Environmental Assessment for Proposed Utility Corridors at Edwards Air Force Base, California

DTIC Science & Technology

2016-07-01

AFB. Coordinating with local communities will serve to ensure all communications towers, wind turbines , residential development and other...Minimis Thresholds in Nonattainment Areas ...................................................................... 35 Table 3-4 Wind Erodibility...125 Table 4-3 Summary of Cultural Resources Associated with Proposed Utility Corridors ........................ 126 Table 4-4 Wind

Meteorological Controls on Local and Regional Volcanic Ash Dispersal.

PubMed

Poulidis, Alexandros P; Phillips, Jeremy C; Renfrew, Ian A; Barclay, Jenni; Hogg, Andrew; Jenkins, Susanna F; Robertson, Richard; Pyle, David M

2018-05-02

Volcanic ash has the capacity to impact human health, livestock, crops and infrastructure, including international air traffic. For recent major eruptions, information on the volcanic ash plume has been combined with relatively coarse-resolution meteorological model output to provide simulations of regional ash dispersal, with reasonable success on the scale of hundreds of kilometres. However, to predict and mitigate these impacts locally, significant improvements in modelling capability are required. Here, we present results from a dynamic meteorological-ash-dispersion model configured with sufficient resolution to represent local topographic and convectively-forced flows. We focus on an archetypal volcanic setting, Soufrière, St Vincent, and use the exceptional historical records of the 1902 and 1979 eruptions to challenge our simulations. We find that the evolution and characteristics of ash deposition on St Vincent and nearby islands can be accurately simulated when the wind shear associated with the trade wind inversion and topographically-forced flows are represented. The wind shear plays a primary role and topographic flows a secondary role on ash distribution on local to regional scales. We propose a new explanation for the downwind ash deposition maxima, commonly observed in volcanic eruptions, as resulting from the detailed forcing of mesoscale meteorology on the ash plume.

The role of remote wind forcing in the subinertial current variability in the central and northern parts of the South Brazil Bight

NASA Astrophysics Data System (ADS)

Dottori, Marcelo; Castro, Belmiro Mendes

2018-06-01

Data analysis of continental shelf currents and coastal sea level, together with the application of a semi-analytical model, are used to estimate the importance of remote wind forcing on the subinertial variability of the current in the central and northern areas of the South Brazil Bight. Results from both the data analysis and from the semi-analytical model are robust in showing subinertial variability that propagates along-shelf leaving the coast to the left in accordance with theoretical studies of Continental Shelf Waves (CSW). Both the subinertial variability observed in along-shelf currents and sea level oscillations present different propagation speeds for the narrow northern part of the SBB ( 6-7 m/s) and the wide central SBB region ( 11 m/s), those estimates being in agreement with the modeled CSW propagation speed. On the inner and middle shelf, observed along-shelf subinertial currents show higher correlation coefficients with the winds located southward and earlier in time than with the local wind at the current meter mooring position and at the time of measurement. The inclusion of the remote (located southwestward) wind forcing improves the prediction of the subinertial currents when compared to the currents forced only by the local wind, since the along-shelf-modeled currents present correlation coefficients with observed along-shelf currents up to 20% higher on the inner and middle shelf when the remote wind is included. For most of the outer shelf, on the other hand, this is not observed since usually, the correlation between the currents and the synoptic winds is not statistically significant.

The role of remote wind forcing in the subinertial current variability in the central and northern parts of the South Brazil Bight

NASA Astrophysics Data System (ADS)

Dottori, Marcelo; Castro, Belmiro Mendes

2018-05-01

Data analysis of continental shelf currents and coastal sea level, together with the application of a semi-analytical model, are used to estimate the importance of remote wind forcing on the subinertial variability of the current in the central and northern areas of the South Brazil Bight. Results from both the data analysis and from the semi-analytical model are robust in showing subinertial variability that propagates along-shelf leaving the coast to the left in accordance with theoretical studies of Continental Shelf Waves (CSW). Both the subinertial variability observed in along-shelf currents and sea level oscillations present different propagation speeds for the narrow northern part of the SBB ( 6-7 m/s) and the wide central SBB region ( 11 m/s), those estimates being in agreement with the modeled CSW propagation speed. On the inner and middle shelf, observed along-shelf subinertial currents show higher correlation coefficients with the winds located southward and earlier in time than with the local wind at the current meter mooring position and at the time of measurement. The inclusion of the remote (located southwestward) wind forcing improves the prediction of the subinertial currents when compared to the currents forced only by the local wind, since the along-shelf-modeled currents present correlation coefficients with observed along-shelf currents up to 20% higher on the inner and middle shelf when the remote wind is included. For most of the outer shelf, on the other hand, this is not observed since usually, the correlation between the currents and the synoptic winds is not statistically significant.

Intra-seasonal sea level variability along the west coast of India

NASA Astrophysics Data System (ADS)

Dhage, Laxmikant; Strub, P. Ted

2016-11-01

The importance of local versus distant forcing is studied for the wind-driven intra-seasonal (30-120 day) sea level anomaly (SLA) variations along the west coast of India. Significant correlations of altimeter-derived SLA on the west coast are found with the mid-basin SLA east of Sri Lanka and SLA as far as Sumatra and the equator, with increased lags, connecting with the remote forcing from the equator in the form of reflected Rossby waves. The highest correlations between SLA on the west coast and winds are found with the winds at the southern tip of India. Coherence calculations help to identify the importance of a narrow band (40-60 day) for the interactions of winds with the intra-seasonal SLA variations. A multivariate regression model, along with the coherences within this narrower band, suggest the lags of SLA on the west coast with winds to range from 0 to 2 days with the local forcing to 11-13 days with the forcing along south east coast of India. Hovmöller diagrams illustrate the propagation of signals by estimating phase speed for Rossby waves (57 cm/s) across the Indian Ocean from Sumatra and Coastal Trapped Waves (CTWs) along the west coast of India (178 cm/s). Propagation from the south-east coast of India is not as robust as Rossby waves from Sumatra.

Applied Meteorology Unit (AMU) Quarterly Report Third Quarter FY-08

NASA Technical Reports Server (NTRS)

Bauman, William; Crawford, Winifred; Barrett, Joe; Watson, Leela; Dreher, Joseph

2008-01-01

This report summarizes the Applied Meteorology Unit (AMU) activities for the third quarter of Fiscal Year 2008 (April - June 2008). Tasks reported on are: Peak Wind Tool for User Launch Commit Criteria (LCC), Anvil Forecast Tool in AWIPS Phase II, Completion of the Edward Air Force Base (EAFB) Statistical Guidance Wind Tool, Volume Averaged Height Integ rated Radar Reflectivity (VAHIRR), Impact of Local Sensors, Radar Scan Strategies for the PAFB WSR-74C Replacement, VAHIRR Cost Benefit Analysis, and WRF Wind Sensitivity Study at Edwards Air Force Base

Dynamics of Andaman Sea circulation and its role in connecting the equatorial Indian Ocean to the Bay of Bengal

NASA Astrophysics Data System (ADS)

Chatterjee, Abhisek; Shankar, D.; McCreary, J. P.; Vinayachandran, P. N.; Mukherjee, A.

2017-04-01

Circulation in the Bay of Bengal (BoB) is driven not only by local winds, but are also strongly forced by the reflection of equatorial Kelvin waves (EKWs) from the eastern boundary of the Indian Ocean. The equatorial influence attains its peak during the monsoon-transition period when strong eastward currents force the strong EKWs along the equator. The Andaman Sea, lying between the Andaman and Nicobar island chains to its west and Indonesia, Thailand, and Myanmar to the south, east, and north, is connected to the equatorial ocean and the BoB by three primary passages, the southern (6°N), middle (10°N), and northern (15°N) channels. We use ocean circulation models, together with satellite altimeter data, to study the pathways by which equatorial signals pass through the Andaman Sea to the BoB and associated dynamical interactions in the process. The mean coastal circulation within the Andaman Sea and around the islands is primarily driven by equatorial forcing, with the local winds forcing a weak sea-level signal. On the other hand, the current forced by local winds is comparable to that forced remotely from the equator. Our results suggest that the Andaman and Nicobar Islands not only influence the circulation within the Andaman Sea, but also significantly alter the circulation in the interior bay and along the east coast of India, implying that they need to be represented accurately in numerical models of the Indian Ocean.

3D CFD Quantification of the Performance of a Multi-Megawatt Wind Turbine

NASA Astrophysics Data System (ADS)

Laursen, J.; Enevoldsen, P.; Hjort, S.

2007-07-01

This paper presents the results of 3D CFD rotor computations of a Siemens SWT-2.3-93 variable speed wind turbine with 45m blades. In the paper CFD is applied to a rotor at stationary wind conditions without wind shear, using the commercial multi-purpose CFD-solvers ANSYS CFX 10.0 and 11.0. When comparing modelled mechanical effects with findings from other models and measurements, good agreement is obtained. Similarly the computed force distributions compare very well, whereas some discrepancies are found when comparing with an in-house BEM model. By applying the reduced axial velocity method the local angle of attack has been derived from the CFD solutions, and from this knowledge and the computed force distributions, local airfoil profile coefficients have been computed and compared to BEM airfoil coefficients. Finally, the transition model of Langtry and Menter is tested on the rotor, and the results are compared with the results from the fully turbulent setup.

Weather Research and Forecasting Model Wind Sensitivity Study at Edwards Air Force Base, CA

NASA Technical Reports Server (NTRS)

Watson, Leela R.; Bauman, William H., III; Hoeth, Brian

2009-01-01

This abstract describes work that will be done by the Applied Meteorology Unit (AMU) in assessing the success of different model configurations in predicting "wind cycling" cases at Edwards Air Force Base, CA (EAFB), in which the wind speeds and directions oscillate among towers near the EAFB runway. The Weather Research and Forecasting (WRF) model allows users to choose among two dynamical cores - the Advanced Research WRF (ARW) and the Non-hydrostatic Mesoscale Model (NMM). There are also data assimilation analysis packages available for the initialization of the WRF model - the Local Analysis and Prediction System (LAPS) and the Advanced Regional Prediction System (ARPS) Data Analysis System (ADAS). Having a series of initialization options and WRF cores, as well as many options within each core, creates challenges for local forecasters, such as determining which configuration options are best to address specific forecast concerns. The goal of this project is to assess the different configurations available and determine which configuration will best predict surface wind speed and direction at EAFB.

Sensitivity of local air quality to the interplay between small- and large-scale circulations: a large-eddy simulation study

NASA Astrophysics Data System (ADS)

Wolf-Grosse, Tobias; Esau, Igor; Reuder, Joachim

2017-06-01

Street-level urban air pollution is a challenging concern for modern urban societies. Pollution dispersion models assume that the concentrations decrease monotonically with raising wind speed. This convenient assumption breaks down when applied to flows with local recirculations such as those found in topographically complex coastal areas. This study looks at a practically important and sufficiently common case of air pollution in a coastal valley city. Here, the observed concentrations are determined by the interaction between large-scale topographically forced and local-scale breeze-like recirculations. Analysis of a long observational dataset in Bergen, Norway, revealed that the most extreme cases of recurring wintertime air pollution episodes were accompanied by increased large-scale wind speeds above the valley. Contrary to the theoretical assumption and intuitive expectations, the maximum NO2 concentrations were not found for the lowest 10 m ERA-Interim wind speeds but in situations with wind speeds of 3 m s-1. To explain this phenomenon, we investigated empirical relationships between the large-scale forcing and the local wind and air quality parameters. We conducted 16 large-eddy simulation (LES) experiments with the Parallelised Large-Eddy Simulation Model (PALM) for atmospheric and oceanic flows. The LES accounted for the realistic relief and coastal configuration as well as for the large-scale forcing and local surface condition heterogeneity in Bergen. They revealed that emerging local breeze-like circulations strongly enhance the urban ventilation and dispersion of the air pollutants in situations with weak large-scale winds. Slightly stronger large-scale winds, however, can counteract these local recirculations, leading to enhanced surface air stagnation. Furthermore, this study looks at the concrete impact of the relative configuration of warmer water bodies in the city and the major transport corridor. We found that a relatively small local water body acted as a barrier for the horizontal transport of air pollutants from the largest street in the valley and along the valley bottom, transporting them vertically instead and hence diluting them. We found that the stable stratification accumulates the street-level pollution from the transport corridor in shallow air pockets near the surface. The polluted air pockets are transported by the local recirculations to other less polluted areas with only slow dilution. This combination of relatively long distance and complex transport paths together with weak dispersion is not sufficiently resolved in classical air pollution models. The findings have important implications for the air quality predictions over urban areas. Any prediction not resolving these, or similar local dynamic features, might not be able to correctly simulate the dispersion of pollutants in cities.

Origins of Eddy Kinetic Energy in the Bay of Bengal

NASA Astrophysics Data System (ADS)

Chen, Gengxin; Li, Yuanlong; Xie, Qiang; Wang, Dongxiao

2018-03-01

By analyzing satellite observational data and ocean general circulation model experiments, this study investigates the key processes that determine the spatial distribution and seasonality of intraseasonal eddy kinetic energy (EKE) within the Bay of Bengal (BOB). It is revealed that a complicated mechanism involving both local and remote wind forcing and ocean internal instability is responsible for the generation and modulation of EKE in this region. High-level EKE mainly resides in four regions: east of Sri Lanka (Region 1), the western BOB (Region 2), northwest of Sumatra (Region 3), and the coastal rim of the BOB (Region 4). The high EKE levels in Regions 1 and 2 are predominantly produced by ocean internal instability, which contributes 90% and 79%, respectively. Prominent seasonality is also observed in these two regions, with higher EKE levels in boreal spring and fall due to enhanced instability of the East Indian Coast Current and the Southwest Monsoon Current, respectively. In contrast, ocean internal instability contributes 49% and 52% of the total EKE in Regions 3 and 4, respectively, whereas the atmospheric forcing of intraseasonal oscillations (ISOs) also plays an important role. ISOs produce EKE mainly through wind stress, involving both the remote effect of equatorial winds and the local effect of monsoonal winds. Equatorial-origin wave signals significantly enhance the EKE levels in Regions 3 and 4, in the form of reflected Rossby waves and coastal Kelvin waves, respectively. The local wind forcing effect through Ekman pumping also has a significant contribution in Regions 3 and 4 (24% and 22%, respectively).

Viscous Forces in Velocity Boundary Layers around Planetary Ionospheres.

PubMed

Pérez-De-Tejada

1999-11-01

A discussion is presented to examine the role of viscous forces in the transport of solar wind momentum to the ionospheric plasma of weakly magnetized planets (Venus and Mars). Observational data are used to make a comparison of the Reynolds and Maxwell stresses that are operative in the interaction of the solar wind with local plasma (planetary ionospheres). Measurements show the presence of a velocity boundary layer formed around the flanks of the ionosphere where the shocked solar wind has reached super-Alfvénic speeds. It is found that the Reynolds stresses in the solar wind at that region can be larger than the Maxwell stresses and thus are necessary in the local acceleration of the ionospheric plasma. From an order-of-magnitude calculation of the Reynolds stresses, it is possible to derive values of the kinematic viscosity and the Reynolds number that are suitable to the gyrotropic motion of the solar wind particles across the boundary layer. The value of the kinematic viscosity is comparable to those inferred from studies of the transport of solar wind momentum to the earth's magnetosphere and thus suggest a common property of the solar wind around planetary obstacles. Similar conditions could also be applicable to velocity boundary layers formed in other plasma interaction problems in astrophysics.

Modeling waves and circulation in Lake Pontchartrain, Louisiana

USGS Publications Warehouse

Signell, Richard P.; List, Jeffrey H.

1997-01-01

The U.S. Geological Survey is conducting a study of storm-driven sediment resuspension and transport in Lake Pontchartrain, Louisiana. Two critical processes related to sediment transport in the lake are (1) the resuspension of sediments due to wind-generated storm waves and (2) the movement of resuspended material by lake currents during storm wind events. The potential for sediment resuspension is being studied with the wave prediction model which simulates local generation of waves by wind and shallow-water effects on waves (refraction, shoaling, bottom friction, and breaking). Long-term wind measurements are then used to determine the regional "climate" of bottom orbital velocity (showing the spatial and temporal variability of wave-induced currents at the bottom). The circulation of the lake is being studied with a three-dimensional hydrodynamic model. Results of the modeling effort indicate that remote forcing due to water levels in Mississippi Sound dominate the circulation near the passes in the eastern end of the lake, while local wind forcing dominates water movement in the western end. During typical storms with winds from the north-northeast or the south-southeast, currents along the south coast near New Orleans generally transport material westward, while material in the central region moves against the wind. When periods of sustained winds are followed by a drop in coastal sea level, a large amount of suspended sediment can be flushed from the lake.

Physical response of a back-barrier estuary to a post-tropical cyclone

USGS Publications Warehouse

Beudin, Alexis; Ganju, Neil Kamal; Defne, Zafer; Aretxabaleta, Alfredo

2017-01-01

This paper presents a modeling investigation of the hydrodynamic and sediment transport response of Chincoteague Bay (VA/MD, USA) to Hurricane Sandy using the Coupled Ocean-Atmosphere-Wave-Sediment-Transport (COAWST) modeling system. Several simulation scenarios with different combinations of remote and local forces were conducted to identify the dominant physical processes. While 80% of the water level increase in the bay was due to coastal sea level at the peak of the storm, a rich spatial and temporal variability in water surface slope was induced by local winds and waves. Local wind increased vertical mixing, horizontal exchanges, and flushing through the inlets. Remote waves (swell) enhanced southward flow through wave setup gradients between the inlets, and increased locally generated wave heights. Locally generated waves had a negligible effect on water level but reduced the residual flow up to 70% due to enhanced apparent roughness and breaking-induced forces. Locally generated waves dominated bed shear stress and sediment resuspension in the bay. Sediment transport patterns mirrored the interior coastline shape and generated deposition on inundated areas. The bay served as a source of fine sediment to the inner shelf, and the ocean-facing barrier island accumulated sand from landward-directed overwash. Despite the intensity of the storm forcing, the bathymetric changes in the bay were on the order of centimeters. This work demonstrates the spectrum of responses to storm forcing, and highlights the importance of local and remote processes on back-barrier estuarine function.

Subtidal sea level variability in a shallow Mississippi River deltaic estuary, Louisiana

USGS Publications Warehouse

Snedden, G.A.; Cable, J.E.; Wiseman, W.J.

2007-01-01

The relative roles of river, atmospheric, and tidal forcings on estuarine sea level variability are examined in Breton Sound, a shallow (0.7 m) deltaic estuary situated in an interdistributary basin on the Mississippi River deltaic plain. The deltaic landscape contains vegetated marshes, tidal flats, circuitous channels, and other features that frictionally dissipate waves propagating through the system. Direct forcing by local wind stress over the surface of the estuary is minimal, owing to the lack of significant fetch due to landscape features of the estuary. Atmospheric forcing occurs almost entirely through remote forcing, where alongshore winds facilitate estuary-shelf exchange through coastal Ekman convergence. The highly frictional nature of the deltaic landscape causes the estuary to act as a low-pass filter to remote atmospheric forcing, where high-frequency, coastally-induced fluctuations are significantly damped, and the damping increases with distance from the estuary mouth. During spring, when substantial quantities of controlled Mississippi River inputs (q?? = 62 m3 s-1) are discharged into the estuary, upper estuary subtidal sea levels are forced by a combination of river and remote atmospheric forcings, while river effects are less clear downestuary. During autumn (q?? = 7 m3 s-1) sea level variability throughout the estuary is governed entirely by coastal variations at the marine boundary. A frequency-dependent analytical model, previously used to describe sea level dynamics forced by local wind stress and coastal forcing in deeper, less frictional systems, is applied in the shallow Breton Sound estuary. In contrast to deeper systems where coastally-induced fluctuations exhibit little or no frictional attenuation inside the estuary, these fluctuations in the shallow Breton Sound estuary show strong frequency-dependent amplitude reductions that extend well into the subtidal frequency spectrum. ?? 2007 Estuarine Research Federation.

What Drives the Variability of the Atlantic Water Circulation in the Arctic Ocean?

NASA Astrophysics Data System (ADS)

Lique, C.; Johnson, H. L.

2016-02-01

The Atlantic Water (AW) layer in the Arctic Basin is isolated from the atmosphere by the overlaying surface layer; yet observations of the AW pan-Arctic boundary current have revealed that the velocities in this layer exhibit significant variations on all timescales. Here, analysis of a global ocean/sea ice model hindcast, complemented by experiments performed with an idealized process model, are used to investigate what controls the variability of AW circulation, with a focus on the role of wind forcing. The AW circulation carries the imprint of wind variations, both remotely over the Nordic and Barents seas where they force variability on the AW inflow to the Arctic Basin, and locally over the Arctic Basin through the forcing of the wind-driven Beaufort gyre, which modulates and transfers the wind variability to the AW layer. Our results further suggest that understanding variability in the large amount of heat contained within the AW layer requires a better understanding of the circulation within both AW and surface layers.

Hydrodynamic Models of Line-Driven Accretion Disk Winds III: Local Ionization Equilibrium

NASA Technical Reports Server (NTRS)

Pereyra, Nicolas Antonio; Kallman, Timothy R.; White, Nicholas E. (Technical Monitor)

2002-01-01

We present time-dependent numerical hydrodynamic models of line-driven accretion disk winds in cataclysmic variable systems and calculate wind mass-loss rates and terminal velocities. The models are 2.5-dimensional, include an energy balance condition with radiative heating and cooling processes, and includes local ionization equilibrium introducing time dependence and spatial dependence on the line radiation force parameters. The radiation field is assumed to originate in an optically thick accretion disk. Wind ion populations are calculated under the assumption that local ionization equilibrium is determined by photoionization and radiative recombination, similar to a photoionized nebula. We find a steady wind flowing from the accretion disk. Radiative heating tends to maintain the temperature in the higher density wind regions near the disk surface, rather than cooling adiabatically. For a disk luminosity L (sub disk) = solar luminosity, white dwarf mass M(sub wd) = 0.6 solar mass, and white dwarf radii R(sub wd) = 0.01 solar radius, we obtain a wind mass-loss rate of M(sub wind) = 4 x 10(exp -12) solar mass yr(exp -1) and a terminal velocity of approximately 3000 km per second. These results confirm the general velocity and density structures found in our earlier constant ionization equilibrium adiabatic CV wind models. Further we establish here 2.5D numerical models that can be extended to QSO/AGN winds where the local ionization equilibrium will play a crucial role in the overall dynamics.

Simulation of Turbulent Flow Inside and Above Wind Farms: Model Validation and Layout Effects

NASA Astrophysics Data System (ADS)

Wu, Yu-Ting; Porté-Agel, Fernando

2013-02-01

A recently-developed large-eddy simulation framework is validated and used to investigate turbulent flow within and above wind farms under neutral conditions. Two different layouts are considered, consisting of thirty wind turbines occupying the same total area and arranged in aligned and staggered configurations, respectively. The subgrid-scale (SGS) turbulent stress is parametrized using a tuning-free Lagrangian scale-dependent dynamic SGS model. The turbine-induced forces are modelled using two types of actuator-disk models: (a) the `standard' actuator-disk model (ADM-NR), which calculates only the thrust force based on one-dimensional momentum theory and distributes it uniformly over the rotor area; and (b) the actuator-disk model with rotation (ADM-R), which uses blade-element momentum theory to calculate the lift and drag forces (that produce both thrust and rotation), and distributes them over the rotor disk based on the local blade and flow characteristics. Validation is performed by comparing simulation results with turbulence measurements collected with hot-wire anemometry inside and above an aligned model wind farm placed in a boundary-layer wind tunnel. In general, the ADM-R model yields improved predictions compared with the ADM-NR in the wakes of all the wind turbines, where including turbine-induced flow rotation and accounting for the non-uniformity of the turbine-induced forces in the ADM-R appear to be important. Another advantage of the ADM-R model is that, unlike the ADM-NR, it does not require a priori specification of the thrust coefficient (which varies within a wind farm). Finally, comparison of simulations of flow through both aligned and staggered wind farms shows important effects of farm layout on the flow structure and wind-turbine performance. For the limited-size wind farms considered in this study, the lateral interaction between cumulated wakes is stronger in the staggered case, which results in a farm wake that is more homogeneous in the spanwise direction, thus resembling more an internal boundary layer. Inside the staggered farm, the relatively longer separation between consecutive downwind turbines allows the wakes to recover more, exposing the turbines to higher local wind speeds (leading to higher turbine efficiency) and lower turbulence intensity levels (leading to lower fatigue loads), compared with the aligned farm. Above the wind farms, the area-averaged velocity profile is found to be logarithmic, with an effective wind-farm aerodynamic roughness that is larger for the staggered case.

The impact of snow and glaciers on meteorological variables in the Khumbu Valley, Nepalese Himalaya.

NASA Astrophysics Data System (ADS)

Potter, E.; Orr, A.; Willis, I.

2017-12-01

Previous observational studies have suggested that snow and glaciers have a big impact on local meteorological variables in the Himalayas, in particular affecting near surface temperature and the localised wind system. Understanding the impact of changing surface conditions on these systems and is crucial in improving future predictions of glacier melt and precipitation in the Himalayas. However, the mechanisms that control the local meteorology remain poorly understood due to the lack of in-situ data and detailed modelling studies. To investigate these mechanisms, we run the Weather Research and Forecasting (WRF) model at kilometre scale resolution for one month during the monsoon over the Khumbu Valley, Nepalese Himalaya. The model is run with and without snow and glacier coverage at the surface. The impact of adding debris cover into the model is also investigated. In the control run with snow and ice, thermally-driven near-surface winds are found to travel up valley during the day except over the glacier slopes. When the snow and ice is removed from the model, the up valley winds extend over the entire slope. Removal of the snow and ice also results in changes to cloud cover and hydrometeors. A momentum budget approach is used to fully understand the mechanisms that maintain the localised wind system, e.g. to determine the contributions from local forcing or synoptic forcing.

Pacific decadal variability in the view of linear equatorial wave theory

NASA Astrophysics Data System (ADS)

Emile-Geay, J. B.; Cane, M. A.

2006-12-01

It has recently been proposed, within the framework of the linear shallow water equations, that tropical Pacific decadal variability can be accounted for by basin modes with eigenperiods of 10 to 20 years, amplifying a mid- latitude wind forcing with an essentially white spectrum (Cessi and Louazel 2001; Liu 2003). We question this idea here, using a different formalism of linear equatorial wave theory. We compute the Green's function for the wind forced response of a linear equatorial shallow water ocean, and use the results of Cane and Moore (1981) to obtain a compact, closed form expression for the motion of the equatorial thermocline, which applies to all frequencies lower than seasonal. At very low frequencies (decadal timescales), we recover the planetary geostrophic solution used by Cessi and Louazel (2001), as well as the equatorial wave solution of Liu (2003), and give a formal explanation for this convergence. Using this more general solution to explore more realistic wind forcings, we come to a different interpretation of the results. We find that the equatorial thermocline is inherently more sensitive to local than to remote wind forcing, and that planetary Rossby modes only weakly alter the spectral characteristics of the response. Tropical winds are able to generate a strong equatorial response with periods of 10 to 20 years, while midlatitude winds can only do so for periods longer than about 50 years. Since the decadal pattern of observed winds shows similar amplitude for tropical and midlatitude winds, we conclude that the latter are unlikely to be responsible for the observed decadal tropical Pacific SST variability. References : Cane, M. A., and Moore, D. W., 1981: A note on low-frequency equatorial basin modes. J. Phys. Oceanogr., 11(11), 1578 1584. Cessi, P., and Louazel, S., 2001: Decadal oceanic response to stochastic wind forcing. J. Phys. Oceanogr., 31, 3020 3029. Liu, Z., 2003: Tropical ocean decadal variability and resonance of planetary wave basin modes. J. Clim., 16(18), 1539 1550.

Evaluating meteo marine climatic model inputs for the investigation of coastal hydrodynamics

NASA Astrophysics Data System (ADS)

Bellafiore, D.; Bucchignani, E.; Umgiesser, G.

2010-09-01

One of the major aspects discussed in the recent works on climate change is how to provide information from the global scale to the local one. In fact the influence of sea level rise and changes in the meteorological conditions due to climate change in strategic areas like the coastal zone is at the base of the well known mitigation and risk assessment plans. The investigation of the coastal zone hydrodynamics, from a modeling point of view, has been the field for the connection between hydraulic models and ocean models and, in terms of process studies, finite element models have demonstrated their suitability in the reproduction of complex coastal morphology and in the capability to reproduce different spatial scale hydrodynamic processes. In this work the connection between two different model families, the climate models and the hydrodynamic models usually implemented for process studies, is tested. Together, they can be the most suitable tool for the investigation of climate change on coastal systems. A finite element model, SHYFEM (Shallow water Hydrodynamic Finite Element Model), is implemented on the Adriatic Sea, to investigate the effect of wind forcing datasets produced by different downscaling from global climate models in terms of surge and its coastal effects. The wind datasets are produced by the regional climate model COSMO-CLM (CIRA), and by EBU-POM model (Belgrade University), both downscaling from ECHAM4. As a first step the downscaled wind datasets, that have different spatial resolutions, has been analyzed for the period 1960-1990 to compare what is their capability to reproduce the measured wind statistics in the coastal zone in front of the Venice Lagoon. The particularity of the Adriatic Sea meteo climate is connected with the influence of the orography in the strengthening of winds like Bora, from North-East. The increase in spatial resolution permits the more resolved wind dataset to better reproduce meteorology and to provide a more realistic forcing for hydrodynamic simulations. After this analysis, effects on water level variations, under different wind forcing, has been analyzed to define what is the local effect on sea level changes in the coastal area of the North Adriatic. Surge statistics produced from different climate model forcings for the IPCC A1B scenario have been studied to provide local information on climate change effects on coastal hydrodynamics due to meteorological effect. This typology of application has been considered a suitable tool for coastal management and can be considered a study field that will increase its importance in the more general investigation on scale interaction processes as the effects of global scale climate phenomena on local areas.

Observational study of surface wind along a sloping surface over mountainous terrain during winter

NASA Astrophysics Data System (ADS)

Lee, Young-Hee; Lee, Gyuwon; Joo, Sangwon; Ahn, Kwang-Deuk

2018-03-01

The 2018 Winter Olympic and Paralympic Games will be held in Pyeongchang, Korea, during February and March. We examined the near surface winds and wind gusts along the sloping surface at two outdoor venues in Pyeongchang during February and March using surface wind data. The outdoor venues are located in a complex, mountainous terrain, and hence the near-surface winds form intricate patterns due to the interplay between large-scale and locally forced winds. During February and March, the dominant wind at the ridge level is westerly; however, a significant wind direction change is observed along the sloping surface at the venues. The winds on the sloping surface are also influenced by thermal forcing, showing increased upslope flow during daytime. When neutral air flows over the hill, the windward and leeward flows show a significantly different behavior. A higher correlation of the wind speed between upper- and lower-level stations is shown in the windward region compared with the leeward region. The strong synoptic wind, small width of the ridge, and steep leeward ridge slope angle provide favorable conditions for flow separation at the leeward foot of the ridge. The gust factor increases with decreasing surface elevation and is larger during daytime than nighttime. A significantly large gust factor is also observed in the leeward region.

Seasonal Sea-Level Variations in San Francisco Bay in Response to Atmospheric Forcing, 1980

USGS Publications Warehouse

Wang, Jingyuan; Cheng, R.T.; Smith, P.C.

1997-01-01

The seasonal response of sea level in San Francisco Bay (SFB) to atmospheric forcing during 1980 is investigated. The relations between sea-level data from the Northern Reach, Central Bay and South Bay, and forcing by local wind stresses, sea level pressure (SLP), runoff and the large scale sea level pressure field are examined in detail. The analyses show that the sea-level elevations and slopes respond to the along-shore wind stress T(V) at most times of the year, and to the cross-shore wind stress T(N) during two transition periods in spring and autumn. River runoff raises the sea-level elevation during winter. It is shown that winter precipitation in the SFB area is mainly attributed to the atmospheric circulation associated with the Alcutian Low, which transports the warm, moist air into the Bay area. A multiple linear regression model is employed to estimate the independent contributions of barometric pressure and wind stress to adjusted sea level. These calculations have a simple dynamical interpretation which confirms the importance of along-shore wind to both sea level and north-south slope within the Bay.

Applied Meteorology Unit (AMU)

NASA Technical Reports Server (NTRS)

Bauman, William H., Jr.; Crawford, Winifred; Short, David; Barrett, Joe; Watson, Leela

2008-01-01

This report summarizes the Applied Meteorology Unit (AMU) activities for the second quarter of Fiscal Year 2008 (January - March 2008). Projects described are: (1) Peak Wind Tool for User Launch Commit Criteria (LCC), (2) Peak Wind Tool for General Forecasting, (3) Situational Lightning Climatologies for Central Florida. Phase III, (4) Volume Averaged Height Integrated Radar Reflectivity (VAHIRR), (5) Impact of Local Sensors, (6) Radar Scan Strategies for the PAFB WSR-74C Replacement and (7) WRF Wind Sensitivity Study at Edwards Air Force Base.

Contact stresses modeling at the Panda-type fiber single-layer winding and evaluation of their impact on the fiber optic properties

NASA Astrophysics Data System (ADS)

Lesnikova, Yu I.; Smetannikov, O. Yu; Trufanov, A. N.; Trufanov, N. A.

2017-02-01

The impact of contact transverse forces on the birefringence of the single-mode polarization-maintaining Panda-type fiber is numerically modeled. It has been established that with a single-row power winding on a cylindrical mandrel, the fiber tension at winding is the principal factor that influences birefringence. When coiling the fiber based on the local defect microbending, the birefringence at the microbending point differs from that of the free fiber by 1.3%.

Rocket Plume Scaling for Orion Wind Tunnel Testing

NASA Technical Reports Server (NTRS)

Brauckmann, Gregory J.; Greathouse, James S.; White, Molly E.

2011-01-01

A wind tunnel test program was undertaken to assess the jet interaction effects caused by the various solid rocket motors used on the Orion Launch Abort Vehicle (LAV). These interactions of the external flowfield and the various rocket plumes can cause localized aerodynamic disturbances yielding significant and highly non-linear control amplifications and attenuations. This paper discusses the scaling methodologies used to model the flight plumes in the wind tunnel using cold air as the simulant gas. Comparisons of predicted flight, predicted wind tunnel, and measured wind tunnel forces-and-moments and plume flowfields are made to assess the effectiveness of the selected scaling methodologies.

Dispersal of Sediment in the Western Adriatic during Energetic Wintertime Forcing

NASA Astrophysics Data System (ADS)

Harris, C. K.; Sherwood, C. R.; Mullenbach, B. L.; Pullen, J. D.

2003-12-01

EuroSTRATAFORM aims to relate sediment delivery and reworking to seabed morphology and stratigraphy through observations and modeling of water column transport. The Po River dominates buoyancy and sediment input into the Adriatic Sea, but small Apeninne rivers (the Chienti, Pescara, etc.) may produce locally important signals. Sedimentation is influenced by fluvial supply, resuspension by waves and currents, and transport by oceanographic currents forced by winds and buoyancy. Transport is likely highest during times of energetic forcing; including Bora events with northeasterly winds and Sirocco events with southeasterly winds. It is difficult, from field measurements alone, to characterize dispersal and convergence patterns over the relevant spatial scales. We applied a three-dimensional hydrodynamic model that includes fluvial delivery, transport, resuspension, and deposition of sediment to quantify sediment dispersal with a 2-km resolution over the entire Adriatic. Circulation calculations were driven by spatially- and temporally-varying wind fields for the Fall / Winter of 2002 / 2003 and realistic Po and Apennine river discharges. Waves were hindcast with the SWAN model. Dispersion of both resuspended and river-derived sediment was estimated for periods that contained intense Bora and Sirocco winds. Predicted sediment dispersal rates and patterns are sensitive to forcing winds, buoyancy flux, and wave patterns. Higher sediment flux was predicted during Bora conditions than during Sirocco conditions. Sirocco winds weaken the Western Adriatic Coastal Current (WACC), and because they tend to concentrate over the Eastern Adriatic, they often fail to create especially energetic waves in the Western Adriatic. Bora wind conditions, on the other hand, intensify the WACC and can build high wave energies over the northwestern Adriatic. Most of the sediment transport occurs during Bora, with a net southward flux. These predictions will be compared to field observations made as part of the EuroSTRATAFORM experiment.

Simulations of an Offshore Wind Farm Using Large-Eddy Simulation and a Torque-Controlled Actuator Disc Model

NASA Astrophysics Data System (ADS)

Creech, Angus; Früh, Wolf-Gerrit; Maguire, A. Eoghan

2015-05-01

We present here a computational fluid dynamics (CFD) simulation of Lillgrund offshore wind farm, which is located in the Øresund Strait between Sweden and Denmark. The simulation combines a dynamic representation of wind turbines embedded within a large-eddy simulation CFD solver and uses hr-adaptive meshing to increase or decrease mesh resolution where required. This allows the resolution of both large-scale flow structures around the wind farm, and the local flow conditions at individual turbines; consequently, the response of each turbine to local conditions can be modelled, as well as the resulting evolution of the turbine wakes. This paper provides a detailed description of the turbine model which simulates the interaction between the wind, the turbine rotors, and the turbine generators by calculating the forces on the rotor, the body forces on the air, and instantaneous power output. This model was used to investigate a selection of key wind speeds and directions, investigating cases where a row of turbines would be fully aligned with the wind or at specific angles to the wind. Results shown here include presentations of the spin-up of turbines, the observation of eddies moving through the turbine array, meandering turbine wakes, and an extensive wind farm wake several kilometres in length. The key measurement available for cross-validation with operational wind farm data is the power output from the individual turbines, where the effect of unsteady turbine wakes on the performance of downstream turbines was a main point of interest. The results from the simulations were compared to the performance measurements from the real wind farm to provide a firm quantitative validation of this methodology. Having achieved good agreement between the model results and actual wind farm measurements, the potential of the methodology to provide a tool for further investigations of engineering and atmospheric science problems is outlined.

SAR Observation and Modeling of Gap Winds in the Prince William Sound of Alaska.

PubMed

Liu, Haibo; Olsson, Peter Q; Volz, Karl

2008-08-22

Alaska's Prince William Sound (PWS) is a unique locale tending to have strong gap winds, especially in the winter season. To characterize and understand these strong surface winds, which have great impacts on the local marine and aviation activities, the surface wind retrieval from the Synthetic Aperture Radar data (SAR-wind) is combined with a numerical mesoscale model. Helped with the SAR-wind observations, the mesoscale model is used to study cases of strong winds and relatively weak winds to depict the nature of these winds, including the area of extent and possible causes of the wind regimes. The gap winds from the Wells Passage and the Valdez Arm are the most dominant gap winds in PWS. Though the Valdez Arm is north-south trending and Wells Passage is east-west oriented, gap winds often develop simultaneously in these two places when a low pressure system is present in the Northern Gulf of Alaska. These two gap winds often converge at the center of PWS and extend further out of the Sound through the Hinchinbrook Entrance. The pressure gradients imposed over these areas are the main driving forces for these gap winds. Additionally, the drainage from the upper stream glaciers and the blocking effect of the banks of the Valdez Arm probably play an important role in enhancing the gap wind.

Nearshore circulation on a sea breeze dominated beach during intense wind events

NASA Astrophysics Data System (ADS)

Torres-Freyermuth, Alec; Puleo, Jack A.; DiCosmo, Nick; Allende-Arandía, Ma. Eugenia; Chardón-Maldonado, Patricia; López, José; Figueroa-Espinoza, Bernardo; de Alegria-Arzaburu, Amaia Ruiz; Figlus, Jens; Roberts Briggs, Tiffany M.; de la Roza, Jacobo; Candela, Julio

2017-12-01

A field experiment was conducted on the northern Yucatan coast from April 1 to April 12, 2014 to investigate the role of intense wind events on coastal circulation from the inner shelf to the swash zone. The study area is characterized by a micro-tidal environment, low-energy wave conditions, and a wide and shallow continental shelf. Furthermore, easterly trade winds, local breezes, and synoptic-scale events, associated with the passage of cold-fronts known as Nortes, are ubiquitous in this region. Currents were measured concurrently at different cross-shore locations during both local and synoptic-scale intense wind events to investigate the influence of different forcing mechanisms (i.e., large-scale currents, winds, tides, and waves) on the nearshore circulation. Field observations revealed that nearshore circulation across the shelf is predominantly alongshore-directed (westward) during intense winds. However, the mechanisms responsible for driving instantaneous spatial and temporal current variability depend on the weather conditions and the across-shelf location. During local strong sea breeze events (W > 10 m s-1 from the NE) occurring during spring tide, westward circulation is controlled by the tides, wind, and waves at the inner-shelf, shallow waters, and inside the surf/swash zone, respectively. The nearshore circulation is relaxed during intense land breeze events (W ≈ 9 m s-1 from the SE) associated with the low atmospheric pressure system that preceded a Norte event. During the Norte event (Wmax≈ 15 m s-1 from the NNW), westward circulation dominated outside the surf zone and was correlated to the Yucatan Current, whereas wave breaking forces eastward currents inside the surf/swash zone. The latter finding implies the existence of large alongshore velocity shear at the offshore edge of the surf zone during the Norte event, which enhances mixing between the surf zone and the inner shelf. These findings suggest that both sea breezes and Nortes play an important role in sediment and pollutant transport along/across the nearshore of the Yucatan shelf.

Can a minimalist model of wind forced baroclinic Rossby waves produce reasonable results?

NASA Astrophysics Data System (ADS)

Watanabe, Wandrey B.; Polito, Paulo S.; da Silveira, Ilson C. A.

2016-04-01

The linear theory predicts that Rossby waves are the large scale mechanism of adjustment to perturbations of the geophysical fluid. Satellite measurements of sea level anomaly (SLA) provided sturdy evidence of the existence of these waves. Recent studies suggest that the variability in the altimeter records is mostly due to mesoscale nonlinear eddies and challenges the original interpretation of westward propagating features as Rossby waves. The objective of this work is to test whether a classic linear dynamic model is a reasonable explanation for the observed SLA. A linear-reduced gravity non-dispersive Rossby wave model is used to estimate the SLA forced by direct and remote wind stress. Correlations between model results and observations are up to 0.88. The best agreement is in the tropical region of all ocean basins. These correlations decrease towards insignificance in mid-latitudes. The relative contributions of eastern boundary (remote) forcing and local wind forcing in the generation of Rossby waves are also estimated and suggest that the main wave forming mechanism is the remote forcing. Results suggest that linear long baroclinic Rossby wave dynamics explain a significant part of the SLA annual variability at least in the tropical oceans.

Winds and the orientation of a coastal plane estuary plume

NASA Astrophysics Data System (ADS)

Xia, Meng; Xie, Lian; Pietrafesa, Leonard J.

2010-10-01

Based on a calibrated coastal plane estuary plume model, ideal model hindcasts of estuary plumes are used to describe the evolution of the plume pattern in response to river discharge and local wind forcing by selecting a typical partially mixed estuary (the Cape Fear River Estuary or CFRE). With the help of an existing calibrated plume model, as described by Xia et al. (2007), simulations were conducted using different parameters to evaluate the plume behavior type and its change associated with the variation of wind forcing and river discharge. The simulations indicate that relatively moderate winds can mechanically reverse the flow direction of the plume. Downwelling favorably wind will pin the plume to the coasts while the upwelling plume could induce plume from the left side to right side in the application to CFRE. It was found that six major types of plumes may occur in the estuary and in the corresponding coastal ocean. To better understand these plumes in the CFRE and other similar river estuary systems, we also investigated how the plumes transition from one type to another. Results showed that wind direction, wind speed, and sometimes river discharge contribute to plume transitions.

Observations of a cycle of intense coastal upwelling and downwelling at the research site of the Shirshov Institute of Oceanology in the Black Sea

NASA Astrophysics Data System (ADS)

Zatsepin, A. G.; Silvestrova, K. P.; Kuklev, S. B.; Piotoukh, V. B.; Podymov, O. I.

2016-03-01

The paper presents the results of joint analysis of the response of vertical temperature and current velocity profile distributions in the coastal zone of the Gelendzhik region of the Black Sea to strong wind forcing in the third ten-day period of September 2013. This forcing was caused by the propagation of an atmospheric cyclone, which first initiated coastal upwelling that was later replaced by downwelling. We formulate a criterion for the development of full coastal upwelling and demonstrate its efficiency. We assume that frequent events of incomplete coastal upwelling and downwelling are associated with changes in the water dynamics (variations in the intensity and direction of the alongshore current) generally not related to local wind forcing.

Comparison of shelf currents off central California prior to and during the 1997-1998 El Nino

USGS Publications Warehouse

Ryan, H.F.; Noble, M.A.

2005-01-01

Moored current, temperature, salinity, and pressure data were collected at three sites that transect the narrow continental shelf offshore of Davenport, CA, starting in August 1996 and continuing to the spring of 1998. This data set allowed a comparison of oceanographic conditions prior to (8/96-3/97) and during (8/97-3/98) the last major El Nin??o. During this El Nin??o, mean temperatures over the 8-month time period were about 3??C warmer than during the prior year at all of the sites. Correlations between near-surface and near-bottom temperatures, and between near-surface temperature and wind stress decreased during the El Nin??o compared to conditions the year before. The mean alongshore currents were more strongly poleward during El Nin??o at sites over the mid-shelf and near the shelf break. There was a general tendency for the energy in alongshore currents to move toward lower frequencies during the El Nin??o, particularly at the sites farther offshore. The processes that forced the shelf flows changed in relative importance throughout the study. The local alongshore wind stress was less important in driving shelf currents during the El Nin??o when much of the wind-induced upwelling was confined to less than 5 km of the coast. The observed strong poleward shelf currents on the mid- to outer-shelf were not clearly tied to local forcing, but were remotely driven, most likely by slope currents. The response of the Davenport shelf to an El Nin??o event may differ from other areas since the shelf is narrow, the wind forcing is weaker than areas to the north and south, and the shelf may be at times isolated by fronts that form at strong upwelling centers. In the winter, strong storm-related winds are important in driving currents at periods not only in the synoptic wind band, but also for periods on the order of 20 d and longer.

Analysis of TMT primary mirror control-structure interaction

NASA Astrophysics Data System (ADS)

MacMynowski, Douglas G.; Thompson, Peter M.; Sirota, Mark J.

2008-07-01

The primary mirror control system (M1CS) keeps the 492 segments of the Thirty Meter Telescope primary mirror aligned in the presence of disturbances. A global position control loop uses feedback from inter-segment edge sensors to three actuators behind each segment that control segment piston, tip and tilt. If soft force actuators are used (e.g. voice-coil), then in addition to the global position loop there will be a local servo loop to provide stiffness. While the M1 control system at Keck compensates only for slow disturbances such as gravity and thermal variations, the M1CS for TMT will need to provide some compensation for higher frequency wind disturbances in order to meet stringent error budget targets. An analysis of expected high-wavenumber wind forces on M1 suggests that a 1Hz control bandwidth is required for the global feedback of segment edge-sensorbased position information in order to minimize high spatial frequency segment response for both seeing-limited and adaptive optics performance. A much higher bandwidth is required from the local servo loop to provide adequate stiffness to wind or acoustic disturbances. A related paper presents the control designs for the local actuator servo loops. The disturbance rejection requirements would not be difficult to achieve for a single segment, but the structural coupling between segments mounted on a flexible mirror cell results in controlstructure interaction (CSI) that limits the achievable bandwidth. Using a combination of simplified modeling to build intuition and the full telescope finite element model for verification, we present designs and analysis for both the local servo loop and global loop demonstrating sufficient bandwidth and resulting wind-disturbance rejection despite the presence of CSI.

Response of the Kuroshio Extension path state to near-term global warming in CMIP5 experiments with MIROC4h

NASA Astrophysics Data System (ADS)

Li, Rui; Jing, Zhao; Chen, Zhaohui; Wu, Lixin

2017-04-01

In this study, responses of the Kuroshio Extension (KE) path state to near-term (2006-2035) global warming are investigated using a Kuroshio-resolving atmosphere-ocean coupled model. Under the representative concentration pathway 4.5 (RCP4.5) forcing, the KE system is intensified and its path state tends to move northward and becomes more stable. It is suggested that the local anticyclonic wind stress anomalies in the KE region favor the spin-up of the southern recirculation gyre, and the remote effect induced by the anticyclonic wind stress anomalies over the central and eastern midlatitude North Pacific also contributes to the stabilization of the KE system substantially. The dominant role of wind stress forcing on KE variability under near-term global warming is further confirmed by adopting a linear 1.5 layer reduced-gravity model forced by wind stress curl field from the present climate model. It is also found that the main contributing longitudinal band for KE index (KEI) moves westward in response to the warmed climate. This results from the northwestward expansion of the large-scale sea level pressure (SLP) field.

A Note on the Barotropic Response of Sea Level to Time-Dependent Wind Forcing

NASA Technical Reports Server (NTRS)

Fu, Lee-Lueng; Davidson, Roger A.

1995-01-01

This study examines the extent to which sea level variations at periods between 30 days and 1 year and spatial scales greater than 1000 km can be described by the wind- driven linear barotropic vorticity dynamics. The TOPEX/POSEIDON altimetric observations of sea level and the wind products of the National Meteorological Center are used as the database for the study. Each term of the linear barotropic vorticity equation was evaluated by averaging over regions of 10 deg x 10 deg. In most of the open ocean the result of the analysis suggests that the sea level variabilities at the scales considered cannot be fully described by the equation; the apparent net vorticity change is more than what can be explained by the local wind stress curl. In the few regions where the wind stress curl is strong enough to balance the vorticity budget, predominantly in the northeast Pacific and the southeast Pacific, the balance is basically achieved in terms of the time-dependent topographic Sverdrup relation, namely, the balance between the advection of the planetary vorticity plus the topography-induced vorticity and the forcing by the wind stress curl.

Buoyancy forcing and the MOC: insights from experiments, simulations and global models

NASA Astrophysics Data System (ADS)

White, B. L.; Passaggia, P. Y.; Zemskova, V.

2017-12-01

The driving forces behind the Meridional Overturning Circulation (MOC) have been widely debated, with wind-driven upwelling, surface buoyancy fluxes due to heating/cooling/freshwater input, and vertical diffusion due to turbulent mixing all thought to play significant roles. To explore the specific role of buoyancy forcing we present results from experiments and simulations of Horizontal Convection (HC), where a circulation is driven by differential buoyancy forcing applied along a horizontal surface. We interpret these results using energy budgets based on the local Available Potential Energy framework introduced in [Scotti and White, J. Fluid Mech., 2014]. We first describe HC experiments driven by the diffusion of salt in water across membranes localized at the surface, at Schmidt numbers {Sc}≈ 610 and Rayleigh numbers in the range 1012 < Ra=Δ b L3/(ν κ ) < 1017, where ν is the kinematic viscosity of water, κ is the diffusion coefficient of salt, L=[.5,2,5]m is the length of the different tanks and Δ b=g(ρ salt}-ρ {fresh}/ρ_{fresh is the reduced gravity difference. We show that the scaling follows a Nu ˜ Ra1/4 type scaling recently theorized by Shishkina et; al. (2016). We then present numerical results for rotating horizontal convection with a zonally re-entrant channel to represent the Southern Ocean branch of the MOC. While the zonal wind stress profile is important to the spatial pattern of the circulation, perhaps surprisingly, the energy budget shows only a weak dependence on the magnitude of the wind input, suggesting that surface APE generation by buoyancy forcing is dominant in driving the overturning circulation.

Seasonal variation of the South Indian tropical gyre

NASA Astrophysics Data System (ADS)

Aguiar-González, Borja; Ponsoni, Leandro; Ridderinkhof, Herman; van Aken, Hendrik M.; de Ruijter, Will P. M.; Maas, Leo R. M.

2016-04-01

Based on satellite altimeter data and global atlases of temperature, salinity, wind stress and wind-driven circulation we investigate the seasonal variation of the South Indian tropical gyre and its associated open-ocean upwelling system, known as the Seychelles-Chagos Thermocline Ridge (SCTR). Results show a year-round, altimeter-derived cyclonic gyre where the upwelling regime appears closely related to seasonality of the ocean gyre, a relationship that has not been previously explored in this region. An analysis of major forcing mechanisms suggests that the thermocline ridge results from the constructive interaction of basin-scale wind stress curl, local-scale wind stress forcing and remote forcing driven by Rossby waves of different periodicity: semiannual in the west, under the strong influence of monsoonal winds; and, annual in the east, where the southeasterlies prevail. One exception occurs during winter, when the well-known westward intensification of the upwelling core, the Seychelles Dome, is shown to be largely a response of the wind-driven circulation. At basin-scale, the most outstanding feature is the seasonal shrinkage of the ocean gyre and the SCTR. From late autumn to spring, the eastward South Equatorial Countercurrent (SECC) recirculates early in the east on feeding the westward South Equatorial Current, therefore closing the gyre before arrival to Sumatra. We find this recirculation longitude migrates over 20° and collocates with the westward advance of a zonal thermohaline front emerging from the encounter between (upwelled) Indian Equatorial Water and relatively warmer and fresher Indonesian Throughflow Water. We suggest this front, which we call the Indonesian Throughflow Front, plays an important role as remote forcing to the tropical gyre, generating southward geostrophic flows that contribute to the early recirculation of the SECC.

Strongly-sheared wind-forced currents in the nearshore regions of the central Southern California Bight

USGS Publications Warehouse

Noble, Marlene A.; Rosenberger, Kurt; Robertson, George L.

2015-01-01

Contrary to many previous reports, winds do drive currents along the shelf in the central portion of the Southern California Bight (SCB). Winds off Huntington Beach CA are the dominant forcing for currents over the nearshore region of the shelf (water depths less than 20 m). Winds control about 50–70% of the energy in nearshore alongshelf surface currents. The wind-driven current amplitudes are also anomalously high. For a relatively weak 1 dyne/cm2 wind stress, the alongshelf surface current amplitudes in this region can reach 80 cm/s or more. Mid-depth current amplitudes for the same wind stress are around 30–40 cm/s. These wind-driven surface current amplitudes are much larger than previously measured over other nearshore shelf regions, perhaps because this program is one of the few that measured currents within a meter of the surface. The near-bed cross-shelf currents over the nearshore region of the Huntington Beach shelf have an Ekman response to winds in that they upwell (downwell) for down (up) coast winds. This response disappears further offshore. Hence, there is upwelling in the SCB, but it does not occur across the entire shelf. Subthermocline water in the nearshore region that may contain nutrients and plankton move onshore when winds are southeastward, but subthermocline water over the shelf break is not transported to the beach. The currents over the outer shelf are not predominately controlled by winds, consistent with previous reports. Instead, they are mainly driven by cross-shelf pressure gradients that are independent of local wind stress.

A comparison of remote vs. local influence of El Niño on the coastal circulation of the northeast Pacific

NASA Astrophysics Data System (ADS)

Hermann, Albert J.; Curchitser, Enrique N.; Haidvogel, Dale B.; Dobbins, Elizabeth L.

2009-12-01

A set of spatially nested circulation models is used to explore interannual change in the northeast Pacific (NEP) during 1997-2002, and remote vs. local influence of the 1997-1998 El Niño on this region. Our nested set is based on the primitive equations of motion, and includes a basin-scale model of the north Pacific at ˜40-km resolution (NPac), and a regional model of the Northeast Pacific at ˜10-km resolution. The NEP model spans an area from Baja California through the Bering Sea, from the coast to ˜2000-km offshore. In this context, "remote influence" refers to effects driven by changes in ocean velocity and temperature outside of the NEP domain; "local influence" refers to direct forcing by winds and runoff within the NEP domain. A base run of this model using hindcast winds and runoff for 1996-2002 replicates the dominant spatial modes of sea-surface height anomalies from satellite data, and coastal sea level from tide gauges. We have performed a series of sensitivity runs with the NEP model for 1997-1998, which analyze the response of coastal sea level to: (1) hindcast winds and coastal runoff, as compared to their monthly climatologies and (2) hindcast boundary conditions (from the NPac model), as compared to their monthly climatologies. Results indicate penetration of sea-surface height (SSH) from the basin-scale model into the NEP domain (e.g., remote influence), with propagation as coastal trapped waves from Baja up through Alaska. Most of the coastal sea-level anomaly off Alaska in El Niño years appears due to direct forcing by local winds and runoff (local influence), and such anomalies are much stronger than those produced off California. We quantify these effects as a function of distance along the coastline, and consider how they might impact the coastal ecosystems of the NEP.

Applied Meteorology Unit Quarterly Report, Second Quarter FY-13

NASA Technical Reports Server (NTRS)

Bauman, William; Crawford, Winifred; Watson, Leela; Shafer, Jaclyn; Huddleston, Lisa

2013-01-01

The AMU team worked on six tasks for their customers: (1) Ms. Crawford continued work on the objective lightning forecast task for airports in east-central Florida, and began work on developing a dual-Doppler analysis with local Doppler radars, (2) Ms. Shafer continued work for Vandenberg Air Force Base on an automated tool to relate pressure gradients to peak winds, (3) Dr. Huddleston continued work to develop a lightning timing forecast tool for the Kennedy Space Center/Cape Canaveral Air Force Station area, (4) Dr. Bauman continued work on a severe weather forecast tool focused on east-central Florida, (5) Mr. Decker began developing a wind pairs database for the Launch Services Program to use when evaluating upper-level winds for launch vehicles, and (6) Dr. Watson began work to assimilate observational data into the high-resolution model configurations, she created for Wallops Flight Facility and the Eastern Range.

3D Numerical Simulation of the Wave and Current Loads on a Truss Foundation of the Offshore Wind Turbine During the Extreme Typhoon Event

NASA Astrophysics Data System (ADS)

Lin, C. W.; Wu, T. R.; Chuang, M. H.; Tsai, Y. L.

2015-12-01

The wind in Taiwan Strait is strong and stable which offers an opportunity to build offshore wind farms. However, frequently visited typhoons and strong ocean current require more attentions on the wave force and local scour around the foundation of the turbine piles. In this paper, we introduce an in-house, multi-phase CFD model, Splash3D, for solving the flow field with breaking wave, strong turbulent, and scour phenomena. Splash3D solves Navier-Stokes Equation with Large-Eddy Simulation (LES) for the fluid domain, and uses volume of fluid (VOF) with piecewise linear interface reconstruction (PLIC) method to describe the break free-surface. The waves were generated inside the computational domain by internal wave maker with a mass-source function. This function is designed to adequately simulate the wave condition under observed extreme events based on JONSWAP spectrum and dispersion relationship. Dirichlet velocity boundary condition is assigned at the upper stream boundary to induce the ocean current. At the downstream face, the sponge-layer method combined with pressure Dirichlet boundary condition is specified for dissipating waves and conducting current out of the domain. Numerical pressure gauges are uniformly set on the structure surface to obtain the force distribution on the structure. As for the local scour around the foundation, we developed Discontinuous Bi-viscous Model (DBM) for the development of the scour hole. Model validations were presented as well. The force distribution under observed irregular wave condition was extracted by the irregular-surface force extraction (ISFE) method, which provides a fast and elegant way to integrate the force acting on the surface of irregular structure. From the Simulation results, we found that the total force is mainly induced by the impinging waves, and the force from the ocean current is about 2 order of magnitude smaller than the wave force. We also found the dynamic pressure, wave height, and the projection area of the structure are the main factors to the total force. Detailed results and discussion are presented as well.

Parameterized and resolved Southern Ocean eddy compensation

NASA Astrophysics Data System (ADS)

Poulsen, Mads B.; Jochum, Markus; Nuterman, Roman

2018-04-01

The ability to parameterize Southern Ocean eddy effects in a forced coarse resolution ocean general circulation model is assessed. The transient model response to a suite of different Southern Ocean wind stress forcing perturbations is presented and compared to identical experiments performed with the same model in 0.1° eddy-resolving resolution. With forcing of present-day wind stress magnitude and a thickness diffusivity formulated in terms of the local stratification, it is shown that the Southern Ocean residual meridional overturning circulation in the two models is different in structure and magnitude. It is found that the difference in the upper overturning cell is primarily explained by an overly strong subsurface flow in the parameterized eddy-induced circulation while the difference in the lower cell is mainly ascribed to the mean-flow overturning. With a zonally constant decrease of the zonal wind stress by 50% we show that the absolute decrease in the overturning circulation is insensitive to model resolution, and that the meridional isopycnal slope is relaxed in both models. The agreement between the models is not reproduced by a 50% wind stress increase, where the high resolution overturning decreases by 20%, but increases by 100% in the coarse resolution model. It is demonstrated that this difference is explained by changes in surface buoyancy forcing due to a reduced Antarctic sea ice cover, which strongly modulate the overturning response and ocean stratification. We conclude that the parameterized eddies are able to mimic the transient response to altered wind stress in the high resolution model, but partly misrepresent the unperturbed Southern Ocean meridional overturning circulation and associated heat transports.

Local Climate Changes Forced by Changes in Land Use and topography in the Aburrá Valley, Colombia.

NASA Astrophysics Data System (ADS)

Zapata Henao, M. Z.; Hoyos Ortiz, C. D.

2017-12-01

One of the challenges in the numerical weather models is the adequate representation of soil-vegetation-atmosphere interaction at different spatial scales, including scenarios with heterogeneous land cover and complex mountainous terrain. The interaction determines the energy, mass and momentum exchange at the surface and could affect different variables including precipitation, temperature and wind. In order to quantify the long-term climate impact of changes in local land use and to assess the role of topography, two numerical experiments were examined. The first experiment allows assessing the continuous growth of urban areas within the Aburrá Valley, a complex terrain region located in Colombian Andes. The Weather Research Forecast model (WRF) is used as the basis of the experiment. The basic setup involves two nested domains, one representing the continental scale (18 km) and the other the regional scale (2 km). The second experiment allows drastic topography modification, including changing the valley configuration to a plateau. The control run for both experiments corresponds to a climatological scenario. In both experiments the boundary conditions correspond to the climatological continental domain output. Surface temperature, surface winds and precipitation are used as the main variables to compare both experiments relative to the control run. The results of the first experiment show a strong relationship between land cover and the variables, specially for surface temperature and wind speed, due to the strong forcing land cover imposes on the albedo, heat capacity and surface roughness, changing temperature and wind speed magnitudes. The second experiment removes the winds spatial variability related with hill slopes, the direction and magnitude are modulated only by the trade winds and roughness of land cover.

Golf in the Wind: Exploring the Effect of Wind on the Accuracy of Golf Shots

NASA Astrophysics Data System (ADS)

Yaghoobian, Neda; Mittal, Rajat

2015-11-01

Golf play is highly dependent on the weather conditions with wind being the most significant factor in the unpredictability of the ball landing position. The direction and strength of the wind alters the aerodynamic forces on a ball in flight, and consequently its speed, distance and direction of travel. The fact that local wind conditions on any particular hole change over times-scales ranging all the way from a few seconds to minutes, hours and days introduces an element of variability in the ball trajectory that is not understood. Any such analysis is complicated by the effect of the local terrestrial and vegetation topology, as well as the inherent complexity of golf-ball aerodynamics. In the current study, we use computational modeling to examine the unpredictability of the shots under different wind conditions over Hole-12 at the Augusta National Golf Club, where the Masters Golf Tournament takes place every year. Despite this being the shortest hole on the course, the presence of complex vegetation canopy around this hole introduces a spatial and temporal variability in wind conditions that evokes uncertainty and even fear among professional golfers. We use our model to examine the effect of wind direction and wind-speed on the accuracy of the golf shots at this hole and use the simulations to determine the key aerodynamic factors that affect the accuracy of the shot.

Oceanographic and atmospheric conditions on the continental shelf north of the Monterey Bay during August 2006

NASA Astrophysics Data System (ADS)

Ramp, Steven R.; Lermusiaux, Pierre F. J.; Shulman, Igor; Chao, Yi; Wolf, Rebecca E.; Bahr, Frederick L.

2011-09-01

A comprehensive data set from the ocean and atmosphere was obtained just north of the Monterey Bay as part of the Monterey Bay 2006 (MB06) field experiment. The wind stress, heat fluxes, and sea surface temperature were sampled by the Naval Postgraduate School's TWIN OTTER research aircraft. In situ data were collected using ships, moorings, gliders and AUVs. Four data-assimilating numerical models were additionally run, including the Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS ®) model for the atmosphere and the Harvard Ocean Prediction System (HOPS), the Regional Ocean Modeling System (ROMS), and the Navy Coastal Ocean Model (NCOM) for the ocean. The scientific focus of the Adaptive Sampling and Prediction Experiment (ASAP) was on the upwelling/relaxation cycle and the resulting three-dimensional coastal circulation near a coastal promontory, in this case Point Año Nuevo, CA. The emphasis of this study is on the circulation over the continental shelf as estimated from the wind forcing, two ADCP moorings, and model outputs. The wind stress during August 2006 consisted of 3-10 day upwelling favorable events separated by brief 1-3 day relaxations. During the first two weeks there was some correlation between local winds and currents and the three models' capability to reproduce the events. During the last two weeks, largely equatorward surface wind stress forced the sea surface and barotropic poleward flow occurred over the shelf, reducing model skill at predicting the circulation. The poleward flow was apparently remotely forced by mesoscale eddies and alongshore pressure gradients, which were not well simulated by the models. The small, high-resolution model domains were highly reliant on correct open boundary conditions to drive these larger-scale poleward flows. Multiply-nested models were no more effective than well-initialized local models in this respect.

Two cold-season derechoes in Europe

NASA Astrophysics Data System (ADS)

Gatzen, Christoph; Púčik, Tomas; Ryva, David

2011-06-01

In this study, we apply for the first time the definition of a derecho (Johns and Hirt, 1987) to European cold-season convective storm systems. These occurred on 18 January 2007 and 1 March 2008, respectively, and they are shown to fulfill the criteria of a derecho. Damaging winds were reported over a distance of 1500 km and locally reached F3 intensity. Synoptic analysis for the events reveal strongly forced situations that have been described for cold-season derechoes in the United States. A comparison of swaths of damaging winds, radar structures, detected lightning, cold pool development, and cloud-top temperatures indicates that both derechoes formed along cold fronts that were affected by strong quasi-geostrophic forcing. It seems that the overlap of the cold front position with the strong differential cyclonic vorticity advection at the cyclonic flank of mid-level jet streaks favoured intense convection and high winds. The movement and path width of the two derechoes seemed to be related to this overlap. The wind gust intensity that was also different for both events is discussed and could be related to the component of the mid-level winds perpendicular to the gust fronts.

The AFFDL-Nielsen Flow-Field Study

DTIC Science & Technology

1976-04-01

76-18 1.0 INTRODUCTION This investigation was conducted in the von K ~ n Gas Dynamics Facility (VKF) Supersonic Wind Tunnel (A) for Nielsen...flow field-surveys, using a cone probe rake to determine the local velocity field; (2) pressure distributions on a store model; and (3) force and...moment data on a store model. In addition, free-stream (interference-free) data were obtained with the probe rake and on the force and pressure store

Observation Denial and Performance of a Local Mesoscale Model

NASA Technical Reports Server (NTRS)

Watson, Leela R.; Bauman, William H., III

2009-01-01

.Forecasters at the 45th Weather Squadron (45 WS) use observations from the Kennedy Space Center (KSC) and Cape Canaveral Air Force Station (CCAFS) wind tower network and the CCAFS (XMR) daily rawinsonde observations (RAOB) to issue and verify wind advisories and warnings for operations. These observations are also used by the National Weather Service (NWS) Spaceflight Meteorology Group (SMG) in Houston, Texas and the NWS Melbourne, Florida (NWS MLB) to initialize their locally-run mesoscale models. In addition, SMG uses these observations to support shuttle landings at the Shuttle Landing Facility (SLF). Due to impending budget cuts, some or all of the wind towers on the east-central Florida mainland and the XMR RAOBs may be eliminated. The locations of the mainland towers and XMR RAOB site are shown in Figure 1. The loss of these data may impact the forecast capability of the 45 WS, SMG and NWS MLB.

WIND- THREE DIMENSIONAL POTENTIAL COMPRESSIBLE FLOW ABOUT WIND TURBINE ROTOR BLADES

NASA Technical Reports Server (NTRS)

Dulikravich, D. S.

1994-01-01

This computer program, WIND, was developed to numerically solve the exact, full-potential equation for three-dimensional, steady, inviscid flow through an isolated wind turbine rotor. The program automatically generates a three-dimensional, boundary-conforming grid and iteratively solves the full-potential equation while fully accounting for both the rotating and Coriolis effects. WIND is capable of numerically analyzing the flow field about a given blade shape of the horizontal-axis type wind turbine. The rotor hub is assumed representable by a doubly infinite circular cylinder. An arbitrary number of blades may be attached to the hub and these blades may have arbitrary spanwise distributions of taper and of the twist, sweep, and dihedral angles. An arbitrary number of different airfoil section shapes may be used along the span as long as the spanwise variation of all the geometeric parameters is reasonably smooth. The numerical techniques employed in WIND involve rotated, type-dependent finite differencing, a finite volume method, artificial viscosity in conservative form, and a successive overrelaxation combined with the sequential grid refinement procedure to accelerate the iterative convergence rate. Consequently, WIND is cabable of accurately analyzing incompressible and compressible flows, including those that are locally transonic and terminated by weak shocks. Along with the three-dimensional results, WIND provides the results of the two-dimensional calculations to aid the user in locating areas of possible improvement in the aerodynamic design of the blade. Output from WIND includes the chordwise distribution of the coefficient of pressure, the Mach number, the density, and the relative velocity components at spanwise stations along the blade. In addition, the results specify local values of the lift coefficient and the tangent and axial aerodynamic force components. These are also given in integrated form expressing the total torque and the total axial force acting on the shaft. WIND can also be used to analyze the flow around isolated aircraft propellers and helicopter rotors in hover as long as the relative oncoming flow is subsonic. The WIND program is written in FORTRAN IV for batch execution and has been implemented on an IBM 370 series computer with a central memory requirement of approximately 253K of 8 bit bytes. WIND was developed in 1980.

Wind Loads on Flat Plate Photovoltaic Array Fields

NASA Technical Reports Server (NTRS)

Miller, R.; Zimmerman, D.

1979-01-01

The aerodynamic forces resulting from winds acting on flat plate photovoltaic arrays were investigated. Local pressure distributions and total aerodynamic forces on the arrays are shown. Design loads are presented to cover the conditions of array angles relative to the ground from 20 deg to 60 deg, variable array spacings, a ground clearance gap up to 1.2 m (4 ft) and array slant heights of 2.4 m (8 ft) and 4.8 m (16 ft). Several means of alleviating the wind loads on the arrays are detailed. The expected reduction of the steady state wind velocity with the use of fences as a load alleviation device are indicated to be in excess of a factor of three for some conditions. This yields steady state wind load reductions as much as a factor of ten compared to the load incurred if no fence is used to protect the arrays. This steady state wind load reduction is offset by the increase in turbulence due to the fence but still an overall load reduction of 2.5 can be realized. Other load alleviation devices suggested are the installation of air gaps in the arrays, blocking the flow under the arrays and rounding the edges of the array. A wind tunnel test plan to supplement the theoretical study and to evaluate the load alleviation devices is outlined.

The physical demands of Olympic yacht racing.

PubMed

Mackie, H; Sanders, R; Legg, S

1999-12-01

The primary purpose of this study was to quantify the up wards forces of the feet on the hiking strap and the forces in the mainsheet of four Olympic classes of racing dinghies (Europe, Laser. Finn and 470) during realistic on-water sailing in varying wind conditions. The secondary aim of the study was to measure the joint angles adopted by the sailors and boat heel angles. The tertiary aim was to identify events and sailing conditions associated with large or patterned force production. Forces in the hiking strap and mainsheet of four classes of Olympic sailing dinghies were measured on eleven New Zealand sailors during simulated on-water racing in a range of wind conditions. Up-wind hiking strap forces reached an average of 73-87% of predicted maximal voluntary contraction (pred MVC), with peak forces exceeding 100% pred MVC. Mainsheet forces reached 25-35% pred MVC, with peak forces reaching 40-50% pred MVC. Off-wind hiking strap and mainsheet forces were considerably lower than up-wind forces. Ankle and hip joint angles increased and knee joint angles decreased with increasing wind speed during up-wind sailing. Large forces occurred in the hiking strap and mainsheet when boats reached the tops of wave during up-wind sailing in high wind speeds and when a gust of wind hit the boat. During off-wind sailing large forces were observed in the mainsheet when surfing down waves. It is recommended that the intensities and joint angles found in this study be used as a basis for the development of class specific off-water physical conditioning programmes.

Decoupling of mass flux and turbulent wind fluctuations in drifting snow

NASA Astrophysics Data System (ADS)

Paterna, E.; Crivelli, P.; Lehning, M.

2016-05-01

The wind-driven redistribution of snow has a significant impact on the climate and mass balance of polar and mountainous regions. Locally, it shapes the snow surface, producing dunes and sastrugi. Sediment transport has been mainly represented as a function of the wind strength, and the two processes assumed to be stationary and in equilibrium. The wind flow in the atmospheric boundary layer is unsteady and turbulent, and drifting snow may never reach equilibrium. Our question is therefore: what role do turbulent eddies play in initiating and maintaining drifting snow? To investigate the interaction between drifting snow and turbulence experimentally, we conducted several wind tunnel measurements of drifting snow over naturally deposited snow covers. We observed a coupling between snow transport and turbulent flow only in a weak saltation regime. In stronger regimes it self-organizes developing its own length scales and efficiently decoupling from the wind forcing.

49 CFR 193.2067 - Wind forces.

Code of Federal Regulations, 2014 CFR

2014-10-01

... 49 Transportation 3 2014-10-01 2014-10-01 false Wind forces. 193.2067 Section 193.2067...: FEDERAL SAFETY STANDARDS Siting Requirements § 193.2067 Wind forces. (a) LNG facilities must be designed to withstand without loss of structural or functional integrity: (1) The direct effect of wind forces...

49 CFR 193.2067 - Wind forces.

Code of Federal Regulations, 2013 CFR

2013-10-01

... 49 Transportation 3 2013-10-01 2013-10-01 false Wind forces. 193.2067 Section 193.2067...: FEDERAL SAFETY STANDARDS Siting Requirements § 193.2067 Wind forces. (a) LNG facilities must be designed to withstand without loss of structural or functional integrity: (1) The direct effect of wind forces...

49 CFR 193.2067 - Wind forces.

Code of Federal Regulations, 2012 CFR

2012-10-01

... 49 Transportation 3 2012-10-01 2012-10-01 false Wind forces. 193.2067 Section 193.2067...: FEDERAL SAFETY STANDARDS Siting Requirements § 193.2067 Wind forces. (a) LNG facilities must be designed to withstand without loss of structural or functional integrity: (1) The direct effect of wind forces...

49 CFR 193.2067 - Wind forces.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 49 Transportation 3 2010-10-01 2010-10-01 false Wind forces. 193.2067 Section 193.2067...: FEDERAL SAFETY STANDARDS Siting Requirements § 193.2067 Wind forces. (a) LNG facilities must be designed to withstand without loss of structural or functional integrity: (1) The direct effect of wind forces...

49 CFR 193.2067 - Wind forces.

Code of Federal Regulations, 2011 CFR

2011-10-01

... 49 Transportation 3 2011-10-01 2011-10-01 false Wind forces. 193.2067 Section 193.2067...: FEDERAL SAFETY STANDARDS Siting Requirements § 193.2067 Wind forces. (a) LNG facilities must be designed to withstand without loss of structural or functional integrity: (1) The direct effect of wind forces...

Untangling the roles of wind, run-off and tides in Prince William Sound

NASA Astrophysics Data System (ADS)

Colas, François; Wang, Xiaochun; Capet, Xavier; Chao, Yi; McWilliams, James C.

2013-07-01

Prince William Sound (PWS) oceanic circulation is driven by a combination of local wind, large run-off and strong tides. Using a regional oceanic model of the Gulf of Alaska, adequately resolving the mean circulation and mesoscale eddies, we configure a series of three nested domains. The inner domain zooms in on Prince William Sound with a 1-km horizontal grid resolution. We analyze a set of four experiments with different combinations of run-off, wind and tides to demonstrate the relative influence of these forcing on the central Sound mean circulation cell and its seasonal variability. The mean circulation in the central PWS region is generally characterized by a cyclonic cell. When forced only by the wind, the circulation is cyclonic in winter and fall and strongly anticyclonic in summer. The addition of freshwater run-off greatly enhances the eddy kinetic energy in PWS partly through near-surface baroclinic instabilities. This leads to a much more intermittent circulation in the central Sound, with the presence of intense small-scale turbulence and a disappearance of the summer wind-forced anticyclonic cell. The addition of tides reduces the turbulence intensity (relatively to the experiment with run-off only), particularly in the central Sound. The generation of turbulent motions by baroclinic processes is lowered by tidal mixing and by modification of the exchange at Hinchinbrook Entrance. Tides have an overall stabilizing effect on the central Sound circulation. Tidal rectification currents help maintain a mean cyclonic circulation throughout the year.

Nearshore currents on the southern Namaqua shelf of the Benguela upwelling system

NASA Astrophysics Data System (ADS)

Fawcett, A. L.; Pitcher, G. C.; Shillington, F. A.

2008-05-01

Nearshore currents of the southern Namaqua shelf were investigated using data from a mooring situated three and a half kilometres offshore of Lambert's Bay, downstream of the Cape Columbine upwelling cell, on the west coast of South Africa. This area is susceptible to harmful algal blooms (HABs) and wind-forced variations in currents and water column structure are critical in determining the development, transport and dissipation of blooms. Time series of local wind data, and current and temperature profile data are described for three periods, considered to be representative of the latter part of the upwelling season (27 January-22 February), winter conditions (5-29 May) and the early part of the upwelling season (10 November-12 December) in 2005. Differences observed in mean wind strength and direction between data sets are indicative of seasonal changes in synoptic meteorological conditions. These quasi-seasonal variations in wind forcing affect nearshore current flow, leading to mean northward flow in surface waters early in the upwelling season when equatorward, upwelling-favourable winds are persistent. Mean near-surface currents are southward during the latter part of the upwelling season, consistent with more prolonged periods of relaxation from equatorward winds, and under winter conditions when winds were predominantly poleward. Within these seasonal variations in mean near-surface current direction, two scales of current variability were evident within all data sets: strong inertial oscillations were driven by diurnal winds and introduced vertical shear into the water column enhancing mixing across the thermocline, while sub-inertial current variability was driven by north-south wind reversals at periods of 2-5 days. Sub-inertial currents were found to lag wind reversals by approximately 12 h, with a tendency for near-surface currents to flow poleward in the absence of wind forcing. Consistent with similar sites along the Californian and Iberian coasts, the headland at Cape Columbine is considered to influence currents and circulation patterns during periods of relaxation from upwelling-favourable winds, favouring the development of a nearshore poleward current, leading to poleward advection of warm water, the development of stratification, and the creation of potentially favourable conditions for HAB development.

Formation of the heliospheric boundaries and the induced dynamics of the solar system: a multifluid view

NASA Astrophysics Data System (ADS)

Fahr, Hans-Jörg

2000-05-01

In many papers in the literature it is shown that wind-driving stars with a peculiar motion relative to the ambient interstellar medium within dynamical time periods form a dynamically adapted astropause as separatrix between the stellar wind plasma and the surrounding interstellar plasma. As we shall show in this chapter stars with an adapted astropause are subject to thrust forces finally acting on the wing-generating central body and thus influencing the stellar motion. Thereby the actual magnitude of the resulting thrust force depends on the actual counterflow configuration of stellar and interstellar winds determined by the particular kinematic situation, i.e. the instantaneous Mach number of the motion relative to the ambient medium. We shall study the sensitivity of this configuration to whether the interstellar flow is sub- or supersonic. The resulting net force is shown to vary in a non-monotonic way with the actual peculiar velocity. For subsonic motions this force generally has an accelerating nature, i.e. operating like a rocket thrust motor, whereas for supersonic motions at supercritical Mach numbers μS≥μS,c, to the contrary, it is of a decelerating nature. For an adequate description of a time-dependent circumstellar flow configuration, we shall use an analytic, hydrodynamic modeling of the counterflow configuration representing the case of a stellar wind system in subsonic or supersonic motion with respect to the local interstellar medium. For the purpose of analytical treatability we assume irrotational and incompressible flows downstream of the inner and outer shocks and give quantitative numbers for forces acting on the central star. We also describe long-period evolutions of star motions and give typical acceleration time periods for different types of wind-driving stars. As we shall emphasize here the dynamical influence of these thrust forces onto the central stellar body requires an understanding of how the presence of the counterflowing interstellar plasma is communicated upstream in the supersonic stellar wind up to the origin of this wind, the stellar corona. The answer we shall give is based on the multifluid character of the relevant counterflow situation invalidating the conventional mono-Mach-number concept of hydrodynamical flows. In fact stellar winds can only be described by a poly-Mach-number concept, with stellar-wind protons being supersonic, with pick-up ions being marginally sonic, and with electrons and anomalous cosmic ray particles being strongly subsonic. We shall present solutions for multifluid counterflow configurations based on computational simulations in which a consistent picture of the interaction of all these different species is given. Our final conclusion is that already the solar wind when passing over the Earth's orbit tells us about the interstellar medium beyond the heliopause.

Novel insights into the dynamics of cold-air drainage and pooling on a gentle slope from fiber-optic distributed temperature sensing

NASA Astrophysics Data System (ADS)

Pfister, Lena; Sigmund, Armin; Olesch, Johannes; Thomas, Christoph

2016-04-01

Urban climate can benefit from cold-air drainage as it may help alleviate the urban heat island. In contrast, stable cold-air pools can damage plants especially in rural areas. In this study, we examined the dynamics of cold-air drainage and pooling in a peri-urban setting over a period of 47 days along a 170 m long slope with an inclination of 1.3° located in the Ecological Botany Gardens of the University of Bayreuth. Air and soil temperatures were measured using distributed temperature sensing of an 2-dimensional fiber-optic array at six heights (-2 cm to 100 cm) along the slope sampling every 1 min and every 1 m. Ancillary measurements of winds, turbulence intensity and momentum exchange were collected using two ultrasonic anemometers installed at 0.1 m and 17 m height at the center of the transect. We hypothesized that cold-air drainage, here defined as a gravity-driven density flow near the bottom originating from local radiative cooling of the surface, is decoupled from non-local flows and can thus be predicted from the local topography. The nocturnal data were stratified by classes of longwave radiation balance, wind speed, and wind direction at 0.1 m agl. The four most abundant classes were tested further for decoupling of wind velocities and directions between 17 and 0.1 m. We further computed the vertical and horizontal temperature perturbations of the fiber-optic array as evaluated for these cases, as well as subject the temperature data to a multiresolution decomposition to investigate the spatial two-point correlation coefficient along the transect. Finally, the cold pool intensity was calculated. The results revealed none of the four most abundant classes followed classical textbook knowledge of locally produced cold-air drainage. Instead, we found that the near-surface flow was strongly forced by two possibly competing non-local flow modes. The first mode caused weak (< 0.4 ms-1) near-surface winds directed perpendicular to the local slope and showed strong vertical decoupling of wind velocities and directions. The vertical and horizontal perturbation of the temperature as well as the cold-pool intensity was high and the two-point correlation coefficient decorrelated fast with increasing distance. In contrast, for the second mode the wind was aligned with the local slope and the wind velocities and directions agreed vertically. However, momentum exchange was much enhanced leading to intense shear-generated mixing and almost vanishing temperature perturbations, higher spatial coherence indicated by slower spatial decorrelations, and a cold-pool intensity of close to zero. In conclusion, the first mode was interpreted as a relatively weak non-local valley-scale cold-air drainage modulating the close to stationary cold-air pool filling the shallow depression the Botanical Gardens are located in. Here, the deeper cold-air drainage causes only weak local movements at the surface as both layers are largely decoupled. The second mode is possibly caused by a recirculation of a stronger valley-scale flow with sufficient synoptic forcing. Our findings challenge the common practice to predict cold-air dynamics solely based on micro-topographic analysis.

Development of a Compact Captive Balloon and Its Level Supporting

NASA Astrophysics Data System (ADS)

Nakao, Tatsuya; Fujiwara, Kazuhito; Furukawa, Motoyasu; Hiroe, Tetsuyuki

Many kinds of observation techniques have been developed to obtain the properties of atmospheric conditions. The advanced observation techniques of the flow in relatively large scale are remote sensing by satellite facilities, long range observations by radar or Doppler Sodar, etc., while data from conventional climometers set at fixed places are merely limited information about local scale flow. Captive balloons are also available and feasible for the observation of local flows if their standing mechanics are robust against the strong wind and the motion of balloon are stable for all wind direction and the change of wind direction. In this paper, a compact captive balloon (about 2m diam.) for flow measurement is proposed and the preservation of balloon height level and the stabilization of its motion are challenged by using a kite. The relation between force balances acted on the balloon and the balloon height or position was estimated and confirmed in experiments. Although the lift force of single kite worked successfully, it is found that the performance of plural kites is less in the traction of balloon since the interaction of their tensions. The compact balloon supported by the kite enabled the over 300m floating by virtue of the small size causing only low air resistance.

West Florida shelf circulation and temperature budget for the 1999 spring transition

USGS Publications Warehouse

He, Ruoying; Weisberg, Robert H.

2002-01-01

Mid-latitude continental shelves undergo a spring transition as the net surface heat flux changes from cooling to warming. Using in situ data and a numerical circulation model we investigate the circulation and temperature budget on the West Florida Continental Shelf (WFS) for the spring transition of 1999. The model is a regional adaptation of the primitive equation, Princeton Ocean Model forced by NCEP reanalysis wind and heat flux fields and by river inflows. Based on agreements between the modeled and observed fields we use the model to draw inferences on how the surface momentum and heat fluxes affect the seasonal and synoptic scale variability. We account for a strong southeastward current at mid-shelf by the baroclinic response to combined wind and buoyancy forcing, and we show how this local forcing leads to annually occurring cold and low salinity tongues. Through term-by-term analyses of the temperature budget we describe the WFS temperature evolution in spring. Heat flux largely controls the seasonal transition, whereas ocean circulation largely controls the synoptic scale variability. These two processes, however, are closely linked. Bottom topography and coastline geometry are important in generating regions of convergence and divergence. Rivers contribute to the local hydrography and are important ecologically. Along with upwelling, river inflows facilitate frontal aggregation of nutrients and the spring formation of a high concentration chlorophyll plume near the shelf break (the so-called ‘Green River’) coinciding with the cold, low salinity tongues. These features originate by local, shelf-wide forcing; the Loop Current is not an essential ingredient.

Sediment-transport events on the northern California continental shelf during the 1990 1991 STRESS experiment

NASA Astrophysics Data System (ADS)

Sherwood, C. R.; Butman, B.; Cacchione, D. A.; Drake, D. E.; Gross, T. F.; Sternberg, R. W.; Wiberg, P. L.; Williams, A. J.

1994-08-01

Measurements of currents and light transmission were made at bottom tripods and moorings arrayed across the northern California continental shelf along the Coastal Ocean Dynamics Experiment (CODE) "C" transect as part of the 1990-1991 Sediment Transport Events on Shelves and Slopes (STRESS) experiment. In combination with meteorological and wave data from the National Data Buoy Center Buoy 46013, these measurements provide information about the physical forcing and resultant resuspension and transport of bottom material between 21 November and 8 March. Sixteen events were identified in the wave, wind and current-meter records for this period. Only two were local storms with southerly winds, but they caused about half of the seasonal net transport. Seven were swell events that combined long-period waves generated by distant storms with local currents. At the 90-m site, swells interacted with the mean northward flow to produce northward transport. During six northerly wind events, upwelling-favorable winds often were sufficient to slow or reverse the mean northward flow and thus caused southward transport. A single current event, which produced moderate southward transport, was observed at the 130-m site. Net transport during the winter experiment was offshore at all sites, northward at the inner- and mid-shelf sites, but southward at the outer-shelf site. The results suggest that local storms with southerly winds may dominate seasonal transport, as on the Washington shelf, but significant transport also can occur during fair weather and during periods of northerly winds.

Surface-layer turbulence, energy balance and links to atmospheric circulations over a mountain glacier in the French Alps

NASA Astrophysics Data System (ADS)

Litt, Maxime; Sicart, Jean-Emmanuel; Six, Delphine; Wagnon, Patrick; Helgason, Warren D.

2017-04-01

Over Saint-Sorlin Glacier in the French Alps (45° N, 6.1° E; ˜ 3 km2) in summer, we study the atmospheric surface-layer dynamics, turbulent fluxes, their uncertainties and their impact on surface energy balance (SEB) melt estimates. Results are classified with regard to large-scale forcing. We use high-frequency eddy-covariance data and mean air-temperature and wind-speed vertical profiles, collected in 2006 and 2009 in the glacier's atmospheric surface layer. We evaluate the turbulent fluxes with the eddy-covariance (sonic) and the profile method, and random errors and parametric uncertainties are evaluated by including different stability corrections and assuming different values for surface roughness lengths. For weak synoptic forcing, local thermal effects dominate the wind circulation. On the glacier, weak katabatic flows with a wind-speed maximum at low height (2-3 m) are detected 71 % of the time and are generally associated with small turbulent kinetic energy (TKE) and small net turbulent fluxes. Radiative fluxes dominate the SEB. When the large-scale forcing is strong, the wind in the valley aligns with the glacier flow, intense downslope flows are observed, no wind-speed maximum is visible below 5 m, and TKE and net turbulent fluxes are often intense. The net turbulent fluxes contribute significantly to the SEB. The surface-layer turbulence production is probably not at equilibrium with dissipation because of interactions of large-scale orographic disturbances with the flow when the forcing is strong or low-frequency oscillations of the katabatic flow when the forcing is weak. In weak forcing when TKE is low, all turbulent fluxes calculation methods provide similar fluxes. In strong forcing when TKE is large, the choice of roughness lengths impacts strongly the net turbulent fluxes from the profile method fluxes and their uncertainties. However, the uncertainty on the total SEB remains too high with regard to the net observed melt to be able to recommend one turbulent flux calculation method over another.

Are winds in cities always slower than in the countryside? Modelling the Urban Wind Island Effect

NASA Astrophysics Data System (ADS)

Droste, Arjan; Steeneveld, Gert-Jan

2017-04-01

Though the Urban Heat Island has been extensively studied, relatively little has been documented about differences in wind between the city as a whole and the countryside. Urban winds are difficult to capture in both observations and modelling, due to the complex urban canyon and neighbourhood geometry. This study uses a straightforward mixed-layer model (Tennekes & Driedonks, 1981) to investigate the contrast between the diurnal cycle of wind in the urban and the rural environment. The model contains one urban and one rural column, to identify differences in wind patterns between city and countryside under equal geostrophic forcing. The model has been evaluated against rural observations from the 213 m. Cabauw tower (the Netherlands), and the urban observations from the BUBBLE campaign (Basel, Rotach et al., 2005). The influence of the urban fabric on the wind is investigated by varying the surface underneath the column model using the 10 urban Local Climate Zones, thereby altering building height, fraction of impervious surface, and initial boundary-layer depth. First results show that for high initial urban boundary-layer depths compared to the rural boundary-layer depth, the urban column can be much windier than its rural counterpart: i.e. the urban Wind Island Effect. The effect appears to be most prominent in the morning and the late afternoon (up to 1 m/s), for Local Climate Zones with lower buildings (3 or 7). BUBBLE observations confirm the timing of the Wind Island Effect, though with weaker magnitude.

Intraseasonal variability of sea level and circulation in the Gulf of Thailand: the role of the Madden-Julian Oscillation

NASA Astrophysics Data System (ADS)

Oliver, Eric C. J.

2014-01-01

Intraseasonal variability of the tropical Indo-Pacific ocean is strongly related to the Madden-Julian Oscillation (MJO). Shallow seas in this region, such as the Gulf of Thailand, act as amplifiers of the direct ocean response to surface wind forcing by efficient setup of sea level. Intraseasonal ocean variability in the Gulf of Thailand region is examined using statistical analysis of local tide gauge observations and surface winds. The tide gauges detect variability on intraseasonal time scales that is related to the MJO through its effect on local wind. The relationship between the MJO and the surface wind is strongly seasonal, being most vigorous during the monsoon, and direction-dependent. The observations are then supplemented with simulations of sea level and circulation from a fully nonlinear barotropic numerical ocean model (Princeton Ocean Model). The numerical model reproduces well the intraseasonal sea level variability in the Gulf of Thailand and its seasonal modulations. The model is then used to map the wind-driven response of sea level and circulation in the entire Gulf of Thailand. Finally, the predictability of the setup and setdown signal is discussed by relating it to the, potentially predictable, MJO index.

The influence of spatially and temporally high-resolution wind forcing on the power input to near-inertial waves in the ocean

NASA Astrophysics Data System (ADS)

Rimac, Antonija; von Storch, Jin-Song; Eden, Carsten

2013-04-01

The estimated power required to sustain global general circulation in the ocean is about 2 TW. This power is supplied with wind stress and tides. Energy spectrum shows pronounced maxima at near-inertial frequency. Near-inertial waves excited by high-frequency winds represent an important source for deep ocean mixing since they can propagate into the deep ocean and dissipate far away from the generation sites. The energy input by winds to near-inertial waves has been studied mostly using slab ocean models and wind stress forcing with coarse temporal resolution (e.g. 6-hourly). Slab ocean models lack the ability to reproduce fundamental aspects of kinetic energy balance and systematically overestimate the wind work. Also, slab ocean models do not account the energy used for the mixed layer deepening or the energy radiating downward into the deep ocean. Coarse temporal resolution of the wind forcing strongly underestimates the near-inertial energy. To overcome this difficulty we use an eddy permitting ocean model with high-frequency wind forcing. We establish the following model setup: We use the Max Planck Institute Ocean Model (MPIOM) on a tripolar grid with 45 km horizontal resolution and 40 vertical levels. We run the model with wind forcings that vary in horizontal and temporal resolution. We use high-resolution (1-hourly with 35 km horizontal resolution) and low-resolution winds (6-hourly with 250 km horizontal resolution). We address the following questions: Is the kinetic energy of near-inertial waves enhanced when high-resolution wind forcings are used? If so, is this due to higher level of overall wind variability or higher spatial or temporal resolution of wind forcing? How large is the power of near-inertial waves generated by winds? Our results show that near-inertial waves are enhanced and the near-inertial kinetic energy is two times higher (in the storm track regions 3.5 times higher) when high-resolution winds are used. Filtering high-resolution winds in space and time, the near-inertial kinetic energy reduces. The reduction is faster when a temporal filter is used suggesting that the high-frequency wind forcing is more efficient in generating near-inertial wave energy than the small-scale wind forcing. Using low-resolution wind forcing the wind generated power to near-inertial waves is 0.55 TW. When we use high-resolution wind forcing the result is 1.6 TW meaning that the result increases by 300%.

A Highly Resolved Large-Eddy Simulation of a Wind Turbine using an Actuator Line Model with Optimal Body Force Projection

DOE PAGES

Martinez-Tossas, Luis A.; Churchfield, Matthew J.; Meneveau, Charles

2016-10-03

When representing the blade aerodynamics with rotating actuator lines, the computed forces have to be projected back to the CFD flow field as a volumetric body force. That has been done in the past with a geometrically simple uniform three-dimensional Gaussian at each point along the blade. Here, we argue that the body force can be shaped in a way that better predicts the blade local flow field, the blade load distribution, and the formation of the tip/root vortices. In previous work, we have determined the optimal scales of circular and elliptical Gaussian kernels that best reproduce the local flowmore » field in two-dimensions. Lastly, in this work we extend the analysis and applications by considering the full three-dimensional blade to test our hypothesis in a highly resolved Large Eddy Simulation.« less

A Highly Resolved Large-Eddy Simulation of a Wind Turbine using an Actuator Line Model with Optimal Body Force Projection

DOE Office of Scientific and Technical Information (OSTI.GOV)

Martinez-Tossas, Luis A.; Churchfield, Matthew J.; Meneveau, Charles

When representing the blade aerodynamics with rotating actuator lines, the computed forces have to be projected back to the CFD flow field as a volumetric body force. That has been done in the past with a geometrically simple uniform three-dimensional Gaussian at each point along the blade. Here, we argue that the body force can be shaped in a way that better predicts the blade local flow field, the blade load distribution, and the formation of the tip/root vortices. In previous work, we have determined the optimal scales of circular and elliptical Gaussian kernels that best reproduce the local flowmore » field in two-dimensions. Lastly, in this work we extend the analysis and applications by considering the full three-dimensional blade to test our hypothesis in a highly resolved Large Eddy Simulation.« less

SMALL-SCALE SOLAR WIND TURBULENCE DUE TO NONLINEAR ALFVÉN WAVES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumar, Sanjay; Moon, Y.-J.; Sharma, R. P., E-mail: sanjaykumar@khu.ac.kr

We present an evolution of wave localization and magnetic power spectra in solar wind plasma using kinetic Alfvén waves (AWs) and fast AWs. We use a two-fluid model to derive the dynamical equations of these wave modes and then numerically solve these nonlinear dynamical equations to analyze the power spectra and wave localization at different times. The ponderomotive force associated with the kinetic AW (or pump) is responsible for the wave localization, and these thin slabs (or sheets) become more chaotic as the system evolves with time until the modulational instability (or oscillating two-stream instability) saturates. From our numerical results,more » we notice a steepening of the spectra from the inertial range (k{sup −1.67}) to the dispersion range (k{sup −3.0}). The steepening of the spectra could be described as the energy transference from longer to smaller scales. The formation of complex magnetic thin slabs and the change of the spectral index may be considered to be the main reason for the charged particles acceleration in solar wind plasma.« less

Seasonal circulation over the Catalan inner-shelf (northwest Mediterranean Sea)

USGS Publications Warehouse

Grifoll, Manel; Aretxabaleta, Alfredo L.; Pelegrí, Josep L.; Espino, Manuel; Warner, John C.; Sánchez-Arcilla, Agustín

2013-01-01

This study characterizes the seasonal cycle of the Catalan inner-shelf circulation using observations and complementary numerical results. The relation between seasonal circulation and forcing mechanisms is explored through the depth-averaged momentum balance, for the period between May 2010 and April 2011, when velocity observations were partially available. The monthly-mean along-shelf flow is mainly controlled by the along-shelf pressure gradient and by surface and bottom stresses. During summer, fall, and winter, the along-shelf momentum balance is dominated by the barotropic pressure gradient and local winds. During spring, both wind stress and pressure gradient act in the same direction and are compensated by bottom stress. In the cross-shelf direction the dominant forces are in geostrophic balance, consistent with dynamic altimetry data.

Seasonal circulation over the Catalan inner-shelf (northwest Mediterranean Sea)

NASA Astrophysics Data System (ADS)

Grifoll, Manel; Aretxabaleta, Alfredo L.; Pelegrí, Josep L.; Espino, Manuel; Warner, John C.; Sánchez-Arcilla, Agustín.

2013-10-01

This study characterizes the seasonal cycle of the Catalan inner-shelf circulation using observations and complementary numerical results. The relation between seasonal circulation and forcing mechanisms is explored through the depth-averaged momentum balance, for the period between May 2010 and April 2011, when velocity observations were partially available. The monthly-mean along-shelf flow is mainly controlled by the along-shelf pressure gradient and by surface and bottom stresses. During summer, fall, and winter, the along-shelf momentum balance is dominated by the barotropic pressure gradient and local winds. During spring, both wind stress and pressure gradient act in the same direction and are compensated by bottom stress. In the cross-shelf direction the dominant forces are in geostrophic balance, consistent with dynamic altimetry data.

Mesoscale and Synoptic Summertime Circulations and Their Impact on Visibility in the Arabian Gulf

NASA Astrophysics Data System (ADS)

Eleuterio, D. P.; Walker, A. L.

2005-12-01

Although frequently characterized as a region of relatively persistent northwesterly winds, often referred to as the 40-day shamal, several researchers have recognized significant temporal and spatial variability in the summer low level winds in the Arabian Gulf. In addition to the synoptically driven gradient between the subtropical high to the north and the monsoon trough across the Gulf of Oman and Northern Arabian Sea, there are complex interactions between the Saudi Arabian and Pakistani heat lows, land-sea breeze circulations, and coastal terrain influence due to the proximity of the Zagros Mountains. These interactions frequently result in several distinct wind regimes within the Arabian Gulf, to include weak thermally and dynamically forced southerlies in the southern Gulf, a diurnally varying region of convergence/ divergence across the central Gulf, and northwesterly shamal type flow in the northern Gulf. The relative orientation and strength of these wind regimes and the strength of the subsidence inversion at the top of the marine boundary layer greatly impact the aerosol loading over water and resulting visibility due to wind-blown sand, dust, and smoke. Several case studies are examined to explore the interaction between mesoscale and synoptic forcing and the resulting spatial and temporal variability in visibility and aerosol optical depth. Conditions range from two to three day periods of rapid and persistent regional clearing with freshening northwesterly winds, to persistent periods of moderate to poor visibility in marine haze under light winds, to large scale events that create a distinct wind and dust front, severely reducing visibility through much of Iraq, Kuwait, and Saudi Arabia, and extending well into the Arabian Gulf. These strong, widespread events may be correlated with synoptically forced conditions farther north. Alternatively, smaller scale regional plumes of mobilized dust are often created by mesoscale events which, in conjunction with oil smoke and industrial pollution, can rapidly reduce visibility in localized regions for periods of 1-2 days and are relatively difficult to forecast because of their mesoscale nature.

A summary of wind tunnel research on tilt rotors from hover to cruise flight

NASA Technical Reports Server (NTRS)

Poisson-Quinton, PH.; Cook, W. L.

1972-01-01

An experimental research program has been conducted on a series of tilt rotors designed for a range of blade twist in various wind tunnel facilities. The objective was to obtain precise results on the influence of blade twist and aeroelasticity on tilt rotor performance, from hover to high speed cruise Mach number of about 0.7. global forces on the rotor, local loads and blade torsional deflection measurements were compared with theoretical predictions inside a large Reynolds-Mach envelope. Testing techniques developed during the program are described.

Applied Meteorology Unit (AMU) Quarterly Report Fourth Quarter FY-14

NASA Technical Reports Server (NTRS)

Bauman, William H.; Crawford, Winifred C.; Watson, Leela R.; Shafer, Jaclyn

2014-01-01

Ms. Crawford completed the final report for the dual-Doppler wind field task. Dr. Bauman completed transitioning the 915-MHz and 50-MHz Doppler Radar Wind Profiler (DRWP) splicing algorithm developed at Marshall Space Flight Center (MSFC) into the AMU Upper Winds Tool. Dr. Watson completed work to assimilate data into model configurations for Wallops Flight Facility (WFF) and Kennedy Space Center/Cape Canaveral Air Force Station (KSC/CCAFS). Ms. Shafer began evaluating the a local high-resolution model she had set up previously for its ability to forecast weather elements that affect launches at KSC/CCAFS. Dr. Watson began a task to optimize the data-assimilated model she just developed to run in real time.

The influence of wave-, wind- and tide-forced currents on headland sand bypassing - Study case: Santa Catarina Island north shore, Brazil

NASA Astrophysics Data System (ADS)

Vieira da Silva, Guilherme; Toldo, Elírio E., Jr.; Klein, Antonio H. da F.; Short, Andrew D.

2018-07-01

Investigations of headland sand bypassing are still an under-reported subject in the literature. This paper aims to understand the contribution of currents forced by different mechanisms such as tides, winds (i.e. local wind acting over the ocean surface generating currents, without considering wave generation) and waves (as they approach/break on the coast) to headland sand bypassing. The study was carried out in an area comprising a series of seven headlands with varying wave exposure due to changes in shoreline orientation and increasing tidal influence close to a relatively large bay. This paper uses a calibrated and validated process-based model (Delft3D) to simulate a series of scenarios including spring and neap tides during flood and ebb conditions and a range of wind and wave scenarios that encompass both average and extreme conditions. The results indicate that waves are the main driving force for the headland bypassing as they transport sand at rates two orders of magnitude higher than tide- or wind-driven sediment transport. The tide-driven currents can only transport sediment during spring tides in locations where the currents are intensified. It is also demonstrated that the wave direction plays an important role in sediment transport. In exposed areas with larger headlands a combination of wave directions is required to first transport sediment offshore (out of the beach) and secondly to transport sediment alongshore and back to the next beach. Whereas in areas with little variation in wave direction exposure, the same oblique wave direction is responsible for the entire headland bypassing process. This is the first time the contribution of tide-, winds- and wave-generated sediment transport to headland bypassing have been studied.

Electrohydrodynamic ionic wind, force field, and ionic mobility in a positive dc wire-to-cylinders corona discharge in air

NASA Astrophysics Data System (ADS)

Monrolin, Nicolas; Praud, Olivier; Plouraboué, Franck

2018-06-01

Ionic wind refers to the acceleration of partially ionized air between two high-voltage electrodes. We study the momentum transfer from ions to air, resulting from ionic wind created by two asymmetric electrodes and producing a net thrust. This electrohydrodynamic (EHD) thrust, has already been measured in previous studies with digital scales. In this study, we provide more insights into the electrohydrodynamic momentum transfer for a wire-to-cylinder(s) positive dc corona discharge. We provide a simple and general theoretical derivation for EHD thrust, which is proportional to the current/mobility ratio and also to an effective distance integrated on the surface of the electrodes. By considering various electrode configurations, our investigation brings out the physical origin of previously obtained optimal configurations, associated with a better tradeoff between Coulomb forcing, friction occurring at the collector, and wake interactions. By measuring two-dimensional velocity fields using particle image velocimetry (PIV), we are able to evaluate the resulting local net force, including the pressure gradient. It is shown that the contribution of velocity fluctuations in the wake of the collecting electrode(s) must be taken into account to recover the net thrust. We confirm the proportionality between the EHD force and the current/mobility ratio experimentally, and evaluate the ion mobility from PIV measurements. A spectral analysis of the velocity fluctuations indicates a dominant frequency corresponding to a Strouhal number of 0.3 based on the ionic wind velocity and the collector size. Finally, the effective mobility of charge carriers is estimated by a PIV based method inside the drift region.

Prospects for generating electricity by large onshore and offshore wind farms

NASA Astrophysics Data System (ADS)

Volker, Patrick J. H.; Hahmann, Andrea N.; Badger, Jake; Jørgensen, Hans E.

2017-03-01

The decarbonisation of energy sources requires additional investments in renewable technologies, including the installation of onshore and offshore wind farms. For wind energy to remain competitive, wind farms must continue to provide low-cost power even when covering larger areas. Inside very large wind farms, winds can decrease considerably from their free-stream values to a point where an equilibrium wind speed is reached. The magnitude of this equilibrium wind speed is primarily dependent on the balance between turbine drag force and the downward momentum influx from above the wind farm. We have simulated for neutral atmospheric conditions, the wind speed field inside different wind farms that range from small (25 km2) to very large (105 km2) in three regions with distinct wind speed and roughness conditions. Our results show that the power density of very large wind farms depends on the local free-stream wind speed, the surface characteristics, and the turbine density. In onshore regions with moderate winds the power density of very large wind farms reaches 1 W m-2, whereas in offshore regions with very strong winds it exceeds 3 W m-2. Despite a relatively low power density, onshore regions with moderate winds offer potential locations for very large wind farms. In offshore regions, clusters of smaller wind farms are generally preferable; under very strong winds also very large offshore wind farms become efficient.

Aerosol removal due to precipitation and wind forcings in Milan urban area

NASA Astrophysics Data System (ADS)

Cugerone, Katia; De Michele, Carlo; Ghezzi, Antonio; Gianelle, Vorne

2018-01-01

Air pollution represents a critical issue in Milan urban area (Northern Italy). Here, the levels of fine particles increase, overcoming the legal limits, mostly in wintertime, due to favourable calm weather conditions and large heating and vehicular traffic emissions. The main goal of this work is to quantify the aerosol removal effect due to precipitation at the ground. At first, the scavenging coefficients have been calculated for aerosol particles with diameter between 0.25 and 3 μm. The average values of this coefficient vary between 2 ×10-5 and 5 ×10-5 s-1. Then, the aerosol removal induced separately by precipitation and wind have been compared through the introduction of a removal index. As a matter of fact, while precipitation leads to a proper wet scavenging of the particles from the atmosphere, high wind speeds cause enhanced particle dispersion and dilution, that locally bring to a tangible decrease of aerosol particles' number. The removal triggered by these two forcings showed comparable average values, but different trends. The removal efficiency of precipitation lightly increases with the increase of particle diameters and vice versa happens with strong winds.

Geometeorological data collected by the USGS Desert Winds Project at Gold Spring, Great Basin desert, northeastern Arizona, 1979-1992

USGS Publications Warehouse

Helm, P.J.; Breed, C.S.; Tigges, R.K.; Garcia, P.A.

1995-01-01

The primary purpose of the Desert Winds Project (DWP) is to obtain high-resolution meteorological data and related surface geological and vegetation data for natural (e.g., uncultivated) desert sites where wind is or has been a major erosive or depositional force. The objectives are twofold: (1) to provide the detailed field measurements needed to carry out quantitative studies of wind as an agent of surface geologic change; and (2) to establish a baseline for defining the 'normal' range of climatic conditions that can be expected to occur on a decadal time scale, in areas considered representative of the major American deserts. The Gold Spring locality was selected to represent that part of the Great Basin Desert that extends into northeastern Arizona. The long-term goal for acquiring and analyzing the Desert Winds Project data is to use them to address problems of land resource degradation by wind, whether resulting from climatic variation aridification) or human activities (desertification), or both (see techinfo.doc).

Generation of BBFs and DFs, Formation of Substorm Auroras and Triggers of Substorm Onset

NASA Astrophysics Data System (ADS)

Song, Y.; Lysak, R. L.

2014-12-01

Substorm onset is a dynamical response of the MI coupling system to external solar wind driving conditions and to internal dynamical processes. During the growth phase, the solar wind energy and momentum are transferred into the magnetosphere via MHD mesoscale Alfvenic interactions throughout the magnetopause current sheet. A decrease in momentum transfer from the solar wind into the magnetosphere starts a preconditioning stage, and produces a strong earthward body force acting on the whole magnetotail within a short time period. The strong earthward force will cause localized transients in the tail, such as multiple BBFs, DFs, plasma bubbles, and excited MHD waves. On auroral flux tubes, FACs carried by Alfven waves are generated by Alfvenic interactions between tail earthward flows associated with BBFs/DFs/Bubbles and the ionospheric drag. Nonlinear Alfvenic interaction between the incident and reflected Alfven wave packets in the auroral acceleration region can produce localized parallel electric fields and substorm auroral arcs. During the preconditioning stage prior to substorm onset, the generation of parallel electric fields and auroral arcs can redistribute perpendicular mechanical and magnetic stresses, "decoupling" the magnetosphere from the ionosphere drag. This will enhance the tail earthward flows and rapidly build up stronger parallel electric fields in the auroral acceleration region, leading to a sudden and violent tail energy release and substorm auroral poleward expansion. We suggest that in preconditioning stage, the decrease in the solar wind momentum transfer is a necessary condition of the substorm onset. Additionally, "decoupling" the magnetosphere from ionosphere drag can trigger substorm expansion onset.

Improved double-multiple streamtube model for the Darrieus-type vertical axis wind turbine

NASA Astrophysics Data System (ADS)

Berg, D. E.

Double streamtube codes model the curved blade (Darrieus-type) vertical axis wind turbine (VAWT) as a double actuator fish arrangement (one half) and use conservation of momentum principles to determine the forces acting on the turbine blades and the turbine performance. Sandia National Laboratories developed a double multiple streamtube model for the VAWT which incorporates the effects of the incident wind boundary layer, nonuniform velocity between the upwind and downwind sections of the rotor, dynamic stall effects and local blade Reynolds number variations. The theory underlying this VAWT model is described, as well as the code capabilities. Code results are compared with experimental data from two VAWT's and with the results from another double multiple streamtube and a vortex filament code. The effects of neglecting dynamic stall and horizontal wind velocity distribution are also illustrated.

Circulation and multiple-scale variability in the Southern California Bight

NASA Astrophysics Data System (ADS)

Dong, Changming; Idica, Eileen Y.; McWilliams, James C.

2009-09-01

The oceanic circulation in the Southern California Bight (SCB) is influenced by the large-scale California Current offshore, tropical remote forcing through the coastal wave guide alongshore, and local atmospheric forcing. The region is characterized by local complexity in the topography and coastline. All these factors engender variability in the circulation on interannual, seasonal, and intraseasonal time scales. This study applies the Regional Oceanic Modeling System (ROMS) to the SCB circulation and its multiple-scale variability. The model is configured in three levels of nested grids with the parent grid covering the whole US West Coast. The first child grid covers a large southern domain, and the third grid zooms in on the SCB region. The three horizontal grid resolutions are 20 km, 6.7 km, and 1 km, respectively. The external forcings are momentum, heat, and freshwater flux at the surface and adaptive nudging to gyre-scale SODA reanalysis fields at the boundaries. The momentum flux is from a three-hourly reanalysis mesoscale MM5 wind with a 6 km resolution for the finest grid in the SCB. The oceanic model starts in an equilibrium state from a multiple-year cyclical climatology run, and then it is integrated from years 1996 through 2003. In this paper, the 8-year simulation at the 1 km resolution is analyzed and assessed against extensive observational data: High-Frequency (HF) radar data, current meters, Acoustic Doppler Current Profilers (ADCP) data, hydrographic measurements, tide gauges, drifters, altimeters, and radiometers. The simulation shows that the domain-scale surface circulation in the SCB is characterized by the Southern California Cyclonic Gyre, comprised of the offshore equatorward California Current System and the onshore poleward Southern California Countercurrent. The simulation also exhibits three subdomain-scale, persistent ( i.e., standing), cyclonic eddies related to the local topography and wind forcing: the Santa Barbara Channel Eddy, the Central-SCB Eddy, and the Catalina-Clemente Eddy. Comparisons with observational data reveal that ROMS reproduces a realistic mean state of the SCB oceanic circulation, as well as its interannual (mainly as a local manifestation of an ENSO event), seasonal, and intraseasonal (eddy-scale) variations. We find high correlations of the wind curl with both the alongshore pressure gradient (APG) and the eddy kinetic energy level in their variations on time scales of seasons and longer. The geostrophic currents are much stronger than the wind-driven Ekman flows at the surface. The model exhibits intrinsic eddy variability with strong topographically related heterogeneity, westward-propagating Rossby waves, and poleward-propagating coastally-trapped waves (albeit with smaller amplitude than observed due to missing high-frequency variations in the southern boundary conditions).

Near 7-day response of ocean bottom pressure to atmospheric surface pressure and winds in the northern South China Sea

NASA Astrophysics Data System (ADS)

Zhang, Kun; Zhu, Xiao-Hua; Zhao, Ruixiang

2018-02-01

Ocean bottom pressures, observed by five pressure-recording inverted echo sounders (PIESs) from October 2012 to July 2014, exhibit strong near 7-day variability in the northern South China Sea (SCS) where long-term in situ bottom pressure observations are quite sparse. This variability was strongest in October 2013 during the near two years observation period. By joint analysis with European Center for Medium-Range Weather Forecasts (ECMWF) data, it is shown that the near 7-day ocean bottom pressure variability is closely related to the local atmospheric surface pressure and winds. Within a period band near 7 days, there are high coherences, exceeding 95% significance level, of observed ocean bottom pressure with local atmospheric surface pressure and with both zonal and meridional components of the wind. Ekman pumping/suction caused by the meridional component of the wind in particular, is suggested as one driving mechanism. A Kelvin wave response to the near 7-day oscillation would propagate down along the continental slope, observed at the Qui Nhon in the Vietnam. By multiple and partial coherence analyses, we find that local atmospheric surface pressure and Ekman pumping/suction show nearly equal influence on ocean bottom pressure variability at near 7-day periods. A schematic diagram representing an idealized model gives us a possible mechanism to explain the relationship between ocean bottom pressure and local atmospheric forcing at near 7-day periods in the northern SCS.

The influence of spatially and temporally high-resolution wind forcing on the power input to near-inertial waves in the ocean

NASA Astrophysics Data System (ADS)

Rimac, A.; Eden, C.; von Storch, J.

2012-12-01

Coexistence of stable stratification, the meridional overturning circulation and meso-scale eddies and their influence on the ocean's circulation still raise complex questions concerning the ocean energetics. Oceanic general circulation is mainly forced by the wind field and deep water tides. Its essential energetics are the conversion of kinetic energy of the winds and tides into oceanic potential and kinetic energy. Energy needed for the circulation is bound to internal wave fields. Direct internal wave generation by the wind at the sea surface is one of the sources of this energy. Previous studies using mixed-layer type of models and low frequency wind forcings (six-hourly and daily) left room for improvement. Using mixed-layer models it is not possible to assess the distribution of near-inertial energy into the deep ocean. Also, coarse temporal resolution of wind forcing strongly underestimates the near-inertial wave energy. To overcome this difficulty we use a high resolution ocean model with high frequency wind forcings. We establish the following model setup: We use the Max Planck Institute Ocean Model (MPIOM) on a tripolar grid with 45km horizontal resolution and 40 vertical levels. We run the model with wind forcings that vary in horizontal (250km versus 40km) and temporal resolution (six versus one-hourly). In our study we answer the following questions: How big is the wind kinetic energy input to the near-inertial waves? Is the kinetic energy of the near-inertial waves enhanced when high-frequency wind forcings are used? If so, by how much and why, due to higher level of temporal wind variability or due to better spatial representation of the near-inertial waves? How big is the total power of near-inertial waves generated by the wind at the surface of the ocean? We run the model for one year. Our model results show that the near-inertial waves are excited both using wind forcings of high and low horizontal and temporal resolution. Near-inertial energy is almost two times higher when we force the model with high frequency wind forcings. The influence on the energy mostly depends on the time difference between two forcing fields while the spatial difference has little influence.

The Impact of Coastal Terrain on Offshore Wind and Implications for Wind Energy

NASA Astrophysics Data System (ADS)

Strobach, Edward Justin

The development of offshore wind energy is moving forward as one of several options for carbon-free energy generation along the populous US east coast. Accurate assessments of the wind resource are essential and can significantly lower financing costs that have been a barrier to development. Wind resource assessment in the Mid-Atlantic region is challenging since there are no long-term measurements of winds across the rotor span. Features of the coastal and inland terrain, such as such as the Appalachian mountains and the Chesapeake Bay, are known to lead to complex mesoscale wind regimes onshore, including low-level jets (LLJs), downslope winds and sea breezes. Little is known, however, about whether or how the inland physiography impacts the winds offshore. This research is based on the first comprehensive set of offshore wind observations in the Maryland Wind Energy Area gathered during a UMBC measurement campaign. The presentation will include a case study of a strong nocturnal LLJ that persisted for several hours before undergoing a rapid breakdown and loss of energy to smaller scales. Measurements from an onshore wind profiler and radiosondes, together with North American Regional Analysis (NARR) and a high resolution Weather Research and Forecast (WRF) model simulation, are used to untangle the forcing mechanisms on synoptic, regional and local scales that led to the jet and its collapse. The results suggest that the evolution of LLJs were impacted by a downslope wind from the Appalachians that propagated offshore riding atop a shallow near-surface boundary layer across the coastal plain. Baroclinic forcing from low sea surface temperatures (SSTs) due to coastal upwelling is also discussed. Smaller scale details of the LLJ breakdown are analyzed using a wave/mean flow/turbulence interaction approach. The case study illustrates several characteristics of low-level winds offshore that are important for wind energy, including LLJs, strong wind shear, turbulence and rapid changes in the wind, so-called "ramp events". A 3-year survey based on NARR analyses is used to estimate the likelihood that similar events could occur under the same meteorological conditions.

Wind systems the driving force of evaporation at the Dead Sea

NASA Astrophysics Data System (ADS)

Metzger, Jutta; Corsmeier, Ulrich; Alpert, Pinhas

2017-04-01

The Dead Sea is a unique place on earth. It is located in the Eastern Mediterranean at the lowest point of the Jordan Rift valley and its water level is currently at 429 m below mean sea level. The region is located in a transition zone of semi-arid to arid climate conditions and endangered by severe environmental problems, especially the rapid lake level decline (>1m/year), causing the shifting of fresh/saline groundwater interfaces and the drying up of the lake. Two key features are relevant for these environmental changes: the evaporation from the water surface and its driving mechanisms. The main driver of evaporation at the Dead Sea is the wind velocity and hence the governing wind systems with different scales in space and time. In the framework of the Virtual Institute DEad SEa Research Venue (DESERVE) an extensive field campaign was conducted to study the governing wind systems in the valley and the energy balance of the water and land surface simultaneously. The combination of several in-situ and remote sensing instruments allowed temporally and spatially high-resolution measurements to investigate the frequency of occurrence of the wind systems, their three-dimensional structure, associated wind velocities and their impact on evaporation. The characteristics of the three local wind systems governing the valley's wind field, as well as their impact on evaporation, will be presented. Mostly decoupled from the large scale flow a local lake breeze determines the conditions during the day. Strong downslope winds drive the evaporation in the afternoon, and down valley flows with wind velocities of over 10 m s-1 dominate during the night causing unusually high evaporation rates after sunset.

COMPUTING THE DUST DISTRIBUTION IN THE BOW SHOCK OF A FAST-MOVING, EVOLVED STAR

DOE Office of Scientific and Technical Information (OSTI.GOV)

Van Marle, A. J.; Meliani, Z.; Keppens, R.

2011-06-20

We study the hydrodynamical behavior occurring in the turbulent interaction zone of a fast-moving red supergiant star, where the circumstellar and interstellar material collide. In this wind-interstellar-medium collision, the familiar bow shock, contact discontinuity, and wind termination shock morphology form, with localized instability development. Our model includes a detailed treatment of dust grains in the stellar wind and takes into account the drag forces between dust and gas. The dust is treated as pressureless gas components binned per grain size, for which we use 10 representative grain size bins. Our simulations allow us to deduce how dust grains of varyingmore » sizes become distributed throughout the circumstellar medium. We show that smaller dust grains (radius <0.045 {mu}m) tend to be strongly bound to the gas and therefore follow the gas density distribution closely, with intricate fine structure due to essentially hydrodynamical instabilities at the wind-related contact discontinuity. Larger grains which are more resistant to drag forces are shown to have their own unique dust distribution, with progressive deviations from the gas morphology. Specifically, small dust grains stay entirely within the zone bound by shocked wind material. The large grains are capable of leaving the shocked wind layer and can penetrate into the shocked or even unshocked interstellar medium. Depending on how the number of dust grains varies with grain size, this should leave a clear imprint in infrared observations of bow shocks of red supergiants and other evolved stars.« less

Characteristics of Pressure Sensitive Paint Intrusiveness Effects on Aerodynamic Data

NASA Technical Reports Server (NTRS)

Amer, Tahani R.; Liu, Tianshu; Oglesby, Donald M.

2001-01-01

One effect of using pressure sensitive paint (PSP) is the potential intrusiveness to the aerodynamic characteristics of the model. The paint thickness and roughness may affect the pressure distribution, and therefore, the forces and moments on the wind tunnel model. A study of these potential intrusive effects was carried out at NASA Langley Research Center where a series of wind tunnel tests were conducted using the Modem Design of Experiments (MDOE) test approach. The PSP effects on the integrated forces were measured on two different models at different test conditions in both the Low Turbulence Pressure Tunnel (LTPT) and the Unitary Plan Wind Tunnel (UPWT) at Langley. The paint effect was found to be very small over a range of Reynolds numbers, Mach numbers and angles of attack. This is due to the very low surface roughness of the painted surface. The surface roughness, after applying the NASA Langley developed PSP, was lower than that of the clean wing. However, the PSP coating had a localized effects on the pressure taps, which leads to an appreciable decrease in the pressure tap reading.

On the Interaction Between Gravity Waves and Atmospheric Thermal Tides

NASA Astrophysics Data System (ADS)

Agner, Ryan Matthew

Gravity waves and thermal tides are two of the most important dynamical features of the atmosphere. They are both generated in the lower atmosphere and propagate upward transporting energy and momentum to the upper atmosphere. This dissertation focuses on the interaction of these waves in the Mesosphere and Lower Thermosphere (MLT) region of the atmosphere using both observational data and Global Circulation Model (GCMs). The first part of this work focuses on observations of gravity wave interactions with the tides using both LIDAR data at the Star Fire Optical Range (SOR, 35?N, 106.5?W) and a meteor radar data at the Andes LIDAR Observatory (ALO, 30.3?S, 70.7?W). At SOR, the gravity waves are shown to enhance or damp the amplitude of the diurnal variations dependent on altitude while the phase is always delayed. The results compare well with previous mechanistic model results and with the Japanese Atmospheric General circulation model for Upper Atmosphere Research (JAGUAR) high resolution global circulation model. The meteor radar observed the GWs to almost always enhance the tidal amplitudes and either delay or advance the phase depending on the altitude. When compared to previous radar results from the same meteor radar when it was located in Maui, Hawaii, the Chile results are very similar while the LIDAR results show significant differences. This is because of several instrument biases when calculating GW momentum fluxes that is not significant when determining the winds. The radar needs to perform large amounts of all-sky averaging across many weeks, while the LIDAR directly detects waves in a small section of sky. The second part of this work focuses on gravity wave parameterization scheme effects on the tides in GCMs. The Specified Dynamics Whole Atmosphere Community Climate Model (SD-WACCM) and the extended Canadian Middle Atmosphere Model (eCMAM) are used for this analysis. The gravity wave parameterization schemes in the eCMAM (Hines scheme) have been shown to enhance the tidal amplitudes compared to observations while the parameterization scheme in SD-WACCM (Lindzen scheme) overdamps the tides. It is shown here that the Hines scheme assumption that only small scale gravity waves force the atmosphere do not create enough drag to properly constrain the tidal amplitudes. The Lindzen scheme produces too much drag because all wave scales are assumed to be saturated thus continuing to provide forcing on the atmosphere above the breaking altitude. The final part of this work investigates GWs, tides and their interactions on a local time scale instead of a global scale in the two GCMs. The local time GWs in eCMAM are found to have a strong seasonal dependence, with the majority of the forcings at the winter pole at latitudes where the diurnal variations are weak limiting their interactions. In SD-WACCM, the largest local GW forcings are located at mid latitudes near where the diurnal variations peak causing them to dampen the diurnal amplitudes. On a local time level the diurnal variations may be a summation of many tidal modes. The analysis reveals that in eCMAM the DW1 tidal mode is by far the dominant mode accounting for the local time variations. The high amount of modulation of GWs by the DW1 tidal winds does not allow it to be properly constrained, causing it to dominate the local time diurnal variations. Similarly, the DW1 projection of GW forcing is dominant over all other other modes and contributes the most to the local time diurnal GW variations. The local time wind variations in SD-WACCM are in uenced by several tidal modes because the DW1 tide is of compatible amplitudes to other modes. This is because of the increased damping on the tide by the GWs. It is also found that the local GW diurnal variations have significant contributions from all tidal modes due to the time and location of the forcing being dependent only on the tropospheric source regions and not the at altitude tidal winds.

Design of horizontal-axis wind turbine using blade element momentum method

NASA Astrophysics Data System (ADS)

Bobonea, Andreea; Pricop, Mihai Victor

2013-10-01

The study of mathematical models applied to wind turbine design in recent years, principally in electrical energy generation, has become significant due to the increasing use of renewable energy sources with low environmental impact. Thus, this paper shows an alternative mathematical scheme for the wind turbine design, based on the Blade Element Momentum (BEM) Theory. The results from the BEM method are greatly dependent on the precision of the lift and drag coefficients. The basic of BEM method assumes the blade can be analyzed as a number of independent element in spanwise direction. The induced velocity at each element is determined by performing the momentum balance for a control volume containing the blade element. The aerodynamic forces on the element are calculated using the lift and drag coefficient from the empirical two-dimensional wind tunnel test data at the geometric angle of attack (AOA) of the blade element relative to the local flow velocity.

Causes of the large warm bias in the Angola-Benguela Frontal Zone in the Norwegian Earth System Model

NASA Astrophysics Data System (ADS)

Koseki, Shunya; Keenlyside, Noel; Demissie, Teferi; Toniazzo, Thomas; Counillon, Francois; Bethke, Ingo; Ilicak, Mehmet; Shen, Mao-Lin

2018-06-01

We have investigated the causes of the sea surface temperature (SST) bias in the Angola-Benguela Frontal Zone (ABFZ) of the southeastern Atlantic Ocean simulated by the Norwegian Earth System Model (NorESM). Similar to other coupled-models, NorESM has a warm SST bias in the ABFZ of up to 8 °C in the annual mean. Our analysis of NorESM reveals that a cyclonic surface wind bias over the ABFZ drives a locally excessively strong southward (0.05 m/s (relative to observation)) Angola Current displacing the ABFZ southward. A series of uncoupled stand-alone atmosphere and ocean model simulations are performed to investigate the cause of the coupled model bias. The stand-alone atmosphere model driven with observed SST exhibits a similar cyclonic surface circulation bias; while the stand-alone ocean model forced with the reanalysis data produces a warm SST in the ABFZ with a magnitude approximately half of that in the coupled NorESM simulation. An additional uncoupled sensitivity experiment shows that the atmospheric model's local negative surface wind curl generates anomalously strong Angola Current at the ocean surface. Consequently, this contributes to the warm SST bias in the ABFZ by 2 °C (compared to the reanalysis forced simulation). There is no evidence that local air-sea feedbacks among wind stress curl, SST, and sea level pressure (SLP) affect the ABFZ SST bias. Turbulent surface heat flux differences between coupled and uncoupled experiments explain the remaining 2 °C warm SST bias in NorESM. Ocean circulation, upwelling and turbulent heat flux errors all modulate the intensity and the seasonality of the ABFZ errors.

Objective classification of historical tropical cyclone intensity

NASA Astrophysics Data System (ADS)

Chenoweth, Michael

2007-03-01

Preinstrumental records of historical tropical cyclone activity require objective methods for accurately categorizing tropical cyclone intensity. Here wind force terms and damage reports from newspaper accounts in the Lesser Antilles and Jamaica for the period 1795-1879 are compared with wind speed estimates calculated from barometric pressure data. A total of 95 separate barometric pressure readings and colocated simultaneous wind force descriptors and wind-induced damage reports are compared. The wind speed estimates from barometric pressure data are taken as the most reliable and serve as a standard to compare against other data. Wind-induced damage reports are used to produce an estimated wind speed range using a modified Fujita scale. Wind force terms are compared with the barometric pressure data to determine if a gale, as used in the contemporary newspapers, is consistent with the modern definition of a gale. Results indicate that the modern definition of a gale (the threshold point separating the classification of a tropical depression from a tropical storm) is equivalent to that in contemporary newspaper accounts. Barometric pressure values are consistent with both reported wind force terms and wind damage on land when the location, speed and direction of movement of the tropical cyclone are determined. Damage reports and derived wind force estimates are consistent with other published results. Biases in ships' logbooks are confirmed and wind force terms of gale strength or greater are identified. These results offer a bridge between the earlier noninstrumental records of tropical cyclones and modern records thereby offering a method of consistently classifying storms in the Caribbean region into tropical depressions, tropical storms, nonmajor and major hurricanes.

Effects of reaction control system jet simulation on the stability and control characteristics of a 0.015-scale space shuttle orbiter model in the Ames Research Center 3.5-foot hypersonic wind tunnel

NASA Technical Reports Server (NTRS)

Dziubala, T. J.; Marroquin, J.; Cleary, J. W.; Mellenthin, J. A.

1973-01-01

An experimental investigation was performed in the Ames Research Center 3.5-Foot Hypersonic Wind Tunnel to obtain detailed effects which interactions between the RCS jet flow field and the local orbiter flow field have on orbiter hypersonic stability and control characteristics. Six-component force data were obtained through an angle-of-attack range of 15 to 35 deg with 0 deg angle of sideslip. The test was conducted with yaw, pitch and roll jet simulation at a free-stream Mach number of 10.3. These data simulate two SSV reentry flight conditions at Mach numbers of 28.3 and 10.3. Fuselage base pressures and pressures on the nonmetric RCS pods were obtained in addition to the basic force measurements. Model 42-0 was used for these tests.

Effects of reaction control system jet simulation on the stability and control characteristics of a 0.015 scale space shuttle orbiter model tested in the Langley Research Center unitary plan wind tunnel

NASA Technical Reports Server (NTRS)

Daileda, J. J.; Marroquin, J.

1974-01-01

An experimental investigation was performed in the Langley Research Center Unitary Plan Wind Tunnel (Test 0A70) to obtain the detailed effects that RCS jet flow interactions with local orbiter flow field have on supersonic stability and control characteristics of the space shuttle orbiter. Six-component force data were obtained through an angle-of-attack range from 15 to 35 degrees at angles of sideslip of 0, +5, and -5 degrees. The test was conducted with yaw jet simulation at free-stream Mach numbers of 2.5 and 4.6, simulating SSV re-entry flight conditions at these Mach numbers. In addition to the basic force measurements, fuselage base pressures and pressures on the non-metric RCS pods were obtained.

Decadal variability on the Northwest European continental shelf

NASA Astrophysics Data System (ADS)

Jones, Sam; Cottier, Finlo; Inall, Mark; Griffiths, Colin

2018-02-01

Decadal scale time series of the shelf seas are important for understanding both climate and process studies. Despite numerous investigations of long-term temperature variability in the shelf seas, studies of salinity variability are few. Salt is a more conservative tracer than temperature in shallow seas, and it can reveal changes in local hydrographic conditions as well as transmitted basin-scale changes. Here, new inter-annual salinity time series on the northwest European shelf are developed and a 13 year high resolution salinity record from a coastal mooring in western Scotland is presented and analysed. We find strong temporal variability in coastal salinity on timescales ranging from tidal to inter-annual, with the magnitude of variability greatest during winter months. There is little seasonality and no significant decadal trend in the coastal time series of salinity. We propose 4 hydrographic states to explain salinity variance in the shelf area west of Scotland based on the interaction between a baroclinic coastal current and wind-forced barotropic flow: while wind forcing is important, we find that changes in the buoyancy-driven flow are more likely to influence long-term salinity observations. We calculate that during prevailing westerly wind conditions, surface waters in the Sea of the Hebrides receive a mix of 62% Atlantic origin water to 38% coastal sources. This contrasts with easterly wind conditions, during which the mix is 6% Atlantic to 94% coastal sources on average. This 'switching' between hydrographic states is expected to impact nutrient transport and therefore modify the level of primary productivity on the shelf. This strong local variability in salinity is roughly an order of magnitude greater than changes in the adjacent ocean basin, and we infer from this that Scottish coastal waters are likely to be resilient to decadal changes in ocean climate.

Main Cause of the Poloidal Plasma Motion Inside a Magnetic Cloud Inferred from Multiple-Spacecraft Observations

NASA Astrophysics Data System (ADS)

Zhao, Ake; Wang, Yuming; Chi, Yutian; Liu, Jiajia; Shen, Chenglong; Liu, Rui

2017-04-01

Although the dynamical evolution of magnetic clouds (MCs) has been one of the foci of interplanetary physics for decades, only few studies focus on the internal properties of large-scale MCs. Recent work by Wang et al. ( J. Geophys. Res. 120, 1543, 2015) suggested the existence of the poloidal plasma motion in MCs. However, the main cause of this motion is not clear. In order to find it, we identify and reconstruct the MC observed by the Solar Terrestrial Relations Observatory (STEREO)-A, Wind, and STEREO-B spacecraft during 19 - 20 November 2007 with the aid of the velocity-modified cylindrical force-free flux-rope model. We analyze the plasma velocity in the plane perpendicular to the MC axis. It is found that there was evident poloidal motion at Wind and STEREO-B, but this was not clear at STEREO-A, which suggests a local cause rather than a global cause for the poloidal plasma motion inside the MC. The rotational directions of the solar wind and MC plasma at the two sides of the MC boundary are found to be consistent, and the values of the rotational speeds of the solar wind and MC plasma at the three spacecraft show a rough correlation. All of these results illustrate that the interaction with ambient solar wind through viscosity might be one of the local causes of the poloidal motion. Additionally, we propose another possible local cause: the existence of a pressure gradient in the MC. The significant difference in the total pressure at the three spacecraft suggests that this speculation is perhaps correct.

Phytoplankton pigment patterns and wind forcing off central California

NASA Technical Reports Server (NTRS)

Abbott, Mark R.; Barksdale, Brett

1991-01-01

Mesoscale variability in phytoplankton pigment distributions of central California during the spring-summer upwelling season are studied via a 4-yr time series of high-resolution coastal zone color scanner imagery. Empirical orthogonal functions are used to decompose the time series of spatial images into its dominant modes of variability. The coupling between wind forcing of the upper ocean and phytoplankton distribution on mesoscales is investigated. Wind forcing, in particular the curl of the wind stress, was found to play an important role in the distribution of phytoplankton pigment in the California Current. The spring transition varies in timing and intensity from year to year but appears to be a recurrent feature associated with the rapid onset of the upwelling-favorable winds. Although the underlying dynamics may be dominated by processes other than forcing by wind stress curl, it appears that curl may force the variability of the filaments and hence the pigment patterns.

Pre-Test Assessment of the Use Envelope of the Normal Force of a Wind Tunnel Strain-Gage Balance

NASA Technical Reports Server (NTRS)

Ulbrich, N.

2016-01-01

The relationship between the aerodynamic lift force generated by a wind tunnel model, the model weight, and the measured normal force of a strain-gage balance is investigated to better understand the expected use envelope of the normal force during a wind tunnel test. First, the fundamental relationship between normal force, model weight, lift curve slope, model reference area, dynamic pressure, and angle of attack is derived. Then, based on this fundamental relationship, the use envelope of a balance is examined for four typical wind tunnel test cases. The first case looks at the use envelope of the normal force during the test of a light wind tunnel model at high subsonic Mach numbers. The second case examines the use envelope of the normal force during the test of a heavy wind tunnel model in an atmospheric low-speed facility. The third case reviews the use envelope of the normal force during the test of a floor-mounted semi-span model. The fourth case discusses the normal force characteristics during the test of a rotated full-span model. The wind tunnel model's lift-to-weight ratio is introduced as a new parameter that may be used for a quick pre-test assessment of the use envelope of the normal force of a balance. The parameter is derived as a function of the lift coefficient, the dimensionless dynamic pressure, and the dimensionless model weight. Lower and upper bounds of the use envelope of a balance are defined using the model's lift-to-weight ratio. Finally, data from a pressurized wind tunnel is used to illustrate both application and interpretation of the model's lift-to-weight ratio.

Studies of the relationship between environmental forcing and the structure and dynamics of tornado-like vortices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nolan, David S.; Almgren, Ann S.; Bell, John B.

Axisymmetric numerical simulations continue to provide insight into how the structure, dynamics, and maximum wind speeds of tornadoes, and other convectively-maintained vortices, are influenced by the surrounding environment. This work is continued with a new numerical model of axisymmetric incompressible flow that incorporates adaptive mesh refinement. The model dynamically increases or decreases the resolution in regions of interest as determined by a specified refinement criterion. Here, the criterion used is based on the cell Reynolds number dx dv / nu, so that the flow is guaranteed to be laminar on the scale of the local grid spacing. The model ismore » used to investigate how the altitude and shape of the convective forcing, the size of the domain, and the effective Reynolds number (based on the choice of the eddy viscosity nu) influence the structure and dynamics of the vortex. Over a wide variety of domain and forcing geometries,the vortex Reynolds number Gamma / nu (the ratio of the far-field circulation to the eddy viscosity) is shown to be the most important parameter for determining vortex structure and behavior. Furthermore,it is found that the vertical scale of the convective forcing only affects the vortex inasmuch as this vertical scale contributes to the total strength of the convective forcing. The horizontal scale of the convective forcing, however, is found to be the fundamental length scale in the problem, in that it can determine both the circulation of the fluid that is drawn into the vortex core, and also influences the depth of the swirling boundary layer. Higher mean wind speeds are sustained as the eddy viscosity is decreased; however, it is observed that the highest wind speeds are found in the high-swirl, two-celled vortex regime rather than in the low-swirl, one-celled regime, which is in contrast with some previous results. The conclusions drawn from these results are applied to dimensional simulations with scales similar to the mesocyclone/thunderstorm environment. Tornado-like vortices are reproduced, using a constant eddy viscosity with such values as 40 m2s-1, which have maximum wind speeds, radii of maximum winds, and boundary layer depths which are quite similar to those recently observed with portable Doppler radar. Based on the results of both nondimensional and tornado-scale simulations, scaling laws are empirically derived for the internal length scales in tornado-like vortices, such as the depth of the boundary layer and the radius of maximum winds.« less

Characterization of the Deep Water Surface Wave Variability in the California Current Region

NASA Astrophysics Data System (ADS)

Villas Bôas, Ana B.; Gille, Sarah T.; Mazloff, Matthew R.; Cornuelle, Bruce D.

2017-11-01

Surface waves are crucial for the dynamics of the upper ocean not only because they mediate exchanges of momentum, heat, energy, and gases between the ocean and the atmosphere, but also because they determine the sea state. The surface wave field in a given region is set by the combination of local and remote forcing. The present work characterizes the seasonal variability of the deep water surface wave field in the California Current region, as retrieved from over two decades of satellite altimetry data combined with wave buoys and wave model hindcast (WaveWatch III). In particular, the extent to which the local wind modulates the variability of the significant wave height, peak period, and peak direction is assessed. During spring/summer, regional-scale wind events of up to 10 m/s are the dominant forcing for waves off the California coast, leading to relatively short-period waves (8-10 s) that come predominantly from the north-northwest. The wave climatology throughout the California Current region shows average significant wave heights exceeding 2 m during most of the year, which may have implications for the planning and retrieval methods of the Surface Water and Ocean Topography (SWOT) satellite mission.

Low speed wind tunnel test of a propulsive wing/canard concept in the STOL configuration. Volume 2: Test data

NASA Technical Reports Server (NTRS)

Stewart, V. R.

1987-01-01

A propulsive wind/canard model was tested at STOL operating conditions in the NASA Langley Research Center 4 x 7 meter wind tunnel. Longitudinal and lateral/directional aerodynamic characteristics were measured for various flap deflections, angles of attack and sideslip, and blowing coefficients. Testing was conducted for several model heights to determine ground proximity effects on the aerodynamic characteristics. Flow field surveys of local flow angles and velocities were performed behind both the canard and the wing. This is volume 2 of a 2 volume report. All of the test data in three appendices are presented. Appendix A presented tabulated six component force and moment data, Appendix B presents tabulated wing pressure coefficients, and Appendix C presents the flow field data.

Field Observations of Coastal Air-Sea Interaction

NASA Astrophysics Data System (ADS)

Ortiz-Suslow, D. G.; Haus, B. K.; Williams, N. J.; Graber, H. C.

2016-12-01

In the nearshore zone wind, waves, and currents generated from different forcing mechanisms converge in shallow water. This can profoundly affect the physical nature of the ocean surface, which can significantly modulate the exchange of momentum, heat, and mass across the air-sea interface. For decades, the focus of air-sea interaction research has been on the open ocean while the shallow water regime has been relatively under-explored. This bears implications for efforts to understand and model various coastal processes, such as mixing, surface transport, and air-sea gas flux. The results from a recent study conducted at the New River Inlet in North Carolina showed that directly measured air-sea flux parameters, such as the atmospheric drag coefficient, are strong functions of space as well as the ambient conditions (i.e. wind speed and direction). The drag is typically used to parameterize the wind stress magnitude. It is generally assumed that the wind direction is the direction of the atmospheric forcing (i.e. wind stress), however significant wind stress steering off of the azimuthal wind direction was observed and was found to be related to the horizontal surface current shear. The authors have just returned from a field campaign carried out within Monterey Bay in California. Surface observations made from two research vessels were complimented by an array of beach and inland flux stations, high-resolution wind forecasts, and satellite image acquisitions. This is a rich data set and several case studies will be analyzed to highlight the importance of various processes for understanding the air-sea fluxes. Preliminary findings show that interactions between the local wind-sea and the shoaling, incident swell can have a profound effect on the wind stress magnitude. The Monterey Bay coastline contains a variety of topographical features and the importance of land-air-sea interactions will also be investigated.

Along-shelf current variability on the Catalan inner-shelf (NW Mediterranean)

USGS Publications Warehouse

Grifoll, Manel; Aretxabaleta, Alfredo L.; Espino, Manuel; Warner, John C.

2012-01-01

We examine the circulation over the inner shelf of the Catalan Sea using observations of currents obtained from three ADCPs within the inner-shelf (24 and 50 m depth) during March-April 2011. The along-shelf current fluctuations during that period are mainly controlled by the local wind stress on short time scales and by remote pressure gradients on synoptic time scales. Different forcing mechanisms are involved in the along-shelf momentum balance. During storm conditions, wind stress, sea level gradients and the non-linear terms dominate the balance. During weak wind conditions, the momentum balance is controlled by the pressure gradient, while during periods of moderate wind in the presence of considerable stratification, the balance is established between the Coriolis and wind stress terms. Vertical variations of velocity are affected by the strong observed density gradient. The increased vertical shear is accompanied by the development of stratified conditions due to local heating when the wind is not able to counteract (and destroy) stratification. The occasional influence of the Besòs river plume is observed in time scales of hours to days in a limited area in front of Barcelona. The area affected by the plume depends on the vertical extend of the fresher layer, the fast river discharge peak, and the relaxation of cross-shore velocities after northeast storm events. This contribution provides a first interpretation of the inner-shelf dynamics in the Catalan Sea.

Wind Forcing of the Pacific Ocean Using Scatterometer Wind Data

NASA Technical Reports Server (NTRS)

Kelly, Kathryn A.

1999-01-01

The long-term objective of this research was an understanding of the wind-forced ocean circulation, particularly for the Pacific Ocean. To determine the ocean's response to the winds, we first needed to generate accurate maps of wind stress. For the ocean's response to wind stress we examined the sea surface height (SSH) both from altimeters and from numerical models for the Pacific Ocean.

Non-thermal electron distribution functions through 3D magnetic reconnection instabilities in the solar wind

NASA Astrophysics Data System (ADS)

Alejandro Munoz Sepulveda, Patricio; Buechner, Joerg

2017-04-01

The effects of kinetic instabilities on the solar wind electron velocity distribution functions (eVDFs) are mostly well understood under local homogeneous and stationary conditions. But the solar wind also contains current sheets, which affect the local properties of instabilities, turbulence and thus the observed non-maxwellian features in the eVDFs. Those processes are vastly unexplored. Therefore, we aim to investigate the influence of self-consistently generated turbulence via electron-scale instabilities in reconnecting current sheets on the formation of suprathermal features in the eVDFs. For this sake, we carry out 3D fully-kinetic Particle-in-Cell code numerical simulations of force free current sheets with a guide magnetic field. We find extended tails, anisotropic plateaus and non-gyrotropic features in the eVDFs, correlated with the locations and time where micro-turbulence is enhanced in the current sheet due to current-aligned streaming instabilities. We also discuss the influence of the plasma parameters, such as the ion to electron temperature ratio, on the excitation of current sheet instabilities and their effect on the properties of the eVDFs.

A method of calculation on the airloading of vertical axis wind turbine

NASA Astrophysics Data System (ADS)

Azuma, A.; Kimura, S.

A new method of analyzing the aerodynamic characteristics of the Darrieus Vertical-Axis Wind Turbine (VAWT) by applying the local circulation method is described. The validity of this method is confirmed by analyzing the air load acting on a curved blade. The azimuthwise variation of spanwise airloading, torque, and longitudinal forces are accurately calculated for a variety of operational conditions. The results are found to be in good agreement with experimental ones obtained elsewhere. It is concluded that the present approach can calculate the aerodynamic characteristics of the VAWT with much less computational time than that used by the free vortex model.

Near-surface wind variability over the broader Adriatic region: insights from an ensemble of regional climate models

NASA Astrophysics Data System (ADS)

Belušić, Andreina; Prtenjak, Maja Telišman; Güttler, Ivan; Ban, Nikolina; Leutwyler, David; Schär, Christoph

2018-06-01

Over the past few decades the horizontal resolution of regional climate models (RCMs) has steadily increased, leading to a better representation of small-scale topographic features and more details in simulating dynamical aspects, especially in coastal regions and over complex terrain. Due to its complex terrain, the broader Adriatic region represents a major challenge to state-of-the-art RCMs in simulating local wind systems realistically. The objective of this study is to identify the added value in near-surface wind due to the refined grid spacing of RCMs. For this purpose, we use a multi-model ensemble composed of CORDEX regional climate simulations at 0.11° and 0.44° grid spacing, forced by the ERA-Interim reanalysis, a COSMO convection-parameterizing simulation at 0.11° and a COSMO convection-resolving simulation at 0.02° grid spacing. Surface station observations from this region and satellite QuikSCAT data over the Adriatic Sea have been compared against daily output obtained from the available simulations. Both day-to-day wind and its frequency distribution are examined. The results indicate that the 0.44° RCMs rarely outperform ERA-Interim reanalysis, while the performance of the high-resolution simulations surpasses that of ERA-Interim. We also disclose that refining the grid spacing to a few km is needed to properly capture the small-scale wind systems. Finally, we show that the simulations frequently yield the accurate angle of local wind regimes, such as for the Bora flow, but overestimate the associated wind magnitude. Finally, spectral analysis shows good agreement between measurements and simulations, indicating the correct temporal variability of the wind speed.

Directional Wave Spectra Observed During Intense Tropical Cyclones

NASA Astrophysics Data System (ADS)

Collins, C. O.; Potter, H.; Lund, B.; Tamura, H.; Graber, H. C.

2018-02-01

Two deep-sea moorings were deployed 780 km off the coast of southern Taiwan for 4-5 months during the 2010 typhoon season. Directional wave spectra, wind speed and direction, and momentum fluxes were recorded on two Extreme Air-Sea Interaction buoys during the close passage of Severe Tropical Storm Dianmu and three tropical cyclones (TCs): Typhoon Fanapi, Super Typhoon Megi, and Typhoon Chaba. Conditions sampled include significant wave heights up to 11 m and wind speeds up to 26 m s-1. Details varied for large-scale spectral structure in frequency and direction but were mostly bimodal. The modes were generally composed of a swell system emanating from the most intense storm region and local wind-seas. The peak systems were consistently young, meaning actively forced by winds, when the storms were close. During the peaks of the most intense passages—Chaba at the northern mooring and Megi at the southern—the bimodal seas coalesced. During Chaba, the swell and wind-sea coupling directed the high frequency waves and the wind stress away from the wind direction. A spectral wave model was able reproduce many of the macrofeatures of the directional spectra.

Preliminary study of inphase gusts and moment force wind loads over the first 150 meters at KSC, Florida

NASA Technical Reports Server (NTRS)

Kaufman, J. W.

1985-01-01

A mathematical/statistical analysis of inphase gusts and wind velocity moment forces over the first 150 m at the Kennedy Space Center (KSC) is presented. The wind velocity profile data were acquired at the KSC 150 m ground wind tower. The results show that planetary boundary layer (PBL) winds can sustain near peak speeds for periods up to 60 sec and longer. This is proven from calculating the autocorrelation functions of moment forces for several 10 min cases of wind profile data. The results show that lower atmospheric planetary boundary layer winds have periodic variations for long periods of time. This flow characteristic is valuable as aerospace vehicle engineering and design criteria where wind loading must be determined.

Meteorologic, oceanographic, and geomorphic controls on circulation and residence time in a coral reef-lined embayment: Faga'alu Bay, American Samoa

NASA Astrophysics Data System (ADS)

Storlazzi, C. D.; Cheriton, O. M.; Messina, A. M.; Biggs, T. W.

2018-06-01

Water circulation over coral reefs can determine the degree to which reef organisms are exposed to the overlying waters, so understanding circulation is necessary to interpret spatial patterns in coral health. Because coral reefs often have high geomorphic complexity, circulation patterns and the duration of exposure, or "local residence time" of a water parcel, can vary substantially over small distances. Different meteorologic and oceanographic forcings can further alter residence time patterns over reefs. Here, spatially dense Lagrangian surface current drifters and Eulerian current meters were used to characterize circulation patterns and resulting residence times over different regions of the reefs in Faga'alu Bay, American Samoa, during three distinct forcing periods: calm, strong winds, and large waves. Residence times varied among different geomorphic zones of the reef and were reflected in the spatially varying health of the corals across the embayment. The relatively healthy, seaward fringing reef consistently had the shortest residence times, as it was continually flushed by wave breaking at the reef crest, whereas the degraded, sheltered, leeward fringing reef consistently had the longest residence times, suggesting this area is more exposed to land-based sources of pollution. Strong wind forcing resulted in the longest residence times by pinning the water in the bay, whereas large wave forcing flushed the bay and resulted in the shortest residence times. The effect of these different forcings on residence times was fairly consistent across all reef geomorphic zones, with the shift from wind to wave forcing shortening mean residence times by approximately 50%. Although ecologically significant to the coral organisms in the nearshore reef zones, these shortened residence times were still 2-3 times longer than those associated with the seaward fringing reef across all forcing conditions, demonstrating how the geomorphology of a reef environment sets a first-order control on reef health.

Optical remote sensing of penetration into the lower thermosphere of neutral wind and composition perturbations driven by magnetospheric forcing

NASA Astrophysics Data System (ADS)

Conde, M. G.; Anderson, C.; Hecht, J. H.

2011-12-01

Numerous observations of thermospheric neutral winds at altitudes of 240 km and higher clearly show wind structures occurring at auroral latitudes in response to magnetospheric forcing. It is also known from observations that magnetospheric forcing is not a major driver of winds down at mesopause heights and below. Because it is difficult to measure winds in the intervening "transition region" between these height regimes, very little is known about how deeply the magnetospherically driven neutral wind structures penetrate into the lower thermosphere, what factors affect this penetration, and what consequences it may have for transport of chemical species. Here we will show neutral wind maps obtained at F-region and E-region heights in the auroral zone using Fabry-Perot Doppler spectroscopy of the 630 nm and 558 nm optical emissions. Although thermospheric neutral winds are smoothed by viscosity and inertia, observed responses to magnetospheric forcing still include wind responses on time scales as short as 10 minutes or less, and on length scales shorter than 100 km horizontally and 5 km vertically. The data also show that the degree of penetration of magnetospheric forcing into the lower thermospheric wind field is highly variable from day to day. Signatures of magnetospheric forcing are sometimes seen at altitudes as low as 120 km, whereas at other times the E-region does not seem to respond at all. Possible links will be explored between this variability and the day to day differences seen in the column integrated thermospheric [O]/[N2] ratio over Alaska.

Comparison of TOPEX/Poseidon Sea Level and Linear Model Results forced by Various Wind Products for the Tropical Pacific

NASA Technical Reports Server (NTRS)

Hackert, Eric C.; Busalacchi, Antonio J.

1997-01-01

The goal of this paper is to compare TOPEX/Posaidon (T/P) sea level with sea level results from linear ocean model experiments forced by several different wind products for the tropical Pacific. During the period of this study (October 1992 - October 1995), available wind products include satellite winds from the ERS-1 scatterometer product of [HALP 97] and the passive microwave analysis of SSMI winds produced using the variational analysis method (VAM) of [ATLA 91]. In addition, atmospheric GCM winds from the NCEP reanalysis [KALN 96], ECMWF analysis [ECMW94], and the Goddard EOS-1 (GEOS-1) reanalysis experiment [SCHU 93] are available for comparison. The observed ship wind analysis of FSU [STRI 92] is also included in this study. The linear model of [CANE 84] is used as a transfer function to test the quality of each of these wind products for the tropical Pacific. The various wind products are judged by comparing the wind-forced model sea level results against the T/P sea level anomalies. Correlation and RMS difference maps show how well each wind product does in reproducing the T/P sea level signal. These results are summarized in a table showing area average correlations and RMS differences. The large-scale low-frequency temporal signal is reproduced by all of the wind products, However, significant differences exist in both amplitude and phase on regional scales. In general, the model results forced by satellite winds do a better job reproducing the T/P signal (i.e. have a higher average correlation and lower RMS difference) than the results forced by atmospheric model winds.

An Evaluation of Wind Turbine Technology at Peterson Air Force Base

DTIC Science & Technology

2005-03-01

by the wind speed. Darrieus turbines are ordinarily inexpensive and are used for electricity generation and irrigation. One advantage to a...AN EVALUATION OF WIND TURBINE TECHNOLOGY...02 AN EVALUATION OF WIND TURBINE TECHNOLOGY AT PETERSON AIR FORCE BASE THESIS Presented to the Faculty Department of

Impact of Local Sensors

NASA Technical Reports Server (NTRS)

Watson, Leela R.; Bauman, William H., III

2008-01-01

Forecasters at the 45th Weather Squadron (45 WS) use observations from the Kennedy Space Center (KSC) and Cape Canaveral Air Force Station (CCAFS) wind tower network and the CCAFS (XMR) daily rawinsonde observations (RAOB) to issue and verify wind advisories and warnings for operations. These observations are also used by the National Weather Service (NWS) Spaceflight Meteorology Group (SMG) in Houston, Texas and the NWS Melbourne, Florida (NWS MLB) to initialize their locally-run mesoscale models. In addition, SMG uses these observations to support shuttle landings at the Shuttle Landing Facility (SLF). Due to impending budget cuts, some or all of the KSC/CCAFS wind towers on the east-central Florida mainland and the XMR RAOBs may be eliminated. The locations of the mainland towers and XMR RAOB site are shown in Figure I. The loss of these data may impact the forecast capability of the 45 WS, SMG and NWS MLB. The AMU was tasked to conduct an objective independent modeling study to help determine how important these observations are to the accuracy of the model output used by the forecasters. To accomplish this, the Applied Meteorology Unit (AMU) performed a sensitivity study using the Weather Research and Forecasting (WRF) model initialized with and without KSC/CCAFS wind tower and XMR RAOB data.

Synoptic forcing of wind relaxations at Pt. Conception, California

NASA Astrophysics Data System (ADS)

Fewings, Melanie R.; Washburn, Libe; Dorman, Clive E.; Gotschalk, Christopher; Lombardo, Kelly

2016-08-01

Over the California Current upwelling system in summer, the prevailing upwelling-favorable winds episodically weaken (relax) or reverse direction for a few days. Near Pt. Conception, California, the wind usually does not reverse, but wind relaxation allows poleward oceanic coastal flow with ecological consequences. To determine the offshore extent and synoptic forcing of these wind relaxations, we formed composite averages of wind stress from the QuikSCAT satellite and atmospheric pressure from the North American Regional Reanalysis (NARR) using 67 wind relaxations during summer 2000-2009. Wind relaxations at Pt. Conception are the third stage of an event sequence that repeatedly affects the west coast of North America in summer. First, 5-7 days before the wind weakens near Pt. Conception, the wind weakens or reverses off Oregon and northern California. Second, the upwelling-favorable wind intensifies along central California. Third, the wind relaxes at Pt. Conception, and the area of weakened winds extends poleward to northern California over 3-5 days. The NARR underestimates the wind stress within ˜200 km of coastal capes by a factor of 2. Wind relaxations at Pt. Conception are caused by offshore extension of the desert heat low. This synoptic forcing is related to event cycles that cause wind reversal as in Halliwell and Allen (1987) and Mass and Bond (1996), but includes weaker events. The wind relaxations extend ˜600 km offshore, similarly to the California-scale hydraulic expansion fan shaping the prevailing winds, and ˜1000 km alongshore, limited by an opposing pressure gradient force at Cape Mendocino.

(abstract) Using TOPEX/Poseidon Sea Level Observations to Test the Sensitivity of an Ocean Model to Wind Forcing

NASA Technical Reports Server (NTRS)

Fu, Lee-Lueng; Chao, Yi

1996-01-01

It has been demonstrated that current-generation global ocean general circulation models (OGCM) are able to simulate large-scale sea level variations fairly well. In this study, a GFDL/MOM-based OGCM was used to investigate its sensitivity to different wind forcing. Simulations of global sea level using wind forcing from the ERS-1 Scatterometer and the NMC operational analysis were compared to the observations made by the TOPEX/Poseidon (T/P) radar altimeter for a two-year period. The result of the study has demonstrated the sensitivity of the OGCM to the quality of wind forcing, as well as the synergistic use of two spaceborne sensors in advancing the study of wind-driven ocean dynamics.

Monitoring, modeling and mitigating impacts of wind farms on local meteorology

NASA Astrophysics Data System (ADS)

Baidya Roy, Somnath; Traiteur, Justin; Kelley, Neil

2010-05-01

Wind power is one of the fastest growing sources of energy. Most of the growth is in the industrial sector comprising of large utility-scale wind farms. Recent modeling studies have suggested that such wind farms can significantly affect local and regional weather and climate. In this work, we present observational evidence of the impact of wind farms on near-surface air temperatures. Data from perhaps the only meteorological field campaign in an operational wind farm shows that downwind temperatures are lower during the daytime and higher at night compared to the upwind environment. Corresponding radiosonde profiles at the nearby Edwards Air Force Base WMO meteorological station show that the diurnal environment is unstable while the nocturnal environment is stable during the field campaign. This behavior is consistent with the hypothesis proposed by Baidya Roy et al. (JGR 2004) that states that turbulence generated in the wake of rotors enhance vertical mixing leading to a warming/cooling under positive/negative potential temperature lapse rates. We conducted a set of 306 simulations with the Regional Atmospheric Modeling System (RAMS) to test if regional climate models can capture the thermal effects of wind farms. We represented wind turbines with a subgrid parameterization that assumes rotors to be sinks of momentum and sources of turbulence. The simulated wind farms consistently generated a localized warming/cooling under positive/negative lapse rates as hypothesized. We found that these impacts are inversely correlated with background atmospheric boundary layer turbulence. Thus, if the background turbulence is high due to natural processes, the effects of additional turbulence generated by wind turbine rotors are likely to be small. We propose the following strategies to minimize impacts of wind farms: • Engineering solution: design rotors that generate less turbulence in their wakes. Sensitivity simulations show that these turbines also increase the productivity of wind farms and reduce damages to downwind rotors. • Siting solution: develop wind farms in regions where ABL turbulence is naturally high. Since, turbulence data is not widely recorded, we use surface KE dissipation rate as a proxy for ABL turbulence. Indeed, in our simulations, these 2 parameters are strongly positively correlated (P<0.99). Using the JRA25 dataset, comprising of 25-year long 6-hourly global meteorological data, we identify such regions in the world. These regions that include the Midwest and Great Plains as well as large parts of northern Europe and western China are appropriate sites for low-impact wind farms.

Response of Ocean Circulation to Different Wind Forcing in Puerto Rico and US Virgin Islands

NASA Astrophysics Data System (ADS)

Solano, Miguel; Garcia, Edgardo; Leonardi, Stafano; Canals, Miguel; Capella, Jorge

2013-11-01

The response of the ocean circulation to various wind forcing products has been studied using the Regional Ocean Modeling System. The computational domain includes the main islands of Puerto Rico, Saint John and Saint Thomas, located on the continental shelf dividing the Caribbean Sea and the Atlantic Ocean. Data for wind forcing is provided by an anemometer located in a moored buoy, the Coupled Ocean-Atmosphere Mesoscale Prediction System (COAMPS) model and the National Digital Forecast Database (NDFD). Hindcast simulations have been validated using hydrographic data at different locations in the area of study. Three cases are compared to quantify the impact of high resolution wind forcing on the ocean circulation and the vertical structure of salinity, temperature and velocity. In the first case a constant wind velocity field is used to force the model as measured by an anemometer on top of a buoy. In the second case, a forcing field provided by the Navy's COAMPS model is used and in the third case, winds are taken from NDFD in collaboration with the National Centers for Environmental Prediction. Validated results of ocean currents against data from Acoustic Doppler Current Profilers at different locations show better agreement using high resolution wind data as expected. Thanks to CariCOOS and NOAA.

Numerical simulation of the observed near-surface East India Coastal Current on the continental slope

NASA Astrophysics Data System (ADS)

Mukherjee, A.; Shankar, D.; Chatterjee, Abhisek; Vinayachandran, P. N.

2018-06-01

We simulate the East India Coastal Current (EICC) using two numerical models (resolution 0.1° × 0.1°), an oceanic general circulation model (OGCM) called Modular Ocean Model and a simpler, linear, continuously stratified (LCS) model, and compare the simulated current with observations from moorings equipped with acoustic Doppler current profilers deployed on the continental slope in the western Bay of Bengal (BoB). We also carry out numerical experiments to analyse the processes. Both models simulate well the annual cycle of the EICC, but the performance degrades for the intra-annual and intraseasonal components. In a model-resolution experiment, both models (run at a coarser resolution of 0.25° × 0.25°) simulate well the currents in the equatorial Indian Ocean (EIO), but the performance of the high-resolution LCS model as well as the coarse-resolution OGCM, which is good in the EICC regime, degrades in the eastern and northern BoB. An experiment on forcing mechanisms shows that the annual EICC is largely forced by the local alongshore winds in the western BoB and remote forcing due to Ekman pumping over the BoB, but forcing from the EIO has a strong impact on the intra-annual EICC. At intraseasonal periods, local (equatorial) forcing dominates in the south (north) because the Kelvin wave propagates equatorward in the western BoB. A stratification experiment with the LCS model shows that changing the background stratification from EIO to BoB leads to a stronger surface EICC owing to strong coupling of higher order vertical modes with wind forcing for the BoB profiles. These high-order modes, which lead to energy propagating down into the ocean in the form of beams, are important only for the current and do not contribute significantly to the sea level.

Linking interannual variability in shelf bottom water properties to the California Undercurrent and local processes in the Pacific Northwest

NASA Astrophysics Data System (ADS)

Stone, H. B.; Banas, N. S.; Hickey, B. M.; MacCready, P.

2016-02-01

The Pacific Northwest coast is an unusually productive area with a strong river influence and highly variable upwelling-favorable and downwelling-favorable winds, but recent trends in hypoxia and ocean acidification in this region are troubling to both scientists and the general public. A new ROMS hindcast model of this region makes possible a study of interannual variability. This study of the interannual temperature and salinity variability on the Pacific Northwest coast is conducted using a coastal hindcast model (43°N - 50°N) spanning 2002-2009 from the University of Washington Coastal Modeling Group, with a resolution of 1.5 km over the shelf and slope. Analysis of hindcast model results was used to assess the relative importance of source water variability, including the poleward California Undercurrent, local and remote wind forcing, winter wind-driven mixing, and river influence in explaining the interannual variations in the shelf bottom layer (40 - 80 m depth, 10 m thick) and over the slope (150 - 250 m depth, <100 km from shelf break) at each latitude within the model domain. Characterized through tracking of the fraction of Pacific Equatorial Water (PEW) relative to Pacific Subarctic Upper Water (PSUW) present on the slope, slope water properties at all latitudes varied little throughout the time series, with the largest variability due to patterns of large north-south advection of water masses over the slope. Over the time series, the standard deviation of slope temperature was 0.09 ˚C, while slope salinity standard deviation was 0.02 psu. Results suggest that shelf bottom water interannual variability is not driven primarily by interannual variability in slope water as shelf bottom water temperature and salinity vary nearly 10 times more than those over the slope. Instead, interannual variability in shelf bottom water properties is likely driven by other processes, such as local and remote wind forcing, and winter wind-driven mixing. The relative contributions of these processes to interannual variability in shelf bottom water properties will be addressed. Overall, these results highlight the importance of shelf processes relative to large-scale influences on the interannual timescale in particular. Implications for variability in hypoxia and ocean acidification impacts will be discussed.

The numerical modeling the sensitivity of coastal wind and ozone concentration to different SST forcing

NASA Astrophysics Data System (ADS)

Choi, Hyun-Jung; Lee, Hwa Woon; Jeon, Won-Bae; Lee, Soon-Hwan

2012-01-01

This study evaluated an atmospheric and air quality model of the spatial variability in low-level coastal winds and ozone concentration, which are affected by sea surface temperature (SST) forcing with different thermal gradients. Several numerical experiments examined the effect of sea surface SST forcing on the coastal atmosphere and air quality. In this study, the RAMS-CAMx model was used to estimate the sensitivity to two different resolutions of SST forcing during the episode day as well as to simulate the low-level coastal winds and ozone concentration over a complex coastal area. The regional model reproduced the qualitative effect of SST forcing and thermal gradients on the coastal flow. The high-resolution SST derived from NGSST-O (New Generation Sea Surface Temperature Open Ocean) forcing to resolve the warm SST appeared to enhance the mean response of low-level winds to coastal regions. These wind variations have important implications for coastal air quality. A higher ozone concentration was forecasted when SST data with a high resolution was used with the appropriate limitation of temperature, regional wind circulation, vertical mixing height and nocturnal boundary layer (NBL) near coastal areas.

Modeling of the coupled magnetospheric and neutral wind dynamos

NASA Technical Reports Server (NTRS)

Thayer, Jeff P.

1993-01-01

The solar wind interaction with the earth's magnetosphere generates electric fields and currents that flow from the magnetosphere to the ionosphere at high latitudes. Consequently, the neutral atmosphere is subject to the dissipation and conversion of this electrical energy to thermal and mechanical energy through Joule heating and Lorentz forcing. As a result of the mechanical energy stored within the neutral wind (caused in part by Lorentz--and pressure gradient--forces set up by the magnetospheric flux of electrical energy), electric currents and fields can be generated in the ionosphere through the neutral wind dynamo mechanism. At high latitudes this source of electrical energy has been largely ignored in past studies, owing to the assumed dominance of the solar wind/magnetospheric dynamo as an electrical energy source to the ionosphere. However, other researchers have demonstrated that the available electrical energy provided by the neutral wind is significant at high latitudes, particularly in the midnight sector of the polar cap and in the region of the magnetospheric convection reversal. As a result, the conclusions of a number of broad ranging high-latitude investigations may be modified if the neutral-wind contribution to high-latitude electrodynamics is properly accounted for. These include the following: studies assessing solar wind-magnetospheric coupling by comparing the cross polar cap potential with solar wind parameters; research based on the alignment of particle precipitation with convection or field aligned current boundaries; and synoptic investigations attributing seasonal variations in the observed electric field and current patterns to external sources. These research topics have been initiated by satellite and ground-based observations and have been attributed to magnetospheric causes. However, the contribution of the neutral wind to the high-latitude electric field and current systems and their seasonal and local time dependence has yet to be quantitatively evaluated. In this program, we are evaluating the coupled magnetospheric and neutral wind dynamos at high latitudes under various conditions. In addition to examining the impact of seasonal variations, we are investigating the consequences of the separate dynamos having pure current-source or voltage-source behaviors.

Tidal and meteorological forcing of sediment transport in tributary mudflat channels.

PubMed

Ralston, David K; Stacey, Mark T

2007-06-01

Field observations of flow and sediment transport in a tributary channel through intertidal mudflats indicate that suspended sediment was closely linked to advection and dispersion of a tidal salinity front. During calm weather when tidal forcing was dominant, high concentrations of suspended sediment advected up the mudflat channel in the narrow region between salty water from San Francisco Bay and much fresher runoff from the small local watershed. Salinity and suspended sediment dispersed at similar rates through each tidal inundation, such that during receding ebbs the sediment pulse had spread spatially and maximum concentrations had decreased. Net sediment transport was moderately onshore during the calm weather, as asymmetries in stratification due to tidal straining of the salinity front enhanced deposition, particularly during weaker neap tidal forcing. Sediment transport by tidal forcing was periodically altered by winter storms. During storms, strong winds from the south generated wind waves and temporarily increased suspended sediment concentrations. Increased discharge down the tributary channels due to precipitation had more lasting impact on sediment transport, supplying both buoyancy and fine sediment to the system. Net sediment transport depended on the balance between calm weather tidal forcing and perturbations by episodic storms. Net transport in the tributary channel was generally off-shore during storms and during calm weather spring tides, and on-shore during calm weather neap tides.

Tidal and meteorological forcing of sediment transport in tributary mudflat channels

PubMed Central

Ralston, David K.; Stacey, Mark T.

2011-01-01

Field observations of flow and sediment transport in a tributary channel through intertidal mudflats indicate that suspended sediment was closely linked to advection and dispersion of a tidal salinity front. During calm weather when tidal forcing was dominant, high concentrations of suspended sediment advected up the mudflat channel in the narrow region between salty water from San Francisco Bay and much fresher runoff from the small local watershed. Salinity and suspended sediment dispersed at similar rates through each tidal inundation, such that during receding ebbs the sediment pulse had spread spatially and maximum concentrations had decreased. Net sediment transport was moderately onshore during the calm weather, as asymmetries in stratification due to tidal straining of the salinity front enhanced deposition, particularly during weaker neap tidal forcing. Sediment transport by tidal forcing was periodically altered by winter storms. During storms, strong winds from the south generated wind waves and temporarily increased suspended sediment concentrations. Increased discharge down the tributary channels due to precipitation had more lasting impact on sediment transport, supplying both buoyancy and fine sediment to the system. Net sediment transport depended on the balance between calm weather tidal forcing and perturbations by episodic storms. Net transport in the tributary channel was generally off-shore during storms and during calm weather spring tides, and on-shore during calm weather neap tides. PMID:21499572

A data driven model for dune morphodynamics

NASA Astrophysics Data System (ADS)

Palmsten, M.; Brodie, K.; Spore, N.

2016-12-01

Dune morphology results from a number of competing feedbacks between wave, Aeolian, and biologic processes. Only now are conceptual and numerical models for dunes beginning to incorporate all aspects of the processes driving morphodynamics. Drawing on a 35-year record of observations of dune morphology and forcing conditions at the Army Corps of Engineers Field Research Facility (FRF) at Duck, NC, USA, we hypothesize that local dune morphology results from the competition between dune growth during dry windy periods and erosion during storms. We test our hypothesis by developing a data driven model using a Bayesian network to hindcast dune-crest elevation change, dune position change, and shoreline position change. Model inputs include a description of dune morphology from dune-crest elevation, dune-base elevation, dune width, and beach width. Wave forcing and the effect of moisture is parameterized in terms of the maximum total water level and period that waves impact the dunes, along with precipitation. Aeolian forcing is parameterized in terms of maximum wind speed, direction and period that wind exceeds a critical value for sediment transport. We test the sensitivity of our model to forcing parameters and hindcast the 35-year record of dune morphodynamics at the FRF. We also discuss the role of vegetation on dune morphologic differences observed at the FRF.

Solar Wind Halo Formation by the Scattering of the Strahl via Direct Cluster/PEACE Observations of the 3D Velocity Distribution Function

NASA Technical Reports Server (NTRS)

Figueroa-Vinas, Adolfo; Gurgiolo, Chris A.; Nieves-Chinchilla, Teresa; Goldstein, Melvyn L.

2010-01-01

It has been suggested by a number of authors that the solar wind electron halo can be formed by the scattering of the strahl. On frequent occasions we have observed in electron angular skymaps (Phi/Theta-plots) of the electron 3D velocity distribution functions) a bursty-filament of particles connecting the strahl to the solar wind core-halo. These are seen over a very limited energy range. When the magnetic field is well off the nominal solar wind flow direction such filaments are inconsistent with any local forces and are probably the result of strong scattering. Furthermore, observations indicates that the strahl component is frequently and significantly anisotropic (Tper/Tpal approx.2). This provides a possible free energy source for the excitation of whistler waves as a possible scattering mechanism. The empirical observational evidence between the halo and the strahl suggests that the strahl population may be, at least in part, the source of the halo component.

Moisture convergence using satellite-derived wind fields - A severe local storm case study

NASA Technical Reports Server (NTRS)

Negri, A. J.; Vonder Haar, T. H.

1980-01-01

Five-minute interval 1-km resolution SMS visible channel data were used to derive low-level wind fields by tracking small cumulus clouds on NASA's Atmospheric and Oceanographic Information Processing System. The satellite-derived wind fields were combined with surface mixing ratios to derive horizontal moisture convergence in the prestorm environment of April 24, 1975. Storms began developing in an area extending from southwest Oklahoma to eastern Tennessee 2 h subsequent to the time of the derived fields. The maximum moisture convergence was computed to be 0.0022 g/kg per sec and areas of low-level convergence of moisture were in general indicative of regions of severe storm genesis. The resultant moisture convergence fields derived from two wind sets 20 min apart were spatially consistent and reflected the mesoscale forcing of ensuing storm development. Results are discussed with regard to possible limitations in quantifying the relationship between low-level flow and between low-level flow and satellite-derived cumulus motion in an antecedent storm environment.

Design of a magnetic force exciter for a small-scale windmill using a piezo-composite generating element

NASA Astrophysics Data System (ADS)

Luong, Hung Truyen; Goo, Nam Seo

2011-03-01

We introduce a design for a magnetic force exciter that applies vibration to a piezo-composite generating element (PCGE) for a small-scale windmill to convert wind energy into electrical energy. The windmill can be used to harvest wind energy in urban regions. The magnetic force exciter consists of exciting magnets attached to the device's input rotor, and a secondary magnet that is fixed at the tip of the PCGE. Under an applied wind force, the input rotor rotates to create a magnetic force interaction to excite the PCGE. Deformation of the PCGE enables it to generate the electric power. Experiments were performed to test power generation and battery charging capabilities. In a battery charging test, the charging time for a 40 mAh battery is approximately 1.5 hours for a wind speed of 2.5 m/s. Our experimental results show that the prototype can harvest energy in urban areas with low wind speeds, and convert the wasted wind energy into electricity for city use.

Surface wind convergence as a short-term predictor of cloud-to-ground lightning at Kennedy Space Center: A four-year summary and evaluation

NASA Technical Reports Server (NTRS)

Watson, Andrew I.; Holle, Ronald L.; Lopez, Raul E.; Nicholson, James R.

1991-01-01

Since 1986, USAF forecasters at NASA-Kennedy have had available a surface wind convergence technique for use during periods of convective development. In Florida during the summer, most of the thunderstorm development is forced by boundary layer processes. The basic premise is that the life cycle of convection is reflected in the surface wind field beneath these storms. Therefore the monitoring of the local surface divergence and/or convergence fields can be used to determine timing, location, longevity, and the lightning hazards which accompany these thunderstorms. This study evaluates four years of monitoring thunderstorm development using surface wind convergence, particularly the average over the area. Cloud-to-ground (CG) lightning is related in time and space with surface convergence for 346 days during the summers of 1987 through 1990 over the expanded wind network at KSC. The relationships are subdivided according to low level wind flow and midlevel moisture patterns. Results show a one in three chance of CG lightning when a convergence event is identified. However, when there is no convergence, the chance of CG lightning is negligible.

Production regimes in four eastern boundary current systems

NASA Technical Reports Server (NTRS)

Carr, M. E.; Kearns, E. J.

2003-01-01

High productivity (maxima 3 g C m(sup -2)day(sup -1)) of the Eastern Boundary Currents (EBCs), i.e. the California, Peru-Humboldt, Canary and Benguela Currents, is driven by a combination of local forcing and large-scale circulation. The characteristics of the deep water brought to the surface by upwelling favorable winds depend on the large-scale circulation patterns. Here we use a new hydrographic and nutrient climatology together with satellite measurements ofthe wind vector, sea-surface temperature (SST), chlorophyll concentration, and primary production modeled from ocean color to quantify the meridional and seasonal patterns of upwelling dynamics and biological response. The unprecedented combination of data sets allows us to describe objectively the variability for small regions within each current and to characterize the governing factors for biological production. The temporal and spatial environmental variability was due in most regions to large-scale circulation, alone or in combination with offshore transport (local forcing). The observed meridional and seasonal patterns of biomass and primary production were most highlycorrelated to components representing large-scale circulation. The biomass sustained by a given nutrient concentration in the Atlantic EBCs was twice as large as that of the Pacific EBCs. This apparent greater efficiency may be due toavailability of iron, physical retention, or differences in planktonic community structure.

Mechanisms of long-term mean sea level variability in the North Sea

NASA Astrophysics Data System (ADS)

Dangendorf, Sönke; Calafat, Francisco; Øie Nilsen, Jan Even; Richter, Kristin; Jensen, Jürgen

2015-04-01

We examine mean sea level (MSL) variations in the North Sea on timescales ranging from months to decades under the consideration of different forcing factors since the late 19th century. We use multiple linear regression models, which are validated for the second half of the 20th century against the output of a state-of-the-art tide+surge model (HAMSOM), to determine the barotropic response of the ocean to fluctuations in atmospheric forcing. We demonstrate that local atmospheric forcing mainly triggers MSL variability on timescales up to a few years, with the inverted barometric effect dominating the variability along the UK and Norwegian coastlines and wind (piling up the water along the coast) controlling the MSL variability in the south from Belgium up to Denmark. However, in addition to the large inter-annual sea level variability there is also a considerable fraction of decadal scale variability. We show that on decadal timescales MSL variability in the North Sea mainly reflects steric changes, which are mostly remotely forced. A spatial correlation analysis of altimetry observations and baroclinic ocean model outputs suggests evidence for a coherent signal extending from the Norwegian shelf down to the Canary Islands. This supports the theory of longshore wind forcing along the eastern boundary of the North Atlantic causing coastally trapped waves to propagate along the continental slope. With a combination of oceanographic and meteorological measurements we demonstrate that ~80% of the decadal sea level variability in the North Sea can be explained as response of the ocean to longshore wind forcing, including boundary wave propagation in the Northeast Atlantic. These findings have important implications for (i) detecting significant accelerations in North Sea MSL, (ii) the conceptual set up of regional ocean models in terms of resolution and boundary conditions, and (iii) the development of adequate and realistic regional climate change projections.

Study of ionospheric anomalies due to impact of typhoon using Principal Component Analysis and image processing

NASA Astrophysics Data System (ADS)

LIN, JYH-WOEI

2012-08-01

Principal Component Analysis (PCA) and image processing are used to determine Total Electron Content (TEC) anomalies in the F-layer of the ionosphere relating to Typhoon Nakri for 29 May, 2008 (UTC). PCA and image processing are applied to the global ionospheric map (GIM) with transforms conducted for the time period 12:00-14:00 UT on 29 May, 2008 when the wind was most intense. Results show that at a height of approximately 150-200 km the TEC anomaly is highly localized; however, it becomes more intense and widespread with height. Potential causes of these results are discussed with emphasis given to acoustic gravity waves caused by wind force.

Measuring Tree Properties and Responses Using Low-Cost Accelerometers

DOE PAGES

van Emmerik, Tim; Steele-Dunne, Susan; Hut, Rolf; ...

2017-05-11

Trees play a crucial role in the water, carbon and nitrogen cycle on local, regional and global scales. Understanding the exchange of momentum, heat, water, and CO 2 between trees and the atmosphere is important to assess the impact of drought, deforestation and climate change. Unfortunately, ground measurements of tree properties such as mass and canopy interception of precipitation are often expensive or difficult due to challenging environments. This paper aims to demonstrate the concept of using robust and affordable accelerometers to measure tree properties and responses. Tree sway is dependent on mass, canopy structure, drag coefficient, and wind forcing.more » By measuring tree acceleration, we can relate the tree motion to external forcing (e.g., wind, precipitation and related canopy interception) and tree physical properties (e.g., mass, elasticity). Using five months of acceleration data of 19 trees in the Brazilian Amazon, we show that the frequency spectrum of tree sway is related to mass, canopy interception of precipitation, and canopy–atmosphere turbulent exchange.« less

Measuring Tree Properties and Responses Using Low-Cost Accelerometers

DOE Office of Scientific and Technical Information (OSTI.GOV)

van Emmerik, Tim; Steele-Dunne, Susan; Hut, Rolf

Trees play a crucial role in the water, carbon and nitrogen cycle on local, regional and global scales. Understanding the exchange of momentum, heat, water, and CO 2 between trees and the atmosphere is important to assess the impact of drought, deforestation and climate change. Unfortunately, ground measurements of tree properties such as mass and canopy interception of precipitation are often expensive or difficult due to challenging environments. This paper aims to demonstrate the concept of using robust and affordable accelerometers to measure tree properties and responses. Tree sway is dependent on mass, canopy structure, drag coefficient, and wind forcing.more » By measuring tree acceleration, we can relate the tree motion to external forcing (e.g., wind, precipitation and related canopy interception) and tree physical properties (e.g., mass, elasticity). Using five months of acceleration data of 19 trees in the Brazilian Amazon, we show that the frequency spectrum of tree sway is related to mass, canopy interception of precipitation, and canopy–atmosphere turbulent exchange.« less

The role of forcing agents on biogeochemical variability along the southwestern Adriatic coast: The Gulf of Manfredonia case study

NASA Astrophysics Data System (ADS)

Specchiulli, Antonietta; Bignami, Francesco; Marini, Mauro; Fabbrocini, Adele; Scirocco, Tommaso; Campanelli, Alessandra; Penna, Pierluigi; Santucci, Angela; D'Adamo, Raffaele

2016-12-01

This study investigates how multiple forcing factors such as rivers, surface marine circulation and winds affect hydrology and biogeochemical processes in the Gulf of Manfredonia and the seas around the Gargano peninsula, in the south-western Adriatic Sea. The study adopted an integrated approach, using in situ and remote sensing data, as well as the output of current models. The data reveal variability in the area's hydrography induced by local freshwater sources, the Western Adriatic Current (WAC) flowing from the north along the Italian coast, and the current patterns under different wind regimes. Specifically, exchange with offshore waters in the gulf induces variability in salinity and biogeochemical content, even within the same season, i.e. winter, in our case. This strong dependence on physical and biogeochemical factors makes the Manfredonia-Gargano ecosystem vulnerable to climate change, which could compromise its important role as a nursery area for the Adriatic Sea.

Measuring Tree Properties and Responses Using Low-Cost Accelerometers

PubMed Central

van Emmerik, Tim; Steele-Dunne, Susan; Hut, Rolf; Gentine, Pierre; Guerin, Marceau; Oliveira, Rafael S.; Wagner, Jim; Selker, John; van de Giesen, Nick

2017-01-01

Trees play a crucial role in the water, carbon and nitrogen cycle on local, regional and global scales. Understanding the exchange of momentum, heat, water, and CO2 between trees and the atmosphere is important to assess the impact of drought, deforestation and climate change. Unfortunately, ground measurements of tree properties such as mass and canopy interception of precipitation are often expensive or difficult due to challenging environments. This paper aims to demonstrate the concept of using robust and affordable accelerometers to measure tree properties and responses. Tree sway is dependent on mass, canopy structure, drag coefficient, and wind forcing. By measuring tree acceleration, we can relate the tree motion to external forcing (e.g., wind, precipitation and related canopy interception) and tree physical properties (e.g., mass, elasticity). Using five months of acceleration data of 19 trees in the Brazilian Amazon, we show that the frequency spectrum of tree sway is related to mass, canopy interception of precipitation, and canopy–atmosphere turbulent exchange. PMID:28492477

Material transport in a wind and buoyancy forced mixed layer

NASA Astrophysics Data System (ADS)

Mensa, J. A.; Özgökmen, T.; Poje, A. C.; Imberger, J.

2016-02-01

Flows in the upper ocean mixed layer are responsible for the transport and dispersion of biogeochemical tracers, phytoplankton and buoyant pollutants, such as hydrocarbons from an oil spill. Material dispersion in mixed layer flows subject to diurnal buoyancy forcing and weak winds (|u10|=5ms-1) are investigated using a non-hydrostatic model. Both purely buoyancy-forced and combined wind- and buoyancy-forced flows are sampled using passive tracers, as well as 2D and 3D particles to explore characteristics of horizontal and vertical dispersion. It is found that the surface tracer patterns are determined by the convergence zones created by convection cells within a time scale of just a few hours. For pure convection, the results displayed the classic signature of Rayleigh-Benard cells. When combined with a wind stress, the convective cells become anisotropic in that the along-wind length scale gets much larger than the cross-wind scale. Horizontal relative dispersion computed by sampling the flow fields using both 2D and 3D passive particles is found to be consistent with the Richardson regime. Relative dispersion is an order of magnitude higher and 2D surface releases transition to Richardson regime faster in the wind-forced case. We also show that the buoyancy-forced case results in significantly lower amplitudes of scale-dependent horizontal relative diffusivity, kD(l), than those reported by Okubo (1970), while the wind- and buoyancy forced case shows a good agreement with Okubo's diffusivity amplitude, and scaling consistent with Richardson's 4/3rd law, kD(l) l4/3. The modelling results provide a framework for measuring material dispersion by mixed layer flow in future observational programs.

Material transport in a convective surface mixed layer under weak wind forcing

NASA Astrophysics Data System (ADS)

Mensa, Jean A.; Özgökmen, Tamay M.; Poje, Andrew C.; Imberger, Jörg

2015-12-01

Flows in the upper ocean mixed layer are responsible for the transport and dispersion of biogeochemical tracers, phytoplankton and buoyant pollutants, such as hydrocarbons from an oil spill. Material dispersion in mixed layer flows subject to diurnal buoyancy forcing and weak winds (| u10 | = 5m s-1) are investigated using a non-hydrostatic model. Both purely buoyancy-forced and combined wind- and buoyancy-forced flows are sampled using passive tracers, as well as 2D and 3D particles to explore characteristics of horizontal and vertical dispersion. It is found that the surface tracer patterns are determined by the convergence zones created by convection cells within a time scale of just a few hours. For pure convection, the results displayed the classic signature of Rayleigh-Benard cells. When combined with a wind stress, the convective cells become anisotropic in that the along-wind length scale gets much larger than the cross-wind scale. Horizontal relative dispersion computed by sampling the flow fields using both 2D and 3D passive particles is found to be consistent with the Richardson regime. Relative dispersion is an order of magnitude higher and 2D surface releases transition to Richardson regime faster in the wind-forced case. We also show that the buoyancy-forced case results in significantly lower amplitudes of scale-dependent horizontal relative diffusivity, kD(ℓ), than those reported by Okubo (1970), while the wind- and buoyancy-forced case shows a good agreement with Okubo's diffusivity amplitude, and the scaling is consistent with Richardson's 4/3rd law, kD ∼ ℓ4/3. These modeling results provide a framework for measuring material dispersion by mixed layer flows in future observational programs.

Dispersion of conservative properties for SGD effects by numerical modeling

NASA Astrophysics Data System (ADS)

Gallegos, G.; Marino-Tapia, I.; Enriquez, C.

2013-05-01

The submarine groundwater discharges around de coasts of theYucatán Peninsula are very common because of its karstic nature. These discharges of fresh water into the sea can change the thermohaline conditions of the region. There are several studies that demonstrate that point submarine groundwater discharges can change the superficial temperature and haline conditions near the point-SGD. Furthermore, there is evidence that considerable concentrations of nutrients are transported to the sea via SGDs. In order to quantify the area of influence of a point-SGD and the ability of the coastal system to dissipate the ground water, this study presents a numerical simulation of a point-SGD on the north coast of Yucatán, Dzilam Bravo. Teh flow recorded for this SGD is ~1m^3/s and it is located 200m offshore in waters of less than 2m detph.. The numerical simulation was carried out in the model DELFT-3D which has been calibrated with water level and hydrodynamics data for the region with a grid of 486 x 243 nodes that cover an area of 6 km alongshore by 2 km crosshore with a resolution of 14 m. Three ideal numerical scenarios were simulated: only wind forcing, only tidal forcing and wind-tide forcing. The real cases are for two different wind conditions, the first is a southeast wind, and the second is a breeze with an easterly component; the dominant winds in the region are easterly. Seasonal variation was also simulated; the two conditions that exist in the region are the rainy and dry seasons. The extreme events of ENSO and northerly storms locally known as "nortes" were also simulated. The results of the ideal set of scenarios shows wind as the principal forcing for dispersion and it governs the direction of the salinity gradient. The seasonal variations show that the area of influence in terms of salinity is also a function of the contrast between fresh and sea water, and finally the set of extreme condition simulations shows, in case of the northerly storms, that the wind pushes the flow of low salinity towards the coast and can even reverse the normal eastwards water circulation of the region. The lack of contrast in salinity between the two water masses during the ENSO event shows the importance of including other variables to trace these discharges. One of the questions behind this work is to explain the red tide when the coastal system is not able to dissipate the input of nutrients by groundwater discharge in the coastal system.

Wind Turbine Wakes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kelley, Christopher Lee; Maniaci, David Charles; Resor, Brian R.

2015-10-01

The total energy produced by a wind farm depends on the complex interaction of many wind turbines operating in proximity with the turbulent atmosphere. Sometimes, the unsteady forces associated with wind negatively influence power production, causing damage and increasing the cost of producing energy associated with wind power. Wakes and the motion of air generated by rotating blades need to be better understood. Predicting wakes and other wind forces could lead to more effective wind turbine designs and farm layouts, thereby reducing the cost of energy, allowing the United States to increase the installed capacity of wind energy. The Windmore » Energy Technologies Department at Sandia has collaborated with the University of Minnesota to simulate the interaction of multiple wind turbines. By combining the validated, large-eddy simulation code with Sandia’s HPC capability, this consortium has improved its ability to predict unsteady forces and the electrical power generated by an array of wind turbines. The array of wind turbines simulated were specifically those at the Sandia Scaled Wind Farm Testbed (SWiFT) site which aided the design of new wind turbine blades being manufactured as part of the National Rotor Testbed project with the Department of Energy.« less

Ocean Wave Simulation Based on Wind Field

PubMed Central

2016-01-01

Ocean wave simulation has a wide range of applications in movies, video games and training systems. Wind force is the main energy resource for generating ocean waves, which are the result of the interaction between wind and the ocean surface. While numerous methods to handle simulating oceans and other fluid phenomena have undergone rapid development during the past years in the field of computer graphic, few of them consider to construct ocean surface height field from the perspective of wind force driving ocean waves. We introduce wind force to the construction of the ocean surface height field through applying wind field data and wind-driven wave particles. Continual and realistic ocean waves result from the overlap of wind-driven wave particles, and a strategy was proposed to control these discrete wave particles and simulate an endless ocean surface. The results showed that the new method is capable of obtaining a realistic ocean scene under the influence of wind fields at real time rates. PMID:26808718

Ocean Wave Simulation Based on Wind Field.

PubMed

Li, Zhongyi; Wang, Hao

2016-01-01

Ocean wave simulation has a wide range of applications in movies, video games and training systems. Wind force is the main energy resource for generating ocean waves, which are the result of the interaction between wind and the ocean surface. While numerous methods to handle simulating oceans and other fluid phenomena have undergone rapid development during the past years in the field of computer graphic, few of them consider to construct ocean surface height field from the perspective of wind force driving ocean waves. We introduce wind force to the construction of the ocean surface height field through applying wind field data and wind-driven wave particles. Continual and realistic ocean waves result from the overlap of wind-driven wave particles, and a strategy was proposed to control these discrete wave particles and simulate an endless ocean surface. The results showed that the new method is capable of obtaining a realistic ocean scene under the influence of wind fields at real time rates.

Improving Energy Security for Air Force Installations

DTIC Science & Technology

2015-09-01

Wind power is a mature technology, with wind turbines first being used for electricity in the late 19th century. The Air Force operates two wind ...company, and the military unit receives energy credits back on its bill. Two concepts are important when considering the turbine size for a wind ...generation and consumption must remain balanced for a grid, so wind turbines are rarely used as a sole energy source since power is only generated

Ski jumping takeoff in a wind tunnel with skis.

PubMed

Virmavirta, Mikko; Kivekäs, Juha; Komi, Paavo

2011-11-01

The effect of skis on the force-time characteristics of the simulated ski jumping takeoff was examined in a wind tunnel. Takeoff forces were recorded with a force plate installed under the tunnel floor. Signals from the front and rear parts of the force plate were collected separately to examine the anteroposterior balance of the jumpers during the takeoff. Two ski jumpers performed simulated takeoffs, first without skis in nonwind conditions and in various wind conditions. Thereafter, the same experiments were repeated with skis. The jumpers were able to perform very natural takeoff actions (similar to the actual takeoff) with skis in wind tunnel. According to the subjective feeling of the jumpers, the simulated ski jumping takeoff with skis was even easier to perform than the earlier trials without skis. Skis did not much influence the force levels produced during the takeoff but they still changed the force distribution under the feet. Contribution of the forces produced under the rear part of the feet was emphasized probably because the strong dorsiflexion is needed for lifting the skis to the proper flight position. The results presented in this experiment emphasize that research on ski jumping takeoff can be advanced by using wind tunnels.

On the analysis of an extreme Bora wind event over the northern Adriatic Sea

NASA Astrophysics Data System (ADS)

Colucci, R. R.; Pucillo, A.

2010-09-01

On 10th March 2010 a severe Bora wind event affected the Friuli Venezia Giulia region, northeastern Italy, in particular the gulf of Trieste area (northern Adriatic Sea). Such event has been driven by a widespread westward moving cold pool aloft, coming from the Western Asia, that brought an intense potential vorticity anomaly over the western Mediterranean Sea. It determined a deep cyclogenesis involving all the troposphere. The pressure gradient force in the lowest layers forced a northeastern wind to blow with noticeable strength over the gulf of Trieste area and the Karstic region. The mean ground wind velocity has reached values above 27 m/s (about 100 km/h) for several hours, and maximum gusts exceeded 42 m/s (about 150 km/h) over Trieste town. The northeastern sector of the Adriatic Sea is frequently affected by strong Bora events in particular during the winter semester. This is a characteristic local wind mostly influenced by the orography of the Karstic relieves to the east of Trieste town. The target of this work is to assess the climatological relevance of such an event by comparing it with the most representative events of the past. It has been possible thanks to the long term archive of meteorological observations in Trieste site (I.R. Accademia di Commercio e Nautica, Regio Comitato Talassografico Italiano, Ministero dell'Agricoltura e Foreste, Consiglio Nazionale delle Ricerche): we have found out that this is one of the ten strongest Bora event along the 1871-2010 period. Considerations about the trend and frequency of severe Bora events have been proposed.

Subtidal circulation on the Alabama shelf during the Deepwater Horizon oil spill

NASA Astrophysics Data System (ADS)

Dzwonkowski, Brian; Park, Kyeong

2012-03-01

Water column velocity and hydrographic measurements on the inner Alabama shelf are used to examine the flow field and its forcing dynamics during the Deepwater Horizon oil spill disaster in the spring and summer of 2010. Comparison between two sites provides insight into the flow variability and dynamics of a shallow, highly stratified shelf in the presence of complicating geographic and bathymetric features. Seasonal currents reveal a convergent flow with strong, highly sheared offshore flow near a submarine bank just outside of Mobile Bay. At synoptic time scales, the flow is relatively consistent with typical characteristics of wind-driven Ekman coastal circulation. Analysis of the depth-averaged along-shelf momentum balance indicates that both bottom stress and along-shelf pressure gradient act to counter wind stress. As a consequence of the along-shelf pressure gradient and thermal wind shear, flow reversals in the bottom currents can occur during periods of transitional winds. Despite the relatively short distance between the two sites (14 km), significant spatial variability is observed. This spatial variability is argued to be a result of local variations in the bathymetry and density field as the study region encompasses a submarine bank near the mouth of a major freshwater source. Given the physical parameters of the system, along-shelf flow in this region would be expected to separate from the local isobaths, generating a mean offshore flow. The local, highly variable density field is expected to be, in part, responsible for the differences in the vertical variability in the current profiles.

Intraseasonal-to-semiannual variability of sea-surface height in the eastern, equatorial Indian Ocean and southern Bay of Bengal

NASA Astrophysics Data System (ADS)

Cheng, X.; McCreary, J. P., Jr.; Qiu, B.; Yu, Z.; DU, Y.

2016-12-01

Intraseasonal-to-semiannual variability of sea-surface height (SSH) in the eastern, equatorial Indian Ocean (EEIO) and southern Bay of Bengal (BoB) is investigated using altimetric data, and solutions to 1½-layer (first-baroclinic-mode) and linear, continuously stratified (LCS; multi-baroclinic-mode) models. The amplitude and dominant period of SSH variability differ regionally. Large-amplitude variability is found along the west coast of Sumatra, in a zonal band across the BoB centered along 5°N, east of Sri Lanka, and in the northwestern BoB. Along the Sumatran west coast, SSH variability peaks at 30-60 days, 90 days, and 180 days. Along 5°N and east of Sri Lanka, 30-60-day variability is dominant. Sensitivity experiments using a nonlinear version of the 1½-layer model forced by realistic winds reproduce the observed patterns of intraseasonal variability in the southern BoB. At 30-60 days, the solutions show that eddies (nonlinear Rossby waves) propagating from the east, rather than local wind forcing, account for most of the variance east of Sri Lanka; furthermore, they demonstrate that the variance is significantly enhance by the nonlinear transfer of 90-120-day energy into the intraseasonal band. The LCS solutions show that the first two baroclinic modes explain most of the SSH variance at 90-180 days. The second-baroclinic-mode dominates the SSH variance at 180 days, a consequence of basin resonance and strong wind forcing.

Temporal variability of marine debris deposition at Tern Island in the Northwestern Hawaiian Islands.

PubMed

Agustin, Alyssa E; Merrifield, Mark A; Potemra, James T; Morishige, Carey

2015-12-15

A twenty-two year record of marine debris collected on Tern Island is used to characterize the temporal variability of debris deposition at a coral atoll in the Northwestern Hawaiian Islands. Debris deposition tends to be episodic, without a significant relationship to local forcing processes associated with winds, sea level, waves, and proximity to the Subtropical Convergence Zone. The General NOAA Operational Modeling Environment is used to estimate likely debris pathways for Tern Island. The majority of modeled arrivals come from the northeast following prevailing trade winds and surface currents, with trajectories indicating the importance of the convergence zone, or garbage patch, in the North Pacific High region. Although debris deposition does not generally exhibit a significant seasonal cycle, some debris types contain considerable 3 cycle/yr variability that is coherent with wind and surface pressure over a broad region north of Tern. Copyright © 2015 Elsevier Ltd. All rights reserved.

Thermal and Pressure Characterization of a Wind Tunnel Force Balance Using the Single Vector System. Experimental Design and Analysis Approach to Model Pressure and Temperature Effects in Hypersonic Wind Tunnel Research

NASA Technical Reports Server (NTRS)

Lynn, Keith C.; Commo, Sean A.; Johnson, Thomas H.; Parker, Peter A,

2011-01-01

Wind tunnel research at NASA Langley Research Center s 31-inch Mach 10 hypersonic facility utilized a 5-component force balance, which provided a pressurized flow-thru capability to the test article. The goal of the research was to determine the interaction effects between the free-stream flow and the exit flow from the reaction control system on the Mars Science Laboratory aeroshell during planetary entry. In the wind tunnel, the balance was exposed to aerodynamic forces and moments, steady-state and transient thermal gradients, and various internal balance cavity pressures. Historically, these effects on force measurement accuracy have not been fully characterized due to limitations in the calibration apparatus. A statistically designed experiment was developed to adequately characterize the behavior of the balance over the expected wind tunnel operating ranges (forces/moments, temperatures, and pressures). The experimental design was based on a Taylor-series expansion in the seven factors for the mathematical models. Model inversion was required to calculate the aerodynamic forces and moments as a function of the strain-gage readings. Details regarding transducer on-board compensation techniques, experimental design development, mathematical modeling, and wind tunnel data reduction are included in this paper.

The dynamics of İzmir Bay under the effects of wind and thermohaline forces

NASA Astrophysics Data System (ADS)

Sayın, Erdem; Eronat, Canan

2018-04-01

The dominant circulation pattern of İzmir Bay on the Aegean Sea coast of Turkey is studied taking into consideration the influence of wind and thermohaline forces. İzmir Bay is discussed by subdividing the bay into outer, middle and inner areas. Wind is the most important driving force in the İzmir coastal area. There are also thermohaline forces due to the existence of water types of different physical properties in the bay. In contrast to the two-layer stratification during summer, a homogeneous water column exists in winter. The free surface version of the Princeton model (Killworth's 3-D general circulation model) is applied, with the input data obtained through the measurements made by the research vessel K. Piri Reis. As a result of the simulations with artificial wind, the strong consistent wind generates circulation patterns independent of the seasonal stratification in the bay. Wind-driven circulation causes cyclonic or anticyclonic movements in the middle bay where the distinct İzmir Bay Water (IBW) forms. Cyclonic movement takes place under the influence of southerly and westerly winds. On the other hand, northerly and easterly winds cause an anticyclonic movement in the middle bay. The outer and inner bay also have the wind-driven recirculation patterns expected.

The effect of wind on the dispersal of a tropical small river plume

NASA Astrophysics Data System (ADS)

Zhao, Junpeng; Gong, Wenping; Shen, Jian

2018-03-01

Wanquan River is a small river located in Hainan, a tropical island in China. As the third largest river in Hainan, the river plume plays an important role in the regional terrigenous mass transport, coastal circulation, and the coral reef's ecosystem. Studies have shown that wind forcings significantly influence river plume dynamics. In this study, wind effects on the dispersal of the river plume and freshwater transport were examined numerically using a calibrated, unstructured, finite volume numerical model (FVCOM). Both wind direction and magnitude were determined to influence plume dispersal. Northeasterly (downwelling-favorable) winds drove freshwater down-shelf while southeasterly (onshore) winds drove water up-shelf (in the sense of Kelvin wave propagation), and were confined near the coast. Southwesterly (upwelling-favorable) and north-westerly (offshore) winds transport more freshwater offshore. The transport flux is decomposed into an advection, a vertical shear, and an oscillatory component. The advection flux dominates the freshwater transport in the coastal area and the vertical shear flux is dominant in the offshore area. For the upwelling-favorable wind, the freshwater transport becomes more controlled by the advection transport with an increase in wind stress, due to enhanced vertical mixing. The relative importance of wind forcing and buoyancy force was investigated. It was found that, when the Wedderburn number is larger than one, the plume was dominated by wind forcing, although the importance of wind varies in different parts of the plume. The water column stratification decreased as a whole under the prevailing southwesterly wind, with the exception of the up-shelf and offshore areas.

Numerical Investigation of the Turbulent Wind Flow Through Elevated Windbreak

NASA Astrophysics Data System (ADS)

Agarwal, Ashish; Irtaza, Hassan

2018-06-01

Analysis of airflow through elevated windbreaks is presented in this paper. Permeable nets and impermeable film increases considerable wind forces on the windbreaks which is susceptible to damage during high wind. A comprehensive numerical investigation has been carried out to analyze the effects of wind on standalone elevated windbreak clad with various permeable nets and an impermeable film. The variation of airflow behavior around and through permeable nets and airflow behavior around impermeable film were also been investigated. Computational fluid dynamics techniques using Reynolds Averaged Navier-Stokes equations has been used to predict the wind force coefficient and thus wind forces on panels supporting permeable nets and impermeable film for turbulent wind flow. Elevated windbreak panels were analyzed for seven different permeable nets having various solidity ratio, specific permeability and aerodynamic resistant coefficients. The permeable nets were modelled as porous jump media obeying Forchheimer's law and an impermeable film modelled as rigid wall.

Numerical Investigation of the Turbulent Wind Flow Through Elevated Windbreak

NASA Astrophysics Data System (ADS)

Agarwal, Ashish; Irtaza, Hassan

2018-04-01

Analysis of airflow through elevated windbreaks is presented in this paper. Permeable nets and impermeable film increases considerable wind forces on the windbreaks which is susceptible to damage during high wind. A comprehensive numerical investigation has been carried out to analyze the effects of wind on standalone elevated windbreak clad with various permeable nets and an impermeable film. The variation of airflow behavior around and through permeable nets and airflow behavior around impermeable film were also been investigated. Computational fluid dynamics techniques using Reynolds Averaged Navier-Stokes equations has been used to predict the wind force coefficient and thus wind forces on panels supporting permeable nets and impermeable film for turbulent wind flow. Elevated windbreak panels were analyzed for seven different permeable nets having various solidity ratio, specific permeability and aerodynamic resistant coefficients. The permeable nets were modelled as porous jump media obeying Forchheimer's law and an impermeable film modelled as rigid wall.

Circulation patterns and wave climate along the coast of the Iberian Peninsula

NASA Astrophysics Data System (ADS)

Rasilla Álvarez, D.; García Codrán, J. C.

2010-09-01

Evidences of an active erosion (beach retreat, falling cliffs, damaged infrastructures) are observed in many coastal areas around the Iberian Peninsula. Morphogenetic coastal processes result from individual episodes of storminess that can accelerate or mitigate the expected impacts of the global rising trend of average sea levels. Thus, a good understanding of the local forcing processes is required in order to assess the impacts of future sea levels. The spatial and temporal variability of the wave climate along the cost of the Iberian Peninsula and their relationships with regional scale circulation patterns and local-scale winds are the main objectives of this contribution. The oceanographic data set consists of observed hourly data from 7 buoys disseminated along the Spanish coastline, and hindcasted 3-hourly analogous parameters (SIMAR 44 database), provided by Puertos del Estado. Sea level pressure, surface 10m U and V wind components gridded data were obtained from NCEP Reanalysis, while storm tracks and cyclone statistics were extracted from the CDC Map Room Climate Products Storm Track Data (http://www.cdc.noaa.gov/map/clim/st_data.html). The influence of the local conditions was highlighted comparing meteorological data from the buoys and synop reports from coastal stations. To explore the regional atmospheric mechanisms responsible for the wave variability, a regional Eulerian approach (a synoptic typing) were combined with a larger-scale Lagrangian method, based on the analysis of storm-tracks over the area. The synoptic catalogue was obtained following a well-known procedure that combines Principal Component Analysis (PCA) for reduction purposes and clustering (Ward plus K-means) to define the circulation types. As expected, rougher wave climate are observed along the northern and western coast of the Iberian Peninsula, open to the Atlantic storms. The Mediterranean shorelines experiences calmer conditions, although the Gulf of Lions, Catalonian coast and Balearic Islands suffer stormier episodes than Mar de Alborán. Moderate wave power conditions occurred frequently by circulation patterns predominately stable and characterized by weak (mostly sea breezes) winds. Synoptic situations dominated by extra-tropical cyclones produced the highest, but least frequent wave power conditions. Depending on the location of the shorelines, three types of storm events are defined: 1. Long winds fetch and locally strong westerly and northwesterly winds expose the northern coast of Iberia to episodes of intense storminess. Extratropical disturbances tracking between the 50-60°N parallels are the main forcing mechanism of those episodes, many of them result of a cyclogenesis processes along the eastern coast of North America. In some cases, the systems evolves as a secondary cyclon, crossing the area southward of the 50°N parallel; significant wave heights can be as high as the northernmost cyclones, but the wave period is slightly lower. 2.Cyclones tracking along the 40°N parallel bring stormy conditions to the western coast and the Gulf of Cádiz area, associated to southwesterly winds. 3. Finally, the Mediterranean shoreline suffer the worst conditions during easterly and northeasterly wind events, usually dominanted by local disturbances formed along the Western Mediterranean basin. Trends observed on the different circulation patterns can explain the temporal evolution of the wave climate along the Spanish coast, characterized by calmer conditions on the south and an increase of the wave period on the north, without discernible wave height trend. The overall results indicated that this synoptic climatological approach provides a viable framework to establish and examine links between weather systems and wave conditions.

A Numerical Study on the Influence of the Mid-Atlantic Ridge on Nonlinear Barotropic and First-Mode Baroclinic Rossby Waves Generated by Seasonal Winds.

DTIC Science & Technology

1986-12-01

ridge. Sponge layers protect all boundaries except the eastern one from wave reflexion. The model is forced by a purely fluctuating wind stress curl...which propagate westward. This is a new feature of the time- dependent wind driven ocean circulation. Barnier uses a wind stress curl field patterned...forced by a purely fluctuating wind stress curl derived from the most significant EOF’s of the FGGE winds. A flat bottom and a ridge experiment are

Modelling study of sea breezes in a complex coastal environment

NASA Astrophysics Data System (ADS)

Cai, X.-M.; Steyn, D. G.

This study investigates a mesoscale modelling of sea breezes blowing from a narrow strait into the lower Fraser valley (LFV), British Columbia, Canada, during the period of 17-20 July, 1985. Without a nudging scheme in the inner grid, the CSU-RAMS model produces satisfactory wind and temperature fields during the daytime. In comparison with observation, the agreement indices for surface wind and temperature during daytime reach about 0.6 and 0.95, respectively, while the agreement indices drop to 0.4 at night. In the vertical, profiles of modelled wind and temperature generally agree with tethersonde data collected on 17 and 19 July. The study demonstrates that in late afternoon, the model does not capture the advection of an elevated warm layer which originated from land surfaces outside of the inner grid. Mixed layer depth (MLD) is calculated from model output of turbulent kinetic energy field. Comparison of MLD results with observation shows that the method generates a reliable MLD during the daytime, and that accurate estimates of MLD near the coast require the correct simulation of wind conditions over the sea. The study has shown that for a complex coast environment like the LFV, a reliable modelling study depends not only on local surface fluxes but also on elevated layers transported from remote land surfaces. This dependence is especially important when local forcings are weak, for example, during late afternoon and at night.

The role of external forcing and Pacific trade winds in recent changes of the global climate system

NASA Astrophysics Data System (ADS)

Friedman, Andrew; Gastineau, Guillaume; Khodri, Myriam

2017-04-01

The Pacific trade winds experienced an unprecedented strengthening since the mid 1990s. Several studies have proposed that the increased Pacific trade winds were associated with the reduced rate of global mean surface temperature warming in the first decade of the 21st century, as well as far-reaching atmospheric teleconnections. We designed a set of ensemble partial coupling experiments using the IPSL-CM5A-LR coupled model that allow us to cleanly distinguish the influence of Pacific trade wind variability from that of external forcing over the past few decades. In this study, we quantify the respective impacts of these processes on surface temperature, ocean heat content, and atmospheric teleconnections. We designed two ensembles of coupled simulations using partial coupling with the IPSL-CM5A-LR model to separate the Pacific internal variability and that of external radiative forcing. We prescribe surface wind stress in the tropical Pacific (20°S to 20°N) from 1979-2014 in two ensembles of 30 members each: (1) Prescribed climatological model wind stress, which allows us to estimate the influence of external radiative forcing in the absence of variability within the Pacific Ocean. (2) Wind stress anomalies from ERA-Interim reanalysis added to the model wind stress climatology, which accounts for the effects of both external radiative forcing and the wind stress variability. We find that the observed wind stress anomalies account for the pattern of eastern tropical Pacific cooling when compared to the climatology experiment, so that it resembles the observed trends from 1992-2011. The tropical Pacific shows dominant heat uptake in the western Pacific above the 20°C isotherm, which contributed to slow the warming of tropical SST during the 2000s. The trade wind increase is associated with a strengthening of the Pacific Walker circulation, and zonal shifts in tropical rainfall. Despite tropical SST biases which affect the response of tropical rainfall and the location of deep convection, the wind stress anomaly forcing effectively simulates the wave train pattern emanating from the tropical Pacific, and associated extratropical teleconnections such as a weakening of the Aleutian Low and drought in North America.

Three Dimensional Dynamics of Freshwater Lenses in the Oceans Near Surface Layer

DTIC Science & Technology

2016-09-14

a third new front appeared…” However, this striking effect was observed only when the following con- ditions for the Froude number (Fr) and the... Coriolis forces and, strictly speaking, is valid only for the equatorial region. CONCLUSIONS Convective rains within the ITCZ pro- duce localized...freshwater plumes under the influence of both ambient stratification and wind stress and how they interact to affect plume dynam- ics. The Coriolis

Ice Load Project Final Technical Report

DOE Office of Scientific and Technical Information (OSTI.GOV)

McCoy, Timothy J.; Brown, Thomas; Byrne, Alex

As interest and investment in offshore wind projects increase worldwide, some turbines will be installed in locations where ice of significant thickness forms on the water surface. This ice moves under the driving forces of wind, current, and thermal effects and may result in substantial forces on bottom-fixed support structures. The North and Baltic Seas in Europe have begun to see significant wind energy development and the Great Lakes of the United States and Canada may host wind energy development in the near future. Design of the support structures for these projects is best performed through the use of anmore » integrated tool that can calculate the cumulative effects of forces due to turbine operations, wind, waves, and floating ice. The dynamic nature of ice forces requires that these forces be included in the design simulations, rather than added as static forces to simulation results. The International Electrotechnical Commission (IEC) standard[2] for offshore wind turbine design and the International Organization for Standardization (ISO) standard[3] for offshore structures provide requirements and algorithms for the calculation of forces induced by surface ice; however, currently none of the major wind turbine dynamic simulation codes provides the ability to model ice loads. The scope of work of the project described in this report includes the development of a suite of subroutines, collectively named IceFloe, that meet the requirements of the IEC and ISO standards and couples with four of the major wind turbine dynamic simulation codes. The mechanisms by which ice forces impinge on offshore structures generally include the forces required for crushing of the ice against vertical-sided structures and the forces required to fracture the ice as it rides up on conical-sided structures. Within these two broad categories, the dynamic character of the forces with respect to time is also dependent on other factors such as the velocity and thickness of the moving ice and the response of the structure. In some cases, the dynamic effects are random and in other cases they are deterministic, such as the effect of structural resonance and coupling of the ice forces with the defection of the support structure. The initial versions of the IceFloe routines incorporate modules that address these varied force and dynamic phenomena with seven alternative algorithms that can be specified by the user. The IceFloe routines have been linked and tested with four major wind turbine aeroelastic simulation codes: FAST, a tool developed under the management of the National Renewable Energy Laboratory (NREL) and available free of charge from its web site; Bladed[4], a widely-used commercial package available from DNV GL; ADAMS[5], a general purpose multi-body simulation code used in the wind industry and available from MSC Software; and HAWC2[6], a code developed by and available for purchase from Danmarks Tekniske Universitet (DTU). Interface routines have been developed and tested with full wind turbine simulations for each of these codes and the source code and example inputs and outputs are available from the NREL website.« less

Synthetic thermosphere winds based on CHAMP neutral and plasma density measurements

NASA Astrophysics Data System (ADS)

Gasperini, F.; Forbes, J. M.; Doornbos, E. N.; Bruinsma, S. L.

2016-04-01

Meridional winds in the thermosphere are key to understanding latitudinal coupling and thermosphere-ionosphere coupling, and yet global measurements of this wind component are scarce. In this work, neutral and electron densities measured by the Challenging Minisatellite Payload (CHAMP) satellite at solar low and geomagnetically quiet conditions are converted to pressure gradient and ion drag forces, which are then used to solve the horizontal momentum equation to estimate low latitude to midlatitude zonal and meridional "synthetic" winds. We validate the method by showing that neutral and electron densities output from National Center for Atmospheric Research (NCAR) Thermosphere Ionosphere Mesosphere Electrodynamics-General Circulation Model (TIME-GCM) can be used to derive solutions to the momentum equations that replicate reasonably well (over 85% of the variance) the winds self-consistently calculated within the TIME-GCM. CHAMP cross-track winds are found to share over 65% of the variance with the synthetic zonal winds, providing further reassurance that this wind product should provide credible results. Comparisons with the Horizontal Wind Model 14 (HWM14) show that the empirical model largely underestimates wind speeds and does not reproduce much of the observed variability. Additionally, in this work we reveal the longitude, latitude, local time, and seasonal variability in the winds; show evidence of ionosphere-thermosphere (IT) coupling, with enhanced postsunset eastward winds due to depleted ion drag; demonstrate superrotation speeds of ˜27 m/s at the equator; discuss vertical wave coupling due the diurnal eastward propagating tide with zonal wave number 3 and the semidiurnal eastward propagating tide with zonal wave number 2.

Analysis of vector wind change with respect to time for Vandenberg Air Force Base, California

NASA Technical Reports Server (NTRS)

Adelfang, S. I.

1978-01-01

A statistical analysis of the temporal variability of wind vectors at 1 km altitude intervals from 0 to 27 km altitude taken from a 10-year data sample of twice-daily rawinsode wind measurements over Vandenberg Air Force Base, California is presented.

Use of a magnetic force exciter to vibrate a piezocomposite generating element in a small-scale windmill

NASA Astrophysics Data System (ADS)

Truyen Luong, Hung; Goo, Nam Seo

2012-02-01

A piezocomposite generating element (PCGE) can be used to convert ambient vibrations into electrical energy that can be stored and used to power other devices. This paper introduces a design of a magnetic force exciter for a small-scale windmill that vibrates a PCGE to convert wind energy into electrical energy. A small-scale windmill was designed to be sensitive to low-speed wind in urban regions for the purpose of collecting wind energy. The magnetic force exciter consists of exciting magnets attached to the device’s input rotor and a secondary magnet fixed at the tip of the PCGE. The PCGE is fixed to a clamp that can be adjusted to slide on the windmill’s frame in order to change the gap between exciting and secondary magnets. Under an applied wind force, the input rotor rotates to create a magnetic force interaction that excites the PCGE. The deformation of the PCGE enables it to generate electric power. Experiments were performed with different numbers of exciting magnets and different gaps between the exciting and secondary magnets to determine the optimal configuration for generating the peak voltage and harvesting the maximum wind energy for the same range of wind speeds. In a battery-charging test, the charging time for a 40 mA h battery was approximately 3 h for natural wind in an urban region. The experimental results show that the prototype can harvest energy in urban regions with low wind speeds and convert the wasted wind energy into electricity for city use.

A Comparison of Wind Speed Data from Mechanical and Ultrasonic Anemometers

NASA Technical Reports Server (NTRS)

Short, D.; Wells, L.; Merceret, F.; Roeder, W. P.

2006-01-01

This study compared the performance of mechanical and ultrasonic anemometers at the Eastern Range (ER; Kennedy Space Center and Cape Canaveral Air Force Station on Florida's Atlantic coast) and the Western Range (WR; Vandenberg Air Force Base on California's Pacific coast). Launch Weather Officers, forecasters, and Range Safety analysts need to understand the performance of wind sensors at the ER and WR for weather warnings, watches, advisories, special ground processing operations, launch pad exposure forecasts, user Launch Commit Criteria (LCC) forecasts and evaluations, and toxic dispersion support. The current ER and WR weather tower wind instruments are being changed from the current propeller-and-vane (ER) and cup-and-vane (WR) sensors to ultrasonic sensors through the Range Standardization and Automation (RSA) program. The differences between mechanical and ultrasonic techniques have been found to cause differences in the statistics of peak wind speed in previous studies. The 45th Weather Squadron (45 WS) and the 30th Weather Squadron (30 WS) requested the Applied Meteorology Unit (AMU) to compare data between RSA and current sensors to determine if there are significant differences. Approximately 3 weeks of Legacy and RSA wind data from each range were used in the study, archived during May and June 2005. The ER data spanned the full diurnal cycle, while the WR data was confined to 1000-1600 local time. The sample of 1-minute data from numerous levels on 5 different towers on each range totaled more than 500,000 minutes of data (482,979 minutes of data after quality control). The 10 towers were instrumented at several levels, ranging from 12 ft to 492 ft above ground level. The RSA sensors were collocated at the same vertical levels as the present sensors and typically within 15 ft horizontally of each another. Data from a total of 53 RSA ultrasonic sensors, collocated with present sensors were compared. The 1-minute average wind speed/direction and the 1-second peak wind speed/direction were compared.

30 WS North Base Wind Study

NASA Technical Reports Server (NTRS)

Wheeler, Mark

2011-01-01

The 30 Weather Squadron (30 WS) is concerned about strong winds observed at their northern towers without advance warning. They state that terrain influences along the extreme northern fringes of Vandenberg Air Force Base (VAFB) make it difficult for forecasters to issue timely and accurate high wind warnings for northeasterly wind events. These events tend to occur during the winter or early spring when they are under the influence of the Great Basin high pressure weather regime. The Launch Weather Officers (LWOs) have seen these rapid wind increases in the current northern Towers 60, 70 and 71 in excess of their 35 kt operational warning threshold. For this task, the 30 WS requested the Applied Meteorology Unit (AMU) analyze data from days when these towers reported winds in excess of 35 kt and determine if there were any precursors in the observations that would allow the LWOs to better forecast and warn their operational customers for these wind events. The 30 WS provided wind tower data for the cool season (October - March) from the period January 2004-March 20 IO. The AMU decoded and evaluated the wind tower data for 66 days identified by the 30 WS as having high-wind events. Out of the 66 event days, only 30 had wind speed observations of > or =35 kt from at least one of the three northern towers. The AMU analyzed surface and upper air charts to determine the synoptic conditions for each event day along with tower peak wind speed and direction time series and wind rose charts for all 30 event days. The analysis revealed a trend on all event days in which the tower winds shifted to the northeast for a period of time before the first recorded > or =35 kt wind speed. The time periods for the 30 event days ranged from 20 minutes to several hours, with a median value of 110 minutes. This trend, if monitored, could give the 30 WS forecasters a precursor to assist in issuing an operational warning before a high wind event occurs. The AMU recommends developing a high-wind alert capability for VAFB using a local mesoscale model to forecast these wind events. The model should incorporate all of the VAFB local data sets and have a forecast capability of between 2 to 24 hours. Such a model would allow the meteorologists at VAFB to alert the operational customers of high wind events in a timely manner so protective action could be taken.

An Analysis of Peak Wind Speed Data from Collocated Mechanical and Ultrasonic Anemometers

NASA Technical Reports Server (NTRS)

Short, David A.; Wells, Leonard; Merceret, Francis J.; Roeder, William P.

2007-01-01

This study compared peak wind speeds reported by mechanical and ultrasonic anemometers at Cape Canaveral Air Force Station and Kennedy Space Center (CCAFS/KSC) on the east central coast of Florida and Vandenberg Air Force Base (VAFB) on the central coast of California. Launch Weather Officers, forecasters, and Range Safety analysts need to understand the performance of wind sensors at CCAFS/KSC and VAFB for weather warnings, watches, advisories, special ground processing operations, launch pad exposure forecasts, user Launch Commit Criteria (LCC) forecasts and evaluations, and toxic dispersion support. The legacy CCAFS/KSC and VAFB weather tower wind instruments are being changed from propeller-and-vane (CCAFS/KSC) and cup-and-vane (VAFB) sensors to ultrasonic sensors under the Range Standardization and Automation (RSA) program. Mechanical and ultrasonic wind measuring techniques are known to cause differences in the statistics of peak wind speed as shown in previous studies. The 45th Weather Squadron (45 WS) and the 30th Weather Squadron (30 WS) requested the Applied Meteorology Unit (AMU) to compare data between the RSA ultrasonic and legacy mechanical sensors to determine if there are significant differences. Note that the instruments were sited outdoors under naturally varying conditions and that this comparison was not designed to verify either technology. Approximately 3 weeks of mechanical and ultrasonic wind data from each range from May and June 2005 were used in this study. The CCAFS/KSC data spanned the full diurnal cycle, while the VAFB data were confined to 1000-1600 local time. The sample of 1-minute data from numerous levels on five different towers on each range totaled more than 500,000 minutes of data (482,979 minutes of data after quality control). The ten towers were instrumented at several levels, ranging from 12 ft to 492 ft above ground level. The ultrasonic sensors were collocated at the same vertical levels as the mechanical sensors and typically within 15 ft horizontally of each another. Data from a total of 53 RSA ultrasonic sensors, collocated with mechanical sensors were compared. The 1- minute average wind speed/direction and the 1-second peak wind speed/direction were compared.

The winterstorm ``Vivian'' of 27 February 1990: About the meteorological development, wind forces and damage situation in the forests of Switzerland

NASA Astrophysics Data System (ADS)

Schüepp, M.; Schiesser, H. H.; Huntrieser, H.; Scherrer, H. U.; Schmidtke, H.

1994-09-01

During the months January and February 1990 a series of severe cyclones were responsible for enormous wind-induced damage in Europe. The final of this series, on 27 February 1990, cyclone “Vivian” mainly affected the alpine valleys of Switzerland. 5 Millions m3 of timber were felled by the severe winds, a record number in this century. A complete damage survey of the deforested areas offers in combination with meteorological data an unique data set for a detailed case study of this extreme event. This paper describes the general meteorological development from the synoptic scale down to the mesoscale of Switzerland and presents a general overview of the damage situation. The main results show that a rare situation of a straight frontal zone stretching over the whole Atlantic Ocean and showing a strong gradient in temperature pointed directly toward Central-Europe. Two waves formed along this elongated polar front and deepend rapidly to depressions. The first low travelled on the southernmost trajectory of the whole storm series and affected Switzerland most. North of the Alps the prefrontal warm air was blocked to the east by the arriving coldfront and had to escape into the complex terrain of the alpine valleys. There, the stormy winds were strengthened by channelizing and “Föhn” effects. The large temperature gradient between the prefrontal and the incoming air masses induced thunderstorm activity which vortices and downdrafts might have enhanced locally. As a result most of the damaged forested areas were found between 1200 and 1600 m MSL on slopes, which were mainly exposed toward the prevailing NW-winds. A comparison of extreme wind speeds for the period 1978 1992 revealed that this event's extreme high speed of 74.5 m/s, measured at a high elevated pass station in the mountains, was exceptional. For lower elevated stations the wind speeds were high but in the range of other observed extreme values. In addition to the severe wind forces the duration of sustained high wind speed was exceptionally long during February 1990.

Force instrumentation for cryogenic wind tunnels using one-piece strain-gage balances

NASA Technical Reports Server (NTRS)

Ferris, A. T.

1980-01-01

The use of cryogenic temperatures in wind tunnels to achieve high Reynolds numbers has imposed a harsh operating environment on the force balance. Laboratory tests were conducted to study the effect cryogenic temperatures have on balance materials, gages, wiring, solder, adhesives, and moisture proofing. Wind tunnel tests were conducted using a one piece three component balance to verify laboratory results. These initial studies indicate that satisfactory force data can be obtained under steady state conditions.

High-Frequency Orographically Forced Variability in a Single-Layer Model of the Martian Atmosphere

NASA Technical Reports Server (NTRS)

Keppenne, C. L.; Ingersoll, A. P.

1993-01-01

A shallow water model with realistic topography and idealized zonal wind forcing is used toinvestigate orographically forced modes in the Martian atmosphere. Locally, the model reproduceswell the climatology at the sites of Viking Lander I and II (VL1 and VL2) as inferred from theViking Lander fall and spring observations. Its variability at those sites is dominated by a 3-sol(Martian solar day) oscillation in the region of VL1 and by a 6-sol oscillation in that of VL2. Theseoscillations are forced by the zonal asymmetries of the Martian mountain field. It is suggested thatthey contribute to the observed variability by reinforcing the baroclinic oscillations with nearbyperiods identified in observational studies. The spatial variability associated with the orographicallyforced oscillations is studied by means of extended empirical orthogonal function analysis. The 3-solVL1 oscillation corresponds to a tropical, eastward-traveling, zonal-wavenumber one pattern...

Colliding Stellar Wind Models with Orbital Motion

NASA Astrophysics Data System (ADS)

Wilkin, Francis P.; O'Connor, Brendan

2018-01-01

We present thin-shell models for the collision between two ballistic stellar winds, including orbital motion.The stellar orbits are assumed circular, so that steady-state solutions exist in the rotating frame, where we include centrifugal and Coriolis forces. Exact solutions for the pre-shock winds are incorporated. Here we discuss 2-D model results for equal wind momentum-loss rates, although we allow for the winds to have distinct speeds and mass loss rates. For these unequal wind conditions, we obtain a clear violation of skew-symmetry, despite equal momentum loss rates, due to the Coriolis force.

An Advanced Actuator Line Method for Wind Energy Applications and Beyond

DOE Office of Scientific and Technical Information (OSTI.GOV)

Churchfield, Matthew J.; Schreck, Scott; Martinez-Tossas, Luis A.

The actuator line method to represent rotor aerodynamics within computational fluid dynamics has been in use for over a decade. This method applies a body force to the flow field along rotating lines corresponding to the individual rotor blades and employs tabular airfoil data to compute the force distribution. The actuator line method is attractive because compared to blade-resolved simulations, the required mesh is much simpler and the computational cost is lower. This work proposes a higher fidelity variant of the actuator line method meant to fill the space between current actuator line and blade-resolved simulations. It contains modifications inmore » two key areas. The first is that of freestream velocity vector estimation along the line, which is necessary to compute the lift and drag along the line using tabular airfoil data. Most current methods rely on point sampling in which the location of sampling is ambiguous. Here we test a velocity sampling method that uses a properly weighted integral over space, removing this ambiguity. The second area of improvement is the function used to project the one-dimensional actuator line force onto the three-dimensional fluid mesh as a body force. We propose and test a projection function that spreads the force over a region that looks something like a real blade with the hope that it will produce the blade local and near wake flow features with more accuracy and higher fidelity. Our goal is that between these two improvements, not only will the flow field predictions be enhanced, but also the spanwise loading will be made more accurate. We refer to this combination of improvements as the advanced actuator line method. We apply these improvements to two different wind turbine cases. Although there is a strong wind energy motivation in our work, there is no reason these advanced actuator line ideas cannot be used in other applications, such as helicopter rotors.« less

An Advanced Actuator Line Method for Wind Energy Applications and Beyond: Preprint

DOE Office of Scientific and Technical Information (OSTI.GOV)

Churchfield, Matthew; Schreck, Scott; Martinez-Tossas, Luis A.

The actuator line method to represent rotor aerodynamics within computational fluid dynamics has been in use for over a decade. This method applies a body force to the flow field along rotating lines corresponding to the individual rotor blades and employs tabular airfoil data to compute the force distribution. The actuator line method is attractive because compared to blade-resolved simulations, the required mesh is much simpler and the computational cost is lower. This work proposes a higher fidelity variant of the actuator line method meant to fill the space between current actuator line and blade-resolved simulations. It contains modifications inmore » two key areas. The first is that of freestream velocity vector estimation along the line, which is necessary to compute the lift and drag along the line using tabular airfoil data. Most current methods rely on point sampling in which the location of sampling is ambiguous. Here we test a velocity sampling method that uses a properly weighted integral over space, removing this ambiguity. The second area of improvement is the function used to project the one-dimensional actuator line force onto the three-dimensional fluid mesh as a body force. We propose and test a projection function that spreads the force over a region that looks something like a real blade with the hope that it will produce the blade local and near wake flow features with more accuracy and higher fidelity. Our goal is that between these two improvements, not only will the flow field predictions be enhanced, but also the spanwise loading will be made more accurate. We refer to this combination of improvements as the advanced actuator line method. We apply these improvements to two different wind turbine cases. Although there is a strong wind energy motivation in our work, there is no reason these advanced actuator line ideas cannot be used in other applications, such as helicopter rotors.« less

Intercomparison of oceanic and atmospheric forced and coupled mesoscale simulations. Part I: Surface fluxes

NASA Astrophysics Data System (ADS)

Josse, P.; Caniaux, G.; Giordani, H.; Planton, S.

1999-04-01

A mesoscale non-hydrostatic atmospheric model has been coupled with a mesoscale oceanic model. The case study is a four-day simulation of a strong storm event observed during the SEMAPHORE experiment over a 500 × 500 km2 domain. This domain encompasses a thermohaline front associated with the Azores current. In order to analyze the effect of mesoscale coupling, three simulations are compared: the first one with the atmospheric model forced by realistic sea surface temperature analyses; the second one with the ocean model forced by atmospheric fields, derived from weather forecast re-analyses; the third one with the models being coupled. For these three simulations the surface fluxes were computed with the same bulk parametrization. All three simulations succeed well in representing the main oceanic or atmospheric features observed during the storm. Comparison of surface fields with in situ observations reveals that the winds of the fine mesh atmospheric model are more realistic than those of the weather forecast re-analyses. The low-level winds simulated with the atmospheric model in the forced and coupled simulations are appreciably stronger than the re-analyzed winds. They also generate stronger fluxes. The coupled simulation has the strongest surface heat fluxes: the difference in the net heat budget with the oceanic forced simulation reaches on average 50 Wm-2 over the simulation period. Sea surface-temperature cooling is too weak in both simulations, but is improved in the coupled run and matches better the cooling observed with drifters. The spatial distributions of sea surface-temperature cooling and surface fluxes are strongly inhomogeneous over the simulation domain. The amplitude of the flux variation is maximum in the coupled run. Moreover the weak correlation between the cooling and heat flux patterns indicates that the surface fluxes are not responsible for the whole cooling and suggests that the response of the ocean mixed layer to the atmosphere is highly non-local and enhanced in the coupled simulation.

Stationary hydrodynamic models of Wolf-Rayet stars with optically thick winds.

NASA Astrophysics Data System (ADS)

Heger, A.; Langer, N.

1996-11-01

We investigate the influence of a grey, optically thick wind on the surface and internal structure of Wolf-Rayet (WR) stars. We calculate hydrodynamic models of chemically homogeneous helium stars with stationary outflows, solving the full set of stellar structure equations from the stellar center up to well beyond the sonic point of the wind, including the line force originating from absorption lines in a parameterized way. For specific assumptions about mass loss rate and wind opacity above our outer boundary, we find that the iron opacity peak may lead to local super-Eddington luminosities at the sonic point. By varying the stellar wind parameters over the whole physically plausible range, we show that the radius of the sonic point of the wind flow is always very close to the hydrostatic stellar radius obtained in WR star models which ignore the wind. However, our models confirm the possibility of large values for observable WR radii and correspondingly small effective temperatures found in earlier models. We show further that the energy which is contained in a typical WR wind can not be neglected. The stellar luminosity may be reduced by several 10%, which has a pronounced effect on the mass-luminosity relation, i. e., the WR masses derived for a given luminosity may be considerably larger. Thereby, also the momentum problem of WR winds is considerably reduced, as well as the scatter in the ˙(M) vs. M diagram for observed hydrogen-free WN stars.

Ockham's Razorblade Shaving Wind-Induced Circulation

NASA Astrophysics Data System (ADS)

Bergmann, Juan Carlos

2010-05-01

Terrestrial physical oceanography is fortunate because of the existence of the continents that divide the low-latitude oceans into basins. At first glance, the previous statement appears to be not obvious because an ocean-planet should be much simpler to describe. Simple-case explanation is the central aspect of Ockham's Razorblade: If a theory fails to describe the most-simple case properly, the theory is, at least, ‘not good'. Also Descartes' methodical rules take the most-simple case as starting point. The analysis of wind-induced circulation on an ocean-planet will support the initial statement. Earth's south hemisphere is dominated by the oceans. The continents' influence on the zonal-average zonal-wind climate is relatively small. Therefore, South Hemisphere's zonal wind pattern is a relatively good proxy for that of an ocean planet. Application of this wind-stress pattern to an ocean planet yields reasonable meridional mass-flow results from the polar-regions down to the high-pressure belts: Down-welling and up-welling of water-mass are approximately balanced. However, the entire tropical circulation can in principle not be closed because there is only down-welling - even if the extreme down-welling in the equatorial belt (± 8°, with a singularity at the equator) is disregarded. The only input to the calculations is the observed terrestrial south-hemisphere zonal wind-stress pattern. Meridional stress is irrelevant because it produces a closed zonal Ekman-transport around the ocean planet (sic!). Vertical mass-transport is calculated from the divergence of the wind-induced meridional Ekman-mass-transport, which in its turn is a necessary consequence of angular-momentum conservation. No assumptions are made on how the return-flows at depth are forced because the wind-force equations cannot contribute hereto. This circumstance expresses a fundamental difference to atmospheric circulation, where mechanical forcing is caused by the pressure-fields that result from differential heating/cooling and therefore ‘automatically' comprise the entire circulation system. Wind-caused oceanic flow is exclusively generated by frictional wind-forces at the surface, and other processes in the ocean are not causally connected hereto. In absence of continents it is quite difficult to ‘find' the corresponding forcing for the meridional return-flows - and it can definitely not be wind-force-caused - very strange! The fact that the wind-induced circulation can only be closed by the action of other processes, which are not causally connected to wind-forces, demonstrates that something must be fundamentally wrong. The singularity at the equator and the extreme down-welling in the equatorial belt indicate an additional severe problem that can only be avoided if zonal wind-stress is completely excluded. Escape to additional assumptions is similar to the introduction of the epicycles in order to explain the planets' retrograde motion in maintaining geocentric cosmology. Should the previous analysis be ignored in favour of maintaining the ‘established' ideas of wind-induced circulation or should there be an effort to formulate new ideas that provide closed and balanced circulation without employing other processes than wind-forces?

Spatiotemporal distribution of nitrogen dioxide within and around a large-scale wind farm - a numerical case study

NASA Astrophysics Data System (ADS)

Mo, Jingyue; Huang, Tao; Zhang, Xiaodong; Zhao, Yuan; Liu, Xiao; Li, Jixiang; Gao, Hong; Ma, Jianmin

2017-12-01

As a renewable and clean energy source, wind power has become the most rapidly growing energy resource worldwide in the past decades. Wind power has been thought not to exert any negative impacts on the environment. However, since a wind farm can alter the local meteorological conditions and increase the surface roughness lengths, it may affect air pollutants passing through and over the wind farm after released from their sources and delivered to the wind farm. In the present study, we simulated the nitrogen dioxide (NO2) air concentration within and around the world's largest wind farm (Jiuquan wind farm in Gansu Province, China) using a coupled meteorology and atmospheric chemistry model WRF-Chem. The results revealed an edge effect, which featured higher NO2 levels at the immediate upwind and border region of the wind farm and lower NO2 concentration within the wind farm and the immediate downwind transition area of the wind farm. A surface roughness length scheme and a wind turbine drag force scheme were employed to parameterize the wind farm in this model investigation. Modeling results show that both parameterization schemes yield higher concentration in the immediate upstream of the wind farm and lower concentration within the wind farm compared to the case without the wind farm. We infer this edge effect and the spatial distribution of air pollutants to be the result of the internal boundary layer induced by the changes in wind speed and turbulence intensity driven by the rotation of the wind turbine rotor blades and the enhancement of surface roughness length over the wind farm. The step change in the roughness length from the smooth to rough surfaces (overshooting) in the upstream of the wind farm decelerates the atmospheric transport of air pollutants, leading to their accumulation. The rough to the smooth surface (undershooting) in the downstream of the wind farm accelerates the atmospheric transport of air pollutants, resulting in lower concentration level.

The Sensitivity of a Global Ocean Model to Wind Forcing: A Test Using Sea Level and Wind Observations from Satellites and Operational Analysis

NASA Technical Reports Server (NTRS)

Fu, L. L.; Chao, Y.

1997-01-01

Investigated in this study is the response of a global ocean general circulation model to forcing provided by two wind products: operational analysis from the National Center for Environmental Prediction (NCEP); observations made by the ERS-1 radar scatterometer.

76 FR 42121 - Final Notice of a Finding of No Significant Impact for a Programmatic Environmental Assessment...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-07-18

... for a Programmatic Environmental Assessment Implementing a Wind Energy Program at Marine Forces... Wind Energy Program at Marine Forces Reserve (MARFORRES) Facilities Located Across the United States... final notice that the FONSI for the PEA implementing the MARFORRES Wind Energy Program will not have a...

Impact of tropical cyclones on modeled extreme wind-wave climate

DOE PAGES

Timmermans, Ben; Stone, Daithi; Wehner, Michael; ...

2017-02-16

Here, the effect of forcing wind resolution on the extremes of global wind-wave climate are investigated in numerical simulations. Forcing winds from the Community Atmosphere Model at horizontal resolutions of ~1.0° and ~0.25° are used to drive Wavewatch III. Differences in extreme wave height are found to manifest most strongly in tropical cyclone (TC) regions, emphasizing the need for high-resolution forcing in those areas. Comparison with observations typically show improvement in performance with increased forcing resolution, with a strong influence in the tail of the distribution, although simulated extremes can exceed observations. A simulation for the end of the 21stmore » century under a RCP 8.5 type emission scenario suggests further increases in extreme wave height in TC regions.« less

Impact of tropical cyclones on modeled extreme wind-wave climate

NASA Astrophysics Data System (ADS)

Timmermans, Ben; Stone, Dáithí; Wehner, Michael; Krishnan, Harinarayan

2017-02-01

The effect of forcing wind resolution on the extremes of global wind-wave climate are investigated in numerical simulations. Forcing winds from the Community Atmosphere Model at horizontal resolutions of ˜1.0° and ˜0.25° are used to drive Wavewatch III. Differences in extreme wave height are found to manifest most strongly in tropical cyclone (TC) regions, emphasizing the need for high-resolution forcing in those areas. Comparison with observations typically show improvement in performance with increased forcing resolution, with a strong influence in the tail of the distribution, although simulated extremes can exceed observations. A simulation for the end of the 21st century under a RCP 8.5 type emission scenario suggests further increases in extreme wave height in TC regions.

NACA Engineer Examines Wind Tunnel Compressor Blades

NASA Image and Video Library

1955-09-21

An engineer examines the main compressor for the 10- by 10-Foot Supersonic Wind Tunnel at the National Advisory Committee for Aeronautics (NACA) Lewis Flight Propulsion Laboratory. The engineers were preparing the new wind tunnel for its initial runs in early 1956. The 10- by 10 was the most powerful propulsion wind tunnel in the nation. The facility was part of Congress’ Unitary Plan Act which coordinated wind tunnel construction at the NACA, Air Force, industry, and universities. The 10- by 10 was the largest of the three NACA tunnels built under the act. The 20-foot diameter eight-stage axial flow compressor, seen in this photograph, could generate air flows up to Mach 2.5 through the test section. The stainless steel compressor had 584 blades ranging from 1.8 to 3.25 feet in length. This main compressor was complemented by a secondary axial flow compressor. Working in tandem the two could generate wind streams up to Mach 3.5. The Cleveland Chamber of Commerce presented NACA Lewis photographer Bill Bowles with a second place award for this photograph in their Business and Professional category. The photograph was published in October 1955 edition of its periodical, The Clevelander, which highlighted local professional photographers. Fellow Lewis photographer Gene Giczy won second place in another category for a photograph of Cleveland Municipal Airport.

The inducement of planetary boundary layer mass convergence associated with varying vorticity beneath tropospheric wind maximum

NASA Technical Reports Server (NTRS)

Johnson, D. R.

1984-01-01

The effects of the vorticity distribution are applied to study planetary boundary layer mass convergence beneath free tropospheric wind maximum. For given forcing by viscous and pressure gradient forces beneath a wind maximum, boundary layer cross stream mass transport is increased by anticyclonic vorticity on the right flank and decreased by cyclonic vorticity on the left flank. Such frictionally forced mass transport induces boundary layer mass convergence beneath the relative wind maximum. This result is related to the empirical rule that the most intense convection and severe weather frequently develop beneath the 500 mb zero relative vorticity isopleth.

Common behaviour of the Adriatic and Black Seas level in the 20th century as response to a Mediterranean forcing.

NASA Astrophysics Data System (ADS)

Scarascia, Luca; Stanica, Adrian; Dinu, Irina; Lionello, Piero

2017-04-01

The Adriatic and Black Seas are two marginal seas, both connected with the Eastern Mediterranean Sea, through the Otranto and Bosporus straits respectively. This contribution aims to evidence the fraction of the interannual sea level variability that is common to the two basins, likely an effect of the common forcing produced by Mediterranean Sea. In order to identify the common signal, the effect of the main local factors (wind, inverse barometer effect, steric effects, river runoff) determining the larger fraction of the interannual sea level variability have been identified and subtracted. Using 7 and 5 tide gauge timeseries located along the Adriatic and Black Sea coasts respectively, provided by PSMSL (Permanent Service of Mean Sea Level), two seamless timeseries representing the sea level of the basins from 1900 to 2009 have been produced. The comparison with satellite data, between 1993 and 2009, confirms that these reconstructions are representative of the actual sea level in the two basins (values are 0.87 for the Adriatic and 0.72 for the Black Sea). When considering local factors, for the Adriatic Sea the annual cycle of inverse barometer effect, steric contribution due to local temperature and salinity variations, and wind set-up have been computed. For the Black Sea, the wind factor (negligible in this case) has been replaced by the Danube river contribution estimated from the available discharge data of Sulina (one of the exits of the Danube delta). After subtracting these local factors from the observed sea level of each basin, the correlation between the residual time series amounts to 0.47, suggesting the presence of a common factor acting at Mediterranean scale, which can be attributed to the effect of the large-scale circulation on the mass exchange between the Mediterranean and the two local basins. The present analysis is still unable to explain a non-negligible fraction of interannual variability of sea level of the Black Sea. This is likely, to a substantial extent, due to uncertainties of hydrographic data caused by their irregular distribution in space and time and to the lack of regular records of past river discharge for most rivers contributing to the Black Sea.

Cost of wind energy: comparing distant wind resources to local resources in the midwestern United States.

PubMed

Hoppock, David C; Patiño-Echeverri, Dalia

2010-11-15

The best wind sites in the United States are often located far from electricity demand centers and lack transmission access. Local sites that have lower quality wind resources but do not require as much power transmission capacity are an alternative to distant wind resources. In this paper, we explore the trade-offs between developing new wind generation at local sites and installing wind farms at remote sites. We first examine the general relationship between the high capital costs required for local wind development and the relatively lower capital costs required to install a wind farm capable of generating the same electrical output at a remote site,with the results representing the maximum amount an investor should be willing to pay for transmission access. We suggest that this analysis can be used as a first step in comparing potential wind resources to meet a state renewable portfolio standard (RPS). To illustrate, we compare the cost of local wind (∼50 km from the load) to the cost of distant wind requiring new transmission (∼550-750 km from the load) to meet the Illinois RPS. We find that local, lower capacity factor wind sites are the lowest cost option for meeting the Illinois RPS if new long distance transmission is required to access distant, higher capacity factor wind resources. If higher capacity wind sites can be connected to the existing grid at minimal cost, in many cases they will have lower costs.

On Local Ionization Equilibrium and Disk Winds in QSOs

NASA Astrophysics Data System (ADS)

Pereyra, Nicolas A.

2014-11-01

We present theoretical C IV λλ1548,1550 absorption line profiles for QSOs calculated assuming the accretion disk wind (ADW) scenario. The results suggest that the multiple absorption troughs seen in many QSOs may be due to the discontinuities in the ion balance of the wind (caused by X-rays), rather than discontinuities in the density/velocity structure. The profiles are calculated from a 2.5-dimensional time-dependent hydrodynamic simulation of a line-driven disk wind for a typical QSO black hole mass, a typical QSO luminosity, and for a standard Shakura-Sunyaev disk. We include the effects of ionizing X-rays originating from within the inner disk radius by assuming that the wind is shielded from the X-rays from a certain viewing angle up to 90° ("edge on"). In the shielded region, we assume constant ionization equilibrium, and thus constant line-force parameters. In the non-shielded region, we assume that both the line-force and the C IV populations are nonexistent. The model can account for P-Cygni absorption troughs (produced at edge on viewing angles), multiple absorption troughs (produced at viewing angles close to the angle that separates the shielded region and the non-shielded region), and for detached absorption troughs (produced at an angle in between the first two absorption line types); that is, the model can account for the general types of broad absorption lines seen in QSOs as a viewing angle effect. The steady nature of ADWs, in turn, may account for the steady nature of the absorption structure observed in multiple-trough broad absorption line QSOs. The model parameters are M bh = 109 M ⊙ and L disk = 1047 erg s-1.

Circulation and thermohaline structure of the Aral Sea in the last three years

NASA Astrophysics Data System (ADS)

Izhitskiy, A. S.; Zavialov, P. O.

2012-04-01

The results of the 3 latest expeditions (2009 - 2011) of the Shirshov Institute to the Aral Sea are reported. We analyze the interannual variability of the basin circulation together with the thermohaline structure in order to identify the underlying mechanisms. The study is based on the results of the field surveys of August, 2009, September, 2010, and November, 2011. The vertical profiles of temperature and salinity were obtained using a CTD profiler at 6 stations across the deepest part of the western basin in 2009 and 2010, and 3 stations in 2011. Additionally, during each of the surveys, mooring stations equipped with current meters and pressure gauges were deployed for 3-5 days in the deepest portion of the western basin. A portable automatic meteorological station, continuously recording the wind stress and the principal meteorological parameters, was installed near the mooring sites. The vertical stratification exhibited a 3-layered pattern, with local salinity maxima in the upper mixed layer and near the bottom, while the intermediate layer was characterized by a core of minimum salinity and temperature. Such a pattern persisted throughout the 3 years of observations. Analysis of the current measurements data along with the meteorological data records demonstrated that the mean basin-scale surface circulation of the Large Aral Sea is likely to have remained anticyclonic, whilst the near-bottom circulation appears to be cyclonic. The current velocity and level anomalies responded energetically to winds. Correlation analysis of the velocity and surface level series versus the wind stress allowed to quantify the response of the system to the wind forcing as well as to formulate a conceptual scheme of the lake's response to wind forcing at synoptic temporal scales.

Factors affecting suspended-solids concentrations in South San Francisco Bay, California

USGS Publications Warehouse

Schoellhamer, D.H.

1996-01-01

Measurements of suspended-solids concentration (SSC) were made at two depths at three sites in South San Francisco Bay (South Bay) to determine the factors that affect SSC. Twenty-eight segments of reliable and continuous SSC time series data longer than 14 days were collected from late 1991 or 1992 through September 1993. Spectral analysis and singular spectrum analysis were used to relate these data segments to time series of several potential forcing factors, including diurnal and semidiurnal tides, the spring-neap tidal cycle, wind shear, freshwater runoff, and longitudinal density differences. SSC is greatest during summer when a landward wind shear is applied to South Bay by the afternoon sea breeze. About one half the variance of SSC is caused by the spring-neap cycle, and SSC lags the spring-neap cycle by about 2 days. Relatively short duration of slack water limits the duration of deposition of suspended solids and consolidation of newly deposited bed sediment during the tidal cycle, so suspended solids accumulate in the water column as a spring tide is approached and slowly deposit as a neap tide is approached. Perturbations in SSC caused by wind and local runoff from winter storms during the study period were usually much smaller than SSC variations caused by the spring-neap cycle. Variations of SSC at the study sites at tidal timescales are tidally forced, and nonlinear physical processes are significant. Advective transport dominates during spring tides when water with higher SSC due to wind wave resuspension is advected to the main channel from shallow water, but during neap tides, advective transport is less significant. The findings of this and other studies indicate that the tidally averaged transport of suspended solids responds to seasonal variations of wind shear in South Bay.

CFD study of some factors affecting performance of HAWT with swept blades

NASA Astrophysics Data System (ADS)

Khalafallah, M. G.; Ahmed, A. M.; Emam, M. K.

2017-05-01

Most modern high-power wind turbines are horizontal axis type with straight twisted blades. Upgrading power and performance of these turbines is considered a challenge. A recent trend towards improving the horizontal axis wind turbine (HAWT) performance is to use swept blades or sweep twist adaptive blades. In the present work, the effect of blade curvature, sweep starting point and sweep direction on the wind turbine performance was investigated. The CFD simulation method was validated against available experimental data of a 0.9 m diameter HAWT. The wind turbine power and thrust coefficients at different tip speed ratios were calculated. Flow field, pressure distribution and local tangential and streamwise forces were also analysed. The results show that the downstream swept blade has the highest Cp value at design point as compared with the straight blade profile. However, the improvement in power coefficient is accompanied by a thrust increase. Results also show that the best performance is obtained when the starting blade sweeps at 25% of blade radius for different directions of sweep.

The dynamics of subtidal poleward flows over a narrow continental shelf, Palos Verdes, CA

USGS Publications Warehouse

Noble, M.A.; Ryan, H.F.; Wiberg, P.L.

2002-01-01

The Palos Verdes peninsula is a short, very narrow (< 3 km) shelf in southern California that is bracketed by two large embayments. In May 1992, arrays of up to 4 moorings and 2 benthic tripods were deployed in a yearlong study of the circulation processes over this shelf and the adjacent slope. Wind stress, coastal sea level, atmospheric pressure and wave records were obtained from offshore sites and from coastal stations surrounding Palos Verdes. Bottom stress calculated for the mid-shelf sites using a boundary-layer model and data from the above instruments indicated the bottom drag coefficient over this shelf is about 0.003 Currents flow toward the northwest along the shelf and upper slope. Speeds are generally around 20-30 cm/s. There was no obvious seasonal structure in the flow. The first EOF for subtidal alongshelf current accounted for nearly 70% of the variance at sites on the shelf and upper slope. The dominant fluctuations had periods between 5 and 20 days, periods longer than seen in the regional wind stress field. Coastal sea level and the alongshore gradient in sea level had a similar concentration of energy in the 5-20 day frequency band. About 30% of the alongshelf flow was coherent with the alongshelf pressure gradient; currents flowed down the pressure gradient with minimal phase lag. Winds accounted for only 15-20% of the variance in subtidal currents, but the measured effect of wind stress was large. A 1 dyne/cm2 wind stress was associated with a 20-30 cm/s alongshore current. Both the regional wind stress and the alongshelf pressure gradients had spatial scales much larger than found on this small shelf. Subtidal flows forced by these regional fields were set up in the adjacent, much broader basins. The currents amplified as they moved onto the narrow shelf between the basins. Hence, local wind-driven currents had anomalously large amplitudes. The momentum equations for alongshelf wind or pressure gradients did not balance because some of the measured terms were associated with regional fields, others with local process. Our observations suggest that it is more difficult to determine which measured fields reflect the local processes in regions with rapidly changing topography. ?? 2002 Elsevier Science Ltd. All rights reserved.

Aerodynamic forces on freight trains : volume 1. wind tunnel tests of containers and trailers on flatcars

DOT National Transportation Integrated Search

1976-12-01

The aerodynamic forces on trailers and containers on flatcars have been measured in wind tunnel tests. The forces were measured on the central car of a five-car train consisting of a locomotive, three flatcars with various loadings and a boxcar. Test...

Correlation of side-force and yawing-moment data for TACV configurations at large angles of sideslip

DOT National Transportation Integrated Search

1974-01-01

Methods developed by Woolard and Ruetenik and Zartarian for predicting the side force and yawing moment on TACV configurations due to side winds are compared against available data from wind-tunnel tests. The predicted side force based on slender-bod...

Environmental Assessment for Installation of a New Jet Engine Test Cell, Edwards Air Force Base, California

DTIC Science & Technology

2012-09-01

suspended in the runoff waters around the lakebeds, sealing lakebed surface cracks and filling fissures. Shallow flooding along with consistent winds are...of the recorded specimens consist of isolated fragments of tooth enamel or bone that are not securely dated. Irvingtonian fossil localities have...require frequent repair as well. Concrete floors are cracking throughout all four test cells. Entry doors sag and drag on buckled floors. One-half

Intraseasonal flow and its impact on the chlorophyll-a concentration in the Sunda Strait and its vicinity

NASA Astrophysics Data System (ADS)

Xu, Tengfei; Li, Shujiang; Hamzah, Faisal; Setiawan, Agus; Susanto, R. Dwi; Cao, Guojiao; Wei, Zexun

2018-06-01

Sunda Strait is the outflow strait of the South China Sea branch of the Pacific to Indian Ocean Throughflow. The annual mean volume transport through the Sunda Strait is around 0.25 Sv from the Java Sea to the eastern Indian Ocean, only 2.5% of the IndonesianThroughflow, and thus has been ignored by previous investigations. However, the Nutrient concentrations in the Sunda Strait and its vicinity are found highly related to the water transport through the Sunda Strait. Particularly, our observation shows significant intraseasonal variability (ISV) of currents at period around 25-45 days in the Sunda Strait. Both remote and local wind forcing contribute to the ISVs in the Sunda Strait. The intraseasonal oscillation of sea surface wind in the central Indian Ocean drives upwelling/downwelling equatorial Kelvin waves to propagate along the equator and subsequently along the Sumatra-Java coasts, resulting in negative/positive sea level anomalies in the south of the Sunda Strait. The local intraseasonal sea surface wind anomalies also tend to induce negative/positive sea level anomalies in the south of the Sunda Strait by offshore/onshore Ekman transport while there are upwelling/downwelling events. The ensuring sea level gradient associated with the sea level anomalies in the south of the Sunda Strait induces intraseasonal outflow (from Indian Ocean to Java Sea) and inflow (from Java Sea to Indian Ocean) through the strait. Analyses also show that the chlorophyll-a concentrations in the south of the Sunda Strait are lower/higher during the inflow/outflow period of the ISV events in March through May. The mechanism attributes to both the nutrient-rich water transported by the intraseasonal flow in the Sunda Strait and by the upwelling and Ekman transport driven by the local sea surface wind anomalies.

A wind comparison study using an ocean general circulation model for the 1997-1998 El Niño

NASA Astrophysics Data System (ADS)

Hackert, Eric C.; Busalacchi, Antonio J.; Murtugudde, Ragu

2001-02-01

Predictions of the 1997-1998 El Niño exhibited a wide range of forecast skill that were dependent, in part, on the wind-driven initial conditions for the ocean. In this study the results of a reduced gravity, primitive equation, sigma coordinate ocean general circulation model are compared and contrasted when forced by several different wind products for the 1997-1998 El Niño/La Niña. The different wind products include atmospheric model winds, satellite wind products, and a subjective analysis of ship and in situ winds. The model results are verified against fields of observed sea level anomalies from TOPEX/Poseidon data, sea surface temperature analyses, and subsurface temperature from the Tropical Atmosphere-Ocean buoy array. Depending on which validation data type one chooses, different wind products provide the best forcing fields for simulating the observed signal. In general, the model results forced by satellite winds provide the best simulations of the spatial and temporal signal of the observed sea level. This is due to the accuracy of the meridional gradient of the zonal wind stress component that these products provide. Differences in wind forcing also affect subsurface dynamics and thermodynamics. For example, the wind products with the weakest magnitude best reproduce the sea surface temperature (SST) signal in the eastern Pacific. For these products the mixed layer is shallower, and the thermocline is closer to the surface. For such simulations the subsurface thermocline variability influences the variation in SST more than in reality. The products with the greatest wind magnitude have a strong cold bias of >1.5°C in the eastern Pacific because of increased mixing. The satellite winds along with the analysis winds correctly reproduce the depth of the thermocline and the general subsurface temperature structure.

Effects of anisotropic thermal conduction on wind properties in hot accretion flow

NASA Astrophysics Data System (ADS)

Bu, De-Fu; Wu, Mao-Chun; Yuan, Ye-Fei

2016-06-01

Previous works have clearly shown the existence of winds from black hole hot accretion flow and investigated their detailed properties. In extremely low accretion rate systems, the collisional mean-free path of electrons is large compared with the length-scale of the system, thus thermal conduction is dynamically important. When the magnetic field is present, the thermal conduction is anisotropic and energy transport is along magnetic field lines. In this paper, we study the effects of anisotropic thermal conduction on the wind production in hot accretion flows by performing two-dimensional magnetohydrodynamic simulations. We find that thermal conduction has only moderate effects on the mass flux of wind. But the energy flux of wind can be increased by a factor of ˜10 due to the increase of wind velocity when thermal conduction is included. The increase of wind velocity is because of the increase of driving forces (e.g. gas pressure gradient force and centrifugal force) when thermal conduction is included. This result demonstrates that thermal conduction plays an important role in determining the properties of wind.

Intraseasonal-to-semiannual variability of sea-surface height in the astern, equatorial Indian Ocean and southern Bay of Bengal

NASA Astrophysics Data System (ADS)

Cheng, Xuhua; McCreary, Julian P.; Qiu, Bo; Qi, Yiquan; Du, Yan

2017-05-01

Intraseasonal-to-semiannual variability of sea-surface height (SSH) in the eastern, equatorial Indian Ocean (EEIO) and southern Bay of Bengal (BoB) is investigated using altimetric data, and solutions to 1½ layer (first baroclinic mode) and linear, continuously stratified (LCS; multibaroclinic-mode) models. The amplitude and dominant periods of SSH variability differ regionally. Large-amplitude variability is found along the west coast of Sumatra, in a zonal band across the BoB centered along 5°N, east of Sri Lanka, and in the northwestern BoB, respectively. Along the Sumatran west coast, SSH variability peaks at 30-60, 90, and 180 days. Along 5°N and east of Sri Lanka, the 30-60 day variability is dominant. Sensitivity experiments using a nonlinear version of the 1½ layer model forced by realistic winds reproduce the observed patterns of intraseasonal variability in the southern BoB. At 30-60 days, the solutions show that eddies (nonlinear Rossby waves) propagating from the east, rather than local wind forcing, account for most of the variance east of Sri Lanka; furthermore, they demonstrate that the variance is significantly enhanced by the nonlinear transfer of 90-120 day energy into the intraseasonal band of 30-60 days. The LCS solutions show that the first two baroclinic modes explain most of the SSH variance at 90-180 days. The second baroclinic mode dominates the SSH variance at 180 days, a consequence of basin resonance and strong wind forcing.

Energetic neutral atom and interstellar flow observations with IBEX: Implications for the global heliosphere

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schwadron, N. A., E-mail: nschwadron@unh.edu; Southwest Research Institute, San Antonio, TX, 78238; McComas, D. J.

2016-03-25

Since launch in Oct. 2008, IBEX, with its two energetic neutral atom (ENA) cameras, has provided humankind with the first-ever global images of the complex boundary separating the heliosphere from the local interstellar medium (LISM). IBEX’s energy-resolved all-sky maps, collected every six months, are yielding remarkable new insights into the heliospheres structure as it is shaped by the combined forces of the local interstellar flow, the local interstellar magnetic field (LISMF), and the evolving solar wind. IBEX has also acquired the first images of ENAs backscattered from the surface of the moon as well as global images of the magnetosphericmore » response to solar wind disturbances. IBEX thus addresses all three Heliophysics science objectives set forth in the 2014 Science Plan for NASAs Science Mission Directorate (SMD) as well as the goals in the recent Solar and Space Physics Decadal Survey (NRC 2012). In addition, with the information it provides on the properties of the LISM and the LISMF, IBEX represents a unique bridge between heliophysics and astrophysics, and fills in critical knowledge for understanding the habitability of exoplanetary systems and the future habitability of Earth and the solar system. Because of the few-year time lag due to solar wind and ENA transport, IBEX observed the solar wind/ LISM interaction characteristic of declining phase/solar minimum conditions. In the continuing mission, IBEX captures the response of the interstellar boundaries to the changing structure of the solar wind in its transition toward the “mini” solar maximum and possibly the decline into the next solar minimum. The continuing IBEX mission affords never-to-be-repeated opportunities to coordinate global imaging of the heliospheric boundary with in-situ measurements by the Voyagers as they pass beyond the heliopause and start to directly sample the LISM.« less

Relative contributions of external forcing factors to circulation and hydrographic properties in a micro-tidal bay

NASA Astrophysics Data System (ADS)

Yoon, Seokjin; Kasai, Akihide

2017-11-01

The dominant external forcing factors influencing estuarine circulation differ among coastal environments. A three-dimensional regional circulation model was developed to estimate external influence indices and relative contributions of external forcing factors such as external oceanic forcing, surface heat flux, wind stress, and river discharge to circulation and hydrographic properties in Tango Bay, Japan. Model results show that in Tango Bay, where the Tsushima Warm Current passes offshore of the bay, under conditions of strong seasonal winds and river discharge, the water temperature and salinity are strongly influenced by surface heat flux and river discharge in the surface layer, respectively, while in the middle and bottom layers both are mainly controlled by open boundary conditions. The estuarine circulation is comparably influenced by all external forcing factors, the strong current, surface heat flux, wind stress, and river discharge. However, the influence degree of each forcing factor varies with temporal variations in external forcing factors as: the influence of open boundary conditions is higher in spring and early summer when the stronger current passes offshore of the bay, that of surface heat flux reflects the absolute value of surface heat flux, that of wind stress is higher in late fall and winter due to strong seasonal winds, and that of river discharge is higher in early spring due to snow-melting and summer and early fall due to flood events.

Droplet Depinning on Inclined Surfaces at High Reynolds Numbers

NASA Astrophysics Data System (ADS)

White, Edward; Singh, Natasha; Lee, Sungyon

2017-11-01

Contact angle hysteresis enables a sessile liquid drop to adhere to a solid surface when the surface is inclined, the drop is exposed to gas-phase flow, or the drop is exposed to both forcing modalities. Previous work by Schmucker and White (2012.DFD.M4.6) identified critical depinning Weber numbers for water drops subject to gravity- and wind-dominated forcing. This work extends the Schmucker and White data and finds the critical depinning Weber number obeys a two-slope linear model. Under pure wind forcing at Reynolds numbers above 1500 and with zero surface inclination, Wecrit = 8.0 . For non-zero inclinations, α, Wecrit decreases proportionally to A Bo sinα where A is the drop aspect ratio and Bo is its Bond number. The same relationship holds for α < 0 when gravity resists depinning by wind. Above We 4 , depinning is dominated by wind forcing; at We < 4 , depinning is gravity dominated. While Wecrit depends linearly on A Bo sinα in both forcing regimes, the slopes of the the limit lines depend on the forcing regime. The difference is attributed to different drop shapes and contact angle distributions that arise depending on whether wind or gravity dominates the depinning behavior. Supported by the National Science Foundation through Grant CBET-1605947.

Empirical models of wind conditions on Upper Klamath Lake, Oregon

USGS Publications Warehouse

Buccola, Norman L.; Wood, Tamara M.

2010-01-01

Upper Klamath Lake is a large (230 square kilometers), shallow (mean depth 2.8 meters at full pool) lake in southern Oregon. Lake circulation patterns are driven largely by wind, and the resulting currents affect the water quality and ecology of the lake. To support hydrodynamic modeling of the lake and statistical investigations of the relation between wind and lake water-quality measurements, the U.S. Geological Survey has monitored wind conditions along the lakeshore and at floating raft sites in the middle of the lake since 2005. In order to make the existing wind archive more useful, this report summarizes the development of empirical wind models that serve two purposes: (1) to fill short (on the order of hours or days) wind data gaps at raft sites in the middle of the lake, and (2) to reconstruct, on a daily basis, over periods of months to years, historical wind conditions at U.S. Geological Survey sites prior to 2005. Empirical wind models based on Artificial Neural Network (ANN) and Multivariate-Adaptive Regressive Splines (MARS) algorithms were compared. ANNs were better suited to simulating the 10-minute wind data that are the dependent variables of the gap-filling models, but the simpler MARS algorithm may be adequate to accurately simulate the daily wind data that are the dependent variables of the historical wind models. To further test the accuracy of the gap-filling models, the resulting simulated winds were used to force the hydrodynamic model of the lake, and the resulting simulated currents were compared to measurements from an acoustic Doppler current profiler. The error statistics indicated that the simulation of currents was degraded as compared to when the model was forced with observed winds, but probably is adequate for short gaps in the data of a few days or less. Transport seems to be less affected by the use of the simulated winds in place of observed winds. The simulated tracer concentration was similar between model results when simulated winds were used to force the model, and when observed winds were used to force the model, and differences between the two results did not accumulate over time.

Security and Stability Analysis of Wind Farms Integration into Distribution Network

NASA Astrophysics Data System (ADS)

Guan-yang, Li; Hongzhao, Wang; Guanglei, Li; Yamei, Cheng; Hong-zheng, Liu; Yi, Sun

2017-05-01

With the increasing share of the wind power in the power system, wind power fluctuations will cause obvious negative impacts on weak local grid. This paper firstly establish electromechanical transient simulation model for doubly fed induction wind turbine, then use Matlab/Simulink to achieve power flow calculation and transient simulation of power system including wind farms, the local synchronous generator, load, etc, finally analyze wind power on the impact of the local power grid under typical circumstances. The actual calculated results indicate that wind mutation causes little effect on the power grid, but when the three-phase short circuit fault happens, active power of wind power decreases sharply and the voltage of location of wind power into the grid also drop sharply, finally wind farm split from power system. This situation is not conducive to security and stability of the local power grid. It is necessary to develop security and stability measures in the future.

Wind-forced modulations in crossing sea states over infinite depth water

NASA Astrophysics Data System (ADS)

Debsarma, Suma; Senapati, Sudipta; Das, K. P.

2014-09-01

The present work is motivated by the work of Leblanc ["Amplification of nonlinear surface waves by wind," Phys. Fluids 19, 101705 (2007)] which showed that Stokes waves grow super exponentially under fair wind as a result of modulational instability. Here, we have studied the effect of wind in a situation of crossing sea states characterized by two obliquely propagating wave systems in deep water. It is found that the wind-forced uniform wave solution in crossing seas grows explosively with a super-exponential growth rate even under a steady horizontal wind flow. This is an important piece of information in the context of the formation of freak waves.

Emissions and temperature benefits: The role of wind power in China.

PubMed

Duan, Hongbo

2017-01-01

As a non-fossil technology, wind power has an enormous advantage over coal because of its role in climate change mitigation. Therefore, it is important to investigate how substituting wind power for coal-fired electricity will affect emission reductions, changes in radiative forcing and rising temperatures, particularly in the context of emission limits. We developed an integrated methodology that includes two parts: an energy-economy-environmental (3E) integrated model and an emission-temperature response model. The former is used to simulate the dynamic relationships between economic output, wind energy and greenhouse gas (GHG) emissions; the latter is used to evaluate changes in radiative forcing and warming. Under the present development projection, wind energy cannot serve as a major force in curbing emissions, even under the strictest space-restraining scenario. China's temperature contribution to global warming will be up to 21.76% if warming is limited to 2 degrees. With the wind-for-coal power substitution, the corresponding contribution to global radiative forcing increase and temperature rise will decrease by up to 10% and 6.57%, respectively. Substituting wind power for coal-fired electricity has positive effects on emission reductions and warming control. However, wind energy alone is insufficient for climate change mitigation. It forms an important component of the renewable energy portfolio used to combat global warming. Copyright © 2016 Elsevier Inc. All rights reserved.

Sensitivity analysis of WRF model PBL schemes in simulating boundary-layer variables in southern Italy: An experimental campaign

NASA Astrophysics Data System (ADS)

Avolio, E.; Federico, S.; Miglietta, M. M.; Lo Feudo, T.; Calidonna, C. R.; Sempreviva, A. M.

2017-08-01

The sensitivity of boundary layer variables to five (two non-local and three local) planetary boundary-layer (PBL) parameterization schemes, available in the Weather Research and Forecasting (WRF) mesoscale meteorological model, is evaluated in an experimental site in Calabria region (southern Italy), in an area characterized by a complex orography near the sea. Results of 1 km × 1 km grid spacing simulations are compared with the data collected during a measurement campaign in summer 2009, considering hourly model outputs. Measurements from several instruments are taken into account for the performance evaluation: near surface variables (2 m temperature and relative humidity, downward shortwave radiation, 10 m wind speed and direction) from a surface station and a meteorological mast; vertical wind profiles from Lidar and Sodar; also, the aerosol backscattering from a ceilometer to estimate the PBL height. Results covering the whole measurement campaign show a cold and moist bias near the surface, mostly during daytime, for all schemes, as well as an overestimation of the downward shortwave radiation and wind speed. Wind speed and direction are also verified at vertical levels above the surface, where the model uncertainties are, usually, smaller than at the surface. A general anticlockwise rotation of the simulated flow with height is found at all levels. The mixing height is overestimated by all schemes and a possible role of the simulated sensible heat fluxes for this mismatching is investigated. On a single-case basis, significantly better results are obtained when the atmospheric conditions near the measurement site are dominated by synoptic forcing rather than by local circulations. From this study, it follows that the two first order non-local schemes, ACM2 and YSU, are the schemes with the best performance in representing parameters near the surface and in the boundary layer during the analyzed campaign.

Runaway Signatures in the Transport Description of Solar Wind Electrons: A New Quantitative Steady Electron Runaway Model (SERM)

NASA Astrophysics Data System (ADS)

Scudder, J. D.; Salem, C. S.

2016-12-01

A new model for solar wind electrons provides an explanation for the origin of the non-thermal core-halo-strahl-superhalo VDF ubiquitously observed in the solar wind. Such kurtotic VDF's should be as common as the gradient induced occurrence of finite parallel electric fields that enforce quasi-neutrality in astrophysical plasmas. The velocity space separatrix of coulomb runaway predicts the observed scaling of the break point energy at 1AU of the electron VDF between thermal and suprathermal components and agrees well with the tabulations of its variation with radius. SERM quantitatively reproduces: 14 year IMP archives of the fraction of supra thermal electrons and the observed variation of the supra thermal density with local (nearly asymptotic) solar wind speed; the observed inverse correlation between halo density fraction and Th/Tc; and the reported, but theoretically unusual relative slippage of the core and halo that supports the heat flux. Requirements for quasi-neutrality (in the presence of runaways) lead to a quantitative non-local specification of the required supra thermal density fraction and the lowest even Legendre order approximate VDF that is symmetric, but kurtotic in the proton rest frame. The Stokes drift of the thermals suggested by runaway physics requires a counter drift of the non-locally returning suprathermals which determine the observed heat flux and thermal force contributions and the lowest order odd Legendre dependence of the VDF. The strahl is recovered as an extreme part of the non-local suprathermals. "Direct'' runaways caused by the parallel electric field are identified as an omnipresent source for the observed sunward portion of the non-thermal VDF. The source of the super halo electrons is suggested to be mirrored runaways produced at the base of the corona with subsequent near isotropization in the interplanetary medium.

Multi-Scale Observation and Modelling of Energy and Matter Exchange in the Atmospheric Boundary-Layer (ScaleX Campaigns)

NASA Astrophysics Data System (ADS)

Zeeman, M. J.; Wolz, K.; Adler, B.; Brenner, C.; De Roo, F.; Emeis, S.; Kalthoff, N.; Mauder, M.; Schäfer, K.; Wohlfahrt, G.; Zhao, P.

2016-12-01

We investigated biosphere-atmosphere exchange processes in relation to the atmospheric boundary-layer (ABL) flow in a shallow valley. Land-use heterogeneity and topography can force local atmospheric flow patterns, including local circulations. Such flow patterns can impair current techniques for the quantification and source attribution of surface-exchange fluxes due to flux-divergence, advection and decoupling. Wind field, temperature and humidity structures in the ABL were observed in high resolution with spatially distributed observations in a 1 km3 experimental domain. Remote-sensing observations of wind, temperature and particles in the ABL (Raman-lidar; RASS; ceilometer; microwave radiometer; 3D Doppler-lidar) were combined with a high-resolution network of in-situ observations that included vertical and horizontal profiles of wind, temperature, carbon dioxide, methane and water vapor concentrations. The experiments were co-located with the long-term eddy covariance (EC) observatory Fendt (DE-Fen; ICOS, TERENO) and were part of international cooperative efforts in 2015 and 2016 (the ScaleX campaigns). The gathered experimental data offers a scale-transcending insight in local flow patterns in mountainous terrain and their influence on surface-exchange fluxes of energy and matter as observed by EC and flux-gradient methodology. In addition, the data is used for validation of Large-Eddy Simulations in complex terrain using PALM-LES. Within this modelling framework, virtual measurements are conducted to further assess the importance of three-dimensional advective and horizontal turbulent transport terms.

Harmonic Fluxes and Electromagnetic Forces of Concentric Winding Brushless Permanent Magnet Motor

NASA Astrophysics Data System (ADS)

Ishibashi, Fuminori; Takemasa, Ryo; Matsushita, Makoto; Nishizawa, Takashi; Noda, Shinichi

Brushless permanent magnet motors have been widely used in home applications and industrial fields. These days, high efficiency and low noise motors are demanded from the view point of environment. Electromagnetic noise and iron loss of the motor are produced by the harmonic fluxes and electromagnetic forces. However, order and space pattern of these have not been discussed in detail. In this paper, fluxes, electromagnetic forces and magneto-motive forces of brushless permanent magnet motors with concentric winding were analyzed analytically, experimentally and numerically. Time harmonic fluxes and time electromagnetic forces in the air gap were measured by search coils on the inner surface of the stator teeth and analyzed by FEM. Space pattern of time harmonic fluxes and time electromagnetic forces were worked out with experiments and FEM. Magneto motive forces due to concentric winding were analyzed with equations and checked by FEM.

Indo-Pacific climate during the decaying phase of the 2015/16 El Niño: role of southeast tropical Indian Ocean warming

NASA Astrophysics Data System (ADS)

Chen, Zesheng; Du, Yan; Wen, Zhiping; Wu, Renguang; Wang, Chunzai

2018-06-01

This study investigates the influence of southeast tropical Indian Ocean (SETIO) sea surface temperature (SST) warming on Indo-Pacific climate during the decaying phase of the 2015/16 El Niño by using observations and model experiments. The results show that the SETIO SST warming in spring 2016 enhanced local convection and forced a "C-shape" wind anomaly pattern in the lower troposphere. The "C-shape" wind anomaly pattern over the eastern tropical Indian Ocean consists of anomalous westerly flow south of the equator and anomalous easterly flow north of the equator. The anomalous easterly flow then extended eastward into the western North Pacific (WNP) and facilitates the development or the maintenance of an anomalous anticyclone over the South China Sea (SCS). Correspondingly, the eastern part of the Bay of Bengal, the SCS and the WNP suffered less rainfall. Such precipitation features and the associated "C-shape" wind anomaly pattern shifted northward about five latitudes in summer 2016. Additionally, the SETIO warming can induce local meridional circulation anomalies, which directly affect Indo-Pacific climate. Numerical model experiments further confirm that the SETIO SST warming plays an important role in modulating Indo-Pacific climate.

Western boundary upwelling dynamics off Oman

NASA Astrophysics Data System (ADS)

Vic, Clément; Capet, Xavier; Roullet, Guillaume; Carton, Xavier

2017-05-01

Despite its climatic and ecosystemic significance, the coastal upwelling that takes place off Oman is not well understood. A primitive-equation, regional model forced by climatological wind stress is used to investigate its dynamics and to compare it with the better-known Eastern Boundary Upwellings (EBUs). The solution compares favorably with existing observations, simulating well the seasonal cycles of thermal structure, surface circulation (mean and turbulent), and sea-surface temperature (SST). There is a 1.5-month lag between the maximum of the upwelling-favorable wind-stress-curl forcing and the oceanic response (minima in sea-surface height and SST), which we attribute to onshore-propagating Rossby waves. A southwestward-flowing undercurrent (opposite to the direction of the near-surface flow) is also simulated with a core depth of 1000 m, much deeper than found in EBUs (150-200 m). An EKE budget reveals that, in contrast to EBUs, the upwelling jet is more prone to barotropic than baroclinic instability and the contribution of locally-generated instabilities to EKE is higher by an order of magnitude. Advection and redistribution of EKE by standing mesoscale features also play a significant role in EKE budget.

Analysis of Wind Forces on Roof-Top Solar Panel

NASA Astrophysics Data System (ADS)

Panta, Yogendra; Kudav, Ganesh

2011-03-01

Structural loads on solar panels include forces due to high wind, gravity, thermal expansion, and earthquakes. International Building Code (IBC) and the American Society of Civil Engineers are two commonly used approaches in solar industries to address wind loads. Minimum Design Loads for Buildings and Other Structures (ASCE 7-02) can be used to calculate wind uplift loads on roof-mounted solar panels. The present study is primarily focused on 2D and 3D modeling with steady, and turbulent flow over an inclined solar panel on the flat based roof to predict the wind forces for designing wind management system. For the numerical simulation, 3-D incompressible flow with the standard k- ɛ was adopted and commercial CFD software ANSYS FLUENT was used. Results were then validated with wind tunnel experiments with a good agreement. Solar panels with various aspect ratios for various high wind speeds and angle of attacks were modeled and simulated in order to predict the wind loads in various scenarios. The present study concluded to reduce the strong wind uplift by designing a guide plate or a deflector before the panel. Acknowledgments to Northern States Metal Inc., OH (GK & YP) and School of Graduate Studies of YSU for RP & URC 2009-2010 (YP).

Seasonal variation of the South Indian tropical gyre

NASA Astrophysics Data System (ADS)

Aguiar-González, Borja; Ponsoni, Leandro; Ridderinkhof, Herman; van Aken, Hendrik M.; de Ruijter, Will P. M.; Maas, Leo R. M.

2016-04-01

The South Indian tropical gyre receives and redistributes water masses from the Indonesian Throughflow (ITF), a source of Pacific Ocean water which represents the only low-latitude connector between the world oceans and, therefore, a key component in the global ocean circulation and climate system. We investigate the seasonal variation of the South Indian tropical gyre and its associated open-ocean upwelling system, known as the Seychelles-Chagos Thermocline Ridge (SCTR), based on satellite altimeter data (AVISO) and global atlases of temperature and salinity (CARS09), wind stress (SCOW) and wind-driven circulation. Two novel large-scale features governing the upper geostrophic circulation of the South Indian tropical gyre are revealed. First, the seasonal shrinkage of the ocean gyre. This occurs when the South Equatorial Countercurrent (SECC) recirculates before arrival to Sumatra from winter to spring, in apparent synchronization with the annual cycle of the ITF. Second, the open-ocean upwelling is found to vary following seasonality of the overlying geostrophic ocean gyre, a relationship that has not been previously shown for this region. An analysis of major forcing mechanisms suggests that the thermocline ridge results from the constructive interaction of basin-scale wind stress curl, local-scale wind stress forcing and remote forcing driven by Rossby waves of different periodicity: semiannual in the west, under the strong influence of monsoonal winds; and, annual in the east, where the southeasterlies prevail. One exception occurs during winter, when the well-known westward intensification of the upwelling core, the Seychelles Dome, is shown to be largely a response of the wind-driven circulation. Broadly speaking, the seasonal shrinkage of the ocean gyre (and the SCTR) is the one feature that differs most when the geostrophic circulation is compared to the wind-driven Sverdrup circulation. From late autumn to spring, the eastward SECC recirculates early in the east on feeding the westward South Equatorial Current, therefore closing the gyre before arrival to Sumatra. We find this recirculation longitude migrates over 20° and collocates with the westward advance of a zonal thermohaline front emerging from the encounter between (upwelled) Indian Equatorial Water and relatively warmer and fresher Indonesian Throughflow Water. We suggest this front, which we call the Indonesian Throughflow Front, plays an important role as forcing to the tropical gyre, generating southward geostrophic flows that contribute to the early recirculation of the SECC at longitudes more westward than predicted from the barotropic wind-driven circulation. Because our findings are based on time-averaged seasonal fields from 22 years of satellite altimeter data and from about 60 years of non-systematic sampling of ocean temperature and salinity data (CARS09), we stress the importance of further study on the possibility that interanual variability in the seasonal ITF may cause changes in the seasonal resizing of the ocean gyre and its associated upwelling ridge.

Intracycle angular velocity control of cross-flow turbines

NASA Astrophysics Data System (ADS)

Strom, Benjamin; Brunton, Steven L.; Polagye, Brian

2017-08-01

Cross-flow turbines, also known as vertical-axis turbines, are attractive for power generation from wind and water currents. Some cross-flow turbine designs optimize unsteady fluid forces and maximize power output by controlling blade kinematics within one rotation. One established method is to dynamically pitch the blades. Here we introduce a mechanically simpler alternative: optimize the turbine rotation rate as a function of angular blade position. We demonstrate experimentally that this approach results in a 59% increase in power output over standard control methods. Analysis of fluid forcing and blade kinematics suggest that power increase is achieved through modification of the local flow conditions and alignment of fluid force and rotation rate extrema. The result is a low-speed, structurally robust turbine that achieves high efficiency and could enable a new generation of environmentally benign turbines for renewable power generation.

47 CFR 80.141 - General provisions for ship stations.

Code of Federal Regulations, 2013 CFR

2013-10-01

... storm, subfreezing air temperatures associated with gale force winds causing severe icing on superstructures, or winds of force 10 or above on the Beaufort scale for which no storm warning has been received...

47 CFR 80.141 - General provisions for ship stations.

Code of Federal Regulations, 2012 CFR

2012-10-01

... storm, subfreezing air temperatures associated with gale force winds causing severe icing on superstructures, or winds of force 10 or above on the Beaufort scale for which no storm warning has been received...

47 CFR 80.141 - General provisions for ship stations.

Code of Federal Regulations, 2011 CFR

2011-10-01

... storm, subfreezing air temperatures associated with gale force winds causing severe icing on superstructures, or winds of force 10 or above on the Beaufort scale for which no storm warning has been received...

47 CFR 80.141 - General provisions for ship stations.

Code of Federal Regulations, 2014 CFR

2014-10-01

... storm, subfreezing air temperatures associated with gale force winds causing severe icing on superstructures, or winds of force 10 or above on the Beaufort scale for which no storm warning has been received...

47 CFR 80.141 - General provisions for ship stations.

Code of Federal Regulations, 2010 CFR

2010-10-01

... storm, subfreezing air temperatures associated with gale force winds causing severe icing on superstructures, or winds of force 10 or above on the Beaufort scale for which no storm warning has been received...

On the spatial coherence of temperature within and above a vineyard under drainage conditions

NASA Astrophysics Data System (ADS)

Everard, K.; Giometto, M. G.; Christen, A.; Oldroyd, H. J.; Parlange, M. B.

2017-12-01

We show that turbulent exchange within vineyards under nighttime drainage conditions is controlled by large-scale coherent structures arising from a mixing-layer type instability at the canopy top, h. A combination of measurements and large-eddy simulations (LESs) are here used to characterize the onset and development of such structures as a function of the approaching wind angle over an organized canopy during drainage flows. Measurements were carried out over a west-facing 7° vineyard slope near Oliver, BC, Canada in the Okanagan Valley between July 5 and July 22, 2016. The vineyard canopy had an average height of h = 2.3 m, with parallel rows oriented in the local downslope direction (i.e. east-west). The set-up consisted of an array of five vertically arranged ultrasonic anemometers at z/h = 0.19, 0.39, 0.65, 1.02, and 2.06, and a 2-D grid of 40 fine-wire thermocouples arranged at the same heights as the ultrasonic anemometer array on 8 separate masts extending in the upslope direction at locations up to x/h = 13.91 from the flux tower. To complement observations, pressure-driven open-channel flow LESs are performed over a regular domain where vegetation is accounted for via a space dependent drag force. The drainage flow regime is emulated via a tuned pressure-gradient forcing, and different approaching wind angles are considered. Linear stability analyses show that the most unstable mode at the canopy top strongly depends on the approaching wind angle. Space-lagged correlations from measurements show that the lifetime of such eddies within the canopy also depends on the approaching wind direction, with longer lifetimes observed when wind angles are directed along the vine-rows. LESs are compared with measured quantities to ensure matching, and then used to investigate in detail the influence of the above-canopy wind vectors on eddy lifetimes. The impact of the observed coherent structures on momentum and heat exchange coefficients are also discussed.

Nonlinearity Role in Long-Term Interaction of the Ocean Gravity Waves

DTIC Science & Technology

2012-09-30

3 4 =s We found that in the fetch-limited case the wind forcing index s is similar to the time domain situation, and the wind forcing is given by...of its evolution. Fig.5 gives a graphical summary of four reference cases of self-similar evolution of wind-driven waves. These cases are shown as...different R, tangents of one-parametric dependencies H~TR height-to-period in logarithmic axes. Reference cases of growing wind sea are shown as

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lantz, E.; Tegen, S.

'Community wind' refers to a class of wind energy ownership structures. The extent of local ownership may range from a small minority share to full ownership by persons in the immediate area surrounding the wind project site. Potential project owners include local farmers, businesses, Native American tribes, universities, cooperatives, or any other local entity seeking to invest in wind energy. The opposite of community wind is an 'absentee' project, in which ownership is completely removed from the state and community surrounding the facility. Thus, there is little or no ongoing direct financial benefit to state and local populations aside frommore » salaries for local repair technicians, local property tax payments, and land lease payments. In recent years, the community wind sector has been inhibited by manufacturers' preference for larger turbine orders. This often puts smaller community wind developers and projects at a competitive disadvantage. However, state policies specifically supporting community wind may become a more influential market factor as turbines are now more readily available given manufacturer ramp-ups and the slow-down in the industry that has accompanied the recent economic and financial crises. This report examines existing literature to provide an overview of economic impacts resulting from community wind projects, compares results, and explains variability.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lantz, E.; Tegen, S.

"Community wind" refers to a class of wind energy ownership structures. The extent of local ownership may range from a small minority share to full ownership by persons in the immediate area surrounding the wind project site. Potential project owners include local farmers, businesses, Native American tribes, universities, cooperatives, or any other local entity seeking to invest in wind energy. The opposite of community wind is an "absentee" project, in which ownership is completely removed from the state and community surrounding the facility. Thus, there is little or no ongoing direct financial benefit to state and local populations aside frommore » salaries for local repair technicians, local property tax payments, and land lease payments. In recent years, the community wind sector has been inhibited by manufacturers' preference for larger turbine orders. This often puts smaller community wind developers and projects at a competitive disadvantage. However, state policies specifically supporting community wind may become a more influential market factor as turbines are now more readily available given manufacturer ramp-ups and the slow-down in the industry that has accompanied the recent economic and financial crises. This report examines existing literature to provide an overview of economic impacts resulting from community wind projects, compares results, and explains variability.« less

Erodibility of waste (Loess) soils from construction sites under water and wind erosional forces.

PubMed

Tanner, Smadar; Katra, Itzhak; Argaman, Eli; Ben-Hur, Meni

2018-03-01

Excess soils from construction sites (waste soils) become a problem when exposed to soil erosion by water or wind. Understanding waste soil erodibility can contribute to its proper reuse for various surface applications. The general objective of the study was to provide a better understanding of the effects of soil properties on erodibility of waste soils excavated from various depths in a semiarid region under rainfall and wind erosive forces. Soil samples excavated from the topsoil (0-0.3m) and subsoil layers (0.3-0.9 and >1m depths) were subjected to simulated rainfall and wind. Under rainfall erosive forces, the subsoils were more erodible than the topsoil, in contrast to the results obtained under wind erosive forces. Exchangeable sodium percentage was the main factor controlling soil erodibility (K i ) under rainfall, and a significant logarithmic regression line was found between these two parameters. In addition, a significant, linear regression was found between K i and slaking values for the studied soil samples, suggesting that the former can be predicted from the latter. Soil erodibility under wind erosion force was controlled mainly by the dry aggregate characteristics (mean weight diameter and aggregate density): their higher values in the subsoil layers resulted in lower soil erodibility compared to the topsoil. Copyright © 2017 Elsevier B.V. All rights reserved.

Heat Pipes Cool Power Magnetics

NASA Technical Reports Server (NTRS)

Hansen, I.; Chester, M.; Luedke, E.

1983-01-01

Configurations originally developed for space use are effective in any orientation. Heat pipes integrated into high-power, high-frequency, highvoltage spaceflight magnetics reduce weight and improve reliability by lowering internal tempertures. Two heat pipes integrated in design of power transformer cool unit in any orientation. Electrostatic shield conducts heat from windings to heat pipe evaporator. Technology allows dramatic reductions in size and weight, while significantly improving reliability. In addition, all attitude design of heat pipes allows operation of heat pipes independent of local gravity forces.

Climate of the Kennedy Space Center and vicinity

NASA Technical Reports Server (NTRS)

Mailander, Joseph L.

1990-01-01

Climate plays a large role in determining the biota of a region. Summary data are presented for climate variables of ecological importance including precipitation, temperature, evapotranspiration, wind, isolation, lightning, and humidity. The John F. Kennedy Space Center, Cape Canaveral Air Force Station, and surrounding area are sampled intensively for climatic conditions; data are presented for the barrier island, Merritt Island, and the mainland, which represents the range of conditions in the local area. Climatic figures, database listings, and historic data (pre-1931) are presented in the appendix.

Dynamics of Monsoon-Induced Biennial Variability in ENSO

NASA Technical Reports Server (NTRS)

Kim, Kyu-Myong; Lau, K.-M.; Einaudi, Franco (Technical Monitor)

2000-01-01

The mechanism of the quasi-biennial tendency in El Nino Southern Oscillation (ENSO)-monsoon coupled system is investigated using an intermediate coupled model. The monsoon wind forcing is prescribed as a function of Sea Surface Temperature (SST) anomalies based on the relationship between zonal wind anomalies over the western Pacific to sea level change in the equatorial eastern Pacific. The key mechanism of quasi-biennial tendency in El Nino evolution is found to be in the strong coupling of ENSO to monsoon wind forcing over the western Pacific. Strong boreal summer monsoon wind forcing, which lags the maximum SST anomaly in the equatorial eastern Pacific approximately 6 months, tends to generate Kelvin waves of the opposite sign to anomalies in the eastern Pacific and initiates the turnabout in the eastern Pacific. Boreal winter monsoon forcing, which has zero lag with maximum SST in the equatorial eastern Pacific, tends to damp the ENSO oscillations.

Circular Conditional Autoregressive Modeling of Vector Fields.

PubMed

Modlin, Danny; Fuentes, Montse; Reich, Brian

2012-02-01

As hurricanes approach landfall, there are several hazards for which coastal populations must be prepared. Damaging winds, torrential rains, and tornadoes play havoc with both the coast and inland areas; but, the biggest seaside menace to life and property is the storm surge. Wind fields are used as the primary forcing for the numerical forecasts of the coastal ocean response to hurricane force winds, such as the height of the storm surge and the degree of coastal flooding. Unfortunately, developments in deterministic modeling of these forcings have been hindered by computational expenses. In this paper, we present a multivariate spatial model for vector fields, that we apply to hurricane winds. We parameterize the wind vector at each site in polar coordinates and specify a circular conditional autoregressive (CCAR) model for the vector direction, and a spatial CAR model for speed. We apply our framework for vector fields to hurricane surface wind fields for Hurricane Floyd of 1999 and compare our CCAR model to prior methods that decompose wind speed and direction into its N-S and W-E cardinal components.

Circular Conditional Autoregressive Modeling of Vector Fields*

PubMed Central

Modlin, Danny; Fuentes, Montse; Reich, Brian

2013-01-01

As hurricanes approach landfall, there are several hazards for which coastal populations must be prepared. Damaging winds, torrential rains, and tornadoes play havoc with both the coast and inland areas; but, the biggest seaside menace to life and property is the storm surge. Wind fields are used as the primary forcing for the numerical forecasts of the coastal ocean response to hurricane force winds, such as the height of the storm surge and the degree of coastal flooding. Unfortunately, developments in deterministic modeling of these forcings have been hindered by computational expenses. In this paper, we present a multivariate spatial model for vector fields, that we apply to hurricane winds. We parameterize the wind vector at each site in polar coordinates and specify a circular conditional autoregressive (CCAR) model for the vector direction, and a spatial CAR model for speed. We apply our framework for vector fields to hurricane surface wind fields for Hurricane Floyd of 1999 and compare our CCAR model to prior methods that decompose wind speed and direction into its N-S and W-E cardinal components. PMID:24353452

Numerical simulation of wave-current interaction under strong wind conditions

NASA Astrophysics Data System (ADS)

Larrañaga, Marco; Osuna, Pedro; Ocampo-Torres, Francisco Javier

2017-04-01

Although ocean surface waves are known to play an important role in the momentum and other scalar transfer between the atmosphere and the ocean, most operational numerical models do not explicitly include the terms of wave-current interaction. In this work, a numerical analysis about the relative importance of the processes associated with the wave-current interaction under strong off-shore wind conditions in Gulf of Tehuantepec (the southern Mexican Pacific) was carried out. The numerical system includes the spectral wave model WAM and the 3D hydrodynamic model POLCOMS, with the vertical turbulent mixing parametrized by the kappa-epsilon closure model. The coupling methodology is based on the vortex-force formalism. The hydrodynamic model was forced at the open boundaries using the HYCOM database and the wave model was forced at the open boundaries by remote waves from the southern Pacific. The atmospheric forcing for both models was provided by a local implementation of the WRF model, forced at the open boundaries using the CFSR database. The preliminary analysis of the model results indicates an effect of currents on the propagation of the swell throughout the study area. The Stokes-Coriolis term have an impact on the transient Ekman transport by modifying the Ekman spiral, while the Stokes drift has an effect on the momentum advection and the production of TKE, where the later induces a deepening of the mixing layer. This study is carried out in the framework of the project CONACYT CB-2015-01 255377 and RugDiSMar Project (CONACYT 155793).

Effects of Regional Climate Change on the Wave Conditions in the Western Baltic Sea

NASA Astrophysics Data System (ADS)

Dreier, N.; Fröhle, P.

2017-12-01

The local wave climate in the Western Baltic Sea is mainly generated by the local wind field over the area. Long-term changes of the local wind conditions that are induced e.g. by regional climate change, directly affect the local wave climate and other local wind driven coastal processes like e.g. the longshore sediment transport. The changes of the local wave climate play an important role for the safe functional and structural design of new, or the adaption of existing, coastal protection structures as well as for the assessment of long-term morphological changes of the coastline. In this study, the wave model SWAN is used for the calculation of hourly wave conditions in the Western Baltic Sea between 1960 and 2100. Future wind conditions from two regional climate models (Cosmo-CLM and REMO) that have been forced by different future greenhouse gas emission scenarios used within AR4 (A1B, B1) and AR5 (RCP4.5 and RCP8.5) of IPCC are used as input for the wave model. The changes of the average wave conditions are analyzed from comparisons between the 30 years averages for the future (e.g. 2071-2100) and the reference period 1971-2000. Regarding the emission scenarios A1B and B1, a significant change of the 30 years averages of significant wave height at westerly wind exposed locations with predominant higher values up to +10% is found (cf. Fig. 1). In contrast, the change of the 30 years averages of significant wave height is more weak at easterly wind exposed locations, resulting in higher and lower values between -5% to +5%. Moreover, more wave events from W-NW and fewer events from N-NE can be expected, due to changes of the frequency of occurrence of the 30 years averages of mean wave direction. The changes of extreme wave heights are analyzed based on methods of extreme value analysis and the time series of wave parameters at selected locations nearby the German Baltic Sea coast. No robust changes of the significant wave heights with a return period of 200 years are found for the emission scenarios A1B and B1. Both increases and decreases of the extreme wave heights are possible within a range of -18% to +18% (-0.5m to +0.5m). In the presentation, we will show results from the assessment of the changes of the wave conditions for the emission scenarios RCP4.5 and RCP8.5 and discuss possible impacts for the German Baltic Sea coast.

Experiments on waves under impulsive wind forcing in view of the Phillips (1957) theory

NASA Astrophysics Data System (ADS)

Shemer, Lev; Zavadsky, Andrey

2016-11-01

Only limited information is currently available on the initial stages of wind-waves growth from rest under sudden wind forcing; the mechanisms leading to the appearance of waves are still not well understood. In the present work, waves emerging in a small-scale laboratory facility under the action of step-like turbulent wind forcing are studied using capacitance and laser slope gauges. Measurements are performed at a number of fetches and for a range of wind velocities. Taking advantage of the fully automated experimental procedure, at least 100 independent realizations are recorded for each wind velocity at every fetch. The accumulated data sets allow calculating ensemble-averaged values of the measured parameters as a function of time elapsed from the blower activation. The accumulated results on the temporal variation of wind-wave field initially at rest allow quantitative comparison with the theory of Phillips (1957). Following Phillips, appearance of the initial detectable ripples was considered first, while the growth of short gravity waves at later times was analyzed separately. Good qualitative and partial quantitative agreement between the Phillips predictions and the measurements was obtained for both those stages of the initial wind-wave field evolution.

Preliminary Assessment of Potential Avian Interactions at Four Proposed Wind Energy Facilities on Vandenberg Air Force Base, California

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

The United States Air Force (USAF) is investigating whether to install wind turbines to provide a supplemental source of electricity at Vandenberg Air Force Base (VAFB) near Lompoc, California. As part of that investigation, VAFB sought assistance from the U.S. Department of Energy's National Renewable Energy Laboratory (NREL) to provide a preliminary characterization of the potential risk to wildlife resources (mainly birds and bats) from wind turbine installations. With wind power development expanding throughout North America and Europe, concerns have surfaced over the number of bird fatalities associated with wind turbines. Guidelines developed for the wind industry by the Nationalmore » Wind Coordinating Committee (NWCC) recommend assessing potential impacts to birds, bats, and other potentially sensitive resources before construction. The primary purpose of an assessment is to identify potential conflicts with sensitive resources, to assist developers with identifying their permitting needs, and to develop strategies to avoid impacts or to mitigate their effects. This report provides a preliminary (Phase I) biological assessment of potential impacts to birds and bats that might result from construction and operation of the proposed wind energy facilities on VAFB.« less

Experimental modeling of the effect of hurricane wind forces on driving behavior and vehicle performance.

PubMed

Rodriguez, Jose M; Codjoe, Julius; Osman, Osama; Ishak, Sherif; Wolshon, Brian

2015-01-01

While traffic planning is important for developing a hurricane evacuation plan, vehicle performance on the roads during extreme weather conditions is critical to the success of the planning process. This novel study investigates the effect of gusty hurricane wind forces on the driving behavior and vehicle performance. The study explores how the parameters of a driving simulator could be modified to reproduce wind loadings experienced by three vehicle types (passenger car, ambulance, and bus) during gusty hurricane winds, through manipulation of appropriate software. Thirty participants were then tested on the modified driving simulator under five wind conditions (ranging from normal to hurricane category 4). The driving performance measures used were heading error and lateral displacement. The results showed that higher wind forces resulted in more varied and greater heading error and lateral displacement. The ambulance had the greatest heading errors and lateral displacements, which were attributed to its large lateral surface area and light weight. Two mathematical models were developed to estimate the heading error and lateral displacements for each of the vehicle types for a given change in lateral wind force. Through a questionnaire, participants felt the different characteristics while driving each vehicle type. The findings of this study demonstrate the valuable use of a driving simulator to model the behavior of different vehicle types and to develop mathematical models to estimate and quantify driving behavior and vehicle performance under hurricane wind conditions.

State Enabling Legislation for Commercial-Scale Wind Power Siting and the Local Government Role

DOE Office of Scientific and Technical Information (OSTI.GOV)

McElfish, J.M.; Gersen, S.

Siting of commercial-scale wind facilities (>5MW) is determined primarily by state laws. State laws either leave siting regulation to local governments, prescribe and constrain the role for local governments, establish state standards, or preempt local governance by having state institutions govern siting. Siting regulation is extremely important to the advancement of wind generation in the United States. Major siting decisions lie ahead for state and local governments as the nation diversifies its energy portfolio. An increase in the number of new wind facilities, siting in more locations and in more heavily populated areas, will require attention to the laws andmore » regulations that govern siting. Local governments exercise some authority over commercial-scale wind facility siting in 48 of the 50 states. In 34 states, local governments have substantial autonomy to regulate the siting of most or all commercial-scale wind facilities. A few states authorize local governments to regulate wind facility siting, but make the scope of local regulation subject to limitations defined by state law. Eleven states set size thresholds for state regulatory involvement with local governments in these states regulating smaller facilities and state boards regulating larger ones (either exclusively or concurrently with local governments). In just under a third of the states, siting of most or all commercial-scale wind facilities requires approval by both state and local government bodies. Only a few states reserve the regulation of siting of all or virtually all commercial-scale wind facilities to state boards and commissions. The content of the applicable regulations is more important, in general, than the level of government responsible for the decision. Several states that assign siting responsibilities to local governments have specified some of the content and the limits of local regulation. About 1/5 of the states have directed boards and commissions to develop statewide regulations to deal with wind facility siting issues subject to state approval. These requirements most often specify standards for setbacks, wildlife, noise, decommissioning, and other issues.« less

Surface Buoyancy Fluxes and the Strength of the Subpolar Gyre

NASA Astrophysics Data System (ADS)

Hogg, A. M.; Gayen, B.

2017-12-01

Midlatitude ocean gyres have long been considered to be driven by the mechanical wind stress on the ocean's surface (strictly speaking, the potential vorticity input from wind stress curl). However, surface buoyancy forcing (i.e. heating/cooling or freshening/salinification) also modifies the potential vorticity at the surface. Here, we present a simple argument to demonstrate that ocean gyres may (in principle) be driven by surface buoyancy forcing. This argument is derived in two ways: A Direct Numerical Simulation, driven purely by buoyancy forcing, which generates strong nonlinear gyers in the absence of wind stress; and A series of idealised eddy-resolving numerical ocean model simulations, in which wind stress and buoyancy flux are varied independently and together, are used to understand the relative importance of these two types of forcing. In these simulations, basin-scale gyres and western boundary currents with realistic magnitudes, remain even in the absence of mechanical forcing by surface wind stress. These results support the notion that surface buoyancy forcing can reorganise the potential vorticity in the ocean in such a way as to drive basin-scale gyres. The role of buoyancy is stronger in the subpolar gyre than in the subtropical gyre. We infer that surface buoyancy fluxes are likely to play a contributing role in governing the strength, variability and predictability of the North Atlantic subpolar gyre.

Aerodynamic profiling of terminal building using computational fluid dynamics approach

NASA Astrophysics Data System (ADS)

Vidhya, S.; Pradeep Kumar, R.; Hareesh, M.; Sekar, S. K.

2017-11-01

A case study of isolated building is studied using ANSYS CFX and SAP2000. The plan idea of 30m by 60m is chosen for terminal building. The model is subjected to different wind incidence from 0° to 90° and 45° with 30° interval for 55m/s wind speed. By using tributary area method, the forces at the each mesh node are summed up to get corresponding wind force at that joint within that area. The best effective structural system is determined by designing the structure for each wind incidence. Wind analysis and design is carried out for increasing wind speed above 55m/s to identify the collapse pattern of structure. External supporting members are suggested to withstand that maximum wind speed.

Near-Inertial Surface Currents and their influence on Surface Dispersion in the Northeastern Gulf of Mexico near the Deepwater Horizon Oil Spill

NASA Astrophysics Data System (ADS)

Gough, M.; Reniers, A.; MacMahan, J. H.; Howden, S. D.

2014-12-01

The continental shelf along the northeastern Gulf of Mexico is transected by the critical latitude (30°N) for inertial motions. At this latitude the inertial period is 24 hours and diurnal surface current oscillations can amplify due to resonance with diurnal wind and tidal forcing. Tidal amplitudes are relatively small in this region although K1 tidal currents can be strong over the shelf west of the DeSoto Canyon where the K1 tide propagates onshore as a Sverdrup wave. Other sources of diurnal motions include internal tidal currents, Poincaré waves, and basin resonance. It is therefore very difficult to separate inertial wind-driven motions from other diurnal motions. Spatiotemporal surface currents were measured using hourly 6 km resolution HF radar data collected in June 2010 during the Deepwater Horizon oil spill and July 2012 during the Grand Lagrangian Deployment (GLAD). Surface currents were also measured using GLAD GPS-tracked drifters. NDBC buoy wind data were used to determine wind-forcing, and OSU Tidal Inversion Software (OTIS) were used to predict tidal currents. The relative spatiotemporal influence of diurnal wind and tidal forcing on diurnal surface current oscillations is determined through a series of comparative analyses: phase and amplitude of bandpassed timeseries, wavelet analyses, wind-driven inertial oscillation calculations, and tidal current predictions. The wind-driven inertial ocean response is calculated by applying a simple "slab" model where wind-forcing is allowed to excite a layer of low-density water riding over high density water. The spatial variance of diurnal motions are found to be correlated with satellite turbidity imagery indicating that stratification influences the sea surface inertial response to wind-forcing. Surface dispersion is found to be minimized in regions of high diurnal variance suggesting that mean surface transport is restricted in regions of inertial motions associated with stratification.

On Release of Microbe-Laden Particles from Mars Landers

NASA Technical Reports Server (NTRS)

Bellan, Josette; Harstad, Kenneth

2006-01-01

A paper presents a study in which rates of release of small particles from Mars lander spacecraft into the Martian atmosphere were estimated from first principles. Because such particles can consist of, or be laden with, terrestrial microbes, the study was undertaken to understand their potential for biological contamination of Mars. The study included taking account of forces and energies involved in adhesion of particles and of three mechanisms of dislodgement of particles from the surface of a Mars lander: wind shear, wind-driven impingement of suspended dust, and impingement of wind-driven local saltating sand particles. Wind shear was determined to be effective in dislodging only particles larger than about 10 microns and would probably be of limited interest because such large particles could be removed by pre-flight cleaning of the spacecraft, and their number on the launched spacecraft would thus be relatively small. Dislodgement by wind-driven dust was found to be characterized by an adhesion half-life of the order of 10,000 years judged to be too long to be of concern. Dislodgement by saltating sand particles, including skirts of dust devils, was found to be of potential importance, depending on the sizes of the spacecraft-attached particles and characteristics of both Mars sand-particle and spacecraft surfaces.

Assimilation of Wind Profiles from Multiple Doppler Radar Wind Profilers for Space Launch Vehicle Applications

NASA Technical Reports Server (NTRS)

Decker, Ryan K.; Walker, John R.; Barbre, Robert E., Jr.; Leach, Richard D.

2015-01-01

Atmospheric wind data are required by space launch vehicles in order to assess flight vehicle loads and performance on day-of-launch. Space launch ranges at NASA's Kennedy Space Center co-located with the United States Air Force's (USAF) Eastern Range (ER) at Cape Canaveral Air Force Station and USAF's Western Range (WR) at Vandenberg Air Force Base have extensive networks of in-situ and remote sensing instrumentation to measure atmospheric winds. Each instrument's technique to measure winds has advantages and disadvantages in regards to use within vehicle trajectory analyses. Balloons measure wind at all altitudes necessary for vehicle assessments, but two primary disadvantages exist when applying balloon output. First, balloons require approximately one hour to reach required altitudes. Second, balloons are steered by atmospheric winds down range of the launch site that could significantly differ from those winds along the vehicle ascent trajectory. These issues are mitigated by use of vertically pointing Doppler Radar Wind Profilers (DRWPs). However, multiple DRWP instruments are required to provide wind data over altitude ranges necessary for vehicle trajectory assessments. The various DRWP systems have different operating configurations resulting in different temporal and spatial sampling intervals. Therefore, software was developed to combine data from both DRWP-generated profiles into a single profile for use in vehicle trajectory analyses. This paper will present details of the splicing software algorithms and will provide sample output.

Placing Local Aggregations in a Larger-Scale Context: Hierarchical Modeling of Black-Footed Albatross Dispersion.

PubMed

Michael, P E; Jahncke, J; Hyrenbach, K D

2016-01-01

At-sea surveys facilitate the study of the distribution and abundance of marine birds along standardized transects, in relation to changes in the local environmental conditions and large-scale oceanographic forcing. We analyzed the form and the intensity of black-footed albatross (Phoebastria nigripes: BFAL) spatial dispersion off central California, using five years (2004-2008) of vessel-based surveys of seven replicated survey lines. We related BFAL patchiness to local, regional and basin-wide oceanographic variability using two complementary approaches: a hypothesis-based model and an exploratory analysis. The former tested the strength and sign of hypothesized BFAL responses to environmental variability, within a hierarchical atmosphere-ocean context. The latter explored BFAL cross-correlations with atmospheric / oceanographic variables. While albatross dispersion was not significantly explained by the hierarchical model, the exploratory analysis revealed that aggregations were influenced by static (latitude, depth) and dynamic (wind speed, upwelling) environmental variables. Moreover, the largest BFAL patches occurred along the survey lines with the highest densities, and in association with shallow banks. In turn, the highest BFAL densities occurred during periods of negative Pacific Decadal Oscillation index values and low atmospheric pressure. The exploratory analyses suggest that BFAL dispersion is influenced by basin-wide, regional-scale and local environmental variability. Furthermore, the hypothesis-based model highlights that BFAL do not respond to oceanographic variability in a hierarchical fashion. Instead, their distributions shift more strongly in response to large-scale ocean-atmosphere forcing. Thus, interpreting local changes in BFAL abundance and dispersion requires considering diverse environmental forcing operating at multiple scales.

Biogeochemical Response to Mesoscale Physical Forcing in the California Current System

NASA Technical Reports Server (NTRS)

Niiler, Pearn P.; Letelier, Ricardo; Moisan, John R.; Marra, John A. (Technical Monitor)

2001-01-01

In the first part of the project, we investigated the local response of the coastal ocean ecosystems (changes in chlorophyll, concentration and chlorophyll, fluorescence quantum yield) to physical forcing by developing and deploying Autonomous Drifting Ocean Stations (ADOS) within several mesoscale features along the U.S. west coast. Also, we compared the temporal and spatial variability registered by sensors mounted in the drifters to that registered by the sensors mounted in the satellites in order to assess the scales of variability that are not resolved by the ocean color satellite. The second part of the project used the existing WOCE SVP Surface Lagrangian drifters to track individual water parcels through time. The individual drifter tracks were used to generate multivariate time series by interpolating/extracting the biological and physical data fields retrieved by remote sensors (ocean color, SST, wind speed and direction, wind stress curl, and sea level topography). The individual time series of the physical data (AVHRR, TOPEX, NCEP) were analyzed against the ocean color (SeaWiFS) time-series to determine the time scale of biological response to the physical forcing. The results from this part of the research is being used to compare the decorrelation scales of chlorophyll from a Lagrangian and Eulerian framework. The results from both parts of this research augmented the necessary time series data needed to investigate the interactions between the ocean mesoscale features, wind, and the biogeochemical processes. Using the historical Lagrangian data sets, we have completed a comparison of the decorrelation scales in both the Eulerian and Lagrangian reference frame for the SeaWiFS data set. We are continuing to investigate how these results might be used in objective mapping efforts.

Ring-slope interactions and the formation of the western boundary current in the Gulf of Mexico

NASA Astrophysics Data System (ADS)

Vidal, VíCtor M. V.; Vidal, Francisco V.; Meza, Eustorgio; Portilla, Josué; Zambrano, Lorenzo; Jaimes, BenjamíN.

1999-09-01

Hydrographic data from the Gulf of Mexico (gulf) provide evidence that a western boundary current was set up by the interaction of an anticyclonic Loop Current (LC) ring with the continental margin of the western gulf during March-August 1985. The March 1985 geostrophic circulation reveals a remnant anticyclonic ring colliding with the slope. During this collision, two cyclonic rings were shed as the anticyclone transferred vorticity to the surrounding slope water. During July-August 1985, the ring triad weakened and evolved into a ˜900-km-long, north flowing, along-slope, western boundary current and cyclonic-anticyclonic ring pairs distributed throughout the central and western gulf. This western boundary current attained maximum northward flow speeds of 25 cm s-1 and an 8.3-Sv mass transport between 94°-96°W at 25°N. Our March-August 1985 observations reveal that the residence time and decay period of LC anticyclones in the western gulf may exceed 150 days. Within this time period the western gulf's cyclonic-anticyclonic vorticity field decayed ˜50%. Thus the western boundary current's evolutionary period, from its gestation to its absolute decay, is estimated to be of the order of 300 days. Although the presence of a western boundary current in the gulf has been attributed to the annual wind stress curl cycle [Sturges, 1993], our analyses of the western gulf March and July-August 1985 ring-driven geostrophic circulation and corresponding (January, February and May, June 1985) monthly mean synoptic wind stress curl distributions reveal that these constitute competing forcing mechanisms for the gulf's regional circulation. However, when very strong local forcing such as large eddies are present, the wind-driven background circulation is overwhelmed by such eddy forcing.

Lagrangian mixed layer modeling of the western equatorial Pacific

NASA Technical Reports Server (NTRS)

Shinoda, Toshiaki; Lukas, Roger

1995-01-01

Processes that control the upper ocean thermohaline structure in the western equatorial Pacific are examined using a Lagrangian mixed layer model. The one-dimensional bulk mixed layer model of Garwood (1977) is integrated along the trajectories derived from a nonlinear 1 1/2 layer reduced gravity model forced with actual wind fields. The Global Precipitation Climatology Project (GPCP) data are used to estimate surface freshwater fluxes for the mixed layer model. The wind stress data which forced the 1 1/2 layer model are used for the mixed layer model. The model was run for the period 1987-1988. This simple model is able to simulate the isothermal layer below the mixed layer in the western Pacific warm pool and its variation. The subduction mechanism hypothesized by Lukas and Lindstrom (1991) is evident in the model results. During periods of strong South Equatorial Current, the warm and salty mixed layer waters in the central Pacific are subducted below the fresh shallow mixed layer in the western Pacific. However, this subduction mechanism is not evident when upwelling Rossby waves reach the western equatorial Pacific or when a prominent deepening of the mixed layer occurs in the western equatorial Pacific or when a prominent deepening of the mixed layer occurs in the western equatorial Pacific due to episodes of strong wind and light precipitation associated with the El Nino-Southern Oscillation. Comparison of the results between the Lagrangian mixed layer model and a locally forced Eulerian mixed layer model indicated that horizontal advection of salty waters from the central Pacific strongly affects the upper ocean salinity variation in the western Pacific, and that this advection is necessary to maintain the upper ocean thermohaline structure in this region.

Blast and Impact Resistant Composite Structures for Navy Ships

DTIC Science & Technology

2013-03-15

Navy cargo ships, Air Force tactical shelters, Air Force runway matting, vehicular bridge decks, railcar floors and wind turbine blades. The US Army...bridge decks, railcar floors and wind turbine blades. NAVY RELEVANCE Producing stronger, safer and more cost-effective platforms for the new generation...floors and wind turbine blades. 32 NAVY RELEVANCE Producing stronger, safer and more cost-effective platforms for the new generation naval ships

Beaufort scale of wind force as adapted for use on forested areas of the northern Rocky Mountains

Treesearch

George M. Jemison

1934-01-01

The Beaufort scale of wind force, internationally employed by weather agencies, was not designed for use on mountainous and forested areas like those of the Rocky Mountains of northern Idaho and western Montana. The United States Forest Service has used it to estimate wind velocities in this region, but has found that in too many cases the resulting estimates were...

Radiative forcing and climate response due to the presence of black carbon in cloud droplets

NASA Astrophysics Data System (ADS)

Wang, Zhili; Zhang, Hua; Li, Jiangnan; Jing, Xianwen; Lu, Peng

2013-05-01

Optical properties of clouds containing black carbon (BC) particles in their water droplets are calculated by using the Maxwell Garnett mixing rule and Mie theory. The obtained cloud optical properties were then applied to an interactive system by coupling an aerosol model with a General Circulation Model. This system is used to investigate the radiative forcing and the equilibrium climate response due to BC in cloud droplets. The simulated global annual mean radiative forcing at the top of the atmosphere due to the BC in cloud droplets is found to be 0.086 W m-2. Positive radiative forcing can be seen in Africa, South America, East and South Asia, and West Europe, with a maximum value of 1.5 W m-2 being observed in these regions. The enhanced cloud absorption is shown to increase the global annual mean values of solar heating rate, water vapor, and temperature, but to decrease the global annual mean cloud fraction. Finally, the global annual mean surface temperature is shown to increase by +0.08 K. The local maximum changes are found to be as low as -1.5 K and as high as +0.6 K. We show there has been a significant difference in surface temperature change in the Southern and Northern Hemisphere (+0.19 K and -0.04 K, respectively). Our results show that this interhemispheric asymmetry in surface temperature change could cause a corresponding change in atmospheric dynamics and precipitation. It is also found that the northern trade winds are enhanced in the Intertropical Convergence Zone (ITCZ). This results in northerly surface wind anomalies which cross the equator to converge with the enhanced southern trade winds in the tropics of Southern Hemisphere. This is shown to lead to an increase (a decrease) of vertical ascending motion and precipitation on the south (north) side of the equator, which could induce a southward shift in the tropical rainfall maximum related to the ITCZ.

Radiative forcing and climate response due to the presence of black carbon in cloud droplets

NASA Astrophysics Data System (ADS)

Wang, Z.; Zhang, H.; Li, J.; Jing, X.; Lu, P.

2013-05-01

Optical properties of clouds containing black carbon (BC) particles in their water droplets are calculated by using the Maxwell Garnett mixing rule and Mie theory. The obtained cloud optical properties were then applied to an interactive system by coupling an aerosol model with a General Circulation Model. This system is used to investigate the radiative forcing and the equilibrium climate response due to BC in cloud droplets. The simulated global annual mean radiative forcing at the top of the atmosphere due to the BC in cloud droplets is found to be 0.086 W m-2. Positive radiative forcing can be seen in Africa, South America, East and South Asia and West Europe, with a maximum value of 1.5 W m-2 being observed in these regions. The enhanced cloud absorption is shown to increase the global annual mean values of solar heating rate, water vapor and temperature, but to decrease the global annual mean cloud fraction. Finally, the global annual mean surface temperature is shown to increase by +0.08 K. The local maximum changes are found to be as low as -1.5 K and as high as +0.6 K. We show there has been a significant difference in surface temperature change in the Southern and Northern Hemisphere (+0.19 K and -0.04 K, respectively). Our results show that this interhemispheric asymmetry in surface temperature change could cause a corresponding change in atmospheric dynamics and precipitation. It is also found that the northern trade winds are enhanced in the Intertropical Convergence Zone (ITCZ). This results in northerly surface wind anomalies which cross the equator to converge with the enhanced southern trade winds in the tropics of Southern Hemisphere. This is shown to lead to an increase (a decrease) of vertical ascending motion and precipitation on the south (north) side of the equator, which could induce a southward shift in the tropical rainfall maximum related to the ITCZ.

Thermography of the New River Inlet plume and nearshore currents

NASA Astrophysics Data System (ADS)

Chickadel, C.; Jessup, A.

2012-12-01

As part of the DARLA and RIVET experiments, thermal imaging systems mounted on a tower and in an airplane captured water flow in the New River Inlet, NC, USA. Kilometer-scale, airborne thermal imagery of the inlet details the ebb flow of the estuarine plume water mixing with ocean water. Multiple fronts, corresponding to the preferred channels through the ebb tidal delta, are imaged in the aerial data. A series of internal fronts suggest discreet sources of the tidal plume that vary with time. Focused thermal measurements made from a tower on the south side of the inlet viewed an area within a radius of a few hundred meters. Sub-meter resolution video from the tower revealed fine-scale flow features and the interaction of tidal exchange and wave-forced surfzone currents. Using the tower and airborne thermal image data we plan to provide geophysical information to compare with numerical models and in situ measurements made by other investigators. From the overflights, we will map the spatial and temporal extent of the estuarine plume to correlate with tidal phase and local wind conditions. From the tower data, we will investigate the structure of the nearshore flow using a thermal particle image velocimetry (PIV) technique, which is based on tracking motion of the surface temperature patterns. Long term variability of the mean and turbulent two-dimensional PIV currents will be correlated to local wave, tidal, and wind forcing parameters.

Effects of subsurface ocean dynamics on instability waves in the tropical Pacific

NASA Astrophysics Data System (ADS)

Lawrence, Sean P.; Allen, Myles R.; Anderson, David L. T.; Llewellyn-Jones, David T.

1998-08-01

Tropical instability waves in a primitive equation model of the tropical Pacific Ocean, forced with analyzed wind stresses updated daily, show unexpectedly close phase correspondence with observation through the latter half of 1992. This suggests that these waves are not pure instabilities developing from infinitesimal disturbances, but that their phases and phase speeds are at least partially determined by the wind stress forcing. To quantify and explain this observation, we perfomed several numerical experiments, which indicate that remotely forced Rossby waves can influence both the phase and phase speed of tropical instability waves. We suggest that a remote wind forcing determines the high model/observation phase correspondence of tropical instability waves through a relatively realistic simulation of equatorial Kelvin and Rossby wave activity.

Relative contributions of local wind and topography to the coastal upwelling intensity in the northern South China Sea

NASA Astrophysics Data System (ADS)

Wang, Dongxiao; Shu, Yeqiang; Xue, Huijie; Hu, Jianyu; Chen, Ju; Zhuang, Wei; Zu, TingTing; Xu, Jindian

2014-04-01

Topographically induced upwelling caused by the interaction between large-scale currents and topography was observed during four cruises in the northern South China Sea (NSCS) when the upwelling favorable wind retreated. Using a high-resolution version of the Princeton Ocean Model, we investigate relative contributions of local wind and topography to the upwelling intensity in the NSCS. The results show that the topographically induced upwelling is sensitive to alongshore large-scale currents, which have an important contribution to the upwelling intensity. The topographically induced upwelling is comparable with the wind-driven upwelling at surface and has a stronger contribution to the upwelling intensity than the local wind does at bottom in the near-shore shelf region. The widened shelf to the southwest of Shanwei and west of the Taiwan Banks intensifies the bottom friction, especially off Shantou, which is a key factor for topographically induced upwelling in terms of bottom Ekman transport and Ekman pumping. The local upwelling favorable wind enhances the bottom friction as well as net onshore transport along the 50 m isobath, whereas it has less influence along the 30 m isobath. This implies the local wind is more important in upwelling intensity in the offshore region than in the nearshore region. The contribution of local upwelling favorable wind on upwelling intensity is comparable with that of topography along the 50 m isobath. The effects of local upwelling favorable wind on upwelling intensity are twofold: on one hand, the wind transports surface warm water offshore, and as a compensation of mass the bottom current transports cold water onshore; on the other hand, the wind enhances the coastal current, and the bottom friction in turn increases the topographically induced upwelling intensity.

Interactive Ion-Neutral Dynamics in the Low Latitude Evening Ionosphere

NASA Astrophysics Data System (ADS)

Evonosky, W. R.; Richmond, A. D.; Fang, T. W.; Maute, A. I.

2015-12-01

Neutral winds in the ionosphere drive global electrodynamic phenomena which alter theupper-atmosphere so significantly that they can affect the orbit of satellites andground-to-spacecraft communications. Understanding these winds and what drives them is centralto prediction and risk management associated with such a dynamic upper atmosphere. This studyexamined the relationship between accelerations acting on neutral winds in the ionosphere and theformation of a vertical shear of those winds in low latitudes (between ±30 magnetic) and earlyevening local times (16-22 LT). Accelerations were calculated using variables output by thethermosphere ionosphere electrodynamics general circulation model (TIEGCM) under differentsolar activity and night-time ionization conditions and visualized both spatially and temporally. Ingeneral, with acceleration values averaged along magnetic latitudes between ±30 degrees(inclusive) and only considering medium solar activity conditions, we found that the ionosphereexhibits distinct layering defined by the dominant accelerations in each layer. We also found hintsthat during different night-time ionization levels, ion drag acceleration tends to remain constantwhile ion and neutral velocities change to conserve the difference between them. When consideringspecific latitudes and solar conditions, previously unreported structures appear which involveinteractions between the ion drag and viscous forces.

Helium Star Models with Optically Thick Winds: Implications for the Internal Structures and Mass-loss Rates of Wolf–Rayet Stars

NASA Astrophysics Data System (ADS)

Nakauchi, Daisuke; Saio, Hideyuki

2018-01-01

We construct helium (He) star models with optically thick winds and compare them with the properties of Galactic Wolf–Rayet (WR) stars. Hydrostatic He-core solutions are connected smoothly to trans-sonic wind solutions that satisfy the regularity conditions at the sonic point. Velocity structures in the supersonic parts are assumed by a simple β-type law. By constructing a center-to-surface structure, a mass-loss rate {\\dot{M}}{{w}} can be obtained as an eigenvalue of the equations. Sonic points appear at temperatures ≈ (1.8{--}2.8)× {10}5 {{K}} below the Fe-group opacity peak, where the radiation force becomes comparable to the local gravity. Photospheres are located at radii 3–10 times larger than sonic points. The obtained mass-loss rates are comparable to those of WR stars. Our {\\dot{M}}{{w}}–luminosity relation agrees well with the relation recently obtained by Gräfener et al. Photospheric temperatures of WR stars tend to be cooler than our predictions. We discuss the effects of stellar evolution, detailed radiation transfer, and wind clumping, which are ignored in this paper.

The use of stellite scatterometer winds to drive a primitive equation model of the Indian Ocean: The impact of bandlike sampling

NASA Technical Reports Server (NTRS)

Barnier, Bernard; Capella, Jorge; O'Brien, James J.

1994-01-01

The aim of this study is to evaluate the impact of the bandlike sampling of spaceborne scatterometers on the ability of scatterometer winds to successfully force the mean flow and seasonal cycle of an ocean model in the context of equatorial and tropical dynamics. The equatorial ocean is simulated with a four-layer, primitive equation, reduced gravity model of the Indian Ocean. The variable wind stress used in this study is derived from one year (1988) of 6-hour analyses of the 10-m wind vector over the Indian Ocean performed at the European Centre for Medium-Range Weather Forecasts (ECMWF). It is applied as a forcing at every grid point of the model to drive a reference circulation. Scatterometer winds are simulated from ECMWF winds, using the nominal configurations and orbital parameters of the European Remote Sensing 1 (ERS-1) and NASA Scatterometer (NSCAT) missions. The model is forced in real time under swaths with the raw scatterometer winds of ERS-1 and NSCAT, with a persistence condition (i.e., the wind is kept constsnt until the next passage of the satellite provides a new value). The circulation obtained for each of the scatterometer experiments is compared with the reference circulation. The seasonal circulation of the Indian Ocean with NSCAT winds is very similar to the reference. The perturbations introduced by the bandlike sampling and the persistance condition have an impact similar to that of a small uncorrelated noise added to the reference forcing. The persistence condition for ERS-1 does not give results which are as good as those obtained for NSCAT.

Effect of hurricane paths on storm surge response at Tianjin, China

NASA Astrophysics Data System (ADS)

Feng, Xingru; Yin, Baoshu; Yang, Dezhou

2012-06-01

A hurricane induced storm surge simulation system was developed for Tianjin coast, which consists of a hurricane model and a storm surge model. The peak storm surge result of the simulation agreed well with that of the observation. Three observed paths (Rita, Mimie and WINNIE) and a hypothetical path (Rita2) were chosen as the selective hurricane paths according to their positions relative to Tianjin. The sensitivity of Tianjin storm surge to the four paths was investigated using the validated storm surge simulation system. Three groups of experiments were done. In group one, the models were forced by the wind field and air pressure; in group two and three the models were forced by the wind only and the air pressure only respectively. In the experiments, the hurricane moved with a fixed speed and an intensity of 50 year return period. The simulation results show that path of the type Rita2 is the easiest to cause storm surge disaster in Tianjin, and the effect of air pressure forcing is most evident for path of the type Rita in Tianjin storm surge process. The above conclusions were analyzed through the evolution of the wind fields and the air pressure distributions. Comparing the experiment results of Group one, two and three, it can be seen that the storm surge is mainly induced by the wind forcing and the nonlinear interaction between the effect of wind forcing and air pressure forcing on the storm surge tends to weaken the storm surge.

An integrated CFD/experimental analysis of aerodynamic forces and moments

NASA Technical Reports Server (NTRS)

Melton, John E.; Robertson, David D.; Moyer, Seth A.

1989-01-01

Aerodynamic analysis using computational fluid dynamics (CFD) is most fruitful when it is combined with a thorough program of wind tunnel testing. The understanding of aerodynamic phenomena is enhanced by the synergistic use of both analysis methods. A technique is described for an integrated approach to determining the forces and moments acting on a wind tunnel model by using a combination of experimentally measured pressures and CFD predictions. The CFD code used was FLO57 (an Euler solver) and the wind tunnel model was a heavily instrumented delta wing with 62.5 deg of leading-edge sweep. A thorough comparison of the CFD results and the experimental data is presented for surface pressure distributions and longitudinal forces and moments. The experimental pressures were also integrated over the surface of the model and the resulting forces and moments are compared to the CFD and wind tunnel results. The accurate determination of various drag increments via the combined use of the CFD and experimental pressures is presented in detail.

Peak Wind Forecasts for the Launch-Critical Wind Towers on Kennedy Space Center/Cape Canaveral Air Force Station, Phase IV

NASA Technical Reports Server (NTRS)

Crawford, Winifred

2011-01-01

This final report describes the development of a peak wind forecast tool to assist forecasters in determining the probability of violating launch commit criteria (LCC) at Kennedy Space Center (KSC) and Cape Canaveral Air Force Station (CCAFS). The peak winds arc an important forecast clement for both the Space Shuttle and Expendable Launch Vehicle (ELV) programs. The LCC define specific peak wind thresholds for each launch operation that cannot be exceeded in order to ensure the safety of the vehicle. The 45th Weather Squadron (45 WS) has found that peak winds are a challenging parameter to forecast, particularly in the cool season months of October through April. Based on the importance of forecasting peak winds, the 45 WS tasked the Applied Meteorology Unit (AMU) to update the statistics in the current peak-wind forecast tool to assist in forecasting LCC violations. The tool includes onshore and offshore flow climatologies of the 5-minute mean and peak winds and probability distributions of the peak winds as a function of the 5-minute mean wind speeds.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, Bingbin; Karr, Dale G.; Song, Huimin

It is a fact that developing offshore wind energy has become more and more serious worldwide in recent years. Many of the promising offshore wind farm locations are in cold regions that may have ice cover during wintertime. The challenge of possible ice loads on offshore wind turbines raises the demand of modeling capacity of dynamic wind turbine response under the joint action of ice, wind, wave, and current. The simulation software FAST is an open source computer-aided engineering (CAE) package maintained by the National Renewable Energy Laboratory. In this paper, a new module of FAST for assessing the dynamicmore » response of offshore wind turbines subjected to ice forcing is presented. In the ice module, several models are presented which involve both prescribed forcing and coupled response. For conditions in which the ice forcing is essentially decoupled from the structural response, ice forces are established from existing models for brittle and ductile ice failure. For conditions in which the ice failure and the structural response are coupled, such as lock-in conditions, a rate-dependent ice model is described, which is developed in conjunction with a new modularization framework for FAST. In this paper, analytical ice mechanics models are presented that incorporate ice floe forcing, deformation, and failure. For lower speeds, forces slowly build until the ice strength is reached and ice fails resulting in a quasi-static condition. For intermediate speeds, the ice failure can be coupled with the structural response and resulting in coinciding periods of the ice failure and the structural response. A third regime occurs at high speeds of encounter in which brittle fracturing of the ice feature occurs in a random pattern, which results in a random vibration excitation of the structure. An example wind turbine response is simulated under ice loading of each of the presented models. This module adds to FAST the capabilities for analyzing the response of wind turbines subjected to forces resulting from ice impact on the turbine support structure. The conditions considered in this module are specifically addressed in the International Organization for Standardization (ISO) standard 19906:2010 for arctic offshore structures design consideration. Special consideration of lock-in vibrations is required due to the detrimental effects of such response with regard to fatigue and foundation/soil response. Finally, the use of FAST for transient, time domain simulation with the new ice module is well suited for such analyses.« less

Wind Tunnel Database Development using Modern Experiment Design and Multivariate Orthogonal Functions

NASA Technical Reports Server (NTRS)

Morelli, Eugene A.; DeLoach, Richard

2003-01-01

A wind tunnel experiment for characterizing the aerodynamic and propulsion forces and moments acting on a research model airplane is described. The model airplane called the Free-flying Airplane for Sub-scale Experimental Research (FASER), is a modified off-the-shelf radio-controlled model airplane, with 7 ft wingspan, a tractor propeller driven by an electric motor, and aerobatic capability. FASER was tested in the NASA Langley 12-foot Low-Speed Wind Tunnel, using a combination of traditional sweeps and modern experiment design. Power level was included as an independent variable in the wind tunnel test, to allow characterization of power effects on aerodynamic forces and moments. A modeling technique that employs multivariate orthogonal functions was used to develop accurate analytic models for the aerodynamic and propulsion force and moment coefficient dependencies from the wind tunnel data. Efficient methods for generating orthogonal modeling functions, expanding the orthogonal modeling functions in terms of ordinary polynomial functions, and analytical orthogonal blocking were developed and discussed. The resulting models comprise a set of smooth, differentiable functions for the non-dimensional aerodynamic force and moment coefficients in terms of ordinary polynomials in the independent variables, suitable for nonlinear aircraft simulation.

Development and testing of a unique carousel wind tunnel to experimentally determine the effect of gravity and the interparticle force on the physics of wind-blown particles

NASA Technical Reports Server (NTRS)

Leach, R. N.; Greeley, Ronald; White, Bruce R.; Iversen, James D.

1987-01-01

In the study of planetary aeolian processes the effect of gravity is not readily modeled. Gravity appears in the equations of particle motion along with the interparticle forces but the two are not separable. A wind tunnel that perimits multiphase flow experiments with wind blown particles at variable gravity was built and experiments were conducted at reduced gravity. The equations of particle motion initiation (saltation threshold) with variable gravity were experimentally verified and the interparticle force was separated. A uniquely design Carousel Wind Tunnel (CWT) allows for the long flow distance in a small sized tunnel since the test section if a continuous loop and develops the required turbulent boundary layer. A prototype model of the tunnel where only the inner drum rotates was built and tested in the KC-135 Weightless Wonder 4 zero-g aircraft. Future work includes further experiments with walnut shell in the KC-135 which sharply graded particles of widely varying median sizes including very small particles to see how interparticle force varies with particle size, and also experiments with other aeolian material.

Dynamically Consistent Parameterization of Mesoscale Eddies This work aims at parameterization of eddy effects for use in non-eddy-resolving ocean models and focuses on the effect of the stochastic part of the eddy forcing that backscatters and induces eastward jet extension of the western boundary currents and its adjacent recirculation zones.

NASA Astrophysics Data System (ADS)

Berloff, P. S.

2016-12-01

This work aims at developing a framework for dynamically consistent parameterization of mesoscale eddy effects for use in non-eddy-resolving ocean circulation models. The proposed eddy parameterization framework is successfully tested on the classical, wind-driven double-gyre model, which is solved both with explicitly resolved vigorous eddy field and in the non-eddy-resolving configuration with the eddy parameterization replacing the eddy effects. The parameterization focuses on the effect of the stochastic part of the eddy forcing that backscatters and induces eastward jet extension of the western boundary currents and its adjacent recirculation zones. The parameterization locally approximates transient eddy flux divergence by spatially localized and temporally periodic forcing, referred to as the plunger, and focuses on the linear-dynamics flow solution induced by it. The nonlinear self-interaction of this solution, referred to as the footprint, characterizes and quantifies the induced eddy forcing exerted on the large-scale flow. We find that spatial pattern and amplitude of each footprint strongly depend on the underlying large-scale flow, and the corresponding relationships provide the basis for the eddy parameterization and its closure on the large-scale flow properties. Dependencies of the footprints on other important parameters of the problem are also systematically analyzed. The parameterization utilizes the local large-scale flow information, constructs and scales the corresponding footprints, and then sums them up over the gyres to produce the resulting eddy forcing field, which is interactively added to the model as an extra forcing. Thus, the assumed ensemble of plunger solutions can be viewed as a simple model for the cumulative effect of the stochastic eddy forcing. The parameterization framework is implemented in the simplest way, but it provides a systematic strategy for improving the implementation algorithm.

Using C-Band Dual-Polarization Radar Signatures to Improve Convective Wind Forecasting at Cape Canaveral Air Force Station and NASA Kennedy Space Center

NASA Technical Reports Server (NTRS)

Amiot, Corey G.; Carey, Lawrence D.; Roeder, William P.; McNamara, Todd M.; Blakeslee, Richard J.

2017-01-01

The United States Air Force's 45th Weather Squadron (45WS) is the organization responsible for monitoring atmospheric conditions at Cape Canaveral Air Force Station and NASA Kennedy Space Center (CCAFS/KSC) and issuing warnings for hazardous weather conditions when the need arises. One such warning is issued for convective wind events, for which lead times of 30 and 60 minutes are desired for events with peak wind gusts of 35 knots or greater (i.e., Threshold-1) and 50 knots or greater (i.e., Threshold-2), respectively (Roeder et al. 2014).

Double-sided electromagnetic pump with controllable normal force for rapid solidification of liquid metals

DOEpatents

Kuznetsov, Stephen B.

1987-01-01

A system for casting liquid metals is provided with an electromagnetic pump which includes a pair of primary blocks each having a polyphase winding and being positioned to form a gap through which a movable conductive heat sink passes. A solidifying liquid metal sheet is deposited on the heat sink and the heat sink and sheet are held in compression by forces produced as a result of current flow through the polyphase windings. Shaded-pole interaction between the primary windings, heat sink and solidifying strip produce transverse forces which act to center the strip on the heat sink.

Double-sided electromagnetic pump with controllable normal force for rapid solidification of liquid metals

DOEpatents

Kuznetsov, S.B.

1987-01-13

A system for casting liquid metals is provided with an electromagnetic pump which includes a pair of primary blocks each having a polyphase winding and being positioned to form a gap through which a movable conductive heat sink passes. A solidifying liquid metal sheet is deposited on the heat sink and the heat sink and sheet are held in compression by forces produced as a result of current flow through the polyphase windings. Shaded-pole interaction between the primary windings, heat sink and solidifying strip produce transverse forces which act to center the strip on the heat sink. 5 figs.

Rotor dynamic considerations for large wind power generator systems

NASA Technical Reports Server (NTRS)

Ormiston, R. A.

1973-01-01

Successful large, reliable, low maintenance wind turbines must be designed with full consideration for minimizing dynamic response to aerodynamic, inertial, and gravitational forces. Much of existing helicopter rotor technology is applicable to this problem. Compared with helicopter rotors, large wind turbines are likely to be relatively less flexible with higher dimensionless natural frequencies. For very large wind turbines, low power output per unit weight and stresses due to gravitational forces are limiting factors. The need to reduce rotor complexity to a minimum favors the use of cantilevered (hingeless) rotor configurations where stresses are relieved by elastic deformations.

A surface ice module for wind turbine dynamic response simulation using FAST

DOE PAGES

Yu, Bingbin; Karr, Dale G.; Song, Huimin; ...

2016-06-03

It is a fact that developing offshore wind energy has become more and more serious worldwide in recent years. Many of the promising offshore wind farm locations are in cold regions that may have ice cover during wintertime. The challenge of possible ice loads on offshore wind turbines raises the demand of modeling capacity of dynamic wind turbine response under the joint action of ice, wind, wave, and current. The simulation software FAST is an open source computer-aided engineering (CAE) package maintained by the National Renewable Energy Laboratory. In this paper, a new module of FAST for assessing the dynamicmore » response of offshore wind turbines subjected to ice forcing is presented. In the ice module, several models are presented which involve both prescribed forcing and coupled response. For conditions in which the ice forcing is essentially decoupled from the structural response, ice forces are established from existing models for brittle and ductile ice failure. For conditions in which the ice failure and the structural response are coupled, such as lock-in conditions, a rate-dependent ice model is described, which is developed in conjunction with a new modularization framework for FAST. In this paper, analytical ice mechanics models are presented that incorporate ice floe forcing, deformation, and failure. For lower speeds, forces slowly build until the ice strength is reached and ice fails resulting in a quasi-static condition. For intermediate speeds, the ice failure can be coupled with the structural response and resulting in coinciding periods of the ice failure and the structural response. A third regime occurs at high speeds of encounter in which brittle fracturing of the ice feature occurs in a random pattern, which results in a random vibration excitation of the structure. An example wind turbine response is simulated under ice loading of each of the presented models. This module adds to FAST the capabilities for analyzing the response of wind turbines subjected to forces resulting from ice impact on the turbine support structure. The conditions considered in this module are specifically addressed in the International Organization for Standardization (ISO) standard 19906:2010 for arctic offshore structures design consideration. Special consideration of lock-in vibrations is required due to the detrimental effects of such response with regard to fatigue and foundation/soil response. Finally, the use of FAST for transient, time domain simulation with the new ice module is well suited for such analyses.« less

Is titin a 'winding filament'? A new twist on muscle contraction.

PubMed

Nishikawa, Kiisa C; Monroy, Jenna A; Uyeno, Theodore E; Yeo, Sang Hoon; Pai, Dinesh K; Lindstedt, Stan L

2012-03-07

Recent studies have demonstrated a role for the elastic protein titin in active muscle, but the mechanisms by which titin plays this role remain to be elucidated. In active muscle, Ca(2+)-binding has been shown to increase titin stiffness, but the observed increase is too small to explain the increased stiffness of parallel elastic elements upon muscle activation. We propose a 'winding filament' mechanism for titin's role in active muscle. First, we hypothesize that Ca(2+)-dependent binding of titin's N2A region to thin filaments increases titin stiffness by preventing low-force straightening of proximal immunoglobulin domains that occurs during passive stretch. This mechanism explains the difference in length dependence of force between skeletal myofibrils and cardiac myocytes. Second, we hypothesize that cross-bridges serve not only as motors that pull thin filaments towards the M-line, but also as rotors that wind titin on the thin filaments, storing elastic potential energy in PEVK during force development and active stretch. Energy stored during force development can be recovered during active shortening. The winding filament hypothesis accounts for force enhancement during stretch and force depression during shortening, and provides testable predictions that will encourage new directions for research on mechanisms of muscle contraction.

Is titin a ‘winding filament’? A new twist on muscle contraction

PubMed Central

Nishikawa, Kiisa C.; Monroy, Jenna A.; Uyeno, Theodore E.; Yeo, Sang Hoon; Pai, Dinesh K.; Lindstedt, Stan L.

2012-01-01

Recent studies have demonstrated a role for the elastic protein titin in active muscle, but the mechanisms by which titin plays this role remain to be elucidated. In active muscle, Ca2+-binding has been shown to increase titin stiffness, but the observed increase is too small to explain the increased stiffness of parallel elastic elements upon muscle activation. We propose a ‘winding filament’ mechanism for titin's role in active muscle. First, we hypothesize that Ca2+-dependent binding of titin's N2A region to thin filaments increases titin stiffness by preventing low-force straightening of proximal immunoglobulin domains that occurs during passive stretch. This mechanism explains the difference in length dependence of force between skeletal myofibrils and cardiac myocytes. Second, we hypothesize that cross-bridges serve not only as motors that pull thin filaments towards the M-line, but also as rotors that wind titin on the thin filaments, storing elastic potential energy in PEVK during force development and active stretch. Energy stored during force development can be recovered during active shortening. The winding filament hypothesis accounts for force enhancement during stretch and force depression during shortening, and provides testable predictions that will encourage new directions for research on mechanisms of muscle contraction. PMID:21900329

SAPS effects on thermospheric winds during the 17 March 2013 storm

NASA Astrophysics Data System (ADS)

Sheng, C.; Lu, G.; Wang, W.; Doornbos, E.; Talaat, E. R.

2017-12-01

Strong subauroral polarization streams (SAPS) were observed by DMSP satellites during the main phase of the 17 March 2013 geomagnetic storm. Both DMSP F18 and GOCE satellites sampled at 19 MLT during this period, providing near-simultaneous measurements of ion drifts and neutral winds near dusk. The fortuitous satellite conjunction allows us to directly examine the SAPS effects on thermospheric winds. In addition, two sets of model runs were carried out for this event: (1) the standard TIEGCM run with high-latitude forcing; (2) the SAPS-TIEGCM run by incoporating an empirical model of SAPS in the subauroral zone. The difference between these two runs represents the influence of SAPS forcing. In particular, we examine ion-neutral coupling at subauroral latitudes through detailed forcing term analysis to determine how the SAPS-related strong westward ion drifts alter thermospheric winds.

Comparison of Ares I-X Wind-Tunnel Derived Buffet Environment with Flight Data

NASA Technical Reports Server (NTRS)

Piatak, David J.; Sekula, Martin K.; Rausch, Russ D.

2011-01-01

The Ares I-X Flight Test Vehicle (FTV), launched in October 2009, carried with it over 243 buffet verification pressure sensors and was one of the most heavily instrumented launch vehicle flight tests. This flight test represented a unique opportunity for NASA and its partners to compare the wind-tunnel derived buffet environment with that measured during the flight of Ares I-X. It is necessary to define the launch vehicle buffet loads to ensure that structural components and vehicle subsystems possess adequate strength, stress, and fatigue margins when the vehicle structural dynamic response to buffet forcing functions are considered. Ares I-X buffet forcing functions were obtained via wind-tunnel testing of a rigid buffet model (RBM) instrumented with hundreds of unsteady pressure transducers designed to measure the buffet environment across the desired frequency range. This paper discusses the comparison of RBM and FTV buffet environments, including fluctuating pressure coefficient and normalized sectional buffet forcing function root-mean-square magnitudes, frequency content of power-spectral density functions, and force magnitudes of an alternating flow phenomena. Comparison of wind-tunnel model and flight test vehicle buffet environments show very good agreement with root-mean-square magnitudes of buffet forcing functions at the majority of vehicle stations. Spectra proved a challenge to compare because of different wind-tunnel and flight test conditions and data acquisition rates. However, meaningful and promising comparisons of buffet spectra are presented. Lastly, the buffet loads resulting from the transition of subsonic separated flow to supersonic attached flow were significantly over-predicted by wind-tunnel results.

Assessment of extreme hydrological conditions in the Bothnian Bay, Baltic Sea, and the impact of the nuclear power plant "Hanhikivi-1" on the local thermal regime

NASA Astrophysics Data System (ADS)

Dvornikov, Anton Y.; Martyanov, Stanislav D.; Ryabchenko, Vladimir A.; Eremina, Tatjana R.; Isaev, Alexey V.; Sein, Dmitry V.

2017-04-01

The results of the study aimed to assess the influence of future nuclear power plant Hanhikivi-1 upon the local thermal conditions in the Bothnian Bay in the Baltic Sea are presented. A number of experiments with different numerical models were also carried out in order to estimate the extreme hydro-meteorological conditions in the area of the construction. The numerical experiments were fulfilled both with analytically specified external forcing and with real external forcing for 2 years: a cold year (2010) and a warm year (2014). The study has shown that the extreme values of sea level and water temperature and the characteristics of wind waves and sea ice in the vicinity of the future nuclear power plant can be significant and sometimes catastrophic. Permanent release of heat into the marine environment from an operating nuclear power plant will lead to a strong increase in temperature and the disappearance of ice cover within a 2 km vicinity of the station. These effects should be taken into account when assessing local climate changes in the future.

Control of tropical instability waves in the Pacific

NASA Astrophysics Data System (ADS)

Allen, M. R.; Lawrence, S. P.; Murray, M. J.; Mutlow, C. T.; Stockdale, T. N.; Llewellyn-Jones, D. T.; Anderson, D. L. T.

Westward-propagating waves with periods of 20-30 days and wavelengths of ˜ 1,100km are a prominent feature of sea-surface temperatures (SSTs) in the equatorial Pacific and Atlantic Oceans. They have been attributed to instabilities due to current shear. We compare SST observations from the spaceborne Along Track Scanning Radiometer (ATSR) and TOGA-TAO moored buoys with SSTs from a model of the tropical Pacific forced with observed daily windstress data. The phases of the strongest “Tropical Instability Waves” (TIWs) in the model are in closer correspondence with those observed than we would expect if these waves simply developed from infinitesimal disturbances (in which case their phases would be arbitrary). If we filter out the intraseasonal component of the windstress, all phase-correspondence is lost. We conclude that the phases of these waves are not arbitrary, but partially determined by the intraseasonal winds. The subsurface evolution of the model suggests a possible control mechanism is through interaction with remotely-forced subsurface Kelvin and Rossby waves. This is supported by an experiment which shows how zonal wind bursts in the west Pacific can modify the TIW field, but other mechanisms, such as local feedbacks, are also possible.

Emissions and temperature benefits: The role of wind power in China

DOE Office of Scientific and Technical Information (OSTI.GOV)

Duan, Hongbo, E-mail: hbduan@ucas.ac.cn

Background: As a non-fossil technology, wind power has an enormous advantage over coal because of its role in climate change mitigation. Therefore, it is important to investigate how substituting wind power for coal-fired electricity will affect emission reductions, changes in radiative forcing and rising temperatures, particularly in the context of emission limits. Methods: We developed an integrated methodology that includes two parts: an energy-economy-environmental (3E) integrated model and an emission-temperature response model. The former is used to simulate the dynamic relationships between economic output, wind energy and greenhouse gas (GHG) emissions; the latter is used to evaluate changes in radiativemore » forcing and warming. Results: Under the present development projection, wind energy cannot serve as a major force in curbing emissions, even under the strictest space-restraining scenario. China's temperature contribution to global warming will be up to 21.76% if warming is limited to 2 degrees. With the wind-for-coal power substitution, the corresponding contribution to global radiative forcing increase and temperature rise will decrease by up to 10% and 6.57%, respectively. Conclusions: Substituting wind power for coal-fired electricity has positive effects on emission reductions and warming control. However, wind energy alone is insufficient for climate change mitigation. It forms an important component of the renewable energy portfolio used to combat global warming. - Highlights: • We assess the warming benefits associated with substitution of wind power for coal. • The effect of emission space limits on climate responses is deeply examined. • China is responsible for at most 21.76% of global warming given the 2-degree target. • Wind power alone may not be sufficient to face the challenge of climate change. • A fertile policy soil and an aggressive plan are necessary to boost renewables.« less

Flows, Fields, and Forces in the Mars-Solar Wind Interaction

NASA Astrophysics Data System (ADS)

Halekas, J. S.; Brain, D. A.; Luhmann, J. G.; DiBraccio, G. A.; Ruhunusiri, S.; Harada, Y.; Fowler, C. M.; Mitchell, D. L.; Connerney, J. E. P.; Espley, J. R.; Mazelle, C.; Jakosky, B. M.

2017-11-01

We utilize suprathermal ion and magnetic field measurements from the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission, organized by the upstream magnetic field, to investigate the morphology and variability of flows, fields, and forces in the Mars-solar wind interaction. We employ a combination of case studies and statistical investigations to characterize the interaction in both quasi-parallel and quasi-perpendicular regions and under high and low solar wind Mach number conditions. For the first time, we include a detailed investigation of suprathermal ion temperature and anisotropy. We find that the observed magnetic fields and suprathermal ion moments in the magnetosheath, bow shock, and upstream regions have observable asymmetries controlled by the interplanetary magnetic field, with particularly large asymmetries found in the ion parallel temperature and anisotropy. The greatest temperature anisotropies occur in quasi-perpendicular regions of the magnetosheath and under low Mach number conditions. These results have implications for the growth and evolution of wave-particle instabilities and their role in energy transport and dissipation. We utilize the measured parameters to estimate the average ion pressure gradient, J × B, and v × B macroscopic force terms. The pressure gradient force maintains nearly cylindrical symmetry, while the J × B force has larger asymmetries and varies in magnitude in comparison to the pressure gradient force. The v × B force felt by newly produced planetary ions exceeds the other forces in magnitude in the magnetosheath and upstream regions for all solar wind conditions.

Coaxial Compound Helicopter for Confined Urban Operations

DTIC Science & Technology

2016-01-22

climb or descent power for the aircraft) is obtained from the wind axis drag force and rotor velocity: ! Pp = "XV . The induced power is...speed. The induced and profile power cannot be measured separately in a wind tunnel or flight test, only the sum is available from ! P i + P o = P...XV (if the rotor wind -axis drag force ! X is measured or estimated). Therefore analysis is used to separate induced and profile power. In this

Satellite observations of the onset and growth of severe local storms

NASA Technical Reports Server (NTRS)

Negri, A. J.; Vonderhaar, T. H.

1977-01-01

The mesoscale nature of the forcing and evolution of these storms was investigated, with emphasis on techniques to aid in the early detection of such severe events. In the pre-storm environment (t-4 to t-2 hours), the satellite wind fields were combined with moisture parameters to derive horizontal moisture flux information. Low level moisture convergence was indicative of regions of subsequent severe storm genesis. Dynamic parameters such as boundary layer vorticity production and relative vorticity were also useful prognosticators of subsequent severe activity.

Influence of atmospheric stability on wind-turbine wakes: A large-eddy simulation study

NASA Astrophysics Data System (ADS)

Abkar, Mahdi; Porté-Agel, Fernando

2014-05-01

In this study, large-eddy simulation is combined with a turbine model to investigate the influence of atmospheric stability on wind-turbine wakes. In the simulations, subgrid-scale turbulent fluxes are parameterized using tuning-free Lagrangian scale-dependent dynamic models. These models optimize the local value of the model coefficients based on the dynamics of the resolved scales. The turbine-induced forces are parameterized with an actuator-disk model with rotation. In this technique, blade-element theory is used to calculate the lift and drag forces acting on the blades. Emphasis is placed on the structure and characteristics of wind-turbine wakes in the cases where the incident flows to the turbine have the same mean velocity at the hub height but different stability conditions. The simulation results show that atmospheric stability has a significant effect on the spatial distribution of the mean velocity deficit and turbulent fluxes in the wake region. In particular, the magnitude of the velocity deficit increases with increasing stability in the atmosphere. In addition, the locations of the maximum turbulence intensity and turbulent stresses are closer to the turbine in convective boundary layer compared with neutral and stable ones. Detailed analysis of the resolved turbulent kinetic energy (TKE) budget inside the wake reveals also that the thermal stratification of the incoming wind considerably affects the magnitude and spatial distribution of the turbulent production, transport term and dissipation rate (transfer of energy to the subgrid scales). It is also shown that the near-wake region can be extended to a farther distance downstream in stable condition compared with neutral and unstable counterparts. In order to isolate the effect of atmospheric stability, additional simulations of neutrally-stratified atmospheric boundary layers are performed with the same turbulence intensity at hub height as convective and stable ones. The results show that the turbulence intensity alone is not sufficient to describe the impact of atmospheric stability on the wind-turbine wakes.

Regional Wave Climates along Eastern Boundary Currents

NASA Astrophysics Data System (ADS)

Semedo, Alvaro; Soares, Pedro

2016-04-01

Two types of wind-generated gravity waves coexist at the ocean surface: wind sea and swell. Wind sea waves are waves under growing process. These young growing waves receive energy from the overlaying wind and are strongly coupled to the local wind field. Waves that propagate away from their generation area and no longer receive energy input from the local wind are called swell. Swell waves can travel long distances across entire ocean basins. A qualitative study of the ocean waves from a locally vs. remotely generation perspective is important, since the air sea interaction processes is strongly modulated by waves and vary accordingly to the prevalence of wind sea or swell waves in the area. A detailed climatology of wind sea and swell waves along eastern boundary currents (EBC; California Current, Canary Current, in the Northern Hemisphere, and Humboldt Current, Benguela Current, and Western Australia Current, in the Southern Hemisphere), based on the ECMWF (European Centre for Medium-Range Weather Forecasts) ERA-Interim reanalysis will be presented. The wind regime along EBC varies significantly from winter to summer. The high summer wind speeds along EBC generate higher locally generated wind sea waves, whereas lower winter wind speeds in these areas, along with stronger winter extratropical storms far away, lead to a predominance of swell waves there. In summer, the coast parallel winds also interact with coastal headlands, increasing the wind speed through a process called "expansion fan", which leads to an increase in the height of locally generated waves downwind of capes and points. Hence the spatial patterns of the wind sea or swell regional wave fields are shown to be different from the open ocean along EBC, due to coastal geometry and fetch dimensions. Swell waves will be shown to be considerably more prevalent and to carry more energy in winter along EBC, while in summer locally generated wind sea waves are either more comparable to swell waves or, particularly in the lee of headlands, or even more prevalent and more energized than swell. This study is part of the WRCP-JCOMM COWCLIP (Coordinated Ocean Wave Climate Project) effort.

Wind Texture

NASA Image and Video Library

2011-03-23

On Earth, these wind-derived features are called blowouts, where the force of the wind has carved out a crescent-shaped depression in soft, uncemented material like glacial loess. This image is from NASA Mars Odyssey.

Developing a Peak Wind Probability Forecast Tool for Kennedy Space Center and Cape Canaveral Air Force Station

NASA Technical Reports Server (NTRS)

Lambert, WInifred; Roeder, William

2007-01-01

This conference presentation describes the development of a peak wind forecast tool to assist forecasters in determining the probability of violating launch commit criteria (LCC) at Kennedy Space Center (KSC) and Cape Canaveral Air Force Station (CCAFS) in east-central Florida. The peak winds are an important forecast element for both the Space Shuttle and Expendable Launch Vehicle (ELV) programs. The LCC define specific peak wind thresholds for each launch operation that cannot be exceeded in order to ensure the safety of the vehicle. The 45th Weather Squadron (45 WS) has found that peak winds are a challenging parameter to forecast, particularly in the cool season months of October through April. Based on the importance of forecasting peak winds, the 45 WS tasked the Applied Meteorology Unit (AMU) to develop a short-range peak-wind forecast tool to assist in forecasting LCC violations. The tool will include climatologies of the 5-minute mean and peak winds by month, hour, and direction, and probability distributions of the peak winds as a function of the 5-minute mean wind speeds.

Statistical Short-Range Guidance for Peak Wind Forecasts on Kennedy Space Center/Cape Canaveral Air Force Station, Phase III

NASA Technical Reports Server (NTRS)

Crawford, Winifred

2010-01-01

This final report describes the development of a peak wind forecast tool to assist forecasters in determining the probability of violating launch commit criteria (LCC) at Kennedy Space Center (KSC) and Cape Canaveral Air Force Station (CCAFS). The peak winds are an important forecast element for both the Space Shuttle and Expendable Launch Vehicle (ELV) programs. The LCC define specific peak wind thresholds for each launch operation that cannot be exceeded in order to ensure the safety of the vehicle. The 45th Weather Squadron (45 WS) has found that peak winds are a challenging parameter to forecast, particularly in the cool season months of October through April. Based on the importance of forecasting peak winds, the 45 WS tasked the Applied Meteorology Unit (AMU) to develop a short-range peak-wind forecast tool to assist in forecasting LCC violations.The tool includes climatologies of the 5-minute mean and peak winds by month, hour, and direction, and probability distributions of the peak winds as a function of the 5-minute mean wind speeds.

A Peak Wind Probability Forecast Tool for Kennedy Space Center and Cape Canaveral Air Force Station

NASA Technical Reports Server (NTRS)

Crawford, Winifred; Roeder, William

2008-01-01

This conference abstract describes the development of a peak wind forecast tool to assist forecasters in determining the probability of violating launch commit criteria (LCC) at Kennedy Space Center (KSC) and Cape Canaveral Air Force Station (CCAFS) in east-central Florida. The peak winds are an important forecast element for both the Space Shuttle and Expendable Launch Vehicle (ELV) programs. The LCC define specific peak wind thresholds for each launch operation that cannot be exceeded in order to ensure the safety of the vehicle. The 45th Weather Squadron (45 WS) has found that peak winds are a challenging parameter to forecast, particularly in the cool season months of October through April. Based on the importance of forecasting peak winds, the 45 WS tasked the Applied Meteorology Unit (AMU) to develop a short-range peak-wind forecast tool to assist in forecasting LCC violatioas.The tool will include climatologies of the 5-minute mean end peak winds by month, hour, and direction, and probability distributions of the peak winds as a function of the 5-minute mean wind speeds.

Assimilation of Wind Profiles from Multiple Doppler Radar Wind Profilers for Space Launch Vehicle Applications

NASA Technical Reports Server (NTRS)

Decker, Ryan K.; Barbre, Robert E., Jr.; Brenton, James C.; Walker, James C.; Leach, Richard D.

2015-01-01

Space launch vehicles utilize atmospheric winds in design of the vehicle and during day-of-launch (DOL) operations to assess affects of wind loading on the vehicle and to optimize vehicle performance during ascent. The launch ranges at NASA's Kennedy Space Center co-located with the United States Air Force's (USAF) Eastern Range (ER) at Cape Canaveral Air Force Station and USAF's Western Range (WR) at Vandenberg Air Force Base have extensive networks of in-situ and remote sensing instrumentation to measure atmospheric winds. Each instrument's technique to measure winds has advantages and disadvantages in regards to use for vehicle engineering assessments. Balloons measure wind at all altitudes necessary for vehicle assessments, but two primary disadvantages exist when applying balloon output on DOL. First, balloons need approximately one hour to reach required altitude. For vehicle assessments this occurs at 60 kft (18.3 km). Second, balloons are steered by atmospheric winds down range of the launch site that could significantly differ from those winds along the vehicle ascent trajectory. Figure 1 illustrates the spatial separation of balloon measurements from the surface up to approximately 55 kft (16.8 km) during the Space Shuttle launch on 10 December 2006. The balloon issues are mitigated by use of vertically pointing Doppler Radar Wind Profilers (DRWPs). However, multiple DRWP instruments are required to provide wind data up to 60 kft (18.3 km) for vehicle trajectory assessments. The various DRWP systems have different operating configurations resulting in different temporal and spatial sampling intervals. Therefore, software was developed to combine data from both DRWP-generated profiles into a single profile for use in vehicle trajectory analyses. Details on how data from various wind measurement systems are combined and sample output will be presented in the following sections.

Near-inertial motions in the Brazil Current at 24°S-36°S: Observations by satellite tracked drifters

NASA Astrophysics Data System (ADS)

Assireu, Arcilan T.; Dauhut, Thibaut; dos Santos, Francisco A.; Lorenzzetti, João A.

2017-08-01

Increased spatial and temporal resolution of recent observations and modeling have pointed out the importance of small scale structures (in the range of 1-50 km) for the mixing processes in the ocean. Based on high-frequency drifter measurements, we show here that the near-inertial currents (NICs) can contribute significantly to the surface kinetic energy in the Brazil Current (BC) region and, therefore, should be properly taken into account in the studies of transport and mixing processes. To characterize these submesoscale features, we examine the current response to the wind forcing in the Brazilian ocean margin between 24°S and 36°S using 3-hourly sampled trajectories of satellite-tracked drifters. Our results indicate a preference for anti-cyclonic circular motions, with a rotating period close to the local inertial period, consistent with near-inertial motions in the Southern Hemisphere (SH). Wind stress time series, from three months of wind measurements, along with synoptic weather charts, are used to relate the observed NICs to the atmospheric forcing. During SH spring, NICs occur in 4.7-15 day bursts and account for 15-45% of the total surface current variance. This intermittency is related to atmospheric cold frontal passages, low pressure systems, and sea breeze/land breeze circulations. The predominance of NICs south of 28°S appears to be related to the increased Effective Inertial Frequency (EIF), which is the inertial frequency changed by the sub-inertial background flow.

Formation of intrathermocline eddies at ocean fronts by wind-driven destruction of potential vorticity

NASA Astrophysics Data System (ADS)

Thomas, Leif N.

2008-08-01

A mechanism for the generation of intrathermocline eddies (ITEs) at wind-forced fronts is examined using a high resolution numerical simulation. Favorable conditions for ITE formation result at fronts forced by "down-front" winds, i.e. winds blowing in the direction of the frontal jet. Down-front winds exert frictional forces that reduce the potential vorticity (PV) within the surface boundary in the frontal outcrop, providing a source for the low-PV water that is the materia prima of ITEs. Meandering of the front drives vertical motions that subduct the low-PV water into the pycnocline, pooling it into the coherent anticyclonic vortex of a submesoscale ITE. As the fluid is subducted along the outcropping frontal isopycnal, the low-PV water, which at the surface is associated with strongly baroclinic flow, re-expresses itself as water with nearly zero absolute vorticity. This generation of strong anticyclonic vorticity results from the tilting of the horizontal vorticity of the frontal jet, not from vortex squashing. During the formation of the ITE, high-PV water from the pycnocline is upwelled alongside the subducting low-PV surface water. The positive correlation between the ITE's velocity and PV fields results in an upward, along-isopycnal eddy PV flux that scales with the surface frictional PV flux driven by the wind. The relationship between the eddy and wind-induced frictional PV flux is nonlocal in time, as the eddy PV flux persists long after the wind forcing is shut off. The ITE's PV flux affects the large-scale flow by driving an eddy-induced transport or bolus velocity down the outcropping isopycnal layer with a magnitude that scales with the Ekman velocity.

Coordinated control of wind generation and energy storage for power system frequency regulation

NASA Astrophysics Data System (ADS)

Baone, Chaitanya Ashok

Large-scale centralized synchronous generators have long been the primary actors in exercising active power and frequency control, and much of the existing grid control framework is predicated upon their dynamic terminal characteristics. Important among these characteristics is the inertia of such generators. These play key roles in determining the electromechanical stability of the electric power grid. Modern wind generator systems are partially or fully connected to the grid through power electronic interfaces, and hence do not present the same level of inertial coupling. The absence of inertial frequency response from modern wind generator systems is a topic of growing concern in power engineering practice, as the penetration of wind generation is expected to grow dramatically in the next few years. Solutions proposed in the literature have sought to address this problem by seeking to mimic the inherent inertial response characteristics of traditional synchronous generators via control loops added to wind generators. Recent literature has raised concerns regarding this approach, and the work here will further examine its shortcomings, motivating approaches that seek to optimally design for the characteristics of the equipment exercising the control, rather than forcing new technologies to mimic the characteristics of synchronous machines. In particular, this work will develop a new approach to power system frequency regulation, with features suited to distributed energy storage devices such as grid-scale batteries and wind turbine speed and blade pitch control. The dynamic characteristics of these new technologies are treated along with existing mechanisms, such as synchronous machine governor control, to develop a comprehensive multi-input control design approach. To make the method practically feasible for geographically distributed power systems, an observer-based distributed control design utilizing phasor measurement unit (PMU) signals along with local measurements is developed. In addition to the system-wide objective of frequency regulation, a local objective of reducing the wind turbine drivetrain stress is considered. Also, an algorithm is proposed to characterize the modal degrees of controllability and observability on a subspace of critical modes of the system, so that the most effective sensor and actuator locations to be used in the control design can be found.

Jovian Temperatures--Highest Resolution

NASA Image and Video Library

1997-09-24

This image, bottom panel, from NASA Galileo orbiter indicates the forces powering Jovian winds, and differentiates between areas of strongest upwelling and downwelling winds in the upper part of the atmosphere where winds are strong.

Is the Critical Rotation of Be Stars Really Critical for the Be Phenomenon?

NASA Astrophysics Data System (ADS)

Stee, Ph.; Meilland, A.

We aim to study the effect of the fast rotation, stellar wind and circumstellar disks around active hot stars and their effects on the formation and evolution of these massive stars. For that purpose, we obtained, for the first time, interferometric measurements of three active hot stars, namely α Arae, κ CMa and Achernar, using the VLTI /AMBER and VLTI/MIDI instruments which allow us to study the kinematics of the central star and its surrounding circumstellar matter. These data coupled with our numerical code SIMECA (SIMulation pour Etoiles Chaudes Actives) seem to indicate that the presence of equatorial disks and polar stellar wind around Be stars are not correlated. A polar stellar wind was detected for α Arae and Achernar whereas κ CMa seems to exhibit no stellar wind. On the other hand, these two first Be stars are certainly nearly critical rotators whereas the last one seems to be far from the critical rotation. Thus a polar stellar wind may be due to the nearly critical rotation which induces a local effective temperature change following the von Zeipel theorem, producing a hotter polar region triggering a polar stellar wind. This critical rotation may also explain the formation of a circumstellar disk which is formed by the centrifugal force balancing the equatorial effective gravity of the central star. Following these results we try to investigate if critical rotation may be the clue for the Be phenomenon.

Comparison of weak-wind characteristics across different Surface Types in stable stratification

NASA Astrophysics Data System (ADS)

Freundorfer, Anita; Rehberg, Ingo; Thomas, Christoph

2017-04-01

Atmospheric transport in weak winds and very stable conditions is often characterized by phenomena collectively referred to as submeso motions since their time and spatial scales exceed those of turbulence, but are smaller than synoptic motions. Evidence is mounting that submeso motions invalidate models for turbulent dispersion and diffusion since their physics are not captured by current similarity theories. Typical phenomena in the weak-wind stable boundary layer include meandering motions, quasi two-dimensional pancake-vortices or wavelike motions. These motions may be subject to non-local forcing and sensitive to small topographic undulations. The invalidity of Taylor's hypothesis of frozen turbulence for submeso motions requires the use of sensor networks to provide observations in both time and space domains simultaneously. We present the results from the series of Advanced Resolution Canopy Flow Observations (ARCFLO) experiments using a sensor network consisting of 12 sonic anemometers and 12 thermohygrometers. The objective of ARCFLO was to observe the flow and the turbulent and submeso transport at a high spatial and temporal resolution at 4 different sites in the Pacific Northwest, USA. These sites represented a variable degree of terrain complexity (flat to mountainous) and vegetation architecture (grass to forest, open to dense). In our study, a distinct weak-wind regime was identified for each site using the threshold velocity at which the friction velocity becomes dependent upon the mean horizontal wind speed. Here we used the scalar mean of the wind speed because the friction velocity showed a clearer dependence on the scalar mean compared to the vector mean of the wind velocity. It was found that the critical speed for the weak wind regime is higher in denser vegetation. For an open agricultural area (Botany and Plant Pathology Farm) we found a critical wind speed of v_crit= (0.24±0.05) ms-1 while for a very dense forest (Mary's River Douglas Fir site) with a Leaf Area Index of LAI=9.4 m2m-2, the critical wind speed measures v_crit= (1.0±0.1) ms-1. Further analyses include developing an identification scheme to sample submeso motions using their quasi two-dimensional nature. Once separated from turbulence the properties of submeso motions and the impact of different canopy densities on those motions can be explored. We hypothesize that submeso motions are the main generating mechanism for the locally confined and intermittent turbulence in the weak-wind and stable boundary layers.

Statistical Short-Range Guidance for Peak Wind Speed Forecasts at Edwards Air Force Base, CA

NASA Technical Reports Server (NTRS)

Dreher, Joseph G.; Crawford, Winifred; Lafosse, Richard; Hoeth, Brian; Burns, Kerry

2009-01-01

The peak winds near the surface are an important forecast element for space shuttle landings. As defined in the Flight Rules (FR), there are peak wind thresholds that cannot be exceeded in order to ensure the safety of the shuttle during landing operations. The National Weather Service Spaceflight Meteorology Group (SMG) is responsible for weather forecasts for all shuttle landings, and is required to issue surface average and 10-minute peak wind speed forecasts. They indicate peak winds are a challenging parameter to forecast. To alleviate the difficulty in making such wind forecasts, the Applied Meteorology Unit (AMU) developed a PC-based graphical user interface (GUI) for displaying peak wind climatology and probabilities of exceeding peak wind thresholds for the Shuttle Landing Facility (SLF) at Kennedy Space Center (KSC; Lambert 2003). However, the shuttle occasionally may land at Edwards Air Force Base (EAFB) in southern California when weather conditions at KSC in Florida are not acceptable, so SMG forecasters requested a similar tool be developed for EAFB.

Impact of Dust Radiative Forcing upon Climate. Chapter 13

NASA Technical Reports Server (NTRS)

Miller, Ronald L.; Knippertz, Peter; Perez Garcia-Pando, Carlos; Perlwitz, Jan P.; Tegan, Ina

2014-01-01

Dust aerosols perturb the atmospheric radiative flux at both solar and thermal wavelengths, altering the energy and water cycles. The climate adjusts by redistributing energy and moisture, so that local temperature perturbations, for example, depend upon the forcing over the entire extent of the perturbed circulation. Within regions frequently mixed by deep convection, including the deep tropics, dust particles perturb the surface air temperature primarily through radiative forcing at the top of the atmosphere (TOA). Many models predict that dust reduces global precipitation. This reduction is typically attributed to the decrease of surface evaporation in response to dimming of the surface. A counterexample is presented, where greater shortwave absorption by dust increases evaporation and precipitation despite greater dimming of the surface. This is attributed to the dependence of surface evaporation upon TOA forcing through its influence upon surface temperature and humidity. Perturbations by dust to the surface wind speed and vegetation (through precipitation anomalies) feed back upon the dust aerosol concentration. The current uncertainty of radiative forcing attributed to dust and the resulting range of climate perturbations calculated by models remain a useful test of our understanding of the mechanisms relating dust radiative forcing to the climate response.

Influence of the gap size on the wind loading on heliostats

NASA Astrophysics Data System (ADS)

Poulain, Pierre E.; Craig, Ken J.; Meyer, Josua P.

2016-05-01

Generally built in desert areas, heliostat fields undergo various wind loading conditions. An ANSYS Fluent CFD model of an isolated heliostat in worst-case orientation for the drag force is realized via numerical simulations using the realizable k-ɛ turbulence model. This paper focuses on the gap width between the panels and its influence on the wind loading that heliostats are subjected to. An atmospheric boundary layer profile is generated based on a wind tunnel experiment. For a heliostat in upright and tilted orientations with the wind angle being zero degrees, the gap width is varied and the force and moment coefficients are calculated. In the range tested, all the coefficients globally increase with the widening of the gaps.

Venus general atmosphere circulation described by Pioneer

NASA Technical Reports Server (NTRS)

1981-01-01

The predominant weather pattern for Venus is described. Wind directions and wind velocities are given. Possible driving forces of the winds are presented and include solar heating, planetary rotation, and the greenhouse effect.

The effect of oblateness and gravity darkening on the radiation driving in winds from rapidly rotating B stars

NASA Technical Reports Server (NTRS)

Cranmer, Steven R.; Owocki, Stanley P.

1995-01-01

We calculate the radiative driving force for winds around rapidly rotating oblate B stars, and we estimate the impact these forces should have on the production of a wind compressed disk. The effects of limb darkening, gravity darkening, oblateness, and an arbitrary wind velocity field are included in the computation of vector 'oblate finite disk' (OFD) factors, which depend on both radius and colatitude in the wind. The impact of limb darkening alone, with or without rotation, can increase the mass loss by as much as 10% over values computed using the standard uniformly bright spherical finite disk factor. For rapidly rotating stars, limb darkening makes 'sub-stellar' gravity darkening the dominant effect in the radial and latitudinal OFD factors, and lessens the impact of gravity darkening at other visible latitudes (nearer to the oblate limb). Thus, the radial radiative driving is generally stronger over the poles and weaker over the equator, following the gravity darkening at these latitudes. The nonradial radiative driving is considerably smaller in magnitude than the radial component, but is directed both away from the equatorial plane and in a retrograde azimuthal direction, acting to decrease the effective stellar rotation velocity. These forces thus weaken the equatorward wind compression compared to wind models computed with nonrotating finite disk factors.

Transonic and supersonic ground effect aerodynamics

NASA Astrophysics Data System (ADS)

Doig, G.

2014-08-01

A review of recent and historical work in the field of transonic and supersonic ground effect aerodynamics has been conducted, focussing on applied research on wings and aircraft, present and future ground transportation, projectiles, rocket sleds and other related bodies which travel in close ground proximity in the compressible regime. Methods for ground testing are described and evaluated, noting that wind tunnel testing is best performed with a symmetry model in the absence of a moving ground; sled or rail testing is ultimately preferable, though considerably more expensive. Findings are reported on shock-related ground influence on aerodynamic forces and moments in and accelerating through the transonic regime - where force reversals and the early onset of local supersonic flow is prevalent - as well as more predictable behaviours in fully supersonic to hypersonic ground effect flows.

Generating an Aerodynamic Model for Projectile Flight Simulation Using Unsteady, Time Accurate Computational Fluid Dynamic Results

DTIC Science & Technology

2006-09-01

Figure 17. Station line center of Magnus force vs. Mach number for spin-stabilized projectile...forces and moments on the projectile. It is also relatively easy to change the wind tunnel model to allow detailed parametric effects to be...such as pitch and roll damping, as well as, Magnus force and moment coefficients, are difficult to obtain in a wind tunnel and require a complex

Salty Anomalies Forced by Central American Gap Winds: Aquarius Observations

NASA Astrophysics Data System (ADS)

Grodsky, S. A.; Carton, J.; Bentamy, A.

2014-12-01

Although upwelling normally doesn't have direct impact on the sea surface salinity (SSS), we present observational evidence of upwelling-induced SSS patterns off the Pacific Central American coast. This area is characterized by stable near-surface salinity stratification that is produced by the mixed layer dilution by local rainfall. Here the fresh and warm mixed layer is periodically disrupted by the gap wind-induced uplifts of colder and saltier water. Aquarius SSS data capture these high SSS events. In boreal winter when the intense gap winds are frequent, two tongues of anomalously salty water develop off the Gulfs of Tehuantepec and Papagayo. During that season the average SSS in the meridionally oriented Tehuantepec tongue is about 0.4 psu saltier than background SSS. The zonally elongated Papagayo tongue stands out even more strongly, being 1 to 2 psu saltier than SSS in the neighboring Panama Bight. The spatial locations and orientations of these salty tongues closely correspond to the locations and orientations of the cool SST tongues suggesting they have similar governing mechanisms.

Uncovering a New Current: The Southwest MAdagascar Coastal Current

NASA Astrophysics Data System (ADS)

Ramanantsoa, Juliano D.; Penven, P.; Krug, M.; Gula, J.; Rouault, M.

2018-02-01

Cruise data sets, satellite remote sensing observations, and model data analyses are combined to highlight the existence of a coastal surface poleward flow in the southwest of Madagascar: the Southwest MAdagascar Coastal Current (SMACC). The SMACC is a relatively shallow (<300 m) and narrow (<100 km wide) warm and salty coastal surface current, which flows along the south western coast of Madagascar toward the south, opposite to the dominant winds. The warm water surface signature of the SMACC extends from 22°S (upstream) to 26.4°S (downstream). The SMACC exhibits a seasonal variability: more intense in summer and reduced in winter. The average volume transport of its core is about 1.3 Sv with a mean summer maximum of 2.1 Sv. It is forced by a strong cyclonic wind stress curl associated with the bending of the trade winds along the southern tip of Madagascar. The SMACC directly influences the coastal upwelling regions south of Madagascar. Its existence is likely to influence local fisheries and larval transport patterns, as well as the connectivity with the Agulhas Current, affecting the returning branch of the global overturning circulation.

Quantifying the Effect of Pressure Sensitive Paint On Aerodynamic Data

NASA Technical Reports Server (NTRS)

Amer, T. R.; Obara, C. J.; Liu, T.

2003-01-01

A thin pressure sensitive paint (PSP) coating can slightly modify the overall shape of a wind-tunnel model and produce surface roughness or smoothness that does not exist on the unpainted model. These undesirable changes in model geometry may alter flow over the model, and affect the pressure distribution and aerodynamic forces and moments on the model. This study quantifies the effects of PSP on three models in low-speed, transonic and supersonic flow regimes. At a 95% confidence level, the PSP effects on the integrated forces are insignificant for a slender arrow-wing-fuselage model and delta wing model with two different paints at Mach 0.2, 1.8, and 2.16 relative to the total balance accuracy limit. The data displayed a repeatability of 2.5 drag counts, while the balance accuracy limit was about 5.5 drag counts. At transonic speeds, the paint has a localized effect at high angles of attack and has a resolvable effect on the normal force, which is significant relative to the balance accuracy limit. For low speeds, the PSP coating has a localized effect on the pressure tap measurements, which leads to an appreciable decrease in the pressure tap reading. Moreover, the force and moment measurements had a poor precision, which precluded the ability to measure the PSP effect for this particular test.

Determining effects of turbine blades on fluid motion

DOEpatents

Linn, Rodman Ray [Los Alamos, NM; Koo, Eunmo [Los Alamos, NM

2012-05-01

Disclosed is a technique for simulating wind interaction with wind turbines. A turbine blade is divided into radial sections. The effect that each of these radial sections has on the velocities in Eulerian computational cells they overlap is determined. The effect is determined using Lagrangian techniques such that the calculations need not include wind components in the radial direction. A force on each radial section of turbine blade is determined. This force depends on the axial and azimuthal components of the fluid flow in the computational cell and the geometric properties of the turbine blade. The force on the turbine blade is fed back to effect the fluid flow in the computational cell for the next time step.

Determining effects of turbine blades on fluid motion

DOEpatents

Linn, Rodman Ray [Los Alamos, NM; Koo, Eunmo [Los Alamos, NM

2011-05-31

Disclosed is a technique for simulating wind interaction with wind turbines. A turbine blade is divided into radial sections. The effect that each of these radial sections has on the velocities in Eulerian computational cells they overlap is determined. The effect is determined using Lagrangian techniques such that the calculations need not include wind components in the radial direction. A force on each radial section of turbine blade is determined. This force depends on the axial and azimuthal components of the fluid flow in the computational cell and the geometric properties of the turbine blade. The force on the turbine blade is fed back to effect the fluid flow in the computational cell for the next time step.

Sundowner Winds Contributing to Intensifying Dry Conditions in Santa Barbara, California

NASA Astrophysics Data System (ADS)

Macarewich, S. I.; Carvalho, L. V.; Hall, T.

2015-12-01

Extreme downslope wind and warming events, locally termed as "sundowners," are notorious for accelerating the spread of wildfires in the vicinity of Santa Barbara, California. Unique topographic features characterize the terrain of this region: about 100 km of narrow coastal plains run approximately east-west, and are bordered by a steep mountain range (exceeding elevations of 1200 m), which runs parallel to the coastline. Named for their typical onset during the early to late afternoon, Sundowners are foehn winds associated with gusty winds down the lee slope of the mountains and canyons, abnormal rapid drop in relative humidity and rise in temperature. Some Sundowner events can exceed wind speeds of gale force and temperatures of 40°C (~100°F). Not only do these events disrupt the marine-influenced weather regime, they also cause significant damage to agriculture, threaten urban landscapes, and coincide with nearly every major wildfire. Sundowners are mesoscale phenomena that develop as a result of a north to south pressure gradient at the Santa Ynez Mountains. Here, Sundowners are identified using the Montecito remote operated weather station (MTIC1) from December 1999 to February 2014. The MTIC1 is located within a mountain pass where Sundowner winds are most significant. A Sundowner database, provided by the National Weather Service, is used to identify the events. We show that recordings of maximum temperatures, sustained wind speeds, wind gusts, and minimum relative humidity indicate that Sundowner events are increasing in frequency and intensity, particularly in spring. When compared to normal conditions, Sundowner conditions produce a significant increase in evapotranspiration and net radiation that can increase drought conditions in the region. This study examines environmental impacts and discusses potential drivers of Sundowner behavior.

Distinct wind convergence patterns in the Mexico City basin due to the interaction of the gap winds with the synoptic flow

NASA Astrophysics Data System (ADS)

de Foy, B.; Clappier, A.; Molina, L. T.; Molina, M. J.

2006-04-01

Mexico City lies in a high altitude basin where air quality and pollutant fate is strongly influenced by local winds. The combination of high terrain with weak synoptic forcing leads to weak and variable winds with complex circulation patterns. A gap wind entering the basin in the afternoon leads to very different wind convergence lines over the city depending on the meteorological conditions. Surface and upper-air meteorological observations are analysed during the MCMA-2003 field campaign to establish the meteorological conditions and obtain an index of the strength and timing of the gap wind. A mesoscale meteorological model (MM5) is used in combination with high-resolution satellite data for the land surface parameters and soil moisture maps derived from diurnal ground temperature range. A simple method to map the lines of wind convergence both in the basin and on the regional scale is used to show the different convergence patterns according to episode types. The gap wind is found to occur on most days of the campaign and is the result of a temperature gradient across the southern basin rim which is very similar from day to day. Momentum mixing from winds aloft into the surface layer is much more variable and can determine both the strength of the flow and the pattern of the convergence zones. Northerly flows aloft lead to a weak jet with an east-west convergence line that progresses northwards in the late afternoon and early evening. Westerlies aloft lead to both stronger gap flows due to channelling and winds over the southern and western basin rim. This results in a north-south convergence line through the middle of the basin starting in the early afternoon. Improved understanding of basin meteorology will lead to better air quality forecasts for the city and better understanding of the chemical regimes in the urban atmosphere.

Vandenberg Air Force Base Pressure Gradient Wind Study

NASA Technical Reports Server (NTRS)

Shafer, Jaclyn A.

2013-01-01

Warning category winds can adversely impact day-to-day space lift operations at Vandenberg Air Force Base (VAFB) in California. NASA's Launch Services Program and other programs at VAFB use wind forecasts issued by the 30 Operational Support Squadron Weather Flight (30 OSSWF) to determine if they need to limit activities or protect property such as a launch vehicle. The 30 OSSWF tasked the AMU to develop an automated Excel graphical user interface that includes pressure gradient thresholds between specific observing stations under different synoptic regimes to aid forecasters when issuing wind warnings. This required the AMU to determine if relationships between the variables existed.

Wind Streaks on Venus: Clues to Atmospheric Circulation

NASA Technical Reports Server (NTRS)

Greeley, Ronald; Schubert, Gerald; Limonadi, Daniel; Bender, Kelly C.; Newman, William I.; Thomas, Peggy E.; Weitz, Catherine M.; Wall, Stephen D.

1994-01-01

Magellan images reveal surface features on Venus attributed to wind processes. Sand dunes, wind-sculpted hills, and more than 5830 wind streaks have been identified. The streaks serve as local "wind vanes," representing wind direction at the time of streak formation and allowing the first global mapping of near-surface wind patterns on Venus. Wind streaks are oriented both toward the equator and toward the west. When streaks associated with local transient events, such as impact cratering, are deleted, the westward component is mostly lost but the equatorward component remains. This pattern is consistent with a Hadley circulation of the lower atmosphere.

Turbulent convection in geostrophic circulation with wind and buoyancy forcing

NASA Astrophysics Data System (ADS)

Sohail, Taimoor; Gayen, Bishakhdatta; Hogg, Andy

2017-11-01

We conduct a direct numerical simulation of geostrophic circulation forced by surface wind and buoyancy to model a circumpolar ocean. The imposed buoyancy forcing (represented by Rayleigh number) drives a zonal current and supports small-scale convection in the buoyancy destabilizing region. In addition, we observe eddy activity which transports heat southward, supporting a large amount of heat uptake. Increasing wind stress enhances the meridional buoyancy gradient, triggering more eddy activity inside the boundary layer. Therefore, heat uptake increases with higher wind stress. The majority of dissipation is confined within the surface boundary layer, while mixing is dominant inside the convective plume and the buoyancy destabilizing region of the domain. The relative strength of the mixing and dissipation in the system can be expressed by mixing efficiency. This study finds that mixing is much greater than viscous dissipation, resulting in higher values of mixing efficiency than previously used. Supported by Australian Research Council Grant DP140103706.

RSRA sixth scale wind tunnel test. Tabulated balance data, volume 2

NASA Technical Reports Server (NTRS)

Ruddell, A.; Flemming, R.

1974-01-01

Summaries are presented of all the force and moment data acquired during the RSRA Sixth Scale Wind Tunnel Test. These data include and supplement the data presented in curve form in previous reports. Each summary includes the model configuration, wing and empennage incidences and deflections, and recorded balance data. The first group of data in each summary presents the force and moment data in full scale parametric form, the dynamic pressure and velocity in the test section, and the powered nacelle fan speed. The second and third groups of data are the balance data in nondimensional coefficient form. The wind axis coefficient data corresponds to the parametric data divided by the wing area for forces and divided by the product of the wing area and wing span or mean aerodynamic chord for moments. The stability axis data resolves the wind axis data with respect to the angle of yaw.

Local Wind Influence on Freshwater Plume Behavior: Application to the Catalan Shelf.

NASA Astrophysics Data System (ADS)

Liste, Maria; Grifoll, Manel; Monbaliu, Jaak; Keupers, Ingrid; Komijani, Homayoon

2013-04-01

Introduction Freshwater fluxes are not always considered, and often their 3D character is neglected. The "distributed" continental run-off is seldom taken into consideration. The main aim of the EU-FP7 Field_Ac project (www.field_ac.eu), was to improve operational service for coastal areas and to generate added value for shelf and regional scale predictions including land discharge as a boundary condition. In this paper the dispersal of a fresh water plume in a small part of the Catalan Coast (NW Mediterranean Sea) caused by a flash flood event in March 2011 is presented in response to the local wind forcing. Observations and modeling results are shown for a short period but with a large impact on the receiving coastal waters. Methodology and aim For the coastal circulation model, version 3.0 of the Regional Ocean Modeling System [ROMS, Shchepetkin and McWilliams, 2005] has been chosen. ROMS solves the 3-D Reynolds-Averaged Navier-Stokes equations in sigma coordinates. The code design is modular, so that different choices for advection and mixing, for example, may be applied by simply modifying preprocessor flags. Nested increasing-resolution models have been implemented in order to reproduce with sufficient spatial resolution the coastal circulation and the river plume evolution in a small portion of the Catalan coastal area. The boundary conditions for the largest domain model are obtained from the MyOcean products. River and urban run-off are estimated based on measured or predicted rainfall in the contributing catchments areas. Conceptual models based on a reservoir-type schematization of the river and sewer network have been set up to allow for fast prediction of the different point source boundary conditions [Keupers et al., 2011]. Model output data are compared to in situ data from dedicated campaigns during the Field_AC Project and to data from operational buoys in the Catalan coastal area. Results Wind forcing leads to freshwater spreading. As expected, wind speed and direction and the magnitude of the fresh water discharge affect substantially the plume behavior. This case study illustrates clearly the need to consider both the wind forcing and the fresh water discharge as part of a single system. References Field_AC project (www.field_ac.eu), EU- FP7-SPACE-2009-1-242284. Keupers, I., Willems, P., Fernandez Sainz, J., Bricheno, L., Wolf, J., Polton, J., Howarth, J., Carniel, S., Staneva, J. (2011). Methodology (including best practice guidelines) on how to identify and incorporate 'concentrated' and 'distributed' run-off in pre-operational forecasts, based on the input and requirements from our users. FIELD_AC project, D3.1, 90 pp. MyOcean products (http://www.myocean.eu/). Shchepetkin and McWilliams, 2005. The Regional Ocean Modeling System (ROMS): A split-explicit, free-surface, topography-following coordinates ocean model. Ocean Modelling. Vol. 9 pp. 347-404.

Offshore Wind Turbines Subjected to Hurricanes

NASA Astrophysics Data System (ADS)

Amirinia, Gholamreza

Hurricane Andrew (1992) caused one of the largest property losses in U.S. history, but limited availability of surface wind measurements hindered the advancement of wind engineering research. Many studies have been conducted on regular boundary layer winds (non-hurricane winds) and their effects on the structures. In this case, their results were used in the standards and codes; however, hurricane winds and their effects on the structures still need more studies and observations. Analysis of hurricane surface winds revealed that turbulence spectrum of hurricane winds differs from that of non-hurricane surface winds. Vertical profile of wind velocity and turbulence intensity are also important for determining the wind loads on high-rise structures. Vertical profile of hurricane winds is affected by different parameters such as terrain or surface roughness. Recent studies show that wind velocity profile and turbulence intensity of hurricane winds may be different from those used in the design codes. Most of the studies and available models for analyzing wind turbines subjected to high-winds neglect unsteady aerodynamic forces on a parked wind tower. Since the blade pitch angle in a parked wind turbine is usually about 90°, the drag coefficient on blade airfoils are very small therefore the along-wind aerodynamic forces on the blades are smaller than those on the tower. Hence, the tower in parked condition plays an important role in along-wind responses of the wind turbine. The objectives of this study are, first, to explore the nature of the hurricane surface winds. Next, to establish a time domain procedure for addressing structure-wind-wave-soil interactions. Third, investigating the behavior of wind turbines subjected to hurricane loads resulted form hurricane nature and, lastly, to investigate reconfiguration of turbine structure to reduce wind forces. In order to achieve these objective, first, recent observations on hurricane turbulence models were discussed. Then a new formulation for addressing unsteady wind forces on the tower was introduced and NREL-FAST package was modified with the new formulation. Interaction of wind-wave-soil-structure was also included in the modification. After customizing the package, the tower and blade buffeting responses, the low cycle fatigue during different hurricane categories, and extreme value of the short-term responses were analyzed. In the second part, piezoelectric materials were used to generate perturbations on the surface of a specimen in the wind tunnel. This perturbation was used to combine upward wall motion and surface curvature. For this purpose, a Macro Fiber Composite (MFC) material was mounted on the surface of a cylindrical specimen for generating perturbation in the wind tunnel. Four different perturbation frequencies (1 Hz, 2 Hz, 3 Hz, and 4Hz) as well as the baseline specimen were tested in a low-speed wind tunnel (Re= 2.8x104). Results showed that recently observed turbulence models resulted in larger structural responses and low-cycle fatigue damage than existing models. In addition, extreme value analysis of the short-term results showed that the IEC 61400-3 recommendation for wind turbine class I was sufficient for designing the tower for wind turbine class S subjected to hurricane; however, for designing the blade, IEC 61400-3 recommendations for class I underestimated the responses. In addition, wind tunnel testing results showed that the perturbation of the surface of the specimen increased the turbulence in the leeward in specific distance from the specimen. The surface perturbation technique had potential to reduce the drag by 4.8%.

Aerodynamic Simulation of the MARINTEK Braceless Semisubmersible Wave Tank Tests

NASA Astrophysics Data System (ADS)

Stewart, Gordon; Muskulus, Michael

2016-09-01

Model scale experiments of floating offshore wind turbines are important for both platform design for the industry as well as numerical model validation for the research community. An important consideration in the wave tank testing of offshore wind turbines are scaling effects, especially the tension between accurate scaling of both hydrodynamic and aerodynamic forces. The recent MARINTEK braceless semisubmersible wave tank experiment utilizes a novel aerodynamic force actuator to decouple the scaling of the aerodynamic forces. This actuator consists of an array of motors that pull on cables to provide aerodynamic forces that are calculated by a blade-element momentum code in real time as the experiment is conducted. This type of system has the advantage of supplying realistically scaled aerodynamic forces that include dynamic forces from platform motion, but does not provide the insights into the accuracy of the aerodynamic models that an actual model-scale rotor could provide. The modeling of this system presents an interesting challenge, as there are two ways to simulate the aerodynamics; either by using the turbulent wind fields as inputs to the aerodynamic model of the design code, or by surpassing the aerodynamic model and using the forces applied to the experimental turbine as direct inputs to the simulation. This paper investigates the best practices of modeling this type of novel aerodynamic actuator using a modified wind turbine simulation tool, and demonstrates that bypassing the dynamic aerodynamics solver of design codes can lead to erroneous results.

Marine Layer Stratus Study

NASA Astrophysics Data System (ADS)

Wells, Leonard A.

2007-06-01

The intent of this study is to develop a better understanding of the behavior of late spring through early fall marine layer stratus and fog at Vandenberg Air Force Base, which accounts for a majority of aviation forecasting difficulties. The main objective was to use Leipper (1995) study as a starting point to evaluate synoptic and mesoscale processes involved, and identify specific meteorological parameters that affected the behavior of marine layer stratus and fog. After identifying those parameters, the study evaluates how well the various weather models forecast them. The main conclusion of this study is that weak upper-air dynamic features work with boundary layer motions to influence marine layer behavior. It highlights the importance of correctly forecasting the surface temperature by showing how it ties directly to the wind field. That wind field, modified by the local terrain, establishes the low-level convergence and divergence pattern and the resulting marine layer cloud thicknesses and visibilities.

Linking storm surge activity and circulation variability along the Spanish coast through a synoptic pattern classification

NASA Astrophysics Data System (ADS)

Rasilla Álvarez, Domingo; Garcia Codrón, Juan Carlos

2010-05-01

The potentially negative consequences resulting from the estimations of global sea level rising along the current century are a matter of serious concern in many coastal areas worldwide. Most of the negative consequences of the sea level variability, such as flooding or erosion, are linked to episodic events of strong atmospheric forcing represented by deep atmospheric disturbances, especially if they combine with extreme astronomical high tides. Moreover, the interaction between the prevailing flows during such events and the actual orientation of the coast line might accelerate or mitigate such impacts. This contribution analyses sea surge variations measured at five tide-gauge stations located around the Iberian Peninsula and their relationships with regional scale circulation patterns with local-scale winds. Its aim is to improve the knowledge of surge related-coastal-risks by analysing the relationship between surges and their atmospheric forcing factors at different spatial scales. The oceanographic data set consists of hourly data from 5 tide gauge stations (Santander, Vigo, Bonanza, Málaga, Valencia and Barcelona) disseminated along the Spanish coastline, provided by Puertos del Estado. To explore the atmospheric mechanisms responsible for the sign and magnitude of sea surges, a regional Eulerian approach (a synoptic typing) were combined with a larger-scale Lagrangian method, based on the analysis of storm-tracks over the Atlantic and local information (synop reports) obtained from the closest meteorological stations to the tide gauges. The synoptic catalogue was obtained following a procedure that combines Principal Component Analysis (PCA) for reduction purposes and clustering (Ward plus K-means) to define the circulation types. Sea level pressure, surface 10m U and V wind components gridded data were obtained from NCEP Reanalysis, while storm tracks and cyclone statistics were extracted from the CDC Map Room Climate Products Storm Track Data (http://www.cdc.noaa.gov/map/clim/st_data.html). The second task was to evaluate the performance of each circulation type on the spatial patterns of a daily fire danger risk index (Canadian Fire Weather Index, FWI). Finally, anomaly maps of several surface and low level climate variables, corresponding to the dates of ignition of the very large forest fires within each synoptic pattern, were calculated to provide insight of the specific conditions associated to those extreme events. A principal component analysis upon 6 hourly residuals highlighted the homogeneous behaviour of the tide gauges and provided a regional quantitative index to identify the largest storm surges. The leading PCA displayed a homogeneous spatial pattern, describing the low frequency variability along the entire coast, in spite of different orientations of the coast, accounting for more than 80% of the total variability. The second PCA displayed opposite phases between the Atlantic and the Mediterranean. Furthermore, the results suggest that surges are a regional rather than local phenomenon, probably related to the same single physical forcing. The comparison between extreme surge events and circulation patterns highlighted that single physical mechanism is represented by extratropical cyclonic disturbances located at the north-western corner of the Iberian Peninsula, responsible for an environment characterized by low pressure readings and westerly-southwesterly winds. That wind pattern acquires an onshore component in the Atlantic coast, but becomes offshore in the Mediterranean. So, the main mechanism responsible for those storm surges is the inverse barometer effect, being the wind dragging secondary. The main physical forcing of the storm surges, the extratropical cyclones, have experience a reduction of this frequency and a marked reduction in their strength since 1950, replaced by stable circulations. Both conditions suggest a long term reduction of the frequency and the magnitude of storm surges.

Beyond Tree Throw: Wind, Water, Rock and the Mechanics of Tree-Driven Bedrock Physical Weathering

NASA Astrophysics Data System (ADS)

Marshall, J. A.; Anderson, R. S.; Dawson, T. E.; Dietrich, W. E.; Minear, J. T.

2017-12-01

Tree throw is often invoked as the dominant process in converting bedrock to soil and thus helping to build the Critical Zone (CZ). In addition, observations of tree roots lifting sidewalk slabs, occupying cracks, and prying slabs of rock from cliff faces have led to a general belief in the power of plant growth forces. These common observations have led to conceptual models with trees at the center of the soil genesis process. This is despite the observation that tree throw is rare in many forested settings, and a dearth of field measurements that quantify the magnitude of growth forces. While few trees blow down, every tree grows roots, inserting many tens of percent of its mass below ground. Yet we lack data quantifying the role of trees in both damaging bedrock and detaching it (and thus producing soil). By combing force measurements at the tree-bedrock interface with precipitation, solar radiation, wind speed, and wind-driven tree sway data we quantified the magnitude and frequency of tree-driven soil-production mechanisms from two contrasting climatic and lithologic regimes (Boulder and Eel Creek CZ Observatories). Preliminary data suggests that in settings with relatively thin soils, trees can damage and detach rock due to diurnal fluctuations, wind response and rainfall events. Surprisingly, our data suggests that forces from roots and trunks growing against bedrock are insufficient to pry rock apart or damage bedrock although much more work is needed in this area. The frequency, magnitude and style of wind-driven tree forces at the bedrock interface varies considerably from one to another species. This suggests that tree properties such as mass, elasticity, stiffness and branch structure determine whether trees respond to gusts big or small, move at the same frequency as large wind gusts, or are able to self-dampen near-ground sway response to extended wind forces. Our measurements of precipitation-driven and daily fluctuations in root pressures exerted on bedrock suggest that these fluctuations may impart a cyclic stress fatigue that over the lifetime of a tree could considerably weaken the enfolding rock (104 to 106 days depending on the species). Combined, our results suggest that wind-driven root torque and water uptake may be the primary mechanisms driving bedrock erosion and soil production in thin soil settings.

Forest impact estimated with NOAA AVHRR and landsat TM data related to an empirical hurricane wind-field distribution

USGS Publications Warehouse

Ramsey, Elijah W.; Hodgson, M.E.; Sapkota, S.K.; Nelson, G.A.

2001-01-01

An empirical model was used to relate forest type and hurricane-impact distribution with wind speed and duration to explain the variation of hurricane damage among forest types along the Atchafalaya River basin of coastal Louisiana. Forest-type distribution was derived from Landsat Thematic Mapper image data, hurricane-impact distribution from a suite of transformed advanced very high resolution radiometer images, and wind speed and duration from a wind-field model. The empirical model explained 73%, 84%, and 87% of the impact variances for open, hardwood, and cypress-tupelo forests, respectively. These results showed that the estimated impact for each forest type was highly related to the duration and speed of extreme winds associated with Hurricane Andrew in 1992. The wind-field model projected that the highest wind speeds were in the southern basin, dominated by cypress-tupelo and open forests, while lower wind speeds were in the northern basin, dominated by hardwood forests. This evidence could explain why, on average, the impact to cypress-tupelos was more severe than to hardwoods, even though cypress-tupelos are less susceptible to wind damage. Further, examination of the relative importance of wind speed in explaining the impact severity to each forest type showed that the impact to hardwood forests was mainly related to tropical-depression to tropical-storm force wind speeds. Impacts to cypress-tupelo and open forests (a mixture of willows and cypress-tupelo) were broadly related to tropical-storm force wind speeds and by wind speeds near and somewhat in excess of hurricane force. Decoupling the importance of duration from speed in explaining the impact severity to the forests could not be fully realized. Most evidence, however, hinted that impact severity was positively related to higher durations at critical wind speeds. Wind-speed intervals, which were important in explaining the impact severity on hardwoods, showed that higher durations, but not the highest wind speeds, were concentrated in the northern basin, dominated by hardwoods. The extreme impacts associated with the cypress-tupelo forests in the southeast corner of the basin intersected the highest durations as well as the highest wind speeds. ?? 2001 Published by Elsevier Science Inc.

Large-Eddy Simulation Sensitivities to Variations of Configuration and Forcing Parameters in Canonical Boundary-Layer Flows for Wind Energy Applications

DOE PAGES

Mirocha, Jeffrey D.; Churchfield, Matthew J.; Munoz-Esparza, Domingo; ...

2017-08-28

Here, the sensitivities of idealized Large-Eddy Simulations (LES) to variations of model configuration and forcing parameters on quantities of interest to wind power applications are examined. Simulated wind speed, turbulent fluxes, spectra and cospectra are assessed in relation to variations of two physical factors, geostrophic wind speed and surface roughness length, and several model configuration choices, including mesh size and grid aspect ratio, turbulence model, and numerical discretization schemes, in three different code bases. Two case studies representing nearly steady neutral and convective atmospheric boundary layer (ABL) flow conditions over nearly flat and homogeneous terrain were used to force andmore » assess idealized LES, using periodic lateral boundary conditions. Comparison with fast-response velocity measurements at five heights within the lowest 50 m indicates that most model configurations performed similarly overall, with differences between observed and predicted wind speed generally smaller than measurement variability. Simulations of convective conditions produced turbulence quantities and spectra that matched the observations well, while those of neutral simulations produced good predictions of stress, but smaller than observed magnitudes of turbulence kinetic energy, likely due to tower wakes influencing the measurements. While sensitivities to model configuration choices and variability in forcing can be considerable, idealized LES are shown to reliably reproduce quantities of interest to wind energy applications within the lower ABL during quasi-ideal, nearly steady neutral and convective conditions over nearly flat and homogeneous terrain.« less

Large-Eddy Simulation Sensitivities to Variations of Configuration and Forcing Parameters in Canonical Boundary-Layer Flows for Wind Energy Applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mirocha, Jeffrey D.; Churchfield, Matthew J.; Munoz-Esparza, Domingo

Here, the sensitivities of idealized Large-Eddy Simulations (LES) to variations of model configuration and forcing parameters on quantities of interest to wind power applications are examined. Simulated wind speed, turbulent fluxes, spectra and cospectra are assessed in relation to variations of two physical factors, geostrophic wind speed and surface roughness length, and several model configuration choices, including mesh size and grid aspect ratio, turbulence model, and numerical discretization schemes, in three different code bases. Two case studies representing nearly steady neutral and convective atmospheric boundary layer (ABL) flow conditions over nearly flat and homogeneous terrain were used to force andmore » assess idealized LES, using periodic lateral boundary conditions. Comparison with fast-response velocity measurements at five heights within the lowest 50 m indicates that most model configurations performed similarly overall, with differences between observed and predicted wind speed generally smaller than measurement variability. Simulations of convective conditions produced turbulence quantities and spectra that matched the observations well, while those of neutral simulations produced good predictions of stress, but smaller than observed magnitudes of turbulence kinetic energy, likely due to tower wakes influencing the measurements. While sensitivities to model configuration choices and variability in forcing can be considerable, idealized LES are shown to reliably reproduce quantities of interest to wind energy applications within the lower ABL during quasi-ideal, nearly steady neutral and convective conditions over nearly flat and homogeneous terrain.« less

Countermeasures for Reducing Unsteady Aerodynamic Force Acting on High-Speed Train in Tunnel by Use of Modifications of Train Shapes

NASA Astrophysics Data System (ADS)

Suzuki, Masahiro; Nakade, Koji; Ido, Atsushi

As the maximum speed of high-speed trains increases, flow-induced vibration of trains in tunnels has become a subject of discussion in Japan. In this paper, we report the result of a study on use of modifications of train shapes as a countermeasure for reducing an unsteady aerodynamic force by on-track tests and a wind tunnel test. First, we conduct a statistical analysis of on-track test data to identify exterior parts of a train which cause the unsteady aerodynamic force. Next, we carry out a wind tunnel test to measure the unsteady aerodynamic force acting on a train in a tunnel and examined train shapes with a particular emphasis on the exterior parts identified by the statistical analysis. The wind tunnel test shows that fins under the car body are effective in reducing the unsteady aerodynamic force. Finally, we test the fins by an on-track test and confirmed its effectiveness.

Drag and Side Force Reduction for Cyclicsts in Echelon Formation

NASA Astrophysics Data System (ADS)

Nedyalkov, Ivaylo; Cunningham, Alec; Lovell, Adam

2017-11-01

When riding directly behind another cyclist (drafting), a rider can use up to 30% less energy. This technique is often used during competitions, yet drafting in the presence of a cross wind has not been studied extensively. To investigate the effect of side-wind on drafting, 1:11 scale models of two different cyclists were rapid-prototyped and tested in a wind tunnel. The drag and side forces were measured in formations of up to 4 models. The results suggest that there is a significant decrease in both drag and side force when a cyclist is riding in another cyclist's wake. Positioning with no off-stream-wise offset result in the largest reduction of forces. When riding in a group of four cyclists, the second and third cyclist experience the largest force reduction. The size of the leading cyclist affects the reduction of forces, particularly when the leading cyclist is smaller. The results are dependent on the Reynolds number, but appear to be independent at higher Reynolds numbers. Initial full scale tests were conducted at the UNH Flow Physics Facility.

6. VIEW OF FIVEFOOT WIND TUNNEL WITH AIR STRAIGHTENER AND ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

6. VIEW OF FIVE-FOOT WIND TUNNEL WITH AIR STRAIGHTENER AND OPERATOR STATION IN FOREGROUND (1991). - Wright-Patterson Air Force Base, Area B, Building No. 19, Five-Foot Wind Tunnel, Dayton, Montgomery County, OH

Biogeochemical and ecological impacts of boundary currents in the Indian Ocean

NASA Astrophysics Data System (ADS)

Hood, Raleigh R.; Beckley, Lynnath E.; Wiggert, Jerry D.

2017-08-01

Monsoon forcing and the unique geomorphology of the Indian Ocean basin result in complex boundary currents, which are unique in many respects. In the northern Indian Ocean, several boundary current systems reverse seasonally. For example, upwelling coincident with northward-flowing currents along the coast of Oman during the Southwest Monsoon gives rise to high productivity which also alters nutrient stoichiometry and therefore, the species composition of the resulting phytoplankton blooms. During the Northeast Monsoon most of the northern Indian Ocean boundary currents reverse and favor downwelling. Higher trophic level species have evolved behavioral responses to these seasonally changing conditions. Examples from the western Arabian Sea include vertical feeding migrations of a copepod (Calanoides carinatus) and the reproductive cycle of a large pelagic fish (Scomberomorus commerson). The impacts of these seasonal current reversals and changes in upwelling and downwelling circulations are also manifested in West Indian coastal waters, where they influence dissolved oxygen concentrations and have been implicated in massive fish kills. The winds and boundary currents reverse seasonally in the Bay of Bengal, though the associated changes in upwelling and productivity are less pronounced. Nonetheless, their effects are observed on the East Indian shelf as, for example, seasonal changes in copepod abundance and zooplankton community structure. In contrast, south of Sri Lanka seasonal reversals in the boundary currents are associated with dramatic changes in the intensity of coastal upwelling, chlorophyll concentration, and catch per unit effort of fishes. Off the coast of Java, monsoon-driven changes in the currents and upwelling strongly impact chlorophyll concentrations, seasonal vertical migrations of zooplankton, and sardine catch in Bali Strait. In the southern hemisphere the Leeuwin is a downwelling-favorable current that flows southward along western Australia, though local wind forcing can lead to transient near shore current reversals and localized coastal upwelling. The poleward direction of this eastern boundary current is unique. Due to its high kinetic energy the Leeuwin Current sheds anomalous, relatively high chlorophyll, warm-core, downwelling eddies that transport coastal diatom communities westward into open ocean waters. Variations in the Leeuwin transport and eddy generation impact many higher trophic level species including the recruitment and fate of rock lobster (Panulirus cygnus) larvae. In contrast, the transport of the Agulhas Current is very large, with sources derived from the Mozambique Channel, the East Madagascar Current and the southwest Indian Ocean sub-gyre. Dynamically, the Agulhas Current is upwelling favorable; however, the spatial distribution of prominent surface manifestations of upwelling is controlled by local wind and topographic forcing. Meanders and eddies in the Agulhas Current propagate alongshore and interact with seasonal changes in the winds and topographic features. These give rise to seasonally variable localized upwelling and downwelling circulations with commensurate changes in primary production and higher trophic level responses. Due to the strong influence of the Agulhas Current, many neritic fish species in southeast Africa coastal waters have evolved highly selective behaviors and reproductive patterns for successful retention of planktonic eggs and larvae. For example, part of the Southern African sardine (Sardinops sagax) stock undergoes a remarkable northward migration enhanced by transient cyclonic eddies in the shoreward boundary of the Agulhas Current. There is evidence from the paleoceanographic record that these currents and their biogeochemical and ecological impacts have changed significantly over glacial to interglacial timescales. These changes are explored as a means of providing insight into the potential impacts of climate change in the Indian Ocean.

Basinwide response of the Atlantic Meridional Overturning Circulation to interannual wind forcing

NASA Astrophysics Data System (ADS)

Zhao, Jian

2017-12-01

An eddy-resolving Ocean general circulation model For the Earth Simulator (OFES) and a simple wind-driven two-layer model are used to investigate the role of momentum fluxes in driving the Atlantic Meridional Overturning Circulation (AMOC) variability throughout the Atlantic basin from 1950 to 2010. Diagnostic analysis using the OFES results suggests that interior baroclinic Rossby waves and coastal topographic waves play essential roles in modulating the AMOC interannual variability. The proposed mechanisms are verified in the context of a simple two-layer model with realistic topography and only forced by surface wind. The topographic waves communicate high-latitude anomalies into lower latitudes and account for about 50% of the AMOC interannual variability in the subtropics. In addition, the large scale Rossby waves excited by wind forcing together with topographic waves set up coherent AMOC interannual variability patterns across the tropics and subtropics. The comparisons between the simple model and OFES results suggest that a large fraction of the AMOC interannual variability in the Atlantic basin can be explained by wind-driven dynamics.

Coupled vibrations of rectangular buildings subjected to normally-incident random wind loads

USGS Publications Warehouse

Safak, E.; Foutch, D.A.

1987-01-01

A method for analyzing the three-directional coupled dynamic response of wind-excited buildings is presented. The method is based on a random vibration concept and is parallel to those currently used for analyzing alongwind response. Only the buildings with rectangular cross-section and normally-incident wind are considered. The alongwind pressures and their correlations are represented by the well-known expressions that are available in the literature. The acrosswind forces are assumed to be mainly due to vortex shedding. The torque acting on the building is taken as the sum of the torque due to random alongwind forces plus the torque due to asymmetric acrosswind forces. The study shows the following: (1) amplitude of acrosswind vibrations can be several times greater than that of alongwind vibrations; (2) torsional vibrations are significant if the building has large frontal width, and/or it is asymmetric, and/or its torsional natural frequency is low; (3) even a perfectly symmetric structure with normally incident wind can experience significant torsional vibrations due to the randomness of wind pressures. ?? 1987.

Influence of wind and river discharge on the vertical exchange process in the Pearl River Estuary

NASA Astrophysics Data System (ADS)

Hong, B.; Peng, S.

2016-02-01

Vertical exchange process is controlled by the buoyancy input from river discharge and the momentum input by wind forcing. This study investigates the vertical exchange process in the Pearl River Estuary by using a 3-D numerical model. The vertical exchange time (VET) is used to quantify the magnitude of vertical exchange process in response to changing local wind and river discharge. During the dry season, it only takes about 2 days for the surface layer water mass being transported to the bottom layer. During the wet season, such transport will take more than 20 days in a large portion of the main channel. The water in the slope area can be well ventilated. Linear regression of VET indicates that water column stratification can be used to estimate the VET and up to 71% of the variance can be accounted. The estimation by using river runoff can only account for about 49% of the variance. The effects of wind speed and direction are investigated separately. Neither river runoff nor the stratification can properly predict the VET during the typical wet season. Further investigations are needed to reveal the dynamics of vertical exchange process and find out other factors that influence the VET during the wet season.

WIND Flow Solver Released

NASA Technical Reports Server (NTRS)

Towne, Charles E.

1999-01-01

The WIND code is a general-purpose, structured, multizone, compressible flow solver that can be used to analyze steady or unsteady flow for a wide range of geometric configurations and over a wide range of flow conditions. WIND is the latest product of the NPARC Alliance, a formal partnership between the NASA Lewis Research Center and the Air Force Arnold Engineering Development Center (AEDC). WIND Version 1.0 was released in February 1998, and Version 2.0 will be released in February 1999. The WIND code represents a merger of the capabilities of three existing computational fluid dynamics codes--NPARC (the original NPARC Alliance flow solver), NXAIR (an Air Force code used primarily for unsteady store separation problems), and NASTD (the primary flow solver at McDonnell Douglas, now part of Boeing).

Vehicle to wireless power transfer coupling coil alignment sensor

DOEpatents

Miller, John M.; Chambon, Paul H.; Jones, Perry T.; White, Clifford P.

2016-02-16

A non-contacting position sensing apparatus includes at least one vehicle-mounted receiver coil that is configured to detect a net flux null when the vehicle is optimally aligned relative to the primary coil in the charging device. Each of the at least one vehicle-mounted receiver coil includes a clockwise winding loop and a counterclockwise winding loop that are substantially symmetrically configured and serially connected to each other. When the non-contacting position sensing apparatus is located directly above the primary coil of the charging device, the electromotive forces from the clockwise winding loop and the counterclockwise region cancel out to provide a zero electromotive force, i.e., a zero voltage reading across the coil that includes the clockwise winding loop and the counterclockwise winding loop.

Aeolus -A Mission to Study the Thermal and Wind Environment of Mars

NASA Technical Reports Server (NTRS)

Colaprete, Anthony

2017-01-01

Aeolus is a small satellite mission to observe surface and atmospheric forcing and general circulation of Mars, by measuring surface energy balance, atmospheric temperatures, aerosols and clouds, and winds. Critically, Aeolus will make these measurements at all local times of day, providing information on both seasonal and diurnal variability. To date, direct measurements of Martian wind speeds have only been possible at the surface, only during daylight hours, and over small areas limited by rover traverse capabilities. From orbit, thermal measurements (e.g., estimates from assumed geostrophic balance) as well as images of dust storms and dune migration have provided inputs to derive current data sets on Martian winds. However, Mars General Circulation models demonstrate that wind speeds derived from these indirect measurements may be in error by 50 to 100%. For this reason, direct wind velocity measurements have been deemed "High Priority" by MEPAG (Mars Exploration Program Analysis Group); measuring wind speeds and corresponding thermal data is vital to understanding the climate of Mars. Aeolus will carry four Spatial Heterodyne Spectrometers (SHS), coupled to two orthogonal viewing telescopes. These high-resolution near-infrared spectrometers will measure CO2 (daytime absorption) and O2 (day and night emission) lines in the Martian atmosphere. Doppler shifts in these lines can be measured during Martian day and night, resolving wind speeds down to 5 m/s. Orthogonal views allow the spectrometers to capture wind vectors over all observation locations. Aeolus will also carry the atmospheric limb-viewing Thermal Limb Sounder (TLS) to measure atmospheric temperatures, water ice clouds, and dust abundances across all altitudes where winds are measured. Finally, the Surface Radiometric Sensor Package (SuRSeP), a nadir viewing radiometer, will measure the total reflected solar and emitted thermal radiance, surface temperature, and water cloud and dust total column abundances. The combined spectral and thermal measurements will provide a new understanding of the global energy balance, dust transport processes, and climate cycles in the Martian atmosphere. Aeolus will consist of a single satellite in a near-polar orbit, allowing it to pass over all local times, with the baseline mission observing all seasons of an entire Martian year (two Earth years). Aeolus was one of two Martian smallsat concepts selected for study through the Planetary Science Deep Space SmallSat Studies program. This talk will provide an overview of the mission, including science rationale, instruments, spacecraft, and mission operations concept.

Subtidal currents over the central California slope: Evidence for offshore veering of the undercurrent and for direct, wind-driven slope currents

USGS Publications Warehouse

Noble, M.A.; Ramp, S.R.

2000-01-01

In February 1991, an array of six current-meter moorings was deployed for one year across the central California outer shelf and slope. The main line of the array extended 30 km offshore of the shelf break, out to water depths of 1400 m. A more sparsely-instrumented line, displaced 30 km to the northwest, extended 14 km offshore. Though shorter, the northern line spanned similar water depths because the gradient of the topography steepened in the northern region. A poleward flow pattern, typical of the California undercurrent, was seen across both lines in the array over most of the year. The poleward flow was surface intensified. In general, the portion of the undercurrent that crossed the southern line had larger amplitudes and penetrated more deeply into the water column than the portion that crossed the northern line. Transport over the year ranged from 0 to 2.5 Sverdrups (Sv) poleward across the southern line; 0 to 1 Sv poleward across the northern line. We suggest the difference in transport was caused by topographic constraints, which tended to force the poleward flow offshore of the northern measurement sites. The slope of the topography steepened too abruptly to allow the poleward flow to follow isobaths when currents were strong. When current velocities lessened, a more coherent flow pattern was seen across both lines in the array. In general, the poleward flow patterns in the undercurrent were not affected by local winds or by the local alongshore pressure gradient. Nor was a strong seasonal pattern evident. Rather unexpectedly, a small but statistically significant fraction of the current variance over the mid- and outer slope was driven by the surface wind stress. An alongshelf wind stress caused currents to flow along the slope, parallel to the wind field, down to depths of 400 m below the surface and out to distances of 2 Rossby radii past the shelf break. The transfer functions were weak, 3-4 cm/s per dyn cm-2, but comparable to wind-driven current amplitudes of 4-6 cm/s per unit wind stress over the middle shelf. Equatorward, alongshelf winds also caused water from 200-300 m over the slope to upwell onto the shelf as the surface water moved offshore.

Large eddy simulations and reduced models of the Unsteady Atmospheric Boundary Layer

NASA Astrophysics Data System (ADS)

Momen, M.; Bou-Zeid, E.

2013-12-01

Most studies of the dynamics of Atmospheric Boundary Layers (ABLs) have focused on steady geostrophic conditions, such as the classic Ekman boundary layer problem. However, real-world ABLs are driven by a time-dependent geostrophic forcing that changes at sub-diurnal scales. Hence, to advance our understanding of the dynamics of atmospheric flows, and to improve their modeling, the unsteady cases have to be analyzed and understood. This is particularly relevant to new applications related to wind energy (e.g. short-term forecast of wind power changes) and pollutant dispersion (forecasting of rapid changes in wind velocity and direction after an accidental spill), as well as to classic weather prediction and hydrometeorological applications. The present study aims to investigate the ABL behavior under variable forcing and to derive a simple model to predict the ABL response under these forcing fluctuations. Simplifications of the governing Navier-Stokes equations, with the Coriolis force, are tested using LES and then applied to derive a physical model of the unsteady ABL. LES is then exploited again to validate the analogy and the output of the simpler model. Results from the analytical model, as well as LES outputs, open the way for inertial oscillations to play an important role in the dynamics. Several simulations with different variable forcing patterns are then conducted to investigate some of the characteristics of the unsteady ABL such as resonant frequency, ABL response time, equilibrium states, etc. The variability of wind velocity profiles and hodographs, turbulent kinetic energy, and vertical profiles of the total stress and potential temperature are also examined. Wind Hodograph of the Unsteady ABL at Different Heights - This figure shows fluctuations in the mean u and v components of the velocity as time passes due to variable geostrophic forcing

Modeling the effects of UV variability and the QBO on the troposphere-stratosphere system. Part I: The middle atmosphere

DOE Office of Scientific and Technical Information (OSTI.GOV)

Balachandran, N.K.; Rind, D.

1995-08-01

Results of experiments with a GCM involving changes in UV input ({plus_minus}25%, {plus_minus}10%, {plus_minus}5% at wavelengths below 0.3 {mu}m) and simulated equatorial QBO are presented, with emphasis on the middle atmosphere response. The UV forcing employed is larger than observed during the last solar cycle and does not vary with wavelength, hence the relationship of these results to those from actual solar UV forcing should be treated with caution. The QBO alters the location of the zero wind line and the horizontal shear of the zonal wind in the low to middle stratosphere, while the UV change alters the magnitudemore » of the polar jet and the vertical shear of the zonal wind. Both mechanisms thus affect planetary wave propagation. The east phase of the QBO leads to tropical cooling and high-latitude warming in the lower stratosphere, with opposite effects in the upper stratosphere. This quadrupole pattern is also seen in the observations. The high-latitude responses are due to altered planetary wave effects, while the model`s tropical response in the upper stratosphere is due to gravity wave drag. Increased UV forcing warms tropical latitudes in the middle atmosphere, resulting in stronger extratropical west winds, an effect which peaks in the upper stratosphere/lower mesosphere with the more extreme UV forcing but at lower altitudes and smaller wind variations with the more realistic forcing. The increased vertical gradient of the zonal wind leads to increased vertical propagation of planetary waves, altering energy convergences and temperatures. The exact altitudes affected depend upon the UV forcing applied. Results with combined QBO and UV forcing show that in the Northern Hemisphere, polar warming for the east QBO is stronger when the UV input is reduced by 25% and 5% as increased wave propagation to high latitudes (east QBO effect) is prevented from then propagating vertically (reduced UV effect). 30 refs., 14 figs., 6 tabs.« less

A Model Study of Zonal Forcing in the Equatorial Stratosphere by Convectively Induced Gravity Waves

NASA Technical Reports Server (NTRS)

Alexander, M. J.; Holton, James R.

1997-01-01

A two-dimensional cloud-resolving model is used to examine the possible role of gravity waves generated by a simulated tropical squall line in forcing the quasi-biennial oscillation (QBO) of the zonal winds in the equatorial stratosphere. A simulation with constant background stratospheric winds is compared to simulations with background winds characteristic of the westerly and easterly QBO phases, respectively. In all three cases a broad spectrum of both eastward and westward propagating gravity waves is excited. In the constant background wind case the vertical momentum flux is nearly constant with height in the stratosphere, after correction for waves leaving the model domain. In the easterly and westerly shear cases, however, westward and eastward propagating waves, respectively, are strongly damped as they approach their critical levels, owing to the strongly scale-dependent vertical diffusion in the model. The profiles of zonal forcing induced by this wave damping are similar to profiles given by critical level absorption, but displaced slightly downward. The magnitude of the zonal forcing is of order 5 m/s/day. It is estimated that if 2% of the area of the Tropics were occupied by storms of similar magnitude, mesoscale gravity waves could provide nearly 1/4 of the zonal forcing required for the QBO.

On using scatterometer and altimeter data to improve storm surge forecasting in the Adriatic Sea

NASA Astrophysics Data System (ADS)

Bajo, Marco; Umgiesser, Georg; De Biasio, Francesco; Vignudelli, Stefano; Zecchetto, Stefano

2017-04-01

Satellite data are seldom used in storm surge forecasting. Among the most important issues related to the storm surge forecasting are the quality of the model wind forcing and the initial condition of the sea surface elevation. In this work, focused on storm surge forecasting in the Adriatic Sea, satellite scatterometer wind data are used to correct the wind speed and direction biases of the ECMWF global atmospheric model by tuning the spatial fields, as an alternative to data assimilation. The capability of such an unbiased wind is tested against that of a high resolution wind, produced by a regional non-hydrostatic model. On the other hand, altimeter Total Water Level Envelope (TWLE) data, which provide the sea level elevation, are used to improve the accuracy of the initial state of the model simulations. This is done by assimilating into a storm surge model the TWLE obtained by the altimeter observations along ground tracks, after subtraction of the tidal components. In order to test the methodology, eleven storm surge events recorded in Venice, from 2008 to 2012, have been simulated using different configurations of forcing wind and altimeter data assimilation. Results show that the relative error on the estimation of the maximum surge peak, averaged over the cases considered, decreases from 13% to 7% using both the unbiased wind and the altimeter data assimilation, while forcing the hydrodynamic model with the high resolution wind (no tuning), the altimeter data assimilation reduces the error from 9% to 6%.

46 CFR 42.30-1 - Basis.

Code of Federal Regulations, 2010 CFR

2010-10-01

... following criteria: (1) Summer: not more than 10 percent winds of force 8 Beaufort (34 knots) or more. (2) Tropical: not more than 1 percent winds of force 8 Beaufort (34 knots) or more. Not more than one tropical storm in 10 years in an area of 5° square in any 1 separate calendar month. (b) In certain special areas...

Efficiency of lung ventilation for people performing wind instruments.

PubMed

Brzęk, Anna; Famuła, Anna; Kowalczyk, Anna; Plinta, Ryszard

Wind instruments musicians are particularly prone to excessive respiratory efforts. Prolonged wind instruments performing may lead to changes in respiratory tracts and thus to respiratory muscles overload. It may result in decreasing lung tissue pliability and, as a consequence, in emphysema. Aim of the research has been to describe basic spirometric parameters for wind players and causes of potential changes. Slow and forced spirometry with the use of Micro Lab Viasys (Micro Medical, Great Britain) was conducted on 31 wind musicians (group A). A survey concerning playing time and frequency, weight of instruments, and education on diaphragmatic breathing was conducted. The control group included 34 healthy persons at similar age (group B). The results were statistically described using Excel and Statistica programmes. The respiratory parameters were within the range of physiological norms and forced expiratory volume in 1 s to forced vital capacity (FEV1/FVC) exceeded in both groups the values of 100%. Forced vital capacity and expiratory vital capacity (EVC) values were significantly lower in the group of musicians than in the control group (p < 0.001). In 45% the group A used diaphragmatic breathing, in 31% of examinees mixed respiratory tract was observed. The significant discrepancy of individual parameters was obtained regarding age and the length of time when performing wind instrument. Spirometric parameters relative to standards may prove a good respiratory capacity. Peak expiratory flow (PEF) and FEV1 may indicate that a proper technique of respiration during performance was acquired. The length of time when performing wind instrument may influence parameters of dynamic spirometry. Med Pr 2016;67(4):427-433. This work is available in Open Access model and licensed under a CC BY-NC 3.0 PL license.

Comparison of the ocean surface vector winds over the Nordic Seas and their application for ocean modeling

NASA Astrophysics Data System (ADS)

Dukhovskoy, Dmitry; Bourassa, Mark

2017-04-01

Ocean processes in the Nordic Seas and northern North Atlantic are strongly controlled by air-sea heat and momentum fluxes. The predominantly cyclonic, large-scale atmospheric circulation brings the deep ocean layer up to the surface preconditioning the convective sites in the Nordic Seas for deep convection. In winter, intensive cooling and possibly salt flux from newly formed sea ice erodes the near-surface stratification and the mixed layer merges with the deeper domed layer, exposing the very weakly stratified deep water mass to direct interaction with the atmosphere. Surface wind is one of the atmospheric parameters required for estimating momentum and turbulent heat fluxes to the sea ice and ocean surface. In the ocean models forced by atmospheric analysis, errors in surface wind fields result in errors in air-sea heat and momentum fluxes, water mass formation, ocean circulation, as well as volume and heat transport in the straits. The goal of the study is to assess discrepancies across the wind vector fields from reanalysis data sets and scatterometer-derived gridded products over the Nordic Seas and northern North Atlantic and to demonstrate possible implications of these differences for ocean modeling. The analyzed data sets include the reanalysis data from the National Center for Environmental Prediction Reanalysis 2 (NCEPR2), Climate Forecast System Reanalysis (CFSR), Arctic System Reanalysis (ASR) and satellite wind products Cross-Calibrated Multi-Platform (CCMP) wind product version 1.1 and recently released version 2.0, and Remote Sensing Systems QuikSCAT data. Large-scale and mesoscale characteristics of winds are compared at interannual, seasonal, and synoptic timescales. Numerical sensitivity experiments are conducted with a coupled ice-ocean model forced by different wind fields. The sensitivity experiments demonstrate differences in the net surface heat fluxes during storm events. Next, it is hypothesized that discrepancies in the wind vorticity fields should manifest different behaviors of the isopycnals in the Nordic Seas. Time evolution of isopycnal depths in the sensitivity experiments forced by different wind fields is discussed. Results of these sensitivity experiments demonstrate a relationship between the isopycnal surfaces and the wind stress curl. The numerical experiments are also analyzed to investigate the relationship between the East Greenland Current and the wind stress curl over the Nordic Seas. The transport of the current at this location has substantial contribution from wind-driven large-scale circulation. This wind-driven part of the East Greenland Current is a western-intensified return flow of a wind-driven cyclonic gyre in the central Nordic Seas. The numerical experiments with different wind fields reveal notable sensitivity of the East Greenland Current to differences in the wind forcing.

0.4 Percent Scale Space Launch System Wind Tunnel Test

NASA Image and Video Library

2011-11-15

0.4 Percent Scale Space Launch System Wind Tunnel Test 0.4 Percent Scale SLS model installed in the NASA Langley Research Center Unitary Plan Wind Tunnel Test Section 1 for aerodynamic force and movement testing.

7. VIEW WEST OF SCALE ROOM IN FULLSCALE WIND TUNNEL; ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

7. VIEW WEST OF SCALE ROOM IN FULL-SCALE WIND TUNNEL; SCALES ARE USED TO MEASURE FORCES ACTING ON MODEL AIRCRAFT SUSPENDED ABOVE. - NASA Langley Research Center, Full-Scale Wind Tunnel, 224 Hunting Avenue, Hampton, Hampton, VA

Stellar and wind parameters of massive stars from spectral analysis

NASA Astrophysics Data System (ADS)

Araya, I.; Curé, M.

2017-07-01

The only way to deduce information from stars is to decode the radiation it emits in an appropriate way. Spectroscopy can solve this and derive many properties of stars. In this work we seek to derive simultaneously the stellar and wind characteristics of A and B supergiant stars. Our stellar properties encompass the effective temperature, the surface gravity, the stellar radius, the micro-turbulence velocity, the rotational velocity and, finally, the chemical composition. For wind properties we consider the mass-loss rate, the terminal velocity and the line-force parameters (α, k and δ) obtained from the standard line-driven wind theory. To model the data we use the radiative transport code Fastwind considering the newest hydrodynamical solutions derived with Hydwind code, which needs stellar and line-force parameters to obtain a wind solution. A grid of spectral models of massive stars is created and together with the observed spectra their physical properties are determined through spectral line fittings. These fittings provide an estimation about the line-force parameters, whose theoretical calculations are extremely complex. Furthermore, we expect to confirm that the hydrodynamical solutions obtained with a value of δ slightly larger than ˜ 0.25, called δ-slow solutions, describe quite reliable the radiation line-driven winds of A and late B supergiant stars and at the same time explain disagreements between observational data and theoretical models for the Wind-Momentum Luminosity Relationship (WLR).

Stellar and wind parameters of massive stars from spectral analysis

NASA Astrophysics Data System (ADS)

Araya, Ignacio; Curé, Michel

2017-11-01

The only way to deduce information from stars is to decode the radiation it emits in an appropriate way. Spectroscopy can solve this and derive many properties of stars. In this work we seek to derive simultaneously the stellar and wind characteristics of a wide range of massive stars. Our stellar properties encompass the effective temperature, the surface gravity, the stellar radius, the micro-turbulence velocity, the rotational velocity and the Si abundance. For wind properties we consider the mass-loss rate, the terminal velocity and the line-force parameters α, k and δ (from the line-driven wind theory). To model the data we use the radiative transport code Fastwind considering the newest hydrodynamical solutions derived with Hydwind code, which needs stellar and line-force parameters to obtain a wind solution. A grid of spectral models of massive stars is created and together with the observed spectra their physical properties are determined through spectral line fittings. These fittings provide an estimation about the line-force parameters, whose theoretical calculations are extremely complex. Furthermore, we expect to confirm that the hydrodynamical solutions obtained with a value of δ slightly larger than ~ 0.25, called δ-slow solutions, describe quite reliable the radiation line-driven winds of A and late B supergiant stars and at the same time explain disagreements between observational data and theoretical models for the Wind-Momentum Luminosity Relationship (WLR).

Wind and Current Forces Acting on Canadian Forces Ships During Tug Operations

DTIC Science & Technology

2002-11-01

McTaggart and Sav- age [1] describe model tests conducted on a generic frigate model to determine wind forces influencing ship capsize. Van Manen and van ...Fn will be 0.06. Based on data presented by van Manen and van Oossanen [2], the fric- tional resistance coefficient will be approximately 0.002 and...Conference on Stability of Ships and Ocean Vehicles (Melbourne, Florida, 1994). 2. J.D. van Manen and P. van Oossanen, Principles of Naval Architecture, Volume

Influence of bending stress on flux distribution in toroidal transducers

NASA Astrophysics Data System (ADS)

Goktepe, M.; Meydan, T.

1994-05-01

Amorphous transducers consisting of toroidally wound amorphous ribbon with a magnetising winding and search coil windings have been investigated. The application of displacement to the toroid gives a linear search coil voltage against the applied force characteristics. The position of the search coils with respect to the applied force has been studied and it is shown that the effect of applied force is localised. These results have elucidated the operation of ac amorphous ribbon transducers and enabled improved designs to be produced.

Response of upper ocean cooling off northeastern Taiwan to typhoon passages

NASA Astrophysics Data System (ADS)

Zheng, Zhe-Wen; Zheng, Quanan; Gopalakrishnan, Ganesh; Kuo, Yi-Chun; Yeh, Ting-Kuang

2017-07-01

A comprehensive investigation of the typhoon induced upper ocean processes and responses off northeastern Taiwan was conducted. Using the Regional Ocean Modeling System, the upper ocean responses of all typhoons striking Taiwan between 2005 and 2013 were simulated. In addition to Kuroshio intrusion, the present study demonstrates another important mechanism of typhoon induced near-inertial currents over the continental shelf of East China Sea, which can also trigger a distinct cooling (through entrainment mixing) within this region. Results indicate that the processes of typhoon inducing distinct cooling off northeastern Taiwan are conditional phenomena (only ∼12% of typhoons passing Taiwan triggered extreme cooling there). Subsequently, by executing a series of sensitivity experiments and systematic analyses on the behaviors and background conditions of all those typhoon cases, key criteria determining the occurrences of cooling through both mechanisms were elucidated. Occurrences of cooling through the Kuroshio intrusion mechanism are determined mainly by the strength of the local wind over northeastern Taiwan. A distinct cooling triggered by enhanced near-inertial currents is shown to be associated with the process of wind-current resonance. Both processes of Kuroshio intrusion and enhanced near-inertial currents are dominated by wind forcing rather than upper oceanic conditions. Based on the recent findings on the possible dynamic linkage between sea surface temperature near northeast Taiwan and local weather systems, the results elucidated in this study lay the foundation for further improvement in the regional weather prediction surrounding northeast Taiwan.

Climate-driven variations in thermal forcing across a nearshore reef system during a marine heat wave and its potential impact on coral calcification

NASA Astrophysics Data System (ADS)

Falter, J.; Zhang, Z.; Lowe, R.; Foster, T.; McCulloch, M. T.

2016-02-01

We examined the oceanic and atmospheric forces driving seasonal and spatial variability in water temperature across backreef and lagoonal habitats at Coral Bay at Ningaloo Reef, Western Australia before, during, and after a historically unprecedented marine heat wave and resulting mass bleaching event in 2010-2011. Local deviations in the mean daily temperature of nearshore reef waters from offshore values were a linear function of the combined effect of net atmospheric heating and offshore wave height and period . While intra-annual variation in local heat exchange was driven mainly by seasonal changes in short-wave radiation; intra-annual variation in local cooling was driven mostly by changes in relative humidity (r2 = 0.60) and wind speed (r2 = 0.31) which exhibited no apparent seasonality. We demonstrate good agreement between nearshore reef temperatures modeled from offshore sea surface temperatures (SST), offshore wave forcing, and local atmospheric heat fluxes with observed temperatures using a simple linear model (r2 = 0.31 to 0.69, root-mean-square error = 0.4°C to 0.9°C). Using these modeled nearshore reef temperature records, we show that during the heat wave local thermal stresses across the reef reached as high as 18-34 °C-weeks and were being both intensified and accelerated by regional climate forcing when compared with offshore waters (12.6 °C-weeks max). Measurements of coral calcification made in Coral Bay following the bleaching event appear to lack any distinct seasonality; possibly due to the long-term effects of acute thermal stress. However, similarly minimal seasonality in calcification rates had also been observed in an Acropora-dominated community at Ningaloo years before the heat wave as well as more recently in coral from regions in WA that had avoided mass bleaching. These observations, in conjunction with observations that most of the bleached communities within Coral Bay had recovered their color within 3-6 months of the bleaching event, suggest that how reef building coral respond to a severe thermal stress event can be somewhat nuanced depending on the local and regional setting.

Wind gusts and plant aeroelasticity effects on the aerodynamics of pollen shedding: a hypothetical turbulence-initiated wind-pollination mechanism.

PubMed

Urzay, Javier; Llewellyn Smith, Stefan G; Thompson, Elinor; Glover, Beverley J

2009-08-21

Plant reproduction depends on pollen dispersal. For anemophilous (wind-pollinated) species, such as grasses and many trees, shedding pollen from the anther must be accomplished by physical mechanisms. The unknown nature of this process has led to its description as the 'paradox of pollen liberation'. A simple scaling analysis, supported by experimental measurements on typical wind-pollinated plant species, is used to estimate the suitability of previous resolutions of this paradox based on wind-gust aerodynamic models of fungal-spore liberation. According to this scaling analysis, the steady Stokes drag force is found to be large enough to liberate anemophilous pollen grains, and unsteady boundary-layer forces produced by wind gusts are found to be mostly ineffective since the ratio of the characteristic viscous time scale to the inertial time scale of acceleration of the wind stream is a small parameter for typical anemophilous species. A hypothetical model of a stochastic aeroelastic mechanism, initiated by the atmospheric turbulence typical of the micrometeorological conditions in the vicinity of the plant, is proposed to contribute to wind pollination.

Cryogenic strain gage techniques used in force balance design for the National Transonic Facility

NASA Technical Reports Server (NTRS)

Ferris, A. T.

1986-01-01

A force balance is a strain gage transducer used in wind tunnels to measure the forces and moments on aerodynamic models. Techniques have been established for temperature-compensation of force balances to allow their use over the operating temperature range of a cryogenic wind tunnel (-190C to 60C) without thermal control. This was accomplished by using a patented strain gage matching process to minimize inherent thermal differences, and a thermal compensation procedure to reduce the remaining thermally-induced outputs to acceptable levels. A method of compensating for mechanical movement of the axial force measuring beam caused by thermally-induced stresses under transient temperatures was also included.

Method and apparatus for wind turbine braking

DOEpatents

Barbu, Corneliu [Laguna Hills, CA; Teichmann, Ralph [Nishkayuna, NY; Avagliano, Aaron [Houston, TX; Kammer, Leonardo Cesar [Niskayuna, NY; Pierce, Kirk Gee [Simpsonville, SC; Pesetsky, David Samuel [Greenville, SC; Gauchel, Peter [Muenster, DE

2009-02-10

A method for braking a wind turbine including at least one rotor blade coupled to a rotor. The method includes selectively controlling an angle of pitch of the at least one rotor blade with respect to a wind direction based on a design parameter of a component of the wind turbine to facilitate reducing a force induced into the wind turbine component as a result of braking.

A new method for wind speed forecasting based on copula theory.

PubMed

Wang, Yuankun; Ma, Huiqun; Wang, Dong; Wang, Guizuo; Wu, Jichun; Bian, Jinyu; Liu, Jiufu

2018-01-01

How to determine representative wind speed is crucial in wind resource assessment. Accurate wind resource assessments are important to wind farms development. Linear regressions are usually used to obtain the representative wind speed. However, terrain flexibility of wind farm and long distance between wind speed sites often lead to low correlation. In this study, copula method is used to determine the representative year's wind speed in wind farm by interpreting the interaction of the local wind farm and the meteorological station. The result shows that the method proposed here can not only determine the relationship between the local anemometric tower and nearby meteorological station through Kendall's tau, but also determine the joint distribution without assuming the variables to be independent. Moreover, the representative wind data can be obtained by the conditional distribution much more reasonably. We hope this study could provide scientific reference for accurate wind resource assessments. Copyright © 2017 Elsevier Inc. All rights reserved.

A comparison between the dynamics of horizontal and vertical axis offshore floating wind turbines.

PubMed

Borg, M; Collu, M

2015-02-28

The need to further exploit offshore wind resources in deeper waters has led to a re-emerging interest in vertical axis wind turbines (VAWTs) for floating foundation applications. However, there has been little effort to systematically compare VAWTs to the more conventional horizontal axis wind turbine (HAWT). This article initiates this comparison based on prime principles, focusing on the turbine aerodynamic forces and their impact on the floating wind turbine static and dynamic responses. VAWTs generate substantially different aerodynamic forces on the support structure, in particular, a potentially lower inclining moment and a substantially higher torque than HAWTs. Considering the static stability requirements, the advantages of a lower inclining moment, a lower wind turbine mass and a lower centre of gravity are illustrated, all of which are exploitable to have a less costly support structure. Floating VAWTs experience increased motion in the frequency range surrounding the turbine [number of blades]×[rotational speed] frequency. For very large VAWTs with slower rotational speeds, this frequency range may significantly overlap with the range of wave excitation forces. Quantitative considerations are undertaken comparing the reference NREL 5 MW HAWT with the NOVA 5 MW VAWT. © 2015 The Author(s) Published by the Royal Society. All rights reserved.

On the nature of low-frequency currents over a shallow area of the southern coast of the Gulf of Finland

NASA Astrophysics Data System (ADS)

Lilover, M.-J.; Pavelson, J.; Kõuts, T.

2014-01-01

This study aims to explain those factors influencing low-frequency currents in a shallow unstratified sea with complex topography. Current velocity measurements using a bottom-mounted ADCP, deployed at 8 m depth on the slope of Naissaar Bank (northern entrance to the Tallinn Bay, Gulf of Finland), were performed over five weeks in late autumn 2008. A quasi-steady current from nine sub-periods (two weeks) was relatively well correlated with wind (mean correlation coefficient of 0.70). During moderate to fresh winds, the current is veered to the right relative to the wind direction, by angles in the range of 14-38°. The flow is directed to the left, relative to the wind direction in stronger wind conditions, indicating evidence of topographic forcing. The observed current was reasonably in accordance with the flow predicted by the classical Ekman model. The modelled current speeds (wind speeds < 11 m s- 1) appear to be overestimated by 3-6 cm s- 1, whilst the observed rotation angles were mostly less than those predicted by the model. Inclusion of barotropic forcing to the Ekman model improved its performance. The discrepancies between the model and observations are discussed in terms of topographic steering, baroclinic effect and surface wave induced forcing.

10. INTERIOR VIEW OF WIND TUNNEL (1991). WrightPatterson Air ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

10. INTERIOR VIEW OF WIND TUNNEL (1991). - Wright-Patterson Air Force Base, Area B, Buildings 25 & 24,10-foot & 20-foot Wind Tunnel Complex, Northeast side of block bounded by K, G, Third, & Fifth Streets, Dayton, Montgomery County, OH

9. INTERIOR VIEW OF WIND TUNNEL (1991). WrightPatterson Air ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

9. INTERIOR VIEW OF WIND TUNNEL (1991). - Wright-Patterson Air Force Base, Area B, Buildings 25 & 24,10-foot & 20-foot Wind Tunnel Complex, Northeast side of block bounded by K, G, Third, & Fifth Streets, Dayton, Montgomery County, OH

11. INTERIOR VIEW OF WIND TUNNEL (1991). WrightPatterson Air ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

11. INTERIOR VIEW OF WIND TUNNEL (1991). - Wright-Patterson Air Force Base, Area B, Buildings 25 & 24,10-foot & 20-foot Wind Tunnel Complex, Northeast side of block bounded by K, G, Third, & Fifth Streets, Dayton, Montgomery County, OH

Determining the response of sea level to atmospheric pressure forcing using TOPEX/POSEIDON data

NASA Technical Reports Server (NTRS)

Fu, Lee-Lueng; Pihos, Greg

1994-01-01

The static response of sea level to the forcing of atmospheric pressure, the so-called inverted barometer (IB) effect, is investigated using TOPEX/POSEIDON data. This response, characterized by the rise and fall of sea level to compensate for the change of atmospheric pressure at a rate of -1 cm/mbar, is not associated with any ocean currents and hence is normally treated as an error to be removed from sea level observation. Linear regression and spectral transfer function analyses are applied to sea level and pressure to examine the validity of the IB effect. In regions outside the tropics, the regression coefficient is found to be consistently close to the theoretical value except for the regions of western boundary currents, where the mesoscale variability interferes with the IB effect. The spectral transfer function shows near IB response at periods of 30 degrees is -0.84 +/- 0.29 cm/mbar (1 standard deviation). The deviation from = 1 cm /mbar is shown to be caused primarily by the effect of wind forcing on sea level, based on multivariate linear regression model involving both pressure and wind forcing. The regression coefficient for pressure resulting from the multivariate analysis is -0.96 +/- 0.32 cm/mbar. In the tropics the multivariate analysis fails because sea level in the tropics is primarily responding to remote wind forcing. However, after removing from the data the wind-forced sea level estimated by a dynamic model of the tropical Pacific, the pressure regression coefficient improves from -1.22 +/- 0.69 cm/mbar to -0.99 +/- 0.46 cm/mbar, clearly revealing an IB response. The result of the study suggests that with a proper removal of the effect of wind forcing the IB effect is valid in most of the open ocean at periods longer than 20 days and spatial scales larger than 500 km.

Exploring the Inner Acceleration Region of Solar Wind: A Study Based on Coronagraphic UV and Visible Light Data

NASA Astrophysics Data System (ADS)

Bemporad, A.

2017-09-01

This work combined coronagraphic visible light (VL) and UV data to provide with an unprecedented view of the inner corona where the nascent solar wind is accelerated. The UV (H I Lyα) and VL (polarized brightness) images (reconstructed with SOHO/UVCS, LASCO, and Mauna Loa data) have been analyzed with the Doppler dimming technique to provide for the first time daily 2D images of the radial wind speed between 1 and 6 R ⊙ over 1 month of observations. Results show that both polar and equatorial regions are characterized at the base of the corona by plasma outflows at speeds > 100 km s-1. The plasma is then decelerated within ˜1.5 R ⊙ at the poles and ˜2.0 R ⊙ at the equator, where local minima of the expansion speeds are reached, and gently reaccelerated higher up, reaching speeds typical of fast and slow wind components. The mass flux is highly variable with latitude and time at the equator and more uniform and stable over the poles. The polar flow is asymmetric, with speeds above the south pole lower than those above the north pole. A correlation (anticorrelation) between the wind speed and its density is found below (above) ˜1.8 R ⊙. The 2D distribution of forces responsible for deceleration and reacceleration of solar wind is provided and interpreted in terms of Alfvén waves. These results provide a possible connection between small-scale outflows reported with other instruments at the base of the corona and bulk wind flows measured higher up.

Quantifying the Bering Strait Oceanic Fluxes and their Impacts on Sea-Ice and Water Properties in the Chukchi and Beaufort Seas and Western Arctic Ocean for 2013-2014

DTIC Science & Technology

2016-07-27

has provided climatologies for past and on-going Arctic modeling studies [Woodgate et al., 2005b; Clement-Kinney et al., 2014; Nguyen et al., 2016... climatology of ~ 0.8 Sv. In contrast to previous results which suggested this was previously 1/3rd due to local wind forcing [Woodgate et al., 2012], we...the 1990s climatology of ~ 2500km3/yr. This is a ~ 40% increase in freshwater flux since 2001, and is mostly (90%) due to increased flow, although

Ocean Wave Energy Regimes of the Circumpolar Coastal Zones

NASA Astrophysics Data System (ADS)

Atkinson, D. E.

2004-12-01

Ocean wave activity is a major enviromental forcing agent of the ice-rich sediments that comprise large sections of the arctic coastal margins. While it is instructive to possess information about the wind regimes in these regions, direct application to geomorphological and engineering needs requires knowledge of the resultant wave-energy regimes. Wave energy information has been calculated at the regional scale using adjusted reanalysis model windfield data. Calculations at this scale are not designed to account for local-scale coastline/bathymetric irregularities and variability. Results will be presented for the circumpolar zones specified by the Arctic Coastal Dynamics Project.

Explosive cyclogenesis of extra-tropical cyclone Klaus and its effects in Catalonia. A case study of hurricane force gusts.

NASA Astrophysics Data System (ADS)

Calvo, J.; López, J. A.; Martín, F.; Morales, G.; Pascual, R.

2009-09-01

On 23th and 24th of January 2009, the extra-tropical cyclone Klaus crossed the north of Spain and the south of France producing several deaths and generalized damages. The cyclone of Atlantic origin underwent an explosive deepening of more than 1 hPa per hour at the surface level. Catalonia region was affected by gale-force winds and hurricane gusts. The Atlantic depression underwent a process called explosive cyclogenesis (when a surface cyclone deepens at a rate higher than 1 hPa/hr over 24 hours, approximately) in front of the Spanish Atlantic coasts. In this study we focus on its impact in the Catalonia areas where both synoptic and local effects were important. Also we evaluate the performance of the numerical weather prediction model outputs against observed data.

The Effect of Subauroral Polarization Streams on Ionosphere and Thermosphere During the 2015 St. Patrick's Day Storm: Global Ionosphere-Thermosphere Model Simulations

NASA Astrophysics Data System (ADS)

Guo, Jia-Peng; Deng, Yue; Zhang, Dong-He; Lu, Yang; Sheng, Cheng; Zhang, Shun-Rong

2018-03-01

Using the Millstone Hill incoherent scatter radar observations during 2015 St. Patrick's Day storm, subauroral polarization streams (SAPSs) have been specified in the nonhydrostatic Global Ionosphere-Thermosphere Model simulations. The results reveal that the effect of SAPS on the coupled thermosphere-ionosphere system includes the following: (1) Sudden frictional heating of SAPS results in acoustic-gravity waves in the thermosphere. The vertical oscillation is localized, while the meridional disturbance propagates poleward and equatorward. (2) The SAPS-associated horizontal wind field includes an enhanced westward wind within SAPS channel and a twin of vortex-like winds north (clockwise) and south (anticlockwise) of subauroral latitudes. (3) Due to the neutral-ion drag, ions in the vicinity of SAPS channel oscillate vertically with neutrals, resulting in a perturbation of 0.3 TECu in ionospheric total electron content. The SAPS-induced traveling atmospheric disturbances can elevate the plasma and increase the total electron content in midlatitude ionosphere. (4) It is confirmed that the Coriolis force can contribute to the poleward turning of the neutral wind during the post-SAPS interval. In addition, the traveling atmospheric disturbance induced by the variation of auroral input and high-latitude convection is possibly the primary cause of the poleward neutral wind surge during the magnetic storm on 17-18 March 2015. The combination of the two factors can make the northward meridional wind surge reach a magnitude of 100 m/s. This study improves our understanding of the SAPS's effect on neutral dynamics and ion-neutral coupling processes during geomagnetically disturbed intervals.

Wind-driven Ocean Circulation and the Spatial-temporal Variability of Dissolved Inorganic Carbon in the Gulf of Tehuantepec, North Eastern Tropical Pacific

NASA Astrophysics Data System (ADS)

Chapa, C.; Beier, E.; Durazo, R.; Martin Hernandez-Ayon, J. M.; Alin, S. R.; Lopez-Perez, A.

2016-12-01

The relationship between the surface enrichment of dissolved inorganic carbon (DIC) and wind variability and circulation in the Gulf of Tehuantepec (GT) was examined from satellite images and in situ data from three cruises (June 2010; April and November 2013). Monthly mean wind climatologies (and derived variables), sea surface temperature and sea surface height anomaly fields were analyzed in the GT and part of the NETP. Signal decomposition according to circulation scales (seasonal, inter-annual, mesoscale) was performed using harmonic analysis for the seasonal components, and empirical orthogonal functions for the residuals, applied to satellite sea-level anomaly data. The results show that wind is the main driving force of the variability in the GT. Mesoscale is the variable with the highest percent of local variance (25-75%), due mainly to mesoscale eddies, followed by seasonality (20-55%), and finally the inter-annual signal (10-30%), dominated by ENSO. Mesoscale and seasonality prevailed during the samplings. The changes in circulation led to variations in the concentration of surface DIC ranging between 100 and 300 µmol kg-1 (436 µatm) due to Ekman pumping. The largest enrichment occurred in November 2013 after a strong northerly wind event. However, the predominance of mesoscale events suggests that changes in dissolved inorganic carbon resulting from mesoscale- derived Ekman pumping may become important in the long term and with a larger spatial and temporal coverage. The results suggest that the seasonal cycle of dissolved inorganic carbon may be linked to wind seasonality.

WES feedback and the Atlantic Meridional Mode: observations and CMIP5 comparisons

NASA Astrophysics Data System (ADS)

Amaya, Dillon J.; DeFlorio, Michael J.; Miller, Arthur J.; Xie, Shang-Ping

2017-09-01

The Atlantic Meridional Mode (AMM) is the dominant mode of tropical SST/wind coupled variability. Modeling studies have implicated wind-evaporation-SST (WES) feedback as the primary driver of the AMM's evolution across the Atlantic basin; however, a robust coupling of the SST and winds has not been shown in observations. This study examines observed AMM growth, propagation, and decay as a result of WES interactions. Investigation of an extended maximum covariance analysis shows that boreal wintertime atmospheric forcing generates positive SST anomalies (SSTA) through a reduction of surface evaporative cooling. When the AMM peaks in magnitude during spring and summer, upward latent heat flux anomalies occur over the warmest SSTs and act to dampen the initial forcing. In contrast, on the southwestern edge of the SSTA, SST-forced cross-equatorial flow reduces the strength of the climatological trade winds and provides an anomalous latent heat flux into the ocean, which causes southwestward propagation of the initial atmosphere-forced SSTA through WES dynamics. Additionally, the lead-lag relationship of the ocean and atmosphere indicates a transition from an atmosphere-forcing-ocean regime in the northern subtropics to a highly coupled regime in the northern tropics that is not observed in the southern hemisphere. CMIP5 models poorly simulate the latitudinal transition from a one-way interaction to a two-way feedback, which may explain why they also struggle to reproduce spatially coherent interactions between tropical Atlantic SST and winds. This analysis provides valuable insight on how meridional modes act as links between extratropical and tropical variability and focuses future research aimed at improving climate model simulations.

The Effect of the South Asia Monsoon on the Wind Sea and Swell Patterns in the Arabian Sea

NASA Astrophysics Data System (ADS)

Semedo, Alvaro

2015-04-01

Ocean surface gravity waves have a considerable impact on coastal and offshore infrastructures, and are determinant on ship design and routing. But waves also play an important role on the coastal dynamics and beach erosion, and modulate the exchanges of momentum, and mass and other scalars between the atmosphere and the ocean. A constant quantitative and qualitative knowledge of the wave patterns is therefore needed. There are two types of waves at the ocean surface: wind-sea and swell. Wind-sea waves are growing waves under the direct influence of local winds; as these waves propagate away from their generation area, or when their phase speed overcomes the local wind speed, they are called swell. Swell waves can propagate thousands of kilometers across entire ocean basins. The qualitative analysis of ocean surface waves has been the focus of several recent studies, from the wave climate to the air-sea interaction community. The reason for this interest lies mostly in the fact that waves have an impact on the lower atmosphere, and that the air-sea coupling is different depending on the wave regime. Waves modulate the exchange of momentum, heat, and mass across the air-sea interface, and this modulation is different and dependent on the prevalence of one type of waves: wind sea or swell. For fully developed seas the coupling between the ocean-surface and the overlaying atmosphere can be seen as quasi-perfect, in a sense that the momentum transfer and energy dissipation at the ocean surface are in equilibrium. This can only occur in special areas of the Ocean, either in marginal seas, with limited fetch, or in Open Ocean, in areas with strong and persistent wind speed with little or no variation in direction. One of these areas is the Arabian Sea, along the coasts of Somalia, Yemen and Oman. The wind climate in the Arabian sea is under the direct influence of the South Asia monsoon, where the wind blows steady from the northeast during the boreal winter, and reverses direction to blow also steady but stronger from the southwest during the boreal summer months. During the summer monsoon the wind pattern in the north Arabian Sea is rather intricate, with a large scale synoptic forcing with a high pressure cell over the ocean and a thermal low pressure system in-land, but also with at least two low-level wind jets, the Finlater (or Somali) jet, and the Oman coastal jet. This wind pattern leads to a particular wave pattern and seasonal variability. The monsoon wind pattern has a direct influence in the wave climate in that area, The particular wind-sea and swell climates of the Arabian Sea are presented. The study is based on the ERA-Interim wave reanalysis from the European Centre for Medium-Range Weather Forecasts.

SOFIA 2 model telescope wind tunnel test report

NASA Technical Reports Server (NTRS)

Keas, Paul

1995-01-01

This document outlines the tests performed to make aerodynamic force and torque measurements on the SOFIA wind tunnel model telescope. These tests were performed during the SOFIA 2 wind tunnel test in the 14 ft wind tunnel during the months of June through August 1994. The test was designed to measure the dynamic cross elevation moment acting on the SOFIA model telescope due to aerodynamic loading. The measurements were taken with the telescope mounted in an open cavity in the tail section of the SOFIA model 747. The purpose of the test was to obtain an estimate of the full scale aerodynamic disturbance spectrum, by scaling up the wind tunnel results (taking into account differences in sail area, air density, cavity dimension, etc.). An estimate of the full scale cross elevation moment spectrum was needed to help determine the impact this disturbance would have on the telescope positioning system requirements. A model of the telescope structure, made of a light weight composite material, was mounted in the open cavity of the SOFIA wind tunnel model. This model was mounted via a force balance to the cavity bulkhead. Despite efforts to use a 'stiff' balance, and a lightweight model, the balance/telescope system had a very low resonant frequency (37 Hz) compared to the desired measurement bandwidth (1000 Hz). Due to this mechanical resonance of the balance/telescope system, the balance alone could not provide an accurate measure of applied aerodynamic force at the high frequencies desired. A method of measurement was developed that incorporated accelerometers in addition to the balance signal, to calculate the aerodynamic force.

Computing factors of safety against wind-induced tree stem damage.

PubMed

Niklas, K J

2000-04-01

The drag forces, bending moments and stresses acting on stems differing in size and location within the mechanical infrastructure of a large wild cherry (Prunus serotina Ehrh.) tree are estimated and used to calculate the factor of safety against wind-induced mechanical failure based on the mean breaking stress of intact stems and samples of wood drawn from this tree. The drag forces acting on stems are calculated based on stem projected areas and field measurements of wind speed taken within the canopy and along the length of the trunk. The bending moments and stresses resulting from these forces are shown to increase basipetally in a nearly log-log linear fashion toward the base of the tree. The factor of safety, however, varies in a sinusoidal manner such that the most distal stems have the highest factors of safety, whereas stems of intermediate location and portions of the trunk near ground level have equivalent and much lower factors of safety. This pattern of variation is interpreted to indicate that, as a course of normal growth and development, trees similar to the one examined in this study maintain a cadre of stems prone to wind-induced mechanical damage that can reduce the probability of catastrophic tree failure by reducing the drag forces acting on older portions of the tree. Comparisons among real and hypothetical stems with different taper experiencing different vertical wind speed profiles show that geometrically self-similar stems have larger factors of safety than stems tapering according to elastic or stress self-similarity, and that safety factors are less significantly influenced by the 'geometry' of the wind-profile.

Atmospheric stability and complex terrain: comparing measurements and CFD

NASA Astrophysics Data System (ADS)

Koblitz, T.; Bechmann, A.; Berg, J.; Sogachev, A.; Sørensen, N.; Réthoré, P.-E.

2014-12-01

For wind resource assessment, the wind industry is increasingly relying on Computational Fluid Dynamics models that focus on modeling the airflow in a neutrally stratified surface layer. So far, physical processes that are specific to the atmospheric boundary layer, for example the Coriolis force, buoyancy forces and heat transport, are mostly ignored in state-of-the-art flow solvers. In order to decrease the uncertainty of wind resource assessment, the effect of thermal stratification on the atmospheric boundary layer should be included in such models. The present work focuses on non-neutral atmospheric flow over complex terrain including physical processes like stability and Coriolis force. We examine the influence of these effects on the whole atmospheric boundary layer using the DTU Wind Energy flow solver EllipSys3D. To validate the flow solver, measurements from Benakanahalli hill, a field experiment that took place in India in early 2010, are used. The experiment was specifically designed to address the combined effects of stability and Coriolis force over complex terrain, and provides a dataset to validate flow solvers. Including those effects into EllipSys3D significantly improves the predicted flow field when compared against the measurements.

Enhancement of Feedback Efficiency by Active Galactic Nucleus Outflows via the Magnetic Tension Force in the Inhomogeneous Interstellar Medium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Asahina, Yuta; Ohsuga, Ken; Nomura, Mariko, E-mail: asahina@cfca.jp

By performing three-dimensional magnetohydrodynamics simulations of subrelativistic jets and disk winds propagating into the magnetized inhomogeneous interstellar medium (ISM), we investigate the magnetic effects on the active galactic nucleus feedback. Our simulations reveal that the magnetic tension force promotes the acceleration of the dense gas clouds, since the magnetic field lines, which are initially straight, bend around the gas clouds. In the jet models, the velocity dispersion of the clouds increases with an increase in the initial magnetic fields. The increment of the kinetic energy of the clouds is proportional to the initial magnetic fields, implying that the magnetic tensionmore » force increases the energy conversion efficiency from the jet to the gas clouds. Through simulations of the mildly collimated disk wind and the funnel-shaped disk wind, we confirm that such an enhancement of the energy conversion efficiency via the magnetic fields appears even if the energy is injected via the disk winds. The enhancement of the acceleration of the dense part of the magnetized ISM via the magnetic tension force will occur wherever the magnetized inhomogeneous matter is blown away.« less

Wind Stress Forcing of the North Sea "Pole Tide"

NASA Technical Reports Server (NTRS)

OConnor, William P.; Chao, Benjamin Fong; Zheng, Dawei; Au, Andrew Y.

1998-01-01

We conducted numerical simulations of the wind-forcing of the sea level variations in the North Sea using a barotropic ocean model with realistic geography, bathymetry, and boundary conditions, to examine the forcing of the 14-month "pole tide" which is known to be strong along the Denmark- Netherlands coast. The simulation input is the monthly-mean surface wind stress field from the National Centers for Environmental Prediction (NCEP) reanalysis for the 40-year period 1958-1997. The output sea level response was then compared with 10 coastal tide gauge records from the Permanent Service for Mean Sea Level (PSMSL). Besides the strong seasonal variations, several prominent quasi-periodicities exist at around 7 years, 3 years, 14 months, 9 months, and 6.5 months. Correlation and spectral analyses show remarkable agreement between the model output and the observations, particularly in the 14-month, or Chandler period band. The latter indicates that the enhanced pole tide found in the North Sea along the Denmark-Netherlands coast is actually the coastal setup response to wind stress forcing with a periodicity of 14 months. We find no need to invoke a geophysical explanation involving resonance-enhancement of pole tide in the North Sea to explain the observations.

Complex Dynamics of Equatorial Scintillation

NASA Astrophysics Data System (ADS)

Piersanti, Mirko; Materassi, Massimo; Forte, Biagio; Cicone, Antonio

2017-04-01

Radio power scintillation, namely highly irregular fluctuations of the power of trans-ionospheric GNSS signals, is the effect of ionospheric plasma turbulence. The scintillation patterns on radio signals crossing the medium inherit the ionospheric turbulence characteristics of inter-scale coupling, local randomness and large time variability. On this basis, the remote sensing of local features of the turbulent plasma is feasible by studying radio scintillation induced by the ionosphere. The distinctive character of intermittent turbulent media depends on the fluctuations on the space- and time-scale statistical properties of the medium. Hence, assessing how the signal fluctuation properties vary under different Helio-Geophysical conditions will help to understand the corresponding dynamics of the turbulent medium crossed by the signal. Data analysis tools, provided by complex system science, appear to be best fitting to study the response of a turbulent medium, as the Earth's equatorial ionosphere, to the non-linear forcing exerted by the Solar Wind (SW). In particular we used the Adaptive Local Iterative Filtering, the Wavelet analysis and the Information theory data analysis tool. We have analysed the radio scintillation and ionospheric fluctuation data at low latitude focusing on the time and space multi-scale variability and on the causal relationship between forcing factors from the SW environment and the ionospheric response.

Dynamic Loading Assembly for Testing Actuators of Segmented Mirror Telescope

NASA Astrophysics Data System (ADS)

Deshmukh, Prasanna Gajanan; Parihar, Padmakar; Balasubramaniam, Karthik A.; Mishra, Deepta Sundar; Mahesh, P. K.

Upcoming large telescopes are based on Segmented Mirror Telescope (SMT) technology which uses small hexagonal mirror segments placed side by side to form the large monolithic surface. The segments alignment needs to be maintained against external disturbances like wind, gravity, temperature and structural vibration. This is achieved by using three position actuators per segment working at few-nanometer scale range along with a local closed loop controller. The actuator along with a controller is required to meet very stringent performance requirements, such as track rates up to 300nm/s (90mN/s) with tracking errors less than 5nm, dynamical forces of up to ±40N, ability to reject disturbances introduced by the wind as well as by mechanical vibration generated in the mirror cell, etc. To conduct these performance tests in more realistic manner, we have designed and developed a Dynamic Loading Assembly (DLA) at Indian Institute of Astrophysics (IIA), Bangalore. DLA is a computer controlled force-inducing device, designed in a modular fashion to generate different types of user-defined disturbances in extremely precise and controlled manner. Before realizing the device, using a simple spring-mass-damper-based mathematical model, we ensured that the concept would indeed work. Subsequently, simple concept was converted into a detailed mechanical design and parts were manufactured and assembled. DLA has static and dynamic loading capabilities up to 250N and 18N respectively, with a bandwidth sufficient to generate wind disturbances. In this paper, we present various performance requirements of SMT actuators as well as our effort to develop a dynamic loading device which can be used to test these actuators. Well before using DLA for meaningful testing of the actuator, the DLA itself have gone through various tests and improvements phases. We have successfully demonstrated that DLA can be used to check the extreme performance of two different SMT actuators, which are expected to track the position/force with a few nanometer accuracy.

Numerical simulation and prediction of coastal ocean circulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, P.

1992-01-01

Numerical simulation and prediction of coastal ocean circulation have been conducted in three cases. 1. A process-oriented modeling study is conducted to study the interaction of a western boundary current (WBC) with coastal water, and its responses to upstream topographic irregularities. It is hypothesized that the interaction of propagating WBC frontal waves and topographic Rossby waves are responsible for upstream variability. 2. A simulation of meanders and eddies in the Norwegian Coastal Current (NCC) for February and March of 1988 is conducted with a newly developed nested dynamic interactive model. The model employs a coarse-grid, large domain to account formore » non-local forcing and a fine-grid nested domain to resolve meanders and eddies. The model is forced by wind stresses, heat fluxes and atmospheric pressure corresponding Feb/March of 1988, and accounts for river/fjord discharges, open ocean inflow and outflow, and M[sub 2] tides. The simulation reproduced fairly well the observed circulation, tides, and salinity features in the North Sea, Norwegian Trench and NCC region in the large domain and fairly realistic meanders and eddies in the NCC in the nested region. 3. A methodology for practical coastal ocean hindcast/forecast is developed, taking advantage of the disparate time scales of various forcing and considering wind to be the dominant factor in affecting density fluctuation in the time scale of 1 to 10 days. The density field obtained from a prognostic simulation is analyzed by the empirical orthogonal function method (EOF), and correlated with the wind; these information are then used to drive a circulation model which excludes the density calculation. The method is applied to hindcast the circulation in the New York Bight for spring and summer season of 1988. The hindcast fields compare favorably with the results obtained from the prognostic circulation model.« less

Effects of orography on planetary scale flow

NASA Technical Reports Server (NTRS)

Smith, R. B.

1986-01-01

The earth's orography is composed of a wide variety of scales, each contributing to the spectrum of atmospheric motions. A well studied subject (originating with Charney and Eliassen) is the direct forcing of planetary scale waves by the planetary scale orography: primarily the Tibetan plateau and the Rockies. However, because of the non-linear terms in the equations of dynamic meteorology, even the smallest scales of mountain induced flow can contribute to the planetary scale if the amplitude of the small scale disturbance is sufficintly large. Two possible mechanisms for this are illustrated. First, preferentially located lee cyclones can force planetary waves by their meridional transport of heat and momentum (Hansen and Chen). Recent theories are helping to explain the phenomena of lee cyclogenesis (e.g., Smith, 1984, J.A.S.). Second, mesoscale mountain wave and severe downslope wind phenomena produce such a large local drag, that planetary scale waves can be produced. The mechanism of upscale transfer is easy to understand in this case as the standing planetary scale wave has a wavelength which depends on the mean structure of the atmosphere, and not on the width of the mountain (just as in small scale lee wave theory). An example of a theoretical description of a severe wind flow with very large drag is shown.

Variability of High-Resolution Sea Surface Heights on a Broad, Shallow Continental Shelf

NASA Astrophysics Data System (ADS)

Crout, R. L.; Rice, A. E.

2017-12-01

Recent satellite altimeter technologies and processing methodologies are allowing investigation of the dynamics of the continental shelf as never before. The region seaward of 20 km from the coast is a region where winds, tides, currents, river discharge, and bathymetry interact. All of these are important parameters to understand when applying coastal altimetry to coastal sea level monitoring. Processing of 8 years (July 2008 to July 2016) of Jason-2 altimeter 20 Hz data from the L2 AVISO-PISTACH experimental products yields nearly 300 crossings of the broad continental shelf to the southeast of Delaware Bay from Cape May, NJ. Removal of a mean surface yields individual crossings that, plotted together, form an envelope that shows high water level variability near the coast. Water level changes near the coast begin at a hinge point that occurs approximately 50 km from shore in less than 30 meters of water. Comparison of individual Jason-2 passes with regional weather patterns, cold front passages, local winds, tides, surface currents, river discharge, and regional oceanography provides information regarding the forcing factors for these regional water levels. The water levels farther than 20 km from shore show similar patterns to the low pass filtered tide data at Cape May, NJ and respond primarily to regional forcing.

Mean winds and momemtum fluxes over Jicamarca, Peru, during June and August 1987

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hitchman, M.H.; Bywaters, K.W.; Fritts, D.C.

1992-12-15

Data from the mesophere-stratosphere-troposphere (MST) radar at Jicamarca, Peru, together with other available data, are used to diagnose the mean structure of winds and gravity-wave momentum fluxes from the surface to 90 km during two ten-day campaigns in June and August of 1987. In the stratosphere a layer of maximum eastward flow associated with the quasi-biennial oscillation (QBO) was seen to strengthen and descend rapidly from June to August, overlying persitent westward flow. A layer of enhanced signal return, suggestive of a turbulent layer, was observed just above the descending QBO eastward maximum. Notable zonal asymmetries were present during thismore » transition and the local meridional circulation departed form zonal-mean QBO theory. A substantial northeastward momentum flux was found below 25 km, which may be related to topographic gravity waves excited by southeastward flow across the Andes. In the lower mesosphere a relatively weak second mesopause semiannual oxcillation is confirmed. Gravity-wave zonal and meridional momentum fluxes usually opposed the flow, yielding body forces of [approximately]10-100 ms[sup [minus]1] day [sup [minus]1]. In both the lower stratosphere and mesosphere, body forces were comparable in magnitude to inferred Coriolis torques. 52 refs., 9 figs.« less

14. EXTERIOR VIEW OF OLD TENFOOT WIND TUNNEL (1991). ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

14. EXTERIOR VIEW OF OLD TEN-FOOT WIND TUNNEL (1991). - Wright-Patterson Air Force Base, Area B, Buildings 25 & 24,10-foot & 20-foot Wind Tunnel Complex, Northeast side of block bounded by K, G, Third, & Fifth Streets, Dayton, Montgomery County, OH

13. EXTERIOR VIEW OF OLD TENFOOT WIND TUNNEL (1991). ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

13. EXTERIOR VIEW OF OLD TEN-FOOT WIND TUNNEL (1991). - Wright-Patterson Air Force Base, Area B, Buildings 25 & 24,10-foot & 20-foot Wind Tunnel Complex, Northeast side of block bounded by K, G, Third, & Fifth Streets, Dayton, Montgomery County, OH

3. VIEW OF WIND TUNNEL, LOOKING NORTHWEST (1991). WrightPatterson ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

3. VIEW OF WIND TUNNEL, LOOKING NORTHWEST (1991). - Wright-Patterson Air Force Base, Area B, Buildings 25 & 24,10-foot & 20-foot Wind Tunnel Complex, Northeast side of block bounded by K, G, Third, & Fifth Streets, Dayton, Montgomery County, OH

The response of the East Asia summer precipitation to greenhouse gases and anthropogenic aerosols

NASA Astrophysics Data System (ADS)

Tian, Fangxing; Dong, Buwen; Robson, Jon; Sutton, Rowan

2017-04-01

The changes of precipitation over China since the mid-20th century display a dipole trend pattern over eastern China, which is known as Southern-Flood-Northern-Drought (SFND) pattern. The trends have been attributed to different factors, such as the changes of aerosol and greenhouse gas emissions. However much less is known about the different effects of these factors on generating the SFND pattern. This work investigated the drivers and dynamical mechanisms by using a atmosphere-ocean-mixed-layer model forced by anthropogenic greenhouse gase (GHG), anthropogenic aerosol (AA) and the combined effects. The model experiments with different forcings indicates that the GHG forcing dominates the precipitation increase, which is stronger over south China than over north China. On the other hand, the drought over north China is dominated by the AA forcing. Analysis of physical processes indicates that the GHG forcing increases the moisture and leads to strong convergence over east China, and then more precipitation. The AA forcing leads to north wind anomalies and generates divergent anomalies over north China, which reduces the precipitation. Further analysis indicates that the changes of the circulation which related to the SFND pattern are forced by the enhancement of the Western North Pacific Subtropical High (WNPSH). Both GHG and AA forcing can enhance the WNPSH by changing the local Hadley cell.

Measurements of wind-waves under transient wind conditions.

NASA Astrophysics Data System (ADS)

Shemer, Lev; Zavadsky, Andrey

2015-11-01

Wind forcing in nature is always unsteady, resulting in a complicated evolution pattern that involves numerous time and space scales. In the present work, wind waves in a laboratory wind-wave flume are studied under unsteady forcing`. The variation of the surface elevation is measured by capacitance wave gauges, while the components of the instantaneous surface slope in across-wind and along-wind directions are determined by a regular or scanning laser slope gauge. The locations of the wave gauge and of the laser slope gauge are separated by few centimeters in across-wind direction. Instantaneous wind velocity was recorded simultaneously using Pitot tube. Measurements are performed at a number of fetches and for different patterns of wind velocity variation. For each case, at least 100 independent realizations were recorded for a given wind velocity variation pattern. The accumulated data sets allow calculating ensemble-averaged values of the measured parameters. Significant differences between the evolution patterns of the surface elevation and of the slope components were found. Wavelet analysis was applied to determine dominant wave frequency of the surface elevation and of the slope variation at each instant. Corresponding ensemble-averaged values acquired by different sensors were computed and compared. Analysis of the measured ensemble-averaged quantities at different fetches makes it possible to identify different stages in the wind-wave evolution and to estimate the appropriate time and length scales.

Damage detection of rotating wind turbine blades using local flexibility method and long-gauge fiber Bragg grating sensors

NASA Astrophysics Data System (ADS)

Hsu, Ting-Yu; Shiao, Shen-Yuan; Liao, Wen-I.

2018-01-01

Wind turbines are a cost-effective alternative energy source; however, their blades are susceptible to damage. Therefore, damage detection of wind turbine blades is of great importance for condition monitoring of wind turbines. Many vibration-based structural damage detection techniques have been proposed in the last two decades. The local flexibility method, which can determine local stiffness variations of beam-like structures by using measured modal parameters, is one of the most promising vibration-based approaches. The local flexibility method does not require a finite element model of the structure. A few structural modal parameters identified from the ambient vibration signals both before and after damage are required for this method. In this study, we propose a damage detection approach for rotating wind turbine blades using the local flexibility method based on the dynamic macro-strain signals measured by long-gauge fiber Bragg grating (FBG)-based sensors. A small wind turbine structure was constructed and excited using a shaking table to generate vibration signals. The structure was designed to have natural frequencies as close as possible to those of a typical 1.5 MW wind turbine in real scale. The optical fiber signal of the rotating blades was transmitted to the data acquisition system through a rotary joint fixed inside the hollow shaft of the wind turbine. Reversible damage was simulated by aluminum plates attached to some sections of the wind turbine blades. The damaged locations of the rotating blades were successfully detected using the proposed approach, with the extent of damage somewhat over-estimated. Nevertheless, although the specimen of wind turbine blades cannot represent a real one, the results still manifest that FBG-based macro-strain measurement has potential to be employed to obtain the modal parameters of the rotating wind turbines and then locations of wind turbine segments with a change of rigidity can be estimated effectively by utilizing these identified parameters.

Wind loading on solar concentrators: some general considerations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Roschke, E. J.

A survey has been completed to examine the problems and complications arising from wind loading on solar concentrators. Wind loading is site specific and has an important bearing on the design, cost, performance, operation and maintenance, safety, survival, and replacement of solar collecting systems. Emphasis herein is on paraboloidal, two-axis tracking systems. Thermal receiver problems also are discussed. Wind characteristics are discussed from a general point of view; current methods for determining design wind speed are reviewed. Aerodynamic coefficients are defined and illustrative examples are presented. Wind tunnel testing is discussed, and environmental wind tunnels are reviewed; recent results onmore » heliostat arrays are reviewed as well. Aeroelasticity in relation to structural design is discussed briefly. Wind loads, i.e., forces and moments, are proportional to the square of the mean wind velocity. Forces are proportional to the square of concentrator diameter, and moments are proportional to the cube of diameter. Thus, wind loads have an important bearing on size selection from both cost and performance standpoints. It is concluded that sufficient information exists so that reasonably accurate predictions of wind loading are possible for a given paraboloidal concentrator configuration, provided that reliable and relevant wind conditions are specified. Such predictions will be useful to the design engineer and to the systems engineer as well. Information is lacking, however, on wind effects in field arrays of paraboloidal concentrators. Wind tunnel tests have been performed on model heliostat arrays, but there are important aerodynamic differences between heliostats and paraboloidal dishes.« less

Wind-fuel cell hybrid project in rural Alaska

DOE Office of Scientific and Technical Information (OSTI.GOV)

David Lockard

2000-02-18

This is a summary of the work performed on the Wind-Fuel Cell Hybrid Project: (1) On October 5th, Tim Howell of the Golden Field Office and Tom Anderson of Battelle Labs arrived in Anchorage. They met with David Lockard, Project Manager, and Percy Frisby, Director of the Alaska Rural Energy Programs Group. (2) On October 6th, Tim, Tom and David flew to Nome to inspect the proposed wind turbine site and meet with John Handeland, Director of the Nome Joint Utility System. They visited the proposed site as well as several private, residential-sized wind turbines operating in the Nome area.more » (3)Tim and Tom flew to Unalaska on October 7th to meet with Mike Golat, City of Unalaska Public Utility Director, and to inspect the proposed wind turbine sites at Pyramid Creek and Pyramid Valley. (4)Tim sent a scoping letter on December 17th to a variety of local, state and federal agencies requesting comments on the proposed wind turbine project. (5) David discussed this project with Marc Schwartz and Gerry Nix at NREL. Marc provided David with a list of wind prospectors and meteorologists. (6) Tom raised the question of FAA permits for structures over 200 feet tall. Gerry provided information on NREL's experience with FAA permitting on other projects. David summarized the potential turbine choices and heights in a spreadsheet and initiated contact with the Alaska region FAA office regarding the permitting process. (7) David responded to a list of design questions from Tom regarding the project foundations, power output, and size for use in developing the environmental assessment. (8) David tried to get wind data for the Nome Anvil Mountain White Alice site from the Corps of Engineers and the Air Force, but was not able to find any. (9) David solicited quotes from vendors of wind monitoring equipment and provided cost information to Doug Hooker, federal grant manager in preparation for ordering the equipment.« less

Clothing resultant thermal insulation determined on a movable thermal manikin. Part II: effects of wind and body movement on local insulation

NASA Astrophysics Data System (ADS)

Lu, Yehu; Wang, Faming; Wan, Xianfu; Song, Guowen; Zhang, Chengjiao; Shi, Wen

2015-10-01

Part II of this two-part series study was focused on examining the effects of wind and body movement on local clothing thermal insulation. Seventeen clothing ensembles with different layers (i.e., 1, 2, or 3 layers) were selected for this study. Local thermal insulation with different air velocities (0.15, 1.55, and 4.0 m/s) and walking speeds (0, 0.75, and 1.17 m/s) were investigated on a thermal manikin. Empirical equations for estimating local resultant clothing insulation as a function of local insulation, air velocity, and walking speed were developed. The results showed that the effects of wind and body movement on local resultant thermal resistance are complex and differ distinctively among different body parts. In general, the reductions of local insulation with wind at the chest, abdomen, and pelvis were greater than those at the lower leg and back, and the changes at the body extremity such as the forearm, thigh, and lower leg were higher than such immobile body parts as the chest and back. In addition, the wind effect interacted with the walking effect. This study may have important applications in human local thermal comfort modeling and functional clothing design.

Clothing resultant thermal insulation determined on a movable thermal manikin. Part II: effects of wind and body movement on local insulation.

PubMed

Lu, Yehu; Wang, Faming; Wan, Xianfu; Song, Guowen; Zhang, Chengjiao; Shi, Wen

2015-10-01

Part II of this two-part series study was focused on examining the effects of wind and body movement on local clothing thermal insulation. Seventeen clothing ensembles with different layers (i.e., 1, 2, or 3 layers) were selected for this study. Local thermal insulation with different air velocities (0.15, 1.55, and 4.0 m/s) and walking speeds (0, 0.75, and 1.17 m/s) were investigated on a thermal manikin. Empirical equations for estimating local resultant clothing insulation as a function of local insulation, air velocity, and walking speed were developed. The results showed that the effects of wind and body movement on local resultant thermal resistance are complex and differ distinctively among different body parts. In general, the reductions of local insulation with wind at the chest, abdomen, and pelvis were greater than those at the lower leg and back, and the changes at the body extremity such as the forearm, thigh, and lower leg were higher than such immobile body parts as the chest and back. In addition, the wind effect interacted with the walking effect. This study may have important applications in human local thermal comfort modeling and functional clothing design.

Importance of air-sea interaction on wind waves, storm surge and hurricane simulations

NASA Astrophysics Data System (ADS)

Chen, Yingjian; Yu, Xiping

2017-04-01

It was reported from field observations that wind stress coefficient levels off and even decreases when the wind speed exceeds 30-40 m/s. We propose a wave boundary layer model (WBLM) based on the momentum and energy conservation equations. Taking into account the physical details of the air-sea interaction process as well as the energy dissipation due to the presence of sea spray, this model successfully predicts the decreasing tendency of wind stress coefficient. Then WBLM is embedded in the current-wave coupled model FVCOM-SWAVE to simulate surface waves and storm surge under the forcing of hurricane Katrina. Numerical results based on WBLM agree well with the observed data of NDBC buoys and tide gauges. Sensitivity analysis of different wind stress evaluation methods also shows that large anomalies of significant wave height and surge elevation are captured along the passage of hurricane core. The differences of the local wave height are up to 13 m, which is in accordance with the general knowledge that the ocean dynamic processes under storm conditions are very sensitive to the amount of momentum exchange at the air-sea interface. In the final part of the research, the reduced wind stress coefficient is tested in the numerical forecast of hurricane Katrina. A parabolic formula fitted to WBLM is employed in the atmosphere-ocean coupled model COAWST. Considering the joint effects of ocean cooling and reduced wind drag, the intensity metrics - the minimum sea level pressure and the maximum 10 m wind speed - are in good inconsistency with the best track result. Those methods, which predict the wind stress coefficient that increase or saturate in extreme wind condition, underestimate the hurricane intensity. As a whole, we unify the evaluation methods of wind stress in different numerical models and yield reasonable results. Although it is too early to conclude that WBLM is totally applicable or the drag coefficient does decrease for high wind speed, our current research is considered to be a significant step for the application of air-sea interaction on the ocean and atmosphere modelling.

ON INTERMITTENT TURBULENCE HEATING OF THE SOLAR WIND: DIFFERENCES BETWEEN TANGENTIAL AND ROTATIONAL DISCONTINUITIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang Xin; Tu Chuanyi; He Jiansen

The intermittent structures in solar wind turbulence, studied by using measurements from the WIND spacecraft, are identified as being mostly rotational discontinuities (RDs) and rarely tangential discontinuities (TDs) based on the technique described by Smith. Only TD-associated current sheets (TCSs) are found to be accompanied with strong local heating of the solar wind plasma. Statistical results show that the TCSs have a distinct tendency to be associated with local enhancements of the proton temperature, density, and plasma beta, and a local decrease of magnetic field magnitude. Conversely, for RDs, our statistical results do not reveal convincing heating effects. These resultsmore » confirm the notion that dissipation of solar wind turbulence can take place in intermittent or locally isolated small-scale regions which correspond to TCSs. The possibility of heating associated with RDs is discussed.« less

Relating large-scale climate variability to local species abundance: ENSO forcing and shrimp in Breton Sound, Louisiana, USA

USGS Publications Warehouse

Piazza, Bryan P.; LaPeyre, Megan K.; Keim, B.D.

2010-01-01

Climate creates environmental constraints (filters) that affect the abundance and distribution of species. In estuaries, these constraints often result from variability in water flow properties and environmental conditions (i.e. water flow, salinity, water temperature) and can have significant effects on the abundance and distribution of commercially important nekton species. We investigated links between large-scale climate variability and juvenile brown shrimp Farfantepenaeus aztecus abundance in Breton Sound estuary, Louisiana (USA). Our goals were to (1) determine if a teleconnection exists between local juvenile brown shrimp abundance and the El Niño Southern Oscillation (ENSO) and (2) relate that linkage to environmental constraints that may affect juvenile brown shrimp recruitment to, and survival in, the estuary. Our results identified a teleconnection between winter ENSO conditions and juvenile brown shrimp abundance in Breton Sound estuary the following spring. The physical connection results from the impact of ENSO on winter weather conditions in Breton Sound (air pressure, temperature, and precipitation). Juvenile brown shrimp abundance effects lagged ENSO by 3 mo: lower than average abundances of juvenile brown shrimp were caught in springs following winter El Niño events, and higher than average abundances of brown shrimp were caught in springs following La Niña winters. Salinity was the dominant ENSO-forced environmental filter for juvenile brown shrimp. Spring salinity was cumulatively forced by winter river discharge, winter wind forcing, and spring precipitation. Thus, predicting brown shrimp abundance requires incorporating climate variability into models.

Space Launch System Liftoff and Transition Aerodynamic Characterization in the NASA Langley 14- by 22-Foot Subsonic Wind Tunnel

NASA Technical Reports Server (NTRS)

Pinier, Jeremy T.; Erickson, Gary E.; Paulson, John W.; Tomek, William G.; Bennett, David W.; Blevins, John A.

2015-01-01

A 1.75% scale force and moment model of the Space Launch System was tested in the NASA Langley Research Center 14- by 22-Foot Subsonic Wind Tunnel to quantify the aerodynamic forces that will be experienced by the launch vehicle during its liftoff and transition to ascent flight. The test consisted of two parts: the first was dedicated to measuring forces and moments for the entire range of angles of attack (0deg to 90deg) and roll angles (0 deg. to 360 deg.). The second was designed to measure the aerodynamic effects of the liftoff tower on the launch vehicle for ground winds from all azimuthal directions (0 deg. to 360 deg.), and vehicle liftoff height ratios from 0 to 0.94. This wind tunnel model also included a set of 154 surface static pressure ports. Details on the experimental setup, and results from both parts of testing are presented, along with a description of how the wind tunnel data was analyzed and post-processed in order to develop an aerodynamic database. Finally, lessons learned from experiencing significant dynamics in the mid-range angles of attack due to steady asymmetric vortex shedding are presented.

Vibrational analysis of vertical axis wind turbine blades

NASA Astrophysics Data System (ADS)

Kapucu, Onur

The goal of this research is to derive a vibration model for a vertical axis wind turbine blade. This model accommodates the affects of varying relative flow angle caused by rotating the blade in the flow field, uses a simple aerodynamic model that assumes constant wind speed and constant rotation rate, and neglects the disturbance of wind due to upstream blade or post. The blade is modeled as elastic Euler-Bernoulli beam under transverse bending and twist deflections. Kinetic and potential energy equations for a rotating blade under deflections are obtained, expressed in terms of assumed modal coordinates and then plugged into Lagrangian equations where the non-conservative forces are the lift and drag forces and moments. An aeroelastic model for lift and drag forces, approximated with third degree polynomials, on the blade are obtained assuming an airfoil under variable angle of attack and airflow magnitudes. A simplified quasi-static airfoil theory is used, in which the lift and drag coefficients are not dependent on the history of the changing angle of attack. Linear terms on the resulting equations of motion will be used to conduct a numerical analysis and simulation, where numeric specifications are modified from the Sandia-17m Darrieus wind turbine by Sandia Laboratories.

Simulation of drift of pesticides: development and validation of a model.

PubMed

Brusselman, E; Spanoghe, P; Van der Meeren, P; Gabriels, D; Steurbaut, W

2003-01-01

Over the last decade drift of pesticides has been recognized as a major problem for the environment. High fractions of pesticides can be transported through the air and deposited in neighbouring ecosystems during and after application. A new computer-two steps-drift model is developed: FYDRIMO or F(ph)Ysical DRift MOdel. In the first step the droplet size spectrum of a nozzle is analysed. In this way the volume percentage of droplets with a certain size is known. In the second step the model results in a prediction of deposition of each droplet with a certain size. This second part of the model runs in MATLAB and is grounded on a combination of two physical factors: gravity force and friction forces. In this stage of development corrections are included for evaporation and wind force following a certain measured wind profile. For validation wind tunnel experiments were performed. Salt solutions were sprayed at two wind velocities and variable distance above the floor. Small gutters in the floor filled with filter paper were used to collect the sprayed droplets. After analysing and comparing the wind tunnel results with the model predictions, FYDRIMO seems to have good predicting capacities.

Water-waves frequency upshift of the spectral mean due to wind forcing

NASA Astrophysics Data System (ADS)

Eeltink, Debbie; Chabchoub, Amin; Brunetti, Maura; Kasparian, Jerome; Kimmoun, Olivier; Branger, Hubert

2017-04-01

The effect of wind forcing on monochromatic modulated water waves was investigated both numerically and experimentally in the context of the Modified Non-Linear Schrödinger (MNLS) equation framework. While wind is usually associated with a frequency downshift of the dominant spectral peak, we show that it may induce an upshift of the spectral mean due to an asymmetric amplification of the spectrum. Here the weighted average spectral mean is equal to the ratio of the momentum of the envelope to its norm and it detects any asymmetries in the spectrum (Segur et al. 2005). Wind can however indirectly induce frequency downshifts, by promoting dissipative effects like wave breaking. We highlight that the definition of the up- and downshift in terms of peak frequency or average frequency is critical for a relevant discussion. In our model, the wind input consists of a leading order forcing term that amplifies all frequencies equally and induces a broadening of the spectrum, and a higher order asymmetric term (Brunetti et al. 2014; Brunetti & Kasparian 2014) that amplifies higher frequencies more than lower ones and induces a permanent upshift of the spectral mean. The effect of MNLS + wind is exactly opposite to MNLS + viscosity, where the lower order viscosity terms damp the whole spectrum, while the higher order viscosity terms damp higher frequencies more than lower ones and thus causes a permanent downshift, as evidenced by Carter & Govan (2016). We corroborated the model with wave tank experiments conducted in the IRPHE/Pytheas large wind-wave facility located in Marseille, France. Wave data analysis show the temporary downshift in the spectral peak sense caused by the wind, and the temporary upshift in the spectral mean sense characteristic of the MNLS. As the tank-length was limited, we used long-range simulations to obtain upshift in the spectral mean sense caused by the wind. The limit of the model is reached when breaking events occur. We acknowledge financial support from the Swiss National Science Foundation (project 200021-155970), the Labex MEC (French ANR-10-LABX-0092) and the A*MIDEX project (ANR-11-IDEX-0001-02). • Brunetti, M. and Kasparian, J. 2014 "Modulational instability in wind-forced waves". Physics Letters A, 378: 48, 3626-3630. • Brunetti, M., Marchiando, N., Berti, N. and Kasparian, J. 2014 "Nonlinear fast growth of water waves under wind forcing". Physics Letters A 378: 1415, 1025-1030. • Carter, J. D. and Govan, A. 2016 "Frequency downshift in a viscous fluid." Eur. Journ. Mech. - B/Fluids 59: 177-185. • Segur, H., Henderson, D., Carter, J., Hammack, J., Li, C.-M., Pheiff, D. and Socha, K. 2005 "Stabilizing the Benjamin-Feir instability". Journ. Fluid Mechanics, 539: 229-271.

Assessment of Wind Datasets for Estimating Offshore Wind Energy along the Central California Coast

NASA Astrophysics Data System (ADS)

Wang, Y. H.; Walter, R. K.; Ruttenberg, B.; White, C.

2017-12-01

Offshore renewable energy along the central California coastline has gained significant interest in recent years. We present a comprehensive analysis of near-surface wind datasets available in this region to facilitate future estimates of wind power generation potential. The analyses are based on local NDBC buoys, satellite-based measurements (QuickSCAT and CCMP V2.0), reanalysis products (NARR and MERRA), and a regional climate model (WRF). There are substantial differences in the diurnal signal during different months among the various products (i.e., satellite-based, reanalysis, and modeled) relative to the local buoys. Moreover, the datasets tended to underestimate wind speed under light wind conditions and overestimate under strong wind conditions. In addition to point-to-point comparisons against local buoys, the spatial variations of bias and error in both the reanalysis products and WRF model data in this region were compared against satellite-based measurements. NARR's bias and root-mean-square-error were generally small in the study domain and decreased with distance from coastlines. Although its smaller spatial resolution is likely to be insufficient to reveal local effects, the small bias and error in near-surface winds, as well as the availability of wind data at the proposed turbine hub heights, suggests that NARR is an ideal candidate for use in offshore wind energy production estimates along the central California coast. The framework utilized here could be applied in other site-specific regions where offshore renewable energy is being considered.

Plants and ventifacts delineate late Holocene wind vectors in the Coachella Valley, USA

USGS Publications Warehouse

Griffiths, P.G.; Webb, R.H.; Fisher, M.; Muth, Allan

2009-01-01

Strong westerly winds that emanate from San Gorgonio Pass, the lowest point between Palm Springs and Los Angeles, California, dominate aeolian transport in the Coachella Valley of the western Sonoran Desert. These winds deposit sand in coppice dunes that are critical habitat for several species, including the state and federally listed threatened species Uma inornata, a lizard. Although wind directions are generally defined in this valley, the wind field has complex interactions with local topography and becomes more variable with distance from the pass. Local, dominant wind directions are preserved by growth patterns of Larrea tridentata (creosote bush), a shrub characteristic of the hot North American deserts, and ventifacts. Exceptionally long-lived, Larrea has the potential to preserve wind direction over centuries to millennia, shaped by the abrasive pruning of windward branches and the persistent training of leeward branches. Wind direction preserved in Larrea individuals and clones was mapped at 192 locations. Compared with wind data from three weather stations, Larrea vectors effectively reflect annual prevailing winds. Ventifacts measured at 24 locations record winds 10° more westerly than Larrea and appear to reflect the direction of the most erosive winds. Based on detailed mapping of local wind directions as preserved in Larrea, only the northern half of the Mission-Morongo Creek floodplain is likely to supply sand to protected U. inornata habitat in the Willow Hole ecological reserve.

6. CLOSEUP VIEW OF TENFOOT WIND TUNNEL (1991). WrightPatterson ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

6. CLOSE-UP VIEW OF TEN-FOOT WIND TUNNEL (1991). - Wright-Patterson Air Force Base, Area B, Buildings 25 & 24,10-foot & 20-foot Wind Tunnel Complex, Northeast side of block bounded by K, G, Third, & Fifth Streets, Dayton, Montgomery County, OH

The Legacy of Admiral Beaufort

ERIC Educational Resources Information Center

Heidorn, Keith

1978-01-01

Francis Beaufort was a British naval officer who developed a wind force scale based on the effect of wind strength on frigate sails. Over the years, this scale has been modified, and today it is used internationally to describe the speed of the wind using numerical equivalents. (MA)

Analysis of Rawinsonde Spatial Separation for Space Launch Vehicle Applications at the Eastern Range

NASA Technical Reports Server (NTRS)

Decker, Ryan K.

2017-01-01

Space launch vehicles develop day-of-launch steering commands based upon the upper-level atmospheric environments in order to alleviate wind induced structural loading and optimize ascent trajectory. Historically, upper-level wind measurements to support launch operations at the National Aeronautics and Space Administration's (NASA's) Kennedy Space Center co-located on the United States Air Force's Eastern Range (ER) at the Cape Canaveral Air Force Station use high-resolution rawinsondes. One inherent limitation with rawinsondes consists of taking approximately one hour to generate a vertically complete wind profile. Additionally, rawinsonde drift during ascent by the ambient wind environment can result in the balloon being hundreds of kilometers down range, which results in questioning whether the measured winds represent the wind environment the vehicle will experience during ascent. This paper will describe the use of balloon profile databases to statistically assess the drift distance away from the ER launch complexes during rawinsonde ascent as a function of season and discuss an alternative method to measure upper level wind environments in closer proximity to the vehicle trajectory launching from the ER.

Wind effect on the Atlantic meridional overturning circulation via sea ice and vertical diffusion

NASA Astrophysics Data System (ADS)

Yang, Haijun; Wang, Kun; Dai, Haijin; Wang, Yuxing; Li, Qing

2016-06-01

Effects of wind and fresh water on the Atlantic meridional overturning circulation (AMOC) are investigated using a fully coupled climate model. The AMOC can change significantly when perturbed by either wind stress or freshwater flux in the North Atlantic. This study focuses on wind stress effect. Our model results show that the wind forcing is crucial in maintaining the AMOC. Reducing wind forcing over the ocean can cause immediately weakening of the vertical salinity diffusion and convection in the mid-high latitudes Atlantic, resulting in an enhancement of vertical salinity stratification that restrains the deep water formation there, triggering a slowdown of the thermohaline circulation. As the thermohaline circulation weakens, the sea ice expands southward and melts, providing the upper ocean with fresh water that weakens the thermohaline circulation further. The wind perturbation experiments suggest a positive feedback between sea-ice and thermohaline circulation strength, which can eventually result in a complete shutdown of the AMOC. This study also suggests that sea-ice variability may be also important to the natural AMOC variability on decadal and longer timescales.

Numerical simulation on a straight-bladed vertical axis wind turbine with auxiliary blade

NASA Astrophysics Data System (ADS)

Li, Y.; Zheng, Y. F.; Feng, F.; He, Q. B.; Wang, N. X.

2016-08-01

To improve the starting performance of the straight-bladed vertical axis wind turbine (SB-VAWT) at low wind speed, and the output characteristics at high wind speed, a flexible, scalable auxiliary vane mechanism was designed and installed into the rotor of SB-VAWT in this study. This new vertical axis wind turbine is a kind of lift-to-drag combination wind turbine. The flexible blade expanded, and the driving force of the wind turbines comes mainly from drag at low rotational speed. On the other hand, the flexible blade is retracted at higher speed, and the driving force is primarily from a lift. To research the effects of the flexible, scalable auxiliary module on the performance of SB-VAWT and to find its best parameters, the computational fluid dynamics (CFD) numerical calculation was carried out. The calculation result shows that the flexible, scalable blades can automatic expand and retract with the rotational speed. The moment coefficient at low tip speed ratio increased substantially. Meanwhile, the moment coefficient has also been improved at high tip speed ratios in certain ranges.

Analysis of Rawinsonde Spatial Separation for Space Launch Vehicle Applications at the Eastern Range

NASA Technical Reports Server (NTRS)

Decker, Ryan K.

2017-01-01

Space launch vehicles use day-of-launch steering commands based upon the upper-level (UL) atmospheric environments in order to alleviate wind induced structural loading and optimize ascent trajectory. Historically, UL wind measurements to support launch operations at the National Aeronautics and Space Administration's (NASA) Kennedy Space Center (KSC), co-located on the United States Air Force's Eastern Range (ER) at the Cape Canaveral Air Force Station use high-resolution (HR) rawinsondes. One inherent limitation with rawinsondes is the approximately one-hour sampling time necessary to measure tropospheric winds. Additionally, rawinsonde drift during ascent due to the ambient wind environment can result in the balloon being hundreds of kilometers down range, which results in questioning whether the measured winds represent the wind environment the vehicle will experience during ascent. This paper will describe the use of balloon profile databases to statistically assess the drift distance away from the ER launch complexes during HR rawinsonde ascent as a function of season. Will also discuss an alternative method to measure UL wind environments in closer proximity to the vehicle trajectory when launching from the ER.

Modulation of ENSO evolution by strong tropical volcanic eruptions

NASA Astrophysics Data System (ADS)

Wang, Tao; Guo, Dong; Gao, Yongqi; Wang, Huijun; Zheng, Fei; Zhu, Yali; Miao, Jiapeng; Hu, Yongyun

2017-11-01

The simulated responses of the El Niño-Southern Oscillation (ENSO) to volcanic forcings are controversial, and some mechanisms of these responses are not clear. We investigate the impacts of volcanic forcing on the ENSO using a long-term simulation covering 1400-1999 as simulated by the Bergen Climate Model (BCM) and a group of simulations performed with the Community Atmosphere Model version 4.0 (CAM4) and the BCM's ocean component Miami Isopycanic Coordinated Ocean Model (MICOM). The analysis of the long-term BCM simulation indicates that ENSO has a negative-positive-negative response to strong tropical volcanic eruptions (SVEs), which corresponds to the different stages of volcanic forcing. In the initial forcing stage, a brief and weak La Niña-like response is caused by the cooling along the west coast of the South American continent and associated enhancement of the trade winds. In the peak forcing stage, westerly wind anomalies are excited by both reduced east-west sea level pressure gradients and weakened and equatorward shifted tropical convergence zones. These westerly wind anomalies extend to the equatorial eastern Pacific, leading to an El Niño-like response. At the same time, easterly wind anomalies west of 120°E and strong cooling effects can promote a discharged thermocline state and excite an upwelling Kelvin wave in the western Pacific. In the declining forcing stage, forced by the recovered trade winds, the upwelling Kelvin wave propagates eastward and reaches the equatorial eastern Pacific. Through the Bjerknes feedback, a strong and temporally extended La Niña-like response forms. Additional CAM4 simulations suggest a more important role of the surface cooling over the Maritime Continent and surrounding ocean in shaping the westerly wind anomalies over the equatorial central-eastern Pacific and the easterly wind anomalies west of 120° E, which are key to causing the El Niño-like responses and subsequent La Niña-like responses, respectively. The MICOM sensitivity simulations confirm that SVE-induced tropical atmospheric circulation anomalies play a dominant role in regulating post-eruption ENSO evolution in the observation, while the influences of anomalous buoyance forcing (heat and freshwater fluxes) are secondary. Therefore, SVEs play an important role in modulating the ENSO evolution. Compared with proxy data, the simulated El Niño-like responses and subsequent La Niña-like responses are consistent with the reconstructed ENSO responses to SVEs. However, the simulated initial brief La Niña-like response, which is reproduced by most models, is seen in only one proxy dataset and is absent in most of the reconstructed ENSOs and those observed. The reason for this model-data mismatch will require further investigation.

Applied Meteorology Unit (AMU) Quarterly Report

NASA Technical Reports Server (NTRS)

Bauman, William; Crawford, Winifred; Watson, Leela; Wheeler, Mark

2011-01-01

This Quarter's Highlights include reports on the following tasks: (1) Mr. Wheeler completed a study for the 30th Weather Squadron at Vandenberg Air Force Base in California in which he found precursors in weather observations that will help the forecasters determine when they will get strong wind gusts at their northern towers. The final report is now on the AMU website at http://science.ksc.nasa.gov/amu/final-reports/30ws-north-base-winds.pdf. (2) continued work on the second phase of verifying the performance of the MesoNAM weather model at Kennedy Space Center (KSC) and Cape Canaveral Air Force Station (CCAFS). (3) continued work to improve the AMU peak wind tool by analyzing wind tower data to determine peak wind behavior during times of onshore and offshore flow. (4) continued updating lightning c1imatologies for KSC/CCAFS and other airfields around central Florida and created new c1imatologies for moisture and stability thresholds.

December anomaly in ionosphere using FORMOSAT-3/COSMIC electron density profiles

NASA Astrophysics Data System (ADS)

Dashnyam, G.; Lin, C. C. H.; Rajesh, P. K.; Lin, J. T.

2017-12-01

December anomaly in ionosphere refers to the observation of greater value of global average ionospheric peak electron density (NmF2) in December-January months than in June-July months. So far there has been no satisfactory explanation to account for this difference, which is also known as annual asymmetry, leading to the speculation that forcing from lower atmosphere may be important. In this work, FORMOSAT-3/COSMIC electron density profiles are used to investigate the characteristics of December anomaly at different local times and longitudes in varying levels of solar activity. The observations in the years 2008, 2009 and 2012 are used for the study. The results suggest that the anomaly exists in all the three years, and is pronounced during day. Detailed analysis is carried out using latitude-altitude electron density profiles at selected longitude sectors, revealing that neutral wind may play dominant role. SAMI2 model is used to further examine the role of neutral wind influencing the electron density in different solstices. Tidal decomposition of the wind is carried out to understand the dominant tidal components that give rise to the larger electron density in the December-January months.

The impact of land-surface wetness heterogeneity on mesoscale heat fluxes

NASA Technical Reports Server (NTRS)

Chen, Fei; Avissar, Roni

1994-01-01

Vertical heat fluxes associated with mesoscale circulations generated by land-surface wetness discontinuities are often stronger than turbulent fluxes, especially in the upper part of the atmospheric planetary boundary layer. As a result, they contribute significantly to the subgrid-scale fluxes in large-scale atmospheric models. Yet they are not considered in these models. To provide some insights into the possible parameterization of these fluxes in large-scale models, a state-of-the-art mesoscale numerical model was used to investigate the relationships between mesoscale heat fluxes and atmospheric and land-surface characteristics that play a key role in the generation of mesoscale circulations. The distribution of land-surface wetness, the wavenumber and the wavelength of the land-surface discontinuities, and the large-scale wind speed have a significant impact on the mesoscale heat fluxes. Empirical functions were derived to characterize the relationships between mesoscale heat fluxes and the spatial distribution of land-surface wetness. The strongest mesoscale heat fluxes were obtained for a wavelength of forcing corresponding approximately to the local Rossby deformation radius. The mesoscale heat fluxes are weakened by large-scale background winds but remain significant even with moderate winds.

A case study of the effects of random errors in rawinsonde data on computations of ageostrophic winds

NASA Technical Reports Server (NTRS)

Moore, J. T.

1985-01-01

Data input for the AVE-SESAME I experiment are utilized to describe the effects of random errors in rawinsonde data on the computation of ageostrophic winds. Computer-generated random errors for wind direction and speed and temperature are introduced into the station soundings at 25 mb intervals from which isentropic data sets are created. Except for the isallobaric and the local wind tendency, all winds are computed for Apr. 10, 1979 at 2000 GMT. Divergence fields reveal that the isallobaric and inertial-geostrophic-advective divergences are less affected by rawinsonde random errors than the divergence of the local wind tendency or inertial-advective winds.

Operation and Equivalent Loads of Wind Turbines in Large Wind Farms

NASA Astrophysics Data System (ADS)

Andersen, Soren Juhl; Sorensen, Jens Norkaer; Mikkelsen, Robert Flemming

2017-11-01

Wind farms continue to grow in size and as the technology matures, the design of wind farms move towards including dynamic effects besides merely annual power production estimates. The unsteady operation of wind turbines in large wind farms has been modelled with EllipSys3D(Michelsen, 1992, and Sørensen, 1995) for a number of different scenarios using a fully coupled large eddy simulations(LES) and aero-elastic framework. The turbines are represented in the flow fields using the actuator line method(Sørensen and Shen, 2002), where the aerodynamic forces and deflections are derived from an aero-elastic code, Flex5(Øye, 1996). The simulations constitute a database of full turbine operation in terms of both production and loads for various wind speeds, turbulence intensities, and turbine spacings. The operating conditions are examined in terms of averaged power production and thrust force, as well as 10min equivalent flapwise bending, yaw, and tilt moment loads. The analyses focus on how the performance and loads change throughout a given farm as well as comparing how various input parameters affect the operation and loads of the wind turbines during different scenarios. COMWIND(Grant 2104-09- 067216/DSF), Nordic Consortium on Optimization and Control of Wind Farms, Eurotech Greentech Wind project, Winds2Loads, and CCA LES. Ressources Granted on SNIC and JESS. The Vestas NM80 turbine has been used.

Patterns of interannual climate variability in large marine ecosystems

NASA Astrophysics Data System (ADS)

Soares, Helena Cachanhuk; Gherardi, Douglas Francisco Marcolino; Pezzi, Luciano Ponzi; Kayano, Mary Toshie; Paes, Eduardo Tavares

2014-06-01

The purpose of this study is to investigate the vulnerability of the Brazilian and western African Large Marine Ecosystems (LMEs) to local and remote forcing, including the Pacific Decadal Oscillation (PDO) regime shift. The analyses are based on the total and partial correlation between climate indices (Niño3, tropical South Atlantic (TSA), tropical North Atlantic (TNA) and Antarctic oscillation (AAO) and oceanic and atmospheric variables (sea surface temperature (SST), wind stress, Ekman transport, sea level pressure and outgoing longwave radiation). Differences in the correlation fields between the cold and warm PDO indicate that this mode exerts a significant impact on the thermodynamic balance of the ocean-atmosphere system on the South Atlantic ocean, mainly in the South Brazil and Benguela LMEs. The PDO regime shift also resulted in an increase in the spatial variability of SST and wind stress anomalies, mainly along the western African LMEs. Another important finding is the strong AAO influence on the SST anomalies (SSTA) in the South Brazil LME. It is also striking that TSA modulates the relation between El Niño-Southern Oscillation (ENSO) and SSTA, by reducing the influence of ENSO on SSTA during the warm PDO period in the North and East Brazil LMEs and in the Guinea Current LME. The relation between AAO and SSTA on the tropical area is also influenced by the TSA. The results shown here give a clear indication that future ecosystem-based management actions aimed at the conservation of marine resources under climate change need to consider the high complexity of basin-scale interactions between local and remote climate forcings, including their effects on the ocean-atmosphere system of the South Atlantic ocean.

The Regional Water Cycle and Water Ice Clouds in the Tharsis - Valles Marineris System

NASA Astrophysics Data System (ADS)

Leung, C. W. S.; Rafkin, S. C.

2017-12-01

The regional atmospheric circulation on Mars is highly influenced by local topographic gradients. Terrain-following air parcels forced along the slopes of the major Tharsis volcanoes and the steep canyon walls of Valles Marineris significantly impact the local water vapor concentration and the associated conditions for cloud formation. Using a non-hydrostatic mesoscale atmospheric model with aerosol & cloud microphysics, we investigate the meteorological conditions for water ice cloud formation in the coupled Tharsis - Valles Marineris system near the aphelion season. The usage of a limited area regional model ensures that topographic slopes are well resolved compared to the typical resolutions of a global-coverage general circulation model. The effects of shadowing and slope angle geometries on the energy budget is also taken into account. Diurnal slope winds in complex terrains are typically characterized by the reversal of wind direction twice per sol: upslope during the day, and downslope at night. However, our simulation results of the regional circulation and diurnal water cycle indicate substantial asymmetries in the day-night circulation. The convergence of moist air masses enters Valles Marineris via easterly flows, whereas dry air sweep across the plateau of the canyon system from the south towards the north. We emphasize the non-uniform vertical distribution of water vapor in our model results. Water vapor mixing ratios in the lower planetary boundary layer may be factors greater than the mixing ratio aloft. Water ice clouds are important contributors to the climatic forcing on Mars, and their effects on the mesoscale circulations in the Tharsis - Valles Marineris region significantly contribute to the regional perturbations in the large-scale global atmospheric circulation.

Economic and Technical Feasibility Study of Utility-Scale Wind Generation for the New York Buffalo River and South Buffalo Brownfield Opportunity Areas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Roberts, J. O.; Mosey, G.

2014-04-01

Through the RE-Powering America's Land initiative, the economic and technical feasibility of utilizing contaminated lands in the Buffalo, New York, area for utility-scale wind development is explored. The study found that there is available land, electrical infrastructure, wind resource, and local interest to support a commercial wind project; however, economies of scale and local electrical markets may need further investigation before significant investment is made into developing a wind project at the Buffalo Reuse Authority site.

Response of the Surface Circulation of the Arabian Sea to Monsoonal Forcing

NASA Astrophysics Data System (ADS)

Beal, L. M.; Hormann, V.; Lumpkin, R.; Foltz, G. R.

2014-12-01

We use two decades of drifter and satellite data to examine the monthly evolution of the surface circulation of the Arabian Sea, which reverses annually in response to the Indian monsoon winds. Most significantly, we find that in the transition from winter to summer circulations, northward flow appears along the length of the western boundary as early as March or April, one or two months before the onset of the southwest monsoon winds. This reversal is initiated by annual Rossby waves, which in turn are initiated by wind curl forcing during the previous southwest monsoon. These results lead us to speculate that there is an oceanic mechanism through which one monsoon may precondition the next. Previous studies of monsoon circulations with lower temporal resolution have highlighted basin-wide currents and connections that are not found to exist in the monthly fields. In particular, we find that the Northeast Monsoon Current does not reach the western boundary and there is no counter-rotating gyre system during boreal winter. South of the equator, the eastward-flowing South Equatorial Counter Current (SECC) is present year-round, even though equatorial winds are strongly influenced by the monsoons. Semi-annual variability of the SECC is governed by Ekman pumping over the south equatorial gyre (or Seychelles dome) and, surprisingly, it is weakest during the northeast monsoon. This region has important influence on the atmosphere and its link to the monsoons deserves further investigation. The East African Coastal Current feeds into the SECC from the boundary. During the southwest monsoon it overshoots the equator and splits, feeding both northward into the Somali Current and eastward into the SECC after looping back across the equator. This apparent retroflection of the EACC is what was previously known as the southern gyre and is obscured at the surface by strong, locally wind-driven, cross-equatorial Ekman transport. Finally, there is broad, strong eastward flow at the mouth of the Gulf of Aden throughout the southwest monsoon, which is influenced by the curvature and bifurcation of the atmospheric monsoon jet.

Unsteady Sail Dynamics in Olympic Class Sailboats

NASA Astrophysics Data System (ADS)

Williamson, Charles; Schutt, Riley

2016-11-01

Unsteady sailing techniques have evolved in competitive sailboat fleets, in cases where the relative weight of the sailor is sufficient to impart unsteady motions to the boat and sails. We will discuss three types of motion that are used by athletes to propel their boats on an Olympic race course faster than using the wind alone. In all of our cases, body weight movements induce unsteady sail motion, increasing driving force and speed through the water. In this research, we explore the dynamics of an Olympic class Laser sailboat equipped with a GPS, IMU, wind sensor, and a 6-GoPro camera array. We shall briefly discuss "sail flicking", whereby the helmsman periodically rolls the sail into the apparent wind, at an angle which is distinct from classical heave (in our case, the oscillations are not normal to the apparent flow). We also demonstrate "roll tacking", where there are considerable advantages to rolling the boat during such a maneuver, especially in light wind. In both of the above examples from on-the-water studies, corresponding experiments using a towing tank exhibit increases in the driving force, associated with the formation of strong vortex pairs into the flow. Finally, we focus on a technique known as "S-curving" in the case where the boat sails downwind. In contrast to the previous cases, it is drag force rather than lift force that the sailor is trying to maximise as the boat follows a zig-zag trajectory. The augmented apparent wind strength due to the oscillatory sail motion, and the growth of strong synchronised low-pressure wake vortices on the low-pressure side of the sail, contribute to the increase in driving force, and velocity-made-good downwind.

Dynamical relationship between wind speed magnitude and meridional temperature contrast: Application to an interannual oscillation in Venusian middle atmosphere GCM

NASA Astrophysics Data System (ADS)

Yamamoto, Masaru; Takahashi, Masaaki

2018-03-01

We derive simple dynamical relationships between wind speed magnitude and meridional temperature contrast. The relationship explains scatter plot distributions of time series of three variables (maximum zonal wind speed UMAX, meridional wind speed VMAX, and equator-pole temperature contrast dTMAX), which are obtained from a Venus general circulation model with equatorial Kelvin-wave forcing. Along with VMAX and dTMAX, UMAX likely increases with the phase velocity and amplitude of a forced wave. In the scatter diagram of UMAX versus dTMAX, points are plotted along a linear equation obtained from a thermal-wind relationship in the cloud layer. In the scatter diagram of VMAX versus UMAX, the apparent slope is somewhat steep in the high UMAX regime, compared with the low UMAX regime. The scatter plot distributions are qualitatively consistent with a quadratic equation obtained from a diagnostic equation of the stream function above the cloud top. The plotted points in the scatter diagrams form a linear cluster for weak wave forcing, whereas they form a small cluster for strong wave forcing. An interannual oscillation of the general circulation forming the linear cluster in the scatter diagram is apparent in the experiment of weak 5.5-day wave forcing. Although a pair of equatorial Kelvin and high-latitude Rossby waves with a same period (Kelvin-Rossby wave) produces equatorward heat and momentum fluxes in the region below 60 km, the equatorial wave does not contribute to the long-period oscillation. The interannual fluctuation of the high-latitude jet core leading to the time variation of UMAX is produced by growth and decay of a polar mixed Rossby-gravity wave with a 14-day period.

Revisiting the Processes That Determine Wintertime Intraseasonal SST Variability in the Thermocline Ridge of the Tropical South Indian Ocean

NASA Astrophysics Data System (ADS)

Han, W.; Li, Y.; Shinoda, T.; Wang, C.; Ravichandran, M.; Wang, J. W.

2014-12-01

Intraseasonal sea surface temperature (SST) variability over the Seychelles-Chagos thermocline ridge (SCTR) induced by boreal wintertime Madden-Julian oscillations (MJOs) is investigated by performing a series of OGCM experiments with improved model configuration and the recently available high quality satellite forcing fields. The impact of the ocean interannual variation of the thermocline depth -represented by the depth of 20C isotherm (D20) - in the SCTR is also assessed. The OGCM main run solution agrees well with the observations. The results show that for the 2001-2011 period, surface shortwave radiation (SWR), turbulent heat fluxes associated with wind speed, and wind stress-driven ocean dynamical processes are all important in causing the MJO-related intraseasonal SST variability in the SCTR region. Overall, forcing by SWR contributes ~31%, and forcing by winds (via both surface turbulent heat flux and ocean dynamics) contributes ~62%. The contribution of turbulent heat flux associated with wind speed is ~39% and that of wind-stress driven ocean dynamics is ~23%. The contribution of ocean dynamics, however, is considerably larger during strong ("prime") MJO events under "strong" thermocline condition. The overall effect of interannual variability of D20 on intraseasonal SST during 2001-2011 is significant in the eastern part of the SCTR (70E-85E), where the intraseasonal SST amplitudes are strengthened by about 20%. In general, a shallower/deeper SCTR favors larger/smaller SST responses to the MJO forcing. In the eastern SCTR, both the heat flux forcing and entrainment are greatly amplified under the strong SCTR condition, but only slightly suppressed under the weak SCTR condition, leading to an overall strengthening effect on intraseasonal SST variability.

Relevance of aerodynamic modelling for load reduction control strategies of two-bladed wind turbines

NASA Astrophysics Data System (ADS)

Luhmann, B.; Cheng, P. W.

2014-06-01

A new load reduction concept is being developed for the two-bladed prototype of the Skywind 3.5MW wind turbine. Due to transport and installation advantages both offshore and in complex terrain two-bladed turbine designs are potentially more cost-effective than comparable three-bladed configurations. A disadvantage of two-bladed wind turbines is the increased fatigue loading, which is a result of asymmetrically distributed rotor forces. The innovative load reduction concept of the Skywind prototype consists of a combination of cyclic pitch control and tumbling rotor kinematics to mitigate periodic structural loading. Aerodynamic design tools must be able to model correctly the advanced dynamics of the rotor. In this paper the impact of the aerodynamic modelling approach is investigated for critical operational modes of a two-bladed wind turbine. Using a lifting line free wake vortex code (FVM) the physical limitations of the classical blade element momentum theory (BEM) can be evaluated. During regular operation vertical shear and yawed inflow are the main contributors to periodic blade load asymmetry. It is shown that the near wake interaction of the blades under such conditions is not fully captured by the correction models of BEM approach. The differing prediction of local induction causes a high fatigue load uncertainty especially for two-bladed turbines. The implementation of both cyclic pitch control and a tumbling rotor can mitigate the fatigue loading by increasing the aerodynamic and structural damping. The influence of the time and space variant vorticity distribution in the near wake is evaluated in detail for different cyclic pitch control functions and tumble dynamics respectively. It is demonstrated that dynamic inflow as well as wake blade interaction have a significant impact on the calculated blade forces and need to be accounted for by the aerodynamic modelling approach. Aeroelastic simulations are carried out using the high fidelity multi body simulation software SIMPACK. The aerodynamic loads are calculated using ECN's AeroModule and NREL's BEM code Aerodynl3.

The effects of the stellar wind and orbital motion on the jets of high-mass microquasars

NASA Astrophysics Data System (ADS)

Bosch-Ramon, V.; Barkov, M. V.

2016-05-01

Context. High-mass microquasar jets propagate under the effect of the wind from the companion star, and the orbital motion of the binary system. The stellar wind and the orbit may be dominant factors determining the jet properties beyond the binary scales. Aims: This is an analytical study, performed to characterise the effects of the stellar wind and the orbital motion on the jet properties. Methods: Accounting for the wind thrust transferred to the jet, we derive analytical estimates to characterise the jet evolution under the impact of the stellar wind. We include the Coriolis force effect, induced by orbital motion and enhanced by the wind's presence. Large-scale evolution of the jet is sketched, accounting for wind-to-jet thrust transfer, total energy conservation, and wind-jet flow mixing. Results: If the angle of the wind-induced jet bending is larger than its half-opening angle, the following is expected: (I) a strong recollimation shock; (II) bending against orbital motion, caused by Coriolis forces and enhanced by the wind presence; and (III) non-ballistic helical propagation further away. Even if disrupted, the jet can re-accelerate due to ambient pressure gradients, but wind entrainment can weaken this acceleration. On large scales, the opening angle of the helical structure is determined by the wind-jet thrust relation, and the wind-loaded jet flow can be rather slow. Conclusions: The impact of stellar winds on high-mass microquasar jets can yield non-ballistic helical jet trajectories, jet partial disruption and wind mixing, shocks, and possibly non-thermal emission. Among other observational diagnostics, such as radiation variability at any band, the radio morphology on milliarcsecond scales can be informative on the wind-jet interaction.

A vorticity budget for the Gulf Stream

NASA Astrophysics Data System (ADS)

Le Bras, Isabela; Toole, John

2017-04-01

We develop a depth-averaged vorticity budget framework to diagnose the dynamical balance of the Gulf Stream, and apply this framework to observations and the ECCO state estimate (Wunsch and Heimbach 2013) above the thermocline in the subtropical North Atlantic. Using the hydrographic and ADCP data along the WOCE/CLIVAR section A22 and a variety of wind stress data products, we find that the advective vorticity flux out of the western region is on the same order as the wind stress forcing over the eastern portion of the gyre. This is consistent with a large-scale balance between a negative source of vorticity from wind stress forcing and a positive source of vorticity in the western region. Additionally, the form of the vorticity flux indicates that the Gulf Stream has a significant inertial component. In the ECCO state estimate, we diagnose a seasonal cycle in advective vorticity flux across a meridional section associated with seasonal fluctuations in Gulf Stream transport. This vorticity flux is forced by wind stress over the eastern subtropical North Atlantic and balanced by lateral friction with the western boundary. The lateral friction in ECCO is a necessary parameterization of smaller scale processes that occur in the real ocean, and quantifying these remains an open and interesting question. This simplified framework provides a means to interpret large scale ocean dynamics. In our application, it points to wind stress forcing over the subtropical North Altantic as an important regulator of the Gulf Stream and hence the climate system.

Remote forcing at the Last Glacial Maximum in the Tropical Pacific Ocean

NASA Astrophysics Data System (ADS)

Andreasen, Dyke H.; Ravelo, A. Christina; Broccoli, Anthony J.

2001-01-01

We present results of a Last Glacial Maximum (LGM) wind stress sensitivity experiment using a high-resolution ocean general circulation model of the tropical Pacific Ocean. LGM wind stress, used to drive the ocean model, was generated using an atmospheric general circulation model simulation forced by LGM boundary conditions as part of the Paleoclimate Modeling Intercomparison Project (PMIP) [Broccoli, 2000]. LGM wind stress anomalies were large in the western half of the basin, yet there was a significant hydrographic response in the eastern half. This ocean model experiment hind casts changes that are in close agreement with paleoceanographic data from the entire region, even without the explicit modeling of the air-sea interactions. Data and model both predict that the annual average thermocline tilt across the basin was enhanced. Data and model are consistent with a stronger equatorial undercurrent which shoaled to the west of where it does today, and stronger advection of water from the Peru Current into the east equatorial Pacific and across the equator. Paleoproductivity and sea surface temperature (SST) data are interpreted in light of the modeling results, indicating that paleoproductivity changes were related to wind-forced dynamical changes resulting from LGM boundary conditions, while SST changes were related to independent, possibly radiative, forcing. Overall, our results imply that much of the dynamic response of the tropical Pacific during the LGM can be explained by wind field changes resulting from global LGM boundary conditions.

The Prospects for Using Little Diomede Island as a Base for Monitoring Bering Strait

NASA Astrophysics Data System (ADS)

Cooper, L. W.; Kelly, V.; Codispoti, L. A.; Sheffield, G.; Grebmeier, J. M.

2002-12-01

Diomede, Alaska is arguably the most isolated community in the United States, located on a small island in the center of Bering Strait, one mile from the international dateline, where nutrient-rich waters from the Bering Sea enter the Arctic Ocean. Postal service is once weekly via helicopter, weather permitting and the 140 Native Inupiat residents (2000 census) are highly dependent upon a subsistence lifestyle utilizing local seabirds, marine mammals, and shellfish. Since the summer of 2000, we have worked with the local community to improve analytical capabilities to analyze waters flowing through the Bering Strait. Other goals of the Bering Strait Environmental Observatory include evaluating the biological health and contaminant burdens of marine mammals used for subsistence by island residents. We have also been annually using the Canadian Coast Guard Service Sir Wilfrid Laurier to assess the biological productivity of benthic organisms that are important as food sources in the Bering Strait region for apex predators such as bearded seal, walrus, diving ducks and gray whale. Future infrastructure that is needed includes a subsea water intake system that would be less vulnerable to wave and ice damage than the interim systems we have employed to date. Using a jet well pump in August, 2001, we pumped water onshore through a thermosalinograph, automated nutrient monitoring devices, a fluorometer, and we also collected discrete samples for silica and oxyen-18/oxygen-16 ratios in a small laboratory constructed under the village school. Results indicate that there is a strong relationship between the surface wind regime and the fertility of waters flowing through the center of Bering Strait. Following sustained northerly wind events, and an approximate 72 hour lag period, waters passing Little Diomede Island were predominantly of Alaska Coastal Water origin, with low nutrients and salinity, and comparatively high temperatures. Southerly winds were by contrast significantly correlated with higher nutrients, lower temperatures, and higher salinities following a similar 72-hour period. These observations are consistent with expected Coriolis forcing and suggest that the flux of high nutrient water flowing through Bering Strait may be particularly sensitive to short and long-term variability in surface wind patterns in this localized region.

RANS simulations of wind turbine wakes: optimal tuning of turbulence closure and aerodynamic loads from LiDAR and SCADA data

NASA Astrophysics Data System (ADS)

Letizia, Stefano; Puccioni, Matteo; Zhan, Lu; Viola, Francesco; Camarri, Simone; Iungo, Giacomo Valerio

2017-11-01

Numerical simulations of wakes produced by utility-scale wind turbines still present challenges related to the variability of the atmospheric conditions and, in the most of the cases, the lack of information about the geometry and aerodynamic performance of the wind turbine blades. In order to overcome the mentioned difficulties, we propose a RANS solver for which turbine aerodynamic forcing and turbulence closure are calibrated through LiDAR and SCADA data acquired for an onshore wind farm. The wind farm under examination is located in North Texas over a relatively flat terrain. The experimental data are leveraged to maximize accuracy of the RANS predictions in terms of wake velocity field and power capture for different atmospheric stability conditions and settings of the wind turbines. The optimization of the RANS parameters is performed through an adjoint-RANS formulation and a gradient-based procedure. The optimally-tuned aerodynamic forcing and turbulence closure are then analyzed in order to investigate effects of the atmospheric stability on the evolution of wind turbine wakes and power performance. The proposed RANS solver has low computational costs comparable to those of wake engineering models, which make it a compelling tool for wind farm control and optimization. Acknowledgments: NSF I/UCRC WindSTAR IIP 1362033 and TACC.

Ocean Mixed Layer responses to intense meteorological events during HyMeX-SOP1 from a high-resolution ocean simulation

NASA Astrophysics Data System (ADS)

Lebeaupin Brossier, Cindy; Arsouze, Thomas; Béranger, Karine; Bouin, Marie-Noëlle; Bresson, Emilie; Ducrocq, Véronique; Giordani, Hervé; Nuret, Mathieu; Rainaud, Romain; Taupier-Letage, Isabelle

2014-12-01

The western Mediterranean Sea is a source of heat and humidity for the atmospheric low-levels in autumn. Large exchanges take place at the air-sea interface, especially during intense meteorological events, such as heavy precipitation and/or strong winds. The Ocean Mixed Layer (OML), which is quite thin at this time of year (∼ 20 m-depth), evolves rapidly under such intense fluxes. This study investigates the ocean responses under intense meteorological events that occurred during HyMeX SOP1 (5 September-6 November 2012). The OML conditions and tendencies are derived from a high-resolution ocean simulation using the sub-regional eddy-resolving NEMO-WMED36 model (1/36°-resolution), driven at the surface by hourly air-sea fluxes from the AROME-WMED forecasts (2.5 km-resolution). The high space-time resolution of the atmospheric forcing allows the highly variable surface fluxes, which induce rapid changes in the OML, to be well represented and linked to small-scale atmospheric processes. First, the simulation results are compared to ocean profiles from several platforms obtained during the campaign. Then, this study focuses on the short-term OML evolution during three events. In particular, we examine the OML cooling and mixing under strong wind events, potentially associated with upwelling, as well as the surface freshening under heavy precipitation events, producing low-salinity lenses. Tendencies demonstrate the major role of the surface forcing in the temperature and/or salinity anomaly formation. At the same time, mixing [restratification] rapidly occurs. As expected, the sign of this tendency term is very dependent on the local vertical stratification which varies at fine scale in the Mediterranean. It also controls [disables] the vertical propagation. In the Alboran Sea, the strong dynamics redistribute the OML anomalies, sometimes up to 7 days after their formation. Elsewhere, despite local amplitude modulations due to internal wave excitation by strong winds, the integrated effect of the horizontal advection is almost null on the anomalies' spread and decay. Finally, diffusion has a small contribution.

Downwelling dynamics of the western Adriatic Coastal Current

NASA Astrophysics Data System (ADS)

Geyer, W. R.; Mullenbach, B. L.; Kineke, G. C.; Sherwood, C. R.; Signell, R. P.; Ogston, A. S.; Puig, P.; Traykovski, P.

2004-12-01

The western Adriatic coastal current (WACC) flows for hundreds of kilometers along the east coast of Italy at speeds of 20 to 100 cm/s. It is fed by the buoyancy input from the Po River and other rivers of the northern Adriatic Sea, with typical freshwater discharge rates of 2000 m**3/s. The Bora winds provide the dominant forcing agent of the WACC during the winter months, resulting in peak southeastward flows reaching 100 cm/s. The energy input of the Bora is principally in the northern Adriatic, and the coastal current response is due mainly to the set up of the pressure field, although there is sometimes an accompanying local component of down-coast winds that further augments the coastal current. Downwelling conditions occur during Bora, with or without local wind-forcing, because the bottom Ekman transport occurs in either case. Downwelling results in destratification of the coastal current, due to both vertical mixing and straining of the cross-shore density gradient. The relative contributions of mixing and straining depends on the value of the Kelvin number K=Lf/(g_Oh)**1/2, where L is the width of the coastal current, f is the Coriolis parameter, g_O is reduced gravity, and h is the plume thickness. For a narrow coastal current (K<1), straining occurs more rapidly than vertical mixing. This is the case in the WACC during Bora events, with strain-induced destratification occurring in less than 24 hours. The straining process limits vertical mixing of the coastal current with the ambient Adriatic water, because once the isopycnals become vertical, no more mixing can occur. This limitation of mixing may explain the persistence of the density anomaly of the coastal current in the presence of high stresses. The straining process also has important implications for sediment transport: destratification allows sediment to be distributed throughout the water column during Bora events, resulting in enhanced down-coast fluxes. The influence of the downwelling dynamics on cross-shore sediment transport is still under examination.

A high resolution WRF model for wind energy forecasting

NASA Astrophysics Data System (ADS)

Vincent, Claire Louise; Liu, Yubao

2010-05-01

The increasing penetration of wind energy into national electricity markets has increased the demand for accurate surface layer wind forecasts. There has recently been a focus on forecasting the wind at wind farm sites using both statistical models and numerical weather prediction (NWP) models. Recent advances in computing capacity and non-hydrostatic NWP models means that it is possible to nest mesoscale models down to Large Eddy Simulation (LES) scales over the spatial area of a typical wind farm. For example, the WRF model (Skamarock 2008) has been run at a resolution of 123 m over a wind farm site in complex terrain in Colorado (Liu et al. 2009). Although these modelling attempts indicate a great hope for applying such models for detailed wind forecasts over wind farms, one of the obvious challenges of running the model at this resolution is that while some boundary layer structures are expected to be modelled explicitly, boundary layer eddies into the inertial sub-range can only be partly captured. Therefore, the amount and nature of sub-grid-scale mixing that is required is uncertain. Analysis of Liu et al. (2009) modelling results in comparison to wind farm observations indicates that unrealistic wind speed fluctuations with a period of around 1 hour occasionally occurred during the two day modelling period. The problem was addressed by re-running the same modelling system with a) a modified diffusion constant and b) two-way nesting between the high resolution model and its parent domain. The model, which was run with horizontal grid spacing of 370 m, had dimensions of 505 grid points in the east-west direction and 490 points in the north-south direction. It received boundary conditions from a mesoscale model of resolution 1111 m. Both models had 37 levels in the vertical. The mesoscale model was run with a non-local-mixing planetary boundary layer scheme, while the 370 m model was run with no planetary boundary layer scheme. It was found that increasing the diffusion constant caused damping of the unrealistic fluctuations, but did not completely solve the problem. Using two-way nesting also mitigated the unrealistic fluctuations significantly. It can be concluded that for real case LES modelling of wind farm circulations, care should be taken to ensure the consistency between the mesoscale weather forcing and LES models to avoid exciting spurious noise along the forcing boundary. The development of algorithms that adequately model the sub-grid-scale mixing that cannot be resolved by LES models is an important area for further research. References Liu, Y. Y._W. Liu, W. Y.Y. Cheng, W. Wu, T. T. Warner and K. Parks, 2009: Simulating intra-farm wind variations with the WRF-RTFDDA-LES modeling system. 10th WRF Users' Workshop, Boulder, C, USA. June 23 - 26, 2009. Skamarock, W., J. Dudhia, D.O. Gill, D.M. Barker, M.G.Duda, X-Y. Huang, W. Wang and J.G. Powers, A Description of the Advanced Research WRF version 3, NCAR Technical Note TN-475+STR, NCAR, Boulder, Colorado, 2008.

Role of wind forcing and eddy activity in the intraseasonal variability of the barrier layer in the South China Sea

NASA Astrophysics Data System (ADS)

Liang, Zhanlin; Xie, Qiang; Zeng, Lili; Wang, Dongxiao

2018-03-01

In addition to widely discussed seasonal variability, the barrier layer (BL) of the South China Sea (SCS) also exhibits significant intraseasonal variability (ISV) and plays an important role in the upper heat and salt balances. The characteristics and mechanisms of spatiotemporal variations in the BL are investigated using an eddy-resolving ocean model OFES (OGCM For the Earth Simulator) ouput and related atmospheric and oceanic processes. The active intraseasonal BL variability in the SCS occurs mainly during the late summer/autumn and winter and exhibits remarkable differences between these two periods. The BL ISV in late summer/autumn occurs in the southern basin, while in winter, it is limited to the northwestern basin. To further discuss the evolution and driving thermodynamic mechanisms, we quantify the processes that control the variability of intraseasonal BL. Different mechanisms for the intraseasonal BL variability for these two active periods are investigated based on the case study and composite analysis. During late summer/autumn, the active BL in the southern basin is generated by advected and local freshwater, and then decays rapidly with the enhanced wind. In winter, anticyclonic eddy activity is associated with the evolution of the BL by affecting the thermocline and halocline variations, while wind stress and wind stress curl have no obvious influence on BL.

A time-dependent, three-dimensional model of the Delaware Bay and River system. Part 2: Three-dimensional flow fields and residual circulation

NASA Astrophysics Data System (ADS)

Galperin, Boris; Mellor, George L.

1990-09-01

The three-dimensional model of Delaware Bay, River and adjacent continental shelf was described in Part 1. Here, Part 2 of this two-part paper demonstrates that the model is capable of realistic simulation of current and salinity distributions, tidal cycle variability, events of strong mixing caused by high winds and rapid salinity changes due to high river runoff. The 25-h average subtidal circulation strongly depends on the wind forcing. Monthly residual currents and salinity distributions demonstrate a classical two-layer estuarine circulation wherein relatively low salinity water flows out at the surface and compensating high salinity water from the shelf flows at the bottom. The salinity intrusion is most vigorous along deep channels in the Bay. Winds can generate salinity fronts inside and outside the Bay and enhance or weaken the two-layer circulation pattern. Since the portion of the continental shelf included in the model is limited, the model shelf circulation is locally wind-driven and excludes such effects as coastally trapped waves and interaction with Gulf Stream rings; nevertheless, a significant portion of the coastal elevation variability is hindcast by the model. Also, inclusion of the shelf improves simulation of salinity inside the Bay compared with simulations where the salinity boundary condition is specified at the mouth of the Bay.

Decoupling analysis of a novel bearingless flux-switching permanent magnet motor

NASA Astrophysics Data System (ADS)

Zhao, Chenyin; Zhu, Huangqiu; Qin, Yuemei

2017-05-01

In this paper, a novel 12/10 stator/rotor pole bearingless flux-switching permanent magnet (BFSPM) motor is proposed to overcome the drawbacks of rotor permanent magnet type bearingless motors. The basic motor configuration, including motor configuration and winding configuration, is introduced firstly. Then, based on the principle of reverse direction magnetization for symmetrical rotor teeth, the radial suspension forces generation principle is analyzed in detail. Finally, decoupling performances between suspension force windings and torque windings are investigated. The results show that the proposed BFSPM not only ensures the merits of high torque output capability compared with conventional 12/10 stator/rotor pole FSPM motor, but also achieves stable radial suspension forces which have little mutual effect with torque. The validity of the proposed structure has been verified by finite element analysis (FEA).

Particular Solutions in Four body problem with solar wind drag

NASA Astrophysics Data System (ADS)

Kumari, Reena; Singh Kushvah, Badam

2012-07-01

To study the motion of a group of celestial objects/bodies interacting with each other under gravitational attraction. We formulated a four body problem with solar wind drag of one radiating body, rotating about their common center of mass with central configuration. We suppose that the governing forces of the motion of four body problems are mutual gravitational attractions of bodies and drag force of radiating body. Firstly, we derive the equations of motion using new co-ordinates for the four body problem. Again, we find the integrals of motions under different cases regarding to the mass of the bodies. Then we find the zero velocity surfaces and particular solutions. Finally, we examined the effect of solar wind drag on the motion of the four body problem. Keywords: Four Body Problem; Particular Solutions; Radiation Force; Zero Velocity Surfaces.

Nonstationary Gravity Wave Forcing of the Stratospheric Zonal Mean Wind

NASA Technical Reports Server (NTRS)

Alexander, M. J.; Rosenlof, K. H.

1996-01-01

The role of gravity wave forcing in the zonal mean circulation of the stratosphere is discussed. Starting from some very simple assumptions about the momentum flux spectrum of nonstationary (non-zero phase speed) waves at forcing levels in the troposphere, a linear model is used to calculate wave propagation through climatological zonal mean winds at solstice seasons. As the wave amplitudes exceed their stable limits, a saturation criterion is imposed to account for nonlinear wave breakdown effects, and the resulting vertical gradient in the wave momentum flux is then used to estimate the mean flow forcing per unit mass. Evidence from global, assimilated data sets are used to constrain these forcing estimates. The results suggest the gravity-wave-driven force is accelerative (has the same sign as the mean wind) throughout most of the stratosphere above 20 km. The sense of the gravity wave forcing in the stratosphere is thus opposite to that in the mesosphere, where gravity wave drag is widely believed to play a principal role in decelerating the mesospheric jets. The forcing estimates are further compared to existing gravity wave parameterizations for the same climatological zonal mean conditions. Substantial disagreement is evident in the stratosphere, and we discuss the reasons for the disagreement. The results suggest limits on typical gravity wave amplitudes near source levels in the troposphere at solstice seasons. The gravity wave forcing in the stratosphere appears to have a substantial effect on lower stratospheric temperatures during southern hemisphere summer and thus may be relevant to climate.

Comparison of the NASA Common Research Model European Transonic Wind Tunnel Test Data to NASA Test Data

NASA Technical Reports Server (NTRS)

Rivers, Melissa; Quest, Juergen; Rudnik, Ralf

2015-01-01

Experimental aerodynamic investigations of the NASA Common Research Model have been conducted in the NASA Langley National Transonic Facility, the NASA Ames 11-ft wind tunnel, and the European Transonic Wind Tunnel. In the NASA Ames 11-ft wind tunnel, data have been obtained at only a chord Reynolds number of 5 million for a wing/body/tail = 0 degree incidence configuration. Data have been obtained at chord Reynolds numbers of 5, 19.8 and 30 million for the same configuration in the National Transonic Facility and in the European Transonic Facility. Force and moment, surface pressure, wing bending and twist, and surface flow visualization data were obtained in all three facilities but only the force and moment and surface pressure data are presented herein.

Early Student Support for a Process Study of Oceanic Responses to Typhoons

DTIC Science & Technology

2015-06-21

responses to tropical cyclone forcing are surface waves, wind-driven currents, shear and turbulence, and inertial currents. Quantifying the effect ...Cd is estimated assuming a balance between the time rate change of the depth-integrated horizontal momentum, Coriolis force, and the wind stress. This...negligible pressure gradient effect . Most of the observed horizontal kinetic energy is within the upper 100 m. The available potential energy and

A Case Study on the Need for and Availability of Patient Tracking Systems

DTIC Science & Technology

2007-06-01

Information Carrier RFID Radio Frequency Infrared Device TacMedCS The Tactical Medical Coordination System TATRC Army’s Telemedicine and Advanced...mph near Buras-Triumph, Louisiana.4 At landfall, hurricane-force winds extended outward 120 miles from the center of the storm. Katrina maintained...hurricane force winds to Meridian, Mississippi more than 150 miles inland. Katrina was downgraded to a tropical depression near Clarksville

Numerical simulation of a flow past a triangular sail-type blade of a wind generator using the ANSYS FLUENT software package

NASA Astrophysics Data System (ADS)

Kusaiynov, K.; Tanasheva, N. K.; Min'kov, L. L.; Nusupbekov, B. R.; Stepanova, Yu. O.; Rozhkova, A. V.

2016-02-01

An air flow past a single triangular sail-type blade of a wind turbine is analyzed by numerical simulation for low velocities of the incoming flow. The results of numerical simulation indicate a monotonic increase in the drag force and the lift force as functions of the incoming flow; empirical dependences of these quantities are obtained.

Space shuttle solid rocket booster sting interference wind tunnel test analysis

NASA Technical Reports Server (NTRS)

Conine, B.; Boyle, W.

1981-01-01

Wind tunnel test results from shuttle solid rocket booster (SRB) sting interference tests were evaluated, yielding the general influence of the sting on the normal force and pitching moment coefficients and the side force and yawing moment coefficients. The procedures developed to determine the sting interference, the development of the corrected aerodynamic data, and the development of a new SRB aerodynamic mathematical model are documented.

Rotary Balance Wind Tunnel Testing for the FASER Flight Research Aircraft

NASA Technical Reports Server (NTRS)

Denham, Casey; Owens, D. Bruce

2016-01-01

Flight dynamics research was conducted to collect and analyze rotary balance wind tunnel test data in order to improve the aerodynamic simulation and modeling of a low-cost small unmanned aircraft called FASER (Free-flying Aircraft for Sub-scale Experimental Research). The impetus for using FASER was to provide risk and cost reduction for flight testing of more expensive aircraft and assist in the improvement of wind tunnel and flight test techniques, and control laws. The FASER research aircraft has the benefit of allowing wind tunnel and flight tests to be conducted on the same model, improving correlation between wind tunnel, flight, and simulation data. Prior wind tunnel tests include a static force and moment test, including power effects, and a roll and yaw damping forced oscillation test. Rotary balance testing allows for the calculation of aircraft rotary derivatives and the prediction of steady-state spins. The rotary balance wind tunnel test was conducted in the NASA Langley Research Center (LaRC) 20-Foot Vertical Spin Tunnel (VST). Rotary balance testing includes runs for a set of given angular rotation rates at a range of angles of attack and sideslip angles in order to fully characterize the aircraft rotary dynamics. Tests were performed at angles of attack from 0 to 50 degrees, sideslip angles of -5 to 10 degrees, and non-dimensional spin rates from -0.5 to 0.5. The effects of pro-spin elevator and rudder deflection and pro- and anti-spin elevator, rudder, and aileron deflection were examined. The data are presented to illustrate the functional dependence of the forces and moments on angle of attack, sideslip angle, and angular rate for the rotary contributions to the forces and moments. Further investigation is necessary to fully characterize the control effectors. The data were also used with a steady state spin prediction tool that did not predict an equilibrium spin mode.

Propagation of the Sea of Azov plume in the Black Sea and its relation with atmospheric forcing

NASA Astrophysics Data System (ADS)

Zavialov, Ivan; Osadchiev, Alexander

2017-04-01

This work is devoted to research of the influence of wind forcing on propagation of the Sea of Azov water plume in the Black Sea. The Sea of Azov water is characterized by relatively low salinity and high concentrations of suspended matter, terrigenic nutrients, and anthropogenic pollutants. Thus, the Sea of Azov inflow has significant impacts on physical, chemical, and biological processes in the Black Sea. The increased concentration of the suspended matter in the Sea of Azov plume allows to determine accurately its borders based on remote sensing data. For this purpose, data of the satellite color scanner MERIS/EnviSat with 300-meter spatial resolution were used. Atmospheric forcing on the Sea of Azov plume was investigated with the data of 6-hour reanalysis of winds (MERRA and NCAR/NCEP) with spatial resolution at 1/2 degrees in latitude and 2/3 degrees in longitude. Based on satellite images and wind reanalysis data for 2002-2012 period, it was established that the Azov Sea water inflow is favored by strong N and NE winds, which prevail in the region. It is evident in the processed satellite data that the Sea of Azov plume mainly extends along the east coast of the Crimean peninsula. In some cases under sufficiently strong winds, the Azov waters spread to the southern coast of the Crimea, and sometimes even to its south-west extremity. Factors influencing the propagation of the Azov Sea plume include intensity of water exchange between the Azov and the Black seas, the Rim Current, mesoscale eddies and other dynamic processes. However, the study demonstrated that the influence of wind forcing is dominant. Empirical regressions are derived expressing the dependence of the Azov plume area and its orientation on the magnitude and directions of the wind stress. Satellite-derived statistics of the Azov plume in the Black Sea characteristics are obtained.

Aerodynamic flight evaluation analysis and data base update

NASA Technical Reports Server (NTRS)

Boyle, W. W.; Miller, M. S.; Wilder, G. O.; Reheuser, R. D.; Sharp, R. S.; Bridges, G. I.

1989-01-01

Research was conducted to determine the feasibility of replacing the Solid Rocket Boosters on the existing Space Shuttle Launch Vehicle (SSLV) with Liquid Rocket Boosters (LRB). As a part of the LRB selection process, a series of wind tunnel tests were conducted along with aero studies to determine the effects of different LRB configurations on the SSLV. Final results were tabulated into increments and added to the existing SSLV data base. The research conducted in this study was taken from a series of wind tunnel tests conducted at Marshall's 14-inch Trisonic Wind Tunnel. The effects on the axial force (CAF), normal force (CNF), pitching moment (CMF), side force (CY), wing shear force (CSR), wing torque moment (CTR), and wing bending moment (CBR) coefficients were investigated for a number of candidate LRB configurations. The aero effects due to LRB protuberances, ET/LRB separation distance, and aft skirts were also gathered from the tests. Analysis was also conducted to investigate the base pressure and plume effects due to the new booster geometries. The test results found in Phases 1 and 2 of wind tunnel testing are discussed and compared. Preliminary LRB lateral/directional data results and trends are given. The protuberance and gap/skirt effects are discussed. The base pressure/plume effects study is discussed and results are given.

Oceanic response to buoyancy, wind and tidal forcing in a Greenlandic glacial fjord

NASA Astrophysics Data System (ADS)

Carroll, D.; Sutherland, D.; Shroyer, E.; Nash, J. D.

2013-12-01

The Greenland Ice Sheet is losing mass at an accelerating rate. This acceleration may in part be due to changes in oceanic heat transport to marine-terminating outlet glaciers. Ocean heat transport to glaciers depends upon fjord dynamics, which include buoyancy-driven estuarine exchange flow, tides, internal waves, turbulent mixing, and connections to the continental shelf. A 3D model of Rink Isbrae fjord in West Greenland is used to investigate the role of ocean forcing on heat transport to the glacier face. Initial conditions are prescribed from oceanographic field data collected in Summer 2013; wind and tidal forcing, along with meltwater flux, are varied in individual model runs. Subglacial meltwater flux values range from 25-500 m3 s-1. For low discharge values, a subsurface plume drives circulation in the fjord. Our simulations indicate that offshore wind forcing is the dominant mechanism for exchange flow between the fjord and the continental shelf. These results show that glacial fjord circulation is a complex, 3D process with multi-cell estuarine circulation and large velocity shears due to coastal winds. Our results are a first step towards a realistic 3D representation of a high-latitude glacial fjord in a numerical model, and will provide insight to future observational studies.

Inner Structure of CME Shock Fronts Revealed by the Electromotive Force and Turbulent Transport Coefficients in Helios-2 Observations

NASA Astrophysics Data System (ADS)

Bourdin, Philippe-A.; Hofer, Bernhard; Narita, Yasuhito

2018-03-01

Electromotive force is an essential quantity in dynamo theory. During a coronal mass ejection (CME), magnetic helicity gets decoupled from the Sun and advected into the heliosphere with the solar wind. Eventually, a heliospheric magnetic transient event might pass by a spacecraft, such as the Helios space observatories. Our aim is to investigate the electromotive force, the kinetic helicity effect (α term), the turbulent diffusion (β term), and the cross-helicity effect (γ term) in the inner heliosphere below 1 au. We set up a one-dimensional model of the solar wind velocity and magnetic field for a hypothetic interplanetary CME. Because turbulent structures within the solar wind evolve much slower than this structure needs to pass by the spacecraft, we use a reduced curl operator to compute the current density and vorticity. We test our CME shock-front model against an observed magnetic transient that passes by the Helios-2 spacecraft. At the peak of the fluctuations in this event we find strongly enhanced α, β, and γ terms, as well as a strong peak in the total electromotive force. Our method allows us to automatically identify magnetic transient events from any in situ spacecraft observations that contain magnetic field and plasma velocity data of the solar wind.

A sigma-coordinate primitive equation model for studying the circulation in the South Atlantic Part II: Meridional transports and seasonal variability

NASA Astrophysics Data System (ADS)

Marchesiello, P.; Barnier, B.; de Miranda, A. P.

1998-04-01

The mean and seasonal variability of the circulation and meridional heat transport in the South Atlantic are investigated using a set of numerical experiments. The primitive equation model uses a topography-following (sigma) coordinate. The model domain is limited to the South Atlantic basin. Artificial boundaries at Drake Passage, between Brazil and Angola, and between South Africa and Antarctica are treated as open boundaries. Finally, recent and self-consistent estimates of seasonal fluxes are used to define a model-dependent atmospheric forcing. Quasi-diagnostic simulations forced by constant climatological winds are first conducted to determine the sensitivity of model solutions to bottom topography smoothing, and to diagnose meridional fluxes from a mass field that is relaxed to the annual climatology of Levitus (1982). Model results show good agreement with known climatological circulation features in this basin, especially in the Confluence Region, where coarse resolution models usually give smooth structures. Sensitivity studies show that the more detailed features of the circulation are influenced by the model bathymetry. The model simulates a meridional circulation whose upper branch (the return flow that balances the southward flow of North Atlantic Deep Water) is composed of Intermediate (IW) and Thermocline (TW) Waters. The transport of IW is found to be predominant, and the value of meridional heat transport consequently falls within the low estimates. We notice that the meridional heat balance is sensitive to the position of the Confluence. When this region occurs too far south, the amount of IW contributing to the return flow of the overturning cell is reduced. Prognostic simulations forced by seasonal winds and heat fluxes are studied to quantify the impact of wind forcing on the circulation in the South Atlantic. Particular attention is focused on meridional transports at 30°S. Analysis of the mean annual circulation confirms that the upper branch of the meridional circulation is predominantly composed of IW (9 Sv), rather than TW (5.3 Sv). The mean transport of the lower branch is 16 Sv, in agreement with recent estimates by Schlitzer (1996). The annual meridional heat transport (0.29 PW) is still within the low estimates, but agrees well with other estimates that give a dominant role to IW (Rintoul, 1991). Original results also concern the variability of the upper branch of the meridional circulation. It is shown that the wind creates seasonal variability in the Subtropical Gyre, which has a marked impact on the water mass balance in the South Atlantic. In winter, a large convergence to the north of the Subtropical Gyre (27°S) reduces the northward flow of IW, whereas stronger Ekman pumping favors an equatorward transport of TW. In summer, this convergence disappears and a larger transport of IW is allowed. Thus a more complex scheme is proposed for the meridional circulation, in which local wind forcing in the South Atlantic Basin has a significant role in preconditioning the surface waters of the global overturning cell.

Lift capability prediction for helicopter rotor blade-numerical evaluation

NASA Astrophysics Data System (ADS)

Rotaru, Constantin; Cîrciu, Ionicǎ; Luculescu, Doru

2016-06-01

The main objective of this paper is to describe the key physical features for modelling the unsteady aerodynamic effects found on helicopter rotor blade operating under nominally attached flow conditions away from stall. The unsteady effects were considered as phase differences between the forcing function and the aerodynamic response, being functions of the reduced frequency, the Mach number and the mode forcing. For a helicopter rotor, the reduced frequency at any blade element can't be exactly calculated but a first order approximation for the reduced frequency gives useful information about the degree of unsteadiness. The sources of unsteady effects were decomposed into perturbations to the local angle of attack and velocity field. The numerical calculus and graphics were made in FLUENT and MAPLE soft environments. This mathematical model is applicable for aerodynamic design of wind turbine rotor blades, hybrid energy systems optimization and aeroelastic analysis.

Assimilative modeling of low latitude ionosphere

NASA Technical Reports Server (NTRS)

Pi, Xiaoqing; Wang, Chunining; Hajj, George A.; Rosen, I. Gary; Wilson, Brian D.; Mannucci, Anthony J.

2004-01-01

In this paper we present an observation system simulation experiment for modeling low-latitude ionosphere using a 3-dimensional (3-D) global assimilative ionospheric model (GAIM). The experiment is conducted to test the effectiveness of GAIM with a 4-D variational approach (4DVAR) in estimation of the ExB drift and thermospheric wind in the magnetic meridional planes simultaneously for all longitude or local time sectors. The operational Global Positioning System (GPS) satellites and the ground-based global GPS receiver network of the International GPS Service are used in the experiment as the data assimilation source. 'The optimization of the ionospheric state (electron density) modeling is performed through a nonlinear least-squares minimization process that adjusts the dynamical forces to reduce the difference between the modeled and observed slant total electron content in the entire modeled region. The present experiment for multiple force estimations reinforces our previous assessment made through single driver estimations conducted for the ExB drift only.

Wind energy resource modelling in Portugal and its future large-scale alteration due to anthropogenic induced climate changes =

NASA Astrophysics Data System (ADS)

Carvalho, David Joao da Silva

The high dependence of Portugal from foreign energy sources (mainly fossil fuels), together with the international commitments assumed by Portugal and the national strategy in terms of energy policy, as well as resources sustainability and climate change issues, inevitably force Portugal to invest in its energetic self-sufficiency. The 20/20/20 Strategy defined by the European Union defines that in 2020 60% of the total electricity consumption must come from renewable energy sources. Wind energy is currently a major source of electricity generation in Portugal, producing about 23% of the national total electricity consumption in 2013. The National Energy Strategy 2020 (ENE2020), which aims to ensure the national compliance of the European Strategy 20/20/20, states that about half of this 60% target will be provided by wind energy. This work aims to implement and optimise a numerical weather prediction model in the simulation and modelling of the wind energy resource in Portugal, both in offshore and onshore areas. The numerical model optimisation consisted in the determination of which initial and boundary conditions and planetary boundary layer physical parameterizations options provide wind power flux (or energy density), wind speed and direction simulations closest to in situ measured wind data. Specifically for offshore areas, it is also intended to evaluate if the numerical model, once optimised, is able to produce power flux, wind speed and direction simulations more consistent with in situ measured data than wind measurements collected by satellites. This work also aims to study and analyse possible impacts that anthropogenic climate changes may have on the future wind energetic resource in Europe. The results show that the ECMWF reanalysis ERA-Interim are those that, among all the forcing databases currently available to drive numerical weather prediction models, allow wind power flux, wind speed and direction simulations more consistent with in situ wind measurements. It was also found that the Pleim-Xiu and ACM2 planetary boundary layer parameterizations are the ones that showed the best performance in terms of wind power flux, wind speed and direction simulations. This model optimisation allowed a significant reduction of the wind power flux, wind speed and direction simulations errors and, specifically for offshore areas, wind power flux, wind speed and direction simulations more consistent with in situ wind measurements than data obtained from satellites, which is a very valuable and interesting achievement. This work also revealed that future anthropogenic climate changes can negatively impact future European wind energy resource, due to tendencies towards a reduction in future wind speeds especially by the end of the current century and under stronger radiative forcing conditions.

ARL Summer Student Research Symposium. Volume 2: Compendium of Abstracts

DTIC Science & Technology

2012-08-01

7 Acoustic Localization with Compensation for Wind Au, Brandon Accurate localization of targets is difficult, as we are often unaware of all the...gathered by the arrays. However, many sources of signal interference add noise. While wind will have a negligible effect on sensors close to the...error over 1 m. However, wind data is often not collected or changes rapidly, so blind wind estimation is calculated to best fit the given data. The

Rate of rotation measurement using back-EMFS associated with windings of a brushless DC motor

NASA Technical Reports Server (NTRS)

Howard, David E. (Inventor)

2000-01-01

A system and method are provided for measuring rate of rotation. A brushless DC motor is rotated and produces a back electromagnetic force (emf) on each winding thereof. Each winding's back-emf is integrated and multiplied by the back-emf associated with an adjacent winding. The multiplied outputs associated with each winding are combined to produce a directionally sensitive DC output proportional only to the rate of rotation of the motor's shaft.

Observations of currents and density structure across a buoyant plume front

USGS Publications Warehouse

Gelfenbaum, G.; Stumpf, R.P.

1993-01-01

Observations of the Mobile Bay, Alabama, plume during a flood event in April 1991 reveal significant differences in the current field on either side of a front associated with the buoyant plume. During a strong southeasterly wind, turbid, low salinity water from Mobile Bay was pushed through an opening in the west side of the ebb-tidal delta and moved parallel to the coast. A stable front developed between the low salinity water of the buoyant plume (11‰) and the high salinity coastal water (>23‰) that was being forced landward by the prevailing winds. Despite the shallow water depth of 6 m, measurements of currents, temperature, and salinity show large shears and density gradients in both the vertical and the horizontal directions. At a station outside of the buoyant plume, currents at 0.5 m and 1.5 m below the surface were in the same direction as the wind. Inside the plume, however, currents at 0.5 m below the surface were parallel to the coast, 45°, off the direction of the wind and the magnitude was 45% larger than the magnitude of the surface currents outside the plume. Beneath the level of the plume, the currents were identical to the wind-driven currents in the ambient water south of the front. Our observations suggest that the wind-driven surface currents of the ambient water converged with the buoyant plume at the front and were subducted beneath the plume. The motion of the ambient coastal surface water was in the direction of the local wind stress, however, the motion of the plume had no northerly component of motion. The plume also did not show any flow toward the front, suggesting a balance between the northerly component of wind stress and the southerly component of buoyant spreading. In addition, the motion of the plume did not appear to affect the motion of the underlying ambient water, suggesting a lack of mixing between the two waters.

Wind-driven coastal upwelling and westward circulation in the Yucatan shelf

NASA Astrophysics Data System (ADS)

Ruiz-Castillo, Eugenio; Gomez-Valdes, Jose; Sheinbaum, Julio; Rioja-Nieto, Rodolfo

2016-04-01

The wind-driven circulation and wind-induced coastal upwelling in a large shelf sea with a zonally oriented coast are examined. The Yucatan shelf is located to the north of the Yucatan peninsula in the eastern Gulf of Mexico. This area is a tropical shallow body of water with a smooth sloping bottom and is one of the largest shelves in the world. This study describes the wind-driven circulation and wind-induced coastal upwelling in the Yucatan shelf, which is forced by easterly winds throughout the year. Data obtained from hydrographic surveys, acoustic current profilers and environmental satellites are used in the analysis. Hydrographic data was analyzed and geostrophic currents were calculated in each survey. In addition an analytical model was applied to reproduce the currents. The results of a general circulation model were used with an empirical orthogonal function analysis to study the variability of the currents. The study area is divided in two regions: from the 40 m to the 200 m isobaths (outer shelf) and from the coast to the 40 m isobath (inner shelf). At the outer shelf, observations revealed upwelling events throughout the year, and a westward current with velocities of approximately 0.2 m s-1 was calculated from the numerical model output and hydrographic data. In addition, the theory developed by Pedlosky (2007) for a stratified fluid along a sloping bottom adequately explains the current's primary characteristics. The momentum of the current comes from the wind, and the stratification is an important factor in its dynamics. At the inner shelf, observations and numerical model output show a wind-driven westward current with maximum velocities of 0.20 m s-1. The momentum balance in this region is between local acceleration and friction. A cold-water band is developed during the period of maximum upwelling.

A contrast between nocturnal flow regimes: Observations and modeling simulations of katabatic intrusions in the Laramie Valley

NASA Astrophysics Data System (ADS)

Juliano, Timothy W.

Katabatic winds commonly occur in mountainous regions under statically stable conditions when a sufficient deficit exists in the net radiation budget. Observations of these stable boundary layer (SBL) downslope flows have extended back to the 1930s. Their interactions with other SBL processes, including cold air pools (CAPs) and mountain waves, are quite complex, however, and have only more recently been deeply investigated. The University of Wyoming (UW) wind tower (WT) and flux tower (WT), situated in the Laramie Valley, were utilized in examining a dataset spanning from 14 December 2011 to 12 September 2013. A set of criteria were developed to determine katabatic intrusion events, and establish a climatology of these events, at the WT. The 21-22 December 2012 nighttime period was then studied in detail using data from the aforementioned towers in addition to weather stations throughout the Laramie Valley and the Weather Research and Forecasting (WRF) model. Both observations and modeling results indicated a competition between two strongly contrasting flow regimes: synoptic and katabatic. The synoptic regime was characterized by strong, southwesterly winds, warm temperatures, and turbulent flow, while the katabatic regime featured weaker, southeasterly winds, cooler temperatures, and intermittently turbulent flow. Sonic and propeller anemometers on the WT elucidated the chaotic transition between the regimes. At the WT, it was found that between regimes the wind speed decreased by up to 60%, wind direction often shifted over 120°, and potential temperature usually decreased more than 2°C. The katabatic wind depth was postulated to be variable in time and space, with its head sloping towards the trailing CAP. Topographically generated mountain waves and local terrain forcing are suspected to play an integral role in the development and evolution of the katabatic wind in the Laramie Valley. Results from this research yield promising insight into the intricate relationships between various SBL processes in complex terrain.

Measuring wind turbine wakes and unsteady loading in a micro wind farm model

NASA Astrophysics Data System (ADS)

Bossuyt, Juliaan; Meneveau, Charles; Meyers, Johan

2014-11-01

Very large wind farms, approximating the ``infinite'' asymptotic limit, are often studied with LES using periodic boundary conditions. In order to create an experimental realization of such large wind-turbine arrays in a wind tunnel experiment including over 100 turbines, a very small-scale turbine model based on a 3 cm diameter porous disk is designed. The porous disc matches a realistic thrust coefficient between 0.75--0.85, and the far wake flow characteristics of a rotating wind turbine. As a first step, we characterize the properties of a single model turbine. Hot-wire measurements are performed for uniform inflow conditions with different background turbulence intensity levels. Strain gage measurements are used to measure the mean value and power spectra of the thrust force, power output and wind velocity in front of the turbine. The dynamics of the wind turbine are modeled making it possible to measure force spectra at least up to the natural frequency of the model. This is shown by reproducing the -5/3 spectrum from the incoming flow and the vortex shedding signatures of an upstream obstruction. An array with a large number of these instrumented model turbines is placed in JHU's Corrsin wind tunnel, to study effects of farm layout on total power output and turbine loading. Work supported by ERC (ActiveWindFarms, Grant No: 306471), and by NSF (CBET-113380 and IIA-1243482).

Winds in the meteor zone over Trivandrum

NASA Astrophysics Data System (ADS)

Reddi, C. R.; Rajeev, K.; Ramakumar, Geetha

1991-04-01

The height profiles of the zonal and meridional wind obtained from the meteor wind radar data recorded at Trivandrum (8 deg 36 min N, 77 deg E) are presented. Large wind shears were found to exist in the meteor zone over Trivandrum. The profiles showed quasi-sinusoidal variations with altitude and vertical wavelength of the oscillation in the range 15-25 km. Further, there was a large day-to-day variability in the profiles obtained for the same local time on consecutive days. The results are discussed in the light of the winds due to tides and equatorial waves in the low latitudes. The implications of the large wind shears with reference to the local wind effects on the equatorial electrojet are outlined.

Spectral wave dissipation by submerged aquatic vegetation in a back-barrier estuary

USGS Publications Warehouse

Nowacki, Daniel J.; Beudin, Alexis; Ganju, Neil K.

2017-01-01

Submerged aquatic vegetation is generally thought to attenuate waves, but this interaction remains poorly characterized in shallow-water field settings with locally generated wind waves. Better quantification of wave–vegetation interaction can provide insight to morphodynamic changes in a variety of environments and also is relevant to the planning of nature-based coastal protection measures. Toward that end, an instrumented transect was deployed across a Zostera marina (common eelgrass) meadow in Chincoteague Bay, Maryland/Virginia, U.S.A., to characterize wind-wave transformation within the vegetated region. Field observations revealed wave-height reduction, wave-period transformation, and wave-energy dissipation with distance into the meadow, and the data informed and calibrated a spectral wave model of the study area. The field observations and model results agreed well when local wind forcing and vegetation-induced drag were included in the model, either explicitly as rigid vegetation elements or implicitly as large bed-roughness values. Mean modeled parameters were similar for both the explicit and implicit approaches, but the spectral performance of the explicit approach was poor compared to the implicit approach. The explicit approach over-predicted low-frequency energy within the meadow because the vegetation scheme determines dissipation using mean wavenumber and frequency, in contrast to the bed-friction formulations, which dissipate energy in a variable fashion across frequency bands. Regardless of the vegetation scheme used, vegetation was the most important component of wave dissipation within much of the study area. These results help to quantify the influence of submerged aquatic vegetation on wave dynamics in future model parameterizations, field efforts, and coastal-protection measures.

Wind tunnel investigation of rotor lift and propulsive force at high speed: Data analysis

NASA Technical Reports Server (NTRS)

Mchugh, F.; Clark, R.; Soloman, M.

1977-01-01

The basic test data obtained during the lift-propulsive force limit wind tunnel test conducted on a scale model CH-47b rotor are analyzed. Included are the rotor control positions, blade loads and six components of rotor force and moment, corrected for hub tares. Performance and blade loads are presented as the rotor lift limit is approached at fixed levels of rotor propulsive force coefficients and rotor tip speeds. Performance and blade load trends are documented for fixed levels of rotor lift coefficient as propulsive force is increased to the maximum obtainable by the model rotor. Test data is also included that defines the effect of stall proximity on rotor control power. The basic test data plots are presented in volumes 2 and 3.

Launch Method for Kites in Low-Wind or No-Wind Conditions

NASA Technical Reports Server (NTRS)

Bland, Geoffrey; Miles, Ted

2012-01-01

Airborne observations using lightweight camera systems are desirable for a variety of applications. This system was contemplated as a method to provide a simple remote sensing aerial platform. Kites have been successfully employed for aerial observations, but have historically required natural wind or towing to become airborne. This new method negates this requirement, and widens the applicability of kites for carrying instrumentation. Applicability is primarily limited by the space available on the ground for launching. The innovation is a method for launching kites in low-wind or no-wind conditions. This method will enable instrumentation to be carried aloft using simple (or complex) kite-based systems, to obtain observations from an aerial perspective. This technique will provide access to altitudes of 100 meters or more over any area normally suited for kite flying. The duration of any observation is dependent on wind strength; however, the initial altitude is relatively independent. The system does not require any electrical or combustion-based elements. This technology was developed to augment local-scale airborne measurement capabilities suitable for Earth science research, agricultural productivity, and environmental observations. The method represents an extension of techniques often used in aeronautical applications for launching fixed-wing aircraft, such as sailplanes, using mechanical means not incorporated in the aircraft itself. The innovation consists of an elastic cord (for propulsive force), a tether extension (optional, for additional height), and the kite (instrumentation optional). Operation of the system is accomplished by fixing the elastic cord to ground (or equivalent), attaching the cord with/or without a tether extension to the kite, tensioning the system to store energy, and releasing the kite. The kite will climb until energy is dissipated.

Analysis of a Destructive Wind Storm on 16 November 2008 in Brisbane, Australia

DOE PAGES

Richter, Harald; Peter, Justin; Collis, Scott

2014-08-25

During the late afternoon on 16 November 2008 the Brisbane (Australia) suburb of “The Gap” experienced extensive wind damage caused by an intense local thunderstorm. The CP2 research radar nearby detected near-surface radial velocities exceeding 44 m s -1 above The Gap while hail size reports did not exceed golf ball size, and no tornadoes were reported. This study shows that the storm environment was characterized by a layer of very moist (mixing ratios exceeding 12 g kg -1) near-surface air embedded in strong storm-relative low-level flow, whereas the storm-relative winds aloft were significantly weaker. And while the thermodynamic stormmore » environment contained a range of downdraft promoting ingredients such as a ~4 km high melting level above a ~2 km deep layer with nearly dry adiabatic lapse rates mostly collocated with dry ambient air, a ~1 km deep stable layer near the ground would generally lower expectations of destructive surface winds based on the downburst mechanism. We also found that once observed reflectivities exceed 70 dBZ that downdraft cooling due to hail melting and downdraft acceleration based on hail loading are likely to become non-negligible forcing mechanisms for a strong downdraft. The study found a close proximity of the hydrostatically and dynamically driven mesohigh at the base of the downdraft to a dynamically driven mesolow associated with a radar-observed low-level circulation. This proximity is hypothesized to have been instrumental in the observed anisotropic horizontal acceleration of the near-ground outflow and the ultimate strength of the Gap storm surface winds. Finally, we speculate that the 44 weak storm-relative midlevel winds allowed the downdraft to descend close to the low45 level circulation which set up this strong horizontal perturbation pressure gradient.« less

Directly Driven Ion Outflow

NASA Technical Reports Server (NTRS)

Elliott, H. A.; Comfort, R. H.; Craven, P. D.; Moore, T. E.; Russell, C. T.; Rose, M. Franklin (Technical Monitor)

2001-01-01

We examine ionospheric outflows in the high altitude magnetospheric polar cap during the POLAR satellite's apogee on April 19, 1996 using the Thermal Ion Dynamics Experiment (TIDE) instrument. The elevated levels of O(+) observed in this pass may be due to the geophysical conditions during and prior to the apogee pass. In addition to the high abundance of O(+) relative to H(+), several other aspects of this data are noteworthy. We observe relationships between the density, velocity, and temperature which appear to be associated with perpendicular heating and the mirror force, rather than adiabatic expansion. The H(+) outflow is at a fairly constant flux which is consistent with being source limited by charge exchange at lower altitudes. Local centrifugal acceleration in the polar cap is found to be insufficient to account for the main variations we observe in the outflow velocity. The solar wind speed is high during this pass approximately 700 kilometers per second, and there are Alfve'n waves present in the solar wind such that the solar wind speed and IMF Bx are correlated. In this pass both the H(+) and O(+) outflow velocities correlate with both the solar wind speed and IMF fluctuations. Polar cap magnetometer and Hydra electron data show the same long period wave structure as found in the solar wind and polar cap ion outflow. In addition, the polar cap Poynting flux along the magnetic field direction correlates well with the H(+) temperature (R=0.84). We conclude that the solar wind can drive polar cap ion outflow particularly during polar squalls by setting up a parallel drop that is tens of eV which then causes the ion outflow velocity of O(+) and H(+), the electrons, and magnetic perturbations to vary in a similar fashion.

Surface drifter derived circulation in the northern and middle Adriatic Sea: Response to wind regime and season

USGS Publications Warehouse

Ursella, L.; Poulain, P.-M.; Signell, R.P.

2007-01-01

More than 120 satellite-tracked drifters were deployed in the northern and middle Adriatic (NMA) Sea between September 2002 and November 2003, with the purpose of studying the surface circulation at mesoscale to seasonal scale in relation to wind forcing, river runoff, and bottom topography. Pseudo-Eulerian and Lagrangian statistics were calculated from the low-pass-filtered drifter velocity data between September 2002 and December 2003. The structure of the mean circulation is determined with unprecedented high horizontal resolution by the new data. In particular, mean currents, velocity variance, and kinetic energy levels are shown to be maximal in the Western Adriatic Current (WAC). Separating data into seasons, we found that the mean kinetic energy is maximal in fall, with high values also in winter, while it is significantly weaker in summer. High-resolution Local Area Model Italy winds were used to relate the drifter velocities to the wind fields. The surface currents appear to be significantly influenced by the winds. The mean flow during the northeasterly bora regime shows an intensification of the across-basin recirculating currents. In addition, the WAC is strongly intensified both in intensity and in its offshore lateral extension. In the southeasterly sirocco regime, northward flow without recirculation dominates in the eastern half of the basin, while during northwesterly maestro the WAC is enhanced. Separating the data into low and high Po River discharge rates for low-wind conditions shows that the WAC and the velocity fluctuations in front of the Po delta are stronger for high Po River runoff. Lagrangian covariance, diffusivity, and integral time and space scales are larger in the along-basin direction and are maximal in the southern portion of the WAC. Copyright 2006 by the American Geophysical Union.

Aeroelastic Response from Indicial Functions with a Finite Element Model of a Suspension Bridge

NASA Astrophysics Data System (ADS)

Mikkelsen, O.; Jakobsen, J. B.

2017-12-01

The present paper describes a comprehensive analysis of the aeroelastic bridge response in time-domain, with a finite element model of the structure. The main focus is on the analysis of flutter instability, accounting for the wind forces generated by the bridge motion, including twisting as well as vertical and horizontal translation, i.e. all three global degrees of freedom. The solution is obtained by direct integration of the equations of motion for the bridge-wind system, with motion-dependent forces approximated from flutter derivatives in terms of rational functions. For the streamlined bridge box-girder investigated, the motion dependent wind forces related to the along-wind response are found to have a limited influence on the flutter velocity. The flutter mode shapes in the time-domain and the frequency domain are consistent, and composed of the three lowest symmetrical vertical modes coupled with the first torsional symmetric mode. The method applied in this study provides detailed response estimates and contributes to an increased understanding of the complex aeroelastic behaviour of long-span bridges.

KINEMATIC TREATMENT OF CORONAL MASS EJECTION EVOLUTION IN THE SOLAR WIND

NASA Technical Reports Server (NTRS)

Riley, Pete; Crooker, N. U.

2004-01-01

We present a kinematic study of the evolution of coronal mass ejections (CMEs) in the solar wind. Specifically, we consider the effects of (1) spherical expansion and (2) uniform expansion due to pressure gradients between the interplanetary CME (ICME) and the ambient solar wind. We compare these results with an MHD model that allows us to isolate these effects h m the combined kinematic and dynamical effects, which are included in MHD models. They also provide compelling evidence that the fundamental cross section of so-called "force-free" flux ropes (or magnetic clouds) is neither circular or elliptical, but rather a convex-outward, "pancake" shape. We apply a force-free fit to the magnetic vectors from the MHD simulation to assess how the distortion of the flux rope affects the fit. In spite of these limitations, force-free fits, which are straightforward to apply, do provide an important description of a number of parameters, including the radial dimension, orientation, and chirality of the ICME. Subject headings: MHD - solar wind - Sun: activity - Sun: corona - Sun: coronal mass ejections (CMEs) - On-line material color figures Sun: magnetic fields

Design and calibration of the carousel wind tunnel

NASA Technical Reports Server (NTRS)

Leach, R. N.; Greeley, R.; Iversen, J.; White, B.; Marshall, J. R.

1986-01-01

In the study of planetary aeolian processes the effect of gravity is not readily modeled. Gravity appears in the equations of particle motion along with interparticle forces but the two terms are not separable. A wind tunnel that would permit variable gravity would allow separation of the forces and aid greatly in understanding planetary aeolian processes. The design Carousel Wind Tunnel (CWT) allows for a long flow distance in a small sized tunnel since the test section is a continuo us circuit and allows for a variable pseudo gravity. A prototype design was built and calibrated to gain some understanding of the characteristics of the design and the results presented.

Design and calibration of the carousel wind tunnel

NASA Technical Reports Server (NTRS)

Leach, R. N.; Greeley, Ronald; Iversen, James D.; White, Bruce R.; Marshall, John R.

1987-01-01

In the study of planetary aeolian processes the effect of gravity is not readily modeled. Gravity appears in the equations of particle motion along with interparticle forces but the two terms are not separable. A wind tunnel that would permit variable gravity would allow separation of the forces and aid greatly in understanding planetary aeolian processes. The design of the Carousel Wind Tunnel (CWT) allows for a long flow distance in a small sized tunnel since the test section is a continuous circuit and allows for a variable pseudo-gravity. A prototype design was built and calibrated to gain some understanding of the characteristics of the design and the results presented.

The Global and Local Climatic Response to the Collapse of the West Antarctic Ice Sheet

NASA Astrophysics Data System (ADS)

Huybers, K. M.; Singh, H.; Steiger, N. J.; Frierson, D. M.; Steig, E. J.; Bitz, C. M.

2014-12-01

Glaciologists have suggested that a relatively small external forcing may compromise the stability of the West Antarctic Ice Sheet (WAIS). Further, there is compelling physical evidence that the WAIS has collapsed in the past, at times when the mean global temperature was only a few degrees warmer than it is today. In addition to a rapid increase in global sea level, the collapse of the WAIS could also affect the global circulation of the atmosphere. Ice sheets are some of the largest topographic features on Earth, causing large regional anomalies in albedo and radiative balance. Our work uses idealized aquaplanet models in tandem with a fully coupled ocean/atmosphere/sea-ice model (CCSM4) to compare the atmospheric, radiative, and oceanic response to a complete loss of the WAIS. Initial findings indicate that the loss of the WAIS leads to a weakening and equator-ward shift of the zonal winds, a development of strong zonal asymmetries in the meridional wind, and a northward migration of the Intertropical Convergence Zone. We aim to characterize how the local and global climate is affected by the presence of the WAIS, and how changes in the distribution of Southern Hemisphere ice may be represented in the proxy record.

Wind-tunnel investigation of aerodynamic loading on a 0.237-scale model of a remotely piloted research vehicle with a thick, high-aspect-ratio supercritical wing

NASA Technical Reports Server (NTRS)

Byrdsong, T. A.; Brooks, C. W., Jr.

1983-01-01

Wind-tunnel measurements were made of the wing-surface static-pressure distributions on a 0.237 scale model of a remotely piloted research vehicle equipped with a thick, high-aspect-ratio supercritical wing. Data are presented for two model configurations (with and without a ventral pod) at Mach numbers from 0.70 to 0.92 at angles of attack from -4 deg to 8 deg. Large variations of wing-surface local pressure distributions were developed; however, the characteristic supercritical-wing pressure distribution occurred near the design condition of 0.80 Mach number and 2 deg angle of attack. The significant variations of the local pressure distributions indicated pronounced shock-wave movements that were highly sensitive to angle of attack and Mach number. The effect of the vertical pod varied with test conditions; however at the higher Mach numbers, the effects on wing flow characteristics were significant at semispan stations as far outboard as 0.815. There were large variations of the wing loading in the range of test conditions, both model configurations exhibited a well-defined peak value of normal-force coefficient at the cruise angle of attack (2 deg) and Mach number (0.80).

High-resolution modeling of local air-sea interaction within the Marine Continent using COAMPS

NASA Astrophysics Data System (ADS)

Jensen, T. G.; Chen, S.; Flatau, M. K.; Smith, T.; Rydbeck, A.

2016-12-01

The Maritime Continent (MC) is a region of intense deep atmospheric convection that serves as an important source of forcing for the Hadley and Walker circulations. The convective activity in the MC region spans multiple scales from local mesoscales to regional scales, and impacts equatorial wave propagation, coupled air-sea interaction and intra seasonal oscillations. The complex distribution of islands, shallow seas with fairly small heat storage and deep seas with large heat capacity is challenging to model. Diurnal convection over land-sea is part of a land-sea breeze system on a small scale, and is highly influenced by large variations in orography over land and marginal seas. Daytime solar insolation, run-off from the Archipelago and nighttime rainfall tends to stabilize the water column, while mixing by tidal currents and locally forced winds promote vertical mixing. The runoff from land and rivers and high net precipitation result in fresh water lenses that enhance vertical stability in the water column and help maintain high SST. We use the fully coupled atmosphere-ocean-wave version of the Coupled Ocean-Atmosphere Mesoscale Prediction System (COAMPS) developed at NRL with resolution of a few kilometers to investigate the air-sea interaction associated with the land-sea breeze system in the MC under active and inactive phases of the Madden-Julian Oscillation. The high resolution enables simulation of strong SST gradients associated with local upwelling in deeper waters and strong salinity gradients near rivers and from heavy precipitation.

Winds over Japan.

NASA Astrophysics Data System (ADS)

Plumley, William J.

1994-01-01

Before World War II, weather forecasters had little knowledge of upper-air wind patterns above 20000 feet. Data were seldom avai able at these heights, and the need was not great because commercial aircraft seldom flew at these altitudes. The war in the Pacific changed all that. Wind forecasts for 30000 feet plus became urgent to support the XXI Bomber Command in its bombing mission over Japan.The U.S. Army Air Force Pacific Ocean Area (AAFPOA) placed a Weather Central in the Marianas Islands in 1944 (Saipan in 1944 and Guam in 1945) to provide forecasting support for this mission. A forecasting procedure was put into operation that combined the elements known as "single-station forecasting" and an advanced procedure that used "altirmeter corrections" to analyze upper-airdata and make prognoses. Upper-air charts were drawn for constant pressure surfaces rather than constant height surfaces. The constant pressure surfaces were tied together by means of the atmospheric temperature field represented by specific temperature anomalies between pressure surfaces. Wind forecasts over the Marianas-Japan route made use of space cross sections that provided the data to forecast winds at each 5000-ft level to 35000 ft along the mission flight path. The new procedures allowed the forecaster to construct internally consistent meteorological charts in three dimensions in regions of sparse data.Army air force pilots and their crews from the Marianas were among the first to experience the extreme wind conditions now known as the "jet stream". Air force forecasters demonstrated that, with experience, such winds could reasonably be forecast under difficult operational conditions.

Effects of Sea-Surface Waves and Ocean Spray on Air-Sea Momentum Fluxes

NASA Astrophysics Data System (ADS)

Zhang, Ting; Song, Jinbao

2018-04-01

The effects of sea-surface waves and ocean spray on the marine atmospheric boundary layer (MABL) at different wind speeds and wave ages were investigated. An MABL model was developed that introduces a wave-induced component and spray force to the total surface stress. The theoretical model solution was determined assuming the eddy viscosity coefficient varied linearly with height above the sea surface. The wave-induced component was evaluated using a directional wave spectrum and growth rate. Spray force was described using interactions between ocean-spray droplets and wind-velocity shear. Wind profiles and sea-surface drag coefficients were calculated for low to high wind speeds for wind-generated sea at different wave ages to examine surface-wave and ocean-spray effects on MABL momentum distribution. The theoretical solutions were compared with model solutions neglecting wave-induced stress and/or spray stress. Surface waves strongly affected near-surface wind profiles and sea-surface drag coefficients at low to moderate wind speeds. Drag coefficients and near-surface wind speeds were lower for young than for old waves. At high wind speeds, ocean-spray droplets produced by wind-tearing breaking-wave crests affected the MABL strongly in comparison with surface waves, implying that wave age affects the MABL only negligibly. Low drag coefficients at high wind caused by ocean-spray production increased turbulent stress in the sea-spray generation layer, accelerating near-sea-surface wind. Comparing the analytical drag coefficient values with laboratory measurements and field observations indicated that surface waves and ocean spray significantly affect the MABL at different wind speeds and wave ages.

Calibration Designs for Non-Monolithic Wind Tunnel Force Balances

NASA Technical Reports Server (NTRS)

Johnson, Thomas H.; Parker, Peter A.; Landman, Drew

2010-01-01

This research paper investigates current experimental designs and regression models for calibrating internal wind tunnel force balances of non-monolithic design. Such calibration methods are necessary for this class of balance because it has an electrical response that is dependent upon the sign of the applied forces and moments. This dependency gives rise to discontinuities in the response surfaces that are not easily modeled using traditional response surface methodologies. An analysis of current recommended calibration models is shown to lead to correlated response model terms. Alternative modeling methods are explored which feature orthogonal or near-orthogonal terms.

Characterization of the surface wave variability in the California Current region from satellite altimetry.

NASA Astrophysics Data System (ADS)

Villas Boas, A. B.; Gille, S. T.; Mazloff, M. R.

2016-02-01

Surface gravity waves play a crucial role in upper-ocean dynamics, and they are an important mechanism by which the ocean exchanges energy with the overlying atmosphere. Surface waves are largely wind forced and can also be modulated by ocean currents via nonlinear wave-current interactions, leading to either an amplification or attenuation of the wave amplitude. Even though individual waves cannot be detected by present satellite altimeters, surface waves have the potential to produce a sea-state bias in altimeter measurements and can impact the sea-surface-height spectrum at high wavenumbers or frequencies. Knowing the wave climatology is relevant for the success of future altimeter missions, such as the Surface Water and Ocean Topography (SWOT). We analyse the seasonal, intra-annual and interannual variability of significant wave heights retrieved from over two decades of satellite altimeter data and assess the extent to which the variability of the surface wave field in the California Current region is modulated by the local wind and current fields.

Influence of container shape on scaling of turbulent fluctuations in convection

NASA Astrophysics Data System (ADS)

Foroozani, Najmeh; Niemela, Joseph J.; Armenio, Vincenzo; Sreenivasan, Katepalli R.

2014-11-01

We perform large-eddy simulations of turbulent convection in a cubic enclosure for Rayleigh numbers 1 ×106 <= Ra <= 1 ×1010 and molecular Prandtl number, Pr = 0 . 7 . The simulations were carried out using a second-order-accurate finite-difference method in which subgrid-scale fluxes of momentum and heat were parametrized using a Lagrangian dynamic Smagorinsky model. The scalings of root-mean-square fluctuations of density and velocity in the cell center with Ra differ significantly from those in cylindrical containers, and are in agreement with laboratory observations by, also using a cell with square cross-section. We find that the time-averaged spatial distributions of the local heat flux and temperature fluctuations are inhomogeneous in the horizontal plane, associated with the forced orientation of the mean wind along either one or the other diagonal. Larger values of the steady-state density (temperature) gradients occur at the mid-plane corners of the diagonal opposite to that of the mean wind, due to the presence of strong counter-rotating circulations.

Effect of viscosity of a thermoplastic prepreg and matrix upon winding of rings

NASA Astrophysics Data System (ADS)

Stavrov, V. P.; Markov, A. V.; Zhernovskii, A. V.; Friedrich, K. F.

2000-05-01

The problem of compression of a unidirectional layer and shear of a polymer interlayer during winding of rings is considered. The equations determining the dependence of the layer thickness and stresses on the parameters entering into the power flow law for a prepreg and polymer matrix and on the basic parameters of the winding process—the initial tension of the prepreg, its placement rate, and the radius of a mandrel—are derived. The ring thickness measurements obtained at various temperatures and initial tension forces of plies confirm the adequacy of the model offered. It is found that the viscous properties of the prepreg and matrix upon winding affect the relative change in the layer thickness to a greater extent than the stresses in these layers. With increase in temperature and tension force upon winding, the effect of viscous deformations of the prepreg and matrix increases. A decrease in viscosity and an increase in the tension force of the tape lead to a higher strength of the ring in tension and interlaminar shear; however, the growing percolation of the polymer melt leads to a greater inhomogeneity of the structure of the composite in the ring and to a lower reinforcing effect of the factors mentioned.

Gap Winds in a Fjord: Howe Sound, British Columbia.

NASA Astrophysics Data System (ADS)

Jackson, Peter L.

1993-01-01

Gap, outflow, or Squamish wind, is the cold low level seaward flow of air through fjords which dissect the coastal mountain barrier of northwestern North America. These flows, occurring mainly during winter, can be strong, threatening safety, economic activity and comfort. Howe Sound gap winds were studied using a combination of observations and several types of models. Observations of winds in Howe Sound showed that gap wind strength varied considerably along the channel, across the channel and vertically. Generally, winds increase down the channel, are strongest along the eastern side, and are below 1000 m depth. Observations were unable to answer all questions about gap winds due to data sparseness, particularly in the vertical direction. Therefore, several modelling approaches were used. The modelling began with a complete 3-dimensional quasi-Boussinesq model (CSU RAMS) and ended with the creation and testing of models which are conceptually simpler, and more easily interpreted and manipulated. A gap wind simulation made using RAMS was shown to be mostly successful by statistical evaluation compared to other mesoscale simulations, and by visual inspection of the fields. The RAMS output, which has very high temporal and spatial resolution, provided much additional information about the details of gap flow. In particular, RAMS results suggested a close analogy between gap wind and hydraulic channel flow, with hydraulic features such as supercritical flow and hydraulic jumps apparent. These findings imply gap wind flow could potentially be represented by much simpler models. The simplest possible models containing pressure gradient, advection and friction but not incorporating hydraulic effects, were created, tested, and found lacking. A hydraulic model, which in addition incorporates varying gap wind height and channel geometry, was created and shown to successfully simulate gap winds. Force balance analysis from RAMS and the hydraulic model showed that pressure gradient and advection are the most important forces, followed by friction which becomes an important force in fast supercritical flow. The sensitivity of gap wind speed to various parameters was found from sensitivity tests using the hydraulic model. Results indicated that gap wind speed increases with increasing boundary layer height and speed at the head of channel, and increasing synoptic pressure gradient. Gap wind speed decreases with increasing friction, and increasing boundary layer height at the seaward channel end. Increasing temperature differences between the cold gap wind air and the warmer air aloft was found to increase the variability of the flow--higher maximum but lower mean wind speeds.

The 2014-2015 warming anomaly in the Southern California Current System observed by underwater gliders

NASA Astrophysics Data System (ADS)

Zaba, Katherine D.; Rudnick, Daniel L.

2016-02-01

Large-scale patterns of positive temperature anomalies persisted throughout the surface waters of the North Pacific Ocean during 2014-2015. In the Southern California Current System, measurements by our sustained network of underwater gliders reveal the coastal effects of the recent warming. Regional upper ocean temperature anomalies were greatest since the initiation of the glider network in 2006. Additional observed physical anomalies included a depressed thermocline, high stratification, and freshening; induced biological consequences included changes in the vertical distribution of chlorophyll fluorescence. Contemporaneous surface heat flux and wind strength perturbations suggest that local anomalous atmospheric forcing caused the unusual oceanic conditions.

Characterizing overwater roughness Reynolds number during hurricanes

NASA Astrophysics Data System (ADS)

Hsu, S. A.; Shen, Hui; He, Yijun

2017-11-01

The Reynolds number, which is the dimensionless ratio of the inertial force to the viscous force, is of great importance in the theory of hydrodynamic stability and the origin of turbulence. To investigate aerodynamically rough flow over a wind sea, pertinent measurements of wind and wave parameters from three data buoys during Hurricanes Kate, Lili, Ivan, Katrina, Rita, and Wilma are analyzed. It is demonstrated that wind seas prevail when the wind speed at 10 m and the wave steepness exceed 9 m s-1 and 0.020, respectively. It is found that using a power law the roughness Reynolds number is statistically significantly related to the significant wave height instead of the wind speed as used in the literature. The reason for this characterization is to avoid any self-correlation between Reynolds number and the wind speed. It is found that although most values of R_{*} were below 500, they could reach to approximately 1000 near the radius of maximum wind. It is shown that, when the significant wave height exceeds approximately 2 m in a wind sea, the air flow over that wind sea is already under the fully rough condition. Further analysis of simultaneous measurements of wind and wave parameters using the logarithmic law indicates that the estimated overwater friction velocity is consistent with other methods including the direct (eddy-covariance flux) measurements, the atmospheric vorticity approach, and the sea-surface current measurements during four slow moving super typhoons with wind speed up to 70 m s-1.

Flow deflection over a foredune

NASA Astrophysics Data System (ADS)

Hesp, Patrick A.; Smyth, Thomas A. G.; Nielsen, Peter; Walker, Ian J.; Bauer, Bernard O.; Davidson-Arnott, Robin

2015-02-01

Flow deflection of surface winds is common across coastal foredunes and blowouts. Incident winds approaching obliquely to the dune toe and crestline tend to be deflected towards a more crest-normal orientation across the stoss slope of the foredune. This paper examines field measurements for obliquely incident winds, and compares them to computational fluid dynamics (CFD) modelling of flow deflection in 10° increments from onshore (0°) to alongshore (90°) wind approach angles. The mechanics of flow deflection are discussed, followed by a comparative analysis of measured and modelled flow deflection data that shows strong agreement. CFD modelling of the full range of onshore to alongshore incident winds reveals that deflection of the incident wind flow is minimal at 0° and gradually increases as the incident wind turns towards 30° to the dune crest. The greatest deflection occurs between 30° and 70° incident to the dune crest. The degree of flow deflection depends secondarily on height above the dune surface, with the greatest effect near the surface and toward the dune crest. Topographically forced flow acceleration ("speed-up") across the stoss slope of the foredune is greatest for winds less than 30° (i.e., roughly perpendicular) and declines significantly for winds with more oblique approach angles. There is less lateral uniformity in the wind field when the incident wind approaches from > 60° because the effect of aspect ratio on topographic forcing and streamline convergence is less pronounced.

The Effect of Systematic Error in Forced Oscillation Testing

NASA Technical Reports Server (NTRS)

Williams, Brianne Y.; Landman, Drew; Flory, Isaac L., IV; Murphy, Patrick C.

2012-01-01

One of the fundamental problems in flight dynamics is the formulation of aerodynamic forces and moments acting on an aircraft in arbitrary motion. Classically, conventional stability derivatives are used for the representation of aerodynamic loads in the aircraft equations of motion. However, for modern aircraft with highly nonlinear and unsteady aerodynamic characteristics undergoing maneuvers at high angle of attack and/or angular rates the conventional stability derivative model is no longer valid. Attempts to formulate aerodynamic model equations with unsteady terms are based on several different wind tunnel techniques: for example, captive, wind tunnel single degree-of-freedom, and wind tunnel free-flying techniques. One of the most common techniques is forced oscillation testing. However, the forced oscillation testing method does not address the systematic and systematic correlation errors from the test apparatus that cause inconsistencies in the measured oscillatory stability derivatives. The primary objective of this study is to identify the possible sources and magnitude of systematic error in representative dynamic test apparatuses. Sensitivities of the longitudinal stability derivatives to systematic errors are computed, using a high fidelity simulation of a forced oscillation test rig, and assessed using both Design of Experiments and Monte Carlo methods.

Analysis of unsteady flow over Offshore Wind Turbine in combination with different types of foundations

NASA Astrophysics Data System (ADS)

Alesbe, Israa; Abdel-Maksoud, Moustafa; Aljabair, Sattar

2017-06-01

Environmental effects have an important influence on Offshore Wind Turbine (OWT) power generation efficiency and the structural stability of such turbines. In this study, we use an in-house Boundary Element (BEM)— panMARE code—to simulate the unsteady flow behavior of a full OWT with various combinations of aerodynamic and hydrodynamic loads in the time domain. This code is implemented to simulate potential flows for different applications and is based on a three-dimensional first-order panel method. Three different OWT configurations consisting of a generic 5 MW NREL rotor with three different types of foundations (Monopile, Tripod, and Jacket) are investigated. These three configurations are analyzed using the RANSE solver which is carried out using ANSYS CFX for validating the corresponding results. The simulations are performed under the same environmental atmospheric wind shear and rotor angular velocity, and the wave properties are wave height of 4 m and wave period of 7.16 s. In the present work, wave environmental effects were investigated firstly for the two solvers, and good agreement is achieved. Moreover, pressure distribution in each OWT case is presented, including detailed information about local flow fields. The time history of the forces at inflow direction and its moments around the mudline at each OWT part are presented in a dimensionless form with respect to the mean value of the last three loads and the moment amplitudes obtained from the BEM code, where the contribution of rotor force is lower in the tripod case and higher in the jacket case and the calculated hydrodynamic load that effect on jacket foundation type is lower than other two cases.

Spatial-temporal patterns and driving mechanisms of semiannual variations in the Philippine Sea

NASA Astrophysics Data System (ADS)

Zhao, Jun; Li, Yuanlong; Wang, Fan; Zhai, Fangguo; Yu, Xiaolin

2012-10-01

Satellite altimetric sea surface height (SSH) measurements from 1992 through 2010 are used to explore the oceanic semiannual variations in the Philippine Sea (PS). Pronounced semiannual SSH variations are detected within two zonal bands. One lies east of Luzon Strait (19°-22°N) in the northern PS, while the other is southeast of Mindanao coast (4°-7°N) in the southern PS. In the two near-coast boxes where semiannual harmonic amplitude exceeds 4 cm, the northern box (127°-133°E, 19°-22°N) and the southern box (127°-133°E, 4°-7°N), semiannual changes contribute considerably to the total annual SSH variance by 12% and 17%, respectively. Despite prominent SSH variability, the bifurcation latitude of the North Equatorial Current (NBL) exhibits weak fluctuations with a peak-to-peak difference of only 0.3° on semiannual time scale. While the in-phase annual SSH variations between the two boxes work together to enhance annual NBL changes, their out-of-phase semiannual SSH variations offset each other in driving the NBL displacements. Further analysis with a 11/2-layer reduced-gravity model forced by ECMWF wind stress reveals that the observed semiannual SSH variations are primarily driven by local wind forcing in the far western Pacific. Rossby wave signals propagating from the eastern/central Pacific contribute much less due to along-path dispersion and cancellation. Semiannual signals of wind field in the northern PS reflect mainly the semiannual changes of the Asian Monsoon system, while those in the southern PS arise from the combined effects of Monsoon transition and the annual migration of the intertropical convergence zone (ITCZ).

Time-domain parameter identification of aeroelastic loads by forced-vibration method for response of flexible structures subject to transient wind

NASA Astrophysics Data System (ADS)

Cao, Bochao

Slender structures representing civil, mechanical and aerospace systems such as long-span bridges, high-rise buildings, stay cables, power-line cables, high light mast poles, crane-booms and aircraft wings could experience vortex-induced and buffeting excitations below their design wind speeds and divergent self-excited oscillations (flutter) beyond a critical wind speed because these are flexible. Traditional linear aerodynamic theories that are routinely applied for their response prediction are not valid in the galloping, or near-flutter regime, where large-amplitude vibrations could occur and during non-stationary and transient wind excitations that occur, for example, during hurricanes, thunderstorms and gust fronts. The linear aerodynamic load formulation for lift, drag and moment are expressed in terms of aerodynamic functions in frequency domain that are valid for straight-line winds which are stationary or weakly-stationary. Application of the frequency domain formulation is restricted from use in the nonlinear and transient domain because these are valid for linear models and stationary wind. The time-domain aerodynamic force formulations are suitable for finite element modeling, feedback-dependent structural control mechanism, fatigue-life prediction, and above all modeling of transient structural behavior during non-stationary wind phenomena. This has motivated the developing of time-domain models of aerodynamic loads that are in parallel to the existing frequency-dependent models. Parameters defining these time-domain models can be now extracted from wind tunnel tests, for example, the Rational Function Coefficients defining the self-excited wind loads can be extracted using section model tests using the free vibration technique. However, the free vibration method has some limitations because it is difficult to apply at high wind speeds, in turbulent wind environment, or on unstable cross sections with negative aerodynamic damping. In the current research, new algorithms were developed based on forced vibration technique for direct extraction of the Rational Functions. The first of the two algorithms developed uses the two angular phase lag values between the measured vertical or torsional displacement and the measured aerodynamic lift and moment produced on the section model subject to forced vibration to identify the Rational Functions. This algorithm uses two separate one-degree-of-freedom tests (vertical or torsional) to identify all the four Rational Functions or corresponding Rational Function Coefficients for a two degrees-of-freedom (DOF) vertical-torsional vibration model. It was applied to a streamlined section model and the results compared well with those obtained from earlier free vibration experiment. The second algorithm that was developed is based on direct least squares method. It uses all the data points of displacements and aerodynamic lift and moment instead of phase lag values for more accurate estimates. This algorithm can be used for one-, two- and three-degree-of-freedom motions. A two-degree-of-freedom forced vibration system was developed and the algorithm was shown to work well for both streamlined and bluff section models. The uniqueness of the second algorithms lies in the fact that it requires testing the model at only two wind speeds for extraction of all four Rational Functions. The Rational Function Coefficients that were extracted for a streamlined section model using the two-DOF Least Squares algorithm were validated in a separate wind tunnel by testing a larger scaled model subject to straight-line, gusty and boundary-layer wind.

Weather Research and Forecasting Model Wind Sensitivity Study at Edwards Air Force Base, CA

NASA Technical Reports Server (NTRS)

Watson, Leela R.; Bauman, William H., III

2008-01-01

NASA prefers to land the space shuttle at Kennedy Space Center (KSC). When weather conditions violate Flight Rules at KSC, NASA will usually divert the shuttle landing to Edwards Air Force Base (EAFB) in Southern California. But forecasting surface winds at EAFB is a challenge for the Spaceflight Meteorology Group (SMG) forecasters due to the complex terrain that surrounds EAFB, One particular phenomena identified by SMG is that makes it difficult to forecast the EAFB surface winds is called "wind cycling". This occurs when wind speeds and directions oscillate among towers near the EAFB runway leading to a challenging deorbit bum forecast for shuttle landings. The large-scale numerical weather prediction models cannot properly resolve the wind field due to their coarse horizontal resolutions, so a properly tuned high-resolution mesoscale model is needed. The Weather Research and Forecasting (WRF) model meets this requirement. The AMU assessed the different WRF model options to determine which configuration best predicted surface wind speed and direction at EAFB, To do so, the AMU compared the WRF model performance using two hot start initializations with the Advanced Research WRF and Non-hydrostatic Mesoscale Model dynamical cores and compared model performance while varying the physics options.

United States Air Force Academy (USAFA) Vertical Axis Wind Turbine.

DTIC Science & Technology

1980-09-01

Rotors, SAND76-0131. Albuquerque: July 1977. 10. Oliver, R.C. and P.R. Nixon. "Design Procedure for Coupling Savonius and Darrieus Wind Turbines ", Air...May 17-20, 1976. -65- 16. Blackwell, B.F., R.E. Sheldahl, and L.V. Feltz. Wind Tunnel Performance Data for the Darrieus Wind Turbine with NACA 0012...a 5.8 m/s (13 mph) wind . At 100 rpm, the Darrieus turbine would be fully self-sustaining and acceleration would continue to an operating tip speed

Stator for a rotating electrical machine having multiple control windings

DOEpatents

Shah, Manoj R.; Lewandowski, Chad R.

2001-07-17

A rotating electric machine is provided which includes multiple independent control windings for compensating for rotor imbalances and for levitating/centering the rotor. The multiple independent control windings are placed at different axial locations along the rotor to oppose forces created by imbalances at different axial locations along the rotor. The multiple control windings can also be used to levitate/center the rotor with a relatively small magnetic field per unit area since the rotor and/or the main power winding provides the bias field.

Development of Combined Asymptotic and Numerical Procedures for Transonic and Hypersonic Flows.

DTIC Science & Technology

1996-04-01

11991 thru December 311995 Contract No. F49620-92-C-0006 Prepared for: Air Force Office of Scientific Research, AFOSR/NM Directorate of Mathematical and...MOMOMNO Air Force Office of Scientific Research AGENCY REOT NUMBER AFOSRJNM Directorat of Mathematical and information Sciences Bldg 410 Boiling AFS, DC...128 wind tunnel leading to the generalization of our Transonic Area Rule for Wind Tunnel Wall Interference (TARWI) to test articles of length

The dangerous flat spin and the factors affecting it

NASA Technical Reports Server (NTRS)

Fuchs, Richard; Schmidt, Wilhelm

1931-01-01

This report deals first with the fundamental data required for the investigation. These are chiefly the aerodynamic forces and moments acting on an airplane in a flat spin. It is shown that these forces and moments depend principally on the angle of attack and on the rotation about the path axis, and can therefore either be measured in a wind tunnel or calculated from wind-tunnel measurements of lift, drag and moment about the leading edge of the wing of an airplane model at rest. The lift, drag and moments about the span axis are so greatly altered by the rapid rotation in a flat spin, that they can no longer be regarded as independent of rotation. No substantial change in the angles of attack and glide occurring in a flat spin is involved. The cross-wind force, as compared with the lift and drag, can be disregarded in a flat spin.

Impact and Estimation of Balance Coordinate System Rotations and Translations in Wind-Tunnel Testing

NASA Technical Reports Server (NTRS)

Toro, Kenneth G.; Parker, Peter A.

2017-01-01

Discrepancies between the model and balance coordinate systems lead to biases in the aerodynamic measurements during wind-tunnel testing. The reference coordinate system relative to the calibration coordinate system at which the forces and moments are resolved is crucial to the overall accuracy of force measurements. This paper discusses sources of discrepancies and estimates of coordinate system rotation and translation due to machining and assembly differences. A methodology for numerically estimating the coordinate system biases will be discussed and developed. Two case studies are presented using this methodology to estimate the model alignment. Examples span from angle measurement system shifts on the calibration system to discrepancies in actual wind-tunnel data. The results from these case-studies will help aerodynamic researchers and force balance engineers to better the understand and identify potential differences in calibration systems due to coordinate system rotation and translation.

Ground Cloud Dispersion Measurements During the Titan IV Mission A-18 (23 October 1997) at Vandenberg Air Force Base

DTIC Science & Technology

1999-02-20

958.88 BASE= 0.00 SECOND SELECTED LAYER HEIGHT- (METERS) TOP = 3008.96 BASE= 958.88 SIGMAR (AZ) AT THE SURFACE (DEGREES) 5.7504 SIGMER(EL) AT THE SURFACE... SIGMAR (AZ) AT THE SURFACE (DEGREES) 5.7504 SIGMER(EL) AT THE SURFACE (DEGREES) 1.0344 MET. WIND WIND LAYER WIND SPEED WIND DIRECTION SIGMA OF SIGMA OF NO

Modulation of frontogenetic plankton production along a meandering jet by zonal wind forcing: An application to the Alboran Sea

NASA Astrophysics Data System (ADS)

Oguz, Temel; Mourre, Baptiste; Tintoré, Joaquin

2017-08-01

We present a coupled physical-biological modeling study to elucidate the changes in ageostrophic frontal dynamics and the frontogenetic plankton production characteristics of a meandering jet under the impacts of successive westerly/easterly wind events combined with seasonal variations in the upstream transport and buoyancy flux characteristics of the jet, using a case study for the Alboran Sea (Western Mediterranean). Their nonlinear coupling is shown to result in different forms of physical and biological characteristics of the background jet structure that follows a meandering path around two anticyclonic gyres in the western and eastern basins and a cyclonic eddy in between. The westerly, downfront wind events broaden the jet, and result in stronger cross-frontal density contrast and intensify ageostrophic cross-frontal secondary circulation. Thus, they improve the frontogenetic plankton production with respect to the no-wind case. They also support higher production along the northern coast in response to wind-induced coastal upwelling and spreading of resulting nutrient-rich, productive water by mesoscale stirring. These features weaken gradually as the jet transport reduces. In contrast, stronger and longer-lasting easterlies during the reduced jet transport phase weaken the currents and frontal density structure, change the circular Western Alboran Gyre to an elongated form, and shift the main axis of the jet towards the southern basin. Then, frontogenesis fails to contribute to phytoplankton production that becomes limited to the eddy pumping within cyclones. Apart from the frontogenetic production, eddy pumping, mesoscale stirring, and diapycnal mixing of nutrients support intermittent and localized phytoplankton patches over the basin.