Sample records for wind shear

  1. CAT LIDAR wind shear studies

    NASA Technical Reports Server (NTRS)

    Goff, R. W.

    1978-01-01

    The studies considered the major meteorological factors producing wind shear, methods to define and classify wind shear in terms significant from an aircraft perturbation standpoint, the significance of sensor location and scan geometry on the detection and measurement of wind shear, and the tradeoffs involved in sensor performance such as range/velocity resolution, update frequency and data averaging interval.

  2. Wind Shear Distributions Related

    E-print Network

    Robert Stengel; Wind Rotors; Wake Vortices; Wake Vortices

    for Translational Dynamics! Earth-relative velocity in earth-fixed polar coordinates:! v E = [V E g x] T! Earth-relative velocity in aircraft-fixed polar coordinates (zero wind):! v E = [V E b E a E] T! Body-frame air-mass-relative velocity:

  3. Structure of wind-shear turbulence

    NASA Technical Reports Server (NTRS)

    Trevino, G.; Laituri, T. R.

    1989-01-01

    The statistical characteristics of wind shear turbulence are modelled. Isotropic turbulence serves as the basis of comparison for the anisotropic turbulence which exists in wind shear. The question of turbulence scales in wind shear is addressed from the perspective of power spectral density.

  4. Structure of wind-shear turbulence

    NASA Technical Reports Server (NTRS)

    Trevino, G.; Laituri, T. R.

    1988-01-01

    The statistical characteristics of wind-shear turbulence are modelled. Isotropic turbulence serves as the basis of comparison for the anisotropic turbulence which exists in wind shear. The question of how turbulence scales in a wind shear is addressed from the perspective of power spectral density.

  5. Continuous wave laser for wind shear detection

    NASA Technical Reports Server (NTRS)

    Nelson, Loren

    1991-01-01

    Details of the design and development of a continuous-wave heterodyne carbon dioxide laser which has wind shear detection capabilities are given in viewgraph form. The goal of the development was to investigate the lower cost CW (rather than pulsed) lidar option for look-ahead wind shear detection from aircraft. The device has potential utility for ground based wind shear detection at secondary airports where the high cost of a Terminal Doppler Weather Radar system is not justifiable.

  6. Wind shear modeling for aircraft hazard definition

    NASA Technical Reports Server (NTRS)

    Frost, W.; Camp, D. W.; Wang, S. T.

    1978-01-01

    Mathematical models of wind profiles were developed for use in fast time and manned flight simulation studies aimed at defining and eliminating these wind shear hazards. A set of wind profiles and associated wind shear characteristics for stable and neutral boundary layers, thunderstorms, and frontal winds potentially encounterable by aircraft in the terminal area are given. Engineering models of wind shear for direct hazard analysis are presented in mathematical formulae, graphs, tables, and computer lookup routines. The wind profile data utilized to establish the models are described as to location, how obtained, time of observation and number of data points up to 500 m. Recommendations, engineering interpretations and guidelines for use of the data are given and the range of applicability of the wind shear models is described.

  7. Flight in low-level wind shear

    NASA Technical Reports Server (NTRS)

    Frost, W.

    1983-01-01

    Results of studies of wind shear hazard to aircraft operation are summarized. Existing wind shear profiles currently used in computer and flight simulator studies are reviewed. The governing equations of motion for an aircraft are derived incorporating the variable wind effects. Quantitative discussions of the effects of wind shear on aircraft performance are presented. These are followed by a review of mathematical solutions to both the linear and nonlinear forms of the governing equations. Solutions with and without control laws are presented. The application of detailed analysis to develop warning and detection systems based on Doppler radar measuring wind speed along the flight path is given. A number of flight path deterioration parameters are defined and evaluated. Comparison of computer-predicted flight paths with those measured in a manned flight simulator is made. Some proposed airborne and ground-based wind shear hazard warning and detection systems are reviewed. The advantages and disadvantages of both types of systems are discussed.

  8. Summary Proceedings of a Wind Shear Workshop

    NASA Technical Reports Server (NTRS)

    Enders, J. H.; Melvin, W. W.; Frost, W.; Camp, D. W.

    1983-01-01

    A number of recent program results and current issues were addressed: the data collection phase of the highly successful Joint Airport Weather Study (JAWS) Project and the NASA-B5f7B Gust Gradient Program, the use of these data for flight crew training through educational programs (e.g., films) and with manned flight training simulators, methods for post-accident determination of wind conditions from flight data recorders, the microburst wind shear phenomenon which was positively measured and described the ring vortex as a possible generating mechanism, the optimum flight procedure for use during an unexpected wind shear encounter, evaluation of the low-level wind shear alert system (LLWSAS), and assessment of the demonstrated and viable application of Doppler radar as an operational wind shear warning and detection system.

  9. Wind shear and turbulence simulation

    NASA Technical Reports Server (NTRS)

    Bowles, Roland L.

    1987-01-01

    The aviation community is increasing its reliance on flight simulators. This is true both in pilot training and in research and development. In moving research concepts through the development pipeline, there is a sequence of events which take place: analysis, ground based simulation, inflight simulation, and flight testing. Increasing fidelity as progress toward the flight testing arena is accompanied by increasing cost. The question that seems to be posed in relation to the meteorological aspects of flight simulation is, How much fidelity is enough and can it be quantified. As a part of the Langley Simulation Technology Program, there are three principal areas of focus, one being improved simulation of weather hazards. A close liaison with the JAWS project was established because of the Langley Simulation Technology interests regarding reliable simulation of severe convective weather phenomena and their impact on aviation systems. Simulation offers the only feasible approach for examining the utility of new technology and new procedures for coping with severe convective weather phenomena such as wind shear. These simulation concepts are discussed in detail.

  10. Wind shear related research at Princeton University

    NASA Technical Reports Server (NTRS)

    Stengel, Robert

    1992-01-01

    The topics addressed are: (1) real-time decision aiding-aircraft guidance for wind shear avoidance; (2) reducing the thrust-manual recovery strategies; and (3) dynamic behaviour of and aircraft encountering a single axis vortex.

  11. Pulsed laser Doppler measurements of wind shear

    NASA Technical Reports Server (NTRS)

    Dimarzio, C.; Harris, C.; Bilbro, J. W.; Weaver, E. A.; Burnham, D. C.; Hallock, J. N.

    1979-01-01

    There is a need for a sensor at the airport that can remotely detect, identify, and track wind shears near the airport in order to assure aircraft safety. To determine the viability of a laser wind-shear system, the NASA pulsed coherent Doppler CO2 lidar (Jelalian et al., 1972) was installed in a semitrailer van with a rooftop-mounted hemispherical scanner and was used to monitor thunderstorm gust fronts. Wind shears associated with the gust fronts at the Kennedy Space Center (KSC) between 5 July and 4 August 1978 were measured and tracked. The most significant data collected at KSC are discussed. The wind shears were clearly visible in both real-time velocity vs. azimuth plots and in postprocessing displays of velocities vs. position. The results indicate that a lidar system cannot be used effectively when moderate precipitation exists between the sensor and the region of interest.

  12. An expert system for wind shear avoidance

    NASA Technical Reports Server (NTRS)

    Stengel, Robert F.; Stratton, D. Alexander

    1990-01-01

    A study of intelligent guidance and control concepts for protecting against the adverse effects of wind shear during aircraft takeoffs and landings is being conducted, with current emphasis on developing an expert system for wind shear avoidance. Principal objectives are to develop methods for assessing the likelihood of wind shear encounter (based on real-time information in the cockpit), for deciding what flight path to pursue (e.g., takeoff abort, landing go-around, or normal climbout or glide slope), and for using the aircraft's full potential for combating wind shear. This study requires the definition of both deterministic and statistical techniques for fusing internal and external information , for making go/no-go decisions, and for generating commands to the manually controlled flight. The program has begun with the development of the WindShear Safety Advisor, an expert system for pilot aiding that is based on the FAA Windshear Training Aid; a two-volume manual that presents an overview , pilot guide, training program, and substantiating data provides guidelines for this initial development. The WindShear Safety Advisor expert system currently contains over 200 rules and is coded in the LISP programming language.

  13. Integration of the TDWR and LLWAS wind shear detection system

    NASA Technical Reports Server (NTRS)

    Cornman, Larry

    1991-01-01

    Operational demonstrations of a prototype TDWR/LLWAS (Terminal Doppler Weather Radar/Low Level Wind shear Alarm System) integrated wind shear detection system were conducted. The integration of wind shear detection systems is needed to provide end-users with a single, consensus source of information. A properly implemented integrated system provides wind shear warnings of a higher quality than stand-alone LLWAS or TDWR systems. The algorithmic concept used to generate the TDWR/LLWAS integrated products and several case studies are discussed, indicating the viability and potential of integrated wind shear detection systems. Implications for integrating ground and airborne wind shear detection systems are briefly examined.

  14. Unresolved issues in wind shear encounters

    NASA Technical Reports Server (NTRS)

    Stengel, Robert F.

    1987-01-01

    Much remains to be learned about the hazards of low altitude wind shear to aviation. New research should be conducted on the nature of the atmospheric environment, on aircraft performance, and on guidance and control aids. In conducting this research, it is important to distinguish between near-term and far-term objectives, between basic and applied research, and between uses of results for aircraft design or for real-time implementation. Advances in on-board electronics can be applied to assuring that aircraft of all classes have near optimal protection against wind shear hazards.

  15. Wind shear and turbulence around airports

    NASA Technical Reports Server (NTRS)

    Lewellen, W. S.; Williamson, G. G.

    1976-01-01

    A two part study was conducted to determine the feasibility of predicting the conditions under which wind/turbulence environments hazardous to aviation operations exist. The computer model used to solve the velocity temperature, and turbulence distributions in the atmospheric boundary layer is described, and the results of a parameteric analysis to determine the expected range of wind shear and turbulence to be encountered in the vicinity of airports are given. The second part describes the delineation of an ensemble of aircraft accidents in which low level wind shear and/or turbulence appeared to be causative factors. This set of accidents, encompassing a wide range of meteorological conditions, should prove useful in developing techniques for reconstructing hazardous wind environments for aircraft safety investigation purposes.

  16. Infrared low-level wind shear work

    NASA Technical Reports Server (NTRS)

    Adamson, Pat

    1988-01-01

    Results of field experiments for the detection of clear air disturbance and low level wind shear utilizing an infrared airborne system are given in vugraph form. The hits, misses and nuisance alarms scores are given. Information is given on the infrared spatial resolution technique. The popular index of aircraft hazard (F= WX over g - VN over AS) is developed for a remote temperature sensor.

  17. Progress on Intelligent Guidance and Control for Wind Shear Encounter

    NASA Technical Reports Server (NTRS)

    Stratton, D. Alexander

    1990-01-01

    Low altitude wind shear poses a serious threat to air safety. Avoiding severe wind shear challenges the ability of flight crews, as it involves assessing risk from uncertain evidence. A computerized intelligent cockpit aid can increase flight crew awareness of wind shear, improving avoidance decisions. The primary functions of a cockpit advisory expert system for wind shear avoidance are discussed. Also introduced are computational techniques being implemented to enable these primary functions.

  18. Wind shear training applications for 91/135

    NASA Technical Reports Server (NTRS)

    Arbon, ED

    1991-01-01

    The requirement for wind shear training of all pilots has been demonstrated too often by the accident statistics of past years. Documents were developed to train airline crews on specific aircraft and to teach recognition of the meteorological conditions that are conducive to wind shear and microburst formation. A Wind Shear Training Aid program is discussed.

  19. Wind shear near the ground and aircraft operations.

    NASA Technical Reports Server (NTRS)

    Fichtl, G. H.

    1972-01-01

    The variance of wind shear in the first 150-200 m of the atmosphere is a function of the direction of the mean wind relative to the flight path, the zenith angle of the flight path, the standard deviation of the three components of the turbulence velocity vector, the surface friction velocity, the stability properties of the atmospheric boundary layer, and the heights above natural grade of the beginning and end points of the portion of the flight path over which the shear is to be calculated. The results are applied by calculating wind shear for various risks of occurrence assuming wind shear is a Gaussian process, and it is shown that turbulence produces significantly large dispersions in wind shear about the mean wind shear. The results are interpreted in terms of the ICAO interim shear criteria for reporting wind shear in qualitative terms.

  20. Wind shear predictive detector technology study status

    NASA Technical Reports Server (NTRS)

    Gandolfi, C.

    1990-01-01

    Among the different elements to be investigated when considering the Wind Shear hazard, the Aeronautical Navigation Technical Service (STNA/3E), whose task is to participate in the development of new technologies and equipments, focused its effort on airborne and ground sensors for the detection of low-level wind shear. The first task, initiated in 1986, consists in the evaluation of three candidate techniques for forward-looking sensors: lidar, sodar, and radar. No development is presently foreseen for an infrared based air turbulence advance warning system although some flight experiments took place in the 70's. A Thomson infrared radiometer was then installed on an Air France Boeing 707 to evaluate its capability of detecting clear air turbulence. The conclusion showed that this technique was apparently able to detect cloud layers but that additional experiments were needed; on the other hand, the rarity of the phenomenon and the difficulty in operating on a commercial aircraft were also mentioned.

  1. Microbursts as an aviation wind shear hazard

    NASA Technical Reports Server (NTRS)

    Fujita, T. T.

    1981-01-01

    The downburst-related accidents or near-misses of jet aircraft have been occurring at the rate of once or twice a year since 1975. A microburst with its field comparable to the length of runways can induce a wind shear which endangers landing or liftoff aircraft; the latest near miss landing of a 727 aircraft at Atlanta, Ga. in 1979 indicated that some microbursts are too small to trigger the warning device of the anemometer network at major U.S. airports. The nature of microbursts and their possible detection by Doppler radar are discussed, along with proposed studies of small-scale microbursts.

  2. Airborne infrared low level wind shear predictor

    NASA Technical Reports Server (NTRS)

    Kuhn, P. M.; Kurkowski, R. L.

    1984-01-01

    The operating principles and test performance of an airborne IR (13-16 micron) temperature-sensing detection and warning system for low-level wind shear (LLWS) are presented. The physics of LLWS phenomena and of the IR radiometer are introduced. The cold density-current outflow or gust front related to LLWS is observed in the IR spectrum of CO2 by a radiometer with + or - 0.5-C accuracy at 0.5-Hz sampling rate; LLWS alerts are given on the basis of specific criteria. Test results from the JAWS experiments conducted at Denver in July 1982, are presented graphically and discussed. The feasibility of the passive IR system is demonstrated, with an average warning time of 51 sec, corresponding to a distance from touchdown of about 2 miles.

  3. Impact of Vertical Wind Shear on Tropical Cyclone Rainfall

    NASA Technical Reports Server (NTRS)

    Cecil, Dan; Marchok, Tim

    2014-01-01

    While tropical cyclone rainfall has a large axisymmetric component, previous observational and theoretical studies have shown that environmental vertical wind shear leads to an asymmetric component of the vertical motion and precipitation fields. Composites consistently depict a precipitation enhancement downshear and also cyclonically downwind from the downshear direction. For consistence with much of the literature and with Northern Hemisphere observations, this is subsequently referred to as "Downshear-Left". Stronger shear magnitudes are associated with greater amplitude precipitation asymmetries. Recent work has reinforced the prior findings, and explored details of the response of the precipitation and kinematic fields to environmental vertical wind shear. Much of this research has focused on tropical cyclones away from land, to limit the influence of other processes that might distort the signal related to vertical wind shear. Recent evidence does suggest vertical wind shear can also play a major role in precipitation asymmetries during and after landfall.

  4. Wind shear at turbine rotor heights from Doppler lidar measurements

    NASA Astrophysics Data System (ADS)

    Pichugina, Y.; Banta, R. M.; Kelley, N.; Brewer, A.; Sandberg, S.

    2009-12-01

    As the capacity and size of modern wind turbines increase to take advantage of stronger winds at higher elevations, the confidence in wind resource assessment by “extrapolation method”, routinely used in the wind energy industry, decreases. Error in wind resource approximation at elevated heights can lead to substantial uncertainty in power production and wind farm economics. Remote sensing measurements of wind and turbulence profiles through the entire layer of turbine rotor heights, can provide accurate information on wind flow, thereby improving preliminary evaluation of turbine performance and power production. This paper presents lidar measurements of wind profiles during two experiments in the south-eastern part of the Great Plains and shows mean wind shear at turbine rotor heights as being greater than predicted by the assumption of logarithmic wind profile or power law relation. In addition to the regional climatology over relatively flat terrain, frequent development of the nocturnal Low-Level Jet can lead to significant deviations of wind profile from theoretical extrapolations. Analysis of wind and turbulence characteristics over a wide range of heights, variations of wind shear in time during strong and calm wind nights, along with examples of error in the actual and predicted wind resources will be given.

  5. An experimental cockpit display for TDWR wind shear alerts

    NASA Technical Reports Server (NTRS)

    Campbell, Steven D.; Daly, Peter M.; Demillo, Robert J.

    1991-01-01

    The first successful ground-to-air data link and cockpit display of terminal Doppler weather radar (TDWR) wind shear warnings in real-time are reported. During the summer of 1990, wind shear warnings generated by the TDWR testbed radar at Orlando, Florida, were transmitted in real-time to a research aircraft performing microburst penetrations. Automatic delivery of TDWR wind shear warnings potentially result in decreased controller workload and improved pilot information. Pilot responses indicate that the information provided by the cockpit displays was useful in visualizing the location of wind shear hazards. The graphical display of microburst hazards provided better information than that currently provided by ATC verbal messages and pilot reports. This information was useful in assessing the microburst hazard, deciding whether to continue the approach, and planning escape maneuvers.

  6. Influence of Wind Shear on the Growth of Hail

    Microsoft Academic Search

    Phanindramohan Das

    1962-01-01

    Dessens (1960) has suggested that strong winds aloft favor the growth of hail in thunderstorms building under their influence. The physical implication of this suggestion is examined by making computations on the growth of hailstones in a model cloud under vertical wind shear. The computations are based essentially on the Schumann-Ludlam formulation of the hail problem. The model cloud has

  7. Evaluation of Wind Shear Patterns at Midwest Wind Energy Facilities: Preprint

    Microsoft Academic Search

    K. Smith; G. Randall; D. Malcolm; N. Kelley; B. Smith

    2002-01-01

    The U.S. Department of Energy-Electric Power Research Institute (DOE-EPRI) Wind Turbine Verification Program (TVP) has included several wind energy facilities in the Midwestern United States. At several of these projects, a strong diurnal shear pattern has been observed. During the day, low and sometimes negative shear has been measured. During night hours, very high positive shear is frequently observed. These

  8. Quantifying shear-induced wave transformations in the solar wind

    E-print Network

    Grigol Gogoberidze; Andria Rogava; Stefaan Poedts

    2007-03-20

    The possibility of velocity shear-induced linear transformations of different magnetohydrodynamic waves in the solar wind is studied both analytically and numerically. A quantitative analysis of the wave transformation processes for all possible plasma-$\\beta$ regimes is performed. By applying the obtained criteria for effective wave coupling to the solar wind parameters, we show that velocity shear-induced linear transformations of Alfv\\'en waves into magneto-acoustic waves could effectively take place for the relatively low-frequency Alfv\\'en waves in the energy containing interval. The obtained results are in a good qualitative agreement with the observed features of density perturbations in the solar wind.

  9. Wind shear detection using measurement of aircraft total energy change

    NASA Technical Reports Server (NTRS)

    Joppa, R. G.

    1976-01-01

    Encounters with wind shears are of concern and have caused major accidents, particularly during landing approaches. Changes in the longitudinal component of the wind affect the aircraft by changing its kinetic energy with respect to the air. It is shown that an instrument which will measure and display the rate of change of total energy of the aircraft with respect to the air will give a leading indication of wind shear problems. The concept is outlined and some instrumentation and display considerations are discussed.

  10. Wind speed and direction shears with associated vertical motion during strong surface winds

    NASA Technical Reports Server (NTRS)

    Alexander, M. B.; Camp, D. W.

    1984-01-01

    Strong surface winds recorded at the NASA 150-Meter Ground Winds Tower facility at Kennedy Space Center, Florida, are analyzed to present occurrences representative of wind shear and vertical motion known to be hazardous to the ascent and descent of conventional aircraft and the Space Shuttle. Graphical (percentage frequency distributions) and mathematical (maximum, mean, standard deviation) descriptions of wind speed and direction shears and associated updrafts and downdrafts are included as functions of six vertical layers and one horizontal distance for twenty 5-second intervals of parameters sampled simultaneously at the rate of ten per second during a period of high surface winds.

  11. Temperature lapse rate as an adjunct to wind shear detection

    NASA Technical Reports Server (NTRS)

    Zweifil, Terry

    1991-01-01

    Several meteorological parameters were examined to determine if measurable atmospheric conditions can improve windshear detection devices. Lapse rate, the temperature change with altitude, shows promise as being an important parameter in the prediction of severe wind shears. It is easily measured from existing aircraft instrumentation, and it can be important indicator of convective activity including thunderstorms and microbursts. The meteorological theory behind lapse rate measurement is briefly reviewed, and and FAA certified system is described that is currently implemented in the Honeywell Wind Shear Detection and Guidance System.

  12. Doppler weather radar with predictive wind shear detection capabilities

    NASA Technical Reports Server (NTRS)

    Kuntman, Daryal

    1991-01-01

    The status of Bendix research on Doppler weather radar with predictive wind shear detection capability is given in viewgraph form. Information is given on the RDR-4A, a fully coherent, solid state transmitter having Doppler turbulence capability. Frequency generation data, plans, modifications, system characteristics and certification requirements are covered.

  13. Status of NASA's IR wind shear detection research

    NASA Technical Reports Server (NTRS)

    Mckissick, Burnell

    1991-01-01

    The status of NASA's wind shear detection research is reported in viewgraph form. Information is given on early experience, FLIR detectors, quantities measured by Airborne Warning and Avoidance System 1 (AWAS 1), the time series model for Flight 551, conclusions from NASA 737 flights, conclusions on Orlando 7-7-90, and AWAS 3 mnemonics.

  14. EFFECTS OF WIND SHEAR ON POLLUTION DISPERSION. (R827929)

    EPA Science Inventory

    Using an accurate numerical method for simulating the advection and diffusion of pollution puffs, it is demonstrated that point releases of pollution grow into a shape reflecting the vertical wind shear profile experienced by the puff within a time scale less than 4 h. Fo...

  15. Winds and wind shear in-situ sensors

    NASA Technical Reports Server (NTRS)

    Goff, R. C.

    1980-01-01

    The problem of development of instrumentation for providing wind speed and direction information directly or indirectly to a pilot in the cockpit is considered. The pilots need for horizontal wind information at various stages of flight (i.e., at liftoff, in approach and departure corridors, and even in flight outside the terminal area) are emphasized.

  16. Response of wind shear warning systems to turbulence with implication of nuisance alerts

    NASA Technical Reports Server (NTRS)

    Bowles, Roland L.

    1988-01-01

    The objective was to predict the inherent turbulence response characteristics of candidate wind shear warning system concepts and to assess the potential for nuisance alerts. Information on the detection system and associated signal processing, physical and mathematical models, wind shear factor root mean square turbulence response and the standard deviation of the wind shear factor due to turbulence is given in vugraph form.

  17. The classification of wind shears from the point of view of aerodynamics and flight mechanics

    NASA Technical Reports Server (NTRS)

    Seidler, Fritz; Hensel, Gunter

    1987-01-01

    A study of international statistical data shows that in about three quarters of all serious accidents which occurred with jet propelled airliners wind shear was either one of the main causes of the accident or represented a major contributory cause. Wind shear related problems are examined. The necessity of a use of different concepts, definitions, and divisions is explained, and the concepts and definitions required for the division of wind and wind shear into different categories is discussed. A description of the context between meteorological and aerodynamics-flight mechanics concepts, definitions, and divisions is also provided. Attention is given to wind and wind components, general characteristics of wind shear and the meteorological terms, the basic types of wind shear for aerodynamics-flight mechanics investigations, special types of wind shear for aerodynamics-flight mechanics investigations, and possibilities regarding a change of the wind component.

  18. Air/ground wind shear information integration: Flight test results

    NASA Technical Reports Server (NTRS)

    Hinton, David A.

    1992-01-01

    An element of the NASA/FAA wind shear program is the integration of ground-based microburst information on the flight deck, to support airborne wind shear alerting and microburst avoidance. NASA conducted a wind shear flight test program in the summer of 1991 during which airborne processing of Terminal Doppler Weather Radar (TDWR) data was used to derive microburst alerts. High level microburst products were extracted from TDWR, transmitted to a NASA Boeing 737 in flight via data link, and processed to estimate the wind shear hazard level (F-factor) that would be experienced by the aircraft in the core of each microburst. The microburst location and F-factor were used to derive a situation display and alerts. The situation display was successfully used to maneuver the aircraft for microburst penetrations, during which in situ 'truth' measurements were made. A total of 19 penetrations were made of TDWR-reported microburst locations, resulting in 18 airborne microburst alerts from the TDWR data and two microburst alerts from the airborne in situ measurements. The primary factors affecting alerting performance were spatial offset of the flight path from the region of strongest shear, differences in TDWR measurement altitude and airplane penetration altitude, and variations in microburst outflow profiles. Predicted and measured F-factors agreed well in penetrations near microburst cores. Although improvements in airborne and ground processing of the TDWR measurement would be required to support an airborne executive-level alerting protocol, the feasibility of airborne utilization of TDWR data link data has been demonstrated.

  19. Wind Shear/Turbulence Inputs to Flight Simulation and Systems Certification

    NASA Technical Reports Server (NTRS)

    Bowles, Roland L. (editor); Frost, Walter (editor)

    1987-01-01

    The purpose of the workshop was to provide a forum for industry, universities, and government to assess current status and likely future requirements for application of flight simulators to aviation safety concerns and system certification issues associated with wind shear and atmospheric turbulence. Research findings presented included characterization of wind shear and turbulence hazards based on modeling efforts and quantitative results obtained from field measurement programs. Future research thrusts needed to maximally exploit flight simulators for aviation safety application involving wind shear and turbulence were identified. The conference contained sessions on: Existing wind shear data and simulator implementation initiatives; Invited papers regarding wind shear and turbulence simulation requirements; and Committee working session reports.

  20. Ris-PhD-Report Accounting for the speed shear in wind

    E-print Network

    Risø-PhD-Report Accounting for the speed shear in wind turbine power performance measurement Rozenn for the speed shear in wind turbine power performance measurement Division: Wind Energy Division Abstract: The power curve of a wind turbine is the primary char- acteristic of the machine as it is the basis

  1. The effect of roughness elements on wind erosion: The importance of surface shear stress distribution

    E-print Network

    The effect of roughness elements on wind erosion: The importance of surface shear stress entrainment threshold by the ratio of shear stress on roughness elements to that on the vegetated land surface, and the implications for model accuracy. We use wind tunnel measurements of surface shear stress distributions

  2. A problem formulation for glideslope tracking in wind shear using advanced robust control techniques

    NASA Technical Reports Server (NTRS)

    Belcastro, Christine M.; Chang, B.-C.; Fischl, Robert

    1992-01-01

    A formulation of the longitudinal glideslope tracking of a transport-class aircraft in severe wind shear and turbulence for application to robust control system design is presented. Mathematical wind shear models are incorporated into the vehicle mathematical model, and wind turbulence is modeled as an input disturbance signal. For this problem formulation, the horizontal and vertical wind shear gradients are treated as real uncertain parameters that vary over an entire wind shear profile. The primary objective is to examine the formulation of this problem into an appropriate design format for use in m-synthesis control system design.

  3. Flight guidance research for recovery from microburst wind shear

    NASA Technical Reports Server (NTRS)

    Hinton, David A.

    1990-01-01

    Research is in progress to develop flight strategy concepts for avoidance and recovery from microburst wind shears. The objectives of this study are to evaluate the performance of various strategies for recovery from wind shear encountered during the approach-to-landing, examine the associated piloting factors, and evaluate the payoff of forward-look sensing. Both batch and piloted simulations are utilized. The industry-recommended manual recovery technique is used as a baseline strategy. Two advanced strategies were selected for the piloted tests. The first strategy emulates the recovery characteristics shown by prior optimal trajectory analysis, by initially tracking the glideslope, then commanding a shallow climb. The second strategy generates a flight path angle schedule that is a function of airplane energy state and the instantaneous shear strength. All three strategies are tested with reactive sensing only and with forward-look sensing. Piloted simulation tests are in progress. Tentative results indicate that, using only reactive alerts, there appears to be little difference in performance between the various strategies. With forward-look alerts, the advanced guidance strategies appear to have advantages over the baseline strategy. Relatively short forward-look alert times, on the order of 10 or 15 seconds, produce a far greater recovery benefit than optimizing a recovery from a reactive alert.

  4. Comparison of simulated and actual wind shear radar data products

    NASA Technical Reports Server (NTRS)

    Britt, Charles L.; Crittenden, Lucille H.

    1992-01-01

    Prior to the development of the NASA experimental wind shear radar system, extensive computer simulations were conducted to determine the performance of the radar in combined weather and ground clutter environments. The simulation of the radar used analytical microburst models to determine weather returns and synthetic aperture radar (SAR) maps to determine ground clutter returns. These simulations were used to guide the development of hazard detection algorithms and to predict their performance. The structure of the radar simulation is reviewed. Actual flight data results from the Orlando and Denver tests are compared with simulated results. Areas of agreement and disagreement of actual and simulated results are shown.

  5. Three-Dimensional Numerical Modeling of Convection Produced by Interacting Thunderstorm Outflows. Part II: Variations in Vertical Wind Shear

    Microsoft Academic Search

    Kelvin K. Droegemeier; Robert B. Wilhelmson

    1985-01-01

    In this second paper in a series on outflow interactions, we use the three-dimensional model described in Part I to examine the effects of vertical wind shear variations on cloud development along intersecting thunderstorm outflow boundaries. Three wind shear profiles are used in this study: shear only above cloud base, shear only below cloud base, and shear both above and

  6. Simulations of large winds and wind shears induced by gravity wave breaking in the mesosphere and lower thermosphere (MLT) region

    NASA Astrophysics Data System (ADS)

    Liu, X.; Xu, J.; Liu, H.-L.; Yue, J.; Yuan, W.

    2014-05-01

    Using a fully nonlinear two-dimensional (2-D) numerical model, we simulated gravity waves (GWs) breaking and their contributions to the formation of large winds and wind shears in the mesosphere and lower thermosphere (MLT). An eddy diffusion coefficient is used in the 2-D numerical model to parameterize realistic turbulent mixing. Our study shows that the momentum deposited by breaking GWs accelerates the mean wind. The resultant large background wind increases the GW's apparent horizontal phase velocity and decreases the GW's intrinsic frequency and vertical wavelength. Both the accelerated mean wind and the decreased GW vertical wavelength contribute to the enhancement of wind shears. This, in turn, creates a background condition that favors the occurrence of GW instability, breaking, and momentum deposition, as well as mean wind acceleration, which further enhances the wind shears. We find that GWs with longer vertical wavelengths and faster horizontal phase velocity can induce larger winds, but they may not necessarily induce larger wind shears. In addition, the background temperature can affect the time and height of GW breaking, thus causing accelerated mean winds and wind shears.

  7. How Does the Eye Warm? Part II: Sensitivity to Vertical Wind Shear and a Trajectory Analysis

    E-print Network

    How Does the Eye Warm? Part II: Sensitivity to Vertical Wind Shear and a Trajectory Analysis DANIEL of vertical wind shear on the structure of warming and descent in the eye; results are compared with the no environment, time-averaged eye descent is maximized at 12­13-km height. Warming is not generally maximized

  8. Dominant Role by Vertical Wind Shear in Regulating Aerosol Effects on Deep Convective Clouds

    SciTech Connect

    Fan, Jiwen; Yuan, Tianle; Comstock, Jennifer M.; Ghan, Steven J.; Khain, Alexander; Leung, Lai-Yung R.; Li, Zhanqing; Martins, Vanderlei J.; Ovchinnikov, Mikhail

    2009-11-24

    The impact of aerosols on clouds, especially deep convective clouds (DCCs), is one of the most important and least understood aspects of climate change. Aerosols can either suppress or enhance convection/precipitation in DCCs under different conditions. Here we study the effect of vertical wind shear, a key atmospheric condition, on interactions between aerosol and DCCs. We show a dominant role by vertical wind shear in regulating aerosol effects on DCCs by both modeling and observational evidence. It qualitatively determines whether aerosols suppress or invigorate convective strength: aerosols always suppress convection under strong wind shear and enhance convection under weak wind shear until reaching an optimum loading. In a humid atmosphere, aerosols have the greatest potential to suppress convection when wind shear is strong.

  9. The Effects of Atmospheric Stability and Wind Shear on Wind Farm Power Production

    NASA Astrophysics Data System (ADS)

    Vanderwende, B. J.; Lundquist, J. K.

    2011-12-01

    Power production from wind turbines can vary significantly from manufacturer's ratings due to atmospheric stability and wind shear. In this study, remotely sensed and in-situ data from a wind farm in the High Plains of Central North America were examined to quantify the effects of atmospheric conditions in the boundary layer on power generation. Several approaches for segregating time periods by atmospheric conditions were applied to this dataset, including methods based on the time-of-day, the power law exponent ?, the bulk Richardson number RB, and diurnal cycles in wind and temperature. These classifications were used to generate stability-dependent power curves. For this site, all classification metrics indicated underperformance during stable/night regimes and overperformance during convective/day regimes at moderate wind speeds (7-12m/s). A simple attempt at forecasting power production values proved both the feasibility and the utility of applying meteorological classifications for forecasting applications. The success in diagnosis and forecasting of power production using boundary layer data demonstrate that power output is strongly influenced by boundary layer stability, but further research is required that involves measurements taken across the rotor-disk; remote sensing of such profiles is recommended.

  10. Longitudinal stability and control in wind shear with energy height rate feedback

    NASA Technical Reports Server (NTRS)

    Gera, J.

    1980-01-01

    The longitudinal linearized equations of motion in wind shear were derived for the NASA Terminal Configured Vehicle, a modified Boeing 737 airplane. In addition to the apparent acceleration terms resulting from wind shear, the equations included altitude dependent stability derivatives. A linear analysis of these equations indicates a first order divergence type of instability due to wind shear in which head wind decreased with altitude. Furthermore, this instability cannot be stabilized by attitude control alone. However, attitude control used in combination with an addition feedback loop which consisted of the energy height rate feedback to the throttle proved to be effective in suppressing instability due to wind shear. A brief piloted, real time, nonlinear simulation indicated the desirability of using a display based on the rate of change of energy height rate and of commanded thrust.

  11. Comparison of low-altitude wind-shear statistics derived from measured and proposed standard wind profiles

    NASA Technical Reports Server (NTRS)

    Usry, J. W.

    1983-01-01

    Wind shear statistics were calculated for a simulated set of wind profiles based on a proposed standard wind field data base. Wind shears were grouped in altitude in altitude bands of 100 ft between 100 and 1400 ft and in wind shear increments of 0.025 knot/ft. Frequency distributions, means, and standard deviations for each altitude band were derived for the total sample were derived for both sets. It was found that frequency distributions in each altitude band for the simulated data set were more dispersed below 800 ft and less dispersed above 900 ft than those for the measured data set. Total sample frequency of occurrence for the two data sets was about equal for wind shear values between +0.075 knot/ft, but the simulated data set had significantly larger values for all wind shears outside these boundaries. It is shown that normal distribution in both data sets neither data set was normally distributed; similar results are observed from the cumulative frequency distributions.

  12. Wind turbine blade shear web disbond detection using rotor blade operational sensing and data analysis.

    PubMed

    Myrent, Noah; Adams, Douglas E; Griffith, D Todd

    2015-02-28

    A wind turbine blade's structural dynamic response is simulated and analysed with the goal of characterizing the presence and severity of a shear web disbond. Computer models of a 5?MW offshore utility-scale wind turbine were created to develop effective algorithms for detecting such damage. Through data analysis and with the use of blade measurements, a shear web disbond was quantified according to its length. An aerodynamic sensitivity study was conducted to ensure robustness of the detection algorithms. In all analyses, the blade's flap-wise acceleration and root-pitching moment were the clearest indicators of the presence and severity of a shear web disbond. A combination of blade and non-blade measurements was formulated into a final algorithm for the detection and quantification of the disbond. The probability of detection was 100% for the optimized wind speed ranges in laminar, 30% horizontal shear and 60% horizontal shear conditions. PMID:25583871

  13. A method for three-dimensional modeling of wind-shear environments for flight simulator applications

    NASA Technical Reports Server (NTRS)

    Bray, R. S.

    1984-01-01

    A computational method for modeling severe wind shears of the type that have been documented during severe convective atmospheric conditions is offered for use in research and training flight simulation. The procedure was developed with the objectives of operational flexibility and minimum computer load. From one to five, simple down burst wind models can be configured and located to produce the wind field desired for specific simulated flight scenarios. A definition of related turbulence parameters is offered as an additional product of the computations. The use of the method to model several documented examples of severe wind shear is demonstrated.

  14. TRMM Satellite Shows Bertha's Heavy Rain Pushed From Wind Shear - Duration: 0:13.

    NASA Video Gallery

    TRMM Satellite Shows Bertha's Heavy Rain Pushed From Wind Shear This 3-D flyby of Tropical Storm Bertha on Aug. 1 was created from TRMM satellite data. It shows (from the south) intense thunderstor...

  15. A total energy sensor for glidepath and speed control of a tactical airlifter in wind shear

    E-print Network

    Anderson, Thomas Edward

    1987-01-01

    SHEAR MODELING IV TOTAL ENERGY SENSOR Theory Bench Tests iVIodeling and Verification 29 33 35 TABLE OF CONTENTS (Continued) CHAPTER V TOTAL ENERGY FEEDBACK RESULTS Profile A: 20 knot Tail Wind, MIL-F-8785C, No Wind Profile B: 20 knot Tail... Samples 22. Profile A: 20 knot Tail Wind, MIL-F-8785C, No Wind 44 23. Profile B: 20 knot Tail Wind, ? 0. 3 Gradient, No Wind, First Run 50 24. Stabilizing State Feedback with a-Limiter 55 LIST OF FIGURES (Continued) Figure 25. Profile B: 20 knot...

  16. Importance of wind conditions, fetch, and water levels on wave-generated shear stresses in shallow intertidal basins

    E-print Network

    Fagherazzi, Sergio

    Importance of wind conditions, fetch, and water levels on wave-generated shear stresses in shallow July 2009; published 30 September 2009. [1] Wave-generated shear stresses are the main mechanism, and wind direction on water depth, fetch, and the resulting wave-generated shear stresses. We identify four

  17. Robust Projections of Vertical Wind Shear Changes for the 21st Century

    NASA Astrophysics Data System (ADS)

    Vecchi, G. A.; Soden, B. J.

    2006-12-01

    We explore the changes in tropical vertical wind-shear projected for the 21^{st} Century in response to increased CO2, using a set of 21 climate model experiments performed for the IPCC-AR4. Many features of the shear changes are robust across the various models, in particular an increase on wind-shear in the tropical north Atlantic region. This region is the only one in the world exhibiting a robust increase in shear in the local summer season, the models show robust decreases in wind shear over much of the tropical oceans. The increase in Atlantic wind shear appears related to teleconnections from global-warming-induced reduction in the intensity of large-scale atmospheric circulation, which occurs preferentially in the zonally-asymmetric (i.e., Walker) component of the tropical Pacific circulation - i.e. "El Niño-like" atmospheric changes. Although the mechanisms behind the Pacific changes are distinct from those of El Niño (and are reproduced in both mixed-layer and full ocean dynamics coupled climate models), aspects of climate teleconnections resemble those associated with El Niño. The large-scale shears show a pronounced and robust weakening over the Indian and western tropical Pacific Oceans. The magnitude of the ensemble-mean changes is on the order of 0.5-1 m/s per degree warming, and the robust signals are evident in over 18 of the 21 models. In these models, the spatial structure in the changes to the frequency of extremes in tropical daily cyclonic vorticity show relation to the structure of the changes in wind shear. Effort should be undertaken to understand the extent to which these robust changes in large-scale wind shear may impact hurricane activity, and they should be considered in discussions of projected changes to hurricane intensity and frequency.

  18. Power spectral density analysis of wind-shear turbulence for related flight simulations. M.S. Thesis

    NASA Technical Reports Server (NTRS)

    Laituri, Tony R.

    1988-01-01

    Meteorological phenomena known as microbursts can produce abrupt changes in wind direction and/or speed over a very short distance in the atmosphere. These changes in flow characteristics have been labelled wind shear. Because of its adverse effects on aerodynamic lift, wind shear poses its most immediate threat to flight operations at low altitudes. The number of recent commercial aircraft accidents attributed to wind shear has necessitated a better understanding of how energy is transferred to an aircraft from wind-shear turbulence. Isotropic turbulence here serves as the basis of comparison for the anisotropic turbulence which exists in the low-altitude wind shear. The related question of how isotropic turbulence scales in a wind shear is addressed from the perspective of power spectral density (psd). The role of the psd in related Monte Carlo simulations is also considered.

  19. Improved prediction of the turbulence-shear contribution to wind noise pressure spectra.

    PubMed

    Yu, Jiao; Raspet, Richard; Webster, Jeremy; Abbott, JohnPaul

    2011-12-01

    In previous research [Raspet et al., J. Acoust. Soc. Am. 123(3), 1260-1269 (2008)], predictions of the low frequency turbulence-turbulence and turbulence-mean shear interaction pressure spectra measured by a large wind screen were developed and compared to the spectra measured using large spherical wind screens in the flow. The predictions and measurements agreed well except at very low frequencies where the turbulence-mean shear contribution dominated the turbulence-turbulence interaction pressure. In this region the predicted turbulence-mean shear interaction pressure did not show consistent agreement with microphone measurements. The predicted levels were often much larger than the measured results. This paper applies methods developed to predict the turbulence-shear interaction pressure measured at the ground [Yu et al., J. Acoust. Soc. Am. 129(2), 622-632 (2011)] to improve the prediction of the turbulence-shear interaction pressure above the ground surface by incorporating a realistic wind velocity profile and realistic turbulence anisotropy. The revised prediction of the turbulence-shear interaction pressure spectra compares favorably with wind-screen microphone measurements in large wind screens at low frequency. PMID:22225016

  20. Estimating atmospheric stability from observations and correcting wind shear models accordingly

    NASA Astrophysics Data System (ADS)

    Holtslag, M. C.; Bierbooms, W. A. A. M.; van Bussel, G. J. W.

    2014-12-01

    Atmospheric stability strongly influences wind shear and thus has to be considered when performing load calculations for wind turbine design. Numerous methods exist however for obtaining stability in terms of the Obukhov length L as well as for correcting the logarithmic wind profile. It is therefore questioned to what extend the choice of adopted methods influences results when performing load analyses. Four methods found in literature for obtaining L, and five methods to correct the logarithmic wind profile for stability are included in the analyses (two for unstable, three for stable conditions). The four methods used to estimate stability from observations result in different PDF's of L, which in turn results in differences in estimated lifetime fatigue loads up to 81%. For unstable conditions hardly any differences are found when using either of the proposed stability correction functions, neither in wind shear nor in fatigue loads. For stable conditions however the proposed stability correction functions differ significantly, and the standard correction for stable conditions might strongly overestimate fatigue loads caused by wind shear (up to 15% differences). Due to the large differences found, it is recommended to carefully choose how to obtain stability and correct wind shear models accordingly.

  1. Nocturnal wind direction shear and its potential impact on pollutant transport

    SciTech Connect

    Bowen, B.M.; Baars, J.A.; Stone, G.L.

    1997-09-01

    The estimation of transport and diffusion of airborne pollutants during the nighttime is challenging, especially over complex terrain where gravity driven drainage flows may be overlain with wind from a different direction. This study investigates the character of wind direction shear in the lowest 100 m using tower measurements from a complex, semi-arid site where local thermally-driven flows are common. the effects of wind direction shear on plume transport are studied by simulating a hypothetical elevated term release. This is accomplished by first simulating transport and dispersion using wind measurements from only the 12-m level from a network of towers. This case represents the approach commonly taken at many facilities where a network of short towers is available. Then the release is modeled using wind measurements made at four levels in the lowest 100 m. The differences between the two simulations are significant and would lead to very different responses in an emergency situation.

  2. Nocturnal wind direction shear and its potential impact on pollutant transport

    SciTech Connect

    Bowen, B.M. [Lawrence Livermore National Lab., CA (United States); Baars, J.A.; Stone, G.L. [Los Alamos National Lab., NM (United States)

    1998-12-31

    The estimation of transport and diffusion of airborne pollutants during the nighttime is challenging, especially over complex terrain where gravity driven drainage flows may be overlain with wind from a different direction. This study investigates the character of wind direction shear in the lowest 100 m using tower measurements from a complex, semi-arid site where local thermally-driven flows are common. The effects of wind direction shear on plume transport are studied by simulating a hypothetical elevated term release. This is accomplished by first simulating transport and dispersion using wind measurements from only the 12-m level from a network of towers. This case represents the approach commonly taken at many facilities where a network of short towers is available. Then the release is modeled using wind measurements made at four levels in the lowest 100 m. The differences between the two simulations are significant and would lead to very different responses in an emergency situation.

  3. Response of Atmospheric Convection to Vertical Wind Shear: Cloud Resolving Simulation with Parameterized Large-Scale Circulation

    NASA Astrophysics Data System (ADS)

    Anber, U. M.; Wang, S.; Sobel, A. H.

    2013-12-01

    It was established more than three decades ago that that vertical wind shear can organize convective storms and greatly extend their lifetimes. However, today we still know little about how convection-shear interaction influences tropical convection and surface rainfall in statistical equilibrium. To address the latter question, we have conducted a series of long- term cloud-resolving simulations with parameterized large scale dynamics, to investigate the role of vertical wind shear on the equilibrated tropical cumulus ensembles. We relax the horizontal mean wind strongly towards a simple unidirectional linear vertical shear profile in the troposphere. The strength of the shear is varied as a control parameter. We prescribe surface enthalpy fluxes to exclude complications from air-sea interaction. Our results indicate two distinct flow regimes: for weak wind shear, time-averaged rainfall decreases with shear and convection remains disorganized; for larger wind shear, rainfall in- creases as convection becomes organized into linear mesoscale systems. This non-monotonic dependence of rainfall on shear is observed when the imposed surface fluxes are moderate. For larger surface fluxes, convection in the unsheared basic state is already strongly organized, so increasing wind shear only leads to increasing rainfall. In addition to surface rainfall, we will also discuss the impact of shear on other variables, such as the parameterized large-scale vertical velocity, convective heating and drying, mass fluxes, cloud fraction, and momentum transport.

  4. Climatological characteristics of high altitude wind shear and lapse rate layers

    NASA Technical Reports Server (NTRS)

    Ehernberger, L. J.; Guttman, N. B.

    1981-01-01

    Indications of the climatological distribution of wind shear and temperature lapse and inversion rates as observed by rawinsonde measurements over the western United States are recorded. Frequencies of the strongest shear, lapse rates, and inversion layer strengths were observed for a 1 year period of record and were tabulated for the lower troposphere, the upper troposphere, and five altitude intervals in the lower stratosphere. Selected bivariate frequencies were also tabulated. Strong wind shears, lapse rates, and inversion are observed less frequently as altitude increases from 175 millibars to 20 millibars. On a seasonal basis the frequencies were higher in winter than in summer except for minor influences due to increased tropopause altitude in summer and the stratospheric wind reversal in the spring and fall.

  5. A candidate concept for display of forward-looking wind shear information

    NASA Technical Reports Server (NTRS)

    Hinton, David A.

    1989-01-01

    A concept is proposed which integrates forward-look wind shear information with airplane performance capabilities to predict future airplane energy state as a function of range. The information could be displayed to a crew either in terms of energy height or airspeed deviations. The anticipated benefits of the proposed display information concept are: (1) a wind shear hazard product that scales directly to the performance impact on the airplane and that has intuitive meaning to flight crews; (2) a reduction in flight crew workload by automatic processing of relevant hazard parameters; and (3) a continuous display of predicted airplane energy state if the approach is continued. Such a display may be used to improve pilot situational awareness or improve pilot confidence in wind shear alerts generated by other systems. The display is described and the algorithms necessary for implementation in a simulation system are provided.

  6. The effect of roughness elements on wind erosion: The importance of surface shear stress distribution

    NASA Astrophysics Data System (ADS)

    Webb, Nicholas P.; Okin, Gregory S.; Brown, Shannon

    2014-05-01

    Representation of surface roughness effects on aeolian sediment transport is a key source of uncertainty in wind erosion models. Drag partitioning schemes are used to account for roughness by scaling the soil entrainment threshold by the ratio of shear stress on roughness elements to that on the vegetated land surface. This approach does not explicitly account for the effects of roughness configuration, which may be important for sediment flux. Here we investigate the significance of roughness configuration for aeolian sediment transport, the ability of drag partitioning approaches to represent roughness configuration effects, and the implications for model accuracy. We use wind tunnel measurements of surface shear stress distributions to calculate sediment flux for a suite of roughness configurations, roughness densities, and wind velocities. Roughness configuration has a significant effect on sediment flux, influencing estimates by more than 1 order of magnitude. Measured and modeled drag partitioning approaches overestimate the predicted flux by 2 to 3 orders of magnitude. The drag partition is sensitive to roughness configuration, but current models cannot effectively represent this sensitivity. The effectiveness of drag partitioning approaches is also affected by estimates of the aerodynamic roughness height used to calculate wind shear velocity. Unless the roughness height is consistent with the drag partition, resulting fluxes can show physically implausible patterns. These results should make us question current assessments of the magnitude of vegetated dryland dust emissions. Representing roughness effects on surface shear stress distributions will reduce uncertainty in quantifying wind erosion, enabling better assessment of its impacts and management solutions.

  7. The Formation and Vertical Movement of Dense Ionized Layers in the Ionosphere Due to Neutral Wind Shears

    Microsoft Academic Search

    W. I. Axford

    1963-01-01

    This paper analyzes Dungey's wind-shear mechamsm for the formation of sporadic E layers and the extension of this mechanism, proposed by the author, which causes vertical transport of ionospheric ionization. Approximate equations are derived to describe quasi-steady ionized layers in which forces due to wind shear in the neutral atmosphere are balanced by the effects of pressure gradients and recombination.

  8. Direct Detection of Vertical Wind Shear in Saturn on the Peaks of the Eastward Jets

    NASA Astrophysics Data System (ADS)

    Garcia-Melendo, Enrique; Sánchez-Lavega, A.; Rojas, J. F.; Pérez-Hoyos, S.; Hueso, R.

    2008-09-01

    Up to the present, evidence of the vertical wind shear in Saturn at cloud level has been captured in the equatorial jet. For other regions the vertical shear of the zonal wind system above the main cloud deck of Saturn's atmosphere has been inferred from meridional temperature measurements at different altitudes by using the Cassini CIRS instrument. Here we extend our previous measurements of the equatorial vertical wind shear to the whole southern hemisphere. We have measured the vertical shear of the zonal winds in the cloud-haze upper layer of Saturn using Cassini ISS images obtained in the MT2 (methane absorption band at 725 nm, sensitive to the upper haze) and CB2 (adjacent continuum, sensing lower cloud) bands. We have found that only the peak of the eastward jets show a decrease in velocity with altitude. The velocity decreases by an amount of 20 m/s in the eastward jets with peak at 27ºS, 42ºS, 55ºS and 70ºS planetocentric latitude or 10ms-1H-1. This vertical shear in the jet peaks adds to the previously found at Equatorial latitudes (Sánchez-Lavega et al., Icarus, 187, 2007). Our analysis of direct wind measurements confirms the thermal-wind results recently presented by Fletcher et al. (Science 389, 5859, 2008), and formerly obtained by Conrath and Pirraglia (Icarus 53, 1983). Albedo measurements show that eastward jet peaks divide each peak region in two contrasted albedo bands in MT2. The bright equatorward side band is consistent with high or abundant aerosols transported by ascending motions, while the dark poleward side band indicates low or little aerosols probably depleted by descending motions. These results are fully consistent with the simple model proposed by Conrath and Pirraglia of jets decaying with altitude and related vertical and meridional circulation.

  9. Inversion and shear layer detection using AMDAR and wind profiler soundings

    NASA Astrophysics Data System (ADS)

    Drüe, C.; Hauf, T.; Hoff, A.

    2009-09-01

    The terminal area of Frankfurt airport (EDDF) offers as unique opportunity to campare vertical soundings of the planetary boundary layer (PBL) by two independent sources. One of these sources is a wind and temperature radar profiler (WTR/RASS) located at the western end of the main pair of runways. This wind temperature radar (WTR) is a Scintec "AP1000" radar wind profiler with RASS (radioacoustic sounding system) extension "WT RASS". The WTR/RASS at Frankfurt is the first wind profiler for operational purposes, which uses RASS also for wind measurements. The second source are AMDAR (aircraft meteorological data relay) data collected by commercial passenger aircraft. They contain at least time, position, temperature, wind speed and direction. German weather service (Deutscher Wetterdienst, DWD) collects hourly profiles at the Central European airports. Since Frankfurt is not completely closed at night, this setup leads to a roughly continuous coverage with hourly vertical profiles. Together, both offer a rare opportunity to compare the ability of both systems to identify inversion and wind-shear layers in the terminal area. To asses the degree of consent between layers detected by both systems, we use probability of detection (POD). The mutual inversion POD is in the range 40 to 60%, except at night below 250 m. With the weak shear criteria used to gain sufficient statistics, consenting shear detection is limited to low-level jets and similar structures. Only the lower edges of detected layers agree well. The vertical extent and top heights of layers detected are frequently underestimated by WTR/RASS in general. AMDAR data seem to be more suitable for the detection of elevated inversions (and probably shear layers). In Contrast, WTR/RASS data are more suitable for detecting low and shallow as well as short-lived structures. In turn, data fusion of both systems seems to be advantageous for monitoring of hazardous atmospheric structures in the terminal area.

  10. Low-latitude dusk flank magnetosheath, magnetopause, and boundary layer for low magnetic shear: Wind observations

    Microsoft Academic Search

    D. Larson; J. McFadden; R. P. Lin; C. Carlson; M. Moyer; K. I. Paularena; M. McCarthy; G. K. Parks; H. Rème; T. R. Sanderson; R. P. Lepping

    1997-01-01

    We have studied in detail a Wind spacecraft crossing of the low-latitude dusk flank magnetosheath, magnetopause (MP), and the low-latitude boundary layer (LLBL) when the local magnetic shear across the MP was low (<30°) and the interplanetary magnetic field (IMF) was northward. We find that the magnetosheath flow tangential to the MP slows down initially as one moves from the

  11. Influences of offshore environmental conditions on wind shear profile parameters in Nantucket Sound

    E-print Network

    Massachusetts at Amherst, University of

    Influences of offshore environmental conditions on wind shear profile parameters in Nantucket Sound in Nantucket Sound, off the coast of Massachusetts. These data provide an excellent opportunity to investigate predictions of the `log law' model at this site. In the shallow, protected waters of Nantucket Sound, tidal

  12. The effect of roughness elements on wind erosion: The importance of surface shear stress distribution

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Representation of surface roughness effects on aeolian sediment transport is a key source of uncertainty in wind erosion models. Drag partitioning schemes are used to account for roughness by scaling the soil entrainment threshold by the ratio of shear stress on roughness elements to that on the veg...

  13. Vertical wind shear on Jupiter from Cassini images Liming Li,1

    E-print Network

    Vertical wind shear on Jupiter from Cassini images Liming Li,1 Andrew P. Ingersoll,1 Ashwin R 2006. [1] Multifilter images of Jupiter acquired by the Cassini Imaging Science Subsystem (ISS on Jupiter from Cassini images, J. Geophys. Res., 111, E04004, doi:10.1029/2005JE002556. 1. Introduction [2

  14. Simultaneous measurements of wind shear and temperature gradient spectra in the stratosphere

    SciTech Connect

    Barat, J.; Cot, C. (Service d'Aeronomie du CNRS, Verrieres le Buisson (France))

    1989-10-01

    The authors present in this paper the first high resolution analysis of wind shears and temperature gradient measured over 25 m in the low stratosphere. Their power spectral densities deduced by two different methods show that for vertical wavelengths greater than 500 m the behaviors of the temperature and vertical velocity fluctuating field are significantly different from the saturated wave model predictions.

  15. Computed Responses of Several Aircraft to Atmospheric Turbulence and Discrete Wind Shears

    NASA Technical Reports Server (NTRS)

    Jewell, W. F.; Stapleford, R. L.; Heffley, R. K.

    1977-01-01

    The computed RMS and peak responses due to atmospheric turbulence and discrete wind shears, respectively, are presented for several aircraft in different flight conditions. The responses are presented with and without the effects of a typical second order washout filter. A complete set of dimensional stability derivatives for each aircraft/flight condition combination evaluated is also presented.

  16. Doppler radar spectral width broadening due to beamwidth and wind shear

    E-print Network

    Boyer, Edmond

    Doppler radar spectral width broadening due to beamwidth and wind shear G. D. NastromÃ? Max: 30 January 1997 Abstract. The spectral width observed by Doppler radars can be due to several eects including the atmospheric turbulence within the radar sample volume plus eects associated

  17. Airborne Wind Shear Detection and Warning Systems: Third Combined Manufacturers' and Technologists' Conference, part 1

    NASA Technical Reports Server (NTRS)

    Vicroy, Dan D. (compiler); Bowles, Roland L. (compiler); Schlickenmaier, Herbert (compiler)

    1991-01-01

    Papers presented at the conference on airborne wind shear detection and warning systems are compiled. The following subject areas are covered: terms of reference; case study; flight management; sensor fusion and flight evaluation; Terminal Doppler Weather Radar data link/display; heavy rain aerodynamics; and second generation reactive systems.

  18. Application of infrared radiometers for airborne detection of clear air turbulence and low level wind shear, airborne infrared low level wind shear detection test

    NASA Technical Reports Server (NTRS)

    Kuhn, P. M.

    1985-01-01

    The feasibility of infrared optical techniques for the advance detection and avoidance of low level wind shear (LLWS) or low altitude wind shear hazardous to aircraft operations was investigated. A primary feasibility research effort was conducted with infrared detectors and instrumentation aboard the NASA Ames Research Center Learjet. The main field effort was flown on the NASA-Ames Dryden B57B aircraft. The original approach visualized a forward-looking, infrared transmitting (KRS-5) window through which signals would reach the detector. The present concept of a one inch diameter light pipe with a 45 deg angled mirror enables a much simpler installation virtually anywhere on the aircraft coupled with the possibility of horizontal scanning via rotation of the forward directed mirror. Present infrared detectors and filters would certainly permit ranging and horizontal scanning in a variety of methods. CRT display technology could provide a contoured picture with possible shear intensity levels from the infrared detection system on the weather radar or a small adjunct display. This procedure shoud be further developed and pilot evaluated in a light aircraft such as a Cessna 207 or equivalent.

  19. Dynamical effects of environmental vertical wind shear on tropical cyclone motion, structure, and intensity

    NASA Astrophysics Data System (ADS)

    Zheng, X.; Duan, Y. H.; Yu, H.

    2007-08-01

    A series of numerical experiments on an f plane are conducted using the fifth-generation Pennsylvania State University-National Center for Atmospheric Research Mesoscale Model, version 3 (MM5) to investigate how environmental vertical wind shear affects the motion, structure, and intensity of a tropical cyclone. The results show that a tropical cyclone has a motion component perpendicular to the vertical shear vector, first to the right of the shear and then to the left. An initially axisymmetric, upright tropical cyclone vortex develops a downshear tilt and wavenumber-one asymmetry when embedded in environmental vertical wind shear. In both small-moderate shears, a storm weakens slightly compared to that in a quiescent environment. The circulation centers between 300 hPa and the surface varies from 20 km to over 80 km. The secondary circulation becomes quite asymmetric about the surface cyclone center. As a result, convection on the upshear-right quadrant diminishes, limiting the upward heat transport in the eyewall and thus lowering the warm core and leading to a weakening of the storm. In strong vertical shear (above 12 m s-1), the vertical tilt exceeds 160 km in 48 h of simulation and the secondary circulation on the upshear side is completely destroyed with low-level outflow. The axisymmetric component of eyewall convection weakens remarkably and becomes much less penetrative. As a result, the warm core becomes weak and appears at lower levels and the storm weakens rapidly accordingly. This up-down weakening mechanism discussed in this study is different from those previously discussed. It emphasizes the penetrative role of eyewall convection in transporting heat from the ocean to the mid-upper troposphere, maintaining the warm core structure of the tropical cyclone. The vertical shear is found negative to eyewall penetrative convection.

  20. Airborne Wind Shear Detection and Warning Systems: First Combined Manufacturers' and Technologists' Conference

    NASA Technical Reports Server (NTRS)

    Spady, Amos A., Jr. (compiler); Bowles, Roland L. (compiler); Schlickenmaier, Herbert (compiler)

    1988-01-01

    The purpose of the meeting was to transfer significant, ongoing results gained during the first year of the joint NASA/FAA Airborne Wind Shear Program to the technical industry and to pose problems of current concern to the combined group. It also provided a forum for manufacturers to review forward-looking technology concepts and for technologists to gain an understanding of FAA certification requirements and the problems encountered by the manufacturers during the development of airborne equipment.

  1. Effects of Vertical Wind Shear on the Intensity and Structure of Numerically Simulated Hurricanes

    Microsoft Academic Search

    William M. Frank; Elizabeth A. Ritchie

    2001-01-01

    A series of numerical simulations of tropical cyclones in idealized large-scale environments is performed to examine the effects of vertical wind shear on the structure and intensity of hurricanes. The simulations are performed using the nonhydrostatic Pennsylvania State University-National Center for Atmospheric Research fifth-generation Mesoscale Model using a 5-km fine mesh and fully explicit representation of moist processes. When large-scale

  2. Rossby-Khantadze electromagnetic planetary waves driven by sheared zonal winds in the E-layer ionosphere

    NASA Astrophysics Data System (ADS)

    Futatani, S.; Horton, W.; Kahlon, L. Z.; Kaladze, T. D.

    2015-01-01

    Nonlinear simulations of electromagnetic Rossby and Khantadze planetary waves in the presence of a shearless and sheared zonal flows in the weakly ionized ionospheric E-layer are carried out. The simulations show that the nonlinear action of the vortex structures keeps the solitary character in the presence of shearless zonal winds as well as the ideal solutions of solitary vortex in the absence of zonal winds. In the presence of sheared zonal winds, the zonal flows result in breaking into separate multiple smaller pieces. A passively convected scalar field is shown to clarify the transport associated with the vortices. The work shows that the zonal shear flows provide an energy source into the vortex structure according to the shear rate of the zonal winds.

  3. An Examination of Aviation Accidents Associated with Turbulence, Wind Shear and Thunderstorm

    NASA Technical Reports Server (NTRS)

    Evans, Joni K.

    2013-01-01

    The focal point of the study reported here was the definition and examination of turbulence, wind shear and thunderstorm in relation to aviation accidents. NASA project management desired this information regarding distinct subgroups of atmospheric hazards, in order to better focus their research portfolio. A seven category expansion of Kaplan's turbulence categories was developed, which included wake turbulence, mountain wave turbulence, clear air turbulence, cloud turbulence, convective turbulence, thunderstorm without mention of turbulence, and low altitude wind shear, microburst or turbulence (with no mention of thunderstorms).More than 800 accidents from flights based in the United States during 1987-2008 were selected from a National Transportation Safety Board (NTSB) database. Accidents were selected for inclusion in this study if turbulence, thunderstorm, wind shear or microburst was considered either a cause or a factor in the accident report, and each accident was assigned to only one hazard category. This report summarizes the differences between the categories in terms of factors such as flight operations category, aircraft engine type, the accident's geographic location and time of year, degree of injury to aircraft occupants, aircraft damage, age and certification of the pilot and the phase of flight at the time of the accident.

  4. Flight evaluation of a simple total energy-rate system with potential wind-shear application

    NASA Technical Reports Server (NTRS)

    Ostroff, A. J.; Hueschen, R. M.; Hellbaum, R. F.; Creedon, J. F.

    1981-01-01

    Wind shears can create havoc during aircraft terminal area operations and have been cited as the primary cause of several major aircraft accidents. A simple sensor, potentially having application to the wind-shear problem, was developed to rapidly measure aircraft total energy relative to the air mass. Combining this sensor with either a variometer or a rate-of-climb indicator provides a total energy-rate system which was successfully applied in soaring flight. The measured rate of change of aircraft energy can potentially be used on display/control systems of powered aircraft to reduce glide-slope deviations caused by wind shear. The experimental flight configuration and evaluations of the energy-rate system are described. Two mathematical models are developed: the first describes operation of the energy probe in a linear design region and the second model is for the nonlinear region. The calculated total rate is compared with measured signals for many different flight tests. Time history plots show the tow curves to be almost the same for the linear operating region and very close for the nonlinear region.

  5. A new paradigm for intensity modification of tropical cyclones: thermodynamic impact of vertical wind shear on the inflow layer

    Microsoft Academic Search

    M. Riemer; M. T. Montgomery; M. E. Nicholls

    2010-01-01

    An important roadblock to improved intensity forecasts for tropical cyclones (TCs) is our incomplete understanding of the interaction of a TC with the environmental flow. In this paper we re-visit the canonical problem of a TC in vertical wind shear on an f-plane. A suite of numerical experiments is performed with intense TCs in moderate to strong vertical shear. We

  6. The Influence of Meridional Shear on Planetary Waves. Part 1: Nonsingular Wind Profiles.

    NASA Astrophysics Data System (ADS)

    Boyd, John P.

    1982-04-01

    Using a simple separable model in which the mean wind U(y) is assumed to be a function of latitude only, those effects of latitudinal shear which do not depend on the vanishing of U(y) are examined for planetary waves in the middle atmosphere (the stratosphere and mesosphere).First, it is shown that for nonsingular wind profiles the WKB method and ray tracing may be inaccurate for meridional shear. It is both physically and mathematically preferable to interpret the results of more complex models in terms of vertically propagating modes since the amplitude of the waves as a function of latitude is determined primarily by the modal structure rather than by variations of the mean wind or the refractive index.Second, it is demonstrated that westerly planetary gravity waves, which are vertically trapped as shown by Charney and Drazin (1961), are also latitudinally trapped near the pole where the mean winds are easterly. In consequence, such waves, which form the quasi-stationary spectrum of the summer hemisphere, are unaffected by the critical latitude in the subtropics of the winter hemisphere. The physical implications of these and other findings are discussed.

  7. Journal of Atmospheric and Solar-Terrestrial Physics 68 (2006) 10611074 Seasonal variation of mesopause region wind shears,

    E-print Network

    2006-01-01

    Journal of Atmospheric and Solar-Terrestrial Physics 68 (2006) 1061­1074 Seasonal variation of mesopause region wind shears, convective and dynamic instabilities above Fort Collins, CO: A statistical) temperature and horizontal wind, observed by Colorado State University sodium lidar over Fort Collins, CO (411

  8. A spatial model of wind shear and turbulence for flight simulation. Ph.D. Thesis - Colorado State Univ.

    NASA Technical Reports Server (NTRS)

    Campbell, C. W.

    1984-01-01

    A three dimensional model which combines measurements of wind shear in the real atmosphere with three dimensional Monte Carlo simulated turbulence was developed. The wind field over the body of an aircraft can be simulated and all aerodynamic loads and moments calculated.

  9. First observation of mesospheric wind shear as high as 330 m s-1 km-1

    NASA Astrophysics Data System (ADS)

    Wu, Yong-Fu; Widdel, H.-U.; Offermann, D.

    1995-09-01

    Mesospheric wind profiles with an altitude resolution of 25 m have been obtained by means of radar tracking of foil chaff clouds. Such experiments were performed during winter 1990 at Biscarrosse, France (44°N, 1°W). On one flight, a wind shear as high as 330 m s-1 km-1 at 87.4 km and a region of dynamical instability between 86 and 88 km was measured. This wind shear is believed to be the largest value ever measured in the mesosphere. The region of dynamical instability results from a superposition of two wave motions, and is found to link well with enhanced turbulence and small-scale wave activity. Acknowledgements. I thank D. R. McDiarmid of the Herzberg Institute of Astrophysics, National Research Council, Canada, for important ideas and discussions during the development of this work. I thank the referees for useful comments which have improved the paper. I also thank E.M. Poulter of NIWA for helpful suggestions, and for reading the manuscript and making useful comments. The work was supported by contract CO1309 of the New Zealand Foundation for Research, Science and Technology. Topical Editor C.-G. Fälthammar thanks K. Mursula and W. J. Hughes for their help in evaluating this paper.--> Correspondence to: W. Allan-->

  10. Airborne Wind Shear Detection and Warning Systems: Third Combined Manufacturers' and Technologists' Conference, part 2

    NASA Technical Reports Server (NTRS)

    Vicroy, Dan D. (compiler); Bowles, Roland L. (compiler); Schlickenmaier, Herbert (compiler)

    1991-01-01

    The Third Combined Manufacturers' and Technologists' Conference was held in Hampton, Va., on October 16-18, 1990. The purpose of the meeting was to transfer significant on-going results of the NASA/FAA joint Airborne Wind Shear Program to the technical industry and to pose problems of current concern to the combined group. It also provided a forum for manufacturers to review forward-look technology concepts and for technologists to gain an understanding of the problems encountered by the manufacturers during the development of airborne equipment and the FAA certification requirements.

  11. Airborne Wind Shear Detection and Warning Systems: Fourth Combined Manufacturers' and Technologists' Conference, part 1

    NASA Technical Reports Server (NTRS)

    Vicroy, Dan D. (compiler); Bowles, Roland L. (compiler); Passman, Robert H. (compiler)

    1992-01-01

    The purpose of the meeting was to transfer significant ongoing results of the NASA/FAA joint Airborne Wind Shear Program to the technical industry and to pose problems of current concern to the combined group. It also provided a forum for manufacturers to review forward-look technology concepts and for technologists to gain an understanding of the problems encountered by the manufacturers during the development of airborne equipment and the FAA certification requirements. The present document was compiled to record the essence of the technology updates and discussions which follow each.

  12. Airborne Wind Shear Detection and Warning Systems. Second Combined Manufacturers' and Technologists' Conference, part 1

    NASA Technical Reports Server (NTRS)

    Spady, Amos A., Jr. (compiler); Bowles, Roland L. (compiler); Schlickenmaier, Herbert (compiler)

    1990-01-01

    The Second Combined Manufacturers' and Technologists' Conference hosted jointly by NASA Langley (LaRC) and the Federal Aviation Administration (FAA) was held in Williamsburg, Virginia, on October 18 to 20, 1988. The purpose of the meeting was to transfer significant, ongoing results gained during the second year of the joint NASA/FAA Airborne Wind Shear Program to the technical industry and to pose problems of current concern to the combined group. It also provided a forum for manufacturers to review forward-look technology concepts and for technologists to gain an understanding of the problems encountered by the manufacturers during the development of airborne equipment and the FAA certification requirements.

  13. Convectively generated stratospheric gravity waves - The role of mean wind shear

    NASA Technical Reports Server (NTRS)

    Holton, J. R.; Durran, D.

    1993-01-01

    A two-dimensional numerical simulation of mid-latitude squall lines is used to study the properties of storm-induced stratospheric gravity waves. Owing to the tendency for convective cells to form at the forward edge of a squall line, and then propagate toward the rear, the simulated storms preferentially generate gravity waves that propagate toward the rear of the storm. This anisotropy in gravity wave generation leads to a net vertical transfer of momentum into the stratosphere. Cases with and without stratospheric mean wind shear are compared. In the latter case Doppler shifting of the waves to lower frequencies leads to wave breaking and enhanced wave - mean-flow interaction.

  14. Turbulent transport model of wind shear in thunderstorm gust fronts and warm fronts

    NASA Technical Reports Server (NTRS)

    Lewellen, W. S.; Teske, M. E.; Segur, H. C. O.

    1978-01-01

    A model of turbulent flow in the atmospheric boundary layer was used to simulate the low-level wind and turbulence profiles associated with both local thunderstorm gust fronts and synoptic-scale warm fronts. Dimensional analyses of both type fronts provided the physical scaling necessary to permit normalized simulations to represent fronts for any temperature jump. The sensitivity of the thunderstorm gust front to five different dimensionless parameters as well as a change from axisymmetric to planar geometry was examined. The sensitivity of the warm front to variations in the Rossby number was examined. Results of the simulations are discussed in terms of the conditions which lead to wind shears which are likely to be most hazardous for aircraft operations.

  15. MAGNETIC RECONNECTION IN THE SOLAR WIND AT CURRENT SHEETS ASSOCIATED WITH EXTREMELY SMALL FIELD SHEAR ANGLES

    SciTech Connect

    Gosling, J. T. [Laboratory for Atmospheric and Space Physics, University of Colorado, 3665 Discovery Drive, Boulder, CO 80303 (United States); Phan, T. D., E-mail: jack.gosling@lasp.colorado.edu [Space Sciences Laboratory, University of California, Berkeley, CA 94720 (United States)

    2013-02-01

    Using Wind 3 s plasma and magnetic field data, we have identified nine reconnection exhausts within a solar wind disturbance on 1998 October 18-20 driven by a moderately fast interplanetary coronal mass ejection (ICME). Three of the exhausts within the ICME were associated with current sheets having local field shear angles, {theta}, ranging from 4 Degree-Sign to 9 Degree-Sign , the smallest reported values of {theta} yet associated with reconnection exhausts in a space plasma. They were observed in plasma characterized by extremely low (0.02-0.04) plasma {beta}, and very high (281-383 km s{sup -1}) Alfven speed, V{sub A}. Low {beta} allows reconnection to occur at small {theta} and high V{sub A} leads to exhaust jets that are fast enough relative to the surrounding solar wind to be readily identified. Very small-{theta} current sheets are common in the solar wind at 1 AU, but typically are not associated with particularly low plasma {beta} or high V{sub A}. On the other hand, small-{theta} current sheets should be common in the lower solar corona, a plasma regime of extremely low {beta} and extremely high V{sub A}. Our observations lend credence to models that predict that reconnection at small-{theta} current sheets is primarily responsible for coronal heating.

  16. The Orlando TDWR testbed and airborne wind shear date comparison results

    NASA Technical Reports Server (NTRS)

    Campbell, Steven; Berke, Anthony; Matthews, Michael

    1992-01-01

    The focus of this talk is on comparing terminal Doppler Weather Radar (TDWR) and airborne wind shear data in computing a microburst hazard index called the F factor. The TDWR is a ground-based system for detecting wind shear hazards to aviation in the terminal area. The Federal Aviation Administration will begin deploying TDWR units near 45 airports in late 1992. As part of this development effort, M.I.T. Lincoln Laboratory operates under F.A.A. support a TDWR testbed radar in Orlando, FL. During the past two years, a series of flight tests has been conducted with instrumented aircraft penetrating microburst events while under testbed radar surveillance. These tests were carried out with a Cessna Citation 2 aircraft operated by the University of North Dakota (UND) Center for Aerospace Sciences in 1990, and a Boeing 737 operated by NASA Langley Research Center in 1991. A large data base of approximately 60 instrumented microburst penetrations has been obtained from these flights.

  17. The Structural Changes of Tropical Cyclones Upon Interaction with Vertical Wind Shear

    NASA Technical Reports Server (NTRS)

    Ritchie, Elizabeth A.

    2003-01-01

    The Fourth Convection and Moisture Experiment (CAMEX-4) provided a unique opportunity to observe the distributions and document the roles of important atmospheric factors that impact the development of the core asymmetries and core structural changes of tropical cyclones embedded in vertical wind shear. The state-of-the-art instruments flown on the NASA DC-8 and ER-2, in addition to those on the NOAA aircraft, provided a unique set of observations that documented the core structure throughout the depth of the tropical cyclone. These data have been used to conduct a combined observational and modeling study using a state-of-the-art, high- resolution mesoscale model to examine the role of the environmental vertical wind shear in producing tropical cyclone core asymmetries, and the effects on the structure and intensity of tropical cyclones.The scientific objectives of this study were to obtain in situ measurements that would allow documentation of the physical mechanisms that influence the development of the asymmetric convection and its effect on the core structure of the tropical cyclone.

  18. ``Slab'' modes, quasi-2-D turbulence, shear, and flux tubes in the expanding solar wind

    NASA Astrophysics Data System (ADS)

    Roberts, D. A.; Goldstein, M. L.; Deane, A.; Ghosh, S.

    1999-06-01

    Solar wind fluctuations exhibit anisotropies in both the variances of the vectors and in power spectra. The latter have only been studied observationally in two dimensions, but the result is that there seems to be a preference for power along and transverse to the mean magnetic field, with significant but lower power in between. This observation has led to the idea that the solar wind turbulence consists of two main populations, ``slab-like'' parallel propagating Alfvén waves and ``quasi-2-D'' fluctuations that have both wave vectors and fluctuations confined to a plane perpendicular to the mean field. Recent simulation studies suggest that the perpendicular component of the fluctuations may be due to the shearing of the slab modes, rather than to quasi-2-D fluctuations. Here we examine these scenarios and combinations of them using a compressible three-dimensional MHD code in spherical coordinates. Results show how nearly two-dimensional magnetohydrodynamic turbulence can be initiated and how it evolves with distance in the third dimension. Expanding flows lead to a suppression of the nonlinear cascades, mainly due to the changing transverse length scales. Quasi-2-D velocity fluctuation levels are determined more from the 2-D dynamics than from the expansion except when the velocity fluctuations are initially dominant. With expansion, quasi-2-D magnetic fluctuations always dominate the corresponding velocity fluctuations at late times. The ``slab'' modes produce perpendicular fluctuations when sheared, as in nonexpanding simulations, and these become dominant when initially equipartitioned with the quasi-2-D modes.

  19. A shear sensitive monomer-polymer liquid crystal system for wind tunnel applications

    NASA Technical Reports Server (NTRS)

    Parmar, D. S.; Singh, Jag J.; Eftekhari, Abe

    1992-01-01

    Characteristics of a liquid crystal system, comprised of a shear-sensitive cholesteric-monomer liquid crystal thin-film coated on a liquid-crystal polymer substrate, are described. The system provides stable Grandjean texture, a desirable feature for shear-stress measurements using selective reflection from the monomer liquid-crystal helix structure. Impingement of gas or air flow on the monomer liquid-crystal free surface changes the wavelength of the selective reflection for an incident white light from red toward blue with increase in the rate of gas flow. The contrast of the selectively reflected light improves considerably by providing a thin black coating of about 5 microns at the monomer-polymer interface. The coating thickness is such that the steric interactions are still sufficiently strong to maintain Grandjean texture. For a small angle of incidence of a monochromatic light, the measurement of the reflected light intensity normal to the monomer-polymer liquid-crystal interface enables the determination of the wavelength for selective reflection as a function of the gas-flow differential pressure applied in the plane of the interface. The variation of the wavelength with the pressure is linear with a slope of about 2 nm/mmHg. Furthermore, the shear-stress effects are reversible unlike for monomer liquid crystal-metal systems used for flow visualization on wind-tunnel model surfaces. The present system offers a suitable method for direct on-line measurement of shear stress field from measurements of the wavelength for selective reflection for an incident white light.

  20. Surface Shear Stress Estimates from Geostrophic Winds for Use in Sensible and Latent Heat Flux Formulations

    NASA Astrophysics Data System (ADS)

    Crago, Richard D.

    The surface shear stress (or friction velocity, u_{*}) is found in many formulations for evapotranspiration (LE) and sensible heat flux (H) from land surfaces, but is difficult to estimate without actually measuring wind speeds. Here, ABL (Atmospheric Boundary Layer) similarity theory is used to estimate u _{*} from the geostrophic wind (i.e. from the atmospheric pressure field). Atmospheric pressure is routinely measured at most weather stations across many continents on an hourly basis. Data from the First ISLSCP (International Satellite Land Surface Climatology Project) Field Experiment (FIFE) were analyzed. The values of the similarity variables B and B_{ rm W} were determined, and several formulations for the variables were compared. The optimal formulation (i.e., the one which produced the best match with the reference u_{*} values obtained from surface layer similarity) used the magnitude (G) of the geostrophic wind and a stability-dependent B _{rm W} function. The effects of random errors, baroclinicity, and inertial effects on the results were analyzed. Random measurement errors and the omission of inertial effects in the optimal formulation may cause considerable scatter. No dependence of the similarity variables on baroclinicity or scale-height ratio was discernable amidst the scatter, but they may still at times be important. Contrary to the findings of Hasse and Wagner (1971), no tendency was found in the low wind speed range for near surface wind speeds to be greater than geostrophic wind speeds. The geostrophic drag coefficient (i.e. u_{* }/G) did not vary with stability or baroclinicity; a constant value of 0.1006 (for z_0 = 1.05 m) gave unbiased estimates of u_ {*}, and a higher correlation with the reference values than the optimal ABL similarity formulation. Estimates of H and LE using ABL similarity for temperature, the surface energy budget for LE, and the optimal B_ {rm W} formulation for u _{*} gave correlations with values measured at the surface using the Bowen-ratio with energy -budget method of 0.73 and 0.92, respectively. ABL similarity with measured winds provided better estimates, but is less applicable for widespread use in hydrology. Reduction of measurement error and incorporation of accurate acceleration estimates could improve results.

  1. Airborne Wind Shear Detection and Warning Systems. Fourth Combined Manufacturers' and Technologists' Conference, part 2

    NASA Technical Reports Server (NTRS)

    Vicroy, Dan D. (compiler); Bowles, Roland L. (compiler); Passman, Robert H. (compiler)

    1992-01-01

    The Fourth Combined Manufacturers' and Technologists' Conference was hosted jointly by NASA Langley Research Center (LaRC) and the Federal Aviation Administration (FAA) in Williamsburg, Virginia, on April 14-16, 1992. The meeting was co-chaired by Dr. Roland Bowles of LaRC and Bob Passman of the FAA. The purpose of the meeting was to transfer significant ongoing results of the NASA/FAA Joint Airborne Wind Shear Program to the technical industry and to pose problems of current concern to the combined group. It also provided a forum for manufacturers to review forward-look technology concepts and for technologists to gain an understanding of the problems encountered by the manufacturers during the development of airborne equipment and the FAA certification requirements. The present document has been compiled to record the essence of the technology updates and discussions which follow each.

  2. An airborne FLIR detection and warning system for low altitude wind shear

    NASA Technical Reports Server (NTRS)

    Sinclair, Peter C.; Kuhn, Peter M.

    1991-01-01

    It is shown through some preliminary flight measurement research that a forward looking infrared radiometer (FLIR) system can be used to successfully detect the cool downdraft of downbursts (microbusts/macrobursts) and thunderstorm gust front outflows that are responsible for most of the low altitude wind shear (LAWS) events. The FLIR system provides a much greater safety margin for the pilot than that provided by reactive designs such as inertial air speed systems. Preliminary results indicate that an advanced airborne FLIR system could provide the pilot with remote indication of microburst (MB) hazards along the flight path ahead of the aircraft. Results of a flight test of a prototype FLIR system show that a minimum warning time of one to four minutes (5 to 10 km), depending on aircraft speed, is available to the pilot prior to the microburst encounter.

  3. Marked surface inversions and wind shear: A safety risk for departing aircraft

    NASA Technical Reports Server (NTRS)

    Korhonen, O.

    1983-01-01

    Marked surface inversions occur most frequently in dry continental climates, where low atmospheric humidity allows heat transfer by long wave thermal radiation. In the northern latitudes, surface inversions reach their maximum intensity during the winter, when the incoming Sun's radiation is negligible and radiative cooling is dominant during the long nights. During winter, air mass boundaries are sharp, which causes formation of marked surface inversions. The existence of these inversions and sharp boundaries increase the risk of wind shear. The information should refer to marked inversions exceeding a temperature difference of 10 deg C up to 1000 feet. The need to determine the temperature range over which he information is operationally needed and the magnitude of the inversion required before a notification to pilots prior to departure is warranted are outlined.

  4. Airborne Wind Shear Detection and Warning Systems. Second Combined Manufacturers' and Technologists' Conference, part 2

    NASA Technical Reports Server (NTRS)

    Spady, Amos A., Jr. (compiler); Bowles, Roland L. (compiler); Schlickenmaier, Herbert (compiler)

    1990-01-01

    The Second Combined Manufacturers' and Technologists' Conference was hosted jointly by NASA Langley (LaRC) and the Federal Aviation Administration (FAA) in Williamsburg, Virginia, on October 18 to 20, 1988. The meeting was co-chaired by Dr. Roland Bowles of LaRC and Herbrt Schlickenmaier of the FAA. The purpose of the meeting was to transfer significant, ongoing results gained during the second year of the joint NASA/FAA Airborne Wind Shear Program to the technical industry and to pose problems of current concern to the combined group. It also provided a forum for manufacturers to review forward-look technology concepts and for technologists to gain an understanding of the problems encountered by the manufacturers during the development of airborne equipment and the FAA certification requirements.

  5. A new paradigm for intensity modification of tropical cyclones: thermodynamic impact of vertical wind shear on the inflow layer

    Microsoft Academic Search

    M. Riemer; M. T. Montgomery; M. E. Nicholls

    2009-01-01

    An important roadblock to improved intensity forecasts for tropical cyclones (TCs) is our incomplete understanding of the interaction of a TC with the environmental flow. In this paper we re-visit the classical idealised numerical experiment of tropical cyclones (TCs) in vertical wind shear on an f-plane. We employ a set of simplified model physics - a simple bulk aerodynamic boundary

  6. Piloted-simulation evaluation of escape guidance for microburst wind shear encounters. M.S. Thesis - George Washington Univ.

    NASA Technical Reports Server (NTRS)

    Hinton, David A.

    1989-01-01

    Numerous air carrier accidents and incidents result from encounters with the atmospheric wind shear associated with microburst phenomena, in some cases resulting in heavy loss of life. An important issue in current wind shear research is how to best manage aircraft performance during an inadvertent wind shear encounter. The goals of this study were to: (1) develop techniques and guidance for maximizing an aircraft's ability to recover from microburst encounters following takeoff, (2) develop an understanding of how theoretical predictions of wind shear recovery performance might be achieved in actual use, and (3) gain insight into the piloting factors associated with recovery from microburst encounters. Three recovery strategies were implemented and tested in piloted simulation. Results show that a recovery strategy based on flying a flight path angle schedule produces improved performance over constant pitch attitude or acceleration-based recovery techniques. The best recovery technique was initially counterintuitive to the pilots who participated in the study. Evidence was found to indicate that the techniques required for flight through the turbulent vortex of a microburst may differ from the techniques being developed using classical, nonturbulent microburst models.

  7. 7.2 DISPERSION IN ATMOSPHERIC CONVECTIVE BOUNDARY LAYER WITH WIND SHEARS: FROM LABORATORY MODELS TO COMPLEX SIMULATION STUDIES

    E-print Network

    Fedorovich, Evgeni

    7.2 DISPERSION IN ATMOSPHERIC CONVECTIVE BOUNDARY LAYER WITH WIND SHEARS: FROM LABORATORY MODELS, Oklahoma 1. INTRODUCTION Convective boundary layers (CBLs) driven by buoyancy forcings from the bottom or forcing in the boundary layer is primarily represented by convective heat transfer from a warm underlying

  8. Effects of turbulent eddies and Langmuir circulations on scalar transfer in a sheared wind-driven liquid flow

    NASA Astrophysics Data System (ADS)

    Takagaki, Naohisa; Kurose, Ryoichi; Tsujimoto, Yuta; Komori, Satoru; Takahashi, Keiko

    2015-01-01

    The effects of turbulent eddies and Langmuir circulations in liquid flow on scalar transfer across a sheared wind-driven gas-liquid interface are investigated by means of a direct numerical simulation of a gas-liquid two-phase turbulent flow with a wind-driven nonbreaking wavy interface. The wind-driven wavy gas-liquid interface is captured using an arbitrary Lagrangian-Eulerian method with boundary-fitted coordinates on moving grids. The results show that Langmuir circulations are generated on the liquid side below the sheared wind-driven gas-liquid interface. The marker particles on the gas-liquid interface, the turbulent eddies in the form of streamwise vortices on the liquid side (i.e., the typical horseshoe vortices associated with bursting motions), and the low scalar flux lines on the gas-liquid interface induced by the turbulent eddies on the liquid side tend to locally concentrate in the regions along the downward flows caused by the Langmuir circulations. It is suggested that the turbulent eddies on the liquid side mainly control the scalar transfer across the sheared wind-driven gas-liquid interface, and the effect of the Langmuir circulations is relatively small.

  9. Effects of vertical wind shear on convective development during a landfall of severe tropical storm Bilis (2006)

    NASA Astrophysics Data System (ADS)

    Wang, Donghai; Li, Xiaofan; Tao, Wei-Kuo; Wang, Yuan

    2009-10-01

    Effects of vertical wind shear on convective development during the landfall of tropical storm Bilis (2006) are investigated with a pair of sensitivity experiments using a two-dimensional cloud-resolving model. The validated simulation data from Wang et al. [Wang, D., Li, X., Tao, W.-K., Liu, Y., Zhou, H., 2009: Torrential rainfall processes associated with a landfall of severe tropical storm Bilis (2006): A two-dimensional cloud-resolving modeling study. Atmos. Res., 91, 94-104.] are used as the control experiment. The difference between the control and sensitivity experiments is that vertically varying zonal winds in the control experiment are replaced by their mass-weighted means in the sensitivity experiment. The imposed vertical velocity with ascending motion in the upper troposphere and descending motion in the lower troposphere is responsible for dominant stratiform rainfall on 15 July. The vertical wind shear does not have important impacts on development of stratiform rainfall. One day later, imposed upward motion extends to the lower troposphere. The inclusion of negative vertical wind shear produces well-organized convection and strong convective rainfall because it causes kinetic energy transfer from large-scale forcing to perturbation circulations.

  10. Time-accurate aeroelastic simulations of a wind turbine in yaw and shear using a coupled CFD-CSD method

    NASA Astrophysics Data System (ADS)

    Yu, D. O.; Kwon, O. J.

    2014-06-01

    In the present study, aeroelastic simulations of horizontal-axis wind turbine rotor blades were conducted using a coupled CFD-CSD method. The unsteady blade aerodynamic loads and the dynamic blade response due to yaw misalignment and non-uniform sheared wind were investigated. For this purpose, a CFD code solving the RANS equations on unstructured meshes and a FEM-based CSD beam solver were used. The coupling of the CFD and CSD solvers was made by exchanging the data between the two solvers in a loosely coupled manner. The present coupled CFD-CSD method was applied to the NREL 5MW reference wind turbine rotor, and the results were compared with those of CFD-alone rigid blade calculations. It was found that aeroelastic blade deformation leads to a significant reduction of blade aerodynamic loads, and alters the unsteady load behaviours, mainly due to the torsional deformation. The reduction of blade aerodynamic loads is particularly significant at the advancing rotor blade side for yawed flow conditions, and at the upper half of rotor disk where wind velocity is higher due to wind shear.

  11. Surface and Bulk Oscillations of Sessile Drops: Clearing Up Confusion and Understanding Wind Sheared Drops

    NASA Astrophysics Data System (ADS)

    Milne, Andrew J. B.; Defez Garcia, Beatriz; Cabrerizo Vilchez, Miguel; Amirfazli, Alidad

    2011-11-01

    Sessile drop oscillations are studied in the presence of a shearing airflow, and varying body force. The various possibilities for analysis, (center of mass or drop surface oscillations) are elucidated through presenting a unifying analysis framework based on wavenumber, frequency, and fluid properties. This work examines a range of fluid properties in a single study for the first time. A dispersion relation is found relating the frequency of centroid oscillation and capillary-gravity wave number, depending on the ratio (surface tension/liquid density)^1/2, drop size-3/2 and contact angle. The effects of contact angle are more complex than previously suggested simplifications, or analytic solutions for axisymetric drops and must at present be treated empirically. The growth of sessile drop oscillations is linear at low air velocities and exponential at higher air velocities. This is explained by drawing analogies to drops experiencing a varying body force, and to wind driven capillary-gravity waves on lakes, respectively. Liquid viscosity retards the growth of the waves, and has other important effects.

  12. Simulation and measurement of surface shear stress over isolated and closely spaced transverse dunes in a wind tunnel

    Microsoft Academic Search

    Ian J. Walker; William G. Nickling

    2003-01-01

    Topographic interactions generate multidirectional and unsteady airflow that limits the application of velocity profile approaches for estimating sediment transport over dunes. Results are presented from a series of wind tunnel simulations using Irwin-type surface-mounted pressure sensors to measure shear stress variability directly at the surface over both isolated and closely spaced sharp-crested model dunes. Findings complement existing theories on secondary

  13. Importance of thermal effects and sea surface roughness for wind resource and wind shear at offshore sites

    E-print Network

    Heinemann, Detlev

    the measurement program Rødsand, located in the Danish Baltic Sea. From a given wind speed at one height measured at 10-m height is extrapolated to 50-m height and the power production of a wind turbine to extrapolate wind speed measurements performed at lower heights to the planned hub height of a turbine. Also

  14. Automatic detection of low altitude wind shear due to gust fronts in the terminal Doppler weather radar operational demonstration

    NASA Technical Reports Server (NTRS)

    Klingle-Wilson, Diana

    1990-01-01

    A gust front is the leading edge of the cold air outflow from a thunderstorm. Wind shears and turbulence along the gust front may produce potentially hazardous conditions for an aircraft on takeoff or landing such that runway operations are significantly impacted. The Federal Aviation Administration (FAA) has therefore determined that the detection of gust fronts in the terminal environment be an integral part of the Terminal Doppler Weather Radar (TDWR) system. Detection of these shears by the Gust Front Algorithm permits the generation of warnings that can be issued to pilots on approach and departure. In addition to the detection capability, the algorithm provides an estimate of the wind speed and direction following the gust front (termed wind shift) and the forecasted location of the gust front up to 20 minutes before it impacts terminal operations. This has shown utility as a runway management tool, alerting runway supervisors to approaching wind shifts and the possible need to change runway configurations. The formation and characteristics of gust fronts and their signatures in Doppler radar data are discussed. A brief description of the algorithm and its products for use by Air Traffic Control (ATC), along with an assessment of the algorithm's performance during the 1988 Operational Test and Evaluation, is presented.

  15. Analysis of wind shear models and trends in different terrains M.L. Ray *, A.L. Rogers, and J.G. McGowan

    E-print Network

    Massachusetts at Amherst, University of

    1 Analysis of wind shear models and trends in different terrains M.L. Ray *, A.L. Rogers, and J years. Based on a statistical analysis of the prediction errors, there is no significant difference of data analysis procedures appropriate to the sites that most accurately predict the hub height mean wind

  16. DYNAMICS OF CONVECTIVE ENTRAINMENT IN A HETEROGENEOUSLY STRATIFIED ATMOSPHERE WITH WIND SHEAR

    Microsoft Academic Search

    Robert Conzemius; Evgeni Fedorovich

    Shear and buoyancy are both known to contribute to the development of boundary layers, whose characteristics include turbulent mixing of scalar quantities within the layer. Purely shear-driven boundary layers include airflow over an airplane wing and stream flow over a bottom surface. Buoyancy-driven boundary layers include the atmospheric convective boundary layer (CBL) and the upper levels of the ocean from

  17. Competing mechanisms of plasma transport in inhomogeneous configurations with velocity shear: the solar-wind interaction with earth's magnetosphere.

    PubMed

    Faganello, M; Califano, F; Pegoraro, F

    2008-01-11

    Two-dimensional simulations of the Kelvin-Helmholtz instability in an inhomogeneous compressible plasma with a density gradient show that, in a transverse magnetic field configuration, the vortex pairing process and the Rayleigh-Taylor secondary instability compete during the nonlinear evolution of the vortices. Two different regimes exist depending on the value of the density jump across the velocity shear layer. These regimes have different physical signatures that can be crucial for the interpretation of satellite data of the interaction of the solar wind with the magnetospheric plasma. PMID:18232777

  18. Competing Mechanisms of Plasma Transport in Inhomogeneous Configurations with Velocity Shear: The Solar-Wind Interaction with Earth's Magnetosphere

    SciTech Connect

    Faganello, M.; Califano, F.; Pegoraro, F. [Physics Department, University of Pisa, Pisa (Italy)

    2008-01-11

    Two-dimensional simulations of the Kelvin-Helmholtz instability in an inhomogeneous compressible plasma with a density gradient show that, in a transverse magnetic field configuration, the vortex pairing process and the Rayleigh-Taylor secondary instability compete during the nonlinear evolution of the vortices. Two different regimes exist depending on the value of the density jump across the velocity shear layer. These regimes have different physical signatures that can be crucial for the interpretation of satellite data of the interaction of the solar wind with the magnetospheric plasma.

  19. Experimental evaluation of a wind shear alert and energy management display

    NASA Technical Reports Server (NTRS)

    Kraiss, K.-F.; Baty, D. L.

    1978-01-01

    A method is proposed for onboard measurement and display of specific windshear and energy management data derived from an air data computer. An open-loop simulation study is described which was carried out to verify the feasibility of this display concept, and whose results were used as a basis to develop the respective cockpit instrumentation. The task was to fly a three-degree landing approach under various shear conditions with and without specific information on the shear. Improved performance due to augmented cockpit information was observed. Critical shears with increasing tailwinds could be handled more consistently and with less deviation from the glide path.

  20. Solar-wind turbulence and shear: a superposed-epoch analysis of corotating interaction regions at 1 AU

    SciTech Connect

    Borovsky, Joseph E [Los Alamos National Laboratory; Denton, Michael H [LANCASTER UNIV.

    2009-01-01

    A superposed-epoch analysis of ACE and OMNI2 measurements is performed on 27 corotating interaction regions (CIRs) in 2003-2008, with the zero epoch taken to be the stream interface as determined by the maximum of the plasma vorticity. The structure of CIRs is investigated. When the flow measurements are rotated into the local-Parker-spiral coordinate system the shear is seen to be abrupt and intense, with vorticities on the order of 10{sup -5}-10{sup -4} sec{sup -1}. Converging flows perpendicular to the stream interface are seen in the local-Parker-spiral coordinate system and about half of the CIRs show a layer of divergent rebound flow away from the stream interface. Arguments indicate that any spreading of turbulence away from the region where it is produced is limited to about 10{sup 6} km, which is very small compared with the thickness of a CrR. Analysis of the turbulence across the CrRs is performed. When possible, the effects of discontinuities are removed from the data. Fluctuation amplitudes, the Alfvenicity, and the level of Alfvenic correlations all vary smoothly across the CrR. The Alfven ratio exhibits a decrease at the shear zone of the stream interface. Fourier analysis of 4.5-hr subintervals of ACE data is performed and the results are superposed averaged as an ensemble of realizations. The spectral slopes of the velocity, magnetic-field, and total-energy fluctuations vary smoothly across the CIR. The total-energy spectral slope is {approx} 3/2 in the slow and fast wind and in the CrRs. Analysis of the Elsasser inward-outward fluctuations shows a smooth transition across the CrR from an inward-outward balance in the slow wind to an outward dominance in the fast wind. A number of signatures of turbulence driving at the shear zone are sought (entropy change, turbulence amplitude, Alfvenicity, Alfven ratio, spectral slopes, in-out nature): none show evidence of driving of turbulence by shear.

  1. An airport wind shear detection and warning system using Doppler radar: A feasibility study

    NASA Technical Reports Server (NTRS)

    Mccarthy, J.; Blick, E. F.; Elmore, K. L.

    1981-01-01

    A feasibility study was conducted to determine whether ground based Doppler radar could measure the wind along the path of an approaching aircraft with sufficient accuracy to predict aircraft performance. Forty-three PAR approaches were conducted, with 16 examined in detail. In each, Doppler derived longitudinal winds were compared to aircraft measured winds; in approximately 75 percent of the cases, the Doppler and aircraft winds were in acceptable agreement. In the remaining cases, errors may have been due to a lack of Doppler resolution, a lack of co-location of the two sampling volumes, the presence of eddy or vortex like disturbances within the pulse volume, or the presence of point targets in antenna side lobes. It was further concluded that shrouding techniques would have reduced the side lobe problem. A ground based Doppler radar operating in the optically clear air, provides the appropriate longitudinal winds along an aircraft's intended flight path.

  2. Design and preliminary tests of an IR-airborne LLWS remote sensing system. [Low Level Wind Shear

    NASA Technical Reports Server (NTRS)

    Caracena, F.; Kuhn, P. M.; Kurkowski, R.

    1981-01-01

    Recent history underscores the need for in-cockpit alerts of LLWS for takeoffs and landings. The 13-15 micron portion of the CO2 molecular spectrum can be used to remote sense LLWS in and around thunderstorms. A radiometer with a designed look-distance of about 10 km remote senses an average air temperature along a forward, horizontal path. Wind shear alerts are based on the difference between this forward air temperature and the air temperature near the aircraft. Although spectral ranging, a major design improvement of an IR LLWS alert system, is not at present feasible with noncooled detectors, it is an important technique to keep in mind, given the rapid advance in IR technology.

  3. Simulation comparison of a decoupled longitudinal control system and a velocity vector control wheel steering system during landings in wind shear

    NASA Technical Reports Server (NTRS)

    Kimball, G., Jr.

    1980-01-01

    A simulator comparison of the velocity vector control wheel steering (VCWS) system and a decoupled longitudinal control system is presented. The piloting task was to use the electronic attitude direction indicator (EADI) to capture and maintain a 3 degree glide slope in the presence of wind shear and to complete the landing using the perspective runway included on the EADI. The decoupled control system used constant prefilter and feedback gains to provide steady state decoupling of flight path angle, pitch angle, and forward velocity. The decoupled control system improved the pilots' ability to control airspeed and flight path angle during the final stages of an approach made in severe wind shear. The system also improved their ability to complete safe landings. The pilots preferred the decoupled control system in severe winds and, on a pilot rating scale, rated the approach and landing task with the decoupled control system as much as 3 to 4 increments better than use of the VCWS system.

  4. Air flow and shear stress modifications resulting from annual wind barriers

    E-print Network

    Schwartz, Robert Craig

    1992-01-01

    ) also described an impact threshold condition for the initiation of particle movement when actively saltating grains are 12 introduced from upstream. The impact threshold is approximately 80% of the static threshold friction velocity. Threshold... to the increase in wind velocity. Particles or aggregates ejected under static threshold conditions are usually within the diameter range of O. l to 0. 5 mm and therefore are too large to be suspended by the flow. These saltating particles rise at steep angles...

  5. Lake-size dependency of wind shear and convection as controls on gas exchange

    E-print Network

    California at Santa Barbara, University of

    David P. Hamilton,2 Ankur R. Desai,3 Kevin C. Rose,4,5 Sally MacIntyre,6 John D. Lenters,7 Robyn L. Smyth,5 Paul C. Hanson,8 Jonathan J. Cole,9 Peter A. Staehr,10 James A. Rusak,11 Donald C. Pierson,12 for k predict transfer velocity based only on wind speed measurements [e.g., Cole and Caraco, 1998

  6. The development of convective instability, wind shear, and vertical motion in relation to convection activity and synoptic systems in AVE 4

    NASA Technical Reports Server (NTRS)

    Davis, J. G.; Scoggins, J. R.

    1981-01-01

    Data from the Fourth Atmospheric Variability Experiment were used to investigate conditions/factors responsible for the development (local time rate-of-change) of convective instability, wind shear, and vertical motion in areas with varying degrees of convective activity. AVE IV sounding data were taken at 3 or 6 h intervals during a 36 h period on 24-25 April 1975 over approximately the eastern half of the United States. An error analysis was performed for each variable studied.

  7. Motion and interaction of decaying trailing vortices in spanwise shear wind

    NASA Technical Reports Server (NTRS)

    Liu, C. H.; Lu, T.

    1986-01-01

    A simulation is presented of the drift of trailing vortices in a cross-wind near the ground by an unsteady, two-dimensional, rotational flow field with a concentration of large vorticity in vortical spots (having a finite but small effective size and finite total strength). The problem is analyzed by a combination of the method of matched asymptotic analyses for the decay of the vortical spots and the Euler solution for the unsteady rotational flow. Using the method of averaging, a special numerical method is developed in which the grid size and time step depend only on the length and velocity scales of the background flow and are independent of the effective core size of a vortical spot. The core size can be much smaller than the grid size, whereas the peak velocity in the core is inversely propertional to the spot size. Numerical results are presented to demonstrate the strong interaction between the trajectories of the vortical spots and the change of the vorticity distribution in the background flow field.

  8. Numerical investigation for the effects of the vertical wind shear on the cloud droplet spectra broadening at the lateral boundary of the cumulus clouds

    NASA Astrophysics Data System (ADS)

    Wang, Yongqing; Sun, Jiming

    2014-05-01

    The vortex-structure circulation at the top of cumulus clouds can result in air entrainment at the lateral sides of them. The entrained air at the early developing stage of cumulus clouds can lead to new cloud droplet activation at their lateral sides due to its upward expansion cooling induced by the gradient force of the dynamic perturbation pressure. The vertical wind shear may strengthen such a mechanism for cloud droplet nucleation at the lateral sides of cumulus clouds. In order to investigate the impacts of the vertical wind shear on the cloud droplet spectra broadening at the lateral sides, we used the Weather Research and Forecasting (WRF) Model coupled with an aerosol-cloud interaction bin model with a high spectrum resolution (90 bins for aerosols, 160 bins for water drops) and a high spatial resolution (25m in vertical, 50m in horizontal). We run the Large Eddy Simulation (LES) case in the Tianhe supercomputer with more than 1000 CPUs. In our simulations, a new aerosol parameterization scheme have been proposed in order to investigate the secondary activation of cloud condensation nuclei (CCN). The activated CCN will not be cleaned as the current approach. CCN coming from the evaporated cloud droplets can be explicitly determined. Our results show that the vertical wind shear can enhance the cloud droplet nucleation at the leeward lateral side.

  9. Estimates of the low-level wind shear and turbulence in the vicinity of Kennedy International Airport on 24 June 1975

    NASA Technical Reports Server (NTRS)

    Lewellen, W. S.; Williamson, G. G.

    1976-01-01

    A study was conducted to estimate the type of wind and turbulence distributions which may have existed at the time of the crash of Eastern Airlines Flight 66 while attempting to land. A number of different wind and turbulence profiles are predicted for the site and date of the crash. The morning and mid-afternoon predictions are in reasonably good agreement with magnitude and direction as reported by the weather observer. Although precise predictions cannot be made during the passage of the thunderstorm which coincides with the time of the accident, a number of different profiles which might exist under or in the vicinity of a thunderstorm are presented. The profile that is most probable predicts the mean headwind shear over 100 m (300 feet) altitude change and the average fluctuations about the mean headwind distribution. This combination of means and fluctuations leads to a reasonable probability that the instantaneous headwind shear would equal the maximum value reported in the flight recorder data.

  10. Wind

    NSDL National Science Digital Library

    Iowa Public Television. Explore More Project

    2004-01-01

    What part does the wind play in satisfying energy demands? This informational piece, part of a series about the future of energy, introduces students to wind as an energy source. Here students read about the history, uses, and efficiency of wind power. Information is also provided about benefits, limitations, and geographical considerations of wind power in the United States. Thought-provoking questions afford students chances to reflect on what they've read about the uses of wind power. Supplemental articles and information are available from a sidebar. Three energy-related web links are also provided. Copyright 2005 Eisenhower National Clearinghouse

  11. Use of Dual-Polarization Radar Variables to Assess Low-Level Wind Shear in Severe Thunderstorm Near-storm Environments in the Tennessee Valley

    NASA Technical Reports Server (NTRS)

    Crowe, Christina C.; Schultz, Christopher J.; Kumjian, Matthew; Carey, Lawerence D.; Petersen, Walter A.

    2011-01-01

    The upgrade of the National Weather Service (NWS) network of S ]band dual-polarization radars is currently underway, and the incorporation of polarimetric information into the real ]time forecasting process will enhance the forecaster fs ability to assess thunderstorms and their near ]storm environments. Recent research has suggested that the combination of polarimetric variables differential reflectivity (ZDR) and specific differential phase (KDP) can be useful in the assessment of low level wind shear within a thunderstorm. In an environment with strong low ]level veering of the wind, ZDR values will be largest along the right inflow edge of the thunderstorm near a large gradient in horizontal reflectivity (indicative of large raindrops falling with a relative lack of smaller drops), and take the shape of an arc. Meanwhile, KDP values, which are proportional to liquid water content and indicative of a large number of smaller drops, are maximized deeper into the forward flank precipitation shield than the ZDR arc as the smaller drops are being advected further from the updraft core by the low level winds than the larger raindrops. Using findings from previous work, three severe weather events that occurred in North Alabama were examined in order to assess the utility of these signatures in determining the potential for tornadic activity. The first case is from October 26, 2010, where a large number of storms indicated tornadic potential from a standard reflectivity and velocity analysis but very few storms actually produced tornadoes. The second event is from February 28, 2011, where tornadic storms were present early on in the event, but as the day progressed, the tornado threat transitioned to a high wind threat. The third case is from April 27, 2011, where multiple rounds of tornadic storms ransacked the Tennessee Valley. This event provides a dataset including multiple modes of tornadic development, including QLCS and supercell structures. The overarching goal of examining these three events is to compare dual ]polarization features from this larger dataset to previous work and to determine if these signatures can be a useful indication of the potential for tornadic activity associated with the amount of low ]level wind shear in the near ]storm environment.

  12. NUMERICAL SIMULATION TO DETERMINE THE EFFECTS OF INCIDENT WIND SHEAR AND TURBULENCE LEVEL ON THE FLOW AROUND A BUILDING

    EPA Science Inventory

    The effects of incident shear and turbulence on flow around a cubical building are being investigated by a turbulent kinetic energy dissipation (k-e) model (TEMPEST). he numerical simulations demonstrate significant effects due to the differences in the incident flow. he addition...

  13. Evidence for tropospheric wind shear excitation of high-phase-speed gravity waves reaching the mesosphere using the ray-tracing technique

    NASA Astrophysics Data System (ADS)

    Pramitha, M.; Venkat Ratnam, M.; Taori, A.; Krishna Murthy, B. V.; Pallamraju, D.; Vijaya Bhaskar Rao, S.

    2015-03-01

    Sources and propagation characteristics of high-frequency gravity waves observed in the mesosphere using airglow emissions from Gadanki (13.5° N, 79.2° E) and Hyderabad (17.5° N, 78.5° E) are investigated using reverse ray tracing. Wave amplitudes are also traced back, including both radiative and diffusive damping. The ray tracing is performed using background temperature and wind data obtained from the MSISE-90 and HWM-07 models, respectively. For the Gadanki region, the suitability of these models is tested. Further, a climatological model of the background atmosphere for the Gadanki region has been developed using nearly 30 years of observations available from a variety of ground-based (MST radar, radiosondes, MF radar) and rocket- and satellite-borne measurements. ERA-Interim products are utilized for constructing background parameters corresponding to the meteorological conditions of the observations. With the reverse ray-tracing method, the source locations for nine wave events could be identified to be in the upper troposphere, whereas for five other events the waves terminated in the mesosphere itself. Uncertainty in locating the terminal points of wave events in the horizontal direction is estimated to be within 50-100 km and 150-300 km for Gadanki and Hyderabad wave events, respectively. This uncertainty arises mainly due to non-consideration of the day-to-day variability in the tidal amplitudes. Prevailing conditions at the terminal points for each of the 14 events are provided. As no convection in and around the terminal points is noticed, convection is unlikely to be the source. Interestingly, large (~9 m s-1km-1) vertical shears in the horizontal wind are noticed near the ray terminal points (at 10-12 km altitude) and are thus identified to be the source for generating the observed high-phase-speed, high-frequency gravity waves.

  14. Winds

    NSDL National Science Digital Library

    2012-08-03

    In this problem-based learning (PBL) scenario, students prepare a presentation for investors showing how their fishing company has a significant advantage because it locates upwelling zones and fishing areas using TRMM (Tropical Rainfall Measuring Mission) and other satellite data. Prior to launching the PBL, students learn about wind: the topics of air pressure, coriolis effect, upwelling and the role of differential heating on the atmosphere are explored in classroom demonstrations. Materials required include a beaker, coffee grounds, drinking straw, balloon, flashlight, and turntable. The resource includes teacher background information, glossary, assessment rubric, and an appendix introducing problem-based learning.

  15. WIND ENERGY Wind Energ. (2014)

    E-print Network

    turbine and turbulence simulator (WiTTS hereafter). WiTTS uses a scale-dependent Lagrangian dynamical model of the sub-grid shear stress and actuator lines to simulate the effects of the rotating blades. WiTTS in the near wake. In conclusion, WiTTS performs satisfactorily in the rotor region of wind turbine wakes under

  16. A Simple Method to Predict Threshold Shear Velocity in the Field

    Microsoft Academic Search

    J. Li; G. S. Okin; J. E. Herrick; M. E. Miller; S. M. Munson; J. Belnap

    2009-01-01

    A very important parameter in predicting wind erosion is the threshold shear velocity, which is the minimal shear velocity required to initiate deflation of soil particles. Modeling and wind tunnel are primary methods in predicting threshold shear velocity. However, most models have limited applications in the presence of roughness elements, and running a wind tunnel in the field is labor-intensive

  17. Winding for the wind

    NASA Technical Reports Server (NTRS)

    Weingart, O.

    1981-01-01

    The mechanical properties and construction of epoxy-impregnated fiber-glass blades for wind turbines are discussed, along with descriptions of blades for the Mod 0A and Mod 5A WECS and design goals for a 4 kW WECS. Multicell structure combined with transverse filament tape winding reduces labor and material costs, while placing a high percentage of 0 deg fibers spanwise in the blades yields improved strength and elastic properties. The longitudinal, transverse, and shear modulus are shown to resist stresses exceeding the 50 lb/sq ft requirements, with constant stress resistance expected until fatigue failure is approached. Regression analysis indicates a fatigue life of 400 million operating cycles. The small WECS under prototype development features composite blades, nacelle, and tower. Rated at 5.7 kW in a 15 mph wind, the machine operates over a speed range of 9-53.9 mph and is expected to produce 16,200 kWh annually in a 10 mph average wind measured at 30 ft.

  18. Winding for the wind

    NASA Astrophysics Data System (ADS)

    Weingart, O.

    The mechanical properties and construction of epoxy-impregnated fiber-glass blades for wind turbines are discussed, along with descriptions of blades for the Mod 0A and Mod 5A WECS and design goals for a 4 kW WECS. Multicell structure combined with transverse filament tape winding reduces labor and material costs, while placing a high percentage of 0 deg fibers spanwise in the blades yields improved strength and elastic properties. The longitudinal, transverse, and shear modulus are shown to resist stresses exceeding the 50 lb/sq ft requirements, with constant stress resistance expected until fatigue failure is approached. Regression analysis indicates a fatigue life of 400 million operating cycles. The small WECS under prototype development features composite blades, nacelle, and tower. Rated at 5.7 kW in a 15 mph wind, the machine operates over a speed range of 9-53.9 mph and is expected to produce 16,200 kWh annually in a 10 mph average wind measured at 30 ft.

  19. Satellite-derived rain rates in vertically sheared tropical cyclones

    Microsoft Academic Search

    Daniel J. Cecil

    2007-01-01

    When tropical cyclones interact with environmental vertical wind shear, they often take on an asymmetric structure. Prior observational and modeling studies have identified a preference for rainfall enhancement in the directions that are down shear and also to the left of the shear vector (in the Northern Hemisphere). This study composites hundreds of snapshots of the rain fields for Atlantic

  20. Tornado Wind Patterns

    NSDL National Science Digital Library

    Prentice Hall

    A Flash animation demonstrating how wind patterns lead to the formation of tornados. First, vertical wind shear leads to air spinning parallel to the ground. If an updraft then occurs, a thunderstorm forms and moves the spinning air into a vertical position, potentially creating a full-blown tornado.

  1. Shear-Sensitive Monomer/Polymer Liquid Crystal System

    NASA Technical Reports Server (NTRS)

    Singh, Jag J.; Eftekhari, Abe; Parmar, D. S.

    1993-01-01

    Report describes preliminary investigation of new monomer/polymer liquid crystal system, thin film of shear-sensitive cholesteric monomer liquid crystal (TI 511) on Xydar (STR800) (or equivalent) liquid crystal polymer substrate. Monomer/polymer liquid crystal films applied to surfaces provide quantitative indications of shear stresses caused by winds blowing along surfaces. Effects of shear stresses reversible in new coating system. System provides quantitative data on flows in wind tunnels.

  2. Equivalent Neutral Wind

    NASA Technical Reports Server (NTRS)

    Liu, W. Timothy; Tang, Wenqing

    1996-01-01

    The definition of equivalent neutral wind and the rationale for using it as the geophysical product of a spaceborne scatterometer are reviewed. The differences between equivalent neutral wind and actual wind, which are caused by atmospheric density stratification, are demonstrated with measurements at selected locations. A method of computing this parameter from ship and buoy measurements is described and some common fallacies in accounting for the effects of atmospheric stratification on wind shear are discussed. The computer code for the model to derive equivalent neutral wind is provided.

  3. Inviscid Interactions Between Wake Vortices and Shear Layers

    NASA Technical Reports Server (NTRS)

    Zheng, Z. C.; Baek, K.

    1998-01-01

    Aircraft trailing vortices can be influenced significantly by atmospheric conditions such as crosswind, turbulence, and stratification. According to the NASA 1994 and 1995 field measurement program in Memphis, Tennessee, the descending aircraft wake vortices could stall or be deflected at the top of low-level temperature inversions that usually produce pronounced shear zones. Numerical simulations of vortex/shear interactions with ground effects have been performed by several groups. Burnham used a series of evenly spaced line vortices at a particular altitude to model the ground shear layer of the cross- wind. He found that the wind shear was swept up around the downwind vortex and caused the downwind vortex to move upward, and claimed that the effect was actually produced by the vertical gradient in the wind shear rather than by the wind shear directly, because uniformly distributed wind-shear vortices would have no effect on the trailing vortex vertical motion. Recently, Proctor et al. numerically tested the effects of narrow shear zones on the behavior of the vortex pair, motivated by the observation of the Memphis field data. The shear-layer sensitivity tests indicated that the downwind vortex was more sensitive and deflected to a higher altitude than its upwind counterpart. The downstream vortex contained vorticity of opposite sign to that of the shear. There was no detectable preference for the downwind vortex (or upwind vortex) to weaken (or strengthen) at a greater rate.

  4. Wind turbine acoustics

    NASA Astrophysics Data System (ADS)

    Hubbard, Harvey H.; Shepherd, Kevin P.

    1990-12-01

    Available information on the physical characteristics of the noise generated by wind turbines is summarized, with example sound pressure time histories, narrow- and broadband frequency spectra, and noise radiation patterns. Reviewed are noise measurement standards, analysis technology, and a method of characterizing wind turbine noise. Prediction methods are given for both low-frequency rotational harmonics and broadband noise components. Also included are atmospheric propagation data showing the effects of distance and refraction by wind shear. Human perception thresholds, based on laboratory and field tests, are given. Building vibration analysis methods are summarized. The bibliography of this report lists technical publications on all aspects of wind turbine acoustics.

  5. Wind turbine acoustics

    NASA Technical Reports Server (NTRS)

    Hubbard, Harvey H.; Shepherd, Kevin P.

    1990-01-01

    Available information on the physical characteristics of the noise generated by wind turbines is summarized, with example sound pressure time histories, narrow- and broadband frequency spectra, and noise radiation patterns. Reviewed are noise measurement standards, analysis technology, and a method of characterizing wind turbine noise. Prediction methods are given for both low-frequency rotational harmonics and broadband noise components. Also included are atmospheric propagation data showing the effects of distance and refraction by wind shear. Human perception thresholds, based on laboratory and field tests, are given. Building vibration analysis methods are summarized. The bibliography of this report lists technical publications on all aspects of wind turbine acoustics.

  6. Speed and Direction Shear in the Stable Nocturnal Boundary Layer

    SciTech Connect

    Walter, K.; Weiss, C. C.; Swift, A. H. P.; Chapman, J.; Kelley, N. D.

    2009-02-01

    Numerous previous works have shown that vertical shear in wind speed and wind direction exist in the atmospheric boundary layer. In this work, meteorological forcing mechanisms, such as the Ekman spiral, thermal wind, and inertial oscillation, are discussed as likely drivers of such shears in the statically stable environment. Since the inertial oscillation, the Ekman spiral, and statically stable conditions are independent of geography, potentially significant magnitudes of speed and direction shear are hypothesized to occur to some extent at any inland site in the world. The frequency of occurrence of non-trivial magnitudes of speed and direction shear are analyzed from observation platforms in Lubbock, Texas and Goodland, Indiana. On average, the correlation between speed and direction shear magnitudes and static atmospheric stability are found to be very high. Moreover, large magnitude speed and direction shears are observed in conditions with relatively high hub-height wind speeds. The effects of speed and direction shear on wind turbine power performance are tested by incorporating a simple steady direction shear profile into the fatigue analysis structures and turbulence simulation code from the National Renewable Energy Laboratory. In general, the effect on turbine power production varies with the magnitude of speed and direction shear across the turbine rotor, with the majority of simulated conditions exhibiting power loss relative to a zero shear baseline. When coupled with observational data, the observed power gain is calculated to be as great as 0.5% and depletion as great as 3% relative to a no shear baseline. The average annual power change at Lubbock is estimated to be -0.5%

  7. Microburst vertical wind estimation from horizontal wind measurements

    NASA Technical Reports Server (NTRS)

    Vicroy, Dan D.

    1994-01-01

    The vertical wind or downdraft component of a microburst-generated wind shear can significantly degrade airplane performance. Doppler radar and lidar are two sensor technologies being tested to provide flight crews with early warning of the presence of hazardous wind shear. An inherent limitation of Doppler-based sensors is the inability to measure velocities perpendicular to the line of sight, which results in an underestimate of the total wind shear hazard. One solution to the line-of-sight limitation is to use a vertical wind model to estimate the vertical component from the horizontal wind measurement. The objective of this study was to assess the ability of simple vertical wind models to improve the hazard prediction capability of an airborne Doppler sensor in a realistic microburst environment. Both simulation and flight test measurements were used to test the vertical wind models. The results indicate that in the altitude region of interest (at or below 300 m), the simple vertical wind models improved the hazard estimate. The radar simulation study showed that the magnitude of the performance improvement was altitude dependent. The altitude of maximum performance improvement occurred at about 300 m.

  8. Aircraft control in wake vortex wind shear

    NASA Technical Reports Server (NTRS)

    Wold, Gregory R.

    1995-01-01

    In the past, there have been a number of fatal incidents attributable to wake vortex encounters, involving both general aviation and commercial aircraft. In fact, the wake vortex hazard is considered to be the single dominant safety issue determining the aircraft spacing requirements at airports. As the amount of air traffic increases, the number of dangerous encounters is likely only to increase. It is therefore imperative that a means be found to reduce the danger. That is the purpose of this research: to use nonlinear inverse dynamic (NID) control methods in the design of an aircraft control system which can improve the safety margin in a wake vortex encounter.

  9. Performance testing of a Savonius windmill rotor in shear flows

    NASA Astrophysics Data System (ADS)

    Mojola, O. O.; Onasanya, O. E.

    The effects of flow shear and/or unsteadiness on the power producing performance of a Savonius windmill rotor are studied. Measurements are made in two laboratory statistically-steady shear flows, and in the natural wind, which is both viscous and unsteady. The measurements were made of the speed, torque, and power of the rotor at a number of streamwise stations for each of four values of the bucket overlap ratio. Flow velocity profiles and graphs of wind shear variation are given. It is concluded that even in the presence of shear, the power coefficient of a Savonius windmill rotor is most strongly dependent on the tip speed ratio. As in inviscid flow, the power coefficient peaked at a tip speed ratio = 0.8. The major effect of shear was to reduce the power coefficient below the inviscid flow level, the magnitude of reduction depending on the magnitude of shear present. In field testing of the Savonius rotor, the unsteadiness of the wind proved to be a greater source of power loss than the wind shear.

  10. Influence of wind characteristics on turbine performance Ioannis Antoniou (1)

    E-print Network

    ): Siemens Wind Power (3): Vestas Wind Systems A/S Summary The uncertainty of power performance measurements of measuring the power curve is by using the wind speed at hub height. The assumption behind considerable deviations often occur between the expected and the produced power. Wind shear, directional

  11. Cluster Crystals under Shear

    NASA Astrophysics Data System (ADS)

    Nikoubashman, Arash; Kahl, Gerhard; Likos, Christos N.

    2011-08-01

    We show that a distinct class of colloidal crystals, which consist of mutually overlapping particles, has a novel and universal response to steady shear. After a shear-banding regime at low shear rates, strings parallel to the flow direction form as shear grows, which order on a hexagonal crystal in the gradient-vorticity plane. At even higher shear, lateral fluctuations of the strings, enhanced by hydrodynamics, lead to a disordered, fluid state. Our results are based on appropriate simulation techniques that correctly account for hydrodynamics. We also find that shear vastly accelerates the nucleation rates of supercooled fluids into the cluster crystals.

  12. Interpretation of combined wind profiler and aircraft-measured tropospheric winds and clear air turbulence

    NASA Technical Reports Server (NTRS)

    Thomson, D. W.; Syrett, William J.; Fairall, C. W.

    1991-01-01

    In the first experiment, it was found that wind profilers are far better suited for the detailed examination of jet stream structure than are weather balloons. The combination of good vertical resolution with not previously obtained temporal resolution reveals structural details not seen before. Development of probability-derived shear values appears possible. A good correlation between pilot reports of turbulence and wind shear was found. In the second experiment, hourly measurements of wind speed and direction obtained using two wind profiling Doppler radars during two prolonged jet stream occurrences over western Pennsylvania were analyzed. In particular, the time-variant characteristics of derived shear profiles were examined. Profiler data dropouts were studied in an attempt to determine possible reasons for the apparently reduced performance of profiling radar operating beneath a jet stream. Richardson number and wind shear statistics were examined along with pilot reports of turbulence in the vicinity of the profiler.

  13. VisibleWind: wind profile measurements at low altitude

    NASA Astrophysics Data System (ADS)

    Wilkerson, Tom; Bradford, Bill; Marchant, Alan; Apedaile, Tom; Wright, Cordell

    2009-09-01

    VisibleWindTM is developing an inexpensive rapid response system, for accurately characterizing wind shear and small scale wind phenomena in the boundary layer and for prospecting suitable locations for wind power turbines. The ValidWind system can also collect reliable "ground truth" for other remote wind sensors. The system employs small (0.25 m dia.) lightweight balloons and a tracker consisting of an Impulse 200 XL laser rangefinder coupled to a PC for automated data recording. Experiments on balloon trajectories demonstrate that the laser detection of range (+/- 0.5 m), together with measured azimuth and altitude, is an inexpensive, convenient, and capable alternative to other wind tracking methods. The maximum detection range has been increased to 2200 meters using micro-corner-cube retroreflector tape on balloons. Low power LEDs enable nighttime tracking. To avoid large balloon gyrations about the mean trajectory, we use balloons having low ascent rates and subcritical Reynolds numbers. Trajectory points are typically recorded every 4 - 7 seconds. Atmospheric features observed under conditions of inversions or "light and variable winds" include abrupt onsets of shear at altitudes of 100-250 m, velocity changes of order 1-3 m/s within layers of 10-20 m thickness, and veering of the wind direction by 180 degrees or more as altitude increases from 300 to 500 m. We have previously reported comparisons of balloon-based wind profiles with the output of a co-located sodar. Even with the Impulse rangefinder, our system still requires a "man in the loop" to track the balloon. A future system enhancement will automate balloon tracking, so that laser returns are obtained automatically at 1 Hz. While balloon measurements of large-scale, high altitude wind profiles are well known, this novel measurement system provides high-resolution, real-time characterization of the fluctuating local wind fields at the bottom of the boundary layer where wind power turbines and other remote wind sensors must operate.

  14. Reduced shear power spectrum

    SciTech Connect

    Dodelson, Scott; /Fermilab /Chicago U., Astron. Astrophys. Ctr. /Northwestern U.; Shapiro, Charles; /Chicago U. /KICP, Chicago; White, Martin J.; /UC, Berkeley, Astron.

    2005-08-01

    Measurements of ellipticities of background galaxies are sensitive to the reduced shear, the cosmic shear divided by (1-{kappa}) where {kappa} is the projected density field. They compute the difference between shear and reduced shear both analytically and with simulations. The difference becomes more important an smaller scales, and will impact cosmological parameter estimation from upcoming experiments. A simple recipe is presented to carry out the required correction.

  15. Rotatable shear plate interferometer

    DOEpatents

    Duffus, Richard C. (Livermore, CA)

    1988-01-01

    A rotatable shear plate interferometer comprises a transparent shear plate mounted obliquely in a tubular supporting member at 45.degree. with respect to its horizontal center axis. This tubular supporting member is supported rotatably around its center axis and a collimated laser beam is made incident on the shear plate along this center axis such that defocus in different directions can be easily measured.

  16. Real-time simulation of BLDC-based wind turbine emulator using RT-LAB

    Microsoft Academic Search

    Honghao Guo; Bo Zhou; Jichen Li; Fangshun Cheng; Le Zhang

    2009-01-01

    A novel wind turbine emulator (WTE) based on a torque controlled Brushless DC (BLDC) motor is presented, which can emulate the steady-state and dynamic characteristics of an actual wind turbine. Variable wind speeds, turbine inertia and torque oscillation caused by tower shadow and wind shear are all considered in the construction of the actual wind turbine model and the torque

  17. Ris-R-Report Simulation of shear and turbulence impact on

    E-print Network

    Risø-R-Report Simulation of shear and turbulence impact on wind turbine performance Wagner Rozenn and turbulence impact on wind turbine power performance Division: Wind Energy Risø-R-1722(EN) January 2010 ISSN and the turbulence intensity on the power output of a multi-megawatt turbine. First simulation cases with laminar

  18. Harnessing Wind

    NSDL National Science Digital Library

    2014-09-18

    Students are introduced to the ways that engineers study and harness the wind. They learn about the different kinds of winds and how to measure wind direction. In addition, they learn how air pressure creates winds and how engineers design and test wind turbines to harness renewable wind energy.

  19. Feedback shear layer control for bluff body drag reduction

    Microsoft Academic Search

    Mark Pastoor; Lars Henning; Bernd R. Noack; Rudibert King; Gilead Tadmor

    2008-01-01

    Drag reduction strategies for the turbulent flow around a D-shaped body are examined experimentally and theoretically. A reduced-order vortex model describes the interaction between the shear layer and wake dynamics and guides a path to an efficient feedback control design. The derived feedback controller desynchronizes shear-layer and wake dynamics, thus postponing vortex formation. This actuation is tested in a wind

  20. Microlensing under Shear

    E-print Network

    Yoon-Hyun Ryu; Myeong-Gu Park

    2007-08-18

    We investigate the distortions due to this shear in the microlensing light curves and in the astrometric microlensing centroid shift trajectories. As expected, the light curve deviation increases as the shear increases and the impact parameter decreases. Although the light curve in the presence of a small shear is similar to the simple Paczynski curve with a slightly smaller impact parameter, the detailed difference between the light curve with and without shear reflects the direction and the magnitude of the shear. The centroid shift trajectory also deviates from a simple ellipse in the presence of shear. The distortion of the centroid shift trajectory increases as the impact parameter decreases, and the shape of the trajectory becomes complicated when the impact parameter becomes small enough. The magnitude of the maximum distortion depends on the magnitude and the direction of the shear. For a source trajectory in a given direction, the time of the maximum distortion depends mostly on the impact parameter and hardly on the shear. It is possible to determine the magnitude of the shear and its direction if both the time and the magnitude of the maximum astrometric distortion are measured. The magnitude of the shear produced by the Galactic bulge or a globular cluster falls in the range 10^{-6}--10^{-4} in normalized units. Although the actual determination of the shear from the Galactic sub-structures will not be easy due to complications such as binary companion, future large scale microlensing experiments may enable us to determine the shear in some high amplification events, leading eventually to mapping the Galactic mass distribution.

  1. Shearing stability of lubricants

    NASA Technical Reports Server (NTRS)

    Shiba, Y.; Gijyutsu, G.

    1984-01-01

    Shearing stabilities of lubricating oils containing a high mol. wt. polymer as a viscosity index improver were studied by use of ultrasound. The oils were degraded by cavitation and the degradation generally followed first order kinetics with the rate of degradation increasing with the intensity of the ultrasonic irradiation and the cumulative energy applied. The shear stability was mainly affected by the mol. wt. of the polymer additive and could be determined in a short time by mechanical shearing with ultrasound.

  2. Shear stress transducer concepts

    NASA Astrophysics Data System (ADS)

    Francis, E. C.; Thompson, R. E.; Heerema, S. W.

    1990-07-01

    The measurement of shear stress in a solid propellant rocket motor can be accomplished by discreet transducers embedded in the propellant-insulation interface. However, shear stress transducers and application techniques have not been generally available. CSD has had experience in the past with this type of transducer, and is currently involved in a program that is evaluating new shear transducer concepts. This paper presents the different types of shear stress transducers available, and shows laboratory data on stability and sensitivity. The potential usefulness and drawbacks of each type are presented.

  3. Shear Thinning in Xenon

    NASA Technical Reports Server (NTRS)

    Bergm Robert F.; Moldover, Michael R.; Yao, Minwu; Zimmerli, Gregory A.

    2009-01-01

    We measured shear thinning, a viscosity decrease ordinarily associated with complex liquids such as molten plastics or ketchup, near the critical point of xenon. The data span a wide range of dimensionless shear rate: the product of the shear rate and the relaxation time of critical fluctuations was greater than 0.001 and was less than 700. As predicted by theory, shear thinning occurred when this product was greater than 1. The measurements were conducted aboard the Space Shuttle Columbia to avoid the density stratification caused by Earth's gravity.

  4. Reliability and effect of partially restrained wood shear walls

    Microsoft Academic Search

    John Joseph Gruber

    2012-01-01

    \\u000aRELIABILITY AND EFFECT OF PARTIALLY RESTRAINED WOOD SHEAR WALLS\\u000aby\\u000aJOHN J. GRUBER\\u000aMARCH 2012\\u000aAdvisor:\\u0009Dr. Gongkang Fu\\u000aMajor:\\u0009\\u0009Civil Engineering\\u000aDegree:\\u0009Doctor or Philosophy\\u000aThe prescriptive design of the most widely used residential building code in the United States, the IRC, allows the use of partially restrained wood shear walls to resist wind and seismic loads. Wind load

  5. Buried wire gage for wall shear stress measurements

    NASA Technical Reports Server (NTRS)

    Murthy, V. S.; Rose, W. C.

    1978-01-01

    A buried wire gage for measuring wall shear stress in fluid flow was studied and further developed. Several methods of making this relatively new type of gage were examined to arrive at a successful technique that is well-suited for wind-tunnel testing. A series of measurements was made to demonstrate the adequacy of a two-point calibration procedure for these gages. The buried wire gage is also demonstrated to be ideally suited for quantitative measurement of wall shear stress in wind-tunnel testing.

  6. Principles of Convection III: Shear and Convective Storms

    NSDL National Science Digital Library

    2014-09-14

    This module discusses the role of wind shear in the structure and evolution of convective storms. Using the concept of horizontal vorticity, the module demonstrates how shear enhances uplift, leading to longer-lived supercell and multicell storms. The module also explores the role of shear in the development of mesoscale convective systems, including bow echoes and squall lines. Most of the material in this module previously appeared in the COMET modules developed with Dr. Morris Weisman. This version includes a concise summary for quick reference and a final exam to test your knowledge. The module comes with audio narration, rich graphics, and a companion print version.

  7. An integrated modeling method for wind turbines

    NASA Astrophysics Data System (ADS)

    Fadaeinedjad, Roohollah

    To study the interaction of the electrical, mechanical, and aerodynamic aspects of a wind turbine, a detailed model that considers all these aspects must be used. A drawback of many studies in the area of wind turbine simulation is that either a very simple mechanical model is used with a detailed electrical model, or vice versa. Hence the interactions between electrical and mechanical aspects of wind turbine operation are not accurately taken into account. In this research, it will be shown that a combination of different simulation packages, namely TurbSim, FAST, and Simulink can be used to model the aerodynamic, mechanical, and electrical aspects of a wind turbine in detail. In this thesis, after a review of some wind turbine concepts and software tools, a simulation structure is proposed for studying wind turbines that integrates the mechanical and electrical components of a wind energy conversion device. Based on the simulation structure, a comprehensive model for a three-bladed variable speed wind turbine with doubly-fed induction generator is developed. Using the model, the impact of a voltage sag on the wind turbine tower vibration is investigated under various operating conditions such as power system short circuit level, mechanical parameters, and wind turbine operating conditions. It is shown how an electrical disturbance can cause more sustainable tower vibrations under high speed and turbulent wind conditions, which may disrupt the operation of pitch control system. A similar simulation structure is used to model a two-bladed fixed speed wind turbine with an induction generator. An extension of the concept is introduced by adding a diesel generator system. The model is utilized to study the impact of the aeroelastic aspects of wind turbine (i.e. tower shadow, wind shears, yaw error, turbulence, and mechanical vibrations) on the power quality of a stand-alone wind-diesel system. Furthermore, an IEEE standard flickermeter model is implemented in a Simulink environment to study the flicker contribution of the wind turbine in the wind-diesel system. By using a new wind power plant representation method, a large wind farm (consisting of 96 fixed speed wind turbines) is modelled to study the power quality of wind power system. The flicker contribution of wind farm is also studied with different wind turbine numbers, using the flickermeter model. Keywords. Simulink, FAST, TurbSim, AreoDyn, wind energy, doubly-fed induction generator, variable speed wind turbine, voltage sag, tower vibration, power quality, flicker, fixed speed wind turbine, wind shear, tower shadow, and yaw error.

  8. Perturbed free shear layers

    Microsoft Academic Search

    C.-M. Ho; P. Huerre

    1984-01-01

    The development of free shear layers formed by the mixing of initially separated free streams is examined in a review of recent work. The mixing layer is viewed as a prototype for a class of inviscidly unstable free shear flows including jets and wakes, and the focus is on 2D homogeneous incompressible mixing layers. Major areas covered include dynamical processes

  9. Wind Turbines Adaptation to the Variability of the Wind Field

    NASA Astrophysics Data System (ADS)

    Ulianov, Yuriy; Martynenko, Gennadii; Misaylov, Vitaliy; Soliannikova, Iuliia

    2010-05-01

    WIND TURBINES ADAPTATION TO THE VARIABILITY OF THE WIND FIELD The subject of our scientific research is wind power turbines (WPT) with the horizontal axis which were now common in the world. Efficient wind turbines work is largely determined by non-stationarity of the wind field, expressed in its gustiness, the presence of vertical and horizontal shifts of wind speed and direction. At critical values of the wind parameters WPT has aerodynamic and mechanical overload, leading to breakdowns, premature wear and reduce the life of the wind turbine. To prevent accidents at the peak values of wind speed it is used the regulatory system of windwheels. WPT control systems provide a process orientation of the wind turbine rotor axis in the line of the mean wind. Wind turbines are also equipped with braking device used to protect against breakdowns when a significant increase in the wind. In general, all these methods of regulation are not always effective. Thus, in practice there may be situations when the wind speed is many times greater than the stated limit. For example, if there are microbursts in the atmospheric boundary layer, low-level wind shears caused by its gust front, storms, etc. It is required for a wind power turbine adaptation to intensive short-term wind impulses and considerable vertical wind shifts that the data about them shall be obtained ahead of time. To do this it is necessary to have the information on the real structure of the wind field in the area of the blade sweep for the minimum range against the wind that is determined by the mean speed and the system action time. The implementation of acoustic and laser traditional wind sounding systems is limited by ambient acoustic noise, by heavy rain, snowfall and by fog. There are free of these disadvantages the inclined radioacoustic sounding (IRASS) technique which works for a system of remote detection and control of wind gusts. IRASS technique is realized as low-potential Doppler pulse radar including combined RF-acoustic antenna installed coaxially with the gondola of the wind power turbine. The work of the technique is synchronized with rotation of blades to eliminate their shielding action. Dangerous in terms of dynamic strength is the wind load pulse, the rise time which is comparable with the period of the natural frequency of the wind turbine elements (blade, tower, rotor, etc.). The amplitude decay of resonant vibrations at critical values of the speed of rotation can be realized through the use of mechanical elastic supports with nonlinear artificial dampers. They have a high coefficient of resistance, but may cause self-excited oscillations. We propose the way to deal with raised vibration of wind turbine elements at the expense of short-term increase of damping in the range of critical rotary axis speeds or during impulsive effects of wind loadings (wind gusts). This is possible through the use of non-linear electromagnetic dampers or active magnetic bearings. Their feature is the possibility of varying the mechanical stiffness and damping properties by changing the electrical parameters of electromagnets. The controlling of these parameters is carried out by the control system (CS) with the information feedback on the spatial-temporal structure of the wind field obtained from IRASS. In the composition of the CS can also be included the rotational speed sensor of the WPT rotor. This approach to the adaptation of wind turbines will allow to reduce vibration and to perform early compensation of the load on their components, which arise under the wind gusts. In addition, corrections about the wind field obtained with IRASS, would increase the mean power of WPT.

  10. Generation and manipulation of uniform shear with the use of screens

    Microsoft Academic Search

    U. Karnik; S. Tavoularis

    1987-01-01

    A procedure for the generation of uniformly sheared turbulent flow in the wind-tunnel using separate channels with adjustable blockage is described in detail. Measurements of the reduction of mean shear in a flow crossing transverse grids and gauzes with uniform solidities are also reported: for small flow disturbances, i.e. small relative screen element thickness, d\\/h, the shear reduction factor, A,

  11. Angular shear plate

    DOEpatents

    Ruda, Mitchell C. (Tucson, AZ); Greynolds, Alan W. (Tucson, AZ); Stuhlinger, Tilman W. (Tucson, AZ)

    2009-07-14

    One or more disc-shaped angular shear plates each include a region thereon having a thickness that varies with a nonlinear function. For the case of two such shear plates, they are positioned in a facing relationship and rotated relative to each other. Light passing through the variable thickness regions in the angular plates is refracted. By properly timing the relative rotation of the plates and by the use of an appropriate polynomial function for the thickness of the shear plate, light passing therethrough can be focused at variable positions.

  12. Wave breaking due to internal wave shear flow resonance over a sloping bottom

    Microsoft Academic Search

    Victor I. Shrira; Vyacheslav V. Voronovich; Igor A. Sazonov

    2000-01-01

    A new mechanism of internal wave breaking in the subsurface ocean layer is considered. The breaking is due to the `resonant' interaction of shoaling long internal gravity waves with the subsurface shear current occurring in a resonance zone. Provided the wind-induced shear current is oriented onshore, there exists a wide resonance zone, where internal wave celerity is close to the

  13. A Comparison of Shear and Buoyancy-Driven Planetary Boundary Layer Flows

    Microsoft Academic Search

    Chin-Hoh Moeng; Peter P. Sullivan

    1994-01-01

    Planetary boundary layer (PBL) flows are known to exhibit fundamental differences depending on the relative combination of wind shear and buoyancy forces. These differences are not unexpected in that shear instabilities occur locally, while buoyancy force sets up vigorous thermals, which result in nonlocal transport of heat and momentum. At the same time, these two forces can act together to

  14. 2009 ASME WIND ENERGY SYMPOSIUM Static and Fatigue Testing of Thick Adhesive Joints for

    E-print Network

    1 2009 ASME WIND ENERGY SYMPOSIUM Static and Fatigue Testing of Thick Adhesive Joints for Wind as wind blade size has increased. Typical blade joints use paste adhesives several millimeters thick aircraft, which are also of relevance to wind blades in many instances. The strengths of lap-shear and many

  15. Sliding mode control of wind energy systems with DOIG-power efficiency and torsional dynamics optimization

    Microsoft Academic Search

    H. De Battista; P. F. Puleston; R. J. Mantz; C. F. Christiansen

    2000-01-01

    Wind turbines with double output induction generators can operate at variable speed permitting conversion efficiency maximization over a wide range of wind velocities. However, random wind fluctuations, wind shear and tower shadow, may excite the oscillation mode of the mechanical system, producing large torque ripple. Consequently, damage to drive train components and power quality problems may occur. In this paper,

  16. Radial Heliospheric Magnetic Fields in Solar Wind Rarefaction Regions: Ulysses Observations

    E-print Network

    Sanahuja, Blai

    Radial Heliospheric Magnetic Fields in Solar Wind Rarefaction Regions: Ulysses Observations D it observed solar wind shears from the incursions of high-latitude fast solar wind toward the low-latitude slow solar wind. We look for nearly radial field orientations commonly observed in rarefaction regions

  17. Wind noise under a pine tree canopy.

    PubMed

    Raspet, Richard; Webster, Jeremy

    2015-02-01

    It is well known that infrasonic wind noise levels are lower for arrays placed in forests and under vegetation than for those in open areas. In this research, the wind noise levels, turbulence spectra, and wind velocity profiles are measured in a pine forest. A prediction of the wind noise spectra from the measured meteorological parameters is developed based on recent research on wind noise above a flat plane. The resulting wind noise spectrum is the sum of the low frequency wind noise generated by the turbulence-shear interaction near and above the tops of the trees and higher frequency wind noise generated by the turbulence-turbulence interaction near the ground within the tree layer. The convection velocity of the low frequency wind noise corresponds to the wind speed above the trees while the measurements showed that the wind noise generated by the turbulence-turbulence interaction is near stationary and is generated by the slow moving turbulence adjacent to the ground. Comparison of the predicted wind noise spectrum with the measured wind noise spectrum shows good agreement for four measurement sets. The prediction can be applied to meteorological estimates to predict the wind noise under other pine forests. PMID:25698000

  18. Rail shear test method

    NASA Technical Reports Server (NTRS)

    Garcia, R.; Mcwithey, R. R.

    1979-01-01

    The results of both an experimental test program and a finite element analysis of selected graphite/polyimide rail shear test specimens are discussed. The two dimensional finite element analysis includes both mechanical and thermal loading (differential expansion) of the specimens and their elastic rails. Parameters in this analysis of unidirectional and symmetric, balanced angle-ply laminates include ply layup angles, the effect of flexible rails, the method of load introduction to the specimen and the effect of uniform heating of the specimen and rails. Two types of tensile rail shear fixtures were investigated experimentally: a uniform thickness, bolted-rail shear fixture loaded diagonally across the specimen test section; and a tapered thickness, bonded-rail shear fixture loaded axially along the center-line of the specimen test section. Test results include room-temperature and 589K strain data taken from the center of the specimen test section during loading.

  19. Shear Unzipping of DNA

    E-print Network

    Buddhapriya Chakrabarti; David R. Nelson

    2009-04-09

    We study theoretically the mechanical failure of a simple model of double stranded DNA under an applied shear. Starting from a more microscopic Hamiltonian that describes a sheared DNA, we arrive at a nonlinear generalization of a ladder model of shear unzipping proposed earlier by deGennes [deGennes P. G. C. R. Acad. Sci., Ser. IV; Phys., Astrophys. 2001, 1505]. Using this model and a combination of analytical and numerical methods, we study the DNA "unzipping" transition when the shearing force exceeds a critical threshold at zero temperature. We also explore the effects of sequence heterogeneity and finite temperature and discuss possible applications to determine the strength of colloidal nanoparticle assemblies functionalized by DNA.

  20. Bacteria in shear flow

    E-print Network

    Marcos, Ph.D. Massachusetts Institute of Technology

    2011-01-01

    Bacteria are ubiquitous and play a critical role in many contexts. Their environment is nearly always dynamic due to the prevalence of fluid flow: creeping flow in soil, highly sheared flow in bodily conduits, and turbulent ...

  1. WAVE ACTION AND BOTTOM SHEAR STRESSES IN LAKE ERIE

    EPA Science Inventory

    For Lake Erie, the amplitudes and periods of wind-driven, surface gravity waves were calculated by means of the SMB hindcasting method. Bottom orbital velocities and bottom shear stresses were then calculated using linear wave theory and Kajiura's (1968) turbulent oscillating bou...

  2. Wall Shear stress measurements in the atmosperhic surface layer

    E-print Network

    Marusic, Ivan

    an unprecedented range of Reynolds numbers. The shear stress measurements were made at the unique SLTEST (Sur- face was to further understand similarities that may exist between the SLTEST sur- face layer and the wind tunnel Marusic, Jason Monty, Nicholas Hutchins, and Min Chong Fig. 1. Photograph of the SLTEST measurement site

  3. Wind-induced nearshore sediment resuspension in a lake during a winter storm

    NASA Astrophysics Data System (ADS)

    Reardon, K. E.; Moreno, P. A.; Schladow, S. G.; Bombardelli, F. A.

    2012-12-01

    Sediment resuspension is the process by which sediment is entrained into the water column at the sediment-water interface. It occurs when the bottom shear stress exceeds the critical shear stress and has the potential to negatively impact water quality. Wind-induced sediment resuspension could be a factor contributing to the declining clarity of the nearshore at Lake Tahoe, California-Nevada and is therefore the subject of this study. An observational experiment included vertical profiles of water temperature using a thermistor chain; vertical profiles of water currents as well as surface wave periods and significant wave heights using a Nortek AWAC; high-frequency, near-bed measurements of water velocity using a Nortek Vector and a Sontek ADVOcean Probe; and suspended sediment concentrations using a LISST-100X. During a winter storm event we observed simultaneous peaks in wind speed, significant wave height and wave period, and suspended sediment concentration. Coincident peaks in suspended sediment concentration and wind speed strongly suggested wind-driven resuspension. During this same stormy period currents shifted to align with the wind. Total bottom shear stress was computed from the high-frequency, near-bed velocity data. During this winter storm, measured estimates of total bottom shear stress exceeded the critical shear stress for incipient motion corresponding to an average grain size of 400 ?m. Bottom shear stress was also partitioned according to its provenance (wind-waves; mean currents; and random motions). We implemented the wind-wave model STWAVE to simulate nearshore wind-wave growth and propagation, from which we derived the bottom orbital velocity to estimate bottom shear stress due to wind-waves. When wind directions favored a larger fetch, promoting full development of the wave field, the simulated bottom shear stress from STWAVE was in good agreement with the measured bottom shear stress attributed to wind-waves. We estimated bottom shear stress due to currents as a percentage of the total wind-induced shear stress at the surface of the lake, which was in turn derived from the wind record and the quadratic drag law. Simulated and measured bottom shear stress attributed to mean currents were in good agreement and remained small, which was to be expected. The wind-waves contributed far more to the development of the bottom shear stress during critical periods. For those times when the total bottom shear stress was in excess of the critical shear stress, the sediment entrainment rates were well represented by the 1991 Garcia and Parker formula.

  4. Wind conditions for wind turbine design proposals for revision of the IEC 1400-1 standard

    Microsoft Academic Search

    C. H. J Stork; C. P Butterfield; W Holley; P. H Madsen; P. H Jensen

    1998-01-01

    The International Electrotechnical Commission (IEC) TC88 formed a subcommittee to re-evaluate the external wind condition models defined in the standard for “Wind Turbine Generator Systems, Part I: Safety Requirements” 1400-1. These models define design turbulence conditions, extreme gust transients, extreme wind direction transients and extreme shear transients as well as other normal and extreme conditions. The TC88 subcommittee solicited extreme

  5. Science and Technical Considerations for Wind Farm Siting

    NSDL National Science Digital Library

    This instructional module was created at the 2009 ATEEC Fellows Institute on Wind Power. The following sections are provided: An introduction to wind power classes, Offshore turbine tower foundations, Wind speed lab, Wind shear project, Turbulence and links to supporting resources. The classroom lessons include student worksheets. The entire guide may be downloaded in PDF file format. This resource is free to download. Users must first create a login with ATEEC's website to access the file.

  6. Wild Wind

    NSDL National Science Digital Library

    2014-09-18

    Students learn the difference between global, prevailing and local winds. They make wind vanes out of paper, straws and soda bottles and use them to measure wind direction over time. They analyze their data to draw conclusions about the local prevailing winds.

  7. Meteorology (Wind)

    Atmospheric Science Data Center

    2014-09-25

    Wind speed at 50 m (m/s) The average and percent difference minimum and ... are given.   Percent of time for ranges of wind speed at 50 m (percent) Percentage [frequency] of time that wind ... be adjusted to heights from 10 to 300 meters using the Gipe power law. Wind speeds may be adjusted for different terrain by selecting from ...

  8. Thermal and humidity winds in outer planet atmospheres

    SciTech Connect

    Sun, Zi-Ping; Schubert, G.; Stoker, C.R. (California, University, Los Angeles (USA) NASA, Ames Research Center, Moffett Field, CA (USA))

    1991-05-01

    Among the dynamical consequences of molecular weight variations due to condensation in hydrogen atmospheres is the creation of geostrophic wind variations by horizontal variations in molecular weight. In the present illustrative model, it is shown that such horizontal gradients are generated by methane condensation in the cases of the Uranus and Neptune atmospheres. As a result, the zonal wind shear is different in both magnitude and direction from the value determined while neglecting molecular weight variations. The horizontal molecular weight gradients due to condensation of minor constituents also vertically shear the zonal wind, giving rise to what may be termed the 'humidity wind'. 15 refs.

  9. Amplitude modulation of wind turbine noise

    E-print Network

    Makarewicz, Rufin

    2013-01-01

    Due to swish and thump amplitude modulation, the noise of wind turbines cause more annoyance than other environmental noise of the same average level. The wind shear accounts for the thump modulation (van den Berg effect). Making use of the wind speed measurements at the hub height, as well as at the top and the bottom of the rotor disc (Fig.1), the non-standard wind profile is applied. It causes variations in the A-weighted sound pressure level, LpA. The difference between the maximum and minimum of LpA characterizes thump modulation (Fig.2).

  10. Effect of shear rupture on aggregate scale formation in sea ice Alexander V. Wilchinsky,1

    E-print Network

    Feltham, Daniel

    the fracture of a sea ice cover using a discrete element model that considered compressive and tensile failure convergent wind stresses. The model includes compressive, tensile, and shear rupture of viscous elastic perpendicular to the compression direction and the blocks grow larger. In the standard case, as the wind stress

  11. Converging shear rheometer

    NASA Astrophysics Data System (ADS)

    Baek, Hyung M.; Mix, Adam W.; Giacomin, A. Jeffrey

    2014-05-01

    For highly viscous fluids that slip in parallel sliding plate rheometers, we want to use a slightly converging flow to suppress this wall slip. In this work, we first attack the steady shear flow of a highly viscous Newtonian fluid between two gently converging plates with no slip boundaries using the equation of motion in cylindrical coordinates, which yields no analytical solution. Then we treat the same problem using the lubrication approximation in Cartesian coordinates to yield exact, explicit solutions for dimensionless velocity, pressure and shear stress. This work deepens our understanding of a drag flow through a gently converging slit of arbitrary convergence angle. We also employ the corotational Maxwell model to explore the role of viscoelasticity in this converging shear flow. We then compare these analytical solutions to finite element calculations for both Newtonian and corotational Maxwell cases. A worked example for determining the Newtonian viscosity using a converging shear rheometer is also included. With this work, we provide the framework for exploring other constitutive equations or other boundary conditions in future work. Our results can also be used to design the linear bearings used for the parallel sliding plate rheometer (SPR). This work can also be used to evaluate the error in the shear stress that is caused by bearing misalignment and specify the parallelism tolerance for the linear bearings incorporated into a SPR.

  12. Shear breakage of DNA.

    PubMed

    Dancis, B M

    1978-11-01

    Determinations were made of the mean length of fragments produced after shearing long (greater than 100 kb) native Hela DNA in a VirTis homogenizer. (VirTis Co., Inc., Gardiner, N.Y.). The mean length (L) is a function of the speed of rotation of the homogenizer blades (omega), time of shearing (t), water concentration ([H2O]), solvent viscosity (eta), temperature (T), and energy of activation (E*), but not a function of the initial length so long as the starting molecules sustain an average of three or more breaks. The relationship of the parameters is expressed by the equation L = (b/omegat1/2eta1/2[H2O])eE*/2kBT, where kB is the Boltzmann constant and b is a constant of proportionality. The breakage rate constant k was determined to have the relationship k = (omega2L2eta[H2O]2/2b2)e-E*/kBT. These equations are valid throughout large ranges of the parameters, and a simple method is described which chooses a final mean length between at least 0.15 and 36 kb by choosing the appropriate shearing conditions and initial fragment length. The heterogeneity of shearing conditions within the shearing vessel permits use of the equations at all breakage rates tested. Based on the work of others using more homogeneous shearing conditions and initial fragment lengths, more complicated forms of the equations are necessary at low breakage rates but not at high ones. A proposed model of the breakage mechanism suggests that molecules with stress-induced localized denaturations break at a rate different from that for native DNA. PMID:728525

  13. Bayesian lensing shear measurement

    NASA Astrophysics Data System (ADS)

    Bernstein, Gary M.; Armstrong, Robert

    2014-02-01

    We derive an estimator of weak gravitational lensing shear from background galaxy images that avoids noise-induced biases through a rigorous Bayesian treatment of the measurement. The derived shear estimator disposes with the assignment of ellipticities to individual galaxies that is typical of previous approaches to galaxy lensing. Shear estimates from the mean of the Bayesian posterior are unbiased in the limit of large number of background galaxies, regardless of the noise level on individual galaxies. The Bayesian formalism requires a prior, describing the (noiseless) distribution of the target galaxy population over some parameter space; this prior can be constructed from low-noise images of a subsample of the target population, attainable from long integrations of a fraction of the survey field. We find two ways to combine this exact treatment of noise with rigorous treatment of the effects of the instrumental point spread function (PSF) and sampling. The Bayesian model-fitting (BMF) method assigns a likelihood of the pixel data to galaxy models (e.g. Sérsic ellipses), and requires the unlensed distribution of galaxies over the model parameters as a prior. The Bayesian Fourier domain (BFD) method compresses the pixel data to a small set of weighted moments calculated after PSF correction in Fourier space. It requires the unlensed distribution of galaxy moments as a prior, plus derivatives of this prior under applied shear. A numerical test using a simplified model of a biased galaxy measurement process demonstrates that the Bayesian formalism recovers applied shears to <1 part in 103 accuracy as well as providing accurate uncertainty estimates. BFD is the first shear measurement algorithm that is model free and requires no approximations or ad hoc assumptions in correcting for the effects of PSF, noise, or sampling on the galaxy images. These algorithms are good candidates for attaining the part-per-thousand shear inference required for hemisphere-scale weak gravitational lensing surveys. BMF has the drawback that shear biases will occur since galaxies do not fit any finite-parameter model, but has the advantage of being robust to missing data or non-stationary noise. Both BMF and BFD methods are readily extended to use data from multiple exposures and to inference of lensing magnification.

  14. Wind Turbine

    USGS Multimedia Gallery

    The species of bats that are most susceptible to wind turbines all roost in trees throughout the year, leading some scientists to speculate that they may be visually mistaking wind turbines for trees in which to roost....

  15. Wind Energy

    NSDL National Science Digital Library

    2014-09-18

    Students learn about wind energy by making a pinwheel to model a wind turbine. Just like engineers, they decide where and how their turbine works best by testing it in different areas of the playground.

  16. Determination of surface shear stress with the naphthalene sublimation technique

    NASA Technical Reports Server (NTRS)

    Lee, J. A.; Greeley, Ronald

    1987-01-01

    Aeolian entrainment and transport are functions of surface shear stress and particle characteristics. Measuring surface shear stress is difficult, however, where logarithmic wind profiles are not found, such as regions around large roughness elements. An outline of a method whereby shear stress can be mapped on the surface around an object is presented. The technique involves the sublimation of naphthalene (C10H8) which is a function of surface shear stress and surface temperature. This technique is based on the assumption that the transfer of momentum, heat and mass are analogous (Reynolds analogy). If the Reynolds analogy can be shown to be correct for a given situation, then knowledge of the diffusion of one property allows the determination of the others. The analytical framework and data acquisition for the method are described. The technique was tested in the Planetary Geology Wind Tunnel. Results show that the naphthalene sublimation technique is a reasonably accurate method for determining shear stress, particularly around objects where numerous point values are needed.

  17. Toasty Wind

    NSDL National Science Digital Library

    National Weather Service

    2012-07-24

    In this quick activity, learners use a toaster to investigate the source for the Earth's wind. Learners hold a pinwheel above a toaster to discover that rising heat causes wind. Use this activity to introduce learners to the process of convection as a source for wind. This resource also explains how convection causes thunderstorms and lists important thunderstorm safety tips.

  18. Wind Whispers

    NSDL National Science Digital Library

    The Advanced Technology Environmental and Energy Center (ATEEC) provides this presentation on the career and technical aspects of wind energy. In addition to discussing careers in wind, the presentation covers the siting of wind turbines and some electricity basics. Users must download this resource for viewing, which requires a free log-in. There is no cost to download the item.

  19. Using deformed critters to determine angular shear and shear strain

    NSDL National Science Digital Library

    Angela Moore

    This activity provides a step by step example to help students figure out how to determine the angular shear and shear strain, using fossils with bilateral symmetry. Students first complete the work on an idealized critter, and then on a sheared trilobite using simple graphical techniques and basic trigonometry.

  20. Magnetic energy flow in the solar wind.

    NASA Technical Reports Server (NTRS)

    Modisette, J. L.

    1972-01-01

    Discussion of the effect of rotation (tangential flow) of the solar wind on the conclusions of Whang (1971) suggesting an increase in the solar wind velocity due to the conversion of magnetic energy to kinetic energy. It is shown that the effect of the rotation of the sun on the magnetic energy flow results in most of the magnetic energy being transported by magnetic shear stress near the sun.

  1. Measuring the reduced shear

    SciTech Connect

    Zhang, Jun, E-mail: jzhang@astro.as.utexas.edu [Texas Cosmology Center, The University of Texas at Austin, Austin, TX 78712 (United States)

    2011-11-01

    Neglecting the second order corrections in weak lensing measurements can lead to a few percent uncertainties on cosmic shears, and becomes more important for cluster lensing mass reconstructions. Existing methods which claim to measure the reduced shears are not necessarily accurate to the second order when a point spread function (PSF) is present. We show that the method of Zhang (2008) exactly measures the reduced shears at the second order level in the presence of PSF. A simple theorem is provided for further confirming our calculation, and for judging the accuracy of any shear measurement method at the second order based on its properties at the first order. The method of Zhang (2008) is well defined mathematically. It does not require assumptions on the morphologies of galaxies and the PSF. To reach a sub-percent level accuracy, the CCD pixel size is required to be not larger than 1/3 of the Full Width at Half Maximum (FWHM) of the PSF, regardless of whether the PSF has a power-law or exponential profile at large distances. Using a large ensemble (?>10{sup 7}) of mock galaxies of unrestricted morphologies, we study the shear recovery accuracy under different noise conditions. We find that contaminations to the shear signals from the noise of background photons can be removed in a well defined way because they are not correlated with the source shapes. The residual shear measurement errors due to background noise are consistent with zero at the sub-percent level even when the amplitude of such noise reaches about 1/10 of the source flux within the half-light radius of the source. This limit can in principle be extended further with a larger galaxy ensemble in our simulations. On the other hand, the source Poisson noise remains to be a cause of systematic errors. For a sub-percent level accuracy, our method requires the amplitude of the source Poisson noise to be less than 1/80 ? 1/100 of the source flux within the half-light radius of the source, corresponding to collecting roughly 10{sup 4} source photons.

  2. 24 CFR 3285.403 - Sidewall, over-the-roof, mate-line, and shear wall straps.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ...COMMISSIONER, DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT MODEL MANUFACTURED HOME INSTALLATION STANDARDS Anchorage Against Wind § 3285.403 Sidewall, over-the-roof, mate-line, and shear wall straps. If sidewall, over-the-roof,...

  3. 24 CFR 3285.403 - Sidewall, over-the-roof, mate-line, and shear wall straps.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ...COMMISSIONER, DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT MODEL MANUFACTURED HOME INSTALLATION STANDARDS Anchorage Against Wind § 3285.403 Sidewall, over-the-roof, mate-line, and shear wall straps. If sidewall, over-the-roof,...

  4. 24 CFR 3285.403 - Sidewall, over-the-roof, mate-line, and shear wall straps.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ...COMMISSIONER, DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT MODEL MANUFACTURED HOME INSTALLATION STANDARDS Anchorage Against Wind § 3285.403 Sidewall, over-the-roof, mate-line, and shear wall straps. If sidewall, over-the-roof,...

  5. 24 CFR 3285.403 - Sidewall, over-the-roof, mate-line, and shear wall straps.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ...COMMISSIONER, DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT MODEL MANUFACTURED HOME INSTALLATION STANDARDS Anchorage Against Wind § 3285.403 Sidewall, over-the-roof, mate-line, and shear wall straps. If sidewall, over-the-roof,...

  6. 24 CFR 3285.403 - Sidewall, over-the-roof, mate-line, and shear wall straps.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ...COMMISSIONER, DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT MODEL MANUFACTURED HOME INSTALLATION STANDARDS Anchorage Against Wind § 3285.403 Sidewall, over-the-roof, mate-line, and shear wall straps. If sidewall, over-the-roof,...

  7. Electrostatic Solitary Waves in the Solar Wind: Evidence for Instability at Solar Wind Current Sheets

    NASA Technical Reports Server (NTRS)

    Malaspina, David M.; Newman, David L.; Wilson, Lynn Bruce; Goetz, Keith; Kellogg, Paul J.; Kerstin, Kris

    2013-01-01

    A strong spatial association between bipolar electrostatic solitary waves (ESWs) and magnetic current sheets (CSs) in the solar wind is reported here for the first time. This association requires that the plasma instabilities (e.g., Buneman, electron two stream) which generate ESWs are preferentially localized to solar wind CSs. Distributions of CS properties (including shear angle, thickness, solar wind speed, and vector magnetic field change) are examined for differences between CSs associated with ESWs and randomly chosen CSs. Possible mechanisms for producing ESW-generating instabilities at solar wind CSs are considered, including magnetic reconnection.

  8. Imaging Faults and Shear Zones Using Receiver Functions

    NASA Astrophysics Data System (ADS)

    Schulte-Pelkum, Vera; Mahan, Kevin H.

    2014-11-01

    The geometry of faults at seismogenic depths and their continuation into the ductile zone is of interest for a number of applications ranging from earthquake hazard to modes of lithospheric deformation. Teleseismic passive source imaging of faults and shear zones can be useful particularly where faults are not outlined by local seismicity. Passive seismic signatures of faults may arise from abrupt changes in lithology or foliation orientation in the upper crust, and from mylonitic shear zones at greater depths. Faults and shear zones with less than near-vertical dip lend themselves to detection with teleseismic mode-converted waves (receiver functions) provided that they have either a contrast in isotropic shear velocity ( V s), or a contrast in orientation or strength of anisotropic compressional velocity ( V p). We introduce a detection method for faults and shear zones based on receiver functions. We use synthetic seismograms to demonstrate common features of dipping isotropic interfaces and contrasts in dipping foliation that allows determination of their strike and depth without making further assumptions about the model. We proceed with two applications. We first image a Laramide thrust fault in the western U.S. (the Wind River thrust fault) as a steeply dipping isotropic velocity contrast in the middle crust near the surface trace of the fault; further downdip and across the range, where basin geometry suggests the fault may sole into a subhorizontal shear zone, we identify a candidate shear zone signal from midcrustal depths. The second application is the use of microstructural data from exhumed ductile shear zones in Scotland and in the western Canadian Shield to predict the character of seismic signatures of present-day deep crustal shear zones. Realistic anisotropy in observed shear fabrics generates a signal in receiver functions that is comparable in amplitude to first-order features like the Moho. Observables that can be robustly constrained without significant tradeoffs are foliation strike and the depth of the foliation contrast. We find that an anisotropy of only a few percent in the shear zone is sufficient to generate a strong signal, but that the shear zone width is required to be >2 km for typical frequencies used in receiver function analysis to avoid destructive interference due to the signals from the boundaries of the shear zone.

  9. Application and improvement of Raupach's shear stress partitioning model

    NASA Astrophysics Data System (ADS)

    Walter, B. A.; Lehning, M.; Gromke, C.

    2012-12-01

    Aeolian processes such as the entrainment, transport and redeposition of sand, soil or snow are able to significantly reshape the earth's surface. In times of increasing desertification and land degradation, often driven by wind erosion, investigations of aeolian processes become more and more important in environmental sciences. The reliable prediction of the sheltering effect of vegetation canopies against sediment erosion, for instance, is a clear practical application of such investigations to identify suitable and sustainable counteractive measures against wind erosion. This study presents an application and improvement of a theoretical model presented by Raupach (Boundary-Layer Meteorology, 1992, Vol.60, 375-395 and Journal of Geophysical Research, 1993, Vol.98, 3023-3029) which allows for quantifying the sheltering effect of vegetation against sediment erosion. The model predicts the shear stress ratios ?S'/? and ?S''/?. Here, ?S is the part of the total shear stress ? that acts on the ground beneath the plants. The spatial peak ?S'' of the surface shear stress is responsible for the onset of particle entrainment whereas the spatial mean ?S' can be used to quantify particle mass fluxes. The precise and accurate prediction of these quantities is essential when modeling wind erosion. Measurements of the surface shear stress distributions ?S(x,y) on the ground beneath live vegetation canopies (plant species: lolium perenne) were performed in a controlled wind tunnel environment to determine the model parameters and to evaluate the model performance. Rigid, non-porous wooden blocks instead of the plants were additionally tested for the purpose of comparison, since previous wind tunnel studies used exclusively artificial plant imitations for their experiments on shear stress partitioning. The model constant c, which is needed to determine the total stress ? for a canopy of interest and which remained rather unspecified to date, was found to be c ? 0.27. It was also found that the model parameter m, which relates ?S'' with ?S' and which is needed to determine the peak surface shear stress ?S'', is rather impractically defined in the original model formulation, because m is identified to be a function of the wind velocity, the roughness element shape and the roughness density. We propose an alternative, more universal definition of an a-parameter as a substitute for the m-parameter simply linearly relating ?S'' with ?S'. This strong linear relation is supported by the measurements and can be made plausible with simple fluid dynamical arguments. The advantage of a over m is that a is solely a function of the roughness element shape. Finally, a method is presented to determine the new a-parameter for different kinds of roughness elements with relatively simple experimental methods.

  10. Observations of the trade wind wakes of Kauai and Oahu

    Microsoft Academic Search

    Yang Yang; Jian Ma; Shang-Ping Xie

    2008-01-01

    The Hawaiian islands of Kauai and Oahu stand in the path of the east-northeasterly trade winds, creating wakes in the lee. For the first time, the structure of the wakes and their diurnal cycle were observed on a cruise during 18–20 December 2006. The dynamic wakes, characterized by reduced trades, extend about 1 km in height with strong wind shear

  11. Observations of the trade wind wakes of Kauai and Oahu

    Microsoft Academic Search

    Yang Yang; Jian Ma; Shang-Ping Xie

    2008-01-01

    The Hawaiian islands of Kauai and Oahu stand in the path of the east-northeasterly trade winds, creating wakes in the lee. For the first time, the structure of the wakes and their diurnal cycle were observed on a cruise during 18-20 December 2006. The dynamic wakes, characterized by reduced trades, extend about 1 km in height with strong wind shear

  12. Surface waves in an incompressible fluid - Resonant instability due to velocity shear

    NASA Technical Reports Server (NTRS)

    Hollweg, Joseph V.; Yang, G.; Cadez, V. M.; Gakovic, B.

    1990-01-01

    The effects of velocity shear on the resonance absorption of incompressible MHD surface waves are studied. It is found that there are generally values of the velocity shear for which the surface wave decay rate becomes zero. In some cases, the resonance absorption goes to zero even for very small velocity shears. It is also found that the resonance absorption can be strongly enhanced at other values of the velocity shear, so the presence of flows may be generally important for determining the effects of resonance absorption, such as might occur in the interaction of p-modes with sunspots. Resonances leading to instability of the global surface mode can exist, and instability can occur for velocity shears significantly below the Kelvin-Helmholtz threshold. These instabilities may play a role in the development or turbulence in regions of strong velocity shear in the solar wind or the earth's magnetosphere.

  13. Dynamics of a deformable active particle under shear flow.

    PubMed

    Tarama, Mitsusuke; Menzel, Andreas M; ten Hagen, Borge; Wittkowski, Raphael; Ohta, Takao; Löwen, Hartmut

    2013-09-14

    The motion of a deformable active particle in linear shear flow is explored theoretically. Based on symmetry considerations, we propose coupled nonlinear dynamical equations for the particle position, velocity, deformation, and rotation. In our model, both, passive rotations induced by the shear flow as well as active spinning motions, are taken into account. Our equations reduce to known models in the two limits of vanishing shear flow and vanishing particle deformability. For varied shear rate and particle propulsion speed, we solve the equations numerically in two spatial dimensions and obtain a manifold of different dynamical modes including active straight motion, periodic motions, motions on undulated cycloids, winding motions, as well as quasi-periodic and chaotic motions induced at high shear rates. The types of motion are distinguished by different characteristics in the real-space trajectories and in the dynamical behavior of the particle orientation and its deformation. Our predictions can be verified in experiments on self-propelled droplets exposed to a linear shear flow. PMID:24050364

  14. Rotor equivalent wind speed for power curve measurement - comparative exercise for IEA Wind Annex 32

    NASA Astrophysics Data System (ADS)

    Wagner, R.; Cañadillas, B.; Clifton, A.; Feeney, S.; Nygaard, N.; Poodt, M.; St. Martin, C.; Tüxen, E.; Wagenaar, J. W.

    2014-06-01

    A comparative exercise has been organised within the International Energy Agency (IEA) Wind Annex 32 in order to test the Rotor Equivalent Wind Speed (REWS) method under various conditions of wind shear and measurement techniques. Eight organisations from five countries participated in the exercise. Each member of the group has derived both the power curve based on the wind speed at hub height and the power curve based on the REWS. This yielded results for different wind turbines, located in diverse types of terrain and where the wind speed profile was measured with different instruments (mast or various lidars). The participants carried out two preliminary steps in order to reach consensus on how to implement the REWS method. First, they all derived the REWS for one 10 minute wind speed profile. Secondly, they all derived the power curves for one dataset. The main point requiring consensus was the definition of the segment area used as weighting for the wind speeds measured at the various heights in the calculation of the REWS. This comparative exercise showed that the REWS method results in a significant difference compared to the standard method using the wind speed at hub height in conditions with large shear and low turbulence intensity.

  15. Shearing Strength of Concrete

    E-print Network

    Gallup, R. F.; Russell, F. A.

    1907-01-01

    ­ tained from the shear tests made at Kansas University. Table Ho. 9, page, gives the summary of the shear tests made at Kansas University. Foe 7 70 - 0Z /Z O0 3&/c7z A'o. s 0/c7. 0S~ // 700 3 06 /73 0O 6 07 ZZ 900 7...fl.fi Cosss/ry Ci/. />. CO* Sv/joFATES D01/&/0S / / 6 3 0 Z.6<9 .007 3 - S 3 A 07 9 4./a /•/* /( « Z 0 3 3 9 Z.67 .0/ Z-Z9 A 79 2S.0Z 0-79 // " //03S Z.67 .0/ S-0A Z.0S <9S.&4- /.Z9 7 * Mm&^»- 36^ of voids in aggregate, 68*8 the specifio...

  16. Shear-thinning Fluid

    NASA Technical Reports Server (NTRS)

    2001-01-01

    Whipped cream and the filling for pumpkin pie are two familiar materials that exhibit the shear-thinning effect seen in a range of industrial applications. It is thick enough to stand on its own atop a piece of pie, yet flows readily when pushed through a tube. This demonstrates the shear-thinning effect that was studied with the Critical Viscosity of Xenon Experiment (CVX-2) on the STS-107 Research 1 mission in 2002. CVX observed the behavior of xenon, a heavy inert gas used in flash lamps and ion rocket engines, at its critical point. The principal investigator was Dr. Robert Berg of the National Institutes of Standards and Technology in Gaithersburg, MD.

  17. Cosmic shear and biasing

    E-print Network

    Peter Schneider

    1997-08-29

    The correlation between cosmic shear as measured by the image distortion of high-redshift galaxies and the number counts of foreground galaxies is calculated. For a given power spectrum of the cosmic density fluctuations, this correlation is proportional to the bias factor, which can thus directly be measured. In addition, this correlation provides a first-order measure of cosmic shear and is therefore easier to observe than quadratic measures hitherto proposed. Analytic approximations show that the expected signal-to-noise ratio of the correlation is large, so that a significant detection is possible with a moderate amount of data; in particular, it is predicted that the ongoing ESO Imaging Survey (EIS) will be able to detect this correlation on scales of $\\sim 10'$ at a 3-$\\sigma$ level, and at with higher significance on smaller angular scales.

  18. JAWS multiple Doppler derived winds

    NASA Technical Reports Server (NTRS)

    Elmore, Kimberly L.

    1987-01-01

    An elementary working knowledge is given of the advantages and limitations of the multiple Doppler radar analyses that have recently become available from the Joint Airport Weather Studies (JAWS) project. What Doppler radar is and what it does is addressed and the way Doppler radars were used in the JAWS project to gather wind shear data is described. The working definition of wind shear used is winds that affect aircraft flight over a span of 15 to 45 seconds and turbulence is defined as air motion that cause abrupt aircraft motions. The JAWS data current available contain no turbulence data. The concept of multiple Doppler analysis and the geometry of how it works are described, followed by an explanation of how data gathered in radar space are interpolated to a common Cartesian coordinate system and the limitations involved. A discussion is also presented of the analysis grid and how it was constructed. What the user actually gets is discussed, followed by a discussion of the expected errors in the three orthogonal wind components. Finally, a discussion is presented of why JAWS data are significant.

  19. PILOT and cosmic shear

    E-print Network

    W. Saunders

    2008-01-29

    Cosmic shear offers a remarkbly clean way to measure the equation of state of the Universe and its evolution. Resolution over a wide field is paramount, and Antarctica offers unique possibilities in this respect. There is an order of magnitude gain in speed over temperate sites, or a factor three in surface density. This means that PILOT outperforms much larger telescopes elsewhere, and can compete with the proposed DUNE space mission. Keywords: Antarctic astronomy, Surveys, Adaptive optics, Weak lensing

  20. Micromechanics of shear banding

    SciTech Connect

    Gilman, J.J.

    1992-08-01

    Shear-banding is one of many instabilities observed during the plastic flow of solids. It is a consequence of the dislocation mechanism which makes plastic flow fundamentally inhomogeneous, and is exacerbated by local adiabatic heating. Dislocation lines tend to be clustered on sets of neighboring glide planes because they are heterogeneously generated; especially through the Koehler multiple-cross-glide mechanism. Factors that influence their mobilities also play a role. Strain-hardening decreases the mobilities within shear bands thereby tending to spread (delocalize) them. Strain-softening has the inverse effect. This paper reviews the micro-mechanisms of these phenomena. It will be shown that heat production is also a consequence of the heterogeneous nature of the microscopic flow, and that dislocation dipoles play an important role. They are often not directly observable, but their presence may be inferred from changes in thermal conductivity. It is argued that after deformation at low temperatures dipoles are distributed a la Pareto so there are many more small than large ones. Instability at upper yield point, the shapes of shear-band fronts, and mechanism of heat generation are also considered. It is shown that strain-rate acceleration plays a more important role than strain-rate itself in adiabatic instability.

  1. The role of streamline curvature in sand dune dynamics: evidence from field and wind tunnel measurements

    Microsoft Academic Search

    Giles F. S. Wiggs; Ian Livingstone; Andrew Warren

    1996-01-01

    Field measurements on an unvegetated, 10 m high barchan dune in Oman are compared with measurements over a 1:200 scale fixed model in a wind tunnel. Both the field and wind tunnel data demonstrate similar patterns of wind and shear velocity over the dune, confirming significant flow deceleration upwind of and at the toe of the dune, acceleration of flow

  2. A study of the unification of ground and inflight wind criteria for the space shuttle

    NASA Technical Reports Server (NTRS)

    Scoggins, J. R.; Wilson, G. S.

    1977-01-01

    Wind data measured on a 444-m tower located near Oklahoma City, Oklahoma, were used to investigate the structure of wind and turbulence in the height interval from 150 m to 1 km. The structure of wind and turbulence in the layer not encompassed by the existing design criteria was researched and ways for unifying the ground and inflight criteria were investigated. Steady state vertical wind profiles, directional wind component envelopes, wind shear, wind direction change, gust factor, and turbulence spectra are encompassed. A method is proposed for the specification of steady state wind profiles and shear envelopes for use in the region between 150 m and 1 km without altering in any way the existing design criteria. The data analyzed did not indicate a need for changing the existing criteria in regards to wind direction change, gust factor, or spectra of turbulence.

  3. Wind Generator

    NSDL National Science Digital Library

    The Concord Consortium

    2012-05-21

    Windmills have been used for hundreds of years to collect energy from the wind in order to pump water, grind grain, and more recently generate electricity. There are many possible designs for the blades of a wind generator and engineers are always trying new ones. Design and test your own wind generator, then try to improve it by running a small electric motor connected to a voltage sensor.

  4. Some measurements of molecular mixing in compressible turbulent shear layers

    NASA Astrophysics Data System (ADS)

    Hall, J. L.; Dimotakis, P. E.; Rosemann, H.

    1991-06-01

    A new blowdown wind tunnel facility is used to study reacting and nonreacting compressible, turbulent shear layers. In the reacting experiments reported here, low concentrations of hydrogen, fluorine and nitric oxide are carried by inert diluent gases, with the hydrogen and nitric oxide in the high-speed stream, and fluorine in the low-speed stream. The heat release associated with the resulting chemical reaction serves as a diagnostic for molecular mixing in the shear layer. This molecular mixing has been quantified at two compressibility levels by conducting 'flip' experiments in this new facility. The results indicate that the volume fraction of mixed fluid in the compressible shear layer is substantially reduced as compared to previous incompressible results. These same flip experiments also reveal that compressibility significantly reduces the entrainment ratio as compared to theoretical predictions extrapolated from incompressible models.

  5. Self-sustained oscillations of impinging free shear layers

    Microsoft Academic Search

    D. Rockwell; E. Naudascher

    1979-01-01

    Self-sustaining oscillations have been observed for a wide variety of shear-layer impingement configurations. These oscillations are the source of flow noise and undesirable structural loading, and occur in a range of applications that includes transonic wind tunnels, aircraft components, slotted flumes, high-head gates, velocity probes, and pressure probes. Attention is given to the feedback mechanism, the frequency of oscillation, the

  6. Turbulence and shear stress measurements in hypersonic flow

    NASA Technical Reports Server (NTRS)

    Owen, F. K.

    1990-01-01

    An assessment has been made of the potential for hot wire and laser anemometer measurements of turbulent fluctuations in hypersonic flow fields. The results of laser velocimeter experiments conducted in two hypersonic wind tunnels are reported and comparisons made with previous hot wire turbulence measurements. A new concept for the measurement of the compressible shear stress terms which combines the attributes of both hot wire and laser anemometry is presented.

  7. Assessment of Atmospheric Winds Aloft during NASA Space Shuttle Program Day-of-Launch Operations

    NASA Technical Reports Server (NTRS)

    Decker, Ryan K.; Leach, Richard

    2005-01-01

    The Natural Environments Branch at the National Aeronautics and Space Administration s Marshall Space Flight Center monitors the winds aloft at Kennedy Space Center in support of the Space Shuttle Program day of launch operations. High resolution wind profiles are derived from radar tracked Jimsphere balloons, which are launched at predetermined times preceding the launch, for evaluation. The spatial (shear) and temporal (persistence) wind characteristics are assessed against a design wind database to ensure wind change does not violate wind change criteria. Evaluations of wind profies are reported to personnel at Johnson Space Center.

  8. Wind Engineering

    NASA Technical Reports Server (NTRS)

    1983-01-01

    Dr. Jack Cermak, Director of Fluid Dynamics and Diffusion Laboratory, developed the first wind tunnel to simulate the changing temperatures, directions and velocities of natural winds. In this work, Cermak benefited from NASA technology related to what is known as the atmospheric boundary layer (ABL).

  9. Excited waves in shear layers

    NASA Technical Reports Server (NTRS)

    Bechert, D. W.

    1982-01-01

    The generation of instability waves in free shear layers is investigated. The model assumes an infinitesimally thin shear layer shed from a semi-infinite plate which is exposed to sound excitation. The acoustical shear layer excitation by a source further away from the plate edge in the downstream direction is very weak while upstream from the plate edge the excitation is relatively efficient. A special solution is given for the source at the plate edge. The theory is then extended to two streams on both sides of the shear layer having different velocities and densities. Furthermore, the excitation of a shear layer in a channel is calculated. A reference quantity is found for the magnitude of the excited instability waves. For a comparison with measurements, numerical computations of the velocity field outside the shear layer were carried out.

  10. Wind energy.

    PubMed

    Leithead, W E

    2007-04-15

    From its rebirth in the early 1980s, the rate of development of wind energy has been dramatic. Today, other than hydropower, it is the most important of the renewable sources of power. The UK Government and the EU Commission have adopted targets for renewable energy generation of 10 and 12% of consumption, respectively. Much of this, by necessity, must be met by wind energy. The US Department of Energy has set a goal of 6% of electricity supply from wind energy by 2020. For this potential to be fully realized, several aspects, related to public acceptance, and technical issues, related to the expected increase in penetration on the electricity network and the current drive towards larger wind turbines, need to be resolved. Nevertheless, these challenges will be met and wind energy will, very likely, become increasingly important over the next two decades. An overview of the technology is presented. PMID:17272245

  11. Shear viscosity of nuclear matter

    E-print Network

    Jun Xu

    2013-02-01

    In this talk I report my recent study on the shear viscosity of neutron-rich nuclear matter from a relaxation time approach. An isospin- and momentum-dependent interaction is used in the study. Effects of density, temperature, and isospin asymmetry of nuclear matter on its shear viscosity have been discussed. Similar to the symmetry energy, the symmetry shear viscosity is defined and its density and temperature dependence are studied.

  12. Detection of nocturnal coherent turbulence in the US Great Plains and effects on wind turbine fatigue

    NASA Astrophysics Data System (ADS)

    Dvorak, M. J.; Wiersema, D. J.; Zhou, B.; Chow, F. K.

    2012-12-01

    Strong low-level jet winds that develop in the nocturnal stable boundary layer (SBL) create some of the most energetic wind energy resources in Great Plains of North America. These stratified flows, however, can cause strong wind shear and veer across wind turbine rotors. Additionally, turbulent bursting events triggered by strong vertical wind shear can lead to fatigue and damage of wind turbine blades and components, increasing maintenance costs and reducing wind turbine power production. Coherent structures which are the signature of turbulent bursting events can be observed in heavily instrumented wind farms and in high-resolution simulations. Large-scale adoption of wind energy will benefit from the ability to predict these turbulence events with limited in-situ data. By identifying signatures of these bursting events, new turbine control technologies could be used to reduce wind turbine damage and increase overall wind farm energy yield (for example using algorithms with the ability to proactively and independently pitch blades). This research analyzes SBL turbulence in the Great Plains to develop methods to identify these structures at wind farms. Nested large-eddy simulations down to about 20m horizontal resolution are performed and compared to high-resolution Doppler wind LIDAR data (1 Hz) to determine if the model is able to create similar wind and turbulence conditions. Wavelet analysis of the LIDAR and model wind fields is used to detect coherent turbulent structures at frequencies that could be potentially damaging for wind turbines and provide guidance for design of turbine control technologies.

  13. Effect of wind turbine wakes on summer-time wind profiles in the US Great Plains

    NASA Astrophysics Data System (ADS)

    Rhodes, M. E.; Lundquist, J. K.; Aitken, M.

    2011-12-01

    Wind energy is steadily becoming a significant source of grid electricity in the United States, and the Midwestern United States provides one of the nation's richest wind resources. This study examines the effect of wind turbine wakes on the wind profile in central Iowa. Data were collected using a coherent Doppler LiDAR system located approximately 2.5 rotor diameters north of a row of modern multi-MW wind turbine generators. The prevailing wind direction was from the South allowing the LiDAR to capture wind turbine wake properties; however, a number of periods existed where the LiDAR captured undisturbed flow. The LiDAR system reliably obtained readings up to 200 m above ground level (AGL), spanning the entire rotor disk (~40 m to 120 m AGL) which far surpasses the information provided by traditional wind resource assessment instrumentation. We extract several relevant parameters from the lidar data including: horizontal wind speed, vertical velocity, horizontal turbulence intensity, wind shear, and turbulent kinetic energy (TKE). Each time period at a particular LiDAR measurement height was labeled "wake" or "undisturbed" based on the wind direction at that height. Wake and undisturbed data were averaged separately to create a time-height cross-section averaged day for each parameter. Significant differences between wake and undisturbed data emerge. During the day, wake conditions experience larger values of TKE within the altitudes of the turbine rotor disk while TKE values above the rotor disk are similar between waked and undisturbed conditions. Furthermore, the morning transition of TKE in the atmospheric boundary layer commences earlier during wake conditions than in undisturbed conditions, and the evening decay of TKE persists longer during wake conditions. Waked wind shear is consistently greater than undisturbed periods at the edges of the wind turbine rotor disk (40m & 120m AGL), but especially so during the night where wind shear values during wake conditions are three times larger than in undisturbed conditions. Waked conditions show an increased rate of nocturnal subsidence over that of undisturbed conditions, likely due to the momentum deficit as a result of energy extraction by the turbine. Turbulent intensity shows increased levels and longevity in the waked rotor region when compared to the undisturbed conditions. The presentation will present these differences between waked and undisturbed conditions, and compare these observations to the phenomena accounted for in traditional wind turbine wake models.

  14. Properties of Magnetic Reconnection as a function of magnetic shear

    NASA Astrophysics Data System (ADS)

    Liu, Y.; Daughton, W. S.; Karimabadi, H.; Li, H.; Gary, S. P.; Guo, F.

    2013-12-01

    Observations of reconnection events at the Earth's magnetopause and in the solar wind show that reconnection occurs for a large range in magnetic shear angles extending to the very low shear limit 1. Here we report a fully kinetic study of the influence of the magnetic shear on details of reconnection such as its structure and rate. In previous work, we found that the electron diffusion region bifurcates into two or more distinct layers in regimes with weak magnetic shear2, a new feature that may be observable by NASA's up-coming Magnetospheric Multiscale mission. In this work, we have systematically extended the study to lower shear cases and found a new regime, where the reconnection electric field becomes much smaller and the properties of the reconnection changes significantly. We will discuss the role of various physics mechanisms in determining the observed scaling of the reconnection rate, including the dispersive properties of the waves in the system, the dissipation mechanisms and the tearing instability. 1 J. T. Goslings and T. D. Phan. APJL 763, L39, 2013 2 Yi-Hsin Liu et al. Phys. Rev. Lett. 110 , 265004, 2013

  15. Wind Energy Leasing Handbook

    E-print Network

    Balasundaram, Balabhaskar "Baski"

    Wind Energy Leasing Handbook Wind Energy Leasing Handbook E-1033 Oklahoma Cooperative Extension?..................................................................................................................... 31 What do wind developers consider in locating wind energy projects?............................................................................................ 37 How do companies and individuals invest in wind energy projects?....................................................................

  16. Global Winds

    NSDL National Science Digital Library

    2012-08-03

    On this worksheet, students examine a diagram of global winds and learn the position of the prevailing westerlies, the polar easterlies, the trade winds, the horse latitudes and the doldrums, and that together, the uneven heating of the planet by the Sun and the Coriolis Effect are responsible for the global wind belts. The resource is part of the teacher's guide accompanying the video, NASA Why Files: The Case of the Mysterious Red Light. Lesson objectives supported by the video, additional resources, teaching tips and an answer sheet are included in the teacher's guide.

  17. Stellar Winds

    NASA Astrophysics Data System (ADS)

    Owocki, Stan

    A "stellar wind" is the continuous, supersonic outflow of matter from the surface layers of a star. Our sun has a solar wind, driven by the gas-pressure expansion of the hot (T > 106 K) solar corona. It can be studied through direct in situ measurement by interplanetary spacecraft; but analogous coronal winds in more distant solar-type stars are so tenuous and transparent that that they are difficult to detect directly. Many more luminous stars have winds that are dense enough to be opaque at certain wavelengths of the star's radiation, making it possible to study their wind outflows remotely through careful interpretation of the observed stellar spectra. Red giant stars show slow, dense winds that may be driven by the pressure from magnetohydrodyanmic waves. As stars with initial mass up to 8 M ? evolve toward the Asymptotic Giant Branch (AGB), a combination of stellar pulsations and radiative scattering off dust can culminate in "superwinds" that strip away the entire stellar envelope, leaving behind a hot white dwarf stellar core with less than the Chandrasekhar mass of ˜ ?? 1. 4M ?. The winds of hot, luminous, massive stars are driven by line-scattering of stellar radiation, but such massive stars can also exhibit superwind episodes, either as Red Supergiants or Luminous Blue Variable stars. The combined wind and superwind mass loss can strip the star's hydrogen envelope, leaving behind a Wolf-Rayet star composed of the products of earlier nuclear burning via the CNO cycle. In addition to such direct effects on a star's own evolution, stellar winds can be a substantial source of mass, momentum, and energy to the interstellar medium, blowing open large cavities or "bubbles" in this ISM, seeding it with nuclear processed material, and even helping trigger the formation of new stars, and influencing their eventual fate as white dwarves or core-collapse supernovae. This chapter reviews the properties of such stellar winds, with an emphasis on the various dynamical driving processes and what they imply for key wind parameters like the wind flow speed and mass loss rate.

  18. Wind Tunnel

    NSDL National Science Digital Library

    Lawrence Hall of Science

    2009-01-01

    Scientists use enormous wind tunnels to test the design of planes, helicopters, even the Space Shuttle. In this simulation activity, learners create a miniature wind tunnel test by blowing air with a fan or blow dryer through a large tube, then flying paper airplanes, helicopters and other folded paper models in the "wind." Unless the source of the air is a fan that stands on its own, for example, more than one person will be needed to do the activity.This activity can be combined with the Helicopter Twirl, Parachute Drop and Boomerang activities, also found on the Lawrence Hall of Science Kids Site.

  19. Quadraphonic Wind

    NSDL National Science Digital Library

    National Weather Service

    2012-12-18

    In this activity, learners discover how the extent of various wind speeds changes in each of the four quadrants around a hurricane. Learners use data from the 'present' location of Hurricane Bill (2009) to plot the distance of various wind speeds that extend from the center of the storm. This resource includes brief background information about hurricanes and forecasting as well as an explanation of the Hurricane Bill data used in this activity and how small increases in wind speed can cause increased potential for damage.

  20. Characteristics of shear layer with pyrolysing coal particles in one of the streams

    SciTech Connect

    Gollahalli, S.R.; Butuk, N.

    1998-07-01

    This article presents an experimental study of the growth and structure of a two-dimensional shear layer formed by two gas streams, one of which contained coal particles undergoing pyrolysis. Apparatus consisted of a low speed shear layer wind-tunnel designed to generate two gas streams, initially with uniform velocity profiles and isotropic turbulence, which mix at the end of a splitter plate. A fluidized bed injector system was used to introduce bituminous coal particles into one of the streams which was heated to cause their pyrolysis. The test section was optically accessible. The instrumentation included thermocouple, Pitot tube, laser velocimeter, and gas analyzers. Velocity profiles, temperature profiles, shear layer growth rate parameter, and turbulent intensity measurements were obtained. Results indicate that the presence of coal particles affect the velocity and decreases the shear layer growth rate (visible and vorticity thickness) significantly; however, the mass addition due to pyrolysis alone does not change the shear layer characteristics significantly.

  1. Wind Story

    NSDL National Science Digital Library

    WPSU (Penn State University broadcast station)

    This animation presents the characteristics of wind power as a source of clean energy. The force of moving air generates electricity, by rotating blades around a rotor. The motion of the rotor turns a driveshaft that drives an electric generator.

  2. Wind Surge

    NSDL National Science Digital Library

    Robert A. Dalrymple

    This site features an interactive applet from the University of Delaware. The applet illustrates the way water can pile up against the downwind side (of a basin) due to stresses exerted on the surface by strong wind.

  3. Wind Landforms

    NSDL National Science Digital Library

    Lisa Tranel

    In this assignment, students evaluate depositional and erosional landforms created by wind processes. This exercise looks at sand dune and yardang features using satellite images and topographic maps in an online GIS.

  4. Tubular shear wave source

    SciTech Connect

    Cole, J.H.

    1989-09-19

    This patent describes a vibratory source for imparting seismic shear wave energy into an earth medium, underlying a relatively softer earth surface medium. It comprises: rigid, hollow tube means of elongate, tubular shape having an axis and first and second ends with the first end inserted through the surface medium into firm energy-coupling engagement with the earth medium; a housing means rigidly secured in axially balanced relationship on the second end of the tube means; shaft means rotatably supported in the housing means in axial alignment with the tube means adjacent the type means second end; motor means rigidly secured to the housing means and providing rotational drive to the shaft means; and an eccentric weight rotor secured on the shaft means and generating an orbital force for transmission along the length of the tube means to be the first end thereby to couple seismic wave energy of predetermined frequency and duration into the earth medium.

  5. A comparison of the shear strength of structural composite lumber using torsion and shear block tests

    Microsoft Academic Search

    Rakesh Gupta; Tobias S. Siller

    The objective of this study was to compare the shear strength of structural composite lumber (SCL) based on shear block to that of shear strength based on torsion test. Shear blocks in two different orientations from laminated veneer lumber, parallel strand lumber, and laminated strand lumber (LSL) were tested and their shear strengths were compared to the shear strengths of

  6. Simulated performance of an airborne lidar wind shear detection system

    E-print Network

    Griffith, Kenneth Scott

    1987-01-01

    3, 1 Historical Background 3. 2 Doppler Lidar Theory 3. 3 Atmospheric Effects 3. 4 General Lidar System Description 13 14 20 27 IV. COHERENT LIDAR COMPUTER SIMULATiON . . 4. 1 Elements of Simulation 4. 2 Lidar Instrument Model 4. 3... documented in the literature. Among the preliminary work done in the field of laser Doppler velocimetry is the pioneering effort of Yeh and Cum- mings, s who employed the "reference beam" or "local oscillator heterodyning" technique in measuring fluid flow...

  7. NASA wind shear flight test in situ results

    NASA Technical Reports Server (NTRS)

    Oseguera, Rosa M.

    1992-01-01

    The main objectives in developing the NASA in situ windshear detection algorithm were to provide a measurement standard for validation of forward-look sensors under development, and to demonstrate the algorithm's ability to operate with a suitably low nuisance alert rate. It was necessary to know exactly how the algorithm was implemented and what parameters and filtering were used, in order to be able to fully test its effectiveness and correlate in situ results with forward-look sensor data.

  8. Wind Monitoring Report for Fort Wainwright's Donnelly Training Area

    SciTech Connect

    Orrell, Alice C.; Dixon, Douglas R.

    2011-01-18

    Using the wind data collected at a location in Fort Wainwright’s Donnelly Training Area (DTA) near the Cold Regions Test Center (CRTC) test track, Pacific Northwest National Laboratory (PNNL) estimated the gross and net energy productions that proposed turbine models would have produced exposed to the wind resource measured at the meteorological tower (met tower) location during the year of measurement. Calculations are based on the proposed turbine models’ standard atmospheric conditions power curves, the annual average wind speeds, wind shear estimates, and standard industry assumptions.

  9. Effects of Changing Atmospheric Conditions on Wind Turbine Performance (Poster)

    SciTech Connect

    Clifton, A.

    2012-12-01

    Multi-megawatt, utility-scale wind turbines operate in turbulent and dynamic winds that impact turbine performance in ways that are gradually becoming better understood. This poster presents a study made using a turbulent flow field simulator (TurbSim) and a Turbine aeroelastic simulator (FAST) of the response of a generic 1.5 MW wind turbine to changing inflow. The turbine power output is found to be most sensitive to wind speed and turbulence intensity, but the relationship depends on the wind speed with respect to the turbine's rated wind speed. Shear is found to be poorly correlated to power. A machine learning method called 'regression trees' is used to create a simple model of turbine performance that could be used as part of the wind resource assessment process. This study has used simple flow fields and should be extended to more complex flows, and validated with field observations.

  10. Wind for Schools (Poster)

    Microsoft Academic Search

    Baring-Gould

    2010-01-01

    As the United States dramatically expands wind energy deployment, the industry is challenged with developing a skilled workforce and addressing public resistance. Wind Powering America's Wind for Schools project addresses these issues by developing Wind Application Centers (WACs) at universities; WAC students assist in implementing school wind turbines and participate in wind courses, by installing small wind turbines at community

  11. Smectic Edge Dislocations under Shear

    NASA Astrophysics Data System (ADS)

    Chen, Peilong; Lu, Chun-Yi David

    2011-09-01

    Layer structures around an edge dislocation in a smectic phase under shear are studied with both phase field and order parameter models. It is shown that, contrast to a crystal solid, the conventional picture of the Peach--Koehler force experienced by dislocations when the sample is under a shear stress cannot be readily applied to the smectic phases. Under a uniform shear flow, we obtain the phase field and order parameter solutions around an edge dislocation. The solutions elucidate properties such as the layer distortion range around the dislocation and scaling of inter-dislocation interaction on dislocation separation. Calculations on energy dissipation indicate the extreme shear-thinning behavior that an edge dislocation induces a shear stress independent of the shear rate. Finally in a bulk sample with dislocation forming loops and networks, we argue that the uniform flow component around the dislocation is important to the energy dissipation and we show that its scaling exponent with the shear rate is very close to results from many previous rheology measurements.

  12. Experimental observations of shear patterns in direct shear tests

    NASA Astrophysics Data System (ADS)

    Scarpelli, G.; Wood, D. M.

    A series of simple experiments were performed using direct shear apparatus in order to study the rupture patterns in sands. Measurements of internal displacements were made by observing with X-rays the positions of lead shot placed in a regular array within the sample. Shear displacement was applied manually and radiographs were taken after each increment of horizontal movement in order to observe the incremental strain field. The sand used was 30/52 Leighton Buzzard sand with a grain size between 0.3mm and 0.5mm. It was concluded that, while caution should be exercised in extrapolating the results of these low stress tests, the results matched some theoretical estimates for the orientation of shear bands. It was suggested that characteristic lengths and thicknessess of shear bands might be related to the average particle size of the sand.

  13. Macroscopic Discontinuous Shear Thickening versus Local Shear Jamming in Cornstarch

    NASA Astrophysics Data System (ADS)

    Fall, A.; Bertrand, F.; Hautemayou, D.; Mezière, C.; Moucheront, P.; Lemaître, A.; Ovarlez, G.

    2015-03-01

    We study the emergence of discontinuous shear thickening (DST) in cornstarch by combining macroscopic rheometry with local magnetic resonance imaging measurements. We bring evidence that macroscopic DST is observed only when the flow separates into a low-density flowing and a high-density jammed region. In the shear-thickened steady state, the local rheology in the flowing region is not DST but, strikingly, is often shear thinning. Our data thus show that the stress jump measured during DST, in cornstarch, does not capture a secondary, high-viscosity branch of the local steady rheology but results from the existence of a shear jamming limit at volume fractions quite significantly below random close packing.

  14. Influence of refraction on wind turbine noise

    E-print Network

    Makarewicz, Rufin

    2013-01-01

    A semi-empirical method is applied to calculate the time-average sound level of wind turbine noise generation and propagation. Both are affected by wind shear refraction. Under upwind conditions the partially ensonified zone separates the fully ensonified zone (close to the turbine) and the shadow zone (far away from the turbine). Refraction is described in terms of the wind speed linear profile fitted to the power law profile. The rotating blades are treated as a two-dimensional circular source in the vertical plane. Inside the partially ensonified zone the effective A-weighted sound power decreases to zero when the receiver moves from the turbine toward the shadow zone. The presented results would be useful in practical applications to give a quick estimate of the effect of refraction on wind turbine noise.

  15. Nebraska wind resource assessment first year results

    SciTech Connect

    Hurley, P.J.F.; Vilhauer, R. [RLA Consulting, Inc., Bothell, WA (United States); Stooksbury, D. [Univ. of Nebraska, Lincoln, NE (United States)

    1996-12-31

    This paper presents the preliminary results from a wind resource assessment program in Nebraska sponsored by the Nebraska Power Association. During the first year the measured annual wind speed at 40 meters ranged from 6.5 - 7.5 m/s (14.6 - 16.8 mph) at eight stations across the state. The site selection process is discussed as well as an overview of the site characteristics at the monitoring locations. Results from the first year monitoring period including data recovery rate, directionality, average wind speeds, wind shear, and turbulence intensity are presented. Results from the eight sites are qualitatively compared with other midwest and west coast locations. 5 figs., 2 tabs.

  16. Wind turbine

    DOEpatents

    Cheney, Jr., Marvin C. (Glastonbury, CT)

    1982-01-01

    A wind turbine of the type having an airfoil blade (15) mounted on a flexible beam (20) and a pitch governor (55) which selectively, torsionally twists the flexible beam in response to wind turbine speed thereby setting blade pitch, is provided with a limiter (85) which restricts unwanted pitch change at operating speeds due to torsional creep of the flexible beam. The limiter allows twisting of the beam by the governor under excessive wind velocity conditions to orient the blades in stall pitch positions, thereby preventing overspeed operation of the turbine. In the preferred embodiment, the pitch governor comprises a pendulum (65,70) which responds to changing rotor speed by pivotal movement, the limiter comprising a resilient member (90) which engages an end of the pendulum to restrict further movement thereof, and in turn restrict beam creep and unwanted blade pitch misadjustment.

  17. Structure of Highly Sheared Tropical Storm Chantal during CAMEX-4.

    NASA Astrophysics Data System (ADS)

    Heymsfield, G. M.; Halverson, J.; Ritchie, E.; Simpson, Joanne; Molinari, J.; Tian, L.

    2006-01-01

    Tropical Storm Chantal during August 2001 was a storm that failed to intensify over the few days prior to making landfall on the Yucatan Peninsula. An observational study of Tropical Storm Chantal is presented using a diverse dataset including remote and in situ measurements from the NASA ER-2 and DC-8 and the NOAA WP-3D N42RF aircraft and satellite. The authors discuss the storm structure from the larger-scale environment down to the convective scale. Large vertical shear (850 200-hPa shear magnitude range 8 15 m s-1) plays a very important role in preventing Chantal from intensifying. The storm had a poorly defined vortex that only extended up to 5 6-km altitude, and an adjacent intense convective region that comprised a mesoscale convective system (MCS). The entire low-level circulation center was in the rain-free western side of the storm, about 80 km to the west-southwest of the MCS. The MCS appears to have been primarily the result of intense convergence between large-scale, low-level easterly flow with embedded downdrafts, and the cyclonic vortex flow. The individual cells in the MCS such as cell 2 during the period of the observations were extremely intense, with reflectivity core diameters of 10 km and peak updrafts exceeding 20 m s-1. Associated with this MCS were two broad subsidence (warm) regions, both of which had portions over the vortex. The first layer near 700 hPa was directly above the vortex and covered most of it. The second layer near 500 hPa was along the forward and right flanks of cell 2 and undercut the anvil divergence region above. There was not much resemblance of these subsidence layers to typical upper-level warm cores in hurricanes that are necessary to support strong surface winds and a low central pressure. The observations are compared to previous studies of weakly sheared storms and modeling studies of shear effects and intensification.The configuration of the convective updrafts, low-level circulation, and lack of vertical coherence between the upper- and lower-level warming regions likely inhibited intensification of Chantal. This configuration is consistent with modeled vortices in sheared environments, which suggest the strongest convection and rain in the downshear left quadrant of the storm, and subsidence in the upshear right quadrant. The vertical shear profile is, however, different from what was assumed in previous modeling in that the winds are strongest in the lowest levels and the deep tropospheric vertical shear is on the order of 10 12 m s-1.

  18. Structure of Highly Sheared Tropical Storm Chantal during CAMEX-4

    NASA Technical Reports Server (NTRS)

    Heymsfield, G. M.; Halverson, J.; Ritchie, E.; Simpson, Joanne; Molinari, J.; Tian, L.

    2006-01-01

    Tropical Storm Chantal during August 2001 was a storm that failed to intensify over the few days prior to making landfall on the Yucatan Peninsula. An observational study of Tropical Storm Chantal is presented using a diverse dataset including remote and in situ measurements from the NASA ER-2 and DC-8 and the NOAA WP-3D N42RF aircraft and satellite. The authors discuss the storm structure from the larger-scale environment down to the convective scale. Large vertical shear (850-200-hPa shear magnitude range 8-15 m/s) plays a very important role in preventing Chantal from intensifying. The storm had a poorly defined vortex that only extended up to 5-6-km altitude, and an adjacent intense convective region that comprised a mesoscale convective system (MCS). The entire low-level circulation center was in the rain-free western side of the storm, about 80 km to the west-southwest of the MCS. The MCS appears to have been primarily the result of intense convergence between large-scale, low-level easterly flow with embedded downdrafts, and the cyclonic vortex flow. The individual cells in the MCS such as cell 2 during the period of the observations were extremely intense, with reflectivity core diameters of 10 km and peak updrafts exceeding 20 m/s. Associated with this MCS were two broad subsidence (warm) regions, both of which had portions over the vortex. The first layer near 700 hPa was directly above the vortex and covered most of it. The second layer near 500 hPa was along the forward and right flanks of cell 2 and undercut the anvil divergence region above. There was not much resemblance of these subsidence layers to typical upper-level warm cores in hurricanes that are necessary to support strong surface winds and a low central pressure. The observations are compared to previous studies of weakly sheared storms and modeling studies of shear effects and intensification. The configuration of the convective updrafts, low-level circulation, and lack of vertical coherence between the upper- and lower-level warming regions likely inhibited intensification of Chantal. This configuration is consistent with modeled vortices in sheared environments, which suggest the strongest convection and rain in the downshear left quadrant of the storm, and subsidence in the upshear right quadrant. The vertical shear profile is, however, different from what was assumed in previous modeling in that the winds are strongest in the lowest levels and the deep tropospheric vertical shear is on the order of 10-12 m/s.

  19. Wind Tubes

    NSDL National Science Digital Library

    Exploratorium

    2012-12-14

    In this activity, learners create and experiment with wind tubes. These tubes are a playful and inventive way to explore the effect that moving air has on objects. Construction uses everyday materials such as a fan and embroidery hoops. It’s fun to make things fly out of or float in the tubes, and to adjust the tubes to change the way the objects fly. The activity requires a significant amount of time and resources to build and may require adult help in construction. Experimentation with the wind tubes is engaging for a wide age range of learners.

  20. Are windshear training aid recommendations appropriate for other than large jet transports? Pilot procedures: Shear models

    NASA Technical Reports Server (NTRS)

    Bray, R. S.

    1988-01-01

    Information is given in vugraph form on pilot procedures in windshear, typical winds in a downburst, a downburst encounter at takeoff by a large jet transport and a light turboprop twin, and a comparison of pitch algorithms in an approach encounter with downburst shear. It is observed that the light turboprop appears no less tolerant of a downburst encounter than the large jet.

  1. Study on Hippophae rhamnoides Linn. Roots in Improving the Shear Characteristics of Soil

    Microsoft Academic Search

    Yong-liang Zhang; Jing Liu; Lin-he Wang; Xi-jun Yao; Xin Zhang; Li Yao

    2010-01-01

    In this paper, the author investigates root's soil mechanics' mechanism and influencing factors of a typical soil reinforcing plant- Hippophae rhamnoides Linn. in the area that has been destroyed by wind and water. This investigation has been done from two aspects: shear strength of root-soil composite and friction characteristic of root-soil interface. The results show that when the root diameter

  2. The wind speed profile at offshore wind farm sites

    NASA Astrophysics Data System (ADS)

    Lange, B.; Larsen, S. E.; Højstrup, J.; Barthelmie, R.

    2003-04-01

    The first large offshore wind farms are in the planning phase in several countries in Europe. Their economic viability depends on the favourable wind conditions compared to sites on land. The higher energy yield has to compensate the additional installation and maintenance cost. For project planning and siting a reliable prediction of the wind resource is therefore crucial. For turbine design the wind shear of the marine surface layer is an important design parameter, especially since the growing rotor diameter makes turbines more vulnerable for spatial wind speed variations. Compared to land surfaces the roughness of water is very low. It is commonly described either as a constant (as in the wind resource estimation program WAsP) or by means of the Charnock approach, relating sea surface roughness and friction velocity. While this relation works well for the open oceans it has been found inappropriate for coastal areas where waves are not fully developed. Information about the wave field is needed to model the sea surface roughness more accurately (see e.g. Johnson et al. (1998)). The atmospheric stability differs greatly between land and water areas. It is more important offshore compared to land sites due to the low surface roughness of water. The main influence of the atmospheric stability is on the vertical momentum transport, which is reflected in the vertical wind speed profile. It is usually described with Monin-Obukhov similarity theory. However, other effects not described by this approach might also play an important role: For offshore flow the flow regime at coastal sites is affected by the land-sea discontinuity (Højstrup, 1999). An internal boundary layer develops at the coastline and an inhomogeneous flow field might develop in the coastal zone, especially in stable stratification (see e.g. (Smedman et al. (1997)) Recent data from the measurement at Rødsand, 10 km off the Danish coast in the Baltic Sea, include simultaneous wind and wave data from a 50 m meteorological mast and an acoustic sea bed mounted wave gauge. Wind speed and turbulence intensity profiles are modelled for the Rødsand site using different approaches for stability and roughness. Results are compared with the measured data. For the sea surface roughness the use of the Charnock equation leads to good results. Improvements from using a wave field dependent roughness description are found to be small. For stability induced influences on the profiles M-O-theory works well in the case of unstable stratification. For stable stratification large deviations are found. They can be explained qualitatively as flow regimes with a mixed layer close to the surface and a capping inversion. In such a flow the atmospheric stability is strongly dependent on height and Monin-Obukhov similarity theory fails. For the Rødsand measurement this flow regime has been found to have an important influence on the wind climatology of the site. A wind speed at hub height predicted from a lower measurement with conventional theory will be underestimated. Højstrup, J.: Vertical Extrapolation of Offshore Wind Profiles. Wind energy for the next millennium. Proceedings. 1999 European wind energy conference (EWEC '99), Nice (FR), 1-5 Mar 1999. Petersen, E.L.; Hjuler Jensen, P.; Rave, K.; Helm, P.; Ehmann, H. (eds.), (1999) p. 1220-1223 Smedman, A.-S., H. Bergström and B. Grisogono: Evolution of stable internal boundary layers over a cold sea. Journal of Geophysical Research 102(C1), (1997); pp.1091-1099. Johnson, H.K., J. Højstrup, H.J. Vested, &S.E. Larsen: On the Dependence of Sea Surface Roughness on Wind Waves. Journal of Physical Oceanography. Vol.28 (1998) p. 1702-1716

  3. Wind energy systems

    NASA Technical Reports Server (NTRS)

    Stewart, H. J.

    1978-01-01

    A discussion on wind energy systems involved with the DOE wind energy program is presented. Some of the problems associated with wind energy systems are discussed. The cost, efficiency, and structural design of wind energy systems are analyzed.

  4. Testing the Maximum Magnetic Shear Model with OpenGGCM

    NASA Astrophysics Data System (ADS)

    Maynard, K.; Germaschewski, K.; Lin, L.; Raeder, J.

    2012-12-01

    Magnetic reconnection at Earth's magnetopause can occur as antiparallel or component reconnection depending on the geometry of the magnetic field, and has important implications for plasma entry into the magnetosphere. The maximum magnetic shear model proposed by Trattner et al. [J. Geophys. Res., 112, 2007] is an empirical model for determining the location and type of reconnection based on the solar wind clock angle during times of southward IMF. This model has been tested against reconnection inferred from magnetopause crossings of both the Cluster and THEMIS missions. The observations agree with the model that component reconnection dominates when the IMF points within 60 degrees of the east-west direction; however, observations are limited since the spacecraft must cross the magnetopause near the X-line, and data only exists for a relatively small region of the magnetopause. Numerical simulations can give a view of the global dynamics and geometry of reconnection. We use OpenGGCM, a 3D global MHD code, to test the maximum magnetic shear model using both synthetic solar wind conditions and solar wind observations of some of the events observed by Cluster and THEMIS. In addition, we examine the dynamics of the magnetopause when IMF Bx is greater than 70% of |B|, where observations suggest that antiparallel reconnection usually dominates regardless of clock angle.

  5. Reynolds number effects on surface shear stress patterns around isolated hemispheres

    NASA Technical Reports Server (NTRS)

    Lee, J. A.; Greeley, Ronald

    1987-01-01

    Obstacles projecting into the wind stream alter the shear stress on the surface around them, thus altering the erosion, transportation, and deposition of aeolian sediment. The effect of Reynolds number on the pattern of shear stress on the surface around an isolated hemisphere was investigated. An understanding of Reynolds number effects is necessary if wind tunnel results are to be scaled up to natural situations for meaningful applications. The experiment shows that the surface shear stress pattern is strongly affected by Reynolds number, at least within the range of Re used (1360 to 2977). This is presumably due to a decrease in flow around the sides of the hemisphere and an increase in flow over the object as the Reynolds number increases.

  6. Wind tunnel investigation on wind turbine wakes and wind farms

    NASA Astrophysics Data System (ADS)

    Iungo, G. V.; Coëffé, J.; Porté-Agel, F.

    2012-04-01

    The interaction between atmospheric boundary layer and wind farms leads to flow modifications, which need to be deeply characterized in order to relate them to wind farm performance. The wake flow produced from a wind farm is the result of a strong interaction between multiple turbine wakes, so that the wind farm configuration turns out to be one of the dominant features to enhance power production. For the present work a wind tunnel investigation was carried out with hot-wire anemometry and velocity measurements performed with multi-hole pressure probes. The tested wind farms consist of miniature three-bladed wind turbine models. Preliminarily, the wake flow generated from a single wind turbine is surveyed, which is characterized by a strong velocity defect lying in proximity of the wind turbine hub height. The wake gradually recovers by moving downstream; the characteristics of the incoming boundary layer and wind turbulence intensity can strongly affect the wake recovery, and thus performance of following wind turbines. An increased turbulence level is typically detected downstream of each wind turbine for heights comparable to the wind turbine blade top-tip. These wake flow fluctuations produce increased fatigue loads on the following wind turbines within a wind farm, which could represent a significant hazard for real wind turbines. Dynamics of vorticity structures present in wind turbine wakes are also investigated; particular attention is paid to the downstream evolution of the tip helicoidal vortices and to oscillations of the hub vortex. The effect of wind farm layout on power production is deeply investigated. Particular emphasis is placed on studying how the flow adjusts as it moves inside the wind farm and can affect the power production. Aligned and staggered wind farm configurations are analysed, also with varying separation distances in the streamwise and spanwise directions. The present experimental results are being used to test and guide the development of improved parameterizations of wind turbines in high-resolution numerical models, such as large-eddy simulations (LES).

  7. Shear shocks in fragile networks

    PubMed Central

    Ulrich, Stephan; Upadhyaya, Nitin; van Opheusden, Bas; Vitelli, Vincenzo

    2013-01-01

    A minimal model for studying the mechanical properties of amorphous solids is a disordered network of point masses connected by unbreakable springs. At a critical value of its mean connectivity, such a network becomes fragile: it undergoes a rigidity transition signaled by a vanishing shear modulus and transverse sound speed. We investigate analytically and numerically the linear and nonlinear visco-elastic response of these fragile solids by probing how shear fronts propagate through them. Our approach, which we tentatively label shear front rheology, provides an alternative route to standard oscillatory rheology. In the linear regime, we observe at late times a diffusive broadening of the fronts controlled by an effective shear viscosity that diverges at the critical point. No matter how small the microscopic coefficient of dissipation, strongly disordered networks behave as if they were overdamped because energy is irreversibly leaked into diverging nonaffine fluctuations. Close to the transition, the regime of linear response becomes vanishingly small: the tiniest shear strains generate strongly nonlinear shear shock waves qualitatively different from their compressional counterparts in granular media. The inherent nonlinearities trigger an energy cascade from low to high frequency components that keep the network away from attaining the quasi-static limit. This mechanism, reminiscent of acoustic turbulence, causes a superdiffusive broadening of the shock width. PMID:24309379

  8. Gap Winds

    NSDL National Science Digital Library

    2014-09-14

    This module provides a basic understanding of why gap winds occur, their typical structures, and how gap wind strength and extent are controlled by larger-scale, or synoptic, conditions. You will learn about a number of important gap flows in coastal regions around the world, with special attention given to comprehensively documented gap wind cases in the Strait of Juan de Fuca and the Columbia River Gorge. Basic techniques for evaluating and predicting gap flows are presented. The module reviews the capabilities and limitations of the current generation of mesoscale models in producing realistic gap winds. By the end of this module, you should have sufficient background to diagnose and forecast gap flows around the world, and to use this knowledge to understand their implications for operational decisions. Other features in this module include a concise summary for quick reference and a final exam to test your knowledge. Like other modules in the Mesoscale Meteorology Primer, this module comes with audio narration, rich graphics, and a companion print version.

  9. Wind Chimes

    NSDL National Science Digital Library

    K-12 Outreach Office,

    Students are challenged to design and build wind chimes using their knowledge of physics and sound waves, and under given constraints such as weight, cost and number of musical notes it must generate. They make mathematical computations to determine the pipe lengths.

  10. Extreme wind climate in the Czech Republic

    NASA Astrophysics Data System (ADS)

    Pop, L.; Hanslian, D.; Jiri, H.

    2011-12-01

    Extreme wind events belong to the most damaging weather-related hazards in Czech Republic. Therefore a complex survey is performed to exploit the wind data available over the period of industrial measurements in Czech Republic for extreme wind analysis. The object of the survey is to find the limitations of wind data available, to analyze the conditions for extreme wind events and to try to enhance the knowledge about the statistical behavior of extreme wind. The data quality showed itself as a major issue. The homogeneity of extreme wind data is broken in many cases as the extreme wind values are highly dependent on the measuring instrumentation and changes in neighborhood. It also may be difficult to distinguish between correct high wind data and erroneous values. The individual analysis and quality assessment of wind data used in extremal analysis is therefore essential. There are generally two basic groups of extreme wind events typical in the Czech Republic and generally over the mid-latitudes: The "convective" events (can be also called as "squalls") are primarily initiated by deep convection, whereas the primary cause for "non-convective" (synoptic) events is large-scale pressure gradient. The subject is, however, a bit more complex, as the pressure gradient inducing high wind in higher atmospheric levels or wind shear can be a significant factor in convective events; on the other hand, convection may increase wind speeds in otherwise "non-convective" synoptic-scale windstorms. In addition, there are some special phenomena that should be treated individually: the physical principle and climatological behavior (frequency, magnitude and area affected) of tornadoes make them very different from common convective straight winds; this is in lesser scale also the case of "foehn" or "bora" effects belonging to non-convective events. These effects, however, do not play major role over the Czech Republic. In Czech Republic, the overall impact of convective and non-convective extreme wind events is roughly at the same order. The convective events usually occur from April to August, whereas the non-convective events are typical for cold months from October to March. In mountainous regions, the non-convective events are most important, however, the impact of convective storms is high in lowlands, partially because of the seasonal foliage. The convective events are usually connected with squall lines or frontal waves. The non-convective events are mostly caused by strong southwest to northwest flow; a smaller specific group of these events, typical for some regions, is connected with south to southeast flow.

  11. Shear thickening in highly viscous granular suspensions

    NASA Astrophysics Data System (ADS)

    Xu, Qin; Majumdar, Sayantan; Brown, Eric; Jaeger, Heinrich M.

    2014-09-01

    We experimentally investigate shear thickening in dense granular suspensions under oscillatory shear. Directly imaging the suspension-air interface, we observe dilation beyond a critical strain ?c and the end of shear thickening as the maximum confining stress is reached and the contact line moves. Analyzing the shear profile, we extract the viscosity contributions due to hydrodynamics ?h , dilation ?c and sedimentation ?g . While ?g governs the shear thinning regime, ?h and ?c together determine the shear thickening behavior. As the suspending liquid's viscosity varies from 10 to 1000 cSt, ?h is found to compete with ?c and soften the discontinuous nature of shear thickening.

  12. Evolution of a barotropic shear layer into elliptical vortices.

    PubMed

    Guha, Anirban; Rahmani, Mona; Lawrence, Gregory A

    2013-01-01

    When a barotropic shear layer becomes unstable, it produces the well-known Kelvin-Helmholtz instability (KHI). The nonlinear manifestation of the KHI is usually in the form of spiral billows. However, a piecewise linear shear layer produces a different type of KHI characterized by elliptical vortices of constant vorticity connected via thin braids. Using direct numerical simulation and contour dynamics, we show that the interaction between two counterpropagating vorticity waves is solely responsible for this KHI formation. We investigate the oscillation of the vorticity wave amplitude, the rotation and nutation of the elliptical vortex, and straining of the braids. Our analysis also provides a possible explanation for the formation and evolution of elliptical vortices appearing in geophysical and astrophysical flows, e.g., meddies, stratospheric polar vortices, Jovian vortices, Neptune's Great Dark Spot, and coherent vortices in the wind belts of Uranus. PMID:23410439

  13. Determining ow type, shear rate and shear stress in magmas from bubble shapes and orientations

    E-print Network

    Manga, Michael

    Determining £ow type, shear rate and shear stress in magmas from bubble shapes and orientations A the shapes and orientations of bubbles (vesicles) in obsidian to estimate shear rates and shear stresses shearing that deforms, and surface tension that rerounds. The ratio of these stresses is the capillary

  14. Sand–geotextile interface shear strength by torsional ring shear tests

    Microsoft Academic Search

    S. A Tan; S. H Chew; W. K Wong

    1998-01-01

    The torsional ring shear apparatus was developed to evaluate the residual shear strength of soft soils. It has the advantage of allowing large displacement to take place while shearing. In using geotextiles for geotechnical engineering applications, the soil–geotextile interface shear strength is an important design parameter. Hence this paper describes the evaluation of the soil–geotextile interface shear strength using the

  15. Wind Tunnel Modeling Of Wind Flow Over Complex Terrain

    NASA Astrophysics Data System (ADS)

    Banks, D.; Cochran, B.

    2010-12-01

    This presentation will describe the finding of an atmospheric boundary layer (ABL) wind tunnel study conducted as part of the Bolund Experiment. This experiment was sponsored by Risø DTU (National Laboratory for Sustainable Energy, Technical University of Denmark) during the fall of 2009 to enable a blind comparison of various air flow models in an attempt to validate their performance in predicting airflow over complex terrain. Bohlund hill sits 12 m above the water level at the end of a narrow isthmus. The island features a steep escarpment on one side, over which the airflow can be expected to separate. The island was equipped with several anemometer towers, and the approach flow over the water was well characterized. This study was one of only two only physical model studies included in the blind model comparison, the other being a water plume study. The remainder were computational fluid dynamics (CFD) simulations, including both RANS and LES. Physical modeling of air flow over topographical features has been used since the middle of the 20th century, and the methods required are well understood and well documented. Several books have been written describing how to properly perform ABL wind tunnel studies, including ASCE manual of engineering practice 67. Boundary layer wind tunnel tests are the only modelling method deemed acceptable in ASCE 7-10, the most recent edition of the American Society of Civil Engineers standard that provides wind loads for buildings and other structures for buildings codes across the US. Since the 1970’s, most tall structures undergo testing in a boundary layer wind tunnel to accurately determine the wind induced loading. When compared to CFD, the US EPA considers a properly executed wind tunnel study to be equivalent to a CFD model with infinitesimal grid resolution and near infinite memory. One key reason for this widespread acceptance is that properly executed ABL wind tunnel studies will accurately simulate flow separation, vortex shedding, and local turbulence intensity and wind shear values. To achieve accurate results, attention must of course be paid to issues such as ensuring Reynolds number independence, avoiding blockage issues, and properly matching the velocity power spectrum, but once this is done, the laws of fluid mechanics take care of the rest. There will not be an overproduction of turbulent kinetic energy at the top of escarpments, or unacceptable dissipation of inlet turbulence levels. Modern atmospheric boundary layer wind tunnels are also often used to provide validation data for evaluating the performance of CFD model in complex flow environments. Present day computers have further increased the quality and quantity of data that can be economically obtained in a timely manner, for example through wind speed measurement using a computer controlled 3-D measurement positioning system Given this accuracy and widespread acceptance, it is perhaps surprising that ours was the only wind tunnel model in the Bolund blind experiment, an indication of how seldom physical modelling is used when estimating terrain effect for wind farms. In demonstrating how the Bolund test was modeled, this presentation will provide background on wind tunnel testing, including the governing scaling parameters. And we’ll see how our results compared to the full scale tests.

  16. GPU-based shear-shear correlation calculation

    NASA Astrophysics Data System (ADS)

    Cárdenas-Montes, Miguel; Vega-Rodríguez, Miguel A.; Bonnett, Christopher; Sevilla-Noarbe, Ignacio; Ponce, Rafael; Sánchez Alvaro, Eusebio; Rodríguez-Vázquez, Juan José

    2014-01-01

    Light rays are deflected when travelling through a gravitational potential: this phenomenon is known as gravitational lensing. It causes the observed shapes of distant galaxies to be very slightly distorted by the intervening matter in the Universe, as their light travels towards us. This distortion is called cosmic shear. By measuring this component it is possible to derive the properties of the mass distribution causing the distortion. This in turn can lead to the measurement of the accelerated expansion of the Universe, as matter clumps together differently depending on its dynamics at each cosmological epoch. The measurement of the cosmic shear requires the statistical analysis of the ellipticities of millions of galaxies using very large astronomical surveys. In the past, due to the computational cost of the problem, this kind of analysis was performed by introducing simplifications in the estimation of such statistics. With the advent of scientific computing using graphics processing units, analysis of the shear can be addressed without approximations, even for very large surveys, while maintaining an affordable execution time. In this work, we present the creation and optimization of such a graphics processing unit code to compute the so-called shear-shear correlation function.

  17. WIND ENERGY Wind Energ. (2014)

    E-print Network

    Peinke, Joachim

    2014-01-01

    loads from the wind inflow through rotor aerodynamics, drive train and power electronics is still not fully understood. In this paper, we focus on the local aerodynamic forces at the rotor blade, which stem of their dynamics. Unsteady aerodynamic loads stimulate structural vibrations that can contribute to fatigue

  18. Structural Aspects of Railway Truss Bridges Affecting Transverse Shear Forces in Steel-Concrete Composite Decks

    NASA Astrophysics Data System (ADS)

    Siekierski, Wojciech

    2015-03-01

    At the steel-concrete interface, the horizontal shear forces that are transverse to cross beams occur due to joint action of the steel-concrete composite deck and the truss girders. Numerical analysis showed that values of the forces are big in comparison to the longitudinal shear forces. In both cases extreme force values occur near side edges of a slab. The paper studies possibilities of reduction of these shear forces by structural alterations of the following: rigidity of a concrete slab, arrangement of a wind bracing, arrangement of concrete slab expansion joints. An existing railway truss bridge span has been analysed. Numerical analysis shows that it is possible to reduce the values of shear forces transverse to cross beams. It may reach 20% near the side edges of slabs and 23% in the centre of slab width.

  19. The interaction between a plane shear layer and a slender body

    NASA Astrophysics Data System (ADS)

    Merati, Parviz; Adrian, Ronald J.

    1991-12-01

    The behavior of a shear layer in the neighborood of a thin flat plate is investigated for the cases of different angles of attack and for shear layers changed by the values of plate offset and length. A single stream is split with a plate into two streams in a two-stream plane shear-layer wind tunnel, and the pressure of the lower stream is reduced. Flow photographs are examined, and spectrum and hot-wire-probe measurements are taken to determine streamwise and cross-streamwise velocities. The flat plate is shown to interact with the shear layer by: (1) generating large vertical velocities at the plate's leading-edge stagnation point; (2) affecting a region 30 times plate thickness at zero angle of attack; and (3) generating a high-pressure field at the stagnation region that deflects the mixing layer toward the slower stream at large angles of attack.

  20. Modelling the reorientation of sea-ice faults as the wind changes direction

    E-print Network

    Feltham, Daniel

    , tensile and shear deformation. A constant wind-stress gradient is applied until the initially frozen ice of their length by a particular fraction, the ice pack deformation is neglected and the wind stress is rotated and others (2004) used a discrete-element model to study sea-ice fracture due to different imposed patterns

  1. Yield shear stress and disaggregating shear stress of human blood

    NASA Astrophysics Data System (ADS)

    Jung, Jinmu; Lee, Byoung-Kwon; Shin, Sehyun

    2014-05-01

    This review presents two distinct rheological parameters of blood that have the potential to indicate blood circulation adequacy: yield shear stress (YSS) and disaggregating shear stress (DSS). YSS and DSS reflect the strength of red blood cell (RBC) aggregation in suspension under static and dynamic conditions, respectively. YSS, defined as the critical stress to disperse RBC aggregates under static conditions, was found to be dependent upon hematocrit, fibrinogen, and red cell deformability, but not temperature. DSS, defined as the minimum shear stress to disperse RBC aggregates under dynamic conditions, is dependent upon fibrinogen, red cell deformability, and temperature but not hematocrit. Owing to recent advances in measurement technology, these two parameters can be easily measured, and thus, their clinical significance in blood circulation can be verified.

  2. Isogeometric analysis of shear bands

    NASA Astrophysics Data System (ADS)

    Berger-Vergiat, Luc; McAuliffe, Colin; Waisman, Haim

    2014-08-01

    Numerical modeling of shear bands present several challenges, primarily due to strain softening, strong nonlinear multiphysics coupling, and steep solution gradients with fine solution features. In general it is not known a priori where a shear band will form or propagate, thus adaptive refinement is sometimes necessary to increase the resolution near the band. In this work we explore the use of isogeometric analysis for shear band problems by constructing and testing several combinations of NURBS elements for a mixed finite element shear band formulation. Owing to the higher order continuity of the NURBS basis, fine solution features such as shear bands can be resolved accurately and efficiently without adaptive refinement. The results are compared to a mixed element formulation with linear functions for displacement and temperature and Pian-Sumihara shape functions for stress. We find that an element based on high order NURBS functions for displacement, temperature and stress, combined with gauss point sampling of the plastic strain leads to attractive results in terms of rate of convergence, accuracy and cpu time. This element is implemented with a -bar strain projection method and is shown to be nearly locking free.

  3. The UTRC wind energy conversion system performance analysis for horizontal axis wind turbines (WECSPER)

    NASA Technical Reports Server (NTRS)

    Egolf, T. A.; Landgrebe, A. J.

    1981-01-01

    The theory for the UTRC Energy Conversion System Performance Analysis (WECSPER) for the prediction of horizontal axis wind turbine performance is presented. Major features of the analysis are the ability to: (1) treat the wind turbine blades as lifting lines with a prescribed wake model; (2) solve for the wake-induced inflow and blade circulation using real nonlinear airfoil data; and (3) iterate internally to obtain a compatible wake transport velocity and blade loading solution. This analysis also provides an approximate treatment of wake distortions due to tower shadow or wind shear profiles. Finally, selected results of internal UTRC application of the analysis to existing wind turbines and correlation with limited test data are described.

  4. Wind Technologies & Evolving Opportunities (Presentation)

    SciTech Connect

    Robichaud, R.

    2014-07-01

    This presentation covers opportunities for wind technology; wind energy market trends; an overview of the National Wind Technology Center near Boulder, Colorado; wind energy price and cost trends; wind turbine technology improvements; and wind resource characterization improvements.

  5. 78 FR 29364 - Exelon Corporation, Exelon Wind 1, LLC, Exelon Wind 2, LLC, Exelon Wind 3, LLC, Exelon Wind 4...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-05-20

    ...Exelon Wind 9, LLC, Exelon Wind 10, LLC, Exelon Wind 11, LLC, High Plains Wind Power, LLC v. Xcel Energy Services, Inc., Southwestern...LLC, Exelon Wind 11, LLC, and High Plains Wind Power, LLC (Complainants) filed a formal...

  6. Shear Relaxations of Confined Liquids.

    NASA Astrophysics Data System (ADS)

    Carson, George Amos, Jr.

    Ultrathin (<40 A) films of octamethylcyclotetrasiloxane (OMCTS), hexadecane, and dodecane were subjected to linear and non-linear oscillatory shear between flat plates. Shearing frequencies of 0.1 to 800 s^{-1} were applied at pressures from zero to 0.8 MPa using a surface rheometer only recently developed. In most cases the plates were atomically smooth mica surfaces; the role of surface interactions was examined by replacing these with alkyl chain monolayers. OMCTS and hexadecane were examined at a temperature about 5 Celsius degrees above their melting points and tended to solidify. Newtonian plateaus having enormous viscosities were observed at low shear rates. The onset of shear thinning implied relaxation times of about 0.1 s in the linear structure of the confined liquids. Large activation volumes (~80 nm ^3) suggested that shear involved large-scale collective motion. Dodecane was studied at a much higher temperature relative to its melting point and showed no signs of impending solidification though it exhibited well-defined regions of Newtonian response and power law shear thinning. When treated with molecular sieves before use, dodecane had relaxation times which were short (0.02 s) compared to hexadecane, but still exhibited large-scale collective motion. When treated with silica gel, an unexplained long -time relaxation (10 s) was seen in the Newtonian viscosity of dodecane. The relaxation time of the linear structure, 0.005 s was very small, and the storage modulus was unresolvable. The small activation volume (7nm^3) indicated a much lower level of collective motion. The activation volume remained small when dodecane was confined between tightly bound, low energy, alkyl monolayers. At low strains the storage and loss moduli became very large (>10^4 Pa), probably due to interactions with flaws in the monolayers. Dramatic signs of wall slip were observed at large strains even at low pressures.

  7. Shearing of frictional sphere packings

    E-print Network

    Jean-François Métayer; Donald J. Suntrup III; Charles Radin; Harry L. Swinney; Matthias Schröter

    2011-04-19

    We measure shear response in packings of glass beads by pulling a thin, rough, metal plate vertically through a bed of volume fraction phi, which is set, before the plate is pulled, in the range 0.575 to 0.628. The yield stress is velocity independent over 4 decades and increases exponentially with phi, with a transition at phi approximately 0.595. An analysis of the measured force fluctuations indicates that the shear modulus is significantly smaller than the bulk modulus.

  8. Shearing of frictional sphere packings

    NASA Astrophysics Data System (ADS)

    Métayer, J.-F.; Suntrup, D. J., III; Radin, C.; Swinney, H. L.; Schröter, M.

    2011-03-01

    We measure shear response in packings of glass beads by pulling a thin, rough, metal plate vertically through a bed of volume fraction phi, which is set, before the plate is pulled, in the range from 0.575 to 0.628. The yield stress is velocity independent over 4 decades and increases exponentially with phi, with a transition at phi?0.595. An analysis of the measured force fluctuations indicates that the shear modulus is significantly smaller than the bulk modulus.

  9. Unexpected shear strength change in magnetorheological fluids

    NASA Astrophysics Data System (ADS)

    Tian, Yu; Chen, KaiKai; Shan, Lei; Zhang, Xiangjun; Meng, Yonggang

    2014-09-01

    Smart materials of magnetorheological (MR) fluids could be turned from a liquid state into a solid state, which solidification extent or shear strength often increases monotonically with the applied magnetic field. In this study, the shear stress of a dilute MR fluid decreased with increasing applied magnetic field at a constant shear rate. The dynamic shear stress was significantly higher than the stable counterpart at medium magnetic fields. They are ascribed to the slow particle structure transformation. A higher shear rate and particle volume fraction could reduce the transient time and the shear strength difference.

  10. Shear thickening oscillation in a dilatant fluid

    NASA Astrophysics Data System (ADS)

    Nagahiro, Shin-Ichiro; Nakanishi, Hiizu; Mitarai, Namiko

    2013-03-01

    We report experimental observations of the shear thickening oscillation; spontaneous macroscopic oscillation in the shear flow of severe shear thickening fluids. Using a phenomenological fluid dynamics model for dilatant fluids, we have been predicted theoretically that a dilatant fluid under constant shear stress oscillates due to the shear thickening property coupled with the fluid dynamics. However, such a macroscopic oscillation has never been reported in the literature. In this presentation, we report that strong vibrations of the frequency around 20 Hz is observed using a density-matched starch-water mixture, in the cylindrical shear flow of a few centimeters flow width. The oscillation behavior is consistent with the theoretical prediction.

  11. Use of Acoustic Wind Profilers for Uninhabited Aerial Vehicle Flight Test Activities

    NASA Technical Reports Server (NTRS)

    Donnohue, Casey J.; Underwood, Ken; Bellue, Dan G.

    2001-01-01

    Sonic detection and ranging (SODAR) systems provide crucial information to meteorologists for advising uninhabited aerial vehicle (UAV) flight crews and mission directors on historical, current, and forecasted wind and turbulence conditions. The SODAR system provided advanced warning of increasing surface winds for an X-38 flight on February 6, 1999. The SODAR system has also provided important postflight data for X-38 engineers to review the performance of the parafoil in the presence of strong wind shears near the surface at landing.

  12. The effect of shearing strain-rate on the ultimate shearing resistance of clay

    NASA Technical Reports Server (NTRS)

    Cheng, R. Y. K.

    1976-01-01

    The shearing resistance of cohesive soils subjected to a high rate of shearing strain was investigated. A fast step-loading torque apparatus was used to induce a state of pure shear in a hollow cylindrical soil specimen. The relationship between shearing resistance and rate of shear deformation was established for various soil densities expressed in terms of initial void ratio or water content. For rate of shearing deformation studies to date, the shearing resistance increases initially with shearing velocity but subsequently reaches a terminal value as the shearing velocity increases. The terminal shearing resistance is also found to increase as the density of the soil increases. The results are useful in the rheological study of clay. It is particularly important for mobility problems of soil runways, since the soil resistance is found to be sensitive to the rate of shearing.

  13. The effect of shearing strain-rate on the ultimate shearing resistance of clay

    NASA Technical Reports Server (NTRS)

    Cheng, R. Y. K.

    1975-01-01

    An approach for investigating the shearing resistance of cohesive soils subjected to a high rate of shearing strain is described. A fast step-loading torque apparatus was used to induce a state of pure shear in a hollow cylindrical soil specimen. The relationship between shearing resistance and rate of shear deformation was established for various soil densities expressed in terms of initial void ratio or water content. For rate of shearing deformation studies, the shearing resistance increases initially with shearing velocity, but subsequently reaches a terminal value as the shearing velocity increases. The terminal shearing resistance is also found to increase as the density of the soil increases. The results of this investigation are useful in the rheological study of clay. It is particularly important for mobility problems of soil runways, since the soil resistance is found to be sensitive to the rate of shearing.

  14. Careers in Wind Energy

    ERIC Educational Resources Information Center

    Liming, Drew; Hamilton, James

    2011-01-01

    As a common form of renewable energy, wind power is generating more than just electricity. It is increasingly generating jobs for workers in many different occupations. Many workers are employed on wind farms: areas where groups of wind turbines produce electricity from wind power. Wind farms are frequently located in the midwestern, western, and…

  15. Prospecting for Wind

    ERIC Educational Resources Information Center

    Swapp, Andy; Schreuders, Paul; Reeve, Edward

    2011-01-01

    Many people use wind to help meet their needs. Over the years, people have been able to harness or capture the wind in many different ways. More recently, people have seen the rebirth of electricity-generating wind turbines. Thus, the age-old argument about technology being either good or bad can also be applied to the wind. The wind can be a…

  16. Satellite Winds

    NSDL National Science Digital Library

    2012-08-03

    In this online, interactive module, students learn about the using successive satellite observations of clouds to determine wind direction and speed. The module is part of an online course for grades 7-12 in satellite meteorology, which includes 10 interactive modules. The site also includes lesson plans developed by teachers and links to related resources. Each module is designed to serve as a stand-alone lesson, however, a sequential approach is recommended. Designed to challenge students through the end of 12th grade, middle school teachers and students may choose to skim or skip a few sections.

  17. Windy Wind

    NSDL National Science Digital Library

    2012-08-03

    In this demonstration, students learn that air flows from a high-pressure area to a low pressure area, and greater the differences between pressure areas, the greater the wind speed. The demonstration uses an apparatus made from two 2L beverage bottles, plastic tubing, food coloring, clay and water. The resource is part of the teacher's guide accompanying the video, NASA SCI Files: The Case of the Phenomenal Weather. Lesson objectives supported by the video, additional resources, teaching tips and an answer sheet are included in the teacher's guide.

  18. Wind Streaks

    NASA Technical Reports Server (NTRS)

    2004-01-01

    [figure removed for brevity, see original site]

    Released 12 July 2004 The atmosphere of Mars is a dynamic system. Water-ice clouds, fog, and hazes can make imaging the surface from space difficult. Dust storms can grow from local disturbances to global sizes, through which imaging is impossible. Seasonal temperature changes are the usual drivers in cloud and dust storm development and growth.

    Eons of atmospheric dust storm activity has left its mark on the surface of Mars. Dust carried aloft by the wind has settled out on every available surface; sand dunes have been created and moved by centuries of wind; and the effect of continual sand-blasting has modified many regions of Mars, creating yardangs and other unusual surface forms.

    Windstreaks are features caused by the interaction of wind and topographic landforms. The raised rims and bowls of impact craters causes a complex interaction such that the wind vortex in the lee of the crater can both scour away the surface dust and deposit it back in the center of the lee. If you look closely, you will see evidence of this in a darker 'rim' enclosing a brighter interior.

    Image information: VIS instrument. Latitude 6.9, Longitude 69.4 East (290.6 West). 19 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  19. The Influence of Shearing Velocity on Shear Behavior of Artificial Joints

    NASA Astrophysics Data System (ADS)

    Atapour, Hadi; Moosavi, Mahdi

    2014-09-01

    In this paper, the effects of shear velocity on the shearing behavior of artificial joints have been studied at different normal stress levels. Here, artificial joints with planar and rough surfaces were prepared with the plaster (simulating soft rock joints) and concrete (medium-hard rock joints) materials. The rough joints had triangular shaped asperities with 10° and 20° inclination angles. Direct shear tests were performed on these joints under various shear velocities in the range of 0.3-30 mm/min. The planar plaster-plaster and planer concrete-concrete joints were sheared at three levels of normal stress under constant normal load boundary condition. Also, the rough plaster-plaster and concrete-concrete joints were sheared at one level of normal stress under constant normal stiffness boundary condition. The results of the shear tests show that the shearing parameters of joints, such as shear strength, shear stiffness and friction angle, are related to the shear velocity. Shear strength of planar and rough plaster-plaster joints were decreased when the shear velocity was increased. Shear strength of concrete joints, except for rough joints with 10° inclination, increased with increasing shear velocity. Regardless of the normal stress level, shear stiffness of both planar plaster-plaster and concrete-concrete joints were decreased when the shear velocity was increased.

  20. Effect of shear rupture on aggregate scale formation in sea ice

    NASA Astrophysics Data System (ADS)

    Wilchinsky, Alexander V.; Feltham, Daniel L.; Hopkins, Mark A.

    2010-10-01

    A discrete element model is used to study shear rupture of sea ice under convergent wind stresses. The model includes compressive, tensile, and shear rupture of viscous elastic joints connecting floes that move under the action of the wind stresses. The adopted shear rupture is governed by Coulomb's criterion. The ice pack is a 400 km long square domain consisting of 4 km size floes. In the standard case with tensile strength 10 times smaller than the compressive strength, under uniaxial compression the failure regime is mainly shear rupture with the most probable scenario corresponding to that with the minimum failure work. The orientation of cracks delineating formed aggregates is bimodal with the peaks around the angles given by the wing crack theory determining diamond-shaped blocks. The ice block (floe aggregate) size decreases as the wind stress gradient increases since the elastic strain energy grows faster leading to a higher speed of crack propagation. As the tensile strength grows, shear rupture becomes harder to attain and compressive failure becomes equally important leading to elongation of blocks perpendicular to the compression direction and the blocks grow larger. In the standard case, as the wind stress confinement ratio increases the failure mode changes at a confinement ratio within 0.2-0.4, which corresponds to the analytical critical confinement ratio of 0.32. Below this value, the cracks are bimodal delineating diamond shape aggregates, while above this value failure becomes isotropic and is determined by small-scale stress anomalies due to irregularities in floe shape.

  1. Teaching Case: Scissors and Shears

    NSDL National Science Digital Library

    Ann Velenchik

    This case is the transcript of the 1962 Congressional Testimony of BC Deuschle, President of the Scissors, Shears and Manicure Implement Manufacturers' Association, with regard to the Trade Expansion Act of 1962. Deuschle opposes the act, fearing that reduced protection will destroy his industry. The case includes all of the classic economic and political motives for protection.

  2. Winds Report: Measuring Ocean Winds from Space

    NSDL National Science Digital Library

    Users of this resource can access imagery and animations made from scatterometry data from the SeaWinds instrument, which flies aboard the QuikSCAT satellite. A scatterometer is a radar instrument which bounces electromagnetic energy off the surface of the ocean. Combining the radar return from the same patch of ocean, but as seen from from different directions, allows the calculation of both wind speed and wind direction. In the animations, the background color shows the wind speed: blue is low wind speed and yellow or magenta, high. The direction of the wind field is shown by the direction of motion of imaginary "particles" in the animation.

  3. Shear banding in simulated telechelic polymers

    NASA Astrophysics Data System (ADS)

    Billen, Joris; Wilson, Mark; Baljon, Arlette R. C.

    2015-01-01

    The response of simulated telechelic polymers to shear is investigated. End groups of short polymeric chains form temporary junctions that are continuously broken and formed over time. As in experiments, two shear bands coexist for some shear rates. This allows us to study the microscopic differences between these shear bands. We find that the lifetime of a junction is lower in the high shear rate band. In addition, the average aggregate size is lower in this band since more dangling chains exist. Microstructural differences between the sheared and unsheared system are reported as well. Some of the chains, that bridge between two aggregates before shear is applied, form loops that connect with both ends to the same aggregate instead. In addition and more importantly, an increase of chains connecting the same two aggregates is observed. Such restructuring lowers the network connectivity and hence the stress needed to shear the system.

  4. Residual shear deformations in the coronary artery.

    PubMed

    Wang, Ruoya; Gleason, Rudolph L

    2014-06-01

    Quantifying arterial residual deformations is critical for understanding the stresses and strains within the arterial wall during physiological and pathophysiological conditions. This study presents novel findings on residual shear deformations in the left anterior descending coronary artery. Residual shear deformations are most evident when thin, long axial strips are cut from the artery. These strips deform into helical configurations when placed in isotonic solution. A residual shear angle is introduced as a parameter to quantify the residual shear deformations. Furthermore, a stress analysis is performed to study the effects of residual shear deformations on the intramural shear stress distribution of an artery subjected to pressure, axial stretch, and torsion using numerical simulation. The results from the stress analyses suggest that residual shear deformations can significantly modulate the intramural shear stress across the arterial wall. PMID:24686990

  5. Vertical shears in Saturn's eastward jets at cloud level

    NASA Astrophysics Data System (ADS)

    García-Melendo, Enrique; Sánchez-Lavega, Agustín; Rojas, J. F.; Pérez-Hoyos, S.; Hueso, R.

    2009-06-01

    We have measured the vertical shear of the zonal winds in the cloud-haze upper layer of Saturn using Cassini ISS images obtained in the filters MT2 (753 nm methane absorption band, sensitive to the upper haze) and CB2 (adjacent continuum, sensitive to the lower cloud). Our radiative transfer models indicate that at the eastward jet peaks these filters are sensing clouds at the respective ˜100 mbar and ˜350 mbar levels. We have found a systematic velocity difference between those filters of 15 to 20 m s -1 only in the eastward jets peaks (27° S, 42° S, 55° S and 70° S) which implies a vertical shear of ˜10-20 m s -1 H -1. Our overall results agree with those derived from the thermal-wind relationship using CIRS thermal data [Fletcher, L.N., and 13 colleagues, 2008. Science 319, 79-81] and with previous equatorial measurements [Sánchez-Lavega, A., Hueso, R., Pérez-Hoyos, S., 2007. Icarus 187, 510-519].

  6. Shear viscosity of the quark matter

    E-print Network

    Masaharu Iwasaki; Hiromasa Ohnishi; Takahiko Fukutome

    2007-05-14

    We discuss shear viscosity of the quark matter by using Kubo formula. The shear viscosity is calculated in the framework of the quasi-particle RPA for the Nambu-Jona-Lasinio model. We obtain a formula that the shear viscosity is expressed by the quadratic form of the quark spectral function in the chiral symmetric phase. The magnitude of the shear viscosity is discussed assuming the Breit-Wigner type for the spectral function.

  7. Effects of shear on proteins in solution

    Microsoft Academic Search

    C. R. Thomas; D. Geer

    2011-01-01

    The effects of “shear” on proteins in solution are described and discussed. Research on this topic covers many decades, beginning\\u000a with investigations of possible denaturation of enzymes during processing, whilst more recent concerns are how the quality\\u000a of therapeutic proteins might be affected by shear or shear related effects. The paradigm that emerges from most studies is\\u000a that shear in

  8. Refraction of shear zones in granular materials

    E-print Network

    Tamas Unger

    2007-01-08

    We study strain localization in slow shear flow focusing on layered granular materials. A heretofore unknown effect is presented here. We show that shear zones are refracted at material interfaces in analogy with refraction of light beams in optics. This phenomenon can be obtained as a consequence of a recent variational model of shear zones. The predictions of the model are tested and confirmed by 3D discrete element simulations. We found that shear zones follow Snell's law of light refraction.

  9. Aleutian Pribilof Islands Wind Energy Feasibility Study

    SciTech Connect

    Bruce A. Wright

    2012-03-27

    Under this project, the Aleutian Pribilof Islands Association (APIA) conducted wind feasibility studies for Adak, False Pass, Nikolski, Sand Point and St. George. The DOE funds were also be used to continue APIA's role as project coordinator, to expand the communication network quality between all participants and with other wind interest groups in the state and to provide continued education and training opportunities for regional participants. This DOE project began 09/01/2005. We completed the economic and technical feasibility studies for Adak. These were funded by the Alaska Energy Authority. Both wind and hydro appear to be viable renewable energy options for Adak. In False Pass the wind resource is generally good but the site has high turbulence. This would require special care with turbine selection and operations. False Pass may be more suitable for a tidal project. APIA is funded to complete a False Pass tidal feasibility study in 2012. Nikolski has superb potential for wind power development with Class 7 wind power density, moderate wind shear, bi-directional winds and low turbulence. APIA secured nearly $1M from the United States Department of Agriculture Rural Utilities Service Assistance to Rural Communities with Extremely High Energy Costs to install a 65kW wind turbine. The measured average power density and wind speed at Sand Point measured at 20m (66ft), are 424 W/m2 and 6.7 m/s (14.9 mph) respectively. Two 500kW Vestas turbines were installed and when fully integrated in 2012 are expected to provide a cost effective and clean source of electricity, reduce overall diesel fuel consumption estimated at 130,000 gallons/year and decrease air emissions associated with the consumption of diesel fuel. St. George Island has a Class 7 wind resource, which is superior for wind power development. The current strategy, led by Alaska Energy Authority, is to upgrade the St. George electrical distribution system and power plant. Avian studies in Nikolski and Sand Point have allowed for proper wind turbine siting without killing birds, especially endangered species and bald eagles. APIA continues coordinating and looking for funding opportunities for regional renewable energy projects. An important goal for APIA has been, and will continue to be, to involve community members with renewable energy projects and energy conservation efforts.

  10. Weather: Wind Chill

    NSDL National Science Digital Library

    2010-01-01

    In this activity, students explore the effect of the combination of temperature and wind speed on human comfort. Then they use a formula to compute the Fahrenheit wind chill for a specific wind speed on a specific temperature.

  11. Wind Energy Resource Information

    NSDL National Science Digital Library

    This portal of the U.S. Department of Energy's National Renewable Energy Laboratory offers two major links: Meteorological Field Measurements at Potential and Actual Wind Turbine Sites and Wind Energy Resource Atlas of the United States. In addition, a section called Links to Wind Resource Maps leads to Iowa Energy Centers Iowa Wind Resource Assessment Maps, Wind Maps on NREL's Dynamic Maps and GIS Data website, and Wind Powering America including U.S. State Maps of Wind Resources and Installed U.S. Wind Capacity. Other links include the Colorado Utility Wind Resource Assessment Program (U*WRAP), The State of Hawaii's Wind Energy Fact Sheet and Wind Resource Database of NREL's National Wind Technology Center (NWTC).

  12. An integrated dynamic model of a flexible wind turbine

    NASA Astrophysics Data System (ADS)

    Bongers, Peter M. M.; Bierbooms, Wim A. A.; Dijkstra, Sjoerd; Vanholten, Theo

    1990-06-01

    A model to study the dynamic behavior of flexible wind turbines was developed. The different subsystems of the wind turbine are individually modeled with about the same degree of accuracy. The aerodynamic part describes wind shear, gravity effects, unsteady effects, and dynamic inflow. The rotor blades are provided with degrees of freedom in lag and flap directions. The tower construction is modeled including the first bending mode. The first torsional mode of the transmission is included in the model. The model of synchronous generator with dc link consists of a nonlinear fourth order model, including saturation effects. The different models of the subsystems are coupled into one integrated dynamic model which is implemented as simulation code in the DUWECS (Delf University Wind Energy Converter Simulation Package) program. The DUWECS program is developed in such a manner that it is an easy to handle tool for the study of the dynamic features of wind turbine systems.

  13. Neutrally Buoyant Elliptical Cylinders in Simple Shear

    Microsoft Academic Search

    Claudia Zettner; Minami Yoda

    2000-01-01

    An elliptical cylinder in simple shear is a 2D Lagrangian model of a particle in a dilute sheared suspension. Recent simulations(E. J. Ding and C. K. Aidun ``The dynamics and scaling law for particles suspended in shear flow with inertia'' To appear in J. Fluid Mech.) (2000) have shown that bodies with aspect ratio AR < 1 exhibit two behaviors

  14. Internal and Interface Shear Strength of

    E-print Network

    Zornberg, Jorge G.

    1 Internal and Interface Shear Strength of Geosynthetic Clay Liners (GCLs): Additional Data by John., Zornberg, Jorge G., and Swan, Jr., Robert H. Internal and Interface Shear Strength of Geosynthetic Clay space requirements. However, the internal and interface shear strength of GCLs is known

  15. BEHAVIOUR OF PRECAST CONCRETE SHEAR WALL CONNECTIONS UNDER LARGE REVERSED CYCLIC SHEAR LOADS

    E-print Network

    The performance of precast concrete load bearing shear wall panel structures subjected to earthquakes relies shear wall panels are an economical construction system for low, medium and high rise structuresBEHAVIOUR OF PRECAST CONCRETE SHEAR WALL CONNECTIONS UNDER LARGE REVERSED CYCLIC SHEAR LOADS J

  16. ForReview.Confidential-ACS Homogeneous shear, wall slip and shear banding of

    E-print Network

    Wang, Shi-Qing

    ForReview.Confidential-ACS Homogeneous shear, wall slip and shear banding of entangled polymeric to Macromolecules #12;ForReview.Confidential-ACS 1 Homogeneous shear, wall slip and shear banding of entangled 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 #12;ForReview.Confidential

  17. Shear strength parameters from direct shear tests - influencing factors and their significance

    Microsoft Academic Search

    KARSTEN THERMANN; CHRISTIAN GAU; JOACHIM TIEDEMANN

    The shear strength of soils is essential for any kind of stability analysis. Therefore, it is important to determine reliable values. For this purpose triaxial tests are most appropriate. Nevertheless, direct shear tests are mostly performed to determine the shear strength of soils. This paper deals with the factors affecting the results of direct shear tests. The influence caused by

  18. Shear viscosity and shear thinning in two-dimensional Yukawa , J. Goree2

    E-print Network

    Goree, John

    Shear viscosity and shear thinning in two-dimensional Yukawa liquids Z. Donk´o1 , J. Goree2 , P using two different nonequi- librium molecular dynamics simulation methods. Shear viscosity values.e., the viscosity diminishes with increasing shear rate. It is expected that two-dimensional dusty plasmas

  19. Wind energy manual

    E-print Network

    A. Vieira; Da Rosa; Fundamentals Renewable; Energy Processes; San Diego; Jacob Kirpes; Small Wind

    2013-01-01

    Objectives: The course introduces principles of wind power production, design of wind turbines, location and design of wind farms, control of turbines and wind farms, predictive modeling, diagnostics, operations and maintenance, condition monitoring, health monitoring and of turbine components and systems, wind farm performance optimization, and integration of wind power with a grid. The modeling and analysis aspect of the topics discussed in the class will be illustrated with examples and case studies. Textbook: References:

  20. Wind Erosion Research

    NSDL National Science Digital Library

    2006-02-27

    Wind Erosion Research (WER) provides science-based wind erosion technology for environmentally, economically, and socially sustainable agriculture in the United States. This website introduces the Wind Erosion Equation (WEQ), the first model for estimating soil loss by wind from agricultural fields and the newly developed Wind Erosion Prediction System (WEPS) which provides new capabilities assessing plant damage and calculating suspension loss. Simulation models, multimedia archive and history of wind erosion research are available for educators and students.

  1. Rapid Shear Zones - Unspecific Microstructures

    NASA Astrophysics Data System (ADS)

    Birtel, S.; Stoeckhert, B.

    2008-12-01

    The record of episodic deformation at 500-550°C and 0.7+/-0.2 GPa was identified in eclogite- amphibolites on Rugsundoya island in the Western Gneiss Region of Norway, in the footwall of the low angle Nordfjord Sogn Detachment Zone (Birtel and Stöckhert 2008). An event of fracture formation was followed by inhomogeneous ductile deformation, during which the fractures developed into open cavities sealed by quartz. The structural relations indicate contemporaneous formation of veins and shear zones, also demonstrated by the fact that the quartz veins do nowhere transect the shear zones and the shear zones do nowhere transect the quartz veins. The deformation is ascribed to brittle failure driven by stress redistribution during a large earthquake, followed by an episode of inhomogeneous ductile deformation during postseismic stress relaxation. The peculiar record is thus interpreted to represent a single seismic cycle and to obey the respective time scales, with quasi-instantaneous loading and subsequent stress relaxation over time spans on the order of 102 to 103 years. If this is true, the shear zones linking the open cavities (now quartz veins) must have formed by markedly non-steady state deformation starting at high stress and very high strain rate. Here we examine the microfabrics of the shear zones. The amphibolite facies shear zones are made up of a fine-grained amphibole and plagioclase matrix, with a typical grain size of 0.1 mm for both phases. Millimetre-sized porphyroclasts of amphibole are widespread. The matrix microstructure is characterized by smooth grain and interphase boundaries. The amphiboles reveal a marked shape preferred orientation (SPO) combined with a crystallographic preferred orientation (CPO). In contrast to amphibole, plagioclase shows no CPO. The chemical composition of amphibole and plagioclase within the shear zones corresponds to that in the undeformed host rock, with only slight inhomogeneity and rather unsystematic zoning patterns in both porphyroclasts and matrix amphiboles. The microfabrics of the shear zones are found to be unspecific in terms of deformation mechanisms. The combined CPO and SPO is very common for amphiboles. It does not necessarily indicate deformation by dislocation creep, but can be the product of various processes from anisotropic growth to cataclastic flow (e.g. Brodie and Rutter 1985, Nyman et al. 1992). The unsystematic chemical zoning pattern and the tendency towards a low-energy grain shape indicates that the synkinematic microstructures became erased during annealing at amphibolite facies conditions. The term "blastomylonite" is therefore probably appropriate to characterize the fine-grained amphibolite within the shear zones. We conclude that rapid non-steady state ductile deformation, presumably by a variety of deformation mechanisms sequentially activated at decaying stress, leaves no specific record at the given temperatures of 500-550°C. The synkinematic microfabrics, including those developed at an early stage at exceptionally high strain rate, become obliterated by annealing at such temperatures. References Birtel, S. and Stöckhert, B (2008) Tectonophysics 457: 53-63. Brodie, K. H. and Rutter, E.H. (1985) in Kinetics, Textures, and Deformation. A. B. Thompson and D. C. Rubie. (eds) New York, Springer. 4: 138-179. Nyman, M. W., Law, R. D. and Smelik, E.A. (1992) Geology 20: 455-458.

  2. Dynamics of Sheared Granular Materials

    NASA Technical Reports Server (NTRS)

    Kondic, Lou; Utter, Brian; Behringer, Robert P.

    2002-01-01

    This work focuses on the properties of sheared granular materials near the jamming transition. The project currently involves two aspects. The first of these is an experiment that is a prototype for a planned ISS (International Space Station) flight. The second is discrete element simulations (DES) that can give insight into the behavior one might expect in a reduced-g environment. The experimental arrangement consists of an annular channel that contains the granular material. One surface, say the upper surface, rotates so as to shear the material contained in the annulus. The lower surface controls the mean density/mean stress on the sample through an actuator or other control system. A novel feature under development is the ability to 'thermalize' the layer, i.e. create a larger amount of random motion in the material, by using the actuating system to provide vibrations as well control the mean volume of the annulus. The stress states of the system are determined by transducers on the non-rotating wall. These measure both shear and normal components of the stress on different size scales. Here, the idea is to characterize the system as the density varies through values spanning dense almost solid to relatively mobile granular states. This transition regime encompasses the regime usually thought of as the glass transition, and/or the jamming transition. Motivation for this experiment springs from ideas of a granular glass transition, a related jamming transition, and from recent experiments. In particular, we note recent experiments carried out by our group to characterize this type of transition and also to demonstrate/ characterize fluctuations in slowly sheared systems. These experiments give key insights into what one might expect in near-zero g. In particular, they show that the compressibility of granular systems diverges at a transition or critical point. It is this divergence, coupled to gravity, that makes it extremely difficult if not impossible to characterize the transition region in an earth-bound experiment. In the DE modeling, we analyze dynamics of a sheared granular system in Couette geometry in two (2D) and three (3D) space dimensions. Here, the idea is to both better understand what we might encounter in a reduced-g environment, and at a deeper level to deduce the physics of sheared systems in a density regime that has not been addressed by past experiments or simulations. One aspect of the simulations addresses sheared 2D system in zero-g environment. For low volume fractions, the expected dynamics of this type of system is relatively well understood. However, as the volume fraction is increased, the system undergoes a phase transition, as explained above. The DES concentrate on the evolution of the system as the solid volume fraction is slowly increased, and in particular on the behavior of very dense systems. For these configurations, the simulations show that polydispersity of the sheared particles is a crucial factor that determines the system response. Figures 1 and 2 below, that present the total force on each grain, show that even relatively small (10 %) nonuniformity of the size of the grains (expected in typical experiments) may lead to significant modifications of the system properties, such as velocity profiles, temperature, force propagation, and formation shear bands. The simulations are extended in a few other directions, in order to provide additional insight to the experimental system analyzed above. In one direction, both gravity, and driving due to vibrations are included. These simulations allow for predictions on the driving regime that is required in the experiments in order to analyze the jamming transition. Furthermore, direct comparison of experiments and DES will allow for verification of the modeling assumptions. We have also extended our modeling efforts to 3D. The (preliminary) results of these simulations of an annular system in zero-g environment will conclude the presentation.

  3. Wind Power! Designing a Wind Turbine

    NSDL National Science Digital Library

    Integrated Teaching and Learning Program,

    Students learn how engineers transform wind energy into electrical energy by building their own miniature wind turbines and measuring the electrical current it produces. They explore how design and position affect the electrical energy production.

  4. Wind for Schools (Poster)

    SciTech Connect

    Baring-Gould, I.

    2010-05-01

    As the United States dramatically expands wind energy deployment, the industry is challenged with developing a skilled workforce and addressing public resistance. Wind Powering America's Wind for Schools project addresses these issues by developing Wind Application Centers (WACs) at universities; WAC students assist in implementing school wind turbines and participate in wind courses, by installing small wind turbines at community "host" schools, by implementing teacher training with interactive curricula at each host school. This poster provides an overview of the first two years of the Wind for Schools project, primarily supporting activities in Colorado, Kansas, Nebraska, South Dakota, Montana, and Idaho.

  5. Wind energy bibliography

    SciTech Connect

    None

    1995-05-01

    This bibliography is designed to help the reader search for information on wind energy. The bibliography is intended to help several audiences, including engineers and scientists who may be unfamiliar with a particular aspect of wind energy, university researchers who are interested in this field, manufacturers who want to learn more about specific wind topics, and librarians who provide information to their clients. Topics covered range from the history of wind energy use to advanced wind turbine design. References for wind energy economics, the wind energy resource, and environmental and institutional issues related to wind energy are also included.

  6. Shear strength and shear failure, overview of testing and behavior of ductile metals

    NASA Astrophysics Data System (ADS)

    Meyer, Lothar W.; Halle, Thorsten

    2011-11-01

    Shear dominated states of loading are present in many industrial applications and typical impact processes. The paper gives a review of the well known methods for measuring the high strain rate shear and mixed mode behavior of ductile metals. The testing methods are subdivided into two groups. The first one is to measure the flow behavior under shearing conditions. The second group refers to testing methods for the failure behavior at shear or shear dominated loading states. The main focus is on the measurement of these data at very high strain rates with some of our own, newly developed testing devices. The investigated methods utilize the following specimen geometries "Hat"-, compression/shear-, tension/shear-, shear/ compression-, planar double notched shear-, torsion- and planar torsion shear specimens. The advantages and disadvantages of all presented methods and FEM simulations are compared with the corresponding experimental results. Since no geometry can fulfill all demands, the methods are classified according to their optimal applications.

  7. Shear viscosity and shear thinning in two-dimensional Yukawa liquids

    E-print Network

    Z. Donkó; J. Goree; P. Hartmann; K. Kutasi

    2006-03-24

    A two-dimensional Yukawa liquid is studied using two different nonequilibrium molecular dynamics simulation methods. Shear viscosity values in the limit of small shear rates are reported for a wide range of Coulomb coupling parameter and screening length. At high shear rates it is demonstrated that this liquid exhibits shear thinning, i.e., the viscosity $\\eta$ diminishes with increasing shear rate. It is expected that two-dimensional dusty plasmas will exhibit this effect.

  8. Apparatus for shearing spent nuclear fuel assemblies

    DOEpatents

    Weil, Bradley S. (Knoxville, TN); Metz, III, Curtis F. (Knoxville, TN)

    1980-01-01

    A method and apparatus are described for shearing spent nuclear fuel assemblies of the type comprising an array of fuel pins disposed within an outer metal shell or shroud. A spent fuel assembly is first compacted in a known manner and then incrementally sheared using fixed and movable shear blades having matched laterally projecting teeth which slidably intermesh to provide the desired shearing action. Incremental advancement of the fuel assembly after each shear cycle is limited to a distance corresponding to the lateral projection of the teeth to ensure fuel assembly breakup into small uniform segments which are amenable to remote chemical processing.

  9. Experimental observation of shear thickening oscillation

    NASA Astrophysics Data System (ADS)

    Nagahiro, Shin-ichiro; Nakanishi, Hiizu; Mitarai, Namiko

    2013-10-01

    We report experimental observations of the shear thickening oscillation, i.e. the spontaneous macroscopic oscillation in the shear flow of severe shear thickening fluid. Using a density-matched starch-water mixture, in the cylindrical shear flow of a few centimeters flow width, we observed that well-marked vibrations of frequency around 20 Hz appear via a Hopf bifurcation upon increasing externally applied shear stress. The parameter range and the frequency of the vibration are consistent with those expected by a simple phenomenological model of the dilatant fluid.

  10. Shear thinning of nanoparticle suspensions

    NASA Astrophysics Data System (ADS)

    in 'T Veld, Pieter J.; Petersen, Matt K.; Grest, Gary S.

    2009-02-01

    Results of large scale nonequilibrium molecular dynamics simulations are presented for nanoparticles in an explicit solvent. The nanoparticles are modeled as a uniform distribution of Lennard-Jones particles, while the solvent is represented by standard Lennard-Jones particles. We present results for the shear rheology of spherical nanoparticles of diameter 10 times that of the solvent for a range of nanoparticle volume fractions. By varying the strength of the interactions between nanoparticles and with the solvent, this system can be used to model colloidal gels and glasses as well as hard spherelike nanoparticles. Effect of including the solvent explictly is demonstrated by comparing the pair correlation function of nanoparticles to that in an implicit solvent. The shear rheology for dumbbell nanoparticles made of two fused spheres is similar to that of single nanoparticle.

  11. Semiflexible Polymers in Shear Flow

    NASA Astrophysics Data System (ADS)

    Winkler, Roland G.

    2006-09-01

    The dynamics of semiflexible polymers under the influence of shear flow is studied analytically. Power laws are derived for various conformational and dynamical quantities which are in agreement with experimental findings. In particular, the tumbling motion is analyzed and expressions are provided for the probability distributions of the orientation angles and the tumbling time. The calculations explain the similarities in the behavior of flexible and semiflexible polymers as well as free-draining and nondraining systems.

  12. Shearing of frictional sphere packings

    Microsoft Academic Search

    Jean-François Métayer; Donald J. Suntrup III; Charles Radin; Harry L. Swinney; Matthias Schröter

    2010-01-01

    We measure shear response in packings of glass beads by pulling a thin,\\u000arough, metal plate vertically through a bed of volume fraction phi, which is\\u000aset, before the plate is pulled, in the range 0.575 to 0.628. The yield stress\\u000ais velocity independent over 4 decades and increases exponentially with phi,\\u000awith a transition at phi approximately 0.595. An

  13. Shear Viscosity of Strongly Coupled

    Microsoft Academic Search

    G. Policastro; D. T. Son; A. O. Starinets

    2001-01-01

    Using the anti--de Sitter\\/conformal field theory correspondence, we relate the shear viscosity η of the finite-temperature N=4 supersymmetric Yang-Mills theory in the large N, strong-coupling regime with the absorption cross section of low-energy gravitons by a near-extremal black three-brane. We show that in the limit of zero frequency this cross section coincides with the area of the horizon. From this

  14. Shear thickening of highly viscous granular suspensions

    E-print Network

    Qin Xu; Sayantan Majumdar; Eric Brown; Heinrich M. Jaeger

    2014-04-28

    We experimentally investigate shear thickening in dense granular suspensions under oscillatory shear. Directly imaging the suspension-air interface, we observe dilation beyond a critical strain $\\gamma_c$ and the end of shear thickening as the maximum confining stress is reached and the contact line moves. Analyzing the shear profile, we extract the viscosity contributions due to hydrodynamics $\\eta_\\mu$, dilation $\\eta_c$ and sedimentation $\\eta_g$. While $\\eta_g$ governs the shear thinning regime, $\\eta_\\mu$ and $\\eta_c$ together determine the shear thickening behavior. As the suspending liquid's viscosity varies from 10 to 1000 cst, $\\eta_\\mu$ is found to compete with $\\eta_c$ and soften the discontinuous nature of shear thickening.

  15. A canopy-type similarity model for wind farm optimization

    NASA Astrophysics Data System (ADS)

    Markfort, Corey D.; Zhang, Wei; Porté-Agel, Fernando

    2013-04-01

    The atmospheric boundary layer (ABL) flow through and over wind farms has been found to be similar to canopy-type flows, with characteristic flow development and shear penetration length scales (Markfort et al., 2012). Wind farms capture momentum from the ABL both at the leading edge and from above. We examine this further with an analytical canopy-type model. Within the flow development region, momentum is advected into the wind farm and wake turbulence draws excess momentum in from between turbines. This spatial heterogeneity of momentum within the wind farm is characterized by large dispersive momentum fluxes. Once the flow within the farm is developed, the area-averaged velocity profile exhibits a characteristic inflection point near the top of the wind farm, similar to that of canopy-type flows. The inflected velocity profile is associated with the presence of a dominant characteristic turbulence scale, which may be responsible for a significant portion of the vertical momentum flux. Prediction of this scale is useful for determining the amount of available power for harvesting. The new model is tested with results from wind tunnel experiments, which were conducted to characterize the turbulent flow in and above model wind farms in aligned and staggered configurations. The model is useful for representing wind farms in regional scale models, for the optimization of wind farms considering wind turbine spacing and layout configuration, and for assessing the impacts of upwind wind farms on nearby wind resources. Markfort CD, W Zhang and F Porté-Agel. 2012. Turbulent flow and scalar transport through and over aligned and staggered wind farms. Journal of Turbulence. 13(1) N33: 1-36. doi:10.1080/14685248.2012.709635.

  16. Shear-layer correction after Amiet under consideration of additional temperature gradient. Working diagrams for correction of signals

    NASA Technical Reports Server (NTRS)

    Dobrzynski, W.

    1984-01-01

    Amiet's correction scheme for sound wave transmission through shear-layers is extended to incorporate the additional effects of different temperatures in the flow-field in the surrounding medium at rest. Within a parameter-regime typical for acoustic measurements in wind tunnels amplitude- and angle-correction is calculated and plotted systematically to provide a data base for the test engineer.

  17. WAKE OF A BLOCK VEHICLE IN A SHEAR-FREE BOUNDARY FLOW: AN EXPERIMENTAL AND THEORETICAL STUDY

    EPA Science Inventory

    The wake of a moving vehicle was simulated using a specially-constructed wind tunnel with a moving floor. A 'block-shaped' model vehicle was fixed in position over the test-section floor while the floor moved at the freestream air speed to produce a uniform, shear-free, approach ...

  18. EXPERIMENTAL AND THEORETICAL STUDY OF THE WAKE OF A BLOCK-SHAPED VEHICLE IN A SHEAR-FREE BOUNDARY FLOW

    EPA Science Inventory

    The wake of a moving vehicle was simulated using a specially-constructed wind tunnel with a moving floor. A 'block-shaped' model vehicle was fixed in position over the test-section floor while the floor moved at the freestream air speed to produce a uniform, shear-free, approach ...

  19. Aeolian Shear Stress Ratio Measurements within Mesquite-Dominated Landscapes of the Chihuahuan Desert, New Mexico, USA

    NASA Technical Reports Server (NTRS)

    King, James; Nickling, W. G.; Gilliles, J. A.

    2006-01-01

    A field study was conducted to ascertain the amount of protection that mesquite-dominated communities provide to the surface from wind erosion. The dynamics of the locally accelerated evolution of a mesquite/coppice dune landscape and the undetermined spatial dependence of potential erosion by wind from a shear stress partition model were investigated. Sediment transport and dust emission processes are governed by the amount of protection that can be provided by roughness elements. Although shear stress partition models exist that can describe this, their accuracy has only been tested against a limited dataset because instrumentation has previously been unable to provide the necessary measurements. This study combines the use of meteorological towers and surface shear stress measurements with Irwin sensors to measure the partition of shear stress in situ. The surface shear stress within preferentially aligned vegetation (within coppice dune development) exhibited highly skewed distributions, while a more homogenous surface stress was recorded at a site with less developed coppice dunes. Above the vegetation, the logarithmic velocity profile deduced roughness length (based on 10-min averages) exhibited a distinct correlation with compass direction for the site with vegetation preferentially aligned, while the site with more homogenously distributed vegetation showed very little variation in the roughness length. This distribution in roughness length within an area, defines a distribution of a resolved shear stress partitioning model based on these measurements, ultimately providing potential closure to a previously uncorrelated model parameter.

  20. Zonal winds near Venus' cloud top level - An analytic model of the equatorial wind speed

    NASA Technical Reports Server (NTRS)

    Leovy, Conway B.

    1987-01-01

    A consequence of the presently hypothesized maintenance of the equatorial wind speed near the cloud top level of Venus by a balance between the semidiurnal tide's pumping and the Hadley circulation's vertical advection (both integrated across the thermal driving region) is that the maximum equatorial zonal wind speed is proportional to the product of the buoyancy frequency and the magnitude of the driving region's thickness. The proportionality constant is characterized as a weakly increasing function of the heating rate, and a decreasing function of the product of an inverse length, expressing the mean zonal wind shear, and the driving region thickness. For the class of solutions thus treated, there is a threshold heating rate value below which no equilibrium satisfies the prescribed balance.

  1. Volumetric scans of wind turbine wakes performed with three simultaneous wind LiDARs under different atmospheric stability regimes

    NASA Astrophysics Data System (ADS)

    Valerio Iungo, Giacomo; Porté-Agel, Fernando

    2014-06-01

    Aerodynamic optimization of wind farm layout is a crucial task to reduce wake effects on downstream wind turbines, thus to maximize wind power harvesting. However, downstream evolution and recovery of wind turbine wakes are strongly affected by the characteristics of the incoming atmospheric boundary layer (ABL) flow, such as wind shear and turbulence intensity, which are in turn affected by the ABL thermal stability. In order to characterize the downstream evolution of wakes produced by full-scale wind turbines under different atmospheric conditions, wind velocity measurements were performed with three wind LiDARs. The volumetric scans are performed by continuously sweeping azimuthal and elevation angles of the LiDARs in order to cover a 3D volume that includes the wind turbine wake. The minimum wake velocity deficit is then evaluated as a function of the downstream location for different atmospheric conditions. It is observed that the ABL thermal stability has a significant effect on the wake evolution, and the wake recovers faster under convective conditions.

  2. Severe Convective Wind Environments

    Microsoft Academic Search

    Evan L. Kuchera; Matthew D. Parker

    2006-01-01

    Nontornadic thunderstorm winds from long-lived, widespread convective windstorms can have a tremen- dous impact on human lives and property. To examine environments that support damaging wind producing convection, sounding parameters from Rapid Update Cycle model analyses (at 3-hourly intervals) from 2003 were compared with 7055 reports of damaging winds and 377 081 occurrences of lightning. Ground- relative wind velocity was

  3. Global Wind Map

    ERIC Educational Resources Information Center

    Journal of College Science Teaching, 2005

    2005-01-01

    This brief article describes a new global wind-power map that has quantified global wind power and may help planners place turbines in locations that can maximize power from the winds and provide widely available low-cost energy. The researchers report that their study can assist in locating wind farms in regions known for strong and consistent…

  4. Danish Wind Industry Association

    NSDL National Science Digital Library

    Visitors to this non-profit site can access introductory information about wind turbines and the generation of electricity by wind power. For kids, there is an interactive tour of a wind turbine. For older learners, there is a tutorial that covers all aspects of wind energy. The site is available in several languages, including French and Spanish.

  5. The Power of Wind

    NSDL National Science Digital Library

    Mrs. Andrus

    2010-06-24

    Students should learn about wind energy and why it could possibly be a better option for energy over coal, oil, or gas. Objective: -Students should understand what wind energy is. -Students should learn generally how wind is converted into energy. -Students should learn about the pros and cons of using wind as an energy source. Instructions: View each link to meet the objectives ...

  6. Wind Power Animation

    NSDL National Science Digital Library

    US Department of Energy; Energy Efficiency and Renewable Energy (EERE)

    This animation, from the US Department of Energy, discusses the advantages of wind power, the workings of a wind turbine, and wind resources in the United States. It also describes how wind power is used in small- and large-scale applications.

  7. The effect of the arbitrary level assignment of satellite cloud motion wind vectors on wind analyses in the pre-thunderstorm environment

    NASA Technical Reports Server (NTRS)

    Peslen, C. A.; Koch, S. E.; Uccellini, L. W.

    1985-01-01

    The impact of satellite-derived cloud motion vectors on SESAME rawinsonde wind fields was studied in two separate cases. The effect of wind and moisture gradients on the arbitrary assignment of the satellite data is assessed to coordinate surfaces in a severe storm environment marked by strong vertical wind shear. Objective analyses of SESAME rawinsonde winds and combined winds are produced and differences between these two analyzed fields are used to make an assessment of coordinate level choice. It is shown that the standard method of arbitrarily assigning wind vectors to a low level coordinate surface yields systematic differences between the rawinsonde and combined wind analyses. Arbitrary assignment of cloud motions to the 0.9 sigma surface produces smaller differences than assignment to the 825 mb pressure surface. Systematic differences occur near moisture discontinuities and in regions of horizontal and vertical wind shears. The differences between the combined and SESAME wind fields are made smallest by vertically interpolating cloud motions to either a pressure or sigma surface.

  8. Steel Plate Shear Walls: Efficient Structural Solution for Slender High-Rise in China

    SciTech Connect

    Mathias, Neville; Long, Eric [Skidmore, Owings and Merrill LLP, One Front Street, San Francisco, CA 94111 (United States); Sarkisian, Mark [Skidmore, Owings and Merrill LLP, One Front Street, San Francisco, CA 94111 (United States); Huang Zhihui [Skidmore, Owings and Merrill LLP, One Front Street, San Francisco, CA 94111 (United States)

    2008-07-08

    The 329.6 meter tall 74-story Jinta Tower in Tianjin, China, is expected, when complete, to be the tallest building in the world with slender steel plate shear walls used as the primary lateral load resisting system. The tower has an overall aspect ratio close to 1:8, and the main design challenge was to develop an efficient lateral system capable of resisting significant wind and seismic lateral loads, while simultaneously keeping wind induced oscillations under acceptable perception limits. This paper describes the process of selection of steel plate shear walls as the structural system, and presents the design philosophy, criteria and procedures that were arrived at by integrating the relevant requirements and recommendations of US and Chinese codes and standards, and current on-going research.

  9. Steel Plate Shear Walls: Efficient Structural Solution for Slender High-Rise in China

    NASA Astrophysics Data System (ADS)

    Mathias, Neville; Sarkisian, Mark; Long, Eric; Huang, Zhihui

    2008-07-01

    The 329.6 meter tall 74-story Jinta Tower in Tianjin, China, is expected, when complete, to be the tallest building in the world with slender steel plate shear walls used as the primary lateral load resisting system. The tower has an overall aspect ratio close to 1:8, and the main design challenge was to develop an efficient lateral system capable of resisting significant wind and seismic lateral loads, while simultaneously keeping wind induced oscillations under acceptable perception limits. This paper describes the process of selection of steel plate shear walls as the structural system, and presents the design philosophy, criteria and procedures that were arrived at by integrating the relevant requirements and recommendations of US and Chinese codes and standards, and current on-going research.

  10. Evolution of twist-shear and dip-shear in flaring active region NOAA 10930

    NASA Astrophysics Data System (ADS)

    Gosain, Sanjay; Venkatakrishnan, P.

    2011-08-01

    We study the evolution of magnetic shear angle in a flare productive active region NOAA 10930. The magnetic shear angle is defined as the deviation in the orientation of the observed magnetic field vector with respect to the potential field vector. The shear angle is measured in horizontal as well as vertical plane. The former is computed by taking the difference between the azimuth angles of the observed and potential field and is called the twist-shear, while the latter is computed by taking the difference between the inclination angles of the observed and potential field and is called the dip-shear. The evolution of the two shear angles is then tracked over a small region located over the sheared penumbra of the delta sunspot in NOAA 10930. We find that, while the twist-shear shows an increasing trend after the flare the dip-shear shows a significant drop after the flare.

  11. Galileo entry probe recovery of fine structure in the zonal wind profile at Jupiter

    NASA Astrophysics Data System (ADS)

    Atkinson, D. H.; Pollack, J. B.

    1995-03-01

    The algorithm developed to recover the zonal (east-west) wind profile at Jupiter by Doppler tracking of the Galileo probe is well established in theory and verified by computer simulation. We extend the Doppler wind recovery algorithm to include detection and extraction of microscale wind structure. When the probe encounters regions of high wind shear, turbulence, atmospheric waves, or nonsteady aerodynamics (buffeting) a rapidly varying component is introduced into the probe telemetry Doppler data. These effects can be isolated by their respective Doppler signatures. Analysis of residuals allows fine structure in the wind profile to be located and retrieved. The overall wind recovery is a three-step process: (1) The large-scale zonal wind profile is recovered by converting the probe telemetry frequency residuals (as caused by the Doppler effect) to a velocity and back-projecting it into the local horizontal east-west direction at the probe location. The zonal winds are derived from the velocity residuals by a least squares algorithm. (2) Regions of high zonal wind shear are recovered numerically relative to the large-scale wind structure and serve as a correction to the previously derived large-scale profile. (3) The probe trajectory is updated to reflect both the large- and small-scale wind structure, and the large-scale wind profile is recalculated. The Galileo Doppler wind experiment described previously and the wind microstructure retrieval algorithm outlined here are the only reasonable means by which the vertical profile of the zonal winds at Jupiter can be directly sampled.

  12. Upwelling of Arctic pycnocline associated with shear motion of sea ice

    NASA Technical Reports Server (NTRS)

    McPhee, M. G.; Kwok, R.; Robins, R.; Coon, M.

    2006-01-01

    High-resolution radar imagery shows that the dynamic response of winter sea ice to gradients in large-scale surface wind stress is often localized along quasi-linear fractures hundreds of kilometers long. Relative shearing motion across these narrow fractures can exceed 10 cm/s. In one event recorded during the drift of the SHEBA ice camp, we observed an intense zone of pycnocline upwelling (approx.14 m) associated with significant shear motion near the camp, while upward turbulent heat flux in the ocean boundary layer reached nearly 400 W/sq m, an order of magnitude greater than at any other time during the year-long drift. We attribute the upwelling to Ekman pumping associated with concentrated ice shear. Over the entire Arctic Ocean sea ice cover, this process could be responsible for significant heat exchange between the cold surface layer and warmer subsurface water at the ubiquitous fractures resulting from large-scale atmosphere-ice interactions.

  13. The wind characteristics program

    NASA Astrophysics Data System (ADS)

    Wendell, L. L.

    Wind characteristics research activities emphasize wind resource assessment, site selection and evaluation techniques, and wind characteristics for wind turbine design, performance and operations evaluation. Wind resource analysis shows the greatest area of high wind power resource is in the midsection of the U.S. High wind power is available in other sections of the country and is described in some detail on a state by state basis in twelve regional atlases. To carry the wind prospecting process to a finer scale, site selection techniques for small and large wind turbines were developed, tested, and documented. There is a broad range of sophistication and reliability in these techniques and their application must be matched with the priorities and time available for energy planning efforts. The nature of wind gustiness was evaluated statistically and modeled for calculating fatigue cycles and extreme events.

  14. Streamwise development of the wind turbine boundary layer over a model wind turbine array

    NASA Astrophysics Data System (ADS)

    Newman, Jensen; Lebron, Jose; Meneveau, Charles; Castillo, Luciano

    2013-08-01

    The streamwise development of turbulence statistics and mean kinetic energy in a model wind farm consisting of 3 × 5 wind turbines is studied experimentally in a wind tunnel. The analysis uses planar Particle Image Velocimetry data obtained at the centerline plane of the wind farm, covering the inflow as well as four planes in between five downstream wind turbines. The data analysis is organized by dividing these measurement planes into three regions: the above-rotor, rotor-swept, and below-rotor regions. For each field, flow development is quantified using a properly defined relative difference norm based on an integration over each of the regions. Using this norm, it is found that the mean streamwise velocity approaches a fully developed state most rapidly, whereas the flow development is more gradual for the second-order statistics. The vertical entrainment flux of the mean kinetic energy by the Reynolds shear stress, ?U??u'v'?, is observed to develop at a rate similar to that of the Reynolds shear stress rather than the mean streamwise velocity component. Its development is slowest in the layer nearest to the ground. Analysis of various terms in the mean kinetic energy equation shows that the wind turbine boundary layer has not yet reached fully developed conditions by the fifth turbine but that it is approaching such conditions. By comparing the vertical entrainment flux with the horizontal flux due to the mean flow, it is found that the former increases, whereas the latter decreases, as function of downstream distance, but that the former is already an important contributor in the developing region.

  15. Wind energy offers considerable promise; the wind itself is free,

    E-print Network

    Langendoen, Koen

    Wind energy offers considerable promise; the wind itself is free, wind power is clean. One of these sources, wind energy, offers considerable promise; the wind itself is free, wind power is clean, and it is virtually inexhaustible. In recent years, research on wind energy has accelerated

  16. Estimation of Wind Speed in Connection to a Wind Turbine

    E-print Network

    Estimation of Wind Speed in Connection to a Wind Turbine X. Ma #3; , N. K. Poulsen #3; , H. Bindner y December 20, 1995 Abstract The wind speed varies over the rotor plane of wind turbine making the wind speed on the rotor plane will be estimated by using a wind turbine as a wind measuring device

  17. Separated shear layer transition at low reynolds numbers: Experiments and stability analysis

    Microsoft Academic Search

    Serhiy Yarusevych; John G Kawall; Pierre E Sullivan

    2007-01-01

    Flow transition in the separated shear layer on the upper surface of a NACA 0025 airfoil at low Reynolds numbers was investigated. The study involved wind tunnel experiments and linear stability analysis. Detailed measurements were conducted for Reynolds numbers of 100,000 and 150,000 at 0, 5, and 10-degrees angles of attack. With laminar boundary layer separation occurring on the upper

  18. Nucleation of shear bands in amorphous alloys.

    PubMed

    Perepezko, John H; Imhoff, Seth D; Chen, Ming-Wei; Wang, Jun-Qiang; Gonzalez, Sergio

    2014-03-18

    The initiation and propagation of shear bands is an important mode of localized inhomogeneous deformation that occurs in a wide range of materials. In metallic glasses, shear band development is considered to center on a structural heterogeneity, a shear transformation zone that evolves into a rapidly propagating shear band under a shear stress above a threshold. Deformation by shear bands is a nucleation-controlled process, but the initiation process is unclear. Here we use nanoindentation to probe shear band nucleation during loading by measuring the first pop-in event in the load-depth curve which is demonstrated to be associated with shear band formation. We analyze a large number of independent measurements on four different bulk metallic glasses (BMGs) alloys and reveal the operation of a bimodal distribution of the first pop-in loads that are associated with different shear band nucleation sites that operate at different stress levels below the glass transition temperature, Tg. The nucleation kinetics, the nucleation barriers, and the density for each site type have been determined. The discovery of multiple shear band nucleation sites challenges the current view of nucleation at a single type of site and offers opportunities for controlling the ductility of BMG alloys. PMID:24594599

  19. Numerical modeling of the wind flow over a transverse dune

    PubMed Central

    Araújo, Ascânio D.; Parteli, Eric J. R.; Pöschel, Thorsten; Andrade, José S.; Herrmann, Hans J.

    2013-01-01

    Transverse dunes, which form under unidirectional winds and have fixed profile in the direction perpendicular to the wind, occur on all celestial objects of our solar system where dunes have been detected. Here we perform a numerical study of the average turbulent wind flow over a transverse dune by means of computational fluid dynamics simulations. We find that the length of the zone of recirculating flow at the dune lee — the separation bubble — displays a surprisingly strong dependence on the wind shear velocity, u*: it is nearly independent of u* for shear velocities within the range between 0.2?m/s and 0.8?m/s but increases linearly with u* for larger shear velocities. Our calculations show that transport in the direction opposite to dune migration within the separation bubble can be sustained if u* is larger than approximately 0.39?m/s, whereas a larger value of u* (about 0.49?m/s) is required to initiate this reverse transport. PMID:24091456

  20. Numerical modeling of the wind flow over a transverse dune.

    PubMed

    Araújo, Ascânio D; Parteli, Eric J R; Pöschel, Thorsten; Andrade, José S; Herrmann, Hans J

    2013-01-01

    Transverse dunes, which form under unidirectional winds and have fixed profile in the direction perpendicular to the wind, occur on all celestial objects of our solar system where dunes have been detected. Here we perform a numerical study of the average turbulent wind flow over a transverse dune by means of computational fluid dynamics simulations. We find that the length of the zone of recirculating flow at the dune lee - the separation bubble - displays a surprisingly strong dependence on the wind shear velocity, u: it is nearly independent of u for shear velocities within the range between 0.2 m/s and 0.8 m/s but increases linearly with u for larger shear velocities. Our calculations show that transport in the direction opposite to dune migration within the separation bubble can be sustained if u is larger than approximately 0.39 m/s, whereas a larger value of u (about 0.49 m/s) is required to initiate this reverse transport. PMID:24091456

  1. Numerical modeling of the wind flow over a transverse dune

    E-print Network

    Ascânio D. Araújo; Eric J. R. Parteli; Thorsten Poeschel; José S. Andrade Jr.; Hans J. Herrmann

    2013-09-30

    Transverse dunes, which form under unidirectional winds and have fixed profile in the direction perpendicular to the wind, occur on all celestial objects of our solar system where dunes have been detected. Here we perform a numerical study of the average turbulent wind flow over a transverse dune by means of computational fluid dynamics simulations. We find that the length of the zone of recirculating flow at the dune lee --- the {\\em{separation bubble}} --- displays a surprisingly strong dependence on the wind shear velocity, $u_{\\ast}$: it is nearly independent of $u_{\\ast}$ for shear velocities within the range between $0.2\\,$m$$s and $0.8\\,$m$$s but increases linearly with $u_{\\ast}$ for larger shear velocities. Our calculations show that transport in the direction opposite to dune migration within the separation bubble can be sustained if $u_{\\ast}$ is larger than approximately $0.39\\,$m$$s, whereas a larger value of $u_{\\ast}$ (about $0.49\\,$m$$s) is required to initiate this reverse transport.

  2. Numerical modeling of the wind flow over a transverse dune

    E-print Network

    Araújo, Ascânio D; Poeschel, Thorsten; Andrade, José S; Herrmann, Hans J

    2013-01-01

    Transverse dunes, which form under unidirectional winds and have fixed profile in the direction perpendicular to the wind, occur on all celestial objects of our solar system where dunes have been detected. Here we perform a numerical study of the average turbulent wind flow over a transverse dune by means of computational fluid dynamics simulations. We find that the length of the zone of recirculating flow at the dune lee --- the {\\em{separation bubble}} --- displays a surprisingly strong dependence on the wind shear velocity, $u_{\\ast}$: it is nearly independent of $u_{\\ast}$ for shear velocities within the range between $0.2\\,$m$$s and $0.8\\,$m$$s but increases linearly with $u_{\\ast}$ for larger shear velocities. Our calculations show that transport in the direction opposite to dune migration within the separation bubble can be sustained if $u_{\\ast}$ is larger than approximately $0.39\\,$m$$s, whereas a larger value of $u_{\\ast}$ (about $0.49\\,$m$$s) is required to initiate this reverse transport.

  3. Wind Resource Maps (Postcard)

    SciTech Connect

    Not Available

    2011-07-01

    The U.S. Department of Energy's Wind Powering America initiative provides high-resolution wind maps and estimates of the wind resource potential that would be possible from development of the available windy land areas after excluding areas unlikely to be developed. This postcard is a marketing piece that stakeholders can provide to interested parties; it will guide them to Wind Powering America's online wind energy resource maps.

  4. Wind power. [electricity generation

    NASA Technical Reports Server (NTRS)

    Savino, J. M.

    1975-01-01

    A historical background on windmill use, the nature of wind, wind conversion system technology and requirements, the economics of wind power and comparisons with alternative systems, data needs, technology development needs, and an implementation plan for wind energy are presented. Considerable progress took place during the 1950's. Most of the modern windmills feature a wind turbine electricity generator located directly at the top of their rotor towers.

  5. Wind Power Outlook 2004

    SciTech Connect

    anon.

    2004-01-01

    The brochure, expected to be updated annually, provides the American Wind Energy Association's (AWAE's) up-to-date assessment of the wind industry. It provides a summary of the state of wind power in the U.S., including the challenges and opportunities facing the industry. It provides summary information on the growth of the industry, policy-related factors such as the federal wind energy production tax credit status, comparisons with natural gas, and public views on wind energy.

  6. An Icelandic wind atlas

    NASA Astrophysics Data System (ADS)

    Nawri, Nikolai; Nína Petersen, Gudrun; Bjornsson, Halldór; Arason, Þórður; Jónasson, Kristján

    2013-04-01

    While Iceland has ample wind, its use for energy production has been limited. Electricity in Iceland is generated from renewable hydro- and geothermal source and adding wind energy has not be considered practical or even necessary. However, adding wind into the energy mix is becoming a more viable options as opportunities for new hydro or geothermal power installation become limited. In order to obtain an estimate of the wind energy potential of Iceland a wind atlas has been developed as a part of the Nordic project "Improved Forecast of Wind, Waves and Icing" (IceWind). The atlas is based on mesoscale model runs produced with the Weather Research and Forecasting (WRF) Model and high-resolution regional analyses obtained through the Wind Atlas Analysis and Application Program (WAsP). The wind atlas shows that the wind energy potential is considerable. The regions with the strongest average wind are nevertheless impractical for wind farms, due to distance from road infrastructure and power grid as well as harsh winter climate. However, even in easily accessible regions wind energy potential in Iceland, as measured by annual average power density, is among the highest in Western Europe. There is a strong seasonal cycle, with wintertime power densities throughout the island being at least a factor of two higher than during summer. Calculations show that a modest wind farm of ten medium size turbines would produce more energy throughout the year than a small hydro power plants making wind energy a viable additional option.

  7. Validation of a Wind Farm Parameterisation in COSMO-CLM using large eddy simulations

    NASA Astrophysics Data System (ADS)

    Chatterjee, Fabien; Van Lipzig, Nicole; Meyers, Johan

    2014-05-01

    Offshore wind deployment is foreseen to expand dramatically in the coming years. The strong expansion of offshore wind parks is likely to affect the regional climatology of the coastal areas surrounding the Atlantic, North Sea and Baltic Sea. The main aim of this project is to assess the climate effect of a change in sea use, due to large-scale offshore wind deployment. Wind turbines are shown to have an effect on wind speed and moisture when parameterized in COSMO-CLM. However the magnitude of these is still unclear on the kilometer scale, and direct comparison with offshore wind farm data remains difficult. Large eddy simulations offer insights into processes otherwise parameterised in regional climate models, and are used to validate the wind farm representation. This is done by implementing the wind farm parameterisation in an idealised version of COSMO-CLM and comparing its output with large eddy simulations. Changes in wind speed and shear stresses in and outside of the wind farm are assessed and the effect of wind farms on the geostrophic wind above the boundary layer will be investigated under different wind farm deployments.

  8. An investigation of wind loads on solar collectors. Appendix I - data listing for top and bottom of collector. Final report

    Microsoft Academic Search

    H. W. Tieleman; R. E. Akins; P. Sparks

    1980-01-01

    A wind-tunnel study of a series of model solar-collector installations (flat-plate collectors) immersed in a thick turbulent shear layout was undertaken in order to determine design wind loads on such installations. Wind tunnel measurements were made of the mean and fluctuating pressures on a model of a single flat-plate collector which was a component of different multi-panel installations. The pressures

  9. Application of PVDF Film Sensor to Detect Early Damage in Wind Turbine Blade Components

    Microsoft Academic Search

    Y.-H. Huh; J. I. Kim; J. H. Lee; S. G. Hong; J. H. Park

    2011-01-01

    Monitoring technique for detection of early damage in the wind turbine blade has been investigated using PVDF film sensor and strain gages. The trailing edge component with shear web was prepared by sectioning the full-scale blade with a box spa. Several PVDF film sensors with dimension of 10x10x0.054 mm3 and strain gages were installed on shear web and skin of

  10. Quantification of Critical Shear Stress

    NSDL National Science Digital Library

    Lonnie Leithold

    Ã Photo of angle of repose experiment Provenance: Lonnie Leithold, North Carolina State University at Raleigh Reuse: This item is offered under a Creative Commons Attribution-NonCommercial-ShareAlike license http://creativecommons.org/licenses/by-nc-sa/3.0/ You may reuse this item for non-commercial purposes as long as you provide attribution and offer any derivative works under a similar license. This is a lab activity designed to give students experience with the concept and quantification of critical shear stress.

  11. Shear Viscosity of Quark Matter

    E-print Network

    W. M. Alberico; S. Chiacchiera; H. Hansen; A. Molinari; M. Nardi

    2007-07-30

    We consider the shear viscosity of a system of quarks and its ratio to the entropy density above the critical temperature for deconfinement. Both quantities are derived and computed for different modeling of the quark self-energy, also allowing for a temperature dependence of the effective mass and width. The behaviour of the viscosity and the entropy density is argued in terms of the strength of the coupling and of the main characteristics of the quark self-energy. A comparison with existing results is also discussed.

  12. Inclined granular flows on collisional shear layers

    NASA Astrophysics Data System (ADS)

    Jenkins, James T.; Berzi, Diego

    2013-06-01

    We analyze steady, uniform flow down inclines in which collisions between particles dominate the transfer of momentum and energy in a region of intensely sheared particles at the base of the flow. At the top of the region is an erodible interface that separates two regimes involving colliding particles. Those below the interface participate in the shearing, those above the interface are too concentrated to be sheared. At the bottom of the region, the particles of the flow collide with the fixed particles of a bumpy boundary. Gravity acts throughout the region of shear. The shear stress transmitted through the shear layer to the material above it is determined in terms of the velocity of this material and the total height of the flow.

  13. Generality of shear thickening in dense suspensions.

    PubMed

    Brown, Eric; Forman, Nicole A; Orellana, Carlos S; Zhang, Hanjun; Maynor, Benjamin W; Betts, Douglas E; DeSimone, Joseph M; Jaeger, Heinrich M

    2010-03-01

    Suspensions are of wide interest and form the basis for many smart fluids. For most suspensions, the viscosity decreases with increasing shear rate, that is, they shear thin. Few are reported to do the opposite, that is, shear thicken, despite the longstanding expectation that shear thickening is a generic type of suspension behaviour. Here we resolve this apparent contradiction. We demonstrate that shear thickening can be masked by a yield stress and can be recovered when the yield stress is decreased below a threshold. We show the generality of this argument and quantify the threshold in rheology experiments where we control yield stresses arising from a variety of sources, such as attractions from particle surface interactions, induced dipoles from applied electric and magnetic fields, as well as confinement of hard particles at high packing fractions. These findings open up possibilities for the design of smart suspensions that combine shear thickening with electro- or magnetorheological response. PMID:20118945

  14. Shear Thickening and Migration in Granular Suspensions

    NASA Astrophysics Data System (ADS)

    Fall, Abdoulaye; Lemaître, Anaël; Bertrand, François; Bonn, Daniel; Ovarlez, Guillaume

    2010-12-01

    We study the emergence of shear thickening in dense suspensions of non-Brownian particles. We combine local velocity and concentration measurements using magnetic resonance imaging with macroscopic rheometry experiments. In steady state, we observe that the material is heterogeneous, and we find that the local rheology presents a continuous transition at low shear rate from a viscous to a shear thickening, Bagnoldian, behavior with shear stresses proportional to the shear rate squared, as predicted by a scaling analysis. We show that the heterogeneity results from an unexpectedly fast migration of grains, which we attribute to the emergence of the Bagnoldian rheology. The migration process is observed to be accompanied by macroscopic transient discontinuous shear thickening, which is consequently not an intrinsic property of granular suspensions.

  15. Coronal magnetic fields produced by photospheric shear

    NASA Technical Reports Server (NTRS)

    Sturrock, P. A.; Yang, W.-H.

    1987-01-01

    The magneto-frictional method is used for computing force free fields to examine the evolution of the magnetic field of a line dipole, when there is relative shearing motion between the two polarities. It found that the energy of the sheared field can be arbitrarily large compared with the potential field. It is also found that it is possible to fit the magnetic energy, as a function of shear, by a simple functional form.

  16. Modeling of thermomechanical shear instability in machining

    Microsoft Academic Search

    Zhen Bing Hou; Ranga Komanduri

    1997-01-01

    The modeling of thermomechanical shear instability in the machining of some difficult-to-machine materials leading to shear localization is presented. Shear instability was observed experimentally in high-speed machining (HSM) of some of the difficult-to-machine materials, such as hardened alloy steels (e.g. AISI 4340 steel), titanium alloys (e.g. Ti-6A1-4V), and nickel-base superalloys (e.g. Inconel 718) yielding cyclic chips. Based on an analysis

  17. Measuring cosmic shear with the ring statistics

    Microsoft Academic Search

    T. Eifler; P. Schneider; E. Krause

    2010-01-01

    Context. Commonly used methods of decomposing E- and B-modes in cosmic shear, namely the aperture mass dispersion and the E\\/B-mode shear correlation function, suffer from incomplete knowledge of the two-point correlation function (2PCF) on very small and\\/or very large scales. The ring statistics, the most recently developed cosmic shear measure, improves on this issue and is able to decompose E-

  18. Shear Strength Criteria for Unsaturated Soils

    Microsoft Academic Search

    Daichao Sheng; Annan Zhou; Delwyn G. Fredlund

    2011-01-01

    Shear strength is one of the fundamental properties of unsaturated soils. It has been found to change with matric suction.\\u000a Various shear strength equations have been proposed for predicting the shear strength versus suction relationship for unsaturated\\u000a soils. Some of these equations are based on regression analysis of experimental data, while some are embodied in more complex\\u000a stress–strain constitutive models.

  19. Wind speed forecasting for wind energy applications

    NASA Astrophysics Data System (ADS)

    Liu, Hong

    With more wind energy being integrated into our grid systems, forecasting wind energy has become a necessity for all market participants. Recognizing the market demands, a physical approach to site-specific hub-height wind speed forecasting system has been developed. This system is driven by the outputs from the Canadian Global Environmental Multiscale (GEM) model. A simple interpolation approach benchmarks the forecasting accuracy inherited from GEM. Local, site specific winds are affected on a local scale by a variety of factors including representation of the land surface and local boundary-layer process over heterogeneous terrain which have been a continuing challenge in NWP models like GEM with typical horizontal resolution of order 15-km. In order to resolve these small scale effects, a wind energy industry standard model, WAsP, is coupled with GEM to improve the forecast. Coupling the WAsP model with GEM improves the overall forecasts, but remains unsatisfactory for forecasting winds with abrupt surface condition changes. Subsequently in this study, a new coupler that uses a 2-D RANS model of boundary-layer flow over surface condition changes with improved physics has been developed to further improve the forecasts when winds coming from a water surface to land experience abrupt changes in surface conditions. It has been demonstrated that using vertically averaged wind speeds to represent geostrophic winds for input into the micro-scale models could reduce forecast errors. The hub-height wind speed forecasts could be further improved using a linear MOS approach. The forecasting system has been evaluated, using a wind energy standard evaluation matrix, against data from an 80-m mast located near the north shore of Lake Erie. Coupling with GEM-LAM and a power conversion model using a theoretical power curve have also been investigated. For hub-height wind speeds GEM appears to perform better with a 15-Ian grid than the high resolution GEM-2.5Ian version at the validation site.

  20. Structure of the Highly Sheared Tropical Storm Chantal During CAMEX-4

    NASA Technical Reports Server (NTRS)

    Heymsfield, G. M.; Halverson, J.; Ritchie, E.; Simpson, Joanne; Molinari, J.; Tian, L.

    2004-01-01

    NASA's 4th Convection and Moisture Experiment (CAMEX-4) focused on Atlantic hurricanes during the 2001 hurricane season and it involved both NASA and NOAA participation. The NASA ER-2 and DC-8 aircraft were instrumented with unique remote sensing instruments to help increase the overall understanding of hurricanes. This paper is concerned about one of the storms studied, Tropical Storm Chantal, that was a weak storm which failed to intense into a hurricane. One of the practical questions of high importance is why some tropical stoins intensify into hurricanes, and others remain weak or die altogether. The magnitude of the difference between the horizontal winds at lower levels and upper altitudes in a tropical storm, i.e., the wind shear, is one important quantity that can affect the intensification of a tropical storm. Strong shear as was present during Tropical Storm Chantal s lifetime and it was detrimental to its intensification. The paper presents an analysis of unique aircraft observations collected from Chantal including an on-board radar, radiometers, dropsondes, and flight level measurements. These measurements have enabled us to examine the internal structure of the winds and thermal structure of Chantal. Most of the previous studies have involved intense hurricanes that overcame the effects of shear and this work has provided new insights into what prevents a weaker storm from intensifying. The storm had extremely intense thunderstorms and rainfall, yet its main circulation was confined to low levels of the atmosphere. Chantal's thermal structure was not configured properly for the storm to intensify. It is most typical that huricanes have a warm core structure where warm temperatures in upper levels of a storm s circulation help intensify surface winds and lower its central pressure. Chantal had two weaker warm layers instead of a well-defined warm core. These layers have been related to the horizontal and vertical winds and precipitation structure and have helped us learn more about why this storm didn't develop.

  1. Surface Shear Stress Around a Single Flexible Live Plant and a Rigid Cylinder

    NASA Astrophysics Data System (ADS)

    Walter, B. A.; Gromke, C.; Leonard, K. C.; Clifton, A.; Lehning, M.

    2010-12-01

    The sheltering effect of vegetation against soil erosion and snow transport has direct implications on land degradation and local water storage as snow in many arid and semi arid regions. Plants influence the erosion, transport and redeposition of soil and snow by the wind through momentum absorption, local stress concentration, trapping particles in motion and reducing the area of sediment exposed to the wind. The shear stress distributions on the ground beneath plant canopies determine the onset and magnitude of differential soil and snow erosion on rough or vegetated surfaces, but this has been studied exclusively with artificial and rigid vegetation elements thus far. Real plants have highly irregular structures that can be extremely flexible and porous. They align with the flow at higher wind speeds, resulting in considerable changes to the drag and flow regimes relative to rigid imitations of comparable size. We present measurements in the SLF atmospheric boundary layer wind tunnel of the surface shear stress distribution around a live grass plant (Lolium Perenne) and a solid cylinder of comparable size. Irwin sensors are used to measure pressure differences close to the surface which can be calibrated with surface shear stress velocities. The basal to frontal area index of the plant and the cylinder as well as the Reynolds number of the two experimental setups have been checked for similarity and show good agreement. Distinctive differences between the shear stress pattern around the plant and the cylinder can be attributed to the influence of the plant’s porosity and flexibility. The sheltered zone behind the plant is narrower in cross-stream and longer in streamwise direction than that of the cylinder. For the plant, the lowest shear stresses in the sheltered zone are 50% lower than the mean surface shear stress (? = 0.15 N/m2) in the undisturbed flow. The sheltering was higher behind the cylinder with values reduced by 70% relative to background. “Speed-up” zones on both sides of the roughness elements experienced peak shear stress values 60% above background for the plant and almost 130% higher for the cylinder. While the integral sheltering effect of the plant is smaller in size and magnitude than that of the cylinder, the peak shear stresses in the lateral speed up zones are significantly lower. Since the onset of soil erosion occurs when a critical threshold shear stress is experienced, the lower peak shear stress means that plants provide better protection against soil erosion than rigid elements. This result suggests that parameterizations of flow over vegetated surfaces based on measurements of rigid elements may be incorrect. Further work will investigate sheltering and shear stress concentrations as a function of cylinder / plant density using real canopies instead of single objects.

  2. WIND DATA REPORT Thompson Island

    E-print Network

    Massachusetts at Amherst, University of

    WIND DATA REPORT Thompson Island September 1, 2003 ­ November 30, 2003 Prepared for Massachusetts...................................................................................................................... 9 Wind Speed Time Series............................................................................................................. 9 Wind Speed Distribution

  3. WIND DATA REPORT FALMOUTH, MA

    E-print Network

    Massachusetts at Amherst, University of

    WIND DATA REPORT FALMOUTH, MA June1, 2004 to August 31, 2004. Prepared for Massachusetts Technology...................................................................................................................... 8 Wind Speed Time Series............................................................................................................. 8 Wind Speed Distributions

  4. WIND DATA REPORT Thompson Island

    E-print Network

    Massachusetts at Amherst, University of

    WIND DATA REPORT Thompson Island March 1, 2003 ­ May 31, 2003 Prepared for Massachusetts Technology...................................................................................................................... 9 Wind Speed Time Series............................................................................................................. 9 Wind Speed Distributions

  5. WIND DATA REPORT Thompson Island

    E-print Network

    Massachusetts at Amherst, University of

    WIND DATA REPORT Thompson Island December 1, 2003 ­ February 29, 2004 Prepared for Massachusetts.................................................................................................................... 11 Wind Speed Time Series........................................................................................................... 11 Wind Speed Distribution

  6. WIND DATA REPORT Thompson Island

    E-print Network

    Massachusetts at Amherst, University of

    WIND DATA REPORT Thompson Island June 1, 2004 ­ August 31, 2004 Prepared for Massachusetts...................................................................................................................... 9 Wind Speed Time Series............................................................................................................. 9 Wind Speed Distribution

  7. WIND DATA REPORT Presque Isle

    E-print Network

    Massachusetts at Amherst, University of

    WIND DATA REPORT Presque Isle March 1, 2005 ­ May 31, 2005 Prepared for United States Department.................................................................................................................... 10 Wind Speed Time Series........................................................................................................... 10 Wind Speed Distributions

  8. WIND DATA REPORT Thompson Island

    E-print Network

    Massachusetts at Amherst, University of

    WIND DATA REPORT Thompson Island March 1, 2004 ­ May 31, 2004 Prepared for Massachusetts Technology...................................................................................................................... 9 Wind Speed Time Series............................................................................................................. 9 Wind Speed Distribution

  9. WIND DATA REPORT Thompson Island

    E-print Network

    Massachusetts at Amherst, University of

    WIND DATA REPORT Thompson Island June 1, 2003 ­ August 31, 2003 Prepared for Massachusetts...................................................................................................................... 9 Wind Speed Time Series............................................................................................................. 9 Wind Speed Distribution

  10. WIND DATA REPORT Presque Isle

    E-print Network

    Massachusetts at Amherst, University of

    WIND DATA REPORT Presque Isle June 1, 2005 ­ August 31, 2005 Prepared for United States Department...................................................................................................................... 9 Wind Speed Time Series............................................................................................................. 9 Wind Speed Distributions

  11. WIND DATA REPORT Presque Isle

    E-print Network

    Massachusetts at Amherst, University of

    WIND DATA REPORT Presque Isle December 1, 2004 ­ December 1, 2005 Prepared for United States ......................................................................................................... 9 Wind Speed Time Series........................................................................................................... 10 Wind Speed Distributions

  12. WIND DATA REPORT Presque Isle

    E-print Network

    Massachusetts at Amherst, University of

    WIND DATA REPORT Presque Isle December 1, 2004 ­ February 28, 2005 Prepared for United States.................................................................................................................... 10 Wind Speed Time Series........................................................................................................... 10 Wind Speed Distributions

  13. Novel shear mechanism in nanolayered composites

    SciTech Connect

    Mara, Nathan [Los Alamos National Laboratory; Bhattacharyya, Dhriti [Los Alamos National Laboratory; Hirth, John P [Los Alamos National Laboratory; Dickerson, Patricia O [Los Alamos National Laboratory; Misra, Amit [Los Alamos National Laboratory

    2009-01-01

    Recent studies have shown that two-phase nanocomposite materials with semicoherent interfaces exhibit enhanced strength, deformability, and radiation damage resistance. The remarkable behavior exhibited by these materials has been attributed to the atomistic structure of the bi-metal interface that results in interfaces with low shear strength and hence, strong barriers for slip transmission due to dislocation core spreading along the weak interfaces. In this work, the low interfacial shear strength of Cu/Nb nanoscale multilayers dictates a new mechanism for shear banding and strain softening during micropillar compression. Previous work investigating shear band formation in nanocrystalline materials has shown a connection between insufficient strain hardening and the onset of shear banding in Fe and Fe-10% Cu, but has also shown that hardening does not necessarily offset shear banding in Pd nanomaterials. Therefore, the mechanisms behind shear localization in nanocrystalline materials are not completely understood. Our findings, supported by molecular dynamics simulations, provide insight on the design of nanocomposites with tailored interface structures and geometry to obtain a combination of high strength and deformability. High strength is derived from the ability of the interfaces to trap dislocations through relative ease of interfacial shear, while deformability can be maximized by controlling the effects of loading geometry on shear band formation.

  14. Inertial shear bands in granular materials

    NASA Astrophysics Data System (ADS)

    Berzi, Diego; Jenkins, James T.

    2015-03-01

    We provide numerical solutions to the momentum and energy balance of a kinetic theory for the steady, collisional shearing of identical, inelastic, frictional spheres between two different types of boundaries—rigid-bumpy and erodible, in the absence of gravity. A rigid-bumpy boundary is a source of fluctuation energy for the flow, an erodible boundary is a sink. As a consequence, the characteristics of shearing between two rigid-bumpy boundaries, two erodible boundaries, and a rigid-bumpy and an erodible boundary are all different. Here, we display these differences and relate them to measurements of inhomogeneous shearing and the development of shear bands in laboratory experiments.

  15. Dynamic shear deformation in high purity Fe

    SciTech Connect

    Cerreta, Ellen K [Los Alamos National Laboratory; Bingert, John F [Los Alamos National Laboratory; Trujillo, Carl P [Los Alamos National Laboratory; Lopez, Mike F [Los Alamos National Laboratory; Gray, George T [Los Alamos National Laboratory

    2009-01-01

    The forced shear test specimen, first developed by Meyer et al. [Meyer L. et al., Critical Adiabatic Shear Strength of Low Alloyed Steel Under Compressive Loading, Metallurgical Applications of Shock Wave and High Strain Rate Phenomena (Marcel Decker, 1986), 657; Hartmann K. et al., Metallurgical Effects on Impact Loaded Materials, Shock Waves and High Strain rate Phenomena in Metals (Plenum, 1981), 325-337.], has been utilized in a number of studies. While the geometry of this specimen does not allow for the microstructure to exactly define the location of shear band formation and the overall mechanical response of a specimen is highly sensitive to the geometry utilized, the forced shear specimen is useful for characterizing the influence of parameters such as strain rate, temperature, strain, and load on the microstructural evolution within a shear band. Additionally, many studies have utilized this geometry to advance the understanding of shear band development. In this study, by varying the geometry, specifically the ratio of the inner hole to the outer hat diameter, the dynamic shear localization response of high purity Fe was examined. Post mortem characterization was performed to quantify the width of the localizations and examine the microstructural and textural evolution of shear deformation in a bcc metal. Increased instability in mechanical response is strongly linked with development of enhanced intergranular misorientations, high angle boundaries, and classical shear textures characterized through orientation distribution functions.

  16. [Shear stress and platelet-derived microparticles].

    PubMed

    Nomura, S; Komiyama, Y

    1997-10-01

    One of the responses of activated platelets to certain stimuli is the shedding of microparticles. Many studies have attempted to characterize the role of microparticles under various clinical situations or experimental conditions. Pathological levels of fluid shear stress may occur in diseased small arteries and arterioles partially obstructed by atherosclerosis or vasospasm and such shear stress may induce the activation and aggregation of circulating platelets. We investigated whether high shear stress could cause both platelet aggregation and shedding of microparticles from the platelet plasma membrane. A cone-plate viscometer was used to apply shear stress and microparticle formation was measured by flow cytometry. It was found that microparticle formation increased as the duration of shear stress increased. Both microparticles and remnant platelets showed procoagulant activity on their surfaces. Investigation of the mechanisms involved in shear-dependent microparticle generation showed that binding of von Willebrand factor to platelet glycoprotein Ib, influx of extracellular calcium, and activation of platelet calpain were required to generate microparticles under high shear stress conditions. Activation of protein kinase C promoted shear-dependent microparticle formation. These findings suggest that local generation of microparticles in atherosclerotic arteries, the site at which pathological levels of shear stress could occur, contributes to arterial thrombosis by providing and expanding a catalytic surface for the coagulation cascade. PMID:9369069

  17. Shear Thickening in Concentrated Soft Sphere Colloidal Suspensions: A Shear Induced Phase Transition

    E-print Network

    Joachim Kaldasch; Bernhard Senge; Jozua Laven

    2015-01-09

    A model of shear thickening in dense suspensions of Brownian soft sphere colloidal particles is established. It suggests that shear thickening in soft sphere suspensions can be interpreted as a shear induced phase transition. Based on a Landau model of the coagulation transition of stabilized colloidal particles, taking the coupling between order parameter fluctuations and the local strain-field into account, the model suggests the occurrence of clusters of coagulated particles (subcritical bubbles) by applying a continuous shear perturbation.The critical shear stress of shear thickening in soft sphere suspensions is derived while reversible shear thickening and irreversible shear thickening have the same origin. The comparison of the theory with an experimental investigation of electrically stabilized colloidal suspensions confirms the presented approach.

  18. Combined neutron and rheological studies of polymer systems, revealing shear-instabilities and shear

    E-print Network

    -angle scattering and oscillatory shear instrumentation are effective tools for studying structure and real shear lead to twin structures with {112} planes sharing neighboring twins and [111] axes parallel) 2005. SINQ instruments involved: SANS-II #12;

  19. Q-Winds satellite hurricane wind retrievals and H*Wind comparisons

    E-print Network

    Hennon, Christopher C.

    1 Q-Winds satellite hurricane wind retrievals and H*Wind comparisons Pet Laupattarakasem and W This paper presents a new hurricane ocean vector wind (OVW) product known as Q-Winds produced from the SeaWinds for tropical cyclones. SeaWinds OVW retrievals are presented for ten hurricane passes with near

  20. Analytically Modelling Mean Wind and Stress Profiles in Canopies

    NASA Astrophysics Data System (ADS)

    Wang, Weiguo

    2014-05-01

    An analytical model for mean wind profiles in sparse canopies (W. Wang, Boundary-Layer Meteorol 142:383-399, 2012) has been further developed, with (1) an explicit solution being derived, and (2) a linear term being added to the -closure scheme to improve the shear-stress parametrization when the contribution of non-local transport is significant. Results from large-eddy simulations and from laboratory experiments are used to evaluate the model and adjust model parameters, showing that the model can well simulate canopy wind and stress profiles not only for sparse-canopy scenarios, but also for dense-canopy scenarios. The analytical solution converges exactly to the standard surface-layer logarithmic wind profile in the case of zero canopy density, and tends to an exponential wind profile for a dense canopy.

  1. The gust-front detection and wind-shift algorithms for the Terminal Doppler Weather Radar system

    NASA Technical Reports Server (NTRS)

    Hermes, Laurie G.; Witt, Arthur; Smith, Steven D.; Klingle-Wilson, Diana; Morris, Dale; Stumpf, Gregory J.; Eilts, Michael D.

    1993-01-01

    The Federal Aviation Administration's (FAA) Terminal Doppler Weather Radar (TDWR) system was primarily designed to address the operational needs of pilots in the avoidance of low-altitude wind shears upon takeoff and landing at airports. One of the primary methods of wind-shear detection for the TDWR system is the gust-front detection algorithm. The algorithm is designed to detect gust fronts that produce a wind-shear hazard and/or sustained wind shifts. It serves the hazard warning function by providing an estimate of the wind-speed gain for aircraft penetrating the gust front. The gust-front detection and wind-shift algorithms together serve a planning function by providing forecasted gust-front locations and estimates of the horizontal wind vector behind the front, respectively. This information is used by air traffic managers to determine arrival and departure runway configurations and aircraft movements to minimize the impact of wind shifts on airport capacity. This paper describes the gust-front detection and wind-shift algorithms to be fielded in the initial TDWR systems. Results of a quantitative performance evaluation using Doppler radar data collected during TDWR operational demonstrations at the Denver, Kansas City, and Orlando airports are presented. The algorithms were found to be operationally useful by the FAA airport controllers and supervisors.

  2. 75 FR 23263 - Alta Wind I, LLC; Alta Wind II, LLC; Alta Wind III, LLC; Alta Wind IV, LLC; Alta Wind V, LLC...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-05-03

    ...Alta Wind V, LLC, Alta Wind VI, LLC, Alta Wind VII, LLC, Alta Wind VIII, LLC, Alta Windpower Development, LLC...tie-lines to interconnect Petitioners' full planned wind and solar generation capacity to the integrated...

  3. 77 FR 29633 - Alta Wind VII, LLC, Alta Wind IX, LLC, Alta Wind X, LLC, Alta Wind XI, LLC, Alta Wind XII, LLC...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-05-18

    ...Alta Wind XII, LLC, Alta Wind XIII, LLC, Alta Wind XIV, LLC, Alta Wind XV, LLC, Alta Windpower Development, LLC, and...interconnect the full planned capacity of Petitioners' wind and solar generation projects to the integrated...

  4. Wind Power Career Chat

    SciTech Connect

    Not Available

    2011-01-01

    This document will teach students about careers in the wind energy industry. Wind energy, both land-based and offshore, is expected to provide thousands of new jobs in the next several decades. Wind energy companies are growing rapidly to meet America's demand for clean, renewable, and domestic energy. These companies need skilled professionals. Wind power careers will require educated people from a variety of areas. Trained and qualified workers manufacture, construct, operate, and manage wind energy facilities. The nation will also need skilled researchers, scientists, and engineers to plan and develop the next generation of wind energy technologies.

  5. Wind power today

    SciTech Connect

    NONE

    1998-04-01

    This publication highlights initiatives of the US DOE`s Wind Energy Program. 1997 yearly activities are also very briefly summarized. The first article describes a 6-megawatt wind power plant installed in Vermont. Another article summarizes technical advances in wind turbine technology, and describes next-generation utility and small wind turbines in the planning stages. A village power project in Alaska using three 50-kilowatt turbines is described. Very brief summaries of the Federal Wind Energy Program and the National Wind Technology Center are also included in the publication.

  6. Wind energy information guide

    SciTech Connect

    NONE

    1996-04-01

    This book is divided into nine chapters. Chapters 1--8 provide background and annotated references on wind energy research, development, and commercialization. Chapter 9 lists additional sources of printed information and relevant organizations. Four indices provide alphabetical access to authors, organizations, computer models and design tools, and subjects. A list of abbreviations and acronyms is also included. Chapter topics include: introduction; economics of using wind energy; wind energy resources; wind turbine design, development, and testing; applications; environmental issues of wind power; institutional issues; and wind energy systems development.

  7. On the Modeling of Nonplanar Shear Walls in Shear Wall - Frame Building Structures

    Microsoft Academic Search

    Tolga Akis; Turgut Tokdemir; Cetin Yilmaz

    The objective of this study is to model the non-planar shear walls of asymmetric shear wall-frame building structures in elastic\\u000a range. The modeling work is based on open and closed sections shear wall assemblies for which two different three-dimensional\\u000a models are developed and verified in comparison to common shear wall modeling techniques.\\u000a \\u000a Two-dimensional modeling of symmetric building structures having planar

  8. Effects of shear on vortex shedding patterns in high Reynolds number flow: an experimental study

    SciTech Connect

    none,

    1980-01-01

    Vortex shedding has been identified as a potential major source of loading on the Ocean Thermal Energy Conversion (OTEC) Plant Cold Water Pipe (CWP). To gain a better understanding of the vortex shedding phenomena, a series of model tests has been conducted. The results of this investigation are presented. The effects of current shear on vortex shedding patterns in high Reynolds number (R/sub e/) flow around a circular cylinder used to model the OTEC CWP are addressed. Tests were conducted in a wind tunnel on a 56-inch long, 6-inch diameter circular cylinder for various flow and shear conditions. Measurements were conducted to describe the frequencies of the eddies shed from the cylinder and to investigate the fluctuating surface pressure on the cylinder. From these tests it was determined that shedding for high R/sub e/ sheared flow is characterized by the formation of distinct cells of eddies with constant frequency, that pressure fluctuations on the surface of the cylinder are greater for sheared flow than unsheared flow, and that the mean surface pressures are generally independent of the magnitude of shear.

  9. Laboratory study of wind- and mechanically-generated water waves

    NASA Astrophysics Data System (ADS)

    Waseda, Takuji

    1997-09-01

    Evolution of the wind-wave spectrum and their down- shifting mechanism were studied experimentally, in both the small and the large wind-wave facilities at the Ocean Engineering Laboratory. We made observations in order to investigate: (1) the generation and evolution of the short wind waves (small facility); (2) the infuence of changes in the wind speed on the evolution of wind waves (small facility); (3) the long-time evolution of a non- linear wave train, breaking in groups, including the influence of wind pumping (large facility). We statistically analyzed the first observational results under the assumption of a stationary and Gaussian random process. We revealed that within the short fetch (0-7 m), there exist three stages: (1) initial generation of waves due to a coupled viscous shear instability (initial wavelet); (2) sudden down-shifting of energy to form a rhombic wave pattern, created possibly by the large scale turbulence; (3) growth and down-shifting of the wind-wave spectrum as a result of exchange of energy among energetic wave components in a deterministic fashion. We revealed from the second observational results that wind waves responded to the sudden changes in the wind speed with two distinct time scales, /Delta t1 and /Delta t2. The former is associated with the adjustment of wind waves to achieve a quasi-balance with the new wind speed and the latter is associated with the energy convection in a limited fetch. Some additional findings are: (1) there exists a proportionality between wind pumping and energy dissipation, which leads to a global law between wave height and wave period such as Toba's 3/2 law, satisfied by waves in a quasi-balance with wind; (2) wind wave energy convects along a ray. In the third observational study we successfully conducted an experiment of the sideband wave system with a variety of parameter combinations (ak, /delta f/f and ac/a0). We found that: (1) the breaking event causes a permanent down-shifting, while without the breaking event the wave train demodulates; (2) the existence of wind did not change the characteristics of the side band growth; (3) the inclusion of higher frequency waves is necessary for describing the long time evolution of the wave system as demonstrated by the comparison of the experimental results with the numerical solution of the weakly non-linear theory. The wind wave evolution may be governed by deterministic non-linear processes with a strong coupling of the action of wind and the energy dissipation due to wave breaking.

  10. Sand Transport by Wind on Complex Rough Surfaces: Field Studies in the McMurdo Dry Valleys, Antarctica

    NASA Astrophysics Data System (ADS)

    Lancaster, N.; Nickling, W. G.; Gillies, J. A.; Cupp, K.

    2004-12-01

    Although the physics of the movement of sand-sized particles by wind has been extensively studied, significant uncertainties remain in our understanding of the effects of surface roughness on aeolian transport processes. Accounting for the effects of non-erodible, isolated roughness elements on sediment transport by wind is necessary for the development of models that realistically predict rates of transport for complex surface types on Earth and Mars. Many surfaces in the McMurdo Dry Valleys of Antarctica exhibit a striking resemblance to rocky surfaces on Mars, making this area ideal as a Mars analog site in addition to providing fundamental information on sand transport processes in a cold arid environment. We conducted studies of sand transport rates (using both sand traps and Sensit saltation sensors), boundary layer winds, and surface shear stress at a site in the eastern part of the Victoria Valley for a 3-week period in January 2003, and generated a unique data set on temporal and spatial variations in boundary layer winds, surface shear stress, and sediment transport by wind in a natural setting. The surface in this area consists of a gently undulating sand sheet (median grain size 300 µm) with scattered clusters of poorly sorted angular boulder- and cobble-sized clasts, interspersed with patches of angular medium gravel- to cobble-sized sub-angular rock fragments. Overall roughness density for the area is 0.0039, with an average aerodynamic roughness of 0.0013 m. Surface shear stress was measured using Irwin Sensors with the total shear stress being derived from wind profile parameters. Approximately 20 percent of the regional wind shear stress interacts with the ground surface, indicating a significant partitioning of shear stress, even with a rather sparse roughness element density. Data were obtained for seven sand transport events ranging in duration from 271 to 1451 minutes. The threshold wind shear velocity for sand transport was determined via the time-fraction equivalence method of Stout and Zobeck (1997) and ranged between 0.30 and 0.35 m/s, equivalent to a wind speed at 6 m of 6.2 to 7.4 m/s. This compares to threshold wind shear velocity of 0.29 m/s calculated using the Bagnold formula. Sand transport intermittency as defined by Stout and Zobeck (1997) varied from 0.03 to 0.90, indicating considerable variations between events in the intensity of saltation and in the intermittency function. These variations can be characterized by: (1) a "saltation duration" curve - the cumulative percentage of the event at which different levels of intermittency occur and (2) the percentage of the event during which saltation is continuous (transport intermittency = 1). In turn, these parameters correlate with the overall wind conditions for the event as characterized by the ratio between wind shear velocity and threshold wind shear velocity and the percentage of the time wind shear velocity exceeds the threshold wind shear velocity. The saltation duration curve and percent of time during which saltation is continuous provide means to quantify aeolian activity at a site and can be used to compare levels of aeolian activity among different aeolian environments. Research supported by NSF OPP-0088136.

  11. A study of some effects of vertical shear on thunderstorms

    NASA Technical Reports Server (NTRS)

    Connell, J.

    1976-01-01

    Evidence is presented for the existence of vortices and vortex pairs in thunderstorms. A preliminary parameterized model of the nonthermal generation of thunderstorm vortices derived from field observations of storms and laboratory observations of a jet in crossflow is reported, together with an explanation of how such a model might be used to guide analysis of mesoscale rawinsonde, radar, and satellite data toward an improved capability for prediction of thunderstorm motion and growth. Preliminary analyses of radar and satellite data from Atmospheric Variability Experiment IV are used with available rawinsonde data to develop a correlation between wind shears, instability, and thunderstorm motion and development. Specific studies are recommended for best development of concepts and utilization of data from Atmospheric Variability and Atmospheric Variability Severe Storms Experiments.

  12. Shear strength, force distributions and friction mobilization in sheared packings composed of angular particles

    E-print Network

    Paris-Sud XI, Université de

    materials composed of pentagonal/polyhedral particles with respect to packings composed of circularShear strength, force distributions and friction mobilization in sheared packings composed angularity on the mechanical behavior of sheared granular packings. A first series of contact dynamics

  13. 2008 Wind Energy Projects, Wind Powering America (Poster)

    SciTech Connect

    Not Available

    2009-01-01

    The Wind Powering America program produces a poster at the end of every calendar year that depicts new U.S. wind energy projects. The 2008 poster includes the following projects: Stetson Wind Farm in Maine; Dutch Hill Wind Farm in New York; Grand Ridge Wind Energy Center in Illinois; Hooper Bay, Alaska; Forestburg, South Dakota; Elbow Creek Wind Project in Texas; Glacier Wind Farm in Montana; Wray, Colorado; Smoky Hills Wind Farm in Kansas; Forbes Park Wind Project in Massachusetts; Spanish Fork, Utah; Goodland Wind Farm in Indiana; and the Tatanka Wind Energy Project on the border of North Dakota and South Dakota.

  14. Shear-Stress Partitioning in Live Plant Canopies and Modifications to Raupach's Model

    NASA Astrophysics Data System (ADS)

    Walter, Benjamin; Gromke, Christof; Lehning, Michael

    2012-08-01

    The spatial peak surface shear stress {tau _S^'' on the ground beneath vegetation canopies is responsible for the onset of particle entrainment and its precise and accurate prediction is essential when modelling soil, snow or sand erosion. This study investigates shear-stress partitioning, i.e. the fraction of the total fluid stress on the entire canopy that acts directly on the surface, for live vegetation canopies (plant species: Lolium perenne) using measurements in a controlled wind-tunnel environment. Rigid, non-porous wooden blocks instead of the plants were additionally tested for the purpose of comparison since previous wind-tunnel studies used exclusively artificial plant imitations for their experiments on shear-stress partitioning. The drag partitioning model presented by Raupach (Boundary-Layer Meteorol 60:375-395, 1992) and Raupach et al. (J Geophys Res 98:3023-3029, 1993), which allows the prediction of the total shear stress ? on the entire canopy as well as the peak {(tau _S ^''/tau )^{1/2}} and the average {(tau _S^'/tau )^{1/2}} shear-stress ratios, is tested against measurements to determine the model parameters and the model's ability to account for shape differences of various roughness elements. It was found that the constant c, needed to determine the total stress ? and which was unspecified to date, can be assumed a value of about c = 0.27. Values for the model parameter m, which accounts for the difference between the spatial surface average {tau _S^' and the peak {tau _S ^'' shear stress, are difficult to determine because m is a function of the roughness density, the wind velocity and the roughness element shape. A new definition for a parameter a is suggested as a substitute for m. This a parameter is found to be more closely universal and solely a function of the roughness element shape. It is able to predict the peak surface shear stress accurately. Finally, a method is presented to determine the new a parameter for different kinds of roughness elements.

  15. Wind effects on retention time in highway ponds.

    PubMed

    Bentzen, T R; Larsen, T; Rasmussen, M R

    2008-01-01

    The paper presents results from an experimental and numerical study of wind-induced flows and transportation patterns in highway wet detention ponds. The study presented here is part of a general investigation on road runoff and pollution in respect to wet detention ponds. The objective is to evaluate the quality of long term simulations based on historical rain series of the pollutant discharges from roads and highways. The idea of this paper is to evaluate the effects of wind on the retention time and compare the retention time for the situation of a spatial uniform wind shear stress with the situation of a "real" spatial non-uniform shear stress distribution on the surface of the pond. The result of this paper shows that wind plays a dominant role for the retention time and flow pattern. Furthermore, the results shows that the differences in retention time between the use of uniform and non-uniform wind field distributions are not significant to this study. PMID:18547921

  16. Vandenberg Air Force Base Upper Level Wind Launch Weather Constraints

    NASA Technical Reports Server (NTRS)

    Shafer, Jaclyn A.; Wheeler, Mark M.

    2012-01-01

    The 30th Operational Support Squadron Weather Flight (30 OSSWF) provides comprehensive weather services to the space program at Vandenberg Air Force Base (VAFB) in California. One of their responsibilities is to monitor upper-level winds to ensure safe launch operations of the Minuteman III ballistic missile. The 30 OSSWF tasked the Applied Meteorology Unit (AMU) to analyze VAFB sounding data with the goal of determining the probability of violating (PoV) their upper-level thresholds for wind speed and shear constraints specific to this launch vehicle, and to develop a tool that will calculate the PoV of each constraint on the day of launch. In order to calculate the probability of exceeding each constraint, the AMU collected and analyzed historical data from VAFB. The historical sounding data were retrieved from the National Oceanic and Atmospheric Administration Earth System Research Laboratory archive for the years 1994-2011 and then stratified into four sub-seasons: January-March, April-June, July-September, and October-December. The maximum wind speed and 1000-ft shear values for each sounding in each subseason were determined. To accurately calculate the PoV, the AMU determined the theoretical distributions that best fit the maximum wind speed and maximum shear datasets. Ultimately it was discovered that the maximum wind speeds follow a Gaussian distribution while the maximum shear values follow a lognormal distribution. These results were applied when calculating the averages and standard deviations needed for the historical and real-time PoV calculations. In addition to the requirements outlined in the original task plan, the AMU also included forecast sounding data from the Rapid Refresh model. This information provides further insight for the launch weather officers (LWOs) when determining if a wind constraint violation will occur over the next few hours on day of launch. The interactive graphical user interface (GUI) for this project was developed in Microsoft Excel using Visual Basic for Applications. The GUI displays the critical sounding data easily and quickly for the LWOs on day of launch. This tool will replace the existing one used by the 30 OSSWF, assist the LWOs in determining the probability of exceeding specific wind threshold values, and help to improve the overall upper winds forecast for the launch customer.

  17. The formation of wind curl in the marine atmosphere boundary layer over the East China Sea Kuroshio in spring

    NASA Astrophysics Data System (ADS)

    Zhang, Suping; Kong, Yang

    2014-12-01

    Various data are used to investigate the characteristics of the surface wind field and rainfall on the East China Sea Kuroshio (ESK) in March and April, 2011. In March, the wind speed maximum shows over the ESK front (ESKF) in the 10 meter wind field, which agrees with the thermal wind effect. A wind curl center is generated on the warm flank of the ESKF. The winds are much weaker in April, so is the wind curl. A rainband exists over the ESKF in both the months. The Weather Research and Forecasting (WRF) model is used for further researches. The winds on the top of the marine atmosphere boundary layer (MABL) indicate that in March, a positive wind curl is generated in the whole MABL over the warm flank of the ESKF. The thermal wind effect forced by the strong SST gradient overlying the background wind leads to strong surface northeasterly winds on the ESKF, and a positive shearing vorticity is created over the warm flank of the ESKF to generate wind curl. In the smoothed sea surface temperature experiment, the presence of the ESKF is responsible for the strong northeast winds in the ESKF, and essential for the distribution of the rainfall centers in March, which confirms the mechanism above. The same simulation is made for April, 2011, and the responses from the MABL become weak. The low background wind speed weakens the effect of the thermal wind, thus no strong Ekman pumping is helpful for precipitation. There is no big difference in rainfall between the control run and the smooth SST run. Decomposition of the wind vector shows that local wind acceleration induced by the thermal wind effect along with the variations in wind direction is responsible for the pronounced wind curl/divergence over the ESKF.

  18. On the initiation of surface waves by turbulent shear flow

    NASA Astrophysics Data System (ADS)

    Teixeira, M. A. C.; Belcher, S. E.

    2006-02-01

    An analytical model is developed for the initial stage of surface wave generation at an air-water interface by a turbulent shear flow in either the air or in the water. The model treats the problem of wave growth departing from a flat interface and is relevant for small waves whose forcing is dominated by turbulent pressure fluctuations. The wave growth is predicted using the linearised and inviscid equations of motion, essentially following Phillips [Phillips, O.M., 1957. On the generation of waves by turbulent wind. J. Fluid Mech. 2, 417-445], but the pressure fluctuations that generate the waves are treated as unsteady and related to the turbulent velocity field using the rapid-distortion treatment of Durbin [Durbin, P.A., 1978. Rapid distortion theory of turbulent flows. PhD thesis, University of Cambridge]. This model, which assumes a constant mean shear rate ?, can be viewed as the simplest representation of an oceanic or atmospheric boundary layer. For turbulent flows in the air and in the water producing pressure fluctuations of similar magnitude, the waves generated by turbulence in the water are found to be considerably steeper than those generated by turbulence in the air. For resonant waves, this is shown to be due to the shorter decorrelation time of turbulent pressure in the air (estimated as ? 1/ ?), because of the higher shear rate existing in the air flow, and due to the smaller length scale of the turbulence in the water. Non-resonant waves generated by turbulence in the water, although being somewhat gentler, are still steeper than resonant waves generated by turbulence in the air. Hence, it is suggested that turbulence in the water may have a more important role than previously thought in the initiation of the surface waves that are subsequently amplified by feedback instability mechanisms.

  19. Bats and Wind Energy

    USGS Multimedia Gallery

    USGS biologist Paul Cryan examines the carcass of a hoary bat (Lasiurus cinereus) found beneath a wind turbine. By examining the casualties, biologists hope to learn more about why migratory bats are so susceptible to wind turbines. ...

  20. Wind Energy Facility

    USGS Multimedia Gallery

    Wind energy facility in the Northeastern United States. An unexpected number of dead bats began appearing beneath industrial-scale wind turbines in North America and Europe during the past 10 years....

  1. Solar Wind Five

    NASA Technical Reports Server (NTRS)

    Neugebauer, M. (editor)

    1983-01-01

    Topics of discussion were: solar corona, MHD waves and turbulence, acceleration of the solar wind, stellar coronae and winds, long term variations, energetic particles, plasma distribution functions and waves, spatial dependences, and minor ions.

  2. Wind Energy Benefits

    SciTech Connect

    Not Available

    2005-04-01

    Wind energy provides many benefits, including economic and environmental. This two-sided fact sheet succinctly outlines the top ten wind energy benefits and is especially well suited for general audiences.

  3. Renewable Energy: Wind

    NSDL National Science Digital Library

    John Pratte

    This lesson introduces students to the uses of wind energy. Topics include a history of wind usage (grinding grain, pumping water, transportation), including the development of wind power in the United States and its more recent adaptations for producing electricity. There is also discussion of the physics behind the operation of a windmill and what drives the wind patterns in Earth's atmosphere. The lesson includes an activity in which students use online resources to study the relationship between barometric pressure and wind speed and direction. They will collect data on barometric pressure, wind speed, and wind direction for several days, map it, and look for relationships between wind speed and direction and the isobaric lines on the map.

  4. Residential Wind Power

    E-print Network

    Willis, Gary

    2011-12-16

    This research study will explore the use of residential wind power and associated engineering and environmental issues. There is various wind power generating devices available to the consumer. The study will discuss the dependencies of human...

  5. Animated Wind Capacity Map

    NSDL National Science Digital Library

    National Renewable Energy Laboratory (NREL)

    This map shows how much electrical power is produced from wind in each state from 1999 through 2010. The animation shows a general increase in the amount of wind power produced per state and the number of states producing it.

  6. Applications of hot-film anemometers in hypersonic shear layers

    NASA Technical Reports Server (NTRS)

    Grubb, J. P.; Strike, W. T.

    1991-01-01

    A wind tunnel test was conducted on a flat plate at zero angle of attack with a rearward facing 2D cooling film injector nozzle. The freestream Mach number was 8 and the injector Mach number was 3. The freestream Reynolds number varied from 0.43 to 3.3 million per ft during the test, and the injector flow rate was such that the jet exit and freestream static pressures were matched. The analysis reported herein will focus on data obtained at a freestream Reynolds number of 0.85 million per ft. The data consists of heat-transfer measurements obtained upstream and downstream of the injector nozzle and flowfield surveys obtained downstream of the injector nozzle with a pitot, total temperature, hot-film anemometer and hot-wire anemometer probes. The flowfield surveys were made at stations 0.1 to 9 in. downstream of the injector nozzle from near the model surface to approximately 2 in above the model surface. The hot-film anemometer was used to define the fluctuations in the shear layer separating the flows. The hot-film results are integrated with conventional measurement techniques to obtain a more complete description of the complicated shear layer separating hypersonic and supersonic flows.

  7. A Convective Storm Matrix: Buoyancy/Shear Dependencies

    NSDL National Science Digital Library

    2014-09-14

    In order to help forecasters build a strategy for anticipating convective storm structures, their evolution, and the potential for severe weather, A Convective Storm Matrix provides learners the opportunity for extensive exploration of the relationship between a storm's environment and its structure. The matrix is composed of 54 four-dimensional numerical simulations based on the interactions of 16 different hodographs and 4 thermodynamic profiles. By comparing animated displays of these simulations, learners are able to discern the influences of varying buoyancy and vertical wind shear profiles on storm structure and evolution. A series of questions guides the exploration and helps to reveal key storm/environment relationships evident in the matrix. A synopsis of the physical processes that control storm structure, as well as the current conceptual models of key convective storms types, is included for reference. Subject matter expects for A Convective Storm Matrix: Buoyancy/Shear Dependencies include Mr. Steve Keighton, Mr. Ed Szoke, and Dr. Morris Weisman. Note: This module was originally published on CD-ROM in March 1996 (v1.1) and re-released in 2001 as v1.3 for Microsoft Windows users only. CD-ROM version 1.3 works fairly well with Windows 98/ME/NT4/2000 but has reported to be problematic with Windows XP. Users of version 1.1 should obtain the patch located at http://www.comet.ucar.edu/help/ModuleSupport/matrix_problem.htm or use the new, Web-based module.

  8. Wind Turbines Adaptation to the Variability of the Wind Field

    Microsoft Academic Search

    Yuriy Ulianov; Gennadii Martynenko; Vitaliy Misaylov; Iuliia Soliannikova

    2010-01-01

    WIND TURBINES ADAPTATION TO THE VARIABILITY OF THE WIND FIELD The subject of our scientific research is wind power turbines (WPT) with the horizontal axis which were now common in the world. Efficient wind turbines work is largely determined by non-stationarity of the wind field, expressed in its gustiness, the presence of vertical and horizontal shifts of wind speed and

  9. Subhourly wind forecasting techniques for wind turbine operations

    Microsoft Academic Search

    H. L. Wegley; M. R. Kosorok; W. J. Formica

    1984-01-01

    Three models for making automated forecasts of subhourly wind and wind power fluctuations were examined to determine the models' appropriateness, accuracy, and reliability in wind forecasting for wind turbine operation. Such automated forecasts appear to have value not only in wind turbine control and operating strategies, but also in improving individual wind turbine control and operating strategies, but also in

  10. The Effect of Wind-Turbine Wakes on Summertime US Midwest Atmospheric Wind Profiles as Observed with Ground-Based Doppler Lidar

    NASA Astrophysics Data System (ADS)

    Rhodes, Michael E.; Lundquist, Julie K.

    2013-07-01

    We examine the influence of a modern multi-megawatt wind turbine on wind and turbulence profiles three rotor diameters (D) downwind of the turbine. Light detection and ranging (lidar) wind-profile observations were collected during summer 2011 in an operating wind farm in central Iowa at 20-m vertical intervals from 40 to 220 m above the surface. After a calibration period during which two lidars were operated next to each other, one lidar was located approximately 2D directly south of a wind turbine; the other lidar was moved approximately 3D north of the same wind turbine. Data from the two lidars during southerly flow conditions enabled the simultaneous capture of inflow and wake conditions. The inflow wind and turbulence profiles exhibit strong variability with atmospheric stability: daytime profiles are well-mixed with little shear and strong turbulence, while nighttime profiles exhibit minimal turbulence and considerable shear across the rotor disk region and above. Consistent with the observations available from other studies and with wind-tunnel and large-eddy simulation studies, measurable reductions in wake wind-speeds occur at heights spanning the wind turbine rotor (43-117 m), and turbulent quantities increase in the wake. In generalizing these results as a function of inflow wind speed, we find the wind-speed deficit in the wake is largest at hub height or just above, and the maximum deficit occurs when wind speeds are below the rated speed for the turbine. Similarly, the maximum enhancement of turbulence kinetic energy and turbulence intensity occurs at hub height, although observations at the top of the rotor disk do not allow assessment of turbulence in that region. The wind shear below turbine hub height (quantified here with the power-law coefficient) is found to be a useful parameter to identify whether a downwind lidar observes turbine wake or free-flow conditions. These field observations provide data for validating turbine-wake models and wind-tunnel observations, and for guiding assessments of the impacts of wakes on surface turbulent fluxes or surface temperatures downwind of turbines.

  11. Effect of Shear Displacement Rate on the Internal Shear Strength of GCLs J. S. McCartney1

    E-print Network

    Zornberg, Jorge G.

    1 Effect of Shear Displacement Rate on the Internal Shear Strength of GCLs J. S. McCartney1 , J. G A series of large-scale direct shear strength tests were conducted to evaluate the effect of shear displacement rate on the internal shear strength of reinforced GCLs. Specifically, the tests were conducted

  12. THE ANALYSIS OF FACTORS INFLUENCING THE VALUES OF SOIL SHEAR STRENGTH PARAMETERS OBTAINED BY DIRECT SHEAR TEST

    Microsoft Academic Search

    GIANG NGUYEN

    2009-01-01

    The paper deals with some factors which influence the values of soil shear strength pa- rameters, obtained by direct shear test. The effects of shear speed, shear area changing, conventional test ending linear deformation as well as the number of specimens on test results have been analysed. The analysis is based on actual documents concerning direct shear test, such as

  13. Guided Tour on Wind Energy

    NSDL National Science Digital Library

    The Danish Wind Turbine Manufacturers Association provides the Guided Tour on Wind Energy site. This tour caters to both the expert and the novice of wind energy. Sections included at the site are Wind Energy Resources, Computing Wind Turbine Energy Output, How does a Wind Turbine Work?, Designing a Wind Turbine, Research and Development in Wind Energy, Wind Energy in the Electrical Grid, and Wind Energy and the Environment, among others. Each section offers detailed information as well as images and diagrams. This is a great resource for anyone interested in learning more about wind energy.

  14. BOP Shear Rams for Hydrogen Sulfide Service

    Microsoft Academic Search

    J. R. Canal

    1989-01-01

    The shear rams in a blowout preventer (BOP) are critical components of the drilling system, which is expected to shear drillpipe and to seal the wellbore in all types of drilling fluids. The brittleness of high-strength tool steels when exposed to wellbore fluids containing HâS has been recognized for many years by the drilling industry. The development in recent years

  15. SHEARED NEMATIC LIQUID CRYSTAL POLYMER MONOLAYERS

    Microsoft Academic Search

    Hongyun Wang; Hong Zhou; M. Gregory Forest

    2009-01-01

    We provide a comprehensive study on the planar (2D) orienta- tional distributions of nematic polymers under an imposed shear flow of ar- bitrary strength. We extend previous analysis for persistence of equilibria in steady shear and for transitions to unsteady limit cycles, from closure models (21) to the Doi-Hess 2D kinetic equation. A variation on the Boltzmann distri- bution analysis

  16. Study of shear-stiffened elastomers

    NASA Astrophysics Data System (ADS)

    Tian, Tongfei; Li, Weihua; Ding, Jie; Alici, Gursel; Du, Haiping

    2013-06-01

    Shear thickening fluids, which are usually concentrated colloidal suspensions composed of non-aggregating solid particles suspended in fluids, exhibit a marked increase in viscosity beyond a critical shear rate. This increased viscosity is seen as being both 'field-activated', due to the dependence on shearing rate, as well as reversible. Shear thickening fluids have found good applications as protection materials, such as in liquid body armor, vibration absorber or dampers. This research aims to expand the protection material family by developing a novel solid status shear thickening material, called shear-stiffened elastomers. These new shear-stiffened elastomers were fabricated with the mixture of silicone rubber and silicone oil. A total of four SSE samples were fabricated in this study. Their mechanical and rheological properties under both steady-state and dynamic loading conditions were tested with a parallel-plate. The effects of silicone oil composition and angular frequency were summarized. When raising the angular frequency in dynamic shear test, the storage modulus of conventional silicone rubber shows a small increasing trend with the frequency. However, if silicone oil is selected to be mixed with silicone rubber, the storage modulus increases dramatically when the frequency and strain are both beyond the critical values.

  17. Shear Stress Evaluation of Plastic Packages

    Microsoft Academic Search

    D. Edwards; K. GAIL HEINEN; STEVEN K. GROOTHUIS; JESUS E. MARTINEZ

    1987-01-01

    A study has been performed to determine the impact of package assembly on shear stress phenomena in plastic encapsulated integrated circuits (IC's). Test structures were used which allowed quantitative measurements of compressive stresses along with qualitative observation of shear Stress effects. Results from experiments with various mold compounds, lead frame materials, and mount compounds Will be presented. The experiments led

  18. Shear properties of a magnetorheological elastomer

    Microsoft Academic Search

    G Y Zhou

    2003-01-01

    This paper presents an experiment testing the damped free vibration of a system composed of a magnetorheological elastomer and a mass. The goal of this experiment was to obtain the dependence of the natural frequency and the damping ratio of the structure on the applied magnetic field. The shear properties, including the shear storage modulus and the damping factor, were

  19. Structure and dynamics of sheared mantle plumes

    Microsoft Academic Search

    Ross C. Kerr; Catherine Mériaux

    2004-01-01

    An extensive series of laboratory experiments is used to investigate the behavior of sheared thermal plumes. The plumes are generated by heating a small circular plate on the base of a cylindrical tank filled with viscous fluid and then sheared by rotating a horizontal lid at the fluid surface. The motion of passive tracers in the plumes is visualized by

  20. Shear buckling of square perforated plates

    NASA Technical Reports Server (NTRS)

    Grosskurth, J. F., Jr.; White, R. N.; Gallagher, R. H.; Thomas, G. R.

    1974-01-01

    The behavior of thin square perforated plates under the action of uniform shear deformation is studied experimentally and analytically using finite element analysis. Elastic Shear buckling strength is established as a function of the diameter of a round, centrally located hole in the plate. Post buckling behavior and the behavior of perforated plates with various ring stiffeners are also studied experimentally.

  1. Shear stress in atherosclerotic plaque determination.

    PubMed

    Li, Xiaohong; Yang, Qin; Wang, Zuo; Wei, Dangheng

    2014-12-01

    Atherosclerosis initiates at predictable focal sites near arterial branches and curves, where blood flow is disturbed and shear stress is complex. Endothelial shear stress is the tangential stress derived from the friction of the flowing blood on the endothelial surface of the arterial wall. It is a key factor in modulating endothelial cell gene expression and vascular development and remodeling. Increasing evidences suggest that shear stress patterns have a strong relationship with atherosclerotic features. Moreover, variations in the local artery geometry during atherogenesis further modify flow shear stress characteristics, which contribute to the rupture site at the plaque upstream. In this study, we summarize the mechanistic evidences that associate shear stress patterns with determined atherosclerotic plaque features. An enhanced understanding of the relationship and pathophysiological function of shear stress patterns in atherosclerotic plaque features is essential, which may provide early prediction of clinical risk and guide individualized treatment strategies. In the current review, we analyzed the function of shear stress on the determination of atherosclerotic lesion and provided an update on the mechanotransduction of shear stress, gene expression regulation, and atherosclerotic plaque development and rupture. PMID:25165867

  2. Reliability analysis of shear wall structures

    Microsoft Academic Search

    P. C. Wang; H. Hwang; J. Pires; K. Nakai; M. Reich

    1986-01-01

    This report describes a method for the assessment of the reliability of low-rise shear wall structures, which are often used in nuclear power plants. The shear walls are modeled by stick models with beam elements, and are subjected to dead load, live load and earthquake during their lifetimes. The earthquake load is assumed to be a segment of a stationary

  3. Tensile and shear strength of adhesives

    NASA Technical Reports Server (NTRS)

    Stibolt, Kenneth A.

    1990-01-01

    This experiment is conducted in a freshman-level course: Introduction to Engineering Materials. There are no prerequisites for the course although students should have some knowledge of basic algebra. The objectives are to tension and shear test adhesives and to determine the tensile and shear properties of adhesives. Details of equipment of procedure are given.

  4. Method and apparatus for shear wave logging

    Microsoft Academic Search

    J. R. Hopkins; C. E. Payton; K. H. Waters

    1983-01-01

    A method and apparatus for shear wave logging which utilizes relatively high frequency sweep control transmission and subsequent correlation of received signals in order to define travel times of horizontally polarized shear and\\/or torsional wave energy. The apparatus includes specific sonde structure for effecting firm contact of transmitting and receiving elements with the borehole wall.

  5. Method and apparatus for shear wave logging

    SciTech Connect

    Hopkins, J.R.; Payton, C.E.; Waters, K.H.

    1983-04-19

    A method and apparatus for shear wave logging which utilizes relatively high frequency sweep control transmission and subsequent correlation of received signals in order to define travel times of horizontally polarized shear and/or torsional wave energy. The apparatus includes specific sonde structure for effecting firm contact of transmitting and receiving elements with the borehole wall.

  6. HDPE geomembrane\\/geotextile interface shear strength

    Microsoft Academic Search

    Timothy D. Stark; H. T. Eid; T. A. Williamson

    1996-01-01

    This paper describes torsional ring shear tests on interfaces comprised of high-density polyethylene (HDPE) geomembranes\\/nonwoven geotextiles and a drainage geocomposite. Four textured geomembranes with three different manufacturing techniques are utilized to investigate the effect of geomembrane texturing on interface shear resistance. In addition, the effects of geotextile fiber type, fabric style, polymer composition, calendering, and mass per unit area on

  7. Research on shear strength of galvannealed coatings

    Microsoft Academic Search

    Chun Xu; Z. Q. Lin; S. H. Li; W. G. Zhang

    2007-01-01

    Lap shear test can be generally performed by two kinds of methods. However, the shear strengths measured in both methods (bare and compound sample) may be quite different, which results in some influence on evaluating powdering of galvannealed coating. Samples in uniaxial tensile test are modified to measure their yield stress. The stress–strain curves in tensile test are compared with

  8. Multiple Shear Key Connections for Precast

    E-print Network

    to the high quality control that is achieved at the man ufacturing plant, and the ease and speed of panel for elevator shaft shear wall panelsOne of the main concerns in precast 104 #12;utilize a combination wall panel, as shown in Fig. 1. In addition, the continuity bar and mechanical shear connector system

  9. Dynamic wetting of shear thinning fluids

    NASA Astrophysics Data System (ADS)

    Seevaratnam, G. K.; Suo, Y.; Ramé, E.; Walker, L. M.; Garoff, S.

    2007-01-01

    The impact of non-Newtonian behavior on dynamic wetting is critical since many fluids exhibit such behavior somewhere in the high-shear environment inherent in the wedge flow near a moving contact line. This impact will be different for two broad categories of non-Newtonian behavior, shear thinning, and elasticity. In this paper, we discuss the steady-state wetting of a fluid, aqueous solutions of xanthan gum, dominated by shear thinning but with negligible elasticity. In the shear thinning fluid, viscous bending near the contact line is greatly reduced compared to a Newtonian fluid having the same zero-shear viscosity. Concomitant with this reduction in viscous bending, the effective dynamic contact angle has a much weaker dependence on capillary number, Ca, than is observed in, or predicted for, Newtonian fluids. A simple lubrication model using a constitutive relation with power-law shear thinning at high shear rates and a Newtonian plateau at low shear rates mimics the trends seen in our data and elucidates the origins of the reduced viscous bending.

  10. Dependence of Wind Turbine Curves on Atmospheric Stability Regimes - An Analysis of a West Coast North American Tall Wind Farm

    SciTech Connect

    Wharton, S; Lundquist, J K; Sharp, J; Zulauf, M

    2009-08-24

    Tall wind turbines, with hub heights at 80 m or above, can extract large amounts of energy from the atmosphere because they are likely to encounter higher wind speeds, but they face challenges given the complex nature of wind flow in the boundary layer. Depending on whether the boundary layer is stable, convective or neutral, mean wind speed (U) and turbulence ({sigma}{sub U}) may vary greatly across the tall turbine swept area (40 m to 120 m). This variation can cause a single turbine to produce difference amounts of power during time periods of identical hub height wind speeds. The study examines the influence that atmospheric mixing or stability has on power output at a West Coast North American wind farm. They first examine the accuracy and applicability of two, relatively simple stability parameters, the wind shear-exponent, {alpha}, and the turbulence intensity, I{sub u}, against the physically-based, Obukhov length, L, to describe the wind speed and turbulence profiles in the rotor area. In general, the on-site stability parameters {alpha} and I{sub u} are in high agreement with the off-site, L stability scale parameter. Next, they divide the measurement period into five stability classes (strongly stable, stable, neutral, convective, and strongly convective) to discern stability-effects on power output. When only the mean wind speed profile is taken into account, the dependency of power output on boundary layer stability is only subtly apparent. When turbulence intensity I{sub u} is considered, the power generated for a given wind speed is twenty percent higher during strongly stable conditions than during strongly convective conditions as observed in the spring and summer seasons at this North American wind farm.

  11. Shear viscosity of pion gas

    E-print Network

    Eiji Nakano

    2007-03-21

    Using chiral perturbation theory we investigate the QCD shear viscosity ($\\eta $) to entropy density ($s$) ratio below the deconfinement temperature ($\\sim 170$ MeV) with zero baryon number density. It is found that $\\eta /s$ of QCD is monotonically decreasing in temperature ($T$) and reaches 0.6 with estimated $\\sim 50%$ uncertainty at T=120 MeV. A naive extrapolation of the leading order result shows that $\\eta /s$ reaches the $1/4\\pi $ minimum bound proposed by Kovtun, Son, and Starinets using string theory methods at $T\\sim 210$ MeV. This suggests a phase transition or cross over might occur at $T\\lesssim 210$ MeV in order for the bound to remain valid. Also, it is natural for $\\eta /s$ to stay close to the minimum bound around the phase transition temperature as was recently found in heavy ion collisions.

  12. Steel Shear Walls, Behavior, Modeling and Design

    NASA Astrophysics Data System (ADS)

    Astaneh-Asl, Abolhassan

    2008-07-01

    In recent years steel shear walls have become one of the more efficient lateral load resisting systems in tall buildings. The basic steel shear wall system consists of a steel plate welded to boundary steel columns and boundary steel beams. In some cases the boundary columns have been concrete-filled steel tubes. Seismic behavior of steel shear wall systems during actual earthquakes and based on laboratory cyclic tests indicates that the systems are quite ductile and can be designed in an economical way to have sufficient stiffness, strength, ductility and energy dissipation capacity to resist seismic effects of strong earthquakes. This paper, after summarizing the past research, presents the results of two tests of an innovative steel shear wall system where the boundary elements are concrete-filled tubes. Then, a review of currently available analytical models of steel shear walls is provided with a discussion of capabilities and limitations of each model. We have observed that the tension only "strip model", forming the basis of the current AISC seismic design provisions for steel shear walls, is not capable of predicting the behavior of steel shear walls with length-to-thickness ratio less than about 600 which is the range most common in buildings. The main reasons for such shortcomings of the AISC seismic design provisions for steel shear walls is that it ignores the compression field in the shear walls, which can be significant in typical shear walls. The AISC method also is not capable of incorporating stresses in the shear wall due to overturning moments. A more rational seismic design procedure for design of shear walls proposed in 2000 by the author is summarized in the paper. The design method, based on procedures used for design of steel plate girders, takes into account both tension and compression stress fields and is applicable to all values of length-to-thickness ratios of steel shear walls. The method is also capable of including the effect of overturning moments and any normal forces that might act on the steel shear wall.

  13. Wind energy systems

    Microsoft Academic Search

    R. D. Richardson; GERALD M. MCNERNEY

    1993-01-01

    Wind energy has matured to a level of development where it is ready to become a generally accepted utility generation technology. A brief discussion of this development is presented, and the operating and design principles are discussed. Alternative designs for wind turbines and the tradeoffs that must be considered are briefly compared. Development of a wind energy system and the

  14. Large wind turbine generators

    NASA Technical Reports Server (NTRS)

    Thomas, R. L.; Donovon, R. M.

    1978-01-01

    The development associated with large wind turbine systems is briefly described. The scope of this activity includes the development of several large wind turbines ranging in size from 100 kW to several megawatt levels. A description of the wind turbine systems, their programmatic status and a summary of their potential costs is included.

  15. Wind motor machine

    Microsoft Academic Search

    Goedecke

    1984-01-01

    An improved wind motor machine having a wind rotor rotatable about a vertical axis. The rotor core body of the machine is provided with convexly curved wind application surfaces and coacting outer wing bodies having load supporting airplane wing-shaped cross-sections. The efficiency of the machine is improved by means of stream guiding bodies disposed in the intermediate space between the

  16. The winds of change

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Wind-based power generation has been growing steadily in the United States and around the world, and this growth will continue—and accelerate—in the future, as the following background statistics demonstrate. The U.S. wind industry installed 8,358 megawatts (MW) of new wind generating capacity in 20...

  17. Wind Economic Development (Postcard)

    SciTech Connect

    Not Available

    2011-08-01

    The U.S. Department of Energy's Wind Powering America initiative provides information on the economic development benefits of wind energy. This postcard is a marketing piece that stakeholders can provide to interested parties; it will guide them to the economic development benefits section on the Wind Powering America website.

  18. Wind Powering America

    NSDL National Science Digital Library

    NREL

    This visualization is a utility-scale, land-based, 80-meter wind map. It states, utilities, and wind energy developers use to locate and quantify the wind resource, identifying potentially windy sites within a fairly large region and determining a potential site's economic and technical viability.

  19. Hurricanes, Wind, and Water

    NSDL National Science Digital Library

    In this activity, learners will analyze hurricane data, specifically wind speed data and infrared satellite images, to look for evidence of a relationship between wind speed and cloud-top temperature, and between wind speed and surface type. A link to the data is provided. This activity is part of Event-Based Science (EBS): Remote Sensing Activities.

  20. Energy from the Wind

    ERIC Educational Resources Information Center

    Pelka, David G.; And Others

    1978-01-01

    The large-scale generation of electrical power by wind turbine fields is discussed. It is shown that the maximum power that can be extracted by a wind turbine is 16/27 of the power available in the wind. (BB)

  1. Power from the Wind

    ERIC Educational Resources Information Center

    Roman, Harry T.

    2004-01-01

    Wind energy is the fastest-growing renewable energy source in the world. Over the last 20 years, the wind industry has done a very good job of engineering machines, improving materials, and economies of production, and making this energy source a reality. Like all renewable energy forms, wind energy's successful application is site specific. Also,…

  2. Wind farm electrical system

    DOEpatents

    Erdman, William L.; Lettenmaier, Terry M.

    2006-07-04

    An approach to wind farm design using variable speed wind turbines with low pulse number electrical output. The output of multiple wind turbines are aggregated to create a high pulse number electrical output at a point of common coupling with a utility grid network. Power quality at each individual wind turbine falls short of utility standards, but the aggregated output at the point of common coupling is within acceptable tolerances for utility power quality. The approach for aggregating low pulse number electrical output from multiple wind turbines relies upon a pad mounted transformer at each wind turbine that performs phase multiplication on the output of each wind turbine. Phase multiplication converts a modified square wave from the wind turbine into a 6 pulse output. Phase shifting of the 6 pulse output from each wind turbine allows the aggregated output of multiple wind turbines to be a 24 pulse approximation of a sine wave. Additional filtering and VAR control is embedded within the wind farm to take advantage of the wind farm's electrical impedence characteristics to further enhance power quality at the point of common coupling.

  3. Build a Wind Turbine

    NSDL National Science Digital Library

    Museum of Science and Industry, Chicago

    2012-01-01

    Learners build a wind turbine and test it to see how much energy is created. Learners can build a variety of wind blades, test a variety of wind speeds and see what effect these have on the energy created. Adult supervision recommended.

  4. Wind Power Now!

    ERIC Educational Resources Information Center

    Inglis, David Rittenhouse

    1975-01-01

    The government promotes and heavily subsidizes research in nuclear power plants. Federal development of wind power is slow in comparison even though much research with large wind-electric machines has already been conducted. Unless wind power programs are accelerated it will not become a major energy alternative to nuclear power. (MR)

  5. Wind power outlook 2006

    SciTech Connect

    anon.

    2006-04-15

    This annual brochure provides the American Wind Energy Association's up-to-date assessment of the wind industry in the United States. This 2006 general assessment shows positive signs of growth, use and acceptance of wind energy as a vital component of the U.S. energy mix.

  6. Wind energy in Turkey

    Microsoft Academic Search

    Mehmet Hana?asio?lu

    1999-01-01

    Wind and wind energy has always played an important role in the historical and economical development of Asia Minor and the geographical area covered by the Republic of Turkey today. The ancient city of Troia probably became rich with harbor fees from commercial vessels, which could not sail up the Dardanelles because of strong north-easterly winds and swift currents. As

  7. Determining Shear Stress Distribution in a Laminate

    NASA Technical Reports Server (NTRS)

    Bednarcyk, Brett A.; Aboudi, Jacob; Yarrington, Phillip W.

    2010-01-01

    A "simplified shear solution" method approximates the through-thickness shear stress distribution within a composite laminate based on an extension of laminated beam theory. The method does not consider the solution of a particular boundary value problem; rather, it requires only knowledge of the global shear loading, geometry, and material properties of the laminate or panel. It is thus analogous to lamination theory in that ply-level stresses can be efficiently determined from global load resultants at a given location in a structure and used to evaluate the margin of safety on a ply-by-ply basis. The simplified shear solution stress distribution is zero at free surfaces, continuous at ply boundaries, and integrates to the applied shear load. The method has been incorporated within the HyperSizer commercial structural sizing software to improve its predictive capability for designing composite structures. The HyperSizer structural sizing software is used extensively by NASA to design composite structures. In the case of through-thickness shear loading on panels, HyperSizer previously included a basic, industry-standard, method for approximating the resulting shear stress distribution in sandwich panels. However, no such method was employed for solid laminate panels. The purpose of the innovation is to provide an approximation of the through-thickness shear stresses in a solid laminate given the through-thickness shear loads (Qx and Qy) on the panel. The method was needed for implementation within the HyperSizer structural sizing software so that the approximated ply-level shear stresses could be utilized in a failure theory to assess the adequacy of a panel design. The simplified shear solution method was developed based on extending and generalizing bi-material beam theory to plate-like structures. It is assumed that the through-thickness shear stresses arise due to local bending of the laminate induced by the through-thickness shear load, and by imposing equilibrium both vertically and horizontally, the through-thickness shear stress distribution can be calculated. The resulting shear stresses integrate to the applied shear load, are continuous at the ply interfaces, and are zero at the laminate-free surfaces. If both Qx and Qy shear loads are present, it is assumed that they act independently and that their effects can be superposed. The calculated shear stresses can be rotated within each ply to the principal material coordinates for use in a ply-level failure criterion. The novelty of the simplified shear solution method is its simplicity and the fact that it does not require solution of a particular boundary value problem. The advantages of the innovation are that an approximation of the though-thickness shear stress distribution can be quickly determined for any solid laminate or solid laminate region within a stiffened panel.

  8. Dynamic Jamming Point for Shear Thickening Suspensions

    NASA Astrophysics Data System (ADS)

    Brown, Eric; Jaeger, Heinrich M.

    2009-08-01

    We report on rheometry measurements to characterize the critical behavior in two model shear thickening suspensions: cornstarch in water and glass spheres in oil. The slope of the shear thickening part of the viscosity curve is found to increase dramatically with packing fraction and diverge at a critical packing fraction ?c. The magnitude of the viscosity and the yield stress are also found to have scalings that diverge at ?c. We observe shear thickening as long as the yield stress is less than the stress at the viscosity maximum. Above this point the suspensions transition to purely shear thinning. Based on these data we present a dynamic jamming phase diagram for suspensions and show that a limiting case of shear thickening corresponds to a jammed state.

  9. The Dynamics of Granular Shear Flow: Experiments

    NASA Astrophysics Data System (ADS)

    Gollub, J. P.; Losert, W.; Bocquet, L.; Schalk, D.

    2000-11-01

    We have measured quantitatively the velocity and fluctuation profiles, and the internally generated shear forces, for a granular shear flow in a Couette geometry. The tangential velocity V(y) declines approximately exponentially with distance y from the moving wall. The velocity fluctuations ? V(y) decline also, but more slowly with y. We find that ? V(y) varies as a power law of the local velocity gradient. The shear force is approximately independent of shear rate. A levitating air flow is used to reduce the effective pressure within the material. The shear force decreases approximately linearly with increasing air flow and vanishes at the onset of "bubbling". We find excellent agreement between these experimental results and a locally Newtonian continuum model of granular flow.(W. Losert, L. Bocquet, T.C. Lubensky, and J.P. Gollub, Phys. Rev. Lett. 85), (2000), in press; L. Bocquet, W. Losert, T.C. Lubensky, and J.P. Gollub, to be submitted.

  10. Three dimensional fabric evolution of sheared sand

    SciTech Connect

    Hasan, Alsidqi; Alshibli, Khalid (UWA)

    2012-10-24

    Granular particles undergo translation and rolling when they are sheared. This paper presents a three-dimensional (3D) experimental assessment of fabric evolution of sheared sand at the particle level. F-75 Ottawa sand specimen was tested under an axisymmetric triaxial loading condition. It measured 9.5 mm in diameter and 20 mm in height. The quantitative evaluation was conducted by analyzing 3D high-resolution x-ray synchrotron micro-tomography images of the specimen at eight axial strain levels. The analyses included visualization of particle translation and rotation, and quantification of fabric orientation as shearing continued. Representative individual particles were successfully tracked and visualized to assess the mode of interaction between them. This paper discusses fabric evolution and compares the evolution of particles within and outside the shear band as shearing continues. Changes in particle orientation distributions are presented using fabric histograms and fabric tensor.

  11. Controlling colloidal sedimentation using time dependent shear

    E-print Network

    Matthias Krüger; Joseph M. Brader

    2011-09-10

    Employing a recently developed dynamical density functional theory we study the response of a colloidal sediment above a wall to shear, demonstrating the time dependent changes of the density distribution and its center-of-mass after switching shear either on or off and under oscillatory shear. Following the onset of steady shear we identify two dynamical mechanisms, distinguished by their timescales. Shortly after the onset, a transient enhancement of the packing structure at the wall reflects the self-organization into lanes. On a much longer timescale these effects are transmitted to the bulk, leading to migration away from the wall and an increase in the center-of-mass. Under oscillatory shear flow the center-of-mass enters a stationary state, reminiscent of a driven damped oscillator.

  12. Evolution of slip surface roughness through shear

    NASA Astrophysics Data System (ADS)

    Davidesko, Guy; Sagy, Amir; Hatzor, Yossef H.

    2014-03-01

    A significant part of displacement in fault zones occurs along discrete shear surfaces. The evolution of fault surface topography is studied here in direct shear laboratory experiments. Matching tensile fracture surfaces were sheared under imposed constant normal stress and sliding velocity. The roughness evolution was analyzed using measurements of surface topography before and after slip. We show that shearing reduces the initial surface roughness at all measurement scales. At all wavelengths, the roughness ratio between initial and final roughness increases as a function of the slip distance. For a given test, the roughness ratio increases with wavelength up to a few millimeters, beyond which the ratio becomes wavelength independent. At this region the roughness measured after slip follows a power law similar to that of the initial tensile fracture surface. We interpret this geometrical evolution as a consequence of the deformation stage of interlocked asperities which is followed by shear-induced dilation.

  13. Shear layer excitation, experiment versus theory

    NASA Technical Reports Server (NTRS)

    Bechert, D. W.; Stahl, B.

    1984-01-01

    The acoustical excitation of shear layers is investigated. Acoustical excitation causes the so-called orderly structures in shear layers and jets. Also, the deviations in the spreading rate between different shear layer experiments are due to the same excitation mechanism. Measurements in the linear interaction region close to the edge from which the shear layer is shed are examined. Two sets of experiments (Houston 1981 and Berlin 1983/84) are discussed. The measurements were carried out with shear layers in air using hot wire anemometers and microphones. The agreement between these measurements and the theory is good. Even details of the fluctuating flow field correspond to theoretical predictions, such as the local occurrence of negative phase speeds.

  14. Shear Senses and Viscous Dissipation of Layered Ductile Simple Shear Zones

    NASA Astrophysics Data System (ADS)

    Mulchrone, Kieran F.; Mukherjee, Soumyajit

    2015-02-01

    Velocity profiles and shear heat profiles for inclined, layered Newtonian simple shear zones are considered. Reverse fault-like simple shear of the boundaries and upward net pressure gradient act together in such shear zones. As the velocity of the boundary increases, the point of highest velocity shifts from the lower layer of less viscosity into the upper layer. The shear heat profile shows a temperature peak inside the lower layer. For a more viscous upper layer, the point of highest velocity is located inside the upper layer and shifts towards the upper boundary of the shear zone. The shear heat profile shows a maximum temperature within the upper layer. Depending on the flow parameters of the two layers, the slip rate of the boundary, and the dip and thickness of the shear zone, a shear sense in reverse to the relative movement of the shear zone boundaries may develop. These models can decipher thermo-kinematics of layered shear zones in plate-scale hot orogens.

  15. Validity of Measurement of Shear Modulus by Ultrasound Shear Wave Elastography in Human Pennate Muscle

    PubMed Central

    Miyamoto, Naokazu; Hirata, Kosuke; Kanehisa, Hiroaki; Yoshitake, Yasuhide

    2015-01-01

    Ultrasound shear wave elastography is becoming a valuable tool for measuring mechanical properties of individual muscles. Since ultrasound shear wave elastography measures shear modulus along the principal axis of the probe (i.e., along the transverse axis of the imaging plane), the measured shear modulus most accurately represents the mechanical property of the muscle along the fascicle direction when the probe’s principal axis is parallel to the fascicle direction in the plane of the ultrasound image. However, it is unclear how the measured shear modulus is affected by the probe angle relative to the fascicle direction in the same plane. The purpose of the present study was therefore to examine whether the angle between the principal axis of the probe and the fascicle direction in the same plane affects the measured shear modulus. Shear modulus in seven specially-designed tissue-mimicking phantoms, and in eleven human in-vivo biceps brachii and medial gastrocnemius were determined by using ultrasound shear wave elastography. The probe was positioned parallel or 20° obliquely to the fascicle across the B-mode images. The reproducibility of shear modulus measurements was high for both parallel and oblique conditions. Although there was a significant effect of the probe angle relative to the fascicle on the shear modulus in human experiment, the magnitude was negligibly small. These findings indicate that the ultrasound shear wave elastography is a valid tool for evaluating the mechanical property of pennate muscles along the fascicle direction. PMID:25853777

  16. Analysis of in-flight winds for shuttle Mission STS 51-L

    NASA Technical Reports Server (NTRS)

    Fichtl, George H.; Reynolds, Nathaniel D.; Johnston, Alan E.; Adelfang, Stanley I.; Batts, Wade

    1988-01-01

    Television photos of smoke plumes are analyzed to estimate meridional wind shear on the space shuttle Challenger associated with the accident of Mission 51-L. Gust velocities were obtained by detailed examination of the debris trails. The shuttle exhaust trail was used to establish altitudes of significant features in the photographs. Wind data obtained from the photographs compare favorably with data obtained from a rawinsonde released 9 min after the launch of the shuttle.

  17. Analysis of In-Flight Winds for Shuttle Mission STS 51-L.

    NASA Astrophysics Data System (ADS)

    Fichtl, George H.; Reynolds, Nathaniel D.; Johnston, Alan E.; Adelfang, Stanley I.; Batts, Wade; Lott, Larry; Meyer, Paul J.; Smith, Orvel E.; Swint, Marion S.; Vaughan, Otha H., Jr.

    1988-11-01

    Television photos of smoke plumes an analyzed to estimate meridional wind shear on the space shuttle Challenger associated with the accident of Mission 51-L. Gust velocities were obtained by detailed examination of the debris trails. The shuttle exhaust trail was used to establish altitudes of significant features in the photographs. Wind data obtained from the photographs compare favorably with data obtained from a rawinsonde released 9 min after the launch of the shuttle.

  18. Controlled normal/shear loading and shear fracture in bulk metallic glasses

    SciTech Connect

    Hsueh, Chun-Hway [ORNL; Bei, Hongbin [ORNL; Liu, Chain T [ORNL; George, Easo P [ORNL; Becher, Paul F [ORNL

    2009-01-01

    Limited plasticity inhibits the engineering applications of bulk metallic glasses (BMGs), which often deform by the formation of localized shear bands. Overcoming the brittleness of BMGs necessitates advances in our understanding of the mechanisms of shear band initiation and propagation. Up to now, a major hurdle has been the ability to control the generation of shear bands and the associated fracture (e.g., by conventional uniaxial loading). Here we demonstrate a unique loading fixture that allows one not only to control the locations of shear band formation and shear fracture but also to alter the ratio of the normal to shear stress on the fracture plane. The capability of altering the stress ratio allows one to systematically examine how the normal stress affects shear fracture of BMGs. While some preliminary results with limited data have been presented in a prior publication, a comprehensive description of the unique test fixture is described here.

  19. Reversible shear thickening at low shear rates of electrorheological fluids under electric fields.

    PubMed

    Tian, Yu; Zhang, Minliang; Jiang, Jile; Pesika, Noshir; Zeng, Hongbo; Israelachvili, Jacob; Meng, Yonggang; Wen, Shizhu

    2011-01-01

    By shearing electrorheological (ER) fluids between two concentric cylinders, we show a reversible shear thickening of ER fluids above a low critical shear rate (<1?s(-1)) and a high critical electric field strength (>100 V/mm), which can be characterized by a critical apparent viscosity. Shear thickening and electrostatic particle interaction-induced interparticle friction forces are considered to play an important role in the origin of lateral shear resistance of ER fluids, while the applied electric field controls the extent of shear thickening. The electric-field-controlled reversible shear thickening has implications for high-performance electrorheological-magnetorheological fluid design, clutch fluids with high friction forces triggered by applying a local electric field, other field-responsive materials, and intelligent systems. PMID:21405692

  20. Why do meteorologists use wind vanes? Wind vanes are used to determine the direction of the wind. Wind

    E-print Network

    Nebraska-Lincoln, University of

    Fun Facts Why do meteorologists use wind vanes? Wind vanes are used to determine the direction of the wind. Wind· vanes are also called weather vanes. What do wind vanes look like on a weather station? Wind vanes that are on weather stations look a lot like the one you· made! The biggest differences

  1. 49 CFR 230.27 - Maximum shearing strength of rivets.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... Boilers and Appurtenances Strength of Materials § 230.27 Maximum shearing strength of rivets. The maximum shearing strength of rivets per square inch of...square inch Iron Rivets in Single Shear 38,000 Iron Rivets in...

  2. 49 CFR 230.27 - Maximum shearing strength of rivets.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... Boilers and Appurtenances Strength of Materials § 230.27 Maximum shearing strength of rivets. The maximum shearing strength of rivets per square inch of...square inch Iron Rivets in Single Shear 38,000 Iron Rivets in...

  3. 49 CFR 230.27 - Maximum shearing strength of rivets.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... Boilers and Appurtenances Strength of Materials § 230.27 Maximum shearing strength of rivets. The maximum shearing strength of rivets per square inch of...square inch Iron Rivets in Single Shear 38,000 Iron Rivets in...

  4. 49 CFR 230.27 - Maximum shearing strength of rivets.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... Boilers and Appurtenances Strength of Materials § 230.27 Maximum shearing strength of rivets. The maximum shearing strength of rivets per square inch of...square inch Iron Rivets in Single Shear 38,000 Iron Rivets in...

  5. Characteristic modes and evolution processes of shear-layer vortices in an elevated transverse jet

    NASA Astrophysics Data System (ADS)

    Huang, Rong F.; Lan, Jen

    2005-03-01

    Characteristics and evolution processes of the traveling coherent flow structure in the shear layer of an elevated round jet in crossflow are studied experimentally in an open-loop wind tunnel. Streak pictures of the smoke flow patterns illuminated by the laser-light sheet in the median and horizontal planes are recorded with a high speed digital camera. Time histories of the instantaneous velocity of the vortical flows in the shear layer are digitized by a hot-wire anemometer through a high-speed data acquisition system. By analyzing the streak pictures of the smoke flow visualization, five characteristic flow structures, mixing-layer type vortices, backward-rolling vortices, forward-rolling vortices, swing-induced mushroom vortices, and jet-type vortices, are identified in the shear layer evolving from the up-wind edge of the jet exit. The behaviors and mechanisms of the vortical flow structure in the bent shear layer are prominently distinct in different flow regimes. The frequency characteristics, Strouhal number, power-spectrum density functions, autocorrelation coefficient, as well as the time and length scales of the coherent structure and the Lagrangian integral scales are obtained by processing the measured instantaneous velocity data. The Strouhal number is found to decay exponentially with the increase of the jet-to-crossflow momentum flux ratio. The autocorrelation coefficients provide the information for calculating the statistical time scales of the coherent structure and the integral time scales of turbulence fluctuations. The corresponding length scales of the vortical structure and the integral length scales of turbulence in the shear layer are therefore obtained and discussed.

  6. Wind Turbine Structural Dynamics

    NASA Technical Reports Server (NTRS)

    Miller, D. R. (editor)

    1978-01-01

    A workshop on wind turbine structural dynamics was held to review and document current United States work on the dynamic behavior of large wind turbines, primarily of the horizontal-axis type, and to identify and discuss other wind turbine configurations that may have lower cost and weight. Information was exchanged on the following topics: (1) Methods for calculating dynamic loads; (2) Aeroelasticity stability (3) Wind loads, both steady and transient; (4) Critical design conditions; (5) Drive train dynamics; and (6) Behavior of operating wind turbines.

  7. Wind energy applications guide

    SciTech Connect

    anon.

    2001-01-01

    The brochure is an introduction to various wind power applications for locations with underdeveloped transmission systems, from remote water pumping to village electrification. It includes an introductory section on wind energy, including wind power basics and system components and then provides examples of applications, including water pumping, stand-alone systems for home and business, systems for community centers, schools, and health clinics, and examples in the industrial area. There is also a page of contacts, plus two specific example applications for a wind-diesel system for a remote station in Antarctica and one on wind-diesel village electrification in Russia.

  8. User's guide for a personal computer model of turbulence at a wind turbine rotor

    SciTech Connect

    Connell, J.R.; Powell, D.C.; Gower, G.L.

    1989-08-01

    This document is primarily (1) a user's guide for the personal computer (PC) version of the code for the PNL computational model of the rotationally sampled wind speed (RODASIM11) and (2) a brief guide to the growing literature on the subject of rotationally sampled turbulence, from which the model is derived. The model generates values of turbulence experienced by single points fixed in the rotating frame of reference of an arbitrary wind turbine blade. The character of the turbulence depends on the specification of mean wind speed, the variance of turbulence, the crosswind and along-wind integral scales of turbulence, mean wind shear, and the hub height, radius, and angular speed of rotation of any point at which wind fluctuation is to be calculated. 13 refs., 4 figs., 4 tabs.

  9. Results from utility wind resource assessment programs in Nebraska, Colorado, and Arizona

    SciTech Connect

    Drapeau, C.L. [Global Energy Concepts, Inc., Bothell, WA (United States)

    1997-12-31

    Global Energy Concepts (GEC) has been retained by utilities in Colorado, Nebraska, and Arizona to site, install, and operate 21 wind monitoring stations as part of the Utility Wind Resource Assessment Program (U*WRAP). Preliminary results indicate wind speed averages at 40 meters (132 ft) of 6.5 - 7.4 m/s (14.5-16.5 mph) in Nebraska and 7.6 - 8.9 m/s (17.0-19.9 mph) in Colorado. The Arizona stations are not yet operational. This paper presents the history and current status of the 21 monitoring stations as well as preliminary data results. Information on wind speeds, wind direction, turbulence intensity, wind shear, frequency distribution, and data recovery rates are provided.

  10. Periodic Viscous Shear Heating Instability in Fine-Grained Shear Zones: Mechanism for Intermediate Depth Earthquakes

    NASA Astrophysics Data System (ADS)

    Coon, E.; Kelemen, P.; Hirth, G.; Spiegelman, M.

    2005-12-01

    Kelemen and Hirth (Fall 2004 AGU) presented a model for periodic, viscous shear heating instabilities along pre-existing, fine grained shear zones. This provides an attractive alternative to dehydration embrittlement for explaining intermediate-depth earthquakes, especially those in a narrow thermal window within the mantle section of subducting oceanic plates (Hacker et al JGR03). Ductile shear zones with widths of cm to m are common in shallow mantle massifs and peridotite along oceanic fracture zones. Pseudotachylites in a mantle shear zone show that shear heating temperatures exceeded the mantle solidus (Obata & Karato Tectonophys95). Olivine grain growth in shear zones is pinned by closely spaced pyroxenes; thus, once formed, these features do not `heal' on geological time scales in the absence of melt or fluid (Warren & Hirth EPSL05). Grain-size sensitive creep will be localized within these shear zones, in preference to host rocks with olivine grain size from 1 to 10 mm. Inspired by the work of Whitehead & Gans (GJRAS74), we proposed that such pre-existing shear zones might undergo repeated shear heating instabilities. This is not a new concept; what is new is that viscous deformation is limited to a narrow shear zone, because grain boundary sliding, sensitive to both stress and grain size, may accommodate creep even at high stress and high temperature. These new ideas yield a new result: simple models for a periodic shear heating instability. Last year, we presented a 1D numerical model using olivine flow laws, assuming that viscous deformation remains localized in shear zones, surrounded by host rocks undergoing elastic deformation. Stress evolves due to elastic strain and drives viscous deformation in a shear zone of specified width. Shear heating and thermal diffusion control T. A maximum of 1400 C (substantial melting of peridotite ) was imposed. Grain size evolves due to recrystallization and diffusion. For strain rates of E-13 to E-14 per sec and initial T of 600 to 850 C, this produced periodic viscous shear heating events with periods of 100's to 1000's of years. Strain rates during these events approach 1 per second as temperatures reach 1400. Cooling between events returns the shear zone almost to its initial temperature, though ultimately shear zone temperature between events exceeds 850 C resulting in stable viscous creep. Analysis shows that our system of equations jumps from one steady state to another, depending on a non-dimensional number relating the rate of shear heating to the rate of diffusive cooling. This year, Kelemen and Hirth show that the rate of stress drop during shear heating events is greater than the rate of elastic stress relaxation, so that shear heating events are a runaway instability. Rather than capping the temperature at 1400 C, we parameterize melt fraction as a function of T, and shear viscosity as a function of melt fraction. A problem with our 1D model is that predicted displacements are too large (1 to 20 m) during shear heating events, essentially because there is no resistance at shear zone ends. To address this, Coon and Spiegelman have embarked on a 3D model, incorporating a pre-existing fine-grained, tabular shear zone of finite extent, with a visco-elastic rheology for both shear zone and wall rocks. Preliminary 1D models using this approach show that the more complicated rheology yields the same result as the simpler model. We will present preliminary results, and determine the Maxwell time for this problem, since low strain rates could produce viscous relaxation in both shear zone and wall rocks with negligible shear heating.

  11. Wind mediated vorticity-generation and eddy-confinement, leeward of the Madeira Island: 2008 numerical case study

    NASA Astrophysics Data System (ADS)

    Couvelard, X.; Caldeira, R. M. A.; Araújo, I. B.; Tomé, R.

    2012-11-01

    This study assesses the influence of the atmospheric wind-wake of the Madeira Island on oceanic-eddy generation. Ocean surface wind fields derived from the QuikSCAT scatterometer were compared to the Weather Research and Forecast (WRF) modeled winds at 6 km resolution. The main difference between the two wind products is found southwest of Madeira where QuikSCAT's spatial resolution [0.5°] does not resolve the near-field atmospheric wake dynamics. Nevertheless, high resolution wind extracted from ENVISAT Advanced Synthetic Aperture Radar (ASAR) confirms that WRF is able to realistically reproduce the island-induced wind-wake. The Regional Oceanic Modeling System (ROMS) was used to simulate the oceanic effects of the wind-wake. A “no-wind-wake” case was simulated with ROMS using the QuikSCAT wind, whereas the WRF wind was used for an island-induced wind-wake simulation. Oceanic surface kinetic energy and vorticity are found to increase during the summer months concurrently with strong wind-wake episodes resolved by WRF. The downstream propagation of this oceanic vorticity, as a result of the shedding of the leeward eddies, was captured with an eddy tracking algorithm. In the initial stage, the oceanic leeward eddy corridor was delimited by the zonal wind-shear. This study suggests that the wind-wake is the main contributor to the generation and containment of the oceanic eddies in the lee of the Madeira Island.

  12. Buoyancy and shear characteristics of hurricane-tornado environments

    NASA Technical Reports Server (NTRS)

    Mccaul, Eugene W., Jr.

    1991-01-01

    This study presents detailed composite profiles of temperature, moisture, and wind constructed for tornado environments in tropical cyclones that affected the U.S. between 1948 and 1986. Winds are composited in components radial and tangential to the tropical cyclone center at observation time. Guided by observed patterns of tornado occurrence, composites are constructed for a variety of different stratifications of the data, including proximity to tornadoes, position relative to the cyclone center, time of day, time after cyclone landfall, cyclone translation speed, and landfall location. The composites are also compared to composite soundings from Great Plains tornado environments. A variety of sounding parameters are examined to see which are most closely related to the tornado distribution patterns. Lower-tropospheric vertical shears are found to be stronger in the tropical cyclone tornado environments than on the Great Plains. Buoyancy for the tropical cyclone tornado cases is much smaller than that seen with Great Plains tornado events and exhibits a weak negative correlation with tornado outbreak severity.

  13. SHEAR-WAVE SPLITTING, THE NEW GEOPHYSICS, AND EARTHQUAKE STRESS-FORECASTING SHEAR-WAVE SPLITTING, NEW GEOPHYSICS, AND

    E-print Network

    SHEAR-WAVE SPLITTING, THE NEW GEOPHYSICS, AND EARTHQUAKE STRESS-FORECASTING 1 ___________________________________________ SHEAR-WAVE SPLITTING, NEW GEOPHYSICS, AND EARTHQUAKE STRESS understanding of fluid-rock deformation: a New Geophysics, where earthquakes can be stress-forecast. Shear

  14. Piezoelectric wind turbine

    NASA Astrophysics Data System (ADS)

    Kishore, Ravi Anant; Priya, Shashank

    2013-03-01

    In past few years, there has been significant focus towards developing small scale renewable energy based power sources for powering wireless sensor nodes in remote locations such as highways and bridges to conduct continuous health monitoring. These prior efforts have led to the development of micro-scale solar modules, hydrogen fuel cells and various vibration based energy harvesters. However, the cost effectiveness, reliability, and practicality of these solutions remain a concern. Harvesting the wind energy using micro-to-small scale wind turbines can be an excellent solution in variety of outdoor scenarios provided they can operate at few miles per hour of wind speed. The conventional electromagnetic generator used in the wind mills always has some cogging torque which restricts their operation above certain cut-in wind speed. This study aims to develop a novel piezoelectric wind turbine that utilizes bimorph actuators for electro-mechanical energy conversion. This device utilizes a Savonius rotor that is connected to a disk having magnets at the periphery. The piezoelectric actuators arranged circumferentially around the disk also have magnets at the tip which interacts with the magnetic field of the rotating disk and produces cyclical deflection. The wind tunnel experiments were conducted between 2-12 mph of wind speeds to characterize and optimize the power output of the wind turbine. Further, testing was conducted in the open environment to quantify the response to random wind gusts. An attempt was made towards integration of the piezoelectric wind turbine with the wireless sensor node.

  15. Reduced model of DFIGs wind farms using aggregation of wind turbines and equivalent wind

    Microsoft Academic Search

    L. M. Fernandez; C. A. Garcia; J. R. Saenz; F. Jurado

    2006-01-01

    In this paper, a new reduced model of wind farms with doubly-fed induction generators wind turbines is proposed for representing all the wind turbines of a wind farm by one single equivalent wind turbine. The simulation results demonstrate the effectiveness of the proposed reduced model to represent the collective response of a wind farm in the point of common coupling

  16. Turning to the wind

    NASA Astrophysics Data System (ADS)

    Sorensen, B.

    1981-10-01

    Consideration is given the economic and technological aspects of both free-stream (horizontal-axis) and cross-wind (vertical-axis) wind energy conversion systems, with attention to operational devices ranging in rotor diameter from 10 to 40 m and in output from 22 to 630 kW. After a historical survey of wind turbine design and applications development, the near-term technical feasibility and economic attractiveness of combined wind/fossil-fueled generator and wind/hydroelectric systems are assessed. Also presented are estimates of wind energy potential extraction in the U.S. and Denmark, the industrial requirements of large-scale implementation, energy storage possibilities such as pumped hydro and flywheels, and cost comparisons of electrical generation by large and small wind systems, coal-fired plants, and light-water fission reactors.

  17. Wind tower service lift

    DOEpatents

    Oliphant, David; Quilter, Jared; Andersen, Todd; Conroy, Thomas

    2011-09-13

    An apparatus used for maintaining a wind tower structure wherein the wind tower structure may have a plurality of legs and may be configured to support a wind turbine above the ground in a better position to interface with winds. The lift structure may be configured for carrying objects and have a guide system and drive system for mechanically communicating with a primary cable, rail or other first elongate member attached to the wind tower structure. The drive system and guide system may transmit forces that move the lift relative to the cable and thereby relative to the wind tower structure. A control interface may be included for controlling the amount and direction of the power into the guide system and drive system thereby causing the guide system and drive system to move the lift relative to said first elongate member such that said lift moves relative to said wind tower structure.

  18. Wind energy conversion system

    DOEpatents

    Longrigg, Paul (Golden, CO)

    1987-01-01

    The wind energy conversion system includes a wind machine having a propeller connected to a generator of electric power, the propeller rotating the generator in response to force of an incident wind. The generator converts the power of the wind to electric power for use by an electric load. Circuitry for varying the duty factor of the generator output power is connected between the generator and the load to thereby alter a loading of the generator and the propeller by the electric load. Wind speed is sensed electro-optically to provide data of wind speed upwind of the propeller, to thereby permit tip speed ratio circuitry to operate the power control circuitry and thereby optimize the tip speed ratio by varying the loading of the propeller. Accordingly, the efficiency of the wind energy conversion system is maximized.

  19. Wind-modulated buoyancy circulation over the Texas-Louisiana shelf

    NASA Astrophysics Data System (ADS)

    Zhang, Zhaoru; Hetland, Robert; Zhang, Xiaoqian

    2014-09-01

    This numerical investigation examines buoyancy-driven circulation on the Texas-Louisiana shelf modulated by seasonal winds. In wintertime, with downcoast (in the direction of Kelvin wave propagation) wind forcing, the Mississippi-Atchafalaya River plume exhibits a bottom-advected pattern. The plume is fairly wide and the horizontal density gradients span almost across the entire shelf inshore of 50 m. Within the plume, vertical shear of alongshore flow is in thermal wind balance with the cross-shore density gradient, and the shear causes a slight reversal of alongshore flow near the bottom. An alongshore flow estimated by the thermal wind relation, along with an assumption of zero bottom velocity, generally well agrees with the actual flow near the surface in regions deeper than 20 m. In spring and summer, the thermal-wind-balance-derived flow deviates from the actual alongshore flow, and an Ekman flow driven by strong onshore wind makes the major contribution to the deviation. Besides, the summertime upcoast wind component transforms the plume to a surface-advected state, resulting in reduced cross-shore density gradients and increasing the relative importance of wind-driven, barotropic alongshore flow, which contributes to the remaining deviation.

  20. On liquid migration in sheared granular matter

    NASA Astrophysics Data System (ADS)

    Mani, R.; Kadau, D.; Or, D.; Herrmann, H. J.

    2013-06-01

    Mixing liquids with powders is of great importance, e.g. in process engineering and for pharmaceutical applications. Generally, one might expect that homogeneously shearing or stirring wet granular matter would lead to a homogeneous liquid distribution, however, it is not clear what happens when shear is applied non-homogeneously, e.g. in shear bands. It is commonly accepted that at large liquid contents, liquid flows inside dilating zones as percolating liquid networks prevent air from entering the dilating pores, but it is unknown what happens at low liquid contents. We present experimental measurements showing a decreased liquid concentration inside a shear band where glass beads are sheared in a split bottom shear cell. Furthermore, a microscopic model for liquid transport at low liquid contents is presented, where fluid dynamics between individual liquid structures driven by Laplace pressure differences is taken into account. Our model shows liquid depletion patterns in quantitative agreement with experiments. On the other hand, our model is also applicable to the situation where shear is applied homogeneously, showing diffusive spreading of liquid.