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1

Wind shear detection systems  

NASA Astrophysics Data System (ADS)

The Federal Aviation Administration has established an integrated program to provide wind shear detection and warning at selected airports throughout the United States. The program consists of both ground and aircraft-based sensors, as well as the development of procedures and training aids for pilots and controllers. Selection of airport for ground-based systems was based on the current and projected operations tempo and on the frequency of thunderstorms, the principal cause of hazardous wind shear events. The FAA's procurement of ground-based systems is managed within a wind shear product line in the agency's integrated product team for surveillance and weather. Included in the product line are the terminal doppler weather radar, the low level wind shear alert system, and the airport surveillance radar-weather system processor. These three systems, coupled with new procedures and improved training, bring a truly integrated approach to solving a serious safety problem.

McCullogh, Carl P.

1996-05-01

2

Shearing wind helicity and thermal wind helicity  

NASA Astrophysics Data System (ADS)

Helicity is defined as H = V . omega, where V and omega are the velocity and vorticity vectors, respectively. Many works have pointed out that the larger the helicity is, the longer the life cycle of the weather system is. However, the direct relationship of the helicity to the evolution of the weather system is not quite clear. In this paper, the concept of helicity is generalized as shearing wind helicity (SWH). Dynamically, it is found that the average SWH is directly related to the increase of the average cyclonic rotation of the weather system. Physically, it is also pointed out that the SWH, as a matter of fact, is the sum of the torsion terms and the divergence term in the vorticity equation. Thermal wind helicity (TWH), as a derivative of SWH, is also discussed here because it links the temperature field and the vertical wind field. These two quantities may be effective for diagnosing a weather system. This paper applies these two quantities in cylindrical coordinates to study the development of Hurricane Andrew to validate their practical use. Through analyzing the hurricane, it is found that TWH can well describe the characteristics of the hurricane such as the strong convection and release of latent heat. SWH is not only a good quantity for diagnosing the weather system, but also an effective one for diagnosing the development of the hurricane.

Han, Y.; Wu, R. S.; Fang, J.

2006-07-01

3

Wind-shearing in gaseous protoplanetary disks  

NASA Astrophysics Data System (ADS)

One of the first stages of planet formation is the growth of small planetesimals and their accumulation into large planetesimals and planetary embryos. This early stage occurs much before the dispersal of most of the gas from the protoplanetary disk. Due to their different aerodynamic properties, planetesimals of different sizes/shapes experience different drag forces from the gas at these stage. Such differential forces produce a wind-shearing effect between close by, different size planetesimals. For any two planetesimals, a wind-shearing radius can be considered, at which the differential acceleration due to the wind becomes greater than the mutual gravitational pull between the planetesimals. We find that the wind-shearing radius could be much smaller than the gravitational shearing radius by the Sun (the Hill radius), i.e. during the gas-phase of the disk wind-shearing could play a more important role than tidal perturbations by the Sun. Here we study the wind-shearing radii for planetesimal pairs of different sizes and compare it with gravitational shearing (drag force vs. gravitational tidal forces). We then discuss the role of wind-shearing for the stability and survival of binary planetesimals, and provide stability criteria for binary planetesimals embedded in a gaseous disk.

Perets, Hagai B.; Murray-Clay, Ruth

2011-11-01

4

Wind shear climatology for large wind turbine generators  

SciTech Connect

Climatological wind shear analyses relevant to the design and operation of multimegawatt wind turbines are provided. Insight is provided for relating the wind experienced by a rotating blade in a shear flow to the analysis results. A simple analysis of the wind experienced by a rotating blade for three types of wind shear profiles under steady-state conditions is presented in graphical form. Comparisons of the magnitude and frequency of the variations in 1) the wind sensed by a single blade element, 2) the sum, and 3) the difference of the winds sensed by opposite blade elements show strong sensitivity to profile shape. These three items represent forcing functions that can be related to 1) flatwise bending moment, 2) torque on the shaft, and 3) teeter angle. A computer model was constructed to simulate rotational sampling of 10-s sampled winds from a tall tower for three different types of large wind turbines. Time series produced by the model indicated that the forcing functions on a rotating blade vary according to the shear profile encountered during each revolution as opposed to a profile derived from average wind conditions, e.g., hourly average winds. An analysis scheme was developed to establish a climatology of wind shear profiles derived from 10-s sampled winds and hourly average winds measured over a one-year period at several levels on a tall tower. Because of the sensitivity of the forcing function variability to profile shape, the analyses performed and presented are in the form of joint frequency distributions of velocity differences of the the top-to-hub versus the hub-to-bottom portion of disks of rotation for the three turbine configurations.

Elliott, D.L.; Wendell, L.L.; Heflick, S.K.

1982-10-01

5

Velocity shear generation of solar wind turbulence  

Microsoft Academic Search

A two-dimensional incompressible MHD spectral code is used to show that shear-driven turbulence is a possible means for producing many observed properties of the evolution of the magnetic and velocity fluctuations in the solar wind and, in particular, the evolution of the cross helicity ('Alfvenicity') at small scales. It is shown that large-scale shear can nonlinearly produce a cascade to

D. A. Roberts; Melvyn L. Goldstein; William H. Matthaeus; Sanjoy Ghosh

1992-01-01

6

Velocity shear generation of solar wind turbulence  

Microsoft Academic Search

The authors use a two-dimensional, incompressible MHD spectral code to establish that shear-driven turbulence is a possible means for producing many observed properties of the evolution of the magnetic and velocity fluctuations in the solar wind and, in particular, the evolution of the cross helicity ({open_quotes}Alfvenicity{close_quotes}) at small scales. They find that large-scale shear can nonlinearly produce a cascade to

D. Aaron Roberts; Melvyn L. Goldstein; S. Ghosh; W. H. Matthaeus

1992-01-01

7

Turbulence, wind shear and wind speed downwind of forested terrain  

NASA Astrophysics Data System (ADS)

Wind flows can be significantly affected by the presence of forestry and thereby affect turbines' production and safety. In particular values of wind shear and turbulence intensity can reach significant levels downwind of forested terrain, leading to wind turbine fatigue, vibrations and sometimes failure. Energy yield can also be significantly affected by forestry as wind energy is dissipated by trees. These characteristics of the flow can be assessed using measurements or modeling. However a set of standard curves showing turbulence intensity, wind shear, and wind speed downwind of forested terrain for various forest parameters would prove useful in order to approximately assess wind characteristics before carrying out more in-depth analyses. The Ventos® CFD (Computational Fluid Dynamics) model was used for this purpose, as it includes a state-of-the art canopy model enabling proper modeling of the physics at stake. Forestry height, density and depth were varied within a range of typical values, and values of turbulence intensity, wind shear, and wind speed are provided for each case depending on the distance to the forest and height above ground level. These CFD computations were validated by comparisons with measurements on sites matching the characteristics of the forest to be modeled. Conclusions discuss the approach proposed here and its limitations.

Abiven, Claude; Brady, Oisin; Bugeat, Perrine

2010-05-01

8

Air/Ground Wind Shear Information Integration: Flight Test Results.  

National Technical Information Service (NTIS)

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 ...

D. A. Hinton

1992-01-01

9

Wind Shear Characteristics at Central Plains Tall Towers (presentation)  

SciTech Connect

The objectives of this report are: (1) Analyze wind shear characteristics at tall tower sites for diverse areas in the central plains (Texas to North Dakota)--Turbines hub heights are now 70-100 m above ground and Wind measurements at 70-100+ m have been rare. (2) Present conclusions about wind shear characteristics for prime wind energy development regions.

Schwartz, M.; Elliott, D.

2006-06-05

10

Velocity shear generation of solar wind turbulence  

SciTech Connect

The authors use a two-dimensional, incompressible MHD spectral code to establish that shear-driven turbulence is a possible means for producing many observed properties of the evolution of the magnetic and velocity fluctuations in the solar wind and, in particular, the evolution of the cross helicity ({open_quotes}Alfvenicity{close_quotes}) at small scales. They find that large-scale shear can nonlinearly produce a cascade to smaller scale fluctuations even when the linear Kelvin-Helmholtz mode is stable and that a roughly power law inertial range is established by this process. While the fluctuations thus produced are not Alfvenic, they are nearly equipartitioned between magnetic and kinetic energy. The authors report simulations with Alfvenic fluctuations at high wave numbers, both with and without shear layers and find that it is the low cross helicity at low wave numbers that is critical to the cross helicity evolution, rather than the geometry of the flow or the dominance of kinetic energy at large scales. The fluctuations produced by shear effects are shown to evolve similarly but more slowly in the presence of a larger mean field and to be anisotropic with a preferred direction of spectral transfer perpendicular to the mean field. The evolution found is similar to that seen in some other simulations of HMD turbulence, and thus seems in many respects to be an instance of a more generic turbulent evolution rather than due to specific conditions in the solar wind. 75 refs., 18 figs.

Roberts, D.A.; Goldstein, M.L.; Ghosh, S. [NASA Goddard Space Flight Center, Greenbelt, MD (United States); Matthaeus, W.H. [Univ. of Delaware, Newark, DE (United States)

1992-11-01

11

Wind shear for large wind turbine generators at selected tall tower sites  

SciTech Connect

The objective of the study described in this report is to examine the nature of wind shear profiles and their variability over the height of large horizontal-axis wind turbines and to provide information on wind shear relevant to the design and opertion of large wind turbines. Wind turbine fatigue life and power quality are related through the forcing functions on the blade to the shapes of the wind shear profiles and their fluctuations over the disk of rotation.

Elliott, D.L.

1984-04-01

12

Wind Behavior of Buildings with and without Shear Wall  

NASA Astrophysics Data System (ADS)

Shear walls are specially designed structural walls which are incorporated in buildings to resist lateral forces that are produced in the plane of wall due to wind, earthquake and flexural members. This paper presents the study and comparison of the difference between the wind behavior of buildings with and without shear wall using Staad pro

Rasikan, Alfa; Rajendran, M. G.

2013-03-01

13

Lidar wind shear detection for commercial aircraft  

NASA Astrophysics Data System (ADS)

National attention has focused on the critical problem of detecting and avoiding windshear since the crash on August 2, 1985, of a Lockheed L-1011 at Dallas/Fort Worth International Airport. As part of The NASA/FAA National Integrated Windshear Program, the authors have defined a measurable windshear hazard index that can be remotely sensed from an aircraft, to give the pilot information about the wind conditions he will experience at some later time if he continues along the present flight path. The technology analysis and end- to-end performance simulation, which measures signal-to-noise ratios and resulting wind velocity errors for competing coherent lidar systems, shows that a Ho:YAG lidar at a wavelength of 2.1 micrometers and a CO2 lidar at 10.6 micrometers can give the pilot information about the line-of-sight component of a windshear threat in a region extending from his present position to 2 to 4 km in front of the aircraft. This constitutes a warning time of 20 to 40 s, even under conditions of moderately heavy precipitation. Using these results, a Coherent Lidar Airborne Shear Sensor (CLASS), using a Q-switched CO2 laser at 10.6 micrometers , is being designed and developed for flight evaluation in early 1992.

Targ, Russell; Bowles, Roland L.

1991-08-01

14

The impact of meridonal wind shear on baroclinic life cycle  

NASA Astrophysics Data System (ADS)

In this study, initial-value calculations are performed with a primitive equation model to examine whether the stabilizing effect of the horizontal zonal wind shear in the background state can account for the observed variability in baroclinic life cycles. The life cycle calculations show that a greater maximum eddy energy is attained for the observed basic state with anomalously weak horizontal zonal wind shear, suggesting that the horizontal zonal wind shear indeed plays the dominant role in determining the eddy amplitude. In addition, under this weak shear, the life cycle produces a more pronounced poleward jet shift. Because model simulations of warmer climates tend to show both a poleward jet shift and more intense zonally localized tropical convection which tends to produce the weak shear state, the result of this study provides a mechanism whereby the strengthening of tropical convection can contribute toward the poleward jet shift in warm climates.

Park, Meerea; Lee, Sukyoung

2013-02-01

15

Evolution of salt finger convection with steady wind shear  

NASA Astrophysics Data System (ADS)

In oceanographics situations where salt fingers may be an important mechanism for the transport of heat and salt in the vertical direction, velocity shears may also be present. Salt finger convection is analogous to Bénard convection in that the kinetic energy of the motions is obtained from the potential energy stored in the unstable distribution of a stratifying component. On the basis of the thermal analogy it is of interest to discover whether salt fingers are converted into two-dimensional sheets by wind shear, and how the vertical fluxes of heat and salt are changed by wind shear. Salt finger convection under the effect of steady wind shear is theoretically examined in this paper. The evolution of instability developing in the presence of a vertical density gradient disturbance and the horizontal Couette flow is considered near the onset of salt fingers under a moderate rate of shear. We use velocity as the basic variable and solve the pressure Poisson equation in terms of the associated Green function. Growth competition between the longitudinal rolls (LR) and the transverse rolls (TR), whose axes are, respectively, in the direction parallel to and perpendicular to the Couette flow, is investigated by the weakly nonlinear analysis of coupled-mode equations. The results show that the TR mode is stable under a small wind shear and the LR mode is stable for a higher wind shear.

Yang, Ray-Yeng; Hwung, Hwung-Hweng; Shugan, Igor V.

2011-01-01

16

Wind Shear Characteristics at Central Plains Tall Towers  

Microsoft Academic Search

The object of this study is to analyze wind shear characteristics at tall tower sites in the Central Plains of the United States. The hub heights of modern turbines used for wind farm projects are now 70 meters (m) to 100 m above ground and some advanced turbines under development for deployment during the second half of this decade are

M. Schwartz; D. Elliott

2006-01-01

17

Wind shear coefficients and their effect on energy production  

Microsoft Academic Search

This paper provides realistic values of wind shear coefficients calculated using measured values of wind speed at 20, 30 and 40m above the ground for the first time in Saudi Arabia in particular and, to the best of the authors’ knowledge, in the Gulf region in general. The paper also presents air density values calculated using the measured air temperature

Shafiqur Rehman; Naif M. Al-Abbadi

2005-01-01

18

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

Microsoft Academic Search

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

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

2002-01-01

19

Analysis of vertical wind shear in the Southern Great Plains and potential impacts on estimation of wind energy production  

Microsoft Academic Search

This paper describes the analysis of near-surface wind speeds in Western Oklahoma. The goals of this research are to characterise the nocturnal low-level jet (LLJ) in the region, and to assess the impact wind variability, vertical shear and the LLJ on wind energy calculations. Results show the seasonal variability in wind characteristics as well as in the vertical wind shear,

Scott Greene; Kylah McNabb; Ryan Zwilling; Mark Morrissey; Steve Stadler

2009-01-01

20

Simulation model of wind turbine 3p torque oscillations due to wind shear and tower shadow  

Microsoft Academic Search

To determine the control structures and possible power quality issues, the dynamic torque generated by the blades of a wind turbine must be represented. This paper presents an analytical formulation of the generated aerodynamic torque of a three-bladed wind turbine including the effects of wind shear and tower shadow. The comprehensive model includes turbine-specific parameters such as radius, height, and

Dale S. L. Dolan; Peter W. Lehn

2006-01-01

21

Environmental Vertical Wind Shear with Hurricane Bertha (1996)  

Microsoft Academic Search

Hurricane Bertha (1996) was influenced by vertical wind shear with highly variable direction and magnitude. The paper describes a unique method for determining the vertical tilt of a tropical cyclone vortex using satellite and aircraft data. Hurricane Bertha's vortex tracks at three levels are shown during a period of intensification just prior to landfall. During this period, the hurricane vortex

Raymond M. Zehr

2003-01-01

22

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...

23

Wind shear coefficient, turbulence intensity and wind power potential assessment for Dhulom, Saudi Arabia  

Microsoft Academic Search

The study presents the local values of wind shear coefficient (WSC) estimated using wind speed measurements made at 20, 30 and 40m above ground level (AGL) during November 01, 1998 and October 12, 2002. The study also includes the local values of air density calculated using temperature and pressure measurement made at 2m AGL during the same period. The mean

Shafiqur Rehman; Naif M. Al-Abbadi

2008-01-01

24

Observations of wind shear over the Southern Ocean  

NASA Astrophysics Data System (ADS)

The thermodynamic structure of the lower troposphere over the Southern Ocean is analyzed by employing over 16 years of high resolution upper air soundings from Macquarie Island (54.62°S, 158.85°E). The soundings are analyzed to develop an understanding of the structure of the boundary layer and wind shear occurring through the lower levels over this region, and to compare this to European Centre for Medium-Range Weather Forecasts (ECMWF) model level reanalysis data for the Year of Tropical Convection (YOTC). A multiple layered structure is commonly observed in the high resolution soundings, and is also observed in YOTC, but with a lower frequency. The climatological mean and variability of a number of variables are calculated for both data sets, which reveals that YOTC performs well, but has weaknesses in modeling the observed moisture and wind fields, particularly evident in wind shear profiles. A distinction between a number of boundary layer types is made, and the frequency with which they occur is quantified for both data sets. This highlights important differences between the observations in the Macquarie Island soundings and the reanalysis product. Proxy cloud fields are constructed for the two data sets, and these suggest that clouds are commonly observed in a region between the top of the boundary layer and a secondary temperature inversion, i.e., a "buffer layer" in the words of Russell et al. (1998). The peak relative frequency of observing these clouds lies roughly around 912.5 hPa for both data sets. An examination of the wind shear across the cloud boundaries finds wind shear over cloud base occurs more frequently than cloud top, suggesting that the cloud fields are not embedded in a well-mixed boundary layer.

Hande, L. B.; Siems, S. T.; Manton, M. J.; Belusic, D.

2012-06-01

25

Study of the Methodology of Low-Altitude Wind Shear Detection with Special Emphasis on the Low Level Wind Shear Alert System Concept.  

National Technical Information Service (NTIS)

This basic principles study of the Low Level Wind Shear Alert System (LLWAS) addresses the question of the degree to which a change of algorithm and network geometry can improve the performance of an anemometer-based wind shear detection system to an acce...

F. W. Wilson J. A. Flueck

1986-01-01

26

Wind shear proportional errors in the horizontal wind speed sensed by focused, range gated lidars  

NASA Astrophysics Data System (ADS)

The 10-minute average horizontal wind speeds sensed with lidar and mast mounted cup anemometers, at 60 to 116 meters altitude at HØvsØre, are compared. The lidar deviation from the cup value as a function of wind velocity and wind shear is studied in a 2-parametric regression analysis which reveals an altitude dependent relation between the lidar error and the wind shear. A likely explanation for this relation is an error in the intended sensing altitude. At most this error is estimated to 9 m which induced errors in the horizontal wind velocity of up to 0.5 m/s as compared to a cup at the intended altitude. The altitude errors of focused range gated lidars are likely to arise partly from an unaccounted shift of the weighting functions, describing the sample volume, due to the range dependent collection efficiency of the focused telescope. Possibilities of correcting the lidar measurements both for wind velocity and wind shear dependent errors are discussed. The 2-parametric regression analysis described in this paper is proven to be a better approach when acceptance testing and calibrating lidars.

Lindelöw, P.; Courtney, M.; Parmentier, R.; Cariou, J. P.

2008-05-01

27

ACOUSTIC ARRAY CORRECTIONS FOR COHERENCE LOSS DUE TO THE WIND TUNNEL SHEAR LAYER  

Microsoft Academic Search

Out-of-flow acoustic array measurements in open jet wind tunnels are hampered by the presence of the turbulent shear layer. Signal coher ence between pairs of microphones in the array is reduced because sound from a wind tunnel model passes through the shear layer. As a result, the spatial resolution of the beamforming i mages is significantly lower than without wind,

Pieter Sijtsma

28

The effect of solar-wind structures on the magnetosphere: Current sheets and sudden wind shears  

NASA Astrophysics Data System (ADS)

The solar wind is full of strong current sheets and sudden velocity shears. Often the two types of structures are co-located, so 10 or 20 times per day the Earth simultaneously experiences a sudden change in the magnetic-field direction and a sudden change in the solar-wind flow vector. Using data analysis and simulations, the reaction of the Earth's magnetosphere to these sudden changes is explored.

Borovsky, J. E.; Welling, D. T.; Morley, S.; Birn, J.

2011-12-01

29

A low cost CW CO2 lidar system for low-level wind shear detection  

NASA Astrophysics Data System (ADS)

A CW CO2 lidar sytem developed to determine the feasibility of using such a system for detecting and measuring low-level wind shear is discussed. The system was constructed from off-the-shelf components at a relatively low cost. Results of preliminary testing of the system are included. Wind shear measurements have been achieved but the capability of the system to measure large-scale microburst-generated wind shear has not been determined at this time.

Fetzer, G. J.; Post, M. J.

1990-05-01

30

Lidar wind shear measurements in the planetary boundary layer  

NASA Astrophysics Data System (ADS)

Lidar measurements of wind velocity profiles by slant sounding in the PBL accompanied by ground-based measurements and a comparison with radio- and kytoon data have been carried out in the country during a period of 32 hours. We also carried out similar investigations studying the influence of various micro- and mesoscale phenomena on the wind velocity stratification. In the present work, parts of the preliminary results from two lidar campaigns (1988, 1990) in the region of Sofia are described. Some results of lidar measurements of wind velocity profiles in case of a stable PBL formation after the sunset are presented. The results are obtained during the BLEX'90 (Boundary Layer Experiment). This campaign aimed to perform an investigation of various phenomena and processes in the PBL over an urban area. Some observations of a wind shear appearance during a cold front invasion over the region of Sofia are also presented. These results are derived in the course of the International Boundary Layer Experiment ZOND '88 (teams from the Institute of Atmospheric Optics/Siberian Branch of the USSR Academy of Sciences and from the Institute of Electronics of the Bulgarian Academy of Sciences).

Kolev, Ivan N.; Parvanov, Orlin; Kaprielov, Boiko

1992-08-01

31

a Spatial Model of Wind Shear and Turbulence for Flight Simulation  

Microsoft Academic Search

A three dimensional model which combines measurements of wind shear in the real atmosphere with three-dimensional Monte Carlo simulated turbulence was developed. The measurement of three-dimensional wind shear is a recent development. Measurements were made on a rather coarse ((TURN) 200 m) grid scale so that high frequency, short length scale turbulence information was not included. Some of the missing

C. Warren Campbell

1984-01-01

32

Variation in wind speed and surface shear stress from open floor to porous parallel windbreaks: A wind tunnel study  

Microsoft Academic Search

As vegetative windbreaks become established on a large scale in agricultural ecosystems, understanding the influence of windbreak networks on the momentum budget of the atmospheric boundary layer becomes important. The authors conducted a wind tunnel experiment to study the variation of wind speed profile and surface shear stress of wind flow passing from an open surface to another with parallel

De-Xin Guan; Ye Zhong; Chang-Jie Jin; An-Zhi Wang; Jia-Bing Wu; Ting-Ting Shi; Ting-Yao Zhu

2009-01-01

33

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

SciTech Connect

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.

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

34

Effects of Tropospheric Wind Shear on the Spectrum of Convectively Generated Gravity Waves  

Microsoft Academic Search

ABSTRACT The authors examine,the effects of tropospheric wind shear on the phase speed spectrum,of gravity waves generated by tropical convection. A two-dimensional cloud-resolving model is used to perform numerous,squall line simulations with the vertical shear of the horizontal wind varied in three layers of the troposphere. Several simplified simulations using prescribed heating are also performed,to elucidate the interactions of wind

JADWIGA H. BERES; M. Joan Alexander; James R. Holton

2002-01-01

35

Effect of Wind Shear on the Characteristics of a Rotating Blade of a Field Horizontal Axis Wind Turbine  

Microsoft Academic Search

This paper shows the aerodynamic characteristics at the mid-length of a rotor blade of a 10-m-diameter wind turbine exposed to wind shear. A sonic wind speed meter and six cup-anemometers were installed one diameter upwind of the turbine in order to measure wind profiles. The anemometers at the top, middle and bottom levels were installed at heights of 18.3, 13.3

Takao Maeda; Hideyuki Kawabuchi

2007-01-01

36

The role of vertical shear of the meridional winds in the northward propagation of ITCZ  

NASA Astrophysics Data System (ADS)

A simple linear model was proposed by Jiang et al. (2004) to highlight the mechanism of scale selection during the northward propagation of cloud bands over Bay of Bengal. The easterly shear in zonal winds was shown to be an essential parameter in scale selection. This model was criticized for the use of unrealistic values of the friction and diffusion parameters. The present study extends this model by adding baroclinic vertical shear in the meridional mean winds. The correct rate of propagation is obtained with reasonable values of friction and diffusion parameters. In the present model, the direction of propagation is essentially determined by easterly vertical shear of zonal winds, while vertical shear of meridional wind also contributes to the observed propagation phase speed and instability. The correct phase speed is obtained for southerly mean meridional vertical shear.

Dixit, Vishal; Srinivasan, J.

2011-04-01

37

Factors affecting boundary-layer wind shear over the Indian Ocean during FGGE  

NASA Astrophysics Data System (ADS)

Statistics on the vertical wind shear in the boundary layer over the Indian Ocean were examined for the causes of regional and seasonal changes. Low-level cloud motions and surface ship wind reports were used to define the vertical shear. Temperature data from the ship reports were analyzed for boundary-layer stability related to the observed shears. Smaller wind shears were found in areas of large negative air-sea temperature difference (unstable boundary layers). The ‘thermal wind’ effects were very small over most of the tropical Indian Ocean. The largest factor affecting the speed shear was the strength of the wind itself. Larger speed shear was found under high wind conditions. A small reduction in the direction difference between cloud and ship observations also was found under higher speeds. The scatter of cloud-ship comparisons around the mean (dispersion) also decreased for higher wind speeds. Daily gridded cloud motion and ship wind speed data had a correlation coefficient of 0.8 with a scatter of 1.9 m s-1 (r.m.s.) around the mean difference.

Wylie, Donald P.; Hinton, Barry B.

1984-03-01

38

Microburst Wind Structure and Evaluation of Doppler Radar for Airport Wind Shear Detection.  

NASA Astrophysics Data System (ADS)

Doppler weather radar data from the Joint Airport Weather Studies (JAWS) Project are used to determine the horizontal and vertical structure of airflow within microbursts. Typically, the associated downdraft is about 1 km wide and begins to spread horizontally at a height below 1 km. The median time from initial divergence at the surface to maximum differential wind velocity across the microburst is 5 min. The height of maximum differential velocity is 75 m. The median velocity differential is 22 m s1 over an average distance of 3.1 km. The outflow is asymmetric, averaging twice as strong along the maximum shear axis compared to the minimum axis.Doppler radar could be an effective means for identifying microbursts and warning aircraft of wind shear hazards. For microburst detection such a radar must be able to measure wind velocities in clear air as well as in heavy rain and hail. Scan update rates should be approximately every 2 min and the lowest few hundred meters of the atmosphere must be observed. Ground clutter must be considerably reduced from levels typically obtained with present Doppler radars. New antenna technology and signal processing techniques may solve this problem. Automated range and velocity unfolding is required, as well as automated identification and dissemination techniques.

Wilson, James W.; Roberts, Rita D.; Kessinger, Cathy; McCarthy, John

1984-06-01

39

Wind shear at turbine rotor heights from Doppler lidar measurements  

Microsoft Academic Search

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

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

2009-01-01

40

Behavior of Very Large Aircraft Disturbed by Wind Shear and Atmospheric Turbulence.  

National Technical Information Service (NTIS)

The behavior of very large aircraft disturbed by wind shear and atmospheric turbulence (vertical gust during the landing approach) is analyzed by means of a multiloop system. The aircraft considered were a B-747-like aircraft and two hypothetical aircraft...

W. P. Deboer

1972-01-01

41

Wind shear over the Nice Côte d'Azur airport: case studies  

NASA Astrophysics Data System (ADS)

The Nice Côte d'Azur international airport is subject to horizontal low-level wind shears. Detecting and predicting these hazards is a major concern for aircraft security. A measurement campaign took place over the Nice airport in 2009 including 4 anemometers, 1 wind lidar and 1 wind profiler. Two wind shear events were observed during this measurement campaign. Numerical simulations were carried out with Meso-NH in a configuration compatible with near-real time applications to determine the ability of the numerical model to predict these events and to study the meteorological situations generating an horizontal wind shear. A comparison between numerical simulation and the observation dataset is conducted in this paper.

Boilley, A.; Mahfouf, J.-F.

2013-09-01

42

Vertical wind shear on Jupiter from Cassini images  

Microsoft Academic Search

Multifilter images of Jupiter acquired by the Cassini Imaging Science Subsystem (ISS) are used to derive zonal winds at altitudes above and below the visible cloud deck. Small features unique to the ultraviolet images of ISS are tracked to get the systematic high-altitude zonal winds. Comparison between the zonal winds from ultraviolet images and the vertical profile of zonal winds

Liming Li; Andrew P. Ingersoll; Ashwin R. Vasavada; Amy A. Simon-Miller; Anthony D. Del Genio; Shawn P. Ewald; Carolyn C. Porco; Robert A. West

2006-01-01

43

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

PubMed

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

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

2011-12-01

44

THE DEPENDENCE OF MAGNETIC RECONNECTION ON PLASMA {beta} AND MAGNETIC SHEAR: EVIDENCE FROM SOLAR WIND OBSERVATIONS  

SciTech Connect

We address the conditions for the onset of magnetic reconnection based on a survey of 197 reconnection events in solar wind current sheets observed by the Wind spacecraft. We report the first observational evidence for the dependence of the occurrence of reconnection on a combination of the magnetic field shear angle, {theta}, across the current sheet and the difference in the plasma {beta} values on the two sides of the current sheet, {Delta}{beta}. For low {Delta}{beta}, reconnection occurred for both low and high magnetic shears, whereas only large magnetic shear events were observed for large {Delta}{beta}: Events with shears as low as 11{sup 0} were observed for {Delta}{beta} < 0.1, but for {Delta}{beta} > 1.5 only events with {theta} > 100{sup 0} were detected. Our observations are in quantitative agreement with a theoretical prediction that reconnection is suppressed in high {beta} plasmas at low magnetic shears due to super-Alfvenic drift of the X-line caused by plasma pressure gradients across the current sheet. The magnetic shear-{Delta}{beta} dependence could account for the high occurrence rate of reconnection observed in current sheets embedded within interplanetary coronal mass ejections, compared to those in the ambient solar wind. It would also suggest that reconnection could occur at a substantially higher rate in solar wind current sheets closer to the Sun than at 1 AU and thus may play an important role in the generation and heating of the solar wind.

Phan, T. D.; Pasma, C.; Oeieroset, M.; Larson, D.; Lin, R. P.; Davis, M. S. [SSL, University of California, Berkeley, CA 94720 (United States); Gosling, J. T. [University of Colorado, Boulder, CO (United States); Paschmann, G. [MPE, Garching (Germany); Drake, J. F., E-mail: phan@ssl.berkeley.ed [University of Maryland, College Park, MD (United States)

2010-08-20

45

THIRD MOMENTS AND THE ROLE OF ANISOTROPY FROM VELOCITY SHEAR IN THE SOLAR WIND  

SciTech Connect

We have extended the recent analyses of magnetohydrodynamic third moments as they relate to the turbulent energy cascade in the solar wind to consider the effects of large-scale shear flows. Moments from a large set of Advanced Composition Explorer data have been taken, and chosen data intervals are characterized by the rate of change in the solar wind speed. Mean dissipation rates are obtained in accordance with the predictions of homogeneous shear-driven turbulence. Agreement with predictions is best made for rarefaction intervals where the solar wind speed is decreasing with time. For decreasing speed intervals, we find that the dissipation rates increase with increasing shear magnitude and that the shear-induced fluctuation anisotropy is consistent with a relatively small amount.

Stawarz, Joshua E.; Vasquez, Bernard J.; Smith, Charles W. [Physics Department, Space Science Center, University of New Hampshire, Durham, NH 03824 (United States); Forman, Miriam A. [Department of Physics and Astronomy, State University of New York at Stony Brook, Stony Brook, NY 11794-3800 (United States); Klewicki, Joseph, E-mail: jek32@cisunix.unh.edu, E-mail: Bernie.Vasquez@unh.edu, E-mail: Charles.Smith@unh.edu, E-mail: Miriam.Forman@sunysb.edu, E-mail: Joe.Klewicki@unh.edu [Mechanical Engineering Department, University of New Hampshire, Durham, NH 03824 (United States)

2011-07-20

46

On the Influences of Vertical Wind Shear on Symmetric Tropical Cyclone Structure Derived from AMSU  

Microsoft Academic Search

Axisymmetric temperatures and gradient-balanced winds associated with tropical cyclones derived from the Advanced Microwave Sounding Unit are stratified by the 24-h averaged vector difference of the horizontal wind between 200 and 850 hPa (or vertical wind shear). Using 186 total cases that are limited to tropical cyclones with intensities greater than 33 m s 21 (or mature) and are located

John A. Knaff; Stacey A. Seseske; Mark DeMaria; Julie L. Demuth

2004-01-01

47

The Effect of Desert Shrubs on Shear Stress from the Wind: AN Exploratory Study  

NASA Astrophysics Data System (ADS)

Wind flow near desert surfaces is modified by shrubs, which slow the wind by friction. Shrubs also modify the spatial pattern of the shear stress of wind exerted on the ground surface. This study examines the effect of shrub spacing on these two processes, examined both in a wind tunnel and at field sites in the Mojave and Sonoran Deserts. The wind tunnel experiments involved measurements of wind profiles and surface shear stress for isolated objects and for arrays of objects with varying spacings. The objects used were cylinders and model shrubs. Wind profiles were measured with pitot tubes and surface shear stress was determined with a technique involving the rate of sublimation of naphthalene at points on a naphthalene surface. Flat field sites were selected with scattered shrubs, sufficient fetch, and no nearby topographical obstacles which might modify the wind flow at the site. Wind profiles were obtained with cup anemometers on a seven meter mast and also on a one meter mast which was placed at different locations around a shrub for determination of the near surface flow characteristics. The wind profiles were reduced to determine the values of the profile parameters, which are the zero plane displacement, d, aerodynamic roughness parameter, z _{rm o}, and friction speed, u*. In the wind tunnel, d was consistently negative while z_{rm o} was very high, which indicates that the surface was aerodynamically very rough. In the field, however, the opposite pattern was found, with d above the tops of the shrubs and z_{rm o} very small, showing that wind was effectively skimming over the shrubs and encountering little friction from the surface and the shrubs. The reason for the different wind tunnel and field values of the profile parameters is not known. In the field, there was no discernable pattern in the variation of d with shrub spacing, though z _{rm o} decreased with shrub spacing in a manner consistent with previous studies. The magnitude of the surface shear stress around the cylinders and shrubs in the wind tunnel decreased with object spacing, as expected. The pattern of the surface shear stress also varies with object spacing in that the basic pattern for an isolated object is maintained until the spacing is approximately four times the object height. At denser arrangements, the surface pattern becomes more complex. In the field, a poorly defined trend suggests that surface shear stress also decreases with shrub spacing. No clearly defined spatial pattern of surface stress was found, indicating that the flow is highly complex and generalizations about the pattern will require improved field methods or sample sizes much larger than used in this study.

Lee, Jeffrey Alan

1990-01-01

48

Nocturnal wind direction shear and its potential impact on pollutant transport  

SciTech Connect

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.

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

49

The importance of low-level environmental vertical wind shear to wildfire propagation: Proof of concept  

NASA Astrophysics Data System (ADS)

This study is a proof of concept of the sensitivity of grassfire propagation to vertical shear in the near-surface environmental flow found through four comparative grassfire numerical simulations with a coupled wildfire-atmosphere model. A unidirectional constant wind field, under neutral atmospheric conditions, no surface friction, Coriolis force or topography, and homogeneous fuel, prescribes the model environment. By using the same surface (at 6.2 m above ground level) wind speed for all simulations, analyses of the results can suggest when the behavior and spread rate of the fire may depend more on the interaction of the fire plume with the shear in the above surface wind or more on the magnitude of the mean upstream surface wind speed at the surface. Three aspects of wildfire behavior are investigated: impact of unidirectional vertical shear on surface flow properties and fire line propagation; variability in fire spread and area burnt due to the evolution of the surface flow; and implications of low-level vertical wind shear on the prediction of wildfire, especially extreme or erratic, behavior.

Kochanski, Adam; Jenkins, Mary Ann; Sun, Ruiyu; Krueger, Steven; Abedi, Sepideh; Charney, Joseph

2013-08-01

50

Effects of vertical wind shear, radiation, and ice clouds on a torrential rainfall event in China  

NASA Astrophysics Data System (ADS)

The effects of vertical wind shear, radiation, and ice clouds on surface rainfall processes associated with the torrential rainfall event over Jinan, China, during July 2007 are investigated through a series of sensitivity experiments. All experiments are integrated with an imposed large-scale vertical velocity and zonal wind from the National Centers for Environmental Prediction Global Data Assimilation System for 36 h, while vertical wind shear, cloud radiative effects, cloud-radiation interaction, and ice microphysics are, respectively, suppressed in the sensitivity experiments. The exclusion of ice clouds decreases model domain mean surface rain rate by 12.9%, whereas the mean rain rates are less sensitive to vertical wind shear, cloud radiative effects, and cloud-radiation interaction. The reduction in the mean rain rate resulting from the removal of ice clouds is primarily associated with the decrease in net condensation. The budget analysis of the mean perturbation kinetic energy shows that the barotropic conversion process associated with vertical wind shear does not increase perturbation kinetic energy and thus does not increase the mean rain rate. The increase in radiative cooling resulting from the exclusion of cloud radiative effects is largely offset by the decrease in heat divergence, which results in the insensitivity of the mean rain rate to cloud radiative effects.

Zhou, Yushu

2011-03-01

51

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

Microsoft Academic Search

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.

W. I. Axford

1963-01-01

52

Organization of Tropical Convection in Low Vertical Wind Shears: The Role of Water Vapor  

Microsoft Academic Search

A modeling study is conducted to gain insight into the factors that control the intensity and organization of tropical convection, and in particular to examine if organization occurs in the absence of factors such as vertical wind shear or underlying sea surface temperature (SST) gradient. The control experiment integrates a cloud- resolving model for 15 days using a 3D domain

Adrian M. Tompkins

2001-01-01

53

Wind-induced shear dispersion and genesis of the shelf-break front  

Microsoft Academic Search

Through a simple analytical model, we examine the shear dispersion associated with oscillatory winds in an unstratified coastal ocean. As noted previously in the tidal regime, the vertical-integrated (total) horizontal diffusivity has a maximum where the water depth equals the diffusive depth – defined as the reach of the vertical diffusion during one forcing cycle. Due principally to the long

Hsien-Wang Ou; Dake Chen

2006-01-01

54

Acoustic wave propagation through the shear layer of the DNW large open jet wind tunnel  

Microsoft Academic Search

The adequacy of the sound refraction theory corrections to measurements of the aeroacoustic signals obtained from models immersed in a jet shear in the German-Dutch wind tunnel were evaluated. Four air horns and a speaker served as an aerodynamically shaped model for the calibrated noise source. The test channel is surrounded by an anechoic chamber to eliminate random noise. Data

R. Ross; K. J. Young; R. M. Allen; J. C. A. van Ditshuizen

1983-01-01

55

Inversion and shear layer detection using AMDAR and wind profiler soundings  

NASA Astrophysics Data System (ADS)

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.

Drüe, C.; Hauf, T.; Hoff, A.

2009-09-01

56

Effects of background winds and temperature on bores, strong wind shears and concentric gravity waves in the mesopause region  

NASA Astrophysics Data System (ADS)

Using data from the CSU sodium lidar and Kyoto University OH airglow imager at Fort Collins, CO, this thesis provides a comprehensive, though qualitative, understanding for three different yet related observed fluid-dynamical phenomena in the mesopause region. The first project involves the convection-excited gravity waves observed in the OH airglow layer at 87 km. Case study on May 11, 2004 is discussed in detail along with statistical studies and a ray-tracing modeling. A single convection source matches the center of the concentric gravity waves. The horizontal wavelengths and periods of these gravity waves were measured as functions of both radius and time. The weak mean background wind between the lower and middle atmosphere determines the penetration of the gravity waves into higher altitude. The second project involves mesospheric bores observed by the same OH imager. The observation on October 9, 2007 suggests that when a large-amplitude gravity wave is trapped in a thermal duct, its wave front could steepen and forms bore-like structure in the mesopause. In turn, the large gravity wave and its bore may significantly impact the background. Statistical study reveals the possible link between the jet/front system in the lower atmosphere and the large-scale gravity waves and associated bores in the mesopause region. The third project involves the relationship between large wind shear generation and sustainment and convective/dynamic stabilities measured by the sodium lidar at the altitude of 80--105 km during 2002--2005. The correlation between wind shear, S, and Brunt-Vaisala frequency, N suggests that the maximum sustainable wind shear is determined by the necessary condition for dynamic instability of Richardson number, leading to the result that the maximal wind shear occurs at altitudes of lower thermosphere where the atmosphere is convectively very stable. The dominate source for sustainable large windshears appears to be the semidiurnal tidal-period perturbations with shorter vertical wavelengths and greater amplitude.

Yue, Jia

57

Wave mixed, wind-generated near-surface shear observed over a tidal flat  

NASA Astrophysics Data System (ADS)

Around high tide over a flooded tidal flat, vertical shear measured 0.13-0.4 m beneath the sea surface by upward-looking Acoustic Doppler Profilers (ADPs) was usually aligned with the wind. However, shear did not increase with increasing windspeed, likely owing to an increase in wave heights and wave-generated mixing with increasing windspeed. The associated increase in water-side drag coefficient with windspeed was predicted, with substantial scatter, by a model for near-surface mixing by breaking waves. A depth-independent eddy-viscosity model yielded only slightly less skill than a fitted depth-dependent model. Farther (0.3-0.6 m) from the surface, model skill was low, suggesting that shear at depth was often determined by factors other than wind. Wave heights tended to increase with increasing water depth. Consequently, the simulated wave-generated surface eddy viscosity tended to increase with increasing depth.

Henderson, Stephen M.; Mullarney, Julia C.

58

Wave mixed, wind-generated near-surface shear observed over a tidal flat  

NASA Astrophysics Data System (ADS)

Around high tide over a flooded tidal flat, vertical shear measured 0.13-0.4m beneath the sea surface by upward-looking Acoustic Doppler Profilers (ADPs) was usually aligned with the wind. However, shear did not increase with increasing windspeed, likely owing to an increase in wave heights and wave-generated mixing with increasing windspeed. The associated increase in water-side drag coefficient with windspeed was predicted, with substantial scatter, by a model for near-surface mixing by breaking waves. A depth-independent eddy-viscosity model yielded only slightly less skill than a fitted depth-dependent model. Farther (0.3-0.6m) from the surface, model skill was low, suggesting that shear at depth was often determined by factors other than wind. Wave heights tended to increase with increasing water depth. Consequently, the simulated wave-generated surface eddy viscosity tended to increase with increasing depth.

Henderson, Stephen M.; Mullarney, Julia C.

2013-06-01

59

Wind Energy Resource Assessment and analysis of wind shear in the Southern Great Plains  

Microsoft Academic Search

Summary The Oklahoma Wind Power Initiative has a mission to develop wind resource models and products, to provide educational outreach to state officials and citizens, and to study policies in other states and the nation that are promoting development of wind power. We have modeled statewide wind power densities using an empirically-derived neural net model. Since 1993, Oklahoma has been

Scott Greene; Kylah McNabb; Matt Biddle; Steven Stadler

60

On the vertical wind shear of Saturn's Equatorial Jet at cloud level  

NASA Astrophysics Data System (ADS)

In this work we analyze and compare the vertical cloud structure of Saturn's Equatorial Zone in two different epochs: the first one close to the Voyagers flybys (1979-1981) and the second one in 2004, when the Cassini spacecraft entered its orbit around the planet. Our goal is to retrieve the altitude of cloud features used as zonal wind tracers in both epochs. We reanalyze three different sets of photometrically calibrated published data: ground-based in 1979, Voyager 2 PPS and ISS observations in 1981, and we analyze a new set of Hubble Space Telescope images for 2004. For all situations we reproduced the observed reflectivity by means of a similar vertical model with three layers. The results indicate the presence of a changing tropospheric haze in 1979-1981 ( P˜100 mbar, ?˜10) and in 2004 ( P˜50 mbar, ?˜15) where the tracers are embedded. According to this model the Voyager 2 ISS images locate cloud tracers moving with zonal velocities of 455 to 465 (±2) m/s at a pressure level of 360 ± 140 mbar. For HST observations, our previous works had showed cloud tracers moving with zonal wind speeds of 280±10 m/s at a pressure level of about 50±10 mbar. All these values are calculated in the same region ( 3°±2° N). This speed difference, if interpreted as a vertical wind shear, requires a change of 90-20+50 ms per scale height, two times greater than that estimated from temperature observations. We also perform an initial guess on Cassini ISS vertical sounding levels, retrieving values compatible with HST ones and Cassini CIRS derived vertical wind shear, but not with Voyager wind measurements. We conclude that the wind speed velocity differences measured between 1979-1981 and 2004 cannot be explained as a wind shear effect alone and demand dynamical processes.

Pérez-Hoyos, S.; Sánchez-Lavega, A.

2006-01-01

61

Insight into the role of lower-layer vertical wind shear in tropical cyclone intensification over the western North Pacific  

NASA Astrophysics Data System (ADS)

Vertical wind shear fundamentally influences changes in tropical cyclone (TC) intensity. The effects of vertical wind shear on tropical cyclogenesis and evolution in the western North Pacific basin are not well understood. We present a new statistical study of all named TCs in this region during the period 2000-2006 using a second-generation partial least squares (PLS) regression technique. The results show that the lower-layer (between 850 hPa and 10 m above the sea surface) wind shear is more important than the commonly analyzed deep-layer shear (between 200 and 850 hPa) for changes in TC intensity during the TC intensification period. This relationship is particularly strong for westerly low-level shear. Downdrafts induced by the lower-layer shear bring low ? e air into the boundary layer from above, significantly reducing values of ? e in the TC inflow layer and weakening the TC. Large values of deep-layer shear over the ocean to the east of the Philippine Islands inhibit TC formation, while large values of lower-layer shear over the central and western North Pacific inhibit TC intensification. The critical value of deep-layer shear for TC formation is approximately 10 m s-1, and the critical value of lower-layer shear for TC intensification is approximately ±1.5 m s-1.

Shu, Shoujuan; Wang, Yuan; Bai, Lina

2013-06-01

62

Evolution and Growth Competition of Salt Fingers in Saline Lake with Slight Wind Shear  

NASA Astrophysics Data System (ADS)

Since the discover of double-diffusive convection by Stommel, Arons & Blanchard (1956), 'evidence has accumulated for the widespread presence of double-diffusion throughout the ocean' and for its 'significant effects on global water-mass structure and the thermohaline convection' (Schmitt, 1998). The salt-fingering form of double-diffusion has particularly attracted interest because of salt-finger convection being now widely recognized as an important mechanism for mixing heat and salt both vertically and laterally in the ocean and saline lake. In oceanographic situations or saline lake where salt fingers may be an important mechanism for the transport of heat and salt in the vertical, velocity shears may also be present. Salt finger convection is analogous to Bénard convection in that the kinetic energy of the motions is obtained from the potential energy stored in the unstable distribution of a stratifying component. On the basis of the thermal analogy it is of interest to discover whether salt fingers are converted into two-dimensional sheets by the wind shear, and how the vertical fluxes of heat and salt are changed by the wind shear. Salt finger convection under the effect of steady wind shear is theoretically examined in this paper. The evolution of developing in the presence of a vertical density gradient disturbance and the horizontal Couette flow is considered near the onset of salt fingers in the saline lake under a moderate rate of wind shear. We use velocity as the basic variable and solve the pressure Poisson equation in terms of the associated Green function. Growth competition between the longitudinal rolls (LR) and the transverse rolls (TR), whose axes are respectively in the direction parallel to and perpendicular to the Couette flow, is investigated by the weakly nonlinear analysis of coupled-mode equations. The results show that the TR mode is characterized in some range of the effective Rayleigh number, and that the stability is dominated by the LR mode in the system. KEY WORDS: evolution, saline lake, salt finger convection, wind shear, growth competition, longitudinal rolls, transverse rolls, coupled-mode equations.

Yang, Ray-Yeng; Hwung, Hwung-Hweng; Shugan, Igor

2010-05-01

63

Acoustic wave propagation through the shear layer of the DNW large open jet wind tunnel  

NASA Astrophysics Data System (ADS)

The adequacy of the sound refraction theory corrections to measurements of the aeroacoustic signals obtained from models immersed in a jet shear in the German-Dutch wind tunnel were evaluated. Four air horns and a speaker served as an aerodynamically shaped model for the calibrated noise source. The test channel is surrounded by an anechoic chamber to eliminate random noise. Data were taken with microphones traversing the flow, out of the flow, and in a stationary position. The Amiet shear layer corrections were determined to be valid in most applications. However, with the presence of both high frequency and high Mach number, the refraction angle correction must be used to account for additional shear layer effects on the sound pressure level

Ross, R.; Young, K. J.; Allen, R. M.; van Ditshuizen, J. C. A.

1983-04-01

64

Liquid crystals for surface shear stress visualization on wind turbine airfoils  

SciTech Connect

Experiments were conducted on the Sandia 17-m vertical axis wind turbine to test the liquid-crystal/surface-shear-stress visualization technique in field environments. A Sandia natural-laminar-flow airfoil served as the test surface. Initial feasibility experiments were conducted under high-tip-speed-ratio, high-Reynolds-number conditions, which resulted in low angle-of-attack, quasi-steady flow fields. Data acquisition was accomplished with a tower-mounted movie camera and 35mm color film. Liquid crystal coatings sensitive only to surface shear stress, and insensitive to temperature changes for temperatures below 50/degree/C, were utilized. Observations of coating color changes showed the liquid crystal technique capable of visualizing surface shear stress distributions, including (by contrast) regions of separated flow, under field-test conditions. 10 refs., 3 figs.

Reda, D.C.; Smith, R.W.; Bryant, T.C.; Schluter, L.L.

1988-01-01

65

Simulations of the concept of using a small nonscanning Doppler radar for wind shear detection  

Microsoft Academic Search

The concept of using a small nonscanning Doppler radar, called the weather mini-radar, for automatically detecting and quantitatively measuring low-altitude wind shear along approach and departure paths to airport runways is introduced. This work focuses on the implementation of the weather mini-radar design on a general-purpose pulse Doppler radar computer simulation. This simulation uses microburst model data generated with the

Doyle T. Peed

1990-01-01

66

Doppler radar spectral width broadening due to beamwidth and wind shear  

Microsoft Academic Search

The spectral width observed by Doppler radars can be due to several eÄects including the atmospheric turbulence within the radar sample volume plus eÄects associated with the background flow and the radar geometry and configuration. This study re-exam- ines simple models for the eÄects due to finite beam- width and vertical shear of the horizontal wind. Analytic solutions of 1-

G. D. Nastrom

1997-01-01

67

Wind-shearing in Gaseous Protoplanetary Disks and the Evolution of Binary Planetesimals  

NASA Astrophysics Data System (ADS)

One of the first stages of planet formation is the growth of small planetesimals and their accumulation into large planetesimals and planetary embryos. This early stage occurs much before the dispersal of most of the gas from the protoplanetary disk. Due to their different aerodynamic properties, planetesimals of different sizes and shapes experience different drag forces from the gas during this time. Such differential forces produce a wind-shearing (WISH) effect between close by, different-sized planetesimals. For any two planetesimals, a WISH radius can be considered at which the differential acceleration due to the wind becomes greater than the mutual gravitational pull between the planetesimals. We find that the WISH radius could be much smaller than the gravitational shearing radius by the star (the Hill radius). In other words, during the gas-phase of the disk, WISH could play a more important role than tidal perturbations by the star. Here, we study the WISH radii for planetesimal pairs of different sizes and compare the effects of wind and gravitational shearing (drag force versus gravitational tidal force). We then discuss the role of WISH for the stability and survival of binary planetesimals. Binaries are sheared apart by the wind if they are wider than their WISH radius. WISH-stable binaries can also inspiral, and possibly coalesce, due to gas drag. Here, we calculate the WISH radius and the gas-drag-induced merger timescale, providing stability and survival criteria for gas-embedded binary planetesimals. Our results suggest that even WISH-stable binaries may merge in times shorter than the lifetime of the gaseous disk. This may constrain currently observed binary planetesimals to have formed far from the star or at a late stage after the dispersal of most of the disk gas. We note that the WISH radius may also be important for other processes such as planetesimal erosion and planetesimal encounters and collisions in a gaseous environment.

Perets, Hagai B.; Murray-Clay, Ruth A.

2011-05-01

68

Wind waves on a mudflat: The influence of fetch and depth on bed shear stresses  

NASA Astrophysics Data System (ADS)

Wind waves were measured in the Willapa Bay mudflats, Washington State, USA, for two months. Wave height, period, and bed shear stresses were modulated by water depth (0-3.5m), wind speed (0-20m/s), and fetch (1-5km). Good agreement was found between the measured waves and predictions of the wave spectral model SWAN using either simplified 1D flat bottom or 2D geometries. The relationship between bed shear stress and water depth shows a dependence on fetch: the decay of bed shear stress with increasing water depth is gradual for long fetch and rapid for short fetch. This difference is explained by the coupled effects of water depth, wave height and wave period. Due to the fetch-dependent bed shear stress, different morphological consequences for tidal flats of different size are predicted. In small (˜2km) and sheltered tidal flats, waves cause the largest sediment resuspension when water levels are near mean sea level. In extensive tidal flats (˜20km) or in flats exposed to waves propagating from deep water, waves also are effective in causing substrate erosion during high tides or large storm surges.

Mariotti, Giulio; Fagherazzi, Sergio

2013-06-01

69

Wind waves on a mudflat: The influence of fetch and depth on bed shear stresses  

NASA Astrophysics Data System (ADS)

Wind waves were measured in the Willapa Bay mudflats, Washington State, USA, for two months. Wave height, period, and bed shear stresses were modulated by water depth (0-3.5 m), wind speed (0-20 m/s), and fetch (1-5 km). Good agreement was found between the measured waves and predictions of the wave spectral model SWAN using either simplified 1D flat bottom or 2D geometries. The relationship between bed shear stress and water depth shows a dependence on fetch: the decay of bed shear stress with increasing water depth is gradual for long fetch and rapid for short fetch. This difference is explained by the coupled effects of water depth, wave height and wave period. Due to the fetch-dependent bed shear stress, different morphological consequences for tidal flats of different size are predicted. In small (˜2 km) and sheltered tidal flats, waves cause the largest sediment resuspension when water levels are near mean sea level. In extensive tidal flats (˜20 km) or in flats exposed to waves propagating from deep water, waves also are effective in causing substrate erosion during high tides or large storm surges.

Mariotti, Giulio; Fagherazzi, Sergio

70

Convectively generated internal gravity waves in the lower atmosphere of Venus. I. No wind shear.  

NASA Astrophysics Data System (ADS)

The authors investigate internal gravity wave generation by convection in the lower atmosphere of Venus. A two-dimensional, nonlinear, fully compressible model of a perfect gas is employed. The calculations consider the lower atmosphere from 12- to 60-km altitude, thereby including two convection regions: the lower atmosphere convection layer from roughly 18- to 30-km altitude and the cloud-level convection layer from roughly 48- to 55-km altitude. The gravity waves of interest are located in the stable layer between these two convection regions. This study considers gravity wave generation and propagation in the absence of mean wind shear. In the absence of mean wind shear, internal gravity waves are primarily generated by cloud-level convection. Horizontal wavelengths (?10-15 km) are similar to dominant horizontal scales in the cloud-level penetrative region, and intrinsic horizontal phase speeds are comparable to cloud-level downdraft velocities. Without mean wind shear, there is no effective coupling between the lower atmosphere below 34-km altitude and the overlying stable layer. Simulated wave amplitudes and vertical wavelengths agree well with spacecraft observations, suggesting that gravity waves generated by cloud-level convection through the "mechanical oscillator" effect may be responsible for observed variations in the stable layer.

Baker, R. D.; Schubert, G.; Jones, P. W.

2000-01-01

71

Watershed Scale Shear Stress From Tethersonde Wind Profile Measurements Under Near Neutral and Unstable Atmospheric Stability  

NASA Astrophysics Data System (ADS)

Mean wind speed profiles were measured in the atmospheric surface layer, using a tethersonde system, above the Ojai Valley Watershed in southern California. The valley is mainly planted with mature avocado and orange trees. The surface shear stress and latent and sensible heat fluxes were measured above the trees which are up to 9 m in height. Near-neutral wind speed profile measurements allowed the determination of the watershed surface roughness (z0 = 1.4 m) and the momentum displacement height (d0 = 7.0 m). The wind speed measurements obtained under unstable atmospheric stability were analyzed using Monin-Obukhov similarity theory. New stability correction functions proposed based on theory and experiments of Kader-Yaglom as well as the now classic Businger-Dyer type functions were tested. The watershed shear stress values calculated using the surface layer wind speed profiles with the new Monin-Obukhov stability functions were found to be improved in comparison with the values obtained with the Businger-Dyer functions under strongly unstable stability conditions. The Monin-Obukhov model with the Businger-Dyer stability correction function underpredicted the momentum flux by 25% under strongly unstable stability conditions, while the new Kader-Yaglom formulation compared well on average (R2 = 0.77) with the surface eddy correlation measurements for all atmospheric stability conditions. The unstable 100-m drag coefficient was found to be u*2/V1002 = 0.0182.

Parlange, M. B.; Katul, G. G.

1995-04-01

72

Two-Dimensional Study of the Maximum Power That Can Be Obtained from a Wind Turbine in a Wind Shear Layer.  

National Technical Information Service (NTIS)

For modern large wind turbines there is a considerable velocity gradient in the approaching flow, since the wind flow field above the ground normally is a shear layer with a velocity profile reminding of that of a boundary layer of a wing or a flat plate....

B. C. A. Johansson

1981-01-01

73

Acoustic wave propagation through shear layer of the German-Dutch open jet wind tunnel (DNW)  

NASA Astrophysics Data System (ADS)

The acoustic correction procedures for 1/3 octave analysis in a 20 m long open jet, surrounded by a large anechoic room, were checked with a calibrated noise source using noise data taken inside and outside the flow. Multitone marine horns and an acoustic driver coupled to a horn for broadband and single tone noise were used. The usual instrumentation and wind tunnel corrections can be applied. The usual shear layer correction, based on an infinitely thin shear layer, has to be extended to correct for turbulence and other effects for the case of high tunnel velocity, high frequency, and the most forward and the most rearward propagation angles from the sound source. This correction is insensitive to the position of the model in the flow and type of sound source (tone or broadband).

Ross, R.; Young, K. J.; Allen, R. M.; Vanditschuizen, J. C. A.

1983-01-01

74

Magnetic Reconnection in the Solar Wind at Current Sheets Associated with Extremely Small Field Shear Angles  

NASA Astrophysics Data System (ADS)

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, ?, ranging from 4° to 9°, the smallest reported values of ? yet associated with reconnection exhausts in a space plasma. They were observed in plasma characterized by extremely low (0.02-0.04) plasma ?, and very high (281-383 km s-1) Alfvén speed, V A. Low ? allows reconnection to occur at small ? and high V A leads to exhaust jets that are fast enough relative to the surrounding solar wind to be readily identified. Very small-? current sheets are common in the solar wind at 1 AU, but typically are not associated with particularly low plasma ? or high V A. On the other hand, small-? current sheets should be common in the lower solar corona, a plasma regime of extremely low ? and extremely high V A. Our observations lend credence to models that predict that reconnection at small-? current sheets is primarily responsible for coronal heating.

Gosling, J. T.; Phan, T. D.

2013-02-01

75

Simple kinematic models for the environmental interaction of tropical cyclones in vertical wind shear  

NASA Astrophysics Data System (ADS)

A major impediment to the intensity forecast of tropical cyclones (TCs) is believed to be associated with the interaction of TCs with dry environmental air. However, the conditions under which pronounced TC-environment interaction takes place are not well understood. As a step towards improving our understanding of this problem, we analyze here the flow topology of a TC immersed in an environment of vertical wind shear in an idealized, three-dimensional, convection-permitting numerical experiment. A set of distinct streamlines, the so-called manifolds, can be identified under the assumptions of steady and layer-wise horizontal flow. The manifolds are shown to divide the flow around the TC into distinct regions. The manifold structure in our numerical experiment is more complex than the well-known manifold structure of a non-divergent point vortex in uniform background flow. In particular, one manifold spirals inwards and ends in a limit cycle, a meso-scale dividing streamline encompassing the eyewall above the layer of strong inflow associated with surface friction and below the outflow layer in the upper troposphere. From the perspective of a steady and layer-wise horizontal flow model, the eyewall is well protected from the intrusion of environmental air. In order for the environmental air to intrude into the inner-core convection, time-dependent and/or vertical motions, which are prevalent in the TC inner-core, are necessary. Air with the highest values of moist-entropy resides within the limit cycle. This "moist envelope" is distorted considerably by the imposed vertical wind shear, and the shape of the moist envelope is closely related to the shape of the limit cycle. In a first approximation, the distribution of high- and low-?e air around the TC at low to mid-levels is governed by the stirring of convectively modified air by the steady, horizontal flow. Motivated by the results from the idealized numerical experiment, an analogue model based on a weakly divergent point vortex in background flow is formulated. The simple kinematic model captures the essence of many salient features of the manifold structure in the numerical experiment. A regime diagram representing realistic values of TC intensity and vertical wind shear can be constructed for the point-vortex model. The results indicate distinct scenarios of environmental interaction depending on the ratio of storm intensity and vertical-shear magnitude. Further implications of the new results derived from the manifold analysis for TCs in the real atmosphere are discussed.

Riemer, M.; Montgomery, M. T.

2011-09-01

76

On the vertical wind shear of Saturn's Equatorial Jet at cloud level  

NASA Astrophysics Data System (ADS)

With the aim of retrieving the altitude of cloud features used as zonal wind tracers in Saturn's atmosphere, we have reanalyzed three different sets of photometric and calibrated data corresponding to the Voyager epoch 1979-1981 (ground-based in 1979, Voyager 2 PPS and ISS observations in 1981), and we have analyze a new set of Hubble Space Telescope images for 2004. This analysis is put in the perspective of our previous HST study for 1994-2003 (Pérez-Hoyos et al., Icarus, 176, 155. 2005). A common result is found that the individual cloud tracers are embedded within a variable tropospheric haze. According to our models, the Voyager 2 ISS images locate the cloud tracers moving with zonal velocities of 455 to 465 (± 2) m/s at a pressure level of 360 ± 140 mbar. For HST observations, the cloud tracers moving with zonal wind speeds of 280 ± 10 m/s, locate at a pressure level of about 50 ± 10 mbar. All these values are calculated in the latitude 3 deg North. The speed difference, if interpreted as a vertical wind shear (Porco et al., Science, 307, 1226. 2005), requires a change of 90 m/s per scale height, two times greater than that estimated from Cassini CIRS data (Flasar et al., Science, 307, 1247, 2005). We also perform an initial guess on Cassini ISS vertical sounding levels, retrieving values compatible with the HST ones but not with Voyager wind measurements. We conclude that the wind speed velocity differences measured between 1979-81 and 2004 in the upper troposphere cannot be solely explained as a wind shear effect and demand dynamical processes. We discuss the possible action of Rossby waves or an intrinsic circulation change in the ammonia cloud layer and above, following a large period of equatorial storm activity. Acknowledgments: This work was supported by MCYT AYA2003-03216, FEDER, and Grupos UPV 15946/2004. S.P.-H. acknowledges a PhD fellowship from the Spanish MEC and R. H. a post-doc contract from Gobierno Vasco.

Sánchez-Lavega, A.; Pérez-Hoyos, S.

2005-08-01

77

Torrential rainfall responses to vertical wind shear, radiation and ice clouds: A rainfall partitioning analysis based on surface rainfall budget  

NASA Astrophysics Data System (ADS)

The effects of vertical wind shear, radiation and ice clouds on the torrential rainfall event over Jinan, China during July 2007 are investigated through a rainfall partitioning analysis based on surface rainfall budget. All experiments are integrated with an imposed large-scale vertical velocity and zonal wind from the National Centers for Environmental Prediction (NCEP)/Global Data Assimilation System (GDAS), while vertical wind shear, cloud radiative effects, cloud-radiation interaction and ice clouds are, respectively, suppressed in the sensitivity experiments. The largest change in rainfall contribution from the rainfall with local atmospheric drying, water vapor divergence, and hydrometeor loss/convergence (TfM) caused by the exclusion of vertical wind shear is a decrease associated with the shrink of rainfall area and the decrease in decrease in hydrometeor loss/convergence. The largest change in rainfall contribution from the rainfall with local atmospheric drying, water vapor convergence, and hydrometeor loss/convergence (TFM) caused by the exclusion of ice clouds is an increase associated with the expansion of rainfall area and the enhancements in all rainfall processes. The exclusion of vertical wind shear also causes the increase in rainfall contribution from the rainfall with local atmospheric moistening, water vapor convergence, and hydrometeor loss/convergence (tFM), but the increase is weaker than the decrease in rainfall contribution from TfM. The rainfall contributions from the other rainfall types are less sensitive to these effects than those from the three rainfall types. The cloud radiative effects on rainfall contributions from all rainfall types are weaker than the effects of vertical wind shear and ice clouds.

Zhou, Yushu; Ran, Lingkun

2012-05-01

78

Acoustic Evaluation of the German-Dutch Wind Tunnel (DNW) Shear Layer Correction Using a Model Jet.  

National Technical Information Service (NTIS)

Acoustic tests of a 6-cm model jet were conducted in the German-Dutch Wind Tunnel 6m by 8m free jet facility to evaluate a free jet shear layer correction procedure that adds an empirical correction to the previous theoretical correction. Static-flight ef...

W. H. Herkes F. G. Strout R. Ross J. C. A. Vanditshuizen

1983-01-01

79

Shear layer effects on pure tone sound propagation in open jet wind tunnels using 1\\/3 octave analysis  

Microsoft Academic Search

Wind tunnel tests were performed in the 10th scale DNW pilottunnel to assess the effects of the turbulent shear layer on pure tone sound, propagating from a model in the flow to a microphone outside the flow. The effect is very small when 1\\/3 octave analysis is used, as the spectral broadening of the tone is in general smaller than

R. Ross

1980-01-01

80

Effects of mesoscale convective organization and vertical wind shear on the cumulus-environment interaction  

SciTech Connect

This study is made to understand the thermodynamic and dynamic aspects of cumulus-environment interaction. Specifically, the author examines (1) the similarities and differences of cumulus-environment interactions in the tropical and midlatitude convective systems (2) the impact of the presence of mesoscale circulations on the interpretation of cumulus-environment interaction, and (3) the effects of vertical wind shear on the dynamic interaction of cumulus convection with the large-scale motion. Analysis of PRE-STORM and GATE data show larger moist convective instability, large-scale forcing and vertical wind shear in the mid-latitude MCCs and squall lines than in the tropical non-squall clusters. The interaction mechanism based on the cumulus-induced subsidence and detrainment is capable of explaining most of the observed heating and drying under widely different environment conditions. The Arakawa-Schubert (A-S) quasi-equilibrium assumption is valid. Both the cumulus and stratiform cloud effects are stronger in midlatitude convective systems than in tropical systems. The heat and moisture budget results using the fine resolution SESAME data show pronounced dipole patterns in the horizontal distributions of vertically integrated heat source and moisture sink. Further analysis shows that the dipole pattern is closely related to the horizontal fluxes of heat and moisture due to mesoscale circulations. The quasi-equilibrium assumption becomes more accurate for the data resolving mesoscale circulation. The inclusion of downdrafts is required to accurately predict the cumulus heating and drying. Significant differences are found in vertical transport of horizontal momentum between the MCC and squall line. A new cloud momentum model which includes the convective-scale horizontal pressure gradient force has been developed. The application of the new cloud momentum model shows that the new model can simulate both the upgradient and downgradient transport of cloud momentum.

Wu, Xiaoqing.

1992-01-01

81

Shear layer effects on pure tone sound propagation in open jet wind tunnels using 1/3 octave analysis  

NASA Astrophysics Data System (ADS)

Wind tunnel tests were performed in the 10th scale DNW pilottunnel to assess the effects of the turbulent shear layer on pure tone sound, propagating from a model in the flow to a microphone outside the flow. The effect is very small when 1/3 octave analysis is used, as the spectral broadening of the tone is in general smaller than a 1/3 octave bandwidth. This means that all sound energy is propagated through the shear layer and that only the usual refraction corrections have to be used. It is concluded that sound scattering by shear layer turbulence does not restrict the use of large open wind tunnels, such as DNW, when full scale effective perceived noise levels are to be determined.

Ross, R.

1980-06-01

82

Airglow observations of dynamical (wind shear-induced) instabilities over Adelaide, Australia, associated with atmospheric gravity waves  

NASA Astrophysics Data System (ADS)

While several observations have been made in recent years of instability features in airglow images of atmospheric gravity waves (AGWs), such measurements are still rare. To date, these features are characterized by appearing to be aligned perpendicular to the AGW wave fronts. Multi-instrument observations confirm the theoretical prediction that such features are caused by convective instabilities where the AGW-induced temperature variation causes the total lapse rate to exceed the adiabatic lapse rate. In February 2000, airglow observations were obtained at Buckland Park, Australia, which showed instability features with a different characteristic. These images showed small-scale (less than 10 km horizontal wavelength) features aligned parallel to the larger scale AGW wave fronts. These features were only seen in OH images, not in O2A images, indicating that they originate below 90 km altitude. Simultaneous MF radar wind data reveal the presence of a mean wind shear which, during the period of the small-scale features, was aligned nearly in the direction of AGW propagation. In addition, the larger scale AGW approached a critical level near 90 km altitude. While the wind shear itself is not large enough to cause an instability, an analysis of the data suggests that the small-scale features are the result of a dynamic (wind shear-induced) instability in the 87-90 km altitude region. The instability was due to a combination of the background wind shear and the large shear induced by the passage of the larger scale AGW as it approached the critical level.

Hecht, J. H.; Walterscheid, R. L.; Vincent, R. A.

2001-11-01

83

Eddy and deep chlorophyl maximum response to wind-shear in the lee of Gran Canaria  

NASA Astrophysics Data System (ADS)

The physical and biological properties of the warm wake of Gran Canaria were examined during a survey carried out in June 1998. The sampling region was dominated by the presence of a warm triangular region downwind the island and an anticyclonic eddy spun off the island. Convergent and divergent frontal regions were generated by the wind shear zones extending along either side of the sheltered region of the warm wake. With increasing distance from shore, evidence of convergent/divergent frontal regions weakened, but the influence of the eddy increased. Both structures, frontal regions and the eddy, clearly altered the vertical phytoplankton biomass distribution as indicated by chlorophyll-fluorescence. Downwelling on the convergent boundary moved the 26.2 kg m -3 isopycnal and its associated deep chlorophyll maximum (DCM) below the 1% light zone. Upwelling at the divergent boundary not only elevated the DCM with its associated isopycnal but also, because of the increased light levels, allowed a shift in the DCM to higher (deeper) density surfaces (26.4 kg m -3). However, the highest integrated chlorophyll occurred in the central wake.

Basterretxea, G.; Barton, E. D.; Tett, P.; Sangrá, P.; Navarro-Perez, E.; Ar?´stegui, J.

2002-06-01

84

The ATC evaluation of the prototype Airport Surveillance Radar Wind Shear Processor (ASR-WSP) at Orlando International Airport  

NASA Astrophysics Data System (ADS)

The Airport Surveillance Radar Wind Shear Processor (ASR-WSP), also known as Airport Surveillance Radar-9 (ASR-9) modification for low altitude wind shear detection, is a production ASR-9 with an expanded weather channel for added processing capabilities. The primary mission of the ASR-WSP is to enhance the safety of air travel through the timely detection and reporting of hazardous wind shear in and near the terminal approach and departure zones of the airport. It will also improve the management of air traffic (AT) in the terminal area through the forecast of precipitation, and ultimately the detection of other hazardous weather phenomena. The ASR-WSP may be used as a stand-alone system at airports without a Terminal Doppler Weather Radar (TDWR) or Enhanced-Low Level Wind Shear Alert System (E-LLWAS), or in an integrated mode with either or both the TDWR and E-LLWAS. An operational evaluation of a prototype ASR-WSP, developed by Massachusetts Institute of Technology Lincoln Laboratories (MIT/LL), was conducted at the Orlando International Airport (MCO) in Orlando, Florida, during the period 29 Jun. to 31 Aug. 1992. The objective of the evaluation was to obtain Federal Aviation Administration (FAA) air traffic controller reaction to the prototype ASR-WSP weather data and display equipment. The following are highlights of the evaluation: (1) the ASW-WSP is very useful when making runway configuration changes; (2) the ASR-WSP is not perceived to be as accurate as the prototype TDWR; (3) the gust front prediction feature is not reliable; and (4) the information provided on both the RDT and the GSD is very useful.

Martinez, Radame

1993-03-01

85

Terminal Doppler Weather Radar (TDWR) Low Level Wind Shear Alert System 3 (LLWAS 3) Integration Studies at Orlando International Airport in 1991 and 1992.  

National Technical Information Service (NTIS)

In 1993 the Federal Aviation Administration (FAA) began deploying two new wind shear detection systems: the Terminal Doppler Weather Radar (TDWR) and the third-generation Low Level Windshear Alert System (LLWAS 3). Currently, 9 airports are scheduled to r...

R. E. Cole R. F. Todd

1994-01-01

86

A two-dimensional study of the maximum power that can be obtained from a wind turbine in a wind shear layer  

SciTech Connect

In 1926 Albert Betz derived a one-dimensional stream tube theory for the maximum power that can be obtained from a wind turbine in a uniform flow. However, for modern large wind turbines there is a considerable velocity gradient in the approaching flow, since the wind flow field above the ground normally is a shear layer with a velocity profile reminding of that of a boundary layer of a wing or a flat plate. The present study extends Betz' theory to a two-dimensional case, where the undisturbed velocity field is given and allowed to vary arbitrarily vertically, and the location of the wind turbine is given. The maximum power is calculated by the method of calculus of variations. It is found that for common wind velocity profiles the maximum power is only slightly larger than the power, which is obtained by a constant relative wind speed retardation, equal to Betz' retardation, while for a linear velocity profile there is a considerable difference.

Johansson, B.C.A.

1981-04-01

87

Very High Resolution Numerical Weather Prediction of Wind Shear Event in the Complex Terrain Around Juneau Alaska  

NASA Astrophysics Data System (ADS)

Juneau International Airport is surrounded by complex terrain, often presenting challenging conditions to departing aircraft. General aviation departure procedures for Runway 08 include a 180-degree right turn "as soon as practical" in order to avoid steeply rising terrain. Under strong wind conditions characterized by post-frontal topographically enhanced wind shear, aircraft following these procedures may encounter turbulence or wind shear classified as severe. In January 1993, a Boeing 727 aircraft at a 30-degree bank encountered extreme crosswinds resulting in departure from controlled flight, with successful recovery occurring within only 50 meters of the ground. In this work, we focus on a similar event at Juneau from December 2009. This case has been modeled with WRF at very high resolutions down to 111 m horizontal, with mixed results. The focus of this work is to investigate in more detail the problems, costs and benefits of using very high resolution topography and model runs in a high-wind event in complex terrain. Several model runs will be performed, and results will be compared with each other and station observations available through the Juneau Airport Wind System (JAWS). Two high resolution topographies - the USGS National Elevation Dataset (NED) and the Shuttle Radar Topography Mission (SRTM) - will be compared with the USGS 30s topography in their ability to match the real topography and their influence on forecast winds. Additionally, an attempt will be made to push the model into the realm of Large Eddy Simulation (LES) with a 50 m horizontal resolution in a limited region.

Morton, D.; Arnold, D.; Schicker, I.; Dierking, C.; Harrison, K.

2011-12-01

88

Role of upper-level wind shear on the structure and maintenance of derecho-producing convective systems  

NASA Astrophysics Data System (ADS)

Common large-scale environments associated with the development of derecho-producing convective systems from a large number of events are identified using statistical clustering of the 500-mb geopotential heights as guidance. The majority of the events (72%) fall into three main patterns that include a well-defined upstream trough (40%), a ridge (20%), and a zonal, low-amplitude flow (12%), which is defined as an additional warm-season pattern that is not identified in past studies of derecho environments. Through an analysis of proximity soundings, discrepancies are found in both low-level and deep-tropospheric shear parameters between observations and the shear profiles considered favorable for strong, long-lived convective systems in idealized simulations. To explore the role of upper-level shear in derecho environments, a set of two-dimensional simulations of density currents within a dry, neutrally stable environment are used to examine the ability of a cold pool to lift environmental air within a vertically sheared flow. The results confirm that the addition of upper-level shear to a wind profile with weak to moderate low-level shear increases the vertical displacement of low-level parcels despite a decrease in the vertical velocity along the cold pool interface, as suggested by previous studies. Parcels that are elevated above the surface (1-2 km) overturn and are responsible for the deep lifting in the deep-shear environments. This deep overturning caused by the upper-level shear helps to maintain the tilt of the convective systems in more complex two-dimensional and three dimensional simulations. The overturning also is shown to greatly increase the size of the convective systems in the three-dimensional simulations by facilitating the initiation and maintenance of convective cells along the cold pool. When combined with estimates of the cold pool motion and the storm-relative hodograph, these results may best be used for the prediction of the demise of strong, linear mesoscale convective systems (MCSs) and may provide a conceptual model for the persistence of strong MCSs above a surface nocturnal inversion in situations that are not forced by a low-level jet.

Coniglio, Michael Charles

89

Simultaneous observations of density fluctuations, trimethyl aluminum trail diffusion, wind shears and gravity waves in the turbopause region  

NASA Astrophysics Data System (ADS)

In February 2009, a rocket experiment was launched from Alaska entitled: Where is the tur-bopause? Instabilities, generation and development of turbulence in the 100-km region. The salvo of four rockets obtained in situ wind and temperature profiles, neutral and plasma fluctu-ations, and wave and tidal activity from ground based lidar, radar, and other instrumentation. Among the goals are comparisons of turbulent energy dissipation rates measured by spectral analysis and from chemical trail expansion rates. Based on trimethyl aluminum trail diffusion we identified regions of mixing around 90 km, 95 km, and also above 100 km. The lower re-gion coincided with layers of density fluctuations, while the upper region was characterized by strong wind shear and kilometer-size density structures in the lower thermosphere. Rayleigh and sodium lidar observed a dominant 4-hour wave motion in the upper mesosphere.

Lehmacher, Gerald; Larsen, Miguel; Collins, Richard; Bilen, Sven; Croskey, Charles; Mitchell, John; Luebken, Franz-Josef; Rapp, Markus

90

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

NASA Astrophysics Data System (ADS)

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 layer scheme and "warm rain" microphysics - to foster better understanding of the dynamics and thermodynamics that govern the modification of TC intensity. A suite of experiments is performed with intense TCs in moderate to strong vertical shear. In all experiments the TC is resilient to shear but significant differences in the intensity evolution occur. The ventilation of the TC core with dry environmental air at mid-levels and the dilution of the upper-level warm core are two prevailing hypotheses for the adverse effect of vertical shear on storm intensity. Here we propose an alternative and arguably more effective mechanism how cooler and drier (lower ?e) air - "anti-fuel" for the TC power machine - can enter the core region of the TC. Strong and persistent downdrafts flux low ?e air from the lower and middle troposphere into the boundary layer, significantly depressing the ?e values in the storm's inflow layer. Air with lower ?e values enters the eyewall updrafts, considerably reducing eyewall ?e values in the azimuthal mean. When viewed from the perspective of an idealised Carnot-cycle heat engine a decrease of storm intensity can thus be expected. Although the Carnot cycle model is - if at all - only valid for stationary and axisymmetric TCs, a strong correlation between the downward transport of low ?e into the boundary layer and the intensity evolution offers further evidence in support of our hypothesis. The downdrafts that flush the inflow layer with low ?e air are associated with a quasi-stationary region of convective activity outside the TC's eyewall. We show evidence that, to zero order, the formation of the convective asymmetry is driven by the balanced dynamical response of the TC vortex to the vertical shear forcing. Thus a close link is provided between the thermodynamic impact in the near-core boundary layer and the balanced dynamics governing the TC vortex evolution.

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

2009-05-01

91

Internal Gravity Waves in an Atmosphere with Wind Shear: Validity of the WKB Approximation at Critical Layers in the Presence of Buoyancy Forces  

Microsoft Academic Search

The application of the WKB method to internal gravity waves in a compressible fluid with wind shear is studied from the standpoint of dispersion and of the validity of the method. It is shown that at resonance (the level where the phase speed is Doppler-shifted to zero) the validity is dependent only on the local Richardson number; we accept as

R. C. Whitten; C. A. Riegel

1973-01-01

92

An Operative Wind Shear and Inversion Warning System for Helsinki-Vantaa Airport.  

National Technical Information Service (NTIS)

The system has some data banking capabilities. Real time cross-sections are available in graphical or numerical form at any moment. The station is able to observe low-level wind, temperature, and humidity profiles continuously. Most data are used by the m...

O. Korhonen

1980-01-01

93

The propagation of gravity waves through a critical layer for conditions of moderate wind shear  

Microsoft Academic Search

Solutions of the linearised hydrodynamic equations for a viscous atmosphere using (i) a full-wave integration procedure and (ii) a simplified analytical approach are used to examine the attenuation of gravity waves passing through a critical layer, where the horizontal phase velocity is equal to that of the mean wind. Particular attenuation is paid to the variation of this attenuation with

M. R. Bowman; L. Thomas; R. H. Thomas

1980-01-01

94

Experimental measurements of lee wave interaction with wind shear, wakes, and boundary layers  

NASA Astrophysics Data System (ADS)

We present quantitative whole field measurements of the nonlinear internal wave field generated by a linearly stratified fluid that is perturbed by an idealized isolated ``mountain'' obstacle. We carried out experiments in a recirculating ``Kovasznay'' tank, which allows both the steady wave field to be quasi-stationary in the laboratory frame, and also for the effect of vertical variations in horizontal velocity to be studied straightforwardly. We observe critical layer absorption and total reflection at turning points, and we compare the effect of externally imposed shear with the behaviour associated with boundary layers both in the vicinity of the obstacle, (when the obstacle is located at the base of the tank) and at some distance (when the obstacle is located at the free surface). Post-processing of the experimental data using the Hilbert transform allows us to separate both the emitted outgoing and reflected incoming wave fields. Our results show that the the emission is a fundamentally nonlinear effect, with significant emission and absorption associated with the wake flow structure downstream of the obstacle. Our results suggest that wake effects may be responsible for the wave field observed downstream of many obstacles in atmospheric and oceanographic flows.

Patterson, Michael; Caulfield, Colm; Dalziel, Stuart

2008-11-01

95

Deposition from a volcanic plume under sheared wind condition, origin of double peaked tephra samples.  

NASA Astrophysics Data System (ADS)

The 2011 Grímsvötn eruption started at 17:30 UTC on May the 21st. at around 19:00 UTC the eruption broke through the ice and injected tephra (volcanic ash) into the atmosphere. Peak discharge rate was reached during the first hours of the eruption giving a rise to 20 km high eruption plume. During the first hours of the eruption volcanic tephra was carried from the vent area in two separate directions. The high part of the plume headed towards ESE while the lower part was carried towards SSW by prevailing winds. This caused an unusually wide area (150 km wide at a distance of some 50 km downwind from the volcano) to be affected by the tephra fall. At about 02:00 UTC on the 22nd of May the plume declined and the upper part of the ash cloud was detached from the lower main cloud that continued to carry tephra towards SSW from the volcano. This gave and unexpected opportunity to sample volcanic ash cloud from different levels with accuracy. We shall present some morphological and grain size data from theses sample sets and discuss them in the context of the plume and eruption dynamics. Data from the lower part of the plume do show greater variety in grain size and are in general double peaked, while those sampled from the higher part of the plume are more uniform and single peaked. This suggests that commonly observed double peaks in grain size data do represent less focused sampling from different levels of the plume.

Hoskuldsson, Armann; Thordarsson, Thor; Larsen, Gudrun; Tumi Gudmundsson, Magnus

2013-04-01

96

The use of wind-shear theory to evaluate time variations of sporadic-E-layer parameters  

NASA Astrophysics Data System (ADS)

Sporadic-E-layer parameters measured in Havana during solar eclipses in 1972 and 1973 and on a control day are analyzed with the aim of examining effects connected with wind-system variations. An expression is derived which makes it possible to use ionospheric-observation data to evaluate the characteristics of amplitude variations of the east-west component of the neutral wind. It is concluded that a complex system of winds is generated when an eclipse occurs at sunrise.

Kerblai, T. S.; Palacio, L.; Melendez, B.

1986-04-01

97

A Two-Dimensional Study of the Maximum Power That Can Be Obtained from a Wind Turbine in a Wind Shear Layer.  

National Technical Information Service (NTIS)

In 1926 Albert Betz derived a one-dimensional stream tube theory for the maximum power that can be obtained from a wind turbine in a uniform flow. However, for modern large wind turbines there is a considerable velocity gradient in the approaching flow, s...

B. C. A. Johansson

1981-01-01

98

Wind  

NSDL National Science Digital Library

This document examine wind power as an energy resource. The reading will define wind and discuss topics such as (1) The history of wind machines, (2) Today's windmills, and (3) Types of wind machines. This resource is structured as an informational handout to supplement your energy activities or to generate discussion questions. Copyright 2005 International Technology Education Association

National Energy Education Development (NEED) Project

2003-01-01

99

TRMM-retrieved cloud structure and evolution of MCSs over the northern South China Sea and impacts of CAPE and vertical wind shear  

NASA Astrophysics Data System (ADS)

Cloud structure and evolution of Mesoscale Convective Systems (MCSs) retrieved from the Tropical Rainfall Measuring Mission Microwave Imager (TRMM TMI) and Precipitation Radar (PR) were investigated and compared with some pioneer studies based on soundings and models over the northern South China Sea (SCS). The impacts of Convective Available Potential Energy (CAPE) and environmental vertical wind shear on MCSs were also explored. The main features of MCSs over the SCS were captured well by both TRMM PR and TMI. However, the PR-retrieved surface rainfall in May was less than that in June, and the reverse for TMI. TRMM-retrieved rainfall amounts were generally consistent with those estimated from sounding and models. However, rainfall amounts from sounding-based and PR-based estimates were relatively higher than those retrieved from TRMM-TMI data. The Weather Research and Forecasting (WRF) modeling simulation underestimated the maximum rain rate by 22% compared to that derived from TRMM-PR, and underestimated mean rainfall by 10.4% compared to the TRMM-TMI estimate, and by 12.5% compared to the sounding-based estimate. The warm microphysical processes modeled from both the WRF and the Goddard Cumulus Ensemble (GCE) models were quite close to those based on TMI, but the ice water contents in the models were relatively less compared to that derived from TMI. The CAPE and wind shear induced by the monsoon circulation were found to play critical roles in maintaining and developing the intense convective clouds over SCS. The latent heating rate increased more than twofold during the monsoon period and provided favorable conditions for the upward transportation of energy from the ocean, giving rise to the possibility of inducing large-scale interactions.

Li, Xiangshu; Guo, Xueliang; Fu, Danhong

2013-01-01

100

Aeolian sand transport: a wind tunnel model  

Microsoft Academic Search

Wind sand transport is an important geological process on earth and some other planets. Formulating the wind sand transport model has been of continuing significance. Majority of the existing models relate sand transport rate to the wind shear velocity based on dynamic analysis. However, the wind shear velocity readapted to blown sand is difficult to determine from the measured wind

Zhibao Dong; Xiaoping Liu; Hongtao Wang; Xunming Wang

2003-01-01

101

Wind Speed and Wind Power Characteristics for Gassim, Saudi Arabia  

Microsoft Academic Search

The study presents the wind speed characteristics like wind statistics, local values of wind shear exponent (WSE), Weibull distribution parameters, turbulence intensity (TI), and wind energy yield using wind speed measurements made at 20 m, 30 m, and 40 m above ground level (AGL) from December 5, 1995, to October 24, 1998. At 20, 30, and 40 m above ground

Naif M. Al-Abbadi; Shafiqur Rehman

2009-01-01

102

A Simple Method to Predict Threshold Shear Velocity in the Field  

Microsoft Academic Search

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

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

2009-01-01

103

Winds Observed from July 1968 through November 1970 in the 83 to 216 km Altitude Region.  

National Technical Information Service (NTIS)

Horizontal winds and shears have been computed from 25 rocket released chemical trails. Tables are presented which give vertical profiles of wind speed, heading, and components and the wind shear components. Eight rockets created releases on the up and do...

C. G. Justus H. D. Edwards

1971-01-01

104

Shear Strength  

NSDL National Science Digital Library

Dr. John Atkinson, of the University of the West of England, developed a site for undergraduate students wanting to learn more about soil classification. His site addresses issues such as: shear strength, peak strength, and residual strength testing. Filled with charts, diagrams, statistics, the information is pertinent and easily understood by almost any audience.

Atkinson, John

2008-10-07

105

Measurement of surface shear stress vector distribution using shear-sensitive liquid crystal coatings  

NASA Astrophysics Data System (ADS)

The global wall shear stress measurement technique using shear-sensitive liquid crystal (SSLC) is extended to wind tunnel measurements. Simple and common everyday equipment is used in the measurement; in particular a tungsten-halogen light bulb provides illumination and a saturation of SSLC coating color change with time is found. Spatial wall shear stress distributions of several typical flows are obtained using this technique, including wall-jet flow, vortex flow generated by a delta wing and junction flow behind a thin cylinder, although the magnitudes are not fully calibrated. The results demonstrate that SSLC technique can be extended to wind tunnel measurements with no complicated facilities used.

Zhao, Ji-Song; Scholz, Peter; Gu, Liang-Xian

2012-10-01

106

Wind Energy and Climate: Modeling the Atmospheric Impacts of Wind Energy Turbines  

Microsoft Academic Search

The size and number of wind farms is growing across the globe. Wind energy provides the climatic benefit of producing energy without emitting CO2, however wind energy also produces unintended impacts. Large wind farms directly influence the atmospheric boundary layer by (1.) reducing wind speeds, (2.) generating blade scale turbulence in the wake of the turbines, and (3.) generating shear

A. S. Adams; D. W. Keith

2007-01-01

107

Shear thickening, shear localization and elastic turbulence  

Microsoft Academic Search

The vast majority of complex fluids is shear thinning. The mechanisms of shear thinning are relatively well understood, and the phenomenon is widely used to tailor the rheology of complex fluids. Shear thickening is the exception to this rule, is incompletely understood and hardly ever used to tailor fluid properties. We study shear thickening in granular pastes (cornstarch), and show

Daniel Bonn

2006-01-01

108

The two-stream plasma instability in a velocity shear and its role in the solar wind-Venus ionosphere interaction  

NASA Astrophysics Data System (ADS)

We study the linear development of the two-stream instability in a plasma consisting of cold ions, assumed at rest and taken to represent planetary ions, and a hot, streaming population of electrons, representing the solar wind. The stability of quasi-global perturbations is analyzed as a function of plasma density, temperature and streaming velocity, using a QR algorithm to compute the growth rate of eigenmodes of the coupled fluid equations of motion for both species. The sense of the cross-flow, viscous-like momentum transfer from the streaming plasma to ionospheric ions, is determined on the basis of an heuristic estimation following a Reynolds averaging procedure of the cross-flow momentum flux term in the equation of motion.

Reyes-Ruiz, M.; Aceves, H.; Perez De Tejada, H. A.

2011-12-01

109

Shear strain imaging using shear deformations  

PubMed Central

In this article we investigate the generation of shear strain elastograms induced using a lateral shear deformation. Ultrasound simulation and experimental results demonstrate that the shear strain elastograms obtained under shear deformation exhibit significant differences between bound and unbound inclusions in phantoms, when compared to shear strain images induced upon an axial compression. A theoretical model that estimates the decorrelation between pre- and postdeformation radio frequency signals, as a function of extent of shear deformation, is also developed. Signal-to-noise ratios of shear strain elastograms obtained at different shear angles are investigated theoretically and verified using ultrasound simulations on a uniformly elastic phantom. For the simulation and experiment, a two-dimensinal block-matching-based algorithm is used to estimate the axial and lateral displacement. Shear strains are obtained from the displacement vectors using a least-squares strain estimator. Our results indicate that the signal-to-noise ratio (SNR) of shear strain images increases to reach a maximum and saturates, and then decreases with increasing shear angle. Using typical system parameters, the maximum achievable SNR for shear strain elastography is around 8 (18 dB), which is comparable to conventional axial strain elastography induced by axial compression. Shear strain elastograms obtained experimentally using single inclusion tissue-mimicking phantoms with both bound and unbound inclusions (mimicking cancerous masses and benign fibroadenomas, respectively) demonstrate the characteristic differences in the depiction of these inclusions on the shear strain elastograms.

Rao, Min; Varghese, Tomy; Madsen, Ernest L.

2008-01-01

110

Wind initiation thresholds of the moistened sands  

NASA Astrophysics Data System (ADS)

The widely accepted Bagnold-type function for calculating threshold wind velocity or shear velocity was developed for dry sands, but surface moisture is an extremely important variable controlling the entrainment process of sands by wind because the tensile force between the water molecules and sand grains produces cohesion. Here we report detailed wind tunnel experimental results on the threshold shear velocity of moistened sand of different sizes. The results show that relative threshold shear velocity, which is the ratio of threshold shear velocity of sand in the moistened state to that in the dry state, is better related to moisture content than threshold shear velocity itself. Function, modified after the Bagnold equation has been developed to estimate the threshold shear velocities of moistened sands. For a given grain size, the threshold shear velocity is proportional to (1 + KM)1/2, where, M is the moisture content, and K is a coefficient depending on grain size.

Dong, Zhibao; Liu, Xiaoping; Wang, Xunming

2002-06-01

111

Wind turbine acoustics  

NASA Astrophysics Data System (ADS)

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.

Hubbard, Harvey H.; Shepherd, Kevin P.

1990-12-01

112

In-Plane Shear Resistance of Insulating Concrete Form Walls.  

National Technical Information Service (NTIS)

The efficient use of shear walls in residential construction subjected to wind and seismic loading is of great interest to designers and builders of homes in high hazard areas of the United States. Shear walls are the primary lateral force resisting syste...

2001-01-01

113

An in-plane cantilever for wall shear stress measurement  

NASA Astrophysics Data System (ADS)

A sensor capable of measuring small shear stresses in wind tunnel applications is presented. The sensor utilizes an in-plane cantilever concept for shear stress measurement, designed to minimize intrusiveness into the airflow and allow easy incorporation into wind tunnel test models. The sensor operates independently of input voltage, and can measure <1 Pa shear stresses with a sensitivity of 8.6 (mV V-1) Pa. Altering the geometry of the sensor has a direct effect on the sensitivity and so can be used to adapt the sensor for different applications.

Allen, N. J.; Sims-Williams, D. B.; Wood, D.

2012-07-01

114

Reliability and effect of partially restrained wood shear walls  

Microsoft Academic Search

The 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 is the most common controlling lateral design load for these structures. In contrast, the complimenting building code, the IBC, requires either a restraining dead load or

John J Gruber

2012-01-01

115

Wind-shearing in gaseous protoplanetary disks  

Microsoft Academic Search

One of the first stages of planet formation is the growth of small planetesimals and their accumulation into large planetesimals and planetary embryos. This early stage occurs much before the dispersal of most of the gas from the protoplanetary disk. Due to their different aerodynamic properties, planetesimals of different sizes\\/shapes experience different drag forces from the gas at these stage.

Hagai B. Perets; Ruth Murray-Clay

2011-01-01

116

Wind-shearing in gaseous protoplanetary disks  

Microsoft Academic Search

One of the first stages of planet formation is the growth of small\\u000aplanetesimals and their accumulation into large planetesimals and planetary\\u000aembryos. This early stage occurs much before the dispersal of most of the gas\\u000afrom the protoplanetary disk. Due to their different aerodynamic properties,\\u000aplanetesimals of different sizes\\/shapes experience different drag forces from\\u000athe gas at these stage.

Hagai B. Perets; Ruth Murray-Clay

2010-01-01

117

Aircraft landing control in wind shear condition  

Microsoft Academic Search

Most aircraft accidents occurred during final approach or landing. This study proposes cerebellar model articulation controller (CMAC) to improve the performance of automatic landing system (ALS). The atmospheric disturbances affect not only flying qualities of an airplane but also flight safety. If the flight conditions are beyond the preset envelope, the automatic landing system (ALS) is disabled and the pilot

Chia-Lin Lee; Jih-Gau Juang

2011-01-01

118

Reduced shear power spectrum  

SciTech Connect

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.

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

2005-08-01

119

Feedback shear layer control for bluff body drag reduction  

Microsoft Academic Search

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

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

2008-01-01

120

Strongly sheared stratocumulus convection: an observationally based large-eddy simulation study  

NASA Astrophysics Data System (ADS)

Unusually large wind shears across the inversion in the stratocumulus-topped marine boundary layer (MBL) were frequently observed during VOCALS-REx. To investigate the impact of wind shear on the MBL turbulence structure, a large-eddy simulation (LES) model is used to simulate the strongly sheared MBL observed from Twin-Otter RF 18 on 13 November 2008. The LES simulated turbulence statistics agree in general with those derived from the measurements, with the MBL exhibiting a decoupled structure characterized by an enhanced entrainment and a turbulence intensity minimum just below the clouds. Sensitivity simulations show that the shear tends to reduce the dynamic stability of the inversion, enhance the entrainment mixing, and decrease the cloud water. Consequently, the turbulence intensity in the MBL is significantly weakened by the intense wind shear. The inversion thickens considerably and the MBL top separates from the cloud top, creating a finite cloud-free sublayer of 10-50 m thickness within the inversion, depending on the shear intensity. The wind shear enhances the turbulence buoyant consumption within the inversion, and simultaneously weakens the buoyant production in the cloud layer. These effects may result in different heating rates between the cloud and subcloud layer, leading to a process that tends to decouple the cloud from the subcloud layer. The decoupling process occurs even without solar radiation in the case of an intense wind shear similar to the observations.

Wang, S.; Zheng, X.; Jiang, Q.

2012-02-01

121

Shear Instability Wave along a Snowband: Instability Structure, Evolution, and Energetics Derived from Dual-Doppler Radar Data  

Microsoft Academic Search

This article presents a detailed analysis of a meso-gamma-scale (17 km wavelength) shear instability wave along a snowband using a series of dual-Doppler radar data. The wave developed along a low-level shear line that formed under the strain wind field caused by an adjacent mesoscale vortex. The horizontal wind shear across the line was largest at lower levels, and the

Masayuki Kawashima; Yasushi Fujiyoshi

2005-01-01

122

Reliability and effect of partially restrained wood shear walls  

Microsoft Academic Search

\\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

John Joseph Gruber

2012-01-01

123

Principles of Convection III: Shear and Convective Storms  

NSDL National Science Digital Library

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.

Spangler, Tim

2003-10-01

124

Shear thickening fluid  

Microsoft Academic Search

The instant invention is directed to shear thickening fluids to prevent unwanted flow in wells penetrating subterranean formations. The shear thickening fluids comprise (1) a water swellable granular clay present in sufficient quantity so that, upon interaction with an aqueous phase, a stiff paste rapidly forms having a strength of at least 2000 lbs\\/100 ft², (2) a nonaqueous phase comprising

E. N. Drake; Ch. R. Dawson; M. E. Morrison

1985-01-01

125

Shear thinning vs shear thickening in associating fluids  

Microsoft Academic Search

When one-bond Frenkel dumbbells are allowed to dimerize, as analyzed using the Wertheim theory of association, the resulting fluid exhibits shear thinning or shear thickening behaviors. In contrast, when Gaussian chains undergo shear-assisted association, only shear thickening is possible. The present theory of shear-induced association of non-Newtonian fluids is applied to interpret the shear thickening seen in equimolar solutions of

G. T. Evans

1998-01-01

126

Spatial Distribution of Vertical Shear.  

National Technical Information Service (NTIS)

Spatial variations in small scale vertical shear in the upper ocean are described, relationships between small scale vertical shear and density stratification are investigated, and the potential for predicting mean vertical shear from measurements of the ...

S. L. Patterson F. C. Newman D. M. Rubenstein R. B. Lambert

1981-01-01

127

Nonlinear fluid behavior: from shear thinning to shear thickening  

Microsoft Academic Search

A phenomenological model is introduced which describes both shear thinning and shear thickening behavior. Consequences of this model are presented for plane Couette (simple shear) flow. The non-Newtonian viscosity and normal pressure differences are discussed for a stationary situation. The dynamic behavior - stress growth and relaxation - is analyzed. A stress hysteresis is found in the shear thickening regime.

Ortwin Hess; Siegfried Hess

1994-01-01

128

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

Microsoft Academic Search

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

Chin-Hoh Moeng; Peter P. Sullivan

1994-01-01

129

Wind tunnel investigation of the influence of surface moisture content on the entrainment and erosion of beach sand by wind using sands from tropical humid coastal southern China  

Microsoft Academic Search

Wind erosion has major impacts on dune growth, desertification, and architecture on sea coasts. The deflation threshold shear velocity is a crucial parameter in predicting erosion, and surface moisture greatly affects this threshold and thus sand stability. Wind tunnel studies have shown that reduced moisture contents decrease entrainment thresholds and increase wind erosion, but field and wind tunnel test data

Qingjie Han; Jianjun Qu; Kecun Zhang; Ruiping Zu; Qinghe Niu; Kongtai Liao

2009-01-01

130

Estimates of electromagnetic and turbulent energy dissipation rates under the existence of strong wind shears in the polar lower thermosphere from the European Incoherent Scatter (EISCAT) Svalbard radar observations  

Microsoft Academic Search

Turbulent and electromagnetic energy dissipation rates in the altitude range of ?98–116 km have been estimated using data obtained from the European Incoherent Scatter Svalbard radar (ESR) observations on 22 September 1998 and 12 March 1999. Solar and geomagnetic activities were moderate and quiet during the observational periods, respectively. The horizontal neutral wind fields derived from the ESR observations show

Hitoshi Fujiwara; Sawako Maeda; Miyo Suzuki; Satonori Nozawa; Hiroshi Fukunishi

2004-01-01

131

The effect of shearing on the appetite of the sheep  

Microsoft Academic Search

Twenty 2-tooth Romney wethers were allocated at random into 2 groups: group A on an ad libitum ration and group C on controlled intake. The sheep were individually fed in outdoor pens. Livewcight, wool growth, heart rate, and rectal and skin temperatures were measured. Air temperature and wind velocity were also recorded. After shearing. the appetite of the ad libitum

Manika Wodzicka-Tomaszewska

1963-01-01

132

An Analytical Model of Wake Deflection Due to Shear Flow  

Microsoft Academic Search

The main motivation behind this work is to create a purely analytical engineering model for wind turbine wake upward deflection due to shear flow, by developing a closed form solution of the velocity field due to an oblique vortex ring. The effectiveness of the model is evaluated by comparing the results with those of a free-wake model. The solution of

D. Micallef; C. J. Simao Ferreira; T. Sant; G. J. W. Van Bussel

2010-01-01

133

Shear Banding Driven by Electric Field and Shear Flow  

NASA Astrophysics Data System (ADS)

The shear banding is explored in a granular suspension driven by electric field and shear flow. We find that, given an imposed electric field, there is a critical shear rate determining whether shear banding emerges. A phase diagram of shear banding and fluidization is constructed by using the present experimental data. The evolution in different shear banding phases constitutes an apparent shear thinning phenomenon, probably reflecting an underlying perspective of shear banding. Using the two-phase model, combining with mean field approach and the Onsager least dissipation principle, we give a qualitative explanation of our experimental findings. The results suggest that the stress heterogeneity plays a crucial role for the physical origin of shear banding in this system.

Zheng, Jie; Fu, Wei-Juan; Zhou, Lu-Wei

2013-09-01

134

Wind tunnel test method to study out-of-service tower crane behaviour in storm winds  

Microsoft Academic Search

An experimental method used to study the behaviour of tower cranes in strong winds exposed to the disturbed shear flow induced by the surrounding built environment is proposed. Wind tunnel tests on a tower crane model are described, the tower crane is considered as a rigid body slender structure equipped with a single degree of freedom part: the crane mobile

D. Voisin; G. Grillaud; C. Solliec; A. Beley-Sayettat; J.-L. Berlaud; A. Miton

2004-01-01

135

Observation of shear zone development in ring-shear apparatus with a transparent shear box  

Microsoft Academic Search

Using a new ring-shear apparatus with a transparent shear box and video image analysis system, drained and undrained speed-controlled tests were conducted on coarse-grained silica sands to study the shear-zone formation process in granular materials. Velocity distribution profiles of grains under shear at various stages in the ring shear tests were observed through processing the video image by the Particle

Hiroshi Fukuoka; Kyoji Sassa; Gonghui Wang; Ryo Sasaki

2006-01-01

136

Wind Turbines Adaptation to the Variability of the Wind Field  

NASA Astrophysics Data System (ADS)

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.

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

2010-05-01

137

A linear model of gravity wave drag for hydrostatic sheared flow over elliptical mountains  

Microsoft Academic Search

SUMMARY An analytical model of orographic gravity wave drag due to sheared flow past elliptical mountains is developed. The model extends the domain of applicability of the well-known Phillips model to wind profiles that vary relatively slowly in the vertical, so that they may be treated using a WKB approximation. The model illustrates how linear processes associated with wind profile

M. A. C. Teixeira; P. M. A. Miranda

2006-01-01

138

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.

2013-06-21

139

Design of Thin Shear Blades for Crosscut Shearing of Wood.  

National Technical Information Service (NTIS)

Shear blades have not been acceptable for harvesting sawtimber because they cause splitting. Thin shear blades help to reduce splitting but they have limited structural stability. High speed computers were used to develop critical buckling constants for n...

R. A. Arola T. R. Grimm

1974-01-01

140

Thermal and humidity winds in outer planet atmospheres  

SciTech Connect

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.

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

1991-05-01

141

Determination of surface shear stress with the naphthalene sublimation technique  

NASA Astrophysics Data System (ADS)

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.

Lee, J. A.; Greeley, Ronald

1987-05-01

142

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

Code of Federal Regulations, 2013 CFR

...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,...

2013-04-01

143

Wind power  

Microsoft Academic Search

The fundamentals of wind power utilization are described with emphasis placed on the information needed to determine the basic geometry of wind power devices and to discuss the availability of wind for power generation. The economics and social acceptance of wind power systems at the present time are analyzed.

G. M. Bragg

1979-01-01

144

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

SciTech Connect

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. 27 refs.

Hollweg, J.V.; Yang, G.; Cadez, V.M.; Gakovic, B. (New Hampshire Univ., Durham (USA) Institut za Fiziku, Belgrade (Yugoslavia) Sarajevo Univerzitet (Yugoslavia))

1990-01-01

145

Slicing softly with shear.  

PubMed

A soft solid is more easily sliced using a combination of normal and shearing deformations rather than diced by squeezing down on it normally with the same knife. To explain why this is so, we experimentally probe the slicing and dicing of a soft agar gel with a wire, and complement this with theory and numerical simulations of cutting of a highly deformable solid. We find that purely normal deformations lead to global deformations of the soft solid, so that the blade has to penetrate deeply into the sample, well beyond the linear regime, to reach the relatively large critical stress to nucleate fracture. In contrast, a slicing motion leads to fracture nucleation with minimal deformation of the bulk and thus a much lower barrier. This transition between global and local deformations in soft solids as a function of the angle of shear explains the mechanics of the paper cut and design of guillotine blades. PMID:23368324

Reyssat, E; Tallinen, T; Le Merrer, M; Mahadevan, L

2012-12-10

146

Dynamics of a deformable active particle under shear flow  

NASA Astrophysics Data System (ADS)

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.

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

2013-09-01

147

The mechanism for shear thickening in suspensions  

Microsoft Academic Search

Densely packed suspensions can shear thicken, in which the viscosity increases with shear rate. Video microscopy along with rheology measurements show the shear thickening regime is a transition from negligible particle motion at low stresses to fully developed shear flow at higher stresses. The onset of shear thickening occurs when the shear stress is sufficient to pull particles apart; for

Eric Brown; Heinrich Jaeger

2009-01-01

148

Shear-thickening compositions  

SciTech Connect

Shear-thickening aqueous compositions useful as workover fluids in producing or injection wells, as water diversion agents and mobility control fluids in post-primary oil recovery operations, and as hydraulic fracturing fluids. Well stimulation treatments are provided comprising the reaction product formed from a high molecular weight polyalkylene oxide polymer and a synthetic resin produced from aldehydes and phenols in an alkaline environment.

Swanson, B.L.

1981-10-06

149

A Simple Method to Predict Threshold Shear Velocity in the Field  

NASA Astrophysics Data System (ADS)

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 and time-consuming. Soil crust (both physical and biological) is known to be a crucial factor affecting soil stability and threshold shear velocity. In this report, a simple and portable field method was tested in multiple locations of Utah for the estimation of threshold shear velocity. This method includes measuring size of holes (length and width) induced by shooting a “bullet ball” or “BB” gun, applying a pocket penetrometer, and a torvane on soil surface in the field. In the first stage of the experiment, a conventional wind tunnel was run in combination with BB gun, penetrometer, and torvane in field conditions for a range of soil texture. Results from both the BB gun and penetrometer applied at 45 degree to the ground were significantly correlated with the threshold shear velocity obtained using the wind tunnel (R2=0.70, P<0.001). In the second stage, BB gun and penetrometer method was applied to a serial of sites which have BSNE wind erosion monitors and known horizontal sediment fluxes. Our results showed that a combination of BB gun and penetrometer is able to provide decent prediction of threshold shear velocity in the presence of vegetation under different soil physical and biological conditions.

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

2009-12-01

150

Shear thickening fluid  

SciTech Connect

The instant invention is directed to shear thickening fluids to prevent unwanted flow in wells penetrating subterranean formations. The shear thickening fluids comprise (1) a water swellable granular clay present in sufficient quantity so that, upon interaction with an aqueous phase, a stiff paste rapidly forms having a strength of at least 2000 lbs/100 ft/sup 2/, (2) a nonaqueous phase comprising a hydrocarbon material and a surfactant, and (3) an aqueous phase comprising water and a watersoluble polymer. The granular clay and water-polymer solution are kept separated by the intervening hydrocarbon-surfactant composition, which is the continuous phase. The intervening oil phase prevents the interaction between the water-polymer phase and the granular clay and results in a stable, nonreacting, pumpable composite until such time as the granular clay is fragmented by application of a sufficiently high shear force. Upon such fragmenting, the clay and aqueous phase interact resulting in a semi-rigid high strength paste which plugs any unwanted flow.

Drake, E. N.; Dawson, Ch. R.; Morrison, M. E.

1985-03-05

151

Turbulence measurements in a nearly homogeneous shear flow  

NASA Astrophysics Data System (ADS)

A technique is described for conducting turbulence measurements in a nominally homogeneous turbulent shear flow with a moderate rate of strain. The shear flow was generated in the 7.2-m-long working section of a open-circuit wind tunnel of conventional design, in which a nominally uniform gradient of mean velocity was produced by a shear generator of the type described by Tavoularis and Corrsin (1981). Turbulence measurements were made using a dual-channel DISA 55M01 CTA system with PSI 6141 signal conditioners. Results were found to lie between, and to be broadly consistent with, the results of similar measurements previously taken on flows with higher or lower rates of strain.

Gibson, M. M.; Kanellopoulos, V. E.

152

Field Observations of Shear Waves  

NASA Astrophysics Data System (ADS)

Meanders of the mean alongshore current in the surf zone called shear waves have alongshore propagating velocity fluctuations with periods of a few minutes and alongshore wavelengths of a few hundred meters. Shear wave velocity fluctuations observed within 250 m of the shoreline of a sandy, barred beach for 4 months were approximately horizontally isotropic, with root-mean-square values between 10--40% of the mean alongshore current V. Cross-shore variations of the time-averaged, shear wave momentum flux were consistent with shear wave energy generation in locations where V and the cross-shore shear of the mean alongshore current Vx were high. Farther from the shoreline where V and Vx were weaker, shear wave energy was both dissipated and transfered to the mean flow. In case examples where V is a narrow jet near the shoreline, the observed strong decay of shear wave energy levels seawards of the jet, and the cross- and alongshore structure of shear waves within the jet, were similar to predictions based on the linearly unstable modes of the observed V. Observed shear wave energy levels also were high with a strong, but broad (e.g. weakly sheared) V that is only marginally linearly unstable. This research was supported by the Office of Naval Research and the National Ocean Partnership Program.

Guza, R. T.; Noyes, T. J.; Elgar, S.; Herbers, T. C.

2002-12-01

153

Tropical Cyclone Formation in a Sheared Environment: A Case Study  

Microsoft Academic Search

The development of Hurricane Danny (1997) from depression to hurricane was examined using cloud-to-ground lightning data, reconnaissance aircraft data, and satellite imagery. Vertical wind shear between 850 and 200 hPa of 5 11 m s-1 produced persistent downshear convective outbreaks that became progressively more intense and closer to the center during the development. Early in the period the storm intensified

John Molinari; David Vollaro; Kristen L. Corbosiero

2004-01-01

154

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

NASA Astrophysics Data System (ADS)

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.

Malaspina, D. M.; Newman, D. L.; Wilson, L. B., III; Goetz, K.; Kellogg, P. J.; Kersten, K.

2013-02-01

155

Wind-induced roughening of thin liquid films  

NASA Astrophysics Data System (ADS)

A constant wind shear stress is shown to induce roughness on molecularly thin perfluoropolyether films that are susceptible to dewetting. These wind-induced roughening or dewetting features are pinned to the silicon substrate surface, indicating that these perfluoropolyethers have a heterogeneous interaction with the surface. These results highlight the role of chemical heterogeneity in nucleating dewetting phenomena.

Mate, C. Mathew

2004-01-01

156

Wind Stress Distributions on a Tree-Canopy Sheltered Lake  

Microsoft Academic Search

Wind stress over a lake is generally the most significant driver of whole-lake circulation and lake surface layer mixing. The spatial and temporal distribution of atmospheric flow velocity (and hence wind stress) over the lake is controlled by the roughness transition that the flow encounters as it crosses the shoreline onto the water surface. Well-established shear stress relationships for flat

J. Thill; F. Porte-Agel; H. Stefan

2004-01-01

157

Calibration of a Direct Detection Doppler Wind Lidar System using a Wind Tunnel  

NASA Astrophysics Data System (ADS)

As a critical stage of a Project to develop an airborne Direct-Detection Doppler Wind Lidar System, it was possible to exploit a Wind Tunnel of the VZLU, Prague, Czech Republic for a comprehensive series of tests against calibrated Air Speed generated by the Wind Tunnel. The initial results from these test sequences will be presented. The rms wind speed errors were of order 0.25 m/sec - very satisfactory for this class of Doppler Wind Lidar measurements. The next stage of this Project will exploit a more highly-developed laser and detection system for measurements of wind shear, wake vortex and other potentially hazardous meteorological phenomena at Airports. Following the end of this Project, key parts of the instrumentation will be used for routine ground-based Doppler Wind Lidar measurements of the troposphere and stratosphere.

Rees, David

2012-07-01

158

Shear mode grinding  

SciTech Connect

The thesis of this paper is that shear mode grinding of glass (1) occurs with abrasive particle sizes less than 1/mu/m, (2) that it is the mechanical limit of the the more common mechanical-chemical glass polishing, and (3) that the debris is insufficient in size to perform the function of eroding the binder in the grinding wheel and thus necessitates the addition of an abrasive and/or chemical additions to the coolant to effect wheel-dressing. 13 refs.

Brown, N.J.; Fuchs, B.A.

1989-04-24

159

The Shears Mechanism in Nuclei  

NASA Astrophysics Data System (ADS)

This chapter reviews the experimental properties of shears bands. The most puzzling characteristic of these structures is the emergence of rotational-like behavior while the nucleus retains a small quadrupole deformation. Regardless of the details of particular theoretical models, it can be shown that the most important degree of freedom in describing the shears mechanism is the shears angle. It is then possible to develop a semiclassical description of the shears mechanism, in which the nature (multipole order) of the interaction between valence protons and neutrons constituting the shears "blades" may be derived and the dynamics of the system described. We discuss the competition between the shears mechanism and collective rotation and mention the connection to "magnetic rotation." Directions for future theoretical and experimental efforts are suggested.

Clark, R. M.; Macchiavelli, A. O.

160

Wind Energy  

NSDL National Science Digital Library

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.

Integrated Teaching And Learning Program

161

Magnetorheological dampers in shear mode  

NASA Astrophysics Data System (ADS)

In this study, three types of shear mode damper using magnetorheological (MR) fluids are theoretically analyzed: linear, rotary drum, and rotary disk dampers. The damping performance of these shear mode MR dampers is characterized in terms of the damping coefficient, which is the ratio of the equivalent viscous damping at field-on status to the damping at field-off status. For these three types of shear mode MR damper, the damping coefficient or dynamic range is derived using three different constitutive models: the Bingham-plastic, biviscous, and Herschel-Bulkley models. The impact of constitutive behavior on shear mode MR dampers is theoretically presented and compared.

Wereley, N. M.; Cho, J. U.; Choi, Y. T.; Choi, S. B.

2008-02-01

162

Wind Energy  

Microsoft Academic Search

\\u000a The kinetic energy of wind is harvested using wind turbines to generate electricity. Among various renewable energy sources,\\u000a wind energy is the second most technologically advanced renewable energy source; hydropower is the first. Although there is\\u000a a significant potential for converting wind energy to electricity, a number of issues must be addressed before it can be used\\u000a to its full

Tushar K. Ghosh; Mark A. Prelas

163

TUBE SHEARING VALVE  

DOEpatents

Explosive operated valves can be used to join two or more containers in fluid flow relationship, one such container being a sealed reservoir. The valve is most simply disposed by mounting it on the reservoir so thst a tube extends from the interior of the reservoir through the valve body, terminating at the bottom of the bore in a closed end; other containers may be similarly connected or may be open connected, as desired. The piston of the valve has a cutting edge at its lower end which shears off the closed tube ends and a recess above the cutting edge to provide a flow channel. Intermixing of the fluid being transferred with the explosion gases is prevented by a copper ring at the top of the piston which is force fitted into the bore at the beginning of the stroke. Although designed to avoid backing up of the piston at pressures up to 10,000 psi in the transferred fluid, proper operation is independent of piston position, once the tube ends were sheared.

Wilner, L.B.

1960-05-24

164

Simulation and Estimation of Reliability in a Wind Farm Considering the Wake Effect  

Microsoft Academic Search

In this paper, wake effect is explicitly incorporated in the reliability evaluation of a wind farm. Energy loss resulting from this effect is included in calculating the reliability indices. Three models for wake effect are discussed and the Jensen model is used in this research. In this model, wind shade, shear effect, and wind direction are also reflected. After incorporating

Hagkwen Kim; Chanan Singh; Alex Sprintson

2012-01-01

165

Estimation of turbulent energy dissipation, winds, and ionospheric structure from Dynasonde measurements  

Microsoft Academic Search

A sample of Dynasonde observations at Cleary, Alaska, of the daytime E region, in ionogram and Kinesonde observing modes, is shown to satisfy analysis criteria leading to winds and turbulence. The wind effects on the ionization distribution in the E region are shown to be consistent with the 'wind shear' process for the sporadic E phenomenon at this large magnetic

J. W. Wright; R. D. Hunsucker

1983-01-01

166

Novel alternating frequency Doppler lidar instrument for wind measurements in the lower troposphere  

Microsoft Academic Search

Accurate, spatially resolved wind measurements in the lower atmosphere are critical to improving current weather forecasting models. Wind shear detection for midsized airports, not covered under the Federal Aviation Administration's (FAA's) Terminal Doppler Weather Radars, would significantly reduce personal aircraft accidents. Atmospheric dynamics studies would also benefit from high accuracy, spatially resolved wind profiles within the planetary boundary layer. This

Jeremy Todd Dobler

2005-01-01

167

Wind energy  

Microsoft Academic Search

The 1972 Solar Energy Panel of NASA and the National Science Foundation estimated the potential wind power available in the U.S. to be about 100,000 gigawatts, which is 30 times greater than the projected energy consumption for 1980. Wind energy is discussed with a view of providing a practical foundation and guide to the analysis and application of wind energy

B. Wolff; H. Meyer

1978-01-01

168

Shear rejuvenation, aging and shear banding in yield stress fluids  

Microsoft Academic Search

The purpose of this work is to simulate shear rejuvenation and aging effects in shear thinning yield stress fluids in a typical rotational rheometer and to provide a common framework to describe the behavior of yield stress materials in general. This is particularly important in the determination of material constants under both steady and unsteady conditions. The breakdown and buildup

Andreas N. Alexandrou; Nicholas Constantinou; Georgios Georgiou

2009-01-01

169

Minimal model for chaotic shear banding in shear thickening fluids  

Microsoft Academic Search

We present a minimal model for spatiotemporal oscillation and rheochaos in shear thickening complex fluids at zero Reynolds number. In the model, a tendency towards inhomogeneous flows in the form of shear bands combines with a slow structural dynamics, modeled by delayed stress relaxation. Using Fourier-space numerics, we study the nonequilibrium ``phase diagram'' of the fluid as a function of

A. Aradian; M. E. Cates

2006-01-01

170

Strongly sheared stratocumulus convection: an observationally based large-eddy simulation study  

NASA Astrophysics Data System (ADS)

Unusually large wind shears across the inversion in the stratocumulus-topped marine boundary layer (MBL) were frequently observed during VOCALS-REx. To investigate the impact of wind shear on the MBL turbulence structure, a large-eddy simulation (LES) model is used to simulate the strongly sheared MBL observed from Twin-Otter RF 18 on 13 November 2008. The LES simulated turbulence statistics agree in general with those derived from the measurements, with the MBL exhibiting a decoupled structure characterized by an enhanced entrainment and a turbulence intensity minimum just below the clouds. Sensitivity simulations show that the shear forcing tends to reduce the dynamic stability of the inversion, characterized by the bulk (or gradient) Richardson number. This decrease enhances the entrainment mixing, leading to reduced cloud water. Consequently, the turbulence intensity in the MBL is significantly weakened by the intense wind shear. The inversion thickens considerably and the MBL top separates from the cloud top, creating a finite cloud-free sublayer of 10-50 m thickness within the inversion, depending on the Richardson number. The weakened inversion tends to enhance the turbulence buoyant consumption and simultaneously lead to a reduced buoyant production in the cloud layer due to less radiative cooling. These effects may result in a decoupling process that creates the different heating/moistening rates between the cloud and subcloud layer, leading to a two-layered structure in the strongly sheared stratocumulus-topped MBL.

Wang, S.; Zheng, X.; Jiang, Q.

2012-06-01

171

The third-order law for magnetohydrodynamic turbulence with shear: Numerical investigation  

NASA Astrophysics Data System (ADS)

The scaling laws of third-order structure functions for isotropic, homogeneous, and incompressible magnetohydrodynamic (MHD) turbulence relate the observable structure function with the energy dissipation rate. Recently [Wan et al. Phys. Plasmas 16, 090703 (2009)], the theory was extended to the case in which a constant velocity shear is present, motivated by the application of the third-order law to the solar wind. We use direct numerical simulations of two-dimensional MHD with shear to confirm this new generalization of the theory. The presence of the shear effect broadens the circumstances in which the law can be applied. Important implications for laboratory and space plasmas are discussed.

Wan, M.; Servidio, S.; Oughton, S.; Matthaeus, W. H.

2010-05-01

172

The third-order law for magnetohydrodynamic turbulence with shear: Numerical investigation  

SciTech Connect

The scaling laws of third-order structure functions for isotropic, homogeneous, and incompressible magnetohydrodynamic (MHD) turbulence relate the observable structure function with the energy dissipation rate. Recently [Wan et al. Phys. Plasmas 16, 090703 (2009)], the theory was extended to the case in which a constant velocity shear is present, motivated by the application of the third-order law to the solar wind. We use direct numerical simulations of two-dimensional MHD with shear to confirm this new generalization of the theory. The presence of the shear effect broadens the circumstances in which the law can be applied. Important implications for laboratory and space plasmas are discussed.

Wan, M.; Matthaeus, W. H. [Department of Physics and Astronomy and Bartol Research Institute, University of Delaware, Newark, Delaware 19716 (United States); Servidio, S. [Department of Physics and Astronomy and Bartol Research Institute, University of Delaware, Newark, Delaware 19716 (United States); Dipartimento di Fisica, Universita della Calabria, I-87036 Cosenza (Italy); Oughton, S. [Department of Mathematics, University of Waikato, Hamilton 3240 (New Zealand)

2010-05-15

173

Impact of shear and curvature on surface gravity wave stress  

NASA Astrophysics Data System (ADS)

It has been shown that surface gravity wave stress is sensitive to the low level wind profile shape. The simplest way of incorporating those effects in a theoretical model has been recently proposed, using a second order WKB approach, which leads to closed analytical formulae for the surface stress as a function of stability, low level wind and its two first derivatives (shear and curvature). In the present study, we assess the impact of those calculations on global scale gravity wave stress and the corresponding torque, using 6-hourly data from ERA-40 reanalysis, at full resolution. While the theory shows that linear wind shear leads to a reduced stress and curvature may lead to stress enhancement, the present results indicate that the latter effect is dominant. However, when one looks for regionally integrated stress fields for the large mountain ranges, where cancellation effects take place thorough time and space integration, the overall effect is one of drag enhancement in regions of dominant easterly flow, namely Antarctica and East Africa, leading to a slight reduction of the global westerly torque due to mountain waves. Drag enhancement due to wind profile curvature seems to be an important effect in Antarctic flow, where it accounts for a 50% increase in the mean regional torque, with implied consequences for the dynamics of the polar vortex.

Miranda, P. M. A.; Martins, J. P. A.; Teixeira, M. A. C.

2009-09-01

174

Shear heating and subduction initiation  

NASA Astrophysics Data System (ADS)

Despite it's importance in geodynamics, the processes that result in subduction initiation remain incompletely understood. Shear heating has been put forward as a mechanism to create lithospheric-scale shear zones (e.g. Ogawa 1987, Regenauer-Lieb et al. 2001). A scaling analysis highlighted the governing parameters that control shear localization (Kaus and Podladchikov 2006), and showed that the boundary between localization and no localization is quite sharp. Recently, this scaling analysis was extended to include more realistic lithospheric rheologies and structures and it could be demonstrated that shear-heating induced lithospheric scale localization might occur for Earth-like parameters (Crameri and Kaus, submitted). It however is unclear if all lithospheric-scale shear zones evolve into self-sustaining subduction zones. Here, we therefore use viscoelastoplastic 2D geodynamical numerical simulations to investigate under which conditions lithospheric failure results in the formation of an evolved subduction zone. The results are compared with analytical scaling laws for shear localization in the lithosphere. Crameri, F. and B.J.P. Kaus (subm.) Kaus, B.J.P and Y.Y Podlachikov (2006) Initiation of localized shear zones in viscoelastoplastic rocks, JGR, 111, B04412, doi:10.1029/2005JB003652 Ogawa, M. (1987) Shear Instability in a Viscoelastic Material as the Cause of Deep Focus Earthquakes, JGR, 92, 13,801-13,810 Regenauer-Lieb, K., D. Yuen, and J. Branlund (2001) The initation of subduction: Criticality by addition of water?, Science, 294, 578-580.

Thielmann, Marcel; Kaus, Boris J. P.

2010-05-01

175

Continuous shear wave logging apparatus  

SciTech Connect

Apparatus for continuous shear wave logging of a borehole consisting of a sonde instrument having retractable, expandable coupling arms for rigidly engaging the borehole wall to exert repetitive torqueing action while continuously moving uphole. The sonde includes spaced detector coupling arms in continual contact with the borehole wall and polarized for detection of the repetitive propagated shear waves.

Brown, G. L.

1985-10-29

176

Cavitation Bubble in Shear Flow  

Microsoft Academic Search

In the orifice of liquid injectors at high pressure, cavitation occurs behind the sharp corners, where a strong pressure drop is present due to quick change in the flow direction. In addition, a high level of shear is present inside the boundary layer. Therefore, it is important to understand the influence of the shear on the cavitation. In this study,

Sadegh Dabiri; William Sirignano; Daniel Joseph

2009-01-01

177

Shear dynamics of hydration layers  

NASA Astrophysics Data System (ADS)

Molecular dynamics (MD) simulations have been performed to investigate the shear dynamics of hydration layers of the thickness of D=0.61-2.44 nm confined between two mica surfaces. Emphases are placed on the external shear response and internal relaxation properties of aqueous films. For D=0.92-2.44 nm liquid phase, the shear responses are fluidic and similar to those observed in surface force balance experiments [U. Raviv and J. Klein, Science 297, 1540 (2002)]. However, for the bilayer ice (D=0.61 nm) [Y. S. Leng and P. T. Cummings, J. Chem. Phys. 124, 74711 (2006)] significant shear enhancement and shear thinning over a wide range of shear rates in MD regime are observed. The rotational relaxation time of water molecules in this bilayer ice is found to be as high as 0.017 ms (10-5 s). Extrapolating the shear rate to the inverse of this longest relaxation time, we obtain a very high shear viscosity for the bilayer ice, which is also observed quite recently for D<=0.6+/-0.3 nm hydration layers [H. Sakuma et al., Phys. Rev. Lett. 96, 46104 (2006)]. We further investigate the boundary slip of water molecules and hydrated K+ ions and concluded that no-slip boundary condition should hold for aqueous salt solution under extreme confinement between hydrophilic mica surfaces, provided that the confined film is of Newtonian fluid.

Leng, Yongsheng; Cummings, Peter T.

2006-09-01

178

Shear dynamics of hydration layers.  

PubMed

Molecular dynamics (MD) simulations have been performed to investigate the shear dynamics of hydration layers of the thickness of D=0.61-2.44 nm confined between two mica surfaces. Emphases are placed on the external shear response and internal relaxation properties of aqueous films. For D=0.92-2.44 nm liquid phase, the shear responses are fluidic and similar to those observed in surface force balance experiments [U. Raviv and J. Klein, Science 297, 1540 (2002)]. However, for the bilayer ice (D=0.61 nm) [Y. S. Leng and P. T. Cummings, J. Chem. Phys. 124, 74711 (2006)] significant shear enhancement and shear thinning over a wide range of shear rates in MD regime are observed. The rotational relaxation time of water molecules in this bilayer ice is found to be as high as 0.017 ms (10(-5) s). Extrapolating the shear rate to the inverse of this longest relaxation time, we obtain a very high shear viscosity for the bilayer ice, which is also observed quite recently for D< or =0.6+/-0.3 nm hydration layers [H. Sakuma et al., Phys. Rev. Lett. 96, 46104 (2006)]. We further investigate the boundary slip of water molecules and hydrated K(+) ions and concluded that no-slip boundary condition should hold for aqueous salt solution under extreme confinement between hydrophilic mica surfaces, provided that the confined film is of Newtonian fluid. PMID:16999542

Leng, Yongsheng; Cummings, Peter T

2006-09-14

179

Direct measurement of turbulent shear  

NASA Astrophysics Data System (ADS)

A photon correlation method is introduced for measuring components of the shear rate tensor in a turbulent soap film. This new scheme, which is also applicable to three-dimensional flows, is shown to give the same results as laser Doppler velocimetry, but with less statistical noise. The technique yields the mean shear rate s¯, its standard deviation ?, and a simple mathematical transform of the probability density function P(s) of the shear rate itself. We propose a new method that can directly measure shear in 2 dimensional turbulence. This proposed method has better signal to noise ratio than the conventional method. It also yields information about the probability distribution of shear. The proposed method is inexpensive and applicable to 3 dimensional turbulence.

Stefanus, S.; Steers, S.; Goldburg, W. I.

2011-11-01

180

Electroosmotic shear flow in microchannels.  

PubMed

We generate and study electroosmotic shear flow in microchannels. By chemically or electrically modifying the surface potential of the channel walls a shear flow component with controllable velocity gradient can be added to the electroosmotic flow caused by double layer effects at the channel walls. Chemical modification is obtained by treating the channel wall with a cationic polymer. In case of electric modification, we used gate electrodes embedded in the channel wall. By applying a voltage to the gate electrode, the zeta potential can be varied and a controllable, uniform shear stress can be applied to the liquid in the channel. The strength of the shear stress depends on both the gate voltage and the applied field which drives the electroosmotic shear flow. Although the stress range is still limited, such a microchannel device can be used in principle as an in situ micro-rheometer for lab on a chip purposes. PMID:23089595

Mampallil, Dileep; van den Ende, Dirk

2012-10-02

181

Towards a Wind Energy Climatology at Advanced Turbine Hub-Heights: Preprint  

SciTech Connect

Measurements of wind characteristics over a wide range of heights up to and above 100 m are useful to: (1) characterize the local and regional wind climate; (2) validate wind resource estimates derived from numerical models; and (3) evaluate changes in wind characteristics and wind shear over the area swept by the blades. Developing wind climatology at advanced turbine hub heights for the United States benefits wind energy development. Tall tower data from Kansas, Indiana, and Minnesota (which have the greatest number of tall towers with measurement data) will be the focus of this paper. Analyses of data from the tall towers will start the process of developing a comprehensive climatology.

Schwartz, M.; Elliott, D.

2005-05-01

182

A Wind-Tunnel Investigation of Wind-Turbine Wakes: Boundary-Layer Turbulence Effects  

Microsoft Academic Search

Wind-tunnel experiments were performed to study turbulence in the wake of a model wind turbine placed in a boundary layer\\u000a developed over rough and smooth surfaces. Hot-wire anemometry was used to characterize the cross-sectional distribution of\\u000a mean velocity, turbulence intensity and kinematic shear stress at different locations downwind of the turbine for both surface\\u000a roughness cases. Special emphasis was placed

Leonardo P. Chamorro; Fernando Porté-Agel

2009-01-01

183

A wind-tunnel investigation of wind-turbine wakes: Boundary layer turbulence eects  

Microsoft Academic Search

Abstract. Wind-tunnel experiments were performed to study turbulence in the wake of a model wind turbine placed in a boundary,layer developed over rough and,smooth,surfaces. Hot-wire anemometry,was,used to characterize the cross- sectional distribution of mean velocity, turbulence intensity and kinematic shear stress at dierent,locations downwind of the turbine for both surface roughness cases. Special emphasis was placed on the spatial distribution

Leonardo P. Chamorro; Fernando Port

184

Shear Band Formation in Thermal Viscoplastic Materials.  

National Technical Information Service (NTIS)

Shear strain localization at high strain rates is investigated through the analysis of a one-dimensional model for simple shearing deformation of thermal viscoplastic materials. Analytical investigations of shear band formation are reviewed Understanding ...

R. J. Clifton T. G. Shawki

1989-01-01

185

Wind Flow Characteristics over Rough Surfaces  

NASA Astrophysics Data System (ADS)

The presence of roughness elements such as isolated boulders or sparse vegetation, common to many arid and semi-arid environments, protect the underlying finer-grained sediments from wind erosion, principally by absorbing momentum from the wind. As a result, wind shear stress is partitioned between the isolated roughness elements and the intervening surface. As part of a larger wind erosion study, a series of wind profile measurement experiments were conducted over a relatively flat un-vegetated, crusted field with an area of approximately 10,000 meters square, located at the Jornada Experimental Range, USDA ARS, Las Cruces, NM. Near the upwind margin of the field a triangular shaped area 2000 meters square (with the triangle base located downwind and perpendicular to the dominant wind direction) was covered with up to 1,9250, commercially available, 5-gallon buckets in regularly spaced staggered arrays. The buckets were used to produce four different roughness densities to investigate changes in wind flow patterns and momentum over the roughness configurations. Wind profiles were measured on two 9 m towers located at the upwind and downwind margins of the triangular arrays along the central axis. Wind speed was measured with 8 anemometers spaced logarithmically from 0.5 to 9 m. Wind direction was measured at the top of each tower with a wind vane. Wind speed and direction data were recorded with a data logger at 1s intervals with an averaging time of 10 minutes. Wind profiles at the leading edge of the arrays approaching at angles less than or equal to 10 degrees from normal to the front of the roughness array are associated with the wind flow over the flat, crusted surfaces and are well described by the Prandtl-von Karman log-linear relationship. For the same free stream wind speeds, the profiles at the downwind edge of the arrays are also characteristically log-linear when a displacement height (d) is included in the Prandtl-von Karman equation. A strong linear relationship (R2= 0.97) was found between the ratio of d to inter-element spacing (l) and the roughness density. As well, for similar free stream wind speeds, shear velocity increased markedly between the upwind and down wind towers, the difference of which was dependent on roughness density. Average momentum losses across the arrays (determined from the momentum deficit law) increased linearly with roughness density, indicating the increasing absorption of momentum by the roughness elements as the number of elements per unit area increased.

Bryant, J. M.; Nickling, W. G.; Gillies, J. A.

2004-12-01

186

Accuracy issues of the existing thermospheric wind models: can we rely on them in seeking solutions to wind-driven problems?  

NASA Astrophysics Data System (ADS)

We address the question of the ability of empirical and general circulation model neutral wind profiles in the lower thermosphere to reproduce the observed characteristics of the winds in that part of the atmosphere. The winds in that altitude range are critical for electrodynamic processes, but evaluations of the model winds are generally difficult because of the sparse observational data, which makes an evaluation of the wind predictions over large areas difficult or impossible. In this paper, we use a recently identified characteristic of the winds in the lower thermosphere, namely the enhanced winds and strong shears between 95 and 115 km altitude, as a test of the models, at least in a statistical sense. Our results show that the Horizontal Wind Model (HWM) significantly underestimates the maximum winds and shears in the lower thermosphere, although it has reasonable agreement with the average winds. The NCAR general circulation model used in this study also underestimates the maximum winds and shears significantly when run with standard resolution, as well as producing an unrealistic increase of the wind speed with height. The agreement between the model and the observations improves significantly however, in a statistical sense, when the altitude resolution is increased. The improved height resolution in the model appears to produce a greater improvement in the model predictions than any of the other factors that we examined, such as improving the geomagnetic forcing or the forcing at the lower boundary.

Larsen, M. F.; Fesen, C. G.

2009-06-01

187

Smectic Edge Dislocations under Shear  

NASA Astrophysics Data System (ADS)

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.

Chen, Peilong; Lu, Chun-Yi David

2011-09-01

188

Shear strength of reinforced aerated concrete beams with shear reinforcement  

Microsoft Academic Search

The paper reports on the analysis of shear strength of reinforced beams made of autoclaved aerated concrete with shear reinforcement.\\u000a The test data are taken from three different investigations from three countries, in Europe and Japan, and include 61 tests.\\u000a The analysis of the test data results in regression expressions, suitably modified from a formula used for ordinary concrete\\u000a members,

Samuel Aroni

1990-01-01

189

Parallel Shear Flows Over Cavities.  

National Technical Information Service (NTIS)

Incompressible separated flows have long presented problems to the theoretician. Parallel shear flow over a cavity is an ideal flow configuration to evaluate numerically to shed light on fundamental relationships. It also provides a basis to predict flow ...

V. O'Brien

1970-01-01

190

Proteins in a shear flow  

NASA Astrophysics Data System (ADS)

The conformational dynamics of a single protein molecule in a shear flow is investigated using Brownian dynamics simulations. A structure-based coarse grained model of a protein is used. We consider two proteins, ubiquitin and integrin, and find that at moderate shear rates they unfold through a sequence of metastable states-a pattern which is distinct from a smooth unraveling found in homopolymers. Full unfolding occurs only at very large shear rates. Furthermore, the hydrodynamic interactions between the amino acids are shown to hinder the shear flow unfolding. The characteristics of the unfolding process depend on whether a protein is anchored or not, and if it is, on the choice of an anchoring point.

Szymczak, P.; Cieplak, Marek

2007-10-01

191

Shear thinning of nanoparticle suspensions.  

SciTech Connect

Results of large scale non-equilibrium molecular dynamics (NEMD) 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. Here we present results for the shear rheology of spherical nanoparticles of size 5 to 20 times that of the solvent for a range of nanoparticle volume fractions and interactions. Results from NEMD simulations suggest that for strongly interacting nanoparticle that form a colloidal gel, the shear rheology of the suspension depends only weakly on the size of the nanoparticle, even for nanoparticles as small as 5 times that of the solvent. However for hard sphere-like colloids the size of the nanoparticles strongly affects the shear rheology. The shear rheology for dumbbell nanoparticles made of two fused spheres is also compared to spherical nanoparticles and found to be similar except at very high volume fractions.

Grest, Gary Stephen; Petersen, Matthew K.; in't Veld, Pieter J. (Polymer Research, Ludwigshafen, Germany)

2008-08-01

192

Wind sheltering of a lake by a tree canopy or bluff topography  

NASA Astrophysics Data System (ADS)

A model is developed to quantify the wind sheltering of a lake by a tree canopy or a bluff. The experiment-based model predicts the wind-sheltering coefficient a priori, without calibration, and is useful for one-dimensional (1-D) lake hydrodynamic and water quality modeling. The model is derived from velocity measurements in a boundary layer wind tunnel, by investigating mean velocity profiles and surface shear stress development downwind of two canopies and a bluff. The wind tunnel experiments are validated with field measurements over an ice-covered lake. Both wind tunnel and field experiments show that reduced surface shear stress extends approximately 50 canopy heights downwind from the transition. The reduction in total shear force on the water surface is parameterized by a wind-sheltering coefficient that is related to the reduction of wind-affected lake area. While all measurements are made on solid surfaces, the wind-sheltering coefficient is shown to be applicable to the lake surface. Although several canopy characteristics, such as its height, aerodynamic roughness, and its porosity affect the transition of velocity profiles and surface shear stress onto a lake, a relationship based on canopy height alone provides a sufficiently realistic estimate of the wind-sheltering coefficient. The results compare well with wind-sheltering coefficients estimated by calibration of lake water temperature profile simulations for eight lakes.

Markfort, Corey D.; Perez, Angel L. S.; Thill, James W.; Jaster, Dane A.; Porté-Agel, Fernando; Stefan, Heinz G.

2010-03-01

193

Atmospheric stability affects wind turbine power collection  

NASA Astrophysics Data System (ADS)

The power generated by a wind turbine largely depends on the wind speed. During time periods with identical hub-height wind speeds but different shapes to the wind profile, a turbine will produce different amounts of power. This variability may be induced by atmospheric stability, which affects profiles of mean wind speed, direction and turbulence across the rotor disk. Our letter examines turbine power generation data, segregated by atmospheric stability, in order to investigate power performance dependences at a West Coast North American wind farm. The dependence of power on stability is clear, regardless of whether time periods are segregated by three-dimensional turbulence, turbulence intensity or wind shear. The power generated at a given wind speed is higher under stable conditions and lower under strongly convective conditions: average power output differences approach 15%. Wind energy resource assessment and day ahead power forecasting could benefit from increased accuracy if atmospheric stability impacts were measured and appropriately incorporated in power forecasts, e.g., through the generation of power curves based on a range of turbulence regimes.

Wharton, Sonia; Lundquist, Julie K.

2012-03-01

194

Waves on a Marine Inversion Undergoing Mountain Leeside Wind Shear  

Microsoft Academic Search

Inland penetration of a shallow layer of marine air is a common occurrence along the coast of southern California. The marine air generally is confined to the coastal basin by surrounding mountains and a capping inversion. Air above the inversion is drier and warmer than the marine air below, resulting in different burning conditions for forest fires in mountain areas

William T. Sommers

1981-01-01

195

Wind energy  

Microsoft Academic Search

General resources of wind energy are evaluated, and its main applications are considered, such as conversion into electricity and heat, hydrogen production, and irrigation, along with the associated problem of long-term energy storage. The basic principles of windmill system design and favorable location selection are outlined. The environmental impact of the windmill systems is discussed. It is noted that wind

B. Sorensen

1976-01-01

196

Wind turbine  

Microsoft Academic Search

A wind turbine of the type having an airfoil blade mounted on a flexible beam and a pitch governor which selectively, torsionally twists the flexible beam in response to wind turbine speed thereby setting blade pitch, is provided with a limiter which restricts unwanted pitch change at operating speeds due to torsional creep of the flexible beam. The limiter allows

1982-01-01

197

Wind turbine  

Microsoft Academic Search

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

Marvin C

1982-01-01

198

Resonant interaction of elastic thin bar vibrations with a shear shallow-water flow  

NASA Astrophysics Data System (ADS)

It is demonstrated that resonant interaction of a thin bar with a shear shallow-water flow results in the development of wind instability. The dispersion equation and the instability increment are derived. The wavelength range in which the instability exists is narrowed down when the sound velocity decreases. The frequency and increment of bending waves are estimated numerically for various flow parameters.

Gestrin, S. G.; Sal'Nikov, A. N.; Sergeeva, E. K.

2010-06-01

199

Internal gravity wave-atmospheric wind interaction: a cause of clear air turbulence.  

PubMed

The interaction between an internal gravity wave and a vertical wind shear may be responsible for the production of clear air turbulence in the free atmosphere. A simplified model equation demonstrates the feasibility of the suggested mechanism. PMID:17741981

Bekofske, K; Liu, V C

1972-12-01

200

Internal Gravity Wave-Atmospheric Wind Interaction: A Cause of Clear Air Turbulence  

Microsoft Academic Search

The interaction between an internal gravity wave and a vertical wind shear may be responsible for the production of clear air turbulence in the free atmosphere. A simplified model equation demonstrates the feasibility of the suggested mechanism.

K. Bekofske; V. C. Liu

1972-01-01

201

Dynamic properties of shear thickening colloidal suspensions  

Microsoft Academic Search

The transient shear rheology (i.e., frequency and strain dependence) is compared to the steady rheology for a model colloidal dispersion through the shear thickening transition. Reversible shear thickening is observed and the transition stress compares well to theoretical predictions. Steady and transient shear thickening are observed to occur at the same value of the average stress. The critical strain for

Young Sil Lee; Norman J. Wagner

2003-01-01

202

Generality of shear thickening in dense suspensions  

Microsoft Academic Search

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

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

2010-01-01

203

Effect of high shear on proteins.  

PubMed

Shear is present in almost all bioprocesses and high shear is associated with processes involving agitation and emulsification. The purpose of this study is to investigate the effect of high shear and high shear rate on proteins. Two concentric cylinder-based shear systems were used. One was a closed concentric-cylinder shear device (CCSD) and the other was a homogenizer with a rotor/stator assembly. Mathematical modeling of these systems allowed calculation of the shear rate and shear. The CCSD generated low shear rates (a few hundred s(-1)), whereas the homogenizer could generate very high shear rates (> 10(5) s(-1)). High shear could be achieved in both systems by increasing the processing time. Recombinant human growth hormone (rhGH) and recombinant human deoxyribonuclease (rhDNase) were used as the model proteins in this study. It was found that neither high shear nor high shear rate had a significant effect on protein aggregation. However, a lower melting temperature and enthalpy were detected for highly sheared rhGH by using scanning microcalorimetry, presumably due to some changes in protein's conformation. Also, SDS-PAGE indicated the presence of low molecular-weight fragments, suggesting that peptide bond breakage occurred due to high shear. rhDNase was relatively more stable than rhGH under high shear. No conformational changes and protein fragments were observed. (c) 1996 John Wiley & Sons, Inc. PMID:18629798

Maa, Y F; Hsu, C C

1996-08-20

204

Altitude variations of the horizontal thermospheric winds during geomagnetic storms  

NASA Astrophysics Data System (ADS)

It is generally assumed that viscosity smooths out vertical gradients of the horizontal thermospheric winds in the upper thermosphere, and thus observations of neutral winds at one height can be used at other altitudes in this region. In this paper we present neutral wind simulations of the May 1997 geomagnetic storm using the Coupled Magnetosphere-Ionosphere-Thermosphere (CMIT) model. The model results show that during quiet periods, the assumption of a shearless vertical profile of the horizontal winds is generally valid in low and middle latitudes, although vertical shears do occur in wind profiles in the upper thermosphere in some locations at higher latitudes. During disturbed periods, large variations in the vertical profiles of the upper thermospheric winds are seen globally in the model simulations. A diagnostic analysis of the forcing processes in the neutral momentum equations shows that (1) during quiet time, there are shearing forces, most noticeably the pressure gradient and ion drag, in the upper thermosphere that result in a net momentum forcing that changes with height; this induces altitude variations in the wind profiles at high latitudes and sometime even at middle latitudes. (2) During storm time, momentum advection, which is relatively weak during the quiet time, becomes a dominant force globally. Pressure gradient forces are also significantly enhanced. Ion drag, on the other hand, can be enhanced or suppressed, depending on the location of positive or negative effects. All these forces exhibit significant altitude variations that lead to a net force that is greatly enhanced and has large vertical shears. This produces globally enhanced neutral winds that vary with height. (3) Viscosity is less important than other forcing processes during both the quiet and storm periods and thus cannot prevent shears from occurring in the vertical profiles of the horizontal winds. Viscosity has an insignificant effect on vertical shears that change with height linearly. It, however, does restrict vertical shears that vary nonlinearly with height. The effectiveness of the viscosity in restricting such shears depends on its magnitude. In our simulations, viscosity is weaker than other forcing processes and thus is a relatively slow process, so it will take a few hours for viscosity to reduce such shears.

Wang, W.; Burns, A. G.; Wiltberger, M.; Solomon, S. C.; Killeen, T. L.

2008-02-01

205

Equivalent wind speed model of wind generation  

Microsoft Academic Search

The time series intervals of wind speed and wind power prediction are from a few minutes to ten minutes, which are used for power system energy dispatch, and the power is a mean value in the interval. But physical parameters for wind, such as instantaneous wind speed, maximum wind speed, average wind speed, cannot describe the relationship properly between the

Jing Tian-jun; Yang Ming-hao

2010-01-01

206

Evolution of a barotropic shear layer into elliptical vortices  

NASA Astrophysics Data System (ADS)

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.

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

2013-01-01

207

Wind Monitoring Report for Fort Wainwright's Donnelly Training Area  

SciTech Connect

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.

Orrell, Alice C.; Dixon, Douglas R.

2011-01-18

208

Wind induced sediment resuspension events in shallow tidal basins  

NASA Astrophysics Data System (ADS)

The morphodynamic evolution of shallow tidal basins is crucially affected by wind-wave induced erosion processes. Both in the horizontal and in the vertical planes, wind waves promote erosion processes responsible for the equilibrium configuration and dynamics of tidal-flat surfaces and salt-marsh boundaries. Towards the goal of setting up a theoretical framework which can be used to model wind-wave effects on tidal morphodynamics in a predictive manner, we have used a wind-wave tidal model, forced with observed tidal levels, wind intensities and directions, to analyse the temporal evolution of combined current- and wind-induced exceedances in bottom shear stress over a critical threshold for erosion. Our analyses show that wind-induced resuspensions can be modelled as marked Poisson process, with important consequences for quantitative description of the long-term morphodynamic evolution of tidal landscapes.

D'Alpaos, Andrea; Carniello, Luca; Rinaldo, Andrea

2013-04-01

209

Shear flow instabilities  

NASA Astrophysics Data System (ADS)

The outflows from young, massive protostars are observed to contain, in many instances, more mass than the protostar producing them. Entrainment, spurred on by hydrodynamical or magnetohydrodynamical instabilities, is one possible mechanism of gathering the extra mass. The instability found at a shear flow boundary layer is known as the Kelvin-Helmholtz instability (KHI). This thesis lays the groundwork to start answering the outflow question by examining the KHI in more detail through the use of 2D simulations. I investigate the role of resistivity on the saturation and non-linear evolution of the KHI under the influence of a weak magnetic field. The models run cover magnetic Reynolds numbers ranging from Rm = 1000 toRm = 50000 which, admittedly, is much lower than the Reynolds numbers found in the ISM (Rm ˜ 10 15). Wherever possible, I have tried to postulate the effects of going to even higher Reynolds numbers. Additionally, I have also examined the mixing properties of the KHI by utilizing passive Lagrangian particles initially distributed evenly within the boundary layer. The particles are then tracked as they are advected through the velocity field. Finally, I examine the KHI in a weakly ionized medium. In reality, the molecular interstellar medium is partially ionized, with an ionization fraction Xe ˜ 10-8--10-7. In the absence of collisions, the ions will evolve as the MHD instability does and the neutrals will evolve as the HD instability. However, collisions between the ions and neutrals will affect that evolution. I found that the role of resistivity has a large effect on the non-linear evolution, causing the kinetic and magnetic energy to decay on a much longer timescale. The transport of momentum is greater in the MHD model, with an increasing effect with magnetic Reynolds number, than in the HD model. However, the particle transport remains the same for both the HD and MHD models. The effect is attributed to a large effect on the momentum transport from the Maxwell Stress. Collisions tend to damp out the energy in the instability for a strong magnetic field case.

Palotti, Matthew Lee

210

A Wind Tunnel Measurement of Fluctuations in Infrared Emission from a Turbulent Mixing Layer.  

National Technical Information Service (NTIS)

An investigation is reported of the fluctuating IR emission from hot air in a turbulent shear layer. A wind-tunnel experiment was conducted in which the free shear layer at the exit of a Mach 7 nozzle was observed with an AC radiometer. The radiating spec...

L. D. Lorah J. A. F. Hill J. S. Draper

1964-01-01

211

Study of the turbulent characteristics of the near-wake field of a medium-sized wind turbine operating in high wind conditions  

SciTech Connect

The near-wake turbulent structure that is downwind of a medium-sized, horizontal axis wind turbine at a distance of one rotor diameter is discussed. The experimental site is the Samos Island Wind Park comprising nine wind turbines installed on the top of a 400 m-high saddle. The analysis is based on experimental data obtained mainly under strong wind conditions by two masts erected upstream and downstream of a wind turbine. The field of wind turbulence is examined both in integral and spectral form. Consideration of the perturbation produced by the tower construction is crucial in the interpretation of results. Observations show that the turbulent field varies from the edge to the center of the wake and strongly depends on the incident wind speed. Increased turbulent levels are observed near the blade tips, with evidence of a similar trend around the hub height for all wind speeds. Decreases of wind turbulence are observed in mid frequencies inside the wake due to the reduced shear associated with the flat crosswind velocity profile. This effect seems to dominate in the variation of the integral values of the longitudinal wind component variance. The low frequency portion of wind spectra reverses behavior in high wind speeds, i.e., an increase in energy relative to background values is observed. This is probably due to the shape of the turbine characteristic power curve. Cross-wind profiles of turbulent shear stresses at the lower boundary of the wake are also discussed. 15 refs., 15 figs., 4 tabs.

Papadopoulos, K.H.; Helmis, C.G.; Soilemes, A.T.; Papageorgas, P.G.; Asimakopoulos, D.N. [Lab. of Meteorology, Athens (Greece)

1995-07-01

212

Minimal model for chaotic shear banding in shear thickening fluids.  

PubMed

We present a minimal model for spatiotemporal oscillation and rheochaos in shear thickening complex fluids at zero Reynolds number. In the model, a tendency towards inhomogeneous flows in the form of shear bands combines with a slow structural dynamics, modeled by delayed stress relaxation. Using Fourier-space numerics, we study the nonequilibrium "phase diagram" of the fluid as a function of a steady mean (spatially averaged) stress, and of the relaxation time for structural relaxation. We find several distinct regions of periodic behavior (oscillating bands, traveling bands, and more complex oscillations) and also regions of spatiotemporal rheochaos. A low-dimensional truncation of the model retains the important physical features of the full model (including rheochaos) despite the suppression of sharply defined interfaces between shear bands. Our model maps onto the FitzHugh-Nagumo model for neural network dynamics, with an unusual form of long-range coupling. PMID:16711810

Aradian, A; Cates, M E

2006-04-18

213

Wind Chill!  

NSDL National Science Digital Library

In this activity students use a variety of windchill charts to determine how cold the temperature feels versus how cold it really is. Students experiment with cooling due to evaporation with and without wind. Students tie their knowledge of wind chill to understanding the impact of cold and wind in the polar environment and prevention of dangerous conditions. Students will graph and present their findings, predict and explore how this phenomenon impacts living in polar regions, and suggest measures that can curtail the impact.

Wygoda, Linda

214

Universality of scaling laws in correlation between velocity and shear stress in turbulent boundary layers  

NASA Astrophysics Data System (ADS)

In this study, we analyse simultaneous measurements (at 50 Hz) of velocity at several heights and shear stress at the surface made during the Utah field campaign for the presence of ranges of scales, where distinct scale-to-scale interactions between velocity and shear stress can be identified. We find that our results are similar to those obtained in a previous study [Venugopal et al., 2003] (contrary to the claim in V2003, that the scaling relations might be dependent on Reynolds number) where wind tunnel measurements of velocity and shear stress were analysed. We use a wavelet-based scale-to-scale cross-correlation to detect three ranges of scales of interaction between velocity and shear stress, namely, (a) inertial subrange, where the correlation is negligible; (b) energy production range, where the correlation follows a logarithmic law; and (c) for scales larger than the boundary layer height, the correlation reaches a plateau.

v., V.; Porte-Agel, F.; Heuer, W.; Marusic, I.

2007-05-01

215

Transport suppression by shear reduction  

NASA Astrophysics Data System (ADS)

The relationship between transport and shear is a problem of considerable interest to magnetically confined plasmas. It is well known that there are cases in which an increase of flow shear can lead to a reduction of turbulent transport. However, this is not a generic result, and there are transport problems in which the opposite is the case. In particular, as originally discussed in Ref. footnotetextdel-Castillo-Negrete and Morrison, Phys. Fluids A 5, 948 (1993), barriers to chaotic transport typically form in regions of vanishing shear. This property, which is generic to the so-called non-twist Hamiltonian systems footnotetextdel-Castillo-Negrete, Greene, and Morrison, Physica D 91, 1 (1996), explains the observed resilience of transport barriers in non-monotonic zonal flows in plasmas and fluids and the robustness of shearless magnetic surfaces in reverse shear configurations. Here we study the role of finite Larmor radius (FLR) effects on the suppression of chaotic transport by shear reduction in a simplified model. Following Ref. footnotetextdel-Castillo-Negrete, Phys. Plasmas, 7, 1702 (2000) we consider a model consisting of a superposition of drift waves and a non-monotonic zonal flow. The FLR effects are incorporated by gyroaveraging the E xB velocity, and transport is studied by following the evolution of ensembles of test particles.

Martinell, Julio; Del-Castillo-Negrete, Diego

2009-11-01

216

Bifurcation and Stability in a Model of Moist Convection in a Shearing Environment.  

NASA Astrophysics Data System (ADS)

The six-coefficient spectral model (model I) of two-dimensional shallow moist convection discussed by Shirer and Dutton (1979) is extended to an eleven component system (model II) in order that a height-dependent basic wind V(z) could be added to the problem. In this way, some behavior of atmospheric cloud streets that are usually observed in a shearing environment could be studied qualitatively.In model II, several different types of solutions exist that correspond to a rich variety of physically relevant possibilities. When a basic wind field is present, stationary, advecting or growing and decaying but propagating cloud bands may occur for different magnitudes of the vertical temperature gradient. These two-dimensional rolls are represented by time-dependent or periodic solutions or by an attractor on a two-dimensional torus. At large values of the lapse rate, the invariant set is probably contained on a three-dimensional torus, but whether or not the limit set is composed of a strange attractor (that may be a model of turbulent behavior) is an open question.With use of a minimizing principle, the expected cloud band orientations are obtained. The resulting formulas provide predictions that generally agree with the linear studies of previous investigators, but our equations apply to an arbitrary height-dependent wind field. When the wind direction does not vary with altitude, the branching two-dimensional rolls are longitudinal or aligned parallel to the wind shear vector. But when the basic wind direction changes with height, some wind profiles support longitudinal rolls; other wind fields load to transverse rolls that are oriented perpendicular to the shear. Two or three coexisting cloud band alignments can also occur.

Shirer, Hampton N.

1980-07-01

217

A Conceptual Model to Predict the Deflation Threshold Shear Velocity as Affected by Near-Surface Soil Water  

Microsoft Academic Search

et al., 1996). McKenna-Neuman and Nickling (1989) proposed a theoretical model, in which they solved the A crucial parameter in predicting wind erosion is the deflation capillary force model of Fisher (1926) for cone-shaped threshold shear velocity, which is highly dependent on near-surface sand particles, and simply related the threshold shear soil water. The empirical and theoretical models to predict

Wim M. Cornelis; Donald Gabriels; Roger Hartmann

2004-01-01

218

Wind Surge  

NSDL National Science Digital Library

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.

Dalrymple, Robert A.; Delaware, University O.

219

Colloidal glasses under shear strain  

NASA Astrophysics Data System (ADS)

We have studied the effects of oscillatory shear strain on the structure of a colloidal hard-sphere glass. By light scattering, we measure the kinetic development of ordered structures induced by shearing between parallel plates. Diffusing wave spectroscopy ``echo'' experiments show that for peak to peak oscillatory strain below around 30% the colloidal glass strains approximately reversibly. At higher strains a partly ordered structure develops, the kinetics of the ordering being strongly dependent on strain. Kinetic measurements demonstrate an ``induction'' time for crystallization with a divergentlike behavior as strain decreases toward ~25-30 %. We compare the behavior of glassy samples with that of samples at lower volume fraction, where in equilibrium without shear the sample is fully (poly)crystalline. At the lower volume fraction, irreversible yielding is observed at lower strains. There appears some tendency for very high volume fraction glass samples to ``fracture.'' Similar evidence of fracture is not observed at the lower volume fractions.

Haw, M. D.; Poon, W. C. K.; Pusey, P. N.; Hebraud, P.; Lequeux, F.

1998-10-01

220

Shear relaxations of confined liquids  

SciTech Connect

Ultrathin (<40 [angstrom]) 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[sup [minus]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 Celcius 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 ([approximately]80 nm[sup 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 (7 nm[sup 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[sup 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.

Carson, G.A. Jr.

1992-01-01

221

Measurement of Shear Modulus and Shear Strength of Adhesives.  

National Technical Information Service (NTIS)

This study was conducted to develop an easy - to - use test method suitable for wood adherends, with an accuracy approaching that of the torsion tube method commonly used for metal - bonding adhesives. The simple method would be used to measure the shear ...

B. H. River R. H. Gillespie

1978-01-01

222

On the validity of thermal wind balance in alongshelf currents off the New Jersey coast  

NASA Astrophysics Data System (ADS)

The validity of thermal wind balance (TWB) as an approximation for the observed vertical shear in coastal currents (depth 10-30 m) is analyzed based on the ADCP and CTD transects conducted off the New Jersey coast in early August of 1996. At that time, the study area was forced simultaneously by a brief upwelling-favorable wind event and the arrival of a buoyant plume from the Hudson Estuary. As a result, both downwelling- and upwelling-favorable alongshelf currents resided within the same area, the former inshore and the latter offshore. The very intense pycnocline (buoyancy frequency ˜0.06 s -1) was shaped as a dome and thus the TWB shear of both signs was observed within the same across-shelf transects and under the same wind conditions. In average, the geostrophic (TWB) shear overestimated the observed by a factor of 2. The maximum of the ageostrophic shear (which is the observed minus TWB shear) was within the sloping pycnocline and not near the bottom (where one would expect to find a strong frictional shear). For both upwelling and downwelling-favorable currents, the geostrophic shear had a sharp maximum in the pycnocline (localized within a few meters), while the ageostrophic shear tended to smooth the actual velocity profile, counteracting the TWB shear in the pycnocline and adding to it (changing sign) below. The result was a more linear velocity distribution with depth compared to the TWB prediction. The significant reduction of the TWB shear in the pycnocline described in this study was likely related to the turbulence production by the internal wave breaking. The wind-induced stresses were trapped in the shallow, ˜5 m deep surface layer, and were inhibited below by a strong pycnocline. Nonfrictional mechanisms (inertia or momentum advection) did not contribute significantly to the ageostrophic shear.

Yankovsky, Alexander E.

2006-07-01

223

Review of the Shearing Process for Sheet Steels and Its Effect on Sheared-Edge Stretching  

NASA Astrophysics Data System (ADS)

Failure in sheared-edge stretching often limits the use of advanced high-strength steel sheets in automotive applications. The present study analyzes data in the literature from laboratory experiments on both the shearing process and the characteristics of sheared edges. Shearing produces a surface with regions of rollover, burnish, fracture, and burr. The effect of clearance and tensile strength on the shear face characteristics is quantified. Higher strength, lower ductility steels exhibit an increase in percent fracture region. The shearing process also creates a zone of deformation adjacent to the shear face called the shear-affected zone (SAZ). From an analysis of data in the literature, it is concluded that deformation in the SAZ is the dominant factor in controlling failure during sheared-edge stretching. The characteristics of the shear face are generally important for failures during sheared-edge stretching only as there is a correlation between the characteristics of the shear face and the characteristics of the SAZ. The effect of the shear burr on shear-edge stretching is also related to a correlation with the characteristics of the SAZ. In reviewing the literature, many shearing variables that could affect sheared-edge stretching limits are not identified or if identified, not quantified. It is likely that some of these variables could affect subsequent sheared-edge stretching limits.

Levy, B. S.; Van Tyne, C. J.

2012-07-01

224

Dynamics of Sheared Granular Materials  

Microsoft Academic Search

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.

Lou Kondic; Brian Utter; Robert P. Behringer

2002-01-01

225

Punching shear in concrete slabs  

Microsoft Academic Search

Punching shear in concrete slabs is a serious problem in certain structural systems, such as flat slabs. Current analysis is based either on empirical and simplified analytical techniques or on theoretical models, mainly based on the theory of plasticity. This paper presents a new model, based on rigid post-fractured behavior, utilizing the post fracture properties of concrete at the rough

David Z. Yankelevsky; Orit Leibowitz

1999-01-01

226

Direct Measurement of Turbulent Shear  

NASA Astrophysics Data System (ADS)

Photon Correlation Spectroscopy (PCS) is used to directly measure the mean shear rate s in a turbulent soap film. A 5 mW 633 nm He-Ne laser is focused on the film at a point r, the spot size being w =100 ?m. The scattered light intensity I(t) is analyzed by a correlator that measures the average, over time t, of the correlation function G(?) = /shear s averaged over w and the standard deviation of s. Of special interest is the shear at points r near a solid boundary. The PCS measurements of s (in Hz) are compared with those obtained by laser Doppler velocimetry (LDV). The two techniques yield values of s that agree within a standard deviation. The PCS method has the advantage of compactness and rapid data collection, making it of potential use in biology and medicine. By changing the orientation of the incident and scattered beams, one can measure various components of the shear tensor. The implementation of the PCS method does not require the presence of a mean flow. It can also be applied to three-dimensional turbulence.

Stefanus, Stefanus; Steers, Stanley; Goldburg, Walter

2010-11-01

227

Extreme wind climate in the Czech Republic  

NASA Astrophysics Data System (ADS)

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.

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

2011-12-01

228

Shear Limit Of Nu I-Beams  

National Technical Information Service (NTIS)

Based on the extensive literature review, parametric study, and full scale testing an integrated and simplified shear design model has been developed. It has been found that the proposed model results in a much simpler design without sacrificing the shear...

M. K. Tadros S. A. Yehia

2001-01-01

229

Transport of cross helicity and radial evolution of Alfvénicity in the solar wind  

Microsoft Academic Search

A transport theory including cross helicity, magnetohydrodynamic (MHD) turbulence, and driving by shear and pickup ions, is applied to the radial evolution of the solar wind. The radial decrease of cross helicity observed in the solar wind can be accounted for when sufficient driving is included to overcome the inherent tendency for MHD turbulence to produce Alfvénic states.

W. H. Matthaeus; J. Minnie; B. Breech; S. Parhi; J. W. Bieber; S. Oughton

2004-01-01

230

Analysis of In-Flight Winds for Shuttle Mission STS 51-L  

Microsoft Academic Search

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

George H. Fichtl; Nathaniel D. Reynolds; Alan E. Johnston; Wade Batts; Larry Lott; Paul J. Meyer; Orvel E. Smith; Marion S. Swint; Otha H. Vaughan Jr.

1988-01-01

231

Modelling of tornado and microburst-induced wind loading and failure of a lattice transmission tower  

Microsoft Academic Search

Many transmission line and tower failures worldwide are attributed to high intensity winds (HIW) associated with tornadoes and microbursts. This paper describes models for the wind velocity time–histories of transient tornado and microburst events and the resulting loading on a lattice tower. A dynamic structural analysis has been undertaken for two HIW events, predicting a tornado-induced shear failure, as observed

Eric Savory; Gerard A. R. Parke; Mostafa Zeinoddini; Norman Toy; Peter Disney

2001-01-01

232

A new evaluation of the wind stress coefficient over water surfaces  

Microsoft Academic Search

An analysis of data from numerous investigators, as well as information obtained directly by the authors, indicates that a large portion of the difficulties encountered in the past in establishing a relationship between wind stress coefficient C10 and the wind velocity U10 can be attributed to computationally induced scatter of the data points. However, plots of the shear velocity u*

J. Amorocho; J. J. DeVries

1980-01-01

233

Zircon growth in shear zones  

NASA Astrophysics Data System (ADS)

The possibility of direct dating of the deformation process is critical for understanding of orogenic belts evolution. Establishing the age of deformation by isotopic methods is indispensable in the case of uneven deformation overlapping, when later deformation inherits the structural plan of the early strains, and to distinguish them on the basis of the structural data only is impossible. A good example of zircon from the shear zones is zircon formed under the eclogite facies conditions. On the one hand, the composition of zircon speaks about its formation simultaneously to eclogitic paragenesis (Rubatto, Herman, 1999; Rubatto et al., 2003). On the other hand, geological studies show that mineral reactions of eclogitization are often held only in areas of shear deformations, which provides access of fluid to the rocks (Austrheim, 1987; Jamtveit et al., 2000; Bingen et al., 2004). Zircons from mafic and ultramafic rocks of the Tanaelv and Kolvitsa belts (Kola Peninsula, the Baltic Shield) have showed that the metamorphic zircon growth is probably controlled by the metamorphic fluid regime, as evidenced by an increase of zircon quantity with the degree of shearing. The internal structure of zircon crystals can provide an evidence of zircon growth synchronous with shearing. The studied crystals have a sector zoning and often specific "patchy" zoning (Fig. 1), which speaks about rapid change of growth conditions. Such internal structure can be compared with the "snowball" garnet structure reflecting the rotation of crystals during their growth under a shift. Rapidly changing crystallization conditions can also be associated with a small amount of fluid, where supersaturation is changing even at a constant temperature. Thus, the growth of metamorphic zircon in shear zones is more likely to occur in the fluid flow synchronous with deformation. A distinctive feature of zircons in these conditions is isometric shape and sector "patchy" zoning. The work was supported by Russian Foundation of Basic Research (project: 13-05-00035.) and the DES-6 program.

Kaulina, Tatiana

2013-04-01

234

Windkraft. (Wind power).  

National Technical Information Service (NTIS)

For Schleswig-Holstein, wind energy is the most interesting renewable energy source because the country with its permanent winds is an extensive 'strong wind area'. Therefore, the government significantly emphasizes the development of wind power. The obje...

1989-01-01

235

Wind Power Machines.  

National Technical Information Service (NTIS)

Basic aerodynamic features of wind power and wind wheels are discussed. The adaptation of wind power to running machinery is described. Developments in wind power are illustrated, followed by a brief outline of operating properties. (Author)

U. Hutter

1975-01-01

236

Wind power machines  

Microsoft Academic Search

Basic aerodynamic features of wind power and wind wheels are discussed. The adaptation of wind power to running machinery is described. Developments in wind power are illustrated, followed by a brief outline of operating properties.

U. Hutter

1975-01-01

237

Wind turbine  

DOEpatents

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.

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

1982-01-01

238

Magnetar Winds  

NASA Astrophysics Data System (ADS)

We assume that magnetars - pulsar-like objects with extremely high (around 1015 G) magnetic fields - drive relativistic MHD winds which are Poynting flux dominated. For a non-aligned rotator, the field structure will resemble a Parker spiral. In the pulsar case, such striped winds have been discussed by Coroniti [1], Michel [2] and Lyubarsky and Kirk [3]. We compute the radiation from the reconnection zones of these winds for parameters appropriate to magnetars and discuss the results in the context of Gamma-Ray Burst theories. References: [1] Coroniti, F.V. 1990, ApJ, 349, 538 [2] Michel, F.C. 1994 ApJ, 431, 397 [3] Lyubarsky, Y. & Kirk, J.G., 2001, ApJ, 547, 437

Guthmann, A. W.; Skjæraasen, O.; Kirk, J. G.

239

Wind turbine  

SciTech Connect

A wind turbine of the type having an airfoil blade mounted on a flexible beam and a pitch governor which selectively, torsionally twists the flexible beam in response to wind turbine speed thereby setting blade pitch, is provided with a limiter 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 which responds to changing rotor speed by pivotal movement, the limiter comprising a resilient member which engages an end of the pendulum to restrict further movement thereof, and in turn restrict beam creep and unwanted blade pitch misadjustment.

Cheney, M.C.

1982-10-05

240

A systematic error in MST/ST radar wind measurement induced by a finite range volume effect: 1. Observational results  

NASA Astrophysics Data System (ADS)

Wind measurement by MST/ST radars may be accompanied by a systematic error due to a finite range volume effect which works when a thin turbulent layer is simultaneously located in several adjacent range volumes. The error occurs when the layer coincides with a cross section through the range volume which is not symmetric with respect to the center of the beam. The finite range volume effect appears as a false vertical shear of horizontal wind in a vertical scale of the order of a few hundred meters, even if the ambient wind field is uniform. The false wind shear sometimes exceeds 40 ms-1 km-1 in magnitude or the critical value to induce the Kelvin-Helmholtz instability. Also the effect leads to a false temporal variation of the wind measurement, although the wind field does not change at all. The false wind shear with a magnitude less than 40 ms-1 km-1 cannot be discriminated from a true one in the observed data. It seems hard to indicate directly that the finite range volume effect appears as theoretically conceived. Judging from wind velocity and echo intensity data obtained by the MU radar in Japan, this effect appears quite frequently in the atmosphere. The small vertical scale wind shear as well as the temporal variation found only at a specific range should be treated with great care except when the ambient wind field is weak, where the finite range volume effect is not so important.

Fukao, Shoichiro; Sato, Toru; May, Peter T.; Tsuda, Toshitaka; Kato, Susumu; Inaba, Motoyuki; Kimura, Iwane

1988-01-01

241

Anisotropic thermal conductivity in sheared polypropylene  

Microsoft Academic Search

We discuss the anisotropy of the thermal conductivity tensor in polymer flow in this paper. Isotactic polypropylene (iPP)\\u000a specimens were deformed by injection moulding at high shear rates and by steady shear at low shear rates, and were then quenched.\\u000a The thermal conductivities parallel and perpendicular to the shear direction were measured using modulated differential scanning\\u000a calorimetry (MDSC) in accordance

Shao Cong Dai; Roger I. Tanner

2006-01-01

242

Refraction of shear zones in granular materials.  

PubMed

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. PMID:17358510

Unger, Tamás

2007-01-02

243

Shear piezoelectricity in bone at the nanoscale  

NASA Astrophysics Data System (ADS)

Recent demonstration of shear piezoelectricity in an isolated collagen fibril, which is the origin of piezoelectricity in bone, necessitates investigation of shear piezoelectric behavior in bone at the nanoscale. Using high resolution lateral piezoresponse force microcopy (PFM), shear piezoelectricity in a cortical bone sample was studied at the nanoscale. Subfibrillar structure of individual collagen fibrils with a periodicity of 60-70 nm were revealed in PFM map, indicating the direct contribution of collagen fibrils to the shear piezoelectricity of bone.

Minary-Jolandan, Majid; Yu, Min-Feng

2010-10-01

244

Generality of shear thickening in suspensions  

Microsoft Academic Search

Suspensions are of wide interest and form the basis for many smart fluids.\\u000aFor most suspensions, the viscosity decreases with increasing shear rate, i.e.\\u000athey shear thin. Few are reported to do the opposite, i.e. shear thicken,\\u000adespite the longstanding expectation that shear thickening is a generic type of\\u000asuspension behavior. Here we resolve this apparent contradiction. We\\u000ademonstrate that

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

2009-01-01

245

Optical degradation by turbulent free-shear layers  

NASA Astrophysics Data System (ADS)

The effect of a turbulent, free shear layer is to introduce a random phase variation on a light beam propagating through that layer. It an incoming parallel beam is brought to focus after propagating through the layer, then the effect of this added random phase variation is to scatter energy out of a diffraction limited focused spot and form a halo around the spot. In an imaging system, this could degrade image quality and reduce contrast due to scattering of energy over a large area. The rapid growth of a free shear layer results in a phase screen whose characteristics rapidly change with distance in the flow direction, therefore part of the beam may propagate through a benign region of the flow field, while that part of the beam located further downstream may be severely aberrated. The specific flow condition chosen is one in which the flow separates from a cylindrical turret with a large optical aperture. The spatially varying characteristics of a free shear layer are explicitly accounted for by constructing a spatially varying phase screen, in which the aerodynamic characteristics are based on turbulence measurements made on large scale wind tunnel models, and on flight measurements made on a large aircraft. The resultance Strehl ratios and beam profiles for typical flight conditions are presented.

Kyrazis, Demos T.

1993-12-01

246

Wind Tubes  

NSDL National Science Digital Library

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. Itâs 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.

Exploratorium

2012-12-14

247

In situ Shear Strength Tester for Coal.  

National Technical Information Service (NTIS)

The objective of this research was to develop a device for rapid in situ measurement of rock shearing strength and to compare the shearing strength results with those obtained by other test methods. The rock borehole shear test (RBST) operates by expansio...

R. L. Handy L. E. Engle J. M. Pitt

1976-01-01

248

Supercooled Liquids under Shear: Computational Approach  

Microsoft Academic Search

We examine the microscopic dynamics of supercooled liquids under shear by performing extensive molecular dynamics simulations of a two-dimensional binary liquid with soft-core interactions near, but above, the glass transition tem- perature. Our simulations show that a drastic reduction of the structural relaxation time and the shear viscosity occurs due to shear. The structural relaxation time de- creases as ?

R. Yamamoto; R. Temam; J. Dean; D. Grove; C. Chambers; K. Bruce; E. Bertino

249

Acoustic shear wave displacement measurement using ultrasound  

Microsoft Academic Search

Echo ultrasound can be used to detect and measure acoustic shear waves. Earlier it has been shown that a phase contrast based magnetic resonance imaging technique can be used for cyclic shear wave displacement measurement. Echo ultrasound presents an alternate method for imaging of such shear waves. The ultrasound based method uses the phase of quadrature echo signals to estimate

Vinayak Dutt; Randall R. Kinnick; James F. Greenleaf

1996-01-01

250

REDUCED ORDER MODELING OF REACTING SHEAR FLOW  

Microsoft Academic Search

Thermoacoustic instability in premixed combustors occurs occasionally at multiple frequencies, especially in configurations where flames are stabilized on separating shear layers that form downstream of sudden expansions or bluff bodies. While some of these frequencies are related to the acoustic field, others appear to be related to shear flow instability phenomena. It is shown in this paper that shear flows

Daehyun Wee; Tongxun Yi; Anuradha Annaswamy; Ahmed Ghoniem

251

Glass transitions and shear thickening suspension rheology  

Microsoft Academic Search

We introduce a class of simple models for shear thickening and\\/ or `jamming' in colloidal suspensions. These are based on schematic mode coupling theory (MCT) of the glass transition, having a memory term that depends on a density variable, and on both the shear stress and the shear rate. (Tensorial aspects of the rheology, such as normal stresses, are ignored

C. B. Holmes

2005-01-01

252

Shear induced structures in crystallizing cocoa butter  

Microsoft Academic Search

Cocoa butter is the main structural component of chocolate and many cosmetics. It crystallizes in several polymorphs, called phases I to VI. We used Synchrotron X-ray diffraction to study the effect of shear on its crystallization. A previously unreported phase (phase X) was found and a crystallization path through phase IV under shear was observed. Samples were crystallized under shear

Gianfranco Mazzanti; Sarah E. Guthrie; Eric B. Sirota; Alejandro G. Marangoni; Stefan H. J. Idziak

2004-01-01

253

Hele Shaw Convection with Imposed Shear Flows  

Microsoft Academic Search

We derived the unidirectional shear flows appropriate for Hele Shaw cell when there is no buoyancy driving force. Using the Galerkin spectral method, the linear stability of Hele Shaw convection in shear flows has been analyzed. The results show that all shear flows stabilize the convection. Using a modified perturbation method with a two parameter expansion and a strained time

Huijun Yang

1991-01-01

254

The limited growth of vegetated shear layers  

Microsoft Academic Search

In contrast to free shear layers, which grow continuously downstream, shear layers generated by submerged vegetation grow only to a finite thickness. Because these shear layers are characterized by coherent vortex structures and rapid vertical mixing, their thickness controls exchange between the vegetation and the overlying water. Experiments conducted in a laboratory flume show that the growth of these obstructed

M. Ghisalberti; H. M. Nepf

2004-01-01

255

Steel Shear Walls, Behavior, Modeling and Design  

Microsoft Academic Search

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

Abolhassan Astaneh-Asl; Abolhassan

2008-01-01

256

DUCTILITY OF THIN STEEL PLATE SHEAR WALLS  

Microsoft Academic Search

The idea of using steel plate shear wall as a lateral load resisting system in design and retrofit of structures has attracted the attention of researchers and designers for more than three decades. In this research, the ductility of thin steel plate shear walls are studied based on ATC-24 protocol and Popov's definition. Two three-story unstiffened steel plate shear walls

S. Sabouri-Ghomi; M. Gholhakia

257

Wind tunnel investigation on wind turbine wakes and wind farms  

NASA Astrophysics Data System (ADS)

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).

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

2012-04-01

258

Near-inertial mixing: Modulation of shear, strain and microstructure at low latitude  

NASA Astrophysics Data System (ADS)

We report direct, quantitative measurements of mixing associated with three cycles of a single, energetic, downward-propagating near-inertial wave in the Banda Sea at 6.5°S, 128°E during October 1998. The wave dominates the shear, containing 70% of the total variance. Simultaneous depth/time series of shear, strain, Froude number (Fr), and microstructure allow direct computation of their coherence and phase from 50-120 m, for 14 days. In this depth range, 72% of diapycnal diffusivity (68% of dissipation) occurs in three distinct pulses, spaced at the inertial period of 4.4 days. These are collocated with maxima of transverse shear, strain and Fr. Inertial-band log diapycnal diffusivity, log10 K?, is coherent at the 95% confidence level with both components of shear and Froude number. In this data set, strain is more important than shear in modulating Fr. Owing to the low latitude, the inertial frequency (fo = 1/4.4 cycles per day) is much smaller than the diurnal and tidal frequencies. Consequently, near-inertial motions may be studied separately from tides and other motions via time-domain filtering. Semiempirical WKB plane-wave solutions with observed frequency ?o = 1.02fo and vertical scale 100 m explain 66% and 42% of inertial-band shear and strain variance, respectively. On the basis of the observed phase relationship between shear and strain, the wave is propagating equatorward, toward 295° true. Ratios of shear to strain and of parallel to transverse shear suggest that the wave's intrinsic frequency ?I ? 1.18feff. This indicates that background vorticity ? has lowered the effective Coriolis frequency, feff = fo + ?/2, relative to its planetary value, fo [Kunze, 1985]. Ray tracing suggests that the wave was generated near 6.9°S, 130.6°E, ˜20 days prior to the cruise, coincident with the end of high winds associated with the SE monsoon. A slab mixed layer model [Pollard and Millard, 1970], forced with National Center for Environmental Prediction (NCEP) model surface winds, confirms that fluxes from the wind to the ocean at this time were sufficient to generate the wave. A very simple model shows that mixing by monsoon-generated inertial waves may add an important and strongly time-dependent aspect to some regions' energy budgets.

Alford, Matthew H.; Gregg, Michael C.

2001-08-01

259

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

Microsoft Academic Search

This paper presents the results of 3D CFD rotor computations of a Siemens SWT-2.3-93 variable speed wind turbine with 45m blades. In the paper CFD is applied to a rotor at stationary wind conditions without wind shear, using the commercial multi-purpose CFD-solvers ANSYS CFX 10.0 and 11.0. When comparing modelled mechanical effects with findings from other models and measurements, good

J Laursen; P Enevoldsen; S Hjort

2007-01-01

260

Crossing of Shears Bands in P  

SciTech Connect

Subpicosecond lifetimes of states in shears band 1 in {sup 197}Pb were measured by means of the recoil distance method employing Gammasphere and the New Yale Plunger Device. The extracted reduced matrix elements, B(M1) , show a clear sensitivity to the crossing of different shears configurations reflecting the closing and reopening of the shears blades. The energies and B(M1) values in the band crossing region are successfully described in the framework of the semiclassical model of the shears bands. The relevance of core rotation contributions are shown. The results point to the existence of shears states with an angular momentum coupling angle larger than 90{sup o} .

Cooper, J. R.; Kruecken, R.; Beausang, C. W.; Novak, J. R.; Dewald, A.; Klug, T.; Kemper, G.; von Brentano, P.; Carpenter, M. P.; Janssens, R. V. F. (and others)

2001-09-24

261

Shearing and compression of elliptical particles  

NASA Astrophysics Data System (ADS)

We have performed 2D biaxial shearing and compression experiments for elliptical photoelastic particles in order to understand the effect of particle shape on microscopic and macroscopic properties of a granular system. The shearing experiment was conducted via a series of small forward and reverse steps using pure shear. We study the evolution of particle orientations and the average number of contacts following each step of shear or compression. Using photoelastic particles enables us to visualize the stress state of the system at the particle scale level. The ongoing analysis addresses the statistical properties of jammed state, including jamming that is reached through compression or through shear.

Farhadi, Somayeh; Behringer, Robert

2009-11-01

262

Apparatus for shearing spent nuclear fuel assemblies  

DOEpatents

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.

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

1980-01-01

263

Weakly nonlinear analysis of wind-driven gravity waves  

Microsoft Academic Search

We study the weakly nonlinear development of shear-driven gravity waves induced by the physical mechanism first proposed by Miles, and furthermore investigate the mixing properties of the finite-amplitude solutions. Linear theory predicts that gravity waves are amplified by an influx of energy through the critical layer, where the velocity of the wind equals the wave phase velocity. As the wave

Alexandros Alexakis; Yuan-Nan Young; Robert Rosner

2004-01-01

264

Controlled shear/tension fixture  

DOEpatents

A test fixture for simultaneously testing two material test samples is provided. The fixture provides substantially equal shear and tensile stresses in each test specimens. By gradually applying a load force to the fixture only one of the two specimens fractures. Upon fracture of the one specimen, the fixture and the load train lose contact and the second specimen is preserved in a state of upset just prior to fracture. Particular advantages of the fixture are (1) to control the tensile to shear load on the specimen for understanding the effect of these stresses on the deformation behavior of advanced materials, (2) to control the location of fracture for accessing localized material properties including the variation of the mechanical properties and residual stresses across the thickness of advanced materials, (3) to yield a fractured specimen for strength measurement and an unfractured specimen for examining the microstructure just prior to fracture.

Hsueh, Chun-Hway (Knoxville, TN); Liu, Chain-tsuan (Knoxville, TN); George, Easo P. (Knoxville, TN)

2012-07-24

265

Shear stress and plaque development.  

PubMed

Although traditional cardiovascular risk factors 'prime the soil' for atherogenesis systemically, atherosclerosis primarily occurs in a site-specific manner with a predilection towards the inner wall of curvatures and outer wall of bifurcations with sparing of flow-dividers. Wall shear stress is a frictional force exerted parallel to the vessel wall that leads to alteration of the endothelial phenotype, endothelial cell signaling, gene and protein expression leading to a proinflammatory phenotype, reduced nitric oxide availability and disruption of the extracellular matrix, which in turn leads to plaque development. Clinical and experimental data are emerging that suggest the pathobiology associated with abnormal wall shear stress results in atherosclerotic plaque development and progression. PMID:20397828

Dhawan, Saurabh S; Avati Nanjundappa, Ravi P; Branch, Jonathan R; Taylor, W Robert; Quyyumi, Arshed A; Jo, Hanjoong; McDaniel, Michael C; Suo, Jin; Giddens, Don; Samady, Habib

2010-04-01

266

Rheo NMR and shear banding  

Microsoft Academic Search

The phenomenon of shear banding in complex fluids has been investigated using NMR velocimetry and NMR spectroscopy, mostly\\u000a in wormlike micelle systems, but more recently in colloidal systems and multilayer vesicles. A particular advantage of NMR\\u000a is the ability to simultaneously investigate structural ordering and to compare such ordering with local strain rates. In\\u000a this paper, we describe the basics

Paul T. Callaghan

2008-01-01

267

Cavitation Bubble in Shear Flow  

NASA Astrophysics Data System (ADS)

In the orifice of liquid injectors at high pressure, cavitation occurs behind the sharp corners, where a strong pressure drop is present due to quick change in the flow direction. In addition, a high level of shear is present inside the boundary layer. Therefore, it is important to understand the influence of the shear on the cavitation. In this study, the deformation of a cavitation bubble in shear and extensional flows is numerically investigated. The Navier-Stokes equations are solved to observe the three-dimensional behavior of the bubble as it grows and collapses. During the collapse phase of the bubble, two re-entrant jets are observed on two sides of the bubble due to interaction of the bubble with the background flow. Re-entrant jets with enough strength could breakup the bubble into smaller bubbles. Post processing of the results is done to cast the disturbance by the bubble on the liquid velocity field in terms of spherical harmonics. It is found that a quadrupole moment is created in addition to the monopole source. As the bubble collapses regions of high vorticity are created near the bubble interface.

Dabiri, Sadegh; Sirignano, William; Joseph, Daniel

2009-11-01

268

Shear viscosity in hybrid stars  

NASA Astrophysics Data System (ADS)

A study of the shear viscosity of hadrons and quarks in hybrid stars has been performed in the framework of the microscopic transport theory. The neutron-star structure has been determined employing the equation of state from the Brueckner theory with three-body force for the hadron phase, and the equation of state from the MIT bag model for the deconfined quark phase. The nucleon-nucleon cross sections in dense matter have been consistently calculated from the Brueckner G matrix, whereas for the quark-quark cross sections the perturbative QCD has been adopted. Despite that the quark contribution to the shear viscosity is quite small at low temperature, the transition to the deconfined phase makes the equation of state much softer with the result that the baryon viscosity turns out to be enhanced instead of reduced in hybrid stars. The damping time scale of r-modes due to the shear viscosity has been evaluated for several stable configurations of a hybrid star and compared with the neutron-star spin-down time scale induced by the emission gravitation radiation from the r-modes. The enhancement of the total viscosity makes the viscosity time scale comparable with the gravitation radiation one at low temperature.

Jaccarino, D.; Plumari, S.; Greco, V.; Lombardo, U.; Santra, A. B.

2012-05-01

269

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

...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...

2013-05-20

270

Wind turbulence characterization for wind energy development  

Microsoft Academic Search

As part of its support of the U.S. Department of Energy's (DOE's) Federal Wind Energy Program, the Pacific Northwest Laboratory (PNL) has initiated an effort to work jointly with the wind energy community to characterize wind turbulence in a variety of complex terrains at existing or potential sites of wind turbine installation. Five turbulence characterization systems were assembled and installed

L. L. Wendell; G. L. Gower; V. R. Morris; S. D. Tomich

1991-01-01

271

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 ...

272

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 ...

273

Aeolian shear stress ratio measurements within mesquite-dominated landscapes of the Chihuahuan Desert, New Mexico, USA  

NASA Astrophysics Data System (ADS)

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.

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

2006-12-01

274

Parameterization of Wind Farms in a Mesoscale NWP Model  

NASA Astrophysics Data System (ADS)

The interaction between the atmospheric boundary layer and wind turbines has become an important issue with wind energy the fastest growing renewable energy resource worldwide, with increasingly large wind farms in development. The development of a new wind farm parameterization for the mesoscale numerical weather prediction model WRF provides a tool to improve understanding of the interaction between wind farms and the boundary layer. Wind turbines are represented as a sink of momentum and source of turbulence (turbulent kinetic energy) at model levels containing turbine blades. The parameterization can represent a wide range of turbines based on hub height, blade diameter, nominal power and cut-in/cut-out speeds. Results are presented for a series of idealized experiments which investigate the impact of large wind farms on the boundary layer. For an idealized offshore wind farm covering 10x10 km, the wind speed deficit was found to extend throughout the depth of the neutral boundary layer. Downstream, the wake was found to decay with an e-folding length scale of 60 km. However, the turbulent kinetic energy generated within the farm was found to decay much more quickly downstream due to high dissipation within the farm. Above the farm to the top of the boundary layer, the turbulent kinetic energy was increased due to vertical transport and shear production caused by the momentum deficit within the farm. The turbulent kinetic energy was also increased near the surface below the turbines, causing an increase in the wind.

Fitch, A. C.; Olson, J. B.; Lundquist, J. K.; Dudhia, J.; Gupta, A. K.; Michalakes, J.; Barstad, I.

2011-12-01

275

Temporal oscillations of the shear stress and scattered light in a shear-banding--shear-thickening micellar solution.  

PubMed

The results of optical and rheological experiments performed on a viscoelastic solution (cetyltrimethylammonium bromide + sodium salicylate in water) are reported. The flow curve has a horizontal plateau extending between two critical shear rates characteristic of heterogeneous flows formed by two layers of fluid with different viscosities. These two bands which also have different optical anisotropy are clearly seen by direct observation in polarized light. At the end of the plateau, apparent shear thickening is observed in a narrow range of shear rates; in phase oscillations of the shear stress and of the first normal stress difference are recorded in a shearing device operating under controlled strain. The direct observation of the annular gap of a Couette cell in a direction perpendicular to a plane containing the vorticity shows that the turbidity of the whole sample also undergoes time dependent variations with the same period as the shear stress. However no banding is observed during the oscillations and the flow remains homogeneous. PMID:16132153

Azzouzi, H; Decruppe, J P; Lerouge, S; Greffier, O

2005-08-30

276

An Observational Study of Wind Profiles in the Baroclinic Convective Mixed Layer  

NASA Astrophysics Data System (ADS)

A comprehensive planetary boundary-layer (PBL) and synoptic data set is used to isolate the mechanisms that determine the vertical shear of the horizontal wind in the convective mixed layer. To do this, we compare a fair-weather convective PBL with no vertical shear through the mixed layer (10 March 1992), with a day with substantial vertical shear in the north-south wind component (27 February). The approach involves evaluating the terms of the budget equations for the two components of the vertical shear of the horizontal wind; namely: the time-rate-of-change or time-tendency term, differential advection, the Coriolis terms (a thermal wind term and a shear term), and the second derivative of the vertical transport of horizontal momentum with respect to height (turbulent-transport term). The data, gathered during the 1992 STorm-scale Operational and Research Meteorology (STORM) Fronts Experiments Systems Test (FEST) field experiment, are from gust-probe aircraft horizontal legs and soundings, 915-MHz wind profilers, a 5-cm Doppler radar, radiosondes, and surface Portable Automated Mesonet (PAM) stations in a roughly 50 × 50 km boundary-layer array in north-eastern Kansas, nested in a mesoscale-to-synoptic array of radiosondes and surface data.We present evidence that the shear on 27 February is related to the rapid growth of the convective boundary layer. Computing the shear budget over a fixed depth (the final depth of the mixed layer), we find that the time-tendency term dominates, reflecting entrainment of high-shear air from above the boundary layer. We suggest that shear within the mixed layer occurs when the time-tendency term is sufficiently large that the shear-reduction terms - namely the turbulent-transport term and differential advection terms - cannot compensate. In contrast, the tendency term is small for the slowly-growing PBL of 10 March, resulting in a balance between the Coriolis terms and the turbulent-transport term. Thus, the thermal wind appears to influence mixed-layer shear only indirectly, through its role in determining the entrained shear.

Lemone, Margaret A.; Zhou, Mingyu; Moeng, Chin-Hoh; et al.

277

Acoustic evaluation of DNW free jet shear layer correction using a model jet  

Microsoft Academic Search

Acoustic tests of a 6-cm model jet were conducted in the German-Dutch Wind Tunnel (DNW) 6m by 8m free jet facility. The purpose of these tests was to evaluate a new free jet shear layer correction procedure that adds an empirical correction to the theoretical correction previously used at DNW. Static-to-flight effects on jet noise measured in the flow were

W. H. Herkes; F. G. Strout; R. Ross

1983-01-01

278

Prospecting for Wind  

ERIC Educational Resources Information Center

|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…

Swapp, Andy; Schreuders, Paul; Reeve, Edward

2011-01-01

279

What price wind power  

Microsoft Academic Search

Basic considerations in adapting wind power systems for different uses and locations are discussed. The role of such factors as average wind velocity and wind variation in the selection of a wind system design is examined. The advantages and disadvantages of different types of wind power systems, including lift or drag types and horizontal or vertical axis types, are discussed

D. G. Shepherd

1977-01-01

280

Simulation of sheared, caking powder  

NASA Astrophysics Data System (ADS)

We introduce a visco-elastic contact model for DEM simulations, which takes caking into account and investigate the impacts of this time dependent inter particle cohesion force on the bulk behavior under biaxial deformation. Starting from the assumption that the cohesion force between two particles develops on a characteristic timescale tc, we show, that two regimes can be identified. If tc is small compared to the shear rate ??, full cohesion is reached within the typical contact duration. The cohesion strength remains homogeneous throughout the sample. However, if tc >> ?? crystallization bridges at fluctuating contacts never fully recover. Heterogeneous cohesion forces and granules are the consequence.

Weuster, A.; Brendel, L.; Wolf, D. E.

2013-06-01

281

Quasigeostrophic vortices in zonal shear  

NASA Astrophysics Data System (ADS)

We analyze piece-wise uniform distributions of quasigeostrophic potential vorticity and their dynamics in uniform potential vorticity background zonal flows bar-v = (bar-v(sub x)(y))(bar-x). We develop a spectrally accurate boundary integral method for both solving the initial-value problem and calculating families steady-state vortices and their linear stability. We apply these methods to vortices in zonal velocity profiles which have a linear, quadratic, or cubic dependence on the latitudinal variable y. When we have a variable shear zonal profile with a nearby region of adverse (opposite sign) vorticity there is a limit to the size steady vortices can attain. The limiting vortex has a stagnation point on its boundary that mediates the filamentation of vorticity and provides a mechanism for dynamically limiting the vortex size. We also examine vortices in zonal flows, for the case of finite Rossby deformation radius L(sub R). Steady vortices in a same-signed (prograde) background shear of a given strength, have a limit to their latitudinal height but no limit to their longitudinal length, and are always linearly stable. Steady finite L(sub R) vortices of fixed strength in an adverse shear background have a maximum area that they can attain. If a finite L(sub R) vortex in adverse shear initially has an area slightly larger than this maximum, it fissions into two smaller vortices. With a fixed cubic zonal profile and a fixed vortex strength and L(sub R), there exists two types of steady vortex families. For weak vortices or small L(sub R), the limiting zone-like vortex has a maximum latitudinal height, but is infinitely long. While for strong vortices or large L(sub R) there exists a maximum area vortex. Finally we show that the velocity field of the Great Red Spot of Jupiter is not consistent with a quasigeostrophic uniform potential vortex embedded in an average zonal flow that also has uniform potential vorticity.

Vanbuskirk, Robert Daniel

282

The limited growth of vegetated shear layers  

NASA Astrophysics Data System (ADS)

In contrast to free shear layers, which grow continuously downstream, shear layers generated by submerged vegetation grow only to a finite thickness. Because these shear layers are characterized by coherent vortex structures and rapid vertical mixing, their thickness controls exchange between the vegetation and the overlying water. Experiments conducted in a laboratory flume show that the growth of these obstructed shear layers is arrested once the production of shear-layer-scale turbulent kinetic energy (SKE) is balanced by dissipation of SKE within the canopy. This equilibrium condition, along with a mixing length closure scheme, was used in a one-dimensional numerical model to predict the mean velocity profiles of the experimental shear layers. The agreement between model and experiment is very good, but field application of the model is limited by a lack of description of the drag coefficient in a submerged canopy.

Ghisalberti, M.; Nepf, H. M.

2004-07-01

283

Shear Banding in Mesoscopic Dusty Plasma Liquids  

NASA Astrophysics Data System (ADS)

We experimentally demonstrate shear banding and construct a microscopic dynamic picture of a sheared 2D mesoscopic dust Coulomb liquid at the kinetic level. Under the topological constraints from the discreteness and finite boundary, the nonlinear threshold-type response of motion to the local stress induced by thermal and external drives leads to shear thinning and the enhanced avalanche-type local topological transitions with stress relaxation in the form of clusters. It causes the formation of the outer shear bands in which the mean shear rate, the velocity fluctuations, and the structural rearrangement rate are all enhanced, and leaves a weakly perturbed center band. The typical size of the cooperative hopping vortex (about three interparticle distance) sets up a common length scale for the widths of the confinement induced layering and the shear band.

Chan, Chia-Ling; Woon, Wei-Yen; I, Lin

2004-11-01

284

Use of Shears with a “Rolling Cut”  

Microsoft Academic Search

This article examines the advantages and disadvantages of using guillotine shears with an inclined top blade for the cross-cutting of flat-rolled products on modern plate mills. It is shown that it is necessary to use shears of an improved design. After shears with a “rolling cut,” designed by the All-Russia Scientific Research, Planning, and Design Institute of Metallurgical Machinery (VNIImetmash),

V. V. Zyryanov; A. M. Ivanov; I. Yu. Gaitanov

2004-01-01

285

Crystal nucleation of colloidal suspensions under shear.  

PubMed

We use Brownian dynamics simulations in combination with the umbrella sampling technique to study the effect of shear flow on homogeneous crystal nucleation. We find that a homogeneous shear rate leads to a significant suppression of the crystal nucleation rate and to an increase of the size of the critical nucleus. A simple, phenomenological extension of classical nucleation theory accounts for these observations. The orientation of the crystal nucleus is tilted with respect to the shear direction. PMID:15323669

Blaak, Ronald; Auer, Stefan; Frenkel, Daan; Löwen, Hartmut

2004-08-05

286

Glass transitions and shear thickening suspension rheology  

Microsoft Academic Search

We introduce a class of simple models for shear thickening and\\/ or `jamming'\\u000ain colloidal suspensions. These are based on schematic mode coupling theory\\u000a(MCT) of the glass transition, having a memory term that depends on a density\\u000avariable, and on both the shear stress and the shear rate. (Tensorial aspects\\u000aof the rheology, such as normal stresses, are ignored

M. Fuchs; P. Sollich

2005-01-01

287

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.

288

Dynamic shear deformation in high purity Fe  

SciTech Connect

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.

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

289

Measurement of temperature using speckle shearing interferometry.  

PubMed

A laser speckle shearing interferometric technique is used for measuring the temperature profile inside a gaseous flame. The experimental results are compared with the values obtained by a thermocouple and also by speckle photography. Good agreement is seen among the temperatures measured by speckle shearing interferometry, speckle photography, and the thermocouple. Speckle shearing interferometry is easier to implement than speckle photography. This is because in speckle shearing interferometry the accurate positions of the fringes can be known without point-by-point analysis and correction for the halo effect. PMID:20885553

Shakher, C; Nirala, A K

1994-04-10

290

Shear viscosity in antikaon condensed matter  

SciTech Connect

We investigate the shear viscosity of neutron star matter in the presence of an antikaon condensate. The electron and muon number densities are reduced due to the appearance of a K{sup -} condensate in neutron star matter, whereas the proton number density increases. Consequently, the shear viscosity due to scatterings of electrons and muons with themselves and protons is lowered compared to the case without the condensate. On the other hand, the contribution of proton-proton collisions to the proton shear viscosity through electromagnetic and strong interactions becomes important and comparable to the neutron shear viscosity.

Nandi, Rana; Bandyopadhyay, Debades [Theory Division and Centre for Astroparticle Physics, Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata-700064 (India); Banik, Sarmistha [Variable Energy Cyclotron Centre, 1/AF Bidhannagar, Kolkata-700064 (India)

2009-12-15

291

Study on magnetorheological shear thickening fluid  

NASA Astrophysics Data System (ADS)

In this paper, a magnetic-field-controlled and speed-activated magnetorheological shear thickening fluid (MRSTF) is presented. We fabricated a kind of shear thickening fluid (STF) which was composed of nanosize silica particles suspended in a solvent, ethylene glycol, at high concentrations. Then the micron-size carbonyl iron particles with different volume fractions were added to the STF to fabricate the MRSTF. Their dynamic properties in different shear strain rates and magnetic fields were tested by using a rheometer. The suspension shows an abrupt increase in complex viscosity beyond a critical dynamic shear rate and a magnetic-field-controllable characteristic, as well as being reversible.

Zhang, Xianzhou; Li, Weihua; Gong, X. L.

2008-02-01

292

Novel shear mechanism in nanolayered composites  

SciTech Connect

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.

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

293

Shear reinforcement in deep slabs  

NASA Astrophysics Data System (ADS)

A considerable amount of data is available in the literature regarding the behavior of normally proportioned slabs, those with span-to-effective-depth (L/d) ratios greater than approximately 8. However, guidance for shear design and response limits of deep slabs (L/d less than 6) used in protective construction is lacking. Thirteen one-way reinforced concrete deep slabs were statically loaded with uniform water pressure to gain a basic understanding of the behavior of deep slabs with reinforcing details typical of protective construction. The post-ultimate behavior of the slabs indicated that a substantial amount of reserve capacity is available in deep slabs with large quantities of principal reinforcement. Based on this series, the recommended response limit for deep slabs having a principal steel ratio near 0.01 and adequate shear reinforcement is approximately 12 deg. For deep slabs with relatively small quantities of principal steel, the response should probably be limited to approximately 8 deg for design purposes.

Woodson, Stanley C.

1994-11-01

294

Wind Energy Technology: Generating Power from the Wind; (USA)  

Microsoft Academic Search

Wind Energy Technology: Generating Power from the Wind (WET) announces on a biomonthly basis the current worldwide information available on wind turbine concepts and design, including the basic science of wind turbine dynamics as well as advanced components and systems research; wind turbine performance; ancillary wind turbine equipment, including system protection and interconnection devices; wind resource identification; wind turbine project

M. H. Raridon; S. C. Hicks

1991-01-01

295

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

NASA Astrophysics Data System (ADS)

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.

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

2010-12-01

296

A Small Wind Meter  

Microsoft Academic Search

The paper describes a small, rugged, portable, quick period wind meter for measuring the speed of wind and of gusts of wind. The instrument consists essentially of a mica vane and pointer twisting a torsion wire.

E. O. Hulburt

1933-01-01

297

Wind Energy Applications Guide.  

National Technical Information Service (NTIS)

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 basic...

2001-01-01

298

VAWT Stochastic Wind Simulator.  

National Technical Information Service (NTIS)

A stochastic wind simulation for VAWTs (VSTOC) has been developed which yields turbulent wind-velocity fluctuations for rotationally sampled points. This allows three-component wind-velocity fluctuations to be simulated at specified nodal points on the wi...

J. H. Strickland

1987-01-01

299

Wind energy program overview  

NASA Astrophysics Data System (ADS)

This overview emphasizes the amount of electric power that could be provided by wind power rather than traditional fossil fuels. New wind power markets, advances in technology, technology transfer, and wind resources are some topics covered in this publication.

1992-02-01

300

A comparative study of some mathematical models of the mean wind structure and aerodynamic drag of plant canopies  

Microsoft Academic Search

A semi-analytical method for describing the mean wind profile and shear stress within plant canopies and for estimating the roughness length and the displacement height is presented. This method incorporates density and vertical structure of the canopy and includes simple parameterizations of the roughness sublayer and shelter factor. Some of the wind profiles examined are consistent with first-order closure techniques

William Massman

1987-01-01

301

Investigation of the flow field and the starting conditions of wind-induced erosion of the railway embankment  

Microsoft Academic Search

Wind-induced erosion and deposition of an embankment are investigated using a numerical approach. The underlying mechanism is analyzed. Starting from the N-S equations, employing the SIMPLE algorithm in the computational plane, the flow field around a railway embankment in a windy district is simulated. It shows that the Re number and shear intensity of the incoming wind and the profile

J. Zhang; E. Cui; G. Fu

1995-01-01

302

Reversible shear thickening at low shear rates of electrorheological fluids under electric fields  

Microsoft Academic Search

Shear thickening is a phenomenon of significant viscosity increase of\\u000acolloidal suspensions. While electrorheological (ER) fluids can be turned into\\u000aa solid-like material by applying an electric field, their shear strength is\\u000awidely represented by the attractive electrostatic interaction between ER\\u000aparticles. By shearing ER fluids between two concentric cylinders, we show a\\u000areversible shear thickening of ER fluids above

Yu Tian; Minliang Zhang; Jile Jiang; Noshir Pesika; Hongbo Zeng; Jacob Israelachvili; Yonggang Meng; Shizhu Wen

2010-01-01

303

Reversible shear thickening at low shear rates of electrorheological fluids under electric fields  

Microsoft Academic Search

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

Yu Tian; Minliang Zhang; Jile Jiang; Noshir Pesika; Hongbo Zeng; Jacob Israelachvili; Yonggang Meng; Shizhu Wen

2011-01-01

304

Effect of axial compression ratio on shear strength of reinforced light-weight concrete shear walls  

Microsoft Academic Search

For practical reasons, the axial compression ratio has always been a vital element in light-weight concrete shear wall design relating to its own shear strength and ductility. In this paper, based on the experiment, the shear strength and failure mode of mid-rise light-weight concrete shear walls under cyclic loads, especially under different axial loads, are closely examined. By using a

Wang Mingdong

2011-01-01

305

Wind resources of Somalia  

SciTech Connect

The results of wind energy research in Somalia are presented. The wind resource appears to be suitable for power production on 85% of the country, very intense on 10% and uniform on 70%, being regular throughout. Two areas of different wind regimes have been identified and characterized; the wind-distribution characteristics of 11 sites are presented and discussed, together with the territorial maps of the wind intensity and of the wind energy.

Pallabazzer, R. (Univ. della Calabria (Italy)); Gabow, A.A. (Somali National Univ., Mogadisho (Somalia))

1991-01-01

306

Shear transfer mechanism of a multi-storied shear wall with peripheral members  

Microsoft Academic Search

In the current design code, cantilever shear walls are normally assumed to stand on a solid foundation, and foundation beams, slabs and piles are designed separately without considering their interactions. Moreover, the shear transfer mechanisms are neglected, which along the wall base vary depending on the cracks and inelastic deformation levels at the shear wall base. In this study, a

Jiyang WANGV; Masanobu Sakashita; Susumu Kono

2011-01-01

307

Recording wind microstructure with a seismograph  

NASA Astrophysics Data System (ADS)

In an effort to characterize the effects of atmospheric waves on seismic sensors at the surface of the earth, we used geophones to perform some simple experiments allowing us to “watch” the wind. By examining the wind noise on the resulting seismograms, we were able to characterize the microstructure of atmospheric wind gusts at a horizontal scale of 1 to 10 m. In a first experiment to detect the wind-induced wave field, we placed 96 geophones on the ground in a straight line aligned parallel with the wind at intervals of 0.3 m. We recorded the resulting data using a 96-channel exploration seismograph. In essence, the seismograph system served as a linear array of 96 ground-level wind sensors. On a 1- to 2-m scale, wind-gust details became apparent after the seismograph had recorded for a period of 7.5 s. When wind-gust speeds were between 4 and 7 m/s (as measured directly from the time-and-distance relationships obtained from the seismogram), the wavelength of the gusts was between 3 and 6 m. In a second experiment, we used an array consisting of three parallel lines of 32 geophones each and were able to detect the lateral components of wind motion and turbulence relative to the long axis of the array. We noted variations in both space and time in the effect of the wind gusts on the geophones. The sensing system we describe is preliminary; however, when further refined, it may be a useful way of looking at the microstructure of atmospheric motion near the ground. The data we obtained also suggest that when models are constructed and near-ground atmospheric observations are made using grid spacings of more than 1 m, the results may be subject to serious spatial-aliasing effects. The authors offer these results in the hope that they will stimulate new, cross-disciplinary scientific inquiry. Moreover, applications of the technique might include the generation of data to support improved modeling of atmospheric turbulence at meter scales, which could be of interest to those requiring information about wind shear, wind-induced soil erosion, the dispersion of pollutants and toxins, and other subjects of interest.

Steeples, Don W.; Schmeissner, Chris; Macy, Brian

308

A Convective Storm Matrix: Buoyancy/Shear Dependencies  

NSDL National Science Digital Library

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.

Spangler, Tim

1998-01-01

309

Shear Stress-Strain Characteristics of Adhesive Layers  

Microsoft Academic Search

Shear behavior data of adhesives are evaluated by a specially constructed torsion device which enables recording of shear moment displacement relationship for thin adhesive layers. Shear strains and stresses were computed from the recorded torsional moment displacement curve by assuming linear shear strain distribution throughout the adhesive thickness and uniform shear strain distribution at the cross-sectional area. The general trend

Dan Peretz

1978-01-01

310

Shear thickening in a solution undergoing inverse melting  

Microsoft Academic Search

Rheological measurements on a solution undergoing inverse melting are presented as a function of temperature and concentration. Under shear, this solution exhibits the phenomenon of shear thickening; i.e. an increase in apparent viscosity with increasing shear rate . In particular, a shear-thickening transition happens at a critical shear rate , which increases with increasing concentration. It defines two different regimes:

R. Angelini; G. Salvi; G. Ruocco

2008-01-01

311

Wind Power Today: Federal Wind Program Highlights  

SciTech Connect

Wind Power Today is an annual publication that provides an overview of the wind research conducted under the U.S. Department of Energy's Wind and Hydropower Technologies Program. The purpose of Wind Power Today is to show how DOE supports wind turbine research and deployment in hopes of furthering the advancement of wind technologies that produce clean, low-cost, reliable energy. Content objectives include: educate readers about the advantages and potential for widespread deployment of wind energy; explain the program's objectives and goals; describe the program's accomplishments in research and application; examine the barriers to widespread deployment; describe the benefits of continued research and development; facilitate technology transfer; and attract cooperative wind energy projects with industry.

Not Available

2005-04-01

312

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

NASA Astrophysics Data System (ADS)

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.

Walter, Benjamin; Gromke, Christof; Lehning, Michael

2012-08-01

313

Tomographic weak-lensing shear spectra from large N-body and hydrodynamical simulations  

NASA Astrophysics Data System (ADS)

Context. Forthcoming experiments will enable us to determine tomographic shear spectra at a high precision level. Most predictions about them have until now been based on algorithms yielding the expected linear and non-linear spectrum of density fluctuations. Even when simulations have been used, so-called Halofit predictions on fairly large scales have been needed. Aims: We wish to go beyond this limitation. Methods: We perform N-body and hydrodynamical simulations within a sufficiently large cosmological volume to allow a direct connection between simulations and linear spectra. While covering large length-scales, the simulation resolution is good enough to allow us to explore the high-? harmonics of the cosmic shear (up to ? ~ 50 000), well into the domain where baryon physics becomes important. We then compare shear spectra in the absence and in presence of various kinds of baryon physics, such as radiative cooling, star formation, and supernova feedback in the form of galactic winds. Results: We distinguish several typical properties of matter fluctuation spectra in the different simulations and test their impact on shear spectra. Conclusions: We compare our outputs with those obtainable using approximate expressions for non-linear spectra, and identify substantial discrepancies even between our results and those of purely N-body results. Our simulations and the treatment of their outputs however enable us, for the first time, to obtain shear results that are fully independent of any approximate expression, also in the high-? range, where we need to incorporate a non-linear power spectrum of density perturbations and the effects of baryon physics. This will allow us to fully exploit the cosmological information contained in future high-sensitivity cosmic shear surveys, exploring the physics of cosmic shears via weak lensing measurements.

Casarini, L.; Bonometto, S. A.; Borgani, S.; Dolag, K.; Murante, G.; Mezzetti, M.; Tornatore, L.; La Vacca, G.

2012-06-01

314

Structure of the Brevard Zone and Blue Ridge near Lenoir, North Carolina, with observations on oblique crenulation cleavage and a preliminary theory for irrotational structures in shear zones  

NASA Astrophysics Data System (ADS)

Stratigraphy on the eastern flank of the Southern Appalachian Blue Ridge near the Grandfather Mountain window is arranged in a series of fault-bounded lithotectonic belts stacked so that the structural section dips steeply southeast. The Fries block of the Blue Ridge thrust sheet overlies the Grandfather Mountain window along the Linville Falls fault. The Laytown belt overlies the Fries block along the Winding Stairs Mountain fault. The Brevard zone, bounded as its base by the Ripshin Mountain fault and bounded as its top by the Yadkin fault, lies on the Laytown belt. Theoretical models for irrotational structures in two-dimensional plane strain demonstrate that: lines of material particles lying in an oblique irrotational orientation make an angle, alpha, with the shear zone boundaries whose vertex indicates the shear sense for the simple shear component and the oblique irrotational direction could experience a component of simple shear equal in sign to that of the shear zone.

Bobyarchick, A. R.

1983-09-01

315

Wind characteristics for agricultural wind energy applications  

Microsoft Academic Search

Wind energy utilization in agriculture can provide a potentially significant savings in fuel oil consumption and ultimately a cost savings to the farmer. A knowledge of the wind characteristics within a region and at a location can contribute greatly to a more efficient and cost-effective use of this resource. Current research indicates that the important wind characteristics include mean annual

Renne

1979-01-01

316

Wind speed forecasting for wind energy applications  

Microsoft Academic Search

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

Hong Liu

2010-01-01

317

Study of shear-stiffened elastomers  

NASA Astrophysics Data System (ADS)

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.

Tian, Tongfei; Li, Weihua; Ding, Jie; Alici, Gursel; Du, Haiping

2013-06-01

318

White Light Extended Source Shearing Interferometer  

Microsoft Academic Search

A grating lateral shear interferometer is described that can be used with a white light source. The use of the interferometer with certain types of extended sources is also demonstrated. In a recent paper a simple double frequency grat- ing shearing interferometer, similar to a Ronchi in- terferometer, was described for use with a quasi- monochromatic point light source. l

J. C. Wyant

1974-01-01

319

Dynamic shear deformation in high purity Fe  

Microsoft Academic Search

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,

Ellen K Cerreta; John F Bingert; Carl P Trujillo; Mike F Lopez; George T Gray

2009-01-01

320

Structure and dynamics of sheared mantle plumes  

Microsoft Academic Search

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

Ross C. Kerr; Catherine Mériaux

2004-01-01

321

Creep in shear of experimental solder joints  

SciTech Connect

Thermal fatigue failures of solder joints in electronic devices are a great concern in the electronics industry. Since the fatigue load is often in shear the details of thermal fatigue failure in shear are of particular interest. Recent work indicates that similar failure mechanisms operate in both thermal fatigue in shear and unidirectional creep in shear. Additionally, since the operative temperatures during thermal fatigue represent high solder homologous temperatures, creep deformation is certainly involved. These factors and the relative ease of conducting creep experiments encourage the study of solder joints under shear creep conditions. This work presents steady state shear creep rate vs shear stress data for several solder compositions, including the binary eutectic alloy and Pb-Sn alloyed with small amounts of Bi, Cd, In, and Sb, in a joint configuration. These data indicate that conventional creep mechanisms operate in the temperature and shear strain rate ranges studied. Extensive microstructural information is also reported. The microstructural evolution under creep conditions indicates that the instability of the as-cast binary Pb-Sn eutectic microstructure initiates creep failure. Changes of the as-solidified microstructure with the third element addition are reported as are the microstructural responses of each of these alloys to creep deformation. The efficacy of postponing the microstructural instability with the addition of small amounts of ternary elements is discussed. 27 refs., 13 figs., 1 tab.

Tribula, D.; Morris, J.W. Jr.

1989-09-01

322

Vectorial shearing interferometry for combustion application  

Microsoft Academic Search

We applied vectorial shearing interferometer to the visualization of different combustion regions in the flame. Using the shearing interferometer as edge identifier, the following regions are localized: background (no flame), the hottest part of the flame, internal cone and primary flow of air and fuel. In addition to the so-called surface of stoichoimetric balance, we identify a volume where complete

Marija Strojnik; Gonzalo Paez

2006-01-01

323

In-situ Vane Shear Test  

NSDL National Science Digital Library

This article briefly describes the in-situ shear vane test, including images and typical results. This procedure tests the undrained shear strength of soil. Procedures of the test are not outlined, but a general overview is given. The site contains photos, charts, diagrams and instructional test to help guide the user.

2008-09-24

324

Shear Thickening Oscillation in a Dilatant Fluid  

Microsoft Academic Search

By introducing a state variable, we construct a phenomenological fluid dynamical model of a dilatant fluid, i.e., a dense mixture of fluid and granules that shows severe shear thickening. We demonstrate that the fluid shows shear thickening oscillation, namely, the fluid flow oscillates owning to the coupling between the fluid dynamics and the internal dynamics of state. We also demonstrate

Hiizu Nakanishi

2011-01-01

325

Thixotropy of MR shear-thickening fluids  

Microsoft Academic Search

Particle sedimentation is a key issue of conventional magnetorheological (MR) fluids. We recently fabricated MR shear-thickening fluids (MRSTF), which can work as novel MR fluids without particle settling. This merit of the material against particle settling is attributed to the thixotropy property. By using shear-thickening fluids as a base medium, a series of MRSTF samples was prepared and their rheological

Xianzhou Zhang; Weihua Li; Xinglong Gong

2010-01-01

326

Viscous fingering in shear thickening silica suspensions  

Microsoft Academic Search

We make an experimental study of the viscous fingering behavior of air displacing shear thickening silica suspensions in linear Hele-Shaw cells with different cell gaps as a function of the injection pressure. The imposed shear rate defined by the ratio of the finger tip velocity and the half of a cell gap, at which the onset of the viscous fingering

Naoki Kagei; Daisuke Kanie; Masami Kawaguchi

2005-01-01

327

Shear flow over a porous particle  

Microsoft Academic Search

Linear axisymmetric Stokes flow over a porous spherical particle is investigated. An exact analytic solution for the fluid velocity components and the pressure inside and outside the porous particle is obtained. The solution is generalized to include the cases of arbitrary three-dimensional linear shear flow as well as translational-shear Stokes flow. As the permeability of the particle tends to zero,

A. I. Zhurov; A. D. Polyanin; E. D. Potapov

1995-01-01

328

Two fluid shear-free composites  

NASA Astrophysics Data System (ADS)

Shear-free composite fluids are constructed from two Letelier rotated unaligned perfect fluids. The component fluid parameters necessary to construct a shear-free composite are investigated. A metric in the Stephani-Barnes solution family and a simple stationary metric are discussed.

Krisch, J. P.; Glass, E. N.

2013-08-01

329

Shear Localization in a Tungsten Heavy Alloy.  

National Technical Information Service (NTIS)

This paper presents the results of an investigation into the dynamic shearing deformations of a W-Ni-Fe heavy alloy containing 91% W and with the Ni and Fe in a 7:3 ratio. The techniques used to develop the dynamic shearing deformations are the torsional ...

K. T. Ramesh S. Yadav J. A. Davis

1995-01-01

330

Active Feedback Interaction with a Shear Layer.  

National Technical Information Service (NTIS)

Study of the open-loop forcing of shear layer by a pitching airfoil resulted in three major findings: 1) It is possible to induce very large changes in the shear layer growth rate downstream of the disturbance location, while leaving the portion of the la...

P. E. Dimotakis M. M. Koochesfahani

1987-01-01

331

Creep in shear of experimental solder joints.  

National Technical Information Service (NTIS)

Thermal fatigue failures of solder joints in electronic devices are a great concern in the electronics industry. Since the fatigue load is often in shear the details of thermal fatigue failure in shear are of particular interest. Recent work indicates tha...

D. Tribula J. W. Morris

1989-01-01

332

Shear wall experiments and design in Japan  

Microsoft Academic Search

This paper summarizes the results of recent survey studies on the available experimental data bases and design codes\\/standards for reinforced concrete (RC) shear wall structures in Japan. Information related to the seismic design of RC reactor buildings and containment structures was emphasized in the survey. The seismic requirements for concrete structures, particularly those related to shear strength design, are outlined.

Y. J. Park; C. Hofmayer

1994-01-01

333

Reliability analysis of shear wall structures  

Microsoft Academic Search

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

P. C. Wang; H. Hwang; J. Pires; K. Nakai; M. Reich

1986-01-01

334

Shear deformation in granular materials  

SciTech Connect

An investigation into the properties of granular materials is undertaken via numerical simulation. These simulations highlight that frictional contact, a defining characteristic of dry granular materials, and interfacial debonding, an expected deformation mode in plastic bonded explosives, must be properly modeled. Frictional contact and debonding algorithms have been implemented into FLIP, a particle in cell code, and are described. Frictionless and frictional contact are simulated, with attention paid to energy and momentum conservation. Debonding is simulated, with attention paid to the interfacial debonding speed. A first step toward calculations of shear deformation in plastic bonded explosives is made. Simulations are performed on the scale of the grains where experimental data is difficult to obtain. Two characteristics of deformation are found, namely the intermittent binding of grains when rotation and translation are insufficient to accommodate deformation, and the role of the binder as a lubricant in force chains.

Bardenhagen, S.G.; Brackbill, J.U. [Los Alamos National Lab., NM (United States); Sulsky, D.L. [Univ. of New Mexico, Albuquerque, NM (United States)

1998-12-31

335

An Investigation into Shear Resistances of Headed Shear Studs in Solid Concrete Slabs with Local Aggregates in Hong Kong  

Microsoft Academic Search

In general, there are limited experimental reports on the shear resistances of typical interfacial shear connections of headed shear studs and solid concrete slabs with local aggregates in Hong Kong. Moreover, while it is commonly reckoned that the presence of any tensile force in the headed shear stud will reduce its shear resistance significantly, there are few test data in

M. H. Shen; K. F. Chung

2011-01-01

336

Numerical modeling of the wind flow over a transverse dune  

PubMed Central

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.

Araujo, Ascanio D.; Parteli, Eric J. R.; Poschel, Thorsten; Andrade, Jose S.; Herrmann, Hans J.

2013-01-01

337

Numerical modeling of the wind flow over a transverse dune  

NASA Astrophysics Data System (ADS)

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.

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

2013-10-01

338

Numerical modeling of the wind flow over a transverse dune.  

PubMed

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

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

2013-10-04

339

WEAK LENSING MASS RECONSTRUCTION: FLEXION VERSUS SHEAR  

SciTech Connect

Weak gravitational lensing has proven to be a powerful tool to map directly the distribution of dark matter in the universe. The technique, currently used, relies on the accurate measurement of the gravitational shear that corresponds to the first-order distortion of the background galaxy images. More recently, a new technique has been introduced that relies on the accurate measurement of the gravitational flexion that corresponds to the second-order distortion of the background galaxy images. This technique should probe structures on smaller scales than that of shear analysis. The goal of this paper is to compare the ability of shear and flexion to reconstruct the dark matter distribution by taking into account the dispersion in shear and flexion measurements. Our results show that the flexion is less sensitive than shear for constructing the convergence maps on scales that are physically feasible for mapping, meaning that flexion alone should not be used to do convergence map reconstruction, even on small scales.

Pires, S. [Laboratoire AIM, CEA/DSM-CNRS-Universite Paris Diderot, IRFU/SEDI-SAP, Service d'Astrophysique, CEA Saclay, Orme des Merisiers, 91191 Gif-sur-Yvette (France); Amara, A. [Department of Physics, ETH Zurich, Wolfgang-Pauli-Strasse 16, CH-8093 Zurich (Switzerland)

2010-11-10

340

Trapped Electron Precession Shear Induced Fluctuation Decorrelation  

SciTech Connect

We consider the effects of trapped electron precession shear on the microturbulence. In a similar way the strong E x B shear reduces the radial correlation length of ambient fluctuations, the radial variation of the trapped electron precession frequency can reduce the radial correlation length of fluctuations associated with trapped electrons. In reversed shear plasmas, with the explicit dependence of the trapped electron precession shearing rate on B(subscript)theta, the sharp radial gradient of T(subscript)e due to local electron heating inside qmin can make the precession shearing mechanism more effective, and reduce the electron thermal transport constructing a positive feedback loop for the T(subscript)e barrier formation.

T.S. Hahm; P.H. Diamond; E.-J. Kim

2002-07-29

341

Magnetic Field Generation by Relativistic Shear Flows  

NASA Astrophysics Data System (ADS)

We report PIC simulation results of magnetic field generation by relativistic shear flows. We find that the shear flow boundary layer in initially non-magnetic shear flows is unstable to the growth of oblique 2-stream and Weibel instabilities near the boundary layer. Such instabilities generate current sheets and loops which eventually form nonlinear ordered structures resembling magnetic flux tubes with alternating polarity, orthogonal to the shear flow direction. Peak magnetic fields can reach almost equipartition values. The size and amplitude of such magnetic structures reach a steady state when the free energy input of the shear flow is balanced by turbulence dissipation. Nonthermal particles are efficiently accelerated, likely by the drift-kink instability, into a power-law energy distribution. These results have important implications for many astrophysical settings, including multi-component blazar jets and gamma-ray bursts. This work was supported by NSF AST0909167 and NASA Fermi grants.

Liang, Edison; Boettcher, Markus; Smith, Ian

2011-11-01

342

On wind-wave-current interactions during the Shoaling Waves Experiment  

NASA Astrophysics Data System (ADS)

This paper presents a case study of wind-wave-current interaction during the Shoaling Waves Experiment (SHOWEX). Surface current fields off Duck, North Carolina, were measured by a high-frequency Ocean Surface Current Radar (OSCR). Wind, wind stress, and directional wave data were obtained from several Air Sea Interaction Spar (ASIS) buoys moored in the OSCR scanning domain. At several times during the experiment, significant coastal currents entered the experimental area. High horizontal shears at the current edge resulted in the waves at the peak of wind-sea spectra (but not those in the higher-frequency equilibrium range) being shifted away from the mean wind direction. This led to a significant turning of the wind stress vector away from the mean wind direction. The interactions presented here have important applications in radar remote sensing and are discussed in the context of recent radar imaging models of the ocean surface.

Zhang, Fei W.; Drennan, William M.; Haus, Brian K.; Graber, Hans C.

2009-01-01

343

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

NASA Astrophysics Data System (ADS)

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, , 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.

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

2013-08-01

344

Wind profile measurements at the Mod-1 site at Boone, North Carolina  

SciTech Connect

Three components of the wind field, temperature and pressure were measured by means of tethered balloon-borne sondes from the surface to 175 m (577 ft) and by means of a nacelle mounted system, from the surface to hub height of 43 m (140 ft). Measurements were taken over a ten day period at the Mod-1 Site in Boone, NC. Composite wind profiles are presented for different flow and stability regimes. The most extreme shears, on the order of .3 s/sup -1/, were found between 10 m (33 ft) and hub height. Individual profiles of wind and temperature show the effect of nocturnal cooling and accompanying surface stratification on the intensity of thw wind shear. Gustiness measured in terms of departures of one and two standard deviations above and below the mean, occurs at all heights across the rotor of the Mod-1 machine. Most frequent gustiness, however, occurs at and below hub height with periods up to 8 secs. Similar fluctuations are observed in the vertical component of the velocity field and in the direction of the horizontal wind. The depth of the shearing layer is critically related to hub height and rotor radius. The depth of the shearing layer appears to vary most significantly with thermal stratification; strong surface inversions producing shallow intense shearing layers; adiabatic conditions reflecting only topographically induced shear. For a given site and a given generator, hub height should be guided by the depth of the mean shear layer under adiabatic conditions plus the radius of the rotor.

Brown, J.D.

1980-06-18

345

Transient dynamics in dense colloidal suspensions under shear: shear rate dependence  

NASA Astrophysics Data System (ADS)

A combination of confocal microscopy and rheology experiments, Brownian dynamics (BD) and molecular dynamics (MD) simulations and mode coupling theory (MCT) have been applied in order to investigate the effect of shear rate on the transient dynamics and stress-strain relations in supercooled and glassy systems under shear. Immediately after shear is switched on, the microscopic dynamics display super-diffusion and the macroscopic rheology a stress overshoot, which become more pronounced with increasing shear rate. MCT relates both to negative sections of the generalized shear modulus, which grow with increasing shear rate. When the inverse shear rate becomes much smaller than the structural relaxation time of the quiescent system, relaxation through Brownian motion becomes less important. In this regime, larger stresses are accumulated before the system yields and the transition from localization to flow occurs earlier and more abruptly.

Laurati, M.; Mutch, K. J.; Koumakis, N.; Zausch, J.; Amann, C. P.; Schofield, A. B.; Petekidis, G.; Brady, J. F.; Horbach, J.; Fuchs, M.; Egelhaaf, S. U.

2012-11-01

346

Reversible shear thickening at low shear rates of electrorheological fluids under electric fields.  

PubMed

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

Tian, Yu; Zhang, Minliang; Jiang, Jile; Pesika, Noshir; Zeng, Hongbo; Israelachvili, Jacob; Meng, Yonggang; Wen, Shizhu

2011-01-05

347

Recent Advances in Velocity Shear Driven Processes  

NASA Astrophysics Data System (ADS)

Macroscopic flows are commonly encountered in a wide variety of plasmas and it is becoming increasingly apparent that the presence of shear in such flows can have a pronounced effect on the nonlinear evolution. For instance, in tokamak devices, sheared poloidal flows are thought to play a crucial role in the L--H transition. In laser-produced plasmas, strongly sheared plasma jets are believed to lead to the onset of intense lower-hybrid waves. In the natural plasma environment of the Earth's ionosphere and magnetosphere, observations indicate a correlation between inhomogeneous flows, plasma wave activity, and particle energization. Different physical processes in which shear-driven phenomenon may dominate span a wide range of spatiotemporal scales. Cross-scale coupling between them can play a vital role in determining the ultimate state of a plasma system which, for space plasmas, is an important factor responsible for the definition of ``space weather.'' Hence, the origin of sheared flows and the plasma response to them is a topic of considerable interest. Ongoing studies indicate that the influence of velocity shear can be generally classified into two broad categories, dissipative and reactive. In the dissipative category, low levels of shear can affect wave-particle interactions through resonance detuning which can substantially modify the normal modes and dispersive properties of a homogeneous plasma. A transverse velocity shear reduces the growth rates of the modes with frequencies lower than the ion-cyclotron frequency while it enhances those modes with frequencies around the ion-cyclotron frequency or larger. Sufficiently strong shear can induce a new class of oscillations via a reactive mechanism by creating neighboring regions with wave energy density of opposite sign. In general, depending on the magnitude and scale length, velocity shear can give rise to plasma oscillations in a very broad frequency and wavelength range. These properties and their applications to space and laboratory plasmas will be discussed.

Ganguli, G.

1996-11-01

348

49 CFR 230.27 - Maximum shearing strength of rivets.  

Code of Federal Regulations, 2012 CFR

...2012-10-01 false Maximum shearing strength of rivets. 230.27 Section 230...STANDARDS Boilers and Appurtenances Strength of Materials § 230.27 Maximum shearing strength of rivets. The maximum shearing...

2012-10-01

349

49 CFR 230.27 - Maximum shearing strength of rivets.  

Code of Federal Regulations, 2011 CFR

...2011-10-01 false Maximum shearing strength of rivets. 230.27 Section 230...STANDARDS Boilers and Appurtenances Strength of Materials § 230.27 Maximum shearing strength of rivets. The maximum shearing...

2011-10-01

350

49 CFR 230.28 - Higher shearing strength of rivets.  

Code of Federal Regulations, 2010 CFR

...2009-10-01 false Higher shearing strength of rivets. 230.28 Section 230...STANDARDS Boilers and Appurtenances Strength of Materials § 230.28 Higher shearing strength of rivets. A higher shearing...

2009-10-01

351

49 CFR 230.27 - Maximum shearing strength of rivets.  

Code of Federal Regulations, 2010 CFR

...2010-10-01 false Maximum shearing strength of rivets. 230.27 Section 230...STANDARDS Boilers and Appurtenances Strength of Materials § 230.27 Maximum shearing strength of rivets. The maximum shearing...

2010-10-01

352

49 CFR 230.27 - Maximum shearing strength of rivets.  

Code of Federal Regulations, 2010 CFR

...2009-10-01 false Maximum shearing strength of rivets. 230.27 Section 230...STANDARDS Boilers and Appurtenances Strength of Materials § 230.27 Maximum shearing strength of rivets. The maximum shearing...

2009-10-01

353

49 CFR 230.28 - Higher shearing strength of rivets.  

Code of Federal Regulations, 2010 CFR

...2010-10-01 false Higher shearing strength of rivets. 230.28 Section 230...STANDARDS Boilers and Appurtenances Strength of Materials § 230.28 Higher shearing strength of rivets. A higher shearing...

2010-10-01

354

Wind resources of Somalia  

Microsoft Academic Search

The results of wind energy research in Somalia are presented. The wind resource appears to be suitable for power production on 85% of the country, very intense on 10% and uniform on 70%, being regular throughout. Two areas of different wind regimes have been identified and characterized; the wind-distribution characteristics of 11 sites are presented and discussed, together with the

R. Pallabazzer; A. A. Gabow

1991-01-01

355

Global Wind Map  

ERIC Educational Resources Information Center

|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…

Journal of College Science Teaching, 2005

2005-01-01

356

Solar Wind Composition  

NASA Astrophysics Data System (ADS)

To first order the solar wind composition reflects the composition of the source material, which is photospheric (SOLAR ABUNDANCES). However, there are some important distinctions between the solar wind and solar abundances which will be discussed in the following paragraphs. Since solar wind particles feed the CORONA, and solar energetic particles (SEPs; see SOLAR WIND: ENERGETIC PARTICLES) larg...

Bochsler, P.; Murdin, P.

2000-11-01

357

Emergency wind erosion control  

Technology Transfer Automated Retrieval System (TEKTRAN)

February through May is the critical time for wind erosion in Kansas, but wind erosion can happen any time when high winds occur on smooth, wide fields with low vegetation and poor soil structure. The most effective wind erosion control is to ensure a protective cover of residue or growing crop thro...

358

Wind power for India  

Microsoft Academic Search

The technical and economic feasibility of wind power for rural conditions in India is assessed. Early and current wind power and windmill development are surveyed, and wind measurements on record are mentioned. The relative economics of wind power and power taken from the grid (for areas where such power is accessible) are compared for rural electrification, with base prices for

S. K. Tewari

1977-01-01

359

Wind power myths debunked  

Microsoft Academic Search

The natural variability of wind power makes it different from other generating technologies, which can give rise to questions about how wind power can be integrated into the grid successfully. This article aims to answer several important questions that can be raised with regard to wind power. Although wind is a variable resource, grid operators have experience with managing variability

Michael Milligan; Kevin Porter; Edgar DeMeo; Paul Denholm; Hannele Holttinen; Brendan Kirby; Nicholas Miller; Andrew Mills; Mark O'Malley; Matthew Schuerger; Lennart Soder

2009-01-01

360

Wind With Miller  

NSDL National Science Digital Library

Wind With Miller is a collection of classroom activities that provide good background information about wind energy. The site also provides students with opportunities to build small wind turbines, wind socks, and kites and has a section for teachers. There are a variety of exercises to use in the classroom provided on the site including topics such as small shaft, anemometer, and cooling systems.

2007-04-13

361

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.

362

Wind Energy Technology: Generating Power from the Wind  

Microsoft Academic Search

Wind Energy Technology (WET) announces on a bimonthly basis the current worldwide information available on wind turbine concepts and design, including the basic science of wind turbine dynamics as well as advanced components and systems research; wind turbine performance; ancillary wind turbine equipment, including system protection and interconnection devices; wind resource identification; wind turbine project planning and development; legal-institutional implications

B. C. Steele; G. Harman; J. Pitsenbarger

1996-01-01

363

Shear-segregation and mixing of sheared bidisperse granular materials  

NASA Astrophysics Data System (ADS)

We perform experiments on granular size-segregation in an annular Couette apparatus in which a layer of small particles mixes with, and then resegregates from, a layer of large particles beneath it. We model this process using a modification of the Gray-Thornton model in which we impose a nonlinear shear profile typical of boundary-driven, confined flows. The experimentally-measured exponential velocity profile provides an input to this one-dimensional nonlinear PDE and the resulting solution of the initial value problem is non-standard, involving curved characteristics. We further interpret these solutions by numerically connecting the segregation process to changes in packing fraction, and find qualitative agreement with experimental results. As in the experiment, mixing times are observed to be faster than segregation times. Interestingly, while the size-segregation of granular materials has generally been thought to proceed faster the greater the size difference of the particles we observe that the segregation rate is quite sensitive to both the particle-size ratio and the confining pressure on the system. As a result, we observe that particles of both dissimilar and similar sizes segregate more slowly than intermediate particle size ratios and interpret this anomalous behavior in terms of a species-dependent distribution of forces within the system.

Daniels, Karen; Golick, Laura; May, Lindsay; Shearer, Michael

2009-11-01

364

Onset of the summer monsoon during the FGGE 1979 experiment off the East African Coast: A comparison of wind data collected by different means  

SciTech Connect

During FGGE 1979, from March to July, an extensive oceanographic experiment with ships and moored stations was carried out in the Somali Current. The development of the monsoon winds off Somalia during the time of that experiment is described in a comparative analysis of standard ship wind observations, moored buoy wind measurements, low-level cloud winds, and winds from land stations. The onset 1979 is found to be of the multiple type, with northward winds off Somalia beginning around May 5 but dying down into early June; the real onset of sustained high winds starts around June 10. Cloud level wind observation numbers off Somalia decrease drastically with the monsoon onset because of lack of clouds over the quickly developing cold upwelling areas. An intercomparison of cloud level and ship winds for the period May 16 to July 6 at five offshore points shows good agreement in directions but reduction of ship wind speeds against cloud level winds off northern Somalia after the onset, which may explained by the increased vertical wind shear due to high air stability over the upwelled water and by geostrophic shear due to the strong gradients of sea surface temperature. A comparison of 3-day averages of buoy winds measured at 3-m height 30 km offshore, but still inland from the ship lane, with ship winds for the period March 3 to June 10 showed good agreement in directions but lower buoy wind speeds, which could partly be due to sensor height difference and partly due to horizontal wind shear towards the coast. Coastal stations and wind buoys near the coast are found not to be good indicators of the monsoon onset further out in the open ocean.

Schott, F.; Partagas, J.F.

1981-05-20

365

Quasi-3D Modeling of Shear Waves  

NASA Astrophysics Data System (ADS)

Shear waves were first addressed by Oltman-Shay et. al (1989). Since then, they have been studied intensively. Most of these studies are either based on linear stability analysis or direct simulation utilizing nonlinear shallow water equations. One reason that shear waves attract so much attention is that they are believed to be a plausible mechanism that could contribute to the mixing in the nearshore circulation modeling. On the other hand, Svendsen and Putrevu (1994) found that the 3D structure of currents will also introduce momentum mixing which is similar to the dispersion effect discovered by Taylor (1954), and which is at least one order larger than the turbulence mixing. In this work, we will utilize a quasi-3D nearshore circulation model SHORECIRC (Svendsen et. al, 2000) to simulate finite amplitude shear waves. Our purpose was to investigate how the 3D dispersion mixing and the lateral mixing provided by the shear waves affect each other. To achieve this, 2D and quasi-3D numerical experiments are carried out simultaneously. Our calculations showed that shear waves are more organized in the quasi-3D simulation than that in 2D simulation. We also found that under certain circumstances, the mixing provided by shear waves can be even stronger than that of the 3D dispersive mixing. As the shear waves grow, the 3D dispersive mixing decreases.

Zhao, Q.; Svendsen, I.

2001-12-01

366

Microstructural study of adiabatic shear band  

NASA Astrophysics Data System (ADS)

This article presents a study of the microstructural development of the adiabatic shear band in an HY-100 steel. The steel was deformed at a high strain rate by ballistic impact, and subsequent metallographic observations along with electron microscopy were performed. A number of white- etched shear bands were found near the perforated region, and three typical microstructural features of the adiabatic shear band were observed: elongated grain structure at the boundary between the shear band and matrix, fine equiaxed grain structure with high dislocation densities in the middle of the shear band, and relatively coarse-grained structure located between the above two structures. These microstructures might be formed in an extremely short time by the combined effects of the large temperature rise and the highly localized deformation. Since very complex phenomena might occur within the shear band, possible mechanisms, such as dynamic recovery and strain-induced dynamic phase transformation, are suggested to explain the micro- structural development of the adiabatic shear band.

Lee, Sunghak; Cho, Kyung-Mox; Lee, Chang Sun; Choo, Wung Yong

1993-10-01

367

Wind Power Outlook 2004  

SciTech Connect

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.

anon.

2004-01-01

368

VAWT stochastic wind simulator  

Microsoft Academic Search

A stochastic wind simulation for VAWTs (VSTOC) has been developed which yields turbulent wind-velocity fluctuations for rotationally sampled points. This allows three-component wind-velocity fluctuations to be simulated at specified nodal points on the wind-turbine rotor. A first-order convection scheme is used which accounts for the decrease in streamwise velocity as the flow passes through the wind-turbine rotor. The VSTOC simulation

Strickland

1987-01-01

369

Effects of winds on stratification and circulation in a partially mixed estuary  

NASA Astrophysics Data System (ADS)

Numerical experiments are conducted to investigate how axial winds affect stratification and circulation in the partially mixed estuary of Chesapeake Bay. In the absence of rotational effects, stratification in the estuary decreases following both down-estuary and up-estuary winds, but stratification experiences larger reduction and takes longer to recover under up-estuary winds. In the presence of rotational effects, wind-driven lateral circulations cause the lateral straining of density field and weaken the shear in the along-channel flows. Under the down-estuary winds, a counterclockwise lateral circulation steepens isopycnals in the cross-channel sections, while the Coriolis force acting on it decelerates the downwind current in the surface layer and the upwind-directed current in the bottom layer. Under the up-estuary winds, a clockwise lateral circulation flattens isopycnals in the cross-channel sections and reduces the shear between the surface and bottom currents. Hence, in the presence of rotational effects, the lateral straining offsets the effects of longitudinal straining such that the asymmetry in stratification reduction is significantly reduced between the down-estuary and up-estuary winds. Regime diagrams based on Wedderburn (W) and Kelvin (Ke) numbers are constructed to summarize the net effects of winds on estuarine stratification during both wind perturbation and postwind adjustment periods.

Li, Yun; Li, Ming

2011-12-01

370

An Icelandic wind atlas  

NASA Astrophysics Data System (ADS)

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.

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

2013-04-01

371

Response of the Weddell Sea pack ice to wind forcing  

NASA Astrophysics Data System (ADS)

Sea ice drift in the Weddell Sea was studied on the basis of data from seven buoys deployed on ice floes in January-February 1996. Six of the buoys formed an array with initial mutual distances of 50 km, which by October 1996 were stretched to ˜400 km in an east-west direction. The differential kinematical parameters i.e., divergence, shearing rate, and vorticity, were estimated from the buoy array positions by applying a time-dependent method. The large-scale drift of the array was divergent until August 1996, but after the array came under the influence of the Antarctic Circumpolar Current the deformation was mainly shearing. Meteorological data from European Centre for Medium-Range Weather Forecasts analyses and Special Sensor Microwave Imager derived ice concentrations were interpolated at the buoy sites. The drift velocity was highly wind-dependent; it was also wind-dependent in winter when the momentum balance was mainly between the internal ice stress and the air drag. The drift divergence and shearing rate were related to the wind forcing, while the array vorticity correlated better with the air pressure itself. We estimated the air-ice drag coefficient to be 1.8×10-3 at a height of 10 m over the ice and the geostrophic drag coefficient to be 6.1 × 10-4. The stability effects on the coefficients were mostly felt in conditions of light winds. The average ice-water drag coefficient based on 5 day periods was 2.1×10-3. The ice transport through a transect crossing the Weddell Sea was computed on the basis of the geostrophic winds, observed wind-drift dependence, SSM/I-derived ice concentrations, and the literature on ice draft statistics. The resulting annual mean net export in 1996 was 1600 km3 yr-1.

Uotila, J.; Vihma, T.; Launiainen, J.

2000-01-01

372

Method for shearing spent nuclear fuel assemblies  

DOEpatents

A method is disclosed for shearing spent nuclear fuel assemblies of the type wherein a plurality of long metal tubes packed with ceramic fuel are supported in a spaced apart relationship within an outer metal shell or shroud which provides structural support to the assembly. Spent nuclear fuel assemblies are first compacted in a stepwise manner between specially designed gag-compactors and then sheared into short segments amenable to chemical processing by shear blades contoured to mate with the compacted surface of the fuel assembly.

Weil, Bradley S. (Oak Ridge, TN); Watson, Clyde D. (Knoxville, TN)

1977-01-01

373

Shear instability in magnetized, collisional dusty plasmas  

SciTech Connect

The shear instability of magnetized, collisional dusty plasma is investigated in the present work. It is demonstrated that the relative drift between the charged dust and magnetised electrons and ions which give rise to the Hall effect is crucial to this instability. Although the nature of present shear instability is similar to the Kelvin-Helmholtz instability, the role of magnetic field in the present case is important in destabilising waves. The maximum growth rate of the instability is proportional only to the shear gradient and is independent of the ambient magnetic field strength. Most unstable wavenumber is a function of ambient dust parameters.

Pandey, B. P. [Department of Physics and Astronomy, Macquarie University, Sydney, New South Wales 2109 (Australia); Vladimirov, S. V.; Samarian, A. A. [School of Physics, University of Sydney, New South Wales 2006 (Australia)

2012-06-15

374

Axisymmetric shear flow over spheres and spheroids  

NASA Astrophysics Data System (ADS)

Analytical solutions for an inviscid, incompressible, axisymmetric shear flow over a sphere are established. It is determined that if the shear is sufficiently large with respect to the axis velocity, then a recirculating stagnation region is formed. Solutions for prolate and oblate spheroids exhibit the same flow field characteristics as for the sphere. Stagnation bubble formation is delayed on the prolate spheroids and promoted on the oblate spheroids. These results are related to those for the two-dimensional shear flow over cylinders analyzed by Tsien (1943) and Fraenkel (1961).

Rubel, A.

1985-07-01

375

Stress pulse attenuation in shear thickening fluid  

NASA Astrophysics Data System (ADS)

The stress pulse attenuation of the 62 vol/vol. % dense silica particle-ethylene glycol suspension was investigated by using a modified spilt Hopkinson pressure bar. In comparison to the neat ethylene glycol solution, the transmission pulse of the shear thickening is much weaker under the same impact condition. No energy loss is progressed for the neat ethylene glycol solution, thus it can be concluded that the energy dissipation behavior was happened in the silica particle based shear thickening fluid. In this work, the energy dissipation of the shear thickening fluid was reversible.

Jiang, Weifeng; Gong, Xinglong; Xuan, Shouhu; Jiang, Wanquan; Ye, Fang; Li, Xiaofeng; Liu, Taixiang

2013-03-01

376

Modeling of shear localization in materials  

SciTech Connect

The deformation response of a Ti alloy, Ti-6Al-4V, has been studied during shear localization. The study has involved well-controlled laboratory tests involving a double-notch shear sample. The results have been used to provide a comparison between experiment and the predicted response using DYNA2D and two material models (the Johnson-Cook model and an isotropic elastic-plastic-hydrodynamic model). The work will serve as the basis for the development of a new material model which represents the different deformation mechanisms active during shear localization.

Lesuer, D.; LeBlanc, M.; Riddle, B.; Jorgensen, B.

1998-02-11

377

Shear free solutions in general relativity theory  

NASA Astrophysics Data System (ADS)

The Goldberg-Sachs theorem is an exact result on shear-free null geodesics in a vacuum spacetime. It is compared and contrasted with an exact result for pressure-free matter: shear-free flows cannot both expand and rotate. In both cases, the shear-free condition restricts the way distant matter can influence the local gravitational field. This leads to intriguing discontinuities in the relation of the General Relativity solutions to Newtonian solutions in the timelike case, and of the full theory to the linearised theory in the null case.

Ellis, George F. R.

2011-12-01

378

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

...LLC, Alta Wind IX, LLC, Alta Wind X, LLC, Alta Wind XI, LLC, Alta Wind...LLC, Alta Wind IX, LLC, Alta Wind X, LLC, Alta Wind XI, LLC, Alta Wind...projects to the integrated transmission grid and (2) waive Order Numbers 888, 889,...

2012-05-18

379

The Surface Drag and the Vertical Momentum Fluxes Produced by Mountain Waves in Flows with Directional Shear  

NASA Astrophysics Data System (ADS)

In gravity wave drag (GWD) parametrization schemes that are necessary in numerical models of the atmosphere, both the surface GWD and the distribution of the wave momentum flux with height must be specified. The present study addresses these two aspects. Firstly, the impact of a recently-developed approach to the evaluation of surface GWD is assessed. This approach uses linear theory, but incorporates the effects of wind profile shear and curvature, by means of a second-order WKB approximation. While the theory predicts the possibility of either drag enhancement or reduction, depending on the wind profile, results obtained with the ERA-40 reanalysis data clearly indicate the predominance of local drag enhancement. However, the global impact of shear on the atmospheric axial GWD torque comes mostly from regions with predominantly easterly flow, contributing to a slight reduction of the bias found in different studies of the global angular momentum budget. The relative correction due to shear on linear GWD is found not to depend too strongly on the levels chosen for the computation of the low-level wind derivatives. Secondly, the wave momentum flux is investigated within the framework of linear theory for flow with directional wind shear over a circular mountain. The variation of the momentum flux with height is calculated for relatively large shears, extending previous calculations of the surface GWD by the authors. A WKB approximation is used to address flow with generic, but relatively slowly-varying wind profiles. The WKB approximation must be extended to third order to obtain momentum flux expressions that are accurate to second order. Inviscid, steady, non-rotating, hydrostatic flow is assumed. Since the momentum flux only varies vertically due to wave filtering by critical levels, the application of contour integration techniques enables it to be expressed in terms of simple 1D integrals. On the other hand, the momentum flux divergence (which corresponds to the force on the atmosphere that must be represented in GWD parameterizations) is given in closed analytical form. The momentum flux expressions are tested for idealized wind profiles, where they become a function of the Richardson number (Ri). These expressions tend, for high Ri, to those derived by previous authors (where wind profile effects on the surface drag were neglected and critical levels acted as perfect absorbers). The linear results are compared with linear and nonlinear numerical simulations, showing a considerable improvement upon previous models, developed for very high Ri.

Teixeira, M.; Miranda, P. M.; Martins, J. P.

2010-12-01

380

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

...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...

2010-05-03

381

Butterfly patterns in a sheared lamellar system  

NASA Astrophysics Data System (ADS)

We studied the influence of shear on a lyotropic lamellar phase using the ILL Couette type shear cell on the SANS spectrometer D11 at the ILL, Grenoble. Because of the broad range of momentum transfers available on this instrument a characteristic butterfly pattern with a scattering peak along the neutral direction revealing both the structure and the supramolecular structure of the system could be detected at very high shear rates and very low Q. After cessation of flow the butterfly pattern disappeared immediately and the diffraction pattern showed a ring with an intensity maximum still perpendicular to the direction of flow. We present a model in real space describing this new structure of a lamellar phase at high shear rates.

Zipfel, J.; Richtering, W.; Lindner, P.

1998-04-01

382

Influence of magnetic shear on impurity transport  

SciTech Connect

The magnetic shear dependence of impurity transport in tokamaks is studied using a quasilinear fluid model for ion temperature gradient (ITG) and trapped electron (TE) mode driven turbulence in the collisionless limit and the results are compared with nonlinear gyrokinetic results using GYRO [J. Candy and R. E. Waltz, J. Comput. Phys 186, 545 (2003)]. It is shown that the impurity transport is sensitive to the magnetic shear, in particular for weak, negative, and large positive shear where a strong reduction of the effective impurity diffusivity is obtained. The fluid and gyrokinetic results are in qualitative agreement, with the gyrokinetic diffusivities typically a factor 2 larger than the fluid diffusivities. The steady state impurity profiles in source-free plasmas are found to be considerably less peaked than the electron density profiles for moderate shear. Comparisons between anomalous and neoclassical transport predictions are performed for ITER-like profiles [R. Aymar, P. Barabaschi, and Y. Shimomura, Plasma Phys. Controlled Fusion 44, 519 (2002)].

Nordman, H.; Fueloep, T.; Candy, J.; Strand, P.; Weiland, J. [Department of Radio and Space Science, Chalmers University of Technology and Euratom-VR Association, Goeteborg (Sweden); General Atomics, P.O. Box 85608, San Diego, California 92186-5608 (United States); Department of Radio and Space Science, Chalmers University of Technology and Euratom-VR Association, Goeteborg (Sweden)

2007-05-15

383

Steady Incompressible Variable Thickness Shear Layer Aerodynamics.  

National Technical Information Service (NTIS)

A shear flow aerodynamic theory for steady incompressible flows is presented for both the lifting and non lifting problems. The slow variation of the boundary layer thickness is considered. The slowly varying behavior is treated by using multitime scales....

M. R. Chi

1976-01-01

384

Advanced Body Armor Utilizing Shear Thickening Fluids.  

National Technical Information Service (NTIS)

An armor composite material has been invented which contains a ballistic fabric which has been impregnated with shear thickening fluid. This invention offers a ballistic resistant material that is more flexible and less bulky than comparable, conventional...

E. D. Wetzel N. J. Wagner

2003-01-01

385

Shear Instability Mechanisms in High Hardness Steel.  

National Technical Information Service (NTIS)

The causes of shear instability in high strength martensitic steels were studied using both dynamic and quasistatic loading conditions. Detailed strain measurements were made from thin wall torsion tests. An unexpected result of these tests is that the cr...

M. Azrin J. G. Cowie G. B. Olson

1986-01-01

386

Aeroacoustics of Subsonic Turbulent Shear Flows.  

National Technical Information Service (NTIS)

Sound generation in turbulent shear flows is examined. The emphasis is on simultaneous calculation of the turbulent flow along with the resulting sound generation rather than the alternative acoustic analogy approach. The first part of the paper is concer...

M. E. Goldstein

1987-01-01

387

Seismic Shears and Overturning Moments in Buildings.  

National Technical Information Service (NTIS)

Seismic force distributions for simplified computation of shears and over-turning moment for preliminary design of buildings have been generated. A parameter study of the significant variables has been made to determine the applicability of the proposed d...

N. M. Newmark R. Smilowitz

1977-01-01

388

Shear wall experiments and design in Japan.  

National Technical Information Service (NTIS)

This paper summarizes the results of recent survey studies on the available experimental data bases and design codes/standards for reinforced concrete (RC) shear wall structures in Japan. Information related to the seismic design of RC reactor buildings a...

Y. J. Park C. Hofmayer

1994-01-01

389

Planar shear moduli of rigidity of an oriented strand board from bending and shear tests  

Microsoft Academic Search

The planar shear modulus of rigidity has been recently utilised in the structural grading of oriented strand board (OSB).\\u000a However, data on the planar shear moduli of rigidity of oriented strand board are sparse. This has been attributed to the\\u000a nature of existing tests for determination of planar shear properties, which are deemed to be complex and expensive. The planar

W. H. Thomas

2004-01-01

390

Impact behavior of shear-failure-type RC beams without shear rebar  

Microsoft Academic Search

In this study, to establish a rational impact-resistant design procedure of shear-failure-type reinforced concrete (RC) beams, falling-weight impact tests were conducted. Twenty-seven simply supported rectangular RC beams without shear rebar were used. All RC beams were of 150mm width and 250mm depth in cross section, with rebar and shear-span ratios taken as variables. An impact load was applied at the

N. Kishi; H. Mikami; K. G. Matsuoka; T. Ando

2002-01-01

391

Shear resistance of masonry walls and Eurocode 6: shear versus tensile strength of masonry  

Microsoft Academic Search

In the case of masonry structures subjected to seismic loads, shear failure mechanism of walls, characterised by the formation\\u000a of diagonal cracks, by far predominates the sliding shear failure mechanism. However, as assumed by Eurocode 6, the latter\\u000a represents the critical mechanism for the assessment of the shear resistance of structural walls. The results of a series\\u000a of laboratory tests

Miha Tomaževi?

2009-01-01

392

Shear Strength Behavior of Human Trabecular Bone  

PubMed Central

The shear strength of human trabecular bone may influence overall bone strength under fall loading conditions and failure at bone-implant interfaces. Here, we sought to compare shear and compressive yield strengths of human trabecular bone and elucidate the underlying failure mechanisms. We analyzed 54 specimens (5-mm cubes), all aligned with the main trabecular orientation and spanning four anatomic sites, 44 different cadavers, and a wide range of bone volume fraction (0.06–0.38). Micro-CT-based non-linear finite element analysis was used to assess the compressive and shear strengths and the spatial distribution of yielded tissue; the tissue-level constitutive model allowed for kinematic non-linearity and yielding with strength asymmetry. We found that the computed values of both the shear and compressive strengths depended on bone volume fraction via power law relations having an exponent of 1.7 (R2=0.95 shear; R2=0.97 compression). The ratio of shear to compressive strengths (mean ± SD, 0.44 ± 0.16) did not depend on bone volume fraction (p=0.24) but did depend on microarchitecture, most notably the intra-trabecular standard deviation in trabecular spacing (R2=0.23, p<0.005). For shear, the main tissue-level failure mode was tensile yield of the obliquely oriented trabeculae. By contrast, for compression, specimens having low bone volume fraction failed primarily by large-deformation-related tensile yield of horizontal trabeculae and those having high bone volume failed primarily by compressive yield of vertical trabeculae. We conclude that human trabecular bone is generally much weaker in shear than compression at the apparent level, reflecting different failure mechanisms at the tissue level.

Sanyal, Arnav; Gupta, Atul; Bayraktar, Harun H.; Kwon, Ronald Y.; Keaveny, Tony M.

2012-01-01

393

Microstructural study of adiabatic shear band  

Microsoft Academic Search

This article presents a study of the microstructural development of the adiabatic shear band in an HY-100 steel. The steel\\u000a was deformed at a high strain rate by ballistic impact, and subsequent metallographic observations along with electron microscopy\\u000a were performed. A number of white- etched shear bands were found near the perforated region, and three typical microstructural\\u000a features of the

Sunghak Lee; Kyung-Mox Cho; Chang Sun Lee; Wung Yong Choo

1993-01-01

394

Cracks Faster than the Shear Wave Speed  

Microsoft Academic Search

Classical dynamic fracture theories predict the surface wave speed to be the limiting speed for propagation of in-plane cracks in homogeneous, linear elastic materials subjected to remote loading. This report presents experimental ev- idence to the contrary. Intersonic shear-dominated crack growth featuring shear shock waves was observed along weak planes in a brittle polyester resin under far-field asymmetric loading. When

A. J. Rosakis; O. Samudrala; D. Coker

1999-01-01

395

Measurement of shear impedances of viscoelastic fluids  

SciTech Connect

Shear-wave reflection coefficients from a solid/fluid interface are derived for non-Newtonian fluids that can be described by Maxwell, Voigt, and power-law fluid models. Based on model calculations, we have identified the measurable effects on the reflection coefficients due to fluid non-Newtonian behavior. The models are used to interpret the viscosity data obtained by a technique based on shear impedance measurement.

Sheen, Shuh-Haw; Chien, Hual-Te; Raptis, A.C.

1996-12-31

396

Study on magnetorheological shear thickening fluid  

Microsoft Academic Search

In this paper, a magnetic-field-controlled and speed-activated magnetorheological shear thickening fluid (MRSTF) is presented. We fabricated a kind of shear thickening fluid (STF) which was composed of nanosize silica particles suspended in a solvent, ethylene glycol, at high concentrations. Then the micron-size carbonyl iron particles with different volume fractions were added to the STF to fabricate the MRSTF. Their dynamic

Xianzhou Zhang; Weihua Li; X. L. Gong

2008-01-01

397

Modeling of shear localization in materials  

Microsoft Academic Search

The deformation response of a Ti alloy, Ti-6Al-4V, has been studied during shear localization. The study has involved well-controlled laboratory tests involving a double-notch shear sample. The results have been used to provide a comparison between experiment and the predicted response using DYNA2D and two material models (the Johnson-Cook model and an isotropic elastic-plastic-hydrodynamic model). The work will serve as

D. Lesuer; M. LeBlanc; B. Riddle; B. Jorgensen

1998-01-01

398

Reduction in intermittent transport by shearing  

NASA Astrophysics Data System (ADS)

The intermittent transport due to coherent structures (streamers) is shown to be dramatically reduced by the shearing of mean flow in passive scalar field model, with the scaling ~?-3. Here, ? is the shearing rate of the mean flow. This reduction is much stronger than that in turbulent transport (~?-1) [Kim and Diamond, Phys. Rev. Lett. 91, 075001 (2003)] in the same model. Implications for the transition from low to high confinement (L-H transition) are discussed.

Kim, Eun-Jin

2005-04-01

399

Tropical cyclone energy dispersion under vertical shears  

Microsoft Academic Search

Tropical cyclone Rossby wave energy dispersion under easterly and westerly vertical shears is investigated in a baroclinic model. In a resting environment, the model simulates a Rossby wave train that has a baroclinic structure with alternating cyclonic-anticyclonic-cyclonic (anticyclonic-cyclonic-anticyclonic) circulations in the lower (upper) troposphere. A significant asymmetry appears in the wave train development under easterly and westerly vertical shears, that

Xuyang Ge; Tim Li; Xiaqiong Zhou

2007-01-01

400

Avalanches in anisotropic sheared granular media  

Microsoft Academic Search

We study the influence of particle shape anisotropy on the occurrence of avalanches in sheared granular media. We use molecular\\u000a dynamic simulations to calculate the relative movement of two tectonic plates. Our model considers irregular polygonal particles\\u000a constituting the material within the shear zone. We find that the magnitude of the avalanches is approximately independent\\u000a of particle shape and in

Andrés A. Peña; Sean McNamara; Pedro G. Lind; Hans J. Herrmann

2009-01-01

401

Shear strength of reinforced aerated concrete slabs  

Microsoft Academic Search

The paper reports on the analysis of shear strength of reinforced slabs made of autoclaved aerated concrete without shear\\u000a reinforcement. The test data are taken from eleven different investigations from six countries, in Europe and Japan, over\\u000a a period of some twenty years and include 271 tests. The analysis of the test data results in regression expressions, suitably\\u000a modified from

Samuel Aroni; Boris Cividini

1989-01-01

402

A Refined Shear Deformation Plate Theory  

Microsoft Academic Search

An improved higher-order shear deformation theory of plates is presented in this paper. The theory is developed from the transverse shear deformation theory presented by Ambartsumian [11]. The present plate theory contains kinematics of higher-order displacement field of plates, a system of higher-order differential equilibrium equations in terms of the three generalized displacements of bending plates, and a system of

Yucheng Liu

2011-01-01

403

Analysis of In-Flight Winds for Shuttle Mission STS 51-L.  

NASA Astrophysics Data System (ADS)

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.

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

404

A TURBULENCE-DRIVEN MODEL FOR HEATING AND ACCELERATION OF THE FAST WIND IN CORONAL HOLES  

SciTech Connect

A model is presented for generation of fast solar wind in coronal holes, relying on heating that is dominated by turbulent dissipation of MHD fluctuations transported upward in the solar atmosphere. Scale-separated transport equations include large-scale fields, transverse Alfvenic fluctuations, and a small compressive dissipation due to parallel shears near the transition region. The model accounts for proton temperature, density, wind speed, and fluctuation amplitude as observed in remote sensing and in situ satellite data.

Verdini, A. [Observatoire Royale de Belgique, 3 Avenue Circulaire, 1180, Bruxelles (Belgium); Velli, M. [Dipart. di Astronomia e Scienza dello Spazio, Univ. di Firenze, Largo E. Fermi 3, 50125, Firenze (Italy); Matthaeus, W. H. [Department of Physics and Astronomy, University of Delaware, DE 19716 (United States); Oughton, S. [Department of Mathematics, University of Waikato, Hamilton (New Zealand); Dmitruk, P. [Depart. Fisica, Facultad de Ciencias Exactas y Naturales, Univ. de Buenos Aires-Conicet (Argentina)], E-mail: verdini@oma.be

2010-01-10

405

Magnetized stratified rotating shear waves  

NASA Astrophysics Data System (ADS)

We present a spectral linear analysis in terms of advected Fourier modes to describe the behavior of a fluid submitted to four constraints: shear (with rate S), rotation (with angular velocity ?), stratification, and magnetic field within the linear spectral theory or the shearing box model in astrophysics. As a consequence of the fact that the base flow must be a solution of the Euler-Boussinesq equations, only radial and/or vertical density gradients can be taken into account. Ertel's theorem no longer is valid to show the conservation of potential vorticity, in the presence of the Lorentz force, but a similar theorem can be applied to a potential magnetic induction: The scalar product of the density gradient by the magnetic field is a Lagrangian invariant for an inviscid and nondiffusive fluid. The linear system with a minimal number of solenoidal components, two for both velocity and magnetic disturbance fields, is eventually expressed as a four-component inhomogeneous linear differential system in which the buoyancy scalar is a combination of solenoidal components (variables) and the (constant) potential magnetic induction. We study the stability of such a system for both an infinite streamwise wavelength (k1=0, axisymmetric disturbances) and a finite one (k1?0, nonaxisymmetric disturbances). In the former case (k1=0), we recover and extend previous results characterizing the magnetorotational instability (MRI) for combined effects of radial and vertical magnetic fields and combined effects of radial and vertical density gradients. We derive an expression for the MRI growth rate in terms of the stratification strength, which indicates that purely radial stratification can inhibit the MRI instability, while purely vertical stratification cannot completely suppress the MRI instability. In the case of nonaxisymmetric disturbances (k1?0), we only consider the effect of vertical stratification, and we use Levinson's theorem to demonstrate the stability of the solution at infinite vertical wavelength (k3=0): There is an oscillatory behavior for ?>1+|K2/k1|, where ?=St is a dimensionless time and K2 is the radial component of the wave vector at ?=0. The model is suitable to describe instabilities leading to turbulence by the bypass mechanism that can be relevant for the analysis of magnetized stratified Keplerian disks with a purely azimuthal field. For initial isotropic conditions, the time evolution of the spectral density of total energy (kinetic + magnetic + potential) is considered. At k3=0, the vertical motion is purely oscillatory, and the sum of the vertical (kinetic + magnetic) energy plus the potential energy does not evolve with time and remains equal to its initial value. The horizontal motion can induce a rapid transient growth provided K2/k1?1. This rapid growth is due to the aperiodic velocity vortex mode that behaves like Kh/kh where kh(?)=[k12+(K2-k1?)2]1/2 and Kh=kh(0). After the leading phase (?>K2/k1?1), the horizontal magnetic energy and the horizontal kinetic energy exhibit a similar (oscillatory) behavior yielding a high level of total energy. The contribution to energies coming from the modes k1=0 and k3=0 is addressed by investigating the one-dimensional spectra for an initial Gaussian dense spectrum. For a magnetized Keplerian disk with a purely vertical field, it is found that an important contribution to magnetic and kinetic energies comes from the region near k1=0. The limit at k1=0 of the streamwise one-dimensional spectra of energies, or equivalently, the streamwise two-dimensional (2D) energy, is then computed. The comparison of the ratios of these 2D quantities with their three-dimensional counterparts provided by previous direct numerical simulations shows a quantitative agreement.

Salhi, A.; Lehner, T.; Godeferd, F.; Cambon, C.

2012-02-01

406

Wind energy information guide  

SciTech Connect

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.

NONE

1996-04-01

407

Wind ripple analysis  

NASA Astrophysics Data System (ADS)

Efficient and economical utilization of wind power will require the ability to measure and ultimately predict the effects fluctuations in the incident wind will have on a wind turbine. In order to quantitatively assesss these effects, experimental techniques have been developed which allow analysis of full-scale performance of wind turbines with particular emphasis on the effects caused by turbulence in the incident wind. Examples of these techniques are presented using data from the DOE/Sandia Vertical Axis Wind Turbine (VAWT) program.

Akins, R. E.

1981-12-01

408

Wind power today  

SciTech Connect

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.

NONE

1998-04-01

409

Wind ripple analysis  

SciTech Connect

Efficient and economical utilization of wind power will require the ability to measure and ultimately predict the effects fluctuations in the incident wind will have on a wind turbine. In order to quantitatively assesss these effects, experimental techniques have been developed which allow analysis of full-scale performance of wind turbines with particular emphasis on the effects caused by turbulence in the incident wind. Examples of these techniques are presented using data from the DOE/Sandia Vertical Axis Wind Turbine (VAWT) program.

Akins, R.E.

1981-01-01

410

Wind ripple analysis  

SciTech Connect

Efficient and economical utilization of wind power will require the ability to measure and ultimately predict the effects fluctuations in the incident wind will have on a wind turbine. In order to quantitatively assess these effects, experimental techniques have been developed which allow analysis of full-scale performance of wind turbines with particular emphasis on the effects caused by turbulence in the incident wind. Examples of these techniques are presented using data from the DOE/Sandia Vertical Axis Wind Turbine (VAWT) program.

Akins, R.E.

1981-01-01

411

Effects of Critical Levels on Two-Dimensional Back-Sheared Flow over an Isolated Mountain Ridge on an f Plane  

Microsoft Academic Search

It is well known that there exist three singular points, U c = ±f\\/k and U = c, where the corresponding levels will be called inertia critical levels (ICLs) and the classic critical level (CCL), in the equation governing a two-dimensional, rotating, continuously stratified, hydrostatic, back-sheared Boussinesq flow. Here U and c are basic wind and phase speed, respectively; f

Bo-Wen Shen; Yuh-Lang Lin

1999-01-01

412

Representing Sheared Convective Boundary Layer by Zeroth and First-Order-Jump Mixed-Layer Models: Large-Eddy Simulation Verification  

Microsoft Academic Search

Dry convective boundary layers characterized by a significant wind shear on the surface and at the inversion are studied by means of the mixed-layer theory. Two different representations of the entrainment zone, each of which has a different closure of the entrainment heat flux, are considered. The simpler of the two is based on a sharp discontinuity at the inversion

David Pino; Jordi Vilà-Guerau de Arellano; Si-Wan Kim

2006-01-01

413

Shear induced structures in crystallizing cocoa butter  

NASA Astrophysics Data System (ADS)

Cocoa butter is the main structural component of chocolate and many cosmetics. It crystallizes in several polymorphs, called phases I to VI. We used Synchrotron X-ray diffraction to study the effect of shear on its crystallization. A previously unreported phase (phase X) was found and a crystallization path through phase IV under shear was observed. Samples were crystallized under shear from the melt in temperature controlled Couette cells, at final crystallization temperatures of 17.5^oC, 20^oC and 22.5^oC in Beamline X10A of NSLS. The formation of phase X was observed at low shear rates (90 s-1) and low crystallization temperature (17.5^oC), but was absent at high shear (720 s-1) and high temperature (20^oC). The d-spacing and melting point suggest that this new phase is a mixture rich on two of the three major components of cocoa butter. We also found that, contrary to previous reports, the transition from phase II to phase V can happen through the intermediate phase IV, at high shear rates and temperature.

Mazzanti, Gianfranco; Guthrie, Sarah E.; Sirota, Eric B.; Marangoni, Alejandro G.; Idziak, Stefan H. J.

2004-03-01

414

Shear modulus of kaolin containing methane bubbles  

SciTech Connect

Measurements of undrained shear moduli are reported from a program of laboratory tests on reconstituted kaolin samples containing relatively large bubbles of methane gas. The experimental program included low-frequency torsional stress-strain loops and torsional resonant column tests, providing values of shear moduli for shear-strain similitudes from 0.0004% to 0.1%. At all values of strain amplitude, the reduction of shear moduli caused by the presence of gas bubbles was greater than predicted by a theoretical elastic expression. This pattern of behavior was attributed to te formation of local yield zones around the gas-bubble cavities during consolidation prior to shear testing (a phenomenon that would also occur in-situ within offshore sediments). The results of the research program suggest that reductions in shear moduli of up to 50% could be caused by relatively small volumes of gas bubbles, occupying just a few percent of the total soil volume. This would have considerable significance for the displacements of offshore foundations constructed on sediments containing undissolved gas.

Duffy, S.M. (Northern Ireland Road Service, Belfast (United Kingdom)); Wheeler, S.J. (Univ. of Oxford (United Kingdom). Dept. of Engineering Science); Bennell, J.D. (University Coll. of North Wales, Menai Bridge (United Kingdom))

1994-05-01

415

Shear Driven Aggregation in Latex Colloids  

NASA Astrophysics Data System (ADS)

Reynolds number is small in colloidal flow and therefore, colloidal volume fraction and Peclet number are important. AS the volume fraction and attractive coupling between particles increase, relaxation time and Weisenberg number become significant. Shear-induced aggregation of latex colloids is due to the interplay between the shear-induced formation and breakage of latex .particles. While particle size is limited by breakage, their number density increases with the shearing-time. Upon cessation of shear, the particles interconnect into an assembly held by grainy bonds. It results in increase in yield stress and dynamic modulus. A contact model enables aggregates maintaining their structures under low stress while being restructured under high stress. Modeling involves solution of Navier- Stokes equation with moving particles as boundary condition for the flow like using the Lattice Boltzmann approach or by using (accelerated) Stokesian Dynamics. Alternate approach is to model the fluid phase by soft repulsive particles with pair-wise noise and friction, known as dissipative particle dynamics (DPD). This method by construction produces full inertial hydrodynamics, but applying the correct fluid-particle boundary condition is non-trivial. Both particle to particle and particle to wall collisions can be considered using Johnson-Kendall- Roberts (JKR) analysis of collision dynamics of dissipative forces using a soft-sphere modeling technique. Our experimental work used emulsion polymerized latex that was subjected to steady and dynamic shear. Yield stress, dynamic modulus and relaxation time increased on shearing in conjunction with changes in aggregate size.

Ahuja, Suresh

2013-03-01

416

2008 Wind Energy Projects, Wind Powering America (Poster)  

SciTech Connect

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.

Not Available

2009-01-01

417

The Kelvin-Helmholtz vortex in the asymmetric velocity shear layer: PIC simulations  

NASA Astrophysics Data System (ADS)

We have performed full particle (PIC) simulations of the vortex-induced reconnection using asymmetric conditions across the velocity shear layer. The Kelvin-Helmholtz vortex (KHV) has been believed to cause direct entry of the solar-wind plasma into the magnetosphere across the low-latitude magnetopause (i.e., plasma mixing between solar-wind and magnetospheric plasmas) under northward IMF conditions. Recently, our particle simulations with symmetric conditions across the velocity shear layer have revealed that the MHD-scale KHVs generally cause efficient plasma mixing via magnetic reconnection and associated multiple magnetic island formation within the vortex. Indeed, recent Cluster and THEMIS observations are revealing that magnetic islands actually formed between the MHD-scale KHVs. In this study, we further performed particle simulations of the MHD-scale KHVs with density and temperature asymmetries across the boundary, which always exist at the actual magnetopause. Using the simulation results, we succeeded in estimating actual sizes of islands caused within the asymmetric magnetopause and actual mixing rate within the KHVs. In this presentation, we will discuss how important the KHVs are in the solar-wind entry into the magnetosphere.

Nakamura, T.; Hasegawa, H.; Eriksson, S.; Fujimoto, M.; Shinohara, I.

2011-12-01

418

Shear-induced conversion of seismic waves across single fractures  

Microsoft Academic Search

Elastic wave conversions across a fracture in rock subjected to shear stress are observed during laboratory ultrasonic transmission tests. Compressional waves (P-waves) and shear waves (S-waves) normally incident on a sheared fracture are partially converted to waves with particle motions that are not present in the incident waves. The amplitudes of the converted waves increase significantly with increasing shear stress

Seiji Nakagawa; K. T. Nihei; L. R. Myer

2000-01-01

419

User's guide for a personal computer model of turbulence at a wind turbine rotor  

SciTech Connect

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.

Connell, J.R.; Powell, D.C.; Gower, G.L.

1989-08-01

420

Aging of a colloidal glass under a periodic shear.  

PubMed

The aging dynamics under a periodic shear of a concentrated suspension of saponite particles is measured. It is observed that the dynamics is fastened by the application of a moderate shear amplitude. Nevertheless, this acceleration does not affect the dynamics of the suspension when the shear is ceased. By applying a succession of shear of various amplitudes, we conclude that the dynamics of the suspension at a time t(w) after complete rejuvenation is independent of the shear history between times 0 and t(w) , as soon as the amplitude of the applied shear is smaller than the characteristic shear gamma(c) necessary to completely rejuvenate the suspension. PMID:16089955

Kaloun, Soulaimane; Skouri, Mohammed; Knaebel, Alexandra; Münch, Jean-Pierre; Hébraud, Pascal

2005-07-01

421

Wind power today: 1999 Wind Energy program highlights  

Microsoft Academic Search

Wind Power Today is an annual publication that provides an overview for the Department of Energy's Wind Energy Program. The purpose of Wind Power Today is to show how DOE's Wind Energy Program supports wind turbine research and deployment in hopes of furthering the advancement of wind technologies that produce clean, low-cost, reliable energy for the 21st century. Content objectives

Weis-Taylor

2000-01-01

422

Wind Power Today: 2000 Wind Energy Program Highlights  

Microsoft Academic Search

Wind Power Today is an annual publication that provides an overview of the U.S. Department of Energy's Wind Energy Program. The purpose of Wind Power Today is to show how DOE's Wind Energy Program supports wind turbine research and deployment in hopes of furthering the advancement of wind technologies that produce clean, low-cost, reliable energy. Content objectives include: educate readers

Weis-Taylor

2001-01-01

423

Wind speed dynamical model in a wind farm  

Microsoft Academic Search

This paper presents a model for wind speed in a wind farm. The basic purpose of the paper is to calculate approximately the wind speed in the vicinity of each wind turbine in a farm. In this regard the governing equations of flow will be solved for the whole wind farm. In ideal circumstances, the dynamic model for wind flow

Maryam Soleimanzadeh; Rafael Wisniewski

2010-01-01

424

Effect of wind averaging time on wind erosivity estimation  

Technology Transfer Automated Retrieval System (TEKTRAN)

The Wind Erosion Prediction System (WEPS) and Revised Wind Erosion Equation (RWEQ) are widely used for estimating the wind-induced soil erosion at a field scale. Wind is the principal erosion driver in the two models. The wind erosivity, which describes the capacity of wind to cause soil erosion is ...

425

Modification of Saharan air layer and environmental shear over the eastern Atlantic Ocean by dust-radiation effects  

NASA Astrophysics Data System (ADS)

This study investigates the influence of dust-radiation effects on the modification of the Saharan air layer (SAL) and environmental shear. A tracer model based on the Weather Research and Forecast model was developed to examine the influence using a dust outbreak event. Two numerical experiments were conducted with (ON) and without (OFF) the dust-radiation effects. Both simulations reasonably reproduced SAL's features. However, the 700 hPa maximum temperature within SAL was slightly underestimated and shifted northwestward from OFF. These were improved from ON, but the maximum temperature became slightly overestimated, which might be due to inaccurate optical properties. The dust-radiation interactions mainly warmed the dusty air between 750 and 550 hPa because dust shortwave absorption dominated dust longwave cooling. Another major warming area was found near the surface over the ocean due to longwave radiative heating by dust aloft. The modification of temperature resulted in an adjustment of the vertical wind shear. To the south of SAL, where easterly wave disturbances and tropical storms usually occur, the vertical zonal wind shear increased by about 1˜2.5 m s-1 km-1 from 750 to 550 hPa, resulting in a maximum wind change of 3˜5 m s-1, a 30˜40% increase, around the top of this layer. The enhancement of the vertical shear in this layer could potentially have an impact on TC genesis and development. The dust-radiation effects also modified the moisture and dust distribution, which can have a feedback (i.e., a secondary effect) on the heating profile and the vertical shear.

Chen, Shu-Hua; Wang, Sheng-Hsiang; Waylonis, Mark

2010-11-01

426

How to create mylonitic shear zones in the presence of shear heating  

NASA Astrophysics Data System (ADS)

Lithospheric-scale shear zones are commonly defined as regions inhomogeneous and localized deformation. Strain softening has been demonstrated to be necessary for localization in those shear zones, but there is still debate about the physical cause of this softening. Here, we investigate the interplay between two mechanisms that have been suggested to have a significant impact on lithospheric localization: shear heating and grain size reduction. Shear heating has been suggested to play an important role in i) creating deep focus as well as intermediate-depth earthquakes (Ogawa (1987), Kelemen and Hirth (2007)) and ii) creating lithospheric-scale shear zones, thus creating a weak decoupling interface that enables subsequent subduction initiation (Kaus and Podlatchikov (2006), Crameri and Kaus (2010)). As natural shear zones typically have a significantly reduced grain size, it has been put forward that grain size reduction provides the necessary strain softening to localize deformation. As grain size reduces, the dominant deformation mechanism switches from dislocation to diffusion creep, thus requiring less stress to deform the rock. Usually, the equilibrium grain size is thought to follow a piezometric relationship, thus indicating the stress under which a shear zone deformed. Recent work (Austin and Evans (2007), Rozel et al. (2011)) suggests that the equilibrium grain size is not dependent on stress, but rather on the deformational work. In our study, we employ the grain size evolution law of Rozel et al. and use 1D viscoelastic numerical models of simple shear deformation to investigate the influence of both weakening mechanisms and their interaction for a variety of boundary conditions. We find that grain size reduction in pure olivine does not localize very efficiently, as grain size very rapidly reaches a steady state. Even when a fraction of the deformational work is used by grain size reduction processes, shear heating is found to localize very efficiently (Kaus & Podlatchikov (2005), Braeck et al. (2009)) and the significant temperature increase induced by shear heating severely affects the grain size in the shear zone. Generally, we find that the elevated temperature inside the shear zone results in a larger grain size inside the shear zone compared to the surrounding rock matrix. This finding is not compatible with field observations, where shear zones are usually characterized by small grain sizes. This indicates that further mechanisms are needed to keep either the grain size small (e.g. pinning by secondary phases (Herwegh et. al (2011), Bercovici and Ricard (2012) ) or to limit the temperature increase inside the shear zone.

Thielmann, Marcel; Rozel, Antoine; Kaus, Boris; Ricard, Yanick

2013-04-01

427

Mesosphere and lower thermosphere wind and turbulence observations over Puerto Rico during the Coqui 2 Campaign  

NASA Astrophysics Data System (ADS)

As part of the Coqui 2 sounding rocket campaign that was carried out in Puerto Rico in February and March 1998 a series of three rocket launches released the chemical tracer trimethyl aluminum TMA to measure the neutral wind profiles and turbulence structure in the mesosphere and lower thermosphere The first launch was on February 19 when a sodium sudden atom layer was present and the other two launches were on the night of February 24 25 when enhanced gravity wave activity was detected in lidar measurements from the Arecibo Observatory and in ground-based imager data The TMA trails were released on the upleg and downleg portion of each of the flights covering the altitude range from 85 to 150 km thus providing measurements of the horizontal neutral wind velocities as well as the gradients in the winds along a north south direction Large winds and wind shears were found between 95 and 110 km which is a common feature of the wind profile at midlatitudes The talk will focus on the turbulent structure information obtained from the trails in combination with the measurements of O density profiles from on-board photometers and the relation to the large winds and wind shears will be examined

Zhan, T.; Larsen, M. F.; Hecht, J. H.

428

Development of shear flow thermal rheometer for direct measurement of crystallization fraction of polymer melts under shear deformation  

Microsoft Academic Search

Recently viscoelastic measurement has received considerable attention as a complementary method to estimate the crystallization dynamics under shear. However, because of the complex relationship between the crystallization fraction and dynamic mechanical results, it has been difficult to obtain accurate crystallization fraction under shear. To conduct the direct determination of crystallization fraction under shear, the shear flow thermal rheometer (SFTR) having

W. Nagatake; T. Takahashi; Y. Masubuchi; J.-I. Takimoto; K. Koyama

2000-01-01

429

Ultimate Strength and Failure Mechanism of Resistance Spot Weld Subjected to Tensile, Shear, or Combined Tensile\\/Shear Loads  

Microsoft Academic Search

Strength tests were performed to reveal the failure mechanisms of spot weld in lap-shear and cross tension test samples. It is shown the while the lap-shear (cross tension) sample is subjected to shear (normal) load at the structural level the failure mechanism at the spot weld is tensile (shear) mode at the materials level. Based on the observed failure mechanism,

Yuh J. Chao

2003-01-01

430

The Influence of Single Shear Walls on the Behaviour of Coupled Shear Walls in High-rise Structures  

Microsoft Academic Search

This paper presents a simple method of analysis to determine the influence of single shear walls (SSW) on the degree of coupling DoC and on the peak shear demand PSD for beams of coupled shear walls (CSW) in mixed shear wall structures (MSW). Non-coupled lateral load resisting structures such as singular planar walls will reduce primary bending moments in the

J. C. D. Hoenderkamp

2011-01-01

431

Shear transfer constitutive model for pre-cracked RC plate subjected to combined axial and shear stress  

Microsoft Academic Search

This paper proposes the constitutive model for the shear transfer through the cracks of pre-cracked reinforced concrete (RC) plate subjected to combined axial and shear stress. The plate is a scale model of a shear wall of a nuclear power plant (NPP) building. Twelve plate specimens were initially cracked and then loaded to the failure point by increasing cyclic shear

Katsuhiko Umeki; Yoshio Kitada; Takao Nishikawa; Koichi Maekawa; Mamoru Yamada

2003-01-01

432

DARDC Wind Interface.  

National Technical Information Service (NTIS)

The DARDC Wind Interface converts the signals from a Climatronics Mark 10 Wind Sensor into binary-coded-decimal engineering units suitable for transmission by the Device for Automatic Remote Data Collection (DARCD). Three outputs are available from this s...

R. C. Ahlberg

1976-01-01

433

Wind Energy Benefits  

SciTech Connect

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.

Not Available

2005-04-01

434

Wind energy program critique  

Microsoft Academic Search

Recommendations by the U.S. General Accounting Office on how the DOE sponsored Wind Energy Program should be structured are presented. The recommendations urge reevaluation of programs directed to only large-scale wind energy systems.

M. Jr

1977-01-01

435

Filament Winding System.  

National Technical Information Service (NTIS)

An apparatus for winding fine filaments onto stationary long rods includes a supporting base having control mounting and filament mounting regions. The filament winding region includes first and second parallel bearing rods on which are slidably mounted a...

L. E. Sansone B. A. Blakely

1995-01-01

436

Wind Energy Information Directory.  

National Technical Information Service (NTIS)

Wind Energy Information has been prepared to provide researchers, designers, manufacturers, distributors, dealers, and users of wind energy conversion systems with easy access to technical information. This directory lists organizations and publications w...

1979-01-01

437

Renewable Energy: Wind  

NSDL National Science Digital Library

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.

Pratte, John

438

Wind Energy Benefits.  

National Technical Information Service (NTIS)

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.

2005-01-01

439

Effects of shear connectors on plate-reinforced composite coupling beams of short and medium-length spans  

Microsoft Academic Search

Experimental studies on the newly proposed design of plate-reinforced composite (PRC) coupling beams have been carried out. Previous results have demonstrated the useful application of this design in coupling beams of medium span-to-depth ratios (l\\/h) under both inelastic seismic and elastic wind loading. This paper presents further experimental studies on five PRC coupling beams, which investigated the importance of shear

R. K. L. Su; H. J. Pam; W. Y. Lam

2006-01-01

440

Snell's Law for Shear Zone Refraction in Granular Materials  

Microsoft Academic Search

We present experiments on slow shear flow in a split-bottom linear shear\\u000acell, filled with layered granular materials. Shearing through two different\\u000amaterials separated by a flat material boundary is shown to give narrow shear\\u000azones, which refract at the material boundary in accordance with Snell's law in\\u000aoptics. The shear zone is the one that minimizes the dissipation rate

H. A. Knudsen; J. Bergli

2009-01-01

441

Onset of shear thickening in a simple fluid  

Microsoft Academic Search

We report on nonequilibrium molecular-dynamics simulations of the shear-thickening transition in a simple fluid under shear. We relate the shear-thickening transition to the onset of instabilities in the flow profile and to that of dramatic variations in normal stress differences. The dependence of the critical shear rate, which indicates the onset of shear thickening, on density and temperature is rationalized

J. Delhommelle

2004-01-01

442

Shear rheology of molten crumb chocolate.  

PubMed

The shear rheology of fresh molten chocolate produced from crumb was studied over 5 decades of shear rate using controlled stress devices. The Carreau model was found to be a more accurate description than the traditional Casson model, especially at shear rates between 0.1 and 1 s(-1). At shear rates around 0.1 s(-1) (shear stress approximately 7 Pa) the material exhibited a transition to a solid regime, similar to the behavior reported by Coussot (2005) for other granular suspensions. The nature of the suspension was explored by investigating the effect of solids concentration (0.20 < phi < 0.75) and the nature of the particles. The rheology of the chocolate was then compared with the rheology of (1) a synthetic chocolate, which contained sunflower oil in place of cocoa butter, and (2) a suspension of sugar of a similar size distribution (volume mean 15 mum) in cocoa butter and emulsifier. The chocolate and synthetic chocolate showed very similar rheological profiles under both steady shear and oscillatory shear. The chocolate and the sugar suspension showed similar Krieger-Dougherty dependency on volume fraction, and a noticeable transition to a stiff state at solids volume fractions above approximately 0.5. Similar behavior has been reported by Citerne and others (2001) for a smooth peanut butter, which had a similar particle size distribution and solids loading to chocolate. The results indicate that the melt rheology of the chocolate is dominated by hydrodynamic interactions, although at high solids volume fractions the emulsifier may contribute to the departure of the apparent viscosity from the predicted trend. PMID:19323742

Taylor, J E; Van Damme, I; Johns, M L; Routh, A F; Wilson, D I

2009-03-01

443

Solar Wind: Theory  

NASA Astrophysics Data System (ADS)

The supersonic outflow of electrically charged particles, mainly electrons and protons from the solar CORONA, is called the SOLAR WIND. The solar wind was described theoretically by E N PARKER, in 1958. Parker's theory was verified experimentally by in situ observations by Soviet and American spaceprobes. On its way to Venus, in 1962, the MARINER II spacecraft observed the solar wind for 104 days...

Leer, E.; Murdin, P.

2000-11-01

444

Wind Power Now!  

ERIC Educational Resources Information Center

|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)|

Inglis, David Rittenhouse

1975-01-01

445

Small Wind Independent Testing.  

National Technical Information Service (NTIS)

This fact sheet describes the Small Wind Independent Testing at the NWTC and the Regional Test Center's project. NREL and the U.S. Department of Energy's (DOE) Wind and Water Power Program established the Small Wind Independent Testing project in 2008 and...

2010-01-01

446

Wind energy in Turkey  

Microsoft Academic Search

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

Mehmet Hana?asio?lu

1999-01-01

447

Aeroelastic wind energy converter  

Microsoft Academic Search

The principle of aeroelastic wind energy conversion is introduced and an H-section model which works on the basis of torsional aeroelastic instability is described. A mathematical formulation for the prediction of the power coefficient of such wind machines is presented. A small model is constructed and tested in a wind tunnel. Although the efficiency of the model was very low,

G. Ahmadi

1978-01-01

448

Energy from the Wind  

ERIC Educational Resources Information Center

|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)|

Pelka, David G.; And Others

1978-01-01

449

Wind energy - how reliable  

Microsoft Academic Search

The reliability of a wind energy system depends on the size of the propeller and the size of the back-up energy storage. Design of the optimum system for a given reliability level can be performed if a time series of wind speed data is available. However, a design based on conventional meteorological records, which sample the wind speed with a

D. J. Sherman

1980-01-01

450

WIND WATER PUMPING  

Technology Transfer Automated Retrieval System (TEKTRAN)

Wind power has been used to pump water for centuries; however, the development of the modern wind turbine has allowed for more applications for water pumping. This book was written to give a complete overview of wind power water pumping and serve as a design guide for water pumping systems. The bo...

451

Energy from the Wind  

ERIC Educational Resources Information Center

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)

Pelka, David G.; And Others

1978-01-01

452

Session: Offshore wind  

Microsoft Academic Search

This session at the Wind Energy and Birds\\/Bats workshop consisted of two presentations. Due to time constraints, a discussion period was not possible. The session addressed the current state of offshore wind energy development. The first presentation ''Monitoring Program and Results: Horns Rev and Nysted'' by Jette Gaarde summarized selected environmental studies conducted to date at operating offshore wind turbine

Jette Gaarde; Bonnie Ram

2004-01-01

453

Power from the Wind  

ERIC Educational Resources Information Center

|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.…

Roman, Harry T.

2004-01-01

454

Wind Power Now!  

ERIC Educational Resources Information Center

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)

Inglis, David Rittenhouse

1975-01-01

455

Dual Doppler measurement of a sheared, convective boundary layer  

NASA Astrophysics Data System (ADS)

The Phoenix 2 experiment was conducted in the spring of 1984 on the high plains of eastern Colorado, using dual Doppler radar as the primary observing tool in a study of the convective planetary boundary layer. Extensive support was provided by in situ sensors (instrumented aircraft, micrometeorological tower and surface network) for verification and extension of radar data. The two experiment days with the deepest boundary layers (which proved to be strongly sheared) were chosen for intensive study, and six 20-minute segments of continuous data from each day (about one each hour during the afternoon) were analyzed. The time resolution of the data is approximately two minutes, and the resolution of the analysis grid (which is 9 km by 9 km by 4 km deep) is 200 m in all directions. Application of available dual Doppler synthesis and integration techniques to define the four-dimensional velocity fields produced an unacceptably high noise level in the vertical velocity and derived statistics, prompting an exploration of alternative analysis methods, and a revival of coplanar integration to reduce the error variance to an acceptable level. The success of the coplanar technique is also demonstrated in a propagation of error analysis. Pressure and buoyancy fluctuations were retrieved from the wind fields using the Gal-Chen/Hane thermodynamic recovery, although over a smaller range of physical scales. The computed momentum and buoyancy fluxes are the basis of a study of the sheared, convective boundary layer over the course of two afternoons, including turbulent kinetic energy budgets and vertical velocity variance budgets.

Schneider, Jeanne Maples

456

Direct shear loading leads to failure of generator bolts, rotor  

SciTech Connect

Direct shear loading can result in the failure of bolts clamping the rotor flange to the shaft flange of a hydroelectric generator. Such was the case at the California Department of Water Resources 440-MW Gianelli Pumping-Generating Plant. The incident occurred July 5, 1991, when operators were bringing Unit 1 into service for generation. Tremendous forces on one of the unit's two rotors sheared ten 3 1/2-inch-diameter spider flange assembly bolts (ASTM A193-B16 steel) on the rotor, deforming bolt holes in both the spider flange and the shaft flange. The flanges, which allow the generator to transmit power through friction, rubbed and galled before the unit came to rest. The sudden shock load also slightly twisted the spider of the rotor, which during normal operation turns at 120 revolutions per minute at head of 190 to 245 feet. During normal operation, operators open a butterfly valve, allowing water to rush from a penstock to turn an impeller, which is connected to the generator rotor. Each of the plant's eight units is equipped with two rotors mounted on the same shaft. As the butterfly valve is gradually opened, speed of the unit increases. When the generator rotor is spinning at 90 percent of synchronous speed, the main unit breaker closes, energizing the stator windings with 13,800 volts. This rapidly accelerates the generator to approximately 98 percent of synchronous speed. The field breaker then closes, energizing the rotor poles with DC current. The rotor current reaches full strength in 2 to 5 seconds. During this time, the poles on the rotor are attempting to fall into step with the stator's rotating magnetic field.

Flanagan, P.J.; Knittel, D. (California Department of Water Resources, Santa Nella (United States))

1993-02-01

457

Analyzing the Effects of Temporal Wind Patterns on the Value ofWind-Generated Electricity at Different Sites in California and theNorthwest  

SciTech Connect

Wind power production varies on a diurnal and seasonal basis. In this report, we use wind speed data modeled by TrueWind Solutions, LLC (now AWS Truewind) to assess the effects of wind timing on the value of electric power from potential wind farm locations in California and the Northwest. (Data from this dataset are referred to as ''TrueWind data'' throughout this report.) The intra-annual wind speed variations reported in the TrueWind datasets have not previously been used in published work, however, so we also compare them to a collection of anemometer wind speed measurements and to a limited set of actual wind farm production data. The research reported in this paper seeks to answer three specific questions: (1) How large of an effect can the temporal variation of wind power have on the value of wind in different wind resource areas? (2) Which locations are affected most positively or negatively by the seasonal and diurnal timing of wind speeds? (3) How compatible are wind resources in the Northwest and California with wholesale power prices and loads in either region? The latter question is motivated by the fact that wind power projects in the Northwest could sell their output into California (and vice versa), and that California has an aggressive renewable energy policy that may ultimately yield such imports. Based on our research, we reach three key conclusions. (1) Temporal patterns have a moderate impact on the wholesale market value of wind power and a larger impact on the capacity factor during peak hours. The best-timed wind power sites have a wholesale market value that is up to 4 percent higher than the average market price, while the worst-timed sites have a market value that is up to 11 percent below the average market price. The best-timed wind sites could produce as much as 30-40 percent more power during peak hours than they do on average during the year, while the worst timed sites may produce 30-60 percent less power during peak hours. (2) Northwestern markets appear to be well served by Northwestern wind and poorly served by California wind; results are less clear for California markets. Both the modeled TrueWind data and the anemometer data indicate that many Northwestern wind sites are reasonably well-matched to the Northwest's historically winter-peaking wholesale electricity prices and loads, while most California sites are poorly matched to these prices and loads. However, the TrueWind data indicate that most California and Northwestern wind sites are poorly matched to California's summer-afternoon-peaking prices and loads, while the anemometer data suggest that many of these same sites are well matched to California's wholesale prices and loads. (3) TrueWind and anemometer data agree about wind speeds in most times and places, but disagree about California's summer afternoon wind speeds: The TrueWind data indicate that wind speeds at sites in California's coastal mountains and some Northwestern locations dip deeply during summer days and stay low through much of the afternoon. In contrast, the anemometer data indicate that winds at these sites begin to rise during the afternoon and are relatively strong when power is needed most. At other times and locations, the two datasets show good agreement. This disagreement may be due in part to time-varying wind shear between the anemometer heights (20-25m) and the TrueWind reference height (50m or 70m), but may also be due to modeling errors or data collection inconsistencies.

Fripp, Matthias; Wiser, Ryan

2006-05-31

458

Shear Localization in Fluid-Saturated Fault Gouge by Instability of Spatially Uniform, Adiabatic, Undrained Shear  

NASA Astrophysics Data System (ADS)

A number of authors have shown that the thermal expansion of pore fluids may play an important role in the earthquake process. Here, we examine the dynamics of a shear zone of fluid-saturated gouge under homogenous, undrained, adiabatic shear, and show that such deformation is unstable, in a manner that suggests strong shear localization. The material is assumed to follow the Coulomb friction law but to be rate-strengthening, such that its friction coefficient increases with shear strain rate ?? (if rate-weakening, deformation would localize at the onset of shear). This rate-strengthening model is of interest because it applies to stable regions in which rupture cannot nucleate and to initially unstable regions that have been driven into a stable temperature regime by shear heating. We describe an analysis by Rice and Rudnicki (2005) which shows that this shearing is linearly unstable in the sense that small perturbations from uniform shearing result in exponential growth for all wavelengths greater than a critical wavelength. Setting the shear zone width equal to this critical wavelength, they obtain a rough estimate of the largest width h over which uniform shearing is stable, given by h = 4?2 (?th + ?hy) / [(z+2)HV]. Here ?th and ?hy are the thermal and hydraulic diffusivities, 1/H is a characteristic weakening strain of the homogenous solution, V is the net slip rate across the shear zone, and 1/z = (?? df/ d ??)/f is a measure of the strengthening of friction coefficient f with ??. Choosing z = 40 (z ~ 20-60 based on known lab experiments showing rate strengthening, unfortunately all done at low ??), average earthquake slip rate V = 1 m/s, and values [Rice, 2005] ?th = 0.7 mm2/s, ?hy = 4 mm2/s, and H = 0.1 thought to be relevant to deforming ultracataclastic gouge at typical centroidal depths of the crustal seismogenic zone, we estimate h ? 0.04 mm. This mechanism, therefore, may help explain the field observation of sub-millimeter-sized high shear zones [Chester et al., 2003] within a much thicker gouge layer. We also perform a more detailed, numerical analysis that takes into account nonlinearities and pressure and temperature dependencies of the shear zone poromechanical properties. This numerical analysis more accurately describes the dynamics within the shear zone, and demonstrates the approximate validity of some aspects of the linear stability analysis, e.g., in predicting the localized zone thickness, which lie beyond the range of its applicability. A more comprehensive description of this nonlinear work is in preparation [Tsai and Rice, 2005].

Rice, J. R.; Rudnicki, J. W.; Tsai, V. C.

2005-12-01

459

Microstructure of shear zones in granular rock  

NASA Astrophysics Data System (ADS)

On the basis of image analysis, porosity and grain-size changes have been studied inside the shear bands formed in triaxial testing on a Fontainebleau sandstone with initial porosity of 21% under drained and undrained conditions. In drained conditions, it is obtained that for specimens tested under relatively low confining pressure (7 MPa), the porosity reaches a maximal value of about 30% inside the band and decreases rapidly towards the initial value of 21% outside the band. This is interpreted as dilating shear banding at low confining pressure. For specimens tested under relatively high confining pressure (28 MPa), a different patterning is observed. A compacting zone with high grain crushing and low porosity (values between 2 and 19%) is observed in the center of the band. This zone is surrounded by a dilating one with grain cracking and high porosity (up to 36%). These two zones correspond to the thickness of the white coloration as observed on the sample (i.e. the shear band). This shear band is surrounded by third zone with initial porosity and healthy grains. In globally undrained conditions, such changes in the microstructure of the rock allows for local fluid exchanges between compacting zones that expel fluid and dilating ones that absorb it. At high confinement, pore pressure generation inside the band leads locally to liquefaction of the crushed material which results into the formation of connected channels in the heart of the band. One application of this study is the influence of shear banding on the flow of fluids and contaminants. Although permeability was not directly measured in our experiments, microstructural observations highlight several features which may significantly affect fluid flow and hydraulic properties in a deformed sample. Under relatively high confining pressure, the center of the shear band is expected to inhibit fluid migration due to reduced grain size. Actually, the powder inside the band and the corresponding porosity reduction fill the porous space and can be a natural barrier to fluid flows. The zones surrounding the center of the shear band show a strong dilatancy which will allow a high permeability. Another aspect is the induced anisotropy of the rock permeability as the fluid flow can be enhanced in the direction parallel to the shear band and significantly reduced in the direction perpendicular to it. At large scale, similar phenomena can be expected in faulted zones when sheared. Changes in the structure of the gouge material, such as grain crushing and porosity reduction, will then affect the global permeability of the reservoir.

Sulem, J.; Ouffroukh, H.; El Bied, A.

2003-04-01

460

Shear-related fibrillogenesis of fibronectin.  

PubMed

Abstract Biomechanical forces can induce the transformation of fibronectin (Fn) from its compact structure to an extended fibrillar state. Adsorption of plasma proteins onto metallic surfaces may also influence their conformation. We used a cone-plate rheometer to investigate the effect of shear and stainless steel on conformational changes of Fn. In control experiments, cones grafted once or twice with polyethylene glycol were used. Plasma Fn was added at concentrations of 50 or 100 ?g/ml to bovine serum albumin (BSA)- or Fn-coated plates and subsequently exposed to dynamic shear rates stepwise increasing from 50 to 5000 s-1 within 5 min and subsequently decreasing from 5000 to 50 s-1 within 5 min. The viscosity (mPa s) of Fn solutions was recorded over 10 min. Upon exposure to shear, the viscosity in the sample increased, suggesting conformational changes in Fn. Western blotting and densitometric analyses demonstrated that conformational changes of plasma Fn depended both on shear and protein concentration. However, there was no significant difference in fibril formation between BSA- or Fn-coated plates, suggesting that physical properties of stainless steel and biomechanical forces such as shear can affect the molecular structure of Fn. Our model may provide useful information of surface- and flow-induced alterations of plasma proteins. PMID:24030032

Nguyen, Huong T T; Huynh, Khon C; Scharf, Rüdiger E; Stoldt, Volker R

2013-11-01

461

Turbulent mixing in stability stratified shear flows  

SciTech Connect

Vertical mixing of momentum and heat is investigated in turbulent stratified shear flows. It is assumed that the flow has uniform shear and stratification with homogeneous turbulence and that an equilibrium is reached between kinetic and potential energy without gravity wave oscillations. A simple model is derived to estimate vertical diffusivities for Richardson numbers in between 0 and about 1. The model is based on the budgets of kine