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1

Wind shear radar simulation  

NASA Technical Reports Server (NTRS)

Viewgraphs used in a presentation on wind shear radar simulation are given. Information on a microburst model of radar reflectivity and wind velocity, radar pulse output, the calculation of radar return, microburst power spectrum, and simulation plans are given. A question and answer session is transcribed.

Britt, Charles L.

1988-01-01

2

Wind Shear and Its Effects on Aircraft.  

National Technical Information Service (NTIS)

Wind shear has been responsible for several major accidents and many incidents during landing and take off. In aviation terms, wind changes that cause flight path deviations (wind shear) are mainly those occurring over distances between about 150 and 3000...

A. A. Woodfield

1994-01-01

3

Wind shear modeling for aircraft hazard definition  

NASA Technical Reports Server (NTRS)

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

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

1978-01-01

4

Flight in low-level wind shear  

NASA Technical Reports Server (NTRS)

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

Frost, W.

1983-01-01

5

Summary Proceedings of a Wind Shear Workshop  

NASA Technical Reports Server (NTRS)

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

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

1983-01-01

6

Problems pilots face involving wind shear  

NASA Technical Reports Server (NTRS)

Educating pilots and the aviation industry about wind shears presents a major problem associated with this meteorological phenomenon. The pilot's second most pressing problem is the need for a language to discuss wind shear encounters with other pilots so that the reaction of the aircraft to the wind shear encounter can be accurately described. Another problem is the flight director which gives a centered pitch command for a given angular displacement from the glide slope. It was suggested that they should instead be called flight path command and should not center unless the aircraft is actually correcting to the flight path.

Melvin, W. W.

1977-01-01

7

Wind shear and turbulence simulation  

NASA Technical Reports Server (NTRS)

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

Bowles, Roland L.

1987-01-01

8

Wind shear measuring on board an airliner  

NASA Technical Reports Server (NTRS)

A measurement technique which continuously determines the wind vector on board an airliner during takeoff and landing is introduced. Its implementation is intended to deliver sufficient statistical background concerning low frequency wind changes in the atmospheric boundary layer and extended knowledge about deterministic wind shear modeling. The wind measurement scheme is described and the adaptation of apparatus onboard an A300 airbus is shown. Preliminary measurements made during level flight demonstrate the validity of the method.

Krauspe, P.

1984-01-01

9

Wind shear related research at Princeton University  

NASA Technical Reports Server (NTRS)

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

Stengel, Robert

1992-01-01

10

Pulsed laser Doppler measurements of wind shear  

NASA Technical Reports Server (NTRS)

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

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

1979-01-01

11

Worldwide Experience of Wind Shear during 1981-1982.  

National Technical Information Service (NTIS)

Large changes of wind and downdraughts (Wind Shears) have caused several major accidents to airliners. The Royal Aircraft Establishment (RAE), with support from the United Kingdom Civil Aviation Authority and British Airways (BA), have analysed wind shear...

A. A. Woodfield J. F. Woods

1983-01-01

12

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

13

Some aspects of fluctuating vertical wind shears  

SciTech Connect

Fluctuating vertical shears of wind speed have been measured using an array of towers. The statistical distributions of these shears are compared with formulas proposed by Fichtl (1971, 1972) and good agreement is found. A comparison of Fichtl's formula for the standard deviation of the fluctuating shears with a more empirical one proposed by Ramsdell (1978) shows that the latter is consistent with the former under the proper conditions. The probability of occurrence of extreme shears in speed is discussed. Directional shears are not treated. Fluctuating shears two or more times larger than the mean values are shown to be readily obtainable, and their likelihood increases as the mean measuring height increases if ..delta..Z is held fixed.

Doran, J.C.

1981-05-01

14

Evaluation of Wind Shear Patterns at Midwest Wind Energy Facilities.  

National Technical Information Service (NTIS)

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 ha...

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

2002-01-01

15

Wind turbine aerodynamics and loads control in wind shear flow  

Microsoft Academic Search

Wind turbine is subjected to some asymmetrical effects like wind shear, which will lead to unsteady blade airloads and performance. Fatigue loads can lead to damage of turbine components and eventually to failures. It is evident that the variation of the velocity over the rotor disc has an influence on the blade and introduces both flap-wise and edge-wise fatigue damage

Xin Shen; Xiaocheng Zhu; Zhaohui Du

2011-01-01

16

Integration of the TDWR and LLWAS wind shear detection system  

NASA Technical Reports Server (NTRS)

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

Cornman, Larry

1991-01-01

17

History of wind shear turbulence models  

NASA Technical Reports Server (NTRS)

The Office of Flight Operations, Flight Technical Programs Div., at the FAA Headquarters, interfaces with industry, R&D communities and air carriers during the introduction of new types of equipment into operational services. A brief highlight of the need which FAA operations sees for new wind shear and turbulence data sets from the viewpoint of equipment certification and simulation is presented.

Cusimano, Lou

1987-01-01

18

Development of a wind shear performance envelope  

NASA Technical Reports Server (NTRS)

It is quite important that the airplane performance during a continuing headwind loss be understood. Lack of consideration of this characteristic can result in assuming almost twice the performance than that which the airplane actually has during severe wind shear at high descent rates. The example data relates to the Boeing 727-200, but the characteristics are applicable to any airplane.

Bliss, J. H.

1985-01-01

19

Laboratory model of flight through wind shear  

NASA Technical Reports Server (NTRS)

The simulation of an aircraft flying through a downdraft or microburst is presented. The simulation was performed under the conditions of constant takeoff thrust. The resulting wind shear conditions were filmed and examined for possible pilot corrective action in the future.

Frost, W.

1985-01-01

20

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

21

Wind shear predictive detector technology study status  

NASA Technical Reports Server (NTRS)

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

Gandolfi, C.

1990-01-01

22

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

23

An expert system for wind shear avoidance  

NASA Technical Reports Server (NTRS)

The principal objectives are to develop methods for assessing the likelihood of wind shear encounter (based on real-time information in the cockpit), for deciding what flight path to pursue (e.g., takeoff abort, landing go-around, or normal climbout or glide slope), and for using the aircraft's full potential for combating wind shear. This study requires the definition of both deterministic and statistical techniques for fusing internal and external information, for making go/no-go decisions, and for generating commands to the aircraft's autopilot and flight directors for both automatic and manually controlled flight. The expert system for pilot aiding is based on the results of the FAA Windshear Training Aids Program, a two-volume manual that presents an overview, pilot guide, training program, and substantiating data that provides guidelines for this initial development. The Windshear Safety Advisor expert system currently contains over 140 rules and is coded in the LISP programming language for implementation on a Symbolics 3670 LISP Machine.

Stengel, Robert F.; Stratton, D. Alexander

1990-01-01

24

Sources of low-level wind shear around airports  

NASA Technical Reports Server (NTRS)

Some potential sources of low-level wind shear in and around airports and their likely effects are probed and analyzed. Wind shear over flat terrain with near-homogeneous surface properties (roughness, specific heat), the turning layer, shear flows over inhomogeneous terrain (airport + urban areas), thunderstorms, turbulent flowfields over bluff bodies (individual buildings), and recirculating wake flow downstream of three-dimensional block bodies are among the topics covered. Overshoot or undershoot of runways, and induced moments (pitch, roll, yaw) in takeoff and landing, and other potential hazards traceable to wind shear patterns at low heights are discussed, with emphasis on mean flow or steady-state wind shear (time-averaged, say 2-min averaged, wind fields). Wind tunnel studies and V/STOL operations are included in the study.

Fichtl, G. H.; Camp, D. W.; Frost, W.

1977-01-01

25

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

26

Airborne infrared low level wind shear predictor  

NASA Technical Reports Server (NTRS)

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

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

1984-01-01

27

Tropical Cyclone Intensity in Vertical Wind Shear.  

NASA Astrophysics Data System (ADS)

The structure and intensity changes of tropical cyclones (TCs) in environmental vertical wind shear (VWS) are investigated in this study using the fifth-generation Pennsylvania State University National Center for Atmospheric Research (PSU NCAR) Mesoscale Model (MM5). Triply nested domains of 36-, 12-, and 4-km resolution are used with fully explicit moisture physics in the 4-km domain. Idealized environments with easterly shears of 2, 4, 6, 8, and 10 m s-1 between 800 and 200 hPa are applied on an f plane. Under small values of VWS (2 and 4 m s-1), the TC intensities are similar to that of the control (CTRL; i.e., no VWS) after initial adjustments. The TCs under 6 and 8 m s-1 of VWS are not as intense, although they do not weaken during the simulation. On the other hand, the TC in 10 m s-1 of VWS weakened significantly.Given the same VWS, the TC intensity is also found to be sensitive to TC size. Experiments with TCs with a smaller radius of 15 m s-1 wind reveal that while the TC in 2 m s-1 of VWS remains as intense as the CTRL, the TC in the 4 m s-1 VWS case weakened significantly to a minimal hurricane by the end of the simulation. A VWS of 6 m s-1 is strong enough to cause dissipation of the TC in 72 h. These results indicate that the size of a TC has to be taken into account in determining the intensity change of a TC in VWS.In the 10 m s-1 VWS case, the average temperature over the lower half of the troposphere within 50 km from the TC surface center is higher than that of the CTRL throughout the simulation. Such a warming, though of a small magnitude, is also observed for a brief period in the upper half of the troposphere before the rapid weakening of the TC and is related to the asymmetry of temperature required for a tilt of the vortex axis. The evolution of the vortex tilt is found to be similar to the dry simulations in previous studies, with the midlevel center (? = 0.525) located mainly in the southeast quadrant of the surface center. A tendency for the midlevel center to rotate about the surface center is also observed. These results support the idea that the resistance to vertical tilt by the mutual rotation between the low-level and midlevel centers is also valid in the moist simulations.It is hypothesized that the secondary circulation and the associated diabatic heating reduce the vertical tilt and the weakening. Condensation heating offsets the anomalous cooling effect due to the anomalous rising motion ahead of the vortex tilt. For small VWS, the vertical motion asymmetry is not strong enough to destroy the complete secondary circulation and the eyewall. As a result, a large temperature asymmetry and the associated vortex tilt cannot develop. Furthermore, there is no entrainment of cool/dry air in the upper troposphere. Therefore, TCs under small shears can be as intense as the CTRL.Large-scale asymmetries in the form of anticyclones found in previous studies are also observed. These asymmetries are apparently related to the change of shears near the TCs. While the shears at outer radii stay roughly constant with time, the shears near the TC centers can have large temporal fluctuations both in magnitude and orientation. This result suggests that the location at which the VWS is estimated in observational studies could be important in determining the relationship between VWS and TC intensity change.


Wong, Martin L. M.; Chan, Johnny C. L.

2004-08-01

28

Pilot-aircraft system response to wind shear  

NASA Technical Reports Server (NTRS)

The nonlinear aircraft motion and automatic control computer model of Frost and Reddy has been expanded to incorporate the human pilot into simulations of aircraft response to wind shear. Fixed-stick, autopilot, and manned computer simulations are made with an aircraft having characteristics of a Queen Air (small commuter-type aircraft) flown through longitudinal winds measured by a Doppler radar beamed along the glide slope during the SESAME '79 experiments in Oklahoma. Simulations are also made flying a model Boeing 727 through sinusoidal head wind to tail wind shears at the phugoid frequency to evaluate the response of manned aircraft in thunderstorm wind environments.

Turkel, B. S.; Frost, W.; Camp, D. W.

1980-01-01

29

Airborne in situ computation of the wind shear hazard index  

NASA Technical Reports Server (NTRS)

An algorithm for airborne in situ computation of the wind shear hazard index (F-factor) was developed and evaluated in simulation and verified in flight. The algorithm was implemented on NASA's B-737-100 airplane, and tested under severe maneuvering, nonhazardous wind conditions, and normal takeoffs and landings. The airplane was flown through actual microburst conditions in Orlando, FL, where the algorithm produced wind shear measurements which were confirmed by an independent, ground-based radar measurement. Flight test results indicated that the in situ F-factor algorithm correctly measured the effect of the wind environment on the airplane's performance, and produced no nuisance alerts.

Oseguera, Rosa M.; Bowles, Roland L.; Robinson, Paul A.

1992-01-01

30

Shear at the surface of a lake in light winds  

NASA Astrophysics Data System (ADS)

Standard computer cards released at 1-min intervals from the same point beneath a hydrometeorological tower were observed to segregate by color according to their depth of integration of the current. Green cards floated flat at the lake surface. Orange cards, on the other hand, curved downward when placed on the lake surface and averaged the currents in the top 1 cm. The separation of the cards into two distinct plumes resulted from wind-directed shear in the first centimeter below the surface that was superimposed upon a barotropic current flowing crosswind. Using time-lapse aerial photography, the magnitude and direction of the shear was quantified. The mean shear in the top cm was 3.5 s-1 and was aligned with the mean wind direction. The wind-directed shear was similar to that expected for a viscous sublayer in light winds (1.3-1.8 m s-1).

Kenney, Bernard C.

1991-04-01

31

Influence of wind shear on the aerodynamic characteristics of airplanes  

NASA Technical Reports Server (NTRS)

The aerodynamic effect of shear flow through a series of sensitivity studies of the wind velocity gradients and wing planform geometry parameters is investigated and characterized. The wind shear effect is computed using a modified vortex-lattice computer program and characterized through the formulation of wind shear aerodynamic coefficients. The magnitudes if the aerodynamic effects are demonstrated by computation of the resultant change in the aerodynamics of a conventional wing and horizontal stability configuration on a fixed flight path through a simulated microburst. The results indicate that as much as 20 percent of the control authority of the airplane may be required to counteract the wind-shear-induced forces and moments in the microburst environment.

Vicroy, Dan D.

1988-01-01

32

An experimental cockpit display for TDWR wind shear alerts  

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

33

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

34

Low altitude wind shear statistics derived from measured and FAA proposed standard wind profiles  

NASA Technical Reports Server (NTRS)

Wind shear statistics were calculated for a simulated data set using wind profiles proposed as a standard and compared to statistics derived from measured wind profile data. Wind shear values were grouped in altitude bands of 100 ft between 100 and 1400 ft, and in wind shear increments of 0.025 kt/ft between + or - 0.600 kt/ft for the simulated data set and between + or - 0.200 kt/ft for the measured set. No values existed outside the + or - 0.200 kt/ft boundaries for the measured data. Frequency distributions, means, and standard deviations were derived for each altitude band for both data sets, and compared. Also, frequency distributions were derived for the total sample for both data sets and compared. Frequency of occurrence of a given wind shear was about the same for both data sets for wind shears, but less than + or 0.10 kt/ft, but the simulated data set had larger values outside these boundaries. Neglecting the vertical wind component did not significantly affect the statistics for these data sets. The frequency of occurrence of wind shears for the flight measured data was essentially the same for each altitude band and the total sample, but the simulated data distributions were different for each altitude band. The larger wind shears for the flight measured data were found to have short durations.

Dunham, R. E., Jr.; Usry, J. W.

1984-01-01

35

Velocity shear layers in solar winds affect Earth's magnetosphere  

NASA Astrophysics Data System (ADS)

Human society is increasingly reliant on technology that can be disrupted by space weather. For instance, geomagnetic storms can cause high-latitude air fights to be rerouted, costing as much as $100,000 per fight; induce errors of up to 46 meters in GPS systems; and affect satellites and the International Space Station. Space weather is determined by how the solar wind, a stream of hot plasma from the Sun, interacts with Earth's magnetic field. In studying space weather, scientists have largely neglected the fact that the solar wind contains layers of very strong velocity shear. Scientists understand very little about how these wind shears affect space weather.

Bhattacharya, Atreyee

2012-09-01

36

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

NASA Technical Reports Server (NTRS)

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

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

1984-01-01

37

Simulation Model of Wind Turbine 3p Torque Oscillations due to Wind Shear and Tower Shadow  

Microsoft Academic Search

To determine 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 effects of wind shear and tower shadow. The comprehensive model includes turbine specific parameters such as radius, height, and

Dale S. L. Dolan; P. W. Lehn

2006-01-01

38

Effects of wind shear and turbulence on wind turbine power curves.  

National Technical Information Service (NTIS)

It is a common practice to use wind speeds at hub height in determining wind turbine power curves. Although the possible influence of other variables (sub as turbulence and wind shear) is generally neglected in power curve measurements, we discovered the ...

D. L. Elliott J. B. Cadogan

1990-01-01

39

Nonpotential Aerodynamics for Windmills in Shear Wind.  

National Technical Information Service (NTIS)

Several project goals are included in this report: (1) development of a formulation and computer program for a lifting surface aerodynamic analysis of Wind Energy Conversion Systems (WECS); (2) development of a formulation and computer program for a compl...

L. Morino

1975-01-01

40

Status of NASA's IR wind shear detection research  

NASA Technical Reports Server (NTRS)

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

Mckissick, Burnell

1991-01-01

41

Doppler weather radar with predictive wind shear detection capabilities  

NASA Technical Reports Server (NTRS)

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

Kuntman, Daryal

1991-01-01

42

The relationship of an integral wind shear hazard to aircraft performance limitations  

NASA Technical Reports Server (NTRS)

The development and certification of airborne forward-looking wind shear detection systems has required a hazard definition stated in terms of sensor observable wind field characteristics. This paper outlines the definition of the F-factor wind shear hazard index and an average F-factor quantity, calculated over a specified averaging interval, which may be used to judge an aircraft's potential performance loss due to a given wind shear field. A technique for estimating airplane energy changes during a wind shear encounter is presented and used to determine the wind shear intensity, as a function of the averaging interval, that presents significant hazard to transport category airplanes. The wind shear hazard levels are compared to averaged F-factor values at various averaging intervals for four actual wind shear encounters. Results indicate that averaging intervals of about one kilometer could be used in a simple method to discern hazardous shears.

Lewis, M. S.; Robinson, P. A.; Hinton, D. A.; Bowles, R. L.

1994-01-01

43

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

NASA Technical Reports Server (NTRS)

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

Bowles, Roland L.

1988-01-01

44

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

NASA Technical Reports Server (NTRS)

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

Seidler, Fritz; Hensel, Gunter

1987-01-01

45

Wind Shear Characteristics at Central Plains Tall Towers  

SciTech Connect

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 rated at 2-5 megawatts of energy generation with rotor diameters near 100 m and hub heights of 100-120 m. These advanced turbines will take advantage of the higher wind speeds aloft to generate more wind energy. Specific knowledge of important wind shear characteristics near and at turbine hub height is needed to optimize turbine design and wind farm layout. Unfortunately, wind speed shear measurements at heights of 80-120 m were virtually nonexistent a few years ago and are still quite uncommon today. The Central Plains is a prime wind energy development region and knowledge about the wind shear characteristics will reduce uncertainty about the resource and enhance wind farm design. Previous analyses of tall tower data (Schwartz and Elliott, 2005) concentrated on data from specific states. The wind energy community has recognized the need to fill the gap of direct wind speed measurements at levels 70 m and higher above the ground. Programs instituted during the last 5 years at the state level and supported by the U.S. Department of Energy's (DOE) State Energy Program initiative have placed anemometers and vanes at several levels on existing tall (70 m+) communication towers. The Central Plains has a fairly high concentration of tall tower sites. The distribution of tall tower sites varies among the states in the Central Plains, because the tall tower program is new and the available state and federal funding to establish tall towers is variable. Our wind resource assessment group at DOE's National Renewable Energy Laboratory (NREL) has obtained much of these necessary measurement data from both individual state sources and regional organizations. Most of the data are available to the public, though data from one tower in Colorado are proprietary. We have begun to analyze important wind climate parameters, including wind shear from the tall towers. A total of 13 tall towers were used for this study. Eleven of the towers had the highest anemometer level between 100 m and 113 m. Two towers had the highest measurement level between 70 m and 85 m above ground. The distribution of the towers among the states is: two sites in Texas and Oklahoma; six sites in Kansas; and one site each in Colorado, South Dakota, and North Dakota. Figure 1 shows the locations and names of the thirteen towers. The wind resource at these sites can be classified as ranging from good-to-excellent. Eight tall tower sites have Class 3 resource, four sites have Class 4 resource, and one has Class 5 resource at 50 m.

Schwartz, M.; Elliott, D.

2006-01-01

46

Air/ground wind shear information integration: Flight test results  

NASA Technical Reports Server (NTRS)

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

Hinton, David A.

1992-01-01

47

Effects of wind shear and turbulence on wind turbine power curves  

SciTech Connect

It is a common practice to use wind speeds at hub height in determining wind turbine power curves. Although the possible influence of other variables (sub as turbulence and wind shear) is generally neglected in power curve measurements, we discovered the importance of other variables in an analysis of power curves for three 2.5 MW wind turbines. When the power curves were stratified by turbulence intensity. Such a large sensitivity to turbulence was not expected, and further analyses were conducted to determine if other factors accompanying the change in turbulence level could cause or contribute to the observed sensitivity of the power curves to turbulence. In summary, the sensitivity of the observed power curves was largely due to two factors: (1) an actual sensitivity to turbulence in determining the power curve and (2) the deviation of the disk-averaged velocity from the hub-height velocity under low turbulence conditions that were most prevalent at the site. An examination of the wind shear profiles over the height of the rotor disk revealed that low turbulence conditions were characterized by strong shear in the lower half of the rotor disk and weak or negative shear in the upper half. Implications of this analysis are that significant errors in power curve measurements can result if the effects of wind shear and turbulence are ignored. 7 refs., 6 figs.

Elliott, D.L. (Pacific Northwest Lab., Richland, WA (USA)); Cadogan, J.B. (USDOE, Washington, DC (USA))

1990-09-01

48

Wind Shear/Turbulence Inputs to Flight Simulation and Systems Certification  

NASA Technical Reports Server (NTRS)

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

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

1987-01-01

49

Jet transport performance in thunderstorm wind shear conditions  

NASA Technical Reports Server (NTRS)

Several hours of three dimensional wind data were collected in the thunderstorm approach-to-landing environment, using an instrumented Queen Air airplane. These data were used as input to a numerical simulation of aircraft response, concentrating on fixed-stick assumptions, while the aircraft simulated an instrument landing systems approach. Output included airspeed, vertical displacement, pitch angle, and a special approach deterioration parameter. Theory and the results of approximately 1000 simulations indicated that about 20 percent of the cases contained serious wind shear conditions capable of causing a critical deterioration of the approach. In particular, the presence of high energy at the airplane's phugoid frequency was found to have a deleterious effect on approach quality. Oscillations of the horizontal wind at the phugoid frequency were found to have a more serious effect than vertical wind. A simulation of Eastern flight 66, which crashed at JFK in 1975, served to illustrate the points of the research. A concept of a real-time wind shear detector was outlined utilizing these results.

Mccarthy, J.; Blick, E. F.; Bensch, R. R.

1979-01-01

50

Wind shear detection. Forward-looking sensor technology  

NASA Technical Reports Server (NTRS)

A meeting took place at NASA Langley Research Center in February 1987 to discuss the development and eventual use of forward-looking remote sensors for the detection and avoidance of wind shear by aircraft. The participants represented industry, academia, and government. The meeting was structured to provide first a review of the current FAA and NASA wind shear programs, then to define what really happens to the airplane, and finally to give technology updates on the various types of forward-looking sensors. This document is intended to informally record the essence of the technology updates (represented here through unedited duplication of the vugraphs used), and the floor discussion following each presentation. Also given are key issues remaining unresolved.

Bracalente, E. M. (compiler); Delnore, V. E. (compiler)

1987-01-01

51

Stable boundary layer wind shear model for aircraft flight hazard definition  

NASA Technical Reports Server (NTRS)

It is pointed out that wind shear, particularly at the lower altitudes in the terminal area, has been identified as being hazardous to aircraft operations. Accurate and reliable wind profiles are required for use in fast time and manned flight simulation studies aimed at fully defining and understanding the wind shear hazard. A description is presented of wind speed profiles for neutral and stable atmospheric conditions developed for the simulation studies to improve the safety and reliability of operations in the terminal area. The wind shear is mathematically modeled and the mathematical scenarios are presented in a format for direct application to wind shear hazard/flight simulation studies.

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

1978-01-01

52

Coherent Doppler lidar signal covariance including wind shear and wind turbulence  

NASA Technical Reports Server (NTRS)

The performance of coherent Doppler lidar is determined by the statistics of the coherent Doppler signal. The derivation and calculation of the covariance of the Doppler lidar signal is presented for random atmospheric wind fields with wind shear. The random component is described by a Kolmogorov turbulence spectrum. The signal parameters are clarified for a general coherent Doppler lidar system. There are two distinct physical regimes: one where the transmitted pulse determines the signal statistics and the other where the wind field dominates the signal statistics. The Doppler shift of the signal is identified in terms of the wind field and system parameters.

Frehlich, R. G.

1993-01-01

53

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

54

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

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

55

Flight guidance research for recovery from microburst wind shear  

NASA Technical Reports Server (NTRS)

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

Hinton, David A.

1990-01-01

56

THE MUTUAL VARIATION OF WIND, SHEAR, AND BAROCLINICITY IN THE CUMULUS CONVECTIVE ATMOSPHERE OF THE HURRICANE  

Microsoft Academic Search

The enhanced cumulus convection in tropical disturbances acts in two opposing ways. In one sense the con- densation heat from the cumuli acts to warm the inner portions of the disturbance and induce vertical shear of the horizontal wind through the thermal wind relationship. In the opposite sense the cumuli also act to suppress vertical wind shear by transfer of

M. GRAY

57

Comparison of simulated and actual wind shear radar data products  

NASA Technical Reports Server (NTRS)

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

Britt, Charles L.; Crittenden, Lucille H.

1992-01-01

58

The impact of tower shadow, yaw error, and wind shears on power quality in a wind-diesel system  

Microsoft Academic Search

To study the impact of aerodynamic aspects of a wind turbine (i.e. tower shadow, wind shears, yaw error, and turbulence) on the power quality of a wind-diesel system, all electrical, mechanical and aerodynamic aspects of the wind turbine must be studied. Moreover, the contribution of the diesel generator system and its controllers should be considered. This paper, describes how the

R. F. Bahramjerdi; G. Moschopoulos; M. Moallem

2009-01-01

59

Shear and Turbulence Estimates for Calculation of Wind Turbine Loads and Responses Under Hurricane Strength Winds  

NASA Astrophysics Data System (ADS)

Schwartz et al. (2010) recently reported that the total gross energy-generating offshore wind resource in the United States in waters less than 30m deep is approximately 1000 GW. Estimated offshore generating capacity is thus equivalent to the current generating capacity in the United States. Offshore wind power can therefore play important role in electricity production in the United States. However, most of this resource is located along the East Coast of the United States and in the Gulf of Mexico, areas frequently affected by tropical cyclones including hurricanes. Hurricane strength winds, associated shear and turbulence can affect performance and structural integrity of wind turbines. In a recent study Rose et al. (2012) attempted to estimate the risk to offshore wind turbines from hurricane strength winds over a lifetime of a wind farm (i.e. 20 years). According to Rose et al. turbine tower buckling has been observed in typhoons. They concluded that there is "substantial risk that Category 3 and higher hurricanes can destroy half or more of the turbines at some locations." More robust designs including appropriate controls can mitigate the risk of wind turbine damage. To develop such designs good estimates of turbine loads under hurricane strength winds are essential. We use output from a large-eddy simulation of a hurricane to estimate shear and turbulence intensity over first couple of hundred meters above sea surface. We compute power spectra of three velocity components at several distances from the eye of the hurricane. Based on these spectra analytical spectral forms are developed and included in TurbSim, a stochastic inflow turbulence code developed by the National Renewable Energy Laboratory (NREL, http://wind.nrel.gov/designcodes/preprocessors/turbsim/). TurbSim provides a numerical simulation including bursts of coherent turbulence associated with organized turbulent structures. It can generate realistic flow conditions that an operating turbine would encounter under hurricane strength winds. These flow fields can be used to estimate wind turbine loads and responses with AeroDyn (http://wind.nrel.gov/designcodes/simulators/aerodyn/) and FAST (http://wind.nrel.gov/designcodes/simulators/fast/) codes also developed by NREL.

Kosovic, B.; Bryan, G. H.; Haupt, S. E.

2012-12-01

60

Analysis of strong nocturnal shears for wind machine design. Final report  

SciTech Connect

Wind shear data at wind turbine heights from several sites is reviewed and new data is documented in terms of total and component shear. A variety of atmospheric scenarios may combine to give large persistent shear. Among these, strong boundary layer stability is foremost. It occurs with strong nocturnal surface cooling, in low level frontal and subsidence inversions, and in thunderstorm outflows. Strong shears resulting from surface radiation inversions are particularly evident over the High Plains where dry air and high altitude combine to result in strong radiational cooling. Terrain is also an important influence on shear but it is not well understood and is very site specific.

Mahrt, L.; Heald, R.C.

1980-11-01

61

The Impact of Tower Shadow, Yaw Error, and Wind Shears on Power Quality in a Wind–Diesel System  

Microsoft Academic Search

To study the impact of aerodynamic aspects of a wind turbine (WT) (i.e., tower shadow, wind shears, yaw error, and turbulence) on the power quality of a wind-diesel system, all electrical, mechanical, and aerodynamic aspects of the WT must be studied. Moreover, the contribution of the diesel generator system and its controllers should be considered. This paper describes how the

Roohollah Fadaeinedjad; Gerry Moschopoulos; Mehrdad Moallem

2009-01-01

62

Algorithms for airborne Doppler radar wind shear detection  

NASA Technical Reports Server (NTRS)

Honeywell has developed algorithms for the detection of wind shear/microburst using airborne Doppler radar. The Honeywell algorithms use three dimensional pattern recognition techniques and the selection of an associated scanning pattern forward of the aircraft. This 'volumetric scan' approach acquires reflectivity, velocity, and spectral width from a three dimensional volume as opposed to the conventional use of a two dimensional azimuthal slice of data at a fixed elevation. The algorithm approach is based on detection and classification of velocity patterns which are indicative of microburst phenomenon while minimizing the false alarms due to ground clutter return. Simulation studies of microburst phenomenon and x-band radar interaction with the microburst have been performed and results of that study are presented. Algorithm performance indetection of both 'wet' and 'dry' microbursts is presented.

Gillberg, Jeff; Pockrandt, Mitch; Symosek, Peter; Benser, Earl T.

1992-01-01

63

Optimal penetration landing trajectories in the presence of wind shear  

NASA Technical Reports Server (NTRS)

Aircraft penetration landing in the presence of strong-to-severe wind shear is investigated analytically. The optimal-control problem for vertical-plane trajectories is considered, using angle of attack as one control parameter with either (1) a power setting (PS) which remains constant at its preshear value, (2) a PS which increases to its maximum value, or (3) a PS which is controlled (as the second parameter). The problem formulation is explained in detail, and numerical results obtained with the primal sequential gradient-restoration algorithm of Miele and Wang (1986) are presented in extensive tables and graphs. It is found that the touchdown requirements can only be satisfied by optimal trajectories using scheme (1) (but only at low altitudes) or scheme (3); the characteristics of the latter trajectories are explored.

Miele, A.; Wang, T.; Melvin, W. W.; Wang, H.

1988-01-01

64

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

NASA Astrophysics Data System (ADS)

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 and 8.3 meters, respectively, which correspond to the heights of the tip of the blade at the blade top position, the hub height, and the tip of the blade at the blade bottom position, respectively. Our measurements suggest that the normal force coefficients in strong wind shear conditions are lower than those in weak wind shear condition. Even if the local angle of attack is almost the same, the normal force coefficient shows differences due to the hysteresis effect. In particular, the influence of shear is large not only when there is strong wind shear in a vertical direction, but also when there is strong wind shear in a horizontal direction. A remarkable difference appears in the pressure distribution under these conditions.

Maeda, Takao; Kawabuchi, Hideyuki

65

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

NASA Astrophysics Data System (ADS)

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 shear with thermal forcing. It is found that the dominant phase speed range of convectively generated stratospheric gravity waves is primarily determined by the vertical scale of the tropospheric heating and is then modified by the tropospheric wind. The gravity wave spectrum is especially sensitive to shear in the upper troposphere. Through a mechanism similar to critical level filtering, such shear acts to reduce the momentum flux of waves propagating in the same direction as the storm-relative mean wind. Through interaction with convective turrets, shear in the upper troposphere increases the momentum flux of waves propagating opposite to the storm-relative mean wind (the `obstacle effect'). The resulting spectrum of momentum fluxes produced by convectively generated gravity waves is generally not symmetric in the east and west directions; the east-west asymmetry depends primarily on the difference between the wind above the storm and the storm's motion. Thus, it is important that the effects of tropospheric wind shear be included in any attempt to parameterize the effects of gravity wave stress and turbulence in general circulation models.

Beres, Jadwiga H.; Alexander, M. Joan; Holton, James R.

2002-06-01

66

Coherent Doppler lidar signal covariance including wind shear and wind turbulence.  

PubMed

The performance of a coherent Doppler lidar is determined by the statistics of the coherent Doppler signal. The derivation and calculation of the covariance of the Doppler lidar signal for random atmospheric wind fields and wind shear are presented. The signal parameters are defined for a general coherent Doppler lidar system in terms of the atmospheric parameters. There are two distinct physical regimes: one in which the transmitted pulse determines the signal statistics and the other in which the wind field and the atmospheric parameters dominate the signal statistics. When the wind fields dominate the signal statistics, Doppler lidar data are nonstationary and the signal correlation time is proportional to the operating wavelength of the lidar. The signal covariance is derived for signal-shot and multiple-shot conditions. For a single shot, the parameters of the signal covariance depend on the random, instantaneous atmospheric parameters. For multiple shots, various levels of ensemble averaging over the t emporal scales of the atmospheric processes are required. The wind turbulence is described by a Kolmogorov spectrum with an outer scale of turbulence. The effects of the wind turbulence are demonstrated with calculations for a horizontal propagation path in the atmospheric surface layer. PMID:20941185

Frehlich, R

1994-09-20

67

Nocturnal Wind Direction Shear and Its Potential Impact on Pollutant Transport.  

NASA Astrophysics Data System (ADS)

The potential effects of vertical wind direction shear on pollutant transport at a complicated, semiarid site are examined using tower measurements. This high-elevation site is situated on a sloping plateau between mountains to the west and a river valley to the east. The local climate, which favors clear skies, low humidity, and light winds, permits terrain-generated winds to develop frequently. During the night, winds that are oriented along the valley frequently overlie shallow (<50-m deep) drainage winds. Results indicate the nighttime direction shear between the levels at 92 and 12 m above ground exceeds 60° 20% of the time and exceeds 20° 50% of the time. Daytime shear is more modest: it is less than 20° 90% of the time.The effects of vertical wind direction shear on plume transport are studied by performing two model simulations of release at 50 m above ground level during a period when strong directional shear persisted for several hours. In the simulation using the full wind profile, southwest winds above a shallow drainage layer initially transport material to a community located 2 km to the northeast of the release. However, when only the 12-m wind is used, the model predicts that the material impacts a different community located 10 km to the southeast. This simulation demonstrates that ignoring the vertical shear effects can result in serious mistakes in responding to an emergency.

Bowen, Brent M.; Baars, Jeffrey A.; Stone, Gregory L.

2000-03-01

68

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

NASA Technical Reports Server (NTRS)

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

Gera, J.

1980-01-01

69

Wind stress and near-surface shear in the equatorial Atlantic Ocean  

NASA Astrophysics Data System (ADS)

upper ocean response to wind stress is examined using 8 months of unique near-surface moored velocity, temperature, and salinity data at 0°N, 23°W in the equatorial Atlantic. The effects of wind stress and shear on the time-varying eddy viscosity are inferred using the surface shear-stress boundary condition. Parameterizations of eddy viscosity as a function of wind stress and shear versus wind stress alone are then examined. In principle, eddy viscosity should be proportional to the inverse shear, but how it is represented implicitly or explicitly can affect estimates of the near-surface flow field. This result may explain some discrepancies that have arisen from using parameterizations based only on wind stress to characterize the effects of turbulent momentum mixing.

Wenegrat, Jacob O.; McPhaden, Michael J.; Lien, Ren-Chieh

2014-02-01

70

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

NASA Technical Reports Server (NTRS)

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

Usry, J. W.

1983-01-01

71

Wind-Shear Detection Performance Study for Multifunction Phased Array Radar (MPAR) Risk Reduction.  

National Technical Information Service (NTIS)

Multifunction phased array radars (MPARs) of the future that may replace the current terminal wind-shear detection systems will need to meet the Federal Aviation Administrations (FAA) detection requirements. Detection performance issues related to on-airp...

J. Y. N. Cho M. F. Donovan M. S. Veillette P. L. Heinselman R. S. Frankel

2013-01-01

72

NASA Experimental Airborne Doppler Radar and Real Time Processor for Wind Shear Detection.  

National Technical Information Service (NTIS)

The topics are presented in viewgraph form and include the following: experimental radar system capabilities; an experimental radar system block diagram; wind shear radar signal and data processor (WRSDP); WRSDP hardware architecture; WRSDP system design ...

P. H. Schaffner M. A. Richards W. R. Jones L. H. Crittenden

1992-01-01

73

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

National Technical Information Service (NTIS)

The computed RMS and peak responses due to atmospheric turbulence and discrete wind shears, respectively, are presented for several aircraft in different flight conditions. The responses are presented with and without the effects of a typical second order...

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

1977-01-01

74

NASA experimental airborne doppler radar and real time processor for wind shear detection  

NASA Technical Reports Server (NTRS)

The topics are presented in viewgraph form and include the following: experimental radar system capabilities; an experimental radar system block diagram; wind shear radar signal and data processor (WRSDP); WRSDP hardware architecture; WRSDP system design goals; DSP software development tools; OS-9 software development tools; WRSDP digital signal processing; WRSDP display operational modes; WRSDP division of functions; structure of WRSDP signal and data processing algorithms; and the wind shear radar flight experiment.

Schaffner, Philip H.; Richards, Mark A.; Jones, William R.; Crittenden, Lucille H.

1992-01-01

75

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

76

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 a horizontal wind shear. A comparison between numerical simulation and the observation dataset is conducted in this paper.

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

2013-04-01

77

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

NASA Technical Reports Server (NTRS)

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

Laituri, Tony R.

1988-01-01

78

No evidence for the localized heating of solar wind protons at intense velocity shear zones  

NASA Astrophysics Data System (ADS)

measurements from the Wind spacecraft at 1 AU, the heating of protons in the solar wind at locations of intense velocity shear is examined. The 4321 sites of intense shear in fast coronal hole origin plasma are analyzed. The proton temperature, the proton specific entropy, and the proton number density at the locations of the shears are compared with the same quantities in the plasmas adjacent to the shears. A very slight but statistically significant enhancement of the proton temperature is seen at the sites of the shears, but it is accompanied by a larger enhancement of the proton number density at the sites of the shears. Consequently, there is no enhancement of the proton specific entropy at the shear sites, indicating no production of entropy; hence, no evidence for plasma heating is found at the sites of the velocity shears. Since the shearing velocities have appreciable Mach numbers, the authors suggest that there can be a slight adiabatic compression of the plasma at the shear zones.

Borovsky, Joseph E.; Steinberg, John T.

2014-03-01

79

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

Microsoft Academic Search

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

Yushu Zhou

2011-01-01

80

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

81

Wind shear forecasting by Chaotic Oscillatory-based Neural Networks (CONN) with Lee Oscillator (retrograde signalling) model  

Microsoft Academic Search

Wind shear is a conventionally unpredictable meteorological phenomenon which presents a common danger to aircraft, particularly on takeoff and landing at airports. This paper describes a method for forecasting wind shear using an advanced paradigm from computational intelligence, chaotic oscillatory-based neural networks (CONN). The method uses weather data to predict wind velocities and directions over a short time period. This

Max H. Y. Wong; Raymond S. T. Lee; James Nga-kwok Liu

2008-01-01

82

Aircraft Low Altitude Wind Shear Detection and Warning System.  

NASA Astrophysics Data System (ADS)

There is now considerable evidence to substantiate the causal relationship between low altitude wind shear (LAWS) and the recent increase in low-altitude aircraft accidents. The National Research Council has found that for the period 1964 to 1982, LAWS was involved in nearly all the weather-related air carrier fatalities. However, at present, there is no acceptable method, technique, or hardware system that provides the necessary safety margins, for spatial and timely detection of LAWS from an aircraft during the critical phases of landing and takeoff. The Federal Aviation Administration (FAA) has addressed this matter and supports the development of an airborne system for detecting hazardous LAWS with at least a one minute warning of the potential hazard to the pilot. One of the purposes of this paper is to show from some of our preliminary flight measurement research that a forward looking infrared radiometer (FLIR) system can be used to successfully detect the cool downdraft of downbursts [microbursts/macrobursts (MB)] and thunderstorm gust front outflows that are responsible for most of the LAWS events. The FLIR system provides a much greater safety margin for the pilot than that provided by reactive designs such as inertial-air speed systems that require the actual penetration of the MB before a pilot warning can be initiated. Our preliminary results indicate that an advanced airborne FLIR system could provide the pilot with remote indication of MB threat, location, movement, and predicted MB hazards along the flight path ahead of the aircraft.In a proof-of-concept experiment, we have flight tested a prototype FLIR system (nonscanning, fixed range) near and within Colorado MBs with excellent detectability. The results show that a minimum warning time of one-four minutes (5×10 km), depending on aircraft speed, is available to the pilot prior to a MB encounter. Analysis of the flight data with respect to a modified `hazard index' indicates the severe hazard that the apparently weak and innocuous MBs present to both commercial transport pilots as well as the much larger number of pilots who fly the smaller general aviation and executive aircraft.

Sinclair, Peter C.; Kuhn, Peter M.

1991-01-01

83

Anemometer siting criteria for low level wind shear alert system  

NASA Astrophysics Data System (ADS)

The development of an anemometer siting guide for Federal Aviation Administration use is described. The siting guide included the influence of change in surface roughness, placement within a forest with upwind fetch, the influence of 2D obstacles such as tree lines, the influence of 3D bluff obstacles such as buildings or clumps of trees, the influence of forests on winds downwind of the end of the forest, the influence of 2D and 3D isolated hills on the acceleration of flow over a hilltop, and shielding downwind of hills. A physical model study was performed in a boundary layer wind tunnel capable of simulating wind flow in the atmospheric boundary layer. Profiles of mean velocity were measured for neutrally stable wind flow over proposed anemometer sites to determine the minimum anemometer height required to escape most the shielding effects of the surroundings. Wind velocity profiles in complex terrain compared to runway wind speed are illustrated.

Peterka, Jon A.

84

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

85

Airside velocity measurements over the wind-sheared water surface using particle image velocimetry  

Microsoft Academic Search

An experimental investigation of the airflow structure in the near surface region over the wind-sheared air–water interface\\u000a is reported. The two-dimensional velocity fields in a plane perpendicular to the water surface were measured using particle\\u000a image velocimetry (PIV) technique over a wind speed range from 1.5 to 4.4 m s?1. The results show a reduction in the mean velocity magnitudes and

Nasiruddin Shaikh; Kamran Siddiqui

2008-01-01

86

Dual hologram shearing interference technique with enhanced sensitivity for wind tunnel testing  

Microsoft Academic Search

A novel optical diagnostic approach, namely, a dual hologram shearing interferometry with enhanced sensitivity, is proposed\\u000a for visualization, and for measuring the density gradients of the flow in wind tunnels. The technique is especially useful\\u000a for strong turbulent and\\/or unsteady regions flows. The features of the technique make it tolerant to vibrational disturbances\\u000a typical to many wind tunnel facilities. The

G. Toker; D. Levin; A. Lessin

1998-01-01

87

Generation of auroral Omega bands by shear instability of the neutral winds  

NASA Technical Reports Server (NTRS)

Thermospheric neutral wind acceleration via ion drag in the conducting E-region of the ionosphere is greatly increased by electron precipitation associated with auroras. This increased acceleration can lead to the development of significant horizontal wind shears, which were found to be unstable to the Kelvin-Helmholtz shear instability. Numerical simulation of the neutral response to an intense, postmidnight, diffuse aurora shows tne formation of an E-region 'jet stream' within the aurora, with peak winds speeds greather than 700 m/s after one hour. It is proposed that this jet stream produces unstable Kelvin-Helmholtz waves, which can drive waves of discrete aurora along the poleward boundary of the preexisting diffuse aurora. It is suggested that such auroral waves, driven by the neutral winds, form eastward propagating waves (omega bands) occasionally observed along the poleward boundary of postmidnight diffuse auroras. It was found that neutral wind shears that develop in response to discrete auroral arcs are unstable; however, the resulting wind waves are not expected to drive significant auroral waves along discrete arcs.

Lyons, L. R.; Walterscheid, R. L.

1985-01-01

88

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

89

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 exceeding

Adrian M. Tompkins

2001-01-01

90

Igy and Igc Data on Vertical Wind Shears in Jet Streams over the Southern USSR.  

National Technical Information Service (NTIS)

The paper examines studies of vertical wind shears in arctic-front, polar-front, and subtropical jet streams made in winter and summer in the period 1957 through 1959. Calculations are made of the distribution of frequencies of various gradations of verti...

M. V. Burkova P. Z. Levina

1966-01-01

91

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

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

92

Cumulus Convection in the Atmosphere with Vertical Wind Shear : Numerical Experiment  

Microsoft Academic Search

The behavior of cumulus convection in a prevailing wind with vertical shear is studied by integrating a set of dynamic equations numerically. The motion is considered under the solenoidal condition in a vertical two dimensional plane. Aside from the eddy exchange, the pseudo-adiabatic process is assumed in which the motion is moist adiabatic in saturated ascending air and dry adiabatic

Tomio Asai

1964-01-01

93

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

SciTech Connect

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

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

1989-10-01

94

The Effect of Blockage in Shear Flow in the Wind Tunnel.  

National Technical Information Service (NTIS)

In an attempt to isolate and quantify the effects of blockage in shear flow, the pressure fields around two-dimensional Gaussian hills in an industrial wind tunnel were measured. The results obtained were compared with computed results for an unbounded tu...

P. P. Kirrane S. J. Stewart

1978-01-01

95

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

NASA Technical Reports Server (NTRS)

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

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

1977-01-01

96

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 three reconnection exhausts within a large magnetic flux rope embedded within an interplanetary coronal mass ejection in the solar wind on 19 October 1998. These exhausts were associated with current sheets having local field shear angles ranging from 4.1 to 9.3 degrees, the smallest field shear angles (strongest guide fields) yet associated with identified reconnection exhausts in a space plasma. They were observed in plasma characterized by extremely low (<0.01) proton beta and very high (281 - 383 km/s) Alfvén speed. The very low external plasma beta in these events minimized the effect of diamagnetic drift of the X-line and thus allowed reconnection to occur in a sustained fashion. And, the very high external Alfvén speed translated into sufficiently fast (> 10 km/s) exhaust jets that could be adequately resolved by the Wind 3DP plasma experiment. Thin, very small field shear-angle current sheets are common in the solar wind, but typically are not associated with particularly low plasma beta or particularly high Alfvén speeds. On the other hand, small field shear angle current sheets must also be dominant in topologically complex environments such as the solar corona where the plasma beta is often less than 0.01 and the Alfvén speed is high. Our observations thus suggest that reconnection at thin, low field shear angle current sheets should commonly occur in the corona, and lend some credence to models that suggest that reconnection at low field shear angle current sheets contributes substantially to coronal heating.

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

2012-12-01

97

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

NASA Technical Reports Server (NTRS)

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

Kuhn, P. M.

1985-01-01

98

The effect of wind shear and pitch control delaying on wind turbine blade loading  

Microsoft Academic Search

The loading analysis model of wind turbine blade is established according to strip theory of rotor aerodynamics. For a 1.5MW wind turbine, the force distribution on blade at rated wind speed and the moments of the blade root in various work case are dealt with by this model. The Effect of pitch control delaying on the loads of wind turbine

Jie Fu; Hui-ling Zhang; Bin He; Qin-shan Fan

2011-01-01

99

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

NASA Astrophysics Data System (ADS)

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

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

2007-08-01

100

Solid-state coherent laser radar wind shear measuring systems  

NASA Technical Reports Server (NTRS)

Coherent Technologies, Inc. (CTI) was established in 1984 to engage in the development of coherent laser radar systems and subsystems with applications in atmospheric remote sensing, and in target tracking, ranging and imaging. CTI focuses its capabilities in three major areas: (1) theoretical performance and design of coherent laser radar system; (2) development of coherent laser radar systems for government agencies such as DoD and NASA; and (3) development of coherent laser radar systems for commercial markets. The topics addressed are: (1) 1.06 micron solid-state coherent laser radar system; (2) wind measurement using 1.06 micron system; and flashlamp-pumped 2.09 micron solid-state coherent laser radar system.

Huffaker, R. Milton

1992-01-01

101

Contributions on the Subject of Longitudinal Movements of Aircraft in Wind Shears. Ph.D. Thesis - Technischen Univ., 1983  

NASA Technical Reports Server (NTRS)

The effect of downburst-type wind shears on the longitudinal dynamic behavior of an unguided aircraft is simulated numerically on the basis of published meteorological data and the flight characteristics of an A300-B passenger jet. The nonlinear differential equations of the aircraft motion are linearized by conventional methods, and the wind effects are introduced via the linear derivatives of the wind components referred to the wind gradients to obtain simplified technical models of the longitudinal response to all possible types of constant-gradient wind shears during the first 20-60 sec. Graphs, maps, and diagrams are provided, and a number of accidents presumed to have involved wind shears are analyzed in detail.

Krauspe, P.

1985-01-01

102

Effects of Shear and Wind Profile Curvature on Gravity Wave Drag  

NASA Astrophysics Data System (ADS)

Numerical simulations with mesoscale models indicate that surface gravity wave drag is sensitive to the shape of the wind profile. This is a well known feature of flow past large mountains, where resonant flows may be established for some background profiles of wind and stability. In the limit of linear flow, the effect of linear shear has been studied in recent years and found to lead to a reduction of drag. This paper develops an analytical model that incorporates more general wind profiles, which are characterized by both wind shear and curvature, using a linearized set of equations that treats nonlinearities associated with the vertical variation of wind speed using a WKB approximation. The results of that model indicate that curvature effects may be substantial, and lead to significant increases in the surface drag. Results of that analytical model compare very well with sets of numerical simulations with a mesoscale model. It is suggested that the simple formula that come out of the analytical model may be incorporated into parameterization schemes.

Teixeira, M.; Miranda, P. M.; Valente, M. A.

2003-12-01

103

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

104

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

105

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

106

Liquid crystals for surface shear stress visualization on wind turbine airfoils  

NASA Astrophysics Data System (ADS)

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 35 mm color film. Liquid crystal coatings sensitive only to surface shear stress, and insensitive to temperature changes for temperatures below 50 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.

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

107

Liquid crystals for surface shear stress visualization on wind turbine airfoils  

Microsoft Academic Search

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 35 mm color film.

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

1988-01-01

108

WIND-SHEARING IN GASEOUS PROTOPLANETARY DISKS AND THE EVOLUTION OF BINARY PLANETESIMALS  

SciTech Connect

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. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street Cambridge, MA 02338 (United States)

2011-05-20

109

Modeling of Neutral Turbulence Driven by Large Amplitude Wind Shears to Form Sporadic- E Layer Structures  

NASA Astrophysics Data System (ADS)

The evidence for wind-shear driven modulation of the E-Layer is strong. Large amplitude wind shears are seen with both TMA and LIDAR Observations. The neutral turbulence as observed by TMA Trails provides turbulence levels consistent with Richardson numbers that yield excitation of Kelvin-Helholtz (KH) instability in the neutral atmosphere. Ri ~ 0.2 KH billows are obtained during the from SEEK2 experiment by Larsen et al., AG, 2006. Electron density images show billows and longitudinal tube structures. Billows are seen in ISR scans by Miller and Smith [JGR 1978] and Hysell and Larsen [AG 2004]. Radio induced aurora images over Puerto Rico [Bernhardt et al., JGR, 2003] show both zonal KH scale structures and longitudinal ripples in E- layer density. Finally, the SEEK2 tomographic images by Bernhardt et al.,[AG, 2006] show layer separation consistent with KH billows. Electrodynamic models show that the KH Instability is a significant source of E- Layer structure. The wind-driven shear instability is a primary source of sporadic-E structures and may also be a seed for plasma instabilities such as proposed by Cosgove and Tsunoda.

Bernhardt, P. A.

2006-05-01

110

A Phenomenological Model for Wind Speed and Shear Stress Profiles in Vegetation Cover Layers.  

NASA Astrophysics Data System (ADS)

A phenomenological model for the mean wind speed and Reynolds shear stress profiles with height in a vegetation cover layer is derived from forms suggested by truncation of the equations of turbulent fluid motion at second order in fluctuating velocity products. The initial formulation is unique in that the force per unit volume resisting fluid motion is treated as a body force having a height-dependent character. The body force is assumed to be proportional to the instantaneous speed squared and in the opposite direction from the instantaneous velocity. Viscous forces are ignored as are all pressure forces except for a steady vertical pressure gradient. Closure of the, equations is effected by a phenomenological assumption linking the static pressure and the square of the mean wind speed. The mean wind speed profile predicted by the model is an exponential in the cumulative drag area per unit planform area as a function of height, which is a simple exponential in height for cover with uniform plant area density. Comparisons of predicted profiles of wind speed and Reynolds shear stress with measurements show the model to be relatively robust.

Albini, F. A.

1981-11-01

111

Morphology of sporadic E layer retrieved from COSMIC GPS radio occultation measurements: Wind shear theory examination  

NASA Astrophysics Data System (ADS)

the basis of the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC)-measured fluctuations in the signal-to-noise ratio and excess phase of the GPS signal piercing through ionospheric sporadic E (Es) layers, the general morphologies of these layers are presented for the period from July 2006 to May 2011. It is found that the latitudinal variation in the Es layer occurrence is substantially geomagnetically controlled, most frequent in the summer hemisphere within the geomagnetic latitude region between 10° and 70° and very rare in the geomagnetic equatorial zone. Model simulations show that the summer maximum (winter minimum) in the Es layer occurrence is very likely attributed to the convergence of the Fe+ concentration flux driven by the neutral wind. In addition to seasonal and spatial distributions, the height-time variations in the Es layer occurrence in the midlatitude (>30°) region in summer and spring are primarily dominated by the semidiurnal tides, which start to appear at local time around 6 and 18 h in the height range 110-120 km and gradually descend at a rate of about 0.9-1.6 km/h. In the low-latitude (<30°) region, the diurnal tide dominates. The Horizontal Wind Model (HWM07) indicates that the height-time distribution of Es layers at middle latitude (30°-60°) is highly coincident with the zonal neutral wind shear. However, Es layer occurrences in low-latitude and equatorial regions do not correlate well with the zonal wind shear.

Chu, Y. H.; Wang, C. Y.; Wu, K. H.; Chen, K. T.; Tzeng, K. J.; Su, C. L.; Feng, W.; Plane, J. M. C.

2014-03-01

112

Reflection and transmission of atmospheric gravity waves in a stably sheared horizontal wind field  

NASA Astrophysics Data System (ADS)

Applying a second-order fully nonlinear numerical scheme, we have investigated the characteristics of reflection and transmission of atmospheric gravity wave packets in a vertically sheared horizontal wind. When the leading edge of incident wave arrives at the reflecting level predicted by the linear theory, the wave reflection begins to occur. In the reflection process, the reflection and incident waves are superposed with obvious phase staggering, which is different from the wave reflection in a meridionally sheared horizontal wind. In the evanescent region, the wave phase has only weak variation; the wave amplitude decays with the sheared wind growth and vice versa, which is in good agreement with the evanescent wave configuration predicted by the linear theory. Some spectral components of the incident wave can penetrate through the evanescent region and produce a transmitted wave. Both the reflection and transmission coefficients slightly decrease with the moderate increase of the initial amplitude of the incident wave, which is because a large-amplitude wave can induce a strong mean flow; moreover, the wave-induced mean flow plays a more significant role in transferring the energy from the waves to the background flow than in enhancing the transmission of the waves. This is distinguished from the wave reflection in a sheared flow under the wave propagation distance smaller than the density scale height, in which the mean flow induced by a larger-amplitude wave significantly strengthens the transmission of the wave. The simulation shows that the reflection loop predicted by the linear theory is not a common phenomenon in the wave reflection. Several groups of simulated cases indicate that the reflection and transmission coefficients depend on not only the amplitude, frequency, and wavenumbers of the incident wave but also the strength and thickness of the evanescent region. The reflection coefficient increases but the transmission coefficient decreases with the relative evanescent thickness growth, and once the strength and thickness of the evanescent region are large enough, the wave hardly penetrates through the sheared wind zone, and the reflection coefficient approaches a constant value, too. Except for the disappearance of the evanescent region, the total sum of the reflection and transmission coefficients of the wave pseudoenergy flux is slightly <1 because of the interaction between the wave and flow. These results suggest that the effects of wave reflection and transmission should be correctly included in the parameterization of gravity waves to attain more realistic middle atmospheric climatology from general circulation models.

Huang, Kai Ming; Zhang, Shao Dong; Yi, Fan

2010-08-01

113

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

NASA Technical Reports Server (NTRS)

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

Campbell, C. W.

1984-01-01

114

The Velocity Induced by the Wake of a Wind Turbine in a Shear Layer, Including Ground Effect.  

National Technical Information Service (NTIS)

A theory is developed for the calculation of the velocity field induced by the wake of a horizontal axis wind turbine in a wind shear layer and in the vicinity of a plane ground surface, when the force distribution of the turbine is known. The turbine is ...

B. C. A. Johansson

1980-01-01

115

An Analytical Model of Mountain Wave Drag for Wind Profiles withShear and Curvature.  

NASA Astrophysics Data System (ADS)

An analytical model is developed to predict the surface drag exerted by internal gravity waves on an isolated axisymmetric mountain over which there is a stratified flow with a velocity profile that varies relatively slowly with height. The model is linear with respect to the perturbations induced by the mountain, and solves the Taylor Goldstein equation with variable coefficients using a Wentzel Kramers Brillouin (WKB) approximation, formally valid for high Richardson numbers, Ri. The WKB solution is extended to a higher order than in previous studies, enabling a rigorous treatment of the effects of shear and curvature of the wind profile on the surface drag. In the hydrostatic approximation, closed formulas for the drag are derived for generic wind profiles, where the relative magnitude of the corrections to the leading-order drag (valid for a constant wind profile) does not depend on the detailed shape of the orography. The drag is found to vary proportionally to Ri-1, decreasing as Ri decreases for a wind that varies linearly with height, and increasing as Ri decreases for a wind that rotates with height maintaining its magnitude. In these two cases the surface drag is predicted to be aligned with the surface wind. When one of the wind components varies linearly with height and the other is constant, the surface drag is misaligned with the surface wind, especially for relatively small Ri. All these results are shown to be in fairly good agreement with numerical simulations of mesoscale nonhydrostatic models, for high and even moderate values of Ri.


Teixeira, Miguel A. C.; Miranda, Pedro M. A.; Valente, Maria Antónia

2004-05-01

116

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

117

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

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

118

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

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

119

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

Microsoft Academic Search

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

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

1984-01-01

120

A case study illustrating time scales and operational responses for a wind shear episode during the JAWS project. [Joint Airport Weather Studies Project  

NASA Technical Reports Server (NTRS)

A microburst event on 14 July 1983 illustrates the short time scales involved in responding to this type of wind shear. The event also illustrates how a controller used information from several sources in helping a number of aircraft avoid a dangerous wind shear situation. The implications of this event are discussed for the design of future wind shear detection systems, and these observations are related to data obtained during the JAWS experiment.

Bedard, A. J., Jr.; Mccarthy, J.

1984-01-01

121

Intense winds and shears in the equatorial lower thermosphere measured by high-resolution nonspecular meteor radar  

NASA Astrophysics Data System (ADS)

Large horizontal winds and wind shears have been measured in the lower thermosphere by rockets, lidars, and nonspecular meteor radars. This paper describes a detailed analysis of three multihour nonspecular meteor radar data sets collected at the Jicamarca Radio Observatory. This provides some of the highest-resolution sustained measurements in this part of the atmosphere. These show (1) intense wind speeds, maintaining 180 m/s for half an hour and 160 m/s for another half an hour; (2) winds structured in layers that move up or, more commonly, down in the predawn hours at rates of a few kilometers per hour; (3) intense wind shears that typically persist at around 50 m/s/km but, in one instance, sustains values approaching 100 m/s/km for a few hours.

Oppenheim, M. M.; Arredondo, S.; Sugar, G.

2014-03-01

122

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

123

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

NASA Technical Reports Server (NTRS)

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

Ritchie, Elizabeth A.

2003-01-01

124

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

125

Effects of vertical wind shear, radiation and ice microphysics on precipitation efficiency during a torrential rainfall event in China  

NASA Astrophysics Data System (ADS)

The effects of vertical wind shear, radiation and ice microphysics on precipitation efficiency (PE) were investigated through analysis of modeling data of a torrential rainfall event over Jinan, China during July 2007. Vertical wind shear affected PE by changing the kinetic energy conversion between the mean and perturbation circulations. Cloud-radiation interaction impacted upon PE, but the relationship related to cloud radiative effects on PE was not statistically significant. The reduction in deposition processes associated with the removal of ice microphysics suppressed efficiency. The relationships related to effects of vertical wind shear, radiation and ice clouds on PEs defined in cloud and surface rainfall budgets were more statistically significant than that defined in the rain microphysical budget.

Zhou, Yushu

2013-11-01

126

Spectrum characteristics of Denver and Philadelphia ground clutter and the problem of distinguishing wind shear targets from moving clutter  

NASA Technical Reports Server (NTRS)

Spectral analysis of 1991 wind shear flight data has provided information about the power spectral density, spectral width, and velocity of ground clutter detected by the wind shear radar at several major airports. Ground clutter must be recognized and separated from weather targets before wind shear can be computed. Information will be presented characterizing and comparing ground clutter and weather target spectra. The information includes (1) spectral widths of stationary ground clutter seen at various scan and tilt angles, (2) power spectral density and velocity of moving ground clutter relative to the stationary ground clutter, and (3) spectral widths and velocities of weather targets. A summary of numerical results in the form of histograms and example numerical results in the form of spectral plots are presented.

Mackenzie, Anne I.

1992-01-01

127

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

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

128

Test and evaluation of the Airport Surveillance Radar (ASR)-8 wind shear detection system (phase 2), revision  

NASA Astrophysics Data System (ADS)

A wind shear detection system developed by the Wave Propagation Laboratory (WPL) to operate with the Federal Aviation Administration (FAA) Airport Surveillance Radar (ASR)-8 was installed and is being tested at the FAA technical Center. Initial efforts, previously reported in Report NA-78-59-LR, were directed toward hardware and software shakedown and feasibility determination. Second phase tests compared radar with aircraft and tower winds, evaluated the wind shear measurement capability under various weather conditions, and investigated the effectiveness of a simple two-azimuth pointing strategy and system capabilities and limitations. Results showed the system to be compatible with and to operate satisfactorily with the ASR-8. The processing and spectral display of clear air and precipitation returns is feasible. The accuracy of agreement between radar-measured winds and components of the aircraft-measured winds in both radially oriented flights and runway offset flights, using a two-azimuth pointing technique, was examined. Radar versus tower wind agreement was also examined. Potentially dangerous wind shears associated with weather during these tests were detectable. Certain system limitations also have been defined and considered. It is recommended that tests continue to complete definition of and demonstrate capabilities in all weather situations, to optimize performance, and to provide information to specify system design for possible development of a prototype model.

Offi, D. L.; Lewis, W.; Lee, T.; Delamarche, A.

1980-08-01

129

Explanation of the sporadic-E layer formation by comparing FORMOSAT-3/COSMIC data with meteor and wind shear information  

NASA Astrophysics Data System (ADS)

formation of the sporadic E (Es) layer can be interpreted in several different ways, with wind shear theory and the meteor ionization mechanism being the most commonly used explanations. Nevertheless, neither the wind shear theory nor the meteor ionization mechanism alone can completely explain the formation of the Es layer. The meteor ionization mechanism cannot interpret the different activity in this layer between the Northern and Southern Hemispheres, while the wind shear theory cannot explain the source of the large amount of ionized particles in the Es layer. In this study, the activity in the Es layer is compared with information about meteors and the global vertical speed of ionized particles. The information about meteors is obtained from International Meteor Organization and Radio Meteor Observing Bulletin. The global vertical speed information for ionized particles is calculated using the International Geomagnetic Reference Field model, Horizontal Wind Model (HWM07), and Mass Spectrometer-Incoherent Scatter model. The activity in the Es layer is based on the value of the irregular degree index, which is derived from the signal-to-noise ratio obtained from Formosa Satellite Mission-3/Constellation Observing System for Meteorology, Ionosphere, and Climate (FORMOSAT-3/COSMIC) Global Positioning System radio occultation mission. Taking both wind shear theory and the meteor ionization mechanism together, the source of the ionized particles in the Es layer and the difference in the activity in the Es layer between Northern and Southern Hemispheres can thus be explained more completely.

Yeh, Wen-Hao; Liu, Jann-Yenq; Huang, Cheng-Yung; Chen, Shih-Ping

2014-04-01

130

A Flight Investigation using Variable Glide Path Trajectories to Compensate for Winds and Moderate Wind Shears (Etudes en Vol sous Differentes Trajectoires de Descente pour Compenser les Vents et les Cisaillements Moderes du Vent).  

National Technical Information Service (NTIS)

The influence of wind, wind shears and turbulence on the approach and landing tasks of STOL and V/STOL aircraft has become of significant concern for this evolving class of flight vehicles, particularly during instrument flight operations. Flight experime...

W. S. Hindson R. E. Smith

1976-01-01

131

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

NASA Technical Reports Server (NTRS)

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

Sinclair, Peter C.; Kuhn, Peter M.

1991-01-01

132

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

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

133

1983 lightning, turbulence, wind shear, and Doppler radar studies at the National Severe Storms Laboratory  

NASA Technical Reports Server (NTRS)

As part of continuing research on aviation related weather hazards, numerous experiments were incorporated into the 1983 Spring Observation Program. This year's program was an abbreviated one because of commitments made to the development of the Next Generation Radar (NEXRAD) project. The National Oceanic and Atmospheric Administration's (NOAA) P-3 Orion and the National Aeronautics and Space Administration's (NASA) RB-57B and U-2 were the main aircraft involved in the studies of lightning, wind shear, turbulence, and storm structure. A total of 14 flights were made by these aircraft during the period of May 16 through June 5, 1983. Aircraft instrumentation experiments are described, and resultant data sets available for research are detailed. Aircraft instrumentation and Doppler radar characteristics are detailed.

Lee, J. T.

1984-01-01

134

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

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

135

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

136

Richardson number, vertical wind shear and storm occurrences at Kano, Nigeria  

NASA Astrophysics Data System (ADS)

Radiosonde data for thirteen summer months have been used to relate Richardson under Ri and vertical wind shear to storm occurrences at Kano. It is shown that thunderstorms occur most frequently in association with low-level shears, ?UL, below the Africal Easterly Jet (surface to 700 mb) within -20? ?UL?-5 ms -1 and for the 700-400 layer, ?Um, in the range 0< ?Um<10 m s -1. The Richardson number with which storm occurrences are most common is bi-modal in both lower and middle troposphere: -2? Ri?0 and Ri? -10 in the boundary layer (surface to 900 mb); 1? Ri?4 and Ri?15 in the inflow region (origin) of the downdraft air between 800 and 600 mb. Storms rarely occur (one in every seven cases) if boundary layer Ri>0 and virtually no storm should be expected if the boundary layer Ri>0 and for DDR (the regional origin of down draft air) Ri satisfying 4< Ri<15 simultaneously. The lower cut-off ( Ri ? 1) for the inflow air is close to the value ( Ri?2) obtained by Moncrieff and Miller (1976) for propagating tropical storms.

Omotosho, J. Bayo

137

Large Eddy Simulation of Persistent Contrails in Wind Shear and Atmospheric Turbulence  

NASA Astrophysics Data System (ADS)

A study of contrail evolution was conducted using a three-dimensional Large Eddy Simulation (LES). The LES solves the incompressible Navier-Stokes equations with a Boussinesq approximation for buoyancy forces on an unstructured periodic grid. The numerical scheme uses a second-order finite volume spatial discretization and an implicit fractional-step method for time advancement. Lagrangian contrail particles grow according to a microphysical model of ice deposition and sublimation. The simulation is initialized with the wake of a commercial jet superimposed on a decaying turbulence field. The ambient atmosphere is stable and has a supersaturated relative humidity with respect to ice. Grid resolution is adjusted during the simulation, allowing higher resolution of flow structures than previous studies. We present results of a parametric study in which ambient turbulence levels, vertical wind shear, and aircraft type were varied. We find that higher levels of turbulence and shear promote mixing of aircraft exhaust with supersaturated ambient air, resulting in faster growth of ice and wider dispersion of the exhaust plume. These results provide sensitivity data that improves understanding of the development of persistent contrails into contrail cirrus, a poorly characterized aspect of the climate impact of aviation.

Naiman, Alexander; Ham, Frank; Lele, Sanjiva; Wilkerson, Jordan; Jacobson, Mark

2009-11-01

138

A multiple-source wind tunnel design for producing turbulent shear flows in a stably stratified fluid  

Microsoft Academic Search

The design and construction of a thermally stratified, multiple source wind tunnel for producing linear vertical temperature and velocity profiles is discussed. The tunnel utilizes 10 initially independent layers to produce continuous velocity and temperature profiles for which the turbulence in nominally homogeneous in the lateral direction. The tunnel is capable of producing uniform vertical velocity shears of up to

P. Piccirillo; C. W. Van Atta

1996-01-01

139

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

140

NASA airborne radar wind shear detection algorithm and the detection of wet microbursts in the vicinity of Orlando, Florida  

NASA Technical Reports Server (NTRS)

The algorithms used in the NASA experimental wind shear radar system for detection, characterization, and determination of windshear hazard are discussed. The performance of the algorithms in the detection of wet microbursts near Orlando is presented. Various suggested algorithms that are currently being evaluated using the flight test results from Denver and Orlando are reviewed.

Britt, Charles L.; Bracalente, Emedio M.

1992-01-01

141

Vector Wind and Vector Wind Shear Models 0 to 27 Km Altitude for Cape Kennedy, Florida, and Vandenberg AFB, California.  

National Technical Information Service (NTIS)

The techniques are presented to derive several statistical wind models. The techniques are from the properties of the multivariate normal probability function. Assuming that the winds can be considered as bivariate normally distributed, then (1) the wind ...

O. E. Smith

1976-01-01

142

Wind Shear Enhancement of Entrainment and Refractive Index Structure Parameter at the Top of a Turbulent Mixed Layer.  

NASA Astrophysics Data System (ADS)

where Sk is the inversion wind shear, the lapse rate of v above the inversion and v the buoyancy jump at the inversion. Deardorff's empirical relation for We/ w is used to close the set of equations and to obtain a parameterization for We which applies it Rf is greater than a critical value approximately equal to one-half. The wind shear enhancement of entrainment leads to an increase in the refractive index structure parameter, CN2, in the interfacial region. This increase in CN2 may be significant under conditions of strong geostrophic forcing combined with a low-level inversion or large baroclinic effects associated with horizontal gradients of mixed-layer temperature or inversion height.

Fairall, C. W.

1984-12-01

143

A preliminary look at the large-scale impact of wind shear on mid-latitude convection  

NASA Astrophysics Data System (ADS)

Since pioneering studies by Rotunno, Klemp, and Weisman in the 1980s, wind shear has been known to have important impacts on convective storms. These influences are highly non-linear and are difficult, if not impossible to derive theoretically for convective parameterizations in Global Climate Models (GCMs) with course resolution. As a result, convective parameterizations in GCMs neglect the impact of wind shear. Although strides have been made by incorporating 2-D CRMs into GCMs (so called "super-parameterizations, Randall et al. 2003), the 3-D structure of convection and its relationship to environmental parameters will continue to be a trouble spot for convective parameterizations until models are run at a storm-resolving resolution. For the foreseeable future, at least some aspects of mesoscale convective organization will need to be parameterized. To do so, a collective relationship must be obtained either from observations or high resolution Cloud Resolving Models (CRMs) which explicitly resolve convection. Unfortunately, updraft strength and other convective properties are extremely difficult to observe properly at the large-scales required for GCMs. While these properties can be determined using multiple Doppler radar observations, these datasets are limited to short time periods and small scales. At the present time, the only way to determine the large-scale impacts of wind shear on convection is by using CRMs. These models have taken off in recent years and are now produced by numerous institutions and used by forecasters on a daily basis. Both subjective (Done et al. 2004 and Weisman et al. 2008) and objective (Clark et al. 2010) studies of these simulations have shown that they do a better job than forecasting models with convective parameterizations. In detail, the convective resolving simulations can produce a variety of convective modes (and their 3-D structures) observed in reality such as squall-lines, multicells, and even supercells. In summary, it is now possible to use these simulations to derive convective statistics at the resolution of GCMs for climate related studies. The purpose of this study is to provide a first look at convective statistics from several years of WRF simulations run for the CONUS in support of the NOAA Hazardous Weather Testbed (HWT) spring experiments. These results will be partitioned by thermodynamic and kinematic vertical profiles to understand how wind shear influences properties such as convective area and mean updraft strength at the resolution of climate models. In doing so, it will be possible to quantify how important wind shear is at larger scales.

Kennedy, A. D.

2012-12-01

144

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

NASA Astrophysics Data System (ADS)

A superposed-epoch analysis of ACE and OMNI2 measurements is performed on 27 corotating interaction regions (CIRs) in 2003-2008, with the zero epoch taken to be the stream interface as determined by the maximum of the plasma vorticity. When the measurements are rotated into the local-Parker-spiral coordinate system, the shear is seen to be abrupt. Converging flows are seen; about half of the CIRs show a layer of divergent rebound flow away from the stream interface. Analysis of the turbulence across the CIRs is performed. When possible, the effects of discontinuities are removed. Fluctuation amplitudes, the Alfvenicity, and the level of Alfvenic correlations all vary smoothly across the CIR. The Alfven ratio exhibits a decrease at the shear zone of the stream interface. Fourier analysis of subintervals is performed, and the results are superposed averaged as an ensemble of realizations. The spectral slopes of the velocity, magnetic field, and total energy vary smoothly across the CIR. The total-energy spectral index is ˜3/2 in the slow and fast wind and in the CIRs. Fourier analysis of Elsasser fluctuations shows a smooth transition across the CIR from an inward-outward balance in the slow wind to an outward dominance in the fast wind. Spreading of turbulence away from the region where it is produced is limited to ˜106 km. A number of signatures of turbulence driving at the shear zone are sought (entropy change, turbulence amplitude, Alfvenicity, spectral slopes, and in-out nature): none show evidence of driving of turbulence by shear.

Borovsky, Joseph E.; Denton, Michael H.

2010-10-01

145

The fabrication and integration of a novel shear stress sensor array and its wind tunnel test  

Microsoft Academic Search

A new generation of micro shear stress sensors and flexible PCB for the general purpose of flow separation detection and control\\u000a is presented here. A novel MEMS shear stress sensor array featuring integration of discrete micro sensors and polyimide substrate\\u000a has been developed. Then, CFD (Computational Fluid Dynamics) simulations were performed to estimate the corresponding shear\\u000a stress distribution within the

K. Liu; W. Z. Yuan; B. H. Ma; S. Chen; C. Y. Jiang

2008-01-01

146

Selective excitation of tropical atmospheric waves in wave-CISK: The effect of vertical wind shear  

NASA Technical Reports Server (NTRS)

The growth of waves and the generation of potential energy in wave-CISK require unstable waves to tilt with height oppositely to their direction of propagation. This makes the structures and instability properties of these waves very sensitive to the presence of vertical shear in the basic flow. Equatorial Kelvin and Rossby-gravity waves have opposite phase tilt with height to what they have in the stratosphere, and their growth is selectively favored by basic flows with westward vertical shear and eastward vertical shear, respectively. Similar calculations are also made for gravity waves and Rossby waves. It is shown that eastward vertical shear of the basic flow promotes CISK for westward propagating Rossby-gravity, Rossby, and gravity waves and suppresses CISK for eastward propagating Kelvin and gravity waves, while westward shear of the basic flow has the reverse effects.

Zhang, Minghua; Geller, Marvin A.

1994-01-01

147

Third moments and the role of anisotropy from velocity shear in the solar wind  

NASA Astrophysics Data System (ADS)

In the interplanetary medium, fluctuations in velocity and magnetic field show evidence of turbulent energy cascades. Near 1 AU, Advanced Compositional Explorer (ACE) plasma and magnetic field data have been used by us to compute third-order moments. The cascade rate can be directly evaluated from these moments, and the results are in agreement with rate needed to account for proton heating. Assuming homogeneous shear flow, the total velocity can be split into the sum of a fluctuation and shear part. This approach can be taken to examine the role of velocity shear which at large scales is an important driver of the turbulence at 1 AU. We present results from a linear detrending of velocity for 12 hour samples and provide estimates of the various contributing third-order moments for the fluctuating and shear components. We find that the cascade rate can be recovered with an inferred anisotropy of the fluctuations due to velocity shear.

Smith, C. W.; Stawarz, J. E.; Vasquez, B. J.; Forman, M. A.

2010-12-01

148

Further examination of the thermodynamic modification of the inflow layer of tropical cyclones by vertical wind shear  

NASA Astrophysics Data System (ADS)

Recent work has developed a new framework for the impact of vertical wind shear on the intensity evolution of tropical cyclones. A focus of this framework is on the frustration of the tropical cyclone's power machine by shear-induced, persistent downdrafts that flush relatively cool and dry (lower equivalent potential temperature, ?e) air into the storm's inflow layer. These previous results have been based on idealised numerical experiments for which we have deliberately chosen a simple set of physical parameterisations. Before efforts are undertaken to test the proposed framework with real atmospheric data, we assess here the robustness of our previous results in a more realistic and representative experimental setup by surveying and diagnosing five additional numerical experiments. The modifications of the experimental setup comprise the values of the exchange coefficients of surface heat and momentum fluxes, the inclusion of experiments with ice microphysics, and the consideration of weaker, but still mature tropical cyclones. In all experiments, the depression of the inflow layer ?e values is significant and all tropical cyclones exhibit the same general structural changes when interacting with the imposed vertical wind shear. Tropical cyclones in which strong downdrafts occur more frequently exhibit a more pronounced depression of inflow layer ?e outside of the eyewall in our experiments. The magnitude of the ?e depression underneath the eyewall early after shear is imposed in our experiments correlates well with the magnitude of the ensuing weakening of the respective tropical cyclone. Based on the evidence presented, it is concluded that the newly proposed framework is a robust description of intensity modification in our suite of experiments.

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

2013-01-01

149

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

PubMed

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

Faganello, M; Califano, F; Pegoraro, F

2008-01-11

150

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

SciTech Connect

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

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

2008-01-11

151

Experimental evaluation of a wind shear alert and energy management display  

NASA Technical Reports Server (NTRS)

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

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

1978-01-01

152

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

153

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

Microsoft Academic Search

Characteristics of a liquid crystal system, comprised of a shear-sensitive cholesteric-monomer liquid crystal thin-film coated on a liquid-crystal polymer substrate, are described. The system provides stable Grandjean texture, a desirable feature for shear-stress measurements using selective reflection from the monomer liquid-crystal helix structure. Impingement of gas or air flow on the monomer liquid-crystal free surface changes the wavelength of the

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

1992-01-01

154

Dual hologram shearing interference technique for wind tunnel flow fields testing  

Microsoft Academic Search

A novel optical diagnostic technique, dual hologram shearing interferometry, for measuring density gradients of different\\u000a phase objects is proposed and demonstrated. The lateral shearing is achieved by using a phase grating. A holographic interferometer\\u000a has been developed and designed on the base of a single pass Z type conventional schlieren device. The interferometer’s scheme is insensitive to acoustical disturbances, similarly

G. Toker; D. Levin; J. Stricker

1997-01-01

155

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

SciTech Connect

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

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

2009-01-01

156

A model of wind shear and turbulence in the surface boundary layer  

NASA Technical Reports Server (NTRS)

A model of wind and turbulence has been described for the surface boundary layer. The wind structure in the surface layer is considered to be a function of the surface parameters, stability, and height. The surface parameters considered are: (1) the surface roughness length; (2) the surface friction velocity; and (3) the zero plane displacement height. The stability parameter, Z/L, where L is the Monin-Obukov stability length, describes the thermal effect on the wind profile. The logarithmic wind profile is used to describe the mean wind field in the neutral boundary layer, and a logarithmic profile with a stability defect is used to describe the stable and unstable atmospheric conditions. For the very stable conditions, the logarithmic wind law does not hold. Under this condition, the layers of the atmosphere become disconnected and large scale frontal motions are the predominate factor in defining the wind profile. Figures are presented which represent some typical wind profiles in the very stable condition.

Luers, J. K.

1973-01-01

157

Wind shear and wet and dry thermodynamic indices as predictors of thunderstorm motion and severity and application to the AVE 4 experimental data  

NASA Technical Reports Server (NTRS)

Two types of parameters are computed and mapped for use in assessing their individual merits as predictors of occurrence and severity of thunderstorms. The first group is comprised of equivalent potential temperature, potential temperature, water vapor mixing ratio, and wind speed. Equivalent potential temperature maxima and strong gradients of equivalent potential temperature at the surface correlate well with regions of thunderstorm activity. The second type, comprised of the energy index, shear index, and energy shear index, incorporates some model dynamics of thunderstorms, including nonthermodynamic forcing. The energy shear index is found to improve prediction of tornadic and high-wind situations slightly better than other indices. It is concluded that further development and refinement of nonthermodynamic aspects of predictive indices are definitely warranted.

Connell, J. R.; Ey, L.

1977-01-01

158

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

159

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

NASA Technical Reports Server (NTRS)

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

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

1981-01-01

160

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

EPA Science Inventory

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

161

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

NASA Technical Reports Server (NTRS)

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

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

2011-01-01

162

Statistics of shallow convection on Mars based on large-eddy simulations. Part 2: effects of wind shear  

Microsoft Academic Search

Effects of wind on quasi-steady, shallow convection in the Martian boundary layer are studied using a large-eddy simulation\\u000a model. Convection in the model is generated by the radiative flux divergence and the strength of the surface heat flux, which\\u000a do not vary in time. The resulting convective boundary layer exhibits transient, irregular, horizontal cellular structures,\\u000a transported by wind, and a

Zbigniew Sorbjan

2007-01-01

163

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

164

On the source of dense outflows from T Tauri stars - III. Winds driven from the star-disc shear layer  

NASA Astrophysics Data System (ADS)

Ultraviolet observations of classical T Tauri Stars (cTTSs) have shown that there is a hot (Te? 80 000 K) and dense (ne? 1010 cm-3) component associated with the large-scale jet. This hot component is formed very close to the base of the jet providing fundamental information on the jet formation mechanism. In this series, we have investigated whether this component can be formed in disc winds, either cool or warm. To conclude the series, jet launching from the interface between the magnetic rotor (the star) and the disc is studied. Synthetic profiles are calculated from numerical simulations of outflow launching by star-disc interaction. Profiles are calculated for several possible configurations of the stellar field: dipolar (with surface strengths B* of 1, 2 and 5 kG) or dynamo fed. Also two types of discs, passive or subjected to an ??-dynamo, are considered. These profiles have been used to define the locus of the various models in the observational diagram: dispersion versus centroid, for the profiles of the Si III] line. Bulk motions produce an increasing broadening of the profile as the lever arm launching the jet becomes more efficient; predicted profiles are however sensitive to the disc inclination. Models are compared with observations of the Si III] lines obtained with the Hubble Space Telescope. In addition, it is shown that the non-stationary nature of star-disc winds produce a flickering of the profile during quiescence with variations in the line flux of about 10 per cent. At outburst, accretion signatures appear in the profiles together with an enhancement of the wind, producing the correlation between accretion and outflow as reported from RU Lup, AA Tau and RW Aur observations.

Gómez de Castro, Ana I.; von Rekowski, Brigitta

2011-02-01

165

Winds  

NSDL National Science Digital Library

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

166

Wind turbine wake aerodynamics  

Microsoft Academic Search

The aerodynamics of horizontal axis wind turbine wakes is studied. The contents is directed towards the physics of power extraction by wind turbines and reviews both the near and the far wake region. For the near wake, the survey is restricted to uniform, steady and parallel flow conditions, thereby excluding wind shear, wind speed and rotor setting changes and yawed

L. J. Vermeer; J. N. Sørensen; A. Crespo

2003-01-01

167

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

168

Velocity fluctuations in the wake behind wind breakers and at the edge of the shear layer, and their correlations with the free stream  

Microsoft Academic Search

Wind tunnel tests and field experiments have been performed in order to compare, for neutral conditions, aspects of the wake flow in the external mixing layer of the upper region of a porous wire mesh fence, with a porosity of 70%, a tree canopy (cypress macrocarpa) with a porosity of 80%, and a dense wheat field.

U. Boldes; J. Colman; V. Nadal Mora; A. Zumarraga

1995-01-01

169

Shear-Sensitive Monomer/Polymer Liquid Crystal System  

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

170

Winding for the wind  

NASA Technical Reports Server (NTRS)

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

Weingart, O.

1981-01-01

171

Winding for the wind  

NASA Astrophysics Data System (ADS)

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

Weingart, O.

172

Windtunnel studies of surface shear stress vector distribution measurement using shear sensitive liquid crystal coatings  

Microsoft Academic Search

Shear sensitive liquid crystal coating (SSLCC) can measure surface shear stress vector distribution efficiently with a high\\u000a spatial resolution. The purpose of the present paper is to modify and extend the surface shear stress measurement technique\\u000a determined by Reda et al. to wind tunnel studies. All the facilities employed in the technique are very common and simple.\\u000a The measurement technique

JiSong Zhao; Peter Scholz; LiangXian Gu

173

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

174

Periodic pulsations from a three-bladed wind turbine  

Microsoft Academic Search

In this paper, periodic power pulsations from a three-bladed wind turbine are analyzed. The influence of wind shear, wind speed, turbulence intensity, rotor position and tower oscillation is investigated. No clear dependence between the periodic power components and the wind shear or turbulence intensity has been verified. The investigated turbine sometimes produces large power pulsations at the tower resonance frequency.

Torbjörn Thiringer; Jan-Åke Dahlberg

2001-01-01

175

Tornado Wind Patterns  

NSDL National Science Digital Library

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

Hall, Prentice

176

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

177

Shear wave anisotropy imaging  

Microsoft Academic Search

Shear wave anisotropy imaging (SWAI) is a novel method that images local variations in tissue shear wave velocity. A commercial ultrasound scanner is used to generate and track propagating shear waves. Radiation force from a brief high-energy pulse generates the shear waves. The pulse and resultant shear waves are steered in order to launch the waves at oblique angles. The

Stephen J. Hsu; Mark L. Palermi; Kathryn R. Nightingale; Stephen A. McAleavey; Jeremy D. Dahl; Gregg E. Trahey

2003-01-01

178

Role of velocity shears in turbulent dissipation  

NASA Astrophysics Data System (ADS)

The discussion about what processes are important in solar wind plasma heating usually concentrates on wave particle interactions or on energization by low frequency structures like current sheets and reconnection sites. Less attention has been paid to the role of local velocity shears in plasma heating. We study this problem using Hall-FLR MHD and hybrid codes. We see that the velocity shear sites are related to hot spots and most of the dissipated energy comes from velocity shears. The ultimate energy deposition mechanism is electromagnetic interactions but these interactions are enhanced at the velocity shear sites making them an attractive candidate for sites of dissipation along with magnetic shear sites like the current sheets and reconnection sites.

Parashar, T. N.; Ghosh, S.

2013-12-01

179

Disruption of a helmet streamer by photospheric shear  

NASA Technical Reports Server (NTRS)

Helmet streamers on the Sun have been observed to be the site of coronal mass ejections, dynamic events that eject coronal plasma and magnetic fields into the solar wind. We develop a two-dimensional (azimuthally symmetric) helmet streamer configuration by computing solutions of the time-dependent magnetohydrodynamic (MHD) equations, and we investigate the evolution of the configuration when photospheric shearing motions are imposed. We find that the configuration disrupts when a critical shear is exceeded, ejecting a plasmoid into the solar wind. The results are similar to the case of a sheared dipole magnetic field in a hydrostatic atmosphere (Mikic & Linker 1994). However, the presence of the outflowing solar wind makes the disruption significantly more energetic when a helmet streamer is sheared. Our resutls suggest that shearing of helmet streamers may initiate coronal mass ejections.

Linker, Jon A.; Mikic, Zoran

1995-01-01

180

Mountain Waves in Two-Layer Sheared Flows: Critical-Level Effects, Wave Reflection, and Drag Enhancement  

Microsoft Academic Search

Internal gravity waves generated in two-layer stratified shear flows over mountains are investigated here using linear theory and numerical simulations. The impact on the gravity wave drag of wind profiles with constant unidirectional or directional shear up to a certain height and zero shear above, with and without critical levels, is evaluated. This kind of wind profile, which is more

Miguel A. C. Teixeira; Pedro M. A. Miranda; José L. Argaín

2008-01-01

181

Speed and Direction Shear in the Stable Nocturnal Boundary Layer  

SciTech Connect

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

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

2009-02-01

182

Shear wave anisotropy imaging  

Microsoft Academic Search

Shear wave anisotropy imaging is a novel method that images local variations in tissue shear wave velocity. A commercial ultrasound scanner is used to generate and track propagating shear waves. Radiation force from a brief high-energy pulse generates shear waves. The pulses are steered in order to launch the waves at oblique angles. The Helmholtz equation is used to extract

Stephen J. Hsu; Mark L. Palermi; Kathryn R. Nightingale; Stephen A. McAleavey; Jeremy D. Dahl; Gregg E. Trahey

2003-01-01

183

Performance testing of a Savonius windmill rotor in shear flows  

SciTech Connect

The effects of flow shear and/or unsteadiness on the power-producing performance of a Savonius windmill rotor are discussed. Measurements were made, in two statistically steady shear flows and in the natural wind, of the speed, torque and (hence) power of the rotor at a number of streamwise stations for each of four values of the bucket overlap ratio. 8 refs.

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

1981-08-01

184

Wind turbine acoustics  

NASA Technical Reports Server (NTRS)

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.

1990-01-01

185

A Dynamic Wind Turbine Simulator of the Wind Turbine Generator System  

Microsoft Academic Search

To study dynamic performances of wind turbine generator system (WTGS), and to determine the control structures in laboratory. The dynamic torque generated by wind turbine (WT) must be simulated. In there paper, a dynamic wind turbine emulator (WTE) is designed, which consider wind shear and tower shadow effect, and a dynamic torque compensation scheme is also developed to compensate the

Lei Lu; Zhen Xie; Xing Zhang; Shuying Yang; Renxian Cao

2012-01-01

186

A simulation model for wind turbine blade fatigue loads  

Microsoft Academic Search

The paper describes a horizontal axis wind turbine time domain simulation and fatigue estimation program written using the DelphiTM language. The program models the flapwise motion of a single rotor blade to determine the blade-root fatigue damage of a medium size wind turbine. The effects of turbulence intensity, mean wind speed, wind shear, vertical wind component, dynamic stall, stall hysteresis,

M. Noda; R. G. J. Flay

1999-01-01

187

History of Wind Shear Turbulence Models.  

National Technical Information Service (NTIS)

The Office of Flight Operations, Flight Technical Programs Div., at the FAA Headquarters, interfaces with industry, R&D communities and air carriers during the introduction of new types of equipment into operational services. A brief highlight of the need...

L. Cusimano

1987-01-01

188

Aircraft control in wake vortex wind shear  

NASA Technical Reports Server (NTRS)

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

Wold, Gregory R.

1995-01-01

189

Advanced technology wind shear prediction system evaluation  

NASA Technical Reports Server (NTRS)

The program overviews: (1) American Airline (AA)/Turbulence Prediction Systems (TPS), which have installed forward looking infrared predictive windshear system on 3 MD-80 aircraft; (2) AA/TPS AWAS III evaluation, which is a joint effort and is installed in the noise landing gear (NLG) area and a data recorder installed in the E/E compartment.

Gering, Greg

1992-01-01

190

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. We compute the difference between shear and reduced shear both analytically and with simulations. The difference becomes more important on smaller scales, and will impact cosmological parameter estimation from upcoming experiments. A simple recipe is presented to carry out the required correction.

Dodelson, Scott [NASA/Fermilab Astrophysics Center, Fermi National Accelerator Laboratory, Batavia, Illinois 60510-0500 (United States); Department of Astronomy and Astrophysics, The University of Chicago, Chicago, Illinois 60637-1433 (United States); Department of Physics and Astronomy, Northwestern University, Evanston, Illinois 60208 (United States); Shapiro, Charles [Department of Physics, The University of Chicago, Chicago, Illinois 60637-1433 (United States); Kavli Institute for Cosmological Physics, The University of Chicago, Chicago, Illinois 60637-1433 (United States); White, Martin [Department of Astronomy, University of California, Berkeley, California 94720 (United States); Department of Physics, University of California, Berkeley, California 94720 (United States)

2006-01-15

191

Directional shear force microscopy  

SciTech Connect

We describe a technique, based on shear force microscopy, that allows one to detect shear forces in a chosen direction at the nanometer scale. The lateral direction of an oscillating probe tip is determined by selecting which of the four quadrants are excited on the piezo driver. The shear forces depend directly on this lateral direction if structural anisotropies are present, as confirmed with polydiacetylene monolayers.

Burns, A. R.; Carpick, R. W.

2001-01-15

192

Shear Thinning in Xenon  

NASA Technical Reports Server (NTRS)

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

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

2009-01-01

193

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

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

194

The Effect of Vertical Shear on Tropical Cyclone Intensity Change  

Microsoft Academic Search

The effect of vertical shear on tropical cyclone intensity change is usually explained in terms of `ventilation' where heat and moisture at upper levels are advected away from the low-level circulation, which inhibits development. A simple two-layer diagnostic balance model is used to provide an alternate explanation of the effect of shear. When the upper-layer wind in the vortex environment

Mark Demaria

1996-01-01

195

WAVES AND SHEAR FLOWS  

Microsoft Academic Search

The exact analytical solution of the extended Rayleigh equation for the case of periodic compressible shear flow is found. The dispersion relation of the problem is the Hill determinant. It is found that the sound waves in shear flow have a dispersion and its velocity field contains a solenoidal part. Besides the sound waves, new wave modes, namely phonon, waveguide

Y. D. Zhugzhda

2003-01-01

196

Weakly nonlinear shear waves  

Microsoft Academic Search

Alongshore propagating low-frequency O(0:01 Hz) waves related to the direction and intensity of the alongshore current were rst observed in the surf zone by Oltman- Shay, Howd & Birkemeier (1989). Based on a linear stability analysis, Bowen & Holman (1989) demonstrated that a shear instability of the alongshore current gives rise to alongshore propagating shear (vorticity) waves. The fully nonlinear

F ALK F EDDERSEN

197

Perturbed free shear layers  

Microsoft Academic Search

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

C.-M. Ho; P. Huerre

1984-01-01

198

Role of magnetic shear in flow shear suppression  

SciTech Connect

The interplay between flow shear and magnetic shear is studied in the three-dimensional reduced magnetohydrodynamic turbulence. It is analytically shown that near the resonance surface, transport quenching by flow shear is weakened by magnetic shear as the latter interferes with shearing process. In particular, anomalous particle transport becomes more efficient in the regime with stronger magnetic shear for a given flow shear while self-regulation of zonal flows becomes less effective. The results suggest that weak magnetic shear could be favorable for the formation of transport barrier.

Kim, Eun-jin [Department of Applied Mathematics, University of Sheffield, Sheffield S3 7RH (United Kingdom)

2007-08-15

199

VisibleWind: wind profile measurements at low altitude  

NASA Astrophysics Data System (ADS)

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

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

2009-09-01

200

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

201

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

Microsoft Academic Search

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

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

2009-01-01

202

Angular shear plate  

DOEpatents

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

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

2009-07-14

203

Flicker contribution of a wind turbine in a stand-alone wind diesel system  

Microsoft Academic Search

To study the impact of aeroelastic aspects of a wind turbine (i.e. tower shadow, wind shear, turbulence, and mechanical vibrations) on the power quality of a wind-diesel system all electrical, mechanical and aerodynamic aspects of the wind turbine must be studied. Moreover, the contribution of the diesel-generator system and its controllers should be considered. This paper, describes how the aerodynamic

Roohollah Fadaeinedjad; Gerry Moschopoulos; Mehrdad Moallem

2008-01-01

204

Viscous shear dampers  

SciTech Connect

In a viscous shear damper, the seismic mass is chamfered at all its corners. Thus, the clearances between the seismic mass and its casing are gaps with oppositely widening out sections separated by middle sections of smallest widths.

Zilahi-Szabo, I.

1980-10-07

205

Rail shear test method  

NASA Technical Reports Server (NTRS)

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

Garcia, R.; Mcwithey, R. R.

1979-01-01

206

Shear-Sensitive Liquid Crystal Flow Visualization Technique Applied to a Supersonic Complex Flow  

Microsoft Academic Search

The ability of shear-sensitive liquid crystals to visualize flow separation, flow reattachment, shocks and vortices were demonstrated at the University of Kansas supersonic wind tunnel facilities. This technique was performed using unsealed shear-sensitive liquid crystals on cavity vortex generator models with two-dimensional convex surfaces. Models with different curvatures and cavity heights were tested at Mach 2.0. The shear-sensitive liquid crystal

Luis Yamamoto; Saeed Farokhi

2000-01-01

207

A semi-empirical approach for estimation of bed shear stress in a tailings pond  

Microsoft Academic Search

Wind-driven waves and currents exert shear stress on the bed of a tailings pond. A semi-empirical approach for estimating\\u000a this bed shear stress is presented in this paper. For the first time in a mine tailings storage facility, the current-induced\\u000a component of the bed shear stress was obtained using 1,200-kHz acoustic Doppler current profiler measurements of in situ currents\\u000a and

Laxmi Kant Kachhwal; Ernest K. Yanful; Colin D. Rennie

208

INITIAL DEVELOPMENT OF A MEMS WALL SHEAR STRESS SENSOR FOR PROPULSION APPLICATIONS  

Microsoft Academic Search

This paper describes preliminary research on the development of a MEMS based shear stress sensor for applications in the hypersonic aeropropulsion wind tunnels at the GASL Division of Allied Aerospace. Typically, when attempting to determine combustor performance (i.e. efficiency) using computer codes, assumptions are made with regards to the skin friction coefficient, required as an input. Obtaining direct shear stress

Mathew McCarthy; Luc G. Fréchette; Vijay Modi; Nicholas Tiliakos

209

Alternative Shear Panel Configurations for Light Wood Construction. Development, Seismic Performance, and Design Guidance  

Microsoft Academic Search

Shear panels are used in light wood construction to resist lateral loads resulting from earthquakes or strong winds. These panels are typically made of wooden sheathing nailed to building frame members, but this standard panel design interferes with the installation of sheet insulation. A non-insulated shear panel conducts heat between the building interior and exterior wasting considerable amounts of energy.

James Wilcoski; Chad Fischer; Tim Allison; Kelly Jo Malach

2002-01-01

210

Harnessing Wind  

NSDL National Science Digital Library

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

Integrated Teaching And Learning Program

211

The evaluation of shear sensitive liquid crystals at Mach 3  

Microsoft Academic Search

This paper examines the performance of a range of shear sensitive liquid crystals (manufactured by Hallcrest) in wind tunnel boundary layers upto Mach 3. The changes in observed color were assessed, using digital analysis of CCD video recordings, in terms of the hue, saturation and intensity. The measurement program included the assessment of crystal behavior under the following conditions: (i)

P. J. Disimile; N. Toy; E. Savory

1995-01-01

212

Disruption of a helmet streamer by photospheric shear  

Microsoft Academic Search

Helmet streamers on the Sun have been observed to be the site of coronal mass ejections, dynamic events that eject coronal plasma and magnetic fields into the solar wind. We develop a two-dimensional (azimuthally symmetric) helmet streamer configuration by computing solutions of the time-dependent magnetohydrodynamic (MHD) equations, and we investigate the evolution of the configuration when photospheric shearing motions are

Jon A. Linker; Zoran Mikic

1995-01-01

213

WAVE ACTION AND BOTTOM SHEAR STRESSES IN LAKE ERIE  

EPA Science Inventory

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

214

Jamming under shear  

NASA Astrophysics Data System (ADS)

We describe experiments in which we consider the jamming of 2D granular materials under shear. We consider experiments involving both pure and simple shear. The particles making up the material are either disks or ellipses, and in both cases, they are fabricated from a photoelastic material. It is then possible to obtain quantitative data for contact forces, and all other relevant grain-scale information. A key observation from these experiments is that initial states with densities below isotropic jamming can be jammed under applied shear in a range of packing fractions between ?min<=?<=?J, where ?J corresponds to the isotropic (zero shear stress) jamming point. We explore the behaviour of the above systems for ?'s in and near this regime. Specifically, we determine particle contacts and the mean contact number per particle, Z, the number of nearest neighbors, the shear and normal stresses, ? and P, and kinematic properties such as particle rotation and displacement. We find that the states of the system lie on a surface in a space consisting of ?, P, and ?. As time permits, we will explore the affine and non-affine motion of particles.

Zhang, Jie; Ren, Jie; Farhadi, Somayeh; Behringer, Robert

2010-03-01

215

Converging shear rheometer  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

216

Shear Stress and Atherosclerosis  

PubMed Central

Hemodynamic shear stress, the frictional force acting on vascular endothelial cells, is crucial for endothelial homeostasis under normal physiological conditions. When discussing blood flow effects on various forms of endothelial (dys)function, one considers two flow patterns: steady laminar flow and disturbed flow because endothelial cells respond differently to these flow types both in vivo and in vitro. Laminar flow which exerts steady laminar shear stress is atheroprotective while disturbed flow creates an atheroprone environment. Emerging evidence has provided new insights into the cellular mechanisms of flow-dependent regulation of vascular function that leads to cardiovascular events such as atherosclerosis, atherothrombosis, and myocardial infarction. In order to study effects of shear stress and different types of flow, various models have been used. In this review, we will summarize our current views on how disturbed flow-mediated signaling pathways are involved in the development of atherosclerosis.

Heo, Kyung-Sun; Fujiwara, Keigi; Abe, Jun-ichi

2014-01-01

217

Aeolian sand transport: a wind tunnel model  

NASA Astrophysics Data System (ADS)

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 profiles when sand movement occurs, especially at high wind velocity. Moreover, the effect of grain size on sand transport is open to argument. Detailed wind tunnel tests were carried out with respect to the threshold velocity, threshold shear velocity, and transport rate of differently sized, loose dry sand at different wind velocities to reformulate the transport model. The results suggest that the relationship between threshold shear velocity and grain size basically follow the Bagnold-type equation for the grain size d>0.1 mm. However, the threshold coefficient A in the equation is not constant as suggested by Bagnold, but decreases with the particle Reynolds number. The threshold velocity at the centerline height of the wind tunnel proved to be directly proportional to the square root of grain diameter. Attempts have been made to relate sand transport rate to both the wind velocity and shear velocity readapted to the blown sand movement. The reformulated transport model for loose dry sand follows the modified O'Brien-Rindlaub-type equation: Q= f1( d)(1- Ru) 2( ?/ g) V3, or the modified Bagnold-type equation: Q= f2( d)(1- Rt) 0.25( ?/ g) U*3. Where Q is the sand transport rate, the sand flux per unit time and per unit width, in kg m -1 s -1; ? is the air density, 1.25 kg m -3; g is the acceleration due to gravity, 9.81 m s -2; Ru= Vt/ V; Rt= U*t/ U*; V is the wind velocity at the centerline of the wind tunnel, in m s -1; Vt is the threshold velocity measured at the same height as V, in m s -1; U* is the shear velocity with saltating flux, in m s -1; U*t is threshold shear velocity, in m s -1; f1( d)=1/(475.24+93.62 d/ D); f2( d)=1.41+4.98exp(-0.5(ln( d/1.55 D)/0.57) 2); d is the grain diameter, in mm; and D is the reference grain diameter, equals 0.25 mm. The Bagnold's equation that asserts for a given wind drag the rate of movement of a fine sand is less than that of a coarse sand is not supported by the reformulated models.

Dong, Zhibao; Liu, Xiaoping; Wang, Hongtao; Wang, Xunming

2003-09-01

218

Measurements of wind friction speeds over lava surfaces and assessment of sediment transport  

NASA Technical Reports Server (NTRS)

Wind velocity profiles were obtained over alluvial plains, lava flows, and a cinder cone in the Mojave Desert to determine the wind shear and the potential for particle transport. It was found that aerodynamic roughness for winds increases nearly a factor of 5 as flow crosses from the alluvium to the lava surface, resulting in wind shear that is 21 percent greater. Thus, wind erosion and sand flux may be substantially enhanced over the lava field. Moreover, wind flow turbulence is enhanced in the wake of the cinder cone, which also increases erosion and sediment transportation by the wind.

Greeley, Ronald; Iversen, James D.

1987-01-01

219

Small scale wind perturbation analysis for vertically rising launch vehicles  

NASA Technical Reports Server (NTRS)

This paper discusses the determination of small-scale vertical wind spectra used with space flight and ballistic technology. In particular, Jimsphere, a precision balloon wind sensor with high radar reflectivity is considered. Gross wind velocity data is analyzed to subtract the steady-state wind and wind change-shear effects. A residue of small wind perturbations is left in the horizontal (scalar) along the vertical direction. An analysis leading to formulation of the covariance function with altitude is presented. The function is decoupled to yield an almost periodic representation of the vertical wind perturbations. Forcing functions are determined when the representation is coupled with the vehicle velocity characteristics.

Chenoweth, H. B.

1980-01-01

220

Sheared lherzolite xenoliths revisited  

Microsoft Academic Search

The microstructures of sheared lherzolite xenoliths from South African kimberlites are investigated using new microstructural analysis techniques and new rheological data. By applying electron backscatter diffraction (EBSD) methods and the M-index technique for quantifying the strength of lattice preferred orientation (LPO), it is demonstrated that olivine and orthopyroxene, after an initial stage of dynamic recrystallization, deformed by different mechanisms: olivine

Philip Skemer; Shun-ichiro Karato

2008-01-01

221

Dissipation in adiabatic shear bands  

SciTech Connect

In the present study of adiabatic shear banding in metals, the region of interest is modelled as a two-material two-temperature body. Specific material laws governing thermoviscous plasticity and heat transfer ate ascribed to the shear-band zone. Momentum and energy balance lead to a system of one-dimensional ordinary differential equations describing the dynamics of the shear localization process. The propagating shear band is viewed as having two distinct regions. The first is the shear-band tip process zone within which adiabatic heating, thermal softening and all shear dissipation are considered to occur. The second is the late-time quasi-steady zone in which the shear stress and dissipation rate are close to zero. The analysis provides the width and displacement of the shear band process zone. In addition, criteria for assessing material shear-banding resistance are investigated in terms of a shear-band dissipation rate, or a. shear-band toughness. Shear-band dissipation and shear-band toughness for a number of metals are calculated and compared.

Grady, D.E.

1992-01-01

222

Dissipation in adiabatic shear bands  

SciTech Connect

In the present study of adiabatic shear banding in metals, the region of interest is modelled as a two-material two-temperature body. Specific material laws governing thermoviscous plasticity and heat transfer ate ascribed to the shear-band zone. Momentum and energy balance lead to a system of one-dimensional ordinary differential equations describing the dynamics of the shear localization process. The propagating shear band is viewed as having two distinct regions. The first is the shear-band tip process zone within which adiabatic heating, thermal softening and all shear dissipation are considered to occur. The second is the late-time quasi-steady zone in which the shear stress and dissipation rate are close to zero. The analysis provides the width and displacement of the shear band process zone. In addition, criteria for assessing material shear-banding resistance are investigated in terms of a shear-band dissipation rate, or a. shear-band toughness. Shear-band dissipation and shear-band toughness for a number of metals are calculated and compared.

Grady, D.E.

1992-11-01

223

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

224

Interaction among Adiabatic Shear Bands,  

National Technical Information Service (NTIS)

The problem of interaction among shear bands in nonpolar materials is studied by analyzing the simple shearing problem for a block of isotropic, homogeneous, and thermoviscoplastic material. Inhomogeneities in the material are modeled by introducing a tem...

R. C. Batra C. H. Kim

1987-01-01

225

Shear banding in polymer solutions  

NASA Astrophysics Data System (ADS)

The current theoretical belief is that the steady-state shear banding in viscoelastic liquids requires a non-monotonic constitutive relationship between shear stress and shear rate. Although existing rheological studies conclude that the constitutive equation for entangled polymers is monotonic, recent experimental evidence suggests shear banding can nevertheless occur in polymer solutions. In this work, we predict, for the first time, steady state shear banding with a realistic monotonic constitutive theory for polymeric liquids. The key is that a proper account must be taken of the coupling of polymer stress to polymer concentration. We also predict multiple steady states at some shear rates as seen experimentally, with shear banding if the flow is ramped quickly enough from rest, but homogeneous linear shear flow otherwise.

Cromer, Michael; Villet, Michael C.; Fredrickson, Glenn H.; Leal, L. Gary

2013-05-01

226

Recent results from data analysis of dynamic stall on wind turbine blades  

Microsoft Academic Search

Wind turbines are subjected to dynamic loading from a variety of different sources. Wind shear and turbulence cause time-varying inflow that results in unsteady airloads. Tower shadow, upwind turbine wakes, and yaw angles also introduce unsteady inflow to wind turbine rotors. Wind turbine designers must predict these loads accurately in order to adequately design blades, hubs, and the remaining support

C. P. Butterfield; D. Simms; S. Huyer

1992-01-01

227

Fatigue loads on wind turbines of different control strategies operating in complex terrain  

Microsoft Academic Search

The impact of complex terrain wind conditions on the loading of wind turbines is examined using state-of-art computational means. The analysis is two folded. The first part considers variations of all the wind defining parameters: the turbulence intensities of the wind inflow, the corresponding length scales, the coherence decay factors, the vertical and lateral mean shears, the yaw misalignment and

Vasilis A. Riziotis; Spyros G. Voutsinas

2000-01-01

228

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

Microsoft Academic Search

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

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

2000-01-01

229

Large-eddy simulations of convective shear flows  

NASA Astrophysics Data System (ADS)

The structure of the instantaneous flow fields and turbulence statistics in oceanic convection affected by wind-induced shear are analysed using a large-eddy simulation (LES) data set. A modified subgrid-scale (SGS) model has been developed in order to overcome known deficiencies of the Smagorinsky SGS model in near-wall flows. The SGS model has been formulated as a second-order moment approach. Three distinct convective flows driven by surface cooling are generated. One is the convectively mixed layer with negligible surface shear corresponding to calm wind conditions. The other two are convectively mixed layers affected by enlarged wind-generated shear stresses corresponding to a wind speed of 7 and 14ms-1, respectively. The heat flux was held constant in order to provide equal thermal forcing. Surface gravity waves are excluded. Instantaneous flow fields reveal the ability of the mean shear to order temperature fluctuations into convective roll-like structures under severe wind conditions, whereas under calm to moderate wind conditions convective cells are formed. The ratio of friction velocity u* to Deardorff velocity w* controls the formation of either cell or roll structures. The well-known non-local effects due to turbulent and pressure transport of turbulent kinetic energy from the surface to the bulk of the convectively mixed layer are confirmed. The flows follow the " {1}/{2}" power law for the Nusselt-Rayleigh number relation (based on eddy viscosity and diffusivity) at high Rayleigh numbers. With increasing shear the heat flux decreases. Rotational effects clearly influence the flows despite the shallow mixed layer of only about 200 m depth. The unstable stratification significantly changes the volume transport of momentum compared to near-neutral stratified flows. Whereas for moderate wind conditions the transport is damped compared to the near-neutral case, the situation under strong wind conditions is completely different and volume transport of momentum is enhanced. As rotation as well as stratification tend to reduce the turbulent length scales, the role of the SGS model becomes more pronounced in the presence of rotation and/or stratification.

Heitmann, S.; Backhaus, J. O.

2005-05-01

230

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

Microsoft Academic Search

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

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

1998-01-01

231

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

232

Slicing Softly with Shear  

NASA Astrophysics Data System (ADS)

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.

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

2012-12-01

233

Shear-thinning Fluid  

NASA Technical Reports Server (NTRS)

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

2001-01-01

234

Observation of Shear-Induced Turbulence Using HARLIE  

NASA Technical Reports Server (NTRS)

Ground-based measurements of atmospheric aerosol structure were made using the Holographic Airborne Rotating Lidar Instrument Experiment (HARLIE) during the HOLO-1 field campaign. The scanning ability of HARLIE affords a unique opportunity to view various atmospheric phenomena. Shear-induced turbulence plays an important role in the transport of kinetic energy in the atmosphere and on March 10, 1999, several instances of shear-induced turbulence were observed via HARLIE. Using the data collected and upper-air wind profiles the nature of the instabilities is discussed.

Miller, David O.; Schwemmer, Geary K.; Wilkerson, Thomas D.; Sanders, Jason; Guerra, David; Moody, Steven

2000-01-01

235

Imaging Faults and Shear Zones Using Receiver Functions  

NASA Astrophysics Data System (ADS)

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

Schulte-Pelkum, Vera; Mahan, Kevin H.

2014-05-01

236

Micromechanics of shear banding  

SciTech Connect

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

Gilman, J.J.

1992-08-01

237

Modeling aeolian sediment transport thresholds on physically rough Martian surfaces: A shear stress partitioning approach  

NASA Astrophysics Data System (ADS)

This paper explores the effect that large roughness elements (0.30 m × 0.26 m × 0.36 m) may have on entrainment of sediment by Martian winds using a shear stress partitioning approach based on a model developed by Raupach et al. (Raupach, M.R., Gillette, D.A., Leys, J.F., 1993. The effect of roughness elements on wind erosion threshold. Journal of Geophysical Research 98(D2), 3023-3029). This model predicts the shear stress partitioning ratio defined as the percent reduction in shear stress on the intervening surface between the roughness elements as compared to the surface in the absence of those elements. This ratio is based on knowledge of the geometric properties of the roughness elements, the characteristic drag coefficients of the elements and the surface, and the assumed effect these elements have on the spatial distribution of the mean and maximum shear stresses. On Mars, unlike on Earth, the shear stress partitioning caused by roughness can be non-linear in that the drag coefficients for the surface as well as for the roughness itself show Reynolds number dependencies for the reported range of Martian wind speeds. The shear stress partitioning model of Raupach et al. is used to evaluate how conditions of the Martian atmosphere will affect the threshold shear stress ratio for Martian surfaces over a range of values of roughness density. Using, as an example, a 125 µm diameter particle with an estimated threshold shear stress on Mars of ? 0.06 N m - 2 (shear velocity, u* ? 2 m s - 1 on a smooth surface), we evaluate the effect of roughness density on the threshold shear stress ratio for this diameter particle. In general, on Mars higher regional shear stresses are required to initiate particle entrainment for surfaces that have the same physical roughness as defined by the roughness density term ( ?) compared with terrestrial surfaces mainly because of the low Martian atmospheric density.

Gillies, John A.; Nickling, William G.; King, James; Lancaster, Nicholas

2010-09-01

238

Application and improvement of Raupach's shear stress partitioning model  

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

239

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

240

Wind information display system user's manual  

NASA Technical Reports Server (NTRS)

The Wind Information Display System (WINDS) provides flexible control through system-user interaction for collecting wind shear data, processing this data in real time, displaying the processed data, storing raw data on magnetic tapes, and post-processing raw data. The data are received from two asynchronous laser Doppler velocimeters (LDV's) and include position, velocity and intensity information. The raw data is written onto magnetic tape for permanent storage and is also processed in real time to depict wind velocities in a given spacial region.

Roe, J.; Smith, G.

1977-01-01

241

Wild Wind  

NSDL National Science Digital Library

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

Integrated Teaching And Learning Program

242

Wind Whistlers  

NSDL National Science Digital Library

In this activity, learners make wind whistlers, or objects that interact with wind to make different noises. Learners make their whistlers out of a paper plate, yarn, and bells or buttons and then hang them from a tree. Learners listen to the sounds from the whistler interacting with the wind. The activity guide contains questions to explore while using the wind whistlers.

Houston, Children'S M.

2013-05-15

243

A sensitivity of squall-line intensity to environmental static stability under various shear and moisture conditions  

Microsoft Academic Search

Squall lines develop in various climate regions having diverse environmental profiles of wind shear, moisture, and temperature. In order to explore the sensitivity of squall lines to these environmental profiles, we have performed an extensive set of numerical simulations under various shear and moisture conditions in midlatitude-continental and tropical–oceanic temperature environments. From the results of the sensitivity simulations and the

Tetsuya Takemi

2007-01-01

244

SHEAR FAILURE AT A CRACK TIP UNDER SHEAR WAVE LOADING  

Microsoft Academic Search

Pressure-shear plate impact experiments are used to study dynamic failure at a crack tip subjected to shear wave loading. Plane, shear-wave loading of an effectively semi-infinite crack is obtained by the impact of a flyer plate and a pre-cracked target plate having a mid-plane, half-through, fatigue crack that is parallel to the impact face. The flyer and target plates are

Z. ZHANG; R. J. CLIFTON

245

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.

246

Shear fracture tests of concrete  

Microsoft Academic Search

Symmetrically notched beam specimens of concrete and mortar, loaded near the notches by concentrated forces that produce a\\u000a concentrated shear force zone, are tested to failure. The cracks do not propagate from the notches in the direction normal\\u000a to the maximum principal stress but in a direction in which shear stresses dominate. Thus, the failure is due essentially\\u000a to shear

Z. P. Bažant; P. A. Pfeiffer

1986-01-01

247

SHERA: SHEar Reconvolution Analysis  

NASA Astrophysics Data System (ADS)

Current and upcoming wide-field, ground-based, broad-band imaging surveys promise to address a wide range of outstanding problems in galaxy formation and cosmology. Several such uses of ground-based data, especially weak gravitational lensing, require highly precise measurements of galaxy image statistics with careful correction for the effects of the point-spread function (PSF). The SHERA (SHEar Reconvolution Analysis) software simulates ground-based imaging data with realistic galaxy morphologies and observing conditions, starting from space-based data (from COSMOS, the Cosmological Evolution Survey) and accounting for the effects of the space-based PSF. This code simulates ground-based data, optionally with a weak lensing shear applied, in a model-independent way using a general Fourier space formalism. The utility of this pipeline is that it allows for a precise, realistic assessment of systematic errors due to the method of data processing, for example in extracting weak lensing galaxy shape measurements or galaxy radial profiles, given user-supplied observational conditions and real galaxy morphologies. Moreover, the simulations allow for the empirical test of error estimates and determination of parameter degeneracies, via generation of many noise maps. The public release of this software, along with a large sample of cleaned COSMOS galaxy images (corrected for charge transfer inefficiency), should enable upcoming ground-based imaging surveys to achieve their potential in the areas of precision weak lensing analysis, galaxy profile measurement, and other applications involving detailed image analysis.

Mandelbaum, Rachel; Hirata, Christopher M.; Leauthaud, Alexie; Massey, Richard J.; Rhodes, Jason

2011-08-01

248

Hydrogen bonding in ethanol under shear  

NASA Astrophysics Data System (ADS)

We study the dependence of viscosity of ethanol on shear rate using constant volume and constant pressure nonequilibrium molecular dynamics simulations, with the emphasis of the interrelationship between breaking, stability, and alignment of hydrogen bonds and shear thinning at high shear rates. We find that although the majority of hydrogen bond breakings occur at low shear rates, we do not observe shear thinning until there is some shear-induced alignment of the hydrogen bonds with the direction of shear.

Petravic, Janka; Delhommelle, Jerome

2005-06-01

249

Magnetic and Velocity Shear Driven Instabilities in the Heliospheric Plasma  

NASA Astrophysics Data System (ADS)

We have addressed the problem of combined magnetic and velocity shear driven instabilities in the context of the heliospheric plasma. New high-order numerical methods have been used to analyze the instability dynamics of the heliospheric current-sheet interacting with the structure determined by the slow component of the solar wind on the solar equatorial plane above the helmet streamers. Preliminary results are presented.

Bettarini, L.; Landi, S.; Velli, M.; Londrillo, P.

2009-04-01

250

Shear Diversity Prevents Collective Synchronization  

NASA Astrophysics Data System (ADS)

Large ensembles of heterogeneous oscillators often exhibit collective synchronization as a result of mutual interactions. If the oscillators have distributed natural frequencies and common shear (or nonisochronicity), the transition from incoherence to collective synchronization is known to occur at large enough values of the coupling strength. However, here we demonstrate that shear diversity cannot be counterbalanced by diffusive coupling leading to synchronization. We present the first analytical results for the Kuramoto model with distributed shear and show that the onset of collective synchronization is impossible if the width of the shear distribution exceeds a precise threshold.

Montbrió, Ernest; Pazó, Diego

2011-06-01

251

True Shear Parallel Plate Viscometer  

NASA Technical Reports Server (NTRS)

This viscometer (which can also be used as a rheometer) is designed for use with liquids over a large temperature range. The device consists of horizontally disposed, similarly sized, parallel plates with a precisely known gap. The lower plate is driven laterally with a motor to apply shear to the liquid in the gap. The upper plate is freely suspended from a double-arm pendulum with a sufficiently long radius to reduce height variations during the swing to negligible levels. A sensitive load cell measures the shear force applied by the liquid to the upper plate. Viscosity is measured by taking the ratio of shear stress to shear rate.

Ethridge, Edwin; Kaukler, William

2010-01-01

252

Magnetic energy flow in the solar wind.  

NASA Technical Reports Server (NTRS)

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

Modisette, J. L.

1972-01-01

253

Study of woven fabric shear behaviour  

Microsoft Academic Search

The paper presents the shear frame test with a new method of gripping the fabric sample to describe the shear behaviour of fabrics used in the garment industry under high shear strain conditions (maximum shear angles of 20°). This shear frame test was also used to compare between hysteresis curves given by the Kawabata evaluation system (KES) test, the bias

B. El Abed; S. Msahli; H. Bel Hadj Salah; F. Sakli

2011-01-01

254

Wind Turbine  

USGS Multimedia Gallery

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

2009-10-19

255

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

256

Wind Power!  

NSDL National Science Digital Library

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

Integrated Teaching And Learning Program

257

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

NASA Technical Reports Server (NTRS)

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

2013-01-01

258

Dissipation in adiabatic shear bands.  

National Technical Information Service (NTIS)

In the present study of adiabatic shear banding in metals, the region of interest is modelled as a two-material two-temperature body. Specific material laws governing thermoviscous plasticity and heat transfer ate ascribed to the shear-band zone. Momentum...

D. E. Grady

1992-01-01

259

Shear strength of granular materials  

Microsoft Academic Search

The shear strength properties of granular materials reflecttheir inherent force and fabric anisotropy. We analyze the role of fabric and force an isotropies with respect to the critical-state shear strength. Then, a model of accessiblegeometrical states in terms of particle connectivity and contact anisotropy is presented. This mod el incorporates in a simple way the fact that, due to steric

Farhang Radjai; Emilien Azéma

2009-01-01

260

Shear strength of granular materials  

Microsoft Academic Search

The shear strength properties of granular materials reflect their inherent force and fabric anisotropy. We analyze the role of fabric and force anisotropies with respect to the critical-state shear strength. Then, a model of accessible geometrical states in terms of particle connectivity and contact anisotropy is presented. This model incorporates in a simple way the fact that, due to steric

Farhang Radjai; Emilien Azéma

2009-01-01

261

Shear Strength of Wood Beams  

Microsoft Academic Search

Experimental shear strength research conducted cooperatively with the USDA Forest Service, Forest Products Laboratory; Washington State University; and the Federal Highway Administration on solid-sawn beams is summarized in this paper. Douglas Fir, Engelmann Spruce, and Southern Pine specimens were tested in a green condition to determine shear strength in members without checks and splits. Sizes tested ranged from nominal 51

Douglas R. Rammer; David I. McLean

262

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

263

Wind Mills  

Microsoft Academic Search

\\u000a Over 5,000 years ago, the ancient Egyptians used wind to sail ships on the Nile River. While the proliferation of water mills\\u000a was in full swing, windmills appeared to harness more inanimate energy by employing wind sails. The wind wheel of Heron of\\u000a Alexandria marks one of the first known instances in history of wind powering a machine [1]. The

J. S. Rao

264

Properties of Magnetic Reconnection as a function of magnetic shear  

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

265

Shear Instabilities as a Probe of Jupiter's Atmosphere  

NASA Technical Reports Server (NTRS)

Linear wave patterns in Jupiter clouds with wavelengths strongly clustered around 300 km are commonly observed in the planet's equatorial atmosphere. We propose that the preferred wavelength is related to the thickness of an unstable shear layer within the clouds. We numerically analyze the linear stability of wavelike disturbances that have nonzero horizontal phase speeds in Jupiter's atmosphere and find that. if the static stability in the strongly clustered around 300 km are commonly observed in the planet's equatorial atmosphere. We propose that the preferred wavelength is related to the thickness of an unstable shear layer within the clouds. We numerically analyze the linear stability of wavelike disturbances that have nonzero horizontal phase speeds in Jupiter's atmosphere and find that. if the static stability in the shear layer is very low (but still nonnegative), a deep vertical shear layer like the one measured by the Galileo probe can generate the instabilities. The fastest growing waves grow exponentially within an hour, and their wavelengths match the observations. Close to zero values of static stability that permit the growth of instabilities are within the range of values measured by the Galileo probe in a hot spot. Our model probes Jupiter's equatorial atmosphere below the cloud deck and suggests that thick regions of wind shear and low static stability exist outside hot spots.

Bosak, Tanja; Ingersoll, Andrew P.

2002-01-01

266

Wind turbine  

Microsoft Academic Search

A wind turbine to convert wind energy into hydraulic energy by a positive displacement hydraulic pump driven by a wind mill. To the oil outlet of the hydraulic pump, a thermo-sensitive control element is attached, which functions when the oil temperature exceeds a certain limit. By the control element, the oil outlet is closed, suppressed, or opened to ensure safety

Kita

1983-01-01

267

Wind Whispers  

NSDL National Science Digital Library

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

2011-03-09

268

Toasty Wind  

NSDL National Science Digital Library

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

Service, National W.

2012-07-24

269

Viscous shear banding in foam  

NASA Astrophysics Data System (ADS)

Shear banding is an important feature of flow in complex fluids. Essentially, shear bands refer to the coexistence of flowing and nonflowing regions in driven material. Understanding the possible sources of shear banding has important implications for a wide range of flow applications. In this regard, quasi-two-dimensional flow offers a unique opportunity to study competing factors that result in shear bands. One proposal for interpretation and analysis is the competition between intrinsic dissipation and an external source of dissipation. In this paper, we report on the experimental observation of the transition between different classes of shear bands that have been predicted to exist in cylindrical geometry as the result of this competition [R. J. Clancy, E. Janiaud, D. Weaire, and S. Hutzlet, Eur. J. Phys. E 21, 123 (2006)].

Krishan, Kapilanjan; Dennin, Michael

2008-11-01

270

Shear deflection of anisotropic plate  

NASA Astrophysics Data System (ADS)

In the thin plate theory, shear deformation is neglected. This theory is unreliable for plates of considerable thickness in the vicinity of the point of application of load, and sandwich plates with shear rigidity which is very low compared with bending rigidity. A widely accepted theory which includes the effects of shear deformation was developed by Reissner and Mindlin. In recent years, composite materials have been widely employed as structure elements. Plates of composite material are characterized by strong anisotropy and low out-of-plane shear rigidity. This paper provides a convenient representation for the stiffness matrix of the finite element in order to analyze a sandwich plate with an anisotropic face plate and core. The formulation is based on the nonconforming element of Zienkiewicz (1977) and is obtained with a modified stiffness matrix in the condition in which the out-of-plane shear strain is constant in two directions within an element.

Katori, Hiroaki; Nishimura, Tohru

1992-01-01

271

Internal-gravity wave structures in the ionosphere with shear flow  

NASA Astrophysics Data System (ADS)

A study is made of the generation and further evolution of internal-gravity wave (IGW) structures in the dissipative ionosphere in the presence of a nonuniform zonal wind (a sheared flow). The efficiency of the linear amplification of IGW structures in their interaction with a nonuniform zonal wind is analyzed. When there are sheared flows, the operators of linear problems are non-self-conjugate and the corresponding eigenfunctions are nonorthogonal, so the canonical modal approach is poorly suited for studying such motions and it is necessary to utilize the so-called nonmodal mathematical analysis. It is shown that, in the linear evolutionary stage, IGW efficiently extract energy from the sheared flow, thereby substantially increasing their amplitude and, accordingly, energy (by several orders). As the shear instability develops and the perturbation amplitude grows, a nonlinear self-localization mechanism comes into play and the process ends with the self-organization of nonlinear, highly localized, solitary IG vortex structures. The system thus acquires a new degree of freedom, thereby providing a new way for the perturbation to evolve in a medium with a sheared flow. Depending on the shape of the sheared flow velocity profile, nonlinear structures can be either purely monopole vortices or vortex streets against the background of the zonal wind. The accumulation of such vortices can lead to a strongly turbulent state in an ionospheric medium.

Chargazia, Khatuna; Kharshiladze, Oleg; Aburjania, George

2014-05-01

272

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

273

Shear-Sensitive Liquid Crystal Flow Visualization Technique Applied to a Supersonic Complex Flow  

NASA Astrophysics Data System (ADS)

The ability of shear-sensitive liquid crystals to visualize flow separation, flow reattachment, shocks and vortices were demonstrated at the University of Kansas supersonic wind tunnel facilities. This technique was performed using unsealed shear-sensitive liquid crystals on cavity vortex generator models with two-dimensional convex surfaces. Models with different curvatures and cavity heights were tested at Mach 2.0. The shear-sensitive liquid crystal coating was used to visualize the characteristics of the flow adjacent to the model surface. This flow visualization technique confirmed the ability of the liquid crystal in identifying flow separation, shocks and vortices in supersonic flow.

Yamamoto, Luis; Farokhi, Saeed

2000-11-01

274

Combined effects of deterministic and random loads in wind turbine design  

Microsoft Academic Search

Deficiencies of modeling the deterministic loading on wind turbine blades as a cumulative sum of wind shear, mean wind, tower shadow, gravitational, and centrifugal forces are examined. It is analytically shown by application of the Palmgren-Miner rule that periodic loadings which coincide in cycle result in damage exceeding the sum of the individual stresses. The necessity of calculating the probability

A. Raab

1980-01-01

275

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

Microsoft Academic Search

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

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

1996-01-01

276

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

277

Panel resonant behavior of wind turbine blades  

Microsoft Academic Search

The principal design drivers in the certification of wind turbine blades are ultimate strength, fatigue resistance, adequate tip-tower clearance, and buckling resistance. Buckling resistance is typically strongly correlated to both ultimate strength and fatigue resistance. A composite shell with spar caps forms the airfoil shape of a blade and reinforcing shear webs are placed inside the blade to stiffen the

Joshua A. Paquette; Daniel Todd Griffith

2010-01-01

278

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

279

Shear instabilities in granular flows.  

PubMed

Unstable waves have been long studied in fluid shear layers. These waves affect transport in the atmosphere and oceans, in addition to slipstream stability behind ships, aeroplanes and heat-transfer devices. Corresponding instabilities in granular flows have not been previously documented, despite the importance of these flows in geophysical and industrial systems. Here we report that breaking waves can form at the interface between two streams of identical grains flowing on an inclined plane downstream of a splitter plate. Changes in either the shear rate or the angle of incline cause such waves to appear abruptly. We analyse a granular flow model that agrees qualitatively with our experimental data; the model suggests that the waves result from competition between shear and extensional strains in the flowing granular bed. We propose a dimensionless shear number that governs the transition between steady and wavy flows. PMID:11797003

Goldfarb, David J; Glasser, Benjamin J; Shinbrot, Troy

2002-01-17

280

Shear transmission in magnetic fluids  

Microsoft Academic Search

The decay length of shear diffusion in magnetic fluids is calculated for various field configurations. This provides information on the rotational friction coefficient ?r, and the magnetic relaxation time ?. A simple experimental set-up is proposed.

Katja Henjes

1995-01-01

281

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

282

Shear cutting of PET film  

Microsoft Academic Search

Poly (ethylene terephthalate) (PET) film was extruded and then successively biaxially stretched and thermofixed to obtain\\u000a a high-strength film with stable dimensions. Next, the film was shear cut by two rotating circular knives. In the first part\\u000a of this paper, a microscopic evaluation of the sheared edges of films, cut under a variety of parameters, i.e. cutting speed,\\u000a film thickness

D. Bollen; J. Deneir; E. Aernoudt; W. Muylle

1989-01-01

283

Shear at the surface of a lake in light winds  

Microsoft Academic Search

Standard computer cards released at 1-min intervals from the same point beneath a hydrometerological tower were observed to segregate by color according to their depth of integration of the current. Green cards floated flat at the lake surface. Orange cards, on the other hand, curved downward when placed on the lake surface and averaged the currents in the top 1

Bernard C. Kenney

1991-01-01

284

Signal processing techniques for clutter filtering and wind shear detection  

NASA Technical Reports Server (NTRS)

An extended Prony algorithm applicable to signal processing techniques for clutter filtering and windshear detection is discussed. The algorithm is based upon modelling the radar return as a time series, and appears to offer potential for improving hazard factor estimates in the presence of strong clutter returns.

Baxa, Ernest G., Jr.; Deshpande, Manohar D

1991-01-01

285

Wind Shear Systems Integration Plan, VICON (VIsual CONfirmation) Reliability Analysis.  

National Technical Information Service (NTIS)

This study supports the system reliability area of the VICON Operational Evaluation Program. VICON is the FAA's VIsual CONfirmation system which visually confirms that an aircraft awaiting takeoff has been verbally cleared for takeoff by the airport contr...

C. W. Hamby J. R. DeMattio

1980-01-01

286

Shear shocks in fragile networks  

PubMed Central

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

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

2013-01-01

287

Wind turbine  

SciTech Connect

The improvement in a wind turbine comprises providing a tower with a freely liftable mount and adapting a nacelle which is fitted with a propeller windwheel consisting of a plurality of rotor blades and provided therein with means for conversion of wind energy to be shifted onto said mount attached to the tower. In case of a violent wind storm, the nacelle can be lowered down to the ground to protect the rotor blades from breakage due to the force of the wind. Required maintenance and inspection of the nacelle and replacement of rotor blades can be safely carried out on the ground.

Abe, M.

1982-01-19

288

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

289

Structure of Highly Sheared Tropical Storm Chantal during CAMEX-4  

NASA Technical Reports Server (NTRS)

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

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

2006-01-01

290

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

291

GPU-based shear-shear correlation calculation  

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

292

Modeling shear flow and postsunset stability in the equatorial F region ionosphere  

NASA Astrophysics Data System (ADS)

Sounding rocket and Altair radar data taken during the NASA EQUIS-II campaign on Kwajalein in August, 2004, are incorporated into a computational model of the electrodynamics of the low-latitude ionosphere. The purpose is to understand and quantify sources of the strong shear flow observed in the bottomside F region around and after sunset and to assess its influence on postsunset stability and the production of equatorial spread F. Possible sources of shear include 1) zonal electric fields on flux tubes with significant Hall conductivity, as are responsible for driving the equatorial electrojet, 2) zonal winds on flux tubes with significant Pedersen conductivity, as drive the E and F region dynamos, 3) vertical winds, a largely unknown quantity, and 4) vertical boundary currents forced from above or below the flux tube in question. The model solves for the electrostatic potential in three dimensions as a function of the background conductivity, background electric field, and the winds. We do not assume equipotential field lines but instead solve for the potential exactly using a multigridded solver. Shear flow may destabilize the postsunset ionosphere through a collisional shear instability related to electrostatic Kelvin Helmholtz [ Hysell and Kudeki, 2004]. Assessing the viability of the instability requires us to identify and rank in importance the sources of the shear.

Hysell, D.; Larsen, M.; Swenson, C.; Wheeler, T.

2005-12-01

293

Simultaneous determination of shear strength and shear modulus in glued-laminated timber using a full-scale shear block specimen  

Microsoft Academic Search

A newly developed full-scale shear block specimen was used to simultaneously determine the shear strength and shear modulus\\u000a of glued-laminated timber. The shear modulus was calculated using the shear strain distribution measured by means of digital\\u000a image correlation. To obtain the exact relationship between shear modulus and shear strength, the shear strain in the intended\\u000a shear plane was measured. A

Seiichiro Ukyo; Hirofumi Ido; Hirofumi Nagao; Hideo Kato

2010-01-01

294

Statistical and structural investigations in homogeneous shear flows  

NASA Astrophysics Data System (ADS)

A statistically stationary and nearly homogeneous turbulent shear flow is established by an additional volume forcing in combination with stress-free boundary conditions in the shear direction. Both turbulent energy and enstrophy are stationary to a much better approximation than in previous simulations that use remeshing (R. S. Rogallo, NASA Tech. Mem. 81835 (1981)). Energy spectra and shear-stress cospectra show that local isotropy is satisfactorily obeyed at the level of second-order moments. However, derivative moments of high-order up to n=7 yield increasing moments for n>3 for the spanwise vorticity and the transverse derivative of the streamwise velocity in a range of Taylor Reynolds numbers between 60 and 100 (J. Schumacher, J. Fluid Mech., vol. 441, 109 (2001)). First results on passive scalar fields with constant mean gradient in the homogeneous shear flow are presented and compared with temperature measurements in a wind tunnel (K. R. Sreenivasan and S. Tavoularis, J. Fluid Mech., vol. 101, 783 (1981)). Coherent structures of the scalar field are identified that are related to its persistent derivative skewness. J.S. wishes to thank the Alexander von Humboldt-Foundation and Yale University for financial support of this work.

Schumacher, Joerg; Sreenivasan, Katepalli R.

2001-11-01

295

Shear flow effects at the onset of equatorial spread F  

NASA Astrophysics Data System (ADS)

Experiments were conducted during the NASA EQUIS II sounding rocket campaign on Kwajalein Atoll to elucidate the electrodynamics and layer structure of the postsunset equatorial F region ionosphere prior to the onset of equatorial spread F (ESF). Experiments took place on August 7 and 15, 2004, each comprised of the launch of an instrumented and two chemical release sounding rockets. The instrumented rockets measured plasma number density, vector electric fields, and other parameters to an apogee of about 450 km. The chemical release rockets yielded lower thermospheric wind profile measurements. The Altair radar was used to monitor coherent and incoherent scatter in UHF and VHF bands. Strong plasma shear flow was evident in both experiments. Bottom-type scattering layers were observed below the shear nodes in westward-drifting plasma strata. The layers were often patchy and distributed periodically in space. We attribute the patchiness to large-scale waves which modulate the layers. The large-scale waves may also serve as seed irregularities for ESF. A three-dimensional electrodynamic model is constructed that can reproduce the observed shear flow. Based on the model, we calculate the linear growth rate for the collisional shear instability and show that it can compete with the generalized Rayleigh Taylor instability. A scenario where the former generates the large-scale waves and initiates the latter is discussed.

Hysell, D.; Larsen, M.; Swenson, C.; Barjatya, A.; Wheeler, T.

2006-05-01

296

Asymptotic Sensitivity of Homogeneous Turbulent Shear Flow to the  

NASA Astrophysics Data System (ADS)

Our recent numerical studies of homogeneous turbulent shear flow suggest the dynamics of the large and small scales are sensitive to the initial value of the shear parameter. In particular for initial values of S^* = S k /?>=10, we find that the asymptotic state of the turbulence depends upon this parameter. Rapid distortion theory (RDT) predicts the dependence of both large- and small-scale statistics on S^* reasonably well, but the theory is applicable only for relatively short times (S t < 2). Direct numerical simulation (DNS) has a somewhat longer window, but it too eventually fails when the integral length scale becomes too large. Motivated by this earlier work, we performed experimental measurements of large- and small-scale velocity statistics in homogeneous turbulent shear flow in a wind tunnel. We are able to vary the initial shear parameter over the relevant range and observe the aforementioned asymptotic statistics. The experimental results will be presented, including detailed comparisons with earlier DNS and RDT.

Isaza, Juan; Warhaft, Zellman; Collins, Lance

2007-11-01

297

Wind mills  

Microsoft Academic Search

A wind mill construction is disclosed, including a rigid tower structure to the upper end of which is connected for rotation about a vertical axis a wind turbine housing to which is journalled for rotation about a horizontal axis a propeller of the two-blade on three-blade type, characterized in that a strip member extends generally helically about the tower structure

Ottosen

1979-01-01

298

Wind Engineering  

NASA Technical Reports Server (NTRS)

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

1983-01-01

299

Quantitative visualization of compressible turbulent shear flows using condensate-enhanced Rayleigh scattering  

Microsoft Academic Search

This paper describes several flow visualization experiments carried out in Mach 3 and Mach 8 turbulent shear flows. The experimental technique was based on laser scattering from particles of H 2O or CO 2 condensate that form in the wind tunnel nozzle expansion process. The condensate particles vaporize extremely rapidly on entering the relatively hot fluid within a turbulent structure, so that

J. Poggie; P. J. Erbland; A. J. Smits; R. B. Miles

2004-01-01

300

Yield shear stress and disaggregating shear stress of human blood  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

301

Calculation of turbulent shear stress in supersonic boundary layer flows  

NASA Technical Reports Server (NTRS)

An analysis of turbulent boundary layer flow characteristics and the computational procedure used are discussed. The integrated mass and momentum flux profiles and differentials of the integral quantities are used in the computations so that local evaluation of the streamwise velocity gradient is not necessary. The computed results are compared with measured shear stress data obtained by using hot wire anemometer and laser velocimeter techniques. The flow measurements were made upstream and downstream of an adiabatic unseparated interaction of an oblique shock wave with the turbulent boundary layer on the flat wall of a two dimensional wind tunnel. A comparison of the numerical analysis and actual measurements is made and the effects of small differences in mean flow profiles on the computed shear stress distributions are discussed.

Sun, C. C.; Childs, M. E.

1974-01-01

302

Evolution of a barotropic shear layer into elliptical vortices.  

PubMed

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

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

2013-01-01

303

Wind field variability in high-resolution simulations for wind energy forecasts and resource assessment  

NASA Astrophysics Data System (ADS)

Wind farm resource assessment, operational wind power forecasting, and wind turbine micrositing may benefit from high-resolution simulations of atmospheric flow over complex terrain. Domains can be refined from mesoscale to finer scales using grid nesting to adequately resolve turbulence and terrain in the atmospheric boundary layer. In previous work, we showed that nesting down to fine resolutions (~100 m horizontal spacing) using the WRF model does not clearly improve mean wind forecasts for our case study wind farm when modeling either synoptically or locally driven events. Differences due to increased vertical resolution or using one- vs. two-way nesting were also minimal. The LES models we tested gave similar results and were only slightly closer to the observations than the RANS models. For this particular domain, it appears that key topographic features are well resolved even at coarser resolutions, so that there is minimal change in mean winds at finer resolutions. In this work, we investigate temporal and spatial variability of predicted fields to gain further insight into possible differences due to changes in grid configuration. We also perform week-long simulations at fine resolutions of 300 or 100 meters to determine if we can obtain more detailed results for wind energy resource assessment. High-resolution representation of the spatial structure of the wind flow might be able to better capture variations in wind velocity that are relevant to wind resource assessment. Improved turbulence closure schemes will also be tested and should be able to better capture the fluctuations in the wind fields which may contribute to turbine fatigue. Long term, fine resolution runs should provide more insight into wind patterns and yield frequency distributions of wind speed, wind shear, TKE, and other factors that are invaluable to wind farm operators in determining appropriate sites for turbines and times for greatest power output.

Marjanovic, N.; Chow, F. K.; Wharton, S.; Lundquist, J. K.

2010-12-01

304

Superstrings in Sheared Polymer Blends  

NASA Astrophysics Data System (ADS)

We report the discovery of a droplet-string-ribbon transition in concentrated polymer blends which occurs when the droplet size of the dispersed component becomes comparable to the gap between the boundary plates. Above a critical shear rate (or gap width), dispersed droplets continuously coalescence and breakup; the upper limit on their size is set by the Taylor length. Below this critical shear rate, droplets coalesce into strings and then ribbons in a four stage kinetic process. The mass ratio of string / droplet can be as large as 10^4. The transition is sharp, occurring over a shear interval of 2droplet-string transition is a manifestation of the weakening of the Rayleigh-Tomatika instability which occurs when the system becomes quasi two-dimensional. Possible applications of this technology are ultra-thin materials of high one-dimensional strength, polymer blend wires, and novel polymeric scaffolds.

Migler, Kalman

2000-03-01

305

High shear rate characterization of magnetorheological fluids  

NASA Astrophysics Data System (ADS)

Shear mode or rotary drum-type magnetorheological energy absorbers (MREAS) are an attractive option for use in occupant or payload protection systems that operate at shear rates well over 25,000 s-1. However, their design is still performed using material properties measured using low-shear rate (<1,000 s-1) characterization techniques. This paper details a method for characterizing MR fluids at high shear rates, and presents characterization results for three commercially available MR fluids. It is proposed to utilize the perspective of apparent viscosity (the ratio of shear stress over shear rate) vs. shear rate to describe the behavior of the fluid at these shear rates. Good agreement between the measured data and predictions of MR fluid behavior are achieved using this framework. By expanding the knowledge of MR fluid behavior to these high shear strain rates, the design of MREAs is enabled for occupant protection systems for crash and mine blast events.

Becnel, Andrew C.; Hu, Wei; Wereley, Norman M.

2012-03-01

306

Quantitative calculation of local shear deformation in adiabatic shear band for Ti6Al4V  

Microsoft Academic Search

JOHNSON-COOK(J-C) model was used to calculate flow shear stress—shear strain curve for Ti-6Al-4V in dynamic torsion test. The predicted curve was compared with experimental result. Gradient-dependent plasticity(GDP) was introduced into J-C model and GDP was involved in the measured flow shear stress—shear strain curve, respectively, to calculate the distribution of local total shear deformation(LTSD) in adiabatic shear band(ASB). The predicted

Xue-bin WANG

2007-01-01

307

Characterization of the Fine Dust Particle Production Process by Wind Erosion for Two Types of Bare Soil Surfaces  

Microsoft Academic Search

Wind erosion is a serious problem in many parts of the world for people and environment. This phenomenon is a physical process caused by erosive winds on various types of soil surface and the result of interaction between several conditions. Wind shear stress and soil surface characteristics are the main factors controlling dust emission. Fine airborne particles emitted into the

M. Sabre; M. V. López; S. C. Alfaro; J. L. Rajot; L. Gomes

308

Quadraphonic Wind  

NSDL National Science Digital Library

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

Service, National W.

2012-12-18

309

Stellar Winds  

NASA Astrophysics Data System (ADS)

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

Owocki, Stan

310

Identification of Shear Band using Elastic Shear Wave Propagation  

Microsoft Academic Search

Localization in soil under high stress level is usually investigated using some indirect measures, e.g., X-ray diffraction method. In the present study, the propagation velocity of shear wave was used to detect localization in sandy soil. Firstly, the general expression to exhibit the stress and density dependencies characteristics under consolidation and triaxial testing conditions of the tested soil was proposed.

T. Nachiengtai; W. Chim-Oye; S. Teachavorasinskun; W. Sa-Ngiamvibool

311

Effects of Upper-Level Shear on the Structure and Maintenance of Strong Quasi-Linear Mesoscale Convective Systems.  

NASA Astrophysics Data System (ADS)

Recent observational studies have shown that strong midlatitude mesoscale convective systems (MCSs) tend to decay as they move into environments with less instability and smaller deep-layer vertical wind shear. These observed shear profiles that contain significant upper-level shear are often different from the shear profiles considered to be the most favorable for the maintenance of strong, long-lived convective systems in some past idealized simulations. Thus, to explore the role of upper-level shear in strong MCS environments, a set of two-dimensional (2D) simulations of density currents within a dry, statically neutral environment is used to quantify the dependence of lifting along an idealized cold pool on the upper-level shear. A set of three-dimensional (3D) simulations of MCSs is produced to gauge the effects of the upper-level shear in a more realistic framework.Results from the 2D experiments show that the addition of upper-level shear to a wind profile with weak to moderate low-level shear increases the vertical displacement of parcels despite a decrease in the vertical velocity along the cold pool interface. Parcels that are elevated above the surface (1 2 km) overturn and are responsible for the deep lifting in the deep-shear environments, while the surface-based parcels typically are lifted through the cold pool region in a rearward-sloping path. This deep overturning helps to maintain the leading convection and greatly increases the size and total precipitation output of the convective systems in more complex 3D simulations, even in the presence of 3D structures. These results show that the shear profile throughout the entire troposphere must be considered to gain a more complete understanding of the structure and maintenance of strong midlatitude MCSs.


Coniglio, Michael C.; Stensrud, David J.; Wicker, Louis J.

2006-04-01

312

Wind profile estimation from point to point laser distortion data  

NASA Technical Reports Server (NTRS)

The author's results on the problem of using laser distortion data to estimate the wind profile along the path of the beam are presented. A new model for the dynamics of the index of refraction in a non-constant wind is developed. The model agrees qualitatively with theoretical predictions for the index of refraction statistics in linear wind shear, and is approximated by the predictions of Taylor's hypothesis in constant wind. A framework for a potential in-flight experiment is presented, and the estimation problem is discussed in a maximum likelihood context.

Leland, Robert

1989-01-01

313

The Role of Environmental Shear and Thermodynamic Conditions in Determining the Structure and Evolution of Mesoscale Convective Systems during TOGA COARE.  

NASA Astrophysics Data System (ADS)

A collection of case studies is used to elucidate the influence of environmental soundings on the structure and evolution of the convection in the mesoscale convective systems sampled by the turboprop aircraft in the Tropical Ocean Global Atmosphere (TOGA) Coupled Ocean-Atmosphere Response Experiment (COARE). The soundings were constructed primarily from aircraft data below 5-6 km and primarily from radiosonde data at higher altitudes.The well-documented role of the vertical shear of the horizontal wind in determining the mesoscale structure of tropical convection is confirmed and extended. As noted by earlier investigators, nearly all convective bands occurring in environments with appreciable shear below a low-level wind maximum are oriented nearly normal to the shear beneath the wind maximum and propagate in the direction of the low-level shear at a speed close to the wind maximum; when there is appreciable shear at middle levels (800-400 mb), convective bands form parallel to the shear. With appreciable shear at both levels, the lower-level shear determines the orientation of the primary convective bands. If the midlevel shear is opposite the low-level shear, secondary bands parallel to the midlevel shear will extend rearward from the primary band in later stages of its evolution; if the midlevel shear is 90 degrees to the low-level shear, the primary band will retain its two-dimensional mesoscale structure. Convection has no obvious mesoscale organization on days with little shear or days with widespread convection.Environmental temperatures and humidities have no obvious effect on the mesoscale convective pattern, but they affect COARE convection in other ways. The high tops of COARE convection are related to high parcel equilibrium levels, which approach 100 mb in some cases. Convective available potential energies are larger than those in the GARP (Global Atmospheric Research Program) Atlantic Tropical Experiment (GATE) mainly because of the higher equilibrium levels. The buoyancy integrated over the lowest 500 mb is similar for the two experiments. Convective inihibitions are small, enabling convection to propagate with only weak forcing. Comparison of slow-moving shear-parallel bands in COARE and GATE suggests that lower relative humidities between the top of the mixed layer and 500 mb can shorten their lifetimes significantly.COARE mesoscale organization and evolution differs from what was observed in GATE. Less-organized convection is more common in COARE. Of the convective bands observed, a greater fraction in COARE are faster-moving, shear-perpendicular squall lines. GATE slow-moving lines tend to be longer lived than those for COARE. The differences are probably traceable to differences in environmental shear and relative humidity, respectively.

Lemone, Margaret A.; Zipser, Edward J.; Trier, Stanley B.

1998-12-01

314

Shear mixing in classical Novae  

NASA Astrophysics Data System (ADS)

The mixing of white dwarf material with the accretion envelope in classical novae scenarios is essential for the later evolution and the outburst. One of the plausible mechanisms for the enrichment involves the coupling of large scale flows like convection or accretion with the breaking interfacial waves at the white dwarf surface. We examine how the interaction of accretion wind with a white dwarf surface can lead to a substantial C/O enrichment that can power a novae. We use the FLASH code to perform two and three dimensional simulations of wind driven gravity waves and investigate their growth and non-linear development for a variety of wind profiles. Our results show that even weak winds generate gravity waves through a resonant mechanism with the wind that grow nonlinear and break leading to spray formation and mixing. The total amount of white dwarf material mixed at late times, is shown to be proportional to the square of the maximum wind velocity, inversely proportional to gravity and independent of the functional form of the wind profile. This work has been supported by the DOE ASCI/Alliances program at the University of Chicago under grant No. B341495.

Alexakis, A.; Calder, A. C.; Dursi, L. J.; Times, F. X.; Truran, J. W.; Rosner, R.; Lamb, D. M.; Mignone, A.; Fryxel, B.; Zingale, M.; Olson, K.; Ricker, P.

2003-03-01

315

Stochastic Analysis of Wind Data  

NASA Astrophysics Data System (ADS)

Autoregressive Moving Average models are used to investigate wind speed and longitudinal component wind speed data. Field data obtained at Texas Tech University's Wind Engineering Research Field Laboratory is used for this investigation. Autoregressive models of order 3, AR(3) models, are shown to adequately describe the 15-minute records collected at the field site. ARMA models provide insight into mechanically generated turbulence observed in the wind field not easily seen in the frequency domain. The AR(3) model parameters exhibit a constant linear correlation. Thus a single model parameter can be used to specify the model. This implies that the mechanically generated turbulence in the wind is a constant process. The underlying processes generating stationary and nonstationary wind records is investigated using the AR(3) models. As used here, the 15-minute records are classified as stationary or nonstationary based on the nonparametric run and reverse arrangements tests. Statistical testing indicates there is not a significant difference between the stationary records and the nonstationary records. The AR(3) model parameters and the white noise variance are shown to be linearly related to roughness length, shear velocity, and height above ground. Thus an AR(3) model is established from physical parameters. This allows extension of these results to other terrains. Using the log law to describe the mean flow in conjunction with the AR(3) model to describe the turbulence provides an simple way to simulate time domain wind data. Simulations using this combination of models are shown to adequately describe field data and to match the spectral results published in the literature. The procedures and results presented in this dissertation are useful to wind tunnel modelers, computational wind engineers and structural analysts solving nonlinear structural dynamics problems. Wind tunnel modelers can use the AR(3) models to verify that their approach flow matches the field conditions. These models may be useful to numerical modelers as an input boundary conditions or to verify the accuracy of their numerical models. The structural analysts can easily generate simulations of wind time histories using these procedures which can then be combined with drag coefficients to generate loads for their structures.

Smith, Douglas Alexander

316

Ring Pattern Formation in 2-d Shear of Freely Suspended Films of a Smectic C Liquid Crystal  

Microsoft Academic Search

Space-time diagrams are used to analyze the dynamics of the liquid-crystal smectic C director in two-dimensional shear. We find a steady-state ring pattern only persists if there are no broken rings. A pair of defects, disclinations, is created when a ring breaks. With broken rings, the pattern dynamics is a sensitive balance between phase winding by shearing and unwinding by

I. Mutabazi; P. L. Finn; J. T. Gleeson; J. W. Goodby; C. D. Andereck; P. E. Cladis

1992-01-01

317

Wind Landforms  

NSDL National Science Digital Library

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

Tranel, Lisa

318

Filament winding  

NASA Astrophysics Data System (ADS)

The major aspects of filament winding are discussed, emphasizing basic reinforcement and matrix materials, winding procedures, process controls, and cured composite properties. Fiberglass (E-glass and S-glass strengths are 500,000 and 665,000 psi respectively) and polyester resins are the principal reinforcement constituent materials. Graphite and aramid reinforcements are being used more frequently, primarily for the more critical pressure vessels. Matrix systems are most commonly based on epoxy as it has superior mechanical properties, fatigue behavior, and heat resistance as compard with polyesters. A fiberglass overwrap of PVC pipe is an anticipated development in on-site winding and combination winding, and the compression molding of filament wound lay-ups will be investigated. The fabrication of weight-sensitive structural components may be achieved by using such moldings.

Shibley, A. M.

319

Shear Wave Propagation in Rocks  

Microsoft Academic Search

WE have demonstrated striking similarities in elastic wave propagation through rocks and single crystals in recent experiments. In particular, we find that two shear waves with displacements perpendicular to one another and with differing velocities are often propagated through rocks. This is illustrated in Fig. 1 at 5 kb pressure for samples of slate and dunite; an ultrasonic technique described

N. I. Christensen

1971-01-01

320

Chemically reacting, turbulent shear layer  

Microsoft Academic Search

A chemically reacting turbulent shear layer between two parallel flowing streams with different speeds is investigated in a new blowdown water tunnel. The two streams contain dilute aqueous solutions of diffusion-limited reactants (phenolphthalein and sodium hydroxide, respectively) which mix in the layer and react to form a visible reaction product. Optical densitometry techniques are used to measure the amount of

R. Breidenthal

1979-01-01

321

Phase-Shifting Shearing Interferometer  

NASA Technical Reports Server (NTRS)

A single-element phase-shifting interferometer has been developed based on the lateral shearing interferometer. This new interferometer requires no precise alignment, and the phase is continuously varied by changes in the voltage across a commercially available liquid-crystal phase retarder.

Griffin, DeVon W.

2001-01-01

322

Pore Pressures in Simple Shear.  

National Technical Information Service (NTIS)

The discussion of the use or misuse of the simple shear apparatus for studying the stress:strain behavior of soils is a subject that always proves controversial. Much of the controversy arises because, while it is desirable to study the behavior of soils ...

D. W. Airey D. M. Wood

1985-01-01

323

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

NASA Technical Reports Server (NTRS)

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

Cheng, R. Y. K.

1975-01-01

324

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

325

Recommendations for a wind profiling network to support Space Shuttle launches  

NASA Technical Reports Server (NTRS)

The feasibility is examined of a network of clear air radar wind profilers to forecast wind conditions before Space Shuttle launches during winter. Currently, winds are measured only in the vicinity of the shuttle launch site and wind loads on the launch vehicle are estimated using these measurements. Wind conditions upstream of the Cape are not monitored. Since large changes in the wind shear profile can be associated with weather systems moving over the Cape, it may be possible to improve wind forecasts over the launch site if wind measurements are made upstream. A radar wind profiling system is in use at the Space Shuttle launch site. This system can monitor the wind profile continuously. The existing profiler could be combined with a number of radars located upstream of the launch site. Thus, continuous wind measurements would be available upstream and at the Cape. NASA-Marshall representatives have set the requirements for radar wind profiling network. The minimum vertical resolution of the network must be set so that the wind shears over the depths greater than or = 1 km will be detected. The network should allow scientists and engineers to predict the wind profile over the Cape 6 hours before a Space Shuttle launch.

Zamora, R. J.

1992-01-01

326

Shear Flows and Turbulence in Nature  

Microsoft Academic Search

Shear flows and turbulence have a major impact on the transport of quantities, from heat to material to pollutants. This article explores transport and its sensitivity to novel interactions between shear flow and turbulence.

David E. Newman; Paul W. Terry; Andrew S. Ware

2007-01-01

327

The mechanism for shear thickening in suspensions  

NASA Astrophysics Data System (ADS)

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 example against gravity for large particles, and can be tuned by inducing electric or magnetic dipoles. Dilation can be observed as particles penetrate the fluid surface in the high stress regime. The maximum stress of the shear thickening regime is shown to match, for a wide range of suspensions, the ratio of surface tension divided by a radius of curvature comparable to the particle size. This suggests the large stress associated with shear thickening comes from capillary forces as a consequence of dilation.

Brown, Eric; Jaeger, Heinrich

2009-11-01

328

Shear modulus estimation with vibrating needle stimulation.  

PubMed

An ultrasonic shear wave imaging technique is being developed for estimating the complex shear modulus of biphasic hydropolymers including soft biological tissues. A needle placed in the medium is vibrated along its axis to generate harmonic shear waves. Doppler pulses synchronously track particle motion to estimate shear wave propagation speed. Velocity estimation is improved by implementing a k-lag phase estimator. Fitting shear-wave speed estimates to the predicted dispersion relation curves obtained from two rheological models, we estimate the elastic and viscous components of the complex shear modulus. The dispersion equation estimated using the standard linear solid-body (Zener) model is compared with that from the Kelvin-Voigt model to estimate moduli in gelatin gels in the 50 to 450 Hz shear wave frequency bandwidth. Both models give comparable estimates that agree with independent shear rheometer measurements obtained at lower strain rates. PMID:20529711

Orescanin, Marko; Insana, Michael

2010-06-01

329

Residual shear deformations in the coronary artery.  

PubMed

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

Wang, Ruoya; Gleason, Rudolph L

2014-06-01

330

Fabric of Kaolinite in Direct Shear Tests.  

National Technical Information Service (NTIS)

Fabric data on kaolinite samples sheared in drained direct shear are obtained from carbowax impregnated samples that were examined by light microscopy and x-ray diffraction. Previous research in this laboratory has repeatedly demonstrated that when proper...

R. T. Martin

1972-01-01

331

Winds and wind system performance  

Microsoft Academic Search

Wind characteristics are discussed with reference to evaluation of wind energy conversion systems performance. Weather data sources and measurement methods are considered, and techniques applicable to large-scale (e.g., large multi-unit arrays) and to small scale (e.g., simple power regression relations) use are described. Calculation of output power is explained, factors relevant to system design, siting, and operation are taken into

C. G. Justus

1978-01-01

332

Rapid Shear Zones - Unspecific Microstructures  

NASA Astrophysics Data System (ADS)

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

Birtel, S.; Stoeckhert, B.

2008-12-01

333

Adiabatic shear banding in a bimetallic body  

Microsoft Academic Search

Summary Thermomechanical deformations of a body made of two different materials and under-going simple shearing deformations are studied with the objectives of finding out when and where adiabatic shear bands will initiate and how they will subsequently grow. Each material is modeled as strain and strain-rate hardening but thermally softening. A shear band is presumed to have formed if the

R. C. Batra; Y. W. Kwon

1989-01-01

334

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

335

Shear dependence of viscosity for perfluoropolyether fluids  

Microsoft Academic Search

The shear dependence of the bulk viscosities of two structurally different types of perfluoropolyether fluids was determined by two different techniques. The first involved direct measurement in a high shear Couette viscometer, the second utilized the time-temperature superposition principle to establish master curves from viscosity determinations at low shear rates and temperature; the results are comparable. Both fluids begin to

M. J. R. Cantow; T. Y. Ting; E. M. Barrall; R. S. Porter; E. R. George

1986-01-01

336

Shear flow vortices in magnetospheric plasmas  

Microsoft Academic Search

Theory and numerical simulations are used to investigate the nonlinear evolution of vortices generated by the Kelvin–Helmholtz (KH) instability of sheared plasma flows in the Earth’s magnetosphere. The extent of broadening of the shear flow, and the energy and enstrophy exchange between the shear flow and KH vortices, is characterized. A new stationary vortex street solution is found, and two

R. Rankin; P. Frycz; J. C. Samson; V. T. Tikhonchuk

1997-01-01

337

High temperature integrated ultrasonic shear wave probes  

NASA Astrophysics Data System (ADS)

Integrated ultrasonic shear wave probes have been fabricated using steel substrates through a paint-on method with the use of mode conversion from longitudinal to shear waves. The probe can be operated up to 150 °C. A probe simultaneously generating and receiving both longitudinal and shear waves is also demonstrated.

Jen, C.-K.; Ono, Y.; Kobayashi, M.

2006-10-01

338

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

339

Scanning tomographic acoustic microscopy using shear waves  

Microsoft Academic Search

We propose to use shear waves instead of longitudinal waves in a novel scanning tomographic acoustic microscope (STAM) in which the specimens are solid. When a specimen with a shear modulus is immersed in the microscope's water bath, mode conversion takes place at the water-solid interface. The shear wave energy is detectable and can be used for image reconstruction. Although

Daesik Ko; A. Meyyappan

1997-01-01

340

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

341

Armchair graphene nanoribbons under shear strain  

NASA Astrophysics Data System (ADS)

The symmetry and electronic properties of armchair graphene nanoribbons (AGNRs) have been investigated using density functional theory calculations. For the shear strained AGNRs, the D6h (6/mmm) symmetry of the hexagonal lattice further turns into 2/m. The stability improves with increasing ribbon width under the same shear strain. Besides, the modification of the energy gap under shear strain is weak.

Qu, Li-Hua; Zhang, Jian-Min; Xu, Ke-Wei; Ji, Vincent

2014-06-01

342

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

Microsoft Academic Search

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

KARSTEN THERMANN; CHRISTIAN GAU; JOACHIM TIEDEMANN

343

Shear strengths of wood measured by various short beam shear test methods  

Microsoft Academic Search

We conducted three types of short beam shear tests of western hemlock ( Tsuga heterophylla Sarg.) under various span\\/depth ratios, and examined whether the maximum shear stress was used as the shear strength. The following results were obtained. (1) In the short beam shear tests under the three-point loading method, it was difficult to have the specimen failing by horizontal

Hiroshi Yoshihara; Toshifumi Furushima

2003-01-01

344

The Effect of Vertical Shear on Tropical Cyclone Intensity Change.  

NASA Astrophysics Data System (ADS)

The effect of vertical shear on tropical cyclone intensity change is usually explained in terms of `ventilation' where heat and moisture at upper levels are advected away from the low-level circulation, which inhibits development. A simple two-layer diagnostic balance model is used to provide an alternate explanation of the effect of shear. When the upper-layer wind in the vortex environment differs from that in the lower layer, the potential vorticity (PV) pattern associated with the vortex circulation becomes tilted in the vertical. The balanced mass field associated with the tilted PV pattern requires an increased midlevel temperature perturbation near the vortex center. It is hypothesized that this midlevel warming reduces the convective activity and inhibits the storm development.Previous studies have shown that diabatic heating near the storm center acts to reduce the vertical tilt of the vortex circulation. These studies have also shown that there is an adiabatic process that acts to reduce the vertical tilt of a vortex. The effectiveness of the adiabatic process depends on the Rossby penetration depth, which increases with latitude, horizontal scale, and vortex amplitude. Large-scale analyses from the 1989-1994 Atlantic hurricane seasons are used to show that high-latitude, large. and intense tropical cyclones tend to be less sensitive to the effect of vertical shear than low-latitude, small, and weak storms.

Demaria, Mark

1996-07-01

345

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

346

Wind Generators  

NASA Technical Reports Server (NTRS)

When Enerpro, Inc. president, Frank J. Bourbeau, attempted to file a patent on a system for synchronizing a wind generator to the electric utility grid, he discovered Marshall Space Flight Center's Frank Nola's power factor controller. Bourbeau advanced the technology and received a NASA license and a patent for his Auto Synchronous Controller (ASC). The ASC reduces generator "inrush current," which occurs when large generators are abruptly brought on line. It controls voltage so the generator is smoothly connected to the utility grid when it reaches its synchronous speed, protecting the components from inrush current damage. Generator efficiency is also increased in light winds by applying lower than rated voltage. Wind energy is utilized to drive turbines to generate electricity for utility companies.

1989-01-01

347

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

348

Shear Viscosity of Strongly Coupled  

Microsoft Academic Search

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

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

2001-01-01

349

Heavy oils: Their shear story  

Microsoft Academic Search

ABSTRACT Heavy oils are important unconventional,hydrocarbon,re- sources with huge reserves and are usually exploited through thermal recovery processes. These thermal recovery processes can be monitored using seismic techniques. Shear-wave proper- ties,inparticular,areexpectedtobemostsensitivetothechanges in the heavy-oil reservoir because heavy oils change from being solid-like at low temperatures to fluid-like at higher tempera- tures. To understand their behavior, we measure the complex shearmodulusandthusalsotheattenuationofaheavy-oil-satu-

Jyoti Behura; Mike Batzle; Ronny Hofmann; John Dorgan

2007-01-01

350

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

351

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

352

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

353

Ignition Due To Macroscopic Shear  

NASA Astrophysics Data System (ADS)

Initiation of heterogeneous explosives is often accomplished by shocks inducing in the explosive pressures in the 10-20 kbars range. These pressures are insufficient to compress the bulk of the material uniformly to a high enough temperature for ignition. Instead, the mechanical work is localized at a number of hot spots the temperature of which rises much higher than the bulk of the material. This is the traditional theory and is successful in predicting initiation due to strong shocks. However, when shear is applied, ignition is often observed at pressures lower than the above theory alone can explain - for example, in the drop-weight test, indicating that macroscopic shear, which is not addressed in the traditional theory, is a viable mechanism of explosive initiation. In the paper, the macroscopic shear induced by uniaxially compressing an explosive sample is quantified for a variety of boundary conditions and constitutive models describing the explosive's material. Uniaxial compression is common in a number of tests, such as the drop-weight test, Split Hopkinson Pressure Bar, etc.

Guirguis, Raafat

1999-06-01

354

Layered Systems Under Shear Flow  

NASA Astrophysics Data System (ADS)

We discuss and review a generalization of the usual hydrodynamic description of smectic A liquid crystals motivated by the experimentally observed shear-induced destabilization and reorientation of smectic A like systems. We include both the smectic layering (via the layer displacement u and the layer normal hat{p}) and the director hat{n} of the underlying nematic order in our macroscopic hydrodynamic description and allow both directions to differ in non equilibrium situations. In a homeotropically aligned sample the nematic director couples to an applied simple shear, whereas the smectic layering stays unchanged. This difference leads to a finite (but usually small) angle between hat{n} and hat{p}, which we find to be equivalent to an effective dilatation of the layers. This effective dilatation leads, above a certain threshold, to an undulation instability of the layers with a wave vector parallel to the vorticity direction of the shear flow. We include the couplings of the velocity field with the order parameters for orientational and positional order and show how the order parameters interact with the undulation instability. We explore the influence of the magnitude of various material parameters on the instability. Comparing our results to available experimental results and molecular dynamic simulations, we find good qualitative agreement for the first instability. In addition, we discuss pathways to higher instabilities leading to the formation of onions (multilamellar vesicles) via cylindrical structures and/or the break-up of layers via large amplitude undulations.

Svenšek, Daniel; Brand, Helmut R.

355

Performance Evaluation of FRP Bridge Deck Under Shear Loads  

Microsoft Academic Search

Shear behavior of glass fiber reinforced polymer (FRP) bridge deck components has been experimentally and theoretically studied under in-plane shear, out-of-plane shear, punching shear, shear of web—flange junction, and system racking shear. Experimental data revealed that the shear modulus of FRP bridge decks ranged from 2.66 to 4.14 GPa and the shear stress to failure ranged from 20.7 to 96.6

Woraphot Prachasaree; Hota V. S. Gangarao; Vimala Shekar

2009-01-01

356

Wind energy systems  

NASA Technical Reports Server (NTRS)

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

Stewart, H. J.

1978-01-01

357

Shear localization in a tungsten heavy alloy  

SciTech Connect

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 Kolsky bar and pressure shear plate impact. The torsional Kolsky bar generates shear rates up to 10(exp 3)/s for times of several hundred micro s. The pressure-shear plate impact technique subjects the deformed material to shearing under superimposed hydrostatic pressure and develops shear rates as high as 1O(exp 5)/s for times of one microsec. Adiabatic shear localization has been observed in the high-rate shearing tests; relatively narrow shear bands are formed, followed immediately by catastrophic fracture. The deformed microstructures are examined using scanning electron microscopy, optical microscopy, and quantitative image analysis of micrographs. Examination of the deformed microstructures supplies new insight into the mechanisms through which large dynamic shearing deformations occur in this heavy tungsten alloy.

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

1995-12-01

358

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

359

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

360

Magnetic shear. II - Hale region 17244  

NASA Technical Reports Server (NTRS)

A B-gamma(delta) sunspot group with growing delta-spots of trailing polarity shows evidence in H-alpha filament structure of a transition from a state of weak magnetic shear to a state of strong shear. The shear develops in the chromosphere and transition region to the corona overlying the photospheric magnetic neutral line separating the delta-spots from the leading polarity at a time when the delta-spots are undergoing rapid growth. Several major flares occur along the sheared portion of the neutral line following the shear development. Other segments of the neutral line far removed from the delta-spots show similar evidence of shear in the H-alpha filament structure and in C IV velocity patterns as well. These 'quiescent' regions of shear are relatively steady or decaying with time and show very little related activity.

Athay, R. G.; Jones, H. P.; Zirin, H.

1985-01-01

361

Wind turbine  

Microsoft Academic Search

An improved wind turbine is described in which the tip portions of the blades are variable in pitch and are cyclically varied in pitch to control the yaw of the rotor and to relieve bending moments on the blades and are collectively varied in pitch to relieve bending moments on the blades and to maximize the power output of the

R. E. Donham; R. L. Heimbold

1981-01-01

362

Wind energy.  

National Technical Information Service (NTIS)

This document presents the conference that took place in Sophia-Antipolis (France) on the first and second of October 1992. Several speeches dealing with wind power are presented in this document, which is divided in 5 main parts. The first part deals wit...

1992-01-01

363

Wind Chimes  

NSDL National Science Digital Library

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

K-12 Outreach Office,

364

Microburst wind structure and evaluation of Doppler radar for airport wind shear detection  

Microsoft Academic Search

The horizontal and vertical structure of airflow within microbursts has been determined using Doppler weather radar data from the Joint Airport Weather Studies (JAWS) Project. It is shown that the downdraft typically associated with microbursts 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

J. W. Wilson; R. D. Roberts; C. Kessinger; J. McCarthy

1984-01-01

365

Alternative methods of estimating hub-height wind speed for small wind turbine performance evaluation  

NASA Astrophysics Data System (ADS)

Current industry standards for evaluating wind turbine power performance require erecting a meteorological mast on site to obtain reference measurements of hub-height wind speed. New considerations for small wind turbines (SWTs) offer the alternative of using an anemometer extending from a lower elevation on the turbine tower. In either case, SWT owners face questions and impracticalities when applying this standard in-situ. Alternative methods of predicting hub-height wind speed for SWT performance evaluation have been assessed experimentally using a Bergey XL.1 SWT collocated with a meteorological mast. Findings indicate that vertical extrapolation can increase the accuracy of tower-mounted anemometry for predicting hub-height wind speed. It is recommended to use concurrent wind speed measurements from anemometers at two elevations to develop site-specific wind shear parameters. Three-dimensional wind speed data from a sonic anemometer were used alongside a theoretical model to determine the optimal location for the topmost anemometer but results were inconclusive.

Ziter, Brett

366

Dynamics of wind-driven circulation in a shallow lagoon with strong horizontal density gradient  

NASA Astrophysics Data System (ADS)

Albemarle-Pamlico Sound (APS) is a shallow lagoonal estuary with weak stratification but strong horizontal density gradient. Idealized and realistic model simulations are conducted to examine the dynamics of wind-driven circulation in APS. Two dimensionless parameters, the Ekman (Ek) and Wedderburn (W) numbers, are found to be two key parameters in controlling the flow pattern and dynamics. Circulation in Albemarle Sound and northern Pamlico Sound is primarily driven by wind-forcing, and shows laterally sheared flows withEk approaching 1 and Wexceeding 1. Analysis of the along-channel momentum equation shows a balance among the wind stress, barotropic pressure gradient due to sea level setup, and bottom friction, while the vertical vorticity is primarily determined by the balance between the wind stress curl and bottom stress curl. In contrast, circulation in southern Pamlico Sound is driven by both wind and gravitational forces, and shows vertically sheared two-layer flows with lowEk and Waround 1. Both baroclinic and barotropic pressure gradients act against the wind stress to drive the two-layer flows. A regime diagram in the parameter space ofEk and W is used to summarize variability of circulation pattern on the seasonal time scale. Northern Pamlico Sound is characterized by high Ek and high W values and laterally sheared currents. Southern Pamlico Sound is usually characterized by low Ek and low W values and vertically sheared flows but featuring laterally sheared flows during the fall when Ek averages to over 0.5.

Jia, Peng; Li, Ming

2012-05-01

367

Eddy viscosity and flow properties of the solar wind: Co-rotating interaction regions, coronal-mass-ejection sheaths, and solar-wind/magnetosphere coupling  

SciTech Connect

The coefficient of magnetohydrodynamic (MHD) eddy viscosity of the turbulent solar wind is calculated to be {nu}{sub eddy}{approx_equal}1.3x10{sup 17} cm{sup 2}/s: this coefficient is appropriate for velocity shears with scale thicknesses larger than the {approx}10{sup 6} km correlation length of the solar-wind turbulence. The coefficient of MHD eddy viscosity is calculated again accounting for the action of smaller-scale turbulent eddies on smaller scale velocity shears in the solar wind. This eddy viscosity is quantitatively tested with spacecraft observations of shear flows in co-rotating interaction regions (CIRs) and in coronal-mass-ejection (CME) sheaths and ejecta. It is found that the large-scale ({approx}10{sup 7} km) shear of the CIR fractures into intense narrow ({approx}10{sup 5} km) slip zones between slabs of differently magnetized plasma. Similarly, it is found that the large-scale shear of CME sheaths also fracture into intense narrow slip zones between parcels of differently magnetized plasma. Using the solar-wind eddy-viscosity coefficient to calculate vorticity-diffusion time scales and comparing those time scales with the {approx}100-h age of the solar-wind plasma at 1 AU, it is found that the slip zones are much narrower than eddy-viscosity theory says they should be. Thus, our concept of MHD eddy viscosity fails testing. For the freestream turbulence effect in solar-wind magnetosphere coupling, the eddy-viscous force of the solar wind on the Earth's magnetosphere is rederived accounting for the action of turbulent eddies smaller than the correlation length, along with other corrections. The improved derivation of the solar-wind driver function for the turbulence effect fails to yield higher correlation coefficients between measurements of the solar-wind driver and measurements of the response of the Earth's magnetosphere.

Borovsky, Joseph E. [Los Alamos National Laboratory Mail Stop D466 Los Alamos, New Mexico 87545 (United States)

2006-05-15

368

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

NASA Technical Reports Server (NTRS)

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

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

1981-01-01

369

Shear Mechanics of the TMJ Disc  

PubMed Central

The temporomandibular joint (TMJ) is a complex hinge and gliding joint that induces significant shear loads onto the fibrocartilage TMJ disc during jaw motion. The purpose of this study was to assess regional variation in the disc’s shear loading characteristics under physiologically relevant loads and to associate those mechanical findings with common clinical observations of disc fatigue and damage. Porcine TMJ discs were compressed between an axially translating bottom platen and a 2.5-cm-diameter indenter within a hydrated testing chamber. Discs were cyclically sheared at 0.5, 1, or 5 Hz to 1, 3, or 5% shear strain. Within the anterior and intermediate regions of the disc when sheared in the anteroposterior direction, both shear and compressive moduli experienced a significant decrease from instantaneous to steady state, while the posterior region’s compressive modulus decreased approximately 5%, and no significant loss of shear modulus was noted. All regions retained their shear modulus within 0.5% of instantaneous values when shear was applied in the mediolateral direction. The results of the disc’s regional shear mechanics suggest an observable and predictable link with the common clinical observation that the posterior region of the disc is most often the zone in which fatigue occurs, which may lead to disc damage and perforation.

Juran, C.M.; Dolwick, M.F.; McFetridge, P.S.

2013-01-01

370

Nucleation of shear bands in amorphous alloys.  

PubMed

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

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

2014-03-18

371

Biomechanics of single chondrocytes under direct shear.  

PubMed

Articular chondrocytes experience a variety of mechanical stimuli during daily activity. One such stimulus, direct shear, is known to affect chondrocyte homeostasis and induce catabolic or anabolic pathways. Understanding how single chondrocytes respond biomechanically and morphologically to various levels of applied shear is an important first step toward elucidating tissue level responses and disease etiology. To this end, a novel videocapture method was developed in this study to examine the effect of direct shear on single chondrocytes, applied via the controlled lateral displacement of a shearing probe. Through this approach, precise force and deformation measurements could be obtained during the shear event, as well as clear pictures of the initial cell-to-probe contact configuration. To further study the non-uniform shear characteristics of single chondrocytes, the probe was positioned in three different placement ranges along the cell height. It was observed that the apparent shear modulus of single chondrocytes decreased as the probe transitioned from being close to the cell base (4.1 +/- 1.3 kPa), to the middle of the cell (2.6 +/- 1.1 kPa), and then near its top (1.7 +/- 0.8 kPa). In addition, cells experienced the greatest peak forward displacement (approximately 30% of their initial diameter) when the probe was placed low, near the base. Forward cell movement during shear, regardless of its magnitude, continued until it reached a plateau at ~35% shear strain for all probe positions, suggesting that focal adhesions become activated at this shear level to firmly adhere the cell to its substrate. Based on intracellular staining, the observed height-specific variation in cell shear stiffness and plateau in forward cell movement appeared to be due to a rearrangement of focal adhesions and actin at higher shear strains. Understanding the fundamental mechanisms at play during shear of single cells will help elucidate potential treatments for chondrocyte pathology and loading regimens related to cartilage health and disease. PMID:19644718

Ofek, Gidon; Dowling, Enda P; Raphael, Robert M; McGarry, J Patrick; Athanasiou, Kyriacos A

2010-04-01

372

Wind turbine with automatic pitch and yaw control  

Microsoft Academic Search

A wind turbine is described which has a flexible central beam member supporting serodynamic blades at opposite ends thereof and fabricated of uni-directional high tensile strength material bonded together into beam form so that the beam is lightweight. The material has high tensile strength to carry the blade centrifugal loads, low shear modulus to permit torsional twisting thereof for turbine

M. C. Jr. Cheney; P. A. M. Spierings

1978-01-01

373

Wind turbine with automatic pitch and yaw control  

Microsoft Academic Search

A wind turbine having a flexible central beam member supporting aerodynamic blades at opposite ends thereof and fabricated of uni-directional high tensile strength material bonded together into beam form so that the beam is lightweight, and has high tensile strength to carry the blade centrifugal loads, low shear modulus to permit torsional twisting thereof for turbine speed control purposes, and

Cheney Jr. Marvin Chapin; Petrus A. M. Spierings

1978-01-01

374

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

375

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 ...

376

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 ...

377

The effects of shear and roughness on vortex shedding patterns behind a circular cylinder at critical Reynolds numbers  

Microsoft Academic Search

Wind tunnel tests were conducted in an effort to understand the vortex shedding patterns to be experienced by the OTEC cold water pipe. Test procedures are described for obtaining the velocity and distribution profiles, the surface pressure measurements, and the eddy characteristics. Results discussed include the surface pressure distribution for both uniform and sheared flow cases, the vortex shedding pattern

D. M. Rooney; R. D. Peltzer

1979-01-01

378

Target Classification and Remote Sensing of Ocean Current Shear Using a Dual-Use Multifrequency HF Radar  

Microsoft Academic Search

In this paper, we describe a high-frequency (HF) radar capable of multifrequency operation over the HF band for dual-use application to ship classification and mapping ocean current shear and vector winds. The radar is based on a digital transceiver peripheral component interconnect (PCI) card family that supports antenna arrays of four to 32 elements with a single computer, with larger

Dennis Trizna

2006-01-01

379

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

NASA Technical Reports Server (NTRS)

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.; Gilliles, J. A.

2006-01-01

380

Wind Tube  

NSDL National Science Digital Library

In this activity, learners explore moving air and the physics of lift and drag by constructing homemade wind tunnels. Use this activity to illustrate Newton's Second Law of Motion (F=ma) and to demonstrate how things heavier than air (like airplanes) are able to fly. Note: a drill and other specialty tools are required for this activity, but are not included in the cost of materials.

Workshop, Fresno C.

2013-01-01

381

Upwelling of Arctic pycnocline associated with shear motion of sea ice  

NASA Technical Reports Server (NTRS)

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

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

2006-01-01

382

The third-order law for magnetohydrodynamic turbulence with constant shear  

NASA Astrophysics Data System (ADS)

Recently, the third-order law was used to evaluate the energy dissipation (heating) of the solar wind. We extend the theory for third-order structure functions in homogeneous incompressible magnetohydrodynamic (MHD) turbulence to the case in which a constant velocity shear is present. A generalization is found of the usual relation [Politano and Pouquet, Phys. Rev. E, 57, 21 (1998)] between third-order structure functions and the dissipation rate in steady inertial range turbulence, in which the shear plays a crucial role. In particular, the presence of shear leads to a third-order law which is not simply proportional to the relative separation. Possible implications for laboratory and space plasmas are discussed. Some numerical examples are presented. (See http://arxiv.org/abs/0907.3571)

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

2009-12-01

383

Influence of shear on polypropylene crystallization kinetics  

NASA Astrophysics Data System (ADS)

Isothermal crystallization kinetics under shear in the melt of iPP was investigated by optical microscopy. It appears that shearing from 200^circ C to the crystallization temperatures enhanced the kinetics, but the shear effect was not obvious if the melt of iPP was sheared only at 200{^circ C}. The experiment results show that relaxation plays an important role during crystallization, and that spherulite growth rates increased with shear rates and were governed by relaxation. The effect of flow on the crystallization kinetics can be understood by considering that the increase of the degree of order due to flow results is an effective change of the melt free energy. The Laurizen-Hoffman theory and the DE-IAA model were used to describe the shear-induced crystallization kinetics of iPP excellently.

Huo, Hong; Meng, Yanfeng; Li, Hongfei; Jiang, Shichun; An, Lijia

2004-10-01

384

Fast Shear Compounding Using Robust 2-D Shear Wave Speed Calculation and Multi-directional Filtering.  

PubMed

A fast shear compounding method was developed in this study using only one shear wave push-detect cycle, such that the shear wave imaging frame rate is preserved and motion artifacts are minimized. The proposed method is composed of the following steps: 1. Applying a comb-push to produce multiple differently angled shear waves at different spatial locations simultaneously; 2. Decomposing the complex shear wave field into individual shear wave fields with differently oriented shear waves using a multi-directional filter; 3. Using a robust 2-D shear wave speed calculation to reconstruct 2-D shear elasticity maps from each filter direction; and 4. Compounding these 2-D maps from different directions into a final map. An inclusion phantom study showed that the fast shear compounding method could achieve comparable performance to conventional shear compounding without sacrificing the imaging frame rate. A multi-inclusion phantom experiment showed that the fast shear compounding method could provide a full field-of-view, 2-D and compounded shear elasticity map with three types of inclusions clearly resolved and stiffness measurements showing excellent agreement to the nominal values. PMID:24613636

Song, Pengfei; Manduca, Armando; Zhao, Heng; Urban, Matthew W; Greenleaf, James F; Chen, Shigao

2014-06-01

385

Could Crop Height Impact the Wind Resource at Agriculturally Productive Wind Farm Sites?  

NASA Astrophysics Data System (ADS)

The agriculture-intensive United States Midwest and Great Plains regions feature some of the best wind resources in the nation. Collocation of cropland and wind turbines introduces complex meteorological interactions that could affect both agriculture and wind power production. Crop management practices may modify the wind resource through alterations of land-surface properties. In this study, we used the Weather Research and Forecasting (WRF) model to estimate the impact of crop height variations on the wind resource in the presence of a large turbine array. We parameterized a hypothetical array of 121 1.8 MW turbines at the site of the 2011 Crop/Wind-energy Experiment field campaign using the WRF wind farm parameterization. We estimated the impact of crop choices on power production by altering the aerodynamic roughness length in a region approximately 65 times larger than that occupied by the turbine array. Roughness lengths of 10 cm and 25 cm represent a mature soy crop and a mature corn crop respectively. Results suggest that the presence of the mature corn crop reduces hub-height wind speeds and increases rotor-layer wind shear, even in the presence of a large wind farm which itself modifies the flow. During the night, the influence of the surface was dependent on the boundary layer stability, with strong stability inhibiting the surface drag from modifying the wind resource aloft. Further investigation is required to determine the optimal size, shape, and crop height of the roughness modification to maximize the economic benefit and minimize the cost of such crop management practices.

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

2013-12-01

386

Magnetofluid Turbulence in the Solar Wind  

NASA Technical Reports Server (NTRS)

The solar wind shows striking characteristics that suggest that it is a turbulent magnetofluid, but the picture is not altogether simple. From the earliest observations, a strong correlation between magnetic fluctuations and plasma velocity fluctuations was noted. The high corrections suggest that the fluctuations are Alfven waves. In addition, the power spectrum of the magnetic fluctuation showed evidence of an inertial range that resembled that seen in fully-developed fluid turbulence. Alfven waves, however, are exact solutions of the equations of incompressible magnetohydrodynamics. Thus, there was a puzzle: how can a magnetofluid consisting of Alfven waves be turbulent? The answer lay in the role of velocity shears in the solar wind that could drive turbulent evolution. Puzzles remain: for example, the power spectrum of the velocity fluctuations is less steep than the slope of the magnetic fluctuations, nor do we understand even now why the solar wind appears to be nearly incompressible with a -5/3 power-spectral index.

Goldstein, Melvyn L.

2008-01-01

387

Recrystallization kinetics within adiabatic shear bands  

Microsoft Academic Search

Small recrystallized grains (0.1-0.2 ?m diameter) are observed to form in adiabatic shear bands of shock-prestrained copper. However, the mechanism for recrystallization under the high strain, high-strain-rate conditions within shear bands is somewhat unclear. The kinetics of two classical mechanisms for recrystallization, high angle boundary migration and subgrain coalescence, are compared with the time-temperature profile determined for these adiabatic shear

J. A. Hines; K. S. Vecchio

1997-01-01

388

Spatial Characteristics of Multiple Adiabatic Shear Bands  

Microsoft Academic Search

The Evolution of multiple adiabatic shear bands was investigated in stainless steel, commercial pure titanium(CP Ti) and Ti-6Al-4V alloy through the radial collapse of a thick-walled cylinder under high-strain-rate deformation ( 104 s-1). The shear-band initiation, propagation, as well as spatial distribution were examined under different effective strains. The evolution of shear band pattern during the deformation process reveals the

Qing Xue; Vitali F. Nesterenko; Marc. A. Meyers

2001-01-01

389

Sizes of Multilamellar Vesicles in Shear  

NASA Astrophysics Data System (ADS)

The dynamics of the multilamellar vesicle (MLV) is analyzed theoretically, where membrane interaction squeezes the solvent to flow between the neighboring membranes. With the applied affine shear, the dynamic free energy density of the MLV develops a minima, which selects the MLV size. The model predicts a terminal shear rate, below which the metastable MLV exists. The scaling relations for the MLV size and the terminal shear are both consistent with the experiments.

Lu, C.-Y. David

2012-09-01

390

Three-dimensional effects in shear waves  

Microsoft Academic Search

Most studies on shear waves to date have assumed the flow is depth uniform (two dimensional). In the present study, we utilize the quasi-three-dimensional (quasi-3D) nearshore circulation model SHORECIRC to study shear waves. Our results show that shear wave flow is more organized in the quasi-3D simulation than in the 2D simulation. In the 2D simulation, the vortices are moving

Qun Zhao; I. A. Svendsen; Kevin Haas

2003-01-01

391

Shear Strength Criteria for Unsaturated Soils  

Microsoft Academic Search

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

Daichao Sheng; Annan Zhou; Delwyn G. Fredlund

2011-01-01

392

CHARACTERIZATION OF GCL SHEAR STRENGTH VARIABILITY  

Microsoft Academic Search

Variability in geosynthetic clay liner (GCL) internal and GCL-geomembrane (GM) interface shear strength measured using large-scale direct shear tests is evaluated in this study. Several sources of GCL peak shear strength uncertainty are identified, including laboratory equipment and procedures, GCL and GM material variability, and conditioning\\/test procedures. Uncertainty related to GCL and GM material variability is found to arise in

John S. McCartney; Jorge G. Zornberg

393

Coronal magnetic fields produced by photospheric shear  

SciTech Connect

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

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

1987-10-01

394

Coronal magnetic fields produced by photospheric shear  

NASA Technical Reports Server (NTRS)

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

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

1987-01-01

395

Shear flow vortices in magnetospheric plasmas  

Microsoft Academic Search

Theory and numerical simulations are used to investigate the nonlinear evolution of vortices generated by the KelvinâHelmholtz (KH) instability of sheared plasma flows in the Earth{close_quote}s magnetosphere. The extent of broadening of the shear flow, and the energy and enstrophy exchange between the shear flow and KH vortices, is characterized. A new stationary vortex street solution is found, and two

R. Rankin; P. Frycz; J. C. Samson; V. T. Tikhonchuk

1997-01-01

396

Shear wall experiments and design in Japan  

SciTech Connect

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. Detailed descriptions are presented on the development of Japanese shear wall equations, design requirements for containment structures, and ductility requirements.

Park, Y.J.; Hofmayer, C.

1994-12-01

397

The Borborema shear zone system, NE Brazil  

Microsoft Academic Search

The Neoproterozoic evolution of the Borborema Province is characterized by the development of a continental-scale network of transcurrent shear zones. These shear zones form a kinematically consistent system over more than 200,000 km2. This shear zone system is coeval with a high-temperature, medium- to low-pressure metamorphism, partial melting of the crust, and synkinematic magmatism involving both crustal- and mantle-derived magmas.

A. Vauchez; S. Neves; R. Caby; M. Corsini; M. Egydio-Silva; M. Arthaud; V. Amaro

1995-01-01

398

Shear wall ultimate drift limits  

SciTech Connect

Drift limits for reinforced-concrete shear walls are investigated by reviewing the open literature for appropriate experimental data. Drift values at ultimate are determined for walls with aspect ratios ranging up to a maximum of 3.53 and undergoing different types of lateral loading (cyclic static, monotonic static, and dynamic). Based on the geometry of actual nuclear power plant structures exclusive of containments and concerns regarding their response during seismic (i.e.,cyclic) loading, data are obtained from pertinent references for which the wall aspect ratio is less than or equal to approximately 1, and for which testing is cyclic in nature (typically displacement controlled). In particular, lateral deflections at ultimate load, and at points in the softening region beyond ultimate for which the load has dropped to 90, 80, 70, 60, and 50 percent of its ultimate value, are obtained and converted to drift information. The statistical nature of the data is also investigated. These data are shown to be lognormally distributed, and an analysis of variance is performed. The use of statistics to estimate Probability of Failure for a shear wall structure is illustrated.

Duffey, T.A. [Duffy, (T.A.) Tijeras, NM (United States); Goldman, A. [Goldman, (A.), Sandia, Los Alamos, NM (United States); Farrar, C.R. [Los Alamos National Lab., NM (United States)

1994-04-01

399

Optical Beam-Shear Sensors  

NASA Technical Reports Server (NTRS)

A technique for measuring optical beam shear is based on collecting light from the four quadrants of the beam and comparing the optical power collected from each quadrant with that from the other three quadrants. As used here, "shear" signifies lateral displacement of a beam of light from a nominal optical axis. A sensor for implementing this technique consists of a modified focusing lens and a quad-cell photodetector, both centered on the nominal optical axis. The modification of the lens consists in cutting the lens into four sectors (corresponding to the four quadrants) by sawing along two orthogonal diameters, then reassembling the lens following either of two approaches described next. In one approach, the lens is reassembled by gluing the sectors back together. In the simplest variant of this approach, the kerf of the saw matches the spacing of the photodetector cells, so that the focus of each sector crosses the axis of symmetry to fall on the opposite photodetector cell (see figure). In another variant of this approach, the lens sectors are spaced apart to make their individual foci to fall on separate photodetector cells, without crossing the optical axis. In the case of a sufficiently wide beam, the modified lens could be replaced with four independent lenses placed in a square array, each focusing onto an independent photodetector

Martin, Stefan; Szwaykowski, Piotr

2007-01-01

400

Time and flow-direction responses of shear-styress-sensitive liquid crystal coatings  

NASA Technical Reports Server (NTRS)

Time and flow-direction responses of shear-stress liquid crystal coatings were exploresd experimentally. For the time-response experiments, coatings were exposed to transient, compressible flows created during the startup and off-design operation of an injector-driven supersonic wind tunnel. Flow transients were visualized with a focusing schlieren system and recorded with a 100 frame/s color video camera.

Reda, Daniel C.; Muraqtore, J. J.; Heinick, James T.

1994-01-01

401

Low-rise shear wall failure modes  

SciTech Connect

A summary of the data that are available concerning the structural response of low-rise shear walls is presented. This data will be used to address two failure modes associated with the shear wall structures. First, data concerning the seismic capacity of the shear walls with emphasis on excessive deformations that can cause equipment failure are examined. Second, data concerning the dynamic properties of shear walls (stiffness and damping) that are necessary to compute the seismic inputs to attached equipment are summarized. This case addresses the failure of equipment when the structure remains functional. 23 refs.

Farrar, C.R. (Los Alamos National Lab., NM (USA)); Hashimoto, P.S. (EQE Engineering, Inc., Costa Mesa, CA (USA)); Reed, J.W. (Benjamin (J.R.) and Associates, Inc., Mountain View, CA (USA))

1991-01-01

402

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

403

Instability of periodic MHD shear flows  

SciTech Connect

The stability of periodic MHD shear flows generated by an external transversal periodic force in magnetized plasma is studied. It is shown that the temporal behaviour of magnetosonic wave spatial Fourier harmonics in such flows is governed by Mathieu equation. Consequently the harmonics with the half frequency of the shear flows grow exponentially in time. Therefore the periodic shear motions are unstable to the perturbations of compressible magnetosonic waves. The motions represent the kinetic part of the transversal oscillation in magnetized plasma. Therefore due to the instability of periodic shear motions, the transversal oscillations may quickly be damped, so transferring their energy to compressible magnetosonic perturbations.

Zaqarashvili, T.V. [Abastumani Astrophysical Observatory, Al. Kazbegi ave. 2a, 380060 Tbilisi (Georgia); Oliver, R.; Ballester, J.L. [Departament de Fisica, Universitat de les Illes Balears, E-07122 Palma de Mallorca (Spain); Belvedere, G. [Dipartimento di Fisica e Astronomia, Sezione Astrofisica, Universita di Catania, Via S.Sofia 78, I-95123 Catania (Italy)

2004-11-12

404

Stability of stratified flow with inhomogeneous shear  

NASA Astrophysics Data System (ADS)

The temporal evolution of perturbations in stratified flow with inhomogeneous shear is examined analytically by an extension of the nonmodal approach to flows with inhomogeneous shear. The solutions of the equations that govern the linear evolution and the weak nonlinear evolution of perturbations of the stream function for stratified flow with monotonic inhomogeneous shear are obtained. It is shown that stabilization of perturbations arises from nonmodal effects due to flow shear. Conditions at which these nonmodal effects may be strong enough to stabilize the Rayleigh-Taylor instability are presented. These analytical results are also compared to numerical simulations of the governing equations performed by Benilov, Naulin, and Rasmussen.

Mikhailenko, Vladimir S.; Scime, Earl E.; Mikhailenko, Vladimir V.

2005-02-01

405

Analysis of turbulence structures in shear flows  

NASA Technical Reports Server (NTRS)

Outline of the research program and a recent progress in the studies of sheared turbulence are described. The research program reported is directed at two goals: (1) understanding of fundamental physics of organized structures in turbulent shear flows; and (2) development of phenomenological models of turbulence based on physical arguments. Three projects that were carried out are: (1) structure of sheared turbulence near a plane boundary; (2) distortion of turbulence by axisymmetric strain and dilation; and (3) study of energy transfer in turbulent shear flow.

Lee, Moon J.

1989-01-01

406

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

407

A Velocity Shear Driven Turbulence Model for Recent ACE Magnetometer Observations  

NASA Astrophysics Data System (ADS)

Recent magnetometer measurements from the ACE spacecraft show magnetic fluctuation enhancements above the normal Kolmogorov cascade levels adjacent the Doppler-shifted proton gyro-scales. It has been suggested that enhanced wave activity associated with a large solar wind structure, such as glancing passage of a CME, could explain the observations; however to date, a physical process has not been explored aside from conjectures that velocity shear-based Kelvin-Helmholtz (KH) instabilities may be present. Here we use a two-and-one-half dimensional compressible MHD code, initialized with plasma parameters and initial conditions consistent with the observations, to show that large-scale velocity shears can lead to spectral enhancements adjacent the proton gyro-scales for appropriate orientations of the solar wind magnetic field and the normal plane of the velocity shears. Our model includes finite frequency (Hall) and finite wavenumber (Finite Larmor Radius) effects. The development of spectral anisotropies due to velocity shears appears as a natural consequence of wave advection and does not depend on threshold conditions of the KH instability. Thus, the range of applicability for our model is somewhat broader than the KH instability.

Ghosh, S.; Roelof, E. C.; Smith, C. W.

2012-12-01

408

The Descent Rates of the Shear Zones of the Equatorial QBO.  

NASA Astrophysics Data System (ADS)

The influence of vertical advection on the descent rate of the zero-wind line in both phases of the equatorial quasi-biennial oscillation (QBO) is investigated with the help of the `THIN AIR' stratosphere two-and-a-half-dimensional model. The model QBO is forced by two symmetric easterly and westerly waves, and yet the model reproduces qualitatively the observed asymmetry in the descent rates of the two shear zones due to the enhanced heating during easterly descent combined with the equatorial heating induced by the extratropical planetary waves. Observations show that the maximum easterly accelerations occur predominantly from May until July, which is when the modeled equatorial planetary-wave-induced heating rates are weakest. Hence, model results are consistent with the theory that vertical advection induced by extratropical planetary waves slows significantly the descent of the easterly shear zone. The model also shows the observed increase in vertical wind shear during stalling of the easterly descent (which increases the impact of vertical advection). In the model, the effect of cross-equatorial advection of momentum by the mean flow is negligible compared to the vertical advection. Changes in the propagation of planetary waves depending on the sign of the equatorial zonal wind have a small effect on the modeled equatorial heating rates and therefore do not play a large part in producing the modeled asymmetry in descent rates.

Kinnersley, Jonathan S.; Pawson, Steven

1996-07-01

409

Careers in Wind Energy  

ERIC Educational Resources Information Center

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

Liming, Drew; Hamilton, James

2011-01-01

410

Shear Strains, Strain Rates and Temperature Changes in Adiabatic Shear Bands.  

National Technical Information Service (NTIS)

Experiments were conducted to determine the shear strains and strain rates in adiabatic shear bands in a Ni-Cr steel (rolled armor). An explosively driven mass was used to punch plugs from plate of the steel and, thereby, create adiabatic shear bands. The...

G. L. Moss

1980-01-01

411

Quantifying the impact of shear wavelength and kernel size on shear wave speed estimation  

Microsoft Academic Search

Quantitative measurements of tissue stiffness can be obtained by measuring the speed of shear waves induced in tissue by acoustic radiation force. In homogeneous media, time-of-flight (TOF) measurements of shear wave speed (SWS) ideally are independent of the size of the region of interest (or reconstruction kernel). However, in heterogeneous media, shear wave morphology is altered by discontinuities in stiffness

Mark L Palmeri; Ned C Rouze; Michael H Wang; Xuan Ding; Kathryn R Nightingale

2010-01-01

412

Aleutian Pribilof Islands Wind Energy Feasibility Study  

SciTech Connect

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

Bruce A. Wright

2012-03-27

413

Satellite Winds  

NSDL National Science Digital Library

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

414

Wind Streaks  

NASA Technical Reports Server (NTRS)

[figure removed for brevity, see original site]

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

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

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

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

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

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

2004-01-01

415

Windy Wind  

NSDL National Science Digital Library

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

416

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.

417

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

418

Initiation and Growth of Adiabatic Shear Bands.  

National Technical Information Service (NTIS)

A simple version of thermo/viscoplasticity theory is used to model the formation of adiabatic shear bands in high rate deformation of solids. The one dimensional shearing deformation of a finite slab is considered. For the constitutive assumptions made in...

T. W. Wright R. C. Batra

1985-01-01

419

Scaling laws for adiabatic shear bands  

Microsoft Academic Search

Mathematical analysis of a simple, one-dimensional, canonical problem has yielded a number of scaling laws that relate various characteristic features of an adiabatic shear band to the physical properties of the material and the ambient conditions. Specific formulas have been obtained from solutions to linear and non-linear problems coupled with asymptotic representations of the results. Examples are shear band width,

T. W. Wright

1995-01-01

420

A different viewpoint on adiabatic shear localization  

Microsoft Academic Search

This short review addresses the adiabatic shear failure mechanism (adiabatic shear banding---ASB) in metals subjected to high strain-rate deformations. ASB is usually considered as an instability resulting from thermal softening effects. We present a different viewpoint, based on experimental observations in which we identify the stored energy of cold work as the driving force for microstructural rearrangement by dynamic recrystallization

D. Rittel

2009-01-01

421

Waves and instabilities of periodical shear flows  

Microsoft Academic Search

The exact analytical solution of the extended Rayleigh (ER) equation for the case of the periodical compressible shear flow is found. The dispersion relation of the problem is the infinite Hill determinant. It is found that sound waves in a shear flow have a dispersion and its velocity field contains a solenoidal part. Besides sound waves, new wave modes such

Y. Zhugzhda

2003-01-01

422

Research on shear strength of galvannealed coatings  

Microsoft Academic Search

Lap shear test can be generally performed by two kinds of methods. However, the shear strengths measured in both methods (bare and compound sample) may be quite different, which results in some influence on evaluating powdering of galvannealed coating. Samples in uniaxial tensile test are modified to measure their yield stress. The stress–strain curves in tensile test are compared with

Chun Xu; Z. Q. Lin; S. H. Li; W. G. Zhang

2007-01-01

423

Quasi3D Modeling of Shear Waves  

Microsoft Academic Search

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

Q. Zhao; I. Svendsen

2001-01-01

424

Conjugate Riedel deformation band shear zones  

Microsoft Academic Search

Our investigations have disclosed that individual Riedel shear zones may organize themselves into broadly distributed though rigorously oriented intraformational conjugate systems which may form without relationship to, or dependence upon, an underlying basement fault zone. The Riedel shear zones we mapped are zones of deformation bands, which developed as the preferred deformation mechanism in porous Navajo Sandstone (Jurassic). In the

George H Davis; Alexander P Bump; Pilar E Garc??a; Stephen G Ahlgren

2000-01-01

425

Compression and Shear Wave Propagation in Explosives.  

National Technical Information Service (NTIS)

The objective of the experimental study was to investigate the occurrence of shear-induced reaction (SIR) in an explosive subjected to the type of one-dimensional compression and shear (1DCS) loading produced by the parallel-inclined impact (PII) techniqu...

M. Cowperthwaite

1989-01-01

426

Measurement of shear waves in tissue  

Microsoft Academic Search

The wavelength of a propagating pulse of shear wave within tissue is related to the local shear modulus and density through the speed of propagation. If the pulse does not produce standing waves, then the wavelength is a function of the tissue properties and not boundary conditions. Methods for imaging such waves using ultrasound and magnetic resonance imaging have recently

J. F. Greenleaf; V. Dutt; R. Muthupillai; A. Manduca; R. L. Ehman

1996-01-01

427

Shear strength properties of wet granular materials  

Microsoft Academic Search

We investigate shear strength properties of wet granular materials in the pendular state (i.e., the state where the liquid phase is discontinuous) as a function of water content. Sand and glass beads were wetted and tested in a direct shear cell and under various confining pressures. In parallel, we carried out three-dimensional molecular dynamics simulations by using an explicit equation

Vincent Richefeu; Moulay Saïd El Youssoufi; Farhang Radjaï

2006-01-01

428

The Shear Strength of Thin Lubricant Films  

Microsoft Academic Search

This paper describes a study of the effects of pressure and temperature on the shear strength of very thin layers of a number of lubricants. The shear strength is deduced from measurements of the tangential (frictional) force required to slide glass spheres over glass plates coated with the lubricant. It is assumed that no glass-glass contact occurs through the lubricant

B. J. Briscoe; B. Scruton; F. R. Willis

1973-01-01

429

Normalized undrained shear strength of clay shales  

Microsoft Academic Search

This paper examines the possibility of normalizing the undrained shear strength behavior of clay shales. Shales are formed in sedimentary basins by diagenetic processes, which turn young clay sediments into compacted and lithified shales. Cementation at grain contacts affects many properties of shales including the apparent preconsolidation and shear strength. Based on a study of 25 different types of materials,

Marte Gutierrez; Runar Nygård; Kaare Høeg; Toralv Berre

2008-01-01

430

The formation of multiple adiabatic shear bands  

NASA Astrophysics Data System (ADS)

In a previous paper, Zhou et al. [2006. A numerical methodology for investigating adiabatic shear band formation. J. Mech. Phys. Solids, 54, 904-926] developed a numerical method for analyzing one-dimensional deformation of thermoviscoplastic materials. The method uses a second order algorithm for integration along characteristic lines, and computes the plastic flow after complete localization with high resolution and efficiency. We apply this numerical scheme to analyze localization in a thermoviscoplastic material where multiple shear bands are allowed to form at random locations in a large specimen. As a shear band develops, it unloads neighboring regions and interacts with other bands. Beginning with a random distribution of imperfections, which might be imagined as arising qualitatively from the microstructure, we obtain the average spacing of shear bands through calculations and compare our results with previously existing theoretical estimates. It is found that the spacing between nucleating shear bands follows the perturbation theory due to Wright and Ockendon [1996. A scaling law for the effect of inertia on the formation of adiabatic shear bands. Int. J. Plasticity 12, 927-934], whereas the spacing between mature shear bands is closer to that predicted by the momentum diffusion theory of Grady and Kipp [1987. The growth of unstable thermoplastic shear with application to steady-wave shock compression in solids. J. Mech. Phys. Solids 35, 95-119]. Scaling laws for the dependence of band spacing on material parameters differ in many respects from either theory.

Zhou, F.; Wright, T. W.; Ramesh, K. T.

2006-07-01

431

Tensile and shear strength of adhesives  

NASA Technical Reports Server (NTRS)

This experiment is conducted in a freshman-level course: Introduction to Engineering Materials. There are no prerequisites for the course although students should have some knowledge of basic algebra. The objectives are to tension and shear test adhesives and to determine the tensile and shear properties of adhesives. Details of equipment of procedure are given.

Stibolt, Kenneth A.

1990-01-01

432

Coronal Magnetic Fields Produced by Photospheric Shear,  

National Technical Information Service (NTIS)

The magneto-frictional method for computing force-free fields examines the evolution of the magnetic field of a line dipole, when there is relative shearing motion between the two polarities. The energy of the sheared field can be arbitrarily large compar...

J. A. Klimchuk P. A. Sturrock W. H. Yang

1988-01-01

433

Coronal Magnetic Fields Produced by Photospheric Shear.  

National Technical Information Service (NTIS)

The magneto-frictional method is used for computing force free fields to examine the evolution of the magnetic field of a line dipole, when there is relative shearing motion between the two polarities. It found that the energy of the sheared field can be ...

P. A. Sturrock W. Yang

1987-01-01

434

HDPE geomembrane\\/geotextile interface shear strength  

Microsoft Academic Search

This paper describes torsional ring shear tests on interfaces comprised of high-density polyethylene (HDPE) geomembranes\\/nonwoven geotextiles and a drainage geocomposite. Four textured geomembranes with three different manufacturing techniques are utilized to investigate the effect of geomembrane texturing on interface shear resistance. In addition, the effects of geotextile fiber type, fabric style, polymer composition, calendering, and mass per unit area on

Timothy D. Stark; H. T. Eid; T. A. Williamson

1996-01-01

435

Simple shear deformation of partially molten aplite  

NASA Astrophysics Data System (ADS)

The tectonic processes which are important for melt distribution and transport in the intermediate and lower crust and which can result in crustal weakening are not yet well understood. Natural migmatites are usually overprinted by annealing and retrogression during uplift and exhumation, largely obliterating the deformation structures and microstructures of their partially molten history. Deformation experiments on partially molten crustal rocks have so far been conducted in pure shear geometry and mostly under low confining pressures in the brittle deformation field, both of which are not representative of nature. We carried out deformation experiments in simple shear that predominates in the crust and especially crustal shear zones. Undrained experiments were carried out on Enfield aplite at ~1.5 GPa, 900° -1000° C, and ˜ 5*10-6 s-1, conditions which favor crystal plastic deformation of quartz and feldspar (Dell'Angelo and Tullis, 1988). Sample slices 1.0-1.5 mm thick were placed between the shear pistons with the shear plane at a 45° -angle to the compression direction. Maximum shear strain in the experiments is ? ?2.8. Despite difficulties in controlling the melt content by varying the amount of added water, we were able to achieve the full range of brittle to crystal plastic deformation mechanisms. With decreasing melt content Enfield aplite displays a transition from discrete fracturing at a high angle (~70-90° ) to the shear plane (>20 vol.% melt), to cataclastic shearing (10-20 vol.% melt) and to crystal plastic deformation (

Stipp, Michael; Tullis, Jan; Berger, Alfons

2013-04-01

436

Scanning tomographic acoustic microscopy using shear waves.  

PubMed

We propose to use shear waves instead of longitudinal waves in a novel scanning tomographic acoustic microscope (STAM) in which the specimens are solid. When a specimen with a shear modulus is immersed in the microscope's water bath, mode conversion takes place at the water-solid interface. The shear wave energy is detectable and can be used for image reconstruction. Although wave transmission in most solid specimens is limited to about 20 degrees for longitudinal waves, it is about twice that for shear waves. Also, velocities of shear waves are lower than those of longitudinal waves and hence the wavelengths at the same frequency are smaller. For these and other reasons we can expect that for many specimens the resolution of a shear-wave STAM to be substantially better than that of a longitudinal-wave STAM. We use computer simulation in order to compare the operation of a shear-wave STAM with that of the conventional longitudinal-wave STAM. We have simulated tomographic reconstruction for each. The corresponding critical angles of incidence are computed and tomographic reconstructions of a particular solid specimen is obtained by using the back-and-forth propagation algorithm (BFP). Our simulation results show that shear-wave STAM has better resolution than longitudinal-wave STAM. PMID:18244140

Ko, D; Meyyappan, A

1997-01-01

437

Shear Effects on Cholesteric Liquid Crystals  

Microsoft Academic Search

On shearing, cholesteric liquid crystal (L.C.) films lose color intensity, but the wavelength of their maximum reflectance does not change appreciably. The rate of recovery of the intensity after cessation of shearing is linear with the logarithm of time.The thickness of the liquid crystal film is not a very strong factor in the behavior of total reflectance as a function

D. F. Ciliberti; G. D. Dixon; L. C. Scala

1973-01-01

438

Buckling of a sheared cholesteric liquid crystal  

Microsoft Academic Search

We present qualitative and quantitative observations on structural instabilities in a cholesteric liquid crystal subjected to static shear. Using a model of a cholesteric that is tilted under shear, we find that, in a Landau-de Gennes coarse-grained picture, buckling instabilities can be created when the strain is larger than a critical value. The analogy with buckling obtained under dilations is

N. Scaramuzza; R. Barberi; F. Simoni; F. Xu; G. Barbero; R. Bartolino

1985-01-01

439

Gaseous bubble nucleation under shear flow  

Microsoft Academic Search

A decompression experiment of a water solution, saturated with methane gas at about 68atm at room temperature, was done to investigate gas bubble nucleation under shear flow. A pressure reduction from 68atm to atmospheric pressure is well below the decompression pressure required for spontaneous bubble nucleation of the methane gas, about 120atm. The application of a shear flow from 5min

Ho-Young Kwak; Ki-Moon Kang

2009-01-01

440

Crosswind Shear Gradient Affect on Wake Vortices  

NASA Technical Reports Server (NTRS)

Parametric simulations with a Large Eddy Simulation (LES) model are used to explore the influence of crosswind shear on aircraft wake vortices. Previous studies based on field measurements, laboratory experiments, as well as LES, have shown that the vertical gradient of crosswind shear, i.e. the second vertical derivative of the environmental crosswind, can influence wake vortex transport. The presence of nonlinear vertical shear of the crosswind velocity can reduce the descent rate, causing a wake vortex pair to tilt and change in its lateral separation. The LES parametric studies confirm that the vertical gradient of crosswind shear does influence vortex trajectories. The parametric results also show that vortex decay from the effects of shear are complex since the crosswind shear, along with the vertical gradient of crosswind shear, can affect whether the lateral separation between wake vortices is increased or decreased. If the separation is decreased, the vortex linking time is decreased, and a more rapid decay of wake vortex circulation occurs. If the separation is increased, the time to link is increased, and at least one of the vortices of the vortex pair may have a longer life time than in the case without shear. In some cases, the wake vortices may never link.

Proctor, Fred H.; Ahmad, Nashat N.

2011-01-01

441

Virtual shearing interferometry by digital holography  

Microsoft Academic Search

A novel method of virtual shearing interferometry (VSI) is proposed. In this method, the shearogram is obtained by interference of a real object wave-front and a virtual object wave-front. The former is optically recorded and then digitally reconstructed; and the latter is introduced digitally by repositioning or reforming the former. The obvious advantages of VSI over conventional shearing interferometry (SI)

L. Z. Cai; X. F. Meng; Y. R. Wang; X. X. Shen; G. Y. Dong; X. L. Yang

2006-01-01

442

Reliability Analysis of Shear Wall Structures.  

National Technical Information Service (NTIS)

The 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 ...

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

1986-01-01

443

Shear strength of empty and infilled cassettes  

Microsoft Academic Search

This paper considers the shear buckling of light gauge steel cassette sections both with and without an infilling of relatively rigid thermal insulation. In cassette construction, in-plane shear stresses usually arise as a consequence of stressed skin (diaphragm) action and, in this context, it is local buckling of the wide flange that usually governs the design. Although there are some

J. M. Davies; A. S. Fragos

2003-01-01

444

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

445

Dynamic wetting of shear thinning fluids  

NASA Astrophysics Data System (ADS)

The impact of non-Newtonian behavior on dynamic wetting is critical since many fluids exhibit such behavior somewhere in the high-shear environment inherent in the wedge flow near a moving contact line. This impact will be different for two broad categories of non-Newtonian behavior, shear thinning, and elasticity. In this paper, we discuss the steady-state wetting of a fluid, aqueous solutions of xanthan gum, dominated by shear thinning but with negligible elasticity. In the shear thinning fluid, viscous bending near the contact line is greatly reduced compared to a Newtonian fluid having the same zero-shear viscosity. Concomitant with this reduction in viscous bending, the effective dynamic contact angle has a much weaker dependence on capillary number, Ca, than is observed in, or predicted for, Newtonian fluids. A simple lubrication model using a constitutive relation with power-law shear thinning at high shear rates and a Newtonian plateau at low shear rates mimics the trends seen in our data and elucidates the origins of the reduced viscous bending.

Seevaratnam, G. K.; Suo, Y.; Ramé, E.; Walker, L. M.; Garoff, S.

2007-01-01

446

Vortex shedding from bluff bodies in a shear flow - A review  

NASA Astrophysics Data System (ADS)

This paper examines the effects of velocity shear on vortex shedding from stationary and vibrating bluff bodies. Experiments with circular cylindrical bodies and other cross sections such as D-section cylinders and rectangular cylinders, which were limited to conditions with length/diameter ratios less than L/D = 15 to 20, have shown that the spanwise cellular structure of the vortex shedding is dependent upon end conditions. The vortex shedding also is influenced strongly by the shear flow steepness parameter which is based upon the incident flow velocity gradient. Experimental evidence is available to show that moderate shear levels of practical importance (a shear flow steepness parameter ranging from 0.01 to 0.015) do not appreciably decrease the probability of occurrence of vortex-excited oscillations for flexible structures and cables. The effects of incident shear on vortex shedding from stationary and vibrating bluff structures in both fluid media should be investigated further for long cylinders which have minimal end boundary effects. More definitive bounds for and details of this fluid-structure interaction are needed for applications in the wind engineering design of buildings and structures, and in the design of marine structures and cable systems.

Griffin, O. M.

1985-09-01

447

Wind Tunnels of NASA.  

National Technical Information Service (NTIS)

The contribution of wind tunnels to aerodynamic studies is described. The development of the wind tunnel and the problems of calibration, scaling, and instrumentation are discussed. The NASA wind tunnels form the basis for the book, but Air Force, univers...

D. D. Baals W. R. Corliss

1981-01-01

448

Wind energy program overview  

SciTech Connect

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. (GHH)

Not Available

1992-02-01

449

Wind Energy Resource Information  

NSDL National Science Digital Library

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

450

Weather: Wind Chill  

NSDL National Science Digital Library

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

2010-01-01

451

Shear layer excitation, experiment versus theory  

NASA Technical Reports Server (NTRS)

The acoustical excitation of shear layers is investigated. Acoustical excitation causes the so-called orderly structures in shear layers and jets. Also, the deviations in the spreading rate between different shear layer experiments are due to the same excitation mechanism. Measurements in the linear interaction region close to the edge from which the shear layer is shed are examined. Two sets of experiments (Houston 1981 and Berlin 1983/84) are discussed. The measurements were carried out with shear layers in air using hot wire anemometers and microphones. The agreement between these measurements and the theory is good. Even details of the fluctuating flow field correspond to theoretical predictions, such as the local occurrence of negative phase speeds.

Bechert, D. W.; Stahl, B.

1984-01-01

452

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

453

Evolution of slip surface roughness through shear  

NASA Astrophysics Data System (ADS)

significant part of displacement in fault zones occurs along discrete shear surfaces. The evolution of fault surface topography is studied here in direct shear laboratory experiments. Matching tensile fracture surfaces were sheared under imposed constant normal stress and sliding velocity. The roughness evolution was analyzed using measurements of surface topography before and after slip. We show that shearing reduces the initial surface roughness at all measurement scales. At all wavelengths, the roughness ratio between initial and final roughness increases as a function of the slip distance. For a given test, the roughness ratio increases with wavelength up to a few millimeters, beyond which the ratio becomes wavelength independent. At this region the roughness measured after slip follows a power law similar to that of the initial tensile fracture surface. We interpret this geometrical evolution as a consequence of the deformation stage of interlocked asperities which is followed by shear-induced dilation.

Davidesko, Guy; Sagy, Amir; Hatzor, Yossef H.

2014-03-01