These are representative sample records from Science.gov related to your search topic.
For comprehensive and current results, perform a real-time search at Science.gov.
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

CAT Lidar Wind Shear Studies.  

National Technical Information Service (NTIS)

The studies considered the major meteorological factors producing wind shear, methods to define and classify wind shear in terms significant from an aircraft perturbation standpoint, the significance of sensor location and scan geometry on the detection a...

R. W. Goff

1978-01-01

3

Structure of wind-shear turbulence  

NASA Technical Reports Server (NTRS)

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

Trevino, G.; Laituri, T. R.

1988-01-01

4

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

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

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

7

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

8

Logarithmic Wind Profile: A Stability Wind Shear Term  

E-print Network

A stability wind shear term of logarithmic wind profile based on the terms of turbulent kinetic energy equation is proposed. The fraction influenced by thermal stratification is considered in the shear production term. This thermally affected shear is compared with buoyant term resulting in a stability wind shear term. It is also considered Reynolds stress as a sum of two components associated with wind shear from mechanical and thermal stratification process. The stability wind shear is responsible to Reynolds stress of thermal stratification term, and also to Reynolds stress of mechanical term at no neutral condition. The wind profile and its derivative are validated with data from Pedra do Sal experiment in a flat terrain and 300m from shoreline located in northeast coast of Brazil. It is close to the Equator line, so the meteorological condition are strongly influenced by trade winds and sea breeze. The site has one 100m tower with five instrumented levels, one 3D sonic anemometer, and a medium-range wind...

Sakagami, Yoshiaki; Haas, Reinaldo; Passos, Julio C; Taves, Frederico F

2014-01-01

9

Airborne Doppler radar for wind shear detection  

NASA Technical Reports Server (NTRS)

There has been extensive discussion concerning the use of ground based Doppler radars for the detection and measurement of microburst features and the mapping of associated wind shears. Recent and planned research at Langley into technology and techniques useful for the future development of airborne Doppler weather radar systems for both turbulence and wind shear detection are addressed. Such systems, if successfully developed, would represent a marked increase in performance over airborne weather radars currently available. A principal difficulty in extending to airborne radars the capabilities of current ground based Doppler radars is emphasized.

Staton, Leo

1987-01-01

10

Unresolved issues in wind shear encounters  

NASA Technical Reports Server (NTRS)

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

Stengel, Robert F.

1987-01-01

11

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

12

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

13

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

14

Lidar wind shear detection for commercial aircraft  

NASA Astrophysics Data System (ADS)

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

Targ, Russell; Bowles, Roland L.

1991-08-01

15

Control of aircraft landing approach in wind shear  

NASA Technical Reports Server (NTRS)

Wind and wind shear components are estimated and used for controlling an externally-blown flap STOL aircraft and a B-727 during landing approach under the JAWS microburst profile. A combination of feedforward and feedback concepts is used. The objective is tracking of airspeed and glide slope. Both an asymptotic disturbance rejection scheme, which is equivalent to MIMO zero assignment, and a linear quadratic scheme prove to be successful. Higher angle-of-attack is used only after thrust saturation. Downdraft is found to be more difficult to counter for STOL aircraft than is horizontal wind shear. A third design formulation based on successive loop closure is also presented. A 'Wind Shear Penetration Index' is described, which offers a simple and quantitative evaluation of an aircraft's ability to safely penetrate a wind shear. This index is particularly useful if used with Doppler radars.

Chu, Peter Yaohwa; Bryson, Arthur E., Jr.

1987-01-01

16

Aircraft Control Strategies by Game Theoretic Approach against Wind Shear  

NASA Astrophysics Data System (ADS)

The safety problem of aircraft that encounters wind shear during the final approach flight phase is addressed using a game theoretic approach. The game consists of two players, an aircraft and wind shear. The control scheme is composed of non-cooperative game between players. In the game, aircraft tries to fly to avoid crashing to ground and down burst attempts to force the aircraft to crash. A new control strategy based on nonlinear receding horizon control is applied to the game. It is shown by simulation that this control strategy is effective against wind shear.

Yamaguchi, Masahiro; Umemura, Akira

17

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

18

United Airlines wind shear incident of May 31, 1984  

NASA Technical Reports Server (NTRS)

An incident involving wind shear on 31 May 1984 is discussed by an airline employee. The specs of the plane are given, the weather conditions are listed, and the actions taken by the flight crew are discussed.

Simmon, David A.

1987-01-01

19

United Airlines wind shear incident of May 31, 1984  

NASA Technical Reports Server (NTRS)

An incident involving wind shear which occured on 31 May 1984 on a United Airlines aircraft is discussed by a member of the National Center for Atmospheric Research. The meteorological parameters important to this incident are detailed.

Mccarthy, John

1987-01-01

20

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

21

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

22

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

23

Detection Probability Modeling for Airport Wind-Shear August 28, 2008  

E-print Network

An objective wind-shear detection probability estimation model is developed for radar, lidar, and sensor the lidar by itself does not yield impressive wind-shear detection statistics, in combination with a radar. This is because the lidar excels at wind-shear detection under low reflectivity conditions when the radar signal

Cho, John Y. N.

24

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

25

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

26

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

27

Shear flow induced wave couplings in the solar wind  

SciTech Connect

A sheared background flow in a plasma induces coupling between different MHD wave modes, resulting in their mutual transformations with corresponding energy redistributing between the modes. In this way, the energy can be transfered from one wave mode to the other, but energy can also be added to or extracted from the background flow. In the present paper it is investigated whether the wave coupling and energy transfer mechanisms can operate under solar wind conditions. It is shown that this is indeed the case. Hence, the long-period waves observed in the solar wind at r > 0.3 AU might be generated by much faster periodic oscillations in the photosphere of the Sun. Other possible consequences for observable beat phenomena in the wind and the acceleration of the solar wind particles are also discussed.

Poedts, S. [KULeuven, Heverlee (Belgium). Centre for Plasma Astrophysics; Rogava, A.D. [Tbilisi State Univ. (Georgia). Dept. of Physics]|[International Centre for Theoretical Physics, Trieste (Italy); Mahajan, S.M. [Univ. of Texas, Austin, TX (United States). Institute for Fusion Studies]|[International Centre for Theoretical Physics, Trieste (Italy)

1998-01-01

28

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

29

A theoretical analysis of airplane longitudinal stability and control as affected by wind shear  

NASA Technical Reports Server (NTRS)

The longitudinal equations of motion with wind shear terms were used to analyze the stability and motions of a jet transport. A positive wind shear gives a decreasing head wind or changes a head wind into a tail wind. A negative wind shear gives a decreasing tail wind or changes a tail wind into a head wind. It was found that wind shear had very little effect on the short period mode and that negative wind shear, although it affected the phugoid, did not cause stability problems. On the other hand, it was found that positive wind shear can cause the phugoid to become aperiodic and unstable. In this case, a stability boundary for the phugoid was found that is valid for most aircraft at all flight speeds. Calculations of aircraft motions confirmed the results of the stability analysis. It was found that a flight path control automatic pilot and an airspeed control system provide good control in all types of wind shear. Appendixes give equations of motion that include the effects of downdrafts and updrafts and extend the longitudinal equations of motion for shear to six degrees of freedom.

Sherman, W. L.

1977-01-01

30

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

31

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

32

The effect of sudden wind shear on the Earth's magnetosphere: Statistics of wind shear events and CCMC simulations of magnetotail disconnections  

NASA Astrophysics Data System (ADS)

The solar wind is filled with strong current sheets and sudden velocity shears; often the two are co-located. Sudden velocity shears at 1 AU are statistically analyzed using ACE measurements from 1998 to 2008. The occurrence rates of passage and the orientations of the shear planes are examined. For shear layers with vector velocity changes |?v| > 50 km/s, an average of ˜12 pass the Earth per day. In the fast wind, ˜60 sudden shear layers pass the Earth per day (about 2.5 per hour). To explore the effects of sudden wind shears on the Earth's magnetosphere, global magnetospheric MHD simulations with four different simulation codes are performed at the Community Coordinated Modeling Center (CCMC) with north-south and east-west wind shears. Windsock movement of the magnetotail is analyzed and comet-like disconnections of the magnetotail and magnetosheath are examined. Sudden changes in the cross-polar-cap potential and ionospheric Joule dissipation are seen as the shear layers pass the Earth. Other potential effects of sudden wind shear on the magnetosphere are discussed.

Borovsky, Joseph E.

2012-06-01

33

Large wind shears and stabilities in the mesopause region observed by Na wind-temperature lidar at midlatitude  

NASA Astrophysics Data System (ADS)

Unexpected large horizontal winds and wind shears in the lower thermosphere have been observed by rocket soundings and lidars for decades. From 4 years of the Colorado State University sodium wind-temperature lidar data set (2002-2005 total of ˜1600 nocturnal h), we observed an altitude distribution of high wind velocity and wind shears between 80 and 105 km, similar to the results of chemical release experiments. Our lidar data show conclusively that when the observed wind shears are plotted as a function of the squared Brunt-Vaisala frequency, N2, they are below the value corresponding to the Richardson number of 1/4, which is a necessary condition of the onset of dynamic instability. This suggests that large wind shears can be sustained in the region of high static stability, for example, in the lower thermosphere, where large wind shears are often observed by rocket sounding. The full-diurnal-cycle lidar data enable the extraction of tidal wave components with periods of 24, 12, 8, and 6 h, therefore allowing us to reveal the strong correlation of 60% between large wind shears (>50 m s-1 km-1) and tidal waves. The lidar-measured seasonal variation in N2 and tidal amplitudes in the mesosphere and lower thermosphere are found to be consistent with the difference in altitude distribution of strong wind shears between winter and summer.

Yue, Jia; She, Chiao-Yao; Liu, Han-Li

2010-10-01

34

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

35

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

E-print Network

SHEAR MODELING IV TOTAL ENERGY SENSOR Theory Bench Tests iVIodeling and Verification 29 33 35 TABLE OF CONTENTS (Continued) CHAPTER V TOTAL ENERGY FEEDBACK RESULTS Profile A: 20 knot Tail Wind, MIL-F-8785C, No Wind Profile B: 20 knot Tail... Wind, ? 0. 3 Gradient. No Wind Profile C: 20 knot Tail Wind. ? 0. 3 Gradient, 20 knot Head Wind Profile D: No Wind, ? 0. 3 Gradsent, 20 knot Head Wind Profile E: 20 knot Head Wind, +0. 3 Gradhent, No Wmd Profile F: 20 knot Head Wind, +0. 1...

Anderson, Thomas Edward

2012-06-07

36

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

37

Vector wind and vector wind shear models 0 to 27 km altitude for Cape Kennedy, Florida, and Vandenberg AFB, California  

NASA Technical Reports Server (NTRS)

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 components and conditional wind components are univariate normally distributed, (2) the wind speed is Rayleigh distributed, (3) the conditional distribution of wind speed given a wind direction is Rayleigh distributed, and (4) the frequency of wind direction can be derived. All of these distributions are derived from the 5-sample parameter of wind for the bivariate normal distribution. By further assuming that the winds at two altitudes are quadravariate normally distributed, then the vector wind shear is bivariate normally distributed and the modulus of the vector wind shear is Rayleigh distributed. The conditional probability of wind component shears given a wind component is normally distributed. Examples of these and other properties of the multivariate normal probability distribution function as applied to Cape Kennedy, Florida, and Vandenberg AFB, California, wind data samples are given. A technique to develop a synthetic vector wind profile model of interest to aerospace vehicle applications is presented.

Smith, O. E.

1976-01-01

38

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

E-print Network

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

39

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

E-print Network

Risø-PhD-Report Accounting for the speed shear in wind turbine power performance measurement Rozenn Wagner Risø-PhD-58(EN) - Short version April 2010 #12;#12;Author: Rozenn Wagner Title: Accounting of a simple method to account for the wind speed shear in the power performance measurement. Ig- noring

40

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

41

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

42

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

43

A method of wind shear detection for powered-lift STOL aircraft  

NASA Technical Reports Server (NTRS)

A new wind shear warning system for powered-lift STOL aircraft was evaluated by using a flight simulator. Wind shear warning systems for CTOL aircraft have been designed to detect horizontal shear only. Because the approach air speed of STOL aircraft is lower than that for CTOL aircraft, STOL aircraft are more vulnerable to vertical wind due to (1) a gradient of horizontal shear that is smaller for STOL than for CTOL aircraft because of slower airspeed; (2) STOL aircraft spend longer time in a downdraft; and (3) vertical wind causes a more radical change in the STOL aircraft's flight path because of its lower airspeed. In order to detect the vertical wind, the wind shear warning system proposed calculates the difference between potential flight path measured on-board during shear traversal and trimmed flight path estimated from aircraft status. The most characteristic feature of this new system is that it utilizes only inertial information and pitot-static airspeed data; this yields a convenient means of on-board implementation. Simulation test results confirm that the new system can detect the vertical shear.

Funabiki, Kohei; Bando, Toshio; Tanaka, Keiji; Hynes, Charles S.; Hardy, Gordon H.

1993-01-01

44

Air flow and shear stress modifications resulting from annual wind barriers  

E-print Network

AIR FLOW AND SHEAR STRESS MODIFICATIONS RESULTING FROM ANNUAL WIND BARRIERS A Thesis by ROBERT CRAIG SCHWARTZ Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree... of MASTER OF SCIENCE May 1992 Major Subject: Soil Science AIR FLOW AND SHEAR STRESS MODIFICATIONS RESULTING FROM ANNUAL WIND BARRIERS A Thesis by ROBERT CRAIG SCHWARTZ Approved as to style and content by. Anthony S. . uo (Co-Chair of Committee...

Schwartz, Robert Craig

2012-06-07

45

Simulation of a STOL airlifter in wind shear, using total energy and glideslope angular error methods for glidepath control  

E-print Network

the wind shear model required the addition of wind shear velocity and gradient terms to the aircraft equations of motion and interpolation methods for the tabular wind shear data. Mathematicai Representation Etkin developed the general equations... the process of selecting paths for the HTTBss. Interpolation Technique In order to spatially use three dimensional wind fields represented 23 Plane al Plane PZ Plane a3 Fig. 6 JAWS Corridor Data Set by tabular data, it was necessary to interpolate...

Johnson, Eric William

2012-06-07

46

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

SciTech Connect

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

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

2010-08-20

47

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

E-print Network

) temperature and horizontal wind, observed by Colorado State University sodium lidar over Fort Collins, CO (411 rights reserved. Keywords: Lidar; Mesopause; Wind shear; Convective instability; Dynamic instability 1 of mesopause region wind shears, convective and dynamic instabilities above Fort Collins, CO: A statistical

48

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

Microsoft Academic Search

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

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

2004-01-01

49

Evaluation of total energy-rate feedback for glidescope tracking in wind shear  

NASA Technical Reports Server (NTRS)

Low-altitude wind shear is recognized as an infrequent but significant hazard to all aircraft during take-off and landing. A total energy-rate sensor, which is potentially applicable to this problem, has been developed for measuring specific total energy-rate of an airplane with respect to the air mass. This paper presents control system designs, with and without energy-rate feedback, for the approach to landing of a transport airplane through severe wind shear and gusts to evaluate application of this sensor. A system model is developed which incorporates wind shear dynamics equations with the airplance equations of motion, thus allowing the control systems to be analyzed under various wind shears. The control systems are designed using optimal output feedback and are analyzed using frequency domain control theory techniques. Control system performance is evaluated using a complete nonlinear simulation of the airplane and a severe wind shear and gust data package. The analysis and simulation results indicate very similar stability and performance characteristics for the two designs. An implementation technique for distributing the velocity gains between airspeed and ground speed in the simulation is also presented, and this technique is shown to improve the performance characteristics of both designs.

Belcastro, C. M.; Ostroff, A. J.

1986-01-01

50

Nocturnal wind direction shear and its potential impact on pollutant transport  

SciTech Connect

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

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

1998-12-31

51

Nocturnal wind direction shear and its potential impact on pollutant transport  

SciTech Connect

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

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

1997-09-01

52

Climatological characteristics of high altitude wind shear and lapse rate layers  

NASA Technical Reports Server (NTRS)

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

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

1981-01-01

53

A parameterisation for the vertical overlap of clouds as a function of wind shear  

NASA Astrophysics Data System (ADS)

More than eight million cloud scenes from CloudSat observation have been analysed in conjunction with co-located ECMWF analysis data to identify an empirical relationship between cloud overlap and wind-shear that can be applied to global models with confidence. The analysis confirms that to a good approximation clouds separated by clear sky gaps are randomly overlapped while continuous cloud layers are close to be maximally overlapped at small separations, but decorrelating in height. The analysis also reveals the very obvious and systematic impact of wind-shear on the decorrelation length-scale, with cloud decorrelating over smaller distances as wind shear increases. A simple linear-fit parametrisation is suggested that is straightforward to add to existing radiation schemes.

Di Giuseppe, Francesca; Tompkins, Adrian

2014-05-01

54

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

55

Performance evaluation of a Doppler radar system for wind shear detection  

NASA Technical Reports Server (NTRS)

Nonlinear stochastic differential equations are used to model wind shear, and extended Kalman filters are used to generate state estimates from measurements received from a Doppler radar onboard an aircraft. Likelihood-ratio tests are then used to detect the presence of wind shear. The performance of the system is evaluated by deriving theoretical expressions for the false alarm and miss error probabiilties. The approach uses a Fokker-Planck equation. The overall methodology is general and should be of interest in other applications.

Khalaf, Camille S.; Hibey, Joseph L.; Staton, Leo D.

1990-01-01

56

The relationship between meteor, wind shear, and sporadic-E layer  

NASA Astrophysics Data System (ADS)

The formation of sporadic-E (Es) layer is explained by several explanations, and wind shear theory and meteor ionized mechanism are mostly used to explain it. If only use each one of wind shear theory and meteor ionized mechanism, it cannot explain the formation of Es layer completely. Only meteor ionized mechanism cannot explain the difference of Es layer activity between north and south hemisphere, and only wind shear theory cannot explain the source of large amount of ionized particle in Es layer. In this study, the activity of Es layer is compared with the meteor information and the global vertical drift information of ionized particles. The global and local meteor information is obtained from International Meteor Organization (IMO) and Radio Meteor Observing Bulletin (RMOB), respectively. The global vertical drift information of ionized particles is calculated by using International Geomagnetic Reference Field (IGRF) model, Horizontal Wind Model (HWM07), and Mass Spectrometer-Incoherent Scatter (MSISE-90) model. The activity of Es layer is based on the value of irregular degree (ID) index, which is derived from the signal to noise ratio (SNR) of Global Positioning System (GPS) radio occultation (RO) data. With both wind shear theory and meteor ionized mechanism, the source of the ionized particles in Es layer and the difference of Es layer activity between north and south hemisphere can be explained completely.

Yeh, W.; Liu, J. G.; Huang, C.; Chen, S.

2013-12-01

57

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

58

Large winds and wind shears caused by the nonlinear interactions between gravity waves and tidal backgrounds in the mesosphere and lower thermosphere  

NASA Astrophysics Data System (ADS)

two-dimensional nonlinear numerical model was used to simulate large winds (? 100 m s-1) and wind shears (? 40 m s-1 km-1) in the mesosphere and lower thermosphere (MLT) that are caused by the interaction between gravity waves (GWs) and migrating tidal background. By varying the wavelengths of GWs and the phases of diurnal and semidiurnal tides, 64 numerical experiments were performed. Our numerical experiments indicate that both migrating diurnal and semidiurnal tides strongly modulate the occurrence of GW breaking, and the resulted large winds and wind shears. The simulated large winds and wind shears are in good agreement with those from the rocket-sounding chemical release measurements. Moreover, the occurrence of large wind shears highly depends on the phases of migrating tides in local time, which is in agreement with the reported lidar observations. The local time dependence of large wind shears is mainly attributed to the filtering and/or hindering effects of diurnal and semidiurnal tidal winds on GWs. Our simulation reveals that the nonlinear interactions between GWs breaking and the migrating diurnal and semidiurnal tides may play an important role in driving the large winds and wind shears in the MLT region and their local time dependence.

Liu, Xiao; Xu, Jiyao; Yue, Jia; Liu, Han Li; Yuan, Wei

2014-09-01

59

Vertical wind shears, turbulence and non-turbulence in the troposphere and stratosphere  

Microsoft Academic Search

A theoretical calculation is made of sigma(h), the standard deviation of vertical wind shears, in terms of the turbulence energy dissipation rate ? and Brunt-Väisälä frequency omegaB. This calculation provides a theoretical basis for the empirical power law relation sigma(h)=A hm obtained by rocket and balloon wind soundings; it also provides a scaling of sigma(h) with atmospheric conditions. The intervals

Jerome Weinstock

1980-01-01

60

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

NASA Astrophysics Data System (ADS)

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

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

2008-09-01

61

Redeployment of the New York TDWR: Technical Analysis of Candidate Sites and Alternative Wind Shear Sensors.  

National Technical Information Service (NTIS)

The John F. Kennedy International Airport (JFK) and LaGuardia Airport (LGA) are protected from wind shear exposure by the New York Terminal Doppler Weather Radar (TDWR), which is currently located at Floyd Bennett Field, New York. Because of a September 1...

J. Y. N. Cho, M. F. Donvan, R. G. Hallowell, R. S. Frankel, S. Huang

2009-01-01

62

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

63

Airborne Doppler lidar detection of wind shear. Results of performance analysis  

NASA Technical Reports Server (NTRS)

Results of a performance analysis of an airborne Doppler radar wind shear detection system are given in vugraph form. It was concluded that both CO sub 2 and Ho:YAG lasers are feasible for dry microburst applications, but with limited performance in wet microbursts. The Ho:YAG performs better than the CO sub 2 for a set of identical lidar parameters.

Huffaker, R. Milton

1988-01-01

64

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

E-print Network

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

65

Inversion and shear layer detection using AMDAR and wind profiler soundings  

NASA Astrophysics Data System (ADS)

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

Drüe, C.; Hauf, T.; Hoff, A.

2009-09-01

66

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

67

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

68

Acquisition of control information in a wind shear  

NASA Technical Reports Server (NTRS)

When an aircraft encounters a change of air mass it may experience a change in horizontal wind sufficient to cause appreciable change in airspeed and, therefore, in lift. It may also suffer a change in vertical wind and, therefore, in vertical speed. The adverse combination of these effects may result in a significant excursion below the correct vertical profile and this may be especially serious if it happens during the latter part of an approach. Appropriate action should then be taken very quickly to avoid a situation from which the aircraft can scarcely recover, implying that suitable information needs to be readily accessible to the pilot. The purpose of this paper is to explore circumstances in which it is difficult to meet this requirement in conventionally equipped aircraft, because of time factors affecting the flow of information.

Naish, J. M.

1977-01-01

69

Importance of wind, fetch and water levels on waves and wave-generated shear stresses in a shallow coastal lagoon  

NASA Astrophysics Data System (ADS)

Wind waves and the bed shear stresses they produce are critical for the morphological and ecological equilibrium of shallow tidal basins. Wave-generated shear stresses are the main mechanism responsible for sediment erosion on tidal flats, and regulate both sediment concentrations in the water column and, together with tidal currents, sediment export to salt marshes and to the ocean. We analyze the response of a system of shallow tidal basins along the Eastern Shore of Virginia, U.S., to wind-wave events, with a specific focus on the interplay of basin morphology, tidal elevation and wind direction on depth, fetch and the resulting wave- generated shear stresses. Our analysis indicates that the potential for erosion is the highest when the salt marshes are submerged. Under these conditions the direction of the wind is critical, with maximum wave heights and erosion potential occurring for winds blowing along the barrier islands of the basin (NNE-SSW). We identify four bottom shear stress regimes produced by wind waves in the Virginia Coastal Reserve as a function of water elevation. For elevations between MLLW and MSL the increase in water depth dominates the increase in wave height thus reducing the bottom shear stresses. For elevations between MSL and MHHW the flooding of the salt marshes increases fetch, wave height and bottom shear stresses, producing the largest resuspesion events in the bay. Finally, for elevations above MHHW, the increase in depth reduces the average bottom shear stresses, thus reducing possible erosion in the tidal flats.

Wiberg, P.; Fagherazzi, S.

2008-12-01

70

Performance analysis and technical assessment of coherent lidar systems for airborne wind shear detection  

NASA Technical Reports Server (NTRS)

Detailed computer simulations of the lidar wind-measuring process have been conducted to evaluate the use of pulsed coherent lidar for airborne windshear monitoring. NASA data fields for an actual microburst event were used in the simulation. Both CO2 and Ho:YAG laser lidar systems performed well in the microburst test case, and were able to measure wind shear in the severe weather of this wet microburst to ranges in excess of 1.4 km. The consequent warning time gained was about 15 sec.

Huffaker, R. Milton; Targ, Russell

1988-01-01

71

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

72

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

73

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

74

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

NASA Technical Reports Server (NTRS)

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

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

1978-01-01

75

Analysis of aircraft control strategies for microburst encounter. [low altitude wind shear  

NASA Technical Reports Server (NTRS)

Analyses have indicated that improved control strategies could reduce the threat posed by the presence of microburst-type wind shear during aircraft takeoffs and landings. The attenuation of flight path response to microburst inputs by feedback control to elevators and throttle was studied for the cases of a jet transport and a general aviation aircraft, using longitudinal equations of motion, root locus analysis, Bode plots of altitude response to wind inputs, and nonlinear numerical simulation. Energy management relative to the airmass, a pitch-up response to the decreasing airspeed, increased phugoid mode damping, and decreased phugoid natural frequency, are found to improve microburst penetration aircraft behavior. Aircraft stall, and throttle saturation, are limiting factors in an aircraft's ability to maintain a given flight path during a microburst encounter.

Stengel, R. F.; Psiaki, M. L.

1984-01-01

76

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

77

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

78

Solar wind driving of magnetospheric ULF waves: Pulsations driven by velocity shear at the magnetopause  

NASA Astrophysics Data System (ADS)

We present results from global, three-dimensional magnetohydrodynamic (MHD) simulations of the solar wind/magnetosphere interaction. These MHD simulations are used to study ultra low frequency (ULF) pulsations in the Earth's magnetosphere driven by shear instabilities at the flanks of the magnetopause. We drive the simulations with idealized, constant solar wind input parameters, ensuring that any discrete ULF pulsations generated in the simulation magnetosphere are not due to fluctuations in the solar wind. The simulations presented in this study are driven by purely southward interplanetary magnetic field (IMF) conditions, changing only the solar wind driving velocity while holding all of the other solar wind input parameters constant. We find surface waves near the dawn and dusk flank magnetopause and show that these waves are generated by the Kelvin-Helmholtz (KH) instability. We also find that two KH modes are generated near the magnetopause boundary. One mode, the magnetopause KH mode, propagates tailward along the magnetopause boundary. The other mode, the inner KH mode, propagates tailward along the inner edge of the boundary layer (IEBL). We find large vortical structures associated with the inner KH mode that are centered on the IEBL. The phase velocities, wavelengths, and frequencies of the two KH modes are computed. The KH waves are found to be fairly monochromatic with well-defined wavelengths. In addition, the inner and magnetopause KH modes are coupled and lead to a coupled oscillation of the low-latitude boundary layer. The boundary layer thickness, d, is computed and we find maximum wave growth for kd = 0.5-1.0, where k is the wave number, consistent with the linear theory of the KH instability. We comment briefly on the effectiveness of these KH waves in the energization and transport of radiation belt electrons.

Claudepierre, S. G.; Elkington, S. R.; Wiltberger, M.

2008-05-01

79

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

80

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

81

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

82

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

83

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

NASA Technical Reports Server (NTRS)

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

Hinton, David A.

1989-01-01

84

4A.2 THE STRUCTURE AND EVOLUTION OF A HURRICANE IN VERTICAL WIND SHEAR: HURRICANE ELENA (1985)  

E-print Network

4A.2 THE STRUCTURE AND EVOLUTION OF A HURRICANE IN VERTICAL WIND SHEAR: HURRICANE ELENA (1985. One of the most complete data sets of a single tropical cyclone was recorded in Hurricane Elena (1985), as it was a slow moving, intensifying, convectively active tropical cyclone in the Gulf of Mexico. Elena

Corbosiero, Kristen L.

85

Dynamic impact of the vertical shear of gradient wind on the tropical cyclone boundary layer wind field  

NASA Astrophysics Data System (ADS)

This work studies the impact of the vertical shear of gradient wind (VSGW) in the free atmosphere on the tropical cyclone boundary layer (TCBL). A new TCBL model is established, which relies on fiveforce balance including the pressure gradient force, Coriolis force, centrifugal force, turbulent friction, and inertial deviation force. This model is then employed to idealize tropical cyclones (TCs) produced by DeMaria's model, under different VSGW conditions (non-VSGW, positive VSGW, negative VSGW, and VSGW increase/decrease along the radial direction). The results show that the free-atmosphere VSGW is particularly important to the intensity of TC. For negative VSGW, the total horizontal velocity in the TCBL is somewhat suppressed. However, with the maximum radial inflow displaced upward and outward, the radial velocity notably intensifies. Consequently, the convergence is enhanced throughout the TCBL, giving rise to a stronger vertical pumping at the TCBL top. In contrast, for positive VSGW, the radial inflow is significantly suppressed, even with divergent outflow in the middle-upper TCBL. For varying VSGW along the radial direction, the results indicate that the sign and value of VSGW is more important than its radial distribution, and the negative VSGW induces stronger convergence and Ekman pumping in the TCBL, which favors the formation and intensification of TC.

Cai, Ninghao; Xu, Xin; Song, Lili; Bai, Lina; Ming, Jie; Wang, Yuan

2014-02-01

86

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

NASA Astrophysics Data System (ADS)

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

Coniglio, Michael Charles

87

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

88

American Institute of Aeronautics and Astronautics Wind Shear over Forested Areas  

E-print Network

. Rogers* , James F. Manwell and Anthony F. Ellis Renewable Energy Research Laboratory, University resource assessment. SODAR data from a forested island offshore of Maine are used to estimate mean shear at a meteorological tower on the island of Vinalhaven, offshore of Maine1 (see Fig. 1). The tower sits on a low

Massachusetts at Amherst, University of

89

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

NASA Astrophysics Data System (ADS)

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

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

2009-05-01

90

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

NASA Astrophysics Data System (ADS)

An important roadblock to improved intensity forecasts for tropical cyclones (TCs) is our incomplete understanding of the interaction of a TC with the environmental flow. In this paper we re-visit the canonical problem of a TC in vertical wind shear on an f-plane. A suite of numerical experiments is performed with intense TCs in moderate to strong vertical shear. We employ a set of simplified model physics - a simple bulk aerodynamic boundary layer scheme and "warm rain" microphysics - to foster better understanding of the dynamics and thermodynamics that govern the modification of TC intensity. In all experiments the TC is resilient to shear but significant differences in the intensity evolution occur. The ventilation of the TC core with dry environmental air at mid-levels and the dilution of the upper-level warm core are two prevailing hypotheses for the adverse effect of vertical shear on storm intensity. Here we propose an alternative and arguably more effective mechanism how cooler and drier (lower ?e) air - "anti-fuel" for the TC power machine - can enter the core region of the TC. Strong and persistent, shear-induced downdrafts flux low ?e air into the boundary layer from above, significantly depressing the ?e values in the storm's inflow layer. Air with lower ?e values enters the eyewall updrafts, considerably reducing eyewall ?e values in the azimuthal mean. When viewed from the perspective of an idealised Carnot-cycle heat engine a decrease of storm intensity can thus be expected. Although the Carnot cycle model is - if at all - only valid for stationary and axisymmetric TCs, a close association of the downward transport of low ?e into the boundary layer and the intensity evolution offers further evidence in support of our hypothesis. The downdrafts that flush the boundary layer with low ?e air are tied to a quasi-stationary, azimuthal wave number 1 convective asymmetry outside of the eyewall. This convective asymmetry and the associated downdraft pattern extends outwards to approximately 150 km. Downdrafts occur on the vortex scale and form when precipitation falls out from sloping updrafts and evaporates in the unsaturated air below. It is argued that, to zero order, the formation of the convective asymmetry is forced by frictional convergence associated with the azimuthal wave number 1 vortex Rossby wave structure of the outer-vortex tilt. This work points to an important connection between the thermodynamic impact in the near-core boundary layer and the asymmetric balanced dynamics governing the TC vortex evolution.

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

2010-04-01

91

VELOCITY-SHEAR-INDUCED MODE COUPLING IN THE SOLAR ATMOSPHERE AND SOLAR WIND: IMPLICATIONS FOR PLASMA HEATING AND MHD TURBULENCE  

SciTech Connect

We analytically consider how velocity shear in the corona and solar wind can cause an initial Alfven wave to drive up other propagating signals. The process is similar to the familiar coupling into other modes induced by non-WKB refraction in an inhomogeneous plasma, except here the refraction is a consequence of velocity shear. We limit our discussion to a low-beta plasma, and ignore couplings into signals resembling the slow mode. If the initial Alfven wave is propagating nearly parallel to the background magnetic field, then the induced signals are mainly a forward-going (i.e., propagating in the same sense as the original Alfven wave) fast mode, and a driven signal propagating like a forward-going Alfven wave but polarized like the fast mode; both signals are compressive and subject to damping by the Landau resonance. For an initial Alfven wave propagating obliquely with respect to the magnetic field, the induced signals are mainly forward- and backward-going fast modes, and a driven signal propagating like a forward-going Alfven wave but polarized like the fast mode; these signals are all compressive and subject to damping by the Landau resonance. A backward-going Alfven wave, thought to be important in the development of MHD turbulence, is also produced, but it is very weak. However, we suggest that for oblique propagation of the initial Alfven wave the induced fast-polarized signal propagating like a forward-going Alfven wave may interact coherently with the initial Alfven wave and distort it at a strong-turbulence-like rate.

Hollweg, Joseph V.; Chandran, Benjamin D. G. [Space Science Center, Morse Hall, University of New Hampshire, Durham, NH 03824 (United States); Kaghashvili, Edisher Kh., E-mail: joe.hollweg@unh.edu, E-mail: ekaghash@aer.com, E-mail: benjamin.chandran@unh.edu [Atmospheric and Environmental Research, A Verisk Analytics Company, 131 Hartwell Avenue, Lexington, MA 02421 (United States)

2013-06-01

92

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

NASA Astrophysics Data System (ADS)

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

Wang, Yongqing; Sun, Jiming

2014-05-01

93

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

94

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.

95

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

96

Effect of shear on aircraft landing  

NASA Technical Reports Server (NTRS)

A simulation study was conducted to determine the effect of wind shear on aircraft landings. The landing of various type of commercial and military aircraft was digitally simulated starting from an initial altitude of 300 feet. Assuming no pilot feedback during descent, the deviation in touchdown point due to vertical profiles of wind shear was determined. The vertical profiles of wind shear are defined in terms of surface roughness, Z sub 0, and stability, L, parameters. The effects on touchdown due to Z sub 0 and L have been calculated for the different type aircraft. Comparisons were made between the following types of aircraft: (1) C-130E, (2) C-135A, (3) C-141, (4) DC-8, (5) Boeing 747, and (6) an augmentor-wing STOL. In addition, the wind shear effect on touchdown resulting from different locations of the center of gravity and gross weights was also analyzed.

Luers, J. K.; Reeves, J. B.

1973-01-01

97

Nonlinear water waves with shear  

NASA Astrophysics Data System (ADS)

Various aspects of nonlinear inviscid gravity waves in the presence of shear in the air and water are investigated. The shear, which appears due to the presence of wind in the air and current in the water, is modeled by a piecewise linear velocity profile. The interaction of short and long gravity waves is studied numerically, using spectral methods, and analytically, using perturbation methods. Special attention is paid to the verification of observations and experimental results. It is confirmed that finite amplitude waves propagating in the same direction as the wind or current are more stable with respect to superharmonic infinitesimal perturbations than the waves moving against the wind or current. Infinitesimal perturbations in the form of side bands are also investigated both numerically and analytically. The nonlinear cubic Schrodinger equation for the wave envelope of a slowly varying wave train is derived. It is shown that depending on the direction of propagation (along or against the shear) of the finite amplitude waves, the effect of the shear on the stability is substantially different. In most cases, however, the shear strength increase first enhances the instability, but later suppresses it. Three-wave interactions of gravity waves with shear in the water are considered. The interaction equations are derived with the help of two different perturbation approaches. The question of stability is addressed for both resonant and near-resonant interactions. The regions of explosive and 'pump-wave' instability are identified for various types of three-wave interactions. A new type of steady two-dimensional gravity waves with water shear is computed numerically. These waves appear at relatively low amplitudes and lack symmetry with respect to any crest or trough. A boundary integral formulation is used to obtain a one-parameter family of non-symmetric solutions through a symmetry-breaking bifurcation.

Baumstein, Anatoly I.

98

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.

99

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

100

Shear Strength  

NSDL National Science Digital Library

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

Atkinson, John

2008-10-07

101

Vertical wind estimation from horizontal wind measurements  

NASA Technical Reports Server (NTRS)

This presentation begins with a brief description of the downdraft measurement problem for airborne Doppler based systems and the importance of the downdraft in assessing the hazard posed by a microburst wind shear. This is followed by a review of research on the feasibility of using simple microburst models to compute the downdraft from horizontal wind measurements. The current methodologies for computing the vertical wind are then discussed. A summary of the results and the plan for future research are also presented.

Vicroy, Dan D.

1992-01-01

102

Shear thickening, shear localization and elastic turbulence  

Microsoft Academic Search

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

Daniel Bonn

2006-01-01

103

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

104

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

105

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. PMID:18383661

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

2008-01-01

106

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

E-print Network

Ultraviolet observations of classical T Tauri Stars (cTTSs) have shown that there is a hot (Te ~ 80,000 K) and dense (ne ~ 1e10 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 alpha/Omega-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 ...

de Castro, Ana I Gomez

2010-01-01

107

Wind prospecting study for Western Massachusetts and Northwestern Connecticut. Phase III. Volume I  

Microsoft Academic Search

Summaries of a wind energy project cover the March 1, 1981 to January 31, 1983 data on wind speed for several sites in Northwestern Connecticut and Western Massachusetts. There is also an extensive analysis describing the manner in which wind speed increases with height above ground level (wind shear) at two sites. The project examined wind shear as a function

F. C. Kaminsky; R. H. Kirchhoff

1983-01-01

108

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

109

Wind turbine acoustics  

NASA Astrophysics Data System (ADS)

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

Hubbard, Harvey H.; Shepherd, Kevin P.

1990-12-01

110

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

111

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

E-print Network

, we roughly simulated the wind speed measurements we may get from a LIDAR mounted on the nacelleRisø-R-Report Simulation of shear and turbulence impact on wind turbine performance Wagner Rozenn and turbulence impact on wind turbine power performance Division: Wind Energy Risø-R-1722(EN) January 2010 ISSN

112

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

113

Cluster Crystals under Shear  

NASA Astrophysics Data System (ADS)

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

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

2011-08-01

114

Reduced shear power spectrum  

SciTech Connect

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

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

2005-08-01

115

Ultrasound shear wave imaging  

Microsoft Academic Search

Shear wave propagation properties including phase velocity and attenuation coefficient are indispensable information in materials characterization and nondestructive evaluation. A computer controlled scanning shear-wave ultrasonic imaging system has been developed. It consists of a pair of focusing broadband pvdf transducers of central frequency of 50 MHz immersed in distilled water. Shear waves in a solid specimen are generated by mode-conversion.

Shigong Ye; Junru Wu

2000-01-01

116

Microburst vertical wind estimation from horizontal wind measurements  

NASA Technical Reports Server (NTRS)

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

Vicroy, Dan D.

1994-01-01

117

Dipole shear anisotropy logging  

SciTech Connect

Sonic-scale shear anisotropy of formations are obtained from dipole-shear measurements acquired by orthogonal source and receiver pairs. These measurements resemble miniature 4-component shear VSP surveys inside the borehole. Data from two orthogonal sources and an array of orthogonal receivers are processed providing three main logs; the fast and slow shear slownesses, and the fast shear polarization angle. Potential applications include: shale anisotropy for better seismic models, maximum stress and fracture/microcrack strike direction for horizontal well drilling and fracture height and azimuth determination in hydraulic fracturing.

Esmersoy, C.; Kane, M. [Schlumberger-Doll Research, Ridgefield, CT (United States); Koster, K.; Williams, M. [Amoco Production, Denver, CO (United States); Boyd, A. [GeoQuest, Aurora, CO (United States)

1994-12-31

118

Shearing stability of lubricants  

NASA Technical Reports Server (NTRS)

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

Shiba, Y.; Gijyutsu, G.

1984-01-01

119

TURBULENT SHEAR ACCELERATION  

SciTech Connect

We consider particle acceleration by large-scale incompressible turbulence with a length scale larger than the particle mean free path. We derive an ensemble-averaged transport equation of energetic charged particles from an extended transport equation that contains the shear acceleration. The ensemble-averaged transport equation describes particle acceleration by incompressible turbulence (turbulent shear acceleration). We find that for Kolmogorov turbulence, the turbulent shear acceleration becomes important on small scales. Moreover, using Monte Carlo simulations, we confirm that the ensemble-averaged transport equation describes the turbulent shear acceleration.

Ohira, Yutaka, E-mail: ohira@phys.aoyama.ac.jp [Department of Physics and Mathematics, Aoyama Gakuin University, 5-10-1 Fuchinobe, Sagamihara 252-5258 (Japan)

2013-04-10

120

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

121

Wind power meteorology. Part I: climate and turbulence  

NASA Astrophysics Data System (ADS)

Wind power meteorology has evolved as an applied science firmly founded on boundary layer meteorology but with strong links to climatology and geography. It concerns itself with three main areas: siting of wind turbines, regional wind resource assessment and short-term prediction of the wind resource. The history, status and perspectives of wind power meteorology are presented, with emphasis on physical considerations and on its practical application. Following a global view of the wind resource, the elements of boundary layer meteorology which are most important for wind energy are reviewed: wind profiles and shear, turbulence and gust, and extreme winds. Copyright

Petersen, Erik L.; Mortensen, Niels G.; Landberg, Lars; Højstrup, Jørgen; Frank, Helmut P.

1998-09-01

122

Angular shear plate  

Microsoft Academic Search

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

Mitchell C. Ruda; Alan W. Greynolds; Tilman W. Stuhlinger

2009-01-01

123

Shear flexibility for structures  

NASA Technical Reports Server (NTRS)

This device comprises a flexible sheet member having cross convolutions oriented 45.degree. to the shear vector with spherical reliefs at the convolution junctions. The spherical reliefs are essential to the shear flexibility by interrupting the principal stress lines that act along the ridges of the convolutions. The spherical reliefs provide convolutions in both directions in the plane of the cross-convolution ridges.

Stangeland, Maynard L. (Inventor)

1976-01-01

124

Shear flexibility for structures  

NASA Technical Reports Server (NTRS)

This device comprises a flexible sheet member having cross convolutions oriented 45.degree. to the shear vector with spherical reliefs at the convolution junctions. The spherical reliefs are essential to the shear flexibility by interrupting the principal stress lines that act along the ridges of the convolutions. The spherical reliefs provide convolutions in both directions in the plane of the cross-convolution ridges.

Stangeland, Maynard L. (Inventor)

1977-01-01

125

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

126

Shear thickening fluid  

Microsoft Academic Search

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

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

1985-01-01

127

Shear thinning vs shear thickening in associating fluids  

Microsoft Academic Search

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

G. T. Evans

1998-01-01

128

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. The module comes with audio narration, rich graphics, and a companion print version.

Comet

2003-11-18

129

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

130

Nonlinear fluid behavior: from shear thinning to shear thickening  

Microsoft Academic Search

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

Ortwin Hess; Siegfried Hess

1994-01-01

131

Shear Unzipping of DNA  

E-print Network

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

Buddhapriya Chakrabarti; David R. Nelson

2009-04-09

132

Cosmic Shear Review  

E-print Network

We present an overview of the cosmic shear results obtained so far. We focus on the 2-point statistics only. Evidences supporting the cosmological origin of the measured signal are reviewed, and issues related to various systematics are discussed.

Van Waerbeke, L; Mellier, Y; Bernardeau, F

2002-01-01

133

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

134

Bacteria in shear flow  

E-print Network

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

Marcos, Ph.D. Massachusetts Institute of Technology

2011-01-01

135

A multiple beam lidar for wind measurement  

Microsoft Academic Search

High-resolution remote measurements of vertical wind profiles by lidar (laser radar) are desirable for a number of reasons, including the detection of shear layers in the atmosphere, and scientific studies of turbulence. Existing methods for the determination of wind speed by lidar involve correlations of several separate lidar signals and are plagued with noise problems and complicated data analysis. A

John Rolland Krieger

2000-01-01

136

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

Microsoft Academic Search

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

Chin-Hoh Moeng; Peter P. Sullivan

1994-01-01

137

Threshold-of-Motion Wind Friction Speeds at the Mars Pathfinder Landing Site  

NASA Astrophysics Data System (ADS)

Threshold-of-motion wind friction speeds are calculated for the Pathfinder site, using IMP windsock results and shear-stress partitioning. Stronger winds than previous estimates must have occurred in the past to explain observed aeolian features.

Sullivan, R. J.

2002-03-01

138

IEEE TRANSACTIONS ON ENERGY CONVERSION, VOL. 21, NO. 3, SEPTEMBER 2006 717 Simulation Model of Wind Turbine 3p Torque  

E-print Network

Turbine 3p Torque Oscillations due to Wind Shear and Tower Shadow Dale S. L. Dolan, Student Member, IEEE quality issues, the dynamic torque generated by the blades of a wind turbine must be represented turbine including the effects of wind shear and tower shadow. The comprehensive model includes turbine

Lehn, Peter W.

139

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. PMID:24781409

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

2014-01-01

140

Shear thickening of cornstarch suspensions  

E-print Network

We study the rheology of cornstarch suspensions, a non-Brownian particle system that exhibits discontinuous shear thickening. Using magnetic resonance imaging (MRI), the local properties of the flow are obtained by the determination of local velocity profiles and concentrations in a Couette cell. For low rotational rates, we observe shear localization characteristic of yield stress fluids. When the overall shear rate is increased, the width of the sheared region increases. The discontinuous shear thickening is found to set in at the end of this shear localization regime when all of the fluid is sheared: the existence of a nonflowing region, thus, seems to prevent or delay shear thickening. Macroscopic observations using different measurement geometries show that the smaller the gap of the shear cell, the lower the shear rate at which shear thickening sets in. We, thus, propose that the discontinuous shear thickening of cornstarch suspensions is a consequence of dilatancy: the system under flow attempts to dilate but instead undergoes a jamming transition, because it is confined. This proposition is confirmed by an independent measurement of the dilation of the suspension as a function of the shear rate. It is also explains the MRI observations: when flow is localized, the nonflowing region plays the role of a "dilatancy reservoir" which allows the material to be sheared without jamming.

Abdoulaye Fall; François Bertrand; Guillaume Ovarlez; Daniel Bonn

2012-06-08

141

Detailed Analysis of a 550MW Installed Capacity Wind Farm in Saudi Arabia  

Microsoft Academic Search

The study presents the wind speed data, frequency distribution, local wind shear exponent, energy yield, air density, and turbulence intensity analysis for a site located in the eastern region of Saudi Arabia. Overall mean wind speed values at 20, 30, and 40 m above ground level were 4.72, 5.34, and 5.74 m\\/s respectively. The mean local wind shear exponent and

Shafiqur Rehman; Aftab Ahmad; Luai M. Al-Hadhrami

2010-01-01

142

Shearing Strength of Concrete  

E-print Network

was to obtain values of shear that might be applied in the design of masonry. BIBLIOGRAPHY. Beu30hanger. In 1878, Herr Bau^changer con­ ducted a series of tests on parte of concrete prisms that had been broken by flexur?. He found concrete two years old.... In making up the apparatus, considerable time was required. It consisted of stone screens, a water­ tight box for determining percentage of wolds in the aggregate, moulds and shears for testing the prisms* fhe rock screens are made of wire netting stapled...

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

1907-01-01

143

Shear thinning and shear thickening characteristics in electrorheological fluids  

NASA Astrophysics Data System (ADS)

The electrorheology (ER) of suspensions based on polystyrene/polyaniline (PS/PANI) core/shell structured microspheres and those based on disk-like zeolite particles at different electric fields and particle volume fractions have been studied, respectively. Both types of ER fluids showed abrupt shear thickening under high electric fields and low shear rates, as well as shear thinning when the shear rate increased. A normalized method that considers the effects of electric field strength, shear rate and particle volume fraction was proposed to compare the rheological curves of the two ER fluids. The curves evaluated from the normalization method showed similar shear thinning at low shear rates and the hydrodynamic effect at high shear rates. Shear thinning represents the structure destroyed by shearing, and shear thickening at low shear regions indicates the dramatic structure change. The particle volume fraction and structure factor effects demonstrate that the mechanical contact between particles and the wall of the electrodes is crucial to the shear strength of ER fluids, indicating an electric/magnetic field modulated friction mechanism of the ER and magnetorheological (MR) effects.

Jiang, Jile; Liu, YingDan; Shan, Lei; Zhang, Xiangjun; Meng, Yonggang; Choi, Hyoung Jin; Tian, Yu

2014-01-01

144

Winding for the wind  

Microsoft Academic Search

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

O. Weingart

1981-01-01

145

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

146

Shear consolidation of powders  

NASA Astrophysics Data System (ADS)

The manufacture of bulk parts from metastable powder materials requires new approaches to cold consolidation. One potential technique is equal-channel angular extrusion (ECAE), a simple shear process. This thesis describes an investigation into the effects of confining pressure (back-pressure) on single-pass, right-angled ECAE consolidation of copper and aluminum 6061 powders below 250°C, using an extrusion machine designed and constructed for this purpose. Empirical relationships for punch pressure requirements as a function of back-pressure and billet length are determined experimentally and compared with published theory. Powder particle boundaries are examined in extruded billets, revealing pores and regions of localized shear formed under low back-pressure conditions. This shear localization is considered with a visualization experiment involving wax spheres in a transparent die, and a linear stability analysis of simple shear of a thin strip of material described by a generalized powder yield function and flow rule. The back-pressures required to obtain homogeneous, pore-free microstructures are determined, and related to the response of the powders during the initial compaction stage of ECAE. Interparticle bond formation in cold powder processing is briefly discussed in the context of multi-pass extrusions.

Hanna, James A.

147

Three Dimensional Dynamic Model Based Wind Field Reconstruction from Lidar Data  

NASA Astrophysics Data System (ADS)

Using the inflowing horizontal and vertical wind shears for individual pitch controller is a promising method if blade bending measurements are not available. Due to the limited information provided by a lidar system the reconstruction of shears in real-time is a challenging task especially for the horizontal shear in the presence of changing wind direction. The internal model principle has shown to be a promising approach to estimate the shears and directions in 10 minutes averages with real measurement data. The static model based wind vector field reconstruction is extended in this work taking into account a dynamic reconstruction model based on Taylor's Frozen Turbulence Hypothesis. The presented method provides time series over several seconds of the wind speed, shears and direction, which can be directly used in advanced optimal preview control. Therefore, this work is an important step towards the application of preview individual blade pitch control under realistic wind conditions. The method is tested using a turbulent wind field and a detailed lidar simulator. For the simulation, the turbulent wind field structure is flowing towards the lidar system and is continuously misaligned with respect to the horizontal axis of the wind turbine. Taylor's Frozen Turbulence Hypothesis is taken into account to model the wind evolution. For the reconstruction, the structure is discretized into several stages where each stage is reduced to an effective wind speed, superposed with a linear horizontal and vertical wind shear. Previous lidar measurements are shifted using again Taylor's Hypothesis. The wind field reconstruction problem is then formulated as a nonlinear optimization problem, which minimizes the residual between the assumed wind model and the lidar measurements to obtain the misalignment angle and the effective wind speed and the wind shears for each stage. This method shows good results in reconstructing the wind characteristics of a three dimensional turbulent wind field in real-time, scanned by a lidar system with an optimized trajectory.

Raach, Steffen; Schlipf, David; Haizmann, Florian; Cheng, Po Wen

2014-06-01

148

Using deformed critters to determine angular shear and shear strain  

NSDL National Science Digital Library

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

Moore, Angela

149

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

E-print Network

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

150

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

151

On horizontal wind gradient variability from the stratosphere to the lower troposphere in the Arctic  

Microsoft Academic Search

Previous studies have demonstrated changes in vertical wind shear in recent decades, with implications for upward-propagating planetary waves, the stratospheric polar vortex, and tracer transport. Changes in vertical wind shear combined with horizontal gradients have also been shown to contribute to an increase in vertical gradients in tracer fields, with important implications for vertical transport. In order to explore the

J. V. Lukovich; D. G. Barber

2009-01-01

152

Meteorology (Wind)  

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

2014-09-25

153

Shear-thickening compositions  

SciTech Connect

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

Swanson, B.L.

1981-10-06

154

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

155

Shear thickening fluid  

SciTech Connect

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

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

1985-03-05

156

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

157

The mechanism for shear thickening in suspensions  

Microsoft Academic Search

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

Eric Brown; Heinrich Jaeger

2009-01-01

158

Dynamics of a deformable active particle under shear flow.  

PubMed

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

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

2013-09-14

159

A Simple Method to Predict Threshold Shear Velocity in the Field  

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

160

Dual-hologram shearing interferometry with regulated sensitivity.  

PubMed

A novel optical diagnostic technique, namely, dual-hologram shearing interferometry with regulated sensitivity, is proposed for visualization and measuring of the density gradients of compressible flows in wind tunnels. It is superior to conventional shearing interferometry in both accuracy and sensitivity. The method is especially useful for strong turbulent or unsteady regions of the flows, including shock flows. The interferometer has proved to be insensitive to mechanical vibrations and has allowed us to record holograms during the noisy wind-tunnel run. The proposed approach is demonstrated by application to a supersonic flow over spherically blunted and sharp nose-cone-cylinder models. We believe that the technique will become an effective tool for receiving optical data in many flow facilities. PMID:18285991

Toker, G R; Levin, D

1998-08-01

161

Excited waves in shear layers  

NASA Technical Reports Server (NTRS)

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

Bechert, D. W.

1982-01-01

162

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

163

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

164

Flexural traveling wave excitation based on shear-shear mode  

Microsoft Academic Search

This paper presents a new mechanism for circular flexture traveling wave excitation, which is based on a shear-shear mode in a single piezoelectric disc with a center hole was poled along its radial direction. Its bottom electrode was divided into four parts, and the top electrode acted as common ground. By use of a pair of alternating current (AC) voltage

Shuxiang Dong; Jindong Zhang; Hyeoung Woo Kim; Michael T. Strauss; Kenji Uchino; Dwight Viehland

2004-01-01

165

Minimal model for chaotic shear banding in shear thickening fluids  

Microsoft Academic Search

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

A. Aradian; M. E. Cates

2006-01-01

166

Shear rejuvenation, aging and shear banding in yield stress fluids  

Microsoft Academic Search

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

Andreas N. Alexandrou; Nicholas Constantinou; Georgios Georgiou

2009-01-01

167

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

168

Passive cyclic pitch control for horizontal axis wind turbines  

NASA Technical Reports Server (NTRS)

A flexible rotor concept, called the balanced pitch rotor, is described. The system provides passive adjustment of cyclic pitch in response to unbalanced pitching moments across the rotor disk. Various applications are described and performance predictions are made for wind shear and cross wind operating conditions. Comparisons with the teetered hub are made and significant cost savings are predicted.

Bottrell, G. W.

1981-01-01

169

Tubular shear wave source  

SciTech Connect

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

Cole, J.H.

1989-09-19

170

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

171

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

172

The limited growth of vegetated shear layers  

E-print Network

In contrast to free shear layers, which grow continuously downstream, shear layers generated by submerged vegetation grow only to a finite thickness. Because these shear layers are characterized by coherent vortex structures ...

Ghisalberti, M.

173

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

NASA Astrophysics Data System (ADS)

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

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

2010-05-01

174

Critical shear stresses in cohesive soils  

E-print Network

Dimensions of the Test Apparatus. 12 12 Testing Procedure 15 Sample Preparation Performing the Scour Tests Summary of Scour Test Procedures. . . . . . . . . . Vane Shear Test Void Ratio and Per Cent Moisture Determinations 15 16 19 20 21 RESULTS... on Vane Shear Strength 32 Regression of Critical Shearing Force on Void Ratio 33 12. Critical Shearing Force at Liquid Limit versus Plasticity Index 39 13. Critical Shearing Force at Liquid Limit versus Per Cent Clay . . 39 Critical Shearing Force...

Rektorik, Robert James

2012-06-07

175

An approach to evaluating reactive airborne wind shear systems  

NASA Technical Reports Server (NTRS)

An approach to evaluating reactive airborne windshear detection systems was developed to support a deployment study for future FAA ground-based windshear detection systems. The deployment study methodology assesses potential future safety enhancements beyond planned capabilities. The reactive airborne systems will be an integral part of planned windshear safety enhancements. The approach to evaluating reactive airborne systems involves separate analyses for both landing and take-off scenario. The analysis estimates the probability of effective warning considering several factors including NASA energy height loss characteristics, reactive alert timing, and a probability distribution for microburst strength.

Gibson, Joseph P., Jr.

1992-01-01

176

Simulated performance of an airborne lidar wind shear detection system  

E-print Network

3, 1 Historical Background 3. 2 Doppler Lidar Theory 3. 3 Atmospheric Effects 3. 4 General Lidar System Description 13 14 20 27 IV. COHERENT LIDAR COMPUTER SIMULATiON . . 4. 1 Elements of Simulation 4. 2 Lidar Instrument Model 4. 3... 3, 1 Historical Background 3. 2 Doppler Lidar Theory 3. 3 Atmospheric Effects 3. 4 General Lidar System Description 13 14 20 27 IV. COHERENT LIDAR COMPUTER SIMULATiON . . 4. 1 Elements of Simulation 4. 2 Lidar Instrument Model 4. 3...

Griffith, Kenneth Scott

2012-06-07

177

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

178

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

NASA Technical Reports Server (NTRS)

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

Decker, Ryan K.; Leach, Richard

2005-01-01

179

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

180

Electroconvection in Sheared Annular Films  

Microsoft Academic Search

We report experiments on electroconvection in thin suspended films of a smectic A liquid crystal (8CB). These films behave as nearly ideal 2D isotropic fluids. The films were annular with radius ratio (inner\\/outer electrode radius) ~ 0.8. Shears may be applied by rotating the inner electrode. When no shear is applied, the film is unstable to a stationary roll state

Z. A. Daya; S. W. Morris; T. C. A. Molteno; J. R. de Bruyn

1996-01-01

181

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

182

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. PMID:24309379

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

2013-01-01

183

Shear shocks in fragile networks.  

PubMed

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

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

2013-12-24

184

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

185

Dynamic properties of shear thickening colloidal suspensions  

Microsoft Academic Search

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

Young Sil Lee; Norman J. Wagner

2003-01-01

186

Generality of shear thickening in dense suspensions  

Microsoft Academic Search

Suspensions are of wide interest and form the basis for many smart fluids. For most suspensions, the viscosity decreases with increasing shear rate, that is, they shear thin. Few are reported to do the opposite, that is, shear thicken, despite the longstanding expectation that shear thickening is a generic type of suspension behaviour. Here we resolve this apparent contradiction. We

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

2010-01-01

187

Shear thickening in highly viscous granular suspensions  

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

188

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

189

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

Microsoft Academic Search

Failure in sheared-edge stretching often limits the use of advanced high-strength steel sheets in automotive applications. The present study analyzes data in the literature from laboratory experiments on both the shearing process and the characteristics of sheared edges. Shearing produces a surface with regions of rollover, burnish, fracture, and burr. The effect of clearance and tensile strength on the shear

B. S. Levy; C. J. van Tyne

2011-01-01

190

Shear Properties of the Temporomandibular Joint Disc in Relation to Compressive and Shear Strain  

Microsoft Academic Search

Shear stress can result in fatigue, damage, and irreversible deformation of the temporomandibular joint disc. Insight into the dynamic shear properties of the disc may give insight into the mechanism inducing tissue failure due to shear. We tested the hypothesis that the dynamic shear properties of the disc depend on the amount of shear and compressive strain. Twenty-four porcine discs

E. Tanaka; N. Kawai; K. Hanaoka; T. van Eijden; A. Sasaki; J. Aoyama; M. Tanaka; K. Tanne

2004-01-01

191

Wind Energy Leasing Handbook  

E-print Network

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

Balasundaram, Balabhaskar "Baski"

192

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

193

Minimal model for chaotic shear banding in shear thickening fluids.  

PubMed

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

Aradian, A; Cates, M E

2006-04-01

194

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

195

Wind Tunnel  

NSDL National Science Digital Library

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

Science, Lawrence H.

2009-01-01

196

Global Winds  

NSDL National Science Digital Library

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

197

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

198

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

199

Isogeometric analysis of shear bands  

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

200

Wind Surge  

NSDL National Science Digital Library

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

Dalrymple, Robert A.; Delaware, University O.

201

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.

202

Wind Monitoring Report for Fort Wainwright's Donnelly Training Area  

SciTech Connect

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

Orrell, Alice C.; Dixon, Douglas R.

2011-01-18

203

The wind characteristics program  

Microsoft Academic Search

Wind characteristics research activities emphasize wind resource assessment, site selection and evaluation techniques, and wind characteristics for wind turbine design, performance and operations evaluation. Wind resource analysis shows the greatest area of high wind power resource is in the midsection of the U.S. High wind power is available in other sections of the country and is described in some detail

L. L. Wendell

1981-01-01

204

Experimental observation of shear thickening oscillation  

E-print Network

We report experimental observation of the shear thickening oscillation, i.e. the spontaneous macroscopic oscillation in the shear flow of severe shear thickening fluid. The shear thickening oscillation is caused by the interplay between the fluid dynamics and the shear thickening, and has been predicted theoretically by the present authors using a phenomenological fluid dynamics model for the dilatant fluid, but never been reported experimentally. Using a density-matched starch-water mixture, in the cylindrical shear flow of a few centimeters flow width, we observed strong vibrations of the frequency around 20 Hz, which is consistent with our theoretical prediction.

Nagahiro, Shin-ichiro; Mitarai, Namiko

2012-01-01

205

Unexpected shear strength change in magnetorheological fluids  

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

206

Noise from turbulent shear flows  

NASA Technical Reports Server (NTRS)

The generation of sound in turbulent shear flows with high Reynolds numbers is discussed. Solid surface effects, representation of incident turbulence, sound generation and the role of instability waves, sound generation by turbulence interacting with itself (the jet noise problem), compressible Rayleigh equations, sound generation from streamwise variations in mean flow, complex turbulent flows, and supersonic flows are among the topics discussed.

Goldstein, M. E.

1991-01-01

207

Teaching Case: Scissors and Shears  

NSDL National Science Digital Library

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

Velenchik, Ann

208

Sheep shearing and sudden death.  

PubMed

A 29-year-old sheep shearer collapsed after walking across a shearing shed floor, holding his hand over an incised wound to his neck. Attempted resuscitation was unsuccessful. At the death scene fine arterial blood spatter was noted and at autopsy a single incised wound to the neck was observed, the patterned edges of which corresponded to the teeth of the shears. Dissection revealed injury to the underlying jugular vein and the mid portion of the common carotid artery. Death was attributed to blood loss from an incised wound of the left side of the neck. This case demonstrates the rare event of an accidental death related to the actions of a sheep. Although a relatively small animal, review of the circumstances and interviews with those present revealed that sudden and unexpected movement of the sheep during shearing had caused the shearer to lose control of his electrical shears resulting in a lethal incised wound to the neck. The blood spatter pattern at the scene was supportive of both witness descriptions and the findings at autopsy. PMID:24237795

Irandoust, Shabnum; Heath, Karen; Byard, Roger W

2013-11-01

209

20% Wind Energy 20% Wind Energy  

E-print Network

(government, industry, utilities, NGOs) Analyzes wind's potential contributions to energy security, economic20% Wind Energy by 2030 20% Wind Energy by 2030 #12;Presentation and Objectives Overview Background scenario for reaching 20% wind energy by 2030 and contrasts it to a scenario in which no new U.S. wind

Powell, Warren B.

210

Wind power and Wind power and  

E-print Network

Wind power and the CDM #12; Wind power and the CDM Emerging practices in developing wind power 2005 Jyoti P. Painuly, Niels-Erik Clausen, Jørgen Fenhann, Sami Kamel and Romeo Pacudan #12; WIND POWER AND THE CDM Emerging practices in developing wind power projects for the Clean Development Mechanism Energy

211

The Influence of Shearing Velocity on Shear Behavior of Artificial Joints  

NASA Astrophysics Data System (ADS)

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

Atapour, Hadi; Moosavi, Mahdi

2014-09-01

212

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

213

External Shear in Quadruply Imaged Lens Systems  

E-print Network

We use publicly available N-body simulations and semi-analytic models of galaxy formation to estimate the levels of external shear due to structure near the lens in gravitational lens systems. We also describe two selection effects, specific to four-image systems, that enhance the probability of observing systems to have higher external shear. Ignoring additional contributions from "cosmic shear" and assuming that lens galaxies are not significantly flattened, we find that the mean shear at the position of a quadruple lens galaxy is 0.11, the rms shear is roughly 0.15, and there is roughly a 45% likelihood of external shear greater than 0.1. This is much larger than previous estimates and in good agreement with typical measured external shear. The higher shear primarily stems from the tendency of early-type galaxies, which are the majority of lenses, to reside in overdense regions.

Gilbert P. Holder; Paul L. Schechter

2002-09-25

214

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

215

Elastic Turbulence in Shear Banding Wormlike Micelles  

E-print Network

We study the dynamics of the Taylor-Couette flow of shear banding wormlike micelles. We focus on the high shear rate branch of the flow curve and show that for sufficiently high Weissenberg numbers, this branch becomes ...

Fardin, Marc-Antoine

216

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

217

Local shear in general magnetic stellarator geometry  

SciTech Connect

A nonlinear ballooning mode formulation in general magnetic coordinates is developed for the cold ion electrostatic drift wave problem in stellarators. It is shown that local ripple shear, not global average shear, radially localizes microturbulent modes which are located along the field lines by local ripple curvature wells. It is argued that microturbulence in stellarators depends dominantly on local ripple shear and curvature and may be rather insensitive to global (or average) shear and curvature.

Waltz, R.E. (General Atomics, P.O. Box 85608, San Diego, California 92186-9784 (United States)); Boozer, A.H. (College of William and Mary, Williamsburg, Virginia 23185 (United States) Max-Planck Instituet fuer Plasmaphysik, D-8046 Garching bei Muenchen (Germany))

1993-07-01

218

Refraction of shear zones in granular materials  

E-print Network

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

Tamas Unger

2006-10-03

219

Effects of shear on proteins in solution  

Microsoft Academic Search

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

C. R. Thomas; D. Geer

2011-01-01

220

Generality of shear thickening in suspensions  

Microsoft Academic Search

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

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

2009-01-01

221

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

222

Measurements in support of wind farm simulations and power forecasts: The Crop/Wind-energy Experiments (CWEX)  

NASA Astrophysics Data System (ADS)

The Midwest US currently is experiencing a large build-out of wind turbines in areas where the nocturnal low-level jet (NLLJ) is a prominent and frequently occurring feature. We describe shear characteristics of the NLLJ and their influence on wind power production. Reports of individual turbine power production and concurrent measurements of near-surface thermal stratification are used to turbine wake interactions and turbine interaction with the overlying atmosphere. Progress in forecasting conditions such as wind ramps and shear are discussed. Finally, the pressure perturbation introduced by a line of turbines produces surface flow convergence that may create a vertical velocity and hence a mesoscale influence on cloud formation by a wind farm.

Takle, E. S.; Rajewski, D. A.; Lundquist, J. K.; Gallus, W. A., Jr.; Sharma, A.

2014-06-01

223

Coherent structure effects on shear layer optics  

Microsoft Academic Search

This experimental research investigated the effects of coherent structures and external perturbation on the optical propagation characteristics of shear layers. A low speed shear layer was generated using two parallel streams of gases (a helium\\/argon mixture and air) and a laser beam was passed perpendicularly through the shear layer. The optical quality of the laser beam was quantified by the

Larry Chew

1990-01-01

224

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

225

Glass transitions and shear thickening suspension rheology  

Microsoft Academic Search

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

C. B. Holmes

2005-01-01

226

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

E-print Network

conduits, the origin of pyroclastic obsidian, and the emplacement history and dynamics of obsidian flows a juvenile obsidian clast from a pyroclastic fall deposit records predominantly simple shear. A third sample and shear stress are recorded by the pyroclastic obsidian (shear rate = 0.01 s31 , shear stress = 60 k

Manga, Michael

227

Rheological Characteristics of Shear Banding Flow of Complex Fluids in an Inhomogeneous Shear Field  

Microsoft Academic Search

The nominal shear stress versus shear rate curve of the shear banding flow in non-Newtonian complex fluids was investigated for the planer rotating disc and plate geometry of the rheometer. By postulating two discrete values of the viscosity that depends on the local stress, an analytically tractable calculation could be performed and two stress-shear rate curves were obtained depending on

Yukio Suezaki

2004-01-01

228

Microviscometry reveals reduced blood viscosity and altered shear rate and shear stress profiles  

E-print Network

Microviscometry reveals reduced blood viscosity and altered shear rate and shear stress profiles in diameter. Radial distributions in blood viscosity, shear stress, and shear rate are obtained and used that the microviscometric method consis- tently predicted a reduction in local and apparent blood viscosity after isovolemic

229

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

230

Non Steady State Granular Shear Flows  

NASA Astrophysics Data System (ADS)

We experimentally investigate the shear flow of granular matter in a cylindrical Couette cell. Since granular flows dissipate energy, they must be continuously driven to remain in a flowing state. Previous experiments on steady state shear flows have found that velocity gradients are confined to a thin shear band, and that the shear force is roughly independent of shear rate if the material is allowed to dilate. Our experiments in a Couette geometry focus on two related questions about non-steady state flows: 1) How does a granular shear flow start? 2) How does a granular system respond to oscillatory shear? In particular, we investigate the role of boundary conditions, which we expect to be of particular importance, since granular flows must be continuously driven (in general from a boundary) in order to be sustained. In our Couette cell a shear flow is generated by moving either the inner cylinder or the outer cylinder or both cylinders. The motion of grains on the top surface is measured directly with fast imaging and particle tracking techniques. Previous studies have indicated that the velocity profile on the top surface is very similar to the velocity profile within the bulk. Measurements of the corresponding shear forces are in progress. Initial experiments determined the steady state flow profiles under different driving conditions, with either inner, outer or both cylinders moving. In steady state, velocity gradients are confined to a roughly exponential shearband several particle diameters wide. The shear band is always located at the inner cylinder. A probable reason for this observation is the slightly smaller surface area of the inner cylinder compared to the outer cylinder. Since shear forces are transmitted from one cylinder to the other, the smaller surface area of the inner cylinder leads to larger shear stresses. Shear flow confined to regions of high stress can be reproduced in continuum mechanics models which include plastic flow, non-Newtonian fluid models, or locally Newtonian hydrodynamic models that include a strong density dependence of viscosity. Most of these models are isotropic with respect to the shear direction. However, anisotropies manifest themselves in two distinct flow transients, when rotation of one of the cylinders is started. When the cylinder had been rotated in the same direction before, the thin shear band immediately forms. When the previous motion of the cylinder had been in the opposite direction, particles far from the moving cylinder are initially more mobile. After an extra displacement of up to six particle diameters, a thin shearband forms again in steady state. The extra displacement of particles far from the shear surface does not strongly depend on the shear rate prior or after the stop, solely on the direction of prior shear. This indicates that the static configuration of grains after a shear flow exhibits anisotropies. The flow transient, at least, can then no longer be modeled with the isotropic form of the models described above. Finally, we investigate oscillatory shear flow. During small amplitude oscillations the shear flow is confined to a thin shear band. In addition, a gradual compaction and strengthening of the granular material is observed. For sufficiently large oscillation amplitudes, the flow resembles a sequence of shear reversals. In oscillatory flows driven by the outer cylinder, coexistence of shearbands at the outer and inner cylinder can be found. In summary, we have elucidated important properties of granular shear flows from non-steady state flow measurements: First, shear bands form preferentially near the inner cylinder, even when the outer cylinder is sheared. Transiently a shear band can also form near the outer cylinder during oscillatory driving. These observations should help refine models of granular shear flow. One challenge in improving models of granular shear flow is the observation that the initial flow transient contains 'memory' of the direction of previously applied shear. In order to incorporate this observation into flow model

Losert, Wolfgang; Kwon, Gene

2002-11-01

231

Gap Winds  

NSDL National Science Digital Library

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

Comet

2003-03-20

232

Vertical shears in Saturn's eastward jets at cloud level  

NASA Astrophysics Data System (ADS)

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

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

2009-06-01

233

Shear shocks in fragile matter  

NASA Astrophysics Data System (ADS)

Random media, like polymer networks, covalent network glasses, or grains under pressure can be viewed as elastic networks composed of springs and balls. The shear moduli of these types of materials typically vanish as the network connectivity z approaches a critical value. In this talk, I show that shear strains propagate as diffusive fronts, whose width diverges and whose transverse speed of sound vanishes, as the transition is approached. Consequently, in this regime, linear theory breaks down, giving rise to nonlinear transverse waves. Comparison of the analytical front profile to molecular dynamics simulations allows the extraction of the material constants of the network. Interestingly, even an undamped network yields a diverging effective viscosity caused by leaking of energy into non-affine degrees of freedom.

Ulrich, Stephan; Vitelli, Vincenzo; Upadhyaya, Nitin

2013-03-01

234

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

Microsoft Academic Search

Failure in sheared-edge stretching often limits the use of advanced high-strength steel sheets in automotive applications.\\u000a The present study analyzes data in the literature from laboratory experiments on both the shearing process and the characteristics\\u000a of sheared edges. Shearing produces a surface with regions of rollover, burnish, fracture, and burr. The effect of clearance\\u000a and tensile strength on the shear

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

235

Shear fatigue crack growth - A literature survey  

NASA Technical Reports Server (NTRS)

Recent studies of shear crack growth are reviewed, emphasizing test methods and data analyses. The combined mode I and mode II elastic crack tip stress fields are considered. The development and design of the compact shear specimen are described, and the results of fatigue crack growth tests using compact shear specimens are reviewed. The fatigue crack growth tests are discussed and the results of inclined cracks in tensile panels, center cracks in plates under biaxial loading, cracked beam specimens with combined bending and shear loading, center-cracked panels and double edge-cracked plates under cyclic shear loading are examined and analyzed in detail.

Liu, H. W.

1985-01-01

236

Experimental observation of shear thickening oscillation  

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

237

Lagrangian Coherent Structure Analysis of Terminal Winds Detected by Lidar. Part I: Turbulence Structures  

E-print Network

Lagrangian Coherent Structure Analysis of Terminal Winds Detected by Lidar. Part I: Turbulence. In this paper, a method is developed to identify Lagrangian coherent structures (LCS) from horizontal lidar, and wind shear. Based on a recently developed finite-domain­finite-time Lyapunov exponent (FDFTLE

Tang, Wenbo

238

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.

239

Shear thickening of highly viscous granular suspensions  

E-print Network

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

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

2014-04-28

240

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

241

The stability of turbulent accretion discs with magnetically influenced winds  

Microsoft Academic Search

The stability of turbulent accretion discs is considered, in which a magnetically influenced wind plays a major role in driving the inflow. The magnetic field is generated by a dynamo operating in the disc, involving radial shear and turbulence. The steady angular momentum balance is found to be linearly stable for a range of radial boundary conditions, and an expression

C. G. Campbell

2001-01-01

242

Surface drift effect on wind energy transfer to waves  

Microsoft Academic Search

The effect of surface drift velocity on the energy transfer from the wind to ocean waves and the growth rate of the dominant surface wave was studied analytically. The model analyzed considered first the airflow above the surface wave to be turbulent, the thin drift shear layer to be viscous, and the flow beneath the drift flow to be potential.

Donghuo Zhou; Cesar Mendoza

1993-01-01

243

AIAA-2004-1184 AN AEROACOUSTIC ANALYSIS OF WIND TURBINES*  

E-print Network

are being considered. These are airfoil self-noise, the effects of blade rotation, and the propagation of sound over large distances. Two aspects of airfoil self-noise are being studied. The first gusts, incoming atmospheric turbulence and wind shear. The unsteady flow simulations are coupled

244

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

E-print Network

Shear thickening is a phenomenon of significant viscosity increase of colloidal suspensions. While electrorheological (ER) fluids can be turned into a solid-like material by applying an electric field, their shear strength is widely represented by the attractive electrostatic interaction between ER particles. By shearing ER fluids between two concentric cylinders, we show a reversible shear thickening of ER fluids above a low critical shear rate (100 V/mm), which could be characterized by a modified Mason number. Shear thickening and electrostatic particle interaction-induced inter-particle friction forces is considered to be the real origin of the high shear strength of ER fluids, while the applied electric field controls the extent of shear thickening. The electric field-controlled reversible shear thickening has implications for high-performance ER/magnetorheological (MR) fluid design, clutch fluids with high friction forces triggered by applying local electric field, other field-responsive materials and intelligent systems.

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

2010-08-24

245

Nucleation of shear bands in amorphous alloys  

PubMed Central

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

2014-01-01

246

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

247

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

PubMed

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

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

2005-08-01

248

Invariant quantities in shear flow  

E-print Network

The dynamics of systems out of thermal equilibrium is usually treated on a case-by-case basis without knowledge of fundamental and universal principles. We address this problem for a class of driven steady states, namely those mechanically driven at the boundaries such as complex fluids under shear. From a nonequilibrium counterpart to detailed balance (NCDB) we derive a remarkably simple set of invariant quantities which remain unchanged when the system is driven. These new nonequilibrium relations are both exact and valid arbitrarily far from equilibrium. Furthermore, they enable the systematic calculation of transition rates in driven systems with state-spaces of arbitrary connectivity.

A. Baule; R. M. L. Evans

2008-08-08

249

Quantification of Critical Shear Stress  

NSDL National Science Digital Library

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

Leithold, Lonnie

250

Conductor shears as iceberg encroaches  

SciTech Connect

Operators in the Arctic regions must protect wellheads from encroaching icebergs and icepack sheets. Diverting ice masses and excavating large holes below scour depth is expensive. Now an alternate approach allows the conductor to shear, shuts in the well, and provides a method of re-entering the well. The new system has been successfully used by Mobil on two exploratory wells in the Hibernia field off eastern Canada. The wells used 18 3/4-in. wellheads rated at 10,000 psi with 36-in. conductor pipe. The performance of the system is discussed.

Not Available

1984-10-01

251

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 ...

252

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 ...

253

Advances in endothelial shear stress proteomics.  

PubMed

The vascular endothelium lining the luminal surface of all blood vessels is constantly exposed to shear stress exerted by the flowing blood. Blood flow with high laminar shear stress confers protection by activation of antiatherogenic, antithrombotic and anti-inflammatory proteins, whereas low or oscillatory shear stress may promote endothelial dysfunction, thereby contributing to cardiovascular disease. Despite the usefulness of proteomic techniques in medical research, however, there are relatively few reports on proteome analysis of cultured vascular endothelial cells employing conditions that mimic in vivo shear stress attributes. This review focuses on the proteome studies that have utilized cultured endothelial cells to identify molecular mediators of shear stress and the roles they play in the regulation of endothelial function, and their ensuing effect on vascular function in general. It provides an overview on current strategies in shear stress-related proteomics and the key proteins mediating its effects which have been characterized so far. PMID:25017810

Firasat, Sabika; Hecker, Markus; Binder, Lutz; Asif, Abdul R

2014-10-01

254

Shear Thickening and Migration in Granular Suspensions  

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

255

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

256

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

257

Wind Streaks  

NASA Technical Reports Server (NTRS)

[figure removed for brevity, see original site]

Released 17 September 2003

Bright wind streaks are present in the lee of craters and other obstacles in this image, located in Sinus Sabaeus, near the Martian equator. These streaks indicate that the local winds blow from the northeast (upper right in the image). The brightness of the streaks indicates that either bright material has been deposited in the lee of the craters, or that the surface has eroded preferentially in the lee of craters, exposing an underlying bright material. Because the streaks are bright regardless of the surrounding surface brightness, the first hypothesis most likely. The streaks probably all represent deposits of the same bright material that settled out of the atmosphere in the wind shelter provided by topographic peaks.

Image information: VIS instrument. Latitude -6.3, Longitude 14.1 East (345.9 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.

2003-01-01

258

Prospecting for Wind  

ERIC Educational Resources Information Center

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

Swapp, Andy; Schreuders, Paul; Reeve, Edward

2011-01-01

259

Accommodating Wind's Natural Behavior  

Microsoft Academic Search

Integration of wind-power plants into the electric power system presents challenges to power-system planners and operators. These challenges stem primarily from the natural characteristics of wind plants, which differ in some respects from conventional plants. Wind plants operate when the wind blows, and their power levels vary with the strength of the wind. Hence, they are not dispatchable in the

Edgar DeMeo; Gary Jordan; Clint Kalich; Jack King; Michael Milligan; Cliff Murley; Brett Oakleaf; Matthew Schuerger

2007-01-01

260

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.

261

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

262

Glass transitions and shear thickening suspension rheology  

Microsoft Academic Search

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

M. Fuchs; P. Sollich

2005-01-01

263

Electroconvection in Sheared Annular Films  

NASA Astrophysics Data System (ADS)

We report experiments on electroconvection in thin suspended films of a smectic A liquid crystal (8CB). These films behave as nearly ideal 2D isotropic fluids. The films were annular with radius ratio (inner/outer electrode radius) ~ 0.8. Shears may be applied by rotating the inner electrode. When no shear is applied, the film is unstable to a stationary roll state when the voltage between the inner and outer edges of the annulus exceeds a critical voltage, V_c^o. The periodic units of the flow pattern are pairs of symmetric counter-rotating vortices. From the current-voltage characteristic of the film, we find the onset to be supercritical. When the inner electrode is rotated at a constant angular velocity ?, the base state is 2D Couette flow. At a critical voltage V_c(?)>V_c^o, the film is unstable to a travelling roll state whose periodic units are pairs of asymmetric counter-rotating vortices. In each pair, the roll whose circulation is in the same sense as the rotation of the inner electrode is narrower while the opposite sense roll is broader. The pattern travels azimuthally at a constant angular speed which depends on ?. From the current-voltage characteristic, we find a subcritical bifurcation with an ?-dependent hysteresis.

Daya, Z. A.; Morris, S. W.; Molteno, T. C. A.; de Bruyn, J. R.

1996-11-01

264

Novel shear mechanism in nanolayered composites  

SciTech Connect

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

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

2009-01-01

265

Shear banding phenomena in a Laponite suspension  

E-print Network

Shear localization in an aqueous clay suspension of Laponite is investigated through dynamic light scattering, which provides access both to the dynamics of the system (homodyne mode) and to the local velocity profile (heterodyne mode). When the shear bands form, a relaxation of the dynamics typical of a gel phase is observed in the unsheared band soon after flow stop, suggesting that an arrested dynamics is present during the shear localization regime. Periodic oscillations of the flow behavior, typical of a stick-slip phenomenon, are also observed when shear localization occurs. Both results are discussed in the light of various theoretical models for soft glassy materials.

Ianni, F; Gentilini, S; Ruocco, G

2007-01-01

266

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

267

Confined Cubic Blue Phases under Shear  

E-print Network

We study the behaviour of confined cubic blue phases under shear flow via lattice Boltzmann simulations. We focus on the two experimentally observed phases, blue phase I and blue phase II. The disinclination network of blue phase II continuously breaks and reforms under shear, leading to an oscillatory stress response in time. The oscillations are only regular for very thin samples. For thicker samples, the shear leads to a "stick-slip" motion of part of the network along the vorticity direction. Blue phase I responds very differently: its defect network undergoes seemingly chaotic rearrangements under shear, irrespective of system size.

O. Henrich; K. Stratford; D. Marenduzzo; P. V. Coveney; M. E. Cates

2011-11-23

268

Confined cubic blue phases under shear.  

PubMed

We study the behaviour of confined cubic blue phases under shear flow via lattice Boltzmann simulations. We focus on the two experimentally observed phases, blue phase I and blue phase II. The disclination network of blue phase II continuously breaks and reforms under shear, leading to an oscillatory stress response in time. The oscillations are only regular for very thin samples. For thicker samples, the shear leads to a 'stick-slip' motion of part of the network along the vorticity direction. Blue phase I responds very differently: its defect network undergoes seemingly chaotic rearrangements under shear, irrespective of system size. PMID:22738991

Henrich, O; Stratford, K; Marenduzzo, D; Coveney, P V; Cates, M E

2012-07-18

269

Three-dimensional shear in granular flow  

E-print Network

The evolution of granular shear flow is investigated as a function of height in a split-bottom Couette cell. Using particle tracking, magnetic-resonance imaging, and large-scale simulations we find a transition in the nature of the shear as a characteristic height $H^*$ is exceeded. Below $H^*$ there is a central stationary core; above $H^*$ we observe the onset of additional axial shear associated with torsional failure. Radial and axial shear profiles are qualitatively different: the radial extent is wide and increases with height while the axial width remains narrow and fixed.

Xiang Cheng; Jeremy B. Lechman; Antonio F. Barbero; Gary S. Grest; Heinrich M. Jaeger; Greg S. Karczmar; Matthias E. Möbius; Sidney R. Nagel

2005-07-20

270

Cyclic shearing deformation behavior of saturated clays  

NASA Astrophysics Data System (ADS)

The apparatus for static and dynamic universal triaxial and torsional shear soil testing is employed to perform stress-controlled cyclic single-direction torsional shear tests and two-direction coupled shear tests under unconsolidated-undrained conditions. Through a series of tests on saturated clay, the effects of initial shear stress and stress reversal on the clay’s strain-stress behavior are examined, and the behavior of pore water pressure is studied. The experimental results indicate that the patterns of stress-strain relations are distinctly influenced by the initial shear stress in the cyclic single-direction shear tests. When the initial shear stress is large and no stress reversal occurs, the predominant deformation behavior is characterized by an accumulative effect. When the initial shear stress is zero and symmetrical cyclic stress occurs, the predominant deformation behavior is characterized by a cyclic effect. The pore water pressure fluctuates around the confining pressure with the increase of cycle number. It seems that the fluctuating amplitude increases with the increase of the cyclic stress. But a buildup of pore water pressure does not occur. The deformations of clay samples under the complex initial and the cyclic coupled stress conditions include the normal deviatoric deformation and horizontal shear deformation, the average deformation and cyclic deformation. A general strain failure criterion taking into account these deformations is recommended and is proved more stable and suitable compared to the strain failure criteria currently used.

Qi, Jianfeng; Luan, Maotian; Feng, Xiuli; Ma, Tailei; Nie, Ying

2007-10-01

271

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.

272

Comparison of transient and quasi-steady aeroelastic analysis of wind turbine blade in steady wind conditions  

NASA Astrophysics Data System (ADS)

In the preliminary design stage of wind turbine blade, faster and simpler methods are preferred to predict the aeroelastic response of the blades in order to get an idea about the appropriateness of the blade stiffness. Therefore, in the present study, applicability of the quasi-steady aeroelastic analysis of wind turbine blade is investigated in terms of how accurately the quasi-steady aeroelastic analysis predicts the deformed state of the blade at certain azimuthal positions. For this purpose, comparative study of transient and quasi-steady aeroelastic analysis of a composite wind turbine blade in steady wind conditions is conducted. To perform the transient analysis, a multi-body wind turbine model is generated with almost rigid components except for the dynamic superelement blade that is inverse designed. Transient analysis of the multi body wind turbine system is performed by imposing constant rotational speed to the main shaft and bypassing the controller. Quasi-steady aeroelastic analysis of the same composite wind turbine blade is performed, by coupling a structural finite element solver with a blade element momentum tool, in steady wind conditions at different azimuthal positions including the effect of the centrifugal and gravitational forces. Results show that for the wind turbine system taken as the case study, reasonably good agreement is obtained between the tip deflections and flapwise root shear forces determined by the transient aeroelastic analysis of the wind turbine and quasi-steady aeroelastic analysis of the blade only.

Sargin, H.; Kayran, A.

2014-06-01

273

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

274

Where do we stand in understanding fast solar wind acceleration?  

NASA Astrophysics Data System (ADS)

Ulysses and SOHO/UVCS were instrumental in confirming the origin of fast solar wind streams in solar coronal holes. In this paper I will try to assess where our understanding of fast solar wind acceleration really stands, illustrating new observations and the most recent models involving reflection-driven Alfvenic turbulence, Alfven waves and compressible interactions, and coronal plumes and microstream shear. Since Alfvenic turbulence is often considered "exotic" I will also try to give an understandable, yet precise, description of the large scale interaction of Alfven waves in the solar wind, including turbulence phenomenologies. While models predicated on turbulence come the closest to describing the fast solar wind correctly, a number of issues, from the precise dissipation mechanisms, to the relative roles of helium and minor ions, to the formation and role of the ubiquitous electron strahl in the fast wind still remain far from resolution.

Velli, Marco

2012-07-01

275

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

Microsoft Academic Search

By shearing electrorheological (ER) fluids between two concentric cylinders, we show a reversible shear thickening of ER fluids above a low critical shear rate (<1 s-1) and a high critical electric field strength (>100 V\\/mm), which can be characterized by a critical apparent viscosity. Shear thickening and electrostatic particle interaction-induced interparticle friction forces are considered to play an important role

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

2011-01-01

276

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

Microsoft Academic Search

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

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

2010-01-01

277

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

278

A numerical examination of shear banding and simple shear non-coaxial flow rules  

Microsoft Academic Search

Strain localisation and shear band formation is frequently observed during the handling and flow of dense phase particulate materials. However, a complete understanding of how shear bands form and what happens inside shear bands is still lacking. In order to address this problem, discrete particle simulations have been carried out to examine the detailed processes that occur at the grain

C. Thornton; L. Zhang

2006-01-01

279

Insitu Rock Shear Device (Development of a New Insitu Shear Strength Measuring Device).  

National Technical Information Service (NTIS)

A new device has been designed to measure the insitu rock shear strength in cored holes. Limited field data indicate that shear strengths obtained by the Rock Shear Device are in good agreement with McVay's laboratory square root (sup 2) method.

C. Hay, D. Bloomquist, M. McVay

2008-01-01

280

Modified Shear Box Test Apparatus for Measuring Shear Strength of Unsaturated Residual Soil  

Microsoft Academic Search

Abstract: Residual soils occur in most countries of the world but the greater areas and depths are normally found in tropical humid areas. Most of these soils exhibit high suctions for most of the year. The shear strength parameters, c’ and ? ’, of soil can be obtained using conventional shear strength tests. However the conventional shear strength test equipments

Bujang B. k. Huat; Faisal Hj. Ali; S. Hashim

2005-01-01

281

Wind resources of Somalia  

SciTech Connect

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

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

1991-01-01

282

Wind Erosion Research  

NSDL National Science Digital Library

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

2006-02-27

283

Extreme Velocity Wind Sensor  

NASA Technical Reports Server (NTRS)

This presentation provides an overview of the development of new hurricane wind sensor (Extreme Velocity Wind Sensor) for the Kennedy Space Center (KSC) which is designed to withstand winds of up to three hundred miles an hour. The proposed Extreme Velocity Wind Sensor contains no moveable components that would be exposed to extreme wind conditions. Topics covered include: need for new hurricane wind sensor, conceptual design, software applications, computational fluid dynamic simulations of design concept, preliminary performance tests, and project status.

Perotti, Jose; Voska, Ned (Technical Monitor)

2002-01-01

284

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

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

285

Shear thickening in a solution undergoing inverse melting  

Microsoft Academic Search

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

R. Angelini; G. Salvi; G. Ruocco

2008-01-01

286

Wind energy bibliography  

SciTech Connect

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

None

1995-05-01

287

Wind for Schools (Poster)  

SciTech Connect

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

Baring-Gould, I.

2010-05-01

288

Quadruple Lap Shear Processing Evaluation  

NASA Technical Reports Server (NTRS)

The Thiokol, Science and Engineering Huntsville Operations (SEHO) Laboratory has previously experienced significant levels of variation in testing Quadruple Lap Shear (QLS) specimens. The QLS test is used at Thiokol / Utah for the qualification of Reusable Solid Rocket Motor (RSRM) nozzle flex bearing materials. A test was conducted to verify that process changes instituted by SEHO personnel effectively reduced variability, even with normal processing variables introduced. A test matrix was designed to progress in a series of steps; the first establishing a baseline, then introducing additional solvents or other variables. Variables included normal test plan delay times, pre-bond solvent hand-wipes and contaminants. Each condition tested utilized standard QLS hardware bonded with natural rubber, two separate technicians and three replicates. This paper will report the results and conclusions of this investigation.

Thornton, Tony N.; McCool, A. (Technical Monitor)

2000-01-01

289

Utilizing Wind: Optimal Wind Farm Placement in the United States  

E-print Network

An Introduction to Wind Energy 1 1.1 Wind, a Brief History . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.2 The Wind Turbine . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 1.3 Advantages and Disadvantages of Wind . . . . . . . . . . . . . . . . . 7 1.3.1 Advantages of Wind

Powell, Warren B.

290

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

291

THE SHEARING BEHAVIOUR OF A SUGAR AGGREGATE  

E-print Network

granules. The present study is therefore an investigation of the shearing response of a loose, dry or moistTHE SHEARING BEHAVIOUR OF A SUGAR AGGREGATE Catherine A. Davy1 , M. D. Bolton2 , N. A. Fleck2 machines remain the only viable option. The development of a High Grade Continuous Centrifuge would

Bolton, Malcolm

292

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

293

Internal and Interface Shear Strength of  

E-print Network

is suitable for quantification of the effects of normal stress during shearing, normal stress during hydration. This report investigates the mechanical behavior of GCLs by providing a state-of-the-art review of internal proposed to address the effect of shear strength variability and field loading conditions on the stability

Zornberg, Jorge G.

294

Compressible Homogeneous Shear: Simulation and Modeling \\Lambda  

E-print Network

Compressible Homogeneous Shear: Simulation and Modeling \\Lambda S. Sarkar, G. Erlebacher, and M numerical simulation of homogeneous shear flow. A primary observation is that the growth of the turbulent and Engineering (ICASE), NASA Langley Research Center, Hampton, VA 23665. i #12; 1 Introduction Homogeneous

Erlebacher, Gordon

295

Study of shear-stiffened elastomers  

NASA Astrophysics Data System (ADS)

Shear thickening fluids, which are usually concentrated colloidal suspensions composed of non-aggregating solid particles suspended in fluids, exhibit a marked increase in viscosity beyond a critical shear rate. This increased viscosity is seen as being both 'field-activated', due to the dependence on shearing rate, as well as reversible. Shear thickening fluids have found good applications as protection materials, such as in liquid body armor, vibration absorber or dampers. This research aims to expand the protection material family by developing a novel solid status shear thickening material, called shear-stiffened elastomers. These new shear-stiffened elastomers were fabricated with the mixture of silicone rubber and silicone oil. A total of four SSE samples were fabricated in this study. Their mechanical and rheological properties under both steady-state and dynamic loading conditions were tested with a parallel-plate. The effects of silicone oil composition and angular frequency were summarized. When raising the angular frequency in dynamic shear test, the storage modulus of conventional silicone rubber shows a small increasing trend with the frequency. However, if silicone oil is selected to be mixed with silicone rubber, the storage modulus increases dramatically when the frequency and strain are both beyond the critical values.

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

2013-06-01

296

Low shear viscosity due to Anderson localization  

SciTech Connect

We study the Anderson localization effect on the shear viscosity in a system with random medium by Kubo formula. We show that this effect can suppress nonperturbatively the shear viscosity and other transport coefficients. The possible relevancy of such a suppression to the near perfect fluid behavior of the quark-gluon plasma created in heavy-ion collisions is discussed.

Giannakis, Ioannis [Physics Department, Rockefeller University, 1230 York Avenue, New York, New York 10021-6399 (United States); Hou Defu; Ren Haicang [Physics Department, Rockefeller University, 1230 York Avenue, New York, New York 10021-6399 (United States); Institute of Particle Physics, Huazhong Normal University, Wuhan, 430079 (China); Li Jiarong [Institute of Particle Physics, Huazhong Normal University, Wuhan, 430079 (China)

2008-01-15

297

Viscous fingering in shear thickening silica suspensions  

Microsoft Academic Search

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

Naoki Kagei; Daisuke Kanie; Masami Kawaguchi

2005-01-01

298

Shear Thickening Oscillation in a Dilatant Fluid  

Microsoft Academic Search

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

Hiizu Nakanishi

2011-01-01

299

Thixotropy of MR shear-thickening fluids  

Microsoft Academic Search

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

Xianzhou Zhang; Weihua Li; Xinglong Gong

2010-01-01

300

White Light Extended Source Shearing Interferometer  

Microsoft Academic Search

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

J. C. Wyant

1974-01-01

301

Wind speed forecasting for wind energy applications  

Microsoft Academic Search

With more wind energy being integrated into our grid systems, forecasting wind energy has become a necessity for all market participants. Recognizing the market demands, a physical approach to site-specific hub-height wind speed forecasting system has been developed. This system is driven by the outputs from the Canadian Global Environmental Multiscale (GEM) model. A simple interpolation approach benchmarks the forecasting

Hong Liu

2010-01-01

302

Visualization of shear banding in colloidal glasses  

NASA Astrophysics Data System (ADS)

Shear banding, i.e. the localization of shear flow, occurs in a manifold of systems ranging from hard materials such as metallic glasses to soft materials such as clays, shaving cream or mayonnaise. We investigate this phenomenon in a dense colloidal system using confocal microscopy that enables to track individual particles in 3D space and time. The particle motions reveal a transition from homogeneous flow to shear localization above a critical shear rate. We elucidate this transition using spatial correlations in the displacement of the particles. The diffusive motion of the particles is correlated over large length, and shows intermittent, scale-free behavior, reminiscent of crystal plasticity. Further, we associate an order parameter with the mobility of particles and demonstrate that shear banding is phase coexistence of regions differing in mobilities.

Chikkadi, Vijayakumar; Schofield, Andrew; Nienhuis, Bernard; Schall, Peter

2010-03-01

303

Dynamic Jamming Point for Shear Thickening Suspensions  

NASA Astrophysics Data System (ADS)

We report on rheometry measurements to characterize the critical behavior in two model shear thickening suspensions: cornstarch in water and glass spheres in oil. The slope of the shear thickening part of the viscosity curve is found to increase dramatically with packing fraction and diverge at a critical packing fraction ?c. The magnitude of the viscosity and the yield stress are also found to have scalings that diverge at ?c. We observe shear thickening as long as the yield stress is less than the stress at the viscosity maximum. Above this point the suspensions transition to purely shear thinning. Based on these data we present a dynamic jamming phase diagram for suspensions and show that a limiting case of shear thickening corresponds to a jammed state.

Brown, Eric; Jaeger, Heinrich M.

2009-08-01

304

Determining Shear Stress Distribution in a Laminate  

NASA Technical Reports Server (NTRS)

A "simplified shear solution" method approximates the through-thickness shear stress distribution within a composite laminate based on an extension of laminated beam theory. The method does not consider the solution of a particular boundary value problem; rather, it requires only knowledge of the global shear loading, geometry, and material properties of the laminate or panel. It is thus analogous to lamination theory in that ply-level stresses can be efficiently determined from global load resultants at a given location in a structure and used to evaluate the margin of safety on a ply-by-ply basis. The simplified shear solution stress distribution is zero at free surfaces, continuous at ply boundaries, and integrates to the applied shear load. The method has been incorporated within the HyperSizer commercial structural sizing software to improve its predictive capability for designing composite structures. The HyperSizer structural sizing software is used extensively by NASA to design composite structures. In the case of through-thickness shear loading on panels, HyperSizer previously included a basic, industry-standard, method for approximating the resulting shear stress distribution in sandwich panels. However, no such method was employed for solid laminate panels. The purpose of the innovation is to provide an approximation of the through-thickness shear stresses in a solid laminate given the through-thickness shear loads (Qx and Qy) on the panel. The method was needed for implementation within the HyperSizer structural sizing software so that the approximated ply-level shear stresses could be utilized in a failure theory to assess the adequacy of a panel design. The simplified shear solution method was developed based on extending and generalizing bi-material beam theory to plate-like structures. It is assumed that the through-thickness shear stresses arise due to local bending of the laminate induced by the through-thickness shear load, and by imposing equilibrium both vertically and horizontally, the through-thickness shear stress distribution can be calculated. The resulting shear stresses integrate to the applied shear load, are continuous at the ply interfaces, and are zero at the laminate-free surfaces. If both Qx and Qy shear loads are present, it is assumed that they act independently and that their effects can be superposed. The calculated shear stresses can be rotated within each ply to the principal material coordinates for use in a ply-level failure criterion. The novelty of the simplified shear solution method is its simplicity and the fact that it does not require solution of a particular boundary value problem. The advantages of the innovation are that an approximation of the though-thickness shear stress distribution can be quickly determined for any solid laminate or solid laminate region within a stiffened panel.

Bednarcyk, Brett A.; Aboudi, Jacob; Yarrington, Phillip W.

2010-01-01

305

Particle acceleration timescales in relativistic shear flows  

E-print Network

We review the acceleration of energetic particles in relativistic astrophysical jets characterized by a significant velocity shear. The possible formation of power-law momentum spectra is discussed and typical acceleration timescales are determined for a variety of different conditions such as parallel and azimuthal shear flows. Special attendance is given to the analysis of parallel shear flows with either a linear decreasing or a Gaussian-type velocity profile. It is shown that in the presence of a gradual shear flow and a particle mean free path scaling with the gyroradius, synchrotron radiation losses may no longer be able to stop the acceleration once it has started to work efficiently. Finally, the relevance of shear acceleration in small- and large-scale relativistic jets is addressed.

Frank M. Rieger; Peter Duffy

2005-06-29

306

Identification of complex shear modulus from measured shear strains on a circular disc subjected to a transient torque  

Microsoft Academic Search

A method for identification of complex shear modulus from measured shear strains on a circular disc subjected to a transient torque at its centre has been established. It is based on the evolution of an outgoing shear wave between two radial positions at which the associated shear strains are measured. The two-dimensional shear wave solutions used are exact in the

S. Mousavi; L. Hillström; B. Lundberg

2008-01-01

307

Lagrangian Coherent Structure Analysis of Terminal Winds Detected by Lidar. Part II: Structure Evolution and Comparison with Flight Data  

E-print Network

Lagrangian Coherent Structure Analysis of Terminal Winds Detected by Lidar. Part II: Structure) ABSTRACT Using observational data from coherent Doppler light detection and ranging (lidar) systems and compare them with onboard wind shear and altitude data collected during airplane approaches. Their results

Tang, Wenbo

308

A Convective Storm Matrix: Buoyancy/Shear Dependencies  

NSDL National Science Digital Library

In order to help forecasters build a strategy for anticipating convective storm structures, their evolution, and the potential for severe weather, A Convective Storm Matrix provides learners the opportunity for extensive exploration of the relationship between a storm's environment and its structure. The matrix is composed of 54 four-dimensional numerical simulations based on the interactions of 16 different hodographs and 4 thermodynamic profiles. By comparing animated displays of these simulations, learners are able to discern the influences of varying buoyancy and vertical wind shear profiles on storm structure and evolution. A series of questions guides the exploration and helps to reveal key storm/environment relationships evident in the matrix. A synopsis of the physical processes that control storm structure, as well as the current conceptual models of key convective storms types, is included for reference. Subject matter expects for A Convective Storm Matrix: Buoyancy/Shear Dependencies include Mr. Steve Keighton, Mr. Ed Szoke, and Dr. Morris Weisman. Note: This module was originally published on CD-ROM in March 1996 (v1.1) and re-released in 2001 as v1.3 for Microsoft Windows users only. CD-ROM version 1.3 works fairly well with Windows 98/ME/NT4/2000 but has reported to be problematic with Windows XP. Users of version 1.1 should obtain the patch located at http://www.comet.ucar.edu/help/ModuleSupport/matrix_problem.htm or use the new, Web-based module.

Comet

2003-04-09

309

Applications of hot-film anemometers in hypersonic shear layers  

NASA Technical Reports Server (NTRS)

A wind tunnel test was conducted on a flat plate at zero angle of attack with a rearward facing 2D cooling film injector nozzle. The freestream Mach number was 8 and the injector Mach number was 3. The freestream Reynolds number varied from 0.43 to 3.3 million per ft during the test, and the injector flow rate was such that the jet exit and freestream static pressures were matched. The analysis reported herein will focus on data obtained at a freestream Reynolds number of 0.85 million per ft. The data consists of heat-transfer measurements obtained upstream and downstream of the injector nozzle and flowfield surveys obtained downstream of the injector nozzle with a pitot, total temperature, hot-film anemometer and hot-wire anemometer probes. The flowfield surveys were made at stations 0.1 to 9 in. downstream of the injector nozzle from near the model surface to approximately 2 in above the model surface. The hot-film anemometer was used to define the fluctuations in the shear layer separating the flows. The hot-film results are integrated with conventional measurement techniques to obtain a more complete description of the complicated shear layer separating hypersonic and supersonic flows.

Grubb, J. P.; Strike, W. T.

1991-01-01

310

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

NASA Astrophysics Data System (ADS)

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

Walter, Benjamin; Gromke, Christof; Lehning, Michael

2012-08-01

311

A canopy-type similarity model for wind farm optimization  

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

312

Physics-controlled thickness of shear zones caused by viscous heating: Implications for crustal shear localization  

NASA Astrophysics Data System (ADS)

We evaluate the parameters that control the thickness of ductile shear zones that are generated by viscous heating. We employ two-dimensional thermomechanical numerical models to simulate shear zone development under compression. Results show that the shear zone thickness is essentially independent on the numerical resolution and the initial size of a weak inclusion that triggers shear localization. A simple scaling law is derived which predicts the thickness with six physical parameters: far-field stress and strain rate, thermal conductivity (both constant and temperature dependent), initial temperature, activation energy, and stress exponent. The scaling law is confirmed by numerical simulations for a wide range of parameters. For crustal deformation conditions typical temperature increase ranges between 50°C and 200°C, and the predicted thickness is between 1 km and 7 km. These thicknesses agree with natural crustal and lithospheric shear zones suggesting that shear heating is a process controlling crustal shear zone formation.

Duretz, T.; Schmalholz, S. M.; Podladchikov, Y. Y.; Yuen, D. A.

2014-07-01

313

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

PubMed

By shearing electrorheological (ER) fluids between two concentric cylinders, we show a reversible shear thickening of ER fluids above a low critical shear rate (<1?s(-1)) and a high critical electric field strength (>100 V/mm), which can be characterized by a critical apparent viscosity. Shear thickening and electrostatic particle interaction-induced interparticle friction forces are considered to play an important role in the origin of lateral shear resistance of ER fluids, while the applied electric field controls the extent of shear thickening. The electric-field-controlled reversible shear thickening has implications for high-performance electrorheological-magnetorheological fluid design, clutch fluids with high friction forces triggered by applying a local electric field, other field-responsive materials, and intelligent systems. PMID:21405692

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

2011-01-01

314

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

Federal Register 2010, 2011, 2012, 2013

...LLC, Alta Wind IX, LLC, Alta Wind X, LLC, Alta Wind XI, LLC, Alta Wind...LLC, Alta Wind IX, LLC, Alta Wind X, LLC, Alta Wind XI, LLC, Alta Wind...capacity of Petitioners' wind and solar generation projects to the integrated...

2012-05-18

315

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

NASA Technical Reports Server (NTRS)

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

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

1985-01-01

316

Relation between ordering and shear thinning in colloidal suspensions  

E-print Network

Colloidal suspensions exhibit shear thinning and shear thickening. The most common interpretation of these phenomena identifies layering of the fluid perpendicular to the shear gradient as the driver for the observed ...

Xu, Xinliang

317

49 CFR 230.27 - Maximum shearing strength of rivets.  

Code of Federal Regulations, 2011 CFR

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

2011-10-01

318

49 CFR 230.27 - Maximum shearing strength of rivets.  

Code of Federal Regulations, 2012 CFR

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

2012-10-01

319

49 CFR 230.27 - Maximum shearing strength of rivets.  

Code of Federal Regulations, 2013 CFR

...2013-10-01 false Maximum shearing strength of rivets. 230.27 Section 230...STANDARDS Boilers and Appurtenances Strength of Materials § 230.27 Maximum shearing strength of rivets. The maximum shearing...

2013-10-01

320

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

NASA Astrophysics Data System (ADS)

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

Valerio Iungo, Giacomo; Porté-Agel, Fernando

2014-06-01

321

Shear-induced fat particle structure variation and the stability of food emulsions: I. Effects of shear history, shear rate and temperature  

Microsoft Academic Search

The shear-induced fat particle structure variation and the stability of food emulsions were investigated by the back-light scattering technique. The effects of temperature, shear rate, and shear history on the fat particle structure and stability of food emulsions were studied. Increasing the shear time initially improves the fat particle structure; afterwards, the fat particle packing structure becomes less ordered. The

Wen Xu; Alex Nikolov; Darsh T. Wasan

2005-01-01

322

Wind environment in the Lee of Kauai Island, Hawaii during trade wind conditions: weather setting for the Helios Mishap  

NASA Astrophysics Data System (ADS)

On 26 June 2003 (approximately 1030 local time) the Helios ultralight aircraft broke apart off the west coast of Kauai Island, Hawaii as it was climbing out of the Kauai wind shadow. Following the aircraft mishap, a study was carried out to understand the conditions on the day of the crash and to better characterize the wind in the lee of Kauai. As part of this effort, both aircraft measurements and numerical modelling studies were carried out. Measurements and models showed the trade wind flow was enhanced around the island creating a region of wind shear surrounding the leeside calm zone. This wind shear region was found to be vertically oriented along the south side but tilted northward with height along the northern side of the calm zone. Several other factors on the day of the crash were investigated including water vapour gradients, diurnal Island heating, and gravity waves but their possible influences on the crash could not be confirmed. While the numerical model captured the general features of the Kauai leeside winds, the orientation of the calm zone was north of the observed one.

Porter, John N.; Stevens, Duane; Roe, Kevin; Kono, Sheldon; Kress, David; Lau, Eric

2007-06-01

323

Numerical modeling of the wind flow over a transverse dune  

PubMed Central

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

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

2013-01-01

324

Wind energy conversion  

Microsoft Academic Search

Effective utilization of wind energy requires systematic studies of the sites available for the location of wind energy conversion systems and careful evaluation of the type and size of machines to be used. The present paper describes an approach currently in use for the siting of wind generators. It describes also the aerodynamic features of various types of wind machines

A. A. Fejer

1978-01-01

325

Wind resources of Somalia  

Microsoft Academic Search

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

R. Pallabazzer; A. A. Gabow

1991-01-01

326

Energy from the wind  

NASA Astrophysics Data System (ADS)

This document provides a brief description of the use of wind power. Windmills from the 18th century are described. Modern wind turbines and wind turbine arrays are discussed. Present and future applications of wind power in the U.S. are explained.

1987-07-01

327

Wind With Miller  

NSDL National Science Digital Library

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

2007-04-13

328

Controls of dust emission fluxes and wind erosion threshold on a wet playa  

NASA Astrophysics Data System (ADS)

The control of dust emissions from crusted surfaces is both highly variable and difficult to measure directly. Seasonal changes in moisture availability, temperature, evaporation, surface roughness, and sediment supply result in a highly complex surface condition that remains to be fully described in the context of wind erosion potential. A highly intensive project on Sua Pan, Botswana using the PI-SWERL (portable wind tunnel) combined with surface measurements of crust and soil properties has led to a new understanding of the controls on wind erosion from these surfaces. The PI-SWERL is a highly portable wind tunnel that applies a wind shear to the surface using a motor-controlled rotating annular blade and measures resulting dust emissions with a DustTrak dust monitor. We undertook a sequence of tests with the PI-SWERL to obtain both the wind erosion threshold (using a slowly increasing shear velocity) and a dust emission flux (using a constant shear velocity) across a 12 km by 12 km grid across the pan surface. A total of just under 1000 wind tunnel tests and 2000 correlated measurements of a variety of surface properties including crust thickness, surface and subsurface soil moisture, shearing strength (shear vane), normal stress resistance (penetrometer), and surface roughness were conducted in August 2011. These results show that wind erosion potential is best described by measurements of normal stress resistance rather than shearing strength at low dust emission fluxes, but despite their frequent use in wind erosion studies of crusted surfaces neither metric provided a good explanation of higher dust emission fluxes. Surface soil moisture explained the most variation in both dust emissions and wind erosion threshold although much variation remains unexplained. Our results suggested that combining measurements of surface roughness, soil moisture, and crust thickness provided a reasonable explanation of wind erosion potential on the salt pan surface. As pan surfaces can exhibit a range of aerodynamic roughness lengths over three orders of magnitude the small-scale partition of wind stress could be considered. Surface soil moisture also had a very large range in which a relatively sharp threshold was found to increase dust emissions when combined with other surface factors. Although the role of surface moisture in dust emissions is understood it remains a very difficult (yet critical) parameter to measure and a call for more precise estimations of this metric is highly encouraged.

Wiggs, G.; King, J.; Thomas, D. S.; Washington, R.

2012-12-01

329

HELICITY CONDENSATION AS THE ORIGIN OF CORONAL AND SOLAR WIND STRUCTURE  

SciTech Connect

Three of the most important and most puzzling features of the Sun's atmosphere are the smoothness of the closed-field corona (the so-called coronal loops), the accumulation of magnetic shear at photospheric polarity inversion lines (PILs; filament channels), and the complex dynamics of the slow wind. We propose that a single process, helicity condensation, is the physical mechanism giving rise to all three features. A simplified model is presented for how helicity is injected and transported in the closed corona by magnetic reconnection. With this model, we demonstrate that magnetic shear must accumulate at PILs and coronal hole boundaries, and estimate the rate of shear growth at PILs and the loss to the wind. Our results can account for many of the observed properties of the corona and wind.

Antiochos, S. K., E-mail: spiro.antiochos@nasa.gov [NASA Goddard Space Flight Center, Greenbelt, MD, 20771 (United States)

2013-07-20

330

Generalized shear of a soft rectangular block  

NASA Astrophysics Data System (ADS)

The problem of the simple shear of a block has been treated in terms of a shear displacement, applied uniformly in a lateral direction and assumed to be a linear function of the height above the base. In this paper, simple shear is generalized: the shear displacement is neither uniform in the lateral direction nor necessarily a linear function of the height. Using second-order isotropic elasticity, the analytical solutions show that the shear displacements are characterized by the product of sine and hyperbolic sine functions of the height and depth variables, respectively. The height dependence of the shear displacement is predicted to be a combination of linear and sinusoidal functions, and is verified against the test data of agar-gelatin cuboidal blocks. If the gravity effect is incorporated, a quadratic dependence on height is additionally predicted. The calculation of stresses reveals the presence of not only negative normal stresses but also sinusoidally varying shear stresses on the lateral planes tending to distort the block about the height direction. These results can be of great importance in tissue/cell mechanics.

Wang, Dong; Wu, M. S.

2014-10-01

331

Shear thinning in deeply supercooled melts  

PubMed Central

We compute, on a molecular basis, the viscosity of a deeply supercooled liquid at high shear rates. The viscosity is shown to decrease at growing shear rates, owing to an increase in the structural relaxation rate as caused by the shear. The onset of this non-Newtonian behavior is predicted to occur universally at a shear rate significantly lower than the typical structural relaxation rate, by approximately two orders of magnitude. This results from a large size—up to several hundred atoms—of the cooperative rearrangements responsible for mass transport in supercooled liquids and the smallness of individual molecular displacements during the cooperative rearrangements. We predict that the liquid will break down at shear rates such that the viscosity drops by approximately a factor of 30 below its Newtonian value. These phenomena are predicted to be independent of the liquid's fragility. In contrast, the degree of nonexponentiality and violation of the Stokes–Einstein law, which are more prominent in fragile substances, will be suppressed by shear. The present results are in agreement with existing measurements of shear thinning in silicate melts.

Lubchenko, Vassiliy

2009-01-01

332

Convectively driven shear and decreased heat flux  

E-print Network

We report on direct numerical simulations of two-dimensional, horizontally periodic Rayleigh-B\\'enard convection, focusing on its ability to drive large-scale horizontal flow that is vertically sheared. For the Prandtl numbers ($Pr$) between 1 and 10 simulated here, this large-scale shear can be induced by raising the Rayleigh number ($Ra$) sufficiently, and we explore the resulting convection for $Ra$ up to $10^{10}$. When present in our simulations, the sheared mean flow accounts for a large fraction of the total kinetic energy, and this fraction tends towards unity as $Ra\\to\\infty$. The shear helps disperse convective structures, and it reduces vertical heat flux; in parameter regimes where one state with large-scale shear and one without are both stable, the Nusselt number of the state with shear is smaller and grows more slowly with $Ra$. When the large-scale shear is present with $Pr\\lesssim2$, the convection undergoes strong global oscillations on long timescales, and heat transport occurs in bursts. N...

Goluskin, David; Flierl, Glenn R; Spiegel, Edward A

2014-01-01

333

On liquid migration in sheared granular matter  

NASA Astrophysics Data System (ADS)

Mixing liquids with powders is of great importance, e.g. in process engineering and for pharmaceutical applications. Generally, one might expect that homogeneously shearing or stirring wet granular matter would lead to a homogeneous liquid distribution, however, it is not clear what happens when shear is applied non-homogeneously, e.g. in shear bands. It is commonly accepted that at large liquid contents, liquid flows inside dilating zones as percolating liquid networks prevent air from entering the dilating pores, but it is unknown what happens at low liquid contents. We present experimental measurements showing a decreased liquid concentration inside a shear band where glass beads are sheared in a split bottom shear cell. Furthermore, a microscopic model for liquid transport at low liquid contents is presented, where fluid dynamics between individual liquid structures driven by Laplace pressure differences is taken into account. Our model shows liquid depletion patterns in quantitative agreement with experiments. On the other hand, our model is also applicable to the situation where shear is applied homogeneously, showing diffusive spreading of liquid.

Mani, R.; Kadau, D.; Or, D.; Herrmann, H. J.

2013-06-01

334

Endothelial gene regulation by laminar shear stress.  

PubMed

Endothelial cells, because of their unique localization, are constantly exposed to fluid mechanical forces derived by the flowing blood. These forces, and more specifically shear stresses; affect endothelial structure and function, both in vivo and in vitro, and are implicated as contributing factors in the development of cardiovascular diseases. We have demonstrated earlier that the shear stress selectively induces the transcription of several endothelial genes, and have defined a shear stress response element (SSRE) in the promoter of platelet-derived-growth-factor B (PDGF-B), that is shared by additional endothelial shear stress responsive genes. Here we further characterize this SSRE and the nuclear factors that bind to it, and imply the possible role of the endothelium cytoskeleton in transducing shear stress, leading to the expression of PDGF-B/SSRE constructs in transfected endothelial cells exposed to shear stress. We also present, yet a new shear stress response element in the Platelet Derived Growth Factor A promoter, that contains a binding site to the transcription factors egr1/sp1. These results further demonstrate the complexity of gene regulation by hemodynamic forces, and support the important part that these forces have in the physiology and pathophysiology of the vessel wall. PMID:9330726

Resnick, N; Yahav, H; Khachigian, L M; Collins, T; Anderson, K R; Dewey, F C; Gimbrone, M A

1997-01-01

335

Surface shear inviscidity of soluble surfactants  

PubMed Central

Foam and emulsion stability has long been believed to correlate with the surface shear viscosity of the surfactant used to stabilize them. Many subtleties arise in interpreting surface shear viscosity measurements, however, and correlations do not necessarily indicate causation. Using a sensitive technique designed to excite purely surface shear deformations, we make the most sensitive and precise measurements to date of the surface shear viscosity of a variety of soluble surfactants, focusing on SDS in particular. Our measurements reveal the surface shear viscosity of SDS to be below the sensitivity limit of our technique, giving an upper bound of order 0.01 ?N·s/m. This conflicts directly with almost all previous studies, which reported values up to 103–104 times higher. Multiple control and complementary measurements confirm this result, including direct visualization of monolayer deformation, for SDS and a wide variety of soluble polymeric, ionic, and nonionic surfactants of high- and low-foaming character. No soluble, small-molecule surfactant was found to have a measurable surface shear viscosity, which seriously undermines most support for any correlation between foam stability and surface shear rheology of soluble surfactants. PMID:24563383

Zell, Zachary A.; Nowbahar, Arash; Mansard, Vincent; Leal, L. Gary; Deshmukh, Suraj S.; Mecca, Jodi M.; Tucker, Christopher J.; Squires, Todd M.

2014-01-01

336

Fluid shear stress threshold regulates angiogenic sprouting.  

PubMed

The density and architecture of capillary beds that form within a tissue depend on many factors, including local metabolic demand and blood flow. Here, using microfluidic control of local fluid mechanics, we show the existence of a previously unappreciated flow-induced shear stress threshold that triggers angiogenic sprouting. Both intraluminal shear stress over the endothelium and transmural flow through the endothelium above 10 dyn/cm(2) triggered endothelial cells to sprout and invade into the underlying matrix, and this threshold is not impacted by the maturation of cell-cell junctions or pressure gradient across the monolayer. Antagonizing VE-cadherin widened cell-cell junctions and reduced the applied shear stress for a given transmural flow rate, but did not affect the shear threshold for sprouting. Furthermore, both transmural and luminal flow induced expression of matrix metalloproteinase 1, and this up-regulation was required for the flow-induced sprouting. Once sprouting was initiated, continuous flow was needed to both sustain sprouting and prevent retraction. To explore the potential ramifications of a shear threshold on the spatial patterning of new sprouts, we used finite-element modeling to predict fluid shear in a variety of geometric settings and then experimentally demonstrated that transmural flow guided preferential sprouting toward paths of draining interstitial fluid flow as might occur to connect capillary beds to venules or lymphatics. In addition, we show that luminal shear increases in local narrowings of vessels to trigger sprouting, perhaps ultimately to normalize shear stress across the vasculature. Together, these studies highlight the role of shear stress in controlling angiogenic sprouting and offer a potential homeostatic mechanism for regulating vascular density. PMID:24843171

Galie, Peter A; Nguyen, Duc-Huy T; Choi, Colin K; Cohen, Daniel M; Janmey, Paul A; Chen, Christopher S

2014-06-01

337

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

E-print Network

and research institutions. Career prospects The number of jobs in the wind energy sector in Europe is expectedWind energy offers considerable promise; the wind itself is free, wind power is clean. One of these sources, wind energy, offers considerable promise; the wind itself is free, wind power

Langendoen, Koen

338

Estimation of Wind Speed in Connection to a Wind Turbine  

E-print Network

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

339

Wind Power Outlook 2004  

SciTech Connect

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

anon.

2004-01-01

340

Bubbles in sheared two-dimensional foams  

E-print Network

Oscillatory shear on two-dimensional monodisperse liquid foams was performed. We show that the effect of the oscillatory shear is to cause the migration of bubbles which size is greater than that of a typical bubble of the foam. These so-called flaws move towards the periphery of the foam in a non random motion, thus realizing size segregation in a system which is by construction gravity insensitive. We also show that elongated cavities in the foam could be relaxed towards a more isotropic form with oscillatory shear, and we discuss the pertinent parameters of this relaxation.

C. Quilliet; M. A. P. Idiart; B. Dollet; L. Berthier; A. Yekini

2005-02-18

341

Stress pulse attenuation in shear thickening fluid  

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

342

Shear viscosity from effective couplings of gravitons  

SciTech Connect

We calculate the shear viscosity of field theories with gravity duals using Kubo formula by calculating the Green function of dual transverse gravitons and confirm that the value of the shear viscosity is fully determined by the effective coupling of transverse gravitons on the horizon. We calculate the effective coupling of transverse gravitons for Einstein and Gauss-Bonnet gravities coupled with matter fields, respectively. Then we apply the resulting formula to the case of AdS Gauss-Bonnet gravity with F{sup 4} term corrections of Maxwell field and discuss the effect of F{sup 4} terms on the ratio of the shear viscosity to entropy density.

Cai Ronggen [Institute of Theoretical Physics, Chinese Academy of Sciences, P.O. Box 2735, Beijing 100190 (China); Nie Zhangyu; Sun Yawen [Institute of Theoretical Physics, Chinese Academy of Sciences, P.O. Box 2735, Beijing 100190 (China); Graduate University of Chinese Academy of Sciences, YuQuan Road 19A, Beijing 100049 (China)

2008-12-15

343

Time accurate simulations of compressible shear flows  

NASA Technical Reports Server (NTRS)

The objectives of this research are to employ direct numerical simulation (DNS) to study the phenomenon of mixing (or lack thereof) in compressible free shear flows and to suggest new means of enhancing mixing in such flows. The shear flow configurations under investigation are those of parallel mixing layers and planar jets under both non-reacting and reacting nonpremixed conditions. During the three-years of this research program, several important issues regarding mixing and chemical reactions in compressible shear flows were investigated.

Givi, Peyman; Steinberger, Craig J.; Vidoni, Thomas J.; Madnia, Cyrus K.

1993-01-01

344

Buoyancy and shear characteristics of hurricane-tornado environments  

NASA Technical Reports Server (NTRS)

This study presents detailed composite profiles of temperature, moisture, and wind constructed for tornado environments in tropical cyclones that affected the U.S. between 1948 and 1986. Winds are composited in components radial and tangential to the tropical cyclone center at observation time. Guided by observed patterns of tornado occurrence, composites are constructed for a variety of different stratifications of the data, including proximity to tornadoes, position relative to the cyclone center, time of day, time after cyclone landfall, cyclone translation speed, and landfall location. The composites are also compared to composite soundings from Great Plains tornado environments. A variety of sounding parameters are examined to see which are most closely related to the tornado distribution patterns. Lower-tropospheric vertical shears are found to be stronger in the tropical cyclone tornado environments than on the Great Plains. Buoyancy for the tropical cyclone tornado cases is much smaller than that seen with Great Plains tornado events and exhibits a weak negative correlation with tornado outbreak severity.

Mccaul, Eugene W., Jr.

1991-01-01

345

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

346

Simplified Shear Solution for Determination of the Shear Stress Distribution in a Composite Panel from the Applied Shear Resultant  

NASA Technical Reports Server (NTRS)

The simplified shear solution method is presented for approximating the through-thickness shear stress distribution within a composite laminate or panel based on laminated beam theory. The method does not consider the solution of a particular boundary value problem; rather it requires only knowledge of the global shear loading, geometry, and material properties of the laminate or panel. It is thus analogous to lamination theory in that ply level stresses can be efficiently determined from global load resultants (as determined, for instance, by finite element analysis) at a given location in a structure and used to evaluate the margin of safety on a ply by ply basis. The simplified shear solution stress distribution is zero at free surfaces, continuous at ply boundaries, and integrates to the applied shear load. Comparisons to existing theories are made for a variety of laminates, and design examples are provided illustrating the use of the method for determining through-thickness shear stress margins in several types of composite panels and in the context of a finite element structural analysis.

Bednarcyk, Brett A.; Aboudi, Jacob; Yarrington, Phillip W.; Collier, Craig S.

2008-01-01

347

Effects of transverse shearing flexibility on the postbuckling of plates loaded by inplane shear  

NASA Technical Reports Server (NTRS)

This paper presents buckling and postbuckling results for plates loaded by inplane shear. The buckling results have been plotted to show the effects of thickness on the stress coefficient for aluminum plates. Results are given for various length-to-width ratios. Postbuckling results for thin plates with transverse shearing flexibility are compared to results from classical theory. The problems considered are the postbuckling response of plates in shear made of aluminum and of a + or - 45 deg graphite-epoxy laminate. Thus the materials are isotropic and orthotropic, respectively. The plates are considered to be long with side edges simply supported, with various inplane edge conditions, and the plates are subject to a constant shearing displacement along the side edges. Characteristic curves presenting the average shear stress resultant as a function of the applied displacement are given. These curves indicate that change in inplane edge conditions influence plate postbuckling stiffness and that transverse shearing is important in some cases.

Stein, Manuel

1987-01-01

348

Shear joint capability versus bolt clearance  

NASA Technical Reports Server (NTRS)

The results of a conservative analysis approach into the determination of shear joint strength capability for typical space-flight hardware as a function of the bolt-hole clearance specified in the design are presented. These joints are comprised of high-strength steel fasteners and abutments constructed of aluminum alloys familiar to the aerospace industry. A general analytical expression was first arrived at which relates bolt-hole clearance to the bolt shear load required to place all joint fasteners into a shear transferring position. Extension of this work allowed the analytical development of joint load capability as a function of the number of fasteners, shear strength of the bolt, bolt-hole clearance, and the desired factor of safety. Analysis results clearly indicate that a typical space-flight hardware joint can withstand significant loading when less than ideal bolt hole clearances are used in the design.

Lee, H. M.

1992-01-01

349

Influence of magnetic shear on impurity transport  

NASA Astrophysics Data System (ADS)

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

Nordman, H.; Fülöp, T.; Candy, J.; Strand, P.; Weiland, J.

2007-05-01

350

Computed Turbulent Free Shear Flow Of Air  

NASA Technical Reports Server (NTRS)

Standard k-epsilon model of turbulence yields fairly accurate results. Symposium paper discusses numerical simulation of turbulent free shear flow of nonreacting compressible fluid. Ability to compute such flows essential to advances in design.

Viegas, J. R.; Rubesin, M. W.

1992-01-01

351

Flow and jamming of sheared granular media  

NASA Astrophysics Data System (ADS)

Granular materials, such as athermal suspensions, can either be jammed and rigid, or yield and flow. Recent experiments on granular suspensions in a annular shear cell (vibrated and/or sheared) show a hysteretic freezing and melting transition [1, 2]: a crystallised state is found, which can be melted by sufficient shear. The question is open on what are the mechanisms underlying these phenomena and which are the control parameters. Via Molecular Dynamics simulations, we study the rheology of vibrated and sheared granular materials [3]. In particular, we aim to understand the nature of a critical line separating crystallised and melted states and the "jammed" region in the phase diagram, as well as the connections with thermal glass formers and colloidal suspensions.

Ciamarra, M. Pica; Nicodemi, M.; Coniglio, A.

2009-06-01

352

Shear acceleration in relativistic astrophysical jets  

E-print Network

We consider the acceleration of energetic particles by a velocity shear in the relativistic background flow containing scattering centers. Three possible acceleration sites for astrophysical jets are identified: (1) gradual velocity shear parallel to the jet axis, such as a velocity profile decreasing linearly outward with radial coordinate, (2) gradual velocity shear perpendicular to the jet axis, such as intrinsic jet rotation, and (3) non-gradual/discontinuous, longitudinal velocity shear at the jet-side boundary. We determine the characteristic acceleration timescales, specify the conditions for efficient acceleration and discuss observational features with respect to each process. In particular, it is shown that in the case of (2) the higher energy emission is expected to be concentrated closer to the jet axis, while in the case of (1) and (3) the higher energy particles are likely to be located near the edges of the jet, thus possibly leading to some form of limb-brightening.

Frank M. Rieger; Peter Duffy

2004-10-11

353

Particle acceleration in astrophysical shear flows  

E-print Network

We consider the acceleration of particles due to a velocity shear in relativistic astrophysical flows. The basic physical picture and the formation of power law momentum spectra is discussed for a non-relativistic velocity field using a microscopic approach. We identify possible sites for shear acceleration in relativistic astrophysical jets and analyze their associated acceleration timescales. It is shown in particular that for a mean scattering time $\\tau$ scaling with the gyro-radius, the acceleration timescale for gradual shear scales in the same manner as the synchrotron cooling timescale, so that losses may no longer be able to stop the acceleration once it has started to work efficiently. Finally, the possible role of shear acceleration is discussed with reference to the relativistic jet in the quasar 3C~273.

Frank M. Rieger; Peter Duffy

2005-01-10

354

Shear lag in truss core sandwich beams  

E-print Network

An experimental study was conducted to investigate the possible influence of shear lag in the discrepancy between the theoretical and measured stiffness of truss core sandwich beams. In previous studies, the measured values ...

Roberts, Ryan (Ryan M.)

2005-01-01

355

Shear thickening, frictionless and frictional rheologies  

E-print Network

Particles suspended in a Newtonian fluid raise the viscosity and also generally give rise to a shear-rate dependent rheology. In particular, pronounced shear thickening is observed at large solid volume fractions. In a recent article (R. Seto, R. Mari, J. F. Morris, and M. M. Denn., Phys. Rev. Lett., 111:218301, 2013) we have considered the minimum set of components to reproduce the experimentally observed shear thickening behavior, including Discontinuous Shear Thickening (DST). We have found frictional contact forces to be essential, and were able to reproduce the experimental behavior by a simulation including this physical ingredient. In the present article, we thoroughly investigate the effect of friction and express it in the framework of the jamming transition. The viscosity divergence at the jamming transition has been a well known phenomenon in suspension rheology, as reflected in many empirical laws for the viscosity. Friction can affect this divergence, and in particular the jamming packing fractio...

Mari, Romain; Morris, Jeffrey F; Denn, Morton M

2014-01-01

356

Periodic Exponential Shear of Complex Fluids  

E-print Network

We define a class of flows with exponential kinematics termed Periodic Exponential Shear (PES) flow which involve periodic exponential stretching of fluid elements along with their rotation. We exhibit analytical and numerical results for PES flow by using the Oldroyd-B model for viscoelastic fluids. We calculate the growth in the shear and the normal stresses analytically as well as demonstrate that repeated application of the flow leads to stable oscillatory shear and normal stresses. We define a material function applicable to a periodic, unsteady shear flow and show numerically that this material function exhibits deformation-rate thickening behavior for viscoelastic fluids subject to PES flow. We demonstrate the feasibility of PES flow by presenting preliminary experimental results from a controlled-strain rate rheometer, using a Newtonian mineral oil.

Chirag Kalelkar; Gareth McKinley

2012-05-31

357

Influence of magnetic shear on impurity transport  

SciTech Connect

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

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

2007-05-15

358

Shear thinning behavior of linear polymer melts under shear flow via nonequilibrium molecular dynamics  

NASA Astrophysics Data System (ADS)

The properties of both untangled and entangled linear polymer melts under shear flow are studied by nonequilibrium molecular dynamics simulations. The results reveal that the dependence of shear viscosity ? on shear rate dot{? }, expressed by ? ˜ dot{? }^{-n}, exhibits three distinct regimes. The first is the well-known Newtonian regime, namely, ? independent of shear rate at small shear rates dot{? }?0^{-1}), the shear dependence of viscosity exhibits a crossover at a critical shear rate dot{? }c dividing this regime into two different regimes, shear thinning regime I (ST-I) and II (ST-II), respectively. In the ST-I regime (?^{-1}_0dot{? }c) a universal power law ? ˜ dot{? }^{-0.37} is found for considered chain lengths. Furthermore, the longer the polymer chain is, the smaller the shear viscosity for a given shear rate in the ST-II regime. The simulation also shows that a characteristic chain length, below which dot{? }c will be equal to ?0^{-1}, lies in the interval 30 < N < 50. For all considered chain lengths in the ST-II regime, we also find that the first and second normal stress differences N1 and N2 follow power laws of N1 ˜ dot{? }^{2/3} and N2 ˜ dot{? }^{0.82}, respectively; the orientation resistance parameter mG follows the relation mG ˜ dot{? }^{0.75} and the tumbling frequency ftb follows f_{tb} ˜ dot{? }^{0.75}. These results imply that the effects of entanglement on the shear dependences of these properties may be negligible in the ST-II regime. These findings may shed some light on the nature of shear thinning in flexible linear polymer melts.

Xu, Xiaolei; Chen, Jizhong; An, Lijia

2014-05-01

359

Shear thinning behavior of linear polymer melts under shear flow via nonequilibrium molecular dynamics.  

PubMed

The properties of both untangled and entangled linear polymer melts under shear flow are studied by nonequilibrium molecular dynamics simulations. The results reveal that the dependence of shear viscosity ? on shear rate ?, expressed by n ~ ?(-n), exhibits three distinct regimes. The first is the well-known Newtonian regime, namely, ? independent of shear rate at small shear rates ? < ?0(-1) (where ?0 is the longest polymer relaxation time at equilibrium). In the non-Newtonian regime (? > ?0(-1)) the shear dependence of viscosity exhibits a crossover at a critical shear rate ?c dividing this regime into two different regimes, shear thinning regime I (ST-I) and II (ST-II), respectively. In the ST-I regime (?0(-1) < ? < ?c), the exponent n increases with increasing chain length N, while in the ST-II regime (? > ?c) a universal power law n ~ ?(-0.37) is found for considered chain lengths. Furthermore, the longer the polymer chain is, the smaller the shear viscosity for a given shear rate in the ST-II regime. The simulation also shows that a characteristic chain length, below which ?c will be equal to ?0(-1), lies in the interval 30 < N < 50. For all considered chain lengths in the ST-II regime, we also find that the first and second normal stress differences N1 and N2 follow power laws of N1 ~ ?(2/3) and N2 ~ ?(0.82), respectively; the orientation resistance parameter mG follows the relation mG ~ ?(0.75) and the tumbling frequency ftb follows ftb ~ ?(0.75). These results imply that the effects of entanglement on the shear dependences of these properties may be negligible in the ST-II regime. These findings may shed some light on the nature of shear thinning in flexible linear polymer melts. PMID:24811663

Xu, Xiaolei; Chen, Jizhong; An, Lijia

2014-05-01

360

Shearing Flows in Liquid Crystal Models  

E-print Network

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2 Classic Continuum Models for Liquid Crystals . . . . . . . . . . . . . 2 1.3 A Simplified Phenomenological Model . . . . . . . . . . . . . . . . . . 12 2 Shearing Flows in a Liquid Crystal Model for Friction 14 2.1 The steady state... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 2.1.1 Existence and multiplicity . . . . . . . . . . . . . . . . . . . . 18 2.1.2 An example of multiple steady states . . . . . . . . . . . . . . 24 2.2 Stability for small shearing speeds . . . . . . . . . . . . . . . . . . . . 25 2.2.1 Linear...

Dorn, Timothy

2012-05-31

361

Shear Strength Behavior of Human Trabecular Bone  

PubMed Central

The shear strength of human trabecular bone may influence overall bone strength under fall loading conditions and failure at bone-implant interfaces. Here, we sought to compare shear and compressive yield strengths of human trabecular bone and elucidate the underlying failure mechanisms. We analyzed 54 specimens (5-mm cubes), all aligned with the main trabecular orientation and spanning four anatomic sites, 44 different cadavers, and a wide range of bone volume fraction (0.06–0.38). Micro-CT-based non-linear finite element analysis was used to assess the compressive and shear strengths and the spatial distribution of yielded tissue; the tissue-level constitutive model allowed for kinematic non-linearity and yielding with strength asymmetry. We found that the computed values of both the shear and compressive strengths depended on bone volume fraction via power law relations having an exponent of 1.7 (R2=0.95 shear; R2=0.97 compression). The ratio of shear to compressive strengths (mean ± SD, 0.44 ± 0.16) did not depend on bone volume fraction (p=0.24) but did depend on microarchitecture, most notably the intra-trabecular standard deviation in trabecular spacing (R2=0.23, p<0.005). For shear, the main tissue-level failure mode was tensile yield of the obliquely oriented trabeculae. By contrast, for compression, specimens having low bone volume fraction failed primarily by large-deformation-related tensile yield of horizontal trabeculae and those having high bone volume failed primarily by compressive yield of vertical trabeculae. We conclude that human trabecular bone is generally much weaker in shear than compression at the apparent level, reflecting different failure mechanisms at the tissue level. PMID:22884967

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

2012-01-01

362

The effect of shear on neurodegeneration  

E-print Network

THE EFFECT OF SHEAR ON NEURODEGENERATION A Thesis by DINA HANDAYANI TRIYOSO Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE August l998 Major... Subject: Chemical Engineering THE EFFECT OF SHEAR ON NEIJRODEGENERATION A Thesis by DINA HANDAYAM TRIYOSO Submitted to Texas A&M University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Approved as to style...

Triyoso, Dina Handayani

2012-06-07

363

Speckle Shearing Interferometry And Its Application  

NASA Astrophysics Data System (ADS)

The paper deals with experiments made to verify the theory of bending of plates and related problems by method of speckle shearing interferometry, which is proved to be highly sensitive. Tests carried out on rubber products: (such as tires)and thin-walled containers have demonstrated the prospects of using image-shearing camera in nondestructive in-situ testing of industrial products, suggesting a potentiality still wider than that of holographic interferometry.

Jingtang, Ke; Hongqing, Zhang; Yeling, He; Yanfu, Chang

1983-12-01

364

Bubble kinematics in a sheared foam  

E-print Network

We characterize the kinematics of bubbles in a sheared two-dimensional foam using statistical measures. We consider the distributions of both bubble velocities and displacements. The results are discussed in the context of the expected behavior for a thermal system and simulations of the bubble model. There is general agreement between the experiments and the simulation, but notable differences in the velocity distributions point to interesting elements of the sheared foam not captured by prevalent models.

Yuhong Wang; Kapilanjan Krishan; Michael Dennin

2006-07-05

365

Shear deflection of composite wood beams  

E-print Network

SHEAR DEFLECTION OF COMPOSITE WOOD BEAMS A Thesis by THOlvlAS DAVID SKAGGS Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE May 1992 Major... Subject: Agricultural Engineering SHEAR DEFLECTION OF COMPOSITE WOOD BEAMS A Thesis by THOMAS DAVID SKAGGS Approved as to style and content by: Don A. Bender (Chair of Committee) erry L. Kohutek (Member) ary igh Wol e (Member) Donald L. Reddell...

Skaggs, Thomas David

2012-06-07

366

Compression and shear wave propagation in explosives  

Microsoft Academic Search

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) technique pioneered by Gupta. The objective of the theoretical study was to formulate a treatment of the reactive flow produced in an explosive subjected to

M. Cowperthwaite; Y. M. Gupta

1989-01-01

367

Liquid migration in sheared unsaturated granular media  

E-print Network

We show how liquid migrates in sheared unsaturated granular media using a grain scale model for capillary bridges. Liquid is redistributed to neighboring contacts after rupture of individual capillary bridges leading to redistribution of liquid on large scales. The liquid profile evolution coincides with a recently developed continuum description for liquid migration in shear bands. The velocity profiles which are linked to the migration of liquid as well as the density profiles of wet and dry granular media are studied.

Roman Mani; Dirk Kadau; Hans J. Herrmann

2012-06-25

368

Measurement of shear impedances of viscoelastic fluids  

SciTech Connect

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

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

1996-12-31

369

Study on magnetorheological shear thickening fluid  

Microsoft Academic Search

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

Xianzhou Zhang; Weihua Li; X. L. Gong

2008-01-01

370

The benefit of wind atlases in wind energy and their verification  

NASA Astrophysics Data System (ADS)

1 INTRODUCTION Wind atlases such as reanalysis data and downscaled data sets are widely used in the wind energy sector, e.g. for long-term correlation of short-term measurements or initial site search. Due to the financial impact of statements derived from wind atlases, their verification is of high importance. Here, different wind atlases are verified in-depth with numerous certified high-quality mast measurements covering a broad range of heights up to 200 m. In contrast to the commonly used weather stations, high masts allow for an evaluation of vertical profiles and atmospheric stability. The following questions will be addressed: What are wind atlases? How well are they performing? Which benefit do wind atlases have in wind energy? 2 APPROACH The performance of commonly used reanalysis data, e.g. MERRA, ERA-Interim, and two data sets downscaled from MERRA reanalysis data is investigated. The first downscaled data set is derived by the mesoscale model MM5 and has a spatial and temporal resolution of 20 km and 10 min, respectively. The second downscaled data set is derived by the WRF model and has a spatial and temporal resolution of 3 km and 10 min, respectively. Certified high-quality measurements of 45 met masts with 160 anemometers covering a range of complexity types, measurement heights between 30 m and 200 m and a time period of 2 years are compared to the wind atlases. Hourly values are analysed. 3 RESULTS The correlation with hourly measurements of wind speed is very good for all data sets. Correlation increases with decreasing terrain complexity. Wind directions are also met very well by all data sets. The frequency distributions of wind speed and therefore, the Weibull parameters are reproduced very well by the downscaled data sets for a broad range of velocities, however underestimating higher velocities. MERRA generally strongly overestimates wind speed. Diurnal and annual cycles as well as vertical profiles are reproduced more accurately by the downscaled data sets than by reanalysis data. Thereby, the WRF based atlas performs best, especially in complex terrain and forest areas. One outstanding result is that the downscaled wind atlases are able to simulate the change of the vertical wind shear during the course of the day and thus, atmospheric stability quite well. In general, the performance of all wind atlases weakens for areas with higher complexity and increased roughness (e.g. forests). For offshore sites an underestimation of the level of wind speed is observed. 4 CONCLUSION Correlations with wind speed and wind direction are high, indicating that all wind atlases are suitable for long-term correlation. However, the downscaled data sets yield an overall better performance when it comes to detailed analysis. This suggests that they are more appropriate for applications where the absolute value is important, e.g. the initial estimation of the wind potential, energy loss calculations or the calculation of revenues regarding changing electricity rates. Thus, value is added by downscaling from reanalysis data. Furthermore, we see an improvement from MM5 to WRF and higher spatial resolutions, especially in complex terrain and forest areas.

Bethke, Julia; Kampmeyer, Jens; Mengelkamp, Heinz-Theo

2014-05-01

371

Statistics of polymer adsorption under shear flow  

E-print Network

Using non-equilibrium Brownian dynamics computer simulations, we have investigated the steady state statistics of a polymer chain under three different shear environments: i) linear shear flow in the bulk (no walls), ii) shear vorticity normal to the adsorbing wall, iii) shear gradient normal to the adsorbing wall. The statistical distribution of the chain end-to-end distance and its orientational angles are calculated within our monomer-resolved computer simulations. Over a wide range of shear rates, this distribution can be mapped onto a simple theoretical finite-extensible-nonlinear-elastic dumbbell model with fitted anisotropic effective spring constants. The tails of the angular distribution functions are consistent with scaling predictions borrowed from the bulk dumbbell model. Finally, the frequency of the characteristic periodic tumbling motion has been investigated by simulation as well and was found to be sublinear with the shear rate for the three set-ups, which extends earlier results done in experiments and simulations for free and tethered polymer molecules without adsorption.

Gui-Li He; René Messina; Hartmut Löwen

2009-10-09

372

Evolution of shear zones in granular materials  

E-print Network

The evolution of wide shear zones (or shear bands) was investigated experimentally and numerically for quasistatic dry granular flows in split bottom shear cells. We compare the behavior of materials consisting of beads, irregular grains (e.g. sand) and elongated particles. Shearing an initially random sample, the zone width was found to significantly decrease in the first stage of the process. The characteristic shear strain associated with this decrease is about unity and it is systematically increasing with shape anisotropy, i.e. when the grain shape changes from spherical to irregular (e.g. sand) and becomes elongated (pegs). The strongly decreasing tendency of the zone width is followed by a slight increase which is more pronounced for rod like particles than for grains with smaller shape anisotropy (beads or irregular particles). The evolution of the zone width is connected to shear induced density change and for nonspherical particles it also involves grain reorientation effects. The final zone width is significantly smaller for irregular grains than for spherical beads.

Balazs Szabo; Janos Torok; Ellak Somfai; Sandra Wegner; Ralf Stannarius; Axel Bose; Georg Rose; Frank Angenstein; Tamas Borzsonyi

2014-07-18

373

Evolution of shear zones in granular materials  

NASA Astrophysics Data System (ADS)

The evolution of wide shear zones or shear bands was investigated experimentally and numerically for quasistatic dry granular flows in split bottom shear cells. We compare the behavior of materials consisting of beads, irregular grains, such as sand, and elongated particles. Shearing an initially random sample, the zone width was found to significantly decrease in the first stage of the process. The characteristic shear strain associated with this decrease is about unity and it is systematically increasing with shape anisotropy, i.e., when the grain shape changes from spherical to irregular (e.g., sand) and becomes elongated (pegs). The strongly decreasing tendency of the zone width is followed by a slight increase which is more pronounced for rodlike particles than for grains with smaller shape anisotropy (beads or irregular particles). The evolution of the zone width is connected to shear-induced packing density change and for nonspherical particles it also involves grain reorientation effects. The final zone width is significantly smaller for irregular grains than for spherical beads.

Szabó, Balázs; Török, János; Somfai, Ellák; Wegner, Sandra; Stannarius, Ralf; Böse, Axel; Rose, Georg; Angenstein, Frank; Börzsönyi, Tamás

2014-09-01

374

Shear induced structures in crystallizing cocoa butter  

NASA Astrophysics Data System (ADS)

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

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

2004-03-01

375

WIND DATA REPORT Thompson Island  

E-print Network

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

Massachusetts at Amherst, University of

376

WIND DATA REPORT Presque Isle  

E-print Network

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

Massachusetts at Amherst, University of

377

WIND DATA REPORT Thompson Island  

E-print Network

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

Massachusetts at Amherst, University of

378

WIND DATA REPORT Presque Isle  

E-print Network

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

Massachusetts at Amherst, University of

379

WIND DATA REPORT Presque Isle  

E-print Network

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

Massachusetts at Amherst, University of

380

WIND DATA REPORT Thompson Island  

E-print Network

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

Massachusetts at Amherst, University of

381

WIND DATA REPORT Presque Isle  

E-print Network

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

Massachusetts at Amherst, University of

382

WIND DATA REPORT FALMOUTH, MA  

E-print Network

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

Massachusetts at Amherst, University of

383

WIND DATA REPORT Thompson Island  

E-print Network

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

Massachusetts at Amherst, University of

384

The brittle-viscous-plastic evolution of shear bands in the South Armorican Shear Zone  

NASA Astrophysics Data System (ADS)

Shear bands are microscale shear zones that obliquely crosscut an existing anisotropy such as a foliation. The resulting S-C fabrics are characterized by angles lower than 45° and the C plane parallel to shear zone boundaries. The S-C fabrics typically occur in granitoids deformed at greenschist facies conditions in the vicinity of major shear zones. Despite their long recognition, mechanical reasons for localization of deformation into shear bands and their evolution is still poorly understood. In this work we focus on microscale characterization of the shear bands in the South Armorican Shear Zone, where the S-C fabrics were first recognized by Berthé et al. (1979). The initiation of shear bands in the right-lateral South Armorican Shear Zone is associated with the occurrence of microcracks crosscutting the recrystallized quartz aggregates that define the S fabric. In more advanced stages of shear band evolution, newly formed dominant K-feldspar, together with plagioclase, muscovite and chlorite occur in the microcracks, and the shear bands start to widen. K-feldspar replaces quartz by progressively bulging into the grain boundaries of recrystallized quartz grains, leading to disintegration of quartz aggregates and formation of fine-grained multiphase matrix mixture. The late stages of shear band development are marked by interconnection of fine-grained white mica into a band that crosscuts the original shear band matrix. In its extremity, the shear band widening may lead to the formation of ultramylonites. With the increasing proportion of shear band matrix from ~1% to ~12%, the angular relationship between S and C fabrics increases from ~30° to ~40°. The matrix phases within shear bands show differences in chemical composition related to distinct evolutionary stages of shear band formation. The chemical evolution is well documented in K-feldspar, where the albite component is highest in porphyroclasts within S fabric, lower in the newly formed grains within microcracks and nearly absent in matrix grains in the well developed C bands. The chemical variation between primary and secondary new-formed micas was clearly identified by the Mg-Ti-Na content. The microstructural analysis documents a progressive decrease in quartz grain size and increasing interconnectivity of K-feldspar and white mica towards more mature shear bands. The contact-frequency analysis demonstrates that the phase distribution in shear bands tends to evolve from quartz aggregate distribution via randomization to K-feldspar aggregate distribution. The boundary preferred orientation is absent in quartz-quartz contacts either inside of outside the C bands, while it changes from random to parallel to the C band for the K-feldspar and and K-feldspar-quartz boundaries. The lack of crystallographic preferred orientation of the individual phases in the mixed matrix of the C planes suggests a dominant diffusion-assisted grain boundary sliding deformation mechanism. In the later stages of shear band development, the deformation is accommodated by crystal plasticity of white mica in micaceous bands. The crystallographic and microstructural data thus indicate two important switches in deformation mechanisms, from (i) brittle to Newtonian viscous behavior in the initial stages of shear band evolution and from (ii) Newtonian viscous to power law in the later evolutionary stages. The evolution of shear bands in the South Armorican Shear Zone thus document the interplay between deformation mechanisms and chemical reactions in deformed granitoids.

Bukovská, Zita; Je?ábek, Petr; Morales, Luiz F. G.; Lexa, Ondrej; Milke, Ralf

2014-05-01

385

Turbulent mixing driven by mean-flow shear and internal gravity waves in oceans and atmospheres  

E-print Network

This study starts with balances deduced by Baumert and Peters (2004, 2005) from results of stratified-shear experiments made in channels and wind tunnels by Itsweire (1984) and Rohr and Van Atta (1987), and of free-decay experiments in a resting stratified tank by Dickey and Mellor (1980). Using a modification of Canuto's (2002) ideas on turbulence and waves, these balances are merged with an (internal) gravity-wave energy balance presented for the open ocean by Gregg (1989), without mean-flow shear. The latter was augmented by a linear (viscous) friction term. Gregg's wave-energy source is interpreted on its long-wave spectral end as internal tides, topography, large-scale wind, and atmospheric low-pressure actions. In addition, internal eigen waves, generated by mean-flow shear, and the aging of the wave field from a virginal (linear) into a saturated state are taken into account. Wave packets and turbulence are treated as particles (vortices, packets) by ensemble kinetics so that the loss terms in all thre...

Baumert, Helmut Z

2012-01-01

386

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

SciTech Connect

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

Schott, F.; Partagas, J.F.

1981-05-20

387

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

E-print Network

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

Hennon, Christopher C.

388

Wind energy information guide  

SciTech Connect

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

NONE

1996-04-01

389

Wind Power Career Chat  

SciTech Connect

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

Not Available

2011-01-01

390

Tangential stress beneath wind-driven air water interfaces  

NASA Astrophysics Data System (ADS)

The detailed structure of the aqueous surface sublayer flow immediately adjacent to the wind-driven air water interface is investigated in a laboratory wind-wave flume using particle image velocimetry (PIV) techniques. The goal is to investigate quantitatively the character of the flow in this crucial, very thin region which is often disrupted by microscale breaking events. In this study, we also examine critically the conclusions of Okuda, Kawai & Toba (1977), who argued that for very short, strongly forced wind-wave conditions, shear stress is the dominant mechanism for transmitting the atmospheric wind stress into the water motion waves and surface drift currents. In strong contrast, other authors have more recently observed very substantial normal stress contributions on the air side. The availability of PIV and associated image technology now permits a timely re-examination of the results of Okuda et al., which have been influential in shaping present perceptions of the physics of this dynamically important region. The PIV technique used in the present study overcomes many of the inherent shortcomings of the hydrogen bubble measurements, and allows reliable determination of the fluid velocity and shear within 200 [mu]m of the instantaneous wind-driven air water interface.

Banner, Michael L.; Peirson, William L.

1998-06-01

391

Vandenberg Air Force Base Upper Level Wind Launch Weather Constraints  

NASA Technical Reports Server (NTRS)

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

Shafer, Jaclyn A.; Wheeler, Mark M.

2012-01-01

392

Cyclic behaviour, deformability and rigidity of stiffened steel shear panels  

Microsoft Academic Search

Shear panels play an important role in improving the seismic behaviour of structures. They generally occur as thin steel plate shear walls (TSPSW) or shear panels created within the web of link beams in eccentrically braced frame (EBF) structures. The post-buckling capacity, deformability and energy dissipation of shear panels are now widely accepted by structural engineers and has resulted in

M. M. Alinia; M. Dastfan

2007-01-01

393

Stochastic Shear Thickening Fluids: Strong Convergence of the Galerkin Approximation  

E-print Network

Stochastic Shear Thickening Fluids: Strong Convergence of the Galerkin Approximation and the Energy) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2 The stochastic shear thickening fluids 4 2.1 Strong convergence of the Galerkin approximation.1) where div = (d j=1 jij )d i=1 . The fluid is said shear thinning if p shear

Yoshida, Nobuo

394

The shear-driven Rayleigh problem for generalised Newtonian fluids  

E-print Network

of the solutions for shear-thickening fluids. For a shear-thickening power-law fluid the boundary layer is strictlyThe shear-driven Rayleigh problem for generalised Newtonian fluids Brian R. Duffya , David- steady, non-Newtonian boundary layers, and in particular the effect of shear thinning or thickening

395

Relation between ordering and shear thinning in colloidal suspensions  

E-print Network

) Colloidal suspensions exhibit shear thinning and shear thickening. The most common interpretation of these phenomena identifies layering of the fluid perpendicular to the shear gradient as the driverRelation between ordering and shear thinning in colloidal suspensions Xinliang Xu1 , Stuart A. Rice

Dinner, Aaron

396

Shear Thickening of Cornstarch Suspensions Abdoulaye Fall1,2  

E-print Network

of the fluid is sheared: the existence of a non-flowing region thus seems to prevent or delay shear thickening1 Shear Thickening of Cornstarch Suspensions Abdoulaye Fall1,2 , François Bertrand2 , Guillaume ­ Brownian particle system that exhibits discontinuous shear thickening. Using Magnetic Resonance Imaging

Paris-Sud XI, Université de

397

Deformation analysis of simple-shear sheet specimens  

Microsoft Academic Search

The shear properties of different simple-shear sheet specimens were investigated using the elastic-plastic finite element method. Tension loaded specimens with a shear zone formed at the center area between two transverse slots were adopted to analyze the shear properties of sheet metals under uniaxial tension. Specimens prepared by single material as well as by bonding two different strength materials together

Fuh-Kuo Chen

1995-01-01

398

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

399

Precursors to the shear failure of rock discontinuities  

NASA Astrophysics Data System (ADS)

geophysical monitoring of potential failure along mechanical discontinuities in rock requires identification of precursory signatures to failure in geophysical signals. Active ultrasonic monitoring of shear failure along frictional discontinuities was performed to determine the signatures of potential failure. An instrumented direct shear apparatus was used to apply a constant shearing rate to a discontinuity that was held under a constant normal stress. Transmitted and reflected compressional and shear waves were recorded during the shearing process. Ultrasonic precursors were identified as distinct maxima in the amplitude of transmitted shear waves as well as minima in the amplitude of reflected shear waves that occurred well before the peak shear strength of a frictional discontinuity. The precursors are linked to changes in the local shear specific stiffness along the discontinuity, while the discontinuity's macroscopic shear strength continues to increase prior to failure.

Hedayat, Ahmadreza; Pyrak-Nolte, Laura J.; Bobet, Antonio

2014-08-01

400

CFD modelling and validation of measured wind field data in a portable wind tunnel  

NASA Astrophysics Data System (ADS)

Computational fluid dynamics (CFD) methods enable the detailed study and analysis of three dimensional flow patterns. This article provides a basic introduction to the fundamentals of CFD and its application as an assessment tool for near-wall boundary layers in internal flows. The Reynolds-averaged Navier-Stokes (RANS) approach with the k- ? turbulence model was used to model the characteristic channel flow properties observed in a portable wind tunnel with a coupled rainfall simulator. Wind velocity fields were measured at four cross-sections and compared to simulated data sets. A good correspondence between simulated and measured velocity profiles was obtained (RMSE 0.5 ms -1). In addition, we simulated the complex flow patterns caused by the specific construction of the wind tunnel and calculated the spatial distribution of derived measures such as wall shear stress and turbulence characteristics. It is shown that these measurements deviated significantly from their theoretical distributions, and an explanatory model for an observed bias in wind erosion and transport rates experimentally derived in the tunnel could be developed. We conclude that CFD is a valuable tool for modelling measured flow fields and to assess the spatial variation of variables that often cannot be sufficiently covered by measurements. Nevertheless, accurate measurements of the wind field are necessary to calibrate and validate such simulations and to provide reliable boundary conditions. CFD is thus a promising tool for aeolian research being complementary, to but never separated from, a measurement setup.

Gartmann, Andres; Fister, Wolfgang; Schwanghart, Wolfgang; Müller, Mathias D.

2011-12-01

401

Analysis of vector wind change with respect to time for Cape Kennedy, Florida  

NASA Technical Reports Server (NTRS)

Multivariate analysis was used to determine the joint distribution of the four variables represented by the components of the wind vector at an initial time and after a specified elapsed time is hypothesized to be quadravariate normal; the fourteen statistics of this distribution, calculated from 15 years of twice-daily rawinsonde data are presented by monthly reference periods for each month from 0 to 27 km. The hypotheses that the wind component changes with respect to time is univariate normal, that the joint distribution of wind component change with respect to time is univariate normal, that the joint distribution of wind component changes is bivariate normal, and that the modulus of vector wind change is Rayleigh are tested by comparison with observed distributions. Statistics of the conditional bivariate normal distributions of vector wind at a future time given the vector wind at an initial time are derived. Wind changes over time periods from 1 to 5 hours, calculated from Jimsphere data, are presented. Extension of the theoretical prediction (based on rawinsonde data) of wind component change standard deviation to time periods of 1 to 5 hours falls (with a few exceptions) within the 95 percentile confidence band of the population estimate obtained from the Jimsphere sample data. The joint distributions of wind change components, conditional wind components, and 1 km vector wind shear change components are illustrated by probability ellipses at the 95 percentile level.

Adelfang, S. I.

1978-01-01

402

Self-organization of ULF electromagnetic wave structures in the shear flow driven dissipative ionosphere  

NASA Astrophysics Data System (ADS)

This work is devoted to investigation of nonlinear dynamics of planetary electromagnetic (EM) ultra-low-frequency wave (ULFW) structures in the rotating dissipative ionosphere in the presence of inhomogeneous zonal wind (shear flow). Planetary EM ULFW appears as a result of interaction of the ionospheric medium with the spatially inhomogeneous geomagnetic field. The shear flow driven wave perturbations effectively extract energy of the shear flow increasing own amplitude and energy. These perturbations undergo self organization in the form of the nonlinear solitary vortex structures due to nonlinear twisting of the perturbation's front. Depending on the features of the velocity profiles of the shear flows the nonlinear vortex structures can be either monopole vortices, or dipole vortex, or vortex streets and vortex chains. From analytical calculation and plots we note that the formation of stationary nonlinear vortex structure requires some threshold value of translation velocity for both non-dissipation and dissipation complex ionospheric plasma. The space and time attenuation specification of the vortices is studied. The characteristic time of vortex longevity in dissipative ionosphere is estimated. The long-lived vortices transfer the trapped medium particles, energy and heat. Thus they represent structural elements of turbulence in the ionosphere.

Aburjania, G.; Chargazia, K.; Kharshiladze, O.; Zimbardo, G.

2014-08-01

403

Venus winds are zonal and retrograde below the clouds  

NASA Technical Reports Server (NTRS)

Winds in the lower atmosphere of Venus, inferred from three-dimensional radio interferometric tracking of the descents of the Pioneer day and north probes, are predominantly easterly with speeds of about 1 M/sec near the surface, 50 at the bottom of the clouds, and more than 200 within the densest, middle cloud layer. Between about 25 and 55 km altitude the average flow was slanted equatorward, with superimposed wavelike motions and alternating layers of high and low shear

Counselman, C. C., III; Gourevitch, S. A.; King, R. W.; Loriot, G. B.; Prinn, R. G.

1979-01-01

404

Wind Energy Benefits  

SciTech Connect

Wind energy provides many benefits, including economic and environmental. This two-sided fact sheet succinctly outlines the top ten wind energy benefits and is especially well suited for general audiences.

Not Available

2005-04-01

405

Solar Wind Five  

NASA Technical Reports Server (NTRS)

Topics of discussion were: solar corona, MHD waves and turbulence, acceleration of the solar wind, stellar coronae and winds, long term variations, energetic particles, plasma distribution functions and waves, spatial dependences, and minor ions.

Neugebauer, M. (editor)

1983-01-01

406

Renewable Energy: Wind  

NSDL National Science Digital Library

This lesson introduces students to the uses of wind energy. Topics include a history of wind usage (grinding grain, pumping water, transportation), including the development of wind power in the United States and its more recent adaptations for producing electricity. There is also discussion of the physics behind the operation of a windmill and what drives the wind patterns in Earth's atmosphere. The lesson includes an activity in which students use online resources to study the relationship between barometric pressure and wind speed and direction. They will collect data on barometric pressure, wind speed, and wind direction for several days, map it, and look for relationships between wind speed and direction and the isobaric lines on the map.

Pratte, John

407

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

Microsoft Academic Search

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

Yuh J. Chao

2003-01-01

408

Dependence of Wind Turbine Curves on Atmospheric Stability Regimes - An Analysis of a West Coast North American Tall Wind Farm  

SciTech Connect

Tall wind turbines, with hub heights at 80 m or above, can extract large amounts of energy from the atmosphere because they are likely to encounter higher wind speeds, but they face challenges given the complex nature of wind flow in the boundary layer. Depending on whether the boundary layer is stable, convective or neutral, mean wind speed (U) and turbulence ({sigma}{sub U}) may vary greatly across the tall turbine swept area (40 m to 120 m). This variation can cause a single turbine to produce difference amounts of power during time periods of identical hub height wind speeds. The study examines the influence that atmospheric mixing or stability has on power output at a West Coast North American wind farm. They first examine the accuracy and applicability of two, relatively simple stability parameters, the wind shear-exponent, {alpha}, and the turbulence intensity, I{sub u}, against the physically-based, Obukhov length, L, to describe the wind speed and turbulence profiles in the rotor area. In general, the on-site stability parameters {alpha} and I{sub u} are in high agreement with the off-site, L stability scale parameter. Next, they divide the measurement period into five stability classes (strongly stable, stable, neutral, convective, and strongly convective) to discern stability-effects on power output. When only the mean wind speed profile is taken into account, the dependency of power output on boundary layer stability is only subtly apparent. When turbulence intensity I{sub u} is considered, the power generated for a given wind speed is twenty percent higher during strongly stable conditions than during strongly convective conditions as observed in the spring and summer seasons at this North American wind farm.

Wharton, S; Lundquist, J K; Sharp, J; Zulauf, M

2009-08-24

409

Molecular Dynamics Simulation of Shear Moduli for Coulomb Crystals  

E-print Network

Torsional (shear) oscillations of neutron stars may have been observed in quasiperiodic oscillations of Magnetar Giant Flares. The frequencies of these modes depend on the shear modulus of neutron star crust. We calculate the shear modulus of Coulomb crystals from molecular dynamics simulations. We find that electron screening reduces the shear modulus by about 10% compared to previous Ogata et al. results. Our MD simulations can be extended to calculate the effects of impurities and or polycrystalline structures on the shear modulus.

C. J. Horowitz; J. Hughto

2008-12-15

410

Snell's Law for Shear Zone Refraction in Granular Materials  

Microsoft Academic Search

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

H. A. Knudsen; J. Bergli

2009-01-01

411

Effects of shear stress on the microalgae Chaetoceros muelleri  

Microsoft Academic Search

The effect of shear stress on the viability of Chaetoceros muelleri was studied using a combination of a rheometer and dedicated shearing devices. Different levels of shear stress were applied\\u000a by varying the shear rates and the medium viscosities. It was possible to quantify the effect of shear stress over a wide\\u000a range, whilst preserving laminar flow conditions through the

Michiel H. A. MichelsAtze; Atze J. van der Goot; Niels-Henrik Norsker; René H. Wijffels

2010-01-01

412

Onset of shear thickening in a simple fluid  

Microsoft Academic Search

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

J. Delhommelle

2004-01-01

413

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

SciTech Connect

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

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

2010-01-10

414

Dispersion in Neptune's zonal wind velocities from NIR Keck AO observations in July 2009  

NASA Astrophysics Data System (ADS)

We report observations of Neptune made in H-(1.4-1.8 ?m) and K'-(2.0-2.4 ?m) bands on 14 and 16 July 2009 from the 10-m W.M. Keck II Telescope using the near-infrared camera NIRC2 coupled to the Adaptive Optics (AO) system. We track the positions of 54 bright atmospheric features over a few hours to derive their zonal and latitudinal velocities, and perform radiative transfer modeling to measure the cloud-top pressures of 50 features seen simultaneously in both bands. We observe one South Polar Feature (SPF) on 14 July and three SPFs on 16 July at ˜65 °S. The SPFs observed on both nights are different features, consistent with the high variability of Neptune's storms. There is significant dispersion in Neptune's zonal wind velocities about the smooth Voyager wind profile fit of Sromovsky et al. (Icarus, 105:140, 1993), much greater than the upper limit we expect from vertical wind shear, with the largest dispersion seen at equatorial and southern mid-latitudes. Comparison of feature pressures vs. residuals in zonal velocity from the smooth Voyager wind profile also directly reveals the dominance of mechanisms over vertical wind shear in causing dispersion in the zonal winds. Vertical wind shear is not the primary cause of the difference in dispersion and deviation in zonal velocities between features tracked in H-band on 14 July and those tracked in K'-band on 16 July. Dispersion in the zonal velocities of features tracked over these short time periods is dominated by one or more mechanisms, other than vertical wind shear, that can cause changes in the dispersion and deviation in the zonal velocities on timescales of hours to days.

Fitzpatrick, Patrick J.; de Pater, Imke; Luszcz-Cook, Statia; Wong, Michael H.; Hammel, Heidi B.

2014-03-01

415

Economic feasibility of wind farm using low wind speed turbine  

Microsoft Academic Search

One of the renewable energy technologies is the wind power technology abundantly used in countries located at high wind speeds. However, most rural areas of developing countries have low wind speeds. Moreover, low wind speed turbine (LWST) has been developed to reduce cost which is currently higher than high wind speed turbine (HWST). Therefore, economic feasibility of wind farm using

U. Sangpanich; G. A. Ault; K. L. Lo

2009-01-01

416

Wind Power Today: 2000 Wind Energy Program Highlights  

Microsoft Academic Search

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

Weis-Taylor

2001-01-01

417

Wind power today: 1999 Wind Energy program highlights  

Microsoft Academic Search

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

Weis-Taylor

2000-01-01

418

Wind energy utilization prospects  

Microsoft Academic Search

The chief technical, economic, and environmental aspects of wind energy utilization are considered. One approach being studied is to allow the aeroturbine RPM to vary with wind velocity and employ variable-speed, constant-frequency generating systems to obtain constant-frequency power to be pumped into existing utility mains. Study of generation costs for wind energy systems indicates that wind energy has the potential

R. Ramakumar; W. L. Hughes; H. J. Allison

1975-01-01

419

Wind Energy Markets, 2. edition  

SciTech Connect

The report provides an overview of the global market for wind energy, including a concise look at wind energy development in key markets including installations, government incentives, and market trends. Topics covered include: an overview of wind energy including the history of wind energy production and the current market for wind energy; key business drivers of the wind energy market; barriers to the growth of wind energy; key wind energy trends and recent developments; the economics of wind energy, including cost, revenue, and government subsidy components; regional and national analyses of major wind energy markets; and, profiles of key wind turbine manufacturers.

NONE

2007-11-15

420

Shear-current effect in a turbulent convection with a large-scale shear.  

PubMed

The shear-current effect in a nonrotating homogeneous turbulent convection with a large-scale constant shear is studied. The large-scale velocity shear causes anisotropy of turbulent convection, which produces the mean electromotive force epsilon (W) proportional to W x J and the mean electric current along the original mean magnetic field, where W is the background mean vorticity due to the shear and J is the mean electric current. This results in a large-scale dynamo even in a nonrotating and nonhelical homogeneous sheared turbulent convection, whereby the alpha effect vanishes. It is found that turbulent convection promotes the shear-current dynamo instability, i.e., the heat flux causes positive contribution to the shear-current effect. However, there is no dynamo action due to the shear-current effect for small hydrodynamic and magnetic Reynolds numbers even in a turbulent convection, if the spatial scaling for the turbulent correlation time is tau(k) proportionalto to k-2, where k is the small-scale wave number. PMID:17500991

Rogachevskii, Igor; Kleeorin, Nathan

2007-04-01

421

Influence of cyclic pre-shearing on undrained behaviour of carbonate sand in simple shear tests  

Microsoft Academic Search

The paper will offer insights regarding the effects of cyclic prestrain history on the undrained behaviour of an uncemented carbonate sand (Quiou sand) through a modified NGI simple shear (SS) apparatus. Tests were carried out on specimens reconstituted at two void ratios (loose and dense) by using the water sedimentation method. The influence of cyclic undrained pre-shearing was investigated by

Daniela Porcino; Vincenzo Marcianò; Vito Nicola Ghionna

2009-01-01

422

Shear-Thickening Response of Fumed Silica Suspensions under Steady and Oscillatory Shear  

PubMed

Suspensions of fumed silica in polypropylene glycol exhibit shear-thickening under steady shear and "strain-thickening" under oscillatory shear. Strain-thickening refers to a sharp increase in the complex viscosity eta* observed at critical combinations of strain-amplitude and frequency. Two regimes of strain-thickening behavior have been found: The first occurs at high critical strains and low frequencies, whereas the second occurs at high critical frequencies and a constant lower strain. Strain-thickening in the first regime can be explicitly correlated with steady shear-thickening, using a modified version of the Cox-Merz rule. Accordingly, strain-thickening data for the complex viscosity eta* as a function of the maximum dynamic shear-rate gamma0omega can be superposed against shear-thickening data for the steady viscosity as a function of the steady shear rate. Such a correlation between the two kinds of thickening phenomena has not been reported previously. The combination of shear- and strain-thickening behavior can be qualitatively explained using a clustering mechanism, which attributes the various phenomena to the formation of temporary, flow-induced clusters. The two regimes of strain-thickening are a result of differences in the relative ease of cluster formation. PMID:9056301

Raghavan; Khan

1997-01-01

423

Experimental assessment of Owen's second hypothesis on surface shear stress induced by a fluid during sediment saltation  

NASA Astrophysics Data System (ADS)

widely used, yet thus far unproven, fluid dynamical hypothesis originally presented by P. R. Owen 50 years ago, states that the surface shear stress induced by a fluid on the ground during equilibrium sediment saltation is constant and independent of the magnitude of the fluid velocity and consequently the particle mass flux. This hypothesis is one of the key elements in almost all current model descriptions of sediment erosion. We measured the surface shear stress in a drifting-sand wind tunnel and found Owen's hypothesis being merely an approximation of the real situation. A significant decrease of the fluid stress with increasing wind velocities was measured for low to intermediate particle mass fluxes. For high particle mass fluxes, Owen's hypothesis essentially holds, although a slight increase of the fluid stress was measured.

Walter, B.; Horender, S.; Voegeli, C.; Lehning, M.

2014-09-01

424

Gravity shear waves atop the cirrus layer of intense convective storms  

NASA Technical Reports Server (NTRS)

Recent visual satellite photographs of certain intense convective storms have revealed concentric wave patterns. A model for the generation and growth of these waves is proposed. The proposed initial generating mechanism is similar to the effect noticed when a pebble is dropped into a calm pond. The penetration of the tropopause by overshooting convection is analogous to the pebble's penetration of the water's surface. The model for wave growth involves instability due to the wind shear resulting from the cirrus outflow. This model is based on an equation for the waves' phase speed which is similar to the Helmholtz equation. It, however, does not assume an incompressible atmosphere, but rather assumes density is a logarithmic function of height. Finally, the model is evaluated on the two mid-latitude and three tropical cases. The data indicate that shearing instability may be a significant factor in the appearance of these waves.

Stobie, J. G.

1975-01-01

425

Sweden considers wind power  

Microsoft Academic Search

During 1988, Sweden increased its number of wind generating facilities from 13 to 22, reflecting a new attitude toward wind power developing in the country. Last fall, a 750 kW wind turbine installed in the archipelago of Gothenburg was connected to the grid. The turbine is the biggest in use in Sweden, operated and maintained by the local energy authority

Baurrau

1989-01-01

426

Aeroelastic wind energy converter  

Microsoft Academic Search

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

G. Ahmadi

1978-01-01

427

Wind Power Now!  

ERIC Educational Resources Information Center

The government promotes and heavily subsidizes research in nuclear power plants. Federal development of wind power is slow in comparison even though much research with large wind-electric machines has already been conducted. Unless wind power programs are accelerated it will not become a major energy alternative to nuclear power. (MR)

Inglis, David Rittenhouse

1975-01-01

428

National Wind Technology Center  

NSDL National Science Digital Library

The Advanced Technology Environmental and Energy Center (ATEEC) provides this presentation on the National Wind Technology Center. The material covers the basics of wind energy technology as well as the outlook for wind energy in the United States. Users must download this resource for viewing, which requires a free log-in. There is no cost to download the item.

Johnson, Jim

2012-09-21

429

Wind energy in Europe  

Microsoft Academic Search

Wind energy should be an important part of the energy supply mix, both at home and abroad, to provide cleaner air and a more stable fuel supply. Not only can wind energy contribute to solving complex global issues, it also can provide a large market for American technological leadership. Even though utilities are paying more attention to wind in a

2009-01-01

430

Wind power outlook 2006  

SciTech Connect

This annual brochure provides the American Wind Energy Association's up-to-date assessment of the wind industry in the United States. This 2006 general assessment shows positive signs of growth, use and acceptance of wind energy as a vital component of the U.S. energy mix.

anon.

2006-04-15

431

Energy from the Wind  

ERIC Educational Resources Information Center

The large-scale generation of electrical power by wind turbine fields is discussed. It is shown that the maximum power that can be extracted by a wind turbine is 16/27 of the power available in the wind. (BB)

Pelka, David G.; And Others

1978-01-01

432

Coherent structures in a boundary layer and shear layer of a turbulent backward-facing step flow  

NASA Technical Reports Server (NTRS)

A wind tunnel experiment has been carried out at the NASA Ames Research Center to analyze the evolution of coherent structures from a boundary layer to a shear layer in a turbulent, backward-facing, step flow. A miniature X-wire/cold-wire probe has been used in conjunction with two arrays of cold wires, one aligned in the plane of main shear and the other in the spanwise direction of the flow, to detect and characterize delta-scale organized structures in the outer regions of the flow and to provide detailed information concerning these structures. Kinematic features of the events associated with the large scale structures were analyzed and topological pictures of the evolving flow, as well as the contributions to the Reynolds shear stress components are presented.

Jovic, Srba; Browne, L. W. B.

1989-01-01

433

Review article: Cosmology with cosmic shear observations  

E-print Network

Cosmic shear is the distortion of images of distant galaxies due to weak gravitational lensing by the large-scale structure in the Universe. Such images are coherently deformed by the tidal field of matter inhomogeneities along the line of sight. By measuring galaxy shape correlations, we can study the properties and evolution of structure on large scales as well as the geometry of the Universe. Thus, cosmic shear has become a powerful probe into the nature of dark matter and the origin of the current accelerated expansion of the Universe. Over the last years, cosmic shear has evolved into a reliable and robust cosmological probe, providing measurements of the expansion history of the Universe and the growth of its structure. We review here the principles of weak gravitational lensing and show how cosmic shear is interpreted in a cosmological context. Then we give an overview of weak-lensing measurements, and present the main observational cosmic-shear results since it was discovered 15 years ago, as well as ...

Kilbinger, Martin

2014-01-01

434

Bottom shear stress in unsteady sewer flow.  

PubMed

The properties of unsteady open-channel turbulent flow were theoretically and experimentally investigated in a circular cross section channel with fixed sediment deposits. Velocity and turbulence distribution data were obtained using an ultrasonic velocity profiler (UVP). Different uniform flow conditions and triangular-shaped hydrographs were analysed. The hydrograph analysis revealed a dynamic wave behaviour, where the time lags of mean cross section velocity, friction velocity, discharge and flow depth were all evident. The bottom shear stress dynamic behaviour was estimated using four different approaches. Measurements of the velocity distribution in the inner region of the turbulent layer and of the Reynolds stress distribution in the turbulent flow provided the analysed data sets of the bottom shear stress. Furthermore, based on the Saint Venant equation, the bottom shear stress time behaviour was studied using both the kinematic and the dynamic flow principles. The dynamic values of the bottom shear stress were compared with those for the steady flow conditions. It is evident that bottom shear stress varies along the generated flood hydrograph and its variation is the function of the flow unsteadiness. Moreover, the kinematic flow principle is not an adequate type of approximation for presented flow conditions. PMID:17120638

Bares, V; Jirák, J; Pollert, J

2006-01-01

435

Pressure-shear experiments on granular materials.  

SciTech Connect

Pressure-shear experiments were performed on granular tungsten carbide and sand using a newly-refurbished slotted barrel gun. The sample is a thin layer of the granular material sandwiched between driver and anvil plates that remain elastic. Because of the obliquity, impact generates both a longitudinal wave, which compresses the sample, and a shear wave that probes the strength of the sample. Laser velocity interferometry is employed to measure the velocity history of the free surface of the anvil. Since the driver and anvil remain elastic, analysis of the results is, in principal, straightforward. Experiments were performed at pressures up to nearly 2 GPa using titanium plates and at higher pressure using zirconium plates. Those done with the titanium plates produced values of shear stress of 0.1-0.2 GPa, with the value increasing with pressure. On the other hand, those experiments conducted with zirconia anvils display results that may be related to slipping at an interface and shear stresses mostly at 0.1 GPa or less. Recovered samples display much greater particle fracture than is observed in planar loading, suggesting that shearing is a very effective mechanism for comminution of the grains.

Reinhart, William Dodd (Sandia National Laboratories, Albuquerque, NM); Thornhill, Tom Finley, III (, Sandia National Laboratories, Albuquerque, NM); Vogler, Tracy John; Alexander, C. Scott (Sandia National Laboratories, Albuquerque, NM)

2011-10-01

436

Viscoelasticity and shear thinning of nanoconfined water  

NASA Astrophysics Data System (ADS)

Understanding flow properties and phase behavior of water confined to nanometer-sized pores and slits is central to a wide range of problems in science, such as percolation in geology, lubrication of future nano-machines, self-assembly and interactions of biomolecules, and transport through porous media in filtration processes. Experiments with different techniques in the past have reported that viscosity of nanoconfined water increases, decreases, or remains close to bulk water. Here we show that water confined to less than 20-nm-thick films exhibits both viscoelasticity and shear thinning. Typically viscoelasticity and shear thinning appear due to shearing of complex non-Newtonian mixtures possessing a slowly relaxing microstructure. The shear response of nanoconfined water in a range of shear frequencies (5 to 25 KHz) reveals that relaxation time diverges with reducing film thickness. It suggests that slow relaxation under confinement possibly arises due to existence of a critical point with respect to slit width. This criticality is similar to the capillary condensation in porous media.

Kapoor, Karan; Amandeep, Patil, Shivprasad

2014-01-01

437

Direct shear loading leads to failure of generator bolts, rotor  

SciTech Connect

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

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

1993-02-01

438

Atmospheric Stability Impacts on Power Curves of Tall Wind Turbines - An Analysis of a West Coast North American Wind Farm  

SciTech Connect

Tall wind turbines, with hub heights at 80 m or above, can extract large amounts of energy from the atmosphere because they are likely to encounter higher wind speeds, but they face challenges given the complex nature of wind flow and turbulence at these heights in the boundary layer. Depending on whether the boundary layer is stable, neutral, or convective, the mean wind speed, direction, and turbulence properties may vary greatly across the tall turbine swept area (40 to 120 m AGL). This variability can cause tall turbines to produce difference amounts of power during time periods with identical hub height wind speeds. Using meteorological and power generation data from a West Coast North American wind farm over a one-year period, our study synthesizes standard wind park observations, such as wind speed from turbine nacelles and sparse meteorological tower observations, with high-resolution profiles of wind speed and turbulence from a remote sensing platform, to quantify the impact of atmospheric stability on power output. We first compare approaches to defining atmospheric stability. The standard, limited, wind farm operations enable the calculation only of a wind shear exponent ({alpha}) or turbulence intensity (I{sub U}) from cup anemometers, while the presence at this wind farm of a SODAR enables the direct observation of turbulent kinetic energy (TKE) throughout the turbine rotor disk. Additionally, a nearby research meteorological station provided observations of the Obukhov length, L, a direct measure of atmospheric stability. In general, the stability parameters {alpha}, I{sub U}, and TKE are in high agreement with the more physically-robust L, with TKE exhibiting the best agreement with L. Using these metrics, data periods are segregated by stability class to investigate power performance dependencies. Power output at this wind farm is highly correlated with atmospheric stability during the spring and summer months, while atmospheric stability exerts little impact on power output during the winter and autumn periods. During the spring and summer seasons, power output for a given wind speed was significantly higher during stable conditions and significantly lower during strongly convective conditions: power output differences approached 20% between stable and convective regimes. The dependency of stability on power output was apparent only when both turbulence and the shape of the wind speed profile were considered. Turbulence is one of the mechanisms by which atmospheric stability affects a turbine's power curve at this particular site, and measurements of turbulence can yield actionable insights into wind turbine behavior.

Wharton, S; Lundquist, J K

2010-02-22

439

Wind mediated vorticity-generation and eddy-confinement, leeward of the Madeira Island: 2008 numerical case study  

NASA Astrophysics Data System (ADS)

This study assesses the influence of the atmospheric wind-wake of the Madeira Island on oceanic-eddy generation. Ocean surface wind fields derived from the QuikSCAT scatterometer were compared to the Weather Research and Forecast (WRF) modeled winds at 6 km resolution. The main difference between the two wind products is found southwest of Madeira where QuikSCAT's spatial resolution [0.5°] does not resolve the near-field atmospheric wake dynamics. Nevertheless, high resolution wind extracted from ENVISAT Advanced Synthetic Aperture Radar (ASAR) confirms that WRF is able to realistically reproduce the island-induced wind-wake. The Regional Oceanic Modeling System (ROMS) was used to simulate the oceanic effects of the wind-wake. A “no-wind-wake” case was simulated with ROMS using the QuikSCAT wind, whereas the WRF wind was used for an island-induced wind-wake simulation. Oceanic surface kinetic energy and vorticity are found to increase during the summer months concurrently with strong wind-wake episodes resolved by WRF. The downstream propagation of this oceanic vorticity, as a result of the shedding of the leeward eddies, was captured with an eddy tracking algorithm. In the initial stage, the oceanic leeward eddy corridor was delimited by the zonal wind-shear. This study suggests that the wind-wake is the main contributor to the generation and containment of the oceanic eddies in the lee of the Madeira Island.

Couvelard, X.; Caldeira, R. M. A.; Araújo, I. B.; Tomé, R.

2012-11-01

440

Wind energy systems  

NASA Astrophysics Data System (ADS)

Wind energy has matured to a level of development where it is ready to become a generally accepted utility generation technology. A brief discussion of this development is presented, and the operating and design principles are discussed. Alternative designs for wind turbines and the tradeoffs that must be considered are briefly compared. Development of a wind energy system and the impacts on the utility network including frequency stability, voltage stability, and power quality are discussed. The assessment of wind power station economics and the key economic factors that determine the economic viability of a wind power plant are presented.

Richardson, R. D.; McNerney, Gerald M.

1993-03-01

441

Wind Turbine Structural Dynamics  

NASA Technical Reports Server (NTRS)

A workshop on wind turbine structural dynamics was held to review and document current United States work on the dynamic behavior of large wind turbines, primarily of the horizontal-axis type, and to identify and discuss other wind turbine configurations that may have lower cost and weight. Information was exchanged on the following topics: (1) Methods for calculating dynamic loads; (2) Aeroelasticity stability (3) Wind loads, both steady and transient; (4) Critical design conditions; (5) Drive train dynamics; and (6) Behavior of operating wind turbines.

Miller, D. R. (editor)

1978-01-01

442

Strength of Footing with Punching Shear Preventers  

PubMed Central

The punching shear failure often governs the strength of the footing-to-column connection. The punching shear failure is an undesirable failure mode, since it results in a brittle failure of the footing. In this study, a new method to increase the strength and ductility of the footing was proposed by inserting the punching shear preventers (PSPs) into the footing. The validation and effectiveness of PSP were verified through a series of experimental studies. The nonlinear finite element analysis was then performed to demonstrate the failure mechanism of the footing with PSPs in depth and to investigate the key parameters that affect the behavior of the footing with PSPs. Finally, the design recommendations for the footing with PSPs were suggested.

Lee, Sang-Sup; Moon, Jiho; Park, Keum-Sung; Bae, Kyu-Woong

2014-01-01

443

Streamline curvature in supersonic shear layers  

NASA Technical Reports Server (NTRS)

Results of an experimental investigation in which a curved shear layer was generated between supersonic flow from a rectangular converging/diverging nozzle and the freestream in a series of open channels