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1

Fighting wind shear  

NASA Astrophysics Data System (ADS)

A “coherent and sustained program” of improved radar detection of weather, pilot training, and better communication between pilots and air controllers can greatly reduce the risk of wind shear to airplanes landing or taking off, according to a National Research Council (NRC) committee.Wind shear, characterized by winds rapidly changing direction and speed, has caused several serious accidents in recent years; among the most notable is the July 8, 1982, crash of a Pan American World Airlines jetliner at the New Orleans International Airport, which killed 153 persons. Following the accident, Congress directed the Federal Aviation Administration (FAA) to contract with the NRC to study wind shear.

2

Wind shear detection systems  

NASA Astrophysics Data System (ADS)

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

McCullogh, Carl P.

1996-05-01

3

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

4

CAT LIDAR wind shear studies  

NASA Technical Reports Server (NTRS)

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

Goff, R. W.

1978-01-01

5

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

6

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 turbulence scales in wind shear is addressed from the perspective of power spectral density.

Trevino, G.; Laituri, T. R.

1989-01-01

7

Design of wind shear filters  

NASA Technical Reports Server (NTRS)

A number of aircraft accidents are caused by the effects of wind shear. In connection with efforts to eliminate or reduce hazards leading to such accidents, the possibility was considered to improve aircraft control systems. However, the effective implementation of the considered approaches will only be possible if suitable filters can be designed for a separation of gusts, which involve higher frequencies from low-frequency wind shear components. Filters of appropriate design should be suited for an employment in connection with all flight conditions. Feasible approaches for obtaining such filters are discussed. A survey is provided regarding the order of magnitude of the improvements which can be achieved, taking into account the performance characteristics of the A300 controller.

Joerck, H.

1984-01-01

8

Flight in low-level wind shear  

NASA Technical Reports Server (NTRS)

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

Frost, W.

1983-01-01

9

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

10

Problems pilots face involving wind shear  

NASA Technical Reports Server (NTRS)

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

Melvin, W. W.

1977-01-01

11

Some aspects of fluctuating vertical wind shears  

SciTech Connect

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

Doran, J.C.

1981-05-01

12

Flight penetration of wind shear: Control strategies  

NASA Technical Reports Server (NTRS)

Wind shear is a dangerous condition where there is a sharp change in the direction and magnitude of the wind velocity over a short distance or time. This condition is especially dangerous to aircraft during landing and takeoff and can cause a sudden loss of lift and thereby height at a critical time. A numerical simulation showed the effective performance of the Linear Quadratic Regulator and the Nonlinear Inverse Dynamics controllers. The major conclusions are listed and discussed.

Joshi, Amit S.

1988-01-01

13

An expert system for wind shear avoidance  

NASA Technical Reports Server (NTRS)

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

Stengel, Robert F.; Stratton, D. Alexander

1989-01-01

14

Infrared low-level wind shear work  

NASA Technical Reports Server (NTRS)

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

Adamson, Pat

1988-01-01

15

Wind shear training applications for 91/135  

NASA Technical Reports Server (NTRS)

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

Arbon, ED

1991-01-01

16

Velocity shear generation of solar wind turbulence  

NASA Technical Reports Server (NTRS)

A two-dimensional incompressible MHD spectral code is used to show that shear-driven turbulence is a possible means for producing many observed properties of the evolution of the magnetic and velocity fluctuations in the solar wind and, in particular, the evolution of the cross helicity ('Alfvenicity') at small scales. It is shown that large-scale shear can nonlinearly produce a cascade to smaller scale fluctuations even when the linear Kelvin-Helmholtz mode is stable, and that a roughly power law inertial range is established by this process. The evolution found is similar to that seen in some other simulations of MHD turbulence.

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

1992-01-01

17

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

18

Microbursts as an aviation wind shear hazard  

NASA Technical Reports Server (NTRS)

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

Fujita, T. T.

1981-01-01

19

Wind shear and vortex wake research in UK, 1982  

NASA Technical Reports Server (NTRS)

A wind shear and vortex wake and their impact on aircraft were investigated. The systems and advice to help pilots, and rational scientific methods to assist in advising certification authorities and those interested in improving flight safety were developed. Wind Shear and Vortex Wakes are related, they are both invisible enemies of aircraft in the form of large disturbances in the atmosphere, both cause major accidents. Problems of building wakes at airports are is considered. Research on wind shear was initiated by the American FAA following the Boston, New York and Denver accidents to civil airliners. This resulted in: useful advice to pilots about wind shear; better attempts by the meteorologists at forecasting wind shear conditions; and useful ideas for wind shear measurement and warning systems. Three major research tasks are outstanding: (1) Worldwide measurements to give reliable estimates of probability and details of the forms of large wind shears; (2) Developments of real time wind shear measuring systems for ground or airborne use; and (3) Establishing relationships between measured wind shear and the potential hazard to an aircraft, or class of aircraft.

Woodfield, A. A.

1983-01-01

20

An expert system for wind shear avoidance  

NASA Technical Reports Server (NTRS)

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

Stengel, Robert F.; Stratton, D. Alexander

1990-01-01

21

Airborne in situ computation of the wind shear hazard index  

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

22

An experimental cockpit display for TDWR wind shear alerts  

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

23

Quantifying shear-induced wave transformations in the solar wind  

E-print Network

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

Grigol Gogoberidze; Andria Rogava; Stefaan Poedts

2007-03-20

24

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

25

EFFECTS OF WIND SHEAR ON POLLUTION DISPERSION. (R827929)  

EPA Science Inventory

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

26

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

NASA Technical Reports Server (NTRS)

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

Bowles, Roland L.

1988-01-01

27

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

Microsoft Academic Search

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

Shafiqur Rehman; Naif M. Al-Abbadi

2008-01-01

28

Wind Shear/Turbulence Inputs to Flight Simulation and Systems Certification  

NASA Technical Reports Server (NTRS)

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

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

1987-01-01

29

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

30

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

31

Magnetohydrodynamic Wave Mixing in Solar Wind Shear Flows  

NASA Astrophysics Data System (ADS)

Magnetohydrodynamic (MHD) wave interactions in a linear shear flow, using a Lagrangian variational approach, are described in terms of the Lagrangian fluid displacement ? and entropy perturbation ? S. The equations are used to study MHD wave interactions in the shear between fast, coronal hole solar wind, and slower streamer belt solar wind at lower helio-latitudes, The spatial Fourier harmonics for the waves (SFHs) in the frame moving with the background shear flow (Kelvin's method) satisfy three coupled oscillator equations, with time dependent coupling coefficients, and with source terms proportional to the entropy perturbation ? S. Normal mode analysis, based on the background flow with no shear, results in a Hamiltonian system of six first order differential equations for the SFHs, corresponding to the backward and forward fast and slow magnetoacoustic and Alfvén modes (this system is referred to as the K-system, since the frequencies and wavenumbers of the modes are constant). An alternative normal mode expansion, based on the background flow including the shear, results in an equivalent Hamiltonian system of six first order differential equations, in which the frequencies and wave numbers evolve in time (the wave number k' in this system evolves according to the ray equations, of geometrical, MHD optics; this system is referred to as the R-system). In the absence of entropy perturbations, both the K-system and the R-system possess the same wave action integral for the eigenmodes (the wave action integral ceases to apply if ? S=0). We present evidence that the R-system provides a more natural physical description of the wave interactions. For sufficiently large shear parameter, the waves exhibit the phenomenon of over-reflection. The forward propagating modes have positive wave action densities (quasi-particle number densities), whereas the backward propagating modes have negative canonical wave energy densities (action densities). Wave transformation, transmission and reflection processes are discussed. The relationship between our approach and that of Gogoberidze et al. (2004) is discussed.

Webb, G. M.; Kaghashvili, E. K.; Zank, G. P.

2005-12-01

32

VOLUME 18, NUMBER 2, 2010 n LINCOLN LABORATORY JOURNAL 47 Wind-Shear System  

E-print Network

Robert G. Hallowell and John Y. N. Cho A series of fatal commercial aviation accidents starting the 1970s, when several fatal commercial aviation accidents were attributed to wind shear. Updating-shear-related accident rate, an updated wind-shear exposure estimate for every airport in the National Airspace System

Cho, John Y. N.

33

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

34

Comparison of simulated and actual wind shear radar data products  

NASA Technical Reports Server (NTRS)

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

Britt, Charles L.; Crittenden, Lucille H.

1992-01-01

35

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

36

Evidence of large zonal winds and wind shears in the MLT region over Fort Collins, CO (41N, 105W)  

NASA Astrophysics Data System (ADS)

In a recent article on the 1998 Coqui 2 sounding rocket campaign, Larsen [2000] reported measurements from three chemical release rockets, all of which show large winds (~100m/s) and wind shears (~25ms-1/km) between 90 and 110 km. He then reviewed a more extensive but less publicized data set on earlier chemical release rocket wind measurements and concluded that large wind speeds and wind shears are a common feature of the nighttime MLT region. The implications of large winds and wind shears as a possible norm in the MLT on neutral dynamics, chemistry and electrodynamics are obvious and deserve more attention and study. In1999 and 2000, the Colorado State Sodium Lidar has conducted two-beam lidar observations. Among other things, 38 nights of data were taken with one beam pointing Zenith and one pointing 30 degree East from Zenith. These measurements yielded simultaneous temperature and zonal wind profiles between 80 and 110 km with excellent data quality between 84 and 101km. A quick glance at the regular analysis results suggests that large zonal winds and/or wind gradients exist in nearly 50% of the nights with data. I propose to re-analyze this data set into temperature and zonal wind profiles with 2km and 1hr resolution, from which wind shears and Brunt-Vais

She, C.

2001-12-01

37

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

38

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

SciTech Connect

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

Mahrt, L.; Heald, R.C.

1980-11-01

39

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

40

Effect of intense wind shear across the inversion on stratocumulus clouds  

NASA Astrophysics Data System (ADS)

A large-eddy simulation model is used to examine the impact of the intense cross-inversion wind shear on the stratocumulus cloud structure. The wind shear enhanced entrainment mixing effectively reduces the cloud water and thickens the inversion layer. It leads to a reduction of the turbulence kinetic energy (TKE) production in the cloud layer due to the weakened cloud-top radiative cooling and the formation of a turbulent and cloud free sublayer within the inversion. The thickness of the sublayer increases with the enhanced wind shear intensity. Under the condition of a weaker inversion, the enhanced shear mixing within the inversion layer even lowers the cloud-top height and reduces the entrainment velocity. Finally, increasing wind shear or reducing inversion strength tends to create an inversion layer with a constant bulk Richardson number (~0.3), suggesting that an equilibrium value of the Richardson number is reached.

Wang, Shouping; Golaz, Jean-Christophe; Wang, Qing

2008-08-01

41

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

E-print Network

Influences of offshore environmental conditions on wind shear profile parameters in Nantucket Sound@ecs.umass.edu ABSTRACT Simultaneous wind resource and oceanographic data are available from an offshore monitoring tower how oceanographic data can be used to aid offshore wind resource assessment evaluations. This study

Massachusetts at Amherst, University of

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

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

44

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

E-print Network

, for turbine design the wind shear is an important design parameter, especially for the large rotor diameters measured at 10-m height is extrapolated to 50-m height and the power production of a wind turbine has been found. This is not usually accounted for in turbine design guidelines, which therefore

Heinemann, Detlev

45

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

NASA Technical Reports Server (NTRS)

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

Bray, R. S.

1984-01-01

46

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

NASA Technical Reports Server (NTRS)

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

Laituri, Tony R.

1988-01-01

47

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

NASA Astrophysics Data System (ADS)

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

Borovsky, Joseph E.; Steinberg, John T.

2014-03-01

48

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

Microsoft Academic Search

The effects of vertical wind shear, radiation, and ice clouds on surface rainfall processes associated with the torrential rainfall event over Jinan, China, during July 2007 are investigated through a series of sensitivity experiments. All experiments are integrated with an imposed large-scale vertical velocity and zonal wind from the National Centers for Environmental Prediction Global Data Assimilation System for 36

Yushu Zhou

2011-01-01

49

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

50

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

PubMed

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

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

2011-12-01

51

Estimating atmospheric stability from observations and correcting wind shear models accordingly  

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

52

Total energy-rate feedback for automatic glide-slope tracking during wind-shear penetration  

NASA Technical Reports Server (NTRS)

Low-altitude wind shear is recognized as an infrequent but significant hazard to all aircraft during the take-off and landing phases of flight. A total energy-rate sensor was developed for measuring the specific total energy rate of an airplane with respect to the air mass. Control-system designs, both with and without energy-rate feedback, for the approach to landing of a transport airplane through a severe-wind-shear and gust environment are presented in order to evaluate this application of the sensor. A system model incorporates wind-shear-dynamics equations with the airplane equations of motion to permit analysis of the control systems under various wind-shear conditions. 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 combined with a severe-wind-shear and gust data package. This evaluation is concerned with control system stability and regulation capability only.

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

1984-01-01

53

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

54

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

NASA Technical Reports Server (NTRS)

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

Hinton, David A.

1989-01-01

55

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

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

Direct Determination of Wind Shears from the Gradients of Satellite Radiance Observations.  

NASA Astrophysics Data System (ADS)

To the extent that the stratosphere wind field is close to geostrophic, the thermal wind is a good approximation to the vertical wind shear (vertical variation of the horizontal wind). And since the thermal wind is proportional to the horizontal temperature gradient, the possibility exists of determining it from satellite radiance observations. Several different methods are developed here for retrieving thermal winds directly from the horizontal gradients of satellite radiance observations, without first retrieving the horizontal temperature gradient. The methods are applied to the determination of thermal winds in the upper troposphere and lower stratosphere over the White Sands Missile Range area. A special series of about 30 concurrent sets of radiance observations from the NDAA-4 VTPR instrument and wind shears from radiosonde observations (for ground truth) distributed throughout one year, is used for these tests. The results obtained with these direct methods are compared with results obtained with 1) a traditional method, in which temperature profiles are first retrieved from the satellite radiances and the thermal winds are then obtained from the horizontal gradients of the retrieved temperatures; and 2) a linear regression between observed radiance gradients and observed wind shears. The latter method serves as an estimate of the upper limit of accuracy to be obtained by any method based on a linear combination of radiance gradients.The results indicate that the direct methods may be divided into two groups, with much better retrievals for one of these groups. The probable reasons for these differences are identified. The best direct methods yield results comparable to the traditional method. In comparison with ground truth none of the methods is particularly skillful. The lack of skill in these particular cases is attributed mainly to the modest wind shears contained in the sample. Errors associated with trying to measure relatively small horizontal radiance gradients over relatively small horizontal distances result in residual uncertainty nearly as large as the variance of the sample. it is suggested that much better results would be obtained if some of the better methods were to be applied over greater horizontal distances or to regions with larger wind shears.

Ohring, George; Neeman, Binyamin; Duncan, Louis D.

1981-11-01

58

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

NASA Astrophysics Data System (ADS)

A novel optical diagnostic approach, namely, a dual hologram shearing interferometry with enhanced sensitivity, is proposed for visualization, and for measuring the density gradients of the flow in wind tunnels. The technique is especially useful for strong turbulent and/or unsteady regions flows. The features of the technique make it tolerant to vibrational disturbances typical to many wind tunnel facilities. The method was demonstrated by its application to a supersonic flow over a spherically blunted nose cone/cylinder model.

Toker, G.; Levin, D.; Lessin, A.

59

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

Microsoft Academic Search

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

W. I. Axford

1963-01-01

60

Effects of Vertical Wind Shear on the Predictability of Tropical Cyclones FUQING ZHANG AND DANDAN TAO  

E-print Network

Effects of Vertical Wind Shear on the Predictability of Tropical Cyclones FUQING ZHANG AND DANDAN of tropical cyclone (TC) intensity during different stages of the TC life cycle. A series of ensemble of tropical cyclones, especially during the formation and rapid intensification stage. The larger the vertical

61

Simulator investigation of wind shear recovery techniques. M.S. Thesis - George Washington Univ.  

NASA Technical Reports Server (NTRS)

The objective was the development of practical flight procedures and guidance for near-optimal trajectories during inadvertent wind shear encounters following takeoff. The approach was to conduct preliminary development of candidate strategies using batch simulation of the point mass B737-100 performance model and to evaluate candidate guidance strategies in piloted, real time, six degrees of freedom simulation.

Hinton, David A.

1988-01-01

62

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

NASA Technical Reports Server (NTRS)

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

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

1977-01-01

63

Doppler radar spectral width broadening due to beamwidth and wind shear  

E-print Network

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

Boyer, Edmond

64

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

Technology Transfer Automated Retrieval System (TEKTRAN)

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

65

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

66

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

E-print Network

, the only LLWAS airport with full microburst coverage was Denver (97% detection probability). Although G. Hallowell Project Report ATC-340 LincolnLaboratory MASSACHUSETTSINSTITUTE OFTECHNOLOGY Lexington An objective wind-shear detection probability estimation model is developed for radar, lidar, and sensor

Cho, John Y. N.

67

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

SciTech Connect

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

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

1989-10-01

68

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

69

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

70

Solid-state coherent laser radar wind shear measuring systems  

NASA Technical Reports Server (NTRS)

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

Huffaker, R. Milton

1992-01-01

71

Liquid crystals for surface shear stress visualization on wind turbine airfoils  

NASA Astrophysics Data System (ADS)

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

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

72

The Effects of Vertical Wind Shear on the Distribution of Convection in Tropical Cyclones  

Microsoft Academic Search

The influence of vertical wind shear on the azimuthal distribution of cloud-to-ground lightning in tropical cyclones was examined using flash locations from the National Lightning Detection Network. The study covers 35 Atlantic basin tropical cyclones from 1985-99 while they were over land and within 400 km of the coast over water. A strong correlation was found between the azimuthal distribution

Kristen L. Corbosiero; John Molinari

2002-01-01

73

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

Microsoft Academic Search

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

William M. Frank; Elizabeth A. Ritchie

2001-01-01

74

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

75

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

NASA Technical Reports Server (NTRS)

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

Evans, Joni K.

2013-01-01

76

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

NASA Technical Reports Server (NTRS)

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

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

1981-01-01

77

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

78

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

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

79

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

80

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

SciTech Connect

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

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

2013-02-01

81

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

82

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

83

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

84

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

NASA Technical Reports Server (NTRS)

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

Korhonen, O.

1983-01-01

85

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

86

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

NASA Technical Reports Server (NTRS)

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

Britt, Charles L.; Bracalente, Emedio M.

1992-01-01

87

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

E-print Network

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

Fedorovich, Evgeni

88

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

89

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

E-print Network

speeds to the desired hub heights. 1.1 Objectives This paper addresses several issues relating to wind.G. McGowan University of Massachusetts, Department of Mechanical & Industrial Engineering Renewable speeds. · A study of the seasonal and annual wind shear variations at selected sites. · A study

Massachusetts at Amherst, University of

90

Correction of open jet wind tunnel measurements for shear layer refraction  

Microsoft Academic Search

The problem of sound refraction by a planar, zero-thickness shear layer is treated by combining a previous solution by Ribner and Miles with geometrical acoustics. Analytical expressions are given that allow one to correct far-field measurement angle and acoustic amplitude for the effects of shear layer refraction. The correction is independent of source type, and the results represent the sound

R. K. Amiet

1975-01-01

91

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

92

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

93

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

NASA Astrophysics Data System (ADS)

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

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

94

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

NASA Technical Reports Server (NTRS)

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

Connell, J. R.; Ey, L.

1977-01-01

95

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

E-print Network

experienced by phytoplankton, as well as controlling diffusive fluxes of partially soluble gases across largely regulated by the balance between solar radia- tion (acting to enhance stratification) and wind and heat loss (acting to destabilize and deepen the layer). Efforts to quantify the generation

California at Santa Barbara, University of

96

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

NASA Technical Reports Server (NTRS)

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

Kimball, G., Jr.

1980-01-01

97

Motion and interaction of decaying trailing vortices in spanwise shear wind  

NASA Technical Reports Server (NTRS)

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

Liu, C. H.; Lu, T.

1986-01-01

98

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

NASA Technical Reports Server (NTRS)

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

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

1981-01-01

99

Wind shear hazard determination  

NASA Technical Reports Server (NTRS)

The topics are presented in viewgraph form and include the following: F-factor relationship with aircraft performance; F-factor formulations; the F-bar index; F-factor hazard limit; F-bar with Doppler sensors; and F-bar profile composite.

Lewis, Michael S.

1992-01-01

100

Wind  

NSDL National Science Digital Library

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

Iowa Public Television. Explore More Project

2004-01-01

101

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

EPA Science Inventory

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

102

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.

103

Shear Activities  

NSDL National Science Digital Library

This page presents activities related to shear from the Science & Engineering in the Lives of Students project. Activities include Craft Stick Shear, Galloping Gertie Video, Shear Video, and Walking on a Beach. Each activity includes a detailed description, list of the materials needed, science concepts covered, and reflection questions.

2013-07-17

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

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

Microsoft Academic Search

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

A. S. Adams; D. W. Keith

2007-01-01

106

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

107

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

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

108

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

109

Performance testing of a Savonius windmill rotor in shear flows  

NASA Astrophysics Data System (ADS)

The effects of flow shear and/or unsteady behavior on the power generation capability of a Savonius wind turbine rotor are assessed in view of measurements conducted, both in two statistically steady shear flows and in the wind, of rotor tip speed and torque at a number of streamwise stations for each of four values of the rotor bucket overlap ratio. It is found that, even in the absence of shear, the power coefficient of a Savonius wind turbine rotor is most strongly dependent on tip speed ratio.

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

110

Direct Measurement of Wall-Shear Stress of Plane Shear Layer with Plasma Synthetic Jet Actuator  

NASA Astrophysics Data System (ADS)

One of the useful ways to measure the effect of the flow control devise is to use the wall-shear stress sensor to measure the wall-shear stress directly. The sensor used in this paper measures the wall-shear stress, which is reduced by the flow control devise. In this paper, the wall-shear stress of the plane shear layer with the plasma synthetic jet actuator (PSJA) is investigated. PSJA is a flow control device composed of electrodes with A.C. signal. The actuator uses electrohydrodynamic (EHD) effect and induces flow around the electrodes. PSJA has great advantage such as miniaturization, maintenance free, and easy to control compared to other actuators. In this paper, the wall-shear stress of plane shear layer in a low-speed turbulent wind tunnel is observed to measure the effect of the PSJA. The results show that the PSJA changes the flow condition of shear layer by accelerating the flow in shear layer. The wall-shear stress reduces and increases according to the displacement of the wall-shear stress sensor and the actuator.

Higuchi, Takehiro; Ogawara, Kakuji; Mochizuki, Shinsuke

111

A Dynamic Wind Turbine Simulator of the Wind Turbine Generator System  

Microsoft Academic Search

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

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

2012-01-01

112

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

113

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

E-print Network

and turbulence impact on wind turbine power performance Division: Wind Energy Risø-R-1722(EN) January 2010 ISSNRisø-R-Report Simulation of shear and turbulence impact on wind turbine performance Wagner Rozenn flow and power law wind speed profiles were compared to the case of a uniform inflow. Secondly

114

Multi-hazard Reliability Assessment of Offshore Wind Turbines  

E-print Network

A probabilistic framework is developed to assess the structural reliability of offshore wind turbines. Probabilistic models are developed to predict the deformation, shear force and bending moment demands on the support structure of wind turbines...

Mardfekri Rastehkenari, Maryam 1981-

2012-12-04

115

Aircraft control in wake vortex wind shear  

NASA Technical Reports Server (NTRS)

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

Wold, Gregory R.

1995-01-01

116

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

117

LiDAR observations of offshore winds at future wind turbine operating heights  

E-print Network

of the wind and the turbulence characteristics in the MABL (Marine Atmospheric Boundary Layer) is still- face Layer: the first 10% of the atmospheric boundary layer) where most of the measure- ments at the Horns Rev offshore wind farm. The influence of atmospheric stability on the surface layer wind shear

118

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

119

Reduced Shear Power Spectrum  

E-print Network

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

Scott Dodelson; Charles Shapiro; Martin White

2005-08-12

120

Rotatable shear plate interferometer  

DOEpatents

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

Duffus, Richard C. (Livermore, CA)

1988-01-01

121

Sea surface wind stress in stratified atmospheric flow  

SciTech Connect

The paper presents the wind shear stress on the sea surface as well as the velocity profile in stably stratified atmospheric boundary layer flow over wind waves by using similarity theory. For a given geostrophic velocity, Coriolis parameter, spectral peak period and stratification parameter the sea surface shear stress is determined. Further, the direction of the sea surface shear stress and the velocity profile are given. Parameterizations of the results are also presented. Finally, the engineering relevance of the results is discussed.

Myrhaug, D. [Norwegian Univ. of Science and Technology, Trondheim (Norway). Dept. of Marine Hydrodynamics; Slaattelid, O.H. [Norwegian Marine Technology Research Inst., Trondheim (Norway)

1996-12-31

122

Harnessing Wind  

NSDL National Science Digital Library

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

Integrated Teaching And Learning Program

123

The Effect of Vertical Shear on Tropical Cyclone Intensity Change  

Microsoft Academic Search

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

Mark Demaria

1996-01-01

124

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

125

Shear Thinning in Xenon  

NASA Technical Reports Server (NTRS)

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

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

2009-01-01

126

Shear stress transducer concepts  

NASA Astrophysics Data System (ADS)

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

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

1990-07-01

127

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

128

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

129

WIND ENERGY Wind Energ. (2014)  

E-print Network

the turbulent atmosphere and the wind turbine wake in order to optimize the design of the wind turbine as well.com). DOI: 10.1002/we.1792 RESEARCH ARTICLE Self-similarity and turbulence characteristics of wind turbine by a single wind turbine are studied in this paper with a new large eddy simulation (LES) code, the wind

130

Wind Turbines Adaptation to the Variability of the Wind Field  

NASA Astrophysics Data System (ADS)

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

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

2010-05-01

131

Angular shear plate  

SciTech Connect

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

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

2009-07-14

132

An Optical MEMS-Based Shear Stress Sensor for High Reynolds Number Applications  

Microsoft Academic Search

In an effort to extend wall shear stress measurements to high Reynolds number flows, a new MEMS- based optical shear stress sensor was fabricated and tested in the 2 feet wind tunnel at the California Institute of Technology for Reynolds numbers of up to 5.6 x 106. The description of this sensor and the test results are reported in this

D. Fourguette; D. Modarress; D. Wilson; M. Koochesfahani; M. Gharib

133

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

134

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

E-print Network

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

Sanahuja, Blai

135

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

Microsoft Academic Search

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

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

2000-01-01

136

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

137

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

138

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

139

WAVE ACTION AND BOTTOM SHEAR STRESSES IN LAKE ERIE  

EPA Science Inventory

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

140

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

Microsoft Academic Search

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

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

1998-01-01

141

Final Report for The Creation of a Physics-based Ground-effect Model, Phase 2 - Inclusion of the Effects of Wind, Stratification, and Shear into the New Ground Effect Model  

NASA Technical Reports Server (NTRS)

The reduction of the separation of the leading and following aircrafts is desirable to enhance the airport capacity provided that there is a physics-based operational model applicable to all regions of the flight domain (out of ground effect, OGE; near ground effect, NGE; and in ground effect, IGE) and that the quality of the quantitative input from the measurements of the prevailing atmospheric conditions and the quality of the total airport operations regarding the safety and the sound interpretation of the prevailing conditions match the quality of the analysis and numerical simulations. In the absence of an analytical solution, the physics of the flow is best expressed by a mathematical model based on numerical simulations, field and laboratory experiments, and heuristic reasoning. This report deals with the creation of a sound physics-based real-time IGE model of the aircraft wake vortices subjected to crosswind, stratification and shear.

Sarpkaya, Turgut

2006-01-01

142

Magnetohydrodynamic Shearing Waves  

E-print Network

I consider the nonaxisymmetric linear theory of a rotating, isothermal magnetohydrodynamic (MHD) shear flow. The analysis is performed in the shearing box, a local model of a thin disk, using a decomposition in terms of shearing waves, i.e., plane waves in a frame comoving with the shear. These waves do not have a definite frequency as in a normal mode decomposition, and numerical integration of a coupled set of amplitude equations is required to characterize their time dependence. Their generic time dependence, however, is oscillatory with slowly-varying frequency and amplitude, and one can construct accurate analytical solutions by applying the Wentzel-Kramers-Brillouin method to the full set of amplitude equations. The solutions have the following properties: 1) Their accuracy increases with wavenumber, so that most perturbations that fit within the disk are well-approximated as modes with time-dependent frequencies and amplitudes. 2) They can be broadly classed as incompressive and compressive perturbations, the former including the nonaxisymmetric extension of magnetorotationally unstable modes, and the latter being the extension of fast and slow modes to a differentially-rotating medium. 3) Wave action is conserved, implying that their energy varies with frequency. 4) Their shear stress is proportional to the slope of their frequency, so that they transport angular momentum outward (inward) when their frequency increases (decreases). The complete set of solutions constitutes a comprehensive linear test suite for numerical MHD algorithms that incorporate a background shear flow. I conclude with a brief discussion of possible astrophysical applications.

Bryan M. Johnson

2007-02-12

143

Wild Wind  

NSDL National Science Digital Library

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

Integrated Teaching And Learning Program

144

Thermal and humidity winds in outer planet atmospheres  

SciTech Connect

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

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

1991-05-01

145

Amplitude modulation of wind turbine noise  

E-print Network

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

Makarewicz, Rufin

2013-01-01

146

Jamming under shear  

NASA Astrophysics Data System (ADS)

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

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

2010-03-01

147

Converging shear rheometer  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

148

Shears from shapelets  

NASA Astrophysics Data System (ADS)

Aims.Accurate measurement of gravitational shear from images of distant galaxies is one of the most direct ways of studying the distribution of mass in the universe. We describe a new implementation of a technique for measuring shear that is based on the shapelets formalism. Methods: .The shapelets technique describes PSF and observed images in terms of Gauss-Hermite expansions (Gaussians times polynomials). It allows the various operations that a galaxy image undergoes before being registered in a camera (gravitational shear, PSF convolution, pixelation) to be modeled in a single formalism, so that intrinsic ellipticities can be derived in a single modeling step. Results: .The resulting algorithm, and tests of it on idealized data as well as more realistic simulated images from the STEP project, are described. Results are very promising, with attained calibration accuracy better than four percent (1 percent for round PSFs) and PSF ellipticity correction better than a factor of 20. Residual calibration problems are discussed.

Kuijken, K.

2006-09-01

149

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

150

Ultrasonic shear wave couplant  

DOEpatents

Ultrasonically testing of an article at high temperatures is accomplished by the use of a compact layer of a dry ceramic powder as a couplant in a method which involves providing an ultrasonic transducer as a probe capable of transmitting shear waves, coupling the probe to the article through a thin compact layer of a dry ceramic powder, propagating a shear wave from the probe through the ceramic powder and into the article to develop echo signals, and analyzing the echo signals to determine at least one physical characteristic of the article.

Kupperman, David S. (Oak Park, IL); Lanham, Ronald N. (Lockport, IL)

1985-01-01

151

Bayesian lensing shear measurement  

NASA Astrophysics Data System (ADS)

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

Bernstein, Gary M.; Armstrong, Robert

2014-02-01

152

Ultrasonic shear wave couplant  

DOEpatents

Ultrasonically testing of an article at high temperatures is accomplished by the use of a compact layer of a dry ceramic powder as a couplant in a method which involves providing an ultrasonic transducer as a probe capable of transmitting shear waves, coupling the probe to the article through a thin compact layer of a dry ceramic powder, propagating a shear wave from the probe through the ceramic powder and into the article to develop echo signals, and analyzing the echo signals to determine at least one physical characteristic of the article.

Kupperman, D.S.; Lanham, R.N.

1984-04-11

153

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

154

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.

155

Magnetic energy flow in the solar wind.  

NASA Technical Reports Server (NTRS)

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

Modisette, J. L.

1972-01-01

156

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

Code of Federal Regulations, 2013 CFR

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

2013-04-01

157

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

Code of Federal Regulations, 2012 CFR

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

2012-04-01

158

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

Code of Federal Regulations, 2011 CFR

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

2011-04-01

159

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

Code of Federal Regulations, 2014 CFR

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

2014-04-01

160

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

Code of Federal Regulations, 2010 CFR

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

2010-04-01

161

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

162

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.

2014-11-01

163

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

164

Shear-thinning Fluid  

NASA Technical Reports Server (NTRS)

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

2001-01-01

165

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

166

Shear degradation of DNA.  

PubMed Central

A concentric-cylinder flow-birefringence instrument is used to generate sufficient shear fields to break T2 DNA (M = 1.2 X 10(8)) and E. coli DNA (M = 2.5 X 10(9)) in dilute solution. Breakage is monitored in situ by measuring the change in birefringence relaxation after the flow has been stopped. The breakage of T2 DNA follows first-order kinetics. Rate constants are obtained as functions of shear rate and viscosity (varied by adding glycerol). The data are fitted by a modified Arrhenius equation, assuming that stess increases the rate by lowering the activation energy. The rate increases with temperature, pH, and water concentration, and appears to be a base-catalyzed hydrolysis of the phosphate-ester linkage. La3+ ions catalyze the reaction. E. coli DNA was reduced to half molecules at a shear stress of 0.4 dynes/cm2, which is about 2500 times less than that required for T2. The difference in rates is accounted for in part by the difference in size of the two, but may also reflect the presence of many single-strand nicks in the coli DNA. PMID:19729

Adam, R E; Zimm, B H

1977-01-01

167

Detection of oppositely directed reconnection jets in a solar wind current sheet  

Microsoft Academic Search

We report the first two-spacecraft (Wind and ACE) detection of oppositely directed plasma jets within a bifurcated current sheet in the solar wind. The event occurred on January 3, 2003 and provides further direct evidence that such jets result from reconnection. The magnetic shear across the bifurcated current sheet at both Wind and ACE was ?150°, indicating that the magnetic

M. S. Davis; T. D. Phan; J. T. Gosling; R. M. Skoug

2006-01-01

168

Detection of oppositely directed reconnection jets in a solar wind current sheet  

Microsoft Academic Search

We report the first two-spacecraft (Wind and ACE) detection of oppositely directed plasma jets within a bifurcated current sheet in the solar wind. The event occurred on January 3, 2003 and provides further direct evidence that such jets result from reconnection. The magnetic shear across the bifurcated current sheet at both Wind and ACE was approximately 150 degrees, indicating that

M. S. Davis; T. D. Phan; J. T. Gosling; R. M. Skoug

2006-01-01

169

Detection of oppositely directed reconnection jets in a solar wind current sheet  

Microsoft Academic Search

We report the first two-spacecraft (Wind and ACE) detection of oppositely directed plasma jets within a bifurcated current sheet in the solar wind. The event occurred on January 3, 2003 and provides further direct evidence that such jets result from reconnection. The magnetic shear across the bifurcated current sheet at both Wind and ACE was ~150°, indicating that the magnetic

M. S. Davis; T. D. Phan; J. T. Gosling; R. M. Skoug

2006-01-01

170

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

Microsoft Academic Search

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

Hagkwen Kim; Chanan Singh; Alex Sprintson

2012-01-01

171

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

Microsoft Academic Search

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

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

1996-01-01

172

Combined effects of deterministic and random loads in wind turbine design  

Microsoft Academic Search

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

A. Raab

1980-01-01

173

Wind Generator  

NSDL National Science Digital Library

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

Consortium, The C.

2012-05-21

174

Dual-hologram shearing interference technique with regulated sensitivity  

NASA Astrophysics Data System (ADS)

A novel optical diagnostic technique,namely, a dual hologram shearing interferometry with regulated sensitivity, is proposed for visualization and measuring the density gradients of compressible flows in wind tunnels. It has advantages over 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 proved to be insensitive to mechanical vibrations and allowed to record holograms during the noisy wind tunnel run. The proposed approach was demonstrated by its application to a supersonic flow over spherically blunted and sharp nose cone/cylinder models. It is believed that the technique will become an effective tool for receiving optical data in many flow facilities.

Toker, Gregory R.; Levin, Daniel

1998-06-01

175

Dual-hologram shearing interferometry with regulated sensitivity  

NASA Astrophysics Data System (ADS)

A novel optical diagnostic technique, namely, a dual hologram shearing interferometry with regulated sensitivity, is proposed for visualization and measuring the density gradients of compressible flows in wind tunnels. It has advantages over 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 proved to be insensitive to mechanical vibrations and allowed to record holograms during the noisy wind tunnel run. The proposed approach was demonstrated by its application to a supersonic flow over spherically blunted and sharp nose cone/cylinder models. It is believed that the technique will become an effective tool for receiving optical data in many flow facilities.

Toker, Gregory R.; Levin, Daniel

1998-07-01

176

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

Microsoft Academic Search

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

Leonardo P. Chamorro; Fernando Port

177

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

Microsoft Academic Search

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

Leonardo P. Chamorro; Fernando Porté-Agel

2009-01-01

178

Using machine learning to predict wind turbine power output  

NASA Astrophysics Data System (ADS)

Wind turbine power output is known to be a strong function of wind speed, but is also affected by turbulence and shear. In this work, new aerostructural simulations of a generic 1.5 MW turbine are used to rank atmospheric influences on power output. Most significant is the hub height wind speed, followed by hub height turbulence intensity and then wind speed shear across the rotor disk. These simulation data are used to train regression trees that predict the turbine response for any combination of wind speed, turbulence intensity, and wind shear that might be expected at a turbine site. For a randomly selected atmospheric condition, the accuracy of the regression tree power predictions is three times higher than that from the traditional power curve methodology. The regression tree method can also be applied to turbine test data and used to predict turbine performance at a new site. No new data are required in comparison to the data that are usually collected for a wind resource assessment. Implementing the method requires turbine manufacturers to create a turbine regression tree model from test site data. Such an approach could significantly reduce bias in power predictions that arise because of the different turbulence and shear at the new site, compared to the test site.

Clifton, A.; Kilcher, L.; Lundquist, J. K.; Fleming, P.

2013-06-01

179

Meteorology (Wind)  

Atmospheric Science Data Center

... is in each range (0-2, 3-6, 7-10, 11-14, 15-18, 19-25 m/s).   Wind Speed at 50 m at 3-hourly intervals (m/s)   ... 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

180

Wind energy  

Microsoft Academic Search

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

B. Sorensen

1976-01-01

181

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

182

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

183

Shear resistance of rock bolts  

Microsoft Academic Search

The effectiveness of rock bolts in resisting shear displacement along preexisting fracture surfaces or slip planes was determined in the laboratory with full-scale bolts and large-scale shear test equipment. The system variables were the type of bolt, orientation of bolt relative to shear surface, and normal pressure on the interface. Results showed that, in general, both conventional bolts and resin-grouted

Haas

1976-01-01

184

Q. J. R. Meteorol. Soc. (2004), 130, pp. 120 Using mesocale model winds for correcting wind-drift errors in radar  

E-print Network

latitudes the radar beam will frequently be sampling the ice. Because the terminal velocity of ice is so particles falling with constant terminal velocity through a region of constant wind shear, with the pattern

Reading, University of

185

Failure During Sheared Edge Stretching  

NASA Astrophysics Data System (ADS)

Failure during sheared edge stretching of sheet steels is a serious concern, especially in advanced high-strength steel (AHSS) grades. The shearing process produces a shear face and a zone of deformation behind the shear face, which is the shear-affected zone (SAZ). A failure during sheared edge stretching depends on prior deformation in the sheet, the shearing process, and the subsequent strain path in the SAZ during stretching. Data from laboratory hole expansion tests and hole extrusion tests for multiple lots of fourteen grades of steel were analyzed. The forming limit curve (FLC), regression equations, measurement uncertainty calculations, and difference calculations were used in the analyses. From these analyses, an assessment of the primary factors that contribute to the fracture during sheared edge stretching was made. It was found that the forming limit strain with consideration of strain path in the SAZ is a major factor that contributes to the failure of a sheared edge during stretching. Although metallurgical factors are important, they appear to play a somewhat lesser role.

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

2008-12-01

186

True Shear Parallel Plate Viscometer  

NASA Technical Reports Server (NTRS)

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

Ethridge, Edwin; Kaukler, William

2010-01-01

187

Experimental observations of shear patterns in direct shear tests  

Microsoft Academic Search

A series of simple experiments were performed using direct shear apparatus in order to study the rupture patterns in sands. Measurements of internal displacements were made by observing with X-rays the positions of lead shot placed in a regular array within the sample. Shear displacement was applied manually and radiographs were taken after each increment of horizontal movement in order

G. Scarpelli; D. M. Wood

1982-01-01

188

20% Wind Energy 20% Wind Energy  

E-print Network

(government, industry, utilities, NGOs) Analyzes wind's potential contributions to energy security, economic · Transmission a challenge #12;Wind Power Class Resource Potential Wind Power Density at 50 m W/m 2 Wind Speed20% Wind Energy by 2030 20% Wind Energy by 2030 #12;Presentation and Objectives Overview Background

Powell, Warren B.

189

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"

190

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

191

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.

2012-08-03

192

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

193

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

194

Atmospheric stability affects wind turbine power collection  

NASA Astrophysics Data System (ADS)

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

Wharton, Sonia; Lundquist, Julie K.

2012-03-01

195

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.

Robert A. Dalrymple

196

Wind Landforms  

NSDL National Science Digital Library

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

Tranel, Lisa

197

Wind Story  

NSDL National Science Digital Library

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

WPSU (Penn State University broadcast station); Domain, Teachers'

198

Simulated performance of an airborne lidar wind shear detection system  

E-print Network

? described and sample validations are presented. 'I'wo (ohereni. , pulsed laser systems are examined: COz at A = 10. o91 pin ancl Ho: YAG at A = 2. 0913. Two base line sets of systena parameters are established to evaluate the measurement capabilities... of both COz zotel IIo. YAG laser systems. These sets of values are considered as the nominal operating points for systenr feasibililv consideratio?s. Systematic base linc parameter variations include examination of the effects of pulse duration...

Griffith, Kenneth Scott

1987-01-01

199

NASA wind shear flight test in situ results  

NASA Technical Reports Server (NTRS)

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

Oseguera, Rosa M.

1992-01-01

200

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

201

The V-Notched Rail Shear Test  

Microsoft Academic Search

A V-notched rail shear test has been developed for measuring the shear modulus and shear strength of composites and other materials. This test method, standardized as ASTM D 7078, incorporates attractive features of the existing Iosipescu and two-rail shear tests. The V-notched rail shear specimen provides a larger gage section than the standard Iosipescu shear specimen and provides enhanced loading

Daniel O. Adams; Joseph M. Moriarty; Adam M. Gallegos; Donald F. Adams

2007-01-01

202

Direct shear testing of polished slickensided surfaces  

Microsoft Academic Search

A series of ring shear and direct shear tests were performed to measure the drained residual strength of three clay soils.\\u000a For each of the soils, slickensided direct shear specimens were prepared by wire-cutting intact specimens, and polishing the\\u000a resulting shear plane on a variety of surfaces to align the clay particles in the direction of shear. Drained direct shear

Christopher L. Meehan; Thomas L. Brandon; J. Michael Duncan; Binod Tiwari

2010-01-01

203

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

SciTech Connect

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

Clifton, A.

2012-12-01

204

Galactic Winds  

NASA Astrophysics Data System (ADS)

Galactic winds have become arguably one of the hottest topics in extragalactic astronomy. This enthusiasm for galactic winds is due in part to the detection of winds in many, if not most, high-redshift galaxies. Galactic winds have also been invoked by theorists to (1) suppress the number of visible dwarf galaxies and avoid the "cooling catastrophe" at high redshift that results in the overproduction of massive luminous galaxies, (2) remove material with low specific angular momentum early on and help enlarge gas disks in CDM + baryons simulations, (3) reduce the dark mass concentrations in galaxies, (4) explain the mass-metallicity relation of galaxies from selective loss of metal-enriched gas from smaller galaxies, (5) enrich and "preheat" the ICM, (6) enrich the IGM without disturbing the Ly?forest significantly, and (7) inhibit cooling flows in galaxy clusters with active cD galaxies. The present paper highlights a few key aspects of galactic winds taken from a recent ARAA review by Veilleux, Cecil, &Bland-Hawthorn (2005; herafter VCBH). Readers interested in a more detailed discussion of this topic are encouraged to refer to the original ARAA article.

Veilleux, Sylvain

205

Wind tower augmentation of wind turbines  

Microsoft Academic Search

The operating principle of the 'Baud-Geers' wind towers traditionally used in Iran for ventilation and passive cooling of architectural structures is presently adapted to house a vertical axis wind turbine. Unlike annular diffuser-augmented, horizontal axis wind turbines, the 'wind tower' does not have to be trained into the wind and generates less noise. It may also be either free standing

M. N. Bahadori

1984-01-01

206

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

207

Experimental study on wind loading on a complicated group-tower  

NASA Astrophysics Data System (ADS)

This paper studied how wind pressures and forces affect rigid sectional models of a complicated group-tower using experimental wind tunnel tests. The group-tower was composed of five separate sub-towers with different diameters and heights. The basic characteristics of the mean and fluctuating wind pressure distributions on typical parts of the sub-towers were analyzed along the heights of each sub-tower, and their distribution trends are discussed. Also, the mean base shear and moment coefficients and their characteristics are presented. The wind pressure and wind force results showed that because the group-tower structure consisted of five separate lofty towers, the mutual aerodynamic interferences were serious; thus, the mean and fluctuating wind pressure, wind force distributions and the mean base shear and moment coefficients were quite complicated.

Ming, Gu; Huang, Peng; Tao, Lin; Zhou, Xuanyi; Fan, Zhong

2010-10-01

208

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

209

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

210

Shear thinning of nanoparticle suspensions.  

SciTech Connect

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

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

2008-08-01

211

Scattering of an acoustic field by a free jet shear layer  

Microsoft Academic Search

This paper deals with scattering of an acoustic field propagating through a large wind tunnel jet shear layer. For a monochromatic wave, the scattering effects are mainly spectral broadening of the incident peak and amplitude and phase fluctuations of the wave. These effects have been studied both experimentally through a parametric study and theoretically by carrying out analyses based on

A. Guedel

1983-01-01

212

Scattering of an acoustic field by a free jet shear layer  

Microsoft Academic Search

This paper deals with scattering of an acoustic field propagating through a large wind-tunnel jet shear layer. For a monochromatic wave, the scattering effects are mainly spectral broadening of the incident peak and amplitude and phase fluctuations of the wave. These effects have been studied both experimentally through a parametric study and theoretically by carrying out analyses based on single

A. Guédel

1985-01-01

213

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

NASA Technical Reports Server (NTRS)

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

Bray, R. S.

1988-01-01

214

The wind speed profile at offshore wind farm sites  

NASA Astrophysics Data System (ADS)

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

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

2003-04-01

215

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

216

Wind energy systems  

NASA Technical Reports Server (NTRS)

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

Stewart, H. J.

1978-01-01

217

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

218

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

219

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

220

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

221

Shear Strength and Fatigue Properties of Human Cortical Bone Determined from Pure Shear Tests  

Microsoft Academic Search

Shear properties of bone have been inferred from torsion tests. However, torsion often causes spiral fracture planes that correspond to tensile rather than shear failure. We measured the shear properties of human cortical bone in both longitudinal and transverse directions using pure shear tests. Shearing applied transverse to the bone long axis caused fracture along a 45 plane that coincided

C. H. Turner; T. Wang; D. B. Burr

2001-01-01

222

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

Microsoft Academic Search

We interpret the shear environments that produced bubble textures in obsidian samples using the results of theoretical, numerical and experimental studies on the deformation of bubbles in shear flows. In particular, we use the shapes and orientations of bubbles (vesicles) in obsidian to estimate shear rates and shear stresses, and assess flow type (simple vs. pure shear). This technique can

A. C. Rust; Michael Manga; K. V. Cashman

2003-01-01

223

Wind Tunnel Modeling Of Wind Flow Over Complex Terrain  

NASA Astrophysics Data System (ADS)

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

Banks, D.; Cochran, B.

2010-12-01

224

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

225

Large-eddy simulation of a wind turbine wake in turbulent  

E-print Network

Large-eddy simulation of a wind turbine wake in turbulent neutral shear flow Shengbai Xie, Cristina-similar velocity profile existing in the wake after a wind turbine? How does the wake influence the vertical turbulent mixing above the ground? Is our large-eddy simulation capable to study such complex problems

Firestone, Jeremy

226

A new evaluation of the wind stress coefficient over water surfaces  

Microsoft Academic Search

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

J. Amorocho; J. J. DeVries

1980-01-01

227

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

228

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

NASA Technical Reports Server (NTRS)

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

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

1981-01-01

229

Wind Technologies & Evolving Opportunities (Presentation)  

SciTech Connect

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

Robichaud, R.

2014-07-01

230

Shear Relaxations of Confined Liquids.  

NASA Astrophysics Data System (ADS)

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

Carson, George Amos, Jr.

231

Shear Force in Radiometric Flows  

NASA Astrophysics Data System (ADS)

The impact of the radiometer vane thickness and edge geometry on the total radiometric force is examined numerically solving the ES BGK model kinetic equation. The flow of argon over a single vane and a multi-vane configurations is considered in the range of Knudsen numbers from 0.02 to 1. The shear force is found to reduce the total radiometric force for most vane configurations. It is shown that a change in the vane shape may offset the losses due to the shear force in a multi-vane geometry.

Gimelshein, Natalia E.; Gimelshein, Sergey F.; Ketsdever, Andrew D.; Selden, Nathaniel P.

2011-05-01

232

Shearing Effectiveness of Integral Stiffening  

NASA Technical Reports Server (NTRS)

Values of coefficients for defining the effectiveness of integral stiffeners in resisting shear deformations of the plate of which they are an integral part are presented for a variety of proportions of rectangular stiffeners with circular fillets. Formulas are given in which these coefficients may be employed to calculate the elastic constants associated with the twisting and shearing of integrally stiffened plates. The size of fillet radius is shown to contribute appreciably to the degree of penetration of the stresses from the skin into the stiffener.

Crawford, Robert F; Libove, Charles

1955-01-01

233

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

NASA Technical Reports Server (NTRS)

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

Cheng, R. Y. K.

1975-01-01

234

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

235

Careers in Wind Energy  

ERIC Educational Resources Information Center

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

Liming, Drew; Hamilton, James

2011-01-01

236

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.

2012-08-03

237

Satellite Winds  

NSDL National Science Digital Library

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

238

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

239

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

240

The Shear Joy of Area.  

ERIC Educational Resources Information Center

Geoboards are viewed as excellent vehicles for developing intuitive understandings of various topics in transformational geometry. The activities described are designed to show pupils that when a triangle or parallelogram is subjected to a transformation called a shear, its area is not changed. Ways for finding areas are detailed. (MP)

Spitler, Gail

1982-01-01

241

Shear banding in simulated telechelic polymers  

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

242

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.

243

Shear viscosity of the quark matter  

E-print Network

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

Masaharu Iwasaki; Hiromasa Ohnishi; Takahiko Fukutome

2007-05-14

244

On double shearing in frictional materials  

NASA Astrophysics Data System (ADS)

This paper evaluates the mechanical behaviour of yielding frictional geomaterials. The general Double Shearing model describes this behaviour. Non-coaxiality of stress and plastic strain increments for plane strain conditions forms an important part of this model. The model is based on a micro-mechanical and macro-mechanical formulation. The stress-dilatancy theory in the model combines the mechanical behaviour on both scales.It is shown that the general Double Shearing formulation comprises other Double Shearing models. These models differ in the relation between the mobilized friction and dilatancy and in non-coaxiality. In order to describe reversible and irreversible deformations the general Double Shearing model is extended with elasticity.The failure of soil masses is controlled by shear mechanisms. These shear mechanisms are determined by the conditions along the shear band. The shear stress ratio of a shear band depends on the orientation of the stress in the shear band. There is a difference between the peak strength and the residual strength in the shear band. While peak stress depends on strength properties only, the residual strength depends upon the yield conditions and the plastic deformation mechanisms and is generally considerably lower than the maximum strength. It is shown that non-coaxial models give non-unique solutions for the shear stress ratio on the shear band. The Double Shearing model is applied to various failure problems of soils such as the direct simple shear test, the biaxial test, infinite slopes, interfaces and for the calculation of the undrained shear strength. Copyright

Teunissen, J. A. M.

2007-01-01

245

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

2007-01-08

246

Wind Energy Resource Information  

NSDL National Science Digital Library

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

247

High resolution numerical simulations of unstable colliding stellar winds  

E-print Network

We investigate the hydrodynamics of the interaction of two supersonic winds in binary systems. The collision of the winds creates two shocks separated by a contact discontinuity. The overall structure depends on the momentum flux ratio eta of the winds. We use the code RAMSES with adaptive mesh refinement to study the shock structure up to smaller values of eta, higher spatial resolution and greater spatial scales than have been previously achieved. 2D and 3D simulations, neglecting orbital motion, are compared to widely-used analytic results and their applicability is discussed. In the adiabatic limit, velocity shear at the contact discontinuity triggers the Kelvin-Helmholtz instability. We quantify the amplitude of the resulting fluctuations and find that they can be significant even with a modest initial shear. Using an isothermal equation of state leads to the development of thin shell instabilities. The initial evolution and growth rates enables us to formally identify the non-linear thin shell instabili...

Lamberts, Astrid; Dubus, Guillaume

2011-01-01

248

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

249

Scaling Effects in Direct Shear Tests  

Microsoft Academic Search

Laboratory experiments of the direct shear test were performed on spherical particles of different materials and diameters. Results of the bulk friction vs. non-dimensional shear displacement are presented as a function of the non-dimensional particle diameter. Simulations of the direct shear test were performed using the Discrete Element Method (DEM). The simulation results show Considerable differences with the physical experiments.

Andrés D. Orlando; Daniel M. Hanes; Hayley H. Shen

2009-01-01

250

Interpretation of strains in torsion shear tests  

Microsoft Academic Search

The normal and shear strains obtained in torsion shear tests may be interpreted in two different ways to gain insight into (1) the type of plastic potential to be employed in hardening plasticity stress–strain models, and (2) the coincidence in physical space of the plastic strain increment direction with the stress direction during principal stress rotation. Thirty-four drained torsion shear

Poul V. Lade; Jungman Nam; Won Pyo Hong

2009-01-01

251

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

Microsoft Academic Search

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

KARSTEN THERMANN; CHRISTIAN GAU; JOACHIM TIEDEMANN

252

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

E-print Network

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

Goree, John

253

Comparison of steady-state shear viscosity and complex shear modulus in Langmuir Monolayers  

E-print Network

1 Comparison of steady-state shear viscosity and complex shear modulus in Langmuir Monolayers-state shear viscosity, , and the complex shear modulus, )(* G . In particular, one might expect to find peak using alternate techniques13 found that the peak in the steady state viscosity, !/= , where

Dennin, Michael

254

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

255

An integrated dynamic model of a flexible wind turbine  

NASA Astrophysics Data System (ADS)

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

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

1990-06-01

256

Dynamics of Sheared Granular Materials  

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

257

Wind Power! Designing a Wind Turbine  

NSDL National Science Digital Library

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

Integrated Teaching And Learning Program

258

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

259

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

260

Wind-driven nearshore sediment resuspension in a deep lake during winter  

NASA Astrophysics Data System (ADS)

public concern over declining water quality at Lake Tahoe, California-Nevada (USA) led to an investigation of wind-driven nearshore sediment resuspension that combined field measurements and modeling. Field data included: wind speed and direction, vertical profiles of water temperature and currents, nearbed velocity, lakebed sediment characteristics, and suspended sediment concentration and particle size distribution. Bottom shear stress was computed from ADV-measured nearbed velocity data, adapting a turbulent kinetic energy method to lakes, and partitioned according to its contributions attributed to wind-waves, mean currents, and random motions. When the total shear stress exceeded the critical shear stress, the contribution to overall shear stress was about 80% from wind-waves and 10% each from mean currents and random motions. Therefore, wind-waves were the dominant mechanism resulting in sediment resuspension as corroborated by simultaneous increases in shear stress and total measured sediment concentration. The wind-wave model STWAVE was successfully modified to simulate wind-wave-induced sediment resuspension for viscous-dominated flow typical in lakes. Previous lake applications of STWAVE have been limited to special instances of fully turbulent flow. To address the validity of expressions for sediment resuspension in lakes, sediment entrainment rates were found to be well represented by a modified 1991 García and Parker formula. Last, in situ measurements of suspended sediment concentration and particle size distribution revealed that the predominance of fine particles (by particle count) that most negatively impact clarity was unchanged by wind-related sediment resuspension. Therefore, we cannot assume that wind-driven sediment resuspension contributes to Lake Tahoe's declining nearshore clarity.

Reardon, Kristin E.; Bombardelli, Fabián. A.; Moreno-Casas, Patricio A.; Rueda, Francisco J.; Schladow, S. Geoffrey

2014-11-01

261

An Experimental Study of Shear Damage Using In-Situ Single Shear Test  

Microsoft Academic Search

An experimental study has been performed to investigate the shear damage mechanism of aluminium alloy 2024T3 by an in-situ single shear test using scanning electron microscope (SEM). The observation of microstructural change and measurement of shear strain in mesoscale have been undertaken simultaneously. Hence, the shear damage mechanism and the shear stress–strain curve have been obtained. By measuring the deformed

C. Y. Tang; T. C. Lee; B. Rao; C. L. Chow

2002-01-01

262

Shear viscosity and shear thinning in two-dimensional Yukawa liquids  

E-print Network

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

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

2006-03-24

263

Shear Viscosity and Shear Thinning in Two-Dimensional Yukawa Liquids  

SciTech Connect

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

Donko, Z.; Hartmann, P.; Kutasi, K. [Research Institute for Solid State Physics and Optics of the Hungarian Academy of Sciences, H-1525 Budapest, P.O. Box 49 (Hungary); Goree, J. [Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242 (United States)

2006-04-14

264

Apparatus for shearing spent nuclear fuel assemblies  

DOEpatents

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

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

1980-01-01

265

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

266

Shear instability in nanoporous Si.  

PubMed

Elastic properties of nanoporous Si (np-Si), which is composed of bulk Si containing ordered, nanometer-sized cylindrical pores, are investigated based on first-principles density functional theory calculations. By separately varying the pore size and spacing, it is demonstrated that the elastic stiffness of np-Si under the shear strain perpendicular to the pore axis turns negative when the volume fraction of pores becomes greater than a critical value. The total energy calculations reveal that the negative values in the stiffness originate from the enhanced strain energy, which leads to significant rotation in bonds near the pore surface. Moreover, the high sensitivity of the elastic stiffness to shear induces a structural transformation in np-Si from tetragonal (D2d) to orthorhombic (C2v) phase, which makes it necessary to properly take the effect of external strain due to substrates or electrical leads into account in np-Si-based applications. PMID:25153784

Lee, Joo-Hyoung

2014-09-10

267

Methods of determination of shear properties of textile composites  

Microsoft Academic Search

Shear properties of four types of composites possessing no planes of weak shear strength and stiffness are experimentally investigated. Shear characteristics measured by Iosipescu test and\\/or its modification Asymmetrical Four-Point Bending (AFPB) are compared with experimental results obtained in the work by seven other shear tests developed for the determination of shear modulus and shear strength of fibrous and layered

Yu. M Tarnopol’skii; A. K Arnautov; V. L Kulakov

1999-01-01

268

Cell disaggregation behavior in shear flow.  

PubMed Central

The disaggregation behavior of erythrocytes in dextran saline solution was investigated by a light reflectometry technique in a Couette flow and in a plane Poiseuille flow. Dextran concentration and mass average molecular weight of the polymer fraction strongly influence the shear stress dependence of the erythrocyte suspension reflectivity in shear flow and the critical hydrodynamic conditions (shear rate or shear stress) for near-complete cell dispersion. We investigated the influence of cell volume fraction and membrane deformability (heat treatment of the erythrocytes) on the reflectivity of the flowing suspension. This study indicates that the intercell adhesiveness and the shear stress are the only parameters that influence rouleau break-up in steady uniform shear flow, thus eliminating cell volume fraction and membrane deformability as possible factors. However, the critical cross-sectional average shear stress for near-complete cell dispersion through the flow cross-section is shown to depend on the flow pattern. The rotation of cells in a shear flow or the nonuniform shear field in Poiseuille flow indeed increases the flow resistance of cell aggregates. We give a theoretical description of the shear-induced cell disaggregation process in Couette flow and in plane Poiseuille flow. The quantitation of shear forces for cell dispersion provides a way for estimating the surface adhesive energy of the bridging membranes by fluid mechanical technique. PMID:2439136

Snabre, P; Bitbol, M; Mills, P

1987-01-01

269

Shear Viscosity of Strongly Coupled  

Microsoft Academic Search

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

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

2001-01-01

270

Steady incompressible variable thickness shear layer aerodynamics  

NASA Technical Reports Server (NTRS)

A shear flow aerodynamic theory for steady incompressible flows is presented for both the lifting and non lifting problems. The slow variation of the boundary layer thickness is considered. The slowly varying behavior is treated by using multitime scales. The analysis begins with the elementary wavy wall problem and, through Fourier superpositions over the wave number space, the shear flow equivalents to the aerodynamic transfer functions of classical potential flow are obtained. The aerodynamic transfer functions provide integral equations which relate the wall pressure and the upwash. Computational results are presented for the pressure distribution, the lift coefficient, and the center of pressure travel along a two dimensional flat plate in a shear flow. The aerodynamic load is decreased by the shear layer, compared to the potential flow. The variable thickness shear layer decreases it less than the uniform thickness shear layer based upon equal maximum shear layer thicknesses.

Chi, M. R.

1976-01-01

271

Minimum cut and shear bands  

NASA Astrophysics Data System (ADS)

We explore the efficacy of network optimisation theory for minimum cut to quantify the evolution of granular fabric and its functionality as a transmission medium in deforming dense granular media. Our focus here is on force transmission in a sheared assembly of polydisperse particles, in a biaxial compression test under constant confining pressure. The granular fabric is examined with respect to the material's force-bearing contact network over that regime when the material has reached its residual strength, and is deforming under a near constant volume in the presence of a fully developed shear band. The structural evolution of the fabric is quantitatively characterized using a representative weighted-directed network that is similarly evolving as the sample deforms. The edges or links, representing the interparticle contacts, are each weighted by the capacity of the contact to transmit force: a scalar that depends solely on the relative motion of the contacting grains. In the large strain failure regime, the minimum cut which represents the bottleneck in force transmission is found to lie in the persistent shear band. This study paves the way for the future analysis of flows and force transmission through an evolving contact network and, in turn, the characterisation of the relationship between the material's contact topology and its capacity to transmit forces through its contact network.

Tordesillas, Antoinette; Cramer, Andrew; Walker, David M.

2013-06-01

272

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

EPA Science Inventory

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

273

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 ...

274

Global Wind Map  

ERIC Educational Resources Information Center

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

Journal of College Science Teaching, 2005

2005-01-01

275

Danish Wind Industry Association  

NSDL National Science Digital Library

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

276

The Power of Wind  

NSDL National Science Digital Library

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

Mrs. Andrus

2010-06-24

277

Wind Power Animation  

NSDL National Science Digital Library

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

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

278

Statistical study of magnetic reconnection observed by WIND in the solar wind  

NASA Astrophysics Data System (ADS)

Magnetic reconnection is a process where the energy stored in the magnetic field dissipates into plasma heating and acceleration. In spacecraft observations, we can identify magnetic reconnection through its exhaust where the plasma on reconnected field lines leaves the reconnection site. We present a statistical study of magnetic reconnection exhausts in the solar wind. The dataset is based on the WIND observations during the period of 1995-2012. We track the reconnection exhaust signatures like correlated and anticorrelated changes of the magnetic field and solar wind velocity and enhancements of the plasma temperature and density. In this study, we present the dependences of magnetic field and plasma parameters within the reconnection exhaust on the shear angle and on the exhaust thickness.

Enzl, Jakub; Nemecek, Zdenek; Safrankova, Jana; Prech, Lubomir

279

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

280

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

SciTech Connect

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

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

2008-07-08

281

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

282

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

283

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

284

Wind Resource Maps (Postcard)  

SciTech Connect

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

Not Available

2011-07-01

285

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

286

Wind power. [electricity generation  

NASA Technical Reports Server (NTRS)

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

Savino, J. M.

1975-01-01

287

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

E-print Network

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

Langendoen, Koen

288

the risk issue of wind measurement for wind turbine operation  

E-print Network

-related issues on wind turbine operation 3/31/2011 2 #12;WIND MEASUREMENT IN METEOROLOGY & WIND FARM DESIGN 3the risk issue of wind measurement for wind turbine operation Po-Hsiung Lin Dept. of Atmospheric Sciences, National Taiwan University #12;outline · Wind measurement in meteorology and wind farm design

Leu, Tzong-Shyng "Jeremy"

289

Spatio-Temporal Surface Shear-Stress Variability in Live Plant Canopies and Cube Arrays  

NASA Astrophysics Data System (ADS)

This study presents spatiotemporally-resolved measurements of surface shear-stress ? s in live plant canopies and rigid wooden cube arrays to identify the sheltering capability against sediment erosion of these different roughness elements. Live plants have highly irregular structures that can be extremely flexible and porous resulting in considerable changes to the drag and flow regimes relative to rigid imitations mainly used in other wind-tunnel studies. Mean velocity and kinematic Reynolds stress profiles show that well-developed natural boundary layers were generated above the 8 m long wind-tunnel test section covered with the roughness elements at four different roughness densities ( ? = 0, 0.017, 0.08, 0.18). Speed-up around the cubes caused higher peak surface shear stress than in experiments with plants at all roughness densities, demonstrating the more effective sheltering ability of the plants. The sheltered areas in the lee of the plants are significantly narrower with higher surface shear stress than those found in the lee of the cubes, and are dependent on the wind speed due to the plants ability to streamline with the flow. This streamlining behaviour results in a decreasing sheltering effect at increasing wind speeds and in lower net turbulence production than in experiments with cubes. Turbulence intensity distributions suggest a suppression of horseshoe vortices in the plant case. Comparison of the surface shear-stress measurements with sediment erosion patterns shows that the fraction of time a threshold skin friction velocity is exceeded can be used to assess erosion of, and deposition on, that surface.

Walter, Benjamin; Gromke, Christof; Leonard, Katherine C.; Manes, Costantino; Lehning, Michael

2012-05-01

290

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

Microsoft Academic Search

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

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

1983-01-01

291

Numerical modeling of the wind flow over a transverse dune  

E-print Network

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

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

2013-01-01

292

Numerical modeling of the wind flow over a transverse dune  

E-print Network

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

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

2013-07-26

293

Numerical modeling of the wind flow over a transverse dune.  

PubMed

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

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

2013-01-01

294

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

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

2013-01-01

295

Numerical modeling of the wind flow over a transverse dune  

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

296

Signatures of shear thinning-thickening transition in dense athermal shear flows  

E-print Network

In non-equilibrium molecular dynamics simulations of dense athermal shear flows, we observe the transition from shear thinning to shear thickening at a crossover shear rate $\\dot\\gamma_c$. Shear thickening occurs when $\\frac{{\\rm d (ln} T_g)}{{\\rm d (ln}\\dot\\gamma)}>2$ with $T_g$ the granular temperature. At the transition, the pair distribution function shows the strongest anisotropy. Meanwhile, the dynamics undergo apparent changes, signified by distinct scaling behaviors of the mean squared displacement and relaxation time on both sides of $\\dot\\gamma_c$. These features serve as robust signatures of the shear thinning-thickening transition.

Wen Zheng; Yu Shi; Ning Xu

2013-04-18

297

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

298

Shear Viscosity of Quark Matter  

E-print Network

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

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

2007-07-30

299

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

300

Generality of shear thickening in suspensions  

E-print Network

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

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

2010-02-05

301

Generality of shear thickening in dense suspensions  

NASA Astrophysics Data System (ADS)

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

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

2010-03-01

302

Measurements of shear characteristics of textile composites  

Microsoft Academic Search

The paper is devoted to experimental study of shear strength and shear modulus of three types of 3D textile composites based on different reinforcing fibres and matrices and made by various technologies, as well as 2D glass fibre\\/epoxy plastic (GFRP) with lay-up of (±45°). Correct measurement of shear properties of 3D textile composites is a complex problem due to the

Yu. M Tarnopol’skii; V. L Kulakov; A. K Aranautov

2000-01-01

303

Scale dependence of direct shear tests  

Microsoft Academic Search

Direct shear test has been widely used to measure the shear strength of soils and other particulate materials in industry\\u000a because of its simplicity. However, the results can be dependent on the specimen size. The ASTM (American Society for Testing\\u000a and Materials) publications suggest that for testing soils the shear box should be at least ten times the diameter of

Qiang Zhou; Hayley H. Shen; Brian T. Helenbrook; HongWu Zhang

2009-01-01

304

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

305

Dynamic shear deformation in high purity Fe  

SciTech Connect

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

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

2009-01-01

306

Method of Detecting Simple-shear  

NASA Astrophysics Data System (ADS)

We have derived a method of detecting simple-shear (MODES), which is characteristic of faults and shear zones, using three-dimensional displacements or velocities. In this poster, we present the theory of MODES and illustrate how it works by analyzing a set of displacements measured with the Global Positioning System in a quadrilateral of stations across the 1999 Chi-Chi earthquake ground rupture south of T'ai-chung City, Taiwan [Yu et al., 2001]. The results are illustrated by means of a three-dimensional diagram, the spherical hamburger, which is reminiscent of the seismologist's ``beach-ball.'' The basic assumption of MODES is that the components of a deformation tensor are continuous within a domain of the earth's surface containing survey stations where three components of displacement have been measured. There are no assumptions made about the styles of deformation or the orientation of shear zones and faults. Instead, these quantities are determined by MODES, which consists of three parts: (1) analysis of a deformation tensor to determine whether it contains simple shear and if so determine the orientation of the simple-shear zone in terms of coordinates where S is the direction, ST is the plane, and N is the normal to the plane of simple-shear, (2) calculation of the deformation tensor in the (S, N, T) coordinates, and (3) determination of the importance of the simple shear by comparison of the amount of simple-shear to the amount of pure-shear.

Griffiths, J. H.; Johnson, A. M.

2005-12-01

307

Optical Beam-Shear Sensors  

NASA Technical Reports Server (NTRS)

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

Martin, Stefan; Szwaykowski, Piotr

2007-01-01

308

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.

309

Design of a modified three-rail shear test for shear fatigue of composites  

Microsoft Academic Search

There are various ways of determining the static in-plane shear properties of a fibre-reinforced composite. One of them is the standard three-rail shear test, as described in “ASTM D 4255\\/D 4255M The standard test method for in-plane shear properties of polymer matrix composite materials by the rail shear method”. This setup, however, requires drilling holes through the specimen. In this

I. De Baere; W. Van Paepegem; J. Degrieck

2008-01-01

310

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

311

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

312

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

Federal Register 2010, 2011, 2012, 2013, 2014

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

2012-05-18

313

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

Federal Register 2010, 2011, 2012, 2013, 2014

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

2010-05-03

314

Mechanical characterization in shear of human femoral cancellous bone: torsion and shear tests  

Microsoft Academic Search

In order to investigate and compare the mechanical behaviour of human cancellous bone during different shear loading modes, two tests were performed to characterise human femoral cancellous bone in shear: a torsion test until failure and a shear test using a sharpened stainless steel tube. Paired cylindrical samples were core drilled from 12 human femoral heads, symmetrically with respect to

K. Bruyère Garnier; R. Dumas; C. Rumelhart; M. E. Arlot

1999-01-01

315

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

E-print Network

the shear environments that produced bubble textures in obsidian samples using the results of theoretical the shapes and orientations of bubbles (vesicles) in obsidian to estimate shear rates and shear stresses conduits, the origin of pyroclastic obsidian, and the emplacement history and dynamics of obsidian flows

Manga, Michael

316

A study of some effects of vertical shear on thunderstorms  

NASA Technical Reports Server (NTRS)

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

Connell, J.

1976-01-01

317

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

318

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

NASA Astrophysics Data System (ADS)

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

Zhang, Suping; Kong, Yang

2014-12-01

319

THE SHEARING H I SPIRAL PATTERN OF NGC 1365  

SciTech Connect

The Tremaine-Weinberg equations are solved for a pattern speed that is allowed to vary with radius. The solution method transforms an integral equation for the pattern speed to a least-squares problem with well-established procedures for statistical analysis. The method applied to the H I spiral pattern of the barred, grand-design galaxy NGC 1365 produces convincing evidence for a radial dependence in the pattern speed. The pattern speed behaves approximately as 1/r and is very similar to the material speed. There are no clear indications of corotation or Lindblad resonances. Tests show that the results are not selection biased, and that the method is not measuring the material speed. Other methods of solving the Tremaine-Weinberg equations for shearing patterns are found to produce results in agreement with those obtained using the current method. Previous estimates that relied on the assumptions of the density-wave interpretation of spiral structure are inconsistent with the results obtained using the current method. The results are consistent with spiral structure theories that allow for shearing patterns, and contradict fundamental assumptions in the density-wave interpretation that are often used for finding spiral arm pattern speeds. The spiral pattern is winding on a characteristic timescale of {approx}500 Myr.

Speights, Jason C.; Westpfahl, David J. [Physics Department, New Mexico Institute of Mining and Technology, Socorro, NM 87801 (United States)

2011-07-20

320

The response of sheared turbulence to additional distortion  

NASA Astrophysics Data System (ADS)

In unidirectional flows, the ratios of Reynolds shear stress to total intensity (except near positions of zero stress) remain remarkably constant from one flow to another, but curvature or strong divergence of the mean flow causes very considerable changes in the stress ratios. A scheme for calculating the changes is described, based on the rapid-distortion approximation of the equations of motion. The results depend to some extent on the effective history of distortion of the turbulence and on the magnitude of an eddy viscosity that models the effect of nonlinear transfer of energy to smaller eddies of the dissipation sequence, but the correspondence with measured values in a distorted wake and in a curved mixing layer is fairly good. In particular, the curious behavior of stress ratios in the curved mixing-layer can be reproduced qualitatively without any difficulty. Small perturbations of wall turbulence provide a simple application, and earlier calculations of the energy transfer between wind and water waves have been repeated including the changes in the stress ratios predicted by the scheme. In the latter case, very large changes in the distributions of pressure and shear stress are found, and the rates of energy transfer are much larger and in better agreement with observations

Townsend, A. A.

1980-05-01

321

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

322

Renaissance for wind power  

SciTech Connect

Wind research and development during the 1970s and recent studies showing wind to be a feasible source of both electrical and mechanical power are behind the rapid expansion of wind energy. Improved technology should make wind energy economical in most countries having sufficient wind and appropriate needs. A form of solar energy, winds form a large pattern of global air circulation because the earth's rotation causes differences in pressure and oceans cause differences in temperature. New development in the ancient art of windmill making date to the 1973 oil embargo, but wind availability must be determined at local sites to determine feasibility. Whether design features of the new technology and the concept of large wind farms will be incorporated in national energy policies will depend on changing attitudes, acceptance by utilities, and the speed with which new information is developed and disseminated. 44 references, 6 figures. (DCK)

Flavin, C.

1981-10-01

323

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

324

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

325

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

326

Animated Wind Capacity Map  

NSDL National Science Digital Library

This map shows how much electrical power is produced from wind in each state from 1999 through 2010. The animation shows a general increase in the amount of wind power produced per state and the number of states producing it.

National Renewable Energy Laboratory (NREL)

327

Shear stress in atherosclerotic plaque determination.  

PubMed

Atherosclerosis initiates at predictable focal sites near arterial branches and curves, where blood flow is disturbed and shear stress is complex. Endothelial shear stress is the tangential stress derived from the friction of the flowing blood on the endothelial surface of the arterial wall. It is a key factor in modulating endothelial cell gene expression and vascular development and remodeling. Increasing evidences suggest that shear stress patterns have a strong relationship with atherosclerotic features. Moreover, variations in the local artery geometry during atherogenesis further modify flow shear stress characteristics, which contribute to the rupture site at the plaque upstream. In this study, we summarize the mechanistic evidences that associate shear stress patterns with determined atherosclerotic plaque features. An enhanced understanding of the relationship and pathophysiological function of shear stress patterns in atherosclerotic plaque features is essential, which may provide early prediction of clinical risk and guide individualized treatment strategies. In the current review, we analyzed the function of shear stress on the determination of atherosclerotic lesion and provided an update on the mechanotransduction of shear stress, gene expression regulation, and atherosclerotic plaque development and rupture. PMID:25165867

Li, Xiaohong; Yang, Qin; Wang, Zuo; Wei, Dangheng

2014-12-01

328

Shear properties of a magnetorheological elastomer  

Microsoft Academic Search

This paper presents an experiment testing the damped free vibration of a system composed of a magnetorheological elastomer and a mass. The goal of this experiment was to obtain the dependence of the natural frequency and the damping ratio of the structure on the applied magnetic field. The shear properties, including the shear storage modulus and the damping factor, were

G Y Zhou

2003-01-01

329

In-situ Vane Shear Test  

NSDL National Science Digital Library

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

2008-09-24

330

Turbulence Modeling for Compressible Shear Flows  

E-print Network

.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2 Research description and contributions . . . . . . . . . . . . . . . . . 2 1.2.1 Pressure-strain correlation modeling for compressible shear flows 2 1.2.2 Algebraic Reynolds... stress model (ARSM) for compressible shear flows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.2.3 Second-moment computations of supersonic boundary layers . 4 1.3 Dissertation outline...

Gomez Elizondo, Carlos Arturo 1981-

2012-11-15

331

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

332

Multiple Shear Key Connections for Precast  

E-print Network

to the high quality control that is achieved at the man ufacturing plant, and the ease and speed of panel for elevator shaft shear wall panelsOne of the main concerns in precast 104 #12;utilize a combination elevator shaft shear wall panels. The tests results were used to develop analytical models to predict

333

Computation of Shear Viscosity: A Systems Approach  

E-print Network

Computation of Shear Viscosity: A Systems Approach Joshua L. Hurst and John T. Wen Dept such as viscosity, diffusivity, conductivity, etc., may be computed by using molecular level simulation. In this paper, we focus on the computation of shear viscosity of a fluid-like material. We take a systems

Wen, John Ting-Yung

334

Direct measurement of piezoelectric shear coefficient  

NASA Astrophysics Data System (ADS)

Piezoelectric materials exhibit electromechanical coupling which has led to their widespread application for sensors, actuators, and energy harvesters. These materials possess anisotropic behavior with the shear coefficient, and have the largest electromechanical coupling coefficient. However, the shear mode is difficult to measure with existing techniques and thus has not been fully capitalized upon in recent devices. Better understanding of the full shear response with respect to the driving electric field would significantly help the design of optimized piezoelectric shear devices. Here, a simple and low cost direct measurement method based on digital image correlation is developed to characterize the shear response of piezoelectric materials and its nonlinear behavior as a function of external field. The piezoelectric shear coefficient (d15) of a commercial shear plate actuator is investigated in both bipolar and unipolar electric fields. Two different nonlinearities and hysteresis behaviors of the actuators were observed, and the relation between the driving field amplitude and the corresponding d15 coefficient is determined. Moreover, the measured transverse displacement of the plate actuator in simple shear condition is validated through a laser interferometry technique.

Malakooti, Mohammad H.; Sodano, Henry A.

2013-06-01

335

Finite element modelling of fabric shear  

NASA Astrophysics Data System (ADS)

In this study, a finite element model to predict shear force versus shear angle for woven fabrics is developed. The model is based on the TexGen geometric modelling schema, developed at the University of Nottingham and orthotropic constitutive models for yarn behaviour, coupled with a unified displacement-difference periodic boundary condition. A major distinction from prior modelling of fabric shear is that the details of picture frame kinematics are included in the model, which allows the mechanisms of fabric shear to be represented more accurately. Meso- and micro-mechanisms of deformation are modelled to determine their contributions to energy dissipation during shear. The model is evaluated using results obtained for a glass fibre plain woven fabric, and the importance of boundary conditions in the analysis of deformation mechanisms is highlighted. The simulation results show that the simple rotation boundary condition is adequate for predicting shear force at large deformations, with most of the energy being dissipated at higher shear angles due to yarn compaction. For small deformations, a detailed kinematic analysis is needed, enabling the yarn shear and rotation deformation mechanisms to be modelled accurately.

Lin, Hua; Clifford, Mike J.; Long, Andrew C.; Sherburn, Martin

2009-01-01

336

Two Fluid Shear-Free Composites  

E-print Network

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

J. P. Krisch; E. N. Glass

2013-07-03

337

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

338

Vortex simulation of reacting shear flow  

Microsoft Academic Search

Issues involved in the vortex simulation of reacting shear flow are discussed. It is shown that maintaining accuracy in the vortex methods requires the application of elaborate vorticity-updating schemes as vortex elements are moved along particle trajectories when shear or a strong strain field is represented. Solutions using 2D and 3D methods are discussed to illustrate some of the most

Ahmed F. Ghoniem

1991-01-01

339

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

340

Wind powering America: Vermont  

SciTech Connect

Wind resources in the state of Vermont show great potential for wind energy development according to the wind resource assessment conducted by the state, its utilities, and NREL. This fact sheet provides a brief description of the resource assessment and a link to the resulting wind resource map produced by NREL. The fact sheet also provides a description of the state's net metering program, its financial incentives, and green power programs as well as a list of contacts for more information.

NREL

2000-04-11

341

The Effect of Wind-Turbine Wakes on Summertime US Midwest Atmospheric Wind Profiles as Observed with Ground-Based Doppler Lidar  

NASA Astrophysics Data System (ADS)

We examine the influence of a modern multi-megawatt wind turbine on wind and turbulence profiles three rotor diameters (D) downwind of the turbine. Light detection and ranging (lidar) wind-profile observations were collected during summer 2011 in an operating wind farm in central Iowa at 20-m vertical intervals from 40 to 220 m above the surface. After a calibration period during which two lidars were operated next to each other, one lidar was located approximately 2D directly south of a wind turbine; the other lidar was moved approximately 3D north of the same wind turbine. Data from the two lidars during southerly flow conditions enabled the simultaneous capture of inflow and wake conditions. The inflow wind and turbulence profiles exhibit strong variability with atmospheric stability: daytime profiles are well-mixed with little shear and strong turbulence, while nighttime profiles exhibit minimal turbulence and considerable shear across the rotor disk region and above. Consistent with the observations available from other studies and with wind-tunnel and large-eddy simulation studies, measurable reductions in wake wind-speeds occur at heights spanning the wind turbine rotor (43-117 m), and turbulent quantities increase in the wake. In generalizing these results as a function of inflow wind speed, we find the wind-speed deficit in the wake is largest at hub height or just above, and the maximum deficit occurs when wind speeds are below the rated speed for the turbine. Similarly, the maximum enhancement of turbulence kinetic energy and turbulence intensity occurs at hub height, although observations at the top of the rotor disk do not allow assessment of turbulence in that region. The wind shear below turbine hub height (quantified here with the power-law coefficient) is found to be a useful parameter to identify whether a downwind lidar observes turbine wake or free-flow conditions. These field observations provide data for validating turbine-wake models and wind-tunnel observations, and for guiding assessments of the impacts of wakes on surface turbulent fluxes or surface temperatures downwind of turbines.

Rhodes, Michael E.; Lundquist, Julie K.

2013-07-01

342

Shear flows and shear viscosity in a two-dimensional Yukawa system (dusty plasma).  

PubMed

The shear viscosity of a two-dimensional liquid-state dusty plasma was measured experimentally. A monolayer of highly charged polymer microspheres, with a Yukawa interaction, was suspended in a plasma sheath. Two counterpropagating Ar+ laser beams pushed the particles, causing shear-induced melting of the monolayer and a shear flow in a planar Couette configuration. By fitting the particle velocity profiles in the shear flow to a Navier-Stokes model, the kinematic viscosity was calculated; it was of order 1 mm(2) s(-1), depending on the monolayer's parameters and shear stress applied. PMID:15524893

Nosenko, V; Goree, J

2004-10-01

343

Shear viscosity of pion gas  

E-print Network

Using chiral perturbation theory we investigate the QCD shear viscosity ($\\eta $) to entropy density ($s$) ratio below the deconfinement temperature ($\\sim 170$ MeV) with zero baryon number density. It is found that $\\eta /s$ of QCD is monotonically decreasing in temperature ($T$) and reaches 0.6 with estimated $\\sim 50%$ uncertainty at T=120 MeV. A naive extrapolation of the leading order result shows that $\\eta /s$ reaches the $1/4\\pi $ minimum bound proposed by Kovtun, Son, and Starinets using string theory methods at $T\\sim 210$ MeV. This suggests a phase transition or cross over might occur at $T\\lesssim 210$ MeV in order for the bound to remain valid. Also, it is natural for $\\eta /s$ to stay close to the minimum bound around the phase transition temperature as was recently found in heavy ion collisions.

Eiji Nakano

2007-03-21

344

Guided Tour on Wind Energy  

NSDL National Science Digital Library

The Danish Wind Turbine Manufacturers Association provides the Guided Tour on Wind Energy site. This tour caters to both the expert and the novice of wind energy. Sections included at the site are Wind Energy Resources, Computing Wind Turbine Energy Output, How does a Wind Turbine Work?, Designing a Wind Turbine, Research and Development in Wind Energy, Wind Energy in the Electrical Grid, and Wind Energy and the Environment, among others. Each section offers detailed information as well as images and diagrams. This is a great resource for anyone interested in learning more about wind energy.

1999-01-01

345

On the onset of surface wind drift at short fetches as observed in a wind wave flume  

NASA Astrophysics Data System (ADS)

Ocean surface drift is of great relevance to properly model wind waves and specially the early stages of surface waves development and ocean-atmosphere fluxes during incipient wind events and storms. In particular, wave models are not so accurate predicting wave behaviour at short fetches, where wind drift onset might be very important. The onset of surface drift induced by wind and waves is being studied through detailed laboratory measurements in a large wind-wave flume. Wind stress over the water surface, waves and surface drift are measured in the 40m long wind-wave tank at IRPHE, Marseille. While momentum fluxes are estimated directly through the eddy correlation method in a station about the middle of the tank, they provide reference information to the corresponding surface drift onset recorded at rather short non-dimensional fetches. At each experimental run very low wind was on (about 1m/s) for a certain period and suddenly it was constantly accelerated to reach about 13 m/s (as well as 8 and 5 m/s during different runs) in about 15 sec to as long as 600 sec. The wind was kept constant at that high speed for 2 to 10 min, and then suddenly and constantly decelerate to 0. Surface drift values were up to 0.5 cm/s for the highest wind while very distinctive shear was detected in the upper 1.5 cm. Rather linear variation of surface drift was observed with depth. Evolution of the surface drift velocity is analysed and onset behaviour is addressed with particular emphasis in accelerated winds. This work represents a RugDiSMar Project (CONACYT 155793) contribution. The support from ANUIES-ECOS M09-U01 project, CONACYT-187112 Estancia Sabática, and Institute Carnot, is greatly acknowledged.

Ocampo-Torres, Francisco J.; Branger, Hubert; Osuna, Pedro; Robles, Lucia

2014-05-01

346

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

347

Colloidal gels under shear: Strain rate effects  

NASA Astrophysics Data System (ADS)

Attractive colloidal particles are trapped in metastable states such as colloidal gels at high attraction strengths and attractive glasses and high volume fractions. Under shear such states flow via a two step yielding process that relates to bond and cluster or cage breaking. We discuss the way the structural properties and related stress response are affected by the shear rate. At low rates colloidal gels yield during start-up shear essentially in a single step, exhibiting a single stress overshoot due to creation of compact flowing clusters. With increasing shear rate a second stress overshoot, linked with further cluster breaking up to individual particles, is becoming more pronounced. We further present the age dependence of the two step yielding and wall slip effects often taking place during rheological experiments of colloidal gels. The latter is related both with the shear rate dependent gel structure as well as the time evolution of the near wall structure.

Koumakis, N.; Ballesta, P.; Besseling, R.; Poon, W. C. K.; Brady, J. F.; Petekidis, G.

2013-02-01

348

Particle acceleration efficiencies in astrophysical shear flows  

E-print Network

The acceleration of energetic particles in astrophysical shear flows is analyzed. We show that in the presence of a non-relativistic gradual velocity shear, power law particle momentum distributions $f(p) \\propto p^{-(3+\\alpha)}$ may be generated, assuming a momentum-dependent scattering time $\\tau \\propto p^{\\alpha}$, with $\\alpha > 0$. We consider possible acceleration sites in astrophysical jets and study the conditions for efficient acceleration. It is shown, for example, that in the presence of a gradual shear flow and a gyro-dependent particle mean free path, synchrotron radiation losses no longer stop the acceleration once it has started to work efficiently. This suggests that shear acceleration may naturally account for a second, non-thermal population of energetic particles in addition to a shock-accelerated one. The possible relevance of shear acceleration is briefly discussed with reference to the relativistic jet in the quasar 3C 273.

F. M. Rieger; P. Duffy

2005-02-04

349

WEAK LENSING MASS RECONSTRUCTION: FLEXION VERSUS SHEAR  

SciTech Connect

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

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

2010-11-10

350

Shear layer excitation, experiment versus theory  

NASA Technical Reports Server (NTRS)

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

Bechert, D. W.; Stahl, B.

1984-01-01

351

Trapped Electron Precession Shear Induced Fluctuation Decorrelation  

SciTech Connect

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

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

2002-07-29

352

Three dimensional fabric evolution of sheared sand  

SciTech Connect

Granular particles undergo translation and rolling when they are sheared. This paper presents a three-dimensional (3D) experimental assessment of fabric evolution of sheared sand at the particle level. F-75 Ottawa sand specimen was tested under an axisymmetric triaxial loading condition. It measured 9.5 mm in diameter and 20 mm in height. The quantitative evaluation was conducted by analyzing 3D high-resolution x-ray synchrotron micro-tomography images of the specimen at eight axial strain levels. The analyses included visualization of particle translation and rotation, and quantification of fabric orientation as shearing continued. Representative individual particles were successfully tracked and visualized to assess the mode of interaction between them. This paper discusses fabric evolution and compares the evolution of particles within and outside the shear band as shearing continues. Changes in particle orientation distributions are presented using fabric histograms and fabric tensor.

Hasan, Alsidqi; Alshibli, Khalid (UWA)

2012-10-24

353

Large wind turbine generators  

NASA Technical Reports Server (NTRS)

The development associated with large wind turbine systems is briefly described. The scope of this activity includes the development of several large wind turbines ranging in size from 100 kW to several megawatt levels. A description of the wind turbine systems, their programmatic status and a summary of their potential costs is included.

Thomas, R. L.; Donovon, R. M.

1978-01-01

354

The winds of change  

Technology Transfer Automated Retrieval System (TEKTRAN)

Wind-based power generation has been growing steadily in the United States and around the world, and this growth will continue—and accelerate—in the future, as the following background statistics demonstrate. The U.S. wind industry installed 8,358 megawatts (MW) of new wind generating capacity in 20...

355

Offshore Wind Geoff Sharples  

E-print Network

Offshore Wind Geoff Sharples geoff@clearpathenergyllc.com #12;Frequently Unanswered Ques?ons · Why don't "they" build more offshore wind? · Why not make States Cape Wind PPA at 18 c/kWh #12;The cycle of non-innova?on Offshore

Kammen, Daniel M.

356

CONGRESSIONAL BRIEFING Offshore Wind  

E-print Network

CONGRESSIONAL BRIEFING Offshore Wind Lessons Learned from Europe: Reducing Costs and Creating Jobs Thursday, June 12, 2014 Capitol Visitors Center, Room SVC 215 Enough offshore wind capacity to power six the past decade. What has Europe learned that is applicable to a U.S. effort to deploy offshore wind off

Firestone, Jeremy

357

Power from the Wind  

ERIC Educational Resources Information Center

Wind energy is the fastest-growing renewable energy source in the world. Over the last 20 years, the wind industry has done a very good job of engineering machines, improving materials, and economies of production, and making this energy source a reality. Like all renewable energy forms, wind energy's successful application is site specific. Also,…

Roman, Harry T.

2004-01-01

358

Wind Economic Development (Postcard)  

SciTech Connect

The U.S. Department of Energy's Wind Powering America initiative provides information on the economic development benefits of wind energy. This postcard is a marketing piece that stakeholders can provide to interested parties; it will guide them to the economic development benefits section on the Wind Powering America website.

Not Available

2011-08-01

359

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

360

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

361

Wind energy systems  

Microsoft Academic Search

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

R. D. Richardson; GERALD M. MCNERNEY

1993-01-01

362

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

363

Wind tower turbine  

Microsoft Academic Search

A wind powered turbine drive for an electric generator is disclosed in which both the generator and the turbine driving it are stationary and remain in a fixed position irrespective of wind direction. This turbine facilitates electric power generation by wind power in those higher power ranges where the greater generator and turbine weights otherwise make it difficult and costly

OHare

1981-01-01

364

Wind electric plant  

Microsoft Academic Search

A multiblade, wind-driven, variable pitch propeller is used in a wind electric plant for the generation of electrical power from wind forces, and the propeller is rotatable in a plane at an angle to the tower axis, enabling larger propellers to be used without propeller-tower interference and also reducing the distance between the propeller and gear case. A snubber arrangement

M. L. Jacobs; P. R. Jacobs

1978-01-01

365

Wind Powering America  

NSDL National Science Digital Library

This visualization is a utility-scale, land-based, 80-meter wind map. It states, utilities, and wind energy developers use to locate and quantify the wind resource, identifying potentially windy sites within a fairly large region and determining a potential site's economic and technical viability.

Nrel; Truepower, Aws; Energy, U. S.

366

Hurricanes, Wind, and Water  

NSDL National Science Digital Library

In this activity, learners will analyze hurricane data, specifically wind speed data and infrared satellite images, to look for evidence of a relationship between wind speed and cloud-top temperature, and between wind speed and surface type. A link to the data is provided. This activity is part of Event-Based Science (EBS): Remote Sensing Activities.

367

Build a Wind Turbine  

NSDL National Science Digital Library

Learners build a wind turbine and test it to see how much energy is created. Learners can build a variety of wind blades, test a variety of wind speeds and see what effect these have on the energy created. Adult supervision recommended.

Museum Of Science And Industry, Chicago

2012-01-01

368

Physical nature of the low-speed solar wind  

Microsoft Academic Search

In situ observations indicate that the low-speed wind is highly variable. It commonly originates on open field lines that thread coronal streamers in the vicinity of the magnetic equator, but transient ejections are also a source of low-speed flows on occasion. Close to the Sun a large flow shear probably is common at the interface between low- and high-speed flows.

J. T. Gosling

1997-01-01

369

Physical nature of the low-speed solar wind  

Microsoft Academic Search

In situ observations indicate that the low-speed wind is highly variable. It commonly originates on open field lines that thread coronal streamers in the vicinity of the magnetic equator, but transient ejections are also a source of low-speed flows on occasion. Close to the Sun a large flow shear probably is common at the interface between low- and high-speed flows.

J. T. Gosling

1996-01-01

370

A hydrodynamical model of shear flow over semi-infinite barriers with application to density currents  

SciTech Connect

Vertically sheared airflow over semi-infinite barriers is investigated with a simple hydrodynamical model. The idealized flow is steady, two-dimensional, neutrally buoyant, and inviscid, bounded on the bottom by a semi-infinite impermeable barrier and on the top by a rigid tropopause lid. With attention further restricted to an exponentially decreasing wind shear, the equations of motion (Euler's equations) reduce, without approximation, to a modified Poisson equation for a pseudo streamfunction and a formula for the Exner function. The free parameters characterizing the model's environment are the tropopause height, the density scale height, the wind speed at ground level, and the wind speed at tropopause level. Additional parameters characterize the barrier geometry. Exact solutions of the equations of motion are obtained for semi-infinite plateau barriers and for a barrier qualitatively resembling the shallow density current associated with some thunderstorm outflows. These solutions are noteworthy in that the reduction of a certain nondimensional shear parameter (through negative values) results in greater vertical parcel displacements over the barrier despite a corresponding reduction in the vertical velocity. This steepening tendency culminates in overturning motions associated with both upstream and down-stream steering levels. In this latter case the low-level inflow impinging on the barrier participates in a mixed jump and overturning updraft reminiscent of updrafts simulated in numerical convective models. Conversely, for large values of the nondimensional shear parameter, parcels undergo small vertical parcel displacements over the barrier despite large vertical velocities. This latter behavior may account for the finding that strong convergence along the leading edge of storm outflows does not always trigger deep convection even in unstable environments.

Shapiro, A. (Univ. of Oklahoma, Norman (United States))

1992-12-01

371

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

372

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

373

Variance Anisotropy of Solar Wind fluctuations  

NASA Astrophysics Data System (ADS)

Solar wind observations at MHD scales indicate that the energy associated with velocity and magnetic field fluctuations transverse to the mean magnetic field is typically much larger than that associated with parallel fluctuations [eg, 1]. This is often referred to as variance anisotropy. Various explanations for it have been suggested, including that the fluctuations are predominantly shear Alfven waves [1] and that turbulent dynamics leads to such states [eg, 2]. Here we investigate the origin and strength of such variance anisotropies, using spectral method simulations of the compressible (polytropic) 3D MHD equations. We report on results from runs with initial conditions that are either (i) broadband turbulence or (ii) fluctuations polarized in the same sense as shear Alfven waves. The dependence of the variance anisotropy on the plasma beta and Mach number is examined [3], along with the timescale for any variance anisotropy to develop. Implications for solar wind fluctuations will be discussed. References: [1] Belcher, J. W. and Davis Jr., L. (1971), J. Geophys. Res., 76, 3534. [2] Matthaeus, W. H., Ghosh, S., Oughton, S. and Roberts, D. A. (1996), J. Geophys. Res., 101, 7619. [3] Smith, C. W., B. J. Vasquez and K. Hamilton (2006), J. Geophys. Res., 111, A09111.

Oughton, S.; Matthaeus, W. H.; Wan, M.; Osman, K.

2013-12-01

374

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

375

Analysis of in-flight winds for shuttle Mission STS 51-L  

NASA Technical Reports Server (NTRS)

Television photos of smoke plumes are analyzed to estimate meridional wind shear on the space shuttle Challenger associated with the accident of Mission 51-L. Gust velocities were obtained by detailed examination of the debris trails. The shuttle exhaust trail was used to establish altitudes of significant features in the photographs. Wind data obtained from the photographs compare favorably with data obtained from a rawinsonde released 9 min after the launch of the shuttle.

Fichtl, George H.; Reynolds, Nathaniel D.; Johnston, Alan E.; Adelfang, Stanley I.; Batts, Wade

1988-01-01

376

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

NASA Astrophysics Data System (ADS)

Television photos of smoke plumes an analyzed to estimate meridional wind shear on the space shuttle Challenger associated with the accident of Mission 51-L. Gust velocities were obtained by detailed examination of the debris trails. The shuttle exhaust trail was used to establish altitudes of significant features in the photographs. Wind data obtained from the photographs compare favorably with data obtained from a rawinsonde released 9 min after the launch of the shuttle.

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

1988-11-01

377

Characteristic modes and evolution processes of shear-layer vortices in an elevated transverse jet  

NASA Astrophysics Data System (ADS)

Characteristics and evolution processes of the traveling coherent flow structure in the shear layer of an elevated round jet in crossflow are studied experimentally in an open-loop wind tunnel. Streak pictures of the smoke flow patterns illuminated by the laser-light sheet in the median and horizontal planes are recorded with a high speed digital camera. Time histories of the instantaneous velocity of the vortical flows in the shear layer are digitized by a hot-wire anemometer through a high-speed data acquisition system. By analyzing the streak pictures of the smoke flow visualization, five characteristic flow structures, mixing-layer type vortices, backward-rolling vortices, forward-rolling vortices, swing-induced mushroom vortices, and jet-type vortices, are identified in the shear layer evolving from the up-wind edge of the jet exit. The behaviors and mechanisms of the vortical flow structure in the bent shear layer are prominently distinct in different flow regimes. The frequency characteristics, Strouhal number, power-spectrum density functions, autocorrelation coefficient, as well as the time and length scales of the coherent structure and the Lagrangian integral scales are obtained by processing the measured instantaneous velocity data. The Strouhal number is found to decay exponentially with the increase of the jet-to-crossflow momentum flux ratio. The autocorrelation coefficients provide the information for calculating the statistical time scales of the coherent structure and the integral time scales of turbulence fluctuations. The corresponding length scales of the vortical structure and the integral length scales of turbulence in the shear layer are therefore obtained and discussed.

Huang, Rong F.; Lan, Jen

2005-03-01

378

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

379

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

380

Wind energy applications guide  

SciTech Connect

The brochure is an introduction to various wind power applications for locations with underdeveloped transmission systems, from remote water pumping to village electrification. It includes an introductory section on wind energy, including wind power basics and system components and then provides examples of applications, including water pumping, stand-alone systems for home and business, systems for community centers, schools, and health clinics, and examples in the industrial area. There is also a page of contacts, plus two specific example applications for a wind-diesel system for a remote station in Antarctica and one on wind-diesel village electrification in Russia.

anon.

2001-01-01

381

Utilization of Wind Energy  

SciTech Connect

A wind energy device comprising a first airfoil having a leading edge, a trailing edge and a tip, means supporting the airfoil above a surface, the airfoil being adapted, when traversed by a prevailing wind, to generate a vortex at its tip, an air deflector associated with the airfoil and arranged so as to deflect prevailing wind traversing the deflector into the vortex to augment the energy of the vortex, means to vary the orientation of the airfoil relative to the prevailing wind, and a rotary device located in the path of the vortex and adapted to be driven by the wind in the vortex.

Archer, J. D.

1984-01-31

382

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

SciTech Connect

This document is primarily (1) a user's guide for the personal computer (PC) version of the code for the PNL computational model of the rotationally sampled wind speed (RODASIM11) and (2) a brief guide to the growing literature on the subject of rotationally sampled turbulence, from which the model is derived. The model generates values of turbulence experienced by single points fixed in the rotating frame of reference of an arbitrary wind turbine blade. The character of the turbulence depends on the specification of mean wind speed, the variance of turbulence, the crosswind and along-wind integral scales of turbulence, mean wind shear, and the hub height, radius, and angular speed of rotation of any point at which wind fluctuation is to be calculated. 13 refs., 4 figs., 4 tabs.

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

1989-08-01

383

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

384

Thermally driven winds  

SciTech Connect

This presentation will summarize the present state of knowledge on slope and valley wind systems, emphasizing physical concepts and recent gains in understanding from observational programs in various parts of the world. The presentation will begin with a discussion of terminology and a summary of the characteristics and relevant physics of slope and valley wind systems. The interrelationships between slope and valley wind systems will be covered as well as the cyclical development of the wind systems during the morning transition, daytime, evening transition, and nighttime periods. The discussion will focus on key physical factors including topography, temperature structure, surface energy budgets, atmospheric heat budgets, strength of overlying flows, etc. that produce variations in wind system behavior from one topographic and climatic setting to another. Deviant wind system behavior and winds associated with special topographic features will also be discussed.

Whiteman, C.D.

1993-04-01

385

Wind energy conversion system  

DOEpatents

The wind energy conversion system includes a wind machine having a propeller connected to a generator of electric power, the propeller rotating the generator in response to force of an incident wind. The generator converts the power of the wind to electric power for use by an electric load. Circuitry for varying the duty factor of the generator output power is connected between the generator and the load to thereby alter a loading of the generator and the propeller by the electric load. Wind speed is sensed electro-optically to provide data of wind speed upwind of the propeller, to thereby permit tip speed ratio circuitry to operate the power control circuitry and thereby optimize the tip speed ratio by varying the loading of the propeller. Accordingly, the efficiency of the wind energy conversion system is maximized.

Longrigg, Paul (Golden, CO)

1987-01-01

386

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

387

Surface shear inviscidity of soluble surfactants.  

PubMed

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 10(3)-10(4) 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

2014-03-11

388

Shear Thickening of Telechelic Ionomer Solutions  

NASA Astrophysics Data System (ADS)

Shear thickening behavior is observed in ionomers and certain block polymers in solution. Shear thickening behavior is characterized by an increase in viscosity at a critical shear rate, followed by a viscosity maximum and the usual shear thinning region. The exact structure in solution of the polymers which exhibit shear thickening is not known, but typically the polymers contain a block which aggregates into an insoluble domain. In the case of ionomers in non-polar solvents, the association strength to remove the insoluble block, or the ion pair from the aggregate is much greater than in block polymer solutions, resulting in the observation of substantially enhanced shear thickening behavior. There are several proposed mechanisms of shear thickening behavior yet only a few experimental studies exist. In this work, molecular weight, association strength and concentration have been varied and the start-up transients, steady state and stress relaxation upon flow cessation data have been collected. The data has been compared to predictions of several theories including (Witten-Cohen, Wang and Marrucci et.al.) The data is best described by the Free Path model of Marrucci et.al.

Bhargava, S.; Cooper, S. L.

1996-03-01

389

Large-Scale Cosmic Shear Measurements  

E-print Network

We present estimates of the gravitational lensing shear variance obtained from images taken at the CFHT using the UH8K CCD mosaic camera. Six fields were observed for a total of 1 hour each in V and I, resulting in catalogs containing approximately 20,000$ galaxies per field, with properly calibrated and optimally weighted shear estimates. These were averaged in cells of sizes ranging from 1'.875 to 30' to obtain estimates of the cosmic shear variance $$, with uncertainty estimated from the scatter among the estimates for the 6 fields. Our most reliable estimator for cosmic shear is provided by the cross-correlation of the shear measured in the two passbands. At scales $\\lsim 10'$ the results are in good agreement with those of van Waerbeke et al. 2000, Bacon et al. 2000 and Wittman et al. 2000 and with currently fashionable cosmological models. At larger scales the shear variance falls below the theoretical predictions, and on the largest scales we find a null detection of shear variance averaged in 30' cells of $ = (0.28 \\pm 1.84) \\times 10^{-5}$.

Nick Kaiser; Gillian Wilson; Gerard A. Luppino

2000-03-22

390

Asymmetric lithospheric instability facilitated by shear modulus contrast: implications for shear zones  

NASA Astrophysics Data System (ADS)

Viscoplasticity has been considered to be a dominant element in causing the nucleation of shear instability leading to lithospheric weakening. Here, we propose that a simple contrast in shear moduli may be sufficient for explaining the fast timescale asymmetric shear instability in a bimaterial setting. Not much attention has been paid to heterogeneous elasticity in geodynamical modelling because it is dominant only for short timescales. Up to now, no studies have been made on asymmetric shear instability induced by elastic modulus contrast. Thermal-mechanical numerical simulations based on high-resolution (from 0.4 km × 0.4 km to 0.2 km × 0.4 km meshes) finite-element methods were performed to understand the effects of shear modulus contrast on inducing asymmetric instabilities. Strain-rate and stress-dependent rheology are used with a wide range of activation energy 0-850 kJ mol-1 for all models. Numerical results with enough shear modulus contrast show asymmetric shear instability, which is generated around the interface and then propagates across the interface. Two parts of the lithosphere with different shear moduli (stiff for higher and soft for lower shear modulus lithospheres), which are simply connected to each other without a pre-defined weak zone, were compressed at a constant rate of 2 cm yr-1. Having different shear modulus is justified by chemical heterogeneity of geological minerals and their pressure-temperature dependence. To explore the dynamical effects generated by the contrast in the elastic modulus, the shear modulus of the soft lithosphere is fixed at 32 GPa, whereas that of stiff lithosphere is increased systematically from 32 up to 640 GPa. We also examined the role of activation energy (0-850 kJ mol-1) on the geometrical pattern and the initiation time of asymmetric shear localization. The shear modulus contrast has to be close to two for triggering asymmetric shear instability and is found to be by far a more important controlling factor in causing shear instability than activation energy of the creep law. The instability develops rapidly between 250 000 and 500 000 yr after deformation begins, and thermal weakening in the shear zone is greater, when a stronger shear modulus contrast is prescribed. Our work suggests that initiation of lithosphere-scale asymmetric instability would be faster than previous considerations. Our finding stresses that naturally occurring shear modulus contrast has also important impact on many geological problems related to bimaterial instability.

So, Byung-Dal; Yuen, David A.; Regenauer-Lieb, Klaus; Lee, Sang-Mook

2012-07-01

391

Wind-modulated buoyancy circulation over the Texas-Louisiana shelf  

NASA Astrophysics Data System (ADS)

numerical investigation examines buoyancy-driven circulation on the Texas-Louisiana shelf modulated by seasonal winds. In wintertime, with downcoast (in the direction of Kelvin wave propagation) wind forcing, the Mississippi-Atchafalaya River plume exhibits a bottom-advected pattern. The plume is fairly wide and the horizontal density gradients span almost across the entire shelf inshore of 50 m. Within the plume, vertical shear of alongshore flow is in thermal wind balance with the cross-shore density gradient, and the shear causes a slight reversal of alongshore flow near the bottom. An alongshore flow estimated by the thermal wind relation, along with an assumption of zero bottom velocity, generally well agrees with the actual flow near the surface in regions deeper than 20 m. In spring and summer, the thermal-wind-balance-derived flow deviates from the actual alongshore flow, and an Ekman flow driven by strong onshore wind makes the major contribution to the deviation. Besides, the summertime upcoast wind component transforms the plume to a surface-advected state, resulting in reduced cross-shore density gradients and increasing the relative importance of wind-driven, barotropic alongshore flow, which contributes to the remaining deviation.

Zhang, Zhaoru; Hetland, Robert; Zhang, Xiaoqian

2014-09-01

392

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

NASA Astrophysics Data System (ADS)

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

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

393

Optimization of Wind Turbine Airfoils/Blades and Wind Farm Layouts  

NASA Astrophysics Data System (ADS)

Shape optimization is widely used in the design of wind turbine blades. In this dissertation, a numerical optimization method called Genetic Algorithm (GA) is applied to address the shape optimization of wind turbine airfoils and blades. In recent years, the airfoil sections with blunt trailing edge (called flatback airfoils) have been proposed for the inboard regions of large wind-turbine blades because they provide several structural and aerodynamic performance advantages. The FX, DU and NACA 64 series airfoils are thick airfoils widely used for wind turbine blade application. They have several advantages in meeting the intrinsic requirements for wind turbines in terms of design point, off-design capabilities and structural properties. This research employ both single- and multi-objective genetic algorithms (SOGA and MOGA) for shape optimization of Flatback, FX, DU and NACA 64 series airfoils to achieve maximum lift and/or maximum lift to drag ratio. The commercially available software FLUENT is employed for calculation of the flow field using the Reynolds-Averaged Navier-Stokes (RANS) equations in conjunction with a two-equation Shear Stress Transport (SST) turbulence model and a three equation k-kl-o turbulence model. The optimization methodology is validated by an optimization study of subsonic and transonic airfoils (NACA0012 and RAE 2822 airfoils). In this dissertation, we employ DU 91-W2-250, FX 66-S196-V1, NACA 64421, and Flat-back series of airfoils (FB-3500-0050, FB-3500-0875, and FB-3500-1750) and compare their performance with S809 airfoil used in NREL Phase II and III wind turbines; the lift and drag coefficient data for these airfoils sections are available. The output power of the turbine is calculated using these airfoil section blades for a given B and lambda and is compared with the original NREL Phase II and Phase III turbines using S809 airfoil section. It is shown that by a suitable choice of airfoil section of HAWT blade, the power generated by the turbine can be significantly increased. Parametric studies are also conducted by varying the turbine diameter. In addition, a simplified dynamic inflow model is integrated into the BEM theory. It is shown that the improved BEM theory has superior performance in capturing the instantaneous behavior of wind turbines due to the existence of wind turbine wake or temporal variations in wind velocity. The dissertation also considers the Wind Farm layout optimization problem using a genetic algorithm. Both the Horizontal --Axis Wind Turbines (HAWT) and Vertical-Axis Wind Turbines (VAWT) are considered. The goal of the optimization problem is to optimally position the turbines within the wind farm such that the wake effects are minimized and the power production is maximized. The reasonably accurate modeling of the turbine wake is critical in determination of the optimal layout of the turbines and the power generated. For HAWT, two wake models are considered; both are found to give similar answers. For VAWT, a very simple wake model is employed. Finally, some preliminary investigation of shape optimization of 3D wind turbine blades at low Reynolds numbers is conducted. The optimization employs a 3D straight untapered wind turbine blade with cross section of NACA 0012 airfoils as the geometry of baseline blade. The optimization objective is to achieve maximum Cl/Cd as well as maximum Cl. The multi-objective genetic algorithm is employed together with the commercially available software FLUENT for calculation of the flow field using the Reynolds-Averaged Navier-Stokes (RANS) equations in conjunction with a one-equation Sparlart-Allmaras turbulence model. The results show excellent performance of the optimized wind turbine blade and indicate the feasibility of optimization on real wind turbine blades with more complex shapes in the future. (Abstract shortened by UMI.)

Chen, Xiaomin

394

On the Effect of Offshore Wind Parks on Ocean Dynamics  

NASA Astrophysics Data System (ADS)

Nowadays renewable energy resources play a key role in the energy supply discussion and especially an increasingly interest in wind energy induces intensified installations of wind parks. At this offshore wind energy gains in popularity in the course of higher and more consistent energy availability than over land. For example Germany's government adopted a national interurban offshore wind energy program comprising the construction of hundreds of wind turbines within Germany's Exclusive Economic Zone to ensure up to 50% of Germany's renewable energy supply. The large number of installation in coastal regions asks for analyzing the impact of offshore wind parks (OWPs) on the atmosphere and the ocean. As known from literature such wind parks excite also-called wake-effect and such an influence on the wind field in turn affects ocean circulation. To cover OWP's impact on ocean dynamics we evaluate model simulations using the Hamburg Shelf-Ocean-Model (HAMSOM). All simulations were driven with a wind forcing produced by the Mesoscale Atmosphere Model of the Hamburg University (METRAS) which has implemented wind turbines. Wind forcing data were generated in collaboration with and by courtesy of the Meteorological Institute of the University of Hamburg, Department Technical Meteorology, Numeric Modeling-METRAS. To evaluate dynamical changes forced by the OWP's wind wake-effect we did a sensitivity study with a theoretical setup of a virtual ocean of 60m depth with a flat bottom and a temperature and salinity stratification according to common North Sea's conditions. Here our results show that already a small OWP of 12 wind turbines, placed in an area of 4 km^2, lead to a complex change in ocean dynamics. Due to the wake-effect zones of upwelling and downwelling are formed within a minute after turning-on wind turbines. The evolving vertical cells have a size of around 15x15 kilometers with a vertical velocity in order of 10^-2 mm/sec influencing the dynamic of an area being hundred times bigger than the wind park itself. The emerged vertical structure is generated due to a newly created geostrophic balance resulting in a redistribution of the ocean mass field. A number of additional upwelling and downwelling cells around the wind park support an intensified vertical dispersion through all layers and incline the thermocline which also influences the lower levels. The disturbances of mass show a dipole structure across the main wind direction with a maximum change in thermocline depth of some meters close to the OWP. Diffusion, mostly driven by direct wind induced surface shear is also modified by the wind turbines and supports a further modification of the vertical patterns. Considering that wind turbines operate only in a special window of wind speed, i.e. wind turbines will stop in case of too weak or too strong wind speeds as well as in case of technical issues, the averaged dimension and intensity of occurring vertical cells depend on the number of rotors and expected wind speeds. Finally we will focus on scenario runs for the North Sea under fully realistic conditions to estimate possible changes in ocean dynamics due to OWPs in future and these results will be further used for process analyzes of the ecosystem. If we assume a continuous operation of North Sea's OWPs in future we expect a fundamental constant change in ocean dynamics and moreover in the ecosystem in its vicinity.

Ludewig, E.; Pohlmann, T.

2012-12-01

395

Shear instability in magnetized, collisional dusty plasmas  

SciTech Connect

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

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

2012-06-15

396

Topological Defects in Gravitational Lensing Shear Fields  

E-print Network

Shear fields due to weak gravitational lensing have characteristic coherent patterns. We describe the topological defects in shear fields in terms of the curvature of the surface described by the lensing potential. A simple interpretation of the characteristic defects is given in terms of the the umbilical points of the potential surface produced by ellipsoidal halos. We show simulated lensing shear maps and point out the typical defect configurations. Finally, we show how statistical properties such as the abundance of defects can be expressed in terms of the correlation function of the lensing potential.

Vitelli, Vincenzo; Kamien, Randall D

2009-01-01

397

Topological defects in gravitational lensing shear fields  

SciTech Connect

Shear fields due to weak gravitational lensing have characteristic coherent patterns. We describe the topological defects in shear fields in terms of the curvature of the surface described by the lensing potential. A simple interpretation of the characteristic defects is given in terms of the the umbilical points of the potential surface produced by ellipsoidal halos. We show simulated lensing shear maps and point out the typical defect configurations. Finally, we show how statistical properties such as the abundance of defects can be expressed in terms of the correlation function of the lensing potential.

Vitelli, Vincenzo [Instituut-Lorentz, Universiteit Leiden, Postbus 9506, 2300 RA Leiden (Netherlands); Jain, Bhuvnesh; Kamien, Randall D., E-mail: vitelli@lorentz.leidenuniv.nl, E-mail: bjain@physics.upenn.edu, E-mail: kamien@physics.upenn.edu [Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA 19104 (United States)

2009-09-01

398

Shear-Induced Birefringence in Critical Mixtures  

NASA Astrophysics Data System (ADS)

A large birefringence ?n has been discovered in the critical binary fluids nitrobenzene-n-hexane and isobutyric-acid-water submitted to a shear flow (rate S). In agreement with the Onuki and Kawasaki theory, two typical regions are in evidence: (i) strong shear, where ?n~S13 and is temperature independent; (ii) weak shear, where ?n~S and varies strongly with temperature. Moreover, this effect confirms the contribution of fluctuations to the critical anomaly of the refractive index in fluids at equilibrium, and could become a new tool for studying critical phenomena.

Beysens, D.; Gbadamassi, M.

1981-09-01

399

Shear free solutions in general relativity theory  

NASA Astrophysics Data System (ADS)

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

Ellis, George F. R.

2011-12-01

400

Shear Viscosity from Effective Couplings of Gravitons  

E-print Network

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 $F^4$ term corrections of Maxwell field and discuss the effect of $F^4$ terms on the ratio of the shear viscosity to entropy density.

Rong-Gen Cai; Zhang-Yu Nie; Ya-Wen Sun

2008-12-12

401

Peak Wind Tool for General Forecasting  

NASA Technical Reports Server (NTRS)

The expected peak wind speed of the day is an important forecast element in the 45th Weather Squadron's (45 WS) daily 24-Hour and Weekly Planning Forecasts. The forecasts are used for ground and space launch operations at the Kennedy Space Center (KSC) and Cape Canaveral Air Force Station (CCAFS). The 45 WS also issues wind advisories for KSC/CCAFS when they expect wind gusts to meet or exceed 25 kt, 35 kt and 50 kt thresholds at any level from the surface to 300 ft. The 45 WS forecasters have indicated peak wind speeds are challenging to forecast, particularly in the cool season months of October - April. In Phase I of this task, the Applied Meteorology Unit (AMU) developed a tool to help the 45 WS forecast non-convective winds at KSC/CCAFS for the 24-hour period of 0800 to 0800 local time. The tool was delivered as a Microsoft Excel graphical user interface (GUI). The GUI displayed the forecast of peak wind speed, 5-minute average wind speed at the time of the peak wind, timing of the peak wind and probability the peak speed would meet or exceed 25 kt, 35 kt and 50 kt. For the current task (Phase II ), the 45 WS requested additional observations be used for the creation of the forecast equations by expanding the period of record (POR). Additional parameters were evaluated as predictors, including wind speeds between 500 ft and 3000 ft, static stability classification, Bulk Richardson Number, mixing depth, vertical wind shear, temperature inversion strength and depth and wind direction. Using a verification data set, the AMU compared the performance of the Phase I and II prediction methods. Just as in Phase I, the tool was delivered as a Microsoft Excel GUI. The 45 WS requested the tool also be available in the Meteorological Interactive Data Display System (MIDDS). The AMU first expanded the POR by two years by adding tower observations, surface observations and CCAFS (XMR) soundings for the cool season months of March 2007 to April 2009. The POR was expanded again by six years, from October 1996 to April 2002, by interpolating 1000-ft sounding data to 100-ft increments. The Phase II developmental data set included observations for the cool season months of October 1996 to February 2007. The AMU calculated 68 candidate predictors from the XMR soundings, to include 19 stability parameters, 48 wind speed parameters and one wind shear parameter. Each day in the data set was stratified by synoptic weather pattern, low-level wind direction, precipitation and Richardson Number, for a total of 60 stratification methods. Linear regression equations, using the 68 predictors and 60 stratification methods, were created for the tool's three forecast parameters: the highest peak wind speed of the day (PWSD), 5-minute average speed at the same time (A WSD), and timing of the PWSD. For PWSD and A WSD, 30 Phase II methods were selected for evaluation in the verification data set. For timing of the PWSD, 12 Phase\\I methods were selected for evaluation. The verification data set contained observations for the cool season months of March 2007 to April 2009. The data set was used to compare the Phase I and II forecast methods to climatology, model forecast winds and wind advisories issued by the 45 WS. The model forecast winds were derived from the 0000 and 1200 UTC runs of the 12-km North American Mesoscale (MesoNAM) model. The forecast methods that performed the best in the verification data set were selected for the Phase II version of the tool. For PWSD and A WSD, linear regression equations based on MesoNAM forecasts performed significantly better than the Phase I and II methods. For timing of the PWSD, none of the methods performed significantly bener than climatology. The AMU then developed the Microsoft Excel and MIDDS GUls. The GUIs display the forecasts for PWSD, AWSD and the probability the PWSD will meet or exceed 25 kt, 35 kt and 50 kt. Since none of the prediction methods for timing of the PWSD performed significantly better thanlimatology, the tool no longer displays this predictand. The Excel and MIDDS GUIs display forecas

Barrett, Joe H., III

2010-01-01

402

Lateral shearing interferometer with variable shearing for measurement of a small beam.  

PubMed

A lateral shearing interferometer with variable shearing for measurement of a small beam is proposed. The interferometer is composed of a polarization beam splitter, a thick birefringent plate, a quarter-wave plate, a mirror, and an image sensor. The shearing amount can be tiny by using the thick birefringent plate as the shear generator. The shearing amount of the interferometer can be continuously adjusted by rotating the thick birefringent plate, and 2D interferograms can be obtained by rotating the thick birefringent plate along the mutually perpendicular directions. The optical path difference is compensated with a double lateral shearing by using a quarter-wave plate and a mirror. The interferometer is verified by simulation and experiment; the experiment result is well coincident with the simulation result. The usefulness of the interferometer is verified. PMID:24686657

Liu, Lei; Zeng, Aijun; Zhu, Linglin; Huang, Huijie

2014-04-01

403

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

404

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

405

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

406

Recent progress in shear punch testing  

SciTech Connect

The shear punch test was developed in response to the needs of the materials development community for small-scale mechanical properties tests. Such tests will be of great importance when a fusion neutron simulation device is built, since such a device is expected to have a limited irradiation volume. The shear punch test blanks a circular disk from a fixed sheet metal specimen, specifically a TEM disk. Load-displacement data generated during the test can be related to uniaxial tensile properties such as yield and ultimate strength. Shear punch and tensile tests were performed at room temperature on a number of unirradiated aluminum, copper, vanadium, and stainless steel alloys and on several irradiated aluminum alloys. Recent results discussed here suggest that the relationship between shear punch strength and tensile strength varies with alloy class, although the relationship determined for the unirradiated condition remains valid for the irradiated aluminum alloys.

Hamilton, M.L. [Pacific Northwest Lab., Richland, WA (United States); Toloczko, M.B.; Lucas, G.E. [Univ. of California, Santa Barbara, CA (United States)

1994-09-01

407

Electrostatic ion cyclotron velocity shear instability  

NASA Technical Reports Server (NTRS)

A local electrostatic dispersion equation is derived for a shear flow perpendicular to an ambient magnetic field, which includes all kinetic effects and involves only one important parameter. The dispersion equation is cast in the form of Gordeyev integrals and is solved numerically. Numerical solutions indicate that an ion cyclotron instability is excited. The instability occurs roughly at multiples of the ion cyclotron frequency (modified by the shear), with the growth rate or the individual harmonics overlapping in the wavenumber. At large values of the shear parameter, the instability is confined to long wavelengths, but at smaller shear, a second distinct branch at shorter wavelengths also appears. The properties of the instability obtained are compared with those obtained in the nonlocal limit by Ganguli et al. (1985, 1988).

Lemons, D. S.; Winske, D.; Gary, S. P.

1992-01-01

408

Scaling and intermittency in incoherent ?-shear dynamo  

NASA Astrophysics Data System (ADS)

We consider mean-field dynamo models with fluctuating ? effect, both with and without large-scale shear. The ? effect is chosen to be Gaussian white noise with zero mean and a given covariance. In the presence of shear, we show analytically that (in infinitely large domains) the mean-squared magnetic field shows exponential growth. The growth rate of the fastest growing mode is proportional to the shear rate. This result agrees with earlier numerical results of Yousef et al. and the recent analytical treatment by Heinemann, McWilliams & Schekochihin who use a method different from ours. In the absence of shear, an incoherent ?2 dynamo may also be possible. We further show by explicit calculation of the growth rate of third- and fourth-order moments of the magnetic field that the probability density function of the mean magnetic field generated by this dynamo is non-Gaussian.

Mitra, Dhrubaditya; Brandenburg, Axel

2012-03-01

409

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

410

Unavailability of wind turbines due to wind-induced accelerations  

Microsoft Academic Search

The malfunctioning of acceleration-sensitive equipment in wind turbines has the potential to affect their annual failure rates during normal operating conditions. Current protective measures for wind turbines are triggered by wind speed. However, this option neglects the structural response of the wind turbines, and limits the possibility of effectively controlling accelerations at the top of the wind towers. In this

Leonardo Dueñas-Osorio; Biswajit Basu

2008-01-01

411

Molecular orientation, “Region I” shear thinning and the cholesteric phase in aqueous hydroxypropylcellulose under shear  

Microsoft Academic Search

Birefringence and flow visualization are used to study molecular orientation, texture, and the cholesteric nature of a 60\\u000a wt% aqueous hydroxypropylcellulose solution at low to moderate shear rates. There is a sharp transition in behavior at a shear\\u000a rate near 0.5 s–1. Below this rate, the sample shows “Region I” shear thinning, takes on a frosted appearance, has low flow-induced

Kwan Hongladarom; Wesly R. Burghardt

1998-01-01

412

Periodic Viscous Shear Heating Instability in Fine-Grained Shear Zones: Mechanism for Intermediate Depth Earthquakes  

Microsoft Academic Search

Kelemen and Hirth (Fall 2004 AGU) presented a model for periodic, viscous shear heating instabilities along pre-existing, fine grained shear zones. This provides an attractive alternative to dehydration embrittlement for explaining intermediate-depth earthquakes, especially those in a narrow thermal window within the mantle section of subducting oceanic plates (Hacker et al JGR03). Ductile shear zones with widths of cm to

E. Coon; P. Kelemen; G. Hirth; M. Spiegelman

2005-01-01

413

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

414

Shear viscosity of degenerate electron matter  

E-print Network

We calculate the partial electron shear viscosity $\\eta_{ee}$ limited by electron-electron collisions in a strongly degenerate electron gas taking into account the Landau damping of transverse plasmons. The Landau damping strongly suppresses $\\eta_{ee}$ in the domain of ultrarelativistic degenerate electrons and modifies its %asymptotic temperature behavior. The efficiency of the electron shear viscosity in the cores of white dwarfs and envelopes of neutron stars is analyzed.

P. S. Shternin

2008-03-27

415

Thermodynamics of dilute gases in shear flow  

NASA Astrophysics Data System (ADS)

We consider the effect of shear and normal viscous pressures on the non-equilibrium entropy of ideal gases in Couette flow. These results extend the previous ones (Bidar et al., Physica A 233 (1996) 163), where normal pressure effects were ignored. Furthermore, we analyze the non-equilibrium contributions to the chemical potential, which may be useful in the analysis of shear-induced effects on colligative properties and chemical equilibrium.

Jou, D.; Criado-Sancho, M.

2001-03-01

416

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

417

Wind energy conversion system  

SciTech Connect

This patent describes a wind energy conversion system comprising: a propeller rotatable by force of wind; a generator of electricity mechanically coupled to the propeller for converting power of the wind to electric power for use by an electric load; means coupled between the generator and the electric load for varying the electric power drawn by the electric load to alter the electric loading of the generator; means for electro-optically sensing the speed of the wind at a location upwind from the propeller; and means coupled between the sensing means and the power varying means for operating the power varying means to adjust the electric load of the generator in accordance with a sensed value of wind speed to thereby obtain a desired ratio of wind speed to the speed of a tip of a blade of the propeller.

Longrigg, P.

1987-03-17

418

Session: Offshore wind  

SciTech Connect

This session at the Wind Energy and Birds/Bats workshop consisted of two presentations. Due to time constraints, a discussion period was not possible. The session addressed the current state of offshore wind energy development. The first presentation ''Monitoring Program and Results: Horns Rev and Nysted'' by Jette Gaarde summarized selected environmental studies conducted to date at operating offshore wind turbine projects in Denmark and lessons from other offshore wind developments in Europe. Wildlife impacts studies from the Danish sites focused on birds, fish, and mammals. The second presentation ''What has the U.S. Wind Industry Learned from the European Example'' by Bonnie Ram provided an update on current permit applications for offshore wind developments in the U.S. as well as lessons that may be drawn from the European experience.

Gaarde, Jette; Ram, Bonnie

2004-09-01

419

SERI Wind Energy Program  

SciTech Connect

The SERI Wind Energy Program manages the areas or innovative research, wind systems analysis, and environmental compatibility for the U.S. Department of Energy. Since 1978, SERI wind program staff have conducted in-house aerodynamic and engineering analyses of novel concepts for wind energy conversion and have managed over 20 subcontracts to determine technical feasibility; the most promising of these concepts is the passive blade cyclic pitch control project. In the area of systems analysis, the SERI program has analyzed the impact of intermittent generation on the reliability of electric utility systems using standard utility planning models. SERI has also conducted methodology assessments. Environmental issues related to television interference and acoustic noise from large wind turbines have been addressed. SERI has identified the causes, effects, and potential control of acoustic noise emissions from large wind turbines.

Noun, R. J.

1983-06-01

420

The shear-stress intensity factor for a centrally cracked stiff-flanged shear web  

NASA Technical Reports Server (NTRS)

By use of the principle of superposition the stiff-flanged shear web is modeled mathematically by an infinite elastic strip with fixed longitudinal edges. The shear-stress intensity factor for a central longitudinal crack is calculated for various values of the ratio of strip width to crack length, h/a, in the range 0.1-10. The interaction of the crack with the boundaries is illustrated by boundary shear-stress distributions for three values of h/a. Some implications of the results for the design of damage-tolerant shear webs are discussed briefly.

Fichter, W. B.

1976-01-01

421

Hemoglobin S polymerization and gelation under shear II. The joint concentration and shear dependence of kinetics.  

PubMed

The kinetics of hemoglobin S gelation are critical in sickle disease because microvascular obstruction can be avoided if red blood cells pass these vessels during the delay time, before polymerization and gelation occur in sufficient degree to rigidify the cells. Kinetics, including the delay time and the closely related exponential progress rate, are highly sensitive to hemoglobin concentration and degree of deoxygenation. Kinetics are also greatly accelerated by shear, an effect that may contribute to pathogenesis, since red blood cells deform and can undergo shear in vivo. Here we examine the joint dependence of kinetics on shear and hemoglobin concentration. As shear rate increases, the concentration dependence of the exponential progress rate decreases. The large decrease in concentration dependence supports the conclusion that acceleration of gelation by shear is due to breakage and not to enhancement of heterogeneous nucleation. Under shear, new fibers are created by breakage of existing ones, as well as by heterogeneous nucleation. At high shear, the rate of new fiber creation by breakage is very great and dominates that by heterogeneous nucleation. Therefore, if breakage depended only on shear rate and were independent of the concentration of hemoglobin in solution, the concentration dependence of kinetics should vanish. Although it decreases, it does not disappear. The concentration dependence that remains at high shear arises from (1) the direct contribution of fiber growth rate to the exponential progress rate, (2) the dependence of breakage rate on fiber growth rate, and (3) the dependence of solution viscosity on hemoglobin concentration. PMID:8241514

Samuel, R E; Guzman, A E; Briehl, R W

1993-12-01

422

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

423

Experimental assessment of air permeability in a concrete shear wall subjected to simulated seismic loading  

SciTech Connect

A safety concern for the proposed Special Nuclear Materials Laboratory (SNML) facility at the Los Alamos National Laboratory was air leakage from the facility if it were to experience a design basis earthquake event. To address this concern, a study was initiated to estimate air leakage, driven by wind-generated pressure gradients, from a seismically damaged concrete structure. This report describes a prototype experiment developed and performed to measure the air permeability in a reinforced concrete shear wall, both before and after simulated seismic loading. A shear wall test structure was fabricated with standard 4000-psi concrete mix. Static load-cycle testing was used to simulate earthquake loading. Permeability measurements were made by pressurizing one side of the shear wall above atmospheric conditions and recording the transient pressure decay. As long as the structure exhibited linear load displacement response, no variation in the air permeability was detected. However, experimental results indicate that the air permeability in the shear wall increased by a factor of 40 after the wall had been damaged (cracked). 17 figs., 8 tabs.

Girrens, S.P.; Farrar, C.R.

1991-07-01

424

Computational studies of horizontal axis wind turbines in high wind speed condition using advanced turbulence models  

NASA Astrophysics Data System (ADS)

Next generation horizontal-axis wind turbines (HAWTs) will operate at very high wind speeds. Existing engineering approaches for modeling the flow phenomena are based on blade element theory, and cannot adequately account for 3-D separated, unsteady flow effects. Therefore, researchers around the world are beginning to model these flows using first principles-based computational fluid dynamics (CFD) approaches. In this study, an existing first principles-based Navier-Stokes approach is being enhanced to model HAWTs at high wind speeds. The enhancements include improved grid topology, implicit time-marching algorithms, and advanced turbulence models. The advanced turbulence models include the Spalart-Allmaras one-equation model, k-epsilon, k-o and Shear Stress Transport (k-o-SST) models. These models are also integrated with detached eddy simulation (DES) models. Results are presented for a range of wind speeds, for a configuration termed National Renewable Energy Laboratory Phase VI rotor, tested at NASA Ames Research Center. Grid sensitivity studies are also presented. Additionally, effects of existing transition models on the predictions are assessed. Data presented include power/torque production, radial distribution of normal and tangential pressure forces, root bending moments, and surface pressure fields. Good agreement was obtained between the predictions and experiments for most of the conditions, particularly with the Spalart-Allmaras-DES model.

Benjanirat, Sarun

425

Wind profiles for large wind turbines  

NASA Astrophysics Data System (ADS)

The 12MW project aimed to describe wind profiles and turbulence at levels high in the atmosphere where large wind turbines operate. During the project observations up to 180 m above sea level were collected using mast and lidar offshore in the North Sea at the Horns Rev wind farm in 2006. Later also land-based observations were collected at the coastal station Høvsøre at the North Sea coast of Jutland, Denmark. The most recent observations include wind profiles up to 300 m above ground. In addition, ceilometers observations were collected. Based on the observations results have been obtained and published. Some of the interesting findings are that the atmospheric planetary boundary layer (PBL) often is rather shallow, and as the logarithmic wind profile is only valid in the lower 10% of the PBL, other scaling parameters than roughness is needed. It has been shown that the height of the PBL is an important scaling parameter. Other results include variations in the wind profile as a function of stability, and in particular, for stable stratification the results deviate much from the simple profile equation. The observations and the new profile equations and the results will be presented. Part of the work in the 12MW project has been to compare mast observations to lidar observations, and the results are good indeed. This has given a basis to merge the observations into profiles using mast data at the lower levels and lidar data at the higher levels, thus extending the wind profiles up to high levels in the atmosphere.

Hasager, C. B.; Peña, A.; Gryning, S.-E.; Mikkelsen, T.; Courtney, M.

2009-04-01

426

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

427

Evolution of shear zones in granular materials.  

PubMed

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. PMID:25314435

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

2014-09-01

428

Analysis of shear banding in twelve materials  

NASA Astrophysics Data System (ADS)

The problem of the initiation and growth of shear bands in 12 different materials, namely, OFHC copper, Cartridge brass, Nickel 200, Armco IF (interstitial free) iron, Carpenter electric iron, 1006 steel, 2024-T351 aluminum, 7039 aluminum, low alloy steel, S-7 tool steel, Tungsten alloy, and Depleted Uranium (DU -0.75 Ti) is studied with the objectives of finding out when a shear band initiates, and upon what parameters does the band width depend. The nonlinear coupled partial differential equations governing the overall simple shearing deformations of a thermally softening viscoplastic block are analyzed. It is assumed that the thermomechanical response of these materials can be adequately represented by the Johnson-Cook law, and the only inhomogeneity present in the block is the variation in its thickness. The effect of the defect size on the initiation and subsequent growth of the band is also studied. It is found that, for each one of these 12 materials, the deformation has become nonhomogeneous by the time the maximum shear stress occurs. Also the band width, computed when the shear stress has dropped to 85 percent of its peak value, does not correlate well with the thermal conductivity of the material. The band begins to grow rapidly when the shear stress has dropped to 90 percent of its maximum value.

Batra, R. C.; Kim, C. H.

429

Shear banding in soft glassy materials  

E-print Network

Many soft materials, including foams, dense emulsions, micro gel bead suspensions, star polymers, dense packing of surfactant onion micelles, and textured morphologies of liquid crystals, share the basic "glassy" features of structural disorder and metastability. These in turn give rise to several notable features in the low frequency shear rheology (deformation and flow properties) of these materials: in particular, the existence of a yield stress below which the material behaves like a solid, and above which it flows like a liquid. In the last decade, intense experimental activity has also revealed that these materials often display a phenomenon known as shear banding, in which the flow profile across the shear cell exhibits macroscopic bands of different viscosity. Two distinct classes of yield stress fluid have been identified: those in which the shear bands apparently persist permanently (for as long as the flow remains applied), and those in which banding arises only transiently during a process in which a steady flowing state is established out of an initial rest state (for example, in a shear startup or step stress experiment). After surveying the motivating experimental data, we describe recent progress in addressing it theoretically, using the soft glassy rheology model and a simple fluidity model. We also briefly place these theoretical approaches in the context of others in the literature, including elasto-plastic models, shear transformation zone theories, and molecular dynamics simulations. We discuss finally some challenges that remain open to theory and experiment alike.

Suzanne M. Fielding

2014-08-20

430

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

2014-08-07

431

Accurate shear measurement with faint sources  

NASA Astrophysics Data System (ADS)

For cosmic shear to become an accurate cosmological probe, systematic errors in the shear measurement method must be unambiguously identified and corrected for. Previous work of this series has demonstrated that cosmic shears can be measured accurately in Fourier space in the presence of background noise and finite pixel size, without assumptions on the morphologies of galaxy and PSF. The remaining major source of error is source Poisson noise, due to the finiteness of source photon number. This problem is particularly important for faint galaxies in space-based weak lensing measurements, and for ground-based images of short exposure times. In this work, we propose a simple and rigorous way of removing the shear bias from the source Poisson noise. Our noise treatment can be generalized for images made of multiple exposures through MultiDrizzle. This is demonstrated with the SDSS and COSMOS/ACS data. With a large ensemble of mock galaxy images of unrestricted morphologies, we show that our shear measurement method can achieve sub-percent level accuracy even for images of signal-to-noise ratio less than 5 in general, making it the most promising technique for cosmic shear measurement in the ongoing and upcoming large scale galaxy surveys.

Zhang, Jun; Luo, Wentao; Foucaud, Sebastien

2015-01-01

432

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

433

Continuous failure state direct shear tests  

NASA Astrophysics Data System (ADS)

The paper deals with a new testing procedure aimed at determining the failure envelopes for peak and residual strength in direct shear tests. In a “continuous failure state” direct shear test the specimen is maintained in a state of permanent sliding while the shear and normal stress are being steadily changed. First of all, the specimen is brought to a state of failure in the conventional manner at a chosen constant normal stress. Then under monotonously increasing shear displacement the normal stress is continuously adjusted so that a straight line is produced in the shear stress-displacement plane. Both an increase in the stresses and a decrease is possible. The proper selection of the inclination of the straight line may involve a stress path which corresponds closely to the failure envelope of the specimen. In the case of smooth joint surfaces or in the residual strength state of rough surfaces it is possible to determine exactly the failure envelope with the aid of a single test specimen. The paper also describes a newly developed shear test apparatus suitable for combination with sophisticated servo-controlled loading machines generally available in rock mechanics laboratories.

Tisa, A.; Kovári, K.

1984-04-01

434

The Solar Wind  

NSDL National Science Digital Library

This site describes the nature of the solar winds and the relationships between its speed and solar features. The effect of the variations in the speed of the solar wind on the magnetosphere of the Earth is also discussed, along with the research results of the Ulysses spacecraft and the Advanced Composition Explorer (ACE) satellite. The site also provides links to solar wind conditions for the last seven days and the last 24 hours.

Hathaway, David

435

The Santa Ana Winds  

NSDL National Science Digital Library

This page demonstrates the development of a Santa Ana wind event in the Los Angeles basin. It includes a brief description of these, hot, dry offshore winds, some legends surrounding them, and some of their potentially damaging effects. A series of images shows how a simulated Santa Ana event develops and evolves, depicting temperature, wind speed, and humidity. The images are also available as animations, and there are links to other sites with related information.

Fovell, Robert G., 1958-

2010-10-27

436

Small Wind Task Analysis  

NSDL National Science Digital Library

The Advanced Technology Environmental and Energy Center (ATEEC) has compiled this document which lists objectives and task analysis for small wind energy system installers. The document is divided into areas including of competencies such as conducting a wind energy site assessment, working safely with small wind energy systems and performing system checkouts and inspection. Users must download this resource for viewing, which requires a free log-in. There is no cost to download the item.

437

Rocket Wind Tunnel  

NSDL National Science Digital Library

In this activity, learners evaluate the potential performance of air rockets placed inside a wind tunnel. Learners measure the rocket's resistance to the flow of air in the tunnel and use the data to construct better rockets. The wind tunnel is prepared by the educator before the activity, but can be built by learners with adult supervision. This lesson plan includes instructions on how to build and use a wind tunnel, extensions, and sample data sheets.

Nasa

2012-05-15

438

Community Wind Project  

NSDL National Science Digital Library

In this thought-provoking activity, learners plan a hypothetical project to build and operate wind turbines in their community. Learners research such topics as available wind source, cost, noise, environmental impact, and local electric power needs, and incorporate their research into their plans. Learners also role play a town hall meeting about the wind project, portraying such community members as an environmental activist, a state legislator, a real estate developer, etc.

Illinois, University O.

2009-01-01

439

The Wind Business  

NSDL National Science Digital Library

It can take years to plan and engineer a state-of-the-art wind farm. It is a problem-solving process that draws on an understanding of algebra, geometry, kinetic energy, electronics and just about everything in between in order to turn one of our most abundant natural resources into a viable business. This 6-minute video covers several aspects, from the construction and siting, wind analysis, and merging of wind farms with agricultural land use.

Channel, The F.

440

On the interface friction in direct shear test  

Microsoft Academic Search

Distinct element simulations for the direct shear box tests on a dense and a loose 2D sample of a mixture of binary diameter cylinders were performed. Special attention is focused on the friction between the internal surface of the shear box and the sample. In the conventional direct shear test, where the up\\/downward movement of the upper shear box is

S. H. Liu; De’an Sun; Hajime Matsuoka

2005-01-01

441

Shear induced orientation of edible fat and chocolate crystals  

Microsoft Academic Search

Shear-induced orientation of fat crystallites was observed during crystallization of cocoa butter, milk fat, stripped milk fat and palm oil. This universal effect was observed in systems crystallized under high shear. The minor polar components naturally present in milk fat were found to decrease the shear-induced orientation effect in this system. The competition between Brownian and shear forces, described by

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

2003-01-01

442

Laboratory measurement of bottom shear stress on a movable bed  

Microsoft Academic Search

A shear plate was developed to obtain direct measurements of bottom shear stress under nonbreaking surface gravity waves on a movable sand bed. The experiments were conducted under regular wave conditions in a large wave tank where time histories of bottom shear stress and surface elevation were obtained from a shear plate and wave gauges. Measurements were made at scales

Kelly L. Rankin; Richard I. Hires

2000-01-01

443

Microwave propagation in a plasma with a sheared magnetic field  

Microsoft Academic Search

The propagation of a plane electromagnetic wave through a Lorentz plasma in a sheared magnetic field is considered. The characteristic waves in a uniformly sheared, but otherwise homogeneous, medium are found, and their properties presented graphically. Some effects introduced by the presence of shear are investigated by means of elementary applications of the uniform-shear theory. By suggested extensions of the

M A Heald

1964-01-01

444

Shearing of frictional sphere packings J-F. Metayer1  

E-print Network

measure shear response in packings of glass beads by pulling a thin, rough, metal plate vertically through response to shear stress. We examine here the response to shear of beds of glass beads of diameter 200 µm of the bed to shear by pulling a thin, rough, metal plate embedded in the material. We find a transition

Texas at Austin. University of

445

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

446

Residential Wind Power  

E-print Network

renewableenergyworld.com. The AWEA has a lot of useful information on alternative energy sources. The AWEA produces many case studies in which there is abundant wind power to incorporate as a source to the US power grid. It is a conclusion of the AWEA that wind... manufacturers addressing residential wind power. One product that is very prevalent, and a pioneer within the industry, is SkyStream 3.7 produced by Southwest Wind Power. (skystream.com, 2011) This product can range in price based on installation and size...

Willis, Gary

2011-12-16

447

Dissipation in Pulsar Winds  

E-print Network

I review the constraints placed on relativistic pulsar winds by comparing optical and X-ray images of the inner Crab Nebula on the one hand with two-dimensional MHD simulations on the other. The various proposals in the literature for achieving the low magnetisation required at the inner edge of the Nebula, are then discussed, emphasising that of dissipation in the striped-wind picture. The possibility of direct observation of the wind is examined. Based on the predicted orientation of the polarisation vector, I outline a new argument suggesting that the off-pulse component of the optical emission of the Crab pulsar originates in the wind.

J. G. Kirk

2005-04-19

448

Vertical axis wind turbines  

DOEpatents

A vertical axis wind turbine is described. The wind turbine can include a top ring, a middle ring and a lower ring, wherein a plurality of vertical airfoils are disposed between the rings. For example, three vertical airfoils can be attached between the upper ring and the middle ring. In addition, three more vertical airfoils can be attached between the lower ring and the middle ring. When wind contacts the vertically arranged airfoils the rings begin to spin. By connecting the rings to a center pole which spins an alternator, electricity can be generated from wind.

Krivcov, Vladimir (Miass, RU); Krivospitski, Vladimir (Miass, RU); Maksimov, Vasili (Miass, RU); Halstead, Richard (Rohnert Park, CA); Grahov, Jurij (Miass, RU)

2011-03-08

449

Wind Engineering & Natural Disaster Mitigation  

E-print Network

Wind Engineering & Natural Disaster Mitigation For more than 45 years, Western University has been internationally recognized as the leading university for wind engineering and wind- related research. Its of environmental disaster mitigation, with specific strengths in wind and earthquake research. Boundary Layer Wind

Denham, Graham

450

Wind Energy and Spatial Technology  

E-print Network

2/3/2011 1 Wind Energy and Spatial Technology Lori Pelech Why Wind Energy? A clean, renewable 2,600 tons of carbon emissions annually ­ The economy · Approximately 85,000 wind energy workers to Construct a Wind Farm... Geo-Spatial Components of Wind Farm Development Process Selecting a Project Site

Schweik, Charles M.

451

Dynamic Analysis of Wind Generators  

Microsoft Academic Search

Wind power does not make any pollution and it also create a recyclable energy. The wind blade speeds significantly affect the measured output power. It is necessary to keep the wind blade tip speed to obtain maximum power. The wind blade speeds significantly affect the energy losses and the power coefficients. It is required to keep the wind blade tip

Ming-Hung Hsu

2007-01-01

452

Preliminary Assumptions for Wind Technologies  

E-print Network

installed wind capacity is in BPA balancing authority ~2,000 MW new wind installed in 2012; not much Wind Task 26: The Past and Future Cost of Wind Energy" (May 2012) Significant growth of rotor diameterm rotors Increasing capacity factors Allows development of suboptimal wind sites Increased

453

Module Handbook Specialisation Wind Energy  

E-print Network

Module Handbook Specialisation Wind Energy 2nd Semester for the Master Programme REMA/EUREC Course 2008/2009 NTU Athens Specialisation Provider: Wind Energy #12;Specialisation Wind Energy, NTU Athens, 2nd Semester Module 1/Wind Energy: Wind potential, Aerodynamics & Loading

Habel, Annegret

454

Wind energy potential in Turkey  

Microsoft Academic Search

Lewis's methods are employed to evaluate the wind energy potentials of four selected locations, which have experienced relatively high wind velocities. In addition to Lewis's methods, the relations connecting the instantaneous and average wind powers, total and maximum wind energies for a given period of time are derived. Characteristics of wind energy, including rotor radius and tower height, are estimated

H. Külünk

1993-01-01

455

Where Does the Wind Blow?  

NSDL National Science Digital Library

In this activity, learners investigate wind by comparing the force of wind in different locations. Learners build wind-o-meters out of wooden sticks and strips of paper. Then, learners predict how the wind-o-meters will respond to wind in various locations outside (i.e. high vs. low elevation).

Museum, Kohl C.

2012-01-01

456

DISPERSAL OF PROTOPLANETARY DISKS BY CENTRAL WIND STRIPPING  

SciTech Connect

We present a model for the dispersal of protoplanetary disks by winds from either the central star or the inner disk. These winds obliquely strike the flaring disk surface and strip away disk material by entraining it in an outward radial-moving flow at the wind-disk interface, which lies several disk scale heights above the midplane. The disk dispersal time depends on the entrainment velocity, v{sub d} = {epsilon}c{sub s} , at which disk material flows into this turbulent shear layer interface, where {epsilon} is a scale factor and c{sub s} is the local sound speed in the disk surface just below the entrainment layer. If {epsilon} {approx} 0.1, a likely upper limit, the dispersal time at 1 AU is {approx}6 Myr for a disk with a surface density of 10{sup 3} g cm{sup -2}, a solar mass central star, and a wind with an outflow rate M-dot{sub w}=10{sup -8}M{sub odot}yr{sup -1} and terminal velocity v{sub w} = 200kms{sup -1}. When compared with photoevaporation and viscous evolution, wind stripping can be a dominant mechanism only for the combination of low accretion rates ({approx}<10{sup -8} M{sub sun} yr{sup -1}) and wind outflow rates approaching these accretion rates. This case is unusual since generally outflow rates are {approx}<0.1 of accretion rates.

Matsuyama, I. [Department of Earth and Planetary Science, University of California, Berkeley, 307 McCone Hall, Berkeley, CA 94720 (United States); Johnstone, D. [National Research Council of Canada, Herzberg Institute of Astrophysics, 5071 West Saanich Road, Victoria, BC V9E 2E7 (Canada); Hollenbach, D. [SETI Institute, 515 N. Whisman Road, Mountain View, CA 94043 (United States)], E-mail: isa@berkeley.edu

2009-07-20

457

The Martian slope winds and the nocturnal PBL jet  

NASA Astrophysics Data System (ADS)

The summertime Martian PBL diurnal wind variation, slope winds, and the nocturnal low-level jets were studied using Prandtl's theory, a mesoscale numerical model, and Viking lander observations. During moderate prevailing large-scale flow, nocturnal jets were simulated that were rather similar to those on Earth. They were mainly caused by inertial oscillation after sunset with some contribution from the slope wind effects over sloping regions (which are very common in Mars). During weak large-scale flow, shallow nocturnal drainage flows with strong vertical shear developed over the cold Martian slopes. At middle and high latitudes, these katabatic winds tended to turn to flow along the slope by dawn (due to the Coriolis force). For sufficiently steep slopes, near-surface drainage winds could reach considerable speeds. In contrast, the typical afternoon upslope winds were vertically homogeneous up to 2-3 km and weak (only 1-3 m/s in magnitude), even over relatively steep large-scale slopes.

Savijarvi, H.; Siili, T.

1993-01-01

458

The portrayal of the Australian monsoon equatorial monsoon shear line by GCMs: enhanced greenhouse scenario implications  

NASA Astrophysics Data System (ADS)

A critical test of a general circulation model is its performance on the regional scale. In this paper we examine the summer climatology of the CSIRO4 (4-layer) climate model over the Australian tropical region. The benchmark for the study is the positioning of the monsoon equatorial trough. We compare the CSIRO4 model climatology with the climatologies from the GFDL and GISS models and we report on the sensitivity of the position of the monsoon shear line and the strength of the monsoon westerly winds to the doubling of carbon dioxide in the atmosphere. The model results show that under the greenhouse scenario the monsoon is strengthened, but the average location of the monsoon shear line is not sensitive to the doubling of CO2.

Ryan, Bf; Jones, Da; Gordon, Hb

1992-06-01

459

Shear Layer Refraction Corrections for Off-Axis Sources in a Jet Flow  

NASA Astrophysics Data System (ADS)

A set of equations is derived for converting acoustic measurements taken in a free-jet flight simulation facility, such as the U.K. Noise Test Facility at Pyestock or the French CEPRA-19 wind tunnel at Saclay, to equivalent farfield flight conditions. The equations are based on the high-frequency geometrical acoustics approximation, whose application in the present context was justified in early studies by Morfey and Tester in 1977 and by Amiet in 1978. However, the present work differs by allowing the source to be positioned off the jet centreline, anywhere within the flight stream. The flight stream jet is modelled as an axisymmetric parallel shear flow, with a shear layer thickness which is small compared with the jet diameter. The model also permits the microphone to be located anywhere outside the flow, arbitrarily close to the open jet. The consequences of off-axis source location are illustrated by numerical calculations.

MORFEY, C. L.; JOSEPH, P. F.

2001-01-01

460

Shear-enhanced compaction in viscoplastic rocks  

NASA Astrophysics Data System (ADS)

The phenomenon of mutual influence of compaction and shear deformation was repeatedly reported in the literature over the past years. Dilatancy and shear-enhanced compaction of porous rocks were experimentally observed during both rate-independent and rate-dependent inelastic deformation. Plastic pore collapse was preceding the onset of dilatancy and shear-enhanced compaction. Effective bulk viscosity is commonly used to describe compaction driven fluid flow in porous rocks. Experimental data suggest that bulk viscosity of a fluid saturated rock might be a function of both the effective pressure and the shear stress. Dilatancy and shear-enhanced compaction can alter the transport properties of rocks through their influence on permeability and compaction length scale. Recent investigations show that shear stresses in deep mantle rocks can be responsible for spontaneous development of localized melt-rich bands and segregation of small amounts of melt from the solid rock matrix through shear channeling instability. Usually it is assumed that effective viscosity is a function of porosity only. Thus coupling between compaction and shear deformation is ignored. Spherical model which considers a hollow sphere subjected to homogeneous tractions on the outer boundary as a representative elementary volume succeeded in predicting the volumetric compaction behavior of porous rocks and metals to a hydrostatic pressure in a wide range of porosities. Following the success of this simple model we propose a cylindrical model of void compaction and decompaction due to the non-hydrostatic load. The infinite viscoplastic layer with a cylindrical hole is considered as a representative volume element. The remote boundary of the volume is subjected to a homogeneous non-hydrostatic load such that plane strain conditions are fulfilled through the volume. At some critical values of remote stresses plastic zone develops around the hole. The dependence of the effective bulk viscosity on the properties of individual components as well as on the stress state is examined. We show that bulk viscosity is a function of porosity, effective pressure and shear stress. Decreasing porosity tends to increase bulk viscosity whereas increasing shear stress and increasing effective pressure reduce it.

Yarushina, V. M.; Podladchikov, Y. Y.

2012-04-01

461

Thermospheric neutral wind measurement by three rocket-released Lithium clouds: WIND campaign  

NASA Astrophysics Data System (ADS)

During a Japanese sounding rocket experiment called "WIND" campaign, the S-520-23 rocket was launched from Uchinoura, Japan (131.08° E, 31.25° N) at 19:20 LT on Sep. 2, 2007, in order to investigate interaction between neutral and plasma atmosphere in midlatitude thermosphere. Main purpose of the campaign is to establish a new technology of chemical release in wide altitude range of the thermosphere. Scientific target of the WIND campaign is to measure neutral wind in evening condition of generating MSTID (Medium-Scale Travelling Ionospheric Disturbances). Three Lithium releases were successfully carried out at 230 km, 193 km, and 144 km altitudes by newly developed LES (Lithium Ejection System). Thermospheric neutral wind profile from 250 km down to 120 km was successfully measured along its downleg by taking sequential images from 4 independent ground sites. Imaging of the resonance scattering luminescence of Lithium was operated by newly developed tele-centric lens with wide FOV of 110 degrees with a 20 nm width band-pass filter at around 670.8 nm. At the beginning of 1st release, luminescence intensity more than 1 M rayleigh was observed by 125 g Lithium injection. Triangulation dataset of the three Lithium clouds was obtained until 40 minutes after the 1st release. As a preliminary result, SE-ward wind of 80 m/s or more at 250 km, SSW-ward 100 m/s wind at 200 km, SSW-ward 80 m/s wind at 150 km, and NNE-ward 60 m/s wind at 120 km were obtained, respectively. Strong wind shear in an altitude range between 120 km and 150 km was also found. Observed initial rate of Lithium diffusion speed of 3.2 km/s at 250 km was comparable to thermal diffusion speed in a released temperature condition of 1600 K. Before merging the Lithium clouds into surrounding atmosphere, flight velocity of the rocket itself might affect on the motion of Lithium clouds until about 150 s after the release. In this talk, Lithium release experiment in midlatitude thermosphere will be discussed in detail.

Yamamoto, Masa-Yuki; Yamamoto, Masa-Yuki; Watanabe, Shigeto; Yokoyama, Yuki; Habu, Hiroto; Abe, Takumi; Yamamoto, Mamoru; Otsuka, Yuichi; Saito, Akinori; Ono, Takayuki; Nakamura, Masato

462

Stringlike patterns in critical polymer mixtures under steady shear flow  

NASA Astrophysics Data System (ADS)

Phase-contrast microscopy has been used for a quantitative study of domain deformation in diluted polymer blends undergoing spinodal decomposition in the presence of steady shear flow. Stabilized in the weak-shear limit, nearly spherical droplets of the minority phase elongate and break repeatedly as the shear rate increases, eventually giving way to stringlike patterns in the strong-shear limit. The data are interpreted with the Onuki-Taylor model of emulsionlike critical dispersions under shear.

Hobbie, Erik K.; Kim, Sanghoon; Han, Charles C.

1996-12-01

463

The Solar Wind  

NASA Technical Reports Server (NTRS)

The first evidence of the solar wind was provided through observations of comet tail deflections by L. Biermann in 1951. A cometary ion tail is oriented along the difference between the cometary and solar wind velocities, whereas the dust tail is in the antisunward direction; the ion tail directions demonstrated the existence of an outflow of ionized gas from the Sun (the solar wind) and allowed estimates of solar wind speed. Spacecraft observations have now established that at 1 AU the solar wind has a typical ion number density of about 7 /cc and is composed by number of about 95% protons and 5% Helium, with other minor ions also present. The solar wind as observed at 1 AU in the ecliptic has speeds typically in the range 300-700 km/ s. At such speeds ions travel from the Sun to 1 AU in from 2.5 to 6 days. The impact of the solar wind on planets with magnetic fields (Earth, Jupiter, Saturn, Uranus, Neptune) causes phenomena such as magnetospheres, aurorae, and geomagnetic storms, whereas at objects lacking magnetospheres (Mars, Venus, comets), atmospheric neutrals undergo charge exchange and are picked up by the solar wind flow. The solar wind also shields the Earth from low energy cosmic rays, and is responsible for the existence of the anomalous component of the cosmic rays a low energy component that is created locally rather than in the galaxy. Presented here is a brief introduction to the solar wind and a description of some current topics of research. Solar wind properties vary a great deal due to the changing magnetic structure on the Sun.

Goldstein, B. E.

1998-01-01

464

WIND BRAKING OF MAGNETARS  

SciTech Connect

We explore the wind braking of magnetars considering recent observations challenging the traditional magnetar model. There is evidence for strong multipole magnetic fields in active magnetars, but the dipole field inferred from spin-down measurements may be strongly biased by particle wind. Recent observations challenging the traditional model of magnetars may be explained naturally by the wind braking scenario: (1) the supernova energies of magnetars are of normal value; (2) the non-detection in Fermi observations of magnetars; (3) the problem posed by low magnetic field soft gamma-ray repeaters; (4) the relation between magnetars and high magnetic field pulsars; and (5) a decreasing period derivative during magnetar outbursts. Transient magnetars with L{sub x}<- E-dot{sub rot} may still be magnetic dipole braking. This may explain why low luminosity magnetars are more likely to have radio emissions. A strong reduction of the dipole magnetic field is possible only when the particle wind is very collimated at the star surface. A small reduction of the dipole magnetic field may result from detailed considerations of magnetar wind luminosity. In the wind braking scenario, magnetars are neutron stars with a strong multipole field. For some sources, a strong dipole field may no longer be needed. A magnetism-powered pulsar wind nebula will be one of the consequences of wind braking. For a magnetism-powered pulsar wind nebula, we should see a correlation between the nebula luminosity and the magnetar luminosity. Under the wind braking scenario, a braking index smaller than three is expected. Future braking index measurement of a magnetar may tell us whether magnetars are wind braking or magnetic dipole braking.

Tong, H. [Xinjiang Astronomical Observatory, Chinese Academy of Sciences, Urumqi, Xinjiang 830011 (China); Xu, R. X.; Qiao, G. J. [KIAA and School of Physics, Peking University, Beijing 100871 (China); Song, L. M., E-mail: tonghao@xao.ac.cn [Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049 (China)

2013-05-10

465

The modification of wind turbine performance by statistically distinct atmospheric regimes  

NASA Astrophysics Data System (ADS)

Power production from wind turbines can deviate from the manufacturer’s specifications due to variability in atmospheric inflow characteristics, including stability, wind shear and turbulence. The practice of insufficient data at many operational wind farms has made it difficult to characterize this meteorological forcing. In this study, nacelle wind measurements from a wind farm in the high plains of central North America were examined along with meteorological tower data to quantify the effects of atmospheric stability regimes in the boundary layer on turbine power generation. The wind power law coefficient and the bulk Richardson number were used to segregate time periods by stability to generate regime-dependent power curves. Results indicated underperformance during stable regimes and overperformance during convective regimes at moderate wind speeds (8-12 m s-1). Statistical testing using the Monte Carlo approach demonstrated that these results were robust, despite potential deviations of the nacelle wind speeds from free-stream inflow values due to momentum loss from the turbine structure and spinning rotor. A hypothetical stability dependence between free-stream and nacelle wind speeds was generated that can be evaluated in future analyses. The low instrumentation requirement of our power analysis technique should enable similar studies at many wind sites formerly considered inappropriate.

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

2012-09-01

466

Modern control design for flexible wind turbines  

NASA Astrophysics Data System (ADS)

Control can improve energy capture and reduce dynamic loads in wind turbines. In the 1970s and 1980s wind turbines used classical control designs to regulate power and speed. The methods used, however, were not always successful. These systems often had bandwidths large enough to destabilize low-damped flexible modes leading to high dynamic load fatigue failures. Modern turbines are larger, mounted on taller towers, and are more dynamically active than their predecessors. Control systems to regulate turbine power and maintain stable closed-loop behavior in the presence of turbulent wind inflow will be critical for these designs. New advanced control approaches and paradigms must account for low-damped flexible modes in order to reduce structural dynamic loading and achieve the 20--25 year operational life required of today's machines. This thesis applies modern state-space control design methods to a two-bladed teetering hub upwind machine located at the National Wind Technology Center. The design objective is to regulate turbine speed and enhance damping in several low-damped flexible modes of the turbine. Starting with simpl