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Yuan, Xinzhe, Jian Wang, Bing Han e Xiaoqing Wang. "Study on the Elimination Method of Wind Field Influence in Retrieving a Sea Surface Current Field". Sensors 22, n.º 22 (14 de novembro de 2022): 8781. http://dx.doi.org/10.3390/s22228781.
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An along-the-track interferometric synthetic aperture radar (ATI-SAR) system can estimate the radial velocity of a moving target on the ground and on a sea surface current. This acquires the interference phase by combining two composite SAR images obtained by two antennas spatially separated along the direction of movement of the platform. The key to retrieving the sea surface current is to remove the interference of sea surface waves, wind-generated current, and Bragg phase velocity in the interference Doppler velocity. Previous methods removed the surface waves, Bragg phase velocity, and other interferences based on externally-assisted wind fields (e.g., ECMWF), using the M4S or other models. However, the wind fields obtained from ECMWF and other external information are often average results of a large temporal and spatial scale, while the images obtained from SAR are high-resolution images of sea surface transients, which are quite different in time and space. This paper takes the SAR image data of the Gaofen-3 satellite as the research object and employs an SAR-based wind field retrieval method to obtain an SAR-observed transient wind field. Combined with the CDOP model, the interference of Doppler velocities, such as the sea surface wave, wind-generated current, and Bragg wave phase velocity, was calculated and subtracted from the Doppler velocity, to obtain the sea surface velocity result. Then, the current field measured by the shore-based HF radar was compared with that obtained by correcting the ATI Doppler velocity based on the SAR retrieved wind field and the ECMWF wind field. The comparison of results indicated that the wind field correction result based on the SAR retrieved wind field was closer to the current field measured by the shore-based HF radar than the wind field correction result based on the ECMWF wind field.
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Gonçalves, Rafael C., Mohamed Iskandarani, Tamay Özgökmen e W. Carlisle Thacker. "Reconstruction of Submesoscale Velocity Field from Surface Drifters". Journal of Physical Oceanography 49, n.º 4 (abril de 2019): 941–58. http://dx.doi.org/10.1175/jpo-d-18-0025.1.
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AbstractThe extensive drifter deployment during the Lagrangian Submesoscale Experiment (LASER) provided observations of the surface velocity field in the northern Gulf of Mexico with high resolution in space and time. Here, we estimate the submesoscale velocity field sampled by those drifters using a procedure that statistically interpolates these data both spatially and temporally. Because the spacing of the drifters evolves with the flow, causing the resolution that they provide to vary in space and time, it is important to be able to characterize where and when the estimated velocity field is more or less accurate, which we do by providing fields of interpolation errors. Our interpolation uses a squared-exponential covariance function characterizing correlations in latitude, longitude, and time. Two novelties in our approach are 1) the use of two scales of variation per dimension in the covariance function and 2) allowing the data to determine these scales along with the appropriate amplitude of observational noise at these scales. We present the evolution of the reconstructed velocity field along with maps of relative vorticity, horizontal divergence, and lateral strain rate. The reconstructed velocity field exhibits horizontal length scales of 0.4–3.5 km and time scales of 0.6–3 h, and features with convergence up to 8 times the planetary vorticity f, lateral strain rate up to 10f, and relative vorticity up to 13f. Our results point to the existence of a vigorous and substantial ageostrophic circulation in the submesoscale range.
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Lloyd, Peter M., Peter K. Stansby e David J. Ball. "Unsteady surface-velocity field measurement using particle tracking velocimetry". Journal of Hydraulic Research 33, n.º 4 (julho de 1995): 519–34. http://dx.doi.org/10.1080/00221689509498658.
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Arnold, E., T. Letavic e S. Herko. "High-field electron velocity in silicon surface-accumulation layers". IEEE Electron Device Letters 20, n.º 9 (setembro de 1999): 490–92. http://dx.doi.org/10.1109/55.784462.
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Melville, W. K., e Ronald J. Rapp. "The surface velocity field in steep and breaking waves". Journal of Fluid Mechanics 189 (abril de 1988): 1–22. http://dx.doi.org/10.1017/s0022112088000898.
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Coincident simultaneous measurements of the surface displacement and the horizontal velocity at the surface of steep and breaking waves are presented. The measurements involve a novel use of laser anemometry at the fluctuating air-water interface and clearly show the limitations of surface displacement measurements in characterizing steep and breaking wave fields. The measurements are used to examine the evolution of the surface drift velocity, spectra, wave envelopes, and forced long waves in unstable deep-water waves. Preliminary results of this work were reported by Melville & Rapp (1983).
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Kim, Joon Hyun, e Joo-Hyun Kim. "Thermohydrodynamic Analysis of Surface Roughness in the Flow Field". Journal of Tribology 127, n.º 2 (1 de abril de 2005): 293–301. http://dx.doi.org/10.1115/1.1828072.
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The study deals with the development of a thermohydrodynamic (THD) computational procedure for evaluating the pressure, temperature, and velocity distributions in fluid films with a very rough geometry. A parametric investigation is performed to predict the bearing behaviors in the lubricating film with the absorbed layers and their interfaces as determined by rough surfaces with Gaussian distribution. The layers are expressed as functions of the standard deviations of each surface to characterize flow patterns between both rough surfaces. Velocity variations and heat generation are assumed to occur in the central (shear) zone with the same bearing length and width. The coupled effect of the surface roughness and shear zone dependency on the hydrodynamic pressure and temperature has been found in the noncontact mode. The procedure confirms the numerically determined relationship between the pressure and film gap, provided that its roughness magnitude is smaller than the fluid film thickness.
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Li, Chang He, Zhen Lu Han e Jing Yao Li. "Investigation into Fluid Velocity Field of Wedge-Shaped Gap in Grinding". Applied Mechanics and Materials 37-38 (novembro de 2010): 593–98. http://dx.doi.org/10.4028/www.scientific.net/amm.37-38.593.
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In the grinding process, grinding fluid is delivered for the purposes of chip flushing, cooling, lubrication and chemical protection of work surface. Hence, the conventional method of flood delivering coolant fluid by a nozzle in order to achieve high process performance purposivelly. However, hydrodynamic fluid pressure can be generated ahead of the grinding zone due to the wedge effect between wheel peripheral surface and part surface. In this paper, a theoretical fluid velocity field modeling is presented for flow of coolant fluid of wedge-shaped gap in flood delivery surface grinding, which is based on navier-stokes equation and continuous formulae. The numerical simulation results showed that the velocity in the x direction was dominant and the side-leakage in the y direction existed. The velocity in the z direction was smaller than the others because of the assumption of laminar flow. The smaller the gap is, the larger the velocity in the x direction. The magnitude of the velocity is also proportional to the surface velocity of the wheel.
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BAL, GUILLAUME, e KUI REN. "RECONSTRUCTION OF SINGULAR SURFACES BY SHAPE SENSITIVITY ANALYSIS AND LEVEL SET METHOD". Mathematical Models and Methods in Applied Sciences 16, n.º 08 (agosto de 2006): 1347–73. http://dx.doi.org/10.1142/s021820250600156x.
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We consider the reconstruction of singular surfaces from the over-determined boundary conditions of an elliptic problem. The problem arises in optical and impedance tomography, where void-like structure or cracks may be modeled as diffusion processes supported on co-dimension one surfaces. The reconstruction of such surfaces is obtained theoretically and numerically by combining a shape sensitivity analysis with a level set method. The shape sensitivity analysis is used to define a velocity field, which allows us to update the surface while decreasing a given cost function, which quantifies the error between the prediction of the forward model and the measured data. The velocity field depends on the geometry of the surface and the tangential diffusion process supported on it. The latter process is assumed to be known in this paper. The level set method is next applied to evolve the surface in the direction of the velocity field. Numerical simulations show how the surface may be reconstructed from noisy estimates of the full, or local, Neumann-to-Dirichlet map.
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Hosokawa, Y., e K. Furukawa. "Surface Flow and Particle Settling in a Coastal Reed Field". Water Science and Technology 29, n.º 4 (1 de fevereiro de 1994): 45–53. http://dx.doi.org/10.2166/wst.1994.0154.
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Hydraulic roughness of reed stems in shallow surface flow under low current velocity is discussed. The roughness coefficient, defined as a Manning's formula, depends upon depth and velocity in this flow. Depth and velocity, in turn, are altered by roughness through water surface slope. The interaction between these three parameters must be solved simultaneously for the prediction of the surface flow in a reed wetland. Stem roughness can be expressed as a function of Reynolds' number, similar to that for a single cylinder. Assigning this function, an iteration method easily gives us a suitable set of three parameters. Settling experiments show that stems promote vertical mixing of fine particles in shallow flow. The model of vertically uniform SS concentration is more suitable. Though the observed data fluctuated widely, the apparent settling velocity of fine particles in the flow was very close to the settling velocity in quiescent water. Using the above two models, one for flow and the other for settling in shallow wetland, we can estimate the clarification potential of a reed field under given hydraulic conditions and particle load. Numerical experiments show that fine particles tend to accumulate on the bottom of a reed field, as often observed in natural wetlands.
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Yan, He, Qianru Hou, Guodong Jin, Xing Xu, Gong Zhang e Daiyin Zhu. "Velocity Estimation of Ocean Surface Currents in along-Track InSAR System Based on Conditional Generative Adversarial Networks". Remote Sensing 13, n.º 20 (13 de outubro de 2021): 4088. http://dx.doi.org/10.3390/rs13204088.
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Velocity estimation of ocean surface currents is of great significance in the fields of the fishery, shipping, sewage discharge, and military affairs. Over the last decade, along-track interferometric synthetic aperture radar (along-track InSAR) has been demonstrated to be one of the important instruments for large-area and high-resolution ocean surface current velocity estimation. The calculation method of the traditional ocean surface current velocity, as influenced by the large-scale wave orbital velocity and the Bragg wave phase velocity, cannot easily separate the current velocity, characterized by large error and low efficiency. In this paper, a novel velocity estimation method of ocean surface currents is proposed based on Conditional Generative Adversarial Networks (CGANs). The main processing steps are as follows: firstly, the known ocean surface current field diagrams and their corresponding interferometric phase diagrams are constructed as the training dataset; secondly, the estimation model of the ocean surface current field is constructed based on the pix2pix algorithm and trained by the training dataset; finally, the interferometric phase diagrams in the test dataset are input into the trained model. In the simulation experiment, processing results of the proposed method are compared with those of traditional ocean surface current velocity estimation methods, which demonstrate the efficiency and effectiveness of the novel method.
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Yan, He, Qianru Hou, Guodong Jin, Xing Xu, Gong Zhang e Daiyin Zhu. "Velocity Estimation of Ocean Surface Currents in along-Track InSAR System Based on Conditional Generative Adversarial Networks". Remote Sensing 13, n.º 20 (13 de outubro de 2021): 4088. http://dx.doi.org/10.3390/rs13204088.
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Velocity estimation of ocean surface currents is of great significance in the fields of the fishery, shipping, sewage discharge, and military affairs. Over the last decade, along-track interferometric synthetic aperture radar (along-track InSAR) has been demonstrated to be one of the important instruments for large-area and high-resolution ocean surface current velocity estimation. The calculation method of the traditional ocean surface current velocity, as influenced by the large-scale wave orbital velocity and the Bragg wave phase velocity, cannot easily separate the current velocity, characterized by large error and low efficiency. In this paper, a novel velocity estimation method of ocean surface currents is proposed based on Conditional Generative Adversarial Networks (CGANs). The main processing steps are as follows: firstly, the known ocean surface current field diagrams and their corresponding interferometric phase diagrams are constructed as the training dataset; secondly, the estimation model of the ocean surface current field is constructed based on the pix2pix algorithm and trained by the training dataset; finally, the interferometric phase diagrams in the test dataset are input into the trained model. In the simulation experiment, processing results of the proposed method are compared with those of traditional ocean surface current velocity estimation methods, which demonstrate the efficiency and effectiveness of the novel method.
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Lin, Yao Tsung, Shyh Shin Hwang e Jun An Zhu. "The Study of Velocity Field in Front Opening Unified Pod by CAE". Engineering Innovations 7 (13 de outubro de 2023): 89–94. http://dx.doi.org/10.4028/p-uq3dz7.
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The front opening unified pod (FOUP) is a packing box for contamination control for semiconductor wafer transport. As the wafer fabrication process developes towards nanoor atom level, the semiconductor wafer storage device should advance from the particle prevention function into the airborne molecular contamination (AMC) removal function. Therefore, it is necessary to design/redesign a function for removing AMC or moisture inside the FOUP. This study used the design of leading diffuser tubes in the FOUP and pores in the surfaces of diffuser tubes to generate gas diffusion. This is to achieve a uniform distribution of the wafer surface velocity field and a uniform dehumidification function of the wafer surface. Based on the analysis results, when circular diffuser tubes are introduced in the FOUP and the intake air flow was set at 0.2-0.3 m3/hr, the interlayer wafer surface in the FOUP could achieve uniform distribution of velocity field. As a result, the humidity difference among various zones of wafer surface could be reduced, and the yield and quality of the wafer cutting process could be controlled.
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SAVELSBERG, RALPH, e WILLEM VAN DE WATER. "Experiments on free-surface turbulence". Journal of Fluid Mechanics 619 (25 de janeiro de 2009): 95–125. http://dx.doi.org/10.1017/s0022112008004369.
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We study the free surface of a turbulent flow, in particular the relation between the statistical properties of the wrinkled surface and those of the velocity field beneath it. Channel flow turbulence is generated using an active grid. Through a judicial choice of the stirring protocol the anisotropy of the subsurface turbulence can be controlled. The largest Taylor Reynolds number obtained is Reλ = 258. We characterize the homogeneity and isotropy of the flow and discuss Taylor's frozen turbulence hypothesis, which applies to the subsurface turbulence but not to the surface. The surface gradient field is measured using a novel laser-scanning device. Simultaneously, the velocity field in planes just below the surface is measured using particle image velocimetry (PIV). Several intuitively appealing relations between the surface gradient field and functionals of the subsurface velocity field are tested. For an irregular flow shed off a vertical cylinder, we find that surface indentations are strongly correlated with both vortical and strain events in the velocity field. For fully developed turbulence this correlation is dramatically reduced. This is because the large eddies of the subsurface turbulent flow excite random capillary–gravity waves that travel in all directions across the surface. Therefore, the turbulent surface has dynamics of its own. Nonetheless, it does inherit both the integral scale, which determines the predominant wavelength of the capillary–gravity surface waves, and the (an)isotropy from the subsurface turbulence. The kinematical aspects of the surface–turbulence connection are illustrated by a simple model in which the surface is described in terms of waves originating from Gaussian wave sources that are randomly sprinkled on the moving surface.
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Ali, Fatima, Jan G. Wissink e Herlina Herlina. "Modeling air-water heat transfer induced by buoyant convection". International Journal of Computational Physics Series 1, n.º 2 (28 de fevereiro de 2018): 15–16. http://dx.doi.org/10.29167/a1i2p15-16.
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The instantaneous 2D velocity field obtained at the air-water interface in previously performed direct numerical simulations (DNS) of interfacial heat transfer driven by buoyant convective instability is used to estimate the heat transfer velocity [2]. After reconstructing the three-dimensional velocity field immediately underneath the surface, a Lagrangian particle tracking method was used to assess the surface age. The surface heat transfer velocity, obtained using Danckwerts’ surface renewal model, was found to underestimate the heat transfer velocity acquired directly from the DNS data by about 16%.
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Gecha, V. Ya, M. Yu Zhilenev, V. B. Fyodorov, D. A. Khrychev, Yu I. Hudak e A. V. Shatina. "Velocity field of image points in satellite imagery of planet’s surface". Russian Technological Journal 8, n.º 1 (3 de março de 2020): 97–109. http://dx.doi.org/10.32362/2500-316x-2020-8-1-97-109.
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This paper derives a formula for calculating the velocity of arbitrary point in the field of view of the satellite camera in the process of orbital imagery of the planet's surface. The formula describes the velocity as a function of the point coordinates in the image fixation plane, the focal length of the imaging camera, the orbital parameters of the satellite, the angular velocity of the planet’s rotation, the coordinates of the satellite’s true anomaly in the orbit, the orientation angles of the imaging camera relative to the orbit, and the angular velocity of the camera. The paper also provides examples of the formula use for calculating the velocity field of image points for different sets of imagery parameters.The formula is derived under the assumption that the planet is a homogeneous absolutely solid body, shaped as a ball, and rotating at a constant angular velocity; as a result, the satellite moves in a Keplerian orbit, with the planet located at one of the orbit’s foci. Despite this idealization, the derived formula can be used in developing algorithms for remote sensing of the Earth, for building and optimizing the image blurring compensators, for solving the problem of blurred image recovery, and for a number of other problems related to satellite imagery preparation, execution, and processing the results.
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Bindschadler, R. A., M. A. Fahnestock, P. Skvarca e T. A. Scambos. "Surface-velocity field of the northern Larsen Ice Shelf, Antarctica". Annals of Glaciology 20 (1994): 319–26. http://dx.doi.org/10.3189/1994aog20-1-319-326.
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Three satellite images of the northern Larsen Ice Shelf arc used to derive velocity fields for the periods 1975–86 and 1986 89. Substantial increases in the speed of the ice between these periods are detected to a high degree of confidence. Ice which entered the ice shelf between Fothergill Point and Cape Worsley and ice from Drygalski Glacier has accelerated by approximately 15% over the measurement period. Ice from Bombardier and Dinsmoor Glaciers also exhibits acceleration but by a lesser amount. These accelerations may be the result of either significant retreat experienced by the ice shelf during this period or warming in the Antarctic Peninsula region. Velocities measured by surface survey over a 15 d period in 1991 indicate a slower velocity than the image-derived velocities in the limited region of overlap. These differences appear to be systematic and may be the result of uncontrolled errors in the surface survey. Limited control of one image could also contribute to some of these differences.
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Inaba, H., Y. Itakura e M. Kasahara. "Surface velocity computation of debris flows by vector field measurements". Physics and Chemistry of the Earth, Part B: Hydrology, Oceans and Atmosphere 25, n.º 9 (janeiro de 2000): 741–44. http://dx.doi.org/10.1016/s1464-1909(00)00095-2.
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Bindschadler, R. A., M. A. Fahnestock, P. Skvarca e T. A. Scambos. "Surface-velocity field of the northern Larsen Ice Shelf, Antarctica". Annals of Glaciology 20 (1994): 319–26. http://dx.doi.org/10.1017/s0260305500016633.
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Three satellite images of the northern Larsen Ice Shelf arc used to derive velocity fields for the periods 1975–86 and 1986 89. Substantial increases in the speed of the ice between these periods are detected to a high degree of confidence. Ice which entered the ice shelf between Fothergill Point and Cape Worsley and ice from Drygalski Glacier has accelerated by approximately 15% over the measurement period. Ice from Bombardier and Dinsmoor Glaciers also exhibits acceleration but by a lesser amount. These accelerations may be the result of either significant retreat experienced by the ice shelf during this period or warming in the Antarctic Peninsula region. Velocities measured by surface survey over a 15 d period in 1991 indicate a slower velocity than the image-derived velocities in the limited region of overlap. These differences appear to be systematic and may be the result of uncontrolled errors in the surface survey. Limited control of one image could also contribute to some of these differences.
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Weidle, Christian. "Surface wave phase velocity maps from multiscale wave field interpolation". Computational Geosciences 16, n.º 3 (21 de dezembro de 2011): 535–49. http://dx.doi.org/10.1007/s10596-011-9269-8.
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Noblesse, Francis, Chi Yang e Xiao-Bo Chen. "Boundary-Integral Representation of Linear Free-Surface Potential Flows". Journal of Ship Research 41, n.º 01 (1 de março de 1997): 10–16. http://dx.doi.org/10.5957/jsr.1997.41.1.10.
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A new potential-flow representation, which defines the velocity field ∇ϕ in a potential flow region explicitly in terms of the velocity distribution (u,v,w) at a boundary surface E, is given for the case of wave diffraction-radiation by a ship. This flow representation does not involve the potential ϕ at ϵ (unlike the usual Green identity which expresses ϕ within a flow domain in terms of boundary values of ϕ and ∂ϕ/∂n) and defines the velocity field ∇ϕ directly (i.e., not via numerical differentiation of ϕ). The new flow representation can be useful for extending a given near-field flow into the far field, and for coupling a near-field nonlinear viscous flow calculation method and a far-field linear potential-flow representation.
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Çakır, Özcan, e Nart Coşkun. "LOVE SURFACE WAVES AND ELECTRICAL RESISTIVITY USED TO DELINEATE THE NEAR SURFACE GEOPHYSICAL STRUCTURE: THEORETICAL CONSIDERATIONS". Earth Science Malaysia 5, n.º 2 (29 de dezembro de 2020): 104–13. http://dx.doi.org/10.26480/esmy.02.2021.104.113.
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We invert Love surface waves and electrical resistivities to cooperatively examine the physical properties of the depth range shallower than 50-m. To analyze this depth range is essential for earthquake mitigation efforts. The shear-wave velocity (VS30) is particularly important to describe the dynamic characteristics of shallow Earth. The Love surface waves are treated in terms of both phase and group velocities. The phase velocities are obtained from the slant stacking while for the group velocities the multiple filter technique is utilized. A typical shot-gather is assumed to simulate the field collection of the surface wave data. The phase velocity curve represents the average structure beneath the geophone spread. The group velocity curve represents the average structure from the source to the geophone. In a single-station fashion, for each geophone location one group velocity curve is obtained. A linear system is set up to convert these single-station group velocity curves into local group velocity curves at grid points. The latter group velocities are inverted to attain the shear-wave velocity cross section. A similar approach is adopted to study the electrical resistivity structure of the underground. We simulate the field application using a theoretical model. Multiple electrode Pole-Pole array is assumed for the field collection of the resistivity data. The apparent (measured) resistivity values are inverted to attain the true resistivity structure in terms of a cross section. The inverted structures are one-dimensional reflecting depth dependent shear-wave velocities and electrical resistivities underneath the studied region.
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Zhiwang, Gan, Chen Zhitong e Zhou Meng. "Approaching the characteristic curve of the cutter’s envelope based on a velocity field". Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture 231, n.º 11 (5 de janeiro de 2016): 1904–16. http://dx.doi.org/10.1177/0954405415616788.
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The characteristic curve of the envelope generated by the tool motions is an important medium for measuring the distance between the tool and the desired surface. Via the single parametric surface envelope theory in differential geometry, this article proved the correctness of the characteristic curve obtained by minimum distance pairs. Simultaneously, combined with the existing envelope theory and the longitude method, an algorithm based on a velocity field is proposed to approach the characteristic curve. The torus cutter is first dispersed into longitudes and then the characteristic point on each longitude is determined with the estimated velocity. In the experiments, the actual velocity of the estimated characteristic point is computed by the true trajectory simulation of the tool. Therefore, the deviation of the proposed method could be measured comparing with the actual velocity. In the implementations, the proposed method is validated in machining a flat, a spiral, and a blade surfaces. In machining the spiral, our algorithm improves approximately 7 times accuracy with 1/7 time cost compared with the existing methods. The results in the blade surface example prove the stableness of the proposed algorithm.
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Gunda, Rajendra, e Sandeep Vijayakar. "Computing Radiated Sound Power using Quadratic Power Transfer Vector (QPTV)". INTER-NOISE and NOISE-CON Congress and Conference Proceedings 263, n.º 2 (1 de agosto de 2021): 4257–67. http://dx.doi.org/10.3397/in-2021-2643.
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Pressure Acoustic Transfer Functions or Vectors (PATVs) relate the surface velocity of a structure to the sound pressure level at a field point in the surrounding fluid. These functions depend only on the structure geometry, properties of the fluid medium (sound speed and characteristic density), the excitation frequency and the location of the field point, but are independent of the surface velocity values themselves. Once the pressure acoustic transfer function is computed between a structure and a specified field point, we can compute pressure at this point for any boundary velocity distribution by simply multiplying the forcing function (surface velocity) with the acoustic transfer function. These PATVs are usually computed by application of the Reciprocity Principle, and their computation is well understood. In this work, we present a novel way to compute the Velocity Acoustic Transfer Vector (VATV) which is a relation between the surface velocity of the structure and fluid particle velocity at a field point. To our knowledge, the computation of the VATV is completely new and has not been published in earlier works. By combining the PATVs and VATVs at a number of field points surrounding the structure, we obtain the Quadratic Power Transfer Vector (QPTV) that allows us to compute the sound power radiated by a structure for ANY surface velocity distribution. This allows rapid computation of the sound power for an arbitrary surface velocity distributions and is useful in designing quiet structures by minimizing the sound power radiated.
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Chaudhary, K., A. Sharma e A. K. Jha. "Laminar Mixed Convection Flow from a Vertical Surface with Induced Magnetic Field and Convective Boundary". International Journal of Applied Mechanics and Engineering 23, n.º 2 (1 de maio de 2018): 307–26. http://dx.doi.org/10.2478/ijame-2018-0017.
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AbstractThe objective of this investigation is to study the influence of thermal radiation and radiation absorption parameter on a mixed convection flow over a continuously moving porous vertical plate under the action of transverse applied magnetic field taking into account the induced magnetic field with convective boundary. Under certain assumptions, the solutions for the velocity field, temperature distribution and induced magnetic field are obtained. The influences of various parameters on the velocity, temperature fields and on induced magnetic fields are studied graphically. It is also found that the dimensionless Prandtl number, Grashof number, Schmidt number and magnetic parameter have an appreciable influence on the independent variables.
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Sugiyama, Shin, Daiki Sakakibara, Satoshi Matsuno, Satoru Yamaguchi, Sumito Matoba e Teruo Aoki. "Initial field observations on Qaanaaq ice cap, northwestern Greenland". Annals of Glaciology 55, n.º 66 (2014): 25–33. http://dx.doi.org/10.3189/2014aog66a102.
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AbstractTo study the glaciological processes controlling the mass budget of Greenland’s peripheral glaciers and ice caps, field measurements were carried out on Qaanaaq ice cap, a 20 km long ice cap in northwestern Greenland. In the summer of 2012, we measured surface melt rate, ice flow velocity and ice thickness along a survey route spanning the ice margin (200m a.s.l.) to the ice-cap summit (1110m a.s.l.). Melt rates in the ablation area were clearly influenced by dark materials covering the ice surface, where degree-day factors varied from 5.44 mm w.e. K–1 d–1 on a clean surface to 8.26 mm w.e. K–1 d–1 in the dark regions. Ice velocity showed diurnal variations, indicating the presence of surface-meltwater induced basal sliding. Mean ice thickness along the survey route was 120 m, with a maximum thickness of 165 m. Ice velocity and temperature fields were computed using a thermomechanically coupled numerical glacier model. Modelled ice temperature, obtained by imposing estimated annual mean air temperature as the surface boundary condition, was substantially lower than implied by the observed ice velocity. This result suggests that the ice dynamics and thermodynamics of the ice cap are significantly influenced by heat transfer from meltwater and changing ice geometry.
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Paradkar, B. S., S. M. Chitre e V. Krishan. "Mean field solar surface dynamo in the presence of partially ionized plasmas and sub-surface shear layer". Monthly Notices of the Royal Astronomical Society 488, n.º 3 (25 de julho de 2019): 4329–37. http://dx.doi.org/10.1093/mnras/stz2008.
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Abstract A non-linear α − Ω dynamo in the partially ionized turbulent plasma in the presence of sub-surface velocity shear is studied with mean-field electrodynamics. Such a dynamo is probably operational in the near-surface region of the Sun, where the presence of both neutrals and the velocity shear (due to sub-surface shear layer in the rotation profile) is observationally well established. In particular, we show that the inclusion of ambipolar diffusion leads to a saturation of magnetic field amplitudes in the α − Ω dynamo. We also demonstrate that the temporal evolution of large-scale global magnetic fields follows the well-known pattern similar to the ‘butterfly’ diagram displayed by sunspots. As usual the velocity shear converts part of the poloidal into the toroidal magnetic field which in turn is regenerated largely by the combined kinetic plus Hall helicity, thus closing the dynamo loop. In addition, by allowing temporal variation in the helicity and ambipolar diffusion coefficient we are able to reproduce the grand-minimum type behaviour of the solar dynamo. Details of theoretical model along with numerical computations of dynamo equations in the partially ionized plasma are outlined. The solar surface dynamo model envisaged in this work could operate in conjunction with the global dynamo present in the bulk of the convection zone.
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KACHURIN, NIKOLAY, DMITRY PROKHOROV, DMITRY AMBARTSUMOV e IVAN EROGIN. "AEROGASDYNAMICS AND DUST TRANSPORT OF ANTHROPOGENIC MINERAL FORMATIONS". News of the Tula state university. Sciences of Earth 1, n.º 1 (2023): 531–43. http://dx.doi.org/10.46689/2218-5194-2023-1-1-531-543.
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Of particular interest is the fact that when modeling the convective-turbulent diffusion of dust and gas pollutants, one can use a one-dimensional parabolic type equation, where the convective term will be determined by the wind speed in the surface layer, since the velocity field in the surface layer quickly levels out. The areas of dusty surfaces of a conical AMF do not exceed 60% of its total surface area. When flowing around a spinal-shaped AMT, the air velocity fields can exceed the value of the blow-off velocity of solid particles by almost 30 % of the AMF surface area. At the next stage of research, it is necessary to analyze the simulation results and, on its basis, substantiate technical solutions to ensure the environmental safety of the environment. This will improve the efficiency of technologies to reduce or eliminate the negative impact of AMF on adjacent territories.
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RADWAN, AHMED E. "ALFVEN SURFACE WAVES ALONG ANNULAR GAS JET SURROUNDING TAR COLUMN UNDER OBLIQUE VARYING MAGNETIC FIELD". Tamkang Journal of Mathematics 28, n.º 2 (1 de junho de 1997): 127–33. http://dx.doi.org/10.5556/j.tkjm.28.1997.4326.
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The MFD oscillating Alfven surface waves along a perfectly conducting annular gas jct surrounding a tar column under oblique varying magnetic field has been discussed. Numerous reported works could be recovered as limiting cases. The axial magnetic fields interior and exterior the model are stabilizing while the tenuous azimuthal field is so or not according to restrictions. The thicker the tar column the larger its stabilizing influence; and the oscillation states arc slowed down so easier observations are allowed than in the classical case of full fluid jet in vacuum with constant magnetic fields (Uberio and Somasundaram 1980). The Alfven wave velocity is decreasing with increasing azimuthal-longitudinal magnetic fields intensities ratio. The phase (dispersive) velocity of the wave propagation relative to Alfven wave velocity is monotonic increasing with decreasing the perturbed wavelength.
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Decker, Luke, e Sergey Fomel. "A variational approach for picking optimal surfaces from semblance-like panels". GEOPHYSICS 87, n.º 3 (11 de abril de 2022): U93—U108. http://dx.doi.org/10.1190/geo2021-0336.1.
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We propose and examine a variational method for determining optimal velocity fields from semblance-like volumes using continuation. The proposed approach finds a minimal-cost surface through a volume, which often corresponds to a velocity field within a semblance scan. This allows picked velocity fields to incorporate information from gathers that are spatially near the midpoint in question. The minimization process amounts to solving a nonlinear elliptic partial differential equation, which is accomplished by changing the elliptic problem to a parabolic one and solving it iteratively until it converges to a critical point which minimizes the cost functional. The continuation approach operates by using a variational framework to iteratively minimize the cost of a velocity surface through successively less-smoothed semblance scans. The method works because a global minimum for the velocity cost functional can only exist when the semblance scan varies smoothly in space and convexly in the parameter being scanned. Using a discretization of the functional with a limited-memory Broyden-Fletcher-Goldfarb-Shanno algorithm, we illustrate how the continuation approach is able to avoid local minima that would typically capture the iterative solution of an optimal velocity field determined without continuation by applying the method to seismic processing of a field data set from the Viking Graben. We then use a field data set from the Gulf of Mexico to show how the final velocity model determined by the method using continuation is largely independent of the starting velocity model, producing something resembling a global minimum. Finally, we demonstrate the versatility of the variational picking approach by using it to automatically interpret a seismic horizon from the Heidrun Field.
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Theule, Joshua I., Stefano Crema, Lorenzo Marchi, Marco Cavalli e Francesco Comiti. "Exploiting LSPIV to assess debris-flow velocities in the field". Natural Hazards and Earth System Sciences 18, n.º 1 (3 de janeiro de 2018): 1–13. http://dx.doi.org/10.5194/nhess-18-1-2018.
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Abstract. The assessment of flow velocity has a central role in quantitative analysis of debris flows, both for the characterization of the phenomenology of these processes and for the assessment of related hazards. Large-scale particle image velocimetry (LSPIV) can contribute to the assessment of surface velocity of debris flows, provided that the specific features of these processes (e.g. fast stage variations and particles up to boulder size on the flow surface) are taken into account. Three debris-flow events, each of them consisting of several surges featuring different sediment concentrations, flow stages, and velocities, have been analysed at the inlet of a sediment trap in a stream in the eastern Italian Alps (Gadria Creek). Free software has been employed for preliminary treatment (orthorectification and format conversion) of video-recorded images as well as for LSPIV application. Results show that LSPIV velocities are consistent with manual measurements of the orthorectified imagery and with front velocity measured from the hydrographs in a channel recorded approximately 70 m upstream of the sediment trap. Horizontal turbulence, computed as the standard deviation of the flow directions at a given cross section for a given surge, proved to be correlated with surface velocity and with visually estimated sediment concentration. The study demonstrates the effectiveness of LSPIV in the assessment of surface velocity of debris flows and permit the most crucial aspects to be identified in order to improve the accuracy of debris-flow velocity measurements.
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Hao, J. "Recovering the Pulsation Velocity Distribution on Stellar Surface". Symposium - International Astronomical Union 185 (1998): 383–84. http://dx.doi.org/10.1017/s0074180900238989.
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The analytical expression between the line profile and its corresponding pulsation velocity field is derived by the assumption of Doppler Imaging (DI). Based on this approach, numerical experiments of the recovery of the one dimensional nonradial pulsation velocity distribution from the residual line profiles are presented.
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Yang, Yuande, Bo Sun, Zemin Wang, Minghu Ding, Cheinway Hwang, Songtao Ai, Lianzhong Wang, Yujun Du e Dongchen E. "GPS-derived velocity and strain fields around Dome Argus, Antarctica". Journal of Glaciology 60, n.º 222 (2014): 735–42. http://dx.doi.org/10.3189/2014jog14j078.
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AbstractKnowledge of the surface topography, velocity field and strain field at an ice-core site is critical to the accurate interpretation of ice-core records. At Dome Argus (Dome A), where a Chinese deep ice-core drilling project is being carried out, we have produced an accurate surface digital elevation model from GPS measurements in January 2013 at 47 sites. We identify two peaks at Dome A, with the northern peak ~7 cm higher than the southern peak. Repeat GPS measurements at 12 sites in 2008 and 2013 provide a surface velocity field around the dome. The surface velocity ranges from 3.1±2.6 to 29.4±1.2 cm a–1, with a mean of 11.1 ~2.4 cm a–1. The surface flow directions are near perpendicular to the surface elevation contours. Velocities from GPS are lower than derived from satellite radar interferometry (InSAR). From GPS velocities, the accuracy of velocity from the existing InSAR velocity field is determined, resulting in a standard deviation of 0.570 m a–1 in speed and 117.5º in direction. This result is consistent with the reported accuracy of InSAR, showing the value of in situ GPS measurements for assessing and correcting remote-sensing results. A surface strain field for the drilling site over Dome A is calculated from 24 strain triangles, showing north–south extension, east– west compression and vertical layer thinning.
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Sutherland, Peter, e W. Kendall Melville. "Measuring Turbulent Kinetic Energy Dissipation at a Wavy Sea Surface". Journal of Atmospheric and Oceanic Technology 32, n.º 8 (agosto de 2015): 1498–514. http://dx.doi.org/10.1175/jtech-d-14-00227.1.
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AbstractWave breaking is thought to be the dominant mechanism for energy loss by the surface wave field. Breaking results in energetic and highly turbulent velocity fields, concentrated within approximately one wave height of the surface. To make meaningful estimates of wave energy dissipation in the upper ocean, it is then necessary to make accurate measurements of turbulent kinetic energy (TKE) dissipation very near the surface. However, the surface wave field makes measurements of turbulence at the air–sea interface challenging since the energy spectrum contains energy from both waves and turbulence over the same range of wavenumbers and frequencies. Furthermore, wave orbital velocities can advect the turbulent wake of instrumentation into the sampling volume of the instrument. In this work a new technique for measuring TKE dissipation at the sea surface that overcomes these difficulties is presented. Using a stereo pair of longwave infrared cameras, it is possible to reconstruct the surface displacement and velocity fields. The vorticity of that velocity field can then be considered to be representative of the rotational turbulence and not the irrotational wave orbital velocities. The turbulent kinetic energy dissipation rate can then be calculated by comparing the vorticity spectrum to a universal spectrum. Average surface TKE dissipation calculated in this manner was found to be consistent with near-surface values from the literature, and time-dependent dissipation was found to depend on breaking.
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Çakır, Özcan, e Nart Coşkun. "Theoretical Issues with Rayleigh Surface Waves and Geoelectrical Method Used for the Inversion of Near Surface Geophysical Structure". Journal of Human, Earth, and Future 2, n.º 3 (1 de setembro de 2021): 183–99. http://dx.doi.org/10.28991/hef-2021-02-03-01.
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We numerically simulate the field measurements of Rayleigh surface waves and electrical resistivity in which the target depth is set to be less than 50-m. The Rayleigh surface waves are simulated in terms of fundamental mode group and phase velocities. The seismic field data is assumed to be collected through a conventional shot-gather. The group velocities are found from the application of the multiple filter technique in a single-station fashion while for the phase velocities the slant stacking, or linear radon transform are applied in fashion of multichannel analysis of surface waves (MASW). The average seismic structure from the source to the receiver (or geophone) is represented by the group velocity curve while the average seismic structure underneath the geophone array is represented by the phase velocity curve. The single-station group velocity curves are transformed into local group velocity curves by setting a linear system through grid points. The shear-wave velocity cross section underneath the examined area is constructed by inverting these local group velocity curves. The electrical resistivity structure of the underground is similarly studied. The field compilation of the resistivity data is assumed to be completed by the application of the multiple electrode Pole-Pole array. The actual resistivity assemble underneath the analyzed area is inverted by considering the apparent (measured) resistivity values. Unique forms such as ore body, cavity, sinkhole, melt, salt, and fluid within the Earth may be examined by joint interpretation of electrical resistivities and seismic velocities. These formations may be better outlined by following their distinct signs such as high/low resistivities and high/low seismic velocities. Doi: 10.28991/HEF-2021-02-03-01 Full Text: PDF
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zhu, wu, e Sean F. Wu. "Reconstructing acoustic field based on the normal surface velocity input data". Journal of the Acoustical Society of America 137, n.º 4 (abril de 2015): 2234. http://dx.doi.org/10.1121/1.4920151.
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Arnold, E., T. Letavic e S. Herko. "Corrections to "High-field electron velocity in silicon surface-accumulation layer"". IEEE Electron Device Letters 20, n.º 10 (outubro de 1999): 541. http://dx.doi.org/10.1109/led.1999.791936.
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Hirsa, A., G. M. Korenowski, L. M. Logory e C. D. Judd. "Velocity field and surfactant concentration measurement techniques for free-surface flows". Experiments in Fluids 22, n.º 3 (20 de janeiro de 1997): 239–48. http://dx.doi.org/10.1007/s003480050042.
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Schulz, F., F. J. W. A. Martins e F. Beyrau. "Liquid Pattern And Velocity Field On A Surface During Spray Impingement". Proceedings of the International Symposium on the Application of Laser and Imaging Techniques to Fluid Mechanics 20 (11 de julho de 2022): 1–14. http://dx.doi.org/10.55037/lxlaser.20th.2.
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The process of fuel injection and the associated wall impact is critical for the quality of combustion in engines. Secondary droplets and wall deposits are strongly related to incomplete combustion and soot emissions. To reduce harmful emissions and optimise the combustion, further investigations of the processes of spray impingement, secondary droplet formation and wall film formation are of central importance. In order to obtain a more comprehensive picture of the interaction between spray and wall, light sheet visualizations and particle image velocimetry (PIV) measurements were performed on an impinging gasoline spray within a conditioned pressure vessel. For this purpose, measurements were conducted both perpendicular to the jet axis and parallel to the wall. The focus here is on the conditions in a modern, homogeneously operated gasoline engine with a high-pressure injection valve with a well-known spray. The spray under investigation has already been studied using high-speed shadowgraphs and phase doppler anemometry measurements. The combination of the data allows validation and a better understanding of the present measurements. The injection pressure was 150 bar, the vessel temperature 80°C, and the nozzle-to-wall distance 35 mm. The vessel pressure was varied from 0.4 bar to 6 bar, which represents typical charge conditions in an engine. The measured data allowed the analysis of the internal structure of the spray and the quantification of the flow movements before and after the spray impact. The results obtained provided detailed new insights into the relevant sub-processes.
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Socco, Laura Valentina, Cesare Comina e Farbod Khosro Anjom. "Time-average velocity estimation through surface-wave analysis: Part 1 — S-wave velocity". GEOPHYSICS 82, n.º 3 (1 de maio de 2017): U49—U59. http://dx.doi.org/10.1190/geo2016-0367.1.
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In some areas, the estimation of static corrections for land seismic data is a critical step of the processing workflow. It often requires the execution of additional surveys and data analyses. Surface waves (SWs) in seismic records can be processed to extract local dispersion curves (DCs) that can be used to estimate near-surface S-wave velocity models. Here we focus on the direct estimation of time-average S-wave velocity models from SW DCs without the need to invert the data. Time-average velocity directly provides the value of one-way time, given a datum plan depth. The method requires the knowledge of one 1D S-wave velocity model along the seismic line, together with the relevant DC, to estimate a relationship between SW wavelength and investigation depth on the time-average velocity model. This wavelength/depth relationship is then used to estimate all the other time-average S-wave velocity models along the line directly from the DCs by means of a data transformation. This approach removes the need for extensive data inversion and provides a simple method suitable for industrial workflows. We tested the method on synthetic and field data and found that it is possible to retrieve the time-average velocity models with uncertainties less than 10% in sites with laterally varying velocities. The error on one-way times at various depths of the datum plan retrieved by the time-average velocity models is mostly less than 5 ms for synthetic and field data.
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Ko, B. "Reconstruction of surface velocity field using wavelet transformation and boundary-element method". Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 221, n.º 2 (1 de fevereiro de 2007): 167–75. http://dx.doi.org/10.1243/0954406jmes319.
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This paper shows the application of discrete wavelet transformation (DWT) to inverse acoustics for reconstructing the surface velocity of a noise source. This approach uses the boundary-element analysis based on the measured sound pressure at a set of field points, the Helmholtz integral equations, and wavelet transformation to reconstruct the normal surface velocity field. The reconstructed velocity field can be diverged due to the small measurement errors in the case of nearfield acoustic holography using an inverse boundary-element method. In order to bypass the instability in the inverse problem, the reconstruction process should include some form of regularization for enhancing the resolution of source images. The usual method of regularization has been the truncation of wave vectors associated with small singular values, although the order of an optimal truncation is difficult to determine. In this paper, a DWT is applied to reduce the computation time for inverse acoustics and to enhance the reconstructed surface velocity field. The computational speed-up is achieved, with solution time being reduced to 14.3 per cent.
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Moret, Geoff J. M., William P. Clement, Michael D. Knoll e Warren Barrash. "VSP traveltime inversion: Near‐surface issues". GEOPHYSICS 69, n.º 2 (março de 2004): 345–51. http://dx.doi.org/10.1190/1.1707053.
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P‐wave velocity information obtained from vertical seismic profiles (VSPs) can be useful in imaging subsurface structure, either by directly detecting changes in the subsurface or as an aid to the interpretation of seismic reflection data. In the shallow subsurface, P‐wave velocity can change by nearly an order of magnitude over a short distance, so curved rays are needed to accurately model VSP traveltimes. We used a curved‐ray inversion to estimate the velocity profile and the discrepancy principle to estimate the data noise level and to choose the optimum regularization parameter. The curved‐ray routine performed better than a straight‐ray inversion for synthetic models containing high‐velocity contrasts. The application of the inversion to field data produced a velocity model that agreed well with prior information. These results show that curved‐ray inversion should be used to obtain velocity information from VSPs in the shallow subsurface.
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Ульянов, Олег Николаевич, e Людмила Ильинична Рубина. "On irrotational vector fields with vector lines located on a given surface". Herald of Tver State University. Series: Applied Mathematics, n.º 3(66) (1 de dezembro de 2022): 49–61. http://dx.doi.org/10.26456/vtpmk645.
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Рассматриваются безвихревые векторные поля на поверхности, заданной уравнением $a=z+\alpha(x,y,t)=0$. Изучаются условия, при выполнении которых векторные линии таких полей располагаются на этой поверхности. Получены достаточные условия существования гармонического векторного поля с такими векторными линиями. Изучена переопределенная система уравнений в частных производных, решение которой обеспечивает получение гармонического поля, векторные линии которого лежат на заданной поверхности рассматриваемого вида. Выписано уравнение поверхности, для которой можно найти гармоническое векторное поле с векторными линиями расположенными на этой поверхности. Показано, что для любых поверхностей рассматриваемого вида можно найти безвихревые негармонические векторные поля с векторными линиями, расположенными на заданной поверхности. Приведен ряд поверхностей, для которых указаны гармонические или негармонические безвихревые векторные поля с векторными линиями расположенными на этих поверхностях. Рассмотрена система уравнений Навье - Стокса для вязкой несжимаемой жидкости в безразмерном виде. Для этой системы в предположении потенциальности поля скоростей выписано частное решение, обеспечивающее расположение векторных линии поля скоростей на параболоиде вращения. Irrotational vector fields are considered on the surface given by the equation $a=z+\alpha(x,y,t)=0$. The conditions under which the vector lines of such fields are located on this surface are studied. Sufficient conditions for the existence of a harmonic vector field with such vector lines are obtained. An overdetermined system of partial differential equations is studied, the solution of which provides a harmonic field, the vector lines of which lie on a given surface of the considered type. The equation of the surface is written, for which it is possible to find a harmonic vector field with vector lines located on this surface. It is shown that for any surfaces of the type under consideration, one can find irrotational nonharmonic vector fields with vector lines located on a given surface. A number of surfaces are given for which harmonic or nonharmonic irrotational vector fields with vector lines located on these surfaces are obtained. Navier - Stokes equations for a viscous incompressible fluid in nondimensional form are considered. For this system, under the assumption that the velocity field is potential, a particular solution is written that ensures the location of the vector lines of the velocity field on a paraboloid of revolution.
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Kierulf, Halfdan Pascal, Holger Steffen, Valentina R. Barletta, Martin Lidberg, Jan Johansson, Oddgeir Kristiansen e Lev Tarasov. "A GNSS velocity field for geophysical applications in Fennoscandia". Journal of Geodynamics 146 (julho de 2021): 101845. http://dx.doi.org/10.1016/j.jog.2021.101845.
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Neves, Diogo R. C. B., Moisés Brito, António Alberto Pires-Silva, Conceição Juana Fortes e Jorge Matos. "Experimental Investigation of Air Bubble Curtain Effects on Water Wave Field". Defect and Diffusion Forum 415 (27 de abril de 2022): 81–99. http://dx.doi.org/10.4028/p-9jm010.
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This paper studies the effects of an air bubble curtain on surface water waves. Water particle velocities and free surface elevations were measured simultaneously at two cross-shore locations downstream of the air bubble curtain. Measurements were carried out for regular waves using different air bubble curtain configurations. Free surface elevations were measured using resistive gauges and the instantaneous velocities were acquired using an Acoustic Doppler Velocimeter (ADV). The characteristics of the free surface elevation time series, velocity field and turbulence are analyzed and discussed. The free surface elevation was found to be attenuated by the air bubble curtains. The phase averaged velocity profiles also depict the effect of the air bubbles in the flow field by generating milder longitudinal velocities (u) and by increasing the transverse component of the velocity (w). The increase in the turbulence intensity and the different energy spectrum produced by the air bubble curtain is also observed. The experimental results indicate that the thickness of the air bubble curtain and the total air flow rate affects the wave field.
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Beasley, Craig, e Walt Lynn. "The zero‐velocity layer: Migration from irregular surfaces". GEOPHYSICS 57, n.º 11 (novembro de 1992): 1435–43. http://dx.doi.org/10.1190/1.1443211.
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Seismic data acquired in areas with irregular topography are usually corrected to a flat datum before migration. A time‐honored technique for handling elevation changes is to time shift the data before application of migration. This simple time shift, or elevation‐static correction, cannot properly represent wide‐angle or dipping reflections as they would have been recorded at the datum. As a result, when elevation varies significantly, accuracy in event positioning may be compromised for migration and other wave‐equation processes, such as dip moveout processing (DMO). Traditionally, such over‐ and under‐migration artifacts have been dealt with by increasing or decreasing the migration velocity. However, simple adjustment of the migration velocity cannot undo the wave‐field distortions induced in seismic data acquired over varying elevations. More sophisticated and accurate solutions such as wave‐equation datuming are too computationally demanding for routine use. Here, we propose an efficient and accurate technique for doing migration from irregular surfaces using conventional migration algorithms. As in elevation‐static corrections, surface‐recorded data are time‐shifted to a horizontal datum; for our process, we choose to have that datum elevation lie at or above the highest elevation in the survey. After migration, the datum elevation can always be adjusted to any other level by means of a bulk time shift. In the migration step, the velocity is set to zero (or some very small value) in the layer between the surface and the datum; below the original surface, the interval velocity represents the best estimate of the subsurface geology. By adding a zero‐velocity layer, the migration algorithm is applied to the data from the flat datum and no lateral propagation is allowed until a nonzero velocity is encountered at the recording surface. Synthetic and field data examples demonstrate that use of the “zero‐velocity layer” significantly improves imaging accuracy relative to conventional migration from a flat datum. Moreover, the geologically derived migration‐velocity field need not be adjusted to compensate for shortcomings in the datum‐static procedure. The technique can be extended to prestack processes such as DMO, shot‐ and receiver‐gather downward extrapolation, and migration and thus suggests a unified approach to processing data from irregular surfaces.
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Yao, Congcong, Chengpeng Lu, Wei Qin e Jiayun Lu. "Field Experiments of Hyporheic Flow Affected by a Clay Lens". Water 11, n.º 8 (3 de agosto de 2019): 1613. http://dx.doi.org/10.3390/w11081613.
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As a typical water exchange of surface water and groundwater, hyporheic flow widely exists in streambeds and is significantly affected by the characteristics of sediment and surface water. In this study, a low-permeability clay lens was chosen to investigate the influence of the streambed heterogeneity on the hyporheic flow at a river section of the Xin’an River in Anhui Province, China. A 2D sand tank was constructed to simulate the natural streambed including a clay lens under different velocity of surface water velocity. Heat tracing was used in this study. In particular, six analytical solutions based on the amplitude ratio and phase shift of temperatures were applied to calculate the vertical hyporheic flux. The results of the six methods ranged from −102.4 to 137.5 m/day and showed significant spatial differences. In view of the robustness of the calculations and the rationality of the results, the amplitude ratio method was much better than the phase shift method. The existence of the clay lens had a significant influence on the hyporheic flow. Results shows that the vertical hyporheic flux in the model containing a clay lens was lower than that for the blank control, and the discrepancy of the hyporheic flow field on both sides of the lens was obvious. Several abnormal flow velocity zones appeared around the clay lens where the local hyporheic flow was suppressed or generally enhanced. The hyporheic flow fields at three test points had mild changes when the lens was placed in a shallow layer of the model, indicating that the surface water velocity only affect the hyporheic flow slightly. With the increasing depth of the clay lens, the patterns of the hyporheic flow fields at all test points were very close to those of the hyporheic flow field without a clay lens, indicating that the influence of surface water velocity on hyporheic flow appeared gradually. A probable maximum depth of the clay lens was 30 to 40 cm, which approached the bottom of the model and a clay lens buried lower than this maximum would not affect the hyporheic flow any more. Influenced by the clay lens, hyporheic flow was hindered or enhanced in different regions of streambed, which was also depended on the depth of lens and surface water velocity. Introducing a two-dimensional sand tank model in a field test is an attempt to simulate a natural streambed and may positively influence research on hyporheic flow.
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Eslick, Robert, Georgios Tsoflias e Don Steeples. "Field investigation of Love waves in near-surface seismology". GEOPHYSICS 73, n.º 3 (maio de 2008): G1—G6. http://dx.doi.org/10.1190/1.2901215.
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We examine subsurface conditions and survey parameters suitable for successful exploitation of Love waves in near-surface investigations. Love-wave generation requires the existence of a low shear-velocity surface layer. We examined the minimum thickness of the near-surface layer necessary to generate and record usable Love-wave data sets in the frequency range of [Formula: see text]. We acquired field data on a hillside with flat-lying limestone and shale layers that allowed for the direct testing of varying overburden thicknesses as well as varying acquisition geometry. The resulting seismic records and dispersion images were analyzed, and the Love-wave dispersion relation for two layers was examined analytically. We concluded through theoretical and field data analysis that a minimum thickness of [Formula: see text] of low-velocity material is needed to record usable data in the frequency range of interest in near-surface Love-wave surveys. The results of this study indicate that existing guidelines for Rayleigh-wave data acquisition, such as receiver interval and line length, are also applicable to Love-wave data acquisition.
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Paasche, Hendrik, Ulrike Werban e Peter Dietrich. "Near-surface seismic traveltime tomography using a direct-push source and surface-planted geophones". GEOPHYSICS 74, n.º 4 (julho de 2009): G17—G25. http://dx.doi.org/10.1190/1.3131612.
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Information about seismic velocity distribution in heterogeneous near-surface sedimentary deposits is essential for a variety of environmental and engineering geophysical applications. We have evaluated the suitability of the minimally invasive direct-push technology for near-surface seismic traveltime tomography. Geophones placed at the surface and a seismic source installed temporarily in the subsurface by direct-push technology quickly acquire reversed multioffset vertical seismic profiles (VSPs). The first-arrival traveltimes of these data were used to reconstruct the 2D seismic velocity distribution tomographically. After testing this approach on synthetic data, we applied it to field data collected over alluvial deposits in a former river floodplain. The resulting velocity model contains information about high- and low-velocity anomalies and offers a significantly deeper penetration depth than conventional refraction tomography using surface-planted sources and receivers at the investigated site. A combination of refraction seismic and direct-push data increases resolution capabilities in the unsaturated zone and enables reliable reconstruction of velocity variations in near-surface unconsolidated sediments. The final velocity model structurally matches the results of cone-penetration tests and natural gamma-radiation data acquired along the profile. The suitability of multiple rapidly acquired reverse VSP surveys for 2D tomographic velocity imaging of near-surface unconsolidated sediments was explored.
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Zhang, Enzhan, Liang Li, Weiche Huang, Yucheng Jia, Minghu Zhang, Faming Kang e Hu Da. "Measuring Velocity and Discharge of High Turbidity Rivers Using an Improved Near-Field Remote-Sensing Measurement System". Water 16, n.º 1 (29 de dezembro de 2023): 135. http://dx.doi.org/10.3390/w16010135.
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Large-scale particle image velocimetry (LSPIV) is a computer vision-based technique renowned for its precise and efficient measurement of river surface velocity. However, a crucial prerequisite for utilizing LSPIV involves camera calibration. Conventional techniques rely on ground control points, thus restricting their scope of application. This study introduced a near-field remote-sensing measurement system based on LSPIV, capable of accurately measuring river surface velocity sans reliance on ground control points. The system acquires gravity-acceleration data using a triaxial accelerometer and converts this data into a camera pose, thereby facilitating swift camera calibration. This study validates the system through method verification and field measurements. The method verification results indicate that the system’s method for retroactively deriving ground control-point coordinates achieves an accuracy exceeding 90%. Then, field measurements were performed five times to assess the surface velocity of the Datong River. These measured results were analyzed and compared with data collected from the radar wave velocity meter (RWCM) and the LS1206B velocity meter. Finally, a comprehensive sensitivity analysis of each parameter was conducted to identify those significantly impacting the river’s surface velocity. The findings revealed that this system achieved an accuracy exceeding 92% for all river surface velocities measured.
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Wang, Yufang, e Nannan Wang. "Influence of the Projectile Rotation on the Supersonic Fluidic Element". Aerospace 10, n.º 1 (31 de dezembro de 2022): 35. http://dx.doi.org/10.3390/aerospace10010035.
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The effects of projectile rotation on the internal and external flow fields of the supersonic fluidic element are numerically studied using sliding grid technique and the RNG k-ε turbulence model. The effects of rotating speed on internal and external flow fields, switching time and output characteristics are studied. The results show that: for the external flow field, there is no obvious change in the flow field structure at low angular velocity; when the angular velocity increases to 20 r/s, the flow field structure becomes obviously asymmetric due to the Coriolis force; the flow field far away from the surface of the projectile body (more than 0.3 m) is much more affected than the flow field near the surface of the projectile body. The influence of projectile rotation on the internal flow field is much weaker than on the external flow field, and the change of internal flow field is not obvious when the rotational speed is less than 20 r/s. The switching time decreases with the increase in angular velocity, and within normal range of the angular velocity, the deviation of switching time from that without rotation is within 5%. The change of thrust distribution is not obvious when the rotational speed is less than 20 r/s. However, when the rotational speed reaches 50 r/s, the thrust of the middle part of the right nozzle increases by about 20 N.