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Статті в журналах з теми "Advection velocity correction"
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Shapiro, Alan, Joshua G. Gebauer, Nathan A. Dahl, David J. Bodine, Andrew Mahre, and Corey K. Potvin. "Spatially Variable Advection Correction of Doppler Radial Velocity Data." Journal of the Atmospheric Sciences 78, no. 1 (January 2021): 167–88. http://dx.doi.org/10.1175/jas-d-20-0048.1.
Повний текст джерелаАнотація:
AbstractTechniques to mitigate analysis errors arising from the nonsimultaneity of data collections typically use advection-correction procedures based on the hypothesis (frozen turbulence) that the analyzed field can be represented as a pattern of unchanging form in horizontal translation. It is more difficult to advection correct the radial velocity than the reflectivity because even if the vector velocity field satisfies this hypothesis, its radial component does not—but that component does satisfy a second-derivative condition. We treat the advection correction of the radial velocity (υr) as a variational problem in which errors in that second-derivative condition are minimized subject to smoothness constraints on spatially variable pattern-translation components (U, V). The Euler–Lagrange equations are derived, and an iterative trajectory-based solution is developed in which U, V, and υr are analyzed together. The analysis code is first verified using analytical data, and then tested using Atmospheric Imaging Radar (AIR) data from a band of heavy rainfall on 4 September 2018 near El Reno, Oklahoma, and a decaying tornado on 27 May 2015 near Canadian, Texas. In both cases, the analyzed υr field has smaller root-mean-square errors and larger correlation coefficients than in analyses based on persistence, linear time interpolation, or advection correction using constant U and V. As some experimentation is needed to obtain appropriate parameter values, the procedure is more suitable for non-real-time applications than use in an operational setting. In particular, the degree of spatial variability in U and V, and the associated errors in the analyzed υr field are strongly dependent on a smoothness parameter.
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Shapiro, Alan, Stefan Rahimi, Corey K. Potvin, and Leigh Orf. "On the Use of Advection Correction in Trajectory Calculations." Journal of the Atmospheric Sciences 72, no. 11 (November 1, 2015): 4261–80. http://dx.doi.org/10.1175/jas-d-15-0095.1.
Повний текст джерелаАнотація:
Abstract An advection correction procedure is used to mitigate temporal interpolation errors in trajectory analyses constructed from gridded (in space and time) velocity data. The procedure is based on a technique introduced by Gal-Chen to reduce radar data analysis errors arising for the nonsimultaneity of the data collection. Experiments are conducted using data from a high-resolution Cloud Model 1 (CM1) numerical model simulation of a supercell storm initialized within an environment representative of the 24 May 2011 El Reno, Oklahoma, tornadic supercell storm. Trajectory analyses using advection correction are compared to traditional trajectory analyses using linear time interpolation. Backward trajectories are integrated over a 5-min period for a range of data input time intervals and for velocity-pattern-translation estimates obtained from different analysis subdomain sizes (box widths) and first-guess options. The use of advection correction reduces trajectory end-point position errors for a large majority of the trajectories in the analysis domain, with substantial improvements for trajectories launched in the vicinity of the model storm’s gust front and in bands within the rear-flank downdraft. However, the pattern-translation components retrieved by this procedure may be nonunique if the data input time intervals are too large.
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Shapiro, Alan, Katherine M. Willingham, and Corey K. Potvin. "Spatially Variable Advection Correction of Radar Data. Part I: Theoretical Considerations." Journal of the Atmospheric Sciences 67, no. 11 (November 1, 2010): 3445–56. http://dx.doi.org/10.1175/2010jas3465.1.
Повний текст джерелаАнотація:
Abstract Radar data–based analysis products, such as accumulated rainfall maps, dual-Doppler wind syntheses, and thermodynamic retrievals, are prone to substantial error if the temporal sampling interval is too coarse. Techniques to mitigate these errors typically make use of advection-correction procedures (space-to-time conversions) in which the analyzed radial velocity or reflectivity field is idealized as a pattern of unchanging form that translates horizontally at constant speed. The present study is concerned with an advection-correction procedure for the reflectivity field in which the pattern-advection components vary spatially. The analysis is phrased as a variational problem in which errors in the frozen-turbulence constraint are minimized subject to smoothness constraints. The Euler–Lagrange equations for this problem are derived and a solution is proposed in which the trajectories, pattern-advection fields, and reflectivity field are analyzed simultaneously using a combined analytical and numerical procedure. The potential for solution nonuniqueness is explored.
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Miller, William, and Da-Lin Zhang. "A Three-Dimensional Trajectory Model with Advection Correction for Tropical Cyclones: Algorithm Description and Tests for Accuracy." Monthly Weather Review 147, no. 9 (August 12, 2019): 3145–67. http://dx.doi.org/10.1175/mwr-d-18-0434.1.
Повний текст джерелаАнотація:
Abstract When computing trajectories from model output, gridded winds are often temporally interpolated to a time step shorter than model output intervals to satisfy computational stability constraints. This study investigates whether trajectory accuracy may be improved for tropical cyclone (TC) applications by interpolating the model winds using advection correction (AC) instead of the traditional linear interpolation in time (LI) method. Originally developed for Doppler radar processing, AC algorithms interpolate data in a reference frame that moves with the pattern translation, or advective flow velocity. A previously developed trajectory AC implementation is modified here by extending it to three-dimensional (3D) flows, and the advective flows are defined in cylindrical rather than Cartesian coordinates. This AC algorithm is tested on two model-simulated TC cases, Hurricanes Joaquin (2015) and Wilma (2005). Several variations of the AC algorithm are compared to LI on a sample of 10 201 backward trajectories computed from the modeled 5-min output data, using reference trajectories computed from 1-min output to quantify position errors. Results show that AC of 3D wind vectors using advective flows defined as local gridpoint averages improves the accuracy of most trajectories, with more substantial improvements being found in the inner eyewall where the horizontal flows are dominated by rotating cyclonic wind perturbations. Furthermore, AC eliminates oscillations in vertical velocity along LI backward trajectories run through deep convective updrafts, leading to a ~2.5-km correction in parcel height after 20 min of integration.
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Wildmann, Norman, Eileen Päschke, Anke Roiger, and Christian Mallaun. "Towards improved turbulence estimation with Doppler wind lidar velocity-azimuth display (VAD) scans." Atmospheric Measurement Techniques 13, no. 8 (August 4, 2020): 4141–58. http://dx.doi.org/10.5194/amt-13-4141-2020.
Повний текст джерелаАнотація:
Abstract. The retrieval of turbulence parameters with profiling Doppler wind lidars (DWLs) is of high interest for boundary layer meteorology and its applications. DWLs provide wind measurements above the level of meteorological masts while being easier and less expensive to deploy. Velocity-azimuth display (VAD) scans can be used to retrieve the turbulence kinetic energy (TKE) dissipation rate through a fit of measured azimuth structure functions to a theoretical model. At the elevation angle of 35.3∘ it is also possible to derive TKE. Modifications to existing retrieval methods are introduced in this study to reduce errors due to advection and enable retrievals with a low number of scans. Data from two experiments are utilized for validation: first, measurements at the Meteorological Observatory Lindenberg–Richard-Aßmann Observatory (MOL-RAO) are used for the validation of the DWL retrieval with sonic anemometers on a meteorological mast. Second, distributed measurements of three DWLs during the CoMet campaign with two different elevation angles are analyzed. For the first time, the ground-based DWL VAD retrievals of TKE and its dissipation rate are compared to in situ measurements of a research aircraft (here: DLR Cessna Grand Caravan 208B), which allows for measurements of turbulence above the altitudes that are in range for sonic anemometers. From the validation against the sonic anemometers we confirm that lidar measurements can be significantly improved by the introduction of the volume-averaging effect into the retrieval. We introduce a correction for advection in the retrieval that only shows minor reductions in the TKE error for 35.3∘ VAD scans. A significant bias reduction can be achieved with this advection correction for the TKE dissipation rate retrieval from 75∘ VAD scans at the lowest measurement heights. Successive scans at 35.3 and 75∘ from the CoMet campaign are shown to provide TKE dissipation rates with a good correlation of R>0.8 if all corrections are applied. The validation against the research aircraft encourages more targeted validation experiments to better understand and quantify the underestimation of lidar measurements in low-turbulence regimes and altitudes above tower heights.
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Satheesh, Kiran, Gowtham Srinivas, and Santosh Hemchandra. "An advection velocity correction scheme for interface tracking using the level-set method." Computers & Fluids 168 (May 2018): 232–44. http://dx.doi.org/10.1016/j.compfluid.2018.04.010.
Повний текст джерела
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Oue, Mariko, Pavlos Kollias, Alan Shapiro, Aleksandra Tatarevic, and Toshihisa Matsui. "Investigation of observational error sources in multi-Doppler-radar three-dimensional variational vertical air motion retrievals." Atmospheric Measurement Techniques 12, no. 3 (March 29, 2019): 1999–2018. http://dx.doi.org/10.5194/amt-12-1999-2019.
Повний текст джерелаАнотація:
Abstract. Multi-Doppler-radar network observations have been used in different configurations over the last several decades to conduct three-dimensional wind retrievals in mesoscale convective systems. Here, the impacts of the selected radar volume coverage pattern (VCP), the sampling time for the VCP, the number of radars used, and the added value of advection correction on the retrieval of the vertical air motion in the upper part of convective clouds are examined using the Weather Research and Forecasting (WRF) model simulation, the Cloud Resolving Model Radar SIMulator (CR-SIM), and a three-dimensional variational multi-Doppler-radar retrieval technique. Comparisons between the model truth (i.e., WRF kinematic fields) and updraft properties (updraft fraction, updraft magnitude, and mass flux) retrieved from the CR-SIM-generated multi-Doppler-radar field are used to investigate these impacts. The findings are that (1) the VCP elevation strategy and sampling time have a significant effect on the retrieved updraft properties above 6 km in altitude; (2) 2 min or shorter VCPs have small impacts on the retrievals, and the errors are comparable to retrievals using a snapshot cloud field; (3) increasing the density of elevation angles in the VCP appears to be more effective to reduce the uncertainty than an addition of data from one more radar, if the VCP is performed in 2 min; and (4) the use of dense elevation angles combined with an advection correction applied to the 2 min VCPs can effectively improve the updraft retrievals, but for longer VCP sampling periods (5 min) the value of advection correction is challenging. This study highlights several limiting factors in the retrieval of upper-level vertical velocity from multi-Doppler-radar networks and suggests that the use of rapid-scan radars can substantially improve the quality of wind retrievals if conducted in a limited spatial domain.
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Al-Ibadi, Hasan, Karl Stephen, and Eric Mackay. "Novel Observations of Salinity Transport in Low-Salinity Waterflooding." SPE Journal 24, no. 03 (January 9, 2019): 1108–22. http://dx.doi.org/10.2118/190068-pa.
Повний текст джерелаАнотація:
Summary Low-salinity waterflooding (LSWF) is a promising process that could lead to increased oil recovery. To date, the greatest attention has been paid to the complex oil/water/rock chemical reactions that might explain the mechanisms of LSWF, and it is generally accepted that these result in behavior equivalent to changing oil and water mobility. This behavior is modeled using an effective salinity range and weighting function to gradually switch from high- to low-salinity relative permeability curves. There has been limited attention on physical transport of fluids during LSWF, particularly at large scale. We focus on how the salinity profile interacts with water fronts through the effective salinity range and dispersion to alter the transport behavior and change the flow velocities, particularly for the salinity profile. We examined a numerical simulation of LSWF at the reservoir scale. Various representations of the effective salinity range and weighting function were also examined. The dispersion of salinity was compared with a theoretical form of numerical dispersion based on input parameters. We also compared salinity movement with the analytical solution of the conventional dispersion/advection equation. From simulations we observed that salinity is dispersed as analytically predicted, although the advection velocity might be changed. In advection-dominated flow, the salinity profile moves at the speed of the injected water. However, as dispersion increases, the mixing zone falls under the influence of the faster-moving formation water and, thus, speeds up. To predict the salinity profile theoretically, we have modified the advection term of the analytical solution as a function of the formation- and injected-water velocities, Péclet number, and effective salinity range. This important result enables prediction of the salinity transport by this newly derived modification of the analytical solution for 1D flow. We can understand the correction to the flow behavior and quantify it from the model input parameters. At the reservoir scale, we typically simulate flow on coarse grids, which introduces numerical dispersion or must include physical dispersion from underlying heterogeneity. Corrections to the equations can contribute to improving the precision of the coarse-scale models, and, more generally, the suggested form of the correction can also be used to calculate the movement of any solute that transports across an interface between two mobile fluids. We can also better understand the relative behaviors of passive tracers and those that are adsorbed.
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Maneke-Fiegenbaum, Falk, Otto Klemm, Yen-Jen Lai, Chih-Yuan Hung, and Jui-Chu Yu. "Carbon Exchange between the Atmosphere and a Subtropical Evergreen Mountain Forest in Taiwan." Advances in Meteorology 2018 (November 21, 2018): 1–12. http://dx.doi.org/10.1155/2018/9287249.
Повний текст джерелаАнотація:
Tropical, temperate, and boreal forests are the subject of various eddy covariance studies, but less is known about the subtropical region. As there are large areas of subtropical forests in the East Asian monsoon region with possibly high carbon uptake, we used three years (2011–2013) of eddy covariance data to estimate the carbon balance of a subtropical mountain forest in Taiwan. Two techniques of flux partitioning are applied to evaluate ecosystem respiration, thoroughly evaluate the validity of the estimated fluxes, and arrive at an estimate of the yearly net ecosystem exchange (NEE). We found that advection is a strong player at our site. Further, when used alone, the nighttime flux correction with the so-called u∗ method (u∗ = friction velocity) cannot avoid underestimating the nighttime respiration. By using a two-technique method employing both nighttime and daytime parameterizations for flux corrections, we arrive at an estimate of the three-year mean NEE of −561 (±standard deviation 114) g·C·m−2·yr−1. The corrected flux estimate represents a rather large uptake of CO2 for this mountain cloud forest, but the value is in good agreement with the few existing comparable estimates for other subtropical forests.
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Potvin, Corey K., Alan Shapiro, and Ming Xue. "Impact of a Vertical Vorticity Constraint in Variational Dual-Doppler Wind Analysis: Tests with Real and Simulated Supercell Data." Journal of Atmospheric and Oceanic Technology 29, no. 1 (January 1, 2012): 32–49. http://dx.doi.org/10.1175/jtech-d-11-00019.1.
Повний текст джерелаАнотація:
Abstract One of the greatest challenges to dual-Doppler retrieval of the vertical wind is the lack of low-level divergence information available to the mass conservation constraint. This study examines the impact of a vertical vorticity equation constraint on vertical velocity retrievals when radar observations are lacking near the ground. The analysis proceeds in a three-dimensional variational data assimilation (3DVAR) framework with the anelastic form of the vertical vorticity equation imposed along with traditional data, mass conservation, and smoothness constraints. The technique is tested using emulated radial wind observations of a supercell storm simulated by the Advanced Regional Prediction System (ARPS), as well as real dual-Doppler observations of a supercell storm that occurred in Oklahoma on 8 May 2003. Special attention is given to procedures to evaluate the vorticity tendency term, including spatially variable advection correction and estimation of the intrinsic evolution. Volume scan times ranging from 5 min, typical of operational radar networks, down to 30 s, achievable by rapid-scan mobile radars, are considered. The vorticity constraint substantially improves the vertical velocity retrievals in our experiments, particularly for volume scan times smaller than 2 min.
Дисертації з теми "Advection velocity correction"
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Gowtham, Srinivas R. B. "An advection velocity correction scheme for interface tracking using the level-set method." Thesis, 2018. https://etd.iisc.ac.in/handle/2005/5377.
Повний текст джерелаАнотація:
An advection velocity correction (AVC) scheme for interface tracking using the
level-set method is presented in this thesis. The key idea is to apply a correction
to the interface advection velocity at points adjacent to the zero level-set, so as to
enforce the preservation of the signed distance function property at these points.
As such, the AVC scheme eliminates the need for explicit sub-cell x approaches,
as reinitialization at points adjacent to the zero level-set is not needed. This ap-
proach of correcting the advection velocity eld near the interface and computing
the signed distance function (SDF) to a high order of accuracy near the interface,
rather than applying an explicit sub-cell x during the reinitialization step repre-
sents the key novel aspect of the AVC scheme. In this thesis results from using the
AVC scheme along with advection and reinitialization schemes using upwind finite
differencing on uniform meshes are presented. These results are determined for
four canonical test problems: slotted disk rotation, deforming sphere, interacting
circles and vortex in a box. These results are compared with corresponding results
determined using a recently proposed explicit sub-cell x based reinitialization
scheme (CR2). These comparisons show that the AVC scheme yields significantly
improved conservation of enclosed volume/area within the interface. Note that,
the present AVC scheme achieves this by only modifying velocity field values at
mesh points. Therefore, the AVC algorithm can in principle be used within the
framework of nearly any numerical scheme used to compute interface evolution us-
ing the level-set method, even on non-uniform and unstructured meshes, in order
to achieve improvements in solution quality.
Тези доповідей конференцій з теми "Advection velocity correction"
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Collé, Anthony, Jérôme Limido, Thomas Unfer, and Jean-Paul Vila. "An Accurate SPH Scheme for Hypervelocity Impact Modeling." In 2019 15th Hypervelocity Impact Symposium. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/hvis2019-078.
Повний текст джерелаАнотація:
Abstract We focus in this paper on the use of a meshless numerical method called Smooth Particle Hydrodynamics (SPH), to solve fragmentation issues as Hyper Velocity Impact (HVI). Contrary to classical grid-based methods, SPH does not need any opening criteria which makes it naturally well suited to handle material failure. Nevertheless, SPH schemes suffer from well-known instabilities questioning their accuracy and activating nonphysical processes as numerical fragmentation. Many stabilizing tools are available in the literature based for instance on dissipative terms, artificial repulsive forces, stress points or Particle Shifting Techniques (PST). However, they either raise conservation and consistency issues, or drastically increase the computation times. It limits then their effectiveness as well as their industrial application. To achieve robust and consistent stabilization, we propose an alternative scheme called γ -SPH-ALE. Firstly implemented to solve Monophasic Barotropic flows, it is secondly extended to the solid dynamics. Particularly, based on the ALE framework, its governing equations include advective terms allowing an arbitrary description of motion. Thus, in addition of accounting for a stabilizing low-Mach scheme, a PST is implemented through the arbitrary transport velocity field, the asset of ALE formulations. Through a nonlinear stability analysis, CFL-like conditions are formulated ensuring the scheme conservativity, robustness, stability and consistency. Besides, stability intervals are defined for the scheme parameters determining entirely the stability field. Its implementation on several test cases reveals particularly that the proposed scheme faithfully reproduces the strain localization in adiabatic shear bands, a precursor to failure. By preventing spurious oscillations in elastic waves and correcting the so-called tensile instability, it increases both stability and accuracy with respect to classical approaches.
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Schilling, Oleg. "Reynolds-Averaged Navier-Stokes Modeling of Turbulent Rayleigh-Taylor, Richtmyer-Meshkov, and Kelvin-Helmholtz Mixing Using a Higher-Order Shock-Capturing Method." In ASME-JSME-KSME 2019 8th Joint Fluids Engineering Conference. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/ajkfluids2019-5235.
Повний текст джерелаАнотація:
Abstract A numerical implementation of a large number of Reynolds-averaged Navier–Stokes (RANS) models based on two-, three-, four-equation, and Reynolds stress turbulence models (using either the turbulent kinetic energy dissipation rate or the turbulent lengthscale) in an Eulerian, finite-difference shock-capturing code is described. The code uses third-order weighted essentially nonoscillatory (WENO) reconstruction of the advective fluxes, and second- or fourth-order central difference derivatives for the computation of spatial gradients. A third-order TVD Runge–Kutta time-evolution scheme is used to evolve the fields in time. Improved closures for the turbulence production terms, compressibility corrections, mixture transport coefficients, and a consistent initialization methodology for the turbulent fields are briefly summarized. The code framework allows for systematic comparisons of detailed predictions from a variety of turbulence models of increasing complexity. Applications of the code with selected K–ε based models are illustrated for each of the three instabilities. Simulations of Rayleigh–Taylor unstable flows for Atwood numbers 0.1–0.9 are shown to be consistent with previous implicit LES (ILES) results and with the expectation of increased asymmetry in the mixing layer characteristics with increasing stratification. Simulations of reshocked Richtmyer–Meshkov turbulent mixing corresponding to experiments with light-to-heavy transition in air/sulfur hexafluoride and incident shock Mach number Mas = 1.50, and heavy-to-light transition in sulfur hexafluoride/air with Mas = 1.45 are shown to be in generally good agreement with both pre- and post-reshock mixing layer widths. Finally, simulations of the seven Brown–Roshko Kelvin–Helmholtz experiments with various velocity and density ratios using nitrogen, helium, and air are shown to give mixing layer predictions in good agreement with data. The results indicate that the numerical algorithms and turbulence models are suitable for simulating these classes of inhomogeneous turbulent flows.