Chromospheric Velocity Fields Diagnostics from CaII and MgII Emission Profiles

Abstract We examine the process of convective dissolution in a Hele–Shaw cell. We consider a one-sided configuration and we propose a newly developed method to reconstruct the velocity field from concentration measurements. The great advantage of this Concentration-based Velocity Reconstruction (CVR) method consists of providing both concentration and velocity fields with a single snapshot of the experiment recorded in high resolution. We benchmark our method vis–à–vis against numerical simulations in the instance of Darcy flows, and we also include dispersive effects to the reconstruction process of non-Darcy flows. The absence of laser sources and the presence of one low-speed camera make this method a safe, accurate, and cost-effective alternative to classical PIV/PTV velocimetry processes. Finally, as an example of possible application, we employ the CVR method to analyse the tip splitting phenomena. Graphic abstract

Download Full-text

Upscaling, Computational Aspects, and Statistics of the Velocity Field

Applied Stochastic Hydrogeology ◽

10.1093/oso/9780195138047.003.0011 ◽

2003 ◽

Author(s):

Yoram Rubin

Keyword(s):

High Resolution ◽

Velocity Field ◽

Heterogeneous Media ◽

Effective Properties ◽

Computational Effort ◽

Velocity Fields ◽

Level Of Detail ◽

Small Scale ◽

Scale Heterogeneity ◽

Computationally Intensive

This chapter deals with computing the velocity fields in heterogeneous media. This is a broad area, and we shall concentrate here on upscaling, on the spatial correlation pattern of the velocity, and on accuracy measures for techniques that compute velocity fields. Numerical simulations of velocity fields in heterogeneous media (Ababou et al., 1988, 1989; Bellin et al., 1992, 1994; Bellin and Rubin, 1996; Dykaar and Kitandis, 1992a,b; Hassan et al., 1998a,b; Salandin and Fiorotto, 1998) indicate that to capture accurately the effects of the spatial variability of the conductivity on the velocity field, the conductivity field should be modeled with high resolution. Techniques for generating highly detailed realizations of rock properties were reviewed earlier. Because of the huge level of detail included in these realizations, large-scale flow simulations can become computationally intensive. However, the need for fine detail varies over the aquifer. For example, a high level of detail is needed where the velocity field may vary rapidly, such as near wells, or over areas traversed by a contaminant plume, or for describing small-scale features which dominate the flow, such as high-conductivity channels. Coarsening the grid over areas where high resolution is unnecessary can reduce the computational effort. To be able to do that, a procedure is needed for assigning properties such as conductivity on a coarser scale which is more appropriate for simulation, while avoiding the loss of important details. Such a procedure is called upscaling (also scale-up). Upscaling assigns properties to blocks based on subgrid-scale heterogeneity. Upscaling leads to block-effective properties. Unlike effective properties, block-effective properties depend on the size of the block. In the limit of block dimensions much larger than the integral scale of the heterogeneity, the block-effective properties become equal to the media's effective properties. Unlike the case of effective conductivities, there is no consensus about the definition of block conductivity. For example, Rubin and Gomez-Hernandez (1990) defined the block conductivity as the coefficient of proportionality between the block-averaged flux and the gradient. Indelman and Dagan (1993a, b) stipulated that the block-effective conductivity should dissipate energy at a rate equal to the dissipation due to the small-scale heterogeneity.

Download Full-text

Experimental Validation of Falling Liquid Film Models: Velocity Assumption and Velocity Field Comparison

Polymers ◽

10.3390/polym13081205 ◽

2021 ◽

Vol 13 (8) ◽

pp. 1205

Author(s):

Ruiqi Wang ◽

Riqiang Duan ◽

Haijun Jia

Keyword(s):

Experimental Data ◽

Particle Image Velocimetry ◽

Velocity Field ◽

Experimental Validation ◽

Particle Image ◽

Velocity Fields ◽

Number Range ◽

Comparison Results ◽

Image Velocimetry ◽

Experimental Particle

This publication focuses on the experimental validation of film models by comparing constructed and experimental velocity fields based on model and elementary experimental data. The film experiment covers Kapitza numbers Ka = 278.8 and Ka = 4538.6, a Reynolds number range of 1.6–52, and disturbance frequencies of 0, 2, 5, and 7 Hz. Compared to previous publications, the applied methodology has boundary identification procedures that are more refined and provide additional adaptive particle image velocimetry (PIV) method access to synthetic particle images. The experimental method was validated with a comparison with experimental particle image velocimetry and planar laser induced fluorescence (PIV/PLIF) results, Nusselt’s theoretical prediction, and experimental particle tracking velocimetry (PTV) results of flat steady cases, and a good continuity equation reproduction of transient cases proves the method’s fidelity. The velocity fields are reconstructed based on different film flow model velocity profile assumptions such as experimental film thickness, flow rates, and their derivatives, providing a validation method of film model by comparison between reconstructed velocity experimental data and experimental velocity data. The comparison results show that the first-order weighted residual model (WRM) and regularized model (RM) are very similar, although they may fail to predict the velocity field in rapidly changing zones such as the front of the main hump and the first capillary wave troughs.

Download Full-text

High Resolution Observations of Neutral Hydrogen in M33 - II: THE VELOCITY FIELD

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/163.2.163 ◽

1973 ◽

Vol 163 (2) ◽

pp. 163-182 ◽

Cited By ~ 99

Author(s):

P. J. Warner ◽

M. C. H. Wright ◽

J. E. Baldwin

Keyword(s):

High Resolution ◽

Velocity Field ◽

Neutral Hydrogen

Download Full-text

Solutions for Non-Newtonian Flow Into Elliptical Openings

Journal of Applied Mechanics ◽

10.1115/1.2897268 ◽

1991 ◽

Vol 58 (3) ◽

pp. 820-824 ◽

Cited By ~ 5

Author(s):

A. Bogobowicz ◽

L. Rothenburg ◽

M. B. Dusseault

Keyword(s):

Finite Element Analysis ◽

Finite Element ◽

Steady State ◽

Hydrostatic Pressure ◽

Velocity Field ◽

Velocity Fields ◽

Newtonian Flow ◽

Element Analysis ◽

Elliptical Opening ◽

Elliptical Coordinates

A semi-analytical solution for plane velocity fields describing steady-state incompressible flow of nonlinearly viscous fluid into an elliptical opening is presented. The flow is driven by hydrostatic pressure applied at infinity. The solution is obtained by minimizing the rate of energy dissipation on a sufficiently flexible incompressible velocity field in elliptical coordinates. The medium is described by a power creep law and solutions are obtained for a range of exponents and ellipse eccentricites. The obtained solutions compare favorably with results of finite element analysis.

Download Full-text

A 4D continuous representation of myocardial velocity fields from tissue phase mapping magnetic resonance imaging

PLoS ONE ◽

10.1371/journal.pone.0247826 ◽

2021 ◽

Vol 16 (3) ◽

pp. e0247826

Author(s):

Bård A. Bendiksen ◽

Gary McGinley ◽

Ivar Sjaastad ◽

Lili Zhang ◽

Emil K. S. Espe

Keyword(s):

Velocity Field ◽

Velocity Fields ◽

Tissue Phase Mapping ◽

Continuous Representation ◽

Resonance Imaging ◽

Limits Of Agreement ◽

B Splines ◽

End Point ◽

Tissue Phase ◽

Linear B

Myocardial velocities carry important diagnostic information in a range of cardiac diseases, and play an important role in diagnosing and grading left ventricular diastolic dysfunction. Tissue Phase Mapping (TPM) Magnetic Resonance Imaging (MRI) enables discrete sampling of the myocardium’s underlying smooth and continuous velocity field. This paper presents a post-processing framework for constructing a spatially and temporally smooth and continuous representation of the myocardium’s velocity field from TPM data. In the proposed scheme, the velocity field is represented through either linear or cubic B-spline basis functions. The framework facilitates both interpolation and noise reducing approximation. As a proof-of-concept, the framework was evaluated using artificially noisy (i.e., synthetic) velocity fields created by adding different levels of noise to an original TPM data. The framework’s ability to restore the original velocity field was investigated using Bland-Altman statistics. Moreover, we calculated myocardial material point trajectories through temporal integration of the original and synthetic fields. The effect of noise reduction on the calculated trajectories was investigated by assessing the distance between the start and end position of material points after one complete cardiac cycle (end point error). We found that the Bland-Altman limits of agreement between the original and the synthetic velocity fields were reduced after application of the framework. Furthermore, the integrated trajectories exhibited consistently lower end point error. These results suggest that the proposed method generates a realistic continuous representation of myocardial velocity fields from noisy and discrete TPM data. Linear B-splines resulted in narrower limits of agreement between the original and synthetic fields, compared to Cubic B-splines. The end point errors were also consistently lower for Linear B-splines than for cubic. Linear B-splines therefore appear to be more suitable for TPM data.

Download Full-text

Glacier Image Velocimetry: an open-source toolbox for easy and rapid calculation of high-resolution glacier velocity fields

The Cryosphere ◽

10.5194/tc-15-2115-2021 ◽

2021 ◽

Vol 15 (4) ◽

pp. 2115-2132

Author(s):

Maximillian Van Wyk de Vries ◽

Andrew D. Wickert

Keyword(s):

High Resolution ◽

Open Source ◽

Velocity Fields ◽

Surface Velocity ◽

Displacement Fields ◽

Desktop Computer ◽

Ice Cap ◽

Image Velocimetry ◽

Glacier Ice ◽

Glacier Velocity

Abstract. We present Glacier Image Velocimetry (GIV), an open-source and easy-to-use software toolkit for rapidly calculating high-spatial-resolution glacier velocity fields. Glacier ice velocity fields reveal flow dynamics, ice-flux changes, and (with additional data and modelling) ice thickness. Obtaining glacier velocity measurements over wide areas with field techniques is labour intensive and often associated with safety risks. The recent increased availability of high-resolution, short-repeat-time optical imagery allows us to obtain ice displacement fields using “feature tracking” based on matching persistent irregularities on the ice surface between images and hence, surface velocity over time. GIV is fully parallelized and automatically detects, filters, and extracts velocities from large datasets of images. Through this coupled toolchain and an easy-to-use GUI, GIV can rapidly analyse hundreds to thousands of image pairs on a laptop or desktop computer. We present four example applications of the GIV toolkit in which we complement a glaciology field campaign (Glaciar Perito Moreno, Argentina) and calculate the velocity fields of small mid-latitude (Glacier d'Argentière, France) and tropical glaciers (Volcán Chimborazo, Ecuador), as well as very large glaciers (Vavilov Ice Cap, Russia). Fully commented MATLAB code and a stand-alone app for GIV are available from GitHub and Zenodo (see https://doi.org/10.5281/zenodo.4624831, Van Wyk de Vries, 2021a).

Download Full-text

Improved convergence and stability properties in a three-dimensional higher-order ice sheet model

Geoscientific Model Development Discussions ◽

10.5194/gmdd-4-1569-2011 ◽

2011 ◽

Vol 4 (3) ◽

pp. 1569-1610

Author(s):

J. J. Fürst ◽

O. Rybak ◽

H. Goelzer ◽

B. De Smedt ◽

P. de Groen ◽

...

Keyword(s):

Velocity Field ◽

Finite Difference ◽

Three Dimensional ◽

Ice Sheet ◽

Higher Order ◽

Velocity Fields ◽

Force Balance ◽

Staggered Grid ◽

Comparison Results ◽

Resultant Velocity

Abstract. We present a novel finite difference implementation of a three-dimensional higher-order ice sheet model that performs well both in terms of convergence rate and numerical stability. In order to achieve these benefits the discretisation of the governing force balance equation makes extensive use of information on staggered grid points. Using the same iterative solver, an existing discretisation that operates exclusively on the regular grid serves as a reference. Participation in the ISMIP-HOM benchmark indicates that both discretisations are capable of reproducing the higher-order model inter-comparison results. This allows a direct comparison not only of the resultant velocity fields but also of the solver's convergence behaviour which holds main differences. First and foremost, the new finite difference scheme facilitates convergence by a factor of up to 7 and 2.6 in average. In addition to this decrease in computational costs, the precision for the resultant velocity field can be chosen higher in the novel finite difference implementation. For high precisions, the old discretisation experiences difficulties to converge due to large variation in the velocity fields of consecutive Picard iterations. Finally, changing discretisation prevents build-up of local field irregularites that occasionally cause divergence of the solution for the reference discretisation. The improved behaviour makes the new discretisation more reliable for extensive application to real ice geometries. Higher precision and robust numerics are crucial in time dependent applications since numerical oscillations in the velocity field of subsequent time steps are attenuated and divergence of the solution is prevented. Transient applications also benefit from the increased computational efficiency.

Download Full-text

Analysis of Convective Thunderstorm Split Cells in South-Eastern Romania

International Journal of Atmospheric Sciences ◽

10.1155/2013/162541 ◽

2013 ◽

Vol 2013 ◽

pp. 1-19 ◽

Cited By ~ 3

Author(s):

Daniel Carbunaru ◽

Sabina Stefan ◽

Monica Sasu ◽

Victor Stefanescu

Keyword(s):

Velocity Field ◽

Velocity Fields ◽

Severe Weather ◽

Doppler Velocity ◽

Doppler Weather Radar ◽

Dynamic Features ◽

South Eastern ◽

Wind Profiles ◽

Convective Cells ◽

Splitting Process

The mesoscale configurations are analysed associated withthesplitting process of convective cells responsible for severe weather phenomena in the south-eastern part of Romania. The analysis was performed using products from the S-band Doppler weather radar located in Medgidia. The cases studied were chosen to cover various synoptic configurations when the cell splitting process occurs. To detect the presence and intensity of the tropospheric jet, the Doppler velocity field and vertical wind profiles derived from radar algorithms were used. The relative Doppler velocity field was used to study relative flow associated with convective cells. Trajectories and rotational characteristics associated with convective cells were obtained from reflectivity and relative Doppler velocity fields at various elevations. This analysis highlights the main dynamic features associated with the splitting process of convective cells: the tropospheric jet and vertical moisture flow associated with the configuration of the flow relative to the convective cells for the lower and upper tropospheric layers. These dynamic characteristics seen in the Doppler based velocity field and in the relative Doppler velocity field to the storm can indicate further evolution of convective developments, with direct implications to very short range forecast (nowcasting).

Download Full-text

Large-scale, high-resolution maps of interseismic strain accumulation from Sentinel-1, and incorporation of along-track measurements

10.5194/egusphere-egu21-15946 ◽

2021 ◽

Author(s):

Andy Hooper ◽

Pawan Piromthong ◽

Tim Wright ◽

Jonathan Weiss ◽

Milan Milan Lazecky ◽

...

Keyword(s):

Time Series ◽

High Resolution ◽

Velocity Field ◽

Reference Frame ◽

Line Of Sight ◽

Tectonic Deformation ◽

Low Resolution ◽

Gnss Measurements ◽

Along Track ◽

East West

High-resolution geodetic measurements of crustal deformation from InSAR have the potential to provide crucial constraints on a region&#8217;s tectonics, geodynamics and seismic hazard. Here, we present a high-resolution crustal velocity field for the Alpine-Himalayan Seismic Belt (AHSB) derived from Sentinel-1 InSAR and GNSS. We create time series and average velocities from ~220,000 interferograms covering an area of 15 million km2, with an average of 170 acquisitions per measurement point. We tie the velocities to a Eurasian reference frame by jointly inverting the InSAR data with GNSS data to produce a low-resolution model of 3D surface velocities. We then use the referenced InSAR velocities to invert for high-resolution east-west and sub-vertical velocity fields for the entire region. The sub-vertical velocities, which also include a small component of north-south motion, are dominated by non-tectonic deformation, such as subsidence due to water extraction. The east-west velocity field, however, reveals the tectonics of the AHSB with an unprecedented level of detail.The approach described above only provides good constraints on horizontal displacement in the east-west direction, with the north-south component provided by low-resolution GNSS measurements. Sentinel-1 does also have the potential to provide measurements that are sensitive to north-south motion, through exploitation of the burst overlap areas produced by the TOPS acquisition mode. These along-track measurements have lower precision than line-of-sight InSAR and are more effected by ionospheric noise, but have the advantage of being almost insensitive to tropospheric noise. We present a time series approach to tease out the subtle along-track signals associated with interseismic strain. Our approach includes improvements to the mitigation of ionospheric noise and we also investigate different filtering approaches to optimize the reduction of decorrelation noise. In contrast to the relative measurements of line-of-sight InSAR, these along-track measurements are automatically provided in a global reference frame. We present results from five years of data for the West-Lut Fault in eastern Iran and the Chaman Fault in Pakistan and Afghanistan. Our results agree well with independent GNSS measurements; however, the denser coverage of the technique allows us to also detect the variation in slip rate along the faults.Finally, we demonstrate the improvement in the resolution of horizontal strain rates when including these along-track measurements, in addition to the conventional line-of-sight InSAR measurements.

Download Full-text