scholarly journals Acquisition of a 3 min, two-dimensional glacier velocity field with terrestrial radar interferometry

2017 ◽  
Vol 63 (240) ◽  
pp. 629-636 ◽  
Author(s):  
DENIS VOYTENKO ◽  
TIMOTHY H. DIXON ◽  
DAVID M. HOLLAND ◽  
RYAN CASSOTTO ◽  
IAN M. HOWAT ◽  
...  
Keyword(s):  
Velocity Field ◽  
Flow Field ◽  
Feature Tracking ◽  
High Spatial Resolution ◽  
Velocity Fields ◽  
Radar Interferometry ◽  
Line Of Sight ◽  
Two Dimensional ◽  
Outlet Glacier ◽  
Glacier Velocity

ABSTRACTOutlet glaciers undergo rapid spatial and temporal changes in flow velocity during calving events. Observing such changes requires both high temporal and high spatial resolution methods, something now possible with terrestrial radar interferometry. While a single such radar provides line-of-sight velocity, two radars define both components of the horizontal flow field. To assess the feasibility of obtaining the two-dimensional (2-D) flow field, we deployed two terrestrial radar interferometers at Jakobshavn Isbrae, a major outlet glacier on Greenland's west coast, in the summer of 2012. Here, we develop and demonstrate a method to combine the line-of-sight velocity data from two synchronized radars to produce a 2-D velocity field from a single (3 min) interferogram. Results are compared with the more traditional feature-tracking data obtained from the same radar, averaged over a longer period. We demonstrate the potential and limitations of this new dual-radar approach for obtaining high spatial and temporal resolution 2-D velocity fields at outlet glaciers.

scholarly journals Velocity Field around a Rigid Flapping Wing with a Winglet in Quiescent Water

2020 ◽  
Author(s):  
Srikanth Goli ◽  
Arnab Roy ◽  
Subhransu Roy
Keyword(s):  
Velocity Field ◽  
Flow Field ◽  
Particle Image ◽  
Added Mass ◽  
Velocity Fields ◽  
Flapping Wing ◽  
Residual Flow ◽  
Two Dimensional ◽  
Image Velocimetry ◽  
Phase Angles

This study investigated the effect of a winglet on the velocity field around a rigid flapping wing. Two-dimensional particle image velocimetry was used to capture the velocity field of asymmetric one-degree-of-freedom flapping motion. A comparison was conducted between wings with and without a winglet at two flapping frequencies, namely 1.5 and 2.0 Hz. The effect of the winglet on the velocity field was determined by systematically comparing the velocity fields for several wing phase angles during the downstroke and upstroke. The presence of a winglet considerably affected the flow field around the wingtip, residual flow, and added mass interaction. The added mass was lower and residual flow was weaker for the wings with a winglet than for the wings without a winglet. The added mass and velocity magnitudes of the flow field increased proportionally with the flapping frequency.

Conditions for the Separability of Objects in Two-Dimensional Velocity Fields

1992 ◽  
Vol 35 (4) ◽  
pp. 484-491
Author(s):  
Stephan Foldes
Keyword(s):  
Velocity Field ◽  
Directed Graph ◽  
Velocity Fields ◽  
Sufficient Condition ◽  
Two Dimensional ◽  
Jordan Curves ◽  
Directed Cycles

AbstractWe consider the directed graph representing the obstruction relation between objects moving along the streamlines of a two-dimensional velocity field. A collection of objects is sequentially separable if and only if the corresponding graph has no directed cycles. A sufficient condition for this is the permeability of closed Jordan curves.

scholarly journals Evolving Features of Hβ Doppler Velocity Fields at Sites of Flares

1993 ◽  
Vol 141 ◽  
pp. 267-270
Author(s):  
Wei Li ◽  
Guoxiang Ai ◽  
Hongqi Zhang
Keyword(s):  
Velocity Field ◽  
Active Regions ◽  
Velocity Fields ◽  
Time Sequence ◽  
Line Of Sight ◽  
Doppler Velocity

AbstractWe analyzed eight active regions with more than 600 flare kernels and ribbons, and relevant time sequence Hβ chromospheric Dopplergrams. These data showed that during several hours prior to the flares, the velocity field evolves so that the sites of the flare kernels and ribbons become close to the inversion line of the velocity field. This result holds regardless of whether or not the flare sites are wholly located in blue-shifted areas, or are far from the the inversion line of the line-of-sight velocity field, or are partly within red-shifted areas.

Study of three-dimensional unsteady Oseen flow

1978 ◽  
Vol 86 (4) ◽  
pp. 609-622 ◽  
Author(s):  
S. Murata ◽  
Y. Miyake ◽  
Y. Tsujimoto ◽  
F. Yamamoto
Keyword(s):  
Flow Field ◽  
External Force ◽  
Three Dimensional ◽  
Velocity Fields ◽  
Applied Force ◽  
Two Dimensional ◽  
Uniform Velocity ◽  
Pressure Fields ◽  
Oseen Flow ◽  
Impulsive Pressure

In the present paper, it is intended to give the elementary solutions of three-dimensional unsteady Oseen flow when unsteady concentrated lift and/or drag is applied in the flow field. It is shown that the pressure fields due to concentrated impulsive lift and/or drag can be represented by an impulsive pressure doublet in the direction of the applied force and the corresponding velocity fields by diffusing free doublets in the direction of the external force that are shed from the location of the force application and convected downstream with otherwise uniform velocity. It is also confirmed that combination of the elementary solutions given in the present paper yields the two-dimensional ones.

Density and velocity fields in collisionless flow past a diffusely reflecting cone

1970 ◽  
Vol 48 (13) ◽  
pp. 1628-1631
Author(s):  
James Parker Elliott
Keyword(s):  
Flow Field ◽  
Free Stream ◽  
Angle Of Attack ◽  
Velocity Fields ◽  
Circular Cone ◽  
Two Dimensional ◽  
Transition Flow ◽  
Flow Past ◽  
Monatomic Gas

Results of flow field calculations for the collisionless flow of a neutral, monatomic gas past a diffusely reflecting right circular cone at zero angle of attack with the free stream are presented. Singularities at the vertex and at the shoulder of the base are illustrated and discussed. Comparison is made with similar results for spheres and two-dimensional polygonal bodies and with results for transition flow past sharp cones. Methods for improving the analysis are suggested.

SYMMETRIC LARGE-SCALE VELOCITY FIELDS IN TWO-DIMENSIONAL THERMAL CONVECTION

1994 ◽  
Vol 04 (05) ◽  
pp. 1369-1374 ◽  
Author(s):  
J. PRAT ◽  
I. MERCADER ◽  
J.M. MASSAGUER
Keyword(s):  
Stability Analysis ◽  
Velocity Field ◽  
Velocity Profile ◽  
Numerical Simulations ◽  
Linear Stability Analysis ◽  
Thermal Convection ◽  
Vertical Profile ◽  
Large Scale ◽  
Velocity Fields ◽  
Two Dimensional

Recent experiments on thermal convection in finite containers [Krishnamurti & Howard, 1981; Howard & Krishnamurti, 1986] show the presence of flows spanning the largest dimension of the container. Numerical simulations of 2D thermal convection showing large-scale flows of this kind have been presented elsewhere [Prat et al., 1993a, 1993b]. In every known example the large scale velocity field has been found to display a vertical profile either antisymmetric or showing rather small departures from antisymmetry. In contrast, theoretical group arguments support the existence of symmetric velocity profiles. In the present paper it will be shown that large-scale velocity fields with vertically symmetric velocity profile do exist. In spite of these flows not being dominant in the range of parameters explored, their geometry and dynamics will be discussed on the basis of a linear stability analysis.

scholarly journals Velocity fields in and around sunspots at the highest resolution

2010 ◽  
Vol 6 (S273) ◽  
pp. 204-211
Author(s):  
Carsten Denker ◽  
Meetu Verma
Keyword(s):  
Feature Tracking ◽  
Three Dimensional ◽  
Velocity Fields ◽  
Dimensional Structure ◽  
Line Of Sight ◽  
Proper Motions ◽  
Magnetic Shear ◽  
Flow Channels ◽  
Review Reports

AbstractThe flows in and around sunspots are rich in detail. Starting with the Evershed flow along low-lying flow channels, which are cospatial with the horizontal penumbral magnetic fields, Evershed clouds may continue this motion at the periphery of the sunspot as moving magnetic features in the sunspot moat. Besides these well-ordered flows, peculiar motions are found in complex sunspots, where they contribute to the build-up or relaxation of magnetic shear. In principle, the three-dimensional structure of these velocity fields can be captured. The line-of-sight component of the velocity vector is accessible with spectroscopic measurements, whereas local correlation or feature tracking techniques provide the means to assess horizontal proper motions. The next generation of ground-based solar telescopes will provide spectropolarimetric data resolving solar fine structure with sizes below 50 km. Thus, these new telescopes with advanced post-focus instruments act as a ‘zoom lens’ to study the intricate surface flows associated with sunspots. Accompanied by ‘wide-angle’ observations from space, we have now the opportunity to describe sunspots as a system. This review reports recent findings related to flows in and around sunpots and highlights the role of advanced instrumentation in the discovery process.

scholarly journals Two-Dimensional Rotorcraft Downwash Flow Field Measurements by Lidar-Based Wind Scanners with Agile Beam Steering

2014 ◽  
Vol 31 (4) ◽  
pp. 930-937 ◽  
Author(s):  
Mikael Sjöholm ◽  
Nikolas Angelou ◽  
Per Hansen ◽  
Kasper Hjorth Hansen ◽  
Torben Mikkelsen ◽  
...  
Keyword(s):  
Flow Field ◽  
Wind Energy ◽  
Continuous Wave ◽  
Beam Steering ◽  
Vertical Plane ◽  
Line Of Sight ◽  
Opening Angle ◽  
Wind Component ◽  
Good Resolution ◽  
Two Dimensional

Abstract A major risk to helicopters is the unexpected encounter of degraded visual environments in close-to-ground operations, where a loss of visibility often is caused by clouds of dust (brownout) or snow (whiteout) stirred up by intense downwash. The understanding of the phenomenon is limited, and there is a need for instruments that can measure flow fields on scales larger than a few meters with good resolution. This paper reports on the use of synchronized continuous-wave Doppler lidars for rotorcraft downwash flow field studies. Built from a modified ZephIR wind lidar and a double-prism arrangement for agile beam steering, a wind scanner—WindScanner—has been developed at the Department of Wind Energy at the Technical University of Denmark (DTU) Risø campus. The WindScanner measures the line-of-sight component of the airflow remotely and by rapid steering, the line-of-sight direction and the focus position; all points in space within a cone with a full opening angle of 120° can be reached from about 8 m out to some hundred meters depending on the range resolution required. The first two-dimensional mean wind fields measured in a horizontal plane and in a vertical plane below a hovering search and rescue helicopter are presented. Since the line-of-sight directions of the two synchronized WindScanners were scanned within the plane of interest, the influence of the wind component perpendicular to the plane was avoided. The results also demonstrate the possibilities within less demanding flows encountered within complex terrain and wind-energy-related research for which the WindScanner technology primarily has been developed.

Subharmonic dynamo action of fluid motions with two-dimensional periodicity

1995 ◽  
Vol 448 (1933) ◽  
pp. 237-244 ◽  
Keyword(s):  
Magnetic Field ◽  
Velocity Field ◽  
Velocity Fields ◽  
Two Dimensional ◽  
Dynamo Action ◽  
Spatial Periodicity ◽  
The Magnetic Field ◽  
Steady Velocity

Kinematic dynamos based on steady velocity fields with two-dimensional periodicity are analysed numerically. The velocity fields of the study by G. O. Roberts (1972) are used and the analysis is extended to the case when the spatial periodicity of the magnetic field differs from that of the velocity field not only in the homogeneous third direction. While the solutions of Roberts correspond to the most efficient dynamos in most cases, there are some cases in which spatially subharmonic dynamos are preferred.

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