Optimal navigation in a planar time-varying point-symmetric flow-field

2011 ◽  
Author(s):  
Laszlo Techy
Keyword(s):  
Flow Field ◽  
Time Varying ◽  
Symmetric Flow

Flow field and mass transport analysis in arteries with longitudinal ridges

1976 ◽  
Vol 41 (6) ◽  
pp. 910-919 ◽  
Author(s):  
L. H. Back ◽  
D. W. Crawford ◽  
R. Barndt
Keyword(s):  
Flow Field ◽  
Three Dimensional ◽  
Shear Stresses ◽  
Time Varying ◽  
Intimal Thickening ◽  
Three Dimensional Flow ◽  
Longitudinal Vortices ◽  
Arterial Walls ◽  
Transport Analysis

Recent observations have indicated that the earliest lesions of atherosclerosis frequently take the form of longitudinal and helical ridges in arteries of man. Since longitudinal vortices are expected to be present in the troughs between the longitudinal ridges, an analysis was carried out to investigate the three-dimensional flow field and the trasport of lipoproteins and oxygen molecules to arterial walls in the presence of such vortices. The calculations revealed that local hypoxia and lipoprotein accumulation mayoccur at the ridges, leading to subsequent intimal thickening and ridge growth. Higher shear stresses, calculated in the troughs between ridges, may also partially damage the endothelium and lead to intimal thickening and subsequent merging of the ridges. Meaningful measurements are needed in vivo to determine the strength of the vortices, their time-varying behavior, and the actual transverse variations in shear stress, oxygen transport, and lipoprotein accumulation from trough to ridge regions, in order to appraise the present findings and to learn more about the observed progressive thickening and widening of ridges with increasing degrees of intimal thickening and atherosclerosis.

Impingement of Under-Expanded Jets on a Flat Plate

1990 ◽  
Vol 112 (2) ◽  
pp. 179-184 ◽  
Author(s):  
J. Iwamoto
Keyword(s):  
Shock Wave ◽  
Flow Field ◽  
Flat Plate ◽  
Maximum Pressure ◽  
Axially Symmetric ◽  
Symmetric Flow ◽  
Reversed Flow ◽  
Pressure Distributions ◽  
Sonic Jet ◽  
Wave Forms

When an under-expanded sonic jet impinges on a perpendicular flat plate, a shock wave forms just in front of the plate and some interesting phenomena can occur in the flow field between the shock and the plate. In this paper, experimental and numerical results on the flow pattern of this impinging jet are presented. In the experiments the flow field was visualized using shadow-photography and Mach-Zehnder interferometry. In the numerical calculations, the two-step Lax-Wendroff scheme was applied, assuming inviscid, axially symmetric flow. Some of the pressure distributions on the plate show that the maximum pressure does not occur at the center of the plate and that a region of reversed flow exists near the center of the plate.

scholarly journals Heading Perception Depends on Time-Varying Evolution of Optic Flow

2018 ◽  
Author(s):  
Charlie S. Burlingham ◽  
David J. Heeger
Keyword(s):  
Flow Field ◽  
Optic Flow ◽  
Discrimination Task ◽  
Extended Period ◽  
Time Varying ◽  
Temporal Derivative ◽  
Novel Method ◽  
Considerable Support ◽  
Over Time ◽  
Phase Motion

There is considerable support for the hypothesis that perception of heading in the presence of rotation is mediated by instantaneous optic flow. This hypothesis, however, has never been tested. We introduce a novel method, termed “non-varying phase motion,” for generating a stimulus that conveys a single instantaneous optic flow field, even though the stimulus is presented for an extended period of time. In this experiment, observers viewed stimulus videos and performed a forced choice heading discrimination task. For non-varying phase motion, observers made large errors in heading judgments. This suggests that instantaneous optic flow is insufficient for heading perception in the presence of rotation. These errors were mostly eliminated when the velocity of phase motion was varied over time to convey the evolving sequence of optic flow fields corresponding to a particular heading. This demonstrates that heading perception in the presence of rotation relies on the time-varying evolution of optic flow. We hypothesize that the visual system accurately computes heading, despite rotation, based on optic acceleration, the temporal derivative of optic flow.

scholarly journals Heading perception depends on time-varying evolution of optic flow

2020 ◽  
Vol 117 (52) ◽  
pp. 33161-33169
Author(s):  
Charlie S. Burlingham ◽  
David J. Heeger
Keyword(s):  
Flow Field ◽  
Visual System ◽  
Optic Flow ◽  
Discrimination Task ◽  
Extended Period ◽  
Time Varying ◽  
Temporal Derivative ◽  
Considerable Support ◽  
Over Time ◽  
Phase Motion

There is considerable support for the hypothesis that perception of heading in the presence of rotation is mediated by instantaneous optic flow. This hypothesis, however, has never been tested. We introduce a method, termed “nonvarying phase motion,” for generating a stimulus that conveys a single instantaneous optic flow field, even though the stimulus is presented for an extended period of time. In this experiment, observers viewed stimulus videos and performed a forced-choice heading discrimination task. For nonvarying phase motion, observers made large errors in heading judgments. This suggests that instantaneous optic flow is insufficient for heading perception in the presence of rotation. These errors were mostly eliminated when the velocity of phase motion was varied over time to convey the evolving sequence of optic flow fields corresponding to a particular heading. This demonstrates that heading perception in the presence of rotation relies on the time-varying evolution of optic flow. We hypothesize that the visual system accurately computes heading, despite rotation, based on optic acceleration, the temporal derivative of optic flow.

Video Painting Based on a Stabilized Time-Varying Flow Field

2012 ◽  
Vol 18 (1) ◽  
pp. 58-67 ◽  
Author(s):  
Jong-Chul Yoon ◽  
In-Kwon Lee ◽  
H. Kang
Keyword(s):  
Flow Field ◽  
Time Varying

LES simulation of flow field and pollutant dispersion in a street canyon under time-varying inflows with TimeVarying-SIMPLE approach

2019 ◽  
Vol 157 ◽  
pp. 185-196 ◽  
Author(s):  
Weijun Li ◽  
Yuanping He ◽  
Yunwei Zhang ◽  
Junwei Su ◽  
Chungang Chen ◽  
...  
Keyword(s):  
Flow Field ◽  
Street Canyon ◽  
Pollutant Dispersion ◽  
Simple Approach ◽  
Time Varying

Unsteady Effects on Transonic Turbine Blade-Tip Heat Transfer

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
Nicholas R. Atkins ◽  
Steven J. Thorpe ◽  
Roger W. Ainsworth
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Flow Distribution ◽  
Potential Interaction ◽  
Rotor Blades ◽  
Time Varying ◽  
Trailing Edge ◽  
Blade Tip ◽  
Transonic Turbine ◽  
The Impact

In a gas turbine engine the blade tips of the high-pressure turbine are exposed to high levels of convective heat transfer, because of the so-called tip-leakage phenomenon. The blade-lift distribution is known to control the flow distribution in the blade–tip gap. However, the interaction between upstream nozzle guide vanes and the rotor blades produces a time-varying flow field that induces varying flow conditions around the blade and within the tip gap. Extensive measurements of the unsteady blade-tip heat transfer have been made in an engine representative transonic turbine. These include measurements along the mean camber line of the blade tip, which have revealed significant variation in both time-mean and time-varying heat flux. The influences of potential interaction and the vane trailing edge have been observed. Numerical calculations of the turbine stage using a Reynolds-averaged-Navier-Stokes-based computational fluid dynamics code have also been conducted. In combination with the experimental results, these have enabled the time-varying flow field to be probed in the blade-relative frame of reference. This has allowed a deeper analysis of the unsteady heat-transfer data, and the quantification of the impact of vane potential field and vane trailing edge interaction on the tip-region flow and heat transfer. In particular, the separate effects of time-varying flow temperature and heat-transfer coefficient have been established.

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