Velocity gradient

About: Velocity gradient is a research topic. Over the lifetime, 3013 publications have been published within this topic receiving 77120 citations.

Debris-flow surges : experimental simulation

Abstract: A laboratory moving-bed flume was used to study the development, behaviour and characteristics of high-concentration grain-in-fluid waves. These waves behaved similarly to reported debris-flow pulses. Observation of velocity and concentration profiles within the waves suggests that wave behaviour is mainly controlled by larger grains provided the background slurry of fine grains in water is sufficiently dense; that the front of a pulse is highly erosive while the tail is probably less erosive or depositional; and that the maximum height of a pulse is controlled by the velocity gradient within the flow

Deviation of Velocity Gradient Profiles from the “Gap Loading” and “Surface Loading” Limits in Dynamic Simple Shear Experiments

Abstract: The shear‐wave field generated in a linear viscoelastic medium confined between parallel plates (one fixed, the other oscillating sinusoidally in its own plane) has been evaluated and presented in a graphical form convenient for determination of the role of wave propagation effects in dynamic rheological measurements. The transition from closely spaced planes (“gap loading”) to the freely propagating plane wave (“surface loading”) limit is examined; the importance of deviations in magnitude and phase of the gradient profile from the gap loading limit is discussed in terms of high precision dynamic rheological experiments; significant deviations occur for shear wavelength to gap width ratios of 30 or less.

FENE Dumbbell Model and Its Several Linear and Nonlinear Closure Approximations

Abstract: We present some analytical and numerical studies on the finite extendible nonlinear elasticity (FENE) model of polymeric fluids and its several moment-closure approximations. The well-posedness of the FENE model is established under the influence of a steady flow field. We further infer existence of long-time and steady-state solutions for purely symmetric or antisymmetric velocity gradients. The stability of the steady-state solution for a general velocity gradient is illuminated by the analysis of the FENE-P closure approximation. We also propose a new linear closure approximation utilizing higher moments, which is shown to generate more accurate approximations than other existing closure models for moderate shear or extension rates. An instability phenomenon under a large strain is also investigated. This paper is a sequel to our earlier work [P. Yu, Q. Du, and C. Liu, Multiscale Model. Simul., 3 (2005), pp. 895--917].

Effects of Corner Radius on Stagnation-point Velocity Gradients on Blunt Axisymmetric Bodies

Abstract: Velocity gradient on blunt axisymmetric bodies in stagnation region if pressure distribution is known, using isentropic flow equations

Importance of accurate geometry in the study of the total cavopulmonary connection: computational simulations and in vitro experiments.

Abstract: Previous in vitro studies have shown that total cavopulmonary connection (TCPC) models incorporating offset between the vena cavae are energetically more efficient than those without offsets. In this study, the impact of reducing simplifying assumptions, thereby producing more physiologic models, was investigated by computational fluid dynamics (CFD) and particle flow visualization experiments. Two models were constructed based on angiography measurements. The first model retained planar arrangement of all vessels involved in the TCPC but incorporated physiologic vessel diameters. The second model consisted of constant-diameter vessels with nonplanar vascular features. CFD and in vitro experiments were used to study flow patterns and energy losses within each model. Energy losses were determined using three methods: theoretical control volume, simplified control volume, and velocity gradient based dissipation. Results were compared to a simplified model control. Energy loss in the model with physiologically more accurate vessel diameters was 150% greater than the simplified model. The model with nonplanar features produced an asymmetric flow field with energy losses approximately 10% higher than simplified model losses. With the velocity gradient based dissipation technique, the map of energy dissipation was plotted revealing that most of the energy was dissipated near the pulmonary artery walls. © 2001 Biomedical Engineering Society.