A parametrized three-dimensional model for MEMS thermal shear-stress sensors

The author developed a three-dimensional model for the description of fast plastic deformation of metals in the case of cutting. Shear strain occurring as a result of shear stress has a reverse effect on stress, while the temperature of the material is increasing. These counteracting effects may lead to thermomechanic instability, which may result in aperiodic chaotic conditions besides periodic fluctuation due to the non-linear nature of the process. Apart from bifurcation and multi-cycle periodic deformation, the model also describes aperiodic chaotic deformation, which is proven by experimental results.

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Oxygen mass transfer in a model three-dimensional artery

Journal of The Royal Society Interface ◽

10.1098/rsif.2007.1338 ◽

2008 ◽

Vol 5 (26) ◽

pp. 1067-1075 ◽

Cited By ~ 40

Author(s):

G Coppola ◽

C Caro

Keyword(s):

Mass Transfer ◽

Shear Stress ◽

Vessel Wall ◽

Three Dimensional ◽

Oxygen Mass Transfer ◽

Dimensional Model ◽

Flow Conditions ◽

Human Coronary Artery ◽

Three Dimensional Model ◽

Physiological Flow

Arterial geometry is commonly non-planar and associated with swirling blood flow. In this study, we examine the effect of arterial three-dimensionality on the distribution of wall shear stress (WSS) and the mass transfer of oxygen from the blood to the vessel wall in a U-bend, by modelling the blood vessels as either cylindrical or helical conduits. The results show that under physiological flow conditions, three-dimensionality can reduce both the range and extent of low WSS regions and substantially increase oxygen flux through the walls. The Sherwood number and WSS distributions between the three-dimensional helical model and a human coronary artery show remarkable qualitative agreement, implying that coronary arteries may potentially be described with a relatively simple idealized three-dimensional model, characterized by a small number of well-defined geometric parameters. The flow pattern downstream of a planar bend results in separation of the Sh number and WSS effects, a finding that implies means of investigating them individually.

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Formation of Sand Ripples Under Turbulent Flow Simulated by LES

ASME 2010 3rd Joint US-European Fluids Engineering Summer Meeting: Volume 1, Symposia – Parts A, B, and C ◽

10.1115/fedsm-icnmm2010-30574 ◽

2010 ◽

Author(s):

Yan Cui ◽

John C. Wells ◽

Y. Quoc Nguyen

Keyword(s):

Shear Stress ◽

Numerical Model ◽

Three Dimensional ◽

Sand Wave ◽

Bed Shear Stress ◽

Two Dimensional ◽

Dimensional Model ◽

Three Dimensional Model ◽

Eddy Simulation ◽

Large Eddy

To simulate the initial formation of sedimentary bedforms, constrained to be in hydraulically smooth turbulent flows under bedload conditions, a numerical model based on Large Eddy Simulation (LES) in a doubly periodic domain has been developed. The numerical model comprises three parts. Given the instantaneous bed geometry, the bed shear stress distribution is obtained from a Large-Eddy-Simulation (LES) method coupled with an Immersed-Boundary-Method (IBM). Flux is estimated by the van Rijn’s formula [1]. Finally, evolution of the bed surface is described by the Exner equation. “Two-dimensional bed” [2] and “three-dimensional bed” models employ, respectively, transversely averaged bed shear stress and instantaneous local shear stress to estimate the bedload flux. Based on this model, the evolution of an initial sand wave has been successfully computed. Compared to the “two-dimensional” [2] model, the three-dimensional model leads to a slightly slower propagation and a smaller sand wave. The tendency of the sand wave evolution in three-dimensional model is two-dimensional during the simulated interval.

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Computer Simulation of Flow Dynamics in an Intracranial Aneurysm

Interventional Neuroradiology ◽

10.1177/15910199040100s127 ◽

2004 ◽

Vol 10 (1_suppl) ◽

pp. 155-160 ◽

Cited By ~ 4

Author(s):

N. Kobayashi ◽

S. Miyachi ◽

T. Okamoto ◽

K. Hattori ◽

T. Kojima ◽

...

Keyword(s):

Shear Stress ◽

Flow Pattern ◽

Vessel Wall ◽

Arterial Wall ◽

Three Dimensional ◽

Flow Dynamics ◽

Dimensional Model ◽

Three Dimensional Model ◽

Pressure Peak ◽

Aneurysm Model

Using a supercomputer, the authors studied the effect of vessel wall pulsation on flow dynamics with a three-dimensional model simulating both a rigid and pulsatile style. The design of the aneurysm models was set with a 5 mm dome diameter and a 1 or 3 mm orifice size to simulate a carotid-ophthalmic aneurysm. Flow dynamics were analyzed according to flow pattern, wall pressure and wall shear stress. The flow pattern in the aneurysm sac showed the great difference between rigid and pulsatile models particularly in the small-neck aneurysm model. The arterial wall tended to be exposed to a higher pressure peak in the pulsatile model than in the rigid one, especially at its bifurcation and curved regions. Sites of shear stress peak were found on the aneurysmal dome as well as at the distal end of the orifice in both rigid and pulsatile models. The effects of vessel-wall pulsation should be considered whenever evaluating conditions in and around an aneurysm.

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Impact of the Level of Approximation on Modeling Flushing Waves

Water Practice & Technology ◽

10.2166/wpt.2007.036 ◽

2007 ◽

Vol 2 (2) ◽

Cited By ~ 3

Author(s):

P. Staufer ◽

J. Dettmar ◽

J. Pinnekamp

Keyword(s):

Shear Stress ◽

Numerical Models ◽

Three Dimensional ◽

Shear Stresses ◽

Bottom Shear Stress ◽

Dimensional Model ◽

Three Dimensional Model ◽

Successful Operation ◽

One Dimensional ◽

The One

Sewer cleaning with the means of flushing offers the possibility to place sewers free of deposit if flushing waves are generated continuously or quasi-continuously by suitable flushing devices. Numerical investigations should be carried out regarding different hydraulic circumstances because sewer networks consist of various compounds with complex geometries e.g. cross-section alignment or special structures. To accomplish a stable and successful operation of flushing devices it seems necessary to use different level of approximation on modelling flushing waves. Thereby both accuracy and running-time of simulations with numerical models will be optimized. This paper presents differences and similarities of the simulation results of a one-dimensional and a three-dimensional model of flushing wave within a big sized sewer. As assumed the one-dimensional model becomes less accurate when the complexity of the geometry increases. The three-dimensional model shows an underestimation of velocity and bottom shear-stress at the flushing head due to energy losses within the water body. Contrary, the one-dimensional model overestimates bottom shear-stress at the flushing head because of a stationary basic approach which is used. However, real highly resolved measurements of bottom shear-stresses are required to confirm the results in detail.

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