Dynamic spreading on pillar-arrayed surfaces: Viscous resistance versus molecular friction

A mirror-image model of the Lucy Ashton was covered with two different "mesh-type" roughnesses and tested in a wind tunnel. Total drag and velocity profile measurements are presented. Total drag results are also given for a normal Lucy Ashton model with the same roughness mesh tested in a towing tank. The influence of roughness on the wave drag component was found to be small, implying that the "interdependence" of wavemaking and viscous resistance is small. The importance of considering roughness as a local parameter is demonstrated, and the roughness function results agree well with the fully developed turbulent pipe flow results of Perry and Abell, even though the ship boundary-layer outer flow did not follow any recognized wake function.

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The heart works against gravity

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.1993.265.4.r715 ◽

1993 ◽

Vol 265 (4) ◽

pp. R715-R720 ◽

Cited By ~ 8

Author(s):

R. S. Seymour ◽

A. R. Hargens ◽

T. J. Pedley

Keyword(s):

Blood Pressure ◽

Blood Flow ◽

Potential Energy ◽

Flow Rate ◽

Viscous Resistance ◽

Arterial Blood ◽

Experimental Artifact ◽

Continuous Stream ◽

Laboratory Models ◽

Poiseuille Equation

The circulatory systems of vertebrate animals are closed, and blood leaves and returns to the heart at the same level. It is often concluded, therefore, that the heart works only against the viscous resistance of the system, not against gravity, even in vascular loops above the heart in which the siphon principle operates. However, we argue that the siphon principle does not assist blood flow in superior vascular loops if any of the descending vasculature is collapsible. If central arterial blood pressure is insufficient to support a blood column between the heart and the head, blood flow ceases because of vascular collapse. Furthermore, the siphon principle does not assist the heart even when a continuous stream of blood is flowing in a superior loop. The potential energy gained by blood as it is pumped to the head is lost to friction in partially collapsed descending vessels and thus is not regained. Application of the Poiseuille equation to flow in collapsible vessels is limited; resistance depends on flow rate in partially collapsed vessels with no transmural pressure difference, but flow rate is independent of resistance. Thus the pressure developed by the heart to establish a given flow rate is independent of the resistance occurring in the partially collapsed vessels. The pressure depends only on the height of the blood column and the resistance in the noncollapsed parts of the system. Simple laboratory models, involving water flow in collapsible tubing, dispel the idea that the siphon principle facilitates blood flow and suggest that previously published results may have been affected by experimental artifact.

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The Research of a New Method for Manipulating Magnetic Beads through Multi-Layered Flat Micro-Coils Coupled with Permanent Magnet

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.753-755.1571 ◽

2013 ◽

Vol 753-755 ◽

pp. 1571-1575

Author(s):

Zhi Hua Liu ◽

Yu Feng Huang ◽

Jian Peng Li ◽

Xin Wei Xu

Keyword(s):

Magnetic Field ◽

Permanent Magnet ◽

Flow Velocity ◽

Magnetic Beads ◽

Magnetic Bead ◽

New Method ◽

Viscous Resistance ◽

Main Factors ◽

The Magnetic Field

Magnetic bead droplet's non-contacted manipulation can be realized in Electromagnetic MEMS, but how to achieve magnetic beads manipulation is the major problem. A new method of multi-layered flat coils coupled with permanent magnet was proposed. Firstly, the theory of magnetic bead manipulation was analyzed and the main factors affected the magnetic beads manipulation was identified; then the magnetic field of multi-layered flat coils and Stokes viscous resistance of magnetic beads were analyzed and simulated quantificationally; finally the magnetic bead capture area was got under different flow velocity. Consequently the feasibility and correctness of this method was verified.

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Asymmetric Molecular Friction in Supported Phospholipid Bilayers Revealed by NMR Measurements of Lipid Diffusion

Langmuir ◽

10.1021/la9712810 ◽

1998 ◽

Vol 14 (5) ◽

pp. 982-984 ◽

Cited By ~ 61

Author(s):

M. Hetzer ◽

S. Heinz ◽

S. Grage ◽

T. M. Bayerl

Keyword(s):

Phospholipid Bilayers ◽

Lipid Diffusion ◽

Molecular Friction

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Contribution of Viscous Forces to Avalanche Dynamics

Annals of Glaciology ◽

10.3189/s0260305500007898 ◽

1989 ◽

Vol 13 ◽

pp. 202-206 ◽

Cited By ~ 2

Author(s):

K. Nishimura ◽

N. Maeno

Keyword(s):

Dry Friction ◽

Kinematic Viscosity ◽

Viscosity Coefficient ◽

Viscous Force ◽

Viscous Resistance ◽

Resistance Factors ◽

Viscous Forces ◽

Viscosity Coefficients ◽

Avalanche Dynamics ◽

The Individual

Mini-avalanche systems were constructed both in a low-temperature laboratory and in a snowfield, and the behaviour of the flowing snow was observed in each case. Velocity profiles for the individual snow particles were determined and these implied that a viscous force, which has been neglected in most previous numerical simulations of snow-avalanche motion, needs to be taken into account for many avalanches. Kinematic viscosity coefficients for the fluidized snow were also measured using a modified Stormer-type viscometer. Substituting the dry-friction value and the kinematic viscosity coefficient for fluidized snow into the equation for avalanche motion, numerical simulation of natural events was achieved for the Shiai-dani region. Taking viscous resistance factors into account led to the conclusion that the magnitude of turbulent resistance of snow in avalanche systems is probably much smaller than that represented by the values previously in use.

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An Experimental Study of the Viscous Resistance of a 0,564-CB Form

Journal of Ship Research ◽

10.5957/jsr.1979.23.2.140 ◽

1979 ◽

Vol 23 (02) ◽

pp. 140-156

Author(s):

P. N. Joubert ◽

P. H. Hoffmann

Keyword(s):

Experimental Study ◽

Reynolds Number ◽

Skin Friction ◽

Resistance Coefficient ◽

Viscous Resistance ◽

Local Skin ◽

Friction Resistance ◽

Local Skin Friction ◽

The University ◽

Resistance Coefficients

Wind tunnel tests were performed to determine the viscous resistance and its components for a 0.564-CB model from the BSRA Trawler Series. It was found that the sum of the pressure and skin friction resistance coefficients agreed well with the viscous resistance coefficient determined from drag balance tests. The range of Reynolds number examined was from 1.15 × 106 to 5.17 × 106. The results for the viscous resistance and its components were fitted using least-squares methods to various equations. The results were also compared with the results of previous tests done at the University of Melbourne on models of Lucy Ash-. ton and a 0.80-CB tanker. It was found that the skin friction and viscous resistance coefficients had curves of quite different position and slope. Local skin friction distribution showed noteworthy differences, especially at the stern, with high values at the keel and low values approaching the waterline.

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Variation of Streaming Potentials with Time under Steady Fluid Pressure in Bone

Applied Sciences ◽

10.3390/app9183726 ◽

2019 ◽

Vol 9 (18) ◽

pp. 3726

Author(s):

Liu ◽

Hou ◽

Qin ◽

Fu ◽

Pan

Keyword(s):

Theoretical Model ◽

Fluid Pressure ◽

Fluid Flows ◽

Experimental Setup ◽

Viscous Resistance ◽

Streaming Potentials ◽

Charge Densities ◽

Holding Period ◽

Plate Specimen ◽

Haversian Canals

This paper investigates the streaming potentials’ behaviors when fluid flows through the micropores in bone. An experimental setup was developed for measuring the streaming potentials between two surfaces of a bone plate specimen. It was found that the streaming potentials measured increased almost linearly with time under a constant fluid pressure gradient, which does not agree with the prediction from the classical theory of streaming potentials. To explain the reasons associated with the results obtained, a theoretical model was proposed in which the electric charge densities on the inner surfaces of the capillary are unevenly distributed. A formula was developed for solving the model, and the solutions demonstrate that nonuniform accumulations of electric charges carried by the fluid on the inner surfaces of the microcanals in bone can induce streaming potentials which linearly increase with time during the driving air pressure holding period. This phenomenon represents the specific characteristics of bone. The solution implies that the streaming potentials in Haversian canals, lacunas and canaliculi are not affected by electro-viscous resistance in the bone fluid.

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