An Elastic Collision Model for Impulsive Jumping by Small Planktonic Organisms

Many small marine planktonic organisms converge on similar propulsion mechanisms that involve impulsively generated viscous wake vortex rings, and small-scale fluid physics is key to mechanistically understanding the adaptive values of this important behavioral trait. Here, a theoretical fluid mechanics model is developed for plankton jumping, based on observations that the initial acceleration phase for a jumping plankter to attain its maximum speed is nearly impulsive, taking only a small fraction of the viscous timescale, and therefore can be regarded as nearly inviscid, analogous to a one-dimensional elastic collision. Flow circulation time-series data measured by particle image velocimetry (PIV) are input into the model and Froude propulsion efficiencies are calculated for several plankton species. Jumping by the tailed ciliate Pseudotontonia sp. has a high Froude propulsion efficiency ~0.9. Copepod jumping also has a very high efficiency, usually >0.95. Jumping by the squid Doryteuthis pealeii paralarvae has an efficiency of 0.44 ± 0.16 (SD). Jumping by the small medusa Sarsia tubulosa has an efficiency of 0.38 ± 0.26 (SD). Differences in the calculated efficiencies are attributed to the different ways by which these plankters impart momentum on the water during the initial acceleration phase as well as the accompanied different added mass coefficients.

Magnetorheological Fluid Test and Application

Magnetorheological fluid is a kind of new intelligent materials, because of its good controllable and mechanical properties; therefore it can be widely used in aerospace, mechanical engineering and automotive engineering, precision processing engineering, control engineering and engineering field. This paper introduces magnetorheological fluid mechanics model of MRF, temperature static shear yield stress, and the influence of MRF static shear yield stress test, introduces magnetorheological fluid in the application of variable hardness collar. The application tendency of the magnetic fluid flow is pointed out

Asymptotic Analysis of Flow Processes at Drawing of Single Optical Microfibres

Microstructured optical fibres (i.e. fibres that contain holes) have assumed a high profile in recent years, and given rise to many novel optical devices. The problem of manufacturing such fibres by heating and then drawing a preform is considered for both the cases of annular microfibres and annular capillaries. A fluid-mechanics model suggested in literature that uses asymptotic analysis based on the small aspect ratio of capillaries is analysed and revised. The leading-order equations are examined in some asymptotic limits, many of which give valuable practical information about the control parameters that influence the drawing process. Additionally, the solution obtained for a single capillary provides a suitable basis for describing more complicated fibre structures.

Haemodynamic stresses and the onset and progression of vascular diseases

Abdominal aortic aneurysm (AAA), a common vascular disease among the adult population, forms in the portion of the aorta below the renal arteries and upstream of its bifurcation into the two iliac arteries. While the precise cause of this vascular disease is still unknown, it is believed to be multi-factorial and predominantly degenerative, arising through a complex interplay among several biological factors as well as from specific local changes in the haemodynamic stresses on the vessel's wall. Using a simple mechanical model to simulate the difference in the stiffness of the aorta and iliac arteries, Duclaux, Gallaire & Clanet (J. Fluid Mech., 2010, this issue, vol. 664, pp. 5–32) propose a scaling argument for the transition between homogeneous and inhomogeneous deformation of an elastic tubular membrane that offers a plausible explanation for the observed localization of the AAAs. While neglecting long-term tissue remodelling and other important biological processes, the fluid mechanics model of Duclaux et al. (2010) appears to be consistent with some known associated risk factors.