Motion and wake structure of spherical particles

This paper presents results from a flow visualization study of the wake structures behind solid spheres rising or falling freely in liquids under the action of gravity. These show remarkable differences to the wake structures observed behind spheres held fixed. The two parameters controlling the rise or fall velocity (i.e., the Reynolds number) are the density ratio between sphere and liquid and the Galileo number.Comment: 9 pages, 8 figures. Higher resolution on demand. To appear in Nonlinearity January 200

Frame Capture in IEEE 802.11p Vehicular Networks

IEEE 802.11p is the new standard proposed by the IEEE for wireless connectivity in a vehicular context. It can be used by Advanced Driver Assistance Systems (ADAS) and Intelligent Transport Systems (ITS) to make vehicles aware of the traffic around them and increase vehicle safety with applications like cooperative cruise control, assisted merging and assisted lane switching. It is an amendment to the 802.11 standards family, with a physical layer based on Orthogonal Frequency Division Multiplexing (OFDM) similar to 802.11a. It is designed operate in a harsh environment. The increased degree of movement in a vehicular network creates Doppler shift, for example when vehicles connect to roadside units. Also, the cars on the road generate a significantcant amount of scattering and fast fading effects. This Doppler shift and other effects are accounted for in the design of the physical layer of 802.11p

A brief summary of L. van Wijngaarden's work up till his retirement

This paper attempts to provide an overview of Professor Leen van Wijngaarden's scientific work by briefly summarizing a number of his papers. The review is organized by topic and covers his work on pressure waves in bubbly liquids, bubble dynamics, two-phase flow, standing waves in resonant systems, and flow cavitation noise. A list of publications up till his retirement in March 1997 is provided in the Appendix

On the characteristics of the equations of motion for a bubbly flow and the related problem of critical flow

For the study of transients in gas-liquid flows, the equations of the so-called separated flow model are inadequate, because they possess, in the general case where gas and liquid move at different velocities, complex characteristics. This paper is concerned with the equations of motion for bubbly flow. The equations are discussed with emphasis on the aspects of relative motion and the characteristics are calculated. It is found that all characteristics are real. The results are used to establish a relation between gas velocity, liquid velocity, void fraction and sound velocity at critical flow. This relation agrees very well with experimental data for these quantities as measured by Muir and Eichhorn in the throat of a converging-diverging nozzle

The emission of sound by statistically homogeneous bubble layers

This paper is concerned with the flow of a bubbly fluid along a wavy wall, which is one Fourier component of a linearized hydrofoil. The bubbles are dispersed, not throughout the whole of the liquid, but only over a certain distance from the wall, as occurs in practice with cavitation bubbles. Outside the bubbly regime there is pure liquid. The interface between the bubbly fluid and pure liquid fluctuates for various reasons. One of these is the relative motion between bubbles and liquid. This is considered here in detail. A calculation is made of the sound emitted by the bubbly layer into pure liquid as a result of this stochastic motion of the interface

Wall forces on a sphere in a rotating liquid-filled cylinder

We experimentally study the behavior of a particle slightly denser than the surrounding liquid in solid body rotating flow. Earlier work revealed that a heavy particle has an unstable equilibrium point in unbounded rotation flows. In the confinement of the rotational flow by a cylindrical wall a heavy sphere with density 1.05 g/cm$^3$ describes an orbital motion in our experiments. This is due to the effect of the wall near the sphere, i.e. a repulsive force ($F_w$). We model $F_w$ on the sphere as a function of the distance from the wall ($L$): $F_W \propto L^{-4}$ as proposed by Takemura and Magnaudet (2003). Remarkably, the path from the model including $F_w$ reproduce the experimentally measured trajectory. In addition during an orbital motion the particle does not spin around its axis, and we provide a possible explanation for this phenomenon.Comment: 11 pages, 11 figure

International developments in the position of assisting spouses and the possible implications for the Netherlands

Vergelijking van de situatie van meewerkende vrouwen in Nederland en de overige lidstaten van de Europese Unie. Aandacht wordt besteed aan ontwikkelingen op Europees en Nederlands niveau en de formele erkenning, die onder te verdelen is in professionele erkenning, financiële erkenning, participatieve en representatieve erkenning, en administratieve erkenning.