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Particle-Image-Velocimetry (PIV) has been applied to many different environmental flows in the last twelve years at the Institute for Hydromechanics, Karlsruhe Institute of Technology. The present paper gives an overview about the most important results gained with PIV during this period and summarizes the advantages and disadvantages of this measurement technique. PIV applications to determine velocities at the water surface as well as internal flows characteristics are discussed with respect to physical and technical aspects. It can be concluded that PIV is still not a standard tool, every application needs adaptation and comprises certain limitations. Every element of the measurement system (window size, camera, spatial and temporal resolution, etc.) has to fit exactly the physical problem to be examined. Ó

When flexible polyurethane foam is considered as an effective fluid, the density calculated with the model is much less than the physical density of the absorbent. The inference is that the structure plays little part in the absorptive behaviour. This is confirmed by considering the more elaborate two-fluid model. Ta•. fLUID MOD•.L Or AN ABSOm•ENT HAS BEEN DISCUSSED viously by Ford, Landau, and West. • A longitudinal wave of complex velocity c•* is supposed to propagate in the absorbent, having density p•, which is assumed uniform and isotropic. The normal impedance of a layer of this fluid of thickness d is given by Z• Z• p•C•*coth • • pOC pOC k Ca / The nearfield pressures of a rigid piston (ka=0.906 at f=7.55 kHz) and a flexing piston (ka =2.4 at f=20.0 kHz) in an infinite soft baffle were measured in a tank by means of a toneburst technique. The resulting pressure profiles are presented as isobaric contours, comparable to those for pistons in a rigid baffle derived analytically by H. Stenzel [Handbook for the Calculation