M.J.J. Nijhof

An overview of models for viscothermal wave propagation, including fluid structure interaction

In acoustics, the standard wave propagation models neglect the effects of viscosity and thermal conductivity. When waves propagate in narrow tubes or thin layers these simplifications might not be accurate. This paper presents an overview of models that take the effects of inertia, viscosity, thermal conductivity and compressibility into account. Based on the use of dimensionless parameters, three classes of models are outlined. The most important dimensionless parameter is the shear wave number, an unsteady Reynolds number that indicates the ratio between inertial and viscous effects. These viscothermal wave propagation models can be coupled to structural models to capture the fluid structure interaction. Analytical solutions can be found for these coupled analysis cases only for simple geometries and boundary conditions. For more complex geometries, numerical models were developed. Examples of applications of these models are also presented.

Structural and acoustic noise radiated by compact disk drives

Optical drives inside PCs typically operate at high speed, which may result in significant noise. These drives function both as airborne and structural vibration sources. Three main paths can be distinguished through which noise is emitted to the surroundings: (1) the vibrations of the front of the optical drive emit noise directly into the far field, (2) the sound waves induced by the vibrations of the faces of the optical drives inside the enclosure excites the enclosure, and (3) the structural path from the mounting points of the optical drive to the enclosure. The techniques used to determine the contribution of each path are described and the results of an experimental setup are presented in this paper. The contribution of the structural path is determined by comparing the results of a normal setup with the result of a setup for which the structural path is eliminated by mounting the CD drive on a support that is structurally uncoupled from the PC. Direct measurements of the pressure with a scanning ...