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Standard isentropic acoustic models do not include the dissipative effects of viscous friction and heat conduction. These viscothermal effects can be important, for example in models of small acoustic transducers. Viscothermal acoustics can be modeled in arbitrary geometries with models that contain four or fivecoupled fields. Therefore, these fully coupled models are computationally costly.O nt he other hand, efficient approximate viscothermal acoustic models exist, butthese are only applicable to certain simplified geometries. Anew approximate model is presented which fills the gapbetween these twoextremes. This newmodel can be used for arbitrary geometries and has acomputational efficiencywhich is higher than the full model and lower than the models with geometrical constraints. The newmodel is derivedand demonstrated on several problems, including acoustic-structure interaction problems.

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In elastohydrodynamic lubrication (EHL), one generally imposes force balance, i.e., the contact force resulting from the pressure in the contact is equal to the applied load. When studying the effect of structural vibrations, this force balance equation obviously does not hold and the more general equation of motion is required. In Wijnant and Venner (1996), an EHL contact model was introduced that incorporates both squeeze and entraining motion as well as the equation of motion. It was shown numerically that due to a small initial deviation or initial velocity, the rolling element starts an oscillatory motion around the equilibrium position. This motion is slightly damped because of the viscous losses in the lubricant. Moreover, it was shown that these oscillations cause film thickness modulations with a wavelength, directly related to the dimensionless frequency Ω. This paper compares results from experiments that were carried out on a ball and disk apparatus with results obtained with the EHL contact model. In this experiment, the applied load was rapidly increased by impacting a wedge between the base and the ball holder. This results in an increase of the contact area and, as a result of inertia forces of the ball, disk and supports, and oscillatory motion of the contacting bodies. Modulations in the film thickness which result from these oscillations, are clearly visible. The contact model was tailored to this experiment and a qualitatively close agreement has been found.

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In this paper, it is investigated how accurately current models predict the response of an elasto-hydrodynamically lubricated contact to time varying load conditions. For two patterns of time varying load, under conditions of pure rolling, the results obtained experimentally on a ball on disk interferometry apparatus by Sakamoto et al. (Behaviour of point contact EHL films under pulsating loads. 705-716). The observed film changes are explained and related to the piezoviscous behaviour of the lubricant. Results for two different viscosity pressure relations are presented. It is shown that the details of the viscosity pressure relation have little effect on the local phenomena observed. The agreement between experimental and theoretical results is excellent in terms of the location and width of induced film thickness changes. The accuracy of the amplitude of the predicted changes is less. A more accurate amplitude prediction requires more precise knowledge of the dynamic parameters, which describe the load system used in the experiments.