ABSTRACT. While solving harmonic exterior acoustics problems using the traditional finite element method, the domain is truncated at some finite radius on which appropriate absorbing boundary conditions, like spherical damping condition, approximate the Sommerfeld radiation condition.

In exterior domain acoustic wave propagation, there are no incoming waves as the propagating wave do not meet any surface to be reflected. Jog [1] used this physical fact in formulating the Outward wave favouring (OWF) strategy in [1]. He assumed the acoustic pressure in a special form that is favourable to simulate the “Outgoing” nature of the acoustic wave in the exterior domain. In that special form the highly oscillatory part of the acoustic wave, which is common to all exterior harmonic acoustics problems, is separated out. As we are separating out the highly oscillatory part a priori, the frequency term is contained in that separated known oscillatory term. Therefore, FEM has to capture the relatively gentle unknown part which is problem specific and independent of frequency. Hence, this strategy is highly effective for high-frequency exterior domain problems. In this work, we have demonstrated the coarse mesh accuracy of the OWF formulations with various examples running at higher frequencies.

We have compared OWF formulations with their conventional counterpart in terms of L2 error norm over a range of frequencies. Also, we have done a detailed mesh analysis for various benchmark problems over different frequencies. Also, for achieving some expected level of accuracy with respect to the analytical benchmark solutions, the required time has been compared between conventional and OWF elements.

References 1. CS Jog. An outward-wave-favoring finite element based strategy for exterior acoustic problems. International Journal of Acoustics and Vibration, 18(1):27–38, 2013.

ABSTRACT. In the development phase of the seat, the virtual assessment of the ride comfort would be beneficial to save time and money, improve user experience, and increase competitiveness. It would potentially allow us to evaluate design or material choice and the effects of modifications, all of that cheaply and quickly. Mentioned advantages motivated us to start the development of the finite element model approach to the virtual seat vibration response assessment. This paper describes the finite element model creation from the mesh preparation through the material models’ choice to some aspects of the boundary conditions and contact definition. Furthermore, we depict the static validation of the model, comparing simulation and measurement of the distribution of contact pressure between the seat cushion and buttocks-hips mockup. Finally, we draft a frequency response simulation.

ABSTRACT. The paper presents experimental research on the vibration and modal analysis of a tonearm-cartridge system applied to the mechanical system of a turntable. The high fidelity of the music reproduction depends drastically on the dynamical properties of the tonearm-cartridge system, which has only been simplified and studied empirically. The recently developed techniques on the experimental modal analysis, especially on the operational modal analysis and the damping estimation, open new windows to study this micro but complex system with innovations. The finding of the system natural frequencies of the tonearm structure reveals accurately low frequency resonances of the system and the effect of the tonearm dynamics into the vibration of the whole turntable. Moreover, the finding of the cartridge compliance and damping offer some innovative approaches to reduce the vibration level at the needle. The research recalls much potential attention to the vinyl record reproduction industry.

ABSTRACT. Vibration induced noise in a ship structure can be caused due to propeller shaft vibration. These vibration can cause problems to the passengers in a cruise ship. The purpose of this study is to develop a nonlinear model for a propeller shaft vibration and understand the effectiveness of a nonlinear isolator in reducing the vibration amplitude. The vibration from the propeller shaft is transmitted to the deck plate. The coupled system of propeller shaft and the deck plate is modelled as a two degree of freedom system. The propeller produces high response due to synchronous whirl and instabilities such as oil whirl and dry whip. In order to incorporate the nonlinear modal interactions the propeller shaft is modelled a nonlinear duffing oscillator. Vibration from the propeller shaft is transmitted to the deck plate. The deck plate is modelled as a spring mass system with coincident frequency with the synchronous whirl frequency. The propeller shaft is coupled using a linear and nonlinear isolator to the deck plate. Vibration isolation devices are used to protect systems from unwanted vibration force or displacement. positioned between the source of the disturbance and the equipment that has to be protected. The purpose of the study is understand the influence of isolator in controlling the vibration transmitted to the deck plate Two types of isolators are considered in the study a linear and nonlinear isolator. The passive nonlinear isolator is modelled as a cubic spring which induces a high static and low dynamic stiffness. The nonlinear coupled two DOF system is solved using harmonic balance method and compared using numerical continuation. The result from the study indicates that the nonlinear isolator is effective in reducing the vibration on the deck plate. An uncertainty analysis was also carried out to understand the robustness of the isolator.