The vibration and noise caused by pressure pulsation, referred to as fluid-borne vibration or fluid-borne noise, are some of the most detrimental problems in hydraulic systems. A Helmholtz silencer with multiple degrees of freedom was proposed to attenuate several harmonic frequencies generated in the hydraulic systems. The silencer consists of a cylindrical vessel with several chokes inside the vessel. The final goal of this research project is the development of a multiple-degree-of-freedom type of Helmholtz silencer that can be applied to hydraulic pump systems operated at different speeds. The aim of this report is to establish the design criteria of the silencer specifications. In particular, the effects of the diameter and length of the choke and the cylindrical volume on attenuation performance were analytically and experimentally investigated.

The Helmholtz-type hydraulic silencer is one of the most practical silencers for attenuating pressure pulsations in hydraulic systems owing to its simple structure and reasonable cost. Maximum attenuation performance can be attained at the resonance frequency in accordance with the principle of Helmholtz resonance. Therefore, it is extremely important to precisely determine the resonance frequency at the design stage. It was clarified in our previous study that the shape of the volume vessel affects the resonance frequency of the silencer because of the wave propagation of pressure pulsation inside the volume vessel. In this study, the attenuation characteristics and wave propagation in a silencer with a hemispherical vessel are investigated. A mathematical model that takes into account the propagation of a one-dimensional wave in the radial direction of the hemispherical vessel is proposed and compared with the step section approximation model and the classic lumped parameter model. Furthermore, the effectiveness of the theoretical analysis is verified by experiments wherein the dimensional specifications of the vessel and neck are adjusted.

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