Examination of Some Vibration Isolator Models and Their Effects on Vibration and Structure-borne Noise Transmission

A vibration isolator or mount is often modeled by the Voigt model describing uni-axial (longitudinal) motion with frequency-invariant parameters. However, wave effects due to the mass distribution within the isolator are observed as the frequency is increased. Further, flexural stiffness components play an important role, leading to off-axis and coupling effects. Thus, the simplified mount models could lead to erroneous predictions of the dynamic behavior of an overall system such as automotive powertrain or chassis mounting systems. This article compares various approximate isolator models using a multi-dimensional mobility model that is based on the continuous system theory. Harmonic force and moment excitations are separately applied to a rigid body source to investigate the multi-dimensional vibratory behavior. Analysis is however limited to a linear time-invariant system and the mobility synthesis method is utilized to predict the frequency domain behavior. Alternate receiver models, such as infinite and finite plates, are employed to examine the asymptotic and resonant behaviors of the power-based isolation measures. Finally, an inverted ‘L’ plate receiver is selected to represent a simplified vehicle body structure and sound radiated from this receiver is computed to assess the structure-borne noise transmitted through mounts. The roles and effects of coupling terms, frequency dependency and discrete element modeling of stiffnesses on vibration and sound isolation measures are identified over a broad range of frequencies.