Inclusion of measured frequency- and amplitude-dependent mount properties in vehicle or machinery models

This article proposes several new or refined analytical methods for vehicle or machinery system models that include measured dynamic stiffness of vibration isolators or mounts. Complications arising due to the spectrally varying and/or amplitude-dependent parameters are categorized, and the associated eigenvalue and frequency response problems are defined. First, the real and complex eigenvalue problems that include both viscous and visco-elastic damping models are critically examined and illustrated via examples. Second, a non-linear eigenvalue problem is formulated and the resulting eigensolutions are determined for a two-degree-of-freedom system with frequency-dependent elastic and dissipative parameters. Several approximate methods, including the modal expansion method, are also proposed to calculate the forced harmonic response, and their solution errors are assessed. Third, a quasi-linear method is applied to a 1/2 car model, using measured data of a typical hydraulic engine mount, to see the effect of excitation amplitude-dependent dynamic stiffnesses. Finally, a refined non-linear, frequency domain synthesis method is proposed that includes local non-linearities in the form of measured dynamic stiffness data. The forced harmonic response of the overall system is obtained, and comparing to the corresponding time domain method for a specific 1/4 car vehicle model validates it. (C) 2001 Academic Press.