Forced vibrations of a vehicle in the presence of a shock absorber panel

Forced periodic oscillations of a vehicle model consisting of a body, unsprung masses that model the wheels and suspension elements, as well as an additional absorber panel, are considered. The body and the absorber panel are represented in the form of rigid parallelepipeds. The elements of the model are interconnected by a system of springs and shock absorbers. The dynamics of the proposed model, which can apply to both passenger cars and trucks, is described by the nonlinear dissipative system with 10 degrees of freedom. The values of the natural frequencies and dominant coordinates inherent in the vibration modes of the linearized system, the parameters of which correspond to a specific car, are given. To assess the system's response to external influences, harmonic loads applied to the unsprung masses are considered. Numerical modeling has been used to obtain the frequency responses of the system for five variants of the elastic characteristics of the spring connecting the body and the additional panel, and cases of significantly nonlinear springs are also considered. Some variants essentially belong to the class of so-called “quasi-zero elastic characteristics”. An approximate estimate of the transient time is determined using the eigenvalues the linearized system. The estimate used guarantees that even the slowest mode of natural oscillations will die out to less than 1% of its initial contribution. From this moment on, the system vibrations are almost completely determined by the steady-state mode with the frequency of the external load. The amplitude-frequency characteristic is formed by the maximum absolute values of the amplitudes of the coordinates, which are determined after the transient is excluded. Calculations show that the use of springs with essentially nonlinear characteristics provides a significant reduction in cargo vibrations, which can be located in the center of mass of the additional panel, i.e. in this case, this panel acts as an effective shock absorber. This allows for comfortable and safe transportation of important cargo located on this additional panel.