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This paper presents a model of Total Vehicle Vibration Isolation (TVVI) system for vibration analysis and optimization. The TVVI system can handle any number of flexible and rigid components, frequency independent and frequency dependent parameters of spring-damper subsystems, and considers motion with all six degrees of freedom. The modal mass, stiffness, and damping of the eigenvectors of finite-element (FE) model of the flexible components are included in the total vehicle model, instead of the original FE model. This procedure reduces the number of degree of freedom (DOF) of total vehicle model, so that the practical optimization including large FE model can be performed. Optimization module includes various options of objective functions (six kinds of energy and ride quality) for different design goals. Applications of TVVI include cars, buses trucks or any structure where NVH is an issue.

A semi-empirical formula [1] for predicting noise spectra of an engine cooling fan assembly is developed. In deriving this formulation it is assumed that sound radiation from an axial flow fan is primarily due to fluctuating forces exerted on the fan blade surface. These fluctuating forces are correlated to the total lift force exerted on the fan blade, and is approximated by pressure pulses that decay both in space and time. The radiated acoustic pressure is then expressed in terms of superposition of contributions from these pressure pulses, and the corresponding line spectrum is obtained by taking a Fourier series expansion. To simulate the broad band sounds, a normal distribution-like shape function is designed which divides the frequency into consecutive bands centered at the blade passage frequency and its harmonics. The amplitude of this shape function at the center frequency is unity but decays exponentially. The decay rate decreases with an increase in the number of bands.