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Accurate estimation of inertia properties is crucial in the design and development cycle of mechanical structures. When modeling complex structures and subassemblies, or simulating the dynamics of mechanisms, the rigid body characteristics of a subassembly might be too complex or inaccurate to calculate. Traditionally, inertia properties are obtained by a laborious pendulum test, a very time consuming procedure. A highly accurate alternative is to perform a typical modal test, inertia properties are than achieved based on frequency response function and its mass line characteristic. This paper explains, first of all, how to extract inertia properties such as center of gravity, moments and principal axes of inertia based on frequency response functions (FRF's), and then how to synthesize rigid body characteristics such as rigid body modes with respect to the geometry and the resulted inertia properties. Both an academic case and real-life applications are used to validate the approach.

In the eighties, the main concern in the automotive industry from a designer's standpoint was a level issue. In the nineties, the market has put more stringent requirements on the automotive industry with respect to noise in general and psychoacoustics. The governments have imposed lower limits with respect to pass-by noise standards. Customers are spending more time in their car than in the past and are demanding acoustical comfort. All of this is leading to an environment where a sound quality system is becoming a daily tool in the design and trouble-shooting world. This paper describes what should be looked for in a sound, how to quantify these properties and what tools are needed. These steps are then applied in a case study.