Noise and Vibration Control in Automotive Bodies

5Vehicle Body Sensitivity Analysis and Control

5.1 Introduction

5.1.1 System and Transfer Function

A system is a collection of interacting or interdependent components forming an integrated whole, and has a special function. Any object can be regarded as a system, such as a vehicle body, an engine, etc. A dinner table can be also regarded as a system.

If an input is applied on a system, an output will be generated. The input could be force, temperature, pressure, etc. the output could be force, displacement, speed, etc. Figure 5.1 shows the relationship between the input and the output of a system. The input is also called excitation and the output is called response.

Figure 5.1 Relationship between input and output of a system.

For a dynamic structural system or an acoustic system, both the input and the output signals are functions of frequency and are expressed by X(ω) and Y(ω), respectively. The relationship between the input and the output signals can be characterized by a transfer function. The transfer function is defined as the ratio of the output signal to the input signal, as shown in Eq. (1.4). In order to maintain the integrity of this chapter, Eq. (1.4) is rewritten as follows:

(5.1)

The transfer function is also a function of frequency, which represents ...