TABLE OF CONTENTS Vibration data are usually acquired in the form of continuous electrical (analog) signals generated by transducers (see Chap. 12), where each analog signal represents the instantaneous value of a strain, pressure, force, or motion parameter (displacement, velocity, or acceleration) as a function of time. Such a signal is commonly referred to as a time-history. A sample record is defined as the time-history representing a single vibration measurement x( t) over a finite duration T. Although sample records are usually acquired in the form of time-histories, any other variable of interest can replace time t as the independent variable for analysis purposes. For example, road roughness data are commonly acquired as sample records of road elevation x versus distance d, that is, x( d); 0 ? d< D, where D is the length of the record. However, for clarity, all discussions and equations in this chapter are presented in terms of sample time-history records, where it is understood that any other variable can be substituted for time.
The appropriate analysis procedures for vibration environments depend heavily upon certain basic characteristics of the vibration. The most important distinctions are defined in Chap. 1 and illustrated in Fig. 22.1. These definitions may be summarized as follows:
A stationary vibration is one whose basic properties do not vary with time. Stationary vibrations typically occur when the operating and/or environmental conditions producing the...
