_______7
Statistical Responses for
Single Degree of Freedom
Linear Structures
James F. Wilson
The three commonly used methods for computing the dynamic responses of offshore structures to waves are shown schematically in Figure 7.1. The first two
methods involve the time domain and hâve been discussed in previous chapters.
Here, the time history of structural response is computed either for a single
design wave (the first method), or for multiple waves deduced from the partitioning of measured sea wave spectra (the second method). The third method,
the topic of this chapter, involves the frequency domain. That is, for a single
wave height spectrum and a transfer function relating wave height to structural
loading, the statistical responses of the structure are calculated directly.
1. Time Domain
Simple Design
Wave
Transfer Function
Single Harmonie Load
Time History of
Structural Response
2. Time Domain
Wave Amplitude
Spectral Partitioning
Transfer Function
l
Multiple Harmonie Loads
l
Time History of
Structural Response
3. Frequency Domain
Wave Amplitude
Spectra
1
Transfer Function
l
Load Spectra
l
Statistics of
Structural Response
Figure 7.1 Three approaches to the dynamic analysis of offshore structures.
The statistical structural responses for the single degree of freedom st uct tires
considered in this chapter are those for a single, nondirectional wave spectrum,
165