Page 43 - Marine Structural Design

20 Part I Structural Design Principles

Another important aspect of statistics is the random process distribution, which describes the
likelihood of occurrence of a random process. One of the most common random process
distributions is the normal or Gaussian distribution. Typical examples of Gaussian distribution
can be seen in Figure 2.2. One of the most important features of this Gaussian distribution is
the fact that it may be described entirely in terms of two parameters: the mean value px and
variance a:.
The waves that make up a sea-state are normally described using two parameters, the
significant wave height and the peak period. These two parameters follow a log-normal
distribution which means that their natural logarithm Z = In X, follows a Gaussian distribution.
The surface elevation at any point in the ocean is a random variable, which follows a Gaussian
distribution with zero mean.

"'i"

Figure 2.1 Probability Density Function

-6 -4 -2 0 2 4 6
X
Figure 2.2 Gaussian Probability Density Function, (with CT~ = 1,2, and
3, and with px = 0)