ssc-367 - Ship Structure Committee

Multiplication of the wave spectrum ordinates by the RAO squared is
simple. The two underlying assumptions are that the response varies
linearly with wave amplitude and the assumption that the response to
a wave of one frequency is independent of the response to waves of
other frequencies.
Response spectrum characteristics are taken from the shape of the
spectrum or are calculated from the area under the response spectrum
and the area moments of the response spectrum. Typical
characteristics are significant response amplitude, maximum response
amplitude, mean period of the response, and peak period of the
response spectrum.
The random sea transfer function is the ratio of a response spectrum
characteristic to a wave spectrum characteristic. A random sea
transfer function is usually presented as a function of the random
sea characteristic period. A typical transfer function might be the
ratio of maximum bending moment amplitude per unit significant wave
height. The transfer function is useful for estimating the response
to another wave spectrum with similar form but different amplitude.
.
B.2.2
Transfer Function
A transfer function converts input to output for linear systems. A
transfer function is graphically represented in Figure B-1. A
transfer function can relate motion response to the height of
incident waves directly, or a transfer function can relate motion
response to wave force, or a transfer function can relate member
stresses to wave or wind force.
For typical applications to the design of offshore structures, the
input energy forms are waves, current and wind. The desired output
forms are static displacements, dynamic displacements, and member
stresses.
B-4