Experimental Investigation for the Responses of Semi-submersible Platform Subjected to Bidirectional Waves

It is rare to find unidirectional wave in the
real seas and only multi-directional waves or short
crested waves are found. The short crested waves are
defined as linear summation of different long crested
waves propagated to different directions. The wave
forces generated would be randomly varying in
magnitude and direction. Nowadays, designers tend to
use the directional wave statistics for the design of
offshore structures. The main reason is to obtain the
optimum design of the structures for cost and time
effectiveness. As a part of the research focused on the
dynamic responses of the semi-submersible platform
subjected to short crested waves, this paper presents the
results of the experimental investigation for semisubmersible
platform subjected to short crested bidirectional
wave. The experiment was conducted in the
wave tank of the offshore engineering laboratory at
Universiti Teknologi PETRONAS. The model was
subjected to 5 sets of bi-direction waves crossing angles
of 40°, 45°, 55°, 90° and 120°. The direction of the wave
propagating was found to affect the responses. Two
typical trends of the responses were found for wave
crossing angles of 40°, 90° and 120°; along with 45° and
55° respectively. The optimum wave crossing angle 40°
and 55° give the maximum responses.
Keywords- Semi-submersible, bi-directional wave,
response amplitude operator (RAO), experimental
investigation.