Impacts of Environmental Loads on a Jack-up Offshore Structure

Due to natural depletion of oil/gas reserves in shallow water depths and also
continually increasing the demand for producing these natural resources, steadily
more emphasis has been given to design Jack-up structures that can be used in
deeper water as well as harsher environment with longer operational periods. This
final year project aimed to investigate the impacts of environmental loads (caused
by wave, wind and current) on the major reactions (total base shear force and
overturning moment) of a typical jack-up offshore platform. In order to perform
this research, two real-life jack-up structures were selected and analyzed using
SACS structural analysis package. The first selected jack-up structure is called
West Prospero which is located at Malaysia's Jerneh and Tapis fields, off the east
coast of peninsular Malaysia and the second structure is called MSL model which
is designed for Central North Sea environmental condition. To ensure a sound
application of the commercial software (SACS), a simple in house computer
program facilitating the manual calculations of the total base shear was developed.
Toward verifying the analysis outcomes and better understanding of the way in
which offshore structures react to environmental forces, some laboratory
experiments were carried out on scaled physical model of West Prospero. Given
the large approximations involved, the comparison of the experimental results
with the computerized calculations showed acceptable similarity for the base
shear. The results of sensitivity analysis revealed that the majority of base shear
and overturning moment is caused by wave forces. It was shown that the shear
force is more sensitive to wave height than to other wave parameters or to
diameter of members. However, for the overturning moment the dominant
parameter could be wave height or wave period depending on the range of the
relative change of the respective factors. The relative increase of members'
diameter brings about a low relative change in the overturning moment but a high
change in the base shear.