ABSTRACT
As the development of oil and gas industry has progressed into deeper water depth, the research and development focused on this particular region structures have become essential. In the design of the offshore structures, wave force is always the most significant environmental force among. Literature has been reported that long-crested waves, which widely used in the design of offshore structures, are rarely found in the real sea. Whereby, this condition is well represented by the short-crested waves. The short-crested waves were defined as the waves formed by the linear summation of a series of long-crested waves that propagated to different directions, which is randomly varying in the magnitude and directions. Literature as well has been reported that design considering long-crested waves would be overestimated. Hence, in order to simulate the responses of the structures in real sea condition and provide an optimum design for the structures, short-crested waves are preferable. As per the knowledge of authors, research focused on the investigation of the dynamic responses of semi-submersible particularly focusing on short-crested waves and current concurrently has yet been found. In this study, a numerical comparative study on a typical eight-column semi-submersible model had been conducted. Frequency domain method, which adopted the Morison Equation and wave spectrum, was utilized to obtain the dynamic responses of a semi-submersible platform responses in surge, heave, and pitch in term of Response Amplitude Operator (RAO). The maximum amplitude of each motion was determined and compared. From the results, it has proven that the responses of the semi-submersible platform are smaller as compared to the one due to long-crested waves. Whereby, the results indicated that the dynamic responses for short-crested waves are approximately 50% lower.
