M. J. Ketabdari - Department of Marine Technology Amirkabir University of Technology

Sea waves are one of the most important forces in marine environment. When the ratio of element diameter to wave length is less than 0.2 wave force can be estimated by Morrison Equation. It means that we neglect the effect of diffraction in this process. To design the marine structures generally the inline force of the waves is considered. However, there is no evidence that why we neglect the transverse force due to Vortex shedding. In this paper a spectral analysis was performed to evaluate the wave inline and transverse forces on a Jacket Type Platform in Persian Gulf. Because of the lack of a known wave spectrum for Persian Gulf and according to reference [3] the modified JONSWAP spectrum was used. The results showed that the transverse force is usually more than 10% of the inline force for the condition of Persian Gulf. It means that in quasi static and dynamic analysis of offshore structures the transverse force due to Vortex shedding should be considered.