Mojtaba Ezoji - Master of Science in Marine Structural Engineering, Sahand University of Technology,Tabriz,Iran.
Ahmad Gharabaghi - Associate Professor, Sahand University of Technology,Tabriz,Iran.
Hamzeh Gol zaroudi - Master of Science in Marine Structural Engineering, Iran University of Science and Technology, Tehran, Iran

Amir-Kabir platform is a GVA4000 type semi-submersible platform installed in deep water part of Caspian Sea in order to extract its hydrocarbon resources. In this study, the members of Amir-Kabir platform are modeled by beam and shell elements. Morison and diffraction theories are used to calculate the wave loads on these members of platform considering relative geometry of them to the wave length. After verification of the developed model for a similar platform, the frequency domain analysis is performed. The results are presented for the heave, surge and pitch motions in various environmental conditions. It is shown that by increasing the wave period, the spectrum of platform's heave motion gets closer to the wave spectrum and by increasing the wave height, the spectrum of platform's surge motion gets closer to the desired environmental spectrum. This means that the wave height plays more important role in the surge motion of platform and the period is more effective in its heave motion

Semi-Submersible platform, Coupling Analysis, Frequency Domain Analysis, Mooring lines