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Response Spectrum Method for Extreme Wave Loading With Higher Order Components of Drag Force Tabeshpour Mohammad Reza1*, Fatemi Dezfouli Mani2, Dastan Diznab Mohammad Ali1, Mohajernasab Saied1 and Seif Mohammad Saied1 1. Center of Excellence in Hydrodynamics and Dynamics of Marine Vehicles, Mechanical Engineering Department, Sharif University of Technology, Tehran, Iran 2. Department of Marine Industries, Science and Research Branch, Islamic Azad University, Tehran, Iran Abstract: Response spectra of fixed offshore structures impacted by extreme waves are investigated based on the higher order components of the nonlinear drag force. In this way, steel jacket platforms are simplified as a mass attached to a light cantilever cylinder and their corresponding deformation response spectra are estimated by utilizing a generalized single degree of freedom system. Based on the wave data recorded in the Persian Gulf region, extreme wave loading conditions corresponding to different return periods are exerted on the offshore structures. Accordingly, the effect of the higher order components of the drag force is considered and compared to the linearized state for different sea surface levels. When the fundamental period of the offshore structure is about one third of the main period of wave loading, the results indicate the linearized drag term is not capable of achieving a reliable deformation response spectrum. Keywords: offshore structure design, response spectrum method, wave analysis, Morison equation, higher order components, drag force, wave loading, extreme wave منبع دانلود Tabeshpour_Response Spectrum Method for Extreme Wave.pdf

Perturbation nonlinear response of tension leg platform under regular wave excitation Mohammad Reza Tabeshpour1 • Rahim Shoghi Abstract Conceptual discussion on highly nonlinear Duffing type equation of surge motion of TLP gives a deep view on structural response under environmental loads with some simplifications. Such analytical response is a simple form that clarifies important points in behavior of the structure. This paper presents the dynamic motion responses of a TLP in regular sea waves obtained by applying three methods in time domain using MATLAB software. Surge motion equation of TLP is highly nonlinear because of large displacement and it should be solved with large perturbation parameter in time domain. In this paper, homotopy perturbation method (HPM) is used to solve highly nonlinear differential equation of surge motion. Also the numerical methods such as modified Euler method (MEM) and MATLAB are used to solve the ordinary differential equation of motion. MEM is used for highly nonlinear Duffing type equation of surge motion of TLP, whereas the nonlinear part is not considered in MATLAB solution. Calculated responses by analytical HPM are compared with those obtained from both MEM and MATLAB responses. Keywords Tension leg platform Perturbation Morison equation منبع دانلود Tabeshpour_Shoghi_Perturbation nonlinear response.pdf