One of the economical ways to install an offshore pipeline is Rentis method. With this method the whole pipeline is fabricated onshore and then it is towed toward the sea by the use of two tug boats at both ends. The towing process is such that the pipeline is towed at the sea surface or a little below the surface and this is possible due to the existence of buoyancy tanks. The problem of this method is that the dynamic behavior of the towed pipeline should be carefully known and considered.


Loading on flexible structures due to waves, especially on pipeline, is an interesting problem in offshore engineering. One of the aspects is fluid-structure interaction and this paper will cover the fluid-structure interaction in pipeline which is installed using Rentis Method. With this method, the whole pipeline is fabricated on a yard where the pipeline is then towed toward the sea by the use of tug boats. The interesting thing about this method is the dynamic behavior of the pipeline while it is being towed toward the sea. At that time the pipeline will be excited by the waves, current, wind, etc. along its several kilometers length, where the hydroelasticity interaction between pipeline and the surrounding fluid becomes dominant. Wave loading can be formulated using modified Morison equation which consists of two force components i.e. inertia force and drag force. In Morison equation drag force is a square function of the relative velocity between structure and fluid particle. This relative velocity describes wave force on a pipe moving with an acceleration in an unsteady flow of certain velocity. The interaction will be simulated in time domain and analyzed in frequency domain. Time domain analysis wiII refer to the direct numerical integration of the equilibrium equation of the structure.

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