Computational Analysis On Loads And Motion Of Underwater Risers

Since 1950, a lot of analyses having been done on mechanics characteristics of underwater riser in Molole Project, the static and dynamic analyses of riser have been paid great attention and it is experienced rapid development in the past fifty years.Firstly, the mathematical model of underwater riser is introduced in this paper, and the dynamic equation that governs the motions of riser in the horizontal direction, the wave theory, the current theory and the mothed on computing environmental loads on riser with Morison Equation are shown separately. Secondly the static analysis, dynamic analysis and spectrum analysis for riser motions is shown respectively. A method to modify the time history of the displacement, the bending moment and the axial tension at each node separately by the finite element method is proposed. At last, the Fourier Transform is used to convert the time history of the displacement, and the bending moment at each node to the spectrums of the displacement and the spectrums of the bending moment separately. Of course, the computation programs are written with Fortran.There are also some computational examples.and it has been demonstrated that the results has an acceptable accuracy in engineering. Some conclusions is gotten by analyzing the results in order to validate the former researchers conclusions and help to the followings.The trace of notes on riser is shown in the results of the time domain analysis.but the results on spectrum anslysis is more expedient to analyze the relationship between response and frequency,and it is also more helpful in engeering.The method in this paper is not only applicable to underwater riser but also to the tubal component in offshore structure, but some assumptions and simplications in computation and the ignorance of the vortex release need to be perfected in later analysis.