The Nonlinear Dynamic Response Analysis Of Riser Under The Wave And Current

With the developing of world oil industry, the area of exploration is stepping into deep water gradually. Deepwater drilling risers are absolutely necessary equipment for offshore oil exploration and exploitation, while its integer dynamical response is the important factor of safe operations. So the studies of the risers become to hot issues in academical and industrial area.Firstly, this paper briefly introduce the calculation of the wave force of little member and large member, and some basic theories, such as wave spectrum and Volterra model. The first and the second diffraction force are deduced based on diffraction theory and Volterra model,which established a good foundation for further work.Secondly, the nonlinear dynamic response of rigid riser and flexible riser are discussed in this paper. The nonlinear term of Morrison equation is expand to second order using Volterra nonlinear model in the process of analysis. Besides, the nonlinear dynamic response under white noise excitation is also simulated by MATLAB.Finally, the nonlinear dynamic response analysis of single-degree and multi-degree freedom system under the wave and current is presented. In process of analysis, using the P-M spectrum as input wave excitation and Volterra model, the nonlinear dynamic response system of single-degree and multi-degree freedom system are obtained. For the case of single-degree freedom system, a simplified model of rigid riser is established to analyze nonlinear dynamic response on different conditions, such as different height of wave, different current velocity. For the case of multi-degree freedom system, a simplified flexible riser model is developed by riser units dividing, and the nonlinear dynamic response of multi-degree freedom system on the condition of different height of wave, different current velocity and different water depth. The nonlinear dynamic response of designated unit is obtained under different condition successfully. The results indicate that, the first and the second response will increase in varying degree with the current and significant height of wave increasing. Besides, domain frequency response will reach a maximum value before gradually decreasing, while the low frequency response seems to have no regular pattern.