Effect of internal solitary wave on the dynamic response of a flexible riser

Dynamic responses can arise when a flexible riser encounters the internal solitary wave (ISW) in the ocean. It is thus necessary to explore its dynamical behaviors induced by ISW. Firstly, the governing equations of the flexible riser, ISW and hydrodynamic force are introduced and interpreted. The accordant validations are performed so as to examine the accuracy of the applied models. Then the dynamic response of the flexible riser is studied with the increase of nondimensional ISW amplitude. Representative characteristics, such as vortex-induced vibration (VIV), top tension and stress along the flexible riser, are mainly analyzed and discussed. The results prove that with the propagation of ISW, VIV in both inline (IL) and crossflow (CF) directions can be incurred. The maximum values of IL and CF oscillation frequencies, top tension, inline deflection as well as riser stress can be detected while the ISW trough reaches to the flexible riser. Furthermore, all these four dynamic characteristics show an increasing trend with the increase of nondimensional ISW amplitude. Note that the maximum values of oscillation frequencies, inline deflection and stress on the upper section of the flexible riser tend to be larger compared with those on the lower section. In addition, the maximum inline deflection, top tension and stress along the flexible riser can be affected by VIV responses.