Investigation On Numerical Simulation Of The Fluid-solid Interaction Characteristics For Oceanic Riser

With development of ocean engineering toward deep seas, the security of oceanic risers will become more salient. Under different current profiles, the vortex-induced vibrations (VIV) will always occur for such oceanic risers. The special fluid-solid interaction phenomenon could lead to severe fatigue damage of the riser, and hence threats to its security and performance.Considering the riser as a flexible structure with some density and elastic modulus, this thesis presents a transient coupling method for numerical simulating the Vortex-Induced Vibration of a oceanic riser. With the present method, the wake flow and vibration response of the riser are resolved and analyzed by the commercial software FLUENT and ABAQUS respectively, and the transient coupling between the fluid and the structure is accomplished by use of a novel method with the on-line transmission between fluid dynamic loads and structure response data based on the commercial software MPCCI.The VIV characteristics of the cylinder with a small aspect ratio and the deep-sea riser with a large aspect ratio in a uniform current profile are numerically simulated and analyzed. Results show that the cylinder with the small aspect ratio vibrates at low modes, and its vibration displacement is small due to the uniform current. In particularly, the effect of the axial vibration along such a cylinder can be ignored.Results further show that the vibration responses for the deep-sea riser with the high aspect ratio have remarkable influence on its wake dynamic characteristics, including the remarkable increasing of vortex shedding frequencies and the multi-frequency phenomenon of the vortex shedding.Moreover, despite the inflow current being uniform, the riser is observed to vibrate multi-modally, including not only the vibration responses being consistent with the vortex shedding frequencies, but ones with other frequencies also. In particular, complex bend distortions for such a long riser are observed due to multi-modal vibration responses with high orders.It can be concluded that the present method can be used as an effective tool in analyzing and predicting the VIV characteristics for long deep-sea risers.