ABSTRACT
In this paper, numerical simulation of a flexible riser is carried out at first. Results are compared with the model test to verify the validity of the solver. Then, cases with different KC number with the same motion amplitudes are simulated to explain the effect of KC number in the VIV of the riser in the oscillatory flow. Typical characteristics of the vibration are observed including the modal transition and the "build-up-lock- in-die-out" process. Finally, through wavelet analysis, it was found that the main control modes at different positions were in three states when KC number was 84 and 168.
The development of deep-sea oil and gas resources relies on large-scale oil drilling platforms. The riser connects the seabed mineral deposits and the offshore operation platform. On the one hand, the riser needs to bear its own gravity and top tension, on the other hand, the vortex induced vibration (VIV) of the riser generated under the action of the shaking of the top platform and the current. When the excitation frequency is close to the natural frequency of the riser, the lock-in phenomenon will occur and the response amplitude will increase obviously. Under the influence of these factors, riser becomes the weakest link in offshore platform structure.
Many previous work have been done for the VIV problem. The research work mainly focuses on experimental research, semi empirical semi numerical simulation and CFD method. The results of the experimental study are the most reliable, but it is difficult to carry out the model test, because the test needs to invest a lot of manpower, material and financial resources. Semi empirical and semi numerical simulation methods simplify the original complex phenomena through a series of assumptions, which are widely used in industry, but the accuracy is poor. CFD method can show the details of motion that can not be captured by experimental research, and it is easy to analyze the formation mechanism of the phenomenon, but it has requirements for much computing resources.
