Dynamics calculation for underwater moving slender bodies based on flexible segment model

Long marine risers or cables are underwater slender bodies. In the case of being moved or towed by the mother vessels, they may undergo high tensions and moments with large deformations. To evaluate their underwater safeties, the dynamics calculation is often carried out. The paper provides a dynamics calculation method for underwater moving slender bodies (MSBs) based on a Flexible Segment Model (FSM). In FSM, a slender body is discretized into a series of flexible segments. For each flexible segment, its deflecting feature and external forces are analyzed independently. The deformation of the whole slender body is decomposed into micro-deformations of the flexible segments. And the governing equations are listed according to the moment equilibrium on these segments. A linear iteration scheme is provided to get the numerical solution to the governing equations. To verify the results of the proposed FSM based dynamics calculation method, the comparison between the numerical and experimental results is shown. The numerical results can agree with the experimental results very well if selecting suitable hydrodynamic coefficients.