Hydroelastic Response Study Of Multi-body Floating System In Inhomogeneous Sea Environment

In recent years,with the continuous expansion of the breadth and depth of the development and utilization of marine resources,marine spatial structure,offshore floating body and operation are of increasingly complex forms,and different VLFSs meeting different operating requirements have been designed.This kind of structure is usually designed as a multi module composite structure,and the structure of a single module is various,which can be regarded as a multi rigid body structure.Similar to the conventional multi body floating system,there are significant hydrodynamic interaction between these modules.At the same time,because of its huge size,its overall structure is considerable flexibility,which indicates that the interaction between structure deformation and fluid field can't be ignored,and the hydroelastic theory must be adopted in analysis.In this paper,the classical three-dimensional potential flow theory is summarized.On this basis,combined with some numerical examples,the effect of free surface damping,irregular frequency on hydrodynamic coefficients are discussed.Further,three different numerical methods for calculating second order drift forces are compared both theoretically and numerically.Then,the influence of the floating body spacing on the hydrodynamic performance of multi body floating system.It is difficult to deal with complex problems such as nonlinear structure,nonlinear wave load and inhomogeneous ocean environment in the classical three-dimensional hydroelastic theory,which is based on the modal superposition method.Based on the three-dimensional(3D)potential theory and finite element method(FEM),this paper describes a numerical method that can be used to predict the hydroelastic responses of floating structures.In this method,the continuous floating structure is discretized into rigid body sub-modules connected by finite number of elastic beam elements.Based on the 3D potential theory,the hydrodynamic coefficients and wave forces on each sub-module are firstly obtained considering the hydrodynamic interactions between modules.Next,the equivalent stiffness matrixes for the connection beams between various modules are obtained considering Euler-Bernoulli beam theory together with the St.Venant's torsion theory.Finally,the equations of motion for the entire multi-module floating structure in time domain are established,where the effects of nonlinear wave load and inhomogeneous ocean environment can be considered.Compared with the results of the classical three-dimensional hydroelastic theory,the reliability of the hydroelastic analysis method established in this paper is verified.On this basis,the hydroelastic response of a multi floating body system is further studied under the influence of the inhomogeneous incident wave and the second order differential wave forces.The results show that the hydroelastic response induced by the second order drift forces is relatively small,while the inhomogeneous ocean environment may have a significant effect on the hydroelastic response of the floating body system.Therefore,it is necessary to consider the influence of inhomogeneous sea environment on the prediction of hydroelastic response of multi floating system.