A Direct Coupling Analysis Method Of Hydroelastic Responses Of VLFS In Complicated Ocean Environment

To allow for proper description of the environment influence on a VLFS deployed near seashore or islands and reefs,a direct coupling analysis method of hydroelastic responses of a VLFS in complicated geographical environment was proposed based on the ocean wave propagation theory and the 3D hydroelasticity theory in time domain.Meanwhile,a complete set of model test technologies for multi modules VLFS system,which can consider the influences of complex seabed and the shielding effect of islands and reefs,is developed and applied to provide the verification basis for the new hydroelastic theory and the analysis method.The major achievements contained in this thesis include the following aspects:(1)On the basis of the existing three-dimensional hydroelasticity theory of Wu(1984),the Boussinesq equation,Rankine source method and the hydroelasticity theory in time-domain are combined to establish a direct coupling method of hydroelastic responses of a VLFS in complicated geographical environment,especially for the uneven seabed and inhomogeneous wave condition in space-time distribution.The basic theory derivation,its related numerical solution and the corresponding calculation program and software THAFTS-BR are presented in the thesis.(2)The three-dimensional hydroelasticity test technique is combined with the wave dynamics in shallow water to consider the influence of uneven seabed and sheltering effect of islands on the hydroelastic responses of a VLFS deployed near island and reefs in shallow sea.It provides a technical basis for the understanding of the hydroelastic response mechanism and the test examination in the process of design of VLFSs.(3)The hydroelastic analyses of one single module and three module VLFSs deployed on anuneven seabed are carried out to further validate the correctness and usability of the theoretical methods by comparing the results obtained from the model tests.The general regularity of the influence of complex seabed topography on the hydroelastic responses of VLFSs is given by comparing the results with those under constant water depth.It provides a reference for the dynamic response analysis,optimization design and overall planning of the VLFS arranged near seashore or islands and reefs.(4)A detailed analysis of the hydroelastic responses of an eight-module VLFS under the inhomogeneous wave condition is carried out based on the THAFTS-BR software.The change rules of wave propagation and deformation,motions of floating bodies and connector loads in regular and irregular waves are achieved,and verified by comparison with model test results.It can be found that the connector loads of VLFS appear an obvious increase in inhomogeneous waves through the comparative analysis with the responses in homogeneous waves,which directly shows the importance of considering the effects of inhomogeneous wave conditions for the VLFS in the complicated environments.(5)A series of hydroelastic applications including motions,loads and overall strength assessment is investigated for a hundred-meter scale construction platform,which has been built and will be deployed near a typical island for the development of the South China Sea.The achievements provide an analysis conclusion and a design basis for the analysis of motion responses and the structural safety of this platform in the complicated environment near islands.It accomplishes a transfer from theoretical analysis to engineering application for the first time.The direct coupling analysis method of hydroelastic responses of the VLFS in complicated ocean geographical environment and the related model test technique presented in this thesis can basically solve the hydroelastic problems with complex connotation,such as the transition from deep sea to shallow water,the sea bottom topography,the inhomogeneous waves in space-time and multi modules of the VLFS,etc.The effective technical approach and implementation can be provided for the structural safety prediction,the design evaluation and optimization of the full system VLFS in the complex shallow sea geography and wave environment.