Simulation Of Strongly Nonlinear Wave And Its Interaction With Floating Structure

With the increase of survival water depth of ocean engineering structures, more andmore researchers have been paying attention to rough environment, which may cause severedamages to offshore structures and seriously affects the normal operation. Especially thestrong nonlinear impact phenomenon such as the serious wave run-up around the structure,the large amplitude motion response and green water of the structure, etc, all of these will beinduced by the extreme waves. Traditionally, the potential theory is employed to predict thehydrodynamic coefficients in marine environment. However, the potential theory has somelimitations, which is difficult to consider the effect of nonlinearity and ignores viscosity. Inthis paper, based on the time domain method and viscous flow theory, a viscous numericalwave tank is established through the secondary development of the software to simulate thestrongly nonlinear wave and study the interaction between it and the floating structure. Thecontinuity equation and Navier Stokes equations of the incompressible fluid and structuraldynamic equation are used as the basis equations, Major works done in this thesis are asfollows:(1) Based on the viscous flow theory, the mathematical model of FSI is established andits solution method is elaborated. Using the ANSYS software, the example that an elasticbeam is submerged in the static fluid is investigated to verify the feasibility of the FSIsimulation through System Coupling module.(2) A numerical wave tank with effective wave-making and wave-absorbing function isestablished through UDF programs, which based on the module FLUENT of CFD includedin software package ANSYS14.0. Through the simulation of cosine wave, comparisonamong generating waves by adding mass source, setting velocity-inlet and simulatingpiston-like wave maker is analyzed.(3) Series of cosine waves with different length or height are simulated in the NWTwith piston-like wave maker to research the effect of viscosity on fluid particle movementand wave height attenuation. Then regression analysis is carried by MATLAB program andthe attenuation law is studied by numerical fitting method. Finally, a formula form withsatisfactory fitting effect is presented.(4) JONSWAP spectrum is applied to describe the stochastic process of irregular waves.The focused waves are made by wave energy focusing at a certain position and time. During the entire process, the effective frequency bandwidth min~maxof target spectrum iscalculated by MATLAB and parameters of wave components are computed by C languageprogram. The UDF program is also written in C language. Moreover, some results anddiscussion about the relationship are given among the focused position, motion of wavemaker and the focused waves. Lastly, an improved method about how to determine thedesign focusing position and focusing time by MATLAB program is put forward to increasemodeling accuracy and efficiency.(5) The numerical model of the interaction between focused waves and2D floatingstructure is established in the numerical wave tank. Then a number of cases that the2Dfloating body is with different shape or supported condition are set up. Detailed numericalinvestigations of nonlinear wave-body interaction, including the loads on floating bodyinduced by waves, motion response such as drift, heave and roll, green water and impactdynamic pressure, are carried out in this research. The influences of transverse ship,superstructure, restraining sway, different body loaded position and amplitudes of focusedwaves on the response of structure is also analyzed.