Frequency-domain Simulations Of Wave-current Interaction With Three-dimensional Structures

Waves and currents are generally existing simultaneously.Its coupling action between waves and currents makes the study of the coexistence of waves and currents more complicated.The integrated field is not a simple superposition of pure wave field and pure current field.In this thesis,the high-order boundary element method is developed to simulate the interaction of wave-current with structures in the frequency domain.The influence of currents on the hydrodynamic characteristics of structures is main studied.For the wave-current-body interaction,the integral domain can be limited to a limited area on the bodies surface and the free water surface by using a Green's function,which satisfied the conditions of the free water surface and the far-field boundary.However,the calculation of the Green's function is very time consuming.In order to solve these problems,the perturbation expansion theory is developed.Under the assumption of small forward speed,the velocity potential and the Green's function are perturbed according to the parameters related to the wave steepness and the current,where both are small parameters.After that,using the integral equation,the solid angle coefficient and some singular integrals are eliminated,and the calculation of some Cauchy main integrals in the integral is improved,so that the equation is more simplified and the calculation is more rapid.Three sets of models are selected to examined the accuracy of the numerical model.First,the simplest uniform cylinder model is selected.The hydrodynamic characteristics of the cylinder are simulated,and the calculated results are compared with the results of published semi-analytical and time-domain method.The results are all in good agreement.Then,according to the model experimental done by Kinoshita et al(1995).,the interaction between wave-current and a fixed four-column platform is simulated.The simulated wave force results agree well with the experimental results.Finally,the model is extended to the floating hemisphere model in the infinite water depth,simulating the interaction between wave-current and floating bodies.Comparing the simulation results with the published time domain results,the results are in good agreement.Three sets of models prove the currency of the numerical model.Furthermore,a fixed four-column structure is selected to focus on the interaction between waves and structures under different current parameters.The simulation results show that the first-order exciting force on the structure and the wave-up at each position are analyzed.Finally,the simulation results are analyzed with the trend of the incident wave period and the angles of wave approach.