Frequency Domain Simulation Of Wave Interaction With Two-dimensional Structures In A Two-layer Fluid

Internal waves are widely distributed with various forms and relative studies are valuable in engineering and science. The stratification effects are becoming more and more important factors while developing marine sources. Based on the two-layer fluid model, hydrodynamic characteristics of two-dimensional structures are investigated in a two-layer fluid.In order to investigate complex structures, a linearized frequency-domain model is developed by using series expansion in external domain and higher-order boundary method in internal domain. The continuity boundary condition is employed on the interface between internal and external domain. The boundary element method can reduce dimensions of analyzed problems and the unknowns can be placed only on the surface of computational domain. In internal domain, the Rankine source is adopted to avoid calculating complex Wave Green function, and the velocity potential on both free surface and internal surface can be obtained directly. In external domain, analytical asymptotic expressions are adopted to make the coefficients in expressions be the only unknowns. By comparing with the analytic results and verifying the energy-conservation principle, the proposed model is validated.To analyze the transformation between two wave modes when waves past structures, the reflection and transmission coefficients are defined for each incident wave mode. With the proposed model, by computing the coefficients, the reflection and transmission features are discussed. The influences of parameters in stratification, like density ratio and depth ratio, to the coefficients are studied. The interface is easy to be disturbed when there is small density difference. The added mass and damping coefficient are calculated and analyzed. The amplitudes of waves due to the forced oscillation of structures both on free-surface and interface are showed. Finally, the motion responses under incident waves of both surface-wave mode and internal-wave mode are investigated and the motion responses are sensitive to the change of parameters in stratification.