Study On High Frequency Resonance Response Of Marine Structure Under Two-Dimensional Focused Waves

Nowadays, in the ocean exploration today, marine environment is becoming worse, and the nonlinear effect of waves is more significant. The ringing phenomenon is a transient high frequency resonance response of offshore structures in severe sea condition. The frequency which occurs at is much higher than the dominant wave frequency, and the vibration amplitude may be up to that of the combined effect of the first and the second order wave force and dynamic wind. So it's a great threat to the safety of the structure. The high-frequency wave components of nonlinear waves are an important factor to inducing ringing phenomena of marine structures, therefore the study on the interaction of nonlinear waves and structure is of great importance.In this paper, a 2D fully nonlinear numerical wave tank is developed based on the potential theory. In this model,a high-order boundary element method is used to realize numerical discretization, the mixed Eulerian-Lagrangian method is utilized to trace the free surface and the body surface, and the free surface conditions and the body motion equation are integrated by the fourth-order Runga-Kutta method. The auxiliary functions are introduced to calculate nonlinear wave loads, instead of directly predicting the time derivative of the velocity potential.Firstly, the push-pedal wave-generating method and the given incident-wave- velocity generating method are used to generate regular waves. The wave elevations are presented and in good agreement with the higher order theoretical solution of Stokes waves. The push-pedal wave-generating method is used to generate focused waves. The present results are verified by comparing with the other published results and the experimental results. The difference between the numerical results and the theoretical solutions of Stokes waves is analyzed and summarized in terms of wave nonlinearity. Secondly,the model is applied to study the wave diffraction around a fixed body and the interaction between nonlinear waves and the floating body. The wave elevation, wave forces, and motion responds are presented and verified by comparing with the other published results. Simultaneously, the ringing phenomenon is studied under the action of a regular wave, and the effect of wave amplitude and wave frequency on ringing phenomenon is also discussed.Finally, the numerical wave tank model is used to study the ringing phenomenon of the floating body under the action of focused wave. The forming process and characteristics of ringing phenomena is studied. The prerequisite of ringing and the effect of focused-wave amplitude and peak frequency on ringing phenomenon is also discussed.