Experimental Study Of Regular Wave Impact On Elastic Structure

It is known that wave impact pressure as an impulse load acts on marine structures frequently. The impact force and the wave-induced vibrations may cause structure’s partial damage and overall unstability. In recent years, ocean exploiting expands from inshore shallow water to open sea deep water. Naturally, the size of marine structure is much larger than before because of the water depth increase, which result in the structure’s integral stiffness small. As we all know, the previous study of wave impact is on the basis of rigid body assumption. It is reasonable for the structure of small scale. However, for the large scale structure, the rigid body assumption is not reasonable because of the wave-induced vibration and structure’s elastic deformation may cause wave surface deformation and influence the amplitude and distribution of wave impact pressure. So the structure’s dynamic response should not be neglected. Thus, the study of wave impact on elastic structures and analyse the impact loads as well as the structures’dynamic response are full of theoretical significance and engineering applicable value.In this thesis, the study was conducted in the wave tank in the State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology. Both the wave impact pressure and wave-induced vibration were studied by physical model experiment. The elastic effect was simulated by spring with different stiffness. The physical model experiments were subjected to regular waves. The incident wave height was from8cm to12cm and wave period was from1.0s to1.8s and the relative clearance was from0to0.5.The characteristics of both the impact pressure and wave-induced vibration were summarized in time domain according to the experimental data. The impact pressure and its corresponding vibration acceleration was divided into representative four stages in one period. The four different changing processes were also discussed in detail. The influence of supporter rigidity on impact pressure value, impact duration and the distribution of wave induced pressure with a larger amplitude along the bottom of deck were investigated as well.In order to attain a good and accurate result, the experimental data was denoised using wavelet threshold denoising method firstly, then the frequency domain integrated method was selected to calculated the structure’s velocity and displacement corresponding the acceleration signals. Both the time domain and frequency domain of the acceleration and displacement were investigated. In time domain, the relationship between the relative acceleration and relative stiffness, the relationship between relative displacement and relative stiffness were obtained. In frequency domain, the frequency spetrum distribution of acceleration and displacement were discussed.The continuous wavelet transform method was applied to analyse the impact pressure and acceleration in time-frequency domain. The distribution of wavelet energy spectrum of wave impact pressure and wave-induced vibration acceleration were attained and the stiffness change influence on their distribution was discussed as well.