Study Of Dynamic Responses Of Marine Structures Under Wave Slamming

With the development of the ocean exploitation from inshore shallow water to the open sea deep water, the traditional fixed platform can not meet the needs in the deep water, so more and more complaint marine structures are built. The integrated rigidity of complaint structures is relatively small, thus dynamic responses of the structure under wave slamming will be a huge threaten to structure safety; Meanwhile, as a result of structure's rigidi becoming small, its natural frequency may approach the frequency's of the incident wave load with big energy, hence it will be more likely to cause resonance to the marine structure under wave load. So, the study of the dynamic responses of the marine structure under wave slamming is of very important theoretical and scientific significance and also applicable value in engineering.The experiments were conducted in the oil spilling tank in the State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology. The test wave is regular wave, with the incident wave period from 0.8s to 1.6s, wave height from 6.0cm to 14.0cm and the structure clearance from 0.5cm to 5.0cm. The experimental investigation of the dynamic response under wave impact is carried out after the reasonable combination of the test sets.First of all, the wave impact forces on the structure model with different wave condition and structure clearance is obtained through experimental investigation. The dynamic responses under horizontal and vertical wave impact load of the structure are researched in the time domain. The maximum acceleration response and the time of its occurrence under wave slamming are analyzed. Then, based on the Fast Fourier transformation, the frequency analysis is conducted to horizontal and vertical acceleration responses. The vibration frequency characteristics are obtained in both horizontal and vertical direction. The peak values frequency of the horizontal acceleration responses spectra correspond to the incident wave frequency, the natural frequency of the platform structure and the frequency that is the numbers of wave frequency. The maximum spectra peak values lies in the frequency that is the numbers of the wave frequency approaching the natural frequency. The maximum vertical acceleration spectra peak values close to vertical natural frequency. As a result of the added mass when the structure vibrates in the vertical direction, the maximum spectra peak values below the vertical natural frequency. When the incident wave frequency closed to the horizontal natural frequency, the horizontal acceleration gradually takes its maximum. Because the vertical stiffness of the structure is very large, the vertical natural frequency is higher than the incident wave frequency and at the same time lower than the vertical impact load frequency to a large extent, there will be no resonance in the vertical direction within the experiments.