| Oceans are important places for human to obtain survival and development resources.In recent decades,with the increasing needs in ocean energy exploitation and offshore/coastal transportation,more and more offshore power plant and bridges have been built around the world,especially in China.However,considering the complexity of the ocean environment,the wind wave current flows will induce severe threat to these structures.Through systematic research on the characteristics of ocean wind wave current flows and gaining more knowledge on the dynamic performance of offshore structures under the action of multi-hazard environment,the capacity of disaster prevention and mitigation of offshore structures can be considerably elevated.In this paper,numerical simulation and analysis on ocean wind wave current flows have been carried out.Besides,a systematic investigation of the dynamic performance of the tower of a planned cross-strait bridge under wind-wave actions has been made.The main contents of this dissertation are:(1)A line-distribution mass source wave making method has been established based on the internal wave making method and the ALE surface tracking technique,and a series of numerical study on piston-type and flap-type wave makings has been performed.For comparison,numerical wave tank based on VOF surface capturing technique was built.Based on the comparison and analysis of the results through two methods,it was found the wave surface and flow field obtained by ALE and internal wave making methods was quite satisfying,and the free surface wave by the VOF method has minor decaying wave height in the test section(around 4%)while keeping constant wave period and wave profiles.(2)Based on the multi-layered flow structure concept proposed by Campagne under the free surface,this paper employed the velocity-vorticity correlation structure method to analyse the direct numerical simulation result of an open channel flow.The free surface is modelled as a free slip boundary.Two combinations of the velocity and vorticity correlation structure were chosen and quantified,and together they provided a clear picture of the difference between the coherent structures observed from various layers.The effect of the multi-layered structure were manifested by the evolution of the hairpin vortical structure.(3)The paper carried out a series of experimental study on investigating flow fields under wind and wave actions.The characteristics of the wind and wave field and their dependence on each other were analysed.Based on the VOF method,the wind-wave combined numerical tank has been established.Through the comparison of the numerical results and the experimental data,the capacity of application of the numerical wind-wave tank.(4)For an elastic circular cylinder,experimental investigation has been performed under different water depths and wind-only,wave-only and wind-wave actions to obtain the dynamic responses.Based on the numerical wind-wave tank and the elastic structure dynamic solver,a fluid-structure interaction(FSI)solver has been developed in OpenFOAM,which dealt with the dynamic responses of elastic structures under wind-wave combined conditions.Through comparison with the experimental results,the flow field around the cylinder and the influence of wind-wave actions on the dynamic performance of the cylinder have been revealed.(5)A systematic experimental study has been performed on a typical high-rising bridge tower under wind-wave combined conditions.The dynamic responses under windonly,wave-only and wind-wave actions were compared and analysed to better understand the influence of wind and wave loadings on structural response.The frequency domain buffeting analysis for bridges was extended to incorporate the wave loads,and the dynamic responses of the tower under wind-wave actions were computed and compared with the experimental results. |
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