Numerical Study On The Hydrodynamic Characteristics Of Perforated Plate During Water Entry

With the development of technology in recent years,the public awareness of ocean has increased.Marine resources far away from land have been discovered and exploited in succession.Deep sea fields offshore operations require higher safety standards in comparison with those in shallow sea,to cope with the complex and harsh sea conditions.This includes the lowing and installation operation of marine structures in splash zones.During the installation process,the weight loss of the structure can occur if the slamming load of the structure is greater than the weight of the marine structure during the short time of water entry.The huge impact induces the cable slacking and the structure free falling.Eventually,heavier slamming and even damage occur to the structure.The purpose of this thesis is to investigate the law of water entry of solid or perforated plate structures in marine engineering in different sea conditions.The focus in the thesis is on the evolution of the air cushion appearing in the water entry process and its influence on the slamming load.The purpose is to provide a theoretical basis for the design of marine structures and the standard of offshore operation.The thesis firstly illustrates some classical theories of water entry of structures including two-dimensional wedge and flat plate.The control equations of CFD,VOF model and DFBI model are demonstrated next.Secondly,the numerical method is used to simulate the water entry process of the flat plate in static water.The results are compared with the experimental results to verify the numerical simulation method.After that,the water entry process of the perforated plate is numerical simulated,and the peak of slamming load and the evolution characteristics of the gas cushion are analyzed.The effects of parameters including the speed of entering the water(initial height of the plate)and the perforation ratio of the plate on the slamming load are analyzed.The importance of the gas compressibility in the numerical simulation is explained.In addition,the thesis discusses the negative pressure phenomenon that occurs during the lowing process of the structure.Finally,the effect of waves on the slamming load and evolution of gas cushion are analyzed for free-fall structures.