| As a typical deepwater platform,semi-submersible platform has many advantages,such as strong wind resistance,wide adaptability of working water and strong drilling ability.It has been widely used in offshore oil exploration.Due to the harsh marine environment of semi-submersible platforms,wave slamming is often encountered on platform columns and lower deck.The existence of the four column of the platform leads to the near trapping effect,and the superposition of the waves between the columns lead to the negative air gap under lower deck,which seriously affects the structural safety and the operation efficiency of the platform.Therefore,the study of the slamming load and the near trapping phenomenon is very important for the design and construction of the semi-submersible platform.First,the numerical simulation of the slamming load on the deck and the column of the platform is carried out by the CFD software Fine/Marine.A complete slamming load coefficient library is set up,and the formula of the slamming load coefficient is fitted.Based on the potential flow theory software Aqwa,the motion of platform under different sea conditions in mooring mode is simulated.Combined with the formula of slamming force coefficient,a fast calculation method for slamming load of semi-submersible platform based on potential flow theory is proposed.The numerical simulation of the near trapping of semi-submersible platform under fixed mode is carried out,and the influence of different wave elements on the near trapping is explored.The main contents are as follows:Based on the theory of impulse entry slamming,a numerical model for water entry slamming of lower deck and column is established,which includes structure,water and air interaction.The relationship between slamming load and angle of water entry and velocity is analyzed.The relationship between slamming pressure and spatial position distribution at different longitudinal angles is discussed.According to the results of numerical calculation,a slamming load coefficient library is established.The function equation between maximum slamming pressure coefficient and water entry speed and water entry angle is fitted.Using the fitting equation,the maximum slamming force coefficient can be quickly solved,which is of guiding significance for the safety assessment of the platform structure in engineering.Based on potential flow theory,numerical simulation is carried out on the hydrodynamic responses of semi-submersible platforms and the motion responses under extreme sea conditions.First,the hydrodynamic performance of the platform is calculated under the deep water condition,and the motion response and mooring tension of the platform under the mooring mode under the extreme sea condition are studied.The air gap of the platform is statistically analyzed by setting up monitoring points on the lower deck of the platform.The effects of wave direction,wave height and peak period on the distribution of air gap are discussed.The self motion software is used for post-processing of the platform's motion response and negative air gap value.The velocity,relative deck angle and slamming frequency of the slamming wave at the position of the negative air gap are obtained.The slamming pressure coefficient is calculated by the formula of slamming force coefficient,and the slamming load is solved quickly.The slamming load of the semi-submersible platform based on the potential flow theory is completedBased on CFD,numerical simulation and analysis of near trapping of semi-submersible platforms under different wave elements are carried out.By setting wave height monitoring points,the waveform distribution under the influence of near trapping between platform columns is obtained.Considering the interaction of the front and rear columns and the lower floating bodies,the influence of wave angle and wave period on the waveform distribution of the four columns of the platform is studied.The wave superposition and water shock of the column are summarized and analyzed. |
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