| In the field of Marine engineering and Marine engineering,scholars focus on the blunt body slamming,such as seaplane landing,offshore platform heave,lifeboat entry and so on.Its very short water entry process is difficult to capture,and the structure and the surface of the water impact,resulting in a huge impact load,the surface of the structure or even the internal structure easy to damage,resulting in economic losses and casualties,so the study of the mechanism and the method to reduce the impact load into the water has very important significance.In this thesis,the simplified jet device model of sliding lifeboat was designed,the numerical prediction method of the whole process of jet entry movement of lifeboat was carried out based on STAR-CCM+ fluid simulation software,and the real-time numerical prediction model of the motion response of lifeboat in the process of sliding-jet entry-buoyancy was constructed,and the influence of different motion parameters on the attitude of boat body entering water and the shape of cavitation under the condition of jet was discussed.The slamming load characteristics of lifeboat under different jet conditions were studied and the optimal jet scheme under corresponding conditions was finally given.The research results would provide reliable theoretical and technical support for reducing the percussive load of structures entering water.The main research contents and achievements were as follows:Firstly,the six-degree-of-freedom motion equation of the lifeboat was solved based on RANS equation and overlapping grid technology,and the numerical prediction model of the six-degree-of-freedom motion response of the lifeboat was constructed.The impact load variation of wedge during water entry was studied and compared with the experimental results to verify the reliability of the numerical method.At the same time,the motion response characteristics of the whole process of wedge injection were studied,and the impact load characteristics under different injection flow and different water velocity were studied.This would lay the foundation for the study of the impact load distribution and motion response of lifeboat.Secondly,the motion equations of the lifeboat sliding along the track and dropping process under different circumstances were solved by Matlab self-programming,and the results of the motion response characteristics were shown.The influence of different length and dip Angle of slide on the motion response of lifeboat was analyzed.At the same time,taking the final velocity of the slipway as the initial velocity in the process of dropping,the motion law of the lifeboat under different speeds and angles of dropping was analyzed,and the trajectory curve of dropping was obtained.The stage analysis of the whole boat body is carried out to study the slamming load of the lifeboat under the specific conditions of the jet,and the load dropping characteristics were obtained by comparing with that without the jet.At the same time,the influence of different entry speeds and angles on the hydrodynamic performance and slamming load characteristics during the water entry process was studied.Finally,a reasonable jet model was designed,which was simplified in the process of numerical simulation.The variation law of the percussion load during the lifeboat entering the water under different jet conditions was studied.The six-degree of freedom motion response of the boat body and the development and change of cavitation were analyzed,and the influence characteristics of different jet flow and different jet port layout were qualitatively and quantitatively analyzed.By arranging pressure measurement points on the surface of the boat body,the time-varying law of the bang pressure under the condition of air injection was solved,and the spatial distribution of the bang peak value was obtained by drawing software.Finally,the cavitation morphological changes during the water injection process of the boat body were analyzed. |
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