Numerical Study On The Slamming Of A Trimaran And Application Of Air Cushion

With the development of economic globalization,the demand for high-speed and ocean-going ships is rapidly increasing.As the representative of the high speed ship,the trimaran has developed very fast in recent years.At the high-speed,slamming phenomenon of the trimaran ship often occurs,which causes great damage to the structure at the bridge of this type of ship.The aim of this paper is that studying the law of water slamming of three-body ship,and analyzing the influence of air cushion effect on the slamming load of three-body ship connection bridge.In this paper,STAR-CCM+,a commercial software of computational fluid dynamics,is used to simulate the entry water slamming of a trimaran ship.Then the slamming acceleration and surface pressure at different heights and angles are compared,and the law of slamming is obtained.Based on the above analysis,this paper proposes several different types of bottom sealing plates and selects the best ones through a series of numerical calculation results.Finally,it is applied to the trimaran ship model and is verified by numerical calculation,and a new conceptual design of the trimaran ship connection bridge is proposed.The main research contents of this paper are as follows:(1)This paper introduces some theories of the water entry slamming,including the two most classical two-dimensional wedge theory,some empirical formulas obtained from experiments,the control equation in CFD simulation,turbulence model and the VOF model,which involve three aspects: theory,experiment and numerical value of water entry slamming.Based on the above theory,the physical model needed for this numerical value is established.(2)numerical simulation of the water entry slamming of a trimaran ship is carried out by using the commercial computational fluid dynamics software STAR-CCM+,and the results obtained were compared with the tank entry test conducted by dalian university of technology to confirm the feasibility of the numerical simulation.(3)Based on the above one,The numerical calculation of water entry at different heights and water entry angles is carried out respectively,The water entry law of trimaran ship is analyzed by using the pressure and overall acceleration of the monitoring point,and the change of flow field is also observed.According to the flow field,the lifting of free liquid level,the distribution of gas and liquid on the surface of trimaran ship and the distribution of pressure on the surface are described in detail.(4)The escape velocity of the gas is reduced by limiting the calculation domain size,and the influence of air cushion on water entry slamming is analyzed.Based on air cushion effect put forward several new connection bridge bottom sealing plates and filtered through a series of conditions,the advantages and disadvantages of several kinds of bottom sealing plate is described in detail.after that,the optimal bottom sealing plate form was applied to the trimaran ship to carry out the numerical research.Through different working conditions,the load reduction effect of the bottom seal plate has been verified,and a new conceptual design for the subsequent three-body ship connection bridge structure is proposed.