A Study Of Hull Slamming Based On Analytical And CFD

The modern ships are becoming more faster,as a consequent,the problem of slamming caused by the violent movement of the hull in the waves is getting more and more attention.One of the most important problems affecting the safety of hull structure is that the hull slamming for both single-hull and multi-hull ships such as catamaran and trimaran.Therefore,the study of the slamming load is of great significance to the structural safety and design of ship hulls.Based on the analytical and computational fluid dynamics(CFD)method,the twodimensional slamming mechanism of single-and trimaran ships are studied,and the characteristics of slamming pressure and slamming force are obtained considering the influence of various factors.The main research contents and conclusions are as follows:1.This thesis first introduces the background and significance of the research on hull slamming,and describes the current status of theoretical,experimental and numerical simulation research in the field of slamming.2.The two-dimensional slam analytical calculation model and the Precise Integration Method(PIM,for time integration)are combined to study the slamming process under the condition of free fall with arbitrary two-dimensional symmetric shapes.The slamming process is directly related to the penetration depth,but not affected by the ways of entering the water(i.e.variable speed,uniform speed,etc.).Based on this,the following rule is obtained: under the condition of free fall,if the influence of gravity is ignored(the hydrodynamics at the initial stage of slamming into the water is greater than other factors),the maximum slamming force of a body with certain shape is determined by the mass,and not affected by the entry speed.3.Based on the CFD software STAR-CCM+,the numerical simulation of the slamming of the trimaran is carried out.The simulation results are in good agreement with the experimental results,and the reliability of the numerical model is confirmed.On this basis,the simulations with various conditions are simulated:a)Numerical simulations were carried out on the water slamming in three different motion states: free fall,uniform motion,and simple harmonic motion.We have summarized the differences in the slamming characteristics of the trimaran in three motion states,including the phenomenon of negative pressure under the main body when the wet-deck slamming occurs under free fall condition;b)Numerical simulations are carried out on the slamming of free-falling trimarans with different masses and different water entry velocities.The results show the following pattern: Greater water entry velocity generate larger slamming load.The slamming acceleration(i.e.the second peak)of the wet-deck of the trimaran with different masses increases first and then decreases;the ratio of the first and second slamming peaks of the trimaran gradually increases with larger entry speeds;c)For the simple harmonic motion water slamming conditions with different motion periods(corresponding to different water entry velocity),the pressure measurement point under the main body of the wet-deck slamming is positive,not negative pressure as in the case of free falld)By simulating the conditions of uniform velocity and uniform acceleration of water slamming under different parameters,it is concluded that the impact characteristics of the trimaran hull are not affected by way of water entry(i.e.variable velocity,uniform velocity,etc.),and it is directly coorelated to the penetration depth.This is consistent with the slamming pattern of the single hull based on analytical theory prediction.