Research On Hull Structural Loads Forecast And Structural Response Under Slamming Loads

When the ship is sailing in waves, due to the relative motion between the hull and waves, there exists the slamming phenomenon inevitably. The most prominent problem is the enormous slamming pressure between waves and the hull area in a direct collision, it can cause serious local structural dynamic response, and result in local buckling of the hell when the slamming occurs; Secondly it can cause the instant elastic vibration of the entire hull girder, that has a certain threat on the structural safety of the ship. Thus, in terms of both the structural strength of the hull side, and the ship sailing efficiency, the structural response under load is worthy of our attention.Based on the above reasons, we use the large non-linear finite element software MSC.DYTRAN to conduct a series of numerical simulations, such as two-dimensional wedge, the typical structure of the bow and three-dimensional typical structure of the bow into the water slamming. Especially, two-dimensional ship bow were experimentally studied, and the pressure distribution between slamming surface of the structure in the bow slamming was drawn, and on this basis, the three-dimensional bow pressure and structural response unit structure slamming into the water were further analyzed, fitting out the slamming forecast formula for different conditions were given. Main works are as follows:(1)This paper elaborates the basic theory of the finite element method of the ship. A numerical simulation study of the effect of the air cushion and the air pressure on the 2-D flat bottom structure is carried out, the water slamming pressure and flow field changes when the structural into the water with a certain speed at different oblique angles was analyzed, and the results are compared with the experimental results in the literature to verify the feasibility of the simulation method.(2)In considering the effect of the air cushion, the variation law of the 2-D wedge at different oblique angles and different velocity of the structure surface into the water velocity slamming pressure peak is studied, and the formula of the impact load is obtained. The formula can accurately predict the slamming pressure of the 2-D surface of the wedge, and further provide accurate load input for calculations of hull structure;(3) Based on the structure form of the two typical station of a ship bow, according to the stiffness similarity and certain scale, design a 2-D ship test model with two kinds of stiffness. First, simulating the process of the test model slamming into the water, and obtain the pressure distribution of the model under different conditions. Second, studying the structure of the slamming experiments, then obtain distribution of slamming pressure on the test model under different velocity of different measuring points. The experimental results and the numerical simulation values are compared to verify the accuracy of numerical simulation methods, which lays a foundation for the numerical simulation of the slamming of 3-D structure;(4) First, studying the simulation of the slamming of 3-D rotating structure, experimental results are compared with the references, which verifies the feasibility of the simulation method on calculating the slamming problem of 3-D structure. Second, simulating the slamming process of 3-D ship bow, the effect of different stiffness, different velocity, different thickness and elastic modulus and other factors on slamming pressure of 3-D bow structure are studied. When the structure is rigid, this paper analyzes the relationships between the water pressure of the ship bow structures and velocity, curvature, then puts forward the slamming pressure prediction formula of ship bow; when the ship bow structures is elastic-plastic, this paper analyzes and compares the effects of bow structure response of plate thickness and elastic modulus.