Research On Cumulative Damage Rule Of Hull Girder Under Multiple Underwater Explosions

With the continuous improvement of target protection capability of ships,single underwater explosion is no longer enough to cause fatal damage to ship targets.It is necessary to strike ship targets several times.This paper combines underwater explosion test with numerical simulation calculation to carry out single attack around the cumulative damage regularity of multiple underwater explosions on hull girders.Damage effects of underwater explosion on hull girders and cumulative damage of damaged hull girders under subsequent underwater explosive loads are studied.Characteristic parameters of residual strength of hull girders under multiple underwater explosions are obtained.The effects of explosive equivalent,distance and number of explosions on cumulative damage effects of hull girders are analyzed.A correlation model between multiple underwater explosive loads and residual strength of hull girders is established.The main achievements are as follows:1.The damage mode of hull beam caused by underwater explosion load is studied,the strain field of fixed support plate under underwater explosion load is analyzed,and the overall motion equation of Hull Beam under underwater explosion load is deduced.The research shows that the hull beam does not deform under medium and long field underwater explosion load;under near field,the hull beam will generate middle depression.Two deformation modes are partial plastic deformation and integral plastic bending deformation of mid-arch;under the action of contact explosion,the mid-bottom plate will crack at the center and form a hole.2.Accumulated damage test and numerical simulation research of hull girders caused by multiple underwater explosions were carried out,and a method of cumulative damage level model and numerical simulation study of hull girders caused by multiple underwater explosions was established.The influence laws of impact factor,number of explosions and other damage criteria on cumulative damage were investigated.The results show that the cumulative deflection value and explosion of hull girders under the same conditions are the same.The accumulative loading times of explosion are approximately linear.With the increase of impact factor Q,the deflection value increases and the accumulative effect becomes more obvious.3.Establish the calculation model of residual strength of damaged hull girder,calculate the variation rule of ultimate bending moment under the condition of break and plastic deformation,and obtain the correlation between residual strength of hull girder and underwater explosion load.The results show that during the process of multiple underwater explosions in near field,the value of middle plastic deformation of hull girder increases approximately linearly with the number of accumulations,resulting in no residual strength of hull girder.Increased overall bending will reduce the moment of explosive load on the hull girders under the same conditions,thus the overall structural deflection of the hull girders will increase approximately linearly with the number of accumulations.In this paper,the cumulative damage law of Hull Beam under multiple underwater explosions is studied.The research results can provide a certain reference basis for the cumulative damage of ship targets.The next step is to study the cumulative damage law of relatively complex hull structures and the progressive failure mechanism of damaged hull components.