Study On The Response Mechanism Of Ship Structure Under Underwater Explosion And Sea Wave Loads

As the main combat platform of modern naval warfare,the ship is the main object of the weapon attack,and the survivability of the ship is the primary premise and foundation of naval combat.The ship is in waves for most of the time in service.When it is attacked by underwater weapon,it will not only be subjected to blast loads,but also subjected to wave loads.Whereas,whether in the ship structural strength design or in the research of anti-explosion of ship structure,the effect of wave loads and explosion loads are always separately considered.To meet the needs of actual combat,this article focuses on damage mechanism of ship structure under the combined underwater explosion and sea wave loads.The work carried out and the main conclusions obtained are as follows:(1)Summarized the research actuality of ship wave load,damage of ship to underwater explosion and to the combination of underwater explosion and sea wave loads.Due to the huge difference in duration between the two loads,the mechanical state of ship in wave remains unchanged during the explosion.So,the mechanical state of the ship under wave action should be analyzed first,following the considering of explosion.(2)Reviewed the calculation principle of ship wave load,and based on the calculation results of a container ship,the dangerous wave conditions were found.Three kinds of basic research objects subjected to explosion load were abstracted based on the mechanical state of ship structure,which are structural members considering in-plane stress,and members considering out-of-plane load,and ship beam considering bending moment.(3)Focused on the structural member with in-plane stress,the deformation characteristics of axial prestressed beam subjected impulsive load was studied.And found that,the midpoint residual deflection of compressive prestressed beam is larger than that with no prestress,while the midpoint residual deflection of beam with tensile prestress sometimes bigger and sometimes smaller than that with no prestress.According to the deformation results,the prestress coefficient was introduced and the dimensionless prediction formula of the deflection-thickness ratio under compressive prestress was obtained.The influence mechanism of tension and compression prestress is explained reasonably from energy and stress respectively.The influence of length-thickness ratio and movable boundary on the effect of tension and compression prestress is discussed.It is found that the larger the length-thickness ratio is,the larger the axial tension is when the relative deflection reaches the minimum value.The strength of boundary constraints determines the degree of influence of tensile and compression prestress on transverse deformation of beams,and the weaker the boundary,the greater the degree of influence.(4)Focused on the structural member with out-of-plane load,the superposition of the initial out-of-plane load and explosion load and the way how to quantitatively introduce of the initial transverse load in experiments are concerned.Through the analysis of the deformation characteristics of the beam under the initial transverse load,it is found that the influence of the initial transverse load on the deformation of the beam under the explosion load has exceeded the nonlinear superposition phenomenon of "1+1>2",showing a more significant amplification or inhibition effect.And the dimensionless prediction formula of deflection-thickness ratio was obtained by introducing a transverse load coefficient.A conical shock tube device was designed to study both the initial transverse load and the underwater explosion load.The underwater shock wave characteristics of conical shock tube were investigated,and the general expressions of peak shock wave,specific impulse and energy flow density were obtained considering the conical angle of conical shock tube.Based on this device,experiments with initial hydrostatic pressure were carried out.It is found that the midpoint deflection of the plate increases with the increase of initial hydrostatic pressure.(5)Focused on the ship beam considering bending moment,the main concern was on how to introduce the initial bending moment to a relative magnitude in the experiment.A hanging and adding mass technique is proposed,and by employing this technique,experiments with different initial bending moment of box girder subjected to underwater explosion were carried out.It is found that the bottom of the box girder with no weight on is in slight sag deformation,and the box girder with weights on both ends shows a combined failure mode of whole bending and local deformation,and the box girder with weights on middle shows local deformation with slight whole bending.The initial bending moment and mass distribution are the main reasons for these differences.The mass distribution has more influence on the motion,while the bending moment has more influence on the overall bending.(6)The way on how to consider the influence of wave load in real ship is discussed from two aspects of local and overall: the process of introducing wave preload into the determination of ship’s safety radius and critical radius is proposed.And in the evaluation method of total damage to ship,the shock waves should be considered according to whether dynamic buckling is caused by the combination of shock wave and sea wave loads.