Research On Ship Shock Trial And Response Characteristic For Non-contact Underwater Explosion

The warships is the main equipment to protect the national sovereignty,the survivability is the basic element to ensure the operational performance of the ship,so the response of warships subjected to underwater explosion has been a hot spot in the warships shock resistence field.Various theoretical,numerical and tests research has benn conducted extensively,and the research has achieved fruitful results.The research deepens the mechanism study of the underwater explosion and other related issues,and promotes the further research on the structural response of the warships.However,subject to the constraints of technical and economic factors,researchers mostly use the theory and numerical methods to study the response propertier.And some tests were conducted which mainly aims at the local structural model or shrinkage ratio model.In the process of underwater explosion load applied to the ship,the load input to the structure of the energy in the early only distributes in a very small range of the warship structure.Then,the input energy is transmitted to other parts of the structure in the form of a stress wave.After several times of reflection,refraction,scattering,and the interaction between stress wave and stress wave,finally the ship structure achieves the steady state,the ship produces local vibration and overall vibrationand.So the local structure simulation or tests can not reproduce the full scale ship trail,the local system is unable to replace the whole system characteristics.First of all,based on engineering research background of warships shock resistance,the current underwater explosion research status is summarized respectively from the theoretical,numerical and experimental points,and the problems existing in the current study are pointed out,especially warship underwater explosion test research is reviewed,the main research contents of this paper are identified,and an overview of the main work of this paper are presented.In this paper,the measurement system and method of full scale ship underwater explosion test are described,and the test system are summarized,including the measurement point layout,measuring instruments,test cable and testing process.The key technology used in the test is proposed,including selecting principle of measuring points,signal transmission cable selection and the performance index requirements,the applicable conditions of test instruments and the control system for the test and anti-shock protection system.It provides a reference for the complex and difficult implementation of the underwater explosion trail.Before the underwater explosion test,the prediction of the structure response subjected to underwater explosion load is necessary to make decision for test condition.In order to solve the underwater explosion flow field with large discontinuities,Level Set method was applied to track the interface position of multi-medium flow,Ghost Fluid method was used to calculate the physical parameter of both sides of the interface,time and space were discretized by Runge-Kutta Discontinuous Galerkin Method,Euler equations of the flow field were solved.One-dimensional and two-dimensional assessments were conducted by RKDG approach.With underwater explosion load computation program,the underwater explosion load near wall boundary was simulated.The result shows that the program is suitable for simulating the process of underwater explosion shock wave generation,propagation,reflection and explosion products expansion.Combined with ABAQUS,shock responses and damage characteristics of hull plates under shock load were simulated.The simulation calculation of the full scale ship finite element model is carried out,and the ship response is predicted.For modal aliasing problem of empirical mode decomposition(EMD)method,a set of empirical mode decomposition(EEMD)method is used to anlysis the underwater explosion signal,which is used to eliminate mode aliasing,so that the different order IMF has physical meaning and real time frequency information is obtained.Different spectral information of plate Lamb waves subjected to underwater explosion is extracted.Using the improved HHT method,shock response data of 600 ton and 3000 ton ships subjected to underwater explosion is analysed.The bending wave signal of hull plate subjected to underwater explosion achieves the effective narrow band extraction,Lamb wave dispersion of steel plate was solved theoretically.According to the characteristic of time-frequency,the narrowband Lamb wave dispersion characteristics is calculated,narrow band is extracted by modal decomposition,the group velocity of different narrow band is calculated through the time difference,the obtained Lamb wave group velocity test value is compared with the theoretical value.Through the analysis of Lamb wave dispersion characteristics,dispersion characteristics analysis of bending wave group velocity of the structure response under complex loading is realized,characterization of ship underwater explosion test deck bending wave propagation is represented.Based on the discrete time transfer matrix method combined with the non-homogeneous precise integration method,the hull beam is equivalent to variable cross-section beam,the shock dynamic bending moment of the ship beam model subjected to underwater explosion is constructed.Combined with the boundary conditions,the shock dynamic bending moment of the ship girder sustained underwater explosion load is calculated.The calculation of the shock dynamic bending moment of the full scale warship underwater explosion test through the discrete time precise transfer matrix is realized.Meanwhile,the calculation results are compared with the test values,and the proposed method is verified.According to the test results,the optimization of ship underwater explosion test measuring point layout are realized to get the valid information within limited test scale.According to the experimental data analysis of full scale warship underwater explosion trial,the typical problems affecting the ship's vitality are analyzed,the characteristics of the shock environment are analyzed and given,including the deck acceleration peak frequency feature,and the acceleration peak value distribution,and checking the shock environment by the specification.For the combat surface ships,it is necessary to meet the battle vitality under the underwater weapons attack,besides the wave bending moment Mw and hydrostatic moment Ms,the dynamic bending moment Msd should be considered in the check of total strength.Combined with the ship hull total strength requirements of the specification GJB4000-2000,and the total strength considering dynamic moment is checked,the response of shock dynamic moment is analyzed.Finally,the intrinsic frequency of the hull plate is analyzed by modal identification,,and the boundary conditions of the plate are obtained by comparing the measured results and theoretical calculation results.And the plate stress is calculated.