Research On Material Point Method For Underwater Explosion And Shock Problems

The research of underwater explosion and structural dynamic response under underwaterexplosion load has important significance in the field of military defense and civilconstruction. Due to underwater explosion and shock response is a complex questioninvolving detonation physics, impact dynamics, fluid-structure interaction and theelastic-plastic dynamic, there is a huge challenge in its theoretical analysis and experimentalresearch. In recent years, with the rapid development of computer technology and numericalmethods, numerical simulation has become an important means to study the underwaterexplosion.In the whole process of underwater explosion, there exist special features such as largedeformations, moving material interfaces, fluid-structure interaction and so on which makingthe application of the traditional numerical method based on grid for simulation study ofunderwater explosion problem is a very difficult job. The material point method is a novelmeshless algorithm. it inherits the advantages of both Lagrangian method and Euler method,overcoming mesh distortion problem associated with the traditional grid-based numericalmethods in dealing with large deformation problems. The material point particles haveLagrangian nature, so that it can facilitate the tracking material deformation history as well asan accurate description of the material interface. These advantages make the material pointmethod has been widely used in the field of impact dynamics. The material point method hasbeen further developed and extended to the field of underwater explosion in this paper.The space and time discrete format of the control equation of material point method isdeduced and the explicit integral algorithm of material point method is given. Based on thebasic theory of material point method the corresponding calculation program is developed.The simulation model of high explosive detonation is established. The detonation process ofhigh explosive is simulated using the material point method. The calculated results are ingood agreement with analytical solutions and experimental data and laid the foundation forthe next research of underwater explosion and shock problems. For underwater explosionshock wave propagation in free field with spherical symmetry properties characteristics, aspherically symmetric form of material point method is presented. In order to verify theaccuracy of the proposed method, the spherical charge underwater explosion in the free field is numerical calculated. The calculation results are in good agreement with the experimentaldata and calculation results obtained by the empirical formula. On this basis, the remappingalgorithm based on the material point method is presented. The use of this method caneffectively improve the efficiency in solving the three-dimensional underwater explosionproblem. Two-dimensional underwater explosion is simulated and the calculated results arecompared with the results by the SPH method and empirical formula. The results indicate thatthe calculation accuracy is as high as that of SPH, but the material point method has obviousadvantages in dealing with the material interfaces.A series of phenomenon of underwater explosion near the free surface is numericalcalculated. The solving process of multi-material coupling in material point method ispresented. The cut-off effect of the free surface to the shock wave is studied, and theformation process of water mound near the free surface is reproduced successfully. Thephenomenon of air interlayer decay the shock wave has carried on the quantitative research.The results showed that the air interlayer can reduce the shock waves effectively.Elastoplastic constitutive model of materials as well as the equation of state in thecondition of explosion shock is established and the transient plastic dynamic response ofstructure under explosion shock load is studied. Because of the Cauchy stress materialderivative is affected by the rotation of rigid body, the objective of Jaumann stress rate isintroduced to update stress and the stress update algorithm in the material point method ispresented. Material failure model was introduced to the material point method, and thedynamic failure problems is taken into account in the calculation. In order to overcome thenumerical difficulties of solving the strong discontinuity caused by shock wave, artificialviscosity is introduced in the pressure term. The stress update algorithm is modified after theartificial viscosity was introduced. The solving process of fluid-structure interaction in thematerial point method is presented. The fluid and solid is in the same computational domainin material point method and the fluid-structure interaction solution algorithm is simpe anddirect. It is very suitable for solving fluid-structure interaction problem associated with theunderwater explosion in near field.The meshless method research is still in the initial stage and not perfect yet. Althoughsome commercial software already contains some meshless method calculation module, thefunction of these simple calculation module only as auxiliary functions of the program, its core is still the traditional numerical method based on grid algorithm. The calculationprogram developed based on the material point method provides a new numerical computingplatform for study of underwater explosion problems.