The High Order Inerfacial Treatment And Numerical Investigation Of Explosion And Impact Problem

The high-order numerical simulation of explosion and impact problems has very important theoretical value and engineering applicational prospect in fields of public safety and national defense construction including gas explosions in a coal mine,urban antiterrorism,and weapon equipment development.The key technology of the high-order numerical simulation based on the finite difference method of the explosion and impact problem is how to realize the high-order numerical treatment of the multi-material interface.In present thesis,we greatly focused on this core problem and systematically investigated the high-order treatment of the rigid wall boundary for the reactive Euler/Navier-Stokes governing equations,the interface between the explosive product and the gas/water and the large deformation interface for the elastic plastic problem.The proposed numerical treatments successfully overcame the pollution of the interior numerical results caused by the inappropriate interfacial treatment,improved the conservation of the numerical calculation of the interface and the robustness of the whole code.The self-developed code effectively realized high-order simulations of explosion and impact problems such as flame acceleration,deflagration to detonation transition,detonation wave propagation in complex structures and the elastic plastic large deformation.The main research work and innovations of the thesis are as follows:(1)Considering the complex dynamics of explosion and impact problems coupling thermal,mechanical and chemical processes,we constructed the reactive governing equations which describe the flame acceleration,deflagration to detonation transition and detonation wave propagation,the multi-material coupled dynamic evolution models of air explosion and underwater explosion,and the governing equations of the elastic plastic large deformation under the condition of the high-speed impact.The local characteristic decomposition of the hyperbolic gonverning equation for the explosion and impact problem was realized,and the high-order finite difference WENO(Weighted Essentially NonOscillatory)scheme which has an ability of dealing with strong discontinuity and large deformation was developed;(2)For the reactive Euler/Navier-Stokes dynamic governing equations,the ILW(Inverse Lax-Wendroff)method was utilized.Thus,the normal partial derivative can be submitted by the time derivative of the given boundary conditions and objectively reflected the intricate physical mechanism of the interaction between detonation waves and rigid wall.The high-order WENO-type extrapolation was also constructed.Combining with the highorder Taylor expansion,the presented method overcame the high-order approximation challenge of ghost points in the neighborhood of the rigid wall.The high-order rigid wall treatment presented in this thesis effectively addressed the numerical oscillation caused by the strong discontinuity near boundary,improved the stability of the numerical boundary scheme,and avoided polluting the internal high-order numerical results of the explosion flow field from lower order boundary treatments using straight boundary instead of complex curved boundary in tradition;(3)The adaptive least square interpolation method was deduced to obtain the extrapolated value of any physical quantity at the mirror point and improved the robustness of the numerical scheme for the large deformation problems such as cavity collapse and penetration.Based on the generalized Riemann invariant theory,the coupling relation between the undisturbed initial states and the interface states was established for the general equation of state of the explosion and impact problem,and the double rarefaction wave Riemann approximation solver was realized successfully.By being compared with the analytical solution,the validity of the Riemann approximation solver method was verified.The velocity field near the interface was modified by the interface velocity of the Riemann solution,which realizes the accurate tracking of the interface evolution position.The RGFM method uncoupling the multi-material,which possesses the nice conservation and high accuracy,was utilized together to overcome the numerical oscillation phenomenon of the general numerical scheme in the vicinity of the multimaterial interface,which caused from impedance mismatch on both sides of the multi-material interface.Thus the high-order finite difference WENO scheme can be applied to investigate the underwater explosion,and the elastic plastic large deformation under the condition of the high-speed impact;(4)The fifth order WENO scheme was used to discretize the spacial derivative term,and the third order TVD(Total Variation Diminishing)Runge-Kutta scheme was adopted to discretize the temporal derivative term.Thus,the finite difference code with the ability of simulating the explosion and impact problem with high accuracy was developed.Based on the large scale array storage method of scientific computing language FORTRAN,the enclosed data module for each processor of a high dimensional problem was built,which improved the data communication efficiency between different processors for the high-order and large scale computation,simplified the complexity of FORTRAN parallel code development and made the explosion and impact code possesse the large scale engineering parallel computing capacity;(5)The high-order,large scale parallel explosion and impact code developed in this thesis was utilized to investigate the detonation wave propagation mechanism in the complex tube,we discussed the oblique detonation formation mechanism when interacting between the high Mach number inflow premixed combustible mixture and impacted the oblique rigid wall,in which the single-headed and double-headed triple point structures in the oblique detonation front were revealed,compared the influence mechanism of the different obstacle geometrical configuration with the same blocking ratio on the deflagration to detonation transition process,and performed the numerical simulations of the multi-field coupled large scale deformation problems such as weaking the explosion wave from gaseous interlayer,cavity collapse,copper cylinder impacting copper target and copper rod penetrating steel plate with a high speed;(6)Experiments on near surface explosion were carried out to reveal the propagation mechanism of the explosion in the near surface explosion.The experimental data obtained,the empirical formula and the simulation results from the self-developed high-order explosion and impact code were compared.Agreement validated the reliability of the explosion and impact code.