Development Of Hypervelocity Impact Codes Based On Euler Method And Numerical Study Of The Phase Distribution In Debris Cloud

Optimized design of spacecraft structure has become a crucial task for improving spacecraft safety. Hypervelocity impact is not only an important issue in the study of spacecraft protector design but also a basic problem in shock dynamics. In hypervelocity impact, materials in the target undergo large deformation, fragmentation, and stress-wave-induced spall, producing a debris cloud. Under very high velocity (v> 10 km/s), the pressure and temperature in the target material are so high that the debris cloud will melt, vaporize, and even turn into plasma. Consequently, structure evolution, mass and momentum distributions, and the thermal state and phase distributions of the debris cloud have become key subjects in studies of hypervelocity impact and aircraft protector design. Although many experimental and numerical simulation studies of hypervelocity impacts of v< 7 km/s have been undertaken to investigate the mass and momentum distributions and structure evolution of the debris cloud, studies of the thermal state and phase transition of the debris cloud have been lacking. Melt and vaporization of the debris cloud are important issues in such hypervelocity impacts and will become even more common for v> 10 km/s, which is more common in the real space environment. Experimental research on debris clouds to investigate melt, vaporization, and phase distribution is very difficult because of the limited hypervelocity launch capability and diagnosis tools, so numerical simulation has filled an especially important role in studies of hypervelocity impact. Numerical simulation can improve our understanding of the impact mechanism and can guide aircraft protector design but poses some challenges:One needs 1. numerical methods that can deal with large deformation and multi-material interactions,2. a multi-phase equation of state (EOS) that can describe the solid-liquid-vapor phase transition of materials throughout a large thermal region, and 3. material parameters that are valid over a wide pressure and temperature range. Therefore, this project is devoted to studies of the multi-material Euler numerical method and the solid-liquid-vapor multi-phase EOS, to the construction of a code for hypervelocity simulation, and to the numerical simulation and analysis of the debris cloud distribution in hypervelocity impact. The main research results of this project are as follows:1. Using a multi-material Euler method based on the Level Set function, we developed a uniform method that treats together interface tracking, the mixed-mesh partial volume calculation, and the unsplit material transportation and we constructed a hypervelocity impact multi-material Euler simulation code suitable for complicated three-dimensional geometric modeling.2. Based on the GRAY three-phase incomplete EOS, and by describing the solid phase with the Helmholtz free energy, we devised a new EOS based on the Helmholtz free energy and that covers the complete ranges of solid, liquid, and vapor states. Aluminum material parameters were given to verify the effectiveness of the newly build GRAY three-phase EOS.3. We conducted systematic verification and validation (V&V) for the program, demonstrating that the hypervelocity program based on the Euler method can accurately calculate the planar symmetric collision problem and model shock wave propagation characteristics such as pressure and temperature. The program is also qualitatively correct for describing the debris cloud structure and thermal states of the Whipple protector under hypervelocity impact.4. After V&V, we implemented the program in numerical studies of the debris cloud phase distributions under hypervelocity impact with plane symmetry and hypervelocity impact with a spherical bullet. The mechanism of the solid-liquid-gas phase evolution of the debris cloud in the impact process was analyzed by utilizing one-dimensional shock wave theory, and the phase distribution characteristics and evolution law of the debris cloud under different impact velocities were derived. The calculation results are in good agreement with the experimental results.