A computer program which simulates a hypervelocity impact event(s) is called a hydrocode. Extensive research into the development of realistic physically based codes has been conducted over the past decade, extending the experimental testing capability into regimes not yet attainable within a laboratory. As a result, this approach for developing spacecraft and satellite shielding solutions is becoming more and more prevalent. The HIDPL has access to a variety of numerical models, ranging from simple two dimensional Eulerian codes coupled with extensive hydrodynamic models to modified CTH codes (developed at Sandia Labs) designed to fit the HIDPL's specific requirements.
CTH is a family of codes constantly under refinement at Sandia National Laboratories (SNL) for use in modeling complex multidimensional (one-, two-, and three-dimensional), multi-material problems which are characterized by large deformations and/or strong shocks. A two-step Eulerian solution algorithm is used to solve the mass, momentum, and energy conservation equations. The first step is a Lagrangian step in which the computational mesh distorts to follow material motion. The second step is a remap step in which the distorted mesh is mapped back to the original mesh, resulting in motion of the material through the mesh. CTH has been carefully designed to minimize the numerical dispersion present in many Eulerian codes. All quantities are fluxed through the computational mesh using second-order convection algorithms, and a high resolution interface tracking algorithm is used to prevent unrealisitic breakup and distortion of material interfaces.
CTH is optimized by using one of several models for calculating material response in strong shock, large deformation events. Models accounting for material strength, fractures, distended materials as well as a variety of boundary conditions exist. The material strength model may be designated as elastic or perfectly-plastic with thermal softening, and fractures can be initiated based on either pressure or principal stress. HIDPL also has developed a set of highly accurate analytic equations-of-state which may be used to model single-phase solid, liquid, and vapor states, mixed phase vapor-liquid and solid-liquid states, and solids with solid-solid phase changes as they relate to hypervelocity impact studies.