The original Box_Tree code, written by Derek Richardson, was a hybrid of two computer algorithms, a box code and a tree code and was based on a model developed by Wisdom and Tremaine to study protoplanetary disk dynamics. The code is optimized to allow for the inclusion of external potentials under specificied coordinate systems. This provides a self-consistent model of fractal aggregate dynamics along with a full treatment of rigid body dynamics including rotation. The code also allows for particle and cluster trajectories as well as orientations to be followed explicitly and incorporates a local shearing disk model for planetary rings. The tree code provides a method for rapid calculation of interparticle forces thus allowing them to be included as perturbations to the equations of motion.
The version in use within CASPER has been heavily modified and now allows for the tracking of electrostatic forces between grains, charge rearrangement along fractal aggregates, Debye shielding of grains within dusty plasmas, the inclusion of planetary magnetic fields via spherical harmonic expansions and the inclusion of the gravitational potentials of shepherding moons in ring/disk studies. This provides researchers within the Center extensive modeling capabilities for coagulation calculations including both fractal geometries and dynamic charge allocation along fractal fingers. Additionally, Coulomb crystal models in both 2 and 3 dimensions for bounded (periodic and aperiodic) and unbounded conditions are also being investigated. The code is presently undergoing modifications which will allow investigation into EM energy transfer through dusty plasmas as well as advanced gravitoelectrodynamics studies.
The code is available for a number of operating systems including VMS, Sun, and Linux.
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.