Optimization in Radioss was introduced in version 13.0. It is implemented by invoking the optimization capabilities of
OptiStruct and simultaneously using the Radioss solver for analysis.

In the ALE formulation, the freedom of moving the mesh is very appealing as it helps
to combine the respective advantages of Lagrangian and Eulerian formulations.
However, it is not easy to specify a grid velocity well-suited to the particular
problem under consideration. As a consequence, the practical implementation of the
ALE description requires that an automatic mesh-displacement prescription algorithm
be supplied.

In Radioss, the following automatic grid computations
exist.

/ALE/GRID/DONEA

This is the standard method applicable to the most of problems. It is based upon a
combination of the material and grid velocities of the neighboring
nodes:(1)

Each grid node is connected to neighboring grid nodes through a nonlinear viscous
spring, similar to that shown in Figure 1.

The stiffness of each spring is given by $M\text{\Delta}{t}_{02}$ (where, $M$ is the mass of the node and $\text{\Delta}{t}_{02}$ is a user input typical time step), a viscosity and
a ratio between shear spring stiffness and traction-compression stiffness of the
springs can be defined.

Note: Those springs only affect the grid node velocity; they
have no influence on the material velocity.

This method is very accurate and robust, but highly expensive in terms of CPU
time.

/ALE/GRID/ZERO

No automatic grid calculation is performed for the grid. The grid velocity is either
constant (0 if no initial grid velocity is specified, the formulation is therefore
Eulerian) or imposed by Property TYPE15 for parts with a rigid body movement.