An explicit is solved by calculating results in small time increments or time steps. The size of the time step depends
on many factors but is automatically calculated by Radioss.

Composite materials consist of two or more materials combined each other. Most composites consist
of two materials, binder (matrix) and reinforcement. Reinforcements come in three forms, particulate,
discontinuous fiber, and continuous fiber.

A rigid body is defined by a set of secondary nodes and a main node. It can be compared to a part with an infinite
stiffness. No relative displacement is allowed between secondary nodes, and the general motion of the rigid body manages
the main node.

A rigid wall is a nodal constraint applied to a set of secondary nodes in order to avoid the node penetration to the
wall. If contact is detected, then the secondary node acceleration and velocity are modified.

Interface TYPE2, also called tied interface is a nodal constraint to rigidly connect a set of secondary nodes to a main surface. The secondary nodes forces and
moments are transferred to the main nodes, and then secondary nodes are positioned kinematically according to the
motion of the main nodes.

A cylindrical joint is like a rigid body, except that one specific direction is defined with the first two secondary
nodes. All nodes are free to move along this direction and to rotate around it.

The rigid link option imposes the same velocity on all secondary nodes for one or more directions. Directions are
defined to a skew or a global frame, velocity is computed with momentum conservation.

Gear type joints are more complex than other kinematic joints. They use the Lagrange Multiplier method and
are compatible with all other Lagrange Multiplier kinematic conditions and incompatible with all classical
kinematic conditions.

As nodal constraints are based on kinematic conditions applied on nodal DOF, therefore it is not allowed to apply
two nodal constraints to the same set of nodes, unless the induced kinematic conditions are perfectly orthogonal (for
example: boundary condition in the X-direction and rigid link in the Y-direction).

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.

Gear type joints are more complex than other kinematic joints. They use the Lagrange Multiplier method and
are compatible with all other Lagrange Multiplier kinematic conditions and incompatible with all classical
kinematic conditions.

Gear type joints are more complex than other kinematic joints. They use the
Lagrange Multiplier method and are compatible with all other Lagrange Multiplier
kinematic conditions and incompatible with all classical kinematic
conditions.

Three examples of these joints are explained:

Rotational gear type joint

Rack and pinion joint

Differential gear joint

Mass and inertia may be added to all nodes. MPC joints impose relations between nodes velocities. The MPC cannot be applied to the translational degrees of freedom of a node without mass or the rotational degrees of freedom of a node without inertia.

Rotational Gear Type Joint

This joint is used to impose a rotational velocity relation between input and output node as:

Translational velocities of gear joint nodes are constrained by a rigid link relation. For the
rotational degrees of freedom, a scale factor is imposed between
velocities of nodes N_{1} and
N_{2}, measured in their local
coordinates. The corresponding constraint equations
are:

Where, $\text{\Delta}{\omega}_{1}={\omega}_{1}-{\omega}_{0},\text{}\text{\Delta}{\omega}_{2}={\omega}_{2}-{\omega}_{0}$ are relative rotational
velocities of nodes N_{1} and
N_{2} in respect of the rigid
body rotational velocity.

Rack and Pinion Joint

This joint allows the rotational velocity of node to be transformed to a translational velocity
as:

The constraint equations for these velocities are:(1)