Body Interactions
The Body Interactions folder, under Connections, is used to define global connection options for Explicit Dynamics
– Contact Detection
Trajectory (default)
– Formulation
– Shell Thickness Factor
– Tolerence
Proximity Based
– Pinball Factor
– Timestep Safety Factor
– Limiting Timestep Velocity
– Edge On Edge Contact
– Body Self Contact
– Element Self Contact
Trajectory Contact
Recommended option for impact and sliding contact between Solids, Shells and Beams.
The trajectory of nodes and faces are tracked during the computation cycle. If the trajectory of a node and a face intersects during the cycle a contact event is detected (see figure).
Trajectory based contact does not constrain the time step
– Often provides the most efficient solution.
Nodes which penetrate into another element at the start of the simulation will be ignored for contact and should be avoided.
– To generate duplicate conforming nodes across a contact interface
a) Use the multi-body part option in DesignModeler and set the Shared Topology Method to either Imprint or None
b) In Meshing use Arbitrary Match Control (Sweep) or Match mesh where possible (Patch Independent Tetrahedrons).
Shell Thickness Factor
– The Shell Thickness Factor (STF) defines the shell (surface body) thickness used for contact
A factor of 1.0 takes the true physical shell thickness into account, which means that the contact surface is positioned at half the true shell thickness on both sides of the shell mid plane.
A factor of 0.0 means that the shell has no contact thickness and the contact surface is positioned at the shell mid plane.
Value must be between 0.0 and 5.0
– For shell node on shell face impacts, the node is always located at the mid-surface of the shell.
Formulations
– Penalty Formulation (default, recommended)
A penalty force is calculated to push a penetrating node back to the face.
Penalty forces are calculated to conserve linear and angular momentum.
where D is the depth of penetration M is the effective mass of the node (N) and face (F)
?t is the simulation time step
Nodes will be pushed back towards the contact position, but it will usually take several cycles to satisfy the contact condition.
-Decomposition Response
All contacts that take place at the same point in time are first detected. The response of the system is then calculated to conserve momentum and energy. During this process, forces are calculated to ensure that the resulting position of nodes and faces does not result in further penetration at that time point
The decomposition response algorithm is more impulsive (in a given cycle) than the penalty method. This can in some situations give rise to large hourglass energies and energy errors.
Proximity Based Contact
Alternative option for impact and sliding contact between Solids, Shells and Beams
The external faces, edges and nodes of a mesh are encapsulated by a contact detection zone. If a node enters this zone, it is repelled using a penalty based force that conserves linear and angular momentum
ANSYS-Explicit Dynamics Body Interactions Part B
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