Flex Contact

MotionSolve supports contact between a flexible body and a rigid body or another flexible body. The method to add such a contact to a model is the same as a Rigid to Rigid Contact and uses the same panel as the contact between rigid bodies.

Improving Flex Contact Behavior

The normal flexible body generated using the Craig-Bampton or Craig Chang method may not always provide a very accurate contact behavior due to:
  • The region of contact is unknown during the process.
  • The desired region of contact such as joints could have been rigidified.

In both cases, the flexible body needs additional modes to capture the contact accurately.

There are two options available in MotionView for enhancing the behavior of flexible bodies depending upon type of contact regions. Both options involve regeneration of the flexible body through the component mode synthesis (CMS) process – Craig Chang Contact using the Flexprep utility under FlexTools menu. See the OptiStruct Flexbody Generation topic for additional information.

1. Predicted Contact Loadset

This method is useful when it is desired to capture a higher result accuracy of stress/strain at any pre-defined contact interface. This process extends the traditional CMS (Component Mode Synthesis) process by adding additional mode shapes at the contact region.

This improvement is achieved by the following steps in MotionView.
Step A: Generate a regular flexible body
  1. Generate a regular flexible body h3d using any of the CMS methods available using Flexprep.
  2. Use the flexible body h3d from Step 1 to define a flexible body using the Bodies entity.
Step B: Define contact and other modeling elements
  1. Define contact between the flexible body and other bodies as desired.
  2. Complete the rest of the model building process.
Step C: Generate a predictive contact loadset file
  1. In the Body panel of the flexible body, go to Contact Prediction tab and provide a name for the loadset file.
  2. Use the Run panel to run a predictive solution and generate the loadset file.
Step D: Generate a new flexible body
  1. Use the CMS method – Craig Chang Contact in Flexprep.
  2. Provide the loadset file that is generated in previous step at “Include predicted contact loadset”.
  3. Remember to use a different flexible body h3d name for the new flexible body.
  4. Use the newly generated flexible body for the body definition in the Body panel.

2. Contact at a Joint

This method is useful when there is a joint or a bushing connected to the flex body at an interface node location that has rigid elements (RBE2) connecting the desired area of contact. The intention is to capture a higher result accuracy of stress/strain at the regions near the joint. This process takes the same information that would be used in a traditional CMS (Component Mode Synthesis), but first removes the rigid elements and uses the interface node attachments as the basis for calculating additional flex body mode shapes that account for deformation around joint.

This improvement is achieved by the following steps in MotionView.
Step A: Generate the flexible body
  1. Use the CMS method – Craig Chang Contact in Flexprep.
  2. Provide the interface node information “Include contact modes around rigidified nodes”.
  3. Use the generated flexible body for the body definition in the Body panel.
Step B: Define contact and other modeling elements
  1. Define contact between the flexible body and other bodies as desired at the joint/bushing location.
  2. If the model already contained a joint or a bushing at the above location, deactivate it.
  3. Complete the rest of the model building process.
Note: Both of the above options can be used in the same flexible body generation step.