No convergence of nonlinear model including supports with friction in Robot Structural Analysis

Autodesk Support

Feb 10, 2025

Products and versions covered

Issue:

Nonlinear model including supports with friction does not converge for selected load cases in RSA.

Causes:

  • Incorrectly defined bearing direction for friction support.
  • Considered load cases not including loads defined in bearing direction of friction support.
  • Default (not modified) nonlinear cases calculation parameters used in the model. 

Solution:

Check and correct (if necessary) defined friction support.

Follow these steps:

  1. Edit support label from Geometry > Supports.
  2. Go to the Friction tab.
  3. Check the required bearing direction (it should be perpendicular to surface with friction effect simulated).
  4. Activate Friction checkbox.
  5. Open Friction options.
  6. Define the required friction coefficient and cohesion.

Friction definition

Correctly define the bearing pressure direction.

Set simple load cases (not including loads in direction of the friction bearing pressure as auxiliary). To activate friction effect, calculate only load cases /combinations including loads defined in direction of bearing pressure for friction supports.

Follow these steps:

  1. Open Analysis > Analysis parameters.
  2. Double-click simple load cases, not including loads in direction of the bearing pressure force.
  3. Activate Auxiliary case.
  4. Click OK.

Auxiliary cases definition
 

 

Switch on Large Displacement analysis type in load calculation parameters.

Follow these steps:
  1. Open Analysis > Analysis parameters.
  2. Double-click divergent load case.
  3. Switch on Large displacement option.
  4. Click OK.

Large displacement activation

Modify load calculation parameters.

Follow these steps:

  1. Open Analysis > Analysis parameters.
  2. Double-click divergent load case.
  3. Open Nonlinear analysis parameters.
  4. Switch on Matrix update after each iteration.
  5. Change (decrease) Load increment number.
  6. Change (increase value) required tolerance.
  7. Click OK, then click OK again in the Static Analysis Parameters dialog. 

Nonlinear analysis parameters

Add cohesion parameter for supports with friction defined.

Follow these steps:

  1. Open Geometry > Supports.
  2. Double-click support label with friction defined.
  3. Go to the Friction tab.
  4. Double-click the Friction parameters option.
  5. Define the "Cohesion To" value.
  6. Click OK then Add in Support Definition dialog. 

Cohesion definition

Add weak elastic supports to stabilize calculated structure.

Follow these steps:

  1. Open Geometry > Supports.
  2. Create a new support label (Fictitious).
  3. Go to the Elastic tab.
  4. Define "weak" springs in all directions (0.1 kN/m for UX, UY, and UZ and 0.1 kN*m/deg for RX, RY, and RZ).
  5. Add button.
  6. Assign this fictitious support to selected model nodes. 

Dummy elastic supports

 

 

 
 

Products:

Robot Structural Analysis Products;

Was this information helpful?

Need help? Ask the Autodesk Assistant!

The Assistant can help you find answers or contact an agent.

Ask the Assistant

What level of support do you have?

Different subscription plans provide distinct categories of support. Find out the level of support for your plan.

View levels of support