Contact region troubles

- March 29, 2019 at 4:05 pm
  ansysuser
  Subscriber
  Hello,
  
  I am doing an FSI simulation with transient mechanical and fluent. First I test the mechanical side with all the pressures exerted on the structure to make sure it can solve - and it does solve just fine. But when I couple with fluent through system coupling I get solver errors of the type: "An element has become highly distorted."
  
  When I investigated, I found that several contact regions were becoming separated, as shown in the below picture (true scale). The element listed as the one that became highly distorted is adjacent to these regions. These contacts are listed as Bonded, as they were created in DM by slicing a solid geometry.
  
  So I switched from Bonded to No Separation and I get the same error. The element listed as the one that is highly distorted is on the contact boundary, just like before. The new failure looks like the contacts are still slipping around (I know this is expected. I did this for diagnostics).
  
  How can I make sure these contact zones behave? What settings should I look at? Does anyone know why the solution works just fine before coupling, but after coupling the solution cannot converge even after 2 iterations of the coupled solver?
  
  In Structural:
  - Solver: Direct
  - Substeps: 100
  - Nonlinear: On, Unsymmetric
  - All Pressures ramped by time
  In fluent:
  - Remeshing
  - Smoothing
  - One outlet with zero gauge pressure
  In System Coupling:
  
  Ramped Data Transfer and under relaxation factor set to 0.75
- March 29, 2019 at 11:00 pm
  Sandeep Medikonda
  Ansys Employee
  If you are certain that the contacts are causing the problem. Have you checked what your Pinball radius is? Insert an initial contact tool and verify everything.
  
  In general, highly distorted element errors occur:
  - When material model is unstable.
  - When load increments are to large.
  - Mesh is too distorted at large deformations.
  - Bad shaped elements near contact surface or at high strain regions.
  - High localized forces (sharp edges, contacts, point constraints, etc.,)
  Recommendations:
  - Check the stability of material model and change if needed.
  - Reduce the load increments. Apply the load incrementally using substeps.
  - Refine the mesh or use nonlinear mesh adaptivity to re-mesh distorted elements.
  - Reduce the contacts normal stiffness if necessary.
  - Try avoiding sharp edges; use fillets/chamfer where needed.
  - Review Newton Raphson Residuals and Post Process the available results