CADFamily.com: Workbench-Mechanical Diagnostics

Since some nonlinear structural analyses can be challenging to solve, understanding how to diagnose non-convergence problems is critical in obtaining answers.

The following will be covered in this section:

– Solver Output

– Monitoring the Solution

– Newton-Raphson Residuals

The capabilities described in this section are generally applicable to ANSYS Structural licenses and above.

– Exceptions will be noted accordingly

A. Solution Information

In Chapter 2, the Solution Information branch was introduced

– Recall that with the Solution Information branch, the detailed Solver Output from ANSYS can be reviewed, and convergence graphs, such as the Force Convergence behavior, can be plotted.

A “Messages” Window located directly below the Solution Information Worksheet offers a summary listing of some general warnings and errors.

– RMB on any message to:

--Go to Object (Highlights Project Tree Object relevant to the message)

--Show Full Message in separate expanded window

--Copy message (to separate text file)

--Delete message from list

The Solver Output can provide detailed text output about the solution. It is useful to become familiar with how to read this file.

1) The beginning of the Solver Output simply shows the ANSYS license used (in this case, ANSYS Multiphysics) and the version number.

2) Solver Output records the element technology being activated based on the element order chosen (midside nodes) and the material association. See Appendix B for details on Element Technology.

3) Upon scrolling down until a series of asterisks are encountered, the reading of the finite element data by the solver can be seen.

This listing is useful, as will be shown later, because it not only provides information on how many parts are in the model, but the Contact Region ID numbers are listed here

It is instructive to note that while Contact Regions can be given any name in Simulation, the ANSYS solver treats each Contact Region with a unique number (ID). For debugging purposes, it is useful to find out which Contact Region has which ID number. For example, in the above snippet, Contact Region “Teeth 3” is referenced by contact ID 9 and 10.

4) When the equation solution is initiated, the section of the output will be shown as on the right

The useful things to review here are the equation solver used(if left at “Program Chosen” or manually specified), whether large deflection effects are on or off, whether nonlinear material effects are considered (if plasticity is present), and the number of substeps used.

The review of this section of the Solver Output is not critical, but it indicates when the matrices are being solved and what the solution options specified in Simulation were.

5) Details of contact elements are then printed next.

Here, various options related to contact elements, including the contact Normal Stiffness and Pinball Radius will be listed

Any NOTE or WARNING messages printed in this section are useful to review.

For example, initial penetration or gaps (in active unit length) will be shown in this area