Post-processing and Results Output

In the analysis results output, what exactly is the Shear Angle?

The shear angle is the angle between the element’s horizontal axis and the major principle direction (in the principle co-ordinates as used for a Mohr circle). The shear angle is derived from the in-plane normal and shear stresses.

How can SPC forces be output as a result?

Use the SPCFORCE command in the I/O Options section of the input data.

With this command, loads are written to the .spcf file, an ASCII format results file. Loads are also written to the binary .res and .h3d files (if these formats are selected) and these result formats can be viewed graphically. Additionally, if the .spcf file is written, the reaction force summary, the load summary, and the strain energy residuals for each load case are written to the .out file.

For more information, refer to the SPCFORCE entry in the Reference Guide.

Why doesn't the converged optimization result I obtain contain elements with high density values (0.7 ~ 1.0)?

Some of the most common causes of this result are:
  1. The optimization has not converged. The process has stopped because the optimization has reached the iteration limit. Increase the iteration limit and restart the run.
  2. A huge design space has been given. This situation is normally found in the area of minimize mass or volume response.
  3. Not enough mass or volume has been given to the design problem. This situation is normally found in a design problem in which the mass or volume response is used as a constraint. Increase the mass or volume fraction value in the constraint.

In addition, the DISCRETE parameter on the DOPTPRM Bulk Data Entry, found in HyperMesh under opti control in the Optimization panel, can be used to increase the penalization factor and force densities to go to either 0 or 1.

Why do I still have a huge constraint violation percentage even if the output file indicates that the optimization has converged?

In general, optimization is only considered converged if the constraint violation percentage is zero (or at a very low value). Convergence at huge constraint violations occurs when the given constraints in the design problem are too tight or the design problem is so ill-defined that the design problem cannot be further improved. Thus, the change of design objective falls below the convergence criteria that the user has defined and the optimization process ends.

Can I export the DVGRID information from a topography optimization?

Yes, add OSDIAG, 81, 5 to the top of your deck. This will export the DESVAR and DVGRID information generated from the DTPG cards to the .out file.

Is it possible to reduce the file size of the iges surface generated by OSSmooth?

There are two ways to avoid having huge iges surface file sizes:
  1. Set the surface_reduction parameter to 1 in order to reduce the number of surfaces created.
  2. Use minimum member size control to obtain a more discrete structure. This way, you will get a smaller iges file when using the surface_reduction parameter.

How do I obtain stress/force results for 1D elements?

For CBAR/CBEAM elements, normal stress at the cross-section origin is output by default, and is controlled by the STRESS I/O Option. If stress results are desired for other locations, the first continuation line for the PBAR/PBEAM definition is required. The maximum stress calculated at any of the four allowable stress recovery locations is then reported as the element's axial stress.

Sectional forces and moments for 1D elements can be obtained through the FORCE I/O Option. If FORCE=YES is added to the I/O Options section of the input deck, the .force file is output containing force and moment results.

Why are some parts of the model missing when OSSmooth is used to recover geometry?

This can be attributed to the presence of local coordinate systems. The following steps offer a solution:
  1. Import the model into HyperMesh.
  2. Click Systems and reassign all elements to the global coordinate system.
  3. Delete the local coordinate systems.
  4. Export the file and save with a new file name.
  5. Rename the shape file created during the optimization with the same name used in the previous step.
  6. Run OSSmooth