Taking advantage of symmetry is a great way to improve the efficiency of a simulation study. Complex studies can take a significant amount of time to solve. Using a coarse mesh, simplifying geometry, or idealizing boundary conditions can speed up an analysis, but come at the cost of reduced realism and accuracy. Unlike these methods, taking advantage of symmetry allows for results to be calculated in less time without sacrificing accuracy.
I’m going to split this discussion into 3 parts:
- Using symmetry – when to use symmetry, applying symmetry restraints, viewing results
- Special symmetry cases – non-orthogonal symmetry, symmetry for shell elements
- Extreme symmetry – 2D simplification
So when can we use symmetry? Of course, the geometry has to be symmetrical. It’s necessary for the boundary conditions (fixtures and loads) to be symmetrical as well.
The bracket shown is symmetrical and is loaded symmetrically with fixed hinge restraints on each side and a load of 32,000 N on the center face. This analysis is a perfect candidate for simplification with symmetry, so let’s cut it in half.
Editing the model is as easy as creating a cut feature and I like to keep things organized by using a separate configuration. The setup for the new study is a bit different. We now only have a single fixed hinge restraint and the applied force is 16,000 N (half of the full load).
A symmetry restraint also needs to be applied to the cut face on the symmetry plane. Symmetry can be found under the advanced fixture types. This restrains the selected face to the symmetry plane and is functionally equivalent to a roller/slider fixture. We’re now ready to run our study. Easy!
But wait! There’s more! (Erm… less!) This analysis is symmetrical front and back as well, so we can actually cut it down to a quarter. Like before, we have to remember to use a reduced load; it’s now a quarter of the full load at 8000 N. And a symmetry restraint needs to be applied to both cut faces.
After running the study, the results can be viewed using the same plots and tools as usual. In addition, we have the option to display symmetric results and see plots as if we had analyzed the full model.
Again, taking advantage of symmetry is great because it improves efficiency. This example was quite simple and runs quickly, so I used a fine mesh to help illustrate the differences between the full, half, and quarter studies. All three studies produced the same results, but we can see that the quarter study takes less than a quarter of the time needed to run the full study. And while 10 seconds isn’t a huge amount of time, using symmetry with more complex studies, which can take minutes or hours to solve, makes a massive difference.
The last thing we should discuss here are situations where symmetry should not be used. Since symmetry is represented with a restraint to the symmetry plane, the full model should be use for buckling and frequency studies. Otherwise, any buckling or vibration modes across the symmetry plane will not be identified.
I encourage you to use symmetry when you can in your analyses. Check out the next part of this discussion to learn how to handle non-orthogonal symmetry and symmetry on shell elements in SOLIDWORKS Simulation.
