Inventor Nastran – Assemblies, Meshes and accurate solving


This week has been interesting when it comes to Simulating in Nastran IN CAD,( now renamed to Inventor Nastran).  I was helping out with a demonstration and learnt that there could be a few differences between Nastran and other simulation software where Nastran is very strong in getting meshes to line up between assembly parts and other software packages are not able to do this very efficiently.

I also learnt that analysing the model in how it was drawn and how it solves and visually looks in the end is also very important.

If you have not looked at Inventor Nastran yet, we have 2 different type of objects that are used for the analysis, nodes and elements.  These form together to create a mesh which is used to push the forces that have been applied through the model and see how it reacts.  Getting the ratio of nodes and elements vs the size of the object is very important.  If the object you are analysing is small and size of the elements you are using are very large, you will not get a very accurate result.   Visa versa if the element size is too small then it will take forever to solve the analysis.  Balance.

With this in mind you have to look at time versus accuracy and this will only be gained through experience or phoning a friend.

As Inventor Nastran is a very good mesher, there is a separate mesh control which allows you refine meshes and control how they refine.  for example you can have a large mesh on the majority of the object and then when the object meets another object you then create smaller meshes on both objects at the edge so that you can get more accurate results as well as solve correctly where they meet.

This is because if your nodes do not meet up at the edge the forces will not be able to be projected or transferred correctly between the 2 objects.