Issue with collapsed element in LISA Finite Element Analysis

Question

I'm new to the FEA world and trying to learn the ropes through resources available online. I've imported a model into LISA FEA that I would like to analyze, however, when I press solve to conduct my analysis I'm getting an error message that states the following:

Error: Element 1 is collapsed. More than one local node share the same local node. Warning: Elements 395, 400, ... overlap each other. Failed

Being so new to this, I do not have any idea as to how to interpret this. M question is: how can I tweak my model to get rid of these error messages. Namely, how do I "uncollapse" an element? How do I stop elements from overlapping?

Although this is a LISA specific question, and I would appreciate advice as to how to overcome this directly through LISA, I am also open to general advice applicable to other types of FEA. If anyone could give me a few pointers as to how this issue is dealt with in FEA software, I would be greatly appreciative.

Answer 1

I don't use LISA, but the most likely cause of both problems is that the geometry of the element mesh is invalid.

The "collapsed element" message is saying that two (or more) nodes in element 1 have the same node numbers, or they are at the same position in space. For example if you have a 4-node "rectangular" element, you can't squish it down into a triangle shape by putting two "corners" at the same place, or you can't have a weird shape where two "opposite" sides of the element cross over each other, etc.

The "overlapping element" message is saying that two (or more) elements cover the same area or volume. The elements have to fit together like building blocks, or tiles. They can't overlap in an arbitrary way.

To see exactly what the problem is, display the model and highlight the element numbers in the error messages, and then figure out how to make a mesh that doesn't have those problems.