What is the Global Contact Condition and how does it work?
Often times, users call-in to ask for SOLIDWORKS Simulation advice on why their model is not stable. In many cases, I see right away that they have deleted their global contact condition or changed it from its default setting of bonded to no penetration. In most cases, this is not necessary at all. There are three contact options in the Component Contact command window. (See figure 1 below)
- No Penetration: This option allows two or more faces to touch and develop contact pressures/forces, as well as move away from each other. It does not allow the two faces to flow into each other and take up the same space together.
- Bonded: This allows two touching faces or faces with a specific gap between them (when specified by using the “Non-touching faces” option) to remain touching or to force the gap to remain the same size no matter what loads are placed upon the two faces during the analysis. As far as Simulation is concerned when two parts with two faces are bonded they are actually one part.
- Allow Penetration: This contact feature allows multiple parts to flow into each other during the analysis at the specified faces while the analysis is being run. This contact option is mostly used in frequency and buckling analysis.
Figure 1: Component Contact Command Manager
No Penetration Contact Sets
It is a rare situation where the No Penetration contact set should be used for a global contact set. The reasons for this is because SOLIDWORKS Simulation must constantly check all the No Penetration contact sets in a study to see if they are still meeting the No Penetration criteria. Because of this, No Penetration contact sets are very computationally intensive and can take a considerable amount of time and computer resources to solve accurately during a simulation analysis. This is especially true for large assemblies. No Penetration contact sets do not keep parts together they allow the parts to move apart without resistance. This is why the Global No Penetration contact set could become unstable during the analysis where parts just fly off into space.
All Global Component Contacts default to Bonded. I recommend you leave this on because any component contact and local contact set automatically overrides the Global Component Contact set. You do not need to worry about them negating each other. A good way to think about it is that local contacts always trump global contacts.
To get to the command manager that allows a local contact set to be created first, right click on Connections. Then at the top of the pop-up menu that appears, click on Contact Set to open the Contact Sets Command manager. (See figure 2 below)
Figure 2: Click here to open up the Contact Sets Command Manager
After opening the Contact Sets Command Manager, the Simulation User can specify what type of local contact he/she would like to utilize and then choose the faces that the contact set will be applied to.
Local contact sets are useful because the global contact and component contact set don’t always “grab” and apply the right or even any contact between two or more faces that need to have contact sets for the Simulation to be stable. For example, if an edge or point of one part is meant to be bonded to a face of another part the global contact set would not apply a contact condition to these parts. The user needs to recognize where these types of contacts are and to apply them manually in a local contact set. Computers are not smart enough to recognize every situation and apply the correct contact sets perfectly every time. Simulation users making engineering decisions are always necessary to correctly set up a new simulation. The Global and Component contact command windows may make the job easier, but it is always necessary for the engineer to review all contacts and adjust manually as necessary.
Author: Taran Packer
Taran is a SOLIDWORKS Simulation Technical Support Specialist at GoEngineer. He has a Bachelor’s degree in Biomedical Engineering from the University of Utah. Taran enjoys learning about different tools in SOLIDWORKS Simulation, Flow Simulation, and Plastics.