I'd like to address some of the many COSMOSWorks questions we here at Graphics Systems see come through during training or everyday Technical Support. And we thought that, instead of sharing the answers with lone individuals or just those who took training classes, we'd publish them "for the greater good." To begin with, I'll deal with a couple of mesh-related questions.
- Can the use of mesh control still cause distortion in an element? Great question! The use of Mesh Controls is meant to do just the opposite: fix distorted or failing elements. However, given the right conditions, one could still create an undesirable mesh with poor aspect ratio. We'll deal with aspect ratios below. In general, your use of mesh controls is a considerably safe bet.
- What is a good guideline for aspect ratio check on my mesh? Aspect ratios, which we'll cover more in a future post, are a mathematical check for amount of element distortion (how an element gets mapped along curvilinear geometry) within a mesh. Ideally, every element of a mesh will have an aspect ratio of 1. But that's just not realistic given models that look more like reality than tinker toys. And so it is suggested that if there are approximately 5% of all elements diverging from a ratio of 1, you should be OK. But having very distorted elements isn't neccessarily a bad thing because they may be in areas of your model where accurate results aren't needed. To check this, after a mesh has been created we can create mesh plots of both aspect ratios and Jacobian checks. We'll cover more on this sub-topic as well in a future post.
- With a p-adaptive mesh, what is a good threshold for the "energy norm error?" There are no hard and fast rules for this but, from the kind folks over at COSMOS, it is recommended to target within 10%. Take care, however, that (like above) certain areas of your model may be of less interest than others, and refining the mesh in areas of importance is a good way to go.
Lastly, there are two other questions I'd like to deal with. the first involves the use of a "pin connector." Instead of modeling and including a real pin between components, if one isn't interested in the displacements and stresses within the pin itself, it can be excluded and replaced with a special connector. However, this connector creates special bonded pairs and so no gap can ever exist between the pin and the bore. In order to have and use a gap, a pin must be modeled and included within the study. This means it will have to be meshed and solved along with the rest of the components. You also must create a No Penetration contact condition between the pin and the components it connects.
Finally, for studies with beam elements (versus shell or solids), the user can retrieve the forces on the beams with COSMOSWork 2008 by simply right-mouse clicking the Results folder and selecting "List Beam Forces." Also, if you're new to 2008, check out the other new plots you can now create with studies that use beam elements.
Thanks for reading!