Hello Everyone, I used a simple 2-D UMAT for a Coupled Heat Transfer and Displacement Problem and Generated the Stiffness Matrix through the Input file. I can see few negative nodal id, can anyone suggest what this means?
Negative nodal IDs are used to represent fictitious nodes. Fictitious nodes are used in a variety of ways, but they are most commonly used to model contact or boundary conditions. In the context of your coupled heat transfer and displacement problem, negative nodal IDs could be used to represent the interface between the two domains.
If you are seeing negative nodal IDs in the stiffness matrix generated by your UMAT, it means that your UMAT is correctly incorporating fictitious nodes into the model. This is a good thing, as it indicates that your UMAT is compatible with the coupled heat transfer and displacement solver.
However, it is important to note that fictitious nodes are not physical nodes. They are simply mathematical constructs that are used to represent complex boundary conditions or contact interactions. As a result, it is not possible to directly visualize or measure the displacement or temperature of fictitious nodes.
If you need to visualize or measure the displacement or temperature of the interface between the two domains, you can do so by creating a new set of nodes that are located on the interface. These nodes can be assigned positive nodal IDs, and they can be used to visualize or measure the displacement and temperature of the interface in the same way as any other node in the model.
Moiching Ahamed How do you suggest I can assemble a Stiffness Matrix with Negative Nodal id ?
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