Number of DOFs

[KenLuu]

My research relates to shell element and I'm trying to use Opensees as FEM framework. I want to create a new element with 9 nodes, however the number of dofs at each node is not the same. Can I define nodes with different dofs in Opensees.

In addition, at each node of the shell element there are 3 displacement dofs (u_i) based on Cartesian coordinate, and 2 rotational dofs (theta_i) are based on another specified coordinate. My question is : Is that true all the trial displacements at each node are based on Cartesian coordinate, therefore in my case I need to transform the rotational displacement from Cartesian coordinate to the specified coordinate.

Thank you so much for your attention!

[naba077]

The answer to the first question is "YES". You can define nodes with different dofs. You can define the dofs for each node by fixing it (by 1) or free it (by giving 0) in each direction.
For example;
model BasicBuilder -ndm 3 -ndf 6
node 1 0 0 0
node 2 1 1 1
node 3 2 3 2
fix 1 1 1 1 1 1 1; # node 1 is fixed in all directions
fix 2 0 0 0 1 1 1; # node 2 is fixed in all three rotational directional (freed in translational direction)
fix 3 1 1 1 0 0 0 ; # node 3 is fixed in translational direction (fixed in rotational direction)

[KenLuu]

Thank you for answering my question. Your answer is about restraining the dofs, but that way I think every nodes still have the same number of dofs. My purpose is trying to create an element with 9 nodes, each 8 external nodes have 5 dofs, and 1 internal node has 2 dofs, so in total the local stiffness matrix of the element is 42x42. Is it possible to create that type of node and element in Opensees?

[fmk]

yes it is. some existing elements already are using this feature, e.g.
http://opensees.berkeley.edu/wiki/index ... -p_Element

[KenLuu]

Thank you very much. I think I can start from this example. It is very useful