Question:
When using a line release, I get an error message saying that the model is unstable. What is the reason?
Answer:
Image 01 shows a model where Surfaces 1 and 2 should rest on Members 1 and 2. Members 1 and 2 should be supported by Nodal Supports 1 and 2.
For decoupling the members from the surfaces, a line release type shown in Image 02 is defined. The displacement uz is only released for a tensile force; the other displacements ux, uy as well as the rotation φ-x are always released.
Line Release 1 is defined on Line 5 and releases Member 1 (Image 03).
Line Release 2 is defined on Line 14 and releases Member 2 (Image 04).
Member 1 is now defined on Line 15 generated by the line release with Nodes 12 and Node 13, and Member 2 is defined on Line 16 generated by the line release with Nodes 14 and Node 15 (Image 05). Members 1 and 2 have different nodes (13 and 14) at their intersection and are not connected to them.
Furthermore, Nodal Supports 1 and 2 are defined at Nodes 5 and 10 and thus support the surfaces, but not the members (Image 06).
During the calculation, the instability message shown in Figure 07 is displayed because the members are unsupported.
The connection of Members 1 and 2 can be created by defining Node 13 generated by Line Release 1 as a definition node in Line Release 2 (Image 08). Members 1 and 2 then share the same Node 13 and are connected to it.
Furthermore, you have to define Nodal Supports 1 and 2 at the nodes of Members 1 and 2 (Image 09).
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