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Spring Foundation question (Structural Mechanics)
Posted 7 juin 2018, 15:17 UTC−4 Structural Mechanics Version 5.2a 6 Replies
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Consider a single linear element (linear elastic material) whose end points are constrained by Spring Foundation nodes with some finite spring constant (say 1 N/m). Let's say my nodes are at 0,0 and 0,-1 and this is a 2D simulation. Now I apply Point Load (say 10 N) to the 0,-1 node, for example in the -y direction. Since my example lacks fixed constraints, there is simply nothing to prevent nodes from shifting when force is applied. Once the Point Load is balanced by the spring restoring forces and the tension in the elastic element then we reach a stationary solution. So now I want to do a Stationary study and find out how much the nodes shifted. Seems simple. I go to Results, Point Evaluation, use my Soluton data set, select the two nodes and ask for the y coordinate. When I go to Evaluate this, I get that the nodes are at 0,0 and 0,-1 or in other words they did not shift at all. This makes no physical sense so I am doing something wrong. I hope someone here can point me in the right direction.
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To make the question clearer: When I take a truss and constrain its nodes via Spring Foundation points in Comsol, the simulation then does not show displacement from original node locations if I apply a force to the truss. So... either the Spring Foundation is useable only for stress computations but not strain or I am not reading out strain and displacement correctly. Please help. The documentation that I can find on Spring Foundation is minimal and does not explain how it
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Michael,
Not sure I understand the source of your issue - attached model shows that displacement of the solid with spring foundation is proportional to the applied force.
Regards,
Sergei
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Same issue with your model. If I go to "Results" -> "Derived Values" and add "Point Evaluation" and then within "Setting" panel under "Selection" I select point 1 and under "Expression" I look at Y-coordinate ("+" -> "Component 1" -> "Geometry" and select either Material or Spatial coordinate) then I get zeros for all the forces you put in there. Every way I can think of getting a precise number for displacement, Comsol shows no displacement. That's my issue.
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Also, thank you so much for responding. I appreciate the time.
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Never mind. I figured it out. Thanks again.
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Better checkout the "include geometric nonlinearity" option in the study.
-------------------Noman