Good morning,
I’m working on a simple geometry:
I would like to verify the match with the analytical solution of the reaction forces, which is:
F= P*A= 337.5 *10^4 N
q=F/1500= 2250 N/mm
Reaction forces= 168.75 *10^4 N → One for each edge.
I tried to average the reaction forces obtained, but they are far from the analytical solution.
Thank you
If you have supports on two edges, you can use the following procedure. In the results tab select the forces output in the desired direction: F2. Then use the edge query tool (Tools->Query) and select the edge you are interested in. Take a look at the nodal sum.
This procedure only works if you have disjoint edges in supports. When adjoint edges are used for supports you have to sum the values of individual edges and then subtract the values of the nodes where the edges meet (they are counted once for each individual edge).
You can also use a history output to save the reaction forces.
Thank you so much; it worked with the edge query tool.
What does it mean ‘‘disjoint edges in supports’’? It could be useful to know for further analysis.
Disjoint was meant as unconnected edges. So the edges which do not share a node. In such cases the results with Query are correct. If there are two edges in the support that share a common node, then this node will be counted twice. Once in the query for the first edge and once in the query for the second edge. So summing the values from edges gives you a wrong answer.
For example: edge 1 has nodes n1 and n2 while edge 2 has nodes n2 and n3 (n2 is the node shared by both edges). When the sum of edge 1 is computed it equals e1 = n1 + n2 and similar for edge 2 e2 = n2 + n3. Summing the sums of the edges gives you
e1 + e2 = (n1 + n2) + (n2 + n3) = n1 + 2 * n2 + n3.
So the common node n2 is summed twice.
¿Is there any reason why this could be better this way?
Removing this common node could be an improvement for next version.
The reason is that the Query tool does not allow the selection of multiple items. So only one edge (or surface) can be selected at a time. So the result is the sum of all selected nodes on the edge (or on the surface). But the user might pick another edge and get another sum, which is computed independently from the first selection.
A better way would be to allow multiple edges (surfaces) to be selected at the same time and then the sums would be computed correctly in regard to selection.
Thank you. I have a very last question: How can I display the ‘‘reaction momentum’’? For example from a cantilever beam with a force applied on the opposite edge?
Nodes of solid elements don’t have rotational degrees of freedom so the only way to obtain the reaction moment in such a case is to apply the boundary condition via rigid body constraint.
Exactly, i did the example of the following video: PrePoMax (CalculiX FEA) - Tutorial 8 - Remote load - YouTube.
I found the reaction force in F2 with the step you suggested. But I don’t know how to visualize the reaction moment.
So, following your suggestions, I should put a rigid body constraint on the fixed face, then fix the linked reference point, isn’t it? And then?
Yes, apply the fixed BC to the reference point of rigid body constraint instead of applying it to the bar’s face directly. Then request history output of RF for this ref node.
