topic Instability type 3 in Robot Structural Analysis Forum

Instability type 3

Anonymous — Fri, 13 Jul 2018 10:19:17 GMT

Good day Rafal/Arthur,

Regarding the Type 3 instabilities a have a relatively simple model which gives the warning. I must however remove the instability as per internal company review findings. Can you please check what I am missing if possible?

Re: Instability type 3

Artur.Kosakowski — Fri, 13 Jul 2018 10:26:10 GMT

Hi @Anonymous

Such request may be impossible to be fulfilled when the instability is due to the large difference of stiffness of elements (e.g. short vs very long bars). Try to select all the model and intersect the bars (Edit > Intersect). Then look at the shortest bar and try to eliminate them from the original model by moving their nodes (merging them).

If you still have the instabilities then you may apply very small force or moment in the node where the instability is reported to see what happens in terms of its displacements and rotations as explained during the 16th Robot webinar. The recordings of the webinars are available from https://forums.autodesk.com/t5/robot-structural-analysis-forum/robot-structural-analysis-webinars/td-p/5523337

If I managed to answer your question(s) press the Accept as Solution button please. This will help other users to find solution(s) much faster. Thank you.

Re: Instability type 3

Anonymous — Thu, 19 Jul 2018 08:20:39 GMT

Hi Artur,

Thank you for the reply. I went through the webinar and did the checks as prescribed and found no logical reason why there would be instabilities.