Error message in Strand7 - Rotation at node is too large.

[Alex T.]

Hi, I am trying to run a nonlinear analysis on a suspension tower only with its own weight. I have fixed all four feet, both rotational and translational. I get the message "ERROR[ 13]:Solution has diverged. Rotation at node 157 (3.4884E+08 deg) is too large. "

I have tried to fix them, but then I get other nodes with the same message.

Does anyone here have any tips to how I can solve this?

Thanks!

 

[Erik Panos Kostson]

Good to see a Strand7 question. It is tricky to say, because it says that the node is rotating too much.if you attach your model , I can have a quick look for you. Otherwise check restraints, units, material properties, and that freedom cases is active/ticked in the load increment section of the nonlinear solver.

 

[IDS]

If you have current Strand7 support, contact them, with a copy of your model.

If not, post the model here, after checking the things listed by Erik.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[jhardy1]

A very common cause of this issue is that people model a truss structure, applying three rotational releases to both ends of every truss member (to simulate pins and torsional release at both ends of the member). This leads to one or more nodes not being rotationally "attached" to anything, so the solution will fail. Try making sure that every truss member is torsionally "fixed" at at least one end, if not both.

http://julianh72.blogspot.com

 

[Alex T.]

Thank you so much for your answers. After some hours, I finally found out what was wrong. I ran a linear analysis and looked at the deflections. I found out that I introduced two nodes and forgot to intersect the beams to those nodes...a little embarrassing

 

[Erik Panos Kostson]

Great to see a lot of interest. All answers, are very relevant. Many truss elements representing a member will behave like a chain/cable not having any stiffness in compression, so that could have been a problem. This is is not a problem for beams since they have rotational degrees of freedom, and stiffness. So for trusses there should be one element per member, unless we are modelling a cable (GNL, and pretension is needed for lateral stability,which can be switched off once lateral stiffness develops). Also great idea to run LSA, and see how the structure behaves.

 

[IDS]

Always a good idea to clean the mesh before a run!

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/