Strand7 Error: Global stiffness matrix is singular.

[Arif98]

Hi
I have this 2D oriented Strand7 model where a cantilever beam is connected to a bar element (oriented at 45 degree) which can only take axial stress(assuming to be a truss element) and a spring at a common node. A force is being applied on that node. Orientation of the elements are shown in the attached Strand7 model below.

I have a question that need to be clarified. Lets say the '2D' model is oriented on x-y plane. Do i still need to provide restrain in Z direction?

And also, I tried to run the model. It gives me an error saying,

ERROR[ 4]:Global stiffness matrix is singular.

I tried to play around with the restrains but I am unable to solve this error. Therefore, I am wondering if there is anything else I am doing wrong in this model.

A little bit of help would be appreciated.

 

[r13]

I can't open your file. Let me try to picture your setup - "a cantilever connected to a bar (at 45° to the cantilever) through a node, which behaves like a spring", correct? I think the problem is the spring, it needs to have rotational restraint capacity (k = T/θ), as well as linear (k = F/Δ), otherwise the bar element is unstable.

 

[IDS]

I haven't looked at your file yet, but in reply to:

Lets say the '2D' model is oriented on x-y plane. Do i still need to provide restrain in Z direction?

Yes. The easiest way is to define the Freedom case in the Global menu as a 2D beam analysis. This will restrain displacements in the Z direction, and rotation about the X and Y axes.

Just checked your file. Setting the Freedom Case 1 to 2D beam fixes the problem.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[Arif98]

Thank you retired13 for your reply.
I understood what you meant. Let me explain to you the setup properly.

"I have a horizontal cantilever beam connected to a bar (at 45° to the cantilever) through a node. A vertical spring is connected to the beam and bar right below that common node."



I have attached a picture of the setup. Hopefully you will be able to open it.

 

[Arif98]

Okay I will do that and see if i can manage to solve the issue that i have. Thank you IDS

 

[Arif98]

Yes. I have managed fix the problem. Thank you very much. This forum is full of knowledge!

 

[IDS]

Arif98 - No worries. Any future questions specifically about Strand7 would be better in the general FEA Forum, under Engineering Computer Programs.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[Arif98]

Noted.