Cable design, Instability (type 1), Matrix is not positive definite

[Anonymous]

Dear all,

I would design a cable system, which has several hanged masses between 2 columns. i just made a simplier case with 3 wires and a truss between them subjected to tension.

I don`t understand the warning that I got. I tried to solve the instability with releases (fix the Rz, because Uz has to be free), but it didn`t work. Also the matrix warning, because I thought it appears because of the buckling of the column, but when I made a solid 400mm diameter column, it still appears.

The main goal is to define the prestressing of the cables and I will have this kind of system with 7 cables, therefore I planned to use relative elongation and iterate until I find the right position of the pre-defined nodes, where the point loads has to be.

Please comment my model, I would really appreciate, especially because my first experiences with this forum was great, but so far I didn`t get any other help.

Thanks in advance!

[vanvan11 · Accepted solution]

now when i calc no warnings 

is that ok? is warnings was problem

only thing i make to your model was to separate the upper cable in to 2 pcs couse point 2 which was instable to have conetions whit the upper cable

so i think that was the problem 

tell me if my solution is ok for you

see my model

sry for my bad engl

[Anonymous]

Dear Ivan,

Yes, your solution was right for this model, thank you! However this model was a simplier one, the real structure is like a wire chain with some bars to keep the distance between them.

I attached this model, because still there are the same error messages. I dont know why, because now every cable or wires are seperated respect to the nodes.

[Rafal.Gaweda]

Try with elongation relative -0,0001

[Anonymous]

Dear Rafa.Gaweda,

Thanks for the suggestion, I guess I have to "play" with this elongations to be good for all of the cables to reach more or less zero deflections for the specific nodes.

However, I have now another important issue, because I can not make a proper material definition for these cables. Picture attached.

I would set a smaller Young modulus for the cable due to I would take into consideration that it is more flexible at the installation, also it is a high tension cable, with a larger self-weight which I can not set! Why? (It is Robot 2014 version.)

[Anonymous]

Please disregard my previous message. I have solved the material issue.