How do I preload a cable, which has been already described by an equation?

09 September 2015 4 8K Report

Hello there,

I try to conduct a dynamic simulation of a cable. The part for the cable I import by a self-written python script. I use the cable equation (input: length and pretension) to create a point cloud. This point cloud can be used to define a spline and create a part for a pre-tensioned cable (see attachment).

To include pre-tension in the model before a frequency analysis, the abaqus manuel (Example: Vibration of a piping system) recommends to include a prior general step for pretension. When I am doing so, the geometry of the (already pretensioned) cable gets further stretched (geometry of the initially pretensioned cable by the equation differ from the actual geoemtry - logical).

Another option is to use a bolt load in a static step before the dynamic step. Unfortunately I get errors, and can not solve even the static case. Do you have an explonation for this?

Thank you very much in advance,

Mathias

Cardei Petru

I do not know exactly Problem statement: undeformed geometry, retaining and loading conditions. However I suggest loading a load evenly distributed to achieve pretension (if the cable is not stretched at first). Then, if you stay in the linear elastic sum up the relative motion (axes deformed equations in two issues). However only experiment can confirm the correctness of the solution. However I should see a diagram of the problem ....I need to see the geometry

Mathias Kliem

Hej Cardei,

thanks a lot for your answer and the thoughts on the problem.

I finally solved the problem. The pretension can be included by using bolt-load in a first step (I had to choose the first increment to be very small to prevent the system to stop). In the second step (probably it can all included into one single step) the gravity has to be applied.

After those static steps you should get the same geoemtry of the "pre-tensioned" cable, as it is described by the equation of a pretensioned cable. Now, the frequency analysis can be conducted - the results match perfectly with the literature..

Unfortunately, I got stucked again. The cable should now be mounted on a tower (beam as well). Please find attached the image and the input file. I used tie constraint to connect the Tower with the cable. The configuration of the cable didn't change - just the boundary conditions are not fixed-fixed (but rotation-free) anymore. Does anyone has an idea, what the problem could be??

Thanks a lot in advance!

Best,

Mathias

William J Kirkham

I'm not familiar with ABAQUS, but sometimes pretension can be applied in FEM where temperature can be applied. Thus one can install a cable at one temperature, and the model it at another, providing an internal prestressing mechanism. Best wishes on your project.

Mathias Kliem

Dear William,

thank you very much for your hint with the temperature. Thats actually a good idea.

The pretension for a single fixed-fixed cable is finally working by the use of bolt load and gravity. When I then try to modify the model and replace one boundary condition by a beam (represents the tower), I am getting errors. I don't understand the problem.

Thanks,

Mathias

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