How to consider pretension in spring elements?

1

Hello everyone,

I have been wondering how to consider the pretension of a spring element in CalculiX. Specifically, I would like to account for the initial tension in the spring, where the tension is greater than zero at the beginning of the calculation. I would appreciate it if anyone could provide insights on how to achieve this.

Thank you in advance for your assistance.

Best regards,
Yang

2

For what purpose do you want to preload a spring ? Does it represent a bolt ?

3

Thanks for your reply! No, it reprents a mooring line. I want to couple CalculiX and fluid solver to perfrom FSI simulation for a floating structure with mooring lines.

4

HI Yhuang94 ,

I have tried without fluid interaction (some gravity instead).
Damping will be required but may be tricky to adjust it so it doesn’t alter the solution.

You can apply pretension indirectly with a prestretch using:

*INITIAL CONDITIONS,TYPE=DISPLACEMENT

The hard part is that ccx doesn’t seem to permit to apply it to fixed points. (My first idea was to pre-stretch the Springs on the grounding side.

I have connected the springs to a fixed mooring bard, so the spring nodes are now free to be prestretch with the initial condition.

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Have not tested but the springs (Cables) should be nonlinear SpringA (¿only tension, right?).

You can one vids and how the pretension initially rises up the mass.

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Initial-Conditions

Another option would be an amplitude card.

If you try it even without FSI you will quickly realize this is not an easy problem. Goof Luck and please post some vid if you manage to couple the FSI

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5

Hi @Disla,

Thank you very much for sharing your valuable experience! I have previously attempted to consider the pre-tension of mooring chains using this approach. Although the calculations were relatively stable when considering only the structural aspects, they quickly diverged once fluid-structure interaction was involved. Therefore, I have been continuously searching for a stable method to address this situation. Nonetheless, I sincerely appreciate your response and the sharing of your valuable experience. I will continue to explore alternative approaches, and once I have some promising results, I will post them here.

Yang

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6

Are you damping the system?
Have you been able to get a picture of the system deformation status before the failure?

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