5 Tips for Better Cable Model Convergence
Catenrary Cable elements can be difficult to work with. Non-linear catenary cable analysis is very different to linear-static analysis and is not always fully understood or well covered at University. The result is based on an iterative-process, so it comes with a whole range of complexities that don't exist in linear analysis. A common issue, is that the structure will not converge due to a range of instabilities. This means a reliable result cannot be produced by the software which can lead to a long and frustrating process. So SkyCiv has built out the top 5 tricks you can use to get your cable model to solve!
Remember that if the software is not converging to a solution, then either the cables or other aspects of the model are deflecting too much (i.e. the structure is unstable).
1. Check the Cable Diameter
A cable diameter that is too thin may make the structure unstable as it will continue to deflect and diverge. Meanwhile a diameter that is too thick will produce a higher self-weight making it difficult for the software to solve the catenary shape of the cable at every iteration of the non-linear process. Changing the cable diameter can often lead to a faster convergence.
2. Check Cables are not over/under loaded
This is similar to the point above. Convergence will be difficult if the cables or deflecting too much or if the catenary effect is dominating (not loaded enough).
3. Reduce your Convergence Accuracy
By default SkyCiv aims for 99% convergence accuracy (in Solver Settings) or a 1% convergence error. If you reduce the accuracy to around 90-95% then the software may be able to find a "converged" solution. Even though this might not be the accuracy you're looking for, the solution can give you insight into why the model is not converging with a tighter convergence tolerance. For instance, you may see the deflected shape and realize how the model is unstable, giving you an idea of how to stabilize it so you can reach a better convergence accuracy.
4. Add a Extra Supports
Adding more supports can properly constrain the model so instabilities are mitigated. You can also enable the "Auto Stabilize Model" option in the Solver Settings which will automatically attempt to remove instabilities for you.
5. Check your Other Members
If the cables are connected to other members then they may be in a state of high-tension causing the members they are connected to also deflect too much. Using Point #3 above can give you some insight into how the structure is deflecting. Potentially the members that the cables are connected with may not be able to support the high tension that cables often support.
We hope the tips above help our users (and any other engineers) with getting their cable models to solve. SkyCiv's catenary cable analysis is completely integrated within the SkyCiv Structural 3D Software. Beyond that if you are having troubles getting your model to solve, please email us at firstname.lastname@example.org, or visit our integrated live chat to speak with a qualified Structural Engineer in real time!
CTO and Co-Founder of SkyCiv
BEng Mechanical (Hons1), BCom