## Robot Structural Analysis

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# Is it possible to limit a bar force to a certain value?

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# Re: Is it possible to limit a bar force to a certain value?

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Either using a non-linear release or a non-linear support. Mind to set the parameters of the non-linear analysis as shown on the attached picture.

*If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.*

**Artur Kosakowski**

# Re: Is it possible to limit a bar force to a certain value?

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Hi Artur

That´s exactly what I tried to do except for marking " matrix update after each iteration" . But also doing that I keep getting a zero reaction value where I get 100tf when the UZ direction is fixed

# Re: Is it possible to limit a bar force to a certain value?

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Please send the model and indicate the node number and load case to look at.

**Artur Kosakowski**

# Re: Is it possible to limit a bar force to a certain value?

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Artur,

I solved the problem using Bilinear model with a very high K (10000000)for the 1st spring, zero K for the 2nd spring and a corresponding D1 for the force I wanted to limit.It worked great!

But now I´m having a weird problem when running the model.I have like 120 combinations and ,it takes like 20secs to solve each one .But after something like 25 combinations ,it starts to not converge. So I stopped the calculations ,deleted most of combinations and only left some that robot reported as non convergent.Ran it again without saving the model and to my surprise they converged also in 20secseach and without using " matrix update after each iteration" !!!

Nodes with non linear supports are 10 ,21 ,32 ,33 . Combinations are 41,73,75,89

Model is attached. Rename it to .rar

# Re: Is it possible to limit a bar force to a certain value?

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Try to use the parameters from the attached picture. I have calculated the model and all combinations converge.

Case 132

: 1,35xPP+1,05xSC+0,84xVTsuc+0,84xVT270-1,2xTPgrad

Analysis type:

Nonlin. Combination

Non-linear process: convergent.

Maximum value of process parameter when convergence is obtained

: 1.000

Maximum value of process parameter when convergence is not obtained :

1.000

*If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.*

**Artur Kosakowski**

# Re: Is it possible to limit a bar force to a certain value?

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Thx a lot Artur,

It worked.

But What I don´t understand is why a combination that doesn´t converge in the first run (**without** marking "matrix updating after each iteration"), converges if I use calculation restart without modifying anything?

Why the calculation process behaves differently??

The problem is solved, but I´d like to understand that.

thx

# Re: Is it possible to limit a bar force to a certain value?

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I have to admit that I do not fully understand the sequence of actions you made and the idea behind them. Definitely deleting some of the load cases/combinations while the analysis was terminated and then restart of the analysis is not the thing I personally do. The intention of this option was to change the parameters of the analysis when you can see that the process has got little chance to converge with the current settings. I can try to investigate this situation providing you give me the detailed (step by step) description to follow. As you could see all I did was to use the settings I suggested before

BTW: Have you checked in the calculation report that they actually converged?

**Artur Kosakowski**

# Re: Is it possible to limit a bar force to a certain value?

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Artur,

For just an example to show you ,I limited last load case to be number 41.Combinations 39,40 and 41 don´t converge in the 1st run .After I get the no convergence warning for load case 41 ,I just click OK and do an analysis restart for just case 41 without changing any settings.The result is completely different and now the combination converges

Watch it in this video.

# Re: Is it possible to limit a bar force to a certain value?

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As far as I can see Robot starts to have difficulty to converge the last of many non-linear cases for the BFGS method and the multi-threaded solver (when you restart calculations or delete some of the previous cases then divergent cases will converge). Thank you for pointing this situation out - we will check what exactly happens.

The solution is to either use the Full Newton-Raphson method for the multi-threaded solver (the settings I used) or use the Automatic solver (Sparse_M in this case) for the BFGS method.

**Artur Kosakowski**