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Zizhe Wang

Optiimization not successful

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I have a rocker which should be optimized. I added force and joints, but no matter I try maximize stiffness or minimum mass (there is always "design violations" with the safety factor) the results are not so good.

The picture shows how the rocker works.

The .stmod file is also attached.


Thank you very much!

Best Regards



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Hi Zizhe,

Welcome to the sT Forum!

At first, you might check your loads. Seems like you are trying to analyse and optimize for a non-static loadcase, which would cause movement around your support (and huge deflections).

Once you got the correct loads, you should use a screw/support without any freedom to rotate. You can simply check if you did everything correctly by running a quick analysis.


If you have further questions, you might take a look in the altair university: https://altairuniversity.com/academic/


Hope this helps, ~ and good luck at FSG




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Hi Felix

Thanks for your quick answer!


I need to explain my problems more specifically.

The rocker should have the ability to rotate around one hole. I've watched some of your tutorials. And there is also one tutorial which optimized a rocker.



Based on this tutorial I think I should add a joint in that hole instead of a screw or a support. That's the reason why I added a joint before, the other forces are also added correctly. 

I'm optimizing two of my rockers, front and rear. I faced mainly 2 problems:


1. Front rocker,  the analyse and optimization both are failed. It shows "Error 99"
2. Rear rocker, the analyse and optimization went well, but 
 (a) the result with the optimization using maximum stiffness looks bad (picture shows the result)
 (b) after the analyse I got the factor of safety which is 0 (picture 2)
 (c)  based on B) when I run optimization with minimum mass but the result shows always Design Violations (I tried factor of safety with 0.5, 1.2, 2.0)
I've tried solving this problem for almost one week but still failed and I do really need some help :) 

Rocker front with max stiffness.JPG

Rocker front analyse.JPG

01_Rocker Front.stmod


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All your optimization results are wrong. Your loads are representing a non-static loadcase. They are causing a momentum in your joint e.g. for your rear rocker ~ 170Nm. This is the starting point for the optimization issue you are facing.

Once you got the loads correctly, you should have zero momentum in your Support. Then, you should reduce the degree of freedom for rotation of this support.

For example by using a bolt or a support directly.


You will not achieve any plausible structures by optimization, if you are getting extremly high stresses like you do.


Our tutorial model is statically defined, by using two joints. Yours not, using just one allowing to rotate.




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Hi Felix, 

Is this the right result?


Actually I don't really understand why my loadcase is a non-static loadcase.

The force on the upper hole is the force from spring damper, the force on the right upper hole is the force from wishbone, and the force on the bottom hole is the force from anti-role bar. When the car moving, the rocker can rotate around the left bottom hole. I would be much appreciated if you could help me with my file.





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One explanation: when the wishbone push the rocker (bell crank), the rocker will have a potential to rotate, that means it has the potential to push the spring damper and pull the anti-roll bar, so the spring damper and anti-roll bar will in turn apply forces to the rocker.

I don't really know whether I should apply forces which from the spring damper and anti-roll bar on the rocker or simply only apply the force from wishbone. And also not really know which holes should be applied a Support.


Thank you so much


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