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Posts posted by mOaR89


Hello,
when i start an optimization with optistruct the calculation is finished after 1 Iteration. In the Outputfile i found following Information:
Soft convergence criterion satisfied;
the design did not change during the last Iteration.What does this mean?
I already did a lot of successful shapeoptimizations but in this case i don't really know why the shape didn't change.
I changed the default OBJTOL value from the opti control card but the problem still occurs.
The most interesting thing is:When i change the inital value in the shape panel to 0.5 I don't have any problems and the optimization finds the best shape. When I start with an inital value of 0.0 then i get the problem with the soft convergence criterion.
Thank you
Greets,
Fatih Uysal

Thank you Rahul for the information.
The other problems are solved.
Greets,
Fatih Uysal

Hello,
i want to reduce the dynamic stiffness of a rubber bearing by changing the geometry. I have an approximate idea of the "optimized" geometry of this rubber bearing therefore I created morphvolumes and changed the specified area (solid elements) by translating the handles. I saved these changes as shapes which are my design variables.
I know that the optimum is between the initial model and the changed model. I want to do an optimization with optistruct to find the optimum.
To reduce the dynamic Stiffness i need 3 responses and an equation (dont know another way so far).
The calculation of the dynamic Stiffness is simple: Cdyn = Force/Displacement.
First i defined an equation with the dequationpanel: F(x,y)=x/y > where x is the "frf force (ELFORCE)" and y the displacement (frf displacement) which are two of the three responses.
The Last response is "function" which includes the dequation and the other two responses defined before.
I would like to minimize the response "function" (which is the dynamic stiffness). But it's not possible to create an objective which minimizes my response "function", i get following error:
*** ERROR # 1812 ***
Multiple responses are assigned to the DESOBJ objective function.
A MINMAX/MAXMIN objective function definition with DOBJREF should
be used instead.
Number of responses = 10001) Do you know what the maximum number of responses is?
(It's an frequency response analyis from 0 Hz to 3000 Hz with an increment of 3, thats why its 1000 responses (i guess)) .
I created an obj reference "dobjref" which includes the response "function", then i created MINMAX objective.This works, and i can start the optimization but here i have some questions:
2) When i define the obj reference i can choose neg and pos reference. What can i do with these references?
3) I don't really know what this minmax function does. Does it minimize the maximum value of the equation? It is not my goal to minimize only the maximum value of the equation, it's rather minimizing the area of the function.
4) Is it normal that optistruct finds a solution after 2 iterations? I have two different shapes and i would expect that it takes a lot of time and iterations to find the optimum. I guess i did something wrong or forgot sth.
Sry for asking so many questions and sry for my bad english. I thank you so much in advance.
Regards,
Fatih Uysal

Dear Rahul,
sorry for my late reply. It works perfekt with PELAS and Celas1, so i didn't try it with Celas2.
Regards,Fatih U.


I tried like tinh said but that works only for celas1 and celas3.
Thank you :)
Greets,
Fatih Uysal

Hello everybody,
i guess it is easy to solve but i can't define the stiffness of a celas2element. I created 1D > springs > celas2, Chose 2 nodes, Chose dof (3), Chose property, but still i don't know how to apply the stiffness (K).
It tried with PARAM > ELASSTIF, but it doesn't work.
Thank you in advanceGreets,
Fatih Uysal

Hello,
First of all i want to explain what i did so far.
I performed a frequency response modal Analysis to investigate the dynamic stiffness of my component in Hypermesh/Optistruct. I performed an Analysis with Optistruct and my results are the frequencydepended Displacement (s) and SPCForce (F). Then i plotted the dynamic stiffness by calculating Cdyn=F/s. The results are exactly what i expected.
After that i changed the structure of my component using Mesh Morphing and recalculated the dynamic stiffness of the changed component. This had a huge effect on the dynamic stiffness.
I saved the morphchanges as shapes and created a shape design variable. I want to do a shape optimization to reduce (minimize) the dynamic stiffness.
Now my questions:
1. Is it possible to do a shapeoptimization to reduce the dynamic stiffness (reduce the quotient F/s) with optistruct?
2. When it is possible, can you give me a hint, how i have to proceed with the Responses, constraints and objectives for the optimization?
Regards,
Fatih Uysal 
Dear All,
i hope to find a solution for my problem.
To avoid selfintersection i check my component for intersections and fix problems when intersectionproblems occur.
I would like to use TCL to make this possible. I use following code:
*createmark components 1 "compname"
*checkpenetration components 1 0 0 1 0 0 0 0Using these commands Hypermesh will find intersections which exist on the component. As from now, I need a command to fix all found intersections. I have to do that manually by clicking on the "Automatic Intersection/Penetration Fix" Tool so far. Is there a way to do that automatically?
Thank you very much .

Hi everyone,
I have a tetramesh problem and i hope that you can give me a hint to solve that problem. To understand the problem I have added some pictures.
This picture shows the boundary layer "wall1" (outer cylinder, yellow) and "wall2" (inner cylinder, blue) and the "inlet" (green) and "outlet" (red). These four components together form an enclosed volume, therefore a tetramesh is not a problem.
But I would like to include a third wall ("wall3") within the enclosed volume. "wall3" is a complex triaxial braid as shown in the following picture.
Next picture shows "wall3" within the enclosed volume.
My problem: "Wall3" consists of solid elements. As soon as I try to tetramesh the volume including "wall3" it is not possible. I tried to mesh within the tetramesh panel an had no success. I also tried to mesh with the CFD tetramesh panel but also without results.
The goal is to create a "fluid" component within the enclosed volume and "wall3" is sth. like a "barrier" which should have some influence on the flow.
I would appreciate it if you can help me .
Best regards,
Fatih Uysal

Thank you .
I separated it into two parts and meshed each of them. It worked perfectly.

Hi All,
I'm Newbie and I started working with Hypermesh 2 weeks ago and i hope to find solution here for my problem .
I want to mesh a curved tube. But first I tried to mesh a straight tube, created with two circles and a line connecting these circles, and it worked fine (see picture named "straight_tube") with the skin panel.
Then I tried the same with a curved line using the spline panel. But it only meshes the half of the tube instead of creating a closed mesh (see second picture "curved_tube") and I don't know why.
Do you have any idea of how to fix this problem?
Thank you in advance
Best regards,
Uysal
Change Soft convergence criterion
in Altair OptiStruct
Posted · Report reply
Thank you Rahul for the Information.
Since Optistruct is a gradient based optimizer i guess optistruct stopped optimization after finding a local optimum.
Using a DGLOBALCard helped me to find the global optimum.
Greets,
Fatih Uysal