# michaelv

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1. ## Difference in mass, size optimization

The problem is solved. The difference is due to the fact that in hyperworks the volume of the beams is defined by the beam dimensions from hyperbeam. While in Optistruct, the optimizer uses the initial values specified in the design variables. This explains the difference in volume and therefore also in mass. I was confused by that but now I hope this is also clear for other users. Regards, Michael
2. ## Difference in mass, size optimization

Dear optistruct users, I have a question regarding the sizing optimization. Currently I am performing a size optimization of a truss structure. The model consists of lines which are meshed into Cbeam elements and design variables are generated in order to perform a size optimization. The design is subjected to multiple load cases. The objective of the optimization is to minimize the mass of the structure. Constraints are defined for the member stresses and displacements. The optimization works fine. When I calculate the mass of the structure by using tools --> mass calculation, I obtain a mass of 2.056 ton with a volume of 2.620 * 10^8 mm^3. I have used the standard steel material properties (Rho=7.85 * 10^-9 mm^3). I have defined point masses which are defined in a separate compnent with a total mass of 1.245 ton. When I look at the first iteration step (iteration 0) in the output file. I see that the mass is equal to 2.358 Ton and that the volume is equal to 1.42394*10^8 mm^3. This confuses me. So to make it clear: Before first iteration step: Mass= 2.056 Ton Output file, Iteration zero: Mass = 2.358 - 1.245 = 1.13 ton I understand that the masses of the point masses are incorporated into this mass. But why is the volume changed of the design? On the internet I found the following written about this difference, but it is still not clear for me. Do I make a mistake, how should I interpret these masses? Can someone make this clear for me? Regards, Michael
3. ## Error # 2126

Dear Prakash, Thanks for your help, I did not notice that I had insufficient disk space. I will increase my disk space and rerun the optimization. Your feedback is really appreciated. Regards, Michael
4. ## Error # 2126

Dear Prakash, Thanks for your quick reply. Hm, yes maybe that could be the problem which causes the error. During the set-up of the optimization process, I have set the output card param -> checkel -> to no due to a failure in quality element check. I know this is not suggested but I will try to remesh my model to avoid this error. The output file of the run can be found in the link below. Fixed boom - Design domain.out Regards, Michael
5. ## Error # 2126

Hi everyone, I using optistruct in order to perform a topology optimization. After 36 iterations the optimization process was terminated and the following error was shown. The objective function is to minimize the weighted compliance for a certain volume fraction. *** ERROR # 2126 *** Error encountered when writing to the restart file. error code = 38 Can anyone explain to me to what is error is related to. The results from the optimization process looks alright so far. Is it related to the mesh? Any feedback would be appreciated. Regards, Michael

Hi mike, When the results button is not available, try to save your input file as a new file. Because the results button may dissapear if your overwrite your input file, Try to save as a new input file before you perform the optimization. I had the same problem and this worked for me, so hopefully it works for you too. Regards, Michael
7. ## Topology Optimisation of Trusses problem

Dear @Prakash Pagadala Thanks! Now it works, what did I do wrong? Regards, Michael
8. ## Topology Optimisation of Trusses problem

Hi @Prakash Pagadala Allright,Now I have defined the problem by myself in exactly the same manner as in your .fem file. The strange thing is that the member size are optimized up to the specified lower limit and then the optimization is ended. This should mean that there is something wrong with my constraints, But I cannot see what is wrong. Could you please have a look on my model. Because I would like to set-up these kind op problems by myself. Thanks in advance! Here is the .fem file. 10-bar truss benchmark.fem Regards, Michael
9. ## Topology Optimisation of Trusses problem

Dear Prakash, Thanks for sharing the file. I have changed the support conditions and lower bounds for the cross sectional area. Now the solution is close to the solution of the benchmark problem. The difference is probably due to the fact the these results were obtained by another method. The deviation between the two objective values is 0.4%. I will further investigate your model to check my mistakes. Now I only have one question: Why do you have set the boundary condition only at the lower node (Node 6 in the picture), because this cannot ensure stability. This lower node is only constrained in the X and Y direction (DOF12) and therefore the structure will rotate around the Z-axis. When I run the analysis I do not see anything strange. Is this true or do I miss something? Kind regards, Michael
10. ## Topology Optimisation of Trusses problem

Dear Prakash, Thanks for your reply, I think something went wrong while uploading the file. Because the file had no size at all. Here you can find the model. Thanks for the help. 10-bar truss.fem Regards Michael
11. ## Topology Optimisation of Trusses problem

Dear Prakash, Do you have any updates about my model? Or can you provide me the example file which is mentioned in the link above? Regards, Michael
12. ## Topology Optimisation of Trusses problem

Dear optistruct users, In the meantime, I have tried to set-up the 10 bar truss problem by myself. Unfortunately I am unable to obtain the same results as the benchmark solution. I used the following benchmark solution in order to verify my method. My problem definition can be found in the following file: 10 bar truss.fem The values that I obtain are in the range but they are not the same. Can someone check my model or set-up? Any feedback would be appreciated. In the following link there is a describtion for a 10 bar truss optimization in optistruct, but I couldn't locate the file which belongs to it. https://www.sharcnet.ca/Software/Hyperworks/help/hwsolvers/hwsolvers.htm?size_optimization_of_a_ten_bar_truss.htm Regards, Michael
13. ## Topology Optimisation of Trusses problem

Hi everyone, I have tried to solve this benchmark problem. But i am not able to obtain the contour plot of the element densities. So how can I obtain these values in hyperview? If I understand correctly, the minimum member area is already specified in this problem. Therefore the solver should be able to reduce the member area to zero for all the members that are not structural "optimal" and this should lead to the benchmark solution of the 10 bar truss problem. How can I properly set-up this 10 bar truss problem in order to check my optimization set-up by comparing it to this benchmark solution. Your feedback is welcome. Regards, Michael
14. ## Improve optimization results

Dear Prakash, Thanks for your response, I have checked the convergence history and noticed that the constraints are not satisfied for a long time. This can be seen in the animation. You are right, the best design can be found in the intermediate design iterations. I have rerun the optimization and used the SHRES option to obtain an .sh file for each particular iteration. Now I can select a preferred iteration which is suitable for post-processing. Thanks for sharing your knowledge. Kind regards, Michael
15. ## Improve optimization results

Hi Thanks for the provided information. It is true that the max member size control has no effect in this situation. Therefore I performed a run without maxdim and lowered the objective criteria and increased the amount of iterations, In order to obtain a well converged solution. With the objective set to minimize the compliance with a volume constraint of 25%, I obtained the following result: This is an interesting result and shows clearly the loadpaths in the design but it still consists of disconnected areas. Lowering the ISO value further, results in a blurry and scattered solution. From a structural point of view, I would suggest that material should be present at these disconnected areas in order to maximize the stiffness of the structure. Now when a load is acting on the structure, the load is transferred by bending stresses instead of tensile and compressive stresses, which is less efficient and not beneficial for the compliance of the structure. So my question is, what is the reason for this effect? Does this mean that the solution is still not converged? I am looking forward to your response. Regards, Michael
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