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Found 14 results

1. ## Shape Optimization, Frequency Response Modal Analysis: Minimize dynamic Stiffness

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 dequation-panel: 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 = 1000 1) 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
2. ## What is best constructor for combine topology and size/shape optimization?

Dear friends, I'm looking for a mechanical structure which can applied combine method of topology and size/shape optimization. In many references, the common is truss/beam structure, which can use good for academic research. I mean that the structure highly practical for manufacturing, especially for additive manufacturing. Hoping someone could take some time to give me some suggestion/advice. Thanks!
3. ## Error 7312 During Shape Optimization

Hi Everyone, I'm trying to fine-tune a topology optimized part using free shape optimization on some of the members. Unfortunately when I run Optistruct, it gives me the following: *** ERROR # 7312 *** DSHAPE card 1 contains 2 disconnected patches. Patch(es) listed below contain too few grids that are likely insufficient for defining a smooth surface/curve. I can't find anything on this error. Also, it doesn't list any "patches" so I'm not even sure where it's having problems. Any advice? Thanks! Size_Opt_Setup
4. ## Hypermorph Distribution problem

Hello, I want to move a hole located in the middle of a beam. As I translate the elements of the hole along x axis, I want that the disturbance of the elements are distributed equally to the elements which are in the translation directionso that the meshes are not distort. Is there a way of selecting constraints to equally distribute the disturbances? Thank you
5. ## INTERNAL PROGRAMMING ERROR # 8016

Hi guys, I'm doing a shape optimization on some elements of a 2D Pshell and a size optimization of the shell with optistructoptions : -nt=8 -ln=12000 and i've got an error at the end of the iteration 0 : **** Error 8016 in datamr() during "expand" operation. Data block name "ielmlstsol". Current memory allocation 2864 MB, Unused memory 2510 MB, Number of blocks: 576 used, 22 free. Expanding from 1 MB to 23 MB Need at least 22 MB free (1 MB more than allocated). *** INTERNAL PROGRAMMING ERROR # 8020 *** Failed database modify command: Expanding array ielmlstsol.' * DATAMANAGER ERROR in subroutine "EXPAND". Here is the .out file if needed Thanks in advance, Frederic. shape_size.out
6. ## Change Soft convergence criterion

Hello, when i start an optimization with optistruct the calculation is finished after 1 Iteration. In the Output-file 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 shape-optimizations 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
7. ## Is it possible to perform a Shape Optimization while maintaining constant total volume?

Hi, I am trying to run a model which simulates that of a cantilever beam with circular cuts designed into it at regular intervals. I have a force load applying in compression along the top edge of the beam and would like to perform a shape optimization of the circular cuts while maintaining constant volume of the model under a minimizing compliance (maximizing stiffness) objective. I've tried it a few different ways but can't get the model to converge after more than two iterations (the optimization isn't progressing very far most likely due to the strict volume constraints. So what I would like to know is if it is possible to perform a shape optimization while maintaining constant volume of the model. I understand that this may be a difficult problem for the solver as I'm asking it to make changes while perhaps not giving it room to work with. If an upper and lower bound constraint of the original volume is too tight of a constraint, how loose do I have to make the constraint to allow for a reasonable shape optimization to be performed while maintaining (mostly) a constant total volume? Thanks for your input! I've attached the .HM file as well if you would prefer to take a closer look at the problem setup and optimization parameters. Dylan Stelzer Compressive_Load_(Uniform)_Optimizaton_Setup_1.hm
8. ## Error while running shape optimization in Optistruct: Messages for the job: *** ERROR # 1744 *** Missing BMESH ID 1 referenced by DSHAPE card.

While running shape optimization, I encountered this error message: Messages for the job: *** ERROR # 1744 *** Missing BMESH ID 1 referenced by DSHAPE card. Please, how can I resolve this. I am working in Optistruct. Thank you.
9. ## Responses for composite optimization

What are the upper and lower bounds when creating dconstraint for composite failure response. I did free sizing and now want to start with the second stage of optimization
10. ## Morphing of a tube

Hi, I'm currently working on a shape optimization for a tube. As I want to create the necessary shapes, I'm getting across some problems. I added the file for more visibility. 1. Is there any function to smooth my mesh after morphing? The stress concentration in the "edgy" parts of the mesh is very high. 2. Currently I'm morphing my mesh with "scale" for peripherally located handles. I want to keep the same perimeter as the original tube for manufacturing reasons.. Is there a better way? Thank you very much for your help. Matthias Tube.hm
11. ## Displacement constraints for shape optimization

Hi, After doing the HyperMesh morphing tutorials and the Optistruct shape optimization tutorials, I created a shape optimization file on my own. It consists of a cylindrical cantilever which is loaded sideways at the free end. The goal is to find an optimized cross section. The inner part remains unchanged, for the outer part (connected using equivalence) three different shapes are defined (elliptical morphing along x, along y and circular stretching). When minimizing the volume of the cantilever while limiting the stress in z-direction, the expected elliptical cross section results and the optimization constraint is fulfilled: Shape_opt_stress_constr.hm When limiting the displacement in load direction at the end of the cantilever, the cross section shrinks to a circle of minimum diameter and the displacement is much larger than the specified 0.15. Shape_opt_disp_constr.hm Isn't it possible to use displacement dconstraints for shape optimization? The solver (Optistruct) doesn't recognise the constraint violation and minimizes the volume to the extreme, leading to very high displacements. Thanks in advance for any inputs.
12. ## Frequency Response Modal Analysis: Shape Optimization to reduce dynamic Stiffness

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 frequency-depended Displacement (s) and SPC-Force (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 morph-changes 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 shape-optimization 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
13. ## Is it possible to perform a Shape Optimization while maintaining constant total volume?

Hi, I am trying to run a model which simulates that of a cantilever beam with circular cuts designed into it at regular intervals. I have a force load applying in compression along the top edge of the beam and would like to perform a shape optimization of the circular cuts while maintaining constant volume of the model under a minimizing compliance (maximizing stiffness) objective. I've tried it a few different ways but can't get the model to converge after more than two iterations (the optimization isn't progressing very far most likely due to the strict volume constraints. So what I would like to know is if it is possible to perform a shape optimization while maintaining constant volume of the model. I understand that this may be a difficult problem for the solver as I'm asking it to make changes while perhaps not giving it room to work with. If an upper and lower bound constraint of the original volume is too tight of a constraint, how loose do I have to make the constraint to allow for a reasonable shape optimization to be performed while maintaining (mostly) a constant total volume? Thanks for your input! I've attached the .HM file as well if you would prefer to take a closer look at the problem setup and optimization parameters. Dylan Stelzer Compressive_Load_(Uniform)_Optimizaton_Setup_1.hm
14. ## NLSTAT allowable responses

Hi everybody, I'm doing a shape optimization of a NLSTAT analysis (nonlinear contact and material are involved). I need stress or strain responses but, as soon as I launch the optimization, this error is shown to me: Which responses are possible to use with this type of optimization? It is possible to eventually use plastic strain responses? Best regards, Luke31
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