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Found 20 results

1. ## Explanation for very large maximum constraint violation % in the first iteration

Greetings, I am performing a free-size optimization (iteration summary given below) and trying to understand the explanation behind maximum constraint violation %. So far the following is clear: If constraint violation > 1% : status is V (violated) If constraint violation < 1% : status is A (Active) Large constraint violation % could mean that the constraint is too tight and that the problem itself is ill-defined. the difference between regular and soft convergence is understood as well Problem definition: The thickness of an insert is defined to be the DV. Two stress constraints are defined. The objective is a stress minmax formulation. Question: I am unable to figure out whether the large constraint violation % implies a critical issue. If yes, how does one rectify the problem? Insert_FEM_y.out
2. ## Which constraint should I use on my FEA?

Hello everyone!I'm performing a finite element analysis with a pair of gears and another component around this pair of gears. This system is named as "planetary gears". My model is simplified, just to see how will be the behavior of the system, I'm using the software Hypermesh with the solver OptiStruct. My question is, which degrees of freedom on "FACE 1" and "FACE 2" should I constraint to rotate "GEAR A" and "GEAR B" around the axis X.Degres of freedom:Displacement: x, y and zRotation: x, y and zI have attached the picture. Thanks so much in advance.Henry
3. ## Defining constraint

Hello Group I wanted to know whether its is possible to define output as a constraint in optimisation. I am validating my modell with frequency response test I want to vary values of Material properties like Emodulus, G modulus so that at certain frequencies Frequency Response Function FRF (velocity) is say (+\- 10 % ) of the FRF calculated by test. eg Vary values of E = 1000 mpa to 2000 mpa G= 200 mpa to 400 mpa so that at node 256 Frq frf (test) frf(simulation) 5hz 0.256 (+/- 0.01) of 0.256 10hz 0.586 (+- 0.01) of 0.586 15 hz 1.457 (+- 0.01) of 1.457 etc Is it possible to define constraint this way a suggestion or example tutorial would be quit helpful Thanks and Regards Pratik
4. ## Strain constraint error in free-size optimization

Hello, I have done a free-size optimization with a displacement constraint and it has been successfully solved. However the strains are huge and the model fails. I would like to constrain the strains to obtain the optimized model. Now I have tried to do a free-size optimization with a "composite strain" constraint and then an error appears. I understand that stresses and strains are related, so I don't understand why this error appears if I have defined a 0.007 maximum strain. This is the error: *** ERROR # 1800 *** Stress/strain/force responses are applied to ply 1 which belongs to a topology or free-size domain. For stress-constrained topology or free-size optimization, please use the STRESS option on the design variable definition card. This is my Response panel: This is my Constraints panel: This is my Design Variable panel:
5. ## Optimization constraints

Hello, I have tried running a topology optimization on a simply supported beam. I defined the objective as min. mass but did not introduce any stress or deformation constraints. And the optimization gave results. Is it possible to run a topology optimization without constraints? Then based on which parameter the software optimizes the structure, does it automatically introduce constraints by itself? Thank you, Muge Candogan
6. ## Creating Constraints

What does this size value indicate while creating a constraint for certain nodes in HyperMesh ?
7. ## LAMTHK constraint on element set?

Hi everyone, I'm currently making a free-size composite optimization and I need to add Laminate thickness constraints to set's of elements throughout the part. Is this possible or do I need to have more than one laminate to achieve this? I've founded in the internet a release notes pdf and it says that this is possible but I can't find it in the optimization panel, only for the all laminate and not to a set of elems. Thank you for the help, Best regards, Gonçalo
8. ## COG constraint in optimization

Hello, I am working on an optimization problem and COG is one of my constraints. The COG is defined in 3 ( x,y,z ) coordinates but while assigning the constraint, I am asked to enter only 1 value for upper and lower limit each. When I enter a value, how can I define which axis it will be applied to? Thanks, Muge Candogan
9. ## Constraints for groups of design variables

Hello, I'm searching for an easy way to implement the following constraint for a group of design variables in an optimization study within the Hyperstudy interface. Let's assume we have the variables A, B, and C wich should be varied within the following ranges: A: Lower Bound: 0, Upper Bound: 1, Initial Value: 0.33 B: Lower Bound: 0, Upper Bound: 1, Initial Value: 0.33 C: Lower Bound: 0, Upper Bound: 1, Initial Value: 0.33 Whereas the general constraint A+B+C<=1 musn't be violated. My approach using the function "Link Variables" did not lead to an appropriate result. I would like to avoid a redefinition of the parameters within the solver input file (i.e. by A = A/(A+B+C), in consideration of the explicit assignment between the parameters defined by Hyperstudy and the "real" parameters used within the solver. Does anybody know of an convenient way to implement the constraints as described? Thank you for your efforts in advance. Cheers, Felix
10. ## Optimization with two constraint?

Hello Friends, In my Optimization Inputs before I gave mass as constriant and I got new mass everytime in Responses Table. But now I Need volume also, for that I took one more volume Response and Volume constraint with lower bound Zero, so I can see what happen in upper bound. But it Shows nothing in Response Table. Please help... Thank you, Regards, Jay
11. ## Constraining a hole in limited DOFs

Hello, I am looking to constrain a hole of a 3D model. I am currently using RBE2s (with all 6 DOFs on) within the hole and applying a constraint to the independent node in all 6 DOFs. Doing this I am able to successfully run the optimisation. However, I want to simulate a bar constraint where the model can rotate about the y axis but no others. I have tried deselecting the 5th DOF on both the RBE2s and constraint but this results in the optimisation failing. How do I go about applying constraints to all DOFs but 5 (moment around the y-axis)? Additionally, I am using RBE2s currently as I can apply a constraint to these. However, ideally I would be using RBE3s as these will better represent my problem. Is this possible to set up with the constraint in limited DOFs in mind? Thank you
12. ## setting Compliance constraint

Hi, I have to run a topology optimisation on a simple structure, a kind of fixed-end beam with some loads applied . Known the maximum displacement I want to have, how can I perform a calculation of the compliance so that i can put it as upper bound in DCONSTRAINT settings? Thanks to anybody will answer Valentina
13. ## Constraint degrees of freedom of SPC with respect to local coordinate system and importance of CURVE option in constraint panel

Hi sir/Madam, in constraints panel i do not find any option to select local coordinate, how can i constraint only one degree of freedom with respect to local coordinate system ? and what is use of curve option in constraint panel ? Thank you...
14. ## DOF only locked in one direction

Hello @ all, Is it possible to lock a DOF in only one direction/way? For example: I want to block a DOF in the 'minus x direction', but it should be able to move in the positiv way. Is it possible and how to do this? Thanks for your help. Greets, Thomas
15. ## Lattice structure with stress constraint

Hello I tried to optimize a modell with a lattice structure. This model needs to fullfill a certain stress constraint. The lattice structure is created, but the stress constraint did not implement properly. The full volume does it stick to the stress constraint, but the lattice structure itself does not and achieve too high stresses. What can be done, that the stress constraint is also taken account of the lattice structure. I aded following line to the .fem file: + LATTICE 1 0.1 0.7 10. I thank you in advance for your help!
16. ## Can I define a deflection limit for topology optimization

We want to do topology optimization on the hinge component (red) and the rest parts remain the same. The upper and lower surface of the pin (blue) is constrained (6DOF) and there is a 20N upward force on the edge of the door (yellow) We want the vertical deflection of the loading point on the door be less than 7 mm For now, we set the design constraint as the volume fraction value of the hinge, say 0.4 as the upper bound, and the objective is to minimize the compliance of the hinge. There are two questions: 1. After the topo opt, the linking area between the hinge and the door is really weak, as Figure 2 shown. Is it because that we only considered the compliance of the hinge and hypwework will not consider the linking problem between components? If we modify the design area a little bit (leave the linking area as undesigned space), can we solve this problem? Or there is other ways to deal with it? 2. After we got the topo result, we ran a FEA test and it showed that the deflection of the loading point exceeds the limit. Can we define a deflection limit as the design constraint before we run the topo opt? If so, how can we do that? If not, what can we do to minimize the deflection? (maybe we set a wrong objective?) Thank you!
17. ## Singularity Error in Frequency Response Analysis

Hi, I am running a Frequency Response Analysis. When I change the EIGRL entry to EIGRA, I get following error. *** ERROR # 3432 *** Singularity found in construction of constraint equations. Usually this happens when a dof is defined as slave in more than one constraints. For inertia relief analysis this problem may be overcome with SUPORT definitions and/or PARAM,COUPMASS,1. This error occurs in module "asmbdrv". How this can be resolved ?
18. ## Contraining a hole as a void that will not expeirence deformation

Hello, I would like to simulate a void as a region within my model that should not experience any deformation - to not damage any structure that may be place there e.g. a bearing. This is to be for a topology optimisation simulation, then how (if it is possible) can it be approached so that the optimal topology maintains the shape of the void? To expand, if I have a circular hole where a bearing should be placed and I do not want the deformation of the model to damage this bearing, how can I contrain the hole to maintain its shape during the topology optimisation? I would not like to use RBE2s or a nondesign space as this will effect the way the load paths are transferred. Will RBE3s work? If not, is there an alternative? Thank you in advance.
19. ## Topology optimization not converging and high violations

Hey all! I hope you can help me! I´m doing an optimization for a university project of a bracket but get no convergence and high constraint violations. The model: See the design volume (blue) in Screenshot 1. The yellow areas are not being optimized. There the loads are applied and the model is constrained at the two yellow areas on the top. I had to use TET10 elements because auf geometrical issues. 6 forces apply to the model. I use quite big elements but this is for doing quick calculations...I don´t want to wait 2 hours to see if it is working... but I think this should not be a problem here?! Optimization: I want to reduce the weight/volume. So objective is to minimze volume (I have tried Mass, volfrac). At the nodes, where I´ve applied the forces (basically in the middle of the yellow areas), I have set displacement constraints (betweent 0.5mm and 2mm). I use min member size controll of 0.4 and a stress constraint of 450(N/mm²) My Problem: The solver always reaches the iteration limit of 80 without converging below the tolerance and ist violating the constraints massively. (screenshot). I have tried to let the solver run 120 iterations but without any usable result. Here are the ones with 120 iterations: When I view the results given by the solver at iteration 80 it looks like it is about to find a solution that looks acceptable in my eyes. but the strange thing ist that the density values of the structure often are below 0.1 and not almost 1 as they shpould be. I have tried to check if it ist because of quite low loads (max about 165N) but with a scale factor of 10 the same element densities appear. Results with density values > 0.05: Results with density values > 0.2: Results with density values > 0.5: Has anybody an idea what I am doing wrong? Should I increase the number of iterations further?
20. ## deqatn Dequations help

Hello Optistruct users, I am attempting to run a topology optimization using dequations as a force constraint. I would like to obtain the reaction forces on a bolt (represented as a CBUSH) and calculate the shear forces on the bolt. The shear forces will be calculated using dequations since we can only obtain reaction forces in DOF 1-6 and shear is needed from both DOF 2 and 3 (in this case). I would then like to use the calculated reaction shear force as a constraint. My trouble is relating the reaction forces to the dequation. How do I reference these forces? I am assuming I will need to reference the node number as well. My other concern is relating the dequation to RESP2. When I try to create a response (using function as my response type) I get the response "a dequation must be selected and edited". I am not sure if this is due to my equation not having referenced any forces with my variables or not. Do I need to create my eqation in Hypermath? Being that the equation I need is already a built in funtion as rss I am thinking I do not need to use Hypermath. Also, if there is a better way to establish the same result I am open to suggestions. Thanks, LP
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