Altair RISE

A program to recognize and reward our most engaged community members

Nominate Yourself Now!

Lattice Optimization Confusion

Hi there,

I'm new to lattice optimization and confronted a curious problem.

My test example is a cubic, with dimension 240mm*146mm*1000m for example, after state analysis, the max displacement is about 7.5mm. Then I did lattice optimization, set volume_fraction as constraint and Min_compliance(Max stiffness) as objective. I set the density as Design_variable, with range 0.01~1, as shown in pic attached. And I have two control cards to set optimization process.

My three questions are:

1. What should I choose for 'Config' for these two cards respectively? One just controls interation number and the other control lattice parameter?

2. When I set minimum of lattice radius value, for example10mm, it appears as the maximum radius value in the control card. Why does this happen?

3. Is it possible for me to have a lattice optimized structure having same stiffness(max disp) as the original solid one? And How? Is it possible to achieve it just by changing lattice radius?

Great thanks!

<?xml version="1.0" encoding="UTF-8"?>

Find more posts tagged with

English

OptiStruct

Accepted answers

All comments

Altair Forum User

Hi @Zanlang

DOTPRM controls number iterations and LATPRM controls lattice beam parameters. You can include DOTPRM separately.

2) Lot sure why you are not able to see minimum radius in LATPRM, MINRAD but you should have minimum and maximum radius fields to enter as shown in the images. You can also enter through Optimization>>Lattice Params>>MINRAD/MAXRAD (Don't go with the numbers in the images they are just for demo purpose)

<?xml version="1.0" encoding="UTF-8"?>

Altair Forum User

Hi @Prakash Pagadala, thanks for your reply.

1. I got this answer;

2. I tried to set Maxrad and Minrad in through Optimization>>Lattice Params>>MINRAD/MAXRAD, but it just shows one limit... the maximum radius in the control card. Maybe it's relevant to my Hyperworks edition? Mine is 14.

Do you have some idea about my thrid problem?

Thanks a lot!

Altair Forum User

Hi @Zanlang

Can you update to the latest patch and try again?

Altair Forum User

3. Is it possible for me to have a lattice optimized structure having same stiffness(max disp) as the original solid one? And How? Is it possible to achieve it just by changing lattice radius?

You can try this approach:

Restrict the displacement on selected nodes (maybe nodes where load is applied) by creating a displacement constraint and objective will be minimizing mass.

Altair Forum User

Thank you for your help Prakash, I'll try and see what happends. @Prakash Pagadala

Altair Forum User

You can try this approach:

Restrict the displacement on selected nodes (maybe nodes where load is applied) by creating a displacement constraint and objective will be minimizing mass.

Hi @Prakash Pagadala, I tied your advice, it works. but I have another problem.

I attached some result to this reply. All the case are under same boundary condition, load, and mesh. I added one constraint of max displacement of 7.19, which is the solid-block static response under same load.

1）It seems that the max displace for 2^nd optimization generally becomes larger than the first time result. So which result should I take as a comparison standard?

2）Also it seems that the 2^nd optimization is doing some random refinement based on optimized lattice structure. This is no continuous proportional relationship between volfraction and max displacement.

For your convenience, I also upload my test example file.

Thank you very much for your help!

<?xml version="1.0" encoding="UTF-8"?>

Unable to find an attachment - read this blog

Altair Forum User

Hi,

The file you shared and the results does not match and it is a bit confusing.

Can you try this approach?

1) 1st Optimization Responses: Compliance and Volume Fraction

2) 2nd Optimization Responses: Min Mass with Displacement constraint and constrain radius.

Altair Forum User

Hi, @Prakash Pagadala

Sorry for the misleading file... Let me explain that for you.

What I did yesterday is the exactly 1) approach you mentioned here. I have 3 response: volum frac, compliance, and displacement of 2 nodes. Before lattice optimization, the max displacement of structure is 7.19mm. I want to get an lattce structure with same max displacement. So, I set two design constraints, max displacement <=7.19 and volume fraction less than 0.3( for example, it can change to 0.4, 0.5 and so on). And the design objective is to obtain the lattice structure with min compliance.

And the data of the strategy was already posted. I took 2 times lattice optimization, the first time was run in Hypermesh directly, generating file 'lattice.fem'; and the second time inports 'lattice.fem' into Optistruct and run lattice optimization again, resulting in a file 'lattice_optimized.fem'.

To my understanding, the 2nd optimization is just doing some refinement based on 1st lattice optmization, but why the last max displacement becomes larger?

As for the 2) method you mentioned here. I also tried just now. The data are summarized as attachement table. And my 3 cases is attached as well. The 'MaxDisdisp#' is the max displacement constraint I set.

From the data I have got, it seems that the max constraint has to be larger than the 7.19, which is the max displacement of the original solid part. Otherwise, lattice optimization is meaningless (since the optimized result has even larger mass and volume). But my expectation is that optimized lattice structure should be stiffer and lighter. Also, the same problem that 2^nd optimization doesn’t work as refinement, which is still confusing for me.

If it's conveinient, could you also share me the contact of some support engineer in Altair Troy office？ I can contact some engineer and drop by to solve the problem directly.

Thank you very much!

<?xml version="1.0" encoding="UTF-8"?>

Unable to find an attachment - read this blog

Altair Forum User

@Zanlang

Thanks for sharing the files, I will check and update to you soon.