MINDIM and DISCRETE

Altair Forum User
Altair Forum User
Altair Employee
edited October 2020 in Community Q&A

Hi, 

 

I have read the Optistruct User Guide and I have some issues about this two parameters. It says that DISCRETE corresponds to (p-1) in the formula K(rho)=rho^p*K of the SIMP method. 

After that, it says: 'When minimum member size control is used, the penalty starts at 2 and is increased to 3 for the second and third iterative phases.'

So my question is: when I run an optimisation with MINDIM on, Optistruct automatically sets DISCRETE=3 and DISCRETE=4? So trying to run an optimisation with MINDIM on and DISCRETE equal to a number I decide, is a nonsense?

 

Can anyone answer this question?

Thanks!

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Answers

  • Altair Forum User
    Altair Forum User
    Altair Employee
    edited May 2017
    Altair Forum User said:

    Hi, 

     

     

     

     

    I have read the Optistruct User Guide and I have some issues about this two parameters. It says that DISCRETE corresponds to (p-1) in the formula K(rho)=rho^p*K of the SIMP method. 

     

     

    After that, it says: 'When minimum member size control is used, the penalty starts at 2 and is increased to 3 for the second and third iterative phases.'

     

     

    So my question is: when I run an optimisation with MINDIM on, Optistruct automatically sets DISCRETE=3 and DISCRETE=4? So trying to run an optimisation with MINDIM on and DISCRETE equal to a number I decide, is a nonsense?

     

     

     

     

     

    Can anyone answer this question?

     

     

    Thanks!

     

    Hi Vale, did you find an answer to your question? 

  • Altair Forum User
    Altair Forum User
    Altair Employee
    edited May 2017

    Hi,

     

    Have you tried DISCRETE on DOTPRM card?

     

    Goto OptiControls>>DISCRETE

  • Altair Forum User
    Altair Forum User
    Altair Employee
    edited May 2017

    Hi vale,

     

    Read: 'Member size control for Topology optimization - Minimum member size control', in Optistruct User Guide. I think it has a better explanation.

    Keep in mind that p is only a penalty factor. There must be something to choose which elements are penalized due the MINDIM card and DISCRETE acts on all elements.

    Both MINDIM and DISCRETE work different, as said in the user guide section mentioned above.

    However in my opinion, the only way you will understand it well, is to try both in a simple model such as a plate and analyse carefully the results.

     

    Hope it helps,

     

    Best regards,

    Gonçalo

  • killerswitch
    killerswitch New Altair Community Member
    edited May 2020

    Hi, I have been trying to optimize the frequency of a basic plate with a hole, the plate is fixed on two ends for all 6 DOF's  and a normal modal analysis is being run. The Dimensions for the plate are 550 mm x 550 mm with a thickness of 10 mm.  E = 70000, p = 0.33, density = 2.75e-6, wtmass conversion of .001.

     

    The first mode is coming at 204 Hz.

     

    Now after I add my design variable with the default base thickness in the optimization>topology menu. I proceed to add Volume fraction, and Frequency as my responses. 

    As my aim is to constrain the frequency I add a lower bound of 300 with the objective of minimizing frequency.

     

    now after i run the optimization on obstructionist and attach the s1.h3d file to see what the optimized results frequency are they are lower then the original not optimized plate at 195 Hz.

     

    I do not understand what I am doing wrong here. Any help would be greatly appreciated.

     

    Thank You.

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