Min/Max Member Size

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

I've been running 3D Topology Optimizations and have been playing around with my Min/Max member size.   However, I don't see much change in my results between numerical values for max and min member size, unless I turn the feature off (in which I get a handfull of disconnects).  I took a Optistruct class and have read a few tutorials, but have yet to get a clear answer on what the value for max and min size is actually doing.  Plus, when I decreased my mesh size, I get an warning saying my min size is too big.

 

Can someone please explain what exactly I am setting when I change this value - is it a relation of my mesh size or unit size?  And if so, what should I set it at?  I'm 3D printing so manufacturing limitations aren't significantly pertinent.  However, If I don't set them I get obvious bad results.

 

Thanks

-Dave

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Answers

  • tinh
    tinh Altair Community Member
    edited October 2014

    Hi Dave

    did you read the tutorial about optimization with min size control?

    it said MINDIM should be 3 times larger than average element size. Think that you have a member size is only 1 element (= element size), when you verify result, you may want to remesh it, and after remesh the result is changed, so 1-element member size is not reliable.

  • Altair Forum User
    Altair Forum User
    Altair Employee
    edited October 2014

    Hi Dave,

     

    As Tinh said, MINDIM has a relationship with the element size and is different for 2D and 3D elements.

     

    From OptiStruct help:

     

    The average element size for 2-D elements is calculated as the average of the square root of the area of the elements, and for 3-D elements, as the average of the cubic root of the volume of the elements.

    This recommendation is enforced when combined with other manufacturing constraints, and if the defined MINDIM is less than this value, it will be reset to a default value equal to 3 times the average element size. Similarly, if the defined MINDIM is larger than 12 times the average element size, it will be reset to a value equal to 12 times the average element size. 

     

    Please refer to Member Size Control for Topology Optimization for more information.

  • ElineH
    ElineH Altair Community Member
    edited May 2020

    Hi,

     

    I had a question about this.

     

    I have a model with element size 1. When I optimize it and apply a minimal member size constraint of 1, 2 and 3, all 3 results are different. 

    Can someone explain why since I understood that when I put 1 or 2, the minimal member size will be set to 3 and all 3 results should be the same.

     

    Thank you!

  • tinh
    tinh Altair Community Member
    edited May 2020

    Hi

    I am not sure but you can check it in *.out file

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