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Topology optimization: entire design volume disappears

Topology optimization: entire design volume disappears

Topology optimization: entire design volume disappears

(OP)
Hello,

I want to do a topology optimization on a design volume with 3 other volumes being non-design volumes. All loads and constraints being on the non-design volumes. However I seem to be running into a problem setting up my optimization, I would be most grateful to get some help.

I setup my model in hyperworks and was able to get my results to show on Radioss so I suppose my meshing, loads and constraints have been properly setup.

I setup my optimization as following:

Design variable: PSOLID referencing to the Property I want to be the design volume, which is also PSOLID.

Optimization response: Volume Total

Objective: min / response = volume (my optimization response)

However after running Optistruct and looking at the results in Hyperview I see that the design volume is entirely empty starting from the first iteration and for the following 12 iterations.

Also, my output file shows that there seems to be a difference in volume between each iteration, I do not see the link between what is written there and what's shown in Hyperview:

 ------------------------------------------------------------------------------
 Element     Property          # of     Recommended Range    Max.  Viol.  Elem.
                               Viol.     Lower     Upper    Value  type    No.
 ------- ------------------- -------- --------- --------- --------- --- -------
 TETRA   Edge Angle                16        --     75.00     81.50  U    86159
 

(Scratch disk space usage for starting iteration =       19 MB)
(Running in-core solution)

Objective Function (Minimize VOLUM) =  6.49221E-03
No active constraints
Design Volume Fraction              =  9.00000E-01   Mass     =  1.75290E+01


 Subcase   Compliance
       1  4.525657E-04


                           RETAINED RESPONSES TABLE
------------------------------------------------------------------------------------
Response Type  Response    Subcase Grid/     DOF/   Response     Objective    Viol.
User-ID          Label     /Frqncy Element/  Comp     Value      Reference/     %  
                                   MID/PID/  /Reg                Constraint
                                   Mode No.                        Bound   
------------------------------------------------------------------------------------
       1 VOLUM volume           --       --  TOTL   6.492E-03 MIN
------------------------------------------------------------------------------------

ITERATION   1

Objective Function (Minimize VOLUM) =  4.67824E-03   % change =       -27.94
No active constraints
Design Volume Fraction              =  6.00000E-01   Mass     =  1.26312E+01


 Subcase   Compliance
       1  4.718218E-04


                           RETAINED RESPONSES TABLE
------------------------------------------------------------------------------------
Response Type  Response    Subcase Grid/     DOF/   Response     Objective    Viol.
User-ID          Label     /Frqncy Element/  Comp     Value      Reference/     %  
                                   MID/PID/  /Reg                Constraint
                                   Mode No.                        Bound   
------------------------------------------------------------------------------------
       1 VOLUM volume           --       --  TOTL   4.678E-03 MIN
------------------------------------------------------------------------------------

ITERATION   2

Objective Function (Minimize VOLUM) =  2.86427E-03   % change =       -38.77
No active constraints
Design Volume Fraction              =  3.00000E-01   Mass     =  7.73353E+00


 Subcase   Compliance
       1  6.865162E-04


                           RETAINED RESPONSES TABLE
------------------------------------------------------------------------------------
Response Type  Response    Subcase Grid/     DOF/   Response     Objective    Viol.
User-ID          Label     /Frqncy Element/  Comp     Value      Reference/     %  
                                   MID/PID/  /Reg                Constraint
                                   Mode No.                        Bound   
------------------------------------------------------------------------------------
       1 VOLUM volume           --       --  TOTL   2.864E-03 MIN
------------------------------------------------------------------------------------

ITERATION   3

Objective Function (Minimize VOLUM) =  1.95728E-03   % change =       -31.67
No active constraints
Design Volume Fraction              =  1.50000E-01   Mass     =  5.28467E+00


 Subcase   Compliance
       1  1.495673E-03


Thank you very much for your help,

Hugo

RE: Topology optimization: entire design volume disappears

Have you done the A arm optimisation tutorial right through from beginning to end?

Cheers

Greg Locock

SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.

RE: Topology optimization: entire design volume disappears

(OP)
I tried 3 times, following the exact instructions provided, but I ended up with the following error when running Radioss or Optistruct:

 
Created RAM scratch area: total size 200.00 MB

 INFORMATION #     742
 The dependent rotational d.o.f. of this rigid element is removed.
     RBE2 element id =       4035
 independent grid id =       2656
 a dependent grid id =       1772
 This is because there is no need to constrain the rotational d.o.f. of
 any of the dependent grids.

 INFORMATION #     742
 The dependent rotational d.o.f. of this rigid element is removed.
     RBE2 element id =       4036
 independent grid id =       2656
 a dependent grid id =       1731
 This is because there is no need to constrain the rotational d.o.f. of
 any of the dependent grids.

 INFORMATION #     742
 The dependent rotational d.o.f. of this rigid element is removed.
     RBE2 element id =       4037
 independent grid id =       2656
 a dependent grid id =       1690
 This is because there is no need to constrain the rotational d.o.f. of
 any of the dependent grids.

 INFORMATION #     743
 The total number of rigid elements, whose rotational dependent d.o.f.
 are removed because there is no need to constrain those d.o.f., is        89

 ERROR #     110 FROM SUBROUTINE preprbe2
 The dependent d.o.f. is constrained by grid or spc data.
 RBE2 element id =       4040
         grid id =       1770
       component =          1

                         ***** FATAL INPUT ERROR *****


 ERROR #     110 FROM SUBROUTINE preprbe2
 The dependent d.o.f. is constrained by grid or spc data.
 RBE2 element id =       4080
         grid id =       1605
       component =          2

                         ***** FATAL INPUT ERROR *****

RE: Topology optimization: entire design volume disappears

(OP)
I mostly followed the same step as the A arm for my own problem and seemed to get further without error so I continued with it.

I also tried it with a displacement constraint, but still got a empty design volume from the first iteration.

RE: Topology optimization: entire design volume disappears

HugoR, I pinged the Altair support team and the Director of Support and if you could contact support with a model they can help you.  We can then post the final solution back on eng-tips for everyone to see.

The error message you seen when going through the tutorial is mostly likely caused by placing a constraint on the dependent node of an RBE2.

RE: Topology optimization: entire design volume disappears

(OP)
Well in the example there is a component named rbe2. I am not sure how I placed a constraint on rbe2, so how would I go about not placing a constraint there?

I uploaded my carm example on rapidshare if anyone finds it simpler to find the mistake that way:
http://rapidshare.com/files/293012811/carm_hugo.hm.html

Furthermore the I uploaded my own problem at:
http://rapidshare.com/files/293013907/hugo_optimization.hm.html

Also about contacting support, should I contact them at:
http://www.altairhyperworks.ca/ClientCenterHWSupportForm.aspx?top_nav_str=1&product_id=7

I am not sure if it is okay for me as it seems to be more of a problem with my own Hypermesh skills than a software problem.

Thank you for answering!

Hugo

RE: Topology optimization: entire design volume disappears

(OP)
Hello,

I found out that when implementing my displacement constraint I had forgotten to link it to my loadstep. Once I linked it my model worked.

If anyone reads this with the same problem, my model did not work without a displacement variable and constraint.

RE: Topology optimization: entire design volume disappears

Yes, you can use that link for contacting support.  You can also send an e-mail to hwsupport@altair.com which I like because it saves you from filling out the web form.

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