Topology optimization: entire design volume disappears

[HugoR]

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

 

[GregLocock]

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

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[HugoR]

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 *****

 

[HugoR]

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.

 

[BenAltair]

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.

 

[HugoR]

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

 

[HugoR]

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.

 

[BenAltair]

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.