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Mixing Optimization on Maximal Stiffness (freq) "WITH" Minimal Weight

I am setting up for a "FREE SIZING" optimization,
of a CQUAD4 only structure…
yup… Shell Thickness design variable(s)

I set up:

DRESP1 1 TOT_MASS MASS
DRESP1 2 FRSTMODE FREQ 1
DRESP2 3 COMBINED 222
DRESP1 1 2

DEQATN 222 … blah blah blah (this is not where it fails)

DESOBJ can occur in ONLY ONE PLACE in the Case Control Section

So I try DESOBJ(MAX)=3 above my ANALYSIS MODES Subcase #1
cuz MASS response is 'global'

Failing that I read the OUT file and also read the thoroughly helpless documentation* with a fine tooth comb and discover DESOBJ MUST reside within the Subcase (1 in this case) if it needs the data derived from the subcase, which is indeed the case here cuz MODE 1 eigenvalue(freq) is dependent on it. There's other ways to handle the database internally but some dufus didn't think about this. By the way I come from days of MSC SOL 200 in the 90's and sensitivity analysis in the 80's so I am pretty good at desvar-ing and dresp-ing and sorta know what I am talking about in the realm of size type optimization in any case…

But then again I think from some hacking, MASS wants DESOBJ to link to a 'global' response, and so it desires DESOBJ up ABOVE the SUBCASE. (ROLLS EYES about the over-sight of how someone embellishing this Nastran (lawsuit) derived software got these all to link up)

Mind you, these are ALL "D"RESPonses!!! and privy to internal DMAP databases, where the optimization module could pull response data from.

Anyhoo! My DEQuATioN is in want of a superposition of FREQ and inverse of MASS to try and maximize on and I did this in the 90's successfully. Now they are Oil and Water!
What gives!??!!!

Recapping,,,
DESOBJ(MIN)=1 ABOVE Modal Subcase works
DESOBJ(MAX)=2 WITHIN Modal Subcase works
DESOBJ(MAX)=3 NOWHERE DOESN'T WORK! !@#$%^

ANY MAGICAL UNDOCUMENTED METHODS TO HANDLE THIS PROBLEM?Thank you. ================
Footnote from above regarding 'thoroughly helpless documentation'*
*You know, I keep seeing answer comments about telling the poster to 'go check' on the documentation a lot on this forum as a cop out answer to actually giving it (I mean, when I take some effort to answer questions on social media I usually am considerate enough to actually provide meticulous and thorough answers but,,, oh well, that's just me). The documentation for almost everything I had to look up is such a half-donkeyed slap together of info that is very cryptic. They always seem to miss that one bit of very important infrormation, in perfunctory and irrelevant way of presenting explanation. This forum would be less noisy with some simple questions if some customer-oriented thought went into those documents. Sad~ Sigh~

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MITCHELL_21455

I wonder if Normal (not 'Free') Sizing works any different

Adriano_Koga

i think you can accomplish that by using DRESP2 and the DRESP1L option.

By providing the FREQ resposnse the modal Subcase and for the mass response, leave it as 0.

Then the Response can bo above the subcase section.

I've used a similar approach once, for DRESP3 with Compose.

$$
$$ OPTIRESPONSES Data
$$
DRESP1 1 Mass MASS

DRESP1 5 frf_ac1 FRACCL M-TZ 12795
DRESP1 6 mode FREQ 9

DRESP3 4 K_w COMPOSE Kwh_v2

DRESP1LV 1 0 5 2 ALL

$$
$$ OPTICONSTRAINTS Data
$$
$

MITCHELL_21455

Hello again Adriano

Having seen your answer, I am getting my hopes up and trying to figure out what you are saying. Would you mind making the answer a bit more applicable to my case, because the whole dresp1LV thing and all the subsequent parameters are very very very cryptic. Is it just me…?? go figure.

Anyway… here I am having some trouble understanding:

You wrote: By providing the FREQ resposnse the modal Subcase and for the mass response, leave it as 0. WHAT am I leaving 0 again? does 0 signify something like 'global'?

Can you briefly write out DRESP2 version of what you are indicating?

DESOBJ(MAX)=3

Subcase 1 section
…. ANALYSIS MODES
…. METHOD(STRUCTURE) = 1
… SPC = 1
$ A.Koga indicates DESOBJ doesn't have to be in this subcase section

BEGIN BULK

DSIZE 1 PSHELL 3
+ THICK 0.001 0.2

DRESP1 ……. 1 ……. TOT_MASS …… MASS ……. 0 ???
DRESP1 ……. 2 …….  FRSTMODE …….  FREQ …….  1
DRESP2 ……. 3 ……. COMBINED …….  222
+ ……. DRESP1LV 0? …….  1 …….  2 …… ???

DEQATN 222 … that is a function of DRESP #1 and #2

Adriano_Koga

you're correct;

DRESP1L called inside the DRESP2 means you're calling as SCALAR argument a DRESP1 value TIED to a specific LOADCASE.

DRESP1LV does the same, but for a VECTOR, like FRF response.

So, when calling a DRESP1L inside a DRESP2, you're able to combine a subcase dependent response, such as FREQ and a subcase independent subcase, such as mass, by setting the mass to "loadcase 0" as for global.

For your case it would be probably something like