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Subject: Re: Poll results for xansys - optimization
Author: Paris Altidis
Date: 2001-02-26 12:29:00

Amen.

Paris Altidis
Staff Engineer
Borg Warner Automotive
708-547-2719
paltidis@a...

> -----Original Message-----
> From: s-y.chen@u... [SMTP:s-y.chen@u...]
> Sent: Monday, February 26, 2001 10:28 AM
> To: xansys
> Subject: [xansys] Re: Poll results for xansys - optimization

> I think the numerical optimization is, just like all other computer
> programs, a tool to help you solve the problem, but it is not going to
> solve ALL your problems. This is just like FEA. FEA will help you solve
> your design problems, but not ALL your design problems. Today there are
> still a lot of companies believe FEA is not critical at all, and it is not
> worth the effort. It may be true, and may not be true. Same as numerical
> optimization.

> Optimization is focusing on solving problem with complicateinteraction
> between constraints/objective/etc.. Optimization WILL make you life easier
> if you know how to use it. For example, perhaps everyone already agrees
> today, that the parametric model is the way to go. Ok, we have a
> parametric model, we can iterate it easier, but, except for making
> mistake faster, are we doing anything better ? I doubt.

> Optimization was originated from mathematical programming. The name
> "programming" implies its nature very well - it is a mathematical model
> and methodology, you got to figure out the best way to fit your problem
> into the formulation.

> I have seen a lot of failed examples from the optimization process. From
> my own limited experience, 90% of them are due to improper modeling and
> problem formulation. And, of course a good optimizer is very important.
> It is really sad for a researcher in the field of optimization, to see
> some software vendors claiming they have such and such capability, and
> understand the software is doing something definitely wrong but there is
> nothing he can do about it. Some optimization software vendors just try to
> attract as many customers as possible, without even considering if their
> package can do it. After these users get discouraged, or get the wrong
> education, they usually become the attackers of this technology.

> Believe it or not there are some very famious software vendors doing
> something definitely wrong, which makes them only able to solve very
> simple cases. The users usually get excited about the advertisement, and
> begin to use it. But as the software doesn't get them anywhere for
> practical problems, they get disappointed, and jump to the conlusion that
> optimization is not practical at all.
> Or, even worse, the user believe that the program is correct and think
> there is no way to improve the design anymore. I am not talking about
> ANSYS. The optimizer in ANSYS is not very strong but ANSYS defintely knows
> its limitation and never tried to make the user very excited. I imagine
> that is the reason ANSYS leaves a programable interface to other
> optimizers. And, the architecture of ANSYS is almost for optimization.

> For the issue of parametric model, it was heavily studied in the 80's,
> and today several softwares are already able to rebuild the parametric
> model upon existing FE mesh (only). Usually this is then used to do
> preliminary optimization and give a good idea
> about what the shape should look like. Then the information will be given
> to the designer, and after the prliminary design it is
> given to the analysts again for checking and very detailed design. At this
> stage, usually there is not a lot you can change, and there will be a lot
> of geometric constraints. Then, if the analysts want to use optimization,
> the skills will really come to play now. I submitted a article regarding
> this issue to the ANSYS solution magazine in the end of last year, but I
> am not quite sure what happens since then.........

> This is only based my own experience though.

> Shen-Yeh Chen
> Honeywell Engines & Systems
> Phoenix, Arizona

> --- In xansys@y..., "Altidis, Paris (Bellwood)" wrote:
> > The ideal scheme would be :
> > a) Knowledge base Engineering (Not necessarily in electronic form) - to
> weed out unsuccessful scenarios. Experience may still be under your
> nose. Problem is, we don't look there.
> > b) Use your optimizer for the remainder.

> > Paris Altidis
> > Staff Engineer
> > Borg Warner Automotive
> > 708-547-2719
> > paltidis@a...

> > > -----Original Message-----
> > > From: Christopher Wright [SMTP:chrisw@s...]
> > > Sent: Friday, February 23, 2001 11:30 AM
> > > To: XANSYS
> > > Subject: Re: [xansys] Poll results for xansys - optimization

> > > >I think that I can overcopme the "fiddle factor" with
> optimization
> > > >if I see that the payoff is there.
> > > I may as well chip in here. There's really not much general value
> in
> > > optimization because it's restricted to a very narrow area.
> Problems like
> > > 'optimal' fillet radii are trivial and not worth learning the
> necessary
> > > vocabulary, let alone waiting around for results. Real engineering
> optima
> > > involve matters such as cost, schedule and producibility. Weight
> savings
> > > is sueful, but only if it comes with a cost or time savings. I
> once
> > > worked on a rib-stiffened cylindrical shell where the 'optimized'
> > > structure really saved a lot of weight by adding a great many
> small,
> > > closely spaced stiffeners. But the fabrication costs were
> monstrous--it
> > > wasn't an optimum anything.

> > > Engineering designs often require specific types of
> components--you're
> > > stuck with the off-optimum just because plate and fasteners and
> rolled
> > > shapes in any old size you want.

> > > The biggest problem (apart form inability to import parameterized
> CAD
> > > geometry) is that by the time you have enough information to
> 'optimize' a
> > > design, it's already pretty much cast in concrete, particularly if
> you're
> > > waiting on a CAD model. A good example is a pressure vessel with a
> flat
> > > head--you can figure out the 'optimum' combination of head and
> shell
> > > thickness for the least material, but FEA won't explain that a
> flat head
> > > is a rotten idea from the outset.

> > > OTOH, I daresay situations involving proof of concept lend
> themselves to
> > > both parameterization and optimization but the use of small models
> for
> > > studying physics seems to have gone out of fashion.

> > > Christopher Wright P.E. |"They couldn't hit an elephant from
> > > chrisw@s... | this distance" (last words of Gen.
> > > ___________________________| John Sedgwick, Spotsylvania 1864)
> > > http://www.skypoint.com/~chrisw

Posts possibly associated with message #21371AuthorDateScore
21301Poll results for xansys - optimizationDan Bohlen2001/02/23 
21303Re: Poll results for xansys - optimizationDanny Levine2001/02/23 
21311Re: Poll results for xansys - optimizationParis Altidis2001/02/23 
21321Re: Poll results for xansys - optimizationChristopher Wright1991/02/23 
21323Re: Poll results for xansys - optimizationMark Tate2001/02/23 
21325Re: Poll results for xansys - optimizationParis Altidis2001/02/23 
21334Re: Poll results for xansys - optimizationChristopher Wright1991/02/23 
21342Re: Poll results for xansys - optimizationFrank Exius2001/02/24 
21360Re: Poll results for xansys - optimizationShen-Yeh Chen2001/02/26 
21371Re: Poll results for xansys - optimizationParis Altidis2001/02/26 
25378Re: Poll results for xansys - optimizationChris Rogers2001/06/28