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Subject: Re: Superelement in ANSYS/Substructuring
Author: K.S. Raghavan
Date: 2001-02-01 05:06:00

Christopher Wright wrote:

> >You may be able to figure out how to get at the superelement matrices. As
> >a novice user, the chance of success is not good.

> I'm inclined to agree. You can write the matrices off to a file, but I
> think it'll take a little fiddling to make any use of them. The
> substructure matrices are laid out for running in ANSYS, so there aren't
> any guarantees that anything is transportable to another package.

> When you do a substructure run you can opt to generate a force vector
> which is the equivalent of whatever loads exist when the substructure
> gets generated, but all you can do for variable loadings is to scale the
> vector. I don't think there's any practical way to apply loads otherwise
> except for concentrated forces at master DOF.

> I tried something of the sort with a controls guy looking to design a
> control system for a flexible robot arm and we got nowhere. Part of the
> reason was that neither of us spoke the other's language, but the
> substructure matrices aren't supposed to fit anything but ANSYS. I've
> been up against some seriously confusing situations, but nothing like the
> controls guy trying to explain just what he wanted from the matrix. I did
> some fiddling around with mass matrices once when I was going through a
> verification exercise and I go a sort of feel for things, so if you're
> willing to take the time to do this very carefully you might have a shot.

> 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

Stephane,

Chris has a lot to convey in his post.

I wish to add that , using Substructures approach you are not likely
to get what you have in mind. If a large structure is split into two or more
substructures it is essential that adjoining substructures have matching
set of nodes on common boundaries. You ,thus , cannot have a substructure
with fine mesh adjacent (physically) to another substructure having coarse
mesh. If you deliberately keep mismatching mesh densities some nodes
of the finer mesh remain free and hence the results will be erroneous.

I also wish to reiterate what I said in my earlier post in this thread. If
your sole
interest is in getting accurate results in a specific zone of interest ,
without
recourse to fine mesh over the entire structure , submodelling is the best
bet.
There is nothing scary (other than perhaps submodellophobia)
about the approach and we use it regularly.

OTOH if you wish to generate you wish to generate superelement matrices
you need to know more than what is transparent in the manuals.

Cheers.. raghavan (BHEL , Hyderabad , INDIA)

Posts possibly associated with message #20730AuthorDateScore
20651Superelement in ANSYS/Substructuringsbordas@2001/01/30 
20655Re: Superelement in ANSYS/SubstructuringMark Rodamaker2001/01/30 
20659Re: Superelement in ANSYS/SubstructuringK.S. Raghavan2001/01/30-10
20724Re: Superelement in ANSYS/SubstructuringChristopher Wright2001/01/31 
20730Re: Superelement in ANSYS/SubstructuringK.S. Raghavan2001/02/01 
20735Re: Superelement in ANSYS/SubstructuringJason Husband2001/02/01 
20740Re: Superelement in ANSYS/SubstructuringChristopher Wright1991/02/01 
20742Re: Superelement in ANSYS/SubstructuringOsman Buyukisik2001/02/01 
20747Re: Superelement in ANSYS/SubstructuringChristopher Wright1991/02/01 
20768Re: Superelement in ANSYS/SubstructuringK.S. Raghavan2001/02/02 
20783Re: Superelement in ANSYS/SubstructuringChristopher Wright2001/02/02