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Subject: Re: Superelement in ANSYS/Substructuring
Author: Jason Husband
Date: 2001-02-01 09:10:00

Raghavan
If I remember correctly, the original post was something about a crack
growth in a selected region and using superelements for the rest of the
structure..

Based on this, I strongly disagree with your recommendation for
submodelling. In a coase model used for obtaining cut boundary
displacements, the values are dependent on the size of the crack inside
the region of interest. I believe what you are suggesting will not work
correctly.

I believe superelements are definately the way to go here.

Jason Husband
QuEST
Greenville, South Carolina, USA

K.S. Raghavan wrote:

> 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 #20735AuthorDateScore
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