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Subject: Re: Tet 95 Elements - Slower than Tet 92?
Author: Roberto Muccini
Date: 1999-01-18 05:07:00

Steve Owen wrote:

> From: Steve Owen

> Sorry to respond late to this thread. In thinking about ways to improve
> the pyramid transitions, I would appreciate some input about automating
> the TCHG command

> If the user is using 95s and does a tet mesh, is it reasonable to
> automatically convert all tets to 92s?

If not, then under what
> circumstances should you do the automatic conversion? If there are any
> pyramids in the mesh? Should we provide a keyopt (flag) on 95s to
> specify "always convert to 92s when it is a tet"?

I think this last option is a good compromise between different
needeings.

> Any comments on this would be appreciated.

> Steve Owen

> PS. There was a thread a few weeks ago regarding the FVMESH command. I
> have modified the FVMESH command to work with a set of detached
> elements. It is scheduled for release in Ansys 6.0.

> Steve Owen
> Senior Development Engineer
> ANSYS Inc., Pittsburgh, PA
> http://www.andrew.cmu.edu/user/sowen/

> > -----Original Message-----
> > From: Metrisin, Joseph T. [SMTP:metrisin@p...]
> > Sent: Monday, January 11, 1999 2:27 PM
> > To: 'xansys@o...'
> > Subject: [xansys] Re: Tet 95 Elements - Slower than Tet 92?

> > From: "Metrisin, Joseph T."

> > John,

> > You are correct. tet-shaped solid95's are much more expensive to
> > run than tet-shaped solid92's. ANSYS has a command called TCHG
> > to convert 95-tets to 92-tets. It is documented in version 5.5.1 but
> > is undocumented but available in 5.4. I agree that this should be
> > built into the transition meshing routines instead of having the user
> > run this command manually.

> > Joseph T. Metrisin

> > Structural Methods
> > Pratt & Whitney/Unitetd Technologies
> > M/S: 714-03
> > P.O. Box 109600
> > West Palm Beach, FL. 33410-9600

> > Phone: (561) 796-5967
> > Fax: (561) 796-8993

> > > From: Crawford, John[SMTP:John.Crawford@a...]
> > > Sent: Monday, January 11, 1999 2:11 PM
> > > To: ANSYS Users List
> > > Subject: [xansys] Tet 95 Elements - Slower than Tet 92?

> > > From: "Crawford, John"

> > > When ANSYS creates pyramid elements to transition from brick
> > elements
> > > (SOLID95) to tet elements (SOLID92) it makes them as SOLID95
> > elements.
> > > It also makes tet elements between the pyramid 95 and tet 92
> > elements,
> > > but it makes these transition tet elements as SOLID 95 elements too.
> > I
> > > was curious whether having SOLID95 tet elements instead of SOID92
> > tets
> > > woul have an impact on CPU time, so I made up a test case to
> > > iinvestigate.

> > > The test case was a cantilever beam (classic test problem...) fixed
> > on
> > > one end and loaded with a uniform pressure on it's top surface. The
> > > cantilever is made from 3 volumes. The end volumes are fairly
> > small,
> > > while the middle volume is constitutes maybe 75% of the total beam.
> > The
> > > volume on the fixed end was meshed using SOLID95 brick elements,
> > while
> > > the volume on the tip was meshed using SOLID92 tetrahedral elements.
> > > The large volume between them was meshed using SOLID95 pyramid and
> > tet
> > > elements, which ANSYS automatically makes for the transition between
> > > brick and tet element shapes.

> > > I saved this model, and then used a macro to modify the tetrahedral
> > > elements in the middle volume to be regular SOLID92 tets. I then
> > saved
> > > this model. Both models had 18306 degrees of freedom.

> > > I ran each model 5 times, using a macro to get the starting CPU
> > time,
> > > perform the solution, get the ending CPU time, and display the
> > elapse
> > > CPU time to me. The model which had SOLID95 tet elements averaged
> > > 34.82 CPU seconds to run, while the model which had all tets
> > configured
> > > as SOLID92 elements took an average of 22.74 CPU seconds. Very
> > > interesting. A big difference in speed.

> > > I'd appreciate hearing if anyone else has noticed this behaviour.
> > I'd
> > > also like to hear from someone at ANSYS Inc. why this takes place.
> > I
> > > have a good idea why, but I'd like to hear why this happens. Also,
> > now
> > > that the problem is recongized (assuming my test case is correct and
> > > other people duplicate it) would it be possible for ANSYS Inc. to
> > modify
> > > the meshing algorithm so it will create tets as SOLID92 elements so
> > we
> > > can have the fastest solution possible?

> > > I have appended the macro I wrote to convert the SOLID95 tet
> > elements to
> > > SOLID92 tets if anyone is interested in trying to confirm my
> > results.

> > > John Crawford
> > > AlliedSignal Engines
> > > Phoenix, AZ
> > > john.crawford@a...

> > > /nopr
> > > !
> > > ! brk2tet.mac a macro which converts degenerate SOLID95 tet
> > elements
> > > ! to SOLID92 tet elements
> > > !
> > > ! usage: brk2tet (no arguments)
> > > !
> > > ! written by: John Crawford date:1-6-99
> > > !
> > > ! check to make sure that we have elements selected
> > > *if,elmiqr(0,13),gt,0,then
> > > elid_=0
> > > ! create the type 92 element so we can create tets from bricks
> > > et,etyiqr(0,14)+1,92
> > > type,etyiqr(0,14)
> > > ! turn off shape checking and model associativity to avoid
> > > ! error/warning messages. they will be turn back on later.
> > > shpp,off
> > > modm,noch
> > > *do,i_,1,elmiqr(0,13)
> > > elid_=elnext(elid_)
> > > ! get the current elements mat, real, type values
> > > *get,mat_,elem,elid_,attr,mat
> > > *get,real_,elem,elid_,attr,real
> > > *get,type_,elem,elid_,attr,type
> > > ! get the element name to see if it is a 95
> > > *get,enam_,etyp,type_,attr,enam
> > > *if,enam_,eq,95,then
> > > ! check to see if this element has 10 nodes on it
> > > cm,node_,node
> > > cm,elem_,elem
> > > esel,s,elem,,elid_
> > > nsle,s
> > > ! if we have 10 nodes on this 95 element, convert it to
> > > ! a 92
> > > *if,ndinqr(0,13),eq,10,then
> > > ! set values for mat and real, so they will stay unchanged
> > > mat,mat_
> > > real,real_
> > > ! get the node numbers we need to create the 92 element
> > > n1_=nelem(elid_,1)
> > > n2_=nelem(elid_,2)
> > > n3_=nelem(elid_,3)
> > > n4_=nelem(elid_,5)
> > > n5_=nelem(elid_,9)
> > > n6_=nelem(elid_,10)
> > > n7_=nelem(elid_,12)
> > > n8_=nelem(elid_,17)
> > > n9_=nelem(elid_,18)
> > > n10_=nelem(elid_,19)
> > > ! modify the 95 element, converting it to a 92 and changing
> > > ! the node definition
> > > *msg,info,elid_
> > > Recreating element %i as a SOLID92 element
> > > emod,elid_,type,etyiqr(0,14)
> > > emod,elid_,-1,n1_,n2_,n3_,n4_,n5_,n6_,n7_,n8_
> > > emod,elid_,-9,n9_,n10_
> > > *endif
> > > cmse,s,elem_
> > > cmse,s,node_
> > > cmde,elem_
> > > cmde,node_
> > > *else
> > > *msg,info,elid_
> > > Element %i is not a SOLID95 element and was not recreated as a
> > SOLID92
> > > element
> > > *endif
> > > *enddo
> > > shpp,on
> > > modm,check
> > > *else
> > > *msg,info
> > > No elements are currently selected
> > > *endif
> > > /gopr

Posts possibly associated with message #287AuthorDateScore
177Tet 95 Elements - Slower than Tet 92?John Crawford1999/01/11 
179Re: Tet 95 Elements - Slower than Tet 92?Joe Metrisin1999/01/11 
180Re: Tet 95 Elements - Slower than Tet 92?Robert McClain1999/01/11 
183Re: Tet 95 Elements - Slower than Tet 92?Monte McGlaun1999/01/12 
195Re: Tet 95 Elements - Slower than Tet 92?Steve Ferguson1999/01/12 
284Re: Tet 95 Elements - Slower than Tet 92?Steve Owen1999/01/16 
287Re: Tet 95 Elements - Slower than Tet 92?Roberto Muccini1999/01/18 
288Re: Tet 95 Elements - Slower than Tet 92?Gerhard Mueller1999/01/18 
289Re: Tet 95 Elements - Slower than Tet 92?John Crawford1999/01/18 
297Re: Tet 95 Elements - Slower than Tet 92?Joe Metrisin1999/01/18