XANSYS Message: 179 [Go back to message list]
[bookmark on del.icio.us]
No rating yet
Rate item:

Subject: Re: Tet 95 Elements - Slower than Tet 92?
Author: Joe Metrisin
Date: 1999-01-11 14:26:00

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 #179AuthorDateScore
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