Showing results for 
Search instead for 
Do you mean 
Reply

Prohibit displacement in -z direction with constraints?

Is it possible to set up a constraint to allow translation in positive z (dof3) direction, yet disallow translation in the negative z direction?

User defined constraints only allows the choice between fixed (in both directions), free and displacement.

The point is to be able to simulate a metal plate with that is bolted to and in contact with an underlying platform (the platform is infinitely stiff). A pin welded to the middle of the top of the plate is subjected to a force in the y direction causing the plate to have a rotating moment around the x axis. Because the plate is bolted to a platform displacement in -z (dof3) is not possible. All other directions are. Can I set up this without modeling the bottom platform?

Thanks in advance!

Regards Jakob
6 REPLIES

Re: Prohibit displacement in -z direction with constraints?

Is it possible to set up a constraint to allow translation in positive z (dof3) direction, yet disallow translation in the negative z direction?

User defined constraints only allows the choice between fixed (in both directions), free and displacement.

The point is to be able to simulate a metal plate with that is bolted to and in contact with an underlying platform (the platform is infinitely stiff). A pin welded to the middle of the top of the plate is subjected to a force in the y direction causing the plate to have a rotating moment around the x axis. Because the plate is bolted to a platform displacement in -z (dof3) is not possible. All other directions are. Can I set up this without modeling the bottom platform?

Thanks in advance!

Regards Jakob

Jakob,

This is not possible with constraints. You can use linear contact or CGAP elements to enforce this behavior.

Regards,
Jim
--
Jim Bernard
Advanced Applications Engineer

Siemens PLM Software
2000 Eastman Dr., Milford, OH 45150-2712
www.siemens.com/plm

Re: Prohibit displacement in -z direction with constraints?

Thanks for the tip!
But can I use CGAP elements or linear contact if I only have one body (the plate I wish to simulate)? Or must there be a seperate body to "connect to"?

Re: Prohibit displacement in -z direction with constraints?

Is it possible to set up a constraint to allow translation in positive z (dof3) direction, yet disallow translation in the negative z direction?

User defined constraints only allows the choice between fixed (in both directions), free and displacement.

The point is to be able to simulate a metal plate with that is bolted to and in contact with an underlying platform (the platform is infinitely stiff). A pin welded to the middle of the top of the plate is subjected to a force in the y direction causing the plate to have a rotating moment around the x axis. Because the plate is bolted to a platform displacement in -z (dof3) is not possible. All other directions are. Can I set up this without modeling the bottom platform?

Thanks in advance!

Regards Jakob

for linear contact, you would need a separate body/mesh. For CGAP, you would need a separate grid that you would SPC in all DOF.
--
Jim Bernard
Advanced Applications Engineer

Siemens PLM Software
2000 Eastman Dr., Milford, OH 45150-2712
www.siemens.com/plm

Re: Prohibit displacement in -z direction with constraints?

Thank you Jim. I'll give that a try.

Regards,
Jakob

Re: Prohibit displacement in -z direction with constraints?

Dear Jakob,
Just as add-on to Jim comments: in NX Nastran you can achieve the desired
behavior using a node-to-node CGAP compression-only element "linear contact
constraint", and no need to run a nonlinear analysis, simply linear static
SESTATIC (SOL 101) analysis is OK. The basic properties you must enter to
define the CGAP element in the preprocessor are compression stiffness, gap
allowable displacement (if zero or bigger than zero, then compression-only
gap), gap friction, and gap orientation (also you can enter shear stiffness,
and traction stiffness).
In order to activate the contact algorithm you will have to add BCSET=1 in
the case control section (if running FEMAP preprocessor, just click on "Gaps
as Contacts" in NASTRAN Bulk Data Option. If running NX Advanced Simulation
preprocessor just click on "Treat CGAP as Linear Contact Element" in the
Edit Solution), then the solver will iterate to get a contact converged
solution. The output is similar to the following (solution monitor will also
show the XY Plot of contact convergence progress):
^^^
^^^BEGIN CONTACT ITERATIONS FOR SUBCASE NUMBER 1
^^^
^^^
^^^CONTACT ITERATION NUMBER 1
^^^
^^^NUMBER OF INACTIVE CONTACTS: 0
^^^NUMBER OF ACTIVE OPEN CONTACTS: 2
^^^NUMBER OF STICKING CONTACTS: 0
^^^NUMBER OF SLIDING CONTACTS: 0
^^^BEGIN CONTACT FORCE ITERATION
^^^
^^^
^^^CONTACT ITERATION NUMBER 2
^^^
^^^NUMBER OF CONTACT STATUS CHANGES: 2 (NCHG:
0)
^^^NUMBER OF INACTIVE CONTACTS: 1
^^^NUMBER OF STICKING CONTACTS: 0
^^^NUMBER OF SLIDING CONTACTS: 1
^^^BEGIN CONTACT FORCE ITERATION
^^^CONTACT FORCE CONVERGENCE RATIO: 2.464475E-09 (CTOL:
0.000000E+00)
^^^
^^^
^^^FINAL CONTACT STATUS AT CONVERGENCE
^^^
^^^NUMBER OF CONTACT STATUS CHANGES: 0 (NCHG:
0)
^^^NUMBER OF INACTIVE CONTACTS: 1
^^^NUMBER OF STICKING CONTACTS: 0
^^^NUMBER OF SLIDING CONTACTS: 1
^^^
^^^CONTACT ITERATION CONVERGED
^^^
.../..
C O N T A C T F O R C E S
POINT ID. TYPE T1 T2 T3
R1 R2 R3
8 G 0.0 3.274576E+03 0.0 0.0
0.0 0.0
13 G 0.0 -3.274576E+03 0.0 0.0
0.0 0.0
1 SESTATIC (SOL101)
JANUARY 19, 2010 NX NASTRAN 9/17/09 PAGE 22
0
I N I T I A L C O N T A C T S E P A R A T I O N D I S
T A N C E
POINT ID. TYPE DISTANCE
1 G 0.0
2 G 0.0
1 SESTATIC (SOL101)
JANUARY 19, 2010 NX NASTRAN 9/17/09 PAGE 23
0
D E F O R M E D C O N T A C T S E P A R A T I O N D I
S T A N C E
POINT ID. TYPE DISTANCE
1 G 6.054296E-02
2 G 1.038883E-15
By the way, a bug exist in the POINT ID identification for INITIAL CONTACT
SEPARATION DISTANCE and DEFORMED CONTACT SEPARATION DISTANCE, I will have to
file an IR.
Best regards,
Blas.
--
~~~~~~~~~~~~~~~~~~~~~~
Blas Molero Hidalgo
Ingeniero Industrial
Director
IBERISA
Edificio Ercilla
Rodríguez Arias 23, 3º - Dpto. 19
48011 BILBAO (SPAIN)
Tel. (+34) 94 410 65 50
Fax. (+34) 94 470 26 34
E-mail: info@iberisa.com
WEB: http://www.iberisa.com
"jjung" escribió en el mensaje de
noticias news:jjung.45i4cn@noreply.bbsnotes.ugs.com...
>
> Is it possible to set up a constraint to allow translation in positive z
> (dof3) direction, yet disallow translation in the negative z direction?
>
> User defined constraints only allows the choice between fixed (in both
> directions), free and displacement.
>
> The point is to be able to simulate a metal plate with that is bolted
> to and in contact with an underlying platform (the platform is
> infinitely stiff). A pin welded to the middle of the top of the plate is
> subjected to a force in the y direction causing the plate to have a
> rotating moment around the x axis. Because the plate is bolted to a
> platform displacement in -z (dof3) is not possible. All other directions
> are. Can I set up this without modeling the bottom platform?
>
> Thanks in advance!
>
> Regards Jakob
>
>
> --
> jjung
> ------------------------------------------------------------------------
> jjung's Profile:
> http://bbsnotes.ugs.com/vbulletin/member.php?userid=204112
> View this thread: http://bbsnotes.ugs.com/vbulletin/showthread.php?t=41224
>

Re: Prohibit displacement in -z direction with constraints?

And just to add to this, NX Nastran does allow one-way constraints using the
SUPORT and CDITER entry, but it is described in the documentation as being
obsolete, for reasons that I am not aware. This allows a constraint defined
via the SUPORT entry to be treated as only being allowed to "peel" in the
positive direction of the coordinate direction in which the constraint is
applied (thus you need to ensure you have a coordinate system/axis aligned
in your peel direction - in your case, Z). PARAM,CDITER,n defines the
number of contact iterations you are prepared to accept - which is a little
agricultural, and may be why this method is considered obsolete.
"jjung" wrote in message
news:jjung.45i4cn@noreply.bbsnotes.ugs.com...
>
> Is it possible to set up a constraint to allow translation in positive z
> (dof3) direction, yet disallow translation in the negative z direction?
>
> User defined constraints only allows the choice between fixed (in both
> directions), free and displacement.
>
> The point is to be able to simulate a metal plate with that is bolted
> to and in contact with an underlying platform (the platform is
> infinitely stiff). A pin welded to the middle of the top of the plate is
> subjected to a force in the y direction causing the plate to have a
> rotating moment around the x axis. Because the plate is bolted to a
> platform displacement in -z (dof3) is not possible. All other directions
> are. Can I set up this without modeling the bottom platform?
>
> Thanks in advance!
>
> Regards Jakob
>
>
> --
> jjung
> ------------------------------------------------------------------------
> jjung's Profile:
> http://bbsnotes.ugs.com/vbulletin/member.php?userid=204112
> View this thread: http://bbsnotes.ugs.com/vbulletin/showthread.php?t=41224
>