Is the use of CGAP elements better suited for Sol106 rather than Sol101

[tonmeister]

Hi there, this topic might have been covered in a different thread - I apologize in advance if it is the case.
I am interested to know if the use of CGAP elements is better suited for Sol106 rather than Sol101. Does Sol106 iterate better gap elements than sol101? Any feedback on the topic would be great.


Thanks for any reply.

 

[nlgyro]

CGAP's are suited only for a SOL106.

When CGAP's are used for SOL101, NASTRAN equates them to CELAS's with the CGAP's opening stiffness values.

Linear gaps (CDITER's) are the equivalent for doing a contact analysis in SOL101.

 

[BlasMolero]

Dear Tonmeister,
I run a lot CGAP elements for both linear & nonlinear static models, for simply models are quickly to setup and run, but for complex geometry the use of LINEAR contact surface-to-surface is more powerful, of course. And for complex nonlinear contact (plus other nonlinearities) the use of Advanced Nonlinear module SOL601 is mandatory.

Please note when CGAP elements are included with linear contact using NX NASTRAN (solution 101 and consecutive solutions 103, 111 and 112), the system cell (412) OLDGAPS determines how CGAPs are treated, I will explain:

• When a BCSET case control command exists, CGAP elements are treated as linear contact elements if the system cell (412) OLDGAPS is set to 0 (default). You can use CGAP elements this way with surface-to-surface contact defined (BCTSET bulk entries exist), or without (no BCTSET bulk entries exist). In the case where no surface-to-surface contact is defined, “n” on the BCSET case control command can point to a BCTPARM bulk entry which optionally defines PENN, PENT or PENTYP for the CGAP/linear contact elements, or to nothing if a BCTPARM bulk entry does not exist (an integer value for “n” is still required in this case).

• If the system cell OLDGAPS is set to 1, the CGAP will be treated the same as a linear spring element. Remember, for linear solutions without contact defined, and for all other solution sequences, the CGAP will be treated the same as a linear spring element, and remains linear with the initial stiffness.
• In a linear static analysis (SOL101) if you use FEMAP with NX NASTRAN and you want the CGAP element to run as a contact element (not spring), then make sure to activate GAPS AS CONTACT in the NASTRAN BULK Data Options.

• The CGAP element is treated as a nonlinear gap element when used in the nonlinear solutions 106, 129, 153, and 159, in which the gap conditions update as the nonlinear solution iterates.

Best regards,
Blas.


~~~~~~~~~~~~~~~~~~~~~~
Blas Molero Hidalgo
Ingeniero Industrial
Director

IBERISA
48011 BILBAO (SPAIN)
WEB:

http://www.iberisa.com

Blog de FEMAP & NX Nastran:

http://iberisa.wordpress.com/

 

[tonmeister]

Thank You both for your replies. Blas I appreciate very much the time spent on your detailed answer.
I have used linear gap elements with sol101 for quickness of run and for simplicity. I am aware that sol101 treats the gap pretty much as an MPC (closed versus open). But I was not getting or capturing all the complex deflection in the model with sol101. Also I have started with around 200 gap elements at the interface. I tried to go to a couple of thousand linear gaps with sol101 but I wasn't getting better results. from both of your emails I decided to go for Sol106 for better convergence and for higher number of iterations. We'll see how it goes.
thank you again
Ton