Learning Forum

[Tiisora]

Hi everyone,

I am learning about LS Dyna. When I check the pressure results, the color scale shows some negative pressure. Is this an error? And how can I fix it?

Thanks advance!!

[Raman Babu]

Hello Tisora,

I think you are using pressure option available under stress fringe component for plotting pressure.

This pressure shows a mean stress value which can be negative. If you are interested in contact pressure, please write out intfor file and use it for postprocessing contact Pressure.

[Tiisora]

Hi Raman Babu, 

Thanks for your reply.

I was able to get the desired results.

But I still have some questions, I hope you can help me.

1, When I read in document "Contact force data can be recorded with *DATABASE_RCFORC,*DATABASE_NCFORC, and *DATABASE_BINARY_INTFOR". I didnt see *DATABASE_RCFORC,*DATABASE_NCFORC. it just has RCFORC and NCFORC in ASCII_option, is it ok? and I forgot to select NCFORC but it still has results. So, what is the difference between RCFORC and NCFORC?

2, When I set up, I use Contact_Force_Transducer, is that right? and when I set SURFA and ignore SURFB, I can see the pressure. But when I assign 2 parts to 2 SURF A&B. I only see the pressure in SURFA. if I want to see the pressure in 2 parts, do I need create a Set part for 2 parts? or did I make something wrong during the setup?

[Raman Babu]

Yes, *DATABASE_RCFORC and *DATABASE_NCFORC are available through the ASCII option. You can enable the RCFORC and NCFORC options to generate these files.

• RCFORC contains resultant contact forces for the slave and master sides of each contact interface.
• NCFORC provides contact forces at each node. To generate this file, the *DATABASE_NCFORC command must be included in the input deck. Additionally, one or more contact print flags must be set (SPR and MPR on Card 1 of *CONTACT). Only surfaces with a print flag value of 1 will have their nodal contact forces output to the NCFORC file.

*CONTACT_FORCE_TRANSDUCER_PENALTY is used for single surface contacts to output RCFORC data between the bodies. A force transducer does not produce any contact forces and thus does not affect the results of the simulation. A force transducer simply measures contact forces produced by other contact interfaces defined in the model. 

Please refer below link for more information.

https://www.dynasupport.com/tutorial/contact-modeling-in-ls-dyna/contact-output

 

[Tiisora]

Thank you very much ^^