Cancel
Showing results for 
Search instead for 
Did you mean: 

Center of Gravity Calculation including Non Structural Mass

Pioneer
Pioneer

Hi,

 

I am trying to calculate COG of my assembly but the option Tools>Mass Properties>Mesh Properties only gives me the COG when structured mass is included. I want to add NSM and then calculate my COG. 

 

Is there a way that can be done?

 

Thank You,

Bhumika

7 REPLIES

Re: Center of Gravity Calculation including Non Structural Mass

Siemens Phenom Siemens Phenom
Siemens Phenom

The Mass Properties > Mesh Properties command does take into the value of NSM added to a property.

 

What version are you using?  Also, can you post a sample model - I have a sample attached.

 

2017-10-23_13-17-28.jpg

Best Regards,
Chip Fricke
Principal Applications Engineer - Femap Product Development

Re: Center of Gravity Calculation including Non Structural Mass

Pioneer
Pioneer

Hi Chip,

 

I am using version 11.3.2 

I have a significant amount of NSM which I need to include in the structure. But it does not count towards the structural integrity.

 

Thank You

Re: Center of Gravity Calculation including Non Structural Mass

Siemens Phenom Siemens Phenom
Siemens Phenom

Unfortunately, you cannot assign NSM to Solid Element Properties.

 

As an alternative, for coatings, you can place shell elements with a very low stiffness and zero density and assign the NSM value to the shell property.  You could also use Mass Elements attached to the solids using RBE3 elements that do not add stiffeness.

Best Regards,
Chip Fricke
Principal Applications Engineer - Femap Product Development

Re: Center of Gravity Calculation including Non Structural Mass

Solution Partner Phenom Solution Partner Phenom
Solution Partner Phenom

Dear Bhumika,

As an add-on to great Chip comments, the problem here is not related with FEMAP, but NX NASTRAN. 

According the NX NASTRAN Quick Reference Guide (QRG) for the NSM, NSM1, NSML, and NSML1 nastran entries the properties you can use are PBAR, PBARL, PBEAM, PBEAML, PBCOMP, PCOMP, PCOMPG, PROD, CONROD, PBEND, PSHEAR, PSHELL, PTUBE, and PRAC2D.

Then as you can see, applying the NonStructural Mass Regions to the faces of solid elements is not supported by NX Nastran, therefore FEMAP do not include it in the calculation of Mass Properties and Center of Gravity of solids, OK?. 

For workarounds, the coating technique is my recommendation.

Best regards,
Blas.

Blas Molero Hidalgo, Ingeniero Industrial, Director
IBERISA • 48004 BILBAO (SPAIN)
WEB: http://www.iberisa.com
Blog Femap-NX Nastran: http://iberisa.wordpress.com/

Re: Center of Gravity Calculation including Non Structural Mass

Pioneer
Pioneer

Hello Blas and Chip,

 

I tried adding mass elements to the assembly using RBE3 and when I checked under Tools>Mass properties>mesh property, it still shows me only structural mass included with an added mass which is from mass elements and no NSM.

 

Does it mean that these mass elements add stiffness to my assembly since they are mentioned under structural mass?

 

Thank You 

Re: Center of Gravity Calculation including Non Structural Mass

Pioneer
Pioneer

Hi Blas and Chip,

 

One more question, if the NX Nastran does not allow us to add NSM to solid elements for calculation of COG, is it possible that it takes the NSM applied for solid elements through connection command during analysis? 

 

I tried applying NSM through connect>Non-structural mass region

 

The highlighted is the NSM created with connection command and the other two are mass elements.

Re: Center of Gravity Calculation including Non Structural Mass

Solution Partner Phenom Solution Partner Phenom
Solution Partner Phenom

Hello "CodeCrack",

As said Non Structural Mass (NSM) is not supported by solid element faces, then either you use a coating mesh with shell elements, or use concentrated mass elements CONM2.

  • If you add CONM2 mass elements and use an RBE3 to attach to the structure then this is not NSM, is part of the structural mass summary.
  • Its not correct to define CONTACT CONNECTOR based in Non-Structural-Mass regions, is useless. If you try to select any NSM region deploying either the TARGET or SOURCE menu you will see is empty.

Best regards,
Blas.

Blas Molero Hidalgo, Ingeniero Industrial, Director
IBERISA • 48004 BILBAO (SPAIN)
WEB: http://www.iberisa.com
Blog Femap-NX Nastran: http://iberisa.wordpress.com/