×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Mass summary

Mass summary

Mass summary

(OP)
Dear all,

I am doing a trasient analysis in Ansys10. In the output file, I notice that the mass summary by element type of  300 is not the same as what I input as shown below (type 300 is MASS21).

However, the summation of reactions in a static analysis is correct.

Could you please explain this for me. Something's wrong with my input?

Regards,
Bridge



  *** MASS SUMMARY BY ELEMENT TYPE ***

  TYPE      MASS
     1   401625.    
     2   111050.    
   300   10886.7    

RE: Mass summary

Hi,
   You didn't show us how you input the real constant for MASS21 ,so it's difficult to find what was wrong.
   

RE: Mass summary

Bridge,
You do know that you'll need to multiply mass*gravity to get the proper weight right?

-Brian

RE: Mass summary

(OP)
Hi Liweisc,Brian
This is my input. Please tell me what is wrong. Thank you.

!----------------------
    My1= 4497
    Mrx1= 3481
    Mrz1= 14712
 
    My2= 24103
    Mrx2= 23885
    Mrz2= 170610
 
    Mwy1= 979
    Mwrx1= 493
 
    Mwy2= 1616
    Mwrx2= 821
 
    Mwy3= 1305
    Mwrx3= 657
 
    R, 301, 0, Mwy1, 0, Mwrx1, 0, 0,
    R, 302, 0, Mwy2, 0, Mwrx2, 0, 0,
    R, 303, 0, Mwy3, 0, Mwrx3, 0, 0,
    R, 304, 0, My1, 0, Mrx1, 0, Mrz1,
    R, 305, 0, My2, 0, Mrx2, 0, Mrz2,

I group all of MASS21 to E_MASS and apply gravitational acceleration for Y direction:

    CMACEL, E_MASS, , 10, ,
!----------------------

Sum of all the masses must be = My1+My2+Mwy1+Mwy2+Mwy3= 32500

RE: Mass summary

Hi Bridge,

I don't understand: Mwy1+Mwy2+Mwy3 should have no effect with an linear acceleration. They represent rotational inertia.

Regards,
Alex

RE: Mass summary

(OP)
@Alex,
The real constant for MASS21 is:
     R, SETNo, MASSX, MASSY, MASSZ, IXX, IYY, IZZ

So to my understanding, the mass summation in Y direction is: My1+My2+Mwy1+Mwy2+Mwy3. Is it right?

Regards,
Bridge

RE: Mass summary

No, I don't think so... If I am wrong, then I'm very wrong, but I think if you apply a statically transverse acceleration in y direction, then the supports will react with a force equal to the sum of all y masses times the acceleration.

Regards,
Alex

RE: Mass summary

(OP)
@ Alex,
Yes, the sum of force reactions is correct. However, I am just don't understand the mass summary output.

Regards,
Bridge

RE: Mass summary

In the ansys help stands:

The standard mass summary printout is based on the average of MASSX, MASSY, and MASSZ if (KEYOPT(3) = 0).

Since the MASSX and MASSZ are 0 the mass output should be (My1+My2+Mwy1+Mwy2+Mwy3)/3= 32500/3 = 10833.

I can't say from your mass output summary what element types are mass21 elements, but the values are in any case too big. So I suppose you have a bug in your code. Without any other informations I can't help you...

Regards,
Alex

RE: Mass summary

(OP)
Many thanks for your help Alex. Now, I got it.

According to your post, the mass summary output is correct. So what do you mean by "the values are too big"?

Regards,
Bridge

RE: Mass summary

In your output I see

 *** MASS SUMMARY BY ELEMENT TYPE ***
TYPE MASS
300 10886.7

My hand calculation gives me 10833. So I get a difference of 53.7. I can not say why, and I think this could be an error in your code, since Ansys will only do what you say to it.

Regards,
Alex

RE: Mass summary

(OP)
@ Alex,
Yes, I found the cause of the difference. Now the Mass Summary from Ansys is exactly the same as your hand calculation.

Thank you very much for your posts.

Regards,
Bridge

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources