Mass summary 1

[bridgehl]

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

 

[Lirock]

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

 

[Stringmaker]

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

-Brian

 

[bridgehl]

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

 

[meshparts]

Hi Bridge,

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

Regards,
Alex

 

[bridgehl]

@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

 

[meshparts]

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

 

[bridgehl]

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

Regards,
Bridge

 

[meshparts]

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

 

[bridgehl]

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

 

[meshparts]

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

 

[bridgehl]

@ 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