Application of Load 2

[hmaddy]

Hi All,
Please let me know if there is any difference application of load for quad-4 element and quad-8 element.

I am using an elliptical disturbution of load and when applied for a 4-node element I get the theoritical result.But doing the same way for 8 node element is giving me wrong results..

Thanking you,
Maddy

 

[johnhors]

hmaddy

I assume that you are using *CLOAD to apply point loads at individual nodes ? If so then the answer is simply explained by the different shape functions used by linear and quadratic elements. It is incorrect to apply a distribution of loading directly to the element, you must first calculate a pressure distribution over each element face and then convert this into a set of equivalent nodal forces, this can only be achieved using the element shape functions.

 

[hmaddy]

Thank you very much johnhors.
Yes, I am using *CLOAD and applying nodal forces. I am a little poor in using this shape functions.

Can you or somebody please give me an example how to use the element shape functions for a 4-node(linear) and a 8-node element (quad) in applying loads.

I am having a pressure disturbution over 20 elements and I want to use Gauss integration method.CanI directly use the abcissae and the weights to calculate the nodal forces?

Thanks again,
Maddy.

 

[mrgoldthorpe]

hmaddy,
Is there any reason why you can't apply the elliptical distribution of load using a DLOAD user subroutine and let ABAQUS do the appropriate integration for you? DLOAD is presented with the coordinates of the point in question.
MRG

 

[hmaddy]

Hi Mr.Goldthorpe,

I dont know whether I can use *DLOAD for this elliptical pressure load disturbution cause I never tried (actually never used. always have been using *CLOAD option). But since you say we can use may be I can give a try. But, If I use it does Abaqus do the intergration for me instead of me using shape functions and doing all the integration stuff?

Please confirm that,

Also, as requested earlier, Can you please let me know with a small example how to use shape functions or you could suggest a book or website to look for them cause I really want to learn using them,

Thank you,
HMaddy.

 

[mrgoldthorpe]

hmaddy,

Yes, ABAQUS will do the integration for you. I've put the bones of DLOAD below. You apply the user applied distributed load as follows:

*DLOAD, OP=MOD
ESET , P1NU, 0.0

where in this case "ESET" is the relevant element set and "P1NU" specifies the load is applied to Face 1, "P2NU" would apply to face 2 etc. Run abaqus using the "user=dload.f" option where the file "dload.f" contains the DLOAD subroutine.

SUBROUTINE DLOAD(F, KSTEP, KINC, TIME, NOEL, NPT,
& LAYER,KSPT, COORDS, JLTYP, SNAME )
INCLUDE 'ABA_PARAM.INC'
DIMENSION TIME (2), COORDS(3)
CHARACTER*80 SNAME
C work out the distributed load F according to the
C coordinates etc
C F = ???
RETURN
END

 

[johnhors]

A google search yielded this site on element shape functions (not a difficult task to find this!) :-

http://www.colorado.edu/engineering/CAS/courses.d/IFEM.d/IFEM.Ch18.d/IFEM.Ch18.pdf