Clarification on RHS of UEL

[kyonten]

Hi fellow engineers,

If I'm using non-standard external load (that appears in models such as gradient-enhanced or couple-stress due to higher order terms), it makes sense to do the external force calculation inside UEL subroutine (I guess for such case load type UnNU, as defined in Abaqus manual, should be used).

However, if we are using standard external load (due to traction, body force, etc.) it doesn't make sense to do the calculation inside UEL subroutine. For this case we used load type Un. My question is then, does the RHS vector that is passed in UEL contain the external forces already calculated, and the user simply have to compute the internal force and subtract from it? Or is the RHS simply negative of internal force, which is used somewhere else to compute the residual force? Or is the external force the product of stiffness matrix (AMATRX) and DU (or U)?

Comments and suggestions appreciated!

Thanks.

Karma

 

[vumat721]

I believe Abaqus accounts for any forces that you apply externally, so RHS is the negative of internal forces and you don't have to worry about adding/subtracting the external forces.

Did this not work for you? Or are you just seeking information first?

 

[kyonten]

Thanks for your reply!

I'm setting up input file to test my implementation, and was wondering if I MUST define external load via Un or UnNU load key for the UEL or I could use the standard form. Information regarding the load on the element can be passed via the UEL variables ADLMAG, DDLMAG, JDLTYP,NDLOAD, and MDLOAD. Including external force calculation in the UEL can be done, but it would be unnecessary, if these feature is to be used only for calculation of non-standard external load. I guess I will find out soon.