Dear Azin Lamei,

I suggest you to see links on subject.

-5.2. Shell Elements - SHARCNet

https://www.sharcnet.ca/Software/.../Hlp_E_ShellElements.html

-4.93 SHELL93 8-Node Structural Shell (UP19980821 )

ans2.vm.stuba.sk/html/elem_55/chapter4/ES4-93.htm

-shell281 - SHARCNet

https://www.sharcnet.ca/Software/...2.../Hlp_E_SHELL281.html

-Mechanical APDL Command Reference - SHARCNet

https://www.sharcnet.ca/.../Ansys/16.2.3/.../Hlp_C_CmdTOC.html

-ANSYS Mechanical Workbench Tips: Static Analysis with Inertia Relief

https://www.simutechgroup.com/.../251-fea-tips-tricks-ansys-static-...

-FEA Best Practices

innomet.ttu.ee/martin/MER0070/Loengud/FEA_Best_Practices.pdf

Best regards

This is an idea based in the definition of CG:

*do,i,1,n

Cmsel,s,componentName%i%

Esla,s

*Get,nelem,elem,,count

*Get,emin,elem,,num,min

*Do,j,1,nelem

*Get, xcg,elem,,cent,x

*Get, ycg,elem,,cent,y

*Get,zcg,elem,,cent,z

*Get,volume,elem,,volu

Mass=volume*density

Cmsel,s,componentName%i%

Esla,s

*Get,emin,elem,emin,num,nxth

*Enddo

*Enddo

You must collect cg coordinates, volumes and masses for every element in your model in some arrays.

After that, (e.g. x component) you sum up for every element

Xcg = sum(xcg(i,j)*mass(i,j))/sum(mass(i,j))

Operations for arrays are performed via *vscfun