Dear Mr. Winarski:

Obtaining nodal displacement for a selected set of nodes is straightforward, and I will provide an APDL command set for this purpose. However, please remember that when it comes to modal analysis, the displacements (aka Eigen Vectors) are notional. Mode shapes are not actual (absolute) displacement shapes and are only an aid for visualization (relative).

The reason is, the harder you strike an object with a mallet, the more the amplitude of vibrations will be. The natural frequencies, however, will remain the same regardless of the force of impact. Therefore, while the natural frequencies are absolute, Eigen modes (vectors) are relative. Having said that, here is a simple macro to extract nodal displacements and write it to a file.

/POST1

ALLSEL

SET,1,1 ! Load the first mode into the post-processor

! Select your 38 nodes

NSEL,S,NODE,,1

NSEL,A,NODE,,11

NSEL,A,NODE,,128

! etc., etc.

/OUT,mydisp ! My output displacement file

/OUT

*GET,TOTNODE,NODE,COUNT

*DO,J,1,TOTNODE

*GET,NODEMIN,NODE,0,NUM,MIN ! GET THE MINIMUM NODE NUMBER FROM THE LIST

*GET,MYDISPX,NODE,NODEMIN,D,UX

*GET,MYDISPY,NODE,NODEMIN,D,UY

*GET,MYDISPZ,NODE,NODEMIN,D,UZ

/OUT,mydisp,,append

/COM, NODEMIN,MYDISPX,MYDISPY,MYDISPZ

/OUT

NSEL,U,NODE,NODEMIN

*ENDDO

ALLSEL

I hope, this can help you "! After solving your modal analysis

/SOLU

ANTYPE,MODAL ! Ensure in modal analysis

MODOPT,LANB,5 ! Example for 5 modes

SOLVE

FINISH

/POST1

SET,LIST ! Verify modes are available

! Store your nodes of interest in an array

*DIM,myNodes,ARRAY,38

*VREAD,myNodes(1),'nodes_of_interest.txt',,,38

(F10.0) ! Adjust format to match your input file

! Store results in arrays

*DIM,dispX,ARRAY,38,5 ! 38 nodes, 5 modes - X component

*DIM,dispY,ARRAY,38,5 ! Y component

*DIM,dispZ,ARRAY,38,5 ! Z component

! Loop through modes and nodes

*DO,m,1,5 ! For each mode

SET,1,m ! Read mode m

*DO,n,1,38 ! For each node

*GET,dispX(n,m),NODE,myNodes(n),U,X

*GET,dispY(n,m),NODE,myNodes(n),U,Y

*GET,dispZ(n,m),NODE,myNodes(n),U,Z

*ENDDO

*ENDDO

! Output results

*CFOPEN,'modal_displacements.csv',csv

*VWRITE,'Node','Mode','UX','UY','UZ'

(A5,',',A5,',',A5,',',A5,',',A5)

*DO,n,1,38

*DO,m,1,5

*VWRITE,myNodes(n),m,dispX(n,m),dispY(n,m),dispZ(n,m)

(F10.0,',',I3,',',E15.7,',',E15.7,',',E15.7)

*ENDDO

*ENDDO

*CFCLOSE"