ANSYS APDL BEAM3 Transient Analysis Damping(?)

[hogeol]

Q. Why is there a damping property in this response? How can I heal this?
--
Hello everyone.

I am studying about Impulse response[1].
By this code[2], there is no considering about damping.
But when I look into response during relatively long time window[3], the response slowly decrease[4].

My question: Why is there a damping property in this response? How can I heal this?

Thanks to you all.
--
Reference
[1]

http://www.mece.ualberta.ca/tutorials/ansys/IT/Transient/Transient.html

[2]

http://www.mece.ualberta.ca/tutorials/ansys/CL/CIT/Transient/Print.pdf

[3] attached code file:
finish
/clear

/prep7
K,1,0,0
K,2,1,0

L,1,2

ET,1,BEAM3

R,1,0.0001,8.33e-10,0.01

MP,EX,1,2.068e11
MP,PRXY,1,0.33
MP,DENS,1,7830

LESIZE,ALL,,,10
LMESH,1

FINISH

/SOLU
ANTYPE,4

!TRNOPT,REDUC !v
TRNOPT, REDUC, ,NODAMP !no damping!
LUMPM,0

FLST,2,10,1,ORDE,2
FITEM,2,2
FITEM,2,-11
M,P51X,UY, , ,
FLST,2,1,1,ORDE,1
FITEM,2,1

/GO
D,P51X, , , , , ,ALL, , , , ,

TIME,0
AUTOTS,-1
DELTIM,0.001, , ,1
KBC,0
!*
TSRES,ERASE !default
LSWRITE,1,

FLST,2,1,1,ORDE,1
FITEM,2,2
!*
/GO
F,P51X,FY,-100
!*
TIME,0.001
AUTOTS,-1
DELTIM,0.001, , ,1
KBC,0
!*
TSRES,ERASE

LSWRITE,2,
FLST,2,1,1,ORDE,1
FITEM,2,2
FDELE,P51X,ALL
/REPLOT,RESIZE
!*
TIME,100
AUTOTS,-1
DELTIM,0.001, , ,1
KBC,0
!*
TSRES,ERASE
LSWRITE,3,
LSSOLVE,1,3,1,

/POST26
FILE,'file','rdsp','.'

/UI,COLL,1
NUMVAR,200
NSOL,191,2,UY
STORE,MERGE
FILLDATA,191,,,,1,1
REALVAR,191,191
!*

NSOL,2,2,U,Y, UY_2
STORE,MERGE
!PRVAR,2,
XVAR,1
PLVAR,2,

[4] The result of [3]