Piezoelectric crystal generates electrical signals when a time varying pressure / force is applied. You need to give a time varying force for getting a time varying signals and perhaps vice versa. 

Dear Mr. Pandey,

Are you talking about the output load of a Piezoelectric ( such as BVD equivalent circuit) , you can assume the output load as Resistor (R).

! start transient analysis

/SOLU  

ANTYPE,4

TRNOPT,FULL     !!! specify the analysis type

TINTP,,0.25,0.5,0.5    !!!!assign integration parameters

OUTRES,ALL,ALL 

AUTOTS,ON     ! Auto time step

KBC,0  

*SET,FF,19157   

*SET,PI,3.1415926  

*SET,T,1/FF

*SET,N,20   !! devide a cicle into 16 t0 24 steps, here it is 20 steps

*DO,I,1,N*100   !! Number of the circle

TIME,T/N*I  !!  time for a step

*SET,V,SQRT(2)*200*SIN(2*PI*FF*T/N*I) 

!! type of fixation

CSYS, 13

WPCSYS, 13

NSEL, S, LOC, Z, L1+4*L2-ERROR, L1+4*L2+ ERROR

NSEL, R, LOC, X, R1, R2

D, ALL, UX, 0

D, ALL, UY, 0

D, ALL, UZ, 0

ALLSEL

CSYS, 12

WPCSYS, 12

!! negative electrode of the piezoelectric discs

NSEL, S, LOC, Z, L1 -ERROR, L1 +ERROR

NSEL, A, LOC, Z, L1+2*L2 -ERROR, L1+2*L2+ERROR

NSEL, A, LOC, Z, L1+4*L2 -ERROR, L1+4*L2+ERROR

VSEL, S,,, 1, 4

NSLV, R, 1

D, ALL, VOLT, 0

ALLSEL

!!positive electrode of the piezoelectric discs

NSEL, S, LOC, Z, L1+L2 -ERROR, L1+L2+ERROR

NSEL, A, LOC, Z, L1+3*L2 -ERROR, L1+3*L2+ERROR

VSEL, S,,, 1, 4

NSLV, R, 1

D, ALL, VOLT, V

ALLSEL, ALL

/NUMBER,1  

SOLVE  

*ENDDO 

FINISH 

 Hope you can get something useful from the Command Snippets. The important thing is devide a period into 16 to 20 steps. The period should be 1/f, where fmeans the frequency you needed, In my codes, it stands for the resonant frequency of a ultrasonic transducer.