Drillstring Vibrations: Classic Ideas and Modern Approaches - Wave Propagation in Drilling, Well Logging and Reservoir Applications - page 213

C .
C INITIALIZE AXIAL, ANGULAR AND BENDING DISPLACEMENTS
DO 130 I=1,IMAX
X = XS*(I-1)/(IMAX-1)
UNM1(I) = RHO*G*(X**2)/(2.*ELAST) +WZERO*X/AE
C .
VNM1(I) = 0.
VNM2(I) = 0.
WNM1(I) = 0.
WNM2(I) = 0.
130 CONTINUE
C BEGIN TIMEWISE INTEGRATION
T = 0.
DO 900 N=1,NMAX
T = N*DT
C AXIAL VIBRATIONS
DO 200 I=2,IMAXM1
A(I) = 1.
C(I) = 1.
B(I) = -2.-RHO*DX*DX/(ELAST*DT*DT)-GAMA*DX*DX/(2.*ELAST*DT)
W(I) = -RHO*DX*DX*(2.*UNM1(I)-UNM2(I))/(ELAST*DT*DT)
1 -GAMA*DX*DX*UNM2(I)/(2.*ELAST*DT)+RHO*G*(DX**2)/ELAST
200 CONTINUE
A(IMAX) = -AE/DX
B(IMAX) = TBMASS/(DT**2) +BETA/(2.*DT) +AE/DX +SPRING
C(IMAX) = 99.
W(IMAX) = 2.*TBMASS*UNM1(IMAX)/(DT**2)
1 +(BETA/(2.*DT) -TBMASS/(DT**2))*UNM2(IMAX)-TBMASS*G
A(1) = 99.
VEL = (UNM1(1)-UNM2(1))/DT
IF(VEL.LE.0.) GO TO 205
C .
C TORSIONAL VIBRATIONS
C .
C .
Figure 4.3.3. Fortran listing, lateral vibrations (to be continued).