Geology Reference
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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
C .
C See Chapter 5 for axial vibration code listing with boundary
C condition models for rate-of-penetration and bit bounce, and
C displacement source model, from drill bit kinematic modeling.
C .
C .
C TORSIONAL VIBRATIONS
DO 400 I=2,IMAXM1
A(I) = 1.
C(I) = 1.
B(I) = -2.-RHO*DX*DX/(SHRMOD*DT*DT)-
GAMA2*DX*DX/(2.*SHRMOD*DT)
W(I) = -RHO*DX*DX*(2.*TNM1(I)-TNM2(I))/(SHRMOD*DT*DT)
1 -GAMA2*DX*DX*TNM2(I)/(2.*SHRMOD*DT)
400 CONTINUE
C .
C .
C See Chapters 5 and 7 for finite difference equation
C definition, setup, and boundary condition modeling.
C Immediately below we prescribe constant surface rpm
C via the angular displacement THETAN = RPM*2*PI*T/60.
C
A(IMAX) = 0.
B(IMAX) = 1.
C(IMAX) = 99.
W(IMAX) = RPM*2.*PI*T/60.
C
C The following Fortran indicates that the drillbit torque
C is proportional to the product of a friction coefficient
C FCOEF and the dynamic weight-on-bit as obtained from the
C axial calculations above.
C
A(1) = 99.
B(1) = -1.
C(1) = 1.
W(1) = (FCOEF*AE/GJ)*(UN(2)-UN(1))
C
CALL TRIDI(A,B,C,VECTOR,W,IMAX)
DO 450 I=1,IMAX
THETAN(I) = VECTOR(I)
450 CONTINUE
Figure 4.5.3.
Coupled vibrations, Fortran listing (to be continued).
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