Drillstring Vibrations: Classic Ideas and Modern Approaches - Wave Propagation in Drilling, Well Logging and Reservoir Applications - page 214

C .
C .
C COUPLED BENDING VIBRATIONS
C V LATERAL MODE
DO 600 I=3,IMAXM2
D(I) = EI/DX4
E(I) = EI/DX4
A(I) = -4.*EI/DX4 -AE*DUDX(I)/(DX*DX)
1 +AE*(DUDX(I+1)-DUDX(I-1))/(4.*DX*DX)
C(I) = -4.*EI/DX4 -AE*DUDX(I)/(DX*DX)
1 -AE*(DUDX(I+1)-DUDX(I-1))/(4.*DX*DX)
B(I) = 6.*EI/DX4 +2.*AE*DUDX(I)/(DX*DX)
1 +BEAMK +BEAMB/(2.*DT) +RHO*AREA/(DT**2)
W(I) = Q -GJ*DTHDX(I)*
1 (-WNM1(I-2)+2.*WNM1(I-1)
2 -2.*WNM1(I+1)+WNM1(I+2))/(2.*DX**3)
3 -GJ*(DTHDX(I+1)-DTHDX(I-1))*(1./(2.*DX))*
4 (WNM1(I-1)-2.*WNM1(I)+WNM1(I+1))/(DX**2)
5 +BEAMB*VNM2(I)/(2.*DT)
6 +2.*RHO*AREA*VNM1(I)/(DT**2)
7 -RHO*AREA*VNM2(I)/(DT**2)
600 CONTINUE
C .
C .
C Define downhole and surface beam boundary conditions next,
C reduce pentadiagonal equations to tridiagonal form and solve.
C .
C .
CALL REDUCE(A,B,C,D,E,W,IMAX)
CALL TRIDI(A,B,C,VECTOR,W,IMAX)
DO 650 I=1,IMAX
VBENDN(I) = VECTOR(I)
650 CONTINUE
C W LATERAL MODE
C .
C .
900 CONTINUE
C .
C .
STOP
END
Figure 4.3.3. Fortran listing, lateral vibrations (continued).