The in-line force on the pipe per unit length is
71.8 | 0.5 1.4 sint| (0.5 1.4 sint) 322.3 cost(N m^1 ).
The lift force per unit length is
1.2(0.5 1.4 sint)^2 0.507 cos^2 60°
78.3(0.5 1.4 sint)^2 (N m^1 ).
t Drag Inertia In line Lift Frictional force
force
0 18.0 322.3 304.3 19.6 738
1 11.5 246.9 258.4 12.5 740
2 55.4 56.0 111.4 60.5 726
3 36.4 161.1 124.7 39.8 732
4 0.0 302.9 302.9 0.0 744
5 68.8 302.9 371.7 75.0 722
6 210.5 161.2 371.7 229.7 675
6.5 253.4 56.0 309.4 276.5 661
7 253.4 56.0 197.5 276.5 661
8 140.7 246.9 106.2 153.2 698
9 18.0 322.3 304.3 19.6 738
The frictional force0.3(submerged weight lift). For stability, the
frictional force must be greater than the in-line force. The pipeline is
found to be stable.
Worked Example 14.3
Waves of period 8 s in deep water approach the shore from the south-west,
as shown in Fig. 14.27. In the figure, bed contours are shown as broken
lines. Draw the wave refraction pattern.
Solution
Referring to Fig. 14.27, the steps for drawing the refraction diagram are as
follows.
- Sketch the wave crest at deep water and divide the crest into equal
strips AB, BC, CD, etc. Usually ABCD... are drawn at deep water,
which may be taken to be d0.5L 0. From Fig. 14.4, L 0 100 m for
T8s.
- Compute celerities at A, B, C, D... as cA,cB,cC,cD... using Fig. 14.3.
1030
2
622 WAVES AND OFFSHORE ENGINEERING
