Page 72 - Failure Analysis Case Studies II

57
80
70
60
z 50
e
2 40
e
u
v) 30
E
- 20
IO
0
0 200 400 600 800 IO00
depth m
Fig. 9. Number of turns transferred from the chain when tensioned as a function of water depth.

the suspended weight but still not change the minimal torsional stiffness where the chain tension
is zero.
Figure 9 shows how reduction in water depth reduces the number of turns transferred from the
chain when tensioned, with the other parameters as specified initially. Figure 10 shows how using
ropes of different diameter can influence the turns transferred, with results shown for two different
water depths, 1000 and 700 m. In both figures, allowance has been made for an assumed capacity
for the chain to accommodate 33 of rotation per link before adopting a high torsional stiffness.
This capacity of chain to absorb induced turns can overcome the problem completely in shallower
water (as seen by the effective cut-off in Fig. 9). It is evident from Fig. 10 that significant reductions
in turns can be achieved from the use of rope with greater diameter and hence higher torsional

I40

120
w 100
z
+ 80
c
60
40
4-
20
0
50 60 70 80 90
rope diameter m
Fig. 10. Number of turns transferred from the chain when tensioned as a function of rope diameter, the upper line for
1000 m water depth and the lower for 700 m water depth.