DEPLOYMENT OF AN OTEC PIPELINE
281
143 heave cycles at the dominant heave frequency of uN = 1.5 rad/s, and to
encompass about 3.6 dominant sway cycles of frequency eiwp = 0.0372 rad/s.
Since trial simulation times longer than 600 s produced no further increases in
peak responses, the 600 s simulation was considered in the présent calculations
togive a steady State upper bound on the responses, where the deployment rate
was about 1.7 m/s.
Table 10.3 Peak Pipeline Responses During Deployment for a 600 s Simulation Time, for K = 1.13 x 108 N-m/rad (Asterisks Represent Unbounded
Responses)
Pipeline
Length L, m
Deflection v(L,tc), m Moment Mc(xtt}, 105 N m
Mo =
45400 kg
Mo =
227000 kg
Mo =
45400 kg
Mo =
227 000 kg
61
9.63
7.94
-51 800
-51800
122
24.4
12.5
13000
13000
183
*
55.3
*
-15900
244
6.27
5.84
3390
-3400
305
-6.28
-4.87
-2290
-2290
366
9.85
7.71
-1730
-1730
427
-5.00
-4.14
-1420
-1420
488
13.2
13.6
2 730
2690
549
*
-82.4
*
1190
610
*
*
*
*
671
216
108
40200
20300.
732
*
*
*
♦
793
-108
-45.7
40300
15200
854
-139
-98.0
89 100
60100
915
*
*
*
*
975
*
*
*
*
1037
*
*
*
*
The time historiés of transverse pipe deflection and moment were calculated
at 50 points along each chosen length L. The peak values of those responses, for
two values of ballast mass, are listed in Table 10.3. The peak deflection v(L, tc)
is bounded and occurred at the ballast end (a: = L) and at a critical time t — tc.
However, the peak or critical moment Mc(x,t) usually occurred close to but not
exactly at the barge end (x = 0). It is noted that, for this 9.144 m diameter Steel
pipe where the stiffness El is based on a 6.35-mm wall thickness. the bending
moment at which yielding would begin (for most structural steels) would be
about 1500 x 105 N m. These severe pipe moments are probably due mainly to
the transverse pipe wave forces, which are strongest near the surfact and rop
off exponentially with water depth. Thus for an average deployment rate for
this pipe Of about 1.7 m/s, care must be taken to reduce the bending moment
aear the barge, perhaps by attaching cable stays to the pipe or bv restrainmg
barge motion.
281
143 heave cycles at the dominant heave frequency of uN = 1.5 rad/s, and to
encompass about 3.6 dominant sway cycles of frequency eiwp = 0.0372 rad/s.
Since trial simulation times longer than 600 s produced no further increases in
peak responses, the 600 s simulation was considered in the présent calculations
togive a steady State upper bound on the responses, where the deployment rate
was about 1.7 m/s.
Table 10.3 Peak Pipeline Responses During Deployment for a 600 s Simulation Time, for K = 1.13 x 108 N-m/rad (Asterisks Represent Unbounded
Responses)
Pipeline
Length L, m
Deflection v(L,tc), m Moment Mc(xtt}, 105 N m
Mo =
45400 kg
Mo =
227000 kg
Mo =
45400 kg
Mo =
227 000 kg
61
9.63
7.94
-51 800
-51800
122
24.4
12.5
13000
13000
183
*
55.3
*
-15900
244
6.27
5.84
3390
-3400
305
-6.28
-4.87
-2290
-2290
366
9.85
7.71
-1730
-1730
427
-5.00
-4.14
-1420
-1420
488
13.2
13.6
2 730
2690
549
*
-82.4
*
1190
610
*
*
*
*
671
216
108
40200
20300.
732
*
*
*
♦
793
-108
-45.7
40300
15200
854
-139
-98.0
89 100
60100
915
*
*
*
*
975
*
*
*
*
1037
*
*
*
*
The time historiés of transverse pipe deflection and moment were calculated
at 50 points along each chosen length L. The peak values of those responses, for
two values of ballast mass, are listed in Table 10.3. The peak deflection v(L, tc)
is bounded and occurred at the ballast end (a: = L) and at a critical time t — tc.
However, the peak or critical moment Mc(x,t) usually occurred close to but not
exactly at the barge end (x = 0). It is noted that, for this 9.144 m diameter Steel
pipe where the stiffness El is based on a 6.35-mm wall thickness. the bending
moment at which yielding would begin (for most structural steels) would be
about 1500 x 105 N m. These severe pipe moments are probably due mainly to
the transverse pipe wave forces, which are strongest near the surfact and rop
off exponentially with water depth. Thus for an average deployment rate for
this pipe Of about 1.7 m/s, care must be taken to reduce the bending moment
aear the barge, perhaps by attaching cable stays to the pipe or bv restrainmg
barge motion.