Spread mooring systems (SMS) may experience large-amplitude oscillations in the horizontal plane due to slow-drift loads. In the literature, this phenomenon is attributed to resonance. In this paper, it is shown that this conclusion is only partially correct. This phenomenon is investigated using nonlinear stability and bifurcation analyses which reveal an enhanced picture of the nonlinear dynamics of SMS. Catastrophe sets are developed in a parametric design space to define regions of qualitatively different system dynamics for autonomous SMS, including mean drift forces. Limited time simulations are performed to verify the qualitative conclusions drawn on the nonlinear dynamics of SMS using catastrophe sets. Slowly varying drift forces are studied as an additional excitation on the autonomous SMS and simulations reveal that slow drift may cause resonance or bifurcations with stabilizing or destabilizing morphogeneses. The mathematical model of SMS is based on the slow-motion maneuvering equations in the horizontal plane (surge, sway, yaw), including hydrodynamic forces with terms up to third-order, nonlinear restoring forces from mooring lines, and environmental loads due to current, wind, and wave-drift.

Issue Section:
Research Papers
Topics:
Mooring, Nonlinear dynamics, Stress, Bifurcation, Resonance, Simulation, Excitation, Fluid-dynamic forces, Oscillations, Parametric design, Stability, Surges, System dynamics, Wave drift, Wind, Yaw
1.
Abkowitz, M. A., 1972, Stability and Motion Control of Ocean Vehicles, MIT Press, Cambridge, MA.
2.
API, 1987, “Analysis of Spread Mooring Systems for Floating Drilling Units,” API Recommended Practice 2P (RP2P), Second Edition.
3.
Bernitsas
M. M.
, and
Garza-Rios
L. O.
,
1996
, “
Effect of Mooring Line Arrangement on the Dynamics of Spread Mooring Systems
,”
ASME JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING
, Vol.
118
, pp.
7
–
20
.
4.
Bernitsas
M. M.
, and
Kekridis
N. S.
,
1986
, “
Simulation and Stability of Ship Towing
,”
International Shipbuilding Progress
, Vol.
32
, No.
369
, pp.
112
–
123
.
5.
Bernitsas, M. M., and Papoulias, F. A., 1990, “Nonlinear Stability and Maneuvering Simulation of Single Point Mooring Systems,” Proceedings, Offshore Station Keeping Symposium, SNAME, Houston, TX, pp. 1–19.
6.
Brook, A. K., 1992, “The Static and Dynamic Analysis of Moored Vessels in Irregular Seas,” Proceedings, 6th International Conference of Behavior of Offshore Structures, Vol. 1, Imperial College of Science, Technology and Medicine, London, U.K., pp. 251–264.
7.
Chakrabarti
S. K.
, and
Cotter
D. C.
,
1989
, “
Motions of Articulated Towers and Moored Floating Structures
,”
ASME JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING
, Vol.
111
, pp.
233
–
241
.
8.
Chung
J. S.
, and
Bernitsas
M. M.
,
1992
, “
Dynamics of Two-Line Ship Towing/Mooring Systems: Bifurcation, Singularities of Stability Boundaries, Chaos
,”
Journal of Ship Research
, Vol.
36
, No.
2
, pp.
93
–
105
.
9.
Fernandes, A. C., and Aratanha, M., 1996, “Classical Assessment to the Single Point Mooring and Turret Dynamic Stability Problems,” Proceedings, 15th International Conference on Offshore Mechanics and Arctic Engineering, Vol. I.A, Florence, Italy, pp. 423–430.
10.
Garza-Rios
L. O.
, and
Bernitsas
M. M.
,
1996
, “
Analytical Expressions of the Stability and Bifurcation Boundaries for General Spread Mooring Systems
,”
Journal of Ship Research
, Vol.
40
, No.
4
, pp.
337
–
350
.
11.
Guckenheimer, J., and Holmes, P., 1983, Nonlinear Oscillations, Dynamical Systems, and Bifurcations of Vector Fields, Springer-Verlag, New York, NY.
12.
Hirano, M., Takashina, J., Takaishi, Y., and Saruta, T., 1980, “Ship Turning Trajectory in Regular Waves,” Transactions of the West-Japan Society of Naval Architects, Vol. 60.
13.
Kat, J. O., and Wichers, J. E. W., 1991, “Behavior of a Moored Ship in Unsteady Current, Wind, and Waves,” Marine Technology, pp. 251–264.
14.
McKenna
H. A.
, and
Wong
R. K.
,
1979
, “
Synthetic Fiber Rope, Properties and Calculations Relating to Mooring Systems
,”
Deep Water Mooring and Drilling
, Ocean Engineering, Vol.
7
, pp.
189
–
203
.
15.
Newman, J. N., 1974, “Second-Order Slowly Varying Forces on Vessels in Irregular Waves,” Proceedings, International Symposium on Dynamics of Marine Vehicles and Structures in Waves, London, U.K., pp. 182–186.
16.
Nishimoto, K., Brinati, H. L., and Fucatu, C. H., 1995, “Analysis of Single Point Moored Tanker using Maneuvering Hydrodynamic Model,” Proceedings, 14th International Conference on Offshore Mechanics and Arctic Engineering, Vol. I.B, Copenhagen, Denmark, pp. 253–261.
17.
Ogilvie, T. F., 1983, “Second Order Hydrodynamic Effects on Ocean Platforms,” Proceedings, International Workshop on Ship and Platform Motions, pp. 205–265.
18.
Papoulias
F. A.
, and
Bernitsas
M. M.
,
1988
, “
Autonomous Oscillations, Bifurcations, and Chaotic Response of Moored Vessels
,”
Journal of Ship Research
, Vol.
32
, No.
3
, pp.
220
–
228
.
19.
Seydel, R., 1988, From Equilibrium to Chaos, Elsevier Science Publishing Co., Inc., New York, NY.
20.
van Oortmerssen
G.
,
Pinkster
J. A.
, and
van den Boom
H. J. J.
,
1986
, “
Computer Simulation of Moored Ship Behavior
,”
Journal of Waterway, Port, Coastal and Ocean Engineering
, Vol.
112
, No.
2
, pp.
296
–
308
.
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