Nonlinear response of a moored buoy

The nonlinear dynamic analysis of a multipoint slack moored buoy is performed under the action of first and second order wave forces. The nonlinearity of the system is caused by the geometric nonlinearity of the mooring lines. The resulting nonlinear equation of motion is solved by an incremental time marching scheme. The nonlinear responses of the system are analysed to investigate different kinds of dynamic instability phenomena that may arise due to the nonlinearity of the system. As an illustrative example, a hollow cylindrical buoy anchored to the sea bed by means of six slack mooring lines is considered. The responses of the system are obtained and analysed for three regular waves namely, 5 m/5 s, 12 m/10 s and 18 m/15 s. The results of the study show that different kinds of instability phenomena like nT subharmonic oscillations, symmetry breaking bifurcation and aperiodic responses may occur in slack mooring systems. Further, a second order wave force may considerably influence the dynamic stability of such systems.

[1]  Lyle D. Finn,et al.  Design of Guyed Tower for 1,000 ft of Water , 1984 .

[2]  Demosthenes C. Angelides,et al.  DYNAMIC RESPONSE OF TENSION LEG PLATFORM , 1982 .

[3]  John W. Leonard,et al.  EFFECTS OF CURRENTS ON THE STOCHASTIC RESPONSE TO EARTHQUAKES OF MULTIPLE DEGREE OF FREEDOM MODELS OF GUYED OFFSHORE TOWERS , 1988 .

[4]  Solomon C. Yim,et al.  Nonlinear oscillations, bifurcations and chaos in a multi-point mooring system with a geometric nonlinearity , 1992 .

[5]  Lars Bergdahl,et al.  Frequency-domain dynamic analysis of cables , 1997 .

[6]  Moo-Hyun Kim,et al.  THE NONLINEAR SUM-FREQUENCY WAVE EXCITATION AND RESPONSE OF A TENSION-LEG PLATFORM , 1988 .

[7]  T. K. Datta,et al.  Nonlinear response of guyed tower to random wave forces , 1990 .

[8]  Bohdan W. Oppenheim,et al.  Polynomial approximations to mooring forces in equations of low-frequnecy vessel motions , 1982 .

[9]  Haym Benaroya,et al.  NON-LINEAR DYNAMICS OF AN ARTICULATED TOWER IN THE OCEAN , 1994 .

[10]  Robin S. Langley.  On the time domain simulation of second order wave forces and induced responses , 1986 .

[11]  S. M. Hung,et al.  SECOND ORDER DIFFRACTION FORCES ON A VERTICAL CYLINDER IN REGULAR WAVES , 1987 .

[12]  Subrata K. Chakrabarti,et al.  Nonlinear methods in offshore engineering , 1990 .

[13]  Sander M. Calisal,et al.  Hydrodynamic coefficients for vertical circular cylinders at finite depth , 1981 .

[14]  Denby Grey Morrison.  Guyed Tower with Dynamic Mooring Properties , 1983 .

[15]  M S Triantafyllou,et al.  NONLINEAR CABLE DYNAMICS , 1985 .

[16]  M. Kobayashi,et al.  Study on Dynamic Responses of a TLP in Waves , 1987 .