The dynamics of an oil offloading catenary anchor leg mooring (CALM) buoy coupled with mooring and flow lines are directly related to the fatigue life of a mooring system, necessitating an accurate estimate of the buoy hydrodynamic response. Linear wave theory is used for modeling the surface boundary value problem, and the boundary element method is used to solve the fluid-structure interaction between the buoy hull and the incident waves in the frequency-domain. The radiation problem is solved to estimate the added mass and radiation damping coefficients, and the diffraction problem is solved to determine the linear wave exciting loading. The buoy pitch motion is investigated, and linearizations of the quadratic drag/damping term are performed in the frequency-domain. The pitch motion response is calculated by considering an equivalent linearized drag/damping. Quadratic, cubic, and stochastic linearizations of the nonlinear drag term are employed to derive the equivalent drag/damping. Comparisons between the linear and nonlinear damping effects are presented. Time-domain simulations of the buoy motions are performed in conjunction with Morison’s equation to validate the floating buoy response. The time- and frequency-domain results are finally compared with the experimental model test results for validations. The linearization methods applied result in good estimates for the peak pitch response. However, only the stochastic linearization method shows a good agreement for the period range of the incident wave where typical pitch response estimate has not been correctly estimated.

1.
Ryu
,
S.
,
Duggal
,
A. S.
,
Heyl
,
C. N.
, and
Liu
,
Y.
, 2006, “
Prediction of Deepwater Oil Offloading Buoy Response and Experimental Validation
,”
Int. J. Offshore Polar Eng.
1053-5381,
16
, pp.
290
296
.
2.
Chakrabarti
,
S. K.
, and
Cotter
,
D. C.
, 1992, “
Hydrodynamic Coefficients of a Moored Semisubmersible in Waves
,”
ASME J. Offshore Mech. Arct. Eng.
0892-7219,
114
(
1
), pp.
9
15
.
3.
Lee
,
C. H.
, and
Newman
,
J. N.
, 2006,
WAMIT User Manual
,
WAMIT, Inc.
,
Chestnut Hill, MA
, Versions 6.4, 6.4PC and 6.1S, 6.1S-PC.
4.
Chakrabarti
,
S. K.
, 2001, “
Empirical Calculation of Roll Damping for Ships and Barges
,”
Ocean Eng.
0029-8018,
28
, pp.
915
932
.
5.
Chakrabarti
,
S. K.
, 2002,
The Theory and Practice of Hydrodynamics and Vibration
(
Advanced Series on Ocean Engineering
),
World Scientific
,
River Edge, NJ
, Vol.
20
.
6.
Duggal
,
A. S.
, and
Ryu
,
S.
, 2005, “
The Dynamics of Deepwater Offloading Buoys
,”
Fluid Structure Interactions and Moving Boundary Problems
,
WIT Press
,
UK
, Vol.
84
, pp.
269
278
.
You do not currently have access to this content.