Linearization of Quadratic Drag to Estimate CALM Buoy Pitch Motion in Frequency-Domain and Experimental Validation

Abstract

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.

An Overview on Bonded Marine Hoses for Sustainable Fluid Transfer and (Un)Loading Operations via Floating Offshore Structures (FOS)

“…Different studies have been conducted on the numerical modelling of hose-mooring systems for marine hoses [46][47][48][49][50][51][52][53][54][55][56], CALM buoys [57][58][59][60][61][62][63][64][65][66][67], and offloading systems [68][69][70][71][72][73][74][75][76][77][78]. Most studies on marine hoses does not include mooring line safety ([36,37,42-45,79-88]).…”

An Investigation on the Vortex Effect of a CALM Buoy under Water Waves Using Computational Fluid Dynamics (CFD)

“…Over the years, there has been a number of motion response phenomena of floating CALM buoys, however, there are limited computational fluid dynamics (CFD) investigations presented. Different questions have been answered on marine riser mechanics [20][21][22], CALM buoy dynamics [23][24][25][26][27] and CALM buoy motion stability [28][29][30][31], but few works addressed other issues that encompass the motion response of CALM buoy in CFD, moored aspects of single point mooring (SPM) systems, flow vorticity, pressure distribution on CALM buoy, velocity impact on CALM buoy, and vortex-induced motion (VIM) on CALM buoys or similar floating offshore structures (FOS). The sketch the (un)loading operation on a CALM buoy with wave forces and boundary conditions and configured as (a) Chinese-lantern and (b) Lazy-S configurations in Figure 1.…”

Mathematical Modelling of Bonded Marine Hoses for Single Point Mooring (SPM) Systems, with Catenary Anchor Leg Mooring (CALM) Buoy Application—A Review

“…Thus, having mathematical models for bonded marine hoses on CALM buoys and SPM systems is obviously a requisite for the techno-economic design and operation of these floating structures. Recent innovations in bonded marine hoses include the application of composite materials [8][9][10][11], in composite marine risers [11][12][13][14][15][16][17][18][19], in moored offloading systems with coupled analysis [20][21][22][23][24][25][26][27], and the supporting CALM buoy systems [28][29][30][31][32][33][34][35]. However, these structures, similar to moorings, all depend on existing marine structures such as WECs, breakwater devices, tidal turbines, offshore wind turbines or CALM buoys [36][37][38][39][40][41][42][43][44].…”