Extreme runup events around a ship-shaped floating production, storage and offloading vessel in transient wave groups

Chen, L.F.; Taylor, Paul C.J.; Ning, Dezhi; Cong, Peiwen; Wolgamot, Hugh; Draper, Scott; Cheng, Liang

doi:10.1017/jfm.2020.1072

Cited by 10 publications

(8 citation statements)

References 27 publications

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“…This phase-based harmonic separation method relies on a Stokes-like structure of the studied wave-driven response. It has been used to analyse various nonlinear wave phenomena involving fixed (Fitzgerald et al 2014;Zhao et al 2017;Chen et al 2018) and floating (Roux de Reilhac et al 2011;Chen et al 2021) offshore structures, as well as higher-order responses in coastal problems (Orszaghova et al 2014;Whittaker et al 2017;Judge et al 2019). The above studies utilise short deterministic wave groups.…”

Section: Identifying Nonlinear Resonant Responsesmentioning

confidence: 99%

Wave- and drag-driven subharmonic responses of a floating wind turbine

et al. 2021

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The nonlinear hydrodynamic responses of a novel spar-type soft-moored floating offshore wind turbine are investigated via analysis of motion measurements from a wave-basin campaign. A prototype of the TetraSpar floater, supporting a $1:60$ scale model of the DTU 10 MW reference wind turbine, was subjected to irregular wave forcing (with no wind) and shown to exhibit subharmonic resonant motions, which greatly exceeded the wave-frequency motions. These slow-drift responses are excited nonlinearly, since the rigid-body natural frequencies of the system lie below the incident-wave frequency range. Pitch motion is examined in detail, allowing for identification of different hydrodynamic forcing mechanisms. The resonant response is found to contain odd-harmonic components, in addition to the even harmonics expected a priori and excited by second-order difference-frequency hydrodynamic interactions. Data analysis utilising harmonic separation and signal conditioning suggests that Morison drag excitation or third-order subharmonic potential flow forcing could be at play. In the extreme survival-conditions sea state, the odd resonant responses are identified to be drag-driven. Their importance for the tested floater is appreciable, as their magnitude is comparable to the second-order potential flow effects. Under such severe conditions, the turbine would not be operating, and as such neglecting aerodynamic forcing and motion damping is likely to be reasonable. Additionally, other possible drivers of the resonant pitch response are explored. Both Mathieu-type parametric excitation and wavemaker-driven second-order error waves are found to have negligible influence. However, we note slight contamination of the measurements arising from wave-basin sloshing.

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Section: Identifying Nonlinear Resonant Responsesmentioning

confidence: 99%

Wave- and drag-driven subharmonic responses of a floating wind turbine

et al. 2021

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“…The low-frequency horizontal motions may also require additional damping to represent wave-drift damping. If representing viscous effects more directly is desired, Computational Fluid Dynamics (CFD) models including appropriate turbulence models are likely better suited to simulate the wave-structure interactions (e.g., Hadžić et al, 2005;Wilson et al, 2006;Chen et al, 2021), though at far greater computational cost.…”

Section: Discussionmentioning

confidence: 99%

“…To distinguish between the first-and second-order wave motion, excitation loads and body motions predicted by SWASH; we employ the phase separation method (e.g., Fitzgerald et al, 2014). This methodology assumes that the nonlinear wave-driven processes can be described by a Stokes-type perturbation expansion, and has been successfully applied to study both nonlinear wave processes (e.g., Orszaghova et al, 2014;Whittaker et al, 2017;Zhao et al, 2017) and nonlinear wave dynamics of fixed and moving structures (e.g., Fitzgerald et al, 2014;Chen et al, 2021;Orszaghova et al, 2021). To separate the primary and secondorder contributions with this methodology, we ran a simulation with two different wavemaker signals that are out of phase (i.e., all wave frequencies of the second wavemaker signal are phase shifted by 180 • relative to the first wavemaker signal).…”

Section: Swash Methodologymentioning

confidence: 99%

Non-hydrostatic modelling of the wave-induced response of moored floating structures

Rijnsdorp,

Wolgamot,

Zijlema

2022

Preprint

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Predictions of the wave-induced response of floating structures that are moored in a harbour or coastal waters require an accurate description of the (nonlinear) evolution of waves over variable bottom topography, the interactions of the waves with the structure, and the dynamics of the mooring system. In this paper, we present a new advanced numerical model to simulate the wave-induced response of a floating structure that is moored in an arbitrary nearshore region. The model is based on the non-hydrostatic approach, and implemented in the open-source model SWASH, which provides an efficient numerical framework to simulate the nonlinear wave evolution over variable bottom topographies. The model is extended with a solution to the rigid body equations (governing the motions of the floating structure) that is tightly coupled to the hydrodynamic equations (governing the water motion). The model was validated for two test cases that consider different floating structures of increasing geometrical complexity: a cylindrical geometry that is representative of a wave-energy-converter, and a vessel with a more complex shaped hull. A range of wave conditions were considered, varying from monochromatic to short-crested sea states. Model predictions of the excitation forces, added mass, radiation damping, and the wave-induced response agreed well with benchmark solutions to the potential flow equations. Besides the response to the primary wave (sea-swell) components, the model was also able to capture the second-order difference-frequency forcing and response of the moored vessel. Importantly, the model captured the wave-induced response with a relatively coarse vertical resolution, allowing for applications at the scale of a realistic harbour or coastal region. The proposed model thereby provides a new tool to seamlessly simulate the nonlinear evolution of waves over complex bottom topography and the wave-induced response of a floating structure that is moored in coastal waters.

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“…Separation of the linear and nonlinear contributions of free-surface elevation, loads and response from experimental data is possible through the method of harmonic separation. The method was introduced as two-phase separation in Jonathan & Taylor (1997), Walker, Taylor & Eatock Taylor (2004) and Hunt et al (2002), and has been applied in a series of papers in relation to nonlinear responses of a variety of offshore structures (see for instance Zhao et al 2017;Chen et al 2021) and coastal problems (Orszaghova et al 2014;Judge et al 2019;Zheng et al 2020). While originally based on ensemble averaging of large crest and trough events and enabling separation of odd (dominantly linear) and even (dominantly second-order) response contributions, it has later been extended to four-phase separation of wave forcing (Fitzgerald et al 2014) and applied to long time series produced by repeated experiments of phase-shifted input signals.…”

Section: Introductionmentioning

confidence: 99%

Resonant response of a flexible semi-submersible floating structure: experimental analysis and second-order modelling

Lynggård Hansen,

Bredmose,

Vincent

et al. 2024

J. Fluid Mech.

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The dynamics and nonlinear wave forcing of a flexible floating structure are investigated experimentally and numerically. The floater was designed to match sub-harmonic rigid-body natural frequencies of typical floating wind turbine substructures, with the addition of a flexible bending mode. Experiments were carried out for three sea states with phase-shifted input signals to allow harmonic separation of the measured response. We find for the weakest sea states that sub-harmonic rigid-body motion is driven by even-harmonic difference frequency forcing, and by linear forcing for the strongest sea state. The flexible mode was tested in a soft, linearly forced layout, and a stiff layout, forced by second-, third- and fourth-harmonic frequency content, for increasing severity of the sea state. Further insight is gained by analysis of the amplitude scaling of the resonant response. A new simplified approach is proposed and compared with the recent method of Orszaghova et al. (J. Fluid Mech., vol. 929, 2021, A32). We find that resonant surge and pitch motions are dominated by even-harmonic potential-flow forcing and that odd-harmonic response is mainly potential-flow driven in surge and mainly drag driven in pitch. The measured responses are reproduced numerically with second-order forcing and quadratic drag loads, using a recent and computationally efficient calculation method, extended here for the heave, pitch and flexible motions. We are able to reproduce the response statistics and power spectra for the measurements, including the subharmonic pitch and heave modes and the flexible mode. Deeper analysis reveals that inaccuracies in the even-harmonic forcing content can be compensated by the odd-harmonic loads.

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Extreme runup events around a ship-shaped floating production, storage and offloading vessel in transient wave groups

Abstract: Abstract

Cited by 10 publications

References 27 publications

Wave- and drag-driven subharmonic responses of a floating wind turbine

Wave- and drag-driven subharmonic responses of a floating wind turbine

Non-hydrostatic modelling of the wave-induced response of moored floating structures

Resonant response of a flexible semi-submersible floating structure: experimental analysis and second-order modelling

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