Efficient Nonlinear Hydrodynamic Models for Wave Energy Converter Design—A Scoping Study

Davidson, Josh; Costello, Ronan

doi:10.3390/jmse8010035

Cited by 70 publications

(44 citation statements)

References 270 publications

(369 reference statements)

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“…Therefore, over the past decade, in line with the availability of computationally efficient, nonlinear hydrodynamic models [27], increased attention towards numerical modelling of parametric resonance in WECs can be noted. The first publication in this direction was at the end of the 2000s by Babarit et al [28], which investigated the use of a nonlinear hydrodynamic model to capture the parametric roll resonance in the SeaREV, observed during the earlier experimental tests in Durand et al [14].…”

Section: Parametric Resonance In Wecsmentioning

confidence: 99%

A Real-Time Detection System for the Onset of Parametric Resonance in Wave Energy Converters

Davidson

Kalmár‐Nagy

2020

JMSE

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Parametric resonance is a dynamic instability due to the internal transfer of energy between degrees of freedom. Parametric resonance is known to cause large unstable pitch and/or roll motions in floating bodies, and has been observed in wave energy converters (WECs). The occurrence of parametric resonance can be highly detrimental to the performance of a WEC, since the energy in the primary mode of motion is parasitically transferred into other modes, reducing the available energy for conversion. In addition, the large unstable oscillations produce increased loading on the WEC structure and mooring system, accelerating fatigue and damage to the system. To remedy the negative effects of parametric resonance on WECs, control systems can be designed to mitigate the onset of parametric resonance. A key element of such a control system is a real-time detection system, which can provide an early warning of the likely occurrence of parametric resonance, enabling the control system sufficient time to respond and take action to avert the impending exponential increase in oscillation amplitude. This paper presents the first application of a real-time detection system for the onset of parametric resonance in WECs. The method is based on periodically assessing the stability of a mathematical model for the WEC dynamics, whose parameters are adapted online, via a recursive least squares algorithm, based on online measurements of the WEC motion. The performance of the detection system is demonstrated through a case study, considering a generic cylinder type spar-buoy, a representative of a heaving point absorber WEC, in both monochromatic and polychromatic sea states. The detection system achieved 95% accuracy across nearly 7000 sea states, producing 0.4% false negatives and 4.6% false positives. For the monochromatic waves more than 99% of the detections occurred while the pitch amplitude was less than 1/6 of its maximum amplitude, whereas for the polychromatic waves 63% of the detections occurred while the pitch amplitude was less than 1/6 of its maximum amplitude and 91% while it was less than 1/3 of its maximum amplitude.

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Section: Parametric Resonance In Wecsmentioning

confidence: 99%

A Real-Time Detection System for the Onset of Parametric Resonance in Wave Energy Converters

Davidson

Kalmár‐Nagy

2020

JMSE

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“…This adds an extra uncertainty to the obtained numerical results of the aforementioned numerical models; they not only rely on the numerical simulations' accuracy, but also on those of the experiments or simulations performed to tune the wave absorption coefficients. Furthermore, following the study by Reference [19], where the need for reliable and affordable numerical simulations to increase the technology readiness level (TRL) of the wave energy sector was pointed out, phase average and phase resolving numerical models failed to provide the former. Even though they provided computationally efficient solutions, they lacked the tools to implement proof of concept designs easily and accurately.…”

Section: Introductionmentioning

confidence: 99%

“…The general applicability of different coupled models was studied by Reference [19]. As pointed out in Reference [48], the use of linear models for implementing numerical coupling between to models can lead to underestimations of the WEC motions and poor representation of the PTO behaviour, which would make non-linear coupled models a preferable choice [19].…”

Section: Introductionmentioning

confidence: 99%

Influence of Power Take-Off Modelling on the Far-Field Effects of Wave Energy Converter Farms

Fernandez

Stratigaki

Quartier

et al. 2021

Water

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The study of the potential impact of wave energy converter (WEC) farms on the surrounding wave field at long distances from the WEC farm location (also know as “far field” effects) has been a topic of great interest in the past decade. Typically, “far-field” effects have been studied using phase average or phase resolving numerical models using a parametrization of the WEC power absorption using wave transmission coefficients. Most recent studies have focused on using coupled models between a wave-structure interaction solver and a wave-propagation model, which offer a more complex and accurate representation of the WEC hydrodynamics and PTO behaviour. The difference in the results between the two aforementioned approaches has not been studied yet, nor how different ways of modelling the PTO system can affect wave propagation in the lee of the WEC farm. The Coastal Engineering Research Group of Ghent University has developed both a parameterized model using the sponge layer technique in the mild slope wave propagation model MILDwave and a coupled model MILDwave-NEMOH (NEMOH is a boundary element method-based wave-structure interaction solver), for studying the “far-field” effects of WEC farms. The objective of the present study is to perform a comparison between both numerical approaches in terms of performance for obtaining the “far-field” effects of two WEC farms. Results are given for a series of regular wave conditions, demonstrating a better accuracy of the MILDwave-NEMOH coupled model in obtaining the wave disturbance coefficient (Kd) values around the considered WEC farms. Subsequently, the analysis is extended to study the influence of the PTO system modelling technique on the “far-field” effects by considering: (i) a linear optimal, (ii) a linear sub-optimal and (iii) a non-linear hydraulic PTO system. It is shown that modelling a linear optimal PTO system can lead to an unrealistic overestimation of the WEC motions than can heavily affect the wave height at a large distance in the lee of the WEC farm. On the contrary, modelling of a sub-optimal PTO system and of a hydraulic PTO system leads to a similar, yet reduced impact on the “far-field” effects on wave height. The comparison of the PTO systems’ modelling technique shows that when using coupled models, it is necessary to carefully model the WEC hydrodynamics and PTO behaviour as they can introduce substantial inaccuracies into the WECs’ motions and the WEC farm “far-field” effects.

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“…The numerical model should be able to solve the interaction between incoming waves and floating structures, and to reproduce the behaviour of the PTO systems in an accurate way. Several modelling approaches have been employed to analyse the hydrodynamic response of WECs as shown in the following review papers: Li and Yu (2012); Folley et al (2012); Markel and Ringwood (2016); Penalba et al (2017); Zabala et al (2019); Davidson and Costello (2020). However, only a few numerical pieces of research include the mechanical constraints of the PTO system.…”

Section: Introductionmentioning

confidence: 99%

Efficiency and survivability analysis of a point-absorber wave energy converter using DualSPHysics

et al. 2020

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Smoothed Particle Hydrodynamics (SPH) method is used here to simulate a heaving point-absorber with a Power TakeOff system (PTO). The SPH-based code DualSPHysics is first validated with experimental data of regular waves interacting with the point-absorber. Comparison between the numerical and experimental heave displacement and velocity of the device show a good agreement for a given regular wave condition and different configurations of the PTO system. The validated numerical tool is then employed to investigate the efficiency of the proposed system. The efficiency, which is defined here as the ratio between the power absorbed by the point-absorber and its theoretical maximum, is obtained for different wave conditions and several arrangements of the PTO. Finally, the effects of highly energetic sea states on the buoy are examined through alternative configurations of the initial system. A survivability study is performed by computing the horizontal and vertical forces exerted by focused waves on the wave energy converter (WEC). The yield criterion is used to determine that submerging the heaving buoy at a certain depth is the most effective strategy to reduce the loads acting on the WEC and its structure, while keeping the WEC floating at still water level is the worst-case scenario.

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Efficient Nonlinear Hydrodynamic Models for Wave Energy Converter Design—A Scoping Study

Cited by 70 publications

References 270 publications

A Real-Time Detection System for the Onset of Parametric Resonance in Wave Energy Converters

A Real-Time Detection System for the Onset of Parametric Resonance in Wave Energy Converters

Influence of Power Take-Off Modelling on the Far-Field Effects of Wave Energy Converter Farms

Efficiency and survivability analysis of a point-absorber wave energy converter using DualSPHysics

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