On the importance of nonlinear hydrodynamics and resonance frequencies on power production in multi-mode WECs

Tran, N.; Sergiienko, Nataliia Y.; Cazzolato, B.; Ding, Boyin; Wuillaume, Pierre-Yves; Ghayesh, Mergen H.; Arjomandi, Maziar

doi:10.1016/j.apor.2021.102924

Cited by 12 publications

(3 citation statements)

References 22 publications

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“…where other modes of motion are included and the model is forced by incident waves. Recent work on submerged wave energy convertors (Tran et al., 2021; Tran, Sergiienko, Cazzolato, Ghayesh, & Arjomandi, 2022) suggests that mode coupling is of high importance in power absorption – there would be great value in extending the weakly nonlinear model used in these works to a hybrid model taking better account of shallow water effects. However, this requires further model development and validation experiments.…”

Section: Discussionmentioning

confidence: 99%

Hybrid axisymmetric model for forced heave of a shallowly submerged cylindrical wave energy converter

McCauley,

Wolgamot,

Draper

et al. 2023

Flow

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Shallowly submerged oscillating structures may be found in wave energy devices or semi-submersible vessels. Predicting the force on such structures is critical for design purposes, but complicated due to nonlinear phenomena which can occur in shallow water, including wave breaking and bore formation. Such effects are particularly important around the first ‘resonance’ frequency of the fluid on top of the device, where linear theory predicts large flows on/off the cylinder and corresponding surface elevations and forces. In an effort to create a reliable and efficient model to predict the hydrodynamic force on a shallowly submerged truncated vertical cylinder, an axisymmetric nonlinear hybrid model is developed for forced heave oscillations. The flow above the cylinder is modelled using the nonlinear shallow water equations, and linear potential flow theory is used in the surrounding fluid. The model is compared with experimental results for forced heave oscillations and performs well for predicting the heave force. It is then used to examine linearised heave force for increasing amplitudes of (prescribed) harmonic heave motion. There is a significant reduction in the peaks of radiation damping and added mass coefficients with increasing amplitude, and associated shifts in the frequencies of the peaks.

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Section: Discussionmentioning

confidence: 99%

Hybrid axisymmetric model for forced heave of a shallowly submerged cylindrical wave energy converter

McCauley,

Wolgamot,

Draper

et al. 2023

Flow

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show abstract

“…Haeng Sik Ko et al [8] studied the dynamic behaviour of an asymmetric wave-energy converter and found that the third harmonic moment term is significant in both experimental and OpenFOAM results, especially at higher amplitudes. A multi-mode PA-WEC investigation by Tran et al [9] revealed that higher harmonics in motion response can cause more frequent changes in the projected surface area, which decreases the obtained power. Therefore, harmonic components have been shown to play a crucial role in the hydrodynamic performance of wave-energy converters.…”

Section: Introductionmentioning

confidence: 99%

Experimental and CFD Assessment of Harmonic Characteristics of Point-Absorber Wave-Energy Converters with Nonlinear Power Take-Off System

Yi,

Sun,

Liu

et al. 2023

JMSE

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The wave-energy excitation of point absorbers is highly associated with their resonant movement, and harmonic characteristics are of increasing concern in affecting resonance. However, the commonly used linearized power take-off (PTO) systems underestimate the impact of harmonics. The purpose of this study is to address the knowledge gap in assessing the contribution of hydraulic PTO systems to higher harmonic wave loads and velocities. In the present work, higher harmonics in point-absorber wave-energy converters (PA-WECs) with hydraulic power take-off (PTO) systems are investigated through both experimental and computational fluid dynamics (CFD) methods. The fast Fourier transform is used to decompose the high-order harmonics. To account for the influence of nonlinear wave–wave interaction on harmonics, the isolated PA-WEC is used as a basis for comparison with the paired PA-WECs. The influence of wave steepness is also estimated at two resonance periods. Results indicate that the additional resonance of the paired PA-WECs may be attributed to the harmonic wave loads at longer wave periods. Harmonic wave loads of paired PA-WECs typically have a more substantial impact and increase more rapidly with increasing wave steepness compared to isolated PA-WECs. Furthermore, as the wave steepness increases, there are significant enhancements in both the harmonic wave loads and heaving velocity, which strongly correlate with the instantaneous maximum hydraulic power. Consequently, our study will contribute to enhancing the maximum power output in the design of future point absorber arrays.

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“…Among marine renewables, ocean waves are recognized as one of the most promising sources of clean, reliable, and renewable energy, with an estimated potential that is theoretically equivalent to more than double the world's current electricity demand (IRENA 2020). Nevertheless, the full exploitation of Wave Energy Converters (WECs) is still hindered by deficiencies in wave resource assessments, often overlooking relevant non-linear processes that affect the reliability of theoretical estimates (Hong et al, 2021;Tran et al, 2021), as well as by the need to better characterize their performance in complex multi-device configurations and to develop efficient control systems (Gallutia et al, 2022). In general, WECs have yet to reach the level of commercial viability that would guarantee their competitiveness with alternative energy sources, especially in the absence of synergetic technologies with the potential for hybridization and/or co-location (Foteinis and Tsoutsos, 2017;Clemente et al, 2021;Petracca et al, 2022).…”

Section: Introductionmentioning

confidence: 99%

Exploitation of an operative wave forecast system for energy resource assessment in the Mediterranean Sea

2022

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Ocean Energy is now emerging as a viable long-term form of renewable energy, which might contribute around 10% of EU power demand by 2050, if sufficient support is guaranteed along its road to full commercialization, allowing to further demonstrate the reliability, robustness and overall economic competitiveness of technologies. Although wave energy is still less developed than other marine renewables, its high density, great potential and minimal environmental impact have renewed the interest of developers, investors and governments globally, also in view of the increasing awareness of climate change and of the necessity to reduce carbon emissions. In parallel with technological development, the reliable characterization of wave climate and of the associated energy resource is crucial to the design of efficient Wave Energy Converters and to an effective site-technology matching, especially in low-energy seas. The preliminary scrutiny of suitable technologies and the identification of promising sites for their deployment often rely on wave climatological atlases, yet a more detailed characterization of the local resource is needed to account for high-frequency spatial and temporal variability that significantly impact power generation and the economic viability of WEC farms. We present a high-resolution assessment of the wave energy resource at specific locations in the Mediterranean Sea, based on a 7-years dataset derived from the operative wave forecast system that has been developed at ENEA and has been running since 2013. The selected areas correspond to the target regions of the Blue Deal project, where energy resource estimates were combined with technical and environmental considerations, so as to identify optimal sites for Blue Energy exploitation, from a Maritime Spatial Planning perspective. The available resource at selected sites is analysed together with site theoretical productivity for three state-of-the art WECs, showing interesting potential for future deployment.

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On the importance of nonlinear hydrodynamics and resonance frequencies on power production in multi-mode WECs

Cited by 12 publications

References 22 publications

Hybrid axisymmetric model for forced heave of a shallowly submerged cylindrical wave energy converter

Hybrid axisymmetric model for forced heave of a shallowly submerged cylindrical wave energy converter

Experimental and CFD Assessment of Harmonic Characteristics of Point-Absorber Wave-Energy Converters with Nonlinear Power Take-Off System

Exploitation of an operative wave forecast system for energy resource assessment in the Mediterranean Sea

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