# WEC Modelling Review (2022-08-31)
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## Joinly short-list

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### 2022-09: A model predictive control (MPC)-integrated multiphase immersed boundary (IB) framework for simulating wave energy converters (WECs)
> **Ocean Engineering | Vol.260 |** Cited by: 0.0
> | [https://www.sciencedirect.com/science/article/pii/S0029801822012471](https://www.sciencedirect.com/science/article/pii/S0029801822012471)
> | eid: [2-s2.0-85134944446](2-s2.0-85134944446) | doi: [10.1016/j.oceaneng.2022.111908](10.1016/j.oceaneng.2022.111908)
>
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> Khedkar, Kaustubh; Bhalla, Amneet Pal Singh
>
> ---
> United States
>
> ---
>
> Interested in this?
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> - [x] DF
>
> - [x] PM
>
> Irrelevant (forget this paper)
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> - [ ] DF
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> - [ ] PM
>
> ---

*Adaptive mesh refinement | Brinkman penalization method | CFD | Level set method | Ocean energy | Optimal control | Wave–structure interaction*

In this work, we present a novel MPC-integrated multiphase IB framework that can compute the optimal energy-maximizing ==control== force “on-the-fly” by dynamically interacting with a high-fidelity numerical wave ==tank== (NWT). The computational model closely mimics the working setup of the device at its site of operation. ==Due to the requirement of solving a constrained optimization problem at each time step of the IB simulation, the MPC algorithm utilizes a low-dimensional dynamical model of the device that is based on the linear potential theory (LPT).== The multiphase IB solver, on the other hand, is based on the high-dimensional fictitious domain Brinkman penalization (FD/BP) method, which fully-resolves the hydrodynamic ==non-linear==ities associated with the wave–structure interaction (WSI). A time-series forecasting auto-regressive model is implemented that predicts wave heights (from the past NWT data) to estimate the future wave excitation/Froude–Krylov forces for the MPC algorithm. Moreover, we also ==experiment== with ==non-linear== Froude–Krylov (NLFK) forces for the first time in an MPC formulation. The NLFK forces are computed efficiently using a static Cartesian grid, in which the ==WEC== geometry is implicitly represented by a signed distance function. Under varying sea conditions, the predictions of the MPC-integrated multiphase IB solver are compared to the widely popular LPT-based solvers. In agitated sea conditions and/or under aggressive ==control==, the LPT-based WSI solvers produce too optimistic (and misleading) power output values. Overall, six WSI/MPC solver combinations are compared for a heaving vertical cylinder to determine the reasons for discrepancies between high- and low-fidelity predictions. We also determine the pathway of energy transfer from the waves to the power take-off (PTO) system and verify the relationships using IB simulations. Additionally, three different sea states are simulated within the IB simulation to test the adaptive capability of MPC for ==WEC==s. MPC is demonstrated to adapt to changing sea conditions and find the optimal solution for each sea state. The interaction between the distributed-memory parallel multiphase IB solver (written in C++) and the serial MPC solver (written in MATLAB) is fully described to facilitate reproducibility. A bespoke communication layer between the two solvers is developed, which can be easily modified by the ==WEC== community to ==experiment== with other optimal ==control==lers and computational fluid dynamics (==CFD==) solvers. All codes for this work are made open-source for pedagogical and research purposes.

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### 2020-12: Systematic complexity reduction of wave-to-wire models for wave energy system design
> **Ocean Engineering | Vol.217 |** Cited by: 7.0
> | [https://www.sciencedirect.com/science/article/pii/S0029801818318687](https://www.sciencedirect.com/science/article/pii/S0029801818318687)
> | eid: [2-s2.0-85091209721](2-s2.0-85091209721) | doi: [10.1016/j.oceaneng.2020.107651](10.1016/j.oceaneng.2020.107651)
>
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> Penalba, Markel; Ringwood, John V.
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> ---
> Spain;Ireland
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> ---
>
> Interested in this?
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> - [x] DF
>
> - [x] PM
>
> Irrelevant (forget this paper)
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> - [ ] DF
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> - [ ] PM
>
> ---

*HiFiWEC | Hydraulic power take-off | Systematic complexity reduction | Wave energy | Wave-structure hydrodynamic interactions | Wave-to-wire modelling*

Wave-to-wire models are valuable tools for a variety of applications in the development of successful wave energy converters. However, computational requirements of these ==wave-to-wire== models are often prohibitive for certain applications that require fast mathematical models, such as power assessment or ==control== design. The need for computationally fast models is traditionally achieved by assuming linear hydrodynamics and simplifying power take-off (PTO) dynamics with a linear damper in the mathematical model, though these assumptions can be relatively unjustified. However, these computationally appealing mathematical models can have a fidelity level which compromises their use in particular applications. Therefore, this paper suggests an application-sensitive systematic complexity reduction approach that reduces computational requirements of a high-fidelity simulation platform (HiFiWEC), i.e. a ==CFD==-based numerical wave ==tank== coupled to a high-fidelity PTO model, while retaining a level of fidelity in a sense specific to particular applications. The illustrative case study analysed here includes a point absorber with a hydraulic PTO system. Results show that reduced ==wave-to-wire== models designed via the systematic complexity reduction approach retain the application-relevant fidelity (up to 95% fidelity compared to the HiFiWEC) for similar computational requirements shown by the traditionally used linear mathematical models.

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### 2020-06: Computational modelling and experimental tank testing of the multi float WaveSub under regular wave forcing
> **Renewable Energy | Vol.152 |** Cited by: 14.0
> | [https://www.sciencedirect.com/science/article/pii/S0960148119320257](https://www.sciencedirect.com/science/article/pii/S0960148119320257)
> | eid: [2-s2.0-85078753783](2-s2.0-85078753783) | doi: [10.1016/j.renene.2019.12.146](10.1016/j.renene.2019.12.146)
>
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> Faraggiana, E.; Whitlam, C.; Chapman, J.; Hillis, A.; Roesner, J.; Hann, M.; Greaves, D.; Yu, Y. H.; Ruehl, K.; Masters, I.; Foster, G.; Stockman, G.
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> ---
> United Kingdom;United States;United Kingdom;United States;United Kingdom;United Kingdom
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> ---
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> Interested in this?
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> - [x] DF
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> - [x] PM (tbc - experimental validation, but highly-specific WEC config)
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> Irrelevant (forget this paper)
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> - [ ] DF
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> - [ ] PM
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> ---

*Damping | Renewable energy | Tank testing | Wave energy | Wave potential theory*

A submerged wave device generates energy from the relative motion of floating bodies. In WaveSub, three floats are joined to a reactor; each connected to a spring and generator. Electricity generated damps the orbital movements of the floats. The forces are ==non-linear== and each float interacts with the others. Tuning to the wave climate is achieved by changing the line lengths, so there is a need to understand the performance trade-offs for a large number of configurations. This requires an efficient, large displacement, multidirectional, multi-body numerical scheme. Results from a 1/25 scale wave basin ==experiment== are described. Here, we show that a ==time domain== linear potential flow formulation (==Nemoh==, ==WEC==-Sim) can match the ==tank== testing provided that suitably tuned drag coefficients are employed. Inviscid linear potential models can match some wave device ==experiment==s; however, additional viscous terms generally provide better accuracy. Scale ==experiment==s are also prone to mechanical friction, and we estimate friction terms to improve the correlation further. The resulting error in mean power between numerical and physical models is approximately 10%. Predicted device movement shows a good match. Overall, drag terms in ==time domain== wave energy modelling will improve simulation accuracy in wave renewable energy device design.

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### 2020-01: Numerical analysis and wave tank validation on the optimal design of a two-body wave energy converter
> **Renewable Energy | Vol.145 |** Cited by: 27.0
> | [https://www.sciencedirect.com/science/article/pii/S0960148119307827](https://www.sciencedirect.com/science/article/pii/S0960148119307827)
> | eid: [2-s2.0-85067573453](2-s2.0-85067573453) | doi: [10.1016/j.renene.2019.05.109](10.1016/j.renene.2019.05.109)
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> Martin, Dillon; Li, Xiaofan; Chen, Chien An; Thiagarajan, Krish; Ngo, Khai; Parker, Robert; Zuo, Lei
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> United States;United States
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> ---
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> Interested in this?
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> - [x] DF
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> - [x] PM (tbc - no specific mention of control)
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> Irrelevant (forget this paper)
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> - [ ] DF
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> - [ ] PM
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> ---

*Time domain and frequency domain modelling | Two-body point absorber | Wave energy converter | Wave tank test*

To improve the performance of a ‘point absorber’ type wave energy converter (==WEC==), an additional submerged body can be deployed. The submerged body can be used to increase the equivalent excitation force on the ==WEC==, as well as provide resonance tuning. This paper presents numerical analysis and ==experiment==al ==validation== of a two-body point absorber type ==WEC== using a mechanical motion rectifier (MMR) based power takeoff. The two-body point absorber consists of a floating buoy connected to a neutrally buoyant submerged body via the power-takeoff. The mechanical motion rectifier and a ball screw translate the relative heave motion of the two bodies into unidirectional rotation, which in turn spins a generator. Frequency domain analysis suggests there is an optimal submerged body mass for maximum ==WEC== power absorption. Regular wave simulations in the ==time domain== are compared to the results obtained in the ==frequency domain==. While the ==time domain== and ==frequency domain== results predict the same optimal mass ratio, ==time domain== analysis provides a more complex and accurate power result. To ==validate== the ==time domain== model, ==experiment==al wave ==tank== testing is conducted using a 1:30 scale model ==WEC==. The ==experiment== shows the two-body ==WEC== can produce twice the amount of power as the single-body ==WEC== with same floating buoy and can be further increased by PTO design and power electronics optimization. Wave ==tank== testing also shows the two-body ==WEC== has a capture width ratio up to 58% at 59 kW/m and 51% at 36 kW/m.

## PM first pass (DF reviewing)

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### 2019-09: Investigation on PTO control of a Combined Axisymmetric Buoy-WEC(CAB-WEC)
> **Ocean Engineering | Vol.188 |** Cited by: 4.0
> | [https://www.sciencedirect.com/science/article/pii/S0029801819304238](https://www.sciencedirect.com/science/article/pii/S0029801819304238)
> | eid: [2-s2.0-85070208740](2-s2.0-85070208740) | doi: [10.1016/j.oceaneng.2019.106245](10.1016/j.oceaneng.2019.106245)
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> Kong, Fankai; Su, Weiming; Liu, Hengxu; Collu, Maurizio; Lin, Zi; Chen, Hailong; Zheng, Xiongbo
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> United Kingdom;China
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> ---
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> Interested in this?
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> - [ ] DF
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> - [x] PM (tbc)
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> Irrelevant (forget this paper)
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> - [ ] DF
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> - [ ] PM
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> ---

*CAB-WEC | Experimental method | Numerical analysis | PTO control | Semi-analytical*

The Combined Axisymmetric Buoy (CAB), a vertical axisymmetric buoy, has the potential to deliver a high energy absorption power. Considering the CAB-Wave Energy Converters (==WEC==), in order to achieve higher efficiency, the Power Take Off (PTO) systems, which converts the float motion into energy output, needs to be properly ==control==led. In this paper, a PTO ==control== method for a CAB-==WEC== under irregular wave conditions is proposed. Based on the semi-analytical solution obtained in the ==time domain==, a numerical optimization is carried out. The optimal PTO damping coefficients under different wave conditions are obtained, by considering the parameter defined as “capture width ratio”. The expression of the optimal PTO damping coefficient in the ==frequency domain== is derived by an analytical method. Based on the semi-analytical solution of ==time domain== dynamic characteristics and analytical method, a comparison between ==frequency domain== optimization and ==time domain== optimization is presented. In general, the two approaches arrive to very similar conclusions, even if with the ==time domain== methodology a slightly higher capture width ratio is achieved. The ==experiment==al results have been used to ==validate== the ==time domain== optimization method and the variation in optimal average capture width ratio results.

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### 2019-05: Numerical and experimental study on a hemispheric point-absorber-type wave energy converter with a hydraulic power take-off system
> **Renewable Energy | Vol.135 |** Cited by: 26.0
> | [https://www.sciencedirect.com/science/article/pii/S0960148118311716](https://www.sciencedirect.com/science/article/pii/S0960148118311716)
> | eid: [2-s2.0-85060029935](2-s2.0-85060029935) | doi: [10.1016/j.renene.2018.09.097](10.1016/j.renene.2018.09.097)
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> Kim, Sung Jae; Koo, Weoncheol; Shin, Min Jae
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> South Korea;South Korea
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> ---
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> Interested in this?
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> - [ ] DF
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> - [x] PM (tbc)
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> Irrelevant (forget this paper)
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> - [ ] DF
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> - [ ] PM
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> ---

*Energy loss | Hydraulic PTO system | Numerical wave tank | Point absorber | Viscous damping | Wave energy converter*

This study examined the performance of a hemispherical point-absorber wave energy converter (==WEC==) with a hydraulic power take-off (PTO) system. The hydraulic PTO system for power generation was modeled as an approximate coulomb damping force, which was recently proposed to reduce numerical error. To examine the hydrodynamic performance of the ==WEC==, a three-dimensional ==frequency-domain== numerical wave ==tank== technique was adopted, in which the wave radiation problem and diffraction problem for a hemispherical buoy were solved in succession to obtain the hydrodynamic coefficients. The Cummins equation was also adopted to simulate the buoy displacement and extracted wave power in the ==time domain==. For comparison, a three-dimensional wave ==tank== ==experiment== was conducted. Various viscous damping and energy loss from ==WEC== system and hydraulic cylinder pressure of the PTO system were measured from the ==experiment==al results, and these values were added to the governing equation of buoy motion. Therefore, the final numerical model of the ==WEC== system contained the viscous damping and hydraulic PTO forces as well as the potential-flow-based hydrodynamic coefficients. Using the developed numerical model, the hemispheric buoy displacement and extracted wave power were calculated for various hydraulic pressures and input wave conditions to determine the optimal conditions for the maximum wave power.

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### 2019-03: Numerical calculation and experiment of a heaving-buoy wave energy converter with a latching control
> **Ocean Systems Engineering | Vol.9 |** Cited by: 6.0
> | [nan](nan)
> | eid: [2-s2.0-85065069700](2-s2.0-85065069700) | doi: [10.12989/ose.2019.9.1.001](10.12989/ose.2019.9.1.001)
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> Kim, Jeongrok; Cho, Il Hyoung; Kim, Moo Hyun
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> South Korea;United States
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> ---
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> Interested in this?
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> - [ ] DF
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> - [x] PM (tbc)
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> Irrelevant (forget this paper)
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> - [ ] DF
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> - [ ] PM
>
> ---

*Heave motion | Latching control | Latching duration | Model test | Power extraction*

Latching ==control== was applied to a Wave Energy Converter (==WEC==) buoy with direct linear electric Power Take-Off (PTO) systems oscillating in heave direction in waves. The equation of the motion of the ==WEC== buoy in the ==time-domain== is characterized by the wave exciting, hydrostatic, radiation forces and by several damping forces (PTO, brake, and viscous). By applying numerical schemes, such as the semi-analytical and Newmark β methods, the time series of the heave motion and velocity, and the corresponding extracted power may be obtained. The numerical prediction with the latching ==control== is in accordance with the ==experiment==al results from the systematic 1:10-model test in a wave ==tank== at Seoul National University. It was found that the extraction of wave energy may be improved by applying latching ==control== to the ==WEC==, which particularly affects waves longer than the resonant period.

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### 2018-09: A high-fidelity wave-to-wire simulation platform for wave energy converters: Coupled numerical wave tank and power take-off models
> **Applied Energy | Vol.226 |** Cited by: 48.0
> | [https://www.sciencedirect.com/science/article/pii/S0306261918308754](https://www.sciencedirect.com/science/article/pii/S0306261918308754)
> | eid: [2-s2.0-85048289279](2-s2.0-85048289279) | doi: [10.1016/j.apenergy.2018.06.008](10.1016/j.apenergy.2018.06.008)
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> Penalba, Markel; Davidson, Josh; Windt, Christian; Ringwood, John V.
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> Ireland
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> ---
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> Interested in this?
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> - [ ] DF
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> - [ ] PM
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> Irrelevant (forget this paper)
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> - [ ] DF
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> - [ ] PM
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> ---

*CFD | High-fidelity | Numerical Wave Tank | Power take-off | Wave energy | Wave-to-wire modelling*

Performing rigorous technical and commercial assessment of wave energy converters (==WEC==s) numerically, before engaging in expensive wave ==tank== and open ocean tests, is vital for the economically successful development of prototypes. To that end, this paper presents a high-fidelity ==wave-to-wire== simulation platform (the HiFiWEC), where a Computational Fluid Dynamics (==CFD==)-based numerical wave ==tank== is coupled to a high-fidelity power take-off (PTO) model, which enables assessment of ==WEC== performance with greater accuracy than with previous ==wave-to-wire== approaches. A test case, simulating the performance of a heaving point absorber type ==WEC== in realistic conditions, is presented and compared against traditional lower fidelity modelling methods. The ==WEC== response is evaluated with a number of different approaches, including different techniques to model hydrodynamic wave-structure interactions and the power take-off system, and the benefits of the HiFiWEC are highlighted. The results highlight that excessive simplifications in the modelling of the PTO system can lead to significant overestimation in generated energy output, with relative deviations (∊) of up to 150% compared to the HiFiWEC. In addition, uncertainty in viscous drag parameters added to hydrodynamic models based on boundary element method solvers, reinforce the necessity of ==CFD==-based models for applications where high-fidelity is essential. Finally, it is demonstrated that minor/insignificant inaccuracies in the hydrodynamic model (∊=0.5%) can result in significant differences in the estimation of the final energy generation (∊=7%), highlighting the need for a coupled high-fidelity platform.

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### 2018-09: Numerical and experimental studies of excitation force approximation for wave energy conversion
> **Renewable Energy | Vol.125 |** Cited by: 36.0
> | [https://www.sciencedirect.com/science/article/pii/S0960148118303021](https://www.sciencedirect.com/science/article/pii/S0960148118303021)
> | eid: [2-s2.0-85044008247](2-s2.0-85044008247) | doi: [10.1016/j.renene.2018.03.007](10.1016/j.renene.2018.03.007)
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> Guo, Bingyong; Patton, Ron J.; Jin, Siya; Lan, Jianglin
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> United Kingdom;United Kingdom;United Kingdom
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> ---
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> Interested in this?
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> - [ ] DF
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> - [ ] PM
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> Irrelevant (forget this paper)
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> - [ ] DF
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> - [ ] PM
>
> ---

*Excitation force modelling | Model verification | System identification | Unknown input observer | Wave energy conversion | Wave tank tests*

Past or/and future information of the excitation force is useful for real-time power maximisation ==control== of Wave Energy Converter (==WEC==) systems. Current ==WEC== modelling approaches assume that the wave excitation force is accessible and known. However, it is not directly measurable for oscillating bodies. This study aims to provide accurate approximations of the excitation force for the purpose of enhancing the effectiveness of ==WEC== ==control==. In this work, three approaches are proposed to approximate the excitation force, by (i) identifying the excitation force from wave elevation, (ii) estimating the excitation force from the measurements of pressure, acceleration and displacement, (iii) observing the excitation force via an unknown input observer. These methods are compared with each other to discuss their advantages, drawbacks and application scenarios. To ==validate== and compare the performance of the proposed methods, a 1/50 scale heaving point absorber ==WEC== was tested in a wave ==tank== under variable wave scenarios. The ==experiment==al data were in accordance with the excitation force approximations in both the frequency- and ==time-domain==s based upon both regular and irregular wave excitation. Although the ==experiment==al data were post-processed for model verification, these approaches can be applied for real-time power maximisation ==control== with excitation force prediction.

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### 2018-07: Improving the Computational Performance of Nonlinear Pseudospectral Control of Wave Energy Converters
> **IEEE Transactions on Sustainable Energy | Vol.9 |** Cited by: 14.0
> | [nan](nan)
> | eid: [2-s2.0-85039774009](2-s2.0-85039774009) | doi: [10.1109/TSTE.2017.2786045](10.1109/TSTE.2017.2786045)
>
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> Mérigaud, Alexis; Ringwood, John V.
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> Ireland
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> ---
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> Interested in this?
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> - [ ] DF
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> - [ ] PM
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> Irrelevant (forget this paper)
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> - [ ] DF
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> - [ ] PM
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> ---

*constraints | differential flatness | gradient | Hessian | optimal control | power maximisation | Wave energy converters*

The optimal ==control== problem for a one-degree of freedom wave energy converter (==WEC==) with dynamical ==nonlinear==ities and constraints is formulated in the ==frequency-domain==. The formulation adopted corresponds to a Fourier pseudospectral framework but, in contrast to previous similar approaches found in ==WEC== ==control== literature, it is shown that ==control== force and velocity variables can be eliminated, using a ==frequency-domain== transcription of the ==nonlinear== dynamical equations, thus, resulting in fewer variables and elimination of the equality constraints. Furthermore, it is shown how the gradient and Hessian of the cost function and constraints can be explicitly calculated, which can be used to improve convergence within gradient-based optimisation techniques. The benefits of the proposed developments are illustrated by means of numerical ==experiment==s, for a flap-type ==WEC== with viscous drag, under various constraint configurations. The techniques presented are formulated in a generic way, allowing for easy result transposition to a variety of ==nonlinear== ==WEC== models.

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### 2017-01: Validating a wave-to-wire model for a wave energy converter-part I: The hydraulic transmission system
> **Energies | Vol.10 |** Cited by: 25.0
> | [nan](nan)
> | eid: [2-s2.0-85028613014](2-s2.0-85028613014) | doi: [10.3390/en10070977](10.3390/en10070977)
>
> ---
> Penalba, Markel; Sell, Nathan P.; Hillis, Andy J.; Ringwood, John V.
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> United Kingdom;Ireland
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> ---
>
> Interested in this?
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> - [ ] DF
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> - [x] PM (tbc - hydraulic-based PTO transmission)
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> Irrelevant (forget this paper)
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> - [ ] DF
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> - [ ] PM
>
> ---

*Experimental testing | Hydraulic transmission systems | Schlosser model | Stribeck friction model | Validation | Wave energy | Wave-to-wire modelling*

Considering the full dynamics of the different conversion stages from ocean waves to the electricity grid is essential to evaluate the realistic power flow in the drive train and design accurate model-based ==control== formulations. The power take-off system for wave energy converters (==WEC==s) is one of the essential parts of ==wave-to-wire== (W2W) models, for which hydraulic transmissions are a robust solution and offer the flexibility to design specific drive-trains for specific energy absorption requirements of different ==WEC==s. The potential hydraulic drive train topologies can be classified into two main configuration groups (constant-pressure and variable-pressure configurations), each of which uses specific components and has a particular impact on the preceding and following stages of the drive train. The present paper describes the models for both configurations, including the main ==nonlinear== dynamics, losses and constraints. Results from the mathematical model simulations are compared against ==experiment==al results obtained from two independent test rigs, which represent the two main configurations, and high-fidelity software. Special attention is paid to the impact of friction in the hydraulic cylinder and flow and torque losses in the hydraulic motor. Results demonstrate the effectiveness of the models in reproducing ==experiment==al results, capturing friction effects and showing similar losses.

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## DF authored papers

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### 2022-07: Multi-objective optimisation of a sloped-motion, multibody wave energy converter concept
> **Renewable Energy | Vol.194 |** Cited by: 0.0
> | [https://www.sciencedirect.com/science/article/pii/S0960148122006681](https://www.sciencedirect.com/science/article/pii/S0960148122006681)
> | eid: [2-s2.0-85131257300](2-s2.0-85131257300) | doi: [10.1016/j.renene.2022.05.030](10.1016/j.renene.2022.05.030)
>
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> Cotten, A.; Forehand, D. I.M.
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> United Kingdom
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> ---
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> Interested in this?
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> - [ ] DF
>
> - [ ] PM
>
> Irrelevant (forget this paper)
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> - [ ] DF
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> - [ ] PM
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> ---

*Heuristic optimisation | Hydrodynamic modelling | Multi-objective optimisation | Multibody wave energy converter | Sloped motion wave energy converter | WaveTrain*

The WaveTrain device is a wave energy converter concept designed to extend the high performance of buoys that undergo sloped motion into a deep water environment. It achieves this by mechanically interconnecting a series of sloped modules, amongst which restorative forces can be exchanged in order to prevent detrimental pitching motion, whilst sufficiently free motion along the inclined axis is retained. Importantly, this circumvents the requirement of a rigid seabed connection, but introduces a potential vulnerability of operational failure of the rotational joints that link each connecting strut to the adjacent module. In this paper, the impact of considering the fatigue damage accumulating at the joints, in addition to the power extraction, is investigated with regards to the optimal design of the WaveTrain device. A specially-tailored multi-objective genetic algorithm is used to explore the optimal design candidates with two variants of the pair of conflicting objectives (power extraction and fatigue damage). Some key design criteria are then presented, with reference and comparison to the design criteria that are considered optimal when only power extraction is considered.

## PM second pass

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### 2022-07: Hydrodynamics and load shedding behavior of a variable-geometry oscillating surge wave energy converter (OSWEC)
> **Renewable Energy | Vol.194 |** Cited by: 0.0
> | [https://www.sciencedirect.com/science/article/pii/S0960148122008291](https://www.sciencedirect.com/science/article/pii/S0960148122008291)
> | eid: [2-s2.0-85132231003](2-s2.0-85132231003) | doi: [10.1016/j.renene.2022.05.169](10.1016/j.renene.2022.05.169)
>
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> Choiniere, Michael; Davis, Jacob; Nguyen, Nhu; Tom, Nathan; Fowler, Matthew; Thiagarajan, Krish
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> ---
> United States;United States;United States
>
> ---
>
> Interested in this?
>
> - [ ] DF
>
> - [ ] PM
>
> Irrelevant (forget this paper)
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> - [ ] DF
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> - [ ] PM
>
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*Load shedding | Model tests | Oscillating surge wave energy converter | Response amplitude operator | Wave energy conversion | Wave hydrodynamics*

In order to improve their long-term viability, wave energy converters (==WEC==s) need to be able to shed loads when a threshold wave condition is exceeded. As shown by Tom et al. (2016) [1], provision of adjustable flaps within the body of an oscillating surge wave energy converter (OSWEC) allows wave energy to pass through the device. A ==control== system may then be able to open and close the flaps when waves approaching the device exceed preset thresholds. The variable-geometry OSWEC (VG-OSWEC) concept studied in this paper is a bottom-hinged, rectangular wave paddle with five flaps of elliptical cross-section embedded into the face of the paddle. System ID tests were conducted on this VG-OSWEC device at a 1:14 scale in a wave basin. Free decay tests showed that the ==damping== was distinctly ==nonlinear== when the flaps were fully open, and the natural frequency increased by 40% when compared with the flaps in a fully closed configuration. Tests with regular wave conditions were used to develop the response amplitude operator for the rotational motion about the hinge. These response amplitude operator results when compared with numerical simulations run using ==WEC==-Sim/WAMIT and ANSYS AQWA, show strong agreement with the flap open and closed conditions. The regular-wave condition measurements also show that the wave excitation moment about the hinge was reduced by up to 60% when the flaps were fully open. The ==experiment==s serve to demonstrate the potential of the variable geometry design to shed loads and survive harsh ocean environments.

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### 2021-04: Wave Excitation Force Prediction of a Heaving Wave Energy Converter
> **IEEE Journal of Oceanic Engineering | Vol.46 |** Cited by: 1.0
> | [nan](nan)
> | eid: [2-s2.0-85104387181](2-s2.0-85104387181) | doi: [10.1109/JOE.2020.2984293](10.1109/JOE.2020.2984293)
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> Davis, Andrew F.; Fabien, Brian C.
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> United States;United States
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*Time series | wave energy | wave forecasting*

Optimal ==control== strategies for wave energy converters (==WEC==s) commonly require noncausal knowledge of the incident wave to maximize energy production. To enable these ==control== methods, the prediction capabilities of two autoregressive (AR) models are evaluated. This work utilized autoregressive methods to predict the wave excitation force since they can be implemented in real time to adapt to changing conditions. The two models evaluated in this work are AR and AR with exogenous inputs (ARX) models. These models describe the wave propagation between two devices. To substantiate the validity of the predictions presented here, the wave excitation force was also estimated using an extended Kalman filter (EKF). The EKF incorporated ==nonlinear== heave models of each body to determine the wave excitation force that was formulated as a harmonic disturbance to each system. The combination of the EKF and the AR models presents an opportunity to evaluate the prediction capabilities of what can be currently implemented on board ==WEC==s in real time; there is no need for offline training or postprocessed filtering of the wave. The ARX model incorporating excitation force data from other deployed bodies (the exogenous input) is shown to significantly improve the performance of the wave excitation force prediction. It is concluded that ==WEC==s in a wave farm may be able to improve their energy harvesting performance through enhancing their prediction capabilities by using wave estimation data gathered from other ==WEC==s. ==Experiment==al data from a two-body wave ==tank== test is used for this work.

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### 2020-02: Wave excitation force estimation of wave energy floats using extended Kalman filters
> **Ocean Engineering | Vol.198 |** Cited by: 4.0
> | [https://www.sciencedirect.com/science/article/pii/S0029801820300512](https://www.sciencedirect.com/science/article/pii/S0029801820300512)
> | eid: [2-s2.0-85078207219](2-s2.0-85078207219) | doi: [10.1016/j.oceaneng.2020.106970](10.1016/j.oceaneng.2020.106970)
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> Davis, Andrew F.; Fabien, Brian C.
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> United States;United States
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*Estimation | Excitation force | Extended Kalman filter | Nonlinear model | Wave energy converter*

In many advanced ==control== strategies the wave excitation force is key to determining the ==control== input. However, it is often difficult to measure the excitation force on a Wave Energy Converter (==WEC==). The use of Kalman filters to estimate the wave excitation force based on readily available measurement data can potentially fill the gap between the development of ==WEC== ==control== strategies and the data that is available. Two different estimation methods using an ==nonlinear== Extended Kalman Filter are tested on ==experiment==al wave ==tank== data for a heaving semi-submerged float. The first method relies on directly including the excitation force as a state in the first order dynamics—which allows the “random walk” of the Kalman filter to identify an estimate of the excitation force. The second method of estimation involves modeling the wave excitation force as a harmonic oscillator comprised of sinusoidal components. Both methods are evaluated for a variety of incident waves and additional sensitivity analyses are performed to investigate the susceptibility of these estimation methods to changes in the model, measurement noise, and sampling rate.

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### 2019-02: Experimental and numerical comparisons of self-reacting point absorber wave energy converters in irregular waves
> **Ocean Engineering | Vol.173 |** Cited by: 19.0
> | [https://www.sciencedirect.com/science/article/pii/S0029801819300277](https://www.sciencedirect.com/science/article/pii/S0029801819300277)
> | eid: [2-s2.0-85060327327](2-s2.0-85060327327) | doi: [10.1016/j.oceaneng.2019.01.034](10.1016/j.oceaneng.2019.01.034)
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> Beatty, Scott J.; Bocking, Bryce; Bubbar, Kush; Buckham, Bradley J.; Wild, Peter
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> Canada;Canada;Canada
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*Heave plate | Hydrodynamics | Model testing | Point absorbers | Power take-off | Self reacting | Time domain | Wave energy conversion*

An ==experiment==al and numerical comparison of the performance of two self-reacting point absorber wave energy converter designs is undertaken for heave motions in irregular waves. The ==experiment==s consist of a series of 1:25 scale model tests that feature re-configurable ==WEC== body shapes, a feedback ==control==led power take-off, and a heave motion constraint apparatus. While both designs have the same float, the first design features a streamlined reacting body and the second design features a damper plate reacting body. A ==time domain== numerical model, ==validate==d by the ==experiment==al results, is used to extend the comparisons of the designs in terms of power matrices, capture width matrices, and mean annual power production. Results indicate that the wave energy converter design with damper plate produces 41% higher mean annual energy production than the wave energy converter design with streamlined reacting body at a representative location near the West Coast of Vancouver Island, British Columbia, Canada.

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### 2017-02: Numerical modelling of a point-absorbing wave energy converter in irregular and extreme waves
> **Applied Ocean Research | Vol.63 |** Cited by: 37.0
> | [https://www.sciencedirect.com/science/article/pii/S0141118716302668](https://www.sciencedirect.com/science/article/pii/S0141118716302668)
> | eid: [2-s2.0-85009437793](2-s2.0-85009437793) | doi: [10.1016/j.apor.2017.01.004](10.1016/j.apor.2017.01.004)
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> Chen, Wen Chuang; Dolguntseva, Irina; Savin, Andrej; Zhang, Yong Liang; Li, Wei; Svensson, Olle; Leijon, Mats
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> China;Sweden
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*CFD | Connection rope tension | Extreme waves | Irregular waves | Point-absorbing WEC | Survivability*

Based on the Navier-Stokes (RANS) equations, a three-dimensional (3-D) mathematical model for the hydrodynamics and structural dynamics of a floating point-absorbing wave energy converter (==WEC==) with a stroke ==control== system in irregular and extreme waves is presented. The model is ==validate==d by a comparison of the numerical results with the wave ==tank== ==experiment== results of other researchers. The ==validate==d model is then utilized to examine the effect of wave height on structure displacements and connection rope tension. In the examined cases, the differences in ==WEC=='s performance exhibited by an inviscid fluid and a ==viscous== fluid can be neglected. Our results also reveal that the differences in behavior predicted by boundary element method (BEM) and the RANS-based method can be significant and vary considerably, depending on wave height.

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### 2017-01: An assessment of WEC control performance uncertainty
> **Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE | Vol.10 |** Cited by: 1.0
> | [nan](nan)
> | eid: [2-s2.0-85032007648](2-s2.0-85032007648) | doi: [10.1115/OMAE2017-61912](10.1115/OMAE2017-61912)
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> Coe, Ryan G.; Bacelli, Giorgio; Abdelkhalik, Ossama; Wilson, David G.
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> United States;United States
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*(no keywords)*

A linear dynamic model for a wave energy converter (==WEC==) has been developed based on the results of ==experiment==al wave ==tank== testing. Based on this model, a model predictive ==control== (MPC) strategy has been designed and implemented. To assess the performance of this ==control== strategy, a deployment environment off the coast of Newport, OR has been selected and the ==control==ler has been used to simulate the ==WEC== response in a set of irregular sea states. To better understand the influence of model accuracy on ==control== performance, an uncertainty analysis has been performed by varying the parameters of the model used for the design of the ==control==ler (i.e. the ==control== model), while keeping the ==WEC== dynamic model employed in these simulations (i.e. the plant model) unaltered. The results of this study indicate a relative low sensitivity of the MPC ==control== strategy to uncertainties in the ==control==ler model for the specific case studied here.

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## WECCCOMP

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### 2020-01: Ex-post analysis of the WEC control competition results using a Fourier spectral control approach
> **IFAC-PapersOnLine | Vol.53 |** Cited by: 1.0
> | [https://www.sciencedirect.com/science/article/pii/S2405896320315925](https://www.sciencedirect.com/science/article/pii/S2405896320315925)
> | eid: [2-s2.0-85099352592](2-s2.0-85099352592) | doi: [10.1016/j.ifacol.2020.12.1197](10.1016/j.ifacol.2020.12.1197)
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> Mérigaud, Alexis; Ngo, Caroline; Nguyen, Hoai Nam; Sabiron, Guillaume; Tona, Paolino
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> France
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*Model predictive control | Non-smooth optimal control | Power-maximising control | Spectral control | Wave energy converters*

The wave energy converter ==control== competition (==WEC==CCOMP) allowed several real-time ==control== approaches to be assessed, both in numerical and physical ==experiment==s. The solution retained by IFP Énergies Nouvelles (IFPEN), which won the numerical simulation and ==experiment==al evaluation phases, consists of a receding-horizon MPC algorithm, including an estimator and a predictor for the wave excitation torque. The ==control== objective function, solved by a quadratic programming (QP) optimiser in the real-time implementation, is weighted over the receding time horizon by means of weighting coefficients, which are optimised off-line for each sea state, in order to take into account the non-ideal power take-off (PTO) efficiency. Given the potential complexity of the interaction between the different components involved in the ==control== implementation (estimation, prediction, QP solution, choice of weightings), it is useful to carry out an ex-post analysis, in order to understand if, and how, the solution proposed by IFPEN could have been improved. To that end, a Fourier spectral ==control== algorithm is implemented, which is able to calculate the optimal trajectory and ==control== torque for the totality of a signal, simulated from ==WEC==CCOMP sea states, taking the non-ideal PTO efficiency into account. By comparing MPC results with the theoretically optimal solutions provided by the spectral method, it is found that, in the studied ==WEC==CCOMP sea states, the IFPEN MPC algorithm performance lies within approximately 10% of the optimal solution, in terms of electric power. The influence of the MPC forecast accuracy and prediction horizon is examined. Finally, some challenges associated with the offline MPC weighting optimisation are identified.

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### 2020-01: Experimental assessment of the ifpen solution to the wec control competition
> **Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE | Vol.9 |** Cited by: 2.0
> | [nan](nan)
> | eid: [2-s2.0-85099335683](2-s2.0-85099335683)
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> Tona, Paolino; Sabiron, Guillaume; Nguyen, Hoai Nam; Mérigaud, Alexis; Ngo, Caroline
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> France
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*(no keywords)*

This paper describes the ==experiment==al assessment of the solution developed by IFP Energies nouvelles (IFPEN) for the ==WEC== ==Control== Competition (==WEC==CCOMP), a benchmark devised to compare energy-maximizing ==control==lers for wave energy converters (==WEC==s). For the first round of the competition, carried out in simulation with ==WEC==-Sim, IFPEN had submitted an MPCbased solution, which eventually scored best among the contestants, with respect to the energy-related criterion defined by the organizers and computed on a set of six irregular waves. For the second round of the competition, the performance of this MPC solution has been assessed in a ==tank== test situation, on the same Wavestar-like scale device that had been simulated in ==WEC==-Sim. The paper first recalls the features of the ==control== solution implemented for the competition, an offline-tuned weighted-QP MPC algorithm using short-term prediction from present and past wave excitation force estimates. Then, the major steps of the test plan are described and ==control== design choices are explained. Finally, the ==experiment==al results in closed loop are presented. Despite noise and an imperfectly ==control==led PTO actuator, IFPEN's MPC solution proves efficient and robust: Its ==experiment==al performance in terms of harvested electrical energy is in accordance with the nominal results obtained in simulation using the linear design model, and this, for different realizations of each sea state. This performance has allowed the IFPEN team to win the competition also at the ==experiment==al stage.