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Assessment and Nonlinear Modeling of Wave, Tidal and Wind Energy Converters and Turbines

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A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "A3: Wind, Wave and Tidal Energy".

Deadline for manuscript submissions: closed (30 April 2020) | Viewed by 47545

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Dr. Madjid Karimirad

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School of Natural and Built Environment, Queen’s University Belfast, Belfast, UK
Interests: marine structures; offshore mechanics; floating wind turbines; offshore renewable energy; stochastic dynamics; experimental and numerical assessment
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Dr. Maurizio Collu

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Department of Naval Architecture, Ocean and Marine Engineering, University of Strathclyde, Glasgow G1 1XQ, UK
Interests: wind energy; mooring systems; aerodynamics; hydrodynamics; optimization
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Dear colleagues,

Offshore renewable energy (ORE), such as offshore wind turbines, wave energy converters, and tidal and current turbines, has experiences rapid growth in the past decade. The combination of wave, wind, and current energy devices in hybrid marine platforms to use possible synergies through proper combinations has also been a recent scientific focus. These fields are seeing rapid development and advancement in science, technology, and engineering, which is driven by research regarding new concepts/structures, numerical modeling tools, and simulation methods.

ORE structures are subjected to complicated loads and load effects, which demand a comprehensive numerical modeling representation of the physics. Important factors affecting the design, functionality, structural integrity, and performance of offshore structures include—but are not limited to—fluid–structure interactions, controller actions, intense dynamic effects, nonlinear loadings, extreme and harsh weather conditions, and impact pressure loads. There is interdependence between loads, load effects, and structural strength. To enable further growth in reliable ORE technologies in the coming years, more advanced numerical tools and nonlinear modeling are needed.

We invite researchers and scientists to contribute original research articles that will stimulate the continuing progress of the ORE field, with a focus on the state-of-the-art numerical modeling for ORE engineering. We are particularly interested in articles describing the new methodologies, analytical and numerical tools, as well as theoretical methods dealing with engineering problems in the field of ORE structures for wave, wind, current, and hybrid marine platforms. Potential topics include but are not limited to:

Innovative ORE systems;
Statistical methods and environmental resource assessment;
Wind, wave, and current interactions;
Comprehensive handling of engineering problems, in particular design aspects;
Numerical methods for structural and fluid dynamics;
Computational fluid dynamics (CFD);
Finite element methods (FEM);
Fluid–structure interaction (FSI);
Aero-hydro-servo-geo-elastic models for fixed and floating offshore wind turbines;
Automatic control methods applied for ORE engineering problems;
Robust nonlinear models for fast simulation;
Comprehensive numerical methods for high-fidelity simulation of behavior and functionality;
Verification and validation, code-to-code comparison, as well as experiments;
Insight into the philosophy and power of numerical simulations;
Nonlinearities in physical systems and numerical models;
Coupled effects between floater and mooring system;
Soil–structure interaction with a focus on offshore renewable energy applications;
Higher order wave loads and responses.

Dr. Madjid Karimirad
Dr. Maurizio Collu
Guest Editors

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Keywords

nonlinear modeling
numerical simulations
offshore energy structure (ORE)
wave energy converter (WEC)
tidal turbines
floating wind turbines
finite element modeling (FEM)
computational fluid dynamics (CFD)

Related Special Issue

Numerical Analysis, Field Testing and Experimental Assessment of Offshore Wind Turbines 2023 in Energies (8 articles)

Published Papers (13 papers)

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Research

19 pages, 2197 KiB

Open AccessArticle

An Inter-Comparison of Dynamic, Fully Coupled, Electro-Mechanical, Models of Tidal Turbines

by Arturo Ortega, Joseph Praful Tomy, Jonathan Shek, Stephane Paboeuf and David Ingram

Energies 2020, 13(20), 5389; https://doi.org/10.3390/en13205389 - 15 Oct 2020

Cited by 6 | Viewed by 2366

Abstract

Production of electricity using hydrokinetic tidal turbines has many challenges that must be overcome to ensure reliable, economic and practical solutions. Kinetic energy from flowing water is converted to electricity by a system comprising diverse mechanical and electrical components from the rotor blades up to the electricity grid. To date these have often been modelled using simulations of independent systems, lacking bi-directional, real-time, coupling. This approach leads to critical effects being missed. Turbulence in the flow, results in large velocity fluctuations around the blades, causing rapid variation in the shaft torque and generator speed, and consequently in the voltage seen by the power electronics and so compromising the export power quality. Conversely, grid frequency and voltage changes can also cause the generator speed to change, resulting in changes to the shaft speed and torque and consequently changes to the hydrodynamics acting on the blades. Clearly, fully integrated, bi-directional, models are needed. Here we present two fully coupled models which use different approaches to model the hydrodynamics of rotor blades. The first model uses the Blade Element Momentum Theory (BEMT), resulting in an efficient tool for turbine designers. The second model also uses BEMT, combines this with an actuator line model of the blades coupled to an unsteady computational fluid dynamics simulation by OpenFOAM (CFD/BEMT). Each model is coupled to an OpenModelica model of the electro-mechanical system by an energy balance to compute the shaft speed. Each coupled system simulates the performance of a 1.2 m diameter, three-bladed horizontal axis tidal turbine tested in the University of Edinburgh FloWave Ocean Energy Research Facility. The turbulent flow around the blades and the mechanical-electrical variables during the stable period of operation are analysed. Time series and tabulated average values of thrust, torque, power, and rotational speed, as well as, electrical variables of generator power, electromagnetic torque, voltage and current are presented for the coupled system simulation. The relationship between the mechanical and electrical variables and the results from both tidal turbine approaches are discussed. Our comparison shows that while the BEMT model provides an effective design tool (leading to slightly more conservative designs), the CFD/BEMT simulations show the turbulence influence in the mechanical and electrical variables which can be especially important in assessing an additional source of stresses in the whole electro-mechanical system (though at an increased computational cost). Full article

(This article belongs to the Special Issue Assessment and Nonlinear Modeling of Wave, Tidal and Wind Energy Converters and Turbines)

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19 pages, 5674 KiB

Open AccessArticle

Fatigue Life Assessment for Power Cables in Floating Offshore Wind Turbines

by Mohsen Sobhaniasl, Francesco Petrini, Madjid Karimirad and Franco Bontempi

Energies 2020, 13(12), 3096; https://doi.org/10.3390/en13123096 - 15 Jun 2020

Cited by 15 | Viewed by 4716

Abstract

In this paper, a procedure is proposed to determine the fatigue life of the electrical cable connected to a 5 MW floating offshore wind turbine, supported by a spar-buoy at a water depth of 320 m, by using a numerical approach that takes into account site-specific wave and wind characteristics. The effect of the intensity and the simultaneous actions of waves and wind are investigated and the outcomes for specific cable configurations are shown. Finally, the fatigue life of the cable is evaluated. All analyses have been carried out using the Ansys AQWA computational code, which is a commercial code for the numerical investigation of the dynamic response of floating and fixed marine structures under the combined action of wind, waves and current. Furthermore, this paper applies the FAST NREL numerical code for comparison with the ANSYS AQWA results. Full article

(This article belongs to the Special Issue Assessment and Nonlinear Modeling of Wave, Tidal and Wind Energy Converters and Turbines)

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20 pages, 12280 KiB

Open AccessArticle

Optimal Dimensions of a Semisubmersible Floating Platform for a 10 MW Wind Turbine

by Giulio Ferri, Enzo Marino and Claudio Borri

Energies 2020, 13(12), 3092; https://doi.org/10.3390/en13123092 - 15 Jun 2020

Cited by 14 | Viewed by 3666

Abstract

In this paper, an optimal semisubmersible platform is sought considering two key geometry variables: the diameter of the outer cylinders and their radial distance from the platform centre. The goal is to identify a platform configuration able to most efficiently contrast the combined wind-wave action, keeping the platform dimensions as small as possible. The amplitude of the Response Amplitude Operator (RAO) peaks and the integral area of the RAOs in a range of excited frequencies for the selected degrees of freedom are chosen as targets to be minimised. Through an efficient frequency domain simulation approach, we show that upscaling techniques proposed in the literature may lead to overdesigned platforms and that smaller and more performing platforms can be identified. In particular, the optimised platform shows a reduction of about 51% in parked and 54% in power production of the heave RAO peak, and a reduction of about 37% in parked and 50% in power production of the pitch RAO. Full article

(This article belongs to the Special Issue Assessment and Nonlinear Modeling of Wave, Tidal and Wind Energy Converters and Turbines)

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22 pages, 4356 KiB

Open AccessArticle

Parametric Study for an Oscillating Water Column Wave Energy Conversion System Installed on a Breakwater

by Hsien Hua Lee and Cheng-Han Chen

Energies 2020, 13(8), 1926; https://doi.org/10.3390/en13081926 - 14 Apr 2020

Cited by 9 | Viewed by 2099

Abstract

This study focuses on the analysis of the parameters of an oscillating water column (OWC) wave energy conversion system and wave conditions. Interactions between the dimensions of the OWC chambers and wave conditions are all taken into account to design an alternative OWC converter, called caisson-based OWC type wave energy converting system. A numerical method using an unsteady Navier-Stokes equations theorem in conservation form is used to analyze the proposed analytical model. The objective of this study is to try to apply an OWC wave energy converter to a caisson breakwater, which has been constructed in a harbor. The structure proposed in this study is a series of sets of independent systems, in which each set of converters is composed of three chambers to capture the wave energy, while better ensuring the safety of the caisson breakwater. Responses to be analyzed related to the conversion efficiency of the caisson-based OWC wave energy converting system include the airflow velocity from the air-chamber, the pneumatic power and the conversion efficiency in terms of a ratio between the pneumatic power and the energy of the incident waves. Parameters examined in this study include the dimensions of the OWC chamber features such as the orifice of the air-chamber allowing airflow in/output, the chamber length along the direction of incident waves, the size of the opening gate for incident waves and the submersion depth of the air-chamber. As found from the results, a best conversion efficiency from incident waves of 32% can be obtained for the extreme case where the orifice is very small, but for most other cases in the study, the best efficiency is about 15%. Full article

(This article belongs to the Special Issue Assessment and Nonlinear Modeling of Wave, Tidal and Wind Energy Converters and Turbines)

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21 pages, 5113 KiB

Open AccessArticle

Wave-Turbulence Decomposition Methods Applied to Tidal Energy Site Assessment

by Larissa Perez, Remo Cossu, Camille Couzi and Irene Penesis

Energies 2020, 13(5), 1245; https://doi.org/10.3390/en13051245 - 07 Mar 2020

Cited by 17 | Viewed by 3533

Abstract

High levels of turbulence have been proven to substantially increase the blade loadings on tidal turbines, outlining the need of properly characterizing turbulence parameters in tidal energy sites. The presence of long surface gravity waves may cause a significant bias on the estimation of these parameters, which requires wave-turbulence decomposition methods that are currently missing from guidelines. Here, three techniques of decomposing wave and turbulence are tested: the stopband filter (SB), moving average filter (MA), and synchrosqueezing wavelet transform (SWT). The study site, Banks Strait, Tasmania, is a 16 km wide channel that presents high potential for tidal energy generation. Wave peak periods at the study site were found to vary mostly between 7 and 12 s, with maximum exceeding 15 s. Turbulence intensities (TI), turbulent kinetic energy (TKE), and integral scales are quantified. Our results indicate differences between the estimates obtained from each method. The MA highly underestimates turbulence, resulting in TI values which were nearly 50% lower than those obtained from other decomposition methods. While TI and TKE estimated from the SB and the SWT techniques are quite similar, integral length scales are considerably underestimated by the SB. These findings reveal that the SWT is a more reliable method because of the more accurate estimates of turbulence parameters and indicate the need of establishing guidelines which address wave-turbulence decomposition in tidal stream energy site assessments. Despite having shown to be quite a versatile technique, further investigation of its applicability in data from other prospective tidal energy sites is necessary to fully assess the generality of the SWT technique. Full article

(This article belongs to the Special Issue Assessment and Nonlinear Modeling of Wave, Tidal and Wind Energy Converters and Turbines)

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16 pages, 1120 KiB

Open AccessArticle

Assessment of a Hydrokinetic Energy Converter Based on Vortex-Induced Angular Oscillations of a Cylinder

by Iro Malefaki and Efstathios Konstantinidis

Energies 2020, 13(3), 717; https://doi.org/10.3390/en13030717 - 07 Feb 2020

Cited by 5 | Viewed by 2269

Abstract

Vortex-induced oscillations offer a potential means to harness hydrokinetic energy even at low current speeds. In this study, we consider a novel converter where a cylinder undergoes angular oscillations with respect to a pivot point, in contrast to most previous configurations, where the cylinder undergoes flow-induced oscillations transversely to the incident free stream. We formulate a theoretical model to deal with the coupling of the hydrodynamics and the structural dynamics, and we numerically solve the resulting nonlinear equation of cylinder motion in order to assess the performance of the energy converter. The hydrodynamical model utilizes a novel approach where the fluid forces acting on the oscillating cylinder are split into components acting along and normal to the instantaneous relative velocity between the moving cylinder and the free stream. Contour plots illustrate the effects of the main design parameters (in dimensionless form) on the angular response of the cylinder and the energy efficiency of the converter. Peak efficiencies of approximately 20% can be attained by optimal selection of the main design parameters. Guidelines on the sizing of actual converters are discussed. Full article

(This article belongs to the Special Issue Assessment and Nonlinear Modeling of Wave, Tidal and Wind Energy Converters and Turbines)

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28 pages, 2563 KiB

Open AccessArticle

Wave-to-Wire Model Development and Validation for Two OWC Type Wave Energy Converters

by Pierre Benreguig, James Kelly, Vikram Pakrashi and Jimmy Murphy

Energies 2019, 12(20), 3977; https://doi.org/10.3390/en12203977 - 18 Oct 2019

Cited by 12 | Viewed by 3580

Abstract

The Tupperwave device is a closed-circuit oscillating water column (OWC) wave energy converter that uses non-return valves and two large fixed-volume accumulator chambers to create a smooth unidirectional air flow, harnessed by a unidirectional turbine. In this paper, the relevance of the Tupperwave concept against the conventional OWC concept, that uses a self-rectifying turbine, is investigated. For this purpose, wave-to-wire numerical models of the Tupperwave device and a corresponding conventional OWC device are developed and validated against experimental tests. Both devices have the same floating spar buoy structure and a similar turbine technology. The models include wave-structure hydrodynamic interaction, air turbines and generators, along with their control laws in order to encompass all power conversion stages from wave to electrical power. Hardware-in-the-loop is used to physically emulate the last power conversion stage from mechanic to electrical power and hence validate the control law and the generator numerical model. The dimensioning methodology for turbines and generators for power optimisation is explained. Eventually, the validated wave-to-wire numerical models of the conventional OWC and the Tupperwave device are used to assess and compare the performances of these two OWC type wave energy device concepts in the same wave climate. The benefits of pneumatic power smoothing by the Tupperwave device are discussed and the required efficiency of the non-return valves is investigated. Full article

(This article belongs to the Special Issue Assessment and Nonlinear Modeling of Wave, Tidal and Wind Energy Converters and Turbines)

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24 pages, 2584 KiB

Open AccessArticle

Assessment of Primary Energy Conversion of a Closed-Circuit OWC Wave Energy Converter

by Pierre Benreguig, Vikram Pakrashi and Jimmy Murphy

Energies 2019, 12(10), 1962; https://doi.org/10.3390/en12101962 - 22 May 2019

Cited by 12 | Viewed by 3926

Abstract

Tupperwave is a wave energy device based on the Oscillating-Water-Column (OWC) concept. Unlike a conventional OWC, which creates a bidirectional air flow across the self-rectifying turbine, the Tupperwave device uses rectifying valves to create a smooth unidirectional air flow, which is harnessed by a unidirectional turbine. This paper deals with the development and validation of time-domain numerical models from wave to pneumatic power for the Tupperwave device and the conventional OWC device using the same floating spar buoy structure. The numerical models are built using coupled hydrodynamic and thermodynamic equations. The isentropic assumption is used to describe the thermodynamic processes. A tank testing campaign of the two devices at 1/24th scale is described, and the results are used to validate the numerical models. The capacity of the innovative Tupperwave OWC concept to convert wave energy into useful pneumatic energy to the turbine is assessed and compared to the corresponding conventional OWC. Full article

(This article belongs to the Special Issue Assessment and Nonlinear Modeling of Wave, Tidal and Wind Energy Converters and Turbines)

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16 pages, 3778 KiB

Open AccessArticle

Reducing Tower Fatigue through Blade Back Twist and Active Pitch-to-Stall Control Strategy for a Semi-Submersible Floating Offshore Wind Turbine

by Dawn Ward, Maurizio Collu and Joy Sumner

Energies 2019, 12(10), 1897; https://doi.org/10.3390/en12101897 - 18 May 2019

Cited by 9 | Viewed by 5324

Abstract

The necessity of producing more electricity from renewable sources has been driven predominantly by the need to prevent irreversible climate chance. Currently, industry is looking towards floating offshore wind turbine solutions to form part of their future renewable portfolio. However, wind turbine loads are often increased when mounted on a floating rather than fixed platform. Negative damping must also be avoided to prevent tower oscillations. By presenting a turbine actively pitching-to-stall, the impact on the tower fore–aft bending moment of a blade with back twist towards feather as it approaches the tip was explored, utilizing the time domain FAST v8 simulation tool. The turbine was coupled to a floating semisubmersible platform, as this type of floater suffers from increased fore–aft oscillations of the tower, and therefore could benefit from this alternative control approach. Correlation between the responses of the blade’s flapwise bending moment and the tower base’s fore–aft moment was observed with this back-twisted pitch-to-stall blade. Negative damping was also avoided by utilizing a pitch-to-stall control strategy. At 13 and 18 m/s mean turbulent winds, a 20% and 5.8% increase in the tower axial fatigue life was achieved, respectively. Overall, it was shown that the proposed approach seems to be effective in diminishing detrimental oscillations of the power output and in enhancing the tower axial fatigue life. Full article

(This article belongs to the Special Issue Assessment and Nonlinear Modeling of Wave, Tidal and Wind Energy Converters and Turbines)

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32 pages, 18703 KiB

Open AccessArticle

Proposal of a Novel Semi-Submersible Floating Wind Turbine Platform Composed of Inclined Columns and Multi-Segmented Mooring Lines

by Zhenqing Liu, Qingsong Zhou, Yuangang Tu, Wei Wang and Xugang Hua

Energies 2019, 12(9), 1809; https://doi.org/10.3390/en12091809 - 12 May 2019

Cited by 15 | Viewed by 5134

Abstract

The semi-submersible floating offshore wind turbine has been studied in detail due to its good stability. However, the occurrence of typhoons are very frequent in China’s offshore area, putting forward a higher requirement for the stability of the floating wind turbine system. By changing the connection mode of the mooring line as well as the structural form of the platform based on the original OC4 model, two groups of models were examined by an in-house developed code named as the Analysis Tool of Floating Wind Turbine (AFWT). The influence of the arrangement of the mooring lines and the inclination angle of the upper columns on the motion response were clarified. It was found that the surge motion of the platform would be obviously decreased by decreasing the length of the upper segments of the mooring lines, while the heave motion of the platform would be significantly decreased as increasing the inclined angle of the columns. Therefore, a new model integrating the optimized multi-segmented mooring lines and the optimized inclined columns was proposed. The examinations showed that compared with the response motions of the original OC4 semi-submersible model, the proposed model could reduce both the surge and heave motions of the platform effectively. Full article

(This article belongs to the Special Issue Assessment and Nonlinear Modeling of Wave, Tidal and Wind Energy Converters and Turbines)

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26 pages, 38354 KiB

Open AccessArticle

Performance Optimization of a Kirsten–Boeing Turbine by A Metamodel Based on Neural Networks Coupled with CFD

by Jan-Philipp Küppers, Jens Metzger, Jürgen Jensen and Tamara Reinicke

Energies 2019, 12(9), 1777; https://doi.org/10.3390/en12091777 - 10 May 2019

Cited by 3 | Viewed by 4027

Abstract

The supply of energy is sustainable only if it is predominantly based on renewable or regenerative energies. For this reason, the use of micro-hydropower plants on rivers and streams is considered recently. This is a particular challenge for the preservation of ecologically permeable streams, so that no dams or similar structures can be considered. While the axial turbine design has prevailed in wind power, there is still no consensus for the generation of energy in free water flow conditions. In this work, an existing prototype of an unusual vertical axis Kirsten–Boeing turbine was investigated. A multivariate optimization process was created, in which all important machine parameters were checked and improved. By using neural networks as a metamodel coupled with flow simulations in ANSYS CFX, a broadly applicable optimization strategy is presented that yielded a blade design that is 36% more efficient than its predecessor in experiments. During the process, it was shown how to set up a complex sliding mesh problem with ANSYS expressions while evaluating a free surface problem. Full article

(This article belongs to the Special Issue Assessment and Nonlinear Modeling of Wave, Tidal and Wind Energy Converters and Turbines)

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19 pages, 6280 KiB

Open AccessArticle

A Flower Pollination Method Based Global Maximum Power Point Tracking Strategy for Point-Absorbing Type Wave Energy Converters

by Aqiang Zhao, Weimin Wu, Zuoyao Sun, Lixun Zhu, Kaiyuan Lu, Henry Chung and Frede Blaabjerg

Energies 2019, 12(7), 1343; https://doi.org/10.3390/en12071343 - 08 Apr 2019

Cited by 16 | Viewed by 3353

Abstract

To maximize the generated output power under random waves, the control strategy of maximum power point tracking (MPPT) is incorporated in point-absorbing type wave energy converter (WEC) system. However, due to the influence of mutative wave conditions, the curve of the maximum average power appears in multiple peaks, adding complexity to the tracking process. This paper proposes a new MPPT control technique for a wave power generation system, by using the flower pollination algorithm (FPA) instead of the conventional hill-climbing method. Compared with the hill-climbing method, this method has advantages of achieving a smaller peak-to-average ratio and capturing the more average power under the same sea state. The verification has been carried out through the simulations and the experimental results on a lab test bench. Full article

(This article belongs to the Special Issue Assessment and Nonlinear Modeling of Wave, Tidal and Wind Energy Converters and Turbines)

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32 pages, 2982 KiB

Open AccessArticle

Study of Generalized Interaction Wake Models Systems with ELM Variation for Off-Shore Wind Farms

by Mingcan Li, Hanbin Xiao, Lin Pan and Chengjun Xu

Energies 2019, 12(5), 863; https://doi.org/10.3390/en12050863 - 05 Mar 2019

Cited by 4 | Viewed by 2420

Abstract

This paper reports a novel frandsen generalized wake model and its variation model-frandsen generalized normal distribution wake model for off-shore wind farms. Two different new wake models in off-shore wind farms have been studied comparatively. Their characteristics have been analyzed through mathematical modeling and derivation. Meanwhile, simulation experiments show that the proposed two new wake models have different properties. Furthermore, the distributions of wind speed and wind direction are modeled by the statistical methods and Extreme Learning Machine through the off-shore wind farms of Yangshan Deepwater Harbor in the Port of Shanghai, China. In addition, the data of wind energy are provided to verify and test the correctness and effectiveness of the proposed two models. Wind power has been demonstrated by wind rose and wind resources with real-time data. These techniques contribute to enhance planning, utilization and exploitation for wind power of off-shore wind farms. Full article

(This article belongs to the Special Issue Assessment and Nonlinear Modeling of Wave, Tidal and Wind Energy Converters and Turbines)

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