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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 (31 December 2019) | Viewed by 48912

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Special Issue Editors

Prof. Dr. Muk Chen Ong

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Guest Editor

Department of Mechanical and Structural Engineering and Materials Science, University of Stavanger, 4036 Stavanger, Norway
Interests: offshore wind energy; offshore renewable energy; offshore aquaculture technology; marine hydrodynamics; marine structures; marine operations; marine computational fluid dynamics; scour prediction and protection; sediment transport; soil liquefaction; offshore foundation design
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Dr. Zhiyu Jiang

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Guest Editor

Department of Engineering Sciences, Faculty of Engineering and Science, University of Agder, Postboks 422, 4604 Kristiansand, Norway
Interests: wind turbine dynamics; offshore structures; marine operations

Dr. Zhengshun Cheng

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Guest Editor

1. Department of Marine Technology, Norwegian University of Science and Technology, Otto Nielsens veg 10, 7491 Trondheim, Norway
2. State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
Interests: offshore renewable energy; marine structures; marine operations

Dr. Kai Wang

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Guest Editor

1. Department of Marine Technology, Aker Solutions As, Snarøyveien 20, 1360 Fornebu PO Box 222, 1326 Lysaker, Norway
2. School of Marine Engineering and Technology, Sun Yat-Sen University, Zhuhai 519082, China
Interests: wind turbine aerodynamics; CFD technique; marine hydrodynamics; wind turbine dynamics; offshore structures; ice loads; renewable energy; design and analysis of mooring systems

Special Issue Information

Dear Colleagues,

We are inviting submissions to a Special Issue of the journal Energies on the subject area of “Recent Advances in Offshore Wind Technology.” Offshore wind resources are abundant, yet offshore wind farms experience more issues related to design, installation, operation and maintenance, and lifetime extension compared to onshore wind farms. Almost three decades have passed since the first offshore wind farm was constructed. Today, offshore wind energy has been rapidly evolving with the aim to deploy larger wind turbines at increasing water depths and under complex external conditions. Challenges abound when it comes to the upscaling of wind turbines, and cost-effective operation and maintenance in a life-cycle perspective, and there has been continuous progress in foundation design, control strategy, installation methods, computational methods, and model testing, to name a few. This Special Issue is intended to provide a forum for academic researchers and technical professionals to exchange their recent works on technological advancements.

Prof. Dr. Muk Chen Ong
Assoc. Prof. Dr. Zhiyu Jiang
Dr. Zhengshun Cheng
Dr. Kai Wang
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Energies is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

Innovative concepts and technologies
Hydrodynamics, structural dynamics, and aerodynamics
Dynamics and control
Field measurements and model testing
Drivetrain technology
Metocean conditions and wind farm siting
Scour prediction and protection
Foundation design
Fabrication and installation
Operations, maintenance, lifetime extension and decommissioning

Published Papers (13 papers)

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Research

22 pages, 4998 KiB

Open AccessFeature PaperArticle

Numerical Analysis of the Effect of Offshore Turbulent Wind Inflow on the Response of a Spar Wind Turbine

by Rieska Mawarni Putri, Charlotte Obhrai, Jasna Bogunovic Jakobsen and Muk Chen Ong

Energies 2020, 13(10), 2506; https://doi.org/10.3390/en13102506 - 15 May 2020

Cited by 9 | Viewed by 2780

Abstract

Turbulent wind at offshore sites is known as the main cause for fatigue on offshore wind turbine components. Numerical simulations are commonly used to predict the loads and motions of floating offshore wind turbines; however, the definition of representative wind input conditions is necessary. In this study, the load and motion responses of a spar-type Offshore Code Comparison Collaboration (OC3) wind turbine under different turbulent wind conditions is studied and investigated by using SIMO-Riflex in Simulation Workbench for Marine Applications (SIMA) workbench. Using the two spectral models given in the International Electrotechnical Commission (IEC) standards, it is found that a lower wind lateral coherence under neutral atmospheric stability conditions results in an up to 27% higher tower base side–side bending moment and a 20% higher tower top torsional moment. Comparing different atmospheric stability conditions simulated using a spectral model based on FINO1 wind data measurement, the highest turbulent energy content under very unstable conditions yields a 26% higher tower base side–side bending moment and a 27% higher tower top torsional moment than neutral conditions, which have the lowest turbulent energy content and turbulent intensity. The yaw-mode of the OC3 wind turbine is found to be the most influenced component by assessing variations in both the lateral coherence and the atmospheric stability conditions. Full article

(This article belongs to the Special Issue Recent Advances in Offshore Wind Technology)

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20 pages, 4804 KiB

Open AccessFeature PaperArticle

On-Bottom Stability of Umbilicals and Power Cables for Offshore Wind Applications

by Guomin Ji and Muk Chen Ong

Energies 2019, 12(19), 3635; https://doi.org/10.3390/en12193635 - 24 Sep 2019

Cited by 1 | Viewed by 3087

Abstract

With the increase in offshore wind farms, the demands for umbilicals and power cables have increased. The on-bottom stability of umbilicals and power cables under the combined wave and current loading is the most challenging design issue, due to their light weight and the complex fluid–cable–soil interaction. In the present study, the methodology for dynamic lateral stability analysis is first discussed; and the reliable hydrodynamic load model and cable–soil interaction model based on large experimental test data are described in detail. The requirement of the submerged weight of a cable

w_{s}

to obtain on-bottom stability is investigated for three types of soil (clay, sand and rock), using the finite element program PONDUS, and the results are

w_{s, r o c k} > w_{s, c l a y} > w_{s, s a n d}

under the same load conditions. Several different aspects related to optimization design of the on-bottom stability are explored and addressed. There is a significant benefit for the on-bottom stability analysis to consider the reduction factors, due to penetration for clay and sand soil. The on-bottom stability is very sensitive to the relative initial embedment

z_{0} / D

for clay and sand soil, due to the small diameter of the cables, and therefore, reliable prediction of initial embedment is required. In the energy-based cable–soil interaction model, the friction coefficient

μ

and the development of penetration affect each other and the total effect of friction force

F_{f}

and passive resistance

F_{r}

is complicated. The effect of the friction coefficient

μ

on the on-bottom stability is different from engineering judgement based on the Coulomb friction model. The undrained shear strength of clay is an important parameter for the on-bottom stability of umbilicals and cables. The higher the undrained shear strength of the clay, the larger the lateral displacement. Meanwhile, the submerged weight of sand has a minor effect on the lateral displacement of cables. The method used in the present study significantly improves the reliability of the on-bottom stability analysis of umbilicals and power cables for offshore wind application. Full article

(This article belongs to the Special Issue Recent Advances in Offshore Wind Technology)

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31 pages, 15014 KiB

Open AccessFeature PaperArticle

Numerical Modelling of Dynamic Responses of a Floating Offshore Wind Turbine Subject to Focused Waves

by Yang Zhou, Qing Xiao, Yuanchuan Liu, Atilla Incecik, Christophe Peyrard, Sunwei Li and Guang Pan

Energies 2019, 12(18), 3482; https://doi.org/10.3390/en12183482 - 09 Sep 2019

Cited by 53 | Viewed by 5416

Abstract

In this paper, we present numerical modelling for the investigation of dynamic responses of a floating offshore wind turbine subject to focused waves. The modelling was carried out using a Computational Fluid Dynamics (CFD) tool. We started with the generation of a focused wave in a numerical wave tank based on a first-order irregular wave theory, then validated the developed numerical method for wave-structure interaction via a study of floating production storage and offloading (FPSO) to focused wave. Subsequently, we investigated the wave-/wind-structure interaction of a fixed semi-submersible platform, a floating semi-submersible platform and a parked National Renewable Energy Laboratory (NREL) 5 MW floating offshore wind turbine. To understand the nonlinear effect, which usually occurs under severe sea states, we carried out a systematic study of the motion responses, hydrodynamic and mooring tension loads of floating offshore wind turbine (FOWT) over a range of wave steepness, and compared the results obtained from two potential flow theory tools with each other, i.e., Électricité de France (EDF) in-house code and NREL Fatigue, Aerodynamics, Structures, and Turbulence (FAST). We found that the nonlinearity of the hydrodynamic loading and motion responses increase with wave steepness, revealed by higher-order frequency response, leading to the appearance of discrepancies among different tools. Full article

(This article belongs to the Special Issue Recent Advances in Offshore Wind Technology)

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18 pages, 5832 KiB

Open AccessArticle

Stochastic Dynamic Analysis of an Offshore Wind Turbine Structure by the Path Integration Method

by Yue Zhao, Jijian Lian, Chong Lian, Xiaofeng Dong, Haijun Wang, Chunxi Liu, Qi Jiang and Pengwen Wang

Energies 2019, 12(16), 3051; https://doi.org/10.3390/en12163051 - 08 Aug 2019

Cited by 4 | Viewed by 2921

Abstract

Stochastic dynamic analysis of an offshore wind turbine (OWT) structure plays an important role in the structural safety evaluation and reliability assessment of the structure. In this paper, the OWT structure is simplified as a linear single-degree-of-freedom (SDOF) system and the corresponding joint probability density function (PDF) of the dynamic response is calculated by the implementation of the path integration (PI) method. Filtered Gaussian white noise, which is obtained from the utilization of a second-order filter, is considered as horizontal wind excitation and used to excite the SDOF system. Thus, the SDOF model and the second-order linear filter model constitute a four-dimensional dynamic system. Further, a detailed three-dimensional finite element model is applied to obtain the natural frequency of the OWT and the efficient PI method, which is modified based on the fast Fourier transform (FFT) convolution method, is also utilized to reduce the execution time to obtain the PDF of the response. Two important parameters of wind conditions, i.e., horizontal mean wind speed and turbulence standard deviation, are investigated to highlight the influences on the PDF of the dynamic response and the reliability of the OWT. Full article

(This article belongs to the Special Issue Recent Advances in Offshore Wind Technology)

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16 pages, 2018 KiB

Open AccessArticle

Reliability-Based Serviceability Limit State Design of a Jacket Substructure for an Offshore Wind Turbine

by Jianhua Zhang, Won-Hee Kang, Ke Sun and Fushun Liu

Energies 2019, 12(14), 2751; https://doi.org/10.3390/en12142751 - 18 Jul 2019

Cited by 11 | Viewed by 3314

Abstract

The development of a structurally optimized foundation design has become one of the main research objectives for offshore wind turbines (OWTs). The design process should be carried out in a probabilistic way due to the uncertainties involved, such as using parametric uncertainties regarding material and geometric properties, and model uncertainties in resistance prediction models and regarding environmental loads. Traditional simple deterministic checking procedures do not guarantee an optimized design because the associated uncertainties are not fully considered. In this paper, a reliability analysis framework is proposed to support the optimized design of jacket foundations for OWTs. The reliability analysis mainly considers the serviceability limit state of the structure according to the requirements of the code. The framework consists of two parts: (i) an important parameter identification procedure based on statistical correlation analysis and (ii) a finite element-simulation-based reliability estimation procedure. The procedure is demonstrated through a jacket structure design of a 3 MW OWT. The analysis results show that the statistical correlation analysis can help to identify the parameters necessary for the overall structural performance. The Latin hypercube sampling and the Monte Carlo simulation using FE models effectively and efficiently evaluate the reliability of the structure while not relying on a surrogate limit state function. A comparison between the proposed framework and the deterministic design shows that the framework can help to achieve a better result closer to the target reliability level. Full article

(This article belongs to the Special Issue Recent Advances in Offshore Wind Technology)

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21 pages, 10817 KiB

Open AccessArticle

A Simulation of Non-Simultaneous Ice Crushing Force for Wind Turbine Towers with Large Slopes

by Li Zhou, Shifeng Ding, Ming Song, Junliang Gao and Wei Shi

Energies 2019, 12(13), 2608; https://doi.org/10.3390/en12132608 - 07 Jul 2019

Cited by 11 | Viewed by 3063

Abstract

When the offshore wind energy industry attempts to develop in cold regions, ice load becomes the main technological challenge for offshore wind turbine foundation design. Dynamic ice loads acting on wind turbine foundations should be calculated in a reasonable way. The scope of this study is to present a numerical model that considers the non-simultaneous ice crushing failure acting on the vertical structure of a wind turbine’s foundation. The local ice crushing force at the contact surface between the ice sheet and structure is calculated. The boundary of the ice sheet is updated at each time step based on the indentation length of the ice sheet according to its structure. Ice loads are validated against two model tests with three different structure models developed by other researchers. The time series of the ice forces derived from the simulation and model tests are compared. The proposed numerical model can capture the main trends of ice–wind turbine foundation interaction. The simulation results agree well with measured data from the model tests in terms of maximum ice force, which is a key factor for wind turbine design. The proposed model will be helpful for assisting the initial design of wind turbine foundations in cold regions. Full article

(This article belongs to the Special Issue Recent Advances in Offshore Wind Technology)

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23 pages, 5254 KiB

Open AccessArticle

Coupled Motion Characteristics of Offshore Wind Turbines during the Integrated Transportation Process

by Jijian Lian, Junni Jiang, Xiaofeng Dong, Haijun Wang, Huan Zhou and Pengwen Wang

Energies 2019, 12(10), 2023; https://doi.org/10.3390/en12102023 - 27 May 2019

Cited by 6 | Viewed by 2934

Abstract

The offshore wind turbine (OWT) supported by bucket foundations can be installed in the integrated transportation process by a dedicated vessel. During the integrated transportation process, the wind turbine is considered as a coupling system with the transport ship, which is easily influenced by waves and storms. In view of the motion response and influential factors, the heave and rock stiffness of the entire floating system was proposed, and then the analytical dynamic motion model of the coupling system was established based on the movement mechanism of the traditional floating body in the wave in this paper. Subsequently, the rationality of the proposed motion model was verified based on the field observation data, with the maximum deviation of the motion responses less than 14%. Further, the influence on the heave and pitch motion of the coupling system considering different factors (vessel speed, wave height, wind speed and wave angle) and the factor sensitivity were discussed by the novel analytical model. It is explained that the heave and pitch motion responses rise with the increase of the wave height and wave angle. Simultaneously, the responses decrease as the vessel speed increases considering sailing along the waves. On the contrary, the responses show an obvious increasing trend with the increase of vessel speed in the case of the top wave sailing. In addition, it is also illustrated that the wave height has the greatest influence on the heave and pitch motion responses, followed by the vessel speed. The wave angle has the lowest sensitivity when the heave and pitch motion are far away from its harmonic resonance region. Full article

(This article belongs to the Special Issue Recent Advances in Offshore Wind Technology)

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22 pages, 880 KiB

Open AccessArticle

Vindby—A Serious Offshore Wind Farm Design Game

by Esther Dornhelm, Helene Seyr and Michael Muskulus

Energies 2019, 12(8), 1499; https://doi.org/10.3390/en12081499 - 20 Apr 2019

Cited by 5 | Viewed by 4476

Abstract

To maintain the increasing interest and development in offshore wind energy, novel training tools for engineers and researchers are needed. Concurrently, educational outreach activities are in demand to inform the public about the importance of offshore wind energy. In this paper, the development of a serious game about the design and management of offshore wind farms is presented to address such demands. Such a serious game may enable a new audience to explore the field of offshore wind as well as provide researchers entering the field a better understanding of the intricacies of the industry. This requires a simulation that is realistic but also effective in teaching information and engaging outreach. Ultimately, increased public support and expanded training tools are desired to improve decision-making and to provide opportunities to test and integrate innovative solutions. The work presented here includes the game design and implementation of a prototype game. The game design involves building a game framework and developing a simplified simulation. This simulation addresses weather prediction, offshore wind farm design, operation and maintenance, energy demand, climate change, and finance. Playtesting of the prototype demonstrated immersion and informed decision-making of the players and surveys revealed that knowledge had increased while playing the game. Recommendations for future versions of the game are listed. Full article

(This article belongs to the Special Issue Recent Advances in Offshore Wind Technology)

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17 pages, 5454 KiB

Open AccessArticle

Transient Response Estimation of an Offshore Wind Turbine Support System

by Fushun Liu, Xingguo Li, Zhe Tian, Jianhua Zhang and Bin Wang

Energies 2019, 12(5), 891; https://doi.org/10.3390/en12050891 - 07 Mar 2019

Cited by 3 | Viewed by 2900

Abstract

To obtain reliable estimations of the dynamic responses of high-rising marine structures such as offshore wind turbines with obvious nonzero initial conditions, traditional frequency-domain methods cannot be employed because they provide only steady-state results. A novel frequency-domain transient response estimation method for offshore wind turbines is presented in this paper. This method builds upon a recent, significant theoretical development, which found that expressions of external loads in the frequency domain can be obtained by discretizing their eigenvalues and corresponding complex coefficients rather than directly by discrete Fourier transform (DFT) analysis, which makes it possible to deal with nonzero conditions in the frequency domain. One engineering advantage of this approach is its computational efficiency, as the motion equations of the system can be solved in the frequency domain. In order to demonstrate this approach, a case of a monopile-supported wind turbine with nonzero initial conditions was investigated. The numerical results indicate that the approach matches well with the time-domain method, except for a small, earlier portion of the estimated responses. A second case study of a sophisticated, jacket support wind turbine, involving practical issues such as complex external loads and computation efficiency, is also discussed, and comparisons of the results with the time-domain method and traditional frequency-domain method using the commercial software ANSYS are included here. Full article

(This article belongs to the Special Issue Recent Advances in Offshore Wind Technology)

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14 pages, 4025 KiB

Open AccessArticle

Uncertainty in the Physical Testing of Floating Wind Energy Platforms’ Accuracy versus Precision

by Cian J. Desmond, Jan-Christoph Hinrichs and Jimmy Murphy

Energies 2019, 12(3), 435; https://doi.org/10.3390/en12030435 - 30 Jan 2019

Cited by 16 | Viewed by 4527

Abstract

This paper examines the impact on experimental uncertainty of introducing aerodynamic and rotor gyroscopic loading on a model multirotor floating wind energy platform during physical testing. In addition, a methodology and a metric are presented for the assessment of the uncertainty across the full time series for the response of a floating wind energy platform during wave basin testing. It is shown that there is a significant cost incurred in terms of experimental uncertainty through the addition of rotor thrust in the laboratory environment for the considered platform. A slight reduction in experimental uncertainty is observed through the introduction of gyroscopic rotor loading for most platform responses. Full article

(This article belongs to the Special Issue Recent Advances in Offshore Wind Technology)

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22 pages, 2270 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Crane Overload Protection Controller for Blade Lifting Operation Based on Model Predictive Control

by Zhengru Ren, Roger Skjetne and Zhen Gao

Energies 2019, 12(1), 50; https://doi.org/10.3390/en12010050 - 24 Dec 2018

Cited by 28 | Viewed by 4851

Abstract

Lifting is a frequently used offshore operation. In this paper, a nonlinear model predictive control (NMPC) scheme is proposed to overcome the sudden peak tension and snap loads in the lifting wires caused by lifting speed changes in a wind turbine blade lifting operation. The objectives are to improve installation efficiency and ensure operational safety. A simplified three-dimensional crane-wire-blade model is adopted to design the optimal control algorithm. A crane winch servo motor is controlled by the NMPC controller. The direct multiple shooting approach is applied to solve the nonlinear programming problem. High-fidelity simulations of the lifting operations are implemented based on a turbulent wind field with the MarIn and CaSADi toolkit in MATLAB. By well-tuned weighting matrices, the NMPC controller is capable of preventing snap loads and axial peak tension, while ensuring efficient lifting operation. The performance is verified through a sensitivity study, compared with a typical PD controller. Full article

(This article belongs to the Special Issue Recent Advances in Offshore Wind Technology)

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16 pages, 12445 KiB

Open AccessArticle

An Aero-acoustic Noise Distribution Prediction Methodology for Offshore Wind Farms

by Jiufa Cao, Weijun Zhu, Xinbo Wu, Tongguang Wang and Haoran Xu

Energies 2019, 12(1), 18; https://doi.org/10.3390/en12010018 - 21 Dec 2018

Cited by 6 | Viewed by 4685

Abstract

Recently attention has been paid to wind farm noise due to its negative health impact, not only on human beings, but also to marine and terrestrial organisms. The current work proposes a numerical methodology to generate a numerical noise map for a given wind farm. Noise generation from single wind turbines as well as wind farms has its basis in the nature of aerodynamics, caused by the interactions between the incoming turbulent flow and the wind turbine blades. Hence, understanding the mechanisms of airfoil noise generation, demands access to sophisticated numerical tools. The processes of modeling wind farm noise include three steps: (1) The whole wind farm velocity distributions are modelled with an improved Jensen’s wake model; (2) The individual wind turbine’s noise is simulated by a semi-empirical wind turbine noise source model; (3) Propagations of noise from all wind turbines are carried out by solving the parabolic wave equation. In the paper, the wind farm wake effect from the Horns Rev wind farm is studied. Based on the resulted wind speed distributions in the wind farm, the wind turbine noise source and its propagation are simulated for the whole wind farm. Full article

(This article belongs to the Special Issue Recent Advances in Offshore Wind Technology)

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12 pages, 2693 KiB

Open AccessArticle

Experimental Study on the Performance of a Crashworthy Device for the Monopile Offshore Wind Turbine against Ship Impact

by Nianxin Ren, Wei Li, Zhe Ma, Jinping Ou and Dezhi Ning

Energies 2018, 11(11), 3173; https://doi.org/10.3390/en11113173 - 15 Nov 2018

Viewed by 2620

Abstract

In the present work, a crashworthy device for a monopile offshore wind turbine has been proposed, which consists of the inner two-layer rubber torus and the outer thin steel shell. The performance of the crashworthy device against ship impact has been investigated experimentally. Based on the prototype of a 4 MW monopile wind turbine in the East China Sea, the scale ratio of the test model has been designed to be 1/50. The test ship model has been simplified as a “rigid car” equipped with a high-frequency force sensor in the front, which is available for changing the ship mass with different weights. The ship-impact velocity can be accurately controlled by a motion platform driven by a direct current machine. The effect of the key design parameters of the crashworthy device on its anti-impact performance has been tested and compared under typical ship impact cases. The results indicate that the crashworthy device can effectively reduce both the ship impact force and the top nacelle acceleration, and the physical mechanism that has been clarified. The outer thin steel shell can significantly use its structural deformation to absorb the ship impact energy, which is beneficial for reducing the structural damage of the offshore wind turbine (OWT)’s tower. The inner rubber torus can effectively prolong the ship impact duration, which is available for smoothing the impact force. Finally, the porous design for the outer steel shell of the crashworthy device has been proposed and tested. Full article

(This article belongs to the Special Issue Recent Advances in Offshore Wind Technology)

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