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Special Issue "Marine Energy"

A special issue of Energies (ISSN 1996-1073).

Deadline for manuscript submissions: closed (31 October 2017)

Special Issue Editor

Guest Editor
Dr. Aristides Kiprakis

School of Engineering, University of Edinburgh, UK
Website | E-Mail
Interests: power system modelling & control; smart grids; renewable energy integration; demand response; energy management

Special Issue Information

Dear Colleagues,

In recent years, the marine energy industry has experienced an increasing level of interest and activity across the range of technology readiness levels, from blue skies research to the commercialization of marine energy conversion technologies; from the development of new concepts to sea tests of devices, and in some cases even array deployments. Energies is delighted to announce a timely Special Issue on Marine Energy, aiming to capture the latest advances in marine energy research and development, which will accelerate the uptake of new technologies and the expansion of the industry on a global scale. The issue covers, but is not limited to, the following topics:

  • wave and tidal resource modelling, characterization and assessment;
  • resource-to-wire modelling of wave and tidal energy conversion;
  • design and assessment of novel wave and tidal energy converter components and systems;
  • hydrodynamic and electrical interaction among converters within wave and tidal arrays;
  • control and power system integration of wave and tidal arrays;
  • hybrid wave, tidal and offshore wind arrays;
  • system and component reliability;
  • operational and logistics aspects of marine energy conversion systems;
  • policy, regulatory and commercial practices.

We invite papers on blue skies research as well as reports and case studies illustrating current, state-of-the-art industrial applications. As the Guest Editor of this Energies Special Issue on Marine Energy, I am delighted to extend this invitation to you and I look forward to receiving your contributions.

Dr Aristides E. Kiprakis
Guest Editor

Manuscript Submission Information

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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 1800 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

  • wave energy
  • tidal energy
  • resource modelling
  • hydrodynamics
  • network integration
  • reliability
  • energy policy

Published Papers (18 papers)

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Research

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Open AccessArticle
Design and Experiment Analysis of a Direct-Drive Wave Energy Converter with a Linear Generator
Energies 2018, 11(4), 735; https://doi.org/10.3390/en11040735
Received: 10 February 2018 / Revised: 16 March 2018 / Accepted: 22 March 2018 / Published: 23 March 2018
Cited by 2 | PDF Full-text (19472 KB) | HTML Full-text | XML Full-text
Abstract
Coastal waves are an abundant nonpolluting and renewable energy source. A wave energy converter (WEC) must be designed for efficient and steady operation in highly energetic ocean environments. A direct-drive wave energy conversion (D-DWEC) system with a tubular permanent magnet linear generator (TPMLG) [...] Read more.
Coastal waves are an abundant nonpolluting and renewable energy source. A wave energy converter (WEC) must be designed for efficient and steady operation in highly energetic ocean environments. A direct-drive wave energy conversion (D-DWEC) system with a tubular permanent magnet linear generator (TPMLG) on a wind and solar photovoltaic complementary energy generation platform is proposed to improve the conversion efficiency and reduce the complexity and device volume of WECs. The operating principle of D-DWECs is introduced, and detailed analyses of the proposed D-DWEC’s floater system, wave force characteristics, and conversion efficiency conducted using computational fluid dynamics are presented. A TPMLG with an asymmetric slot structure is designed to increase the output electric power, and detailed analyses of the magnetic field distribution, detent force characteristics, and no-load and load performances conducted using finite element analysis are discussed. The TPMLG with an asymmetric slot, which produces the same power as the TPMLG with a symmetric slot, has one fifth detent force of the latter. An experiment system with a prototype of the TPMLG with a symmetric slot is used to test the simulation results. The experiment and analysis results agree well. Therefore, the proposed D-DWEC fulfills the requirements of WEC systems. Full article
(This article belongs to the Special Issue Marine Energy)
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Open AccessArticle
Characterisation of Tidal Flows at the European Marine Energy Centre in the Absence of Ocean Waves
Energies 2018, 11(1), 176; https://doi.org/10.3390/en11010176
Received: 3 November 2017 / Revised: 20 December 2017 / Accepted: 3 January 2018 / Published: 11 January 2018
Cited by 5 | PDF Full-text (9345 KB) | HTML Full-text | XML Full-text
Abstract
The data analyses and results presented here are based on the field measurement campaign of the Reliable Data Acquisition Platform for Tidal (ReDAPT) project (Energy Technologies Institute (ETI), U.K. 2010–2015). During ReDAPT, a 1 MW commercial prototype tidal turbine was deployed and operated [...] Read more.
The data analyses and results presented here are based on the field measurement campaign of the Reliable Data Acquisition Platform for Tidal (ReDAPT) project (Energy Technologies Institute (ETI), U.K. 2010–2015). During ReDAPT, a 1 MW commercial prototype tidal turbine was deployed and operated at the Fall of Warness tidal test site within the European Marine Energy Centre (EMEC), Orkney, U.K. Mean flow speeds and Turbulence Intensity (TI) at multiple positions proximal to the machine are considered. Through the implemented wave identification techniques, the dataset can be filtered into conditions where the effects of waves are present or absent. Due to the volume of results, only flow conditions in the absence of waves are reported here. The analysis shows that TI and mean flows are found to vary considerably between flood and ebb tides whilst exhibiting sensitivity to the tidal phase and to the specification of spatial averaging and velocity binning. The principal measurement technique was acoustic Doppler profiling provided by seabed-mounted Diverging-beam Acoustic Doppler Profilers (D-ADP) together with remotely-operable Single-Beam Acoustic Doppler Profilers (SB-ADP) installed at mid-depth on the tidal turbine. This novel configuration allows inter-instrument comparisons, which were conducted. Turbulence intensity averaged over the rotor extents of the ReDAPT turbine for flood tides vary between 16.7% at flow speeds above 0.3 m/s and 11.7% when considering only flow speeds in the turbine operating speed range, which reduces to 10.9% (6.8% relative reduction) following the implementation of noise correction techniques. Equivalent values for ebb tides are 14.7%, 10.1% and 9.3% (7.9% relative reduction). For flood and ebb tides, TI values resulting from noise correction are reduced in absolute terms by 3% and 2% respectively across a wide velocity range and approximately 1% for turbine operating speeds. Through comparison with SB-ADP-derived mid-depth TI values, this correction is shown to be conservative since uncorrected SB-ADP results remain, in relative terms, between 10% and 21% below corrected D-ADP values depending on tidal direction and the range of velocities considered. Results derived from other regions of the water column, those important to floating turbine devices for example, are reported for comparison. Full article
(This article belongs to the Special Issue Marine Energy)
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Open AccessArticle
Digital-Control-Based Approximation of Optimal Wave Disturbances Attenuation for Nonlinear Offshore Platforms
Energies 2017, 10(12), 1997; https://doi.org/10.3390/en10121997
Received: 20 October 2017 / Revised: 9 November 2017 / Accepted: 22 November 2017 / Published: 1 December 2017
Cited by 1 | PDF Full-text (851 KB) | HTML Full-text | XML Full-text
Abstract
The irregular wave disturbance attenuation problem for jacket-type offshore platforms involving the nonlinear characteristics is studied. The main contribution is that a digital-control-based approximation of optimal wave disturbances attenuation controller (AOWDAC) is proposed based on iteration control theory, which consists of a feedback [...] Read more.
The irregular wave disturbance attenuation problem for jacket-type offshore platforms involving the nonlinear characteristics is studied. The main contribution is that a digital-control-based approximation of optimal wave disturbances attenuation controller (AOWDAC) is proposed based on iteration control theory, which consists of a feedback item of offshore state, a feedforward item of wave force and a nonlinear compensated component with iterative sequences. More specifically, by discussing the discrete model of nonlinear offshore platform subject to wave forces generated from the Joint North Sea Wave Project (JONSWAP) wave spectrum and linearized wave theory, the original wave disturbances attenuation problem is formulated as the nonlinear two-point-boundary-value (TPBV) problem. By introducing two vector sequences of system states and nonlinear compensated item, the solution of introduced nonlinear TPBV problem is obtained. Then, a numerical algorithm is designed to realize the feasibility of AOWDAC based on the deviation of performance index between the adjacent iteration processes. Finally, applied the proposed AOWDAC to a jacket-type offshore platform in Bohai Bay, the vibration amplitudes of the displacement and the velocity, and the required energy consumption can be reduced significantly. Full article
(This article belongs to the Special Issue Marine Energy)
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Open AccessArticle
Electrical Components for Marine Renewable Energy Arrays: A Techno-Economic Review
Energies 2017, 10(12), 1973; https://doi.org/10.3390/en10121973
Received: 1 November 2017 / Revised: 18 November 2017 / Accepted: 21 November 2017 / Published: 27 November 2017
Cited by 1 | PDF Full-text (619 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents a review of the main electrical components that are expected to be present in marine renewable energy arrays. The review is put in context by appraising the current needs of the industry and identifying the key components required in both [...] Read more.
This paper presents a review of the main electrical components that are expected to be present in marine renewable energy arrays. The review is put in context by appraising the current needs of the industry and identifying the key components required in both device and array-scale developments. For each component, electrical, mechanical and cost considerations are discussed; with quantitative data collected during the review made freely available for use by the community via an open access online repository. This data collection updates previous research and addresses gaps specific to emerging offshore technologies, such as marine and floating wind, and provides a comprehensive resource for the techno-economic assessment of offshore energy arrays. Full article
(This article belongs to the Special Issue Marine Energy)
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Open AccessFeature PaperArticle
Re-Creating Waves in Large Currents for Tidal Energy Applications
Energies 2017, 10(11), 1838; https://doi.org/10.3390/en10111838
Received: 28 September 2017 / Revised: 27 October 2017 / Accepted: 6 November 2017 / Published: 10 November 2017
Cited by 5 | PDF Full-text (3581 KB) | HTML Full-text | XML Full-text
Abstract
Unsteady wave loading on tidal turbines impacts significantly the design, and expected life-time, of turbine blades and other key components. Model-scale testing of tidal turbines in the wave-current environment can provide vital understanding by emulating real-world load cases; however, to reduce uncertainty, it [...] Read more.
Unsteady wave loading on tidal turbines impacts significantly the design, and expected life-time, of turbine blades and other key components. Model-scale testing of tidal turbines in the wave-current environment can provide vital understanding by emulating real-world load cases; however, to reduce uncertainty, it is important to isolate laboratory-specific artefacts from real-world behaviour. In this paper, a variety of realistic combined current-wave scenarios is re-created at the FloWave basin, where the main objective is to understand the characteristics of testing in a combined wave-current environment and assess whether wave effects on the flow field can be predicted. Here, we show that a combination of linear wave-current theory and frequency-domain reflection analysis can be used to effectively predict wave-induced particle velocities and identify velocity components that are experimental artefacts. Load-specific mechanisms present in real-world conditions can therefore be isolated, and equivalent full-scale load cases can be estimated with greater confidence. At higher flow speeds, a divergence from the theory presented is observed due to turbulence-induced non-stationarity. The methodology and results presented increase learning about the wave-current testing environment and provide analysis tools able to improve test outputs and conclusions from scale model testing. Full article
(This article belongs to the Special Issue Marine Energy)
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Open AccessArticle
Cost Assessment Methodology and Economic Viability of Tidal Energy Projects
Energies 2017, 10(11), 1806; https://doi.org/10.3390/en10111806
Received: 15 September 2017 / Revised: 24 October 2017 / Accepted: 6 November 2017 / Published: 9 November 2017
Cited by 4 | PDF Full-text (686 KB) | HTML Full-text | XML Full-text
Abstract
The exploitation of technologies with which to harness the energy from ocean currents will have considerable possibilities in the future thanks to their enormous potential for electricity production and their high predictability. In this respect, the development of methodologies for the economic viability [...] Read more.
The exploitation of technologies with which to harness the energy from ocean currents will have considerable possibilities in the future thanks to their enormous potential for electricity production and their high predictability. In this respect, the development of methodologies for the economic viability of these technologies is fundamental to the attainment of a consistent quantification of their costs and the discovery of their economic viability, while simultaneously attracting investment in these technologies. This paper presents a methodology with which to determine the economic viability of tidal energy projects, which includes a technical study of the life-cycle costs into which the development of a tidal farm can be decomposed: concept and definition, design and development, manufacturing, installation, operation and maintenance and dismantling. These cost structures are additionally subdivided by considering their sub-costs and bearing in mind the main components of the tidal farm: the nacelle, the supporting tidal energy converter structure and the export power system. Furthermore, a technical study is developed in order to obtain an estimation of the annual energy produced (and, consequently, the incomes generated if the electric tariff is known) by considering its principal attributes: the characteristics of the current, the ability of the device to capture energy and its ability to convert and export the energy. The methodology has been applied (together with a sensibility analysis) to the particular case of a farm composed of first generation tidal energy converters in one of the Channel Island Races, the Alderney Race, in the U.K., and the results have been attained by means of the computation of engineering indexes, such as the net present value, the internal rate of return, the discounted payback period and the levelized cost of energy, which indicate that the proposed project is economically viable for all the case studies. Full article
(This article belongs to the Special Issue Marine Energy)
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Open AccessArticle
Simulating Extreme Directional Wave Conditions
Energies 2017, 10(11), 1731; https://doi.org/10.3390/en10111731
Received: 22 September 2017 / Revised: 17 October 2017 / Accepted: 24 October 2017 / Published: 28 October 2017
Cited by 2 | PDF Full-text (7356 KB) | HTML Full-text | XML Full-text
Abstract
Wave tank tests often involve simulating extreme wave conditions as they enable the maximum expected loads to be inferred: a vital parameter for structural design. The definition, and simulation of, extreme conditions are often fairly simplistic, which can result in conditions and associated [...] Read more.
Wave tank tests often involve simulating extreme wave conditions as they enable the maximum expected loads to be inferred: a vital parameter for structural design. The definition, and simulation of, extreme conditions are often fairly simplistic, which can result in conditions and associated loads that are not representative of those that would be observed at the deployment location. Here we present a method of defining, simulating at scale, and validating realistic site-specific extreme wave conditions for survival testing of wave energy converters. Bivariate inverse-first order reliability method (I-FORM) environmental contours define extreme pairs of significant wave height and energy period ( H m 0 T E ), while observed extreme conditions are used to define realistic frequency and directional distributions. These sea states are scaled, simulated and validated at the FloWave Ocean Energy Research Facility to demonstrate that the site-specific extreme wave conditions can be re-created with accuracy. The presented approach enables greater realism to be incorporated into tank testing with survival sea states. The techniques outlined and explored here can provide further and more realistic insight into the response of offshore structures and devices, and can help make important design decisions prior to full-scale deployment. Full article
(This article belongs to the Special Issue Marine Energy)
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Open AccessFeature PaperArticle
A Model Predictive Control-Based Power Converter System for Oscillating Water Column Wave Energy Converters
Energies 2017, 10(10), 1631; https://doi.org/10.3390/en10101631
Received: 1 September 2017 / Revised: 25 September 2017 / Accepted: 3 October 2017 / Published: 17 October 2017
Cited by 4 | PDF Full-text (2965 KB) | HTML Full-text | XML Full-text
Abstract
Despite the predictability and availability at large scale, wave energy conversion (WEC) has still not become a mainstream renewable energy technology. One of the main reasons is the large variations in the extracted power which could lead to instabilities in the power grid. [...] Read more.
Despite the predictability and availability at large scale, wave energy conversion (WEC) has still not become a mainstream renewable energy technology. One of the main reasons is the large variations in the extracted power which could lead to instabilities in the power grid. In addition, maintaining the speed of the turbine within optimal range under changing wave conditions is another control challenge, especially in oscillating water column (OWC) type WEC systems. As a solution to the first issue, this paper proposes the direct connection of a battery bank into the dc-link of the back-to-back power converter system, thereby smoothening the power delivered to the grid. For the second issue, model predictive controllers (MPCs) are developed for the rectifier and the inverter of the back-to-back converter system aiming to maintain the turbine speed within its optimum range. In addition, MPC controllers are designed to control the battery current as well, in both charging and discharging conditions. Operations of the proposed battery direct integration scheme and control solutions are verified through computer simulations. Simulation results show that the proposed integrated energy storage and control solutions are capable of delivering smooth power to the grid while maintaining the turbine speed within its optimum range under varying wave conditions. Full article
(This article belongs to the Special Issue Marine Energy)
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Open AccessArticle
Layout Optimisation of Wave Energy Converter Arrays
Energies 2017, 10(9), 1262; https://doi.org/10.3390/en10091262
Received: 19 July 2017 / Revised: 3 August 2017 / Accepted: 22 August 2017 / Published: 24 August 2017
Cited by 3 | PDF Full-text (1120 KB) | HTML Full-text | XML Full-text
Abstract
This paper proposes an optimisation strategy for the layout design of wave energy converter (WEC) arrays. Optimal layouts are sought so as to maximise the absorbed power given a minimum q-factor, the minimum distance between WECs, and an area of deployment. To [...] Read more.
This paper proposes an optimisation strategy for the layout design of wave energy converter (WEC) arrays. Optimal layouts are sought so as to maximise the absorbed power given a minimum q-factor, the minimum distance between WECs, and an area of deployment. To guarantee an efficient optimisation, a four-parameter layout description is proposed. Three different optimisation algorithms are further compared in terms of performance and computational cost. These are the covariance matrix adaptation evolution strategy (CMA), a genetic algorithm (GA) and the glowworm swarm optimisation (GSO) algorithm. The results show slightly higher performances for the latter two algorithms; however, the first turns out to be significantly less computationally demanding. Full article
(This article belongs to the Special Issue Marine Energy)
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Open AccessArticle
Exploring Marine Energy Potential in the UK Using a Whole Systems Modelling Approach
Energies 2017, 10(9), 1251; https://doi.org/10.3390/en10091251
Received: 5 July 2017 / Revised: 11 August 2017 / Accepted: 16 August 2017 / Published: 23 August 2017
Cited by 3 | PDF Full-text (4281 KB) | HTML Full-text | XML Full-text
Abstract
The key market drivers for marine energy are to reduce carbon emissions, and improve the security and sustainability of supply. There are other technologies that also meet these requirements, and therefore the marine energy market is dependent on the technology being cost effective, [...] Read more.
The key market drivers for marine energy are to reduce carbon emissions, and improve the security and sustainability of supply. There are other technologies that also meet these requirements, and therefore the marine energy market is dependent on the technology being cost effective, and competitive. The potential UK wave and tidal stream energy market is assessed using ETI’s energy systems modelling environment (ESME) which uses a multi-vector approach including energy generation, demand, heat, transport, and infrastructure. This is used to identify scenarios where wave and tidal energy form part of the least-cost energy system for the UK by 2050, and will assess what Levelised Cost of Energy (LCOE) reductions are required to improve the commercialization rate. The results indicate that an installed capacity of 4.9 GW of wave and 2.5 GW of tidal stream could be deployed by 2050 if the LCOE is within 4.5 and 7 p/kWh for each respective technology. If there is a step reduction to the LCOE of wave energy, however, a similar capacity of 5 GW could be deployed by 2050 at a LCOE of 11 p/kWh. Full article
(This article belongs to the Special Issue Marine Energy)
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Open AccessArticle
Validating a Wave-to-Wire Model for a Wave Energy Converter—Part II: The Electrical System
Energies 2017, 10(7), 1002; https://doi.org/10.3390/en10071002
Received: 24 May 2017 / Revised: 3 July 2017 / Accepted: 3 July 2017 / Published: 14 July 2017
Cited by 6 | PDF Full-text (13395 KB) | HTML Full-text | XML Full-text
Abstract
The incorporation of the full dynamics of the different conversion stages of wave energy converters (WECs), from ocean waves to the electricity grid, is essential for a realistic evaluation of the power flow in the drive train. WECs with different power take-off (PTO) [...] Read more.
The incorporation of the full dynamics of the different conversion stages of wave energy converters (WECs), from ocean waves to the electricity grid, is essential for a realistic evaluation of the power flow in the drive train. WECs with different power take-off (PTO) systems, including diverse transmission mechanisms, have been developed in recent decades. However, all the different PTO systems for electricity-producing WECs, regardless of any intermediate transmission mechanism, include an electric generator, linear or rotational. Therefore, accurately modelling the dynamics of electric generators is crucial for all wave-to-wire (W2W) models. This paper presents the models for three popular rotational electric generators (squirrel cage induction machine, permanent magnet synchronous generator and doubly-fed induction generator) and a back-to-back (B2B) power converter and validates such models against experimental data generated using three real electric machines. The input signals for the validation of the mathematical models are designed so that the whole operation range of the electrical generators is covered, including input signals generated using the W2W model that mimic the behaviour of different hydraulic PTO systems. Results demonstrate the effectiveness of the models in accurately reproducing the characteristics of the three electrical machines, including power losses in the different machines and the B2B converter. Full article
(This article belongs to the Special Issue Marine Energy)
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Open AccessArticle
Validating a Wave-to-Wire Model for a Wave Energy Converter—Part I: The Hydraulic Transmission System
Energies 2017, 10(7), 977; https://doi.org/10.3390/en10070977
Received: 24 May 2017 / Revised: 3 July 2017 / Accepted: 6 July 2017 / Published: 12 July 2017
Cited by 6 | PDF Full-text (11556 KB) | HTML Full-text | XML Full-text
Abstract
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 (WECs) [...] Read more.
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 (WECs) 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 WECs. 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 experimental 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 experimental results, capturing friction effects and showing similar losses. Full article
(This article belongs to the Special Issue Marine Energy)
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Open AccessArticle
Optimization of the Runner for Extremely Low Head Bidirectional Tidal Bulb Turbine
Energies 2017, 10(6), 787; https://doi.org/10.3390/en10060787
Received: 28 March 2017 / Revised: 19 May 2017 / Accepted: 2 June 2017 / Published: 7 June 2017
Cited by 2 | PDF Full-text (5013 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents a multi-objective optimization procedure for bidirectional bulb turbine runners which is completed using ANSYS Workbench. The optimization procedure is able to check many more geometries with less manual work. In the procedure, the initial blade shape is parameterized, the inlet [...] Read more.
This paper presents a multi-objective optimization procedure for bidirectional bulb turbine runners which is completed using ANSYS Workbench. The optimization procedure is able to check many more geometries with less manual work. In the procedure, the initial blade shape is parameterized, the inlet and outlet angles (β1, β2), as well as the starting and ending wrap angles (θ1, θ2) for the five sections of the blade profile, are selected as design variables, and the optimization target is set to obtain the maximum of the overall efficiency for the ebb and flood turbine modes. For the flow analysis, the ANSYS CFX code, with a SST (Shear Stress Transport) k-ω turbulence model, has been used to evaluate the efficiency of the turbine. An efficient response surface model relating the design parameters and the objective functions is obtained. The optimization strategy was used to optimize a model bulb turbine runner. Model tests were carried out to validate the final designs and the design procedure. For the four-bladed turbine, the efficiency improvement is 5.5% in the ebb operation direction, and 2.9% in the flood operation direction, as well as 4.3% and 4.5% for the three-bladed turbine. Numerical simulations were then performed to analyze the pressure pulsation in the pressure and suction sides of the blade for the prototype turbine with optimal four-bladed and three-bladed runners. The results show that the runner rotational frequency (fn) is the dominant frequency of the pressure pulsations in the blades for ebb and flood turbine modes, and the gravitational effect, rather than rotor-stator interaction (RSI), plays an important role in a low head horizontal axial turbine. The amplitudes of the pressure pulsations on the blade side facing the guide vanes varies little with the water head. However, the amplitudes of the pressure pulsations on the blade side facing the diffusion tube linearly increase with the water head. These results could provide valuable insight for reducing the pressure amplitudes in the bidirectional bulb turbine. Full article
(This article belongs to the Special Issue Marine Energy)
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Open AccessArticle
Offshore Facilities to Produce Hydrogen
Energies 2017, 10(6), 783; https://doi.org/10.3390/en10060783
Received: 3 April 2017 / Revised: 22 May 2017 / Accepted: 31 May 2017 / Published: 6 June 2017
Cited by 2 | PDF Full-text (4126 KB) | HTML Full-text | XML Full-text
Abstract
As a result of international agreements on the reduction of CO2 emissions, new technologies using hydrogen are being developed. Hydrogen, despite being the most abundant element in Nature, cannot be found in its pure state. Water is one of the most abundant [...] Read more.
As a result of international agreements on the reduction of CO2 emissions, new technologies using hydrogen are being developed. Hydrogen, despite being the most abundant element in Nature, cannot be found in its pure state. Water is one of the most abundant sources of hydrogen on the planet. The proposal here is to use energy from the sea in order to obtain hydrogen from water. If plants to obtain hydrogen were to be placed in the ocean, the impact of long submarines piping to the coast will be reduced. Further, this will open the way for the development of ships propelled by hydrogen. This paper discusses the feasibility of an offshore installation to obtain hydrogen from the sea, using ocean wave energy. Full article
(This article belongs to the Special Issue Marine Energy)
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Open AccessArticle
Scale-Model Experiments for the Surface Wave Influence on a Submerged Floating Ocean-Current Turbine
Energies 2017, 10(5), 702; https://doi.org/10.3390/en10050702
Received: 24 February 2017 / Revised: 11 May 2017 / Accepted: 12 May 2017 / Published: 16 May 2017
Cited by 1 | PDF Full-text (5251 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
In order to harness the kinetic energy of marine currents, we propose a novel ocean-current turbine with a horizontal axis. The turbine can be moored to the seabed and function similarly to kites in a water flow. To operate such turbines in a [...] Read more.
In order to harness the kinetic energy of marine currents, we propose a novel ocean-current turbine with a horizontal axis. The turbine can be moored to the seabed and function similarly to kites in a water flow. To operate such turbines in a marine current, the resulting rotor torque needs to be canceled. Therefore, the proposed turbine is designed with a float at its top and a counterweight at its bottom. Thus far, we have verified the turbine stability and blade performance through towing experiments. As the next step, we constructed a scale-model turbine to confirm the mooring system. This experiment was performed at a circulating water channel with wave-making facilities. The influence of waves on the floating body was also investigated. In this paper, we report the behavior of the scale-model turbine moored to the tank bottom and discuss the influence of surface waves. Full article
(This article belongs to the Special Issue Marine Energy)
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Open AccessArticle
Tidal Current Power Resources and Influence of Sea-Level Rise in the Coastal Waters of Kinmen Island, Taiwan
Energies 2017, 10(5), 652; https://doi.org/10.3390/en10050652
Received: 2 March 2017 / Revised: 31 March 2017 / Accepted: 4 May 2017 / Published: 9 May 2017
Cited by 3 | PDF Full-text (3581 KB) | HTML Full-text | XML Full-text
Abstract
The tidal current power (TCP) resource, the impact of TCP extraction on hydrodynamics and the influence of sea-level rise (SLR) on TCP output in the coastal waters of Kinmen Island (Taiwan) are investigated using a state-of-the-art unstructured-grid depth-integrated numerical model. The model was [...] Read more.
The tidal current power (TCP) resource, the impact of TCP extraction on hydrodynamics and the influence of sea-level rise (SLR) on TCP output in the coastal waters of Kinmen Island (Taiwan) are investigated using a state-of-the-art unstructured-grid depth-integrated numerical model. The model was driven by eight tidal constituents extracted from a global tidal prediction model and verified with time series of measured data for tide level and depth-averaged current. The simulations showed reasonable agreement with the observations; the skill index was in the excellent (0.71–0.93) range with regard to simulating tide level and currents. Model predictions indicated that the channel between Kinmen and Lieyu serves as an appropriate site for deploying the tidal turbines because of its higher tidal current and deeper water depth. The bottom friction approach was utilized to compute the average TCP over a spring-neap cycle (i.e., 15 days). Mean TCP reached its maximum to 45.51 kW for a coverage area of 0.036 km2 when an additional turbine friction coefficient (Ct) increased to 0.08, and a cut-in speed of 0.5 m/s was used. The annual TCP output was estimated to be 1.08 MW. The impact of TCP extraction on the change in current is significant, with a maximum reduction rate of instant current exceeding 60%, and the extent of influence for the average current is 1.26 km in length and 0.30 km in width for the −0.05 m/s contour line. However, the impact of TCP extraction on the change in tide level is insignificant; the maximum change in amplitude is only 0.73 cm for the K2 tide. The influence of SLR on the TCP output in Kinmen waters was also estimated. Modeling assessments showed that due to SLR produces faster tidal current, the annual TCP output increased to 1.52 MW, 2.01 MW, 2.48 MW and 2.97 MW under the same cut-in speed and coverage area conditions when SLR 0.25 m, SLR 0.5 m, SLR 0.75 m and SLR 1.0 m were imposed on the model. Full article
(This article belongs to the Special Issue Marine Energy)
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Open AccessArticle
System Identification of a Heaving Point Absorber: Design of Experiment and Device Modeling
Energies 2017, 10(4), 472; https://doi.org/10.3390/en10040472
Received: 2 January 2017 / Revised: 3 March 2017 / Accepted: 15 March 2017 / Published: 3 April 2017
Cited by 12 | PDF Full-text (2240 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Empirically based modeling is an essential aspect of design for a wave energy converter. Empirically based models are used in structural, mechanical and control design processes, as well as for performance prediction. Both the design of experiments and methods used in system identification [...] Read more.
Empirically based modeling is an essential aspect of design for a wave energy converter. Empirically based models are used in structural, mechanical and control design processes, as well as for performance prediction. Both the design of experiments and methods used in system identification have a strong impact on the quality of the resulting model. This study considers the system identification and model validation process based on data collected from a wave tank test of a model-scale wave energy converter. Experimental design and data processing techniques based on general system identification procedures are discussed and compared with the practices often followed for wave tank testing. The general system identification processes are shown to have a number of advantages, including an increased signal-to-noise ratio, reduced experimental time and higher frequency resolution. The experimental wave tank data is used to produce multiple models using different formulations to represent the dynamics of the wave energy converter. These models are validated and their performance is compared against one another. While most models of wave energy converters use a formulation with surface elevation as an input, this study shows that a model using a hull pressure measurement to incorporate the wave excitation phenomenon has better accuracy. Full article
(This article belongs to the Special Issue Marine Energy)
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Review

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Open AccessFeature PaperEditor’s ChoiceReview
Mathematical Modelling of Mooring Systems for Wave Energy Converters—A Review
Energies 2017, 10(5), 666; https://doi.org/10.3390/en10050666
Received: 1 February 2017 / Revised: 16 March 2017 / Accepted: 3 May 2017 / Published: 11 May 2017
Cited by 14 | PDF Full-text (950 KB) | HTML Full-text | XML Full-text
Abstract
Mathematical analysis is an essential tool for the successful development and operation of wave energy converters (WECs). Mathematical models of moorings systems are therefore a requisite in the overall techno-economic design and operation of floating WECs. Mooring models (MMs) can be applied to [...] Read more.
Mathematical analysis is an essential tool for the successful development and operation of wave energy converters (WECs). Mathematical models of moorings systems are therefore a requisite in the overall techno-economic design and operation of floating WECs. Mooring models (MMs) can be applied to a range of areas, such as WEC simulation, performance evaluation and optimisation, control design and implementation, extreme load calculation, mooring line fatigue life evaluation, mooring design, and array layout optimisation. The mathematical modelling of mooring systems is a venture from physics to numerics, and as such, there are a broad range of details to consider when applying MMs to WEC analysis. A large body of work exists on MMs, developed within other related ocean engineering fields, due to the common requirement of mooring floating bodies, such as vessels and offshore oil and gas platforms. This paper reviews the mathematical modelling of the mooring systems for WECs, detailing the relevant material developed in other offshore industries and presenting the published usage of MMs for WEC analysis. Full article
(This article belongs to the Special Issue Marine Energy)
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