Journal of Marine Science and Engineering

Research

13 pages, 3640 KiB

Open AccessArticle

Modelling Air Compressibility in OWC Devices with Deformable Air Chambers

by Pierre Benreguig and Jimmy Murphy

J. Mar. Sci. Eng. 2019, 7(8), 268; https://doi.org/10.3390/jmse7080268 - 11 Aug 2019

Cited by 7 | Viewed by 4943

Air compressibility effects play an important role in large-scale Oscillating Water Column (OWC) wave energy converters. Air compressibility is however not scalable with Froude similarity law. An existing scaling method enables correctly reproducing the air compressibility at the model scale, but its implementation [...] Read more.

Air compressibility effects play an important role in large-scale Oscillating Water Column (OWC) wave energy converters. Air compressibility is however not scalable with Froude similarity law. An existing scaling method enables correctly reproducing the air compressibility at the model scale, but its implementation is effortful and becomes cumbersome for floating devices and tests at relatively large scales (1/15^th–1/2^th). Air compressibility is therefore commonly ignored in model-scale tank testing of conventional OWC devices, which can lead to substantially unrealistic results on the device performance relative to the full-scale device. In the case of the Tupperwave device, which is a closed circuit OWC device, correctly modelling air compressibility during tank testing is however essential because the device relies on air compressibility to work. In this paper, a new method for modelling air compressibility at the model scale is presented. The method uses variable volume chambers, which mimic air compressibility by storing energy under the form of strain energy. This method reduces the difficulties of implementation and enhances the application of the existing method to larger scales. Various applications to this method are identified and described, including the presentation of a novel OWC concept. Full article

(This article belongs to the Special Issue Advances in Ocean Wave Energy Conversion)

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22 pages, 9953 KiB

Open AccessArticle

Hydrodynamic Performance of Rectangular Heaving Buoys for an Integrated Floating Breakwater

by Xiaoxia Zhang, Qiang Zeng and Zhen Liu

J. Mar. Sci. Eng. 2019, 7(8), 239; https://doi.org/10.3390/jmse7080239 - 24 Jul 2019

Cited by 13 | Viewed by 5694

Abstract

Recently, the integrated development of wave energy converters and breakwaters has become popular, moving from traditional passive wave absorption to active energy capture. In this study, rectangular heaving buoys are considered as floating breakwater modules to absorb wave energy. A numerical wave tank [...] Read more.

Recently, the integrated development of wave energy converters and breakwaters has become popular, moving from traditional passive wave absorption to active energy capture. In this study, rectangular heaving buoys are considered as floating breakwater modules to absorb wave energy. A numerical wave tank is established based on Reynolds Averaged Navier-Stokes equation and User-Define-Function in ANSYS-Fluent commercial software. The numerical results show that incident wave conditions and submerged depth have significant effects on the heaving performance and wave energy absorption of a rectangular buoy. Flow structures around the buoy are shown to exhibit flow separations and vortex shedding, which can provide more information on buoy optimization. Power take-off (PTO) reaction forces are assumed to be a linear function of the translation velocities of the buoy. Numerical results demonstrate that a suitable PTO module can improve the wave power absorption by up to 34.2% for certain buoy and wave conditions, which is valuable for further investigations. Full article

(This article belongs to the Special Issue Advances in Ocean Wave Energy Conversion)

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25 pages, 9066 KiB

Open AccessArticle

Experimental Analysis of a Novel Adaptively Counter-Rotating Wave Energy Converter for Powering Drifters

by Guoheng Wu, Zhongyue Lu, Zirong Luo, Jianzhong Shang, Chongfei Sun and Yiming Zhu

J. Mar. Sci. Eng. 2019, 7(6), 171; https://doi.org/10.3390/jmse7060171 - 1 Jun 2019

Cited by 10 | Viewed by 4033

Abstract

Nowadays, drifters are used for a wide range of applications for researching and exploring the sea. However, the power constraint makes it difficult for their sampling intervals to be smaller, meaning that drifters cannot transmit more accurate measurement data to satellites. Furthermore, due [...] Read more.

Nowadays, drifters are used for a wide range of applications for researching and exploring the sea. However, the power constraint makes it difficult for their sampling intervals to be smaller, meaning that drifters cannot transmit more accurate measurement data to satellites. Furthermore, due to the power constraint, a modern Surface Velocity Program (SVP) drifter lives an average of 400 days before ceasing transmission. To overcome the power constraint of SVP drifters, this article proposes an adaptively counter-rotating wave energy converter (ACWEC) to supply power for drifters. The ACWEC has the advantages of convenient modular integration, simple conversion process, and minimal affection by the crucial sea environment. This article details the design concept and working principle, and the interaction between the wave energy converter (WEC) and wave is presented based on plane wave theory. To verify the feasibility of the WEC, the research team carried out a series of experiments in a wave tank with regular and irregular waves. Through experiments, it was found that the power and efficiency of the ACWEC are greatly influenced by parameters such as wave height and wave frequency. The maximum output power of the small scale WEC in a wave tank is 6.36 W, which allows drifters to detect ocean data more frequently and continuously. Full article

(This article belongs to the Special Issue Advances in Ocean Wave Energy Conversion)

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17 pages, 5395 KiB

Open AccessFeature PaperArticle

A Hamiltonian Surface-Shaping Approach for Control System Analysis and the Design of Nonlinear Wave Energy Converters

by Shadi Darani, Ossama Abdelkhalik, Rush D. Robinett and David Wilson

J. Mar. Sci. Eng. 2019, 7(2), 48; https://doi.org/10.3390/jmse7020048 - 15 Feb 2019

Cited by 3 | Viewed by 3167

Abstract

The dynamic model of Wave Energy Converters (WECs) may have nonlinearities due to several reasons such as a nonuniform buoy shape and/or nonlinear power takeoff units. This paper presents the Hamiltonian Surface-Shaping (HSS) approach as a tool for the analysis and design of [...] Read more.

The dynamic model of Wave Energy Converters (WECs) may have nonlinearities due to several reasons such as a nonuniform buoy shape and/or nonlinear power takeoff units. This paper presents the Hamiltonian Surface-Shaping (HSS) approach as a tool for the analysis and design of nonlinear control of WECs. The Hamiltonian represents the stored energy in the system and can be constructed as a function of the WEC’s system states, its position, and velocity. The Hamiltonian surface is defined by the energy storage, while the system trajectories are constrained to this surface and determined by the power flows of the applied non-conservative forces. The HSS approach presented in this paper can be used as a tool for the design of nonlinear control systems that are guaranteed to be stable. The optimality of the obtained solutions is not addressed in this paper. The case studies presented here cover regular and irregular waves and demonstrate that a nonlinear control system can result in a multiple fold increase in the harvested energy. Full article

(This article belongs to the Special Issue Advances in Ocean Wave Energy Conversion)

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18 pages, 6541 KiB

Open AccessArticle

Experimental Study of a Hybrid Wave Energy Converter Integrated in a Harbor Breakwater

by Paulo Rosa-Santos, Francisco Taveira-Pinto, Daniel Clemente, Tomás Cabral, Felipe Fiorentin, Filipe Belga and Tiago Morais

J. Mar. Sci. Eng. 2019, 7(2), 33; https://doi.org/10.3390/jmse7020033 - 3 Feb 2019

Cited by 43 | Viewed by 5785

Abstract

Sea ports are infrastructures with substantial energy demands and often responsible for air pollution and other environmental problems, which may be minimized by using renewable energy, namely electricity harvested from ocean waves. In this regard, a wide variety of concepts to harvest wave [...] Read more.

Sea ports are infrastructures with substantial energy demands and often responsible for air pollution and other environmental problems, which may be minimized by using renewable energy, namely electricity harvested from ocean waves. In this regard, a wide variety of concepts to harvest wave energy are available and some shoreline technologies are already in an advanced development phase. The SE@PORTS project aims to assess the suitability and viability of existing wave energy conversion technologies to be integrated in harbor breakwaters, in order to take advantage of their high exposure to ocean waves. This paper describes the experimental study carried out to assess the performance of a hybrid wave energy converter (WEC) integrated in the rubble-mound structure that was proposed for the extension of the North breakwater of the Port of Leixões, Portugal. The hybrid concept combines the overtopping and the oscillating water column principles and was tested on a geometric scale of 1/50. This paper is focused on the assessment of the effects of the hybrid WEC integration on the case-study breakwater, both in terms of its stability and functionality. The 2D physical model included the reproduction of the seabed bathymetry in front of the breakwater and the generation of a wide range of irregular sea states, including extreme wave conditions. The experimental results shown that the integration of the hybrid WEC in the breakwater does not worsens the stability of its toe berm blocks and reduces the magnitude of the overtopping events. The conclusions obtained are therefore favorable to the integration of this type of devices on harbor breakwaters. Full article

(This article belongs to the Special Issue Advances in Ocean Wave Energy Conversion)

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17 pages, 9072 KiB

Open AccessArticle

KNSwing—On the Mooring Loads of a Ship-Like Wave Energy Converter

by Kim Nielsen and Jonas Bjerg Thomsen

J. Mar. Sci. Eng. 2019, 7(2), 29; https://doi.org/10.3390/jmse7020029 - 1 Feb 2019

Cited by 6 | Viewed by 3098

Abstract

The critical function of keeping a floating Wave Energy Converter in position is done by a mooring system. Several WECs have been lost due to failed moorings, indicating that extreme loads, reliability and durability are very important aspects. An understanding of the interaction [...] Read more.

The critical function of keeping a floating Wave Energy Converter in position is done by a mooring system. Several WECs have been lost due to failed moorings, indicating that extreme loads, reliability and durability are very important aspects. An understanding of the interaction between the WEC’s motion in large waves and the maximum mooring loads can be gained by investigating the system at model scale supported by numerical models. This paper describes the testing of a novel attenuator WEC design called KNSwing. It is shaped like a ship facing the waves with its bow, which results in low mooring loads and small motions in most wave conditions when the structure is longer than the waves. The concept is tested using an experimental model at scale 1:80 in regular and irregular waves, moored using rubber bands to simulate synthetic moorings. The experimental results are compared to numerical simulations done using the OrcaFlex software. The experimental results show that the WEC and the mooring system survives well, even under extreme and breaking waves. The numerical model coefficient concerning the nonlinear drag term for the surge motion is validated using decay tests. The numerical results compare well to the experiments and, thereby, the numerical model can be further used to optimize the mooring system. Full article

(This article belongs to the Special Issue Advances in Ocean Wave Energy Conversion)

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22 pages, 9777 KiB

Open AccessArticle

Energetic Potential Assessment of Wind-Driven Waves on the South-Southeastern Brazilian Shelf

by Phelype Haron Oleinik, Eduardo de Paula Kirinus, Cristiano Fragassa, Wiliam Correa Marques and Juliana Costi

J. Mar. Sci. Eng. 2019, 7(2), 25; https://doi.org/10.3390/jmse7020025 - 23 Jan 2019

Cited by 6 | Viewed by 3268

Abstract

Global electric energy demand is constantly growing, consequently leading towards the usage of renewable energy sources reducing pollution and increasing sustainability. The ocean is a poorly explored renewable energy source; thus, to evaluate the Brazilian wave energy budget, this study investigated the mean [...] Read more.

Global electric energy demand is constantly growing, consequently leading towards the usage of renewable energy sources reducing pollution and increasing sustainability. The ocean is a poorly explored renewable energy source; thus, to evaluate the Brazilian wave energy budget, this study investigated the mean behaviour of the wave power rate on the south-southeastern Brazilian Shelf as well as analysed the temporal variability of the wave power rate at the most energetic locations near the coast. Three locations were examined, namely Laguna, Ilhabela and Farol Island, based on the criteria of high means and small standard deviations. The mean wave power rate was approximately

9.08

kW

/

m

on Laguna,

10.01

kW

/

m

on Ilhabela and

15.93

kW

/

m

on Farol Island. The standard deviation identified in the three locations reached values of

6.47

kW

/

m

on Laguna,

7.59

kW

/

m

on Ilhabela and

13.51

kW

/

m

on Farol Island. Temporal variability analysis was conducted through wavelet analysis. The results show a dominant yearly cycle with a background presence of synoptic cycles, with little deviation between the locations. The El Niño southern oscillation plays a minor role on the energy spectrum of Laguna and does not have a significant influence on Ilhabela and Farol Island. Full article

(This article belongs to the Special Issue Advances in Ocean Wave Energy Conversion)

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18 pages, 5177 KiB

Open AccessArticle

Modelling Approaches of a Closed-Circuit OWC Wave Energy Converter

by Pierre Benreguig, Miguel Vicente, Adrian Dunne and Jimmy Murphy

J. Mar. Sci. Eng. 2019, 7(2), 23; https://doi.org/10.3390/jmse7020023 - 22 Jan 2019

Cited by 14 | Viewed by 4206

Abstract

The Tupperwave device is a wave energy converter based on the Oscillating Water Column (OWC) concept. Unlike conventional OWC devices, which are opened to the atmosphere, the Tupperwave device works in closed-circuit and uses non-return valves and accumulator chambers to create a smooth [...] Read more.

The Tupperwave device is a wave energy converter based on the Oscillating Water Column (OWC) concept. Unlike conventional OWC devices, which are opened to the atmosphere, the Tupperwave device works in closed-circuit and uses non-return valves and accumulator chambers to create a smooth unidirectional flow across a unidirectional turbine. The EU-funded OceanEraNet project called Tupperwave was undertaken by a consortium of academic and industrial partners, aimed at designing and modelling the Tupperwave device. The device was numerically modelled using two different methods. It was also physically modelled at the laboratory scale. The various modelling methods are discussed and compared. An analysis of the dependence of the device efficiency on the valves and turbine aerodynamic damping is carried out, using both physical and numerical approaches. Full article

(This article belongs to the Special Issue Advances in Ocean Wave Energy Conversion)

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17 pages, 7402 KiB

Open AccessArticle

Numerical Modeling and Dynamic Analysis of a Wave-Powered Reverse-Osmosis System

by Yi-Hsiang Yu and Dale Jenne

J. Mar. Sci. Eng. 2018, 6(4), 132; https://doi.org/10.3390/jmse6040132 - 8 Nov 2018

Cited by 19 | Viewed by 7819

Abstract

A wave energy converter (WEC) system has the potential to convert the wave energy resource directly into the high-pressure flow that is needed by the desalination system to pump saltwater to the reverse-osmosis membrane and provide the required pressure level to generate freshwater. [...] Read more.

A wave energy converter (WEC) system has the potential to convert the wave energy resource directly into the high-pressure flow that is needed by the desalination system to pump saltwater to the reverse-osmosis membrane and provide the required pressure level to generate freshwater. In this study, a wave-to-water numerical model was developed to investigate the potential use of a wave-powered desalination system (WPDS) for water production. The model was developed by coupling a time-domain radiation-and-diffraction method-based numerical tool (WEC-Sim) for predicting the hydrodynamic performance of WECs with a solution-diffusion model that was used to simulate the reverse-osmosis (RO) process. The objective of this research is to evaluate the WPDS dynamics and the overall efficiency of the system. To evaluate the feasibility of the WPDS, the wave-to-water numerical model was applied to simulate a desalination system that used an oscillating surge WEC device to pump seawater through the system. The hydrodynamics WEC-Sim simulation results for the oscillating surge WEC device were validated against existing experimental data. The RO simulation was verified by comparing the results to those from the Dow Chemical Company’s reverse osmosis system analysis (ROSA) model, which has been widely used to design and simulate RO systems. The wave-to-water model was then used to analyze the WPDS under a range of wave conditions and for a two-WECs-coupled RO system to evaluate the influence of pressure and flow rate fluctuation on the WPDS performance. The results show that the instantaneous energy fluctuation from waves has a significant influence on the responding hydraulic pressure and flow rate, as well as the recovery ratio and, ultimately, the water-production quality. Nevertheless, it is possible to reduce the hydraulic fluctuation for different sea states while maintaining a certain level of freshwater production, and a WEC array that produces water can be a viable, near-term solution to the nation’s water supply. A discussion on the dynamic impact of hydraulic fluctuation on the WPDS performance and potential options to reduce the fluctuation and their trade-offs is also presented. Full article

(This article belongs to the Special Issue Advances in Ocean Wave Energy Conversion)

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21 pages, 4083 KiB

Open AccessArticle

Analysis of Different Methods for Wave Generation and Absorption in a CFD-Based Numerical Wave Tank

by Adria Moreno Miquel, Arun Kamath, Mayilvahanan Alagan Chella, Renata Archetti and Hans Bihs

J. Mar. Sci. Eng. 2018, 6(2), 73; https://doi.org/10.3390/jmse6020073 - 14 Jun 2018

Cited by 82 | Viewed by 7656

Abstract

In this paper, the performance of different wave generation and absorption methods in computational fluid dynamics (CFD)-based numerical wave tanks (NWTs) is analyzed. The open-source CFD code REEF3D is used, which solves the Reynolds-averaged Navier–Stokes (RANS) equations to simulate two-phase flow problems. The [...] Read more.

In this paper, the performance of different wave generation and absorption methods in computational fluid dynamics (CFD)-based numerical wave tanks (NWTs) is analyzed. The open-source CFD code REEF3D is used, which solves the Reynolds-averaged Navier–Stokes (RANS) equations to simulate two-phase flow problems. The water surface is computed with the level set method (LSM), and turbulence is modeled with the k-

ω

model. The NWT includes different methods to generate and absorb waves: the relaxation method, the Dirichlet-type method and active wave absorption. A sensitivity analysis has been conducted in order to quantify and compare the differences in terms of absorption quality between these methods. A reflection analysis based on an arbitrary number of wave gauges has been adopted to conduct the study. Tests include reflection analysis of linear, second- and fifth-order Stokes waves, solitary waves, cnoidal waves and irregular waves generated in an NWT. Wave breaking over a sloping bed and wave forces on a vertical cylinder are calculated, and the influence of the reflections on the wave breaking location and the wave forces on the cylinder is investigated. In addition, a comparison with another open-source CFD code, OpenFOAM, has been carried out based on published results. Some differences in the calculated quantities depending on the wave generation and absorption method have been observed. The active wave absorption method is seen to be more efficient for long waves, whereas the relaxation method performs better for shorter waves. The relaxation method-based numerical beach generally results in lower reflected waves in the wave tank for most of the cases simulated in this study. The comparably better performance of the relaxation method comes at the cost of larger computational requirements due to the relaxation zones that have to be included in the domain. The reflections in the NWT in REEF3D are generally lower than the published results for reflections using the active wave absorption method in the NWT based on OpenFOAM. Full article

(This article belongs to the Special Issue Advances in Ocean Wave Energy Conversion)

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21 pages, 4460 KiB

Open AccessArticle

Deployment and Maintenance of Wave Energy Converters at the Lysekil Research Site: A Comparative Study on the Use of Divers and Remotely-Operated Vehicles

by Flore Rémouit, Maria-Angeliki Chatzigiannakou, Anke Bender, Irina Temiz, Jan Sundberg and Jens Engström

J. Mar. Sci. Eng. 2018, 6(2), 39; https://doi.org/10.3390/jmse6020039 - 12 Apr 2018

Cited by 21 | Viewed by 6691

Abstract

Ocean renewable technologies have been rapidly developing over the past years. However, current high installation, operation, maintenance, and decommissioning costs are hindering these offshore technologies to reach a commercialization stage. In this paper we focus on the use of divers and remotely-operated vehicles [...] Read more.

Ocean renewable technologies have been rapidly developing over the past years. However, current high installation, operation, maintenance, and decommissioning costs are hindering these offshore technologies to reach a commercialization stage. In this paper we focus on the use of divers and remotely-operated vehicles during the installation and monitoring phase of wave energy converters. Methods and results are based on the wave energy converter system developed by Uppsala University, and our experience in offshore deployments obtained during the past eleven years. The complexity of underwater operations, carried out by either divers or remotely-operated vehicles, is emphasized. Three methods for the deployment of wave energy converters are economically and technically analyzed and compared: one using divers alone, a fully-automated approach using remotely-operated vehicles, and an intermediate approach, involving both divers and underwater vehicles. The monitoring of wave energy converters by robots is also studied, both in terms of costs and technical challenges. The results show that choosing an autonomous deployment method is more advantageous than a diver-assisted method in terms of operational time, but that numerous factors prevent the wide application of robotized operations. Technical solutions are presented to enable the use of remotely-operated vehicles instead of divers in ocean renewable technology operations. Economically, it is more efficient to use divers than autonomous vehicles for the deployment of six or fewer wave energy converters. From seven devices, remotely-operated vehicles become advantageous. Full article

(This article belongs to the Special Issue Advances in Ocean Wave Energy Conversion)

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24 pages, 1888 KiB

Open AccessArticle

Control of Wave Energy Converters with Discrete Displacement Hydraulic Power Take-Off Units

by Shangyan Zou and Ossama Abdelkhalik

J. Mar. Sci. Eng. 2018, 6(2), 31; https://doi.org/10.3390/jmse6020031 - 2 Apr 2018

Cited by 18 | Viewed by 5472

Abstract

The control of ocean Wave Energy Converters (WECs) impacts the harvested energy. Several control methods have been developed over the past few decades to maximize the harvested energy. Many of these methods were developed based on an unconstrained dynamic model assuming an ideal [...] Read more.

The control of ocean Wave Energy Converters (WECs) impacts the harvested energy. Several control methods have been developed over the past few decades to maximize the harvested energy. Many of these methods were developed based on an unconstrained dynamic model assuming an ideal power take-off (PTO) unit. This study presents numerical tests and comparisons of a few recently developed control methods. The testing is conducted using a numerical simulator that simulates a hydraulic PTO. The PTO imposes constraints on the maximum attainable control force and maximum stroke. In addition, the PTO has its own dynamics, which may impact the performance of some control strategies. Full article

(This article belongs to the Special Issue Advances in Ocean Wave Energy Conversion)

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14 pages, 5349 KiB

Open AccessArticle

Small-Scale Renewable Energy Converters for Battery Charging

by Mohd Nasir Ayob, Valeria Castellucci, Malin Göteman, Joakim Widén, Johan Abrahamsson, Jens Engström and Rafael Waters

J. Mar. Sci. Eng. 2018, 6(1), 26; https://doi.org/10.3390/jmse6010026 - 13 Mar 2018

Cited by 5 | Viewed by 5013

Abstract

This paper presents two wave energy concepts for small-scale electricity generation. In the presented case, these concepts are installed on the buoy of a heaving, point-absorbing wave energy converter (WEC) for large scale electricity production. In the studied WEC, developed by Uppsala University, [...] Read more.

This paper presents two wave energy concepts for small-scale electricity generation. In the presented case, these concepts are installed on the buoy of a heaving, point-absorbing wave energy converter (WEC) for large scale electricity production. In the studied WEC, developed by Uppsala University, small-scale electricity generation in the buoy is needed to power a tidal compensating system designed to increase the performance of the WEC in areas with high tides. The two considered and modeled concepts are an oscillating water column (OWC) and a heaving point absorber. The results indicate that the OWC is too small for the task and does not produce enough energy. On the other hand, the results show that a hybrid system composed of a small heaving point absorber combined with a solar energy system would be able to provide a requested minimum power of around 37.7 W on average year around. The WEC and solar panel complement each other, as the WEC produces enough energy by itself during wintertime (but not in the summer), while the solar panel produces enough energy in the summer (but not in the winter). Full article

(This article belongs to the Special Issue Advances in Ocean Wave Energy Conversion)

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