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4 pages, 186 KiB

Open AccessEditorial

Special Issue “Advances and Challenges in Harvesting Ocean Energy”

by Eugen Rusu

Energies 2021, 14(15), 4543; https://doi.org/10.3390/en14154543 - 27 Jul 2021

Viewed by 1073

Abstract

Climate change has visible effects with growing dynamics in the last decades [...] Full article

(This article belongs to the Special Issue Advances and Challenges in Harvesting Ocean Energy)

Research

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16 pages, 41493 KiB

Open AccessArticle

Evaluation of the Worldwide Wave Energy Distribution Based on ERA5 Data and Altimeter Measurements

by Liliana Rusu and Eugen Rusu

Energies 2021, 14(2), 394; https://doi.org/10.3390/en14020394 - 12 Jan 2021

Cited by 34 | Viewed by 3756

Abstract

There is an increasing necessity in reducing CO₂ emissions and implementing clean energy technologies, and over the years the marine environment has shown a huge potential in terms of renewable energy. From this perspective, extracting marine renewable energy represents one of the [...] Read more.

There is an increasing necessity in reducing CO₂ emissions and implementing clean energy technologies, and over the years the marine environment has shown a huge potential in terms of renewable energy. From this perspective, extracting marine renewable energy represents one of the most important technological challenges of the 21st century. In this context, the objective of the present work is to provide a new and comprehensive understanding concerning the global wave energy resources based on the most recent results coming from two different databases, ERA5 and the European Space Agency Climate Change Initiative for Sea State. In this study, an analysis was first made based only on the ERA5 data and concerns the 30-year period of 1989–2018. The mean wave power, defined as the energy flux per unit of wave-crest length, was evaluated at this step. Besides the spatial distribution of this parameter, its seasonal, inter, and mean annual variability was also assessed on a global scale. As a second step, the mean wave energy density per unit horizontal area was analyzed for a 27-year period (1992–2018) with both ERA5 and the satellite data from the European Space Agency being considered. The comparison indicates a relatively good concordance between the results provided by the two databases in terms of mean wave energy density, although the satellite data indicate slightly higher energy values. Full article

(This article belongs to the Special Issue Advances and Challenges in Harvesting Ocean Energy)

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18 pages, 13275 KiB

Open AccessArticle

Numerical Simulation of Pulsed Gravel Packing Completion in Horizontal Wells

by Zhenxiang Zhang, Jin Yang, Shengnan Chen, Qibin Ou, Yichi Zhang, Ximo Qu and Yafei Guo

Energies 2021, 14(2), 292; https://doi.org/10.3390/en14020292 - 07 Jan 2021

Cited by 3 | Viewed by 1728

Abstract

The gravel packing completion method for horizontal wells has the advantages of maintaining high oil production for a long time, maintaining wellbore stability, and preventing sand production, so it has become the preferred completion method for horizontal wells. At present, this technology still [...] Read more.

The gravel packing completion method for horizontal wells has the advantages of maintaining high oil production for a long time, maintaining wellbore stability, and preventing sand production, so it has become the preferred completion method for horizontal wells. At present, this technology still faces the problems of high sand bed height and poor gravel migration. In order to improve the efficiency of gravel packing in horizontal wells, pulsed gravel packing technology for horizontal wells is proposed for the first time. Based on the mechanism of hydraulic pulse, the Eulerian–Eulerian model, k-ε model based on the renormalization group theory (RNG k-ε model), and Fluent are used to simulate the solid-liquid two-phase flow. By optimizing the parameters such as frequency and amplitude of pulse waveform, the optimal pulse waveform of pulsed gravel packing in horizontal wells is determined. The effects of parameters such as sand-carrying fluid displacement, sand-carrying fluid viscosity, sand-carrying ratio, gravel particle size, and string eccentricity on pulsed gravel packing in horizontal wells are studied, and the distribution law of gravel migration velocity and volume fraction in horizontal wells is obtained. According to the results, it can be seen that with the increase of displacement and viscosity of carrier fluid, the volume fraction of fixed bed and moving bed decreases gradually, while that of suspension bed increases gradually. With the increase of sand-carrying ratio, gravel particle size, and string eccentricity, the volume fraction of fixed bed and moving bed increases gradually, while that of suspended bed decreases gradually. Comparing the effects of conventional gravel packing and pulsed gravel packing in horizontal wells, it can be concluded that the efficiency of pulsed gravel packing in horizontal wells is higher. The volume fraction of fixed bed and moving bed decreased by 30% and 40% respectively, while the volume fraction of suspended bed increased by 20%. The migration velocity of moving bed and suspended bed increased by 40% and 25%, respectively, and the migration ability of gravel improved obviously. Full article

(This article belongs to the Special Issue Advances and Challenges in Harvesting Ocean Energy)

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13 pages, 4114 KiB

Open AccessArticle

Mathematical Modeling and Experimental Verification of a New Wave Energy Converter

by Zhongliang Meng, Yanjun Liu, Jian Qin and Yun Chen

Energies 2021, 14(1), 177; https://doi.org/10.3390/en14010177 - 31 Dec 2020

Cited by 3 | Viewed by 1798

Abstract

As traditional energy sources are increasingly depleting, ocean energy has become an emergent potential clean energy source. Wave energy, as an important part of ocean-derived energy, has been studied and utilized by coastal countries worldwide, which have developed various wave energy converters. In [...] Read more.

As traditional energy sources are increasingly depleting, ocean energy has become an emergent potential clean energy source. Wave energy, as an important part of ocean-derived energy, has been studied and utilized by coastal countries worldwide, which have developed various wave energy converters. In this paper, a new wave energy converter is designed, and water movement in fluid channels is analyzed. The results are, then, used to generate a mathematical model that simulates water movement. Based on this approach, the water movement state is analyzed, and a formula for calculating the natural frequency of water movement in the power generator is derived. The formula shows that the characteristic length of the water movement in the proposed generator and the backboard tilt angle at the exit point of the fluid channel are two design-related variables that can be used to alter the natural frequency; a regular wave experiment is conducted based on the fluid model, which is designed based on the natural frequency formula, to verify the changes in model torque and speed as well as whether the model can operate under normal wave conditions. This study lays a theoretical foundation for the design of further experiments and engineering prototypes to verify the validity of mathematical models by way of experimental analysis. Full article

(This article belongs to the Special Issue Advances and Challenges in Harvesting Ocean Energy)

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25 pages, 3038 KiB

Open AccessArticle

Study Concerning the Expected Dynamics of the Wind Energy Resources in the Iberian Nearshore

by Andrés Ruiz, Florin Onea and Eugen Rusu

Energies 2020, 13(18), 4832; https://doi.org/10.3390/en13184832 - 16 Sep 2020

Cited by 12 | Viewed by 2434

Abstract

The objective of the present study is to show a comprehensive assessment of the wind resource dynamics along the Spanish coastal environment of the Iberian Peninsula. After studying the historical resources (reported at 100 m height) for the 20-year period from 1999 to [...] Read more.

The objective of the present study is to show a comprehensive assessment of the wind resource dynamics along the Spanish coastal environment of the Iberian Peninsula. After studying the historical resources (reported at 100 m height) for the 20-year period from 1999 to 2018 by analyzing the ERA5 time series of wind speed data, the 10 locations with highest historical wind resources are considered. For these, the study of the future dynamics for the 30-year period from 2021 to 2050 under the climate change scenario RCP 4.5 is carried out. After further selection, mean and maximum values, as well as the seasonal and monthly variability of the wind power density, are obtained for six locations along the Spanish coasts. Furthermore, a performance and economic dynamics assessment is presented for four different wind turbine technologies with rated capacities ranging between 3 and 9.5 MW. A further comparison with other locations in the Baltic Sea and the Black Sea is presented to provide a critical image of the Spanish wind resources dynamics in the European framework. The results indicate a noticeable gain of wind resources in various locations of the Atlantic and Mediterranean coasts, with others presenting slight losses. Full article

(This article belongs to the Special Issue Advances and Challenges in Harvesting Ocean Energy)

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23 pages, 6748 KiB

Open AccessArticle

An Evaluation of the Wind Energy Resources along the Spanish Continental Nearshore

by Florin Onea, Andrés Ruiz and Eugen Rusu

Energies 2020, 13(15), 3986; https://doi.org/10.3390/en13153986 - 02 Aug 2020

Cited by 13 | Viewed by 2646

Abstract

The main objective of the present work is to provide a comprehensive picture of the wind conditions in the Spanish continental nearshore considering a state-of-the-art wind dataset. In order to do this, the ERA5 wind data, covering the 20-year time interval from 1999 [...] Read more.

The main objective of the present work is to provide a comprehensive picture of the wind conditions in the Spanish continental nearshore considering a state-of-the-art wind dataset. In order to do this, the ERA5 wind data, covering the 20-year time interval from 1999 to 2018, was processed and evaluated. ERA stands for ’ECMWF Re-Analysis’ and refers to a series of research projects at ECMWF (European Centre for Medium-Range Weather Forecasts) which produced various datasets. In addition to the analysis of the wind resources (reported for a 100 m height), the performances of several wind turbines, ranging from 3 to 9.5 MW, were evaluated. From the analysis of the spatial maps it was observed that the Northern part of this region presents significant wind resources, the mean wind speed values exceeding 9 m/s in some locations. On the other hand, in regard to the Southern sector, more energetic conditions are visible close to the Strait of Gibraltar and to the Gulf of Lion. Nevertheless, from the analysis of the data corresponding to these two Southern nearshore points it was observed that the average wind speed was lower than 8 m/s in both summer and winter months. Regarding the considered wind turbines, the capacity factor did in general not exceed 20%—however, we did observe some peaks that could reach to 30%. Finally, it can be highlighted that the Northern part of the Spanish continental nearshore is significant from the perspective of extracting offshore wind energy, especially considering the technologies based on floating platforms. Furthermore, because of the clear synergy between wind and wave energy, which are characteristic to this coastal environment, an important conclusion of the present work is that the implementation of joint wind–wave projects might be effective in the Northwestern side of the Iberian nearshore. Full article

(This article belongs to the Special Issue Advances and Challenges in Harvesting Ocean Energy)

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15 pages, 4062 KiB

Open AccessArticle

Evaluating the Future Efficiency of Wave Energy Converters along the NW Coast of the Iberian Peninsula

by Américo S. Ribeiro, Maite deCastro, Liliana Rusu, Mariana Bernardino, João M. Dias and Moncho Gomez-Gesteira

Energies 2020, 13(14), 3563; https://doi.org/10.3390/en13143563 - 10 Jul 2020

Cited by 20 | Viewed by 3137

Abstract

The efficiency of wave energy converters (WECs) is generally evaluated in terms of historical wave conditions that do not necessarily represent the conditions that those devices will encounter when put into operation. The main objective of the study is to assess the historical [...] Read more.

The efficiency of wave energy converters (WECs) is generally evaluated in terms of historical wave conditions that do not necessarily represent the conditions that those devices will encounter when put into operation. The main objective of the study is to assess the historical and near future efficiency and energy cost of two WECs (Aqua Buoy and Pelamis). A SWAN model was used to downscale the wave parameters along the NW coast of the Iberian Peninsula both for a historical period (1979–2005) and the near future (2026–2045) under the RCP 8.5 greenhouse scenario. The past and future efficiency of both WECs were computed in terms of two parameters that capture the relationship between sea states and the WEC power matrices: the load factor and the capture width. The wave power resource and the electric power capacity of both the WECs will decrease in the near future. The load factor for Aqua Buoy will decrease in the entire area, while it will remain unchanged for Pelamis in most of the area, except north of 43.5° N. The capture width and cost of energy will increase for both devices. The methodology here applied can be easily applied to any device and coastal domain under different climate change scenarios. Full article

(This article belongs to the Special Issue Advances and Challenges in Harvesting Ocean Energy)

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24 pages, 9237 KiB

Open AccessArticle

A BEM for the Hydrodynamic Analysis of Oscillating Water Column Systems in Variable Bathymetry

by Kostas Belibassakis, Alexandros Magkouris and Eugen Rusu

Energies 2020, 13(13), 3403; https://doi.org/10.3390/en13133403 - 02 Jul 2020

Cited by 12 | Viewed by 2166

Abstract

In this work, a novel Boundary Element Method (BEM) is developed and applied to the investigation of the performance of Oscillating Water Column (OWC) systems, taking into account the interaction of the incident wave field with the bottom topography. The modelling includes the [...] Read more.

In this work, a novel Boundary Element Method (BEM) is developed and applied to the investigation of the performance of Oscillating Water Column (OWC) systems, taking into account the interaction of the incident wave field with the bottom topography. The modelling includes the effect of additional upwave walls and barriers used to modify the resonance characteristics of the device and improve its performance as the U-OWC configuration. Numerical results illustrating the effects of depth variation in conjunction with other parameters—such as chamber dimensions as well as the parameters associated with the turbine and power take-off system—on the device performance are presented and discussed. Finally, a case study is presented regarding the potential installation of an OWC in a selected port site in the Black Sea, characterized by a good wave energy potential, on the coast of Romania. Full article

(This article belongs to the Special Issue Advances and Challenges in Harvesting Ocean Energy)

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22 pages, 55756 KiB

Open AccessArticle

Impacts of Global Climate Change on the Future Ocean Wave Power Potential: A Case Study from the Indian Ocean

by Harshinie Karunarathna, Pravin Maduwantha, Bahareh Kamranzad, Harsha Rathnasooriya and Kasun De Silva

Energies 2020, 13(11), 3028; https://doi.org/10.3390/en13113028 - 11 Jun 2020

Cited by 13 | Viewed by 3931

Abstract

This study investigates the impacts of global climate change on the future wave power potential, taking Sri Lanka as a case study from the northern Indian Ocean. The geographical location of Sri Lanka, which receives long-distance swell waves generated in the Southern Indian [...] Read more.

This study investigates the impacts of global climate change on the future wave power potential, taking Sri Lanka as a case study from the northern Indian Ocean. The geographical location of Sri Lanka, which receives long-distance swell waves generated in the Southern Indian Ocean, favors wave energy-harvesting. Waves projected by a numerical wave model developed using Simulating Waves Nearshore Waves (SWAN) wave model, which is forced by atmospheric forcings generated by an Atmospheric Global Climate Model (AGCM) within two time slices that represent “present” and “future” (end of century) wave climates, are used to evaluate and compare present and future wave power potential around Sri Lanka. The results reveal that there will be a 12–20% reduction in average available wave power along the south-west and south-east coasts of Sri Lanka in future. This reduction is due mainly to changes to the tropical south-west monsoon system because of global climate change. The available wave power resource attributed to swell wave component remains largely unchanged. Although a detailed analysis of monthly and annual average wave power under both “present” and “future” climates reveals a strong seasonal and some degree of inter-annual variability of wave power, a notable decadal-scale trend of variability is not visible during the simulated 25-year periods. Finally, the results reveal that the wave power attributed to swell waves are very stable over the long term. Full article

(This article belongs to the Special Issue Advances and Challenges in Harvesting Ocean Energy)

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