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The entrance in the Sulina channel in the Black Sea is the target area of this study. This represents the southern gate of the seventh Pan-European transport corridor, and it is usually subjected to high navigation traffic. The main objective of the work is to provide a more comprehensive picture concerning the past and future expected dynamics of the environmental matrix in this coastal area, including especially the extreme wind and wave conditions in connection with the possible navigation risks. The methodology considered assumes analyses performed at three different levels. First, an analysis of some in situ measurements at the zero-kilometer point of the Danube is carried out for the 15-year period of 2009–2023. Together with the maximum wind speed and the maximum value of the wind gusts, the water level variation was analyzed at this point. As a second step, the analysis is based on wind speed data provided by regional climate models. Two periods, each spanning 30 years, are considered. These are the recent past (1976–2005), when comparisons with ERA5 reanalysis data were also performed, and the near future (2041–2070), when two different models and three climate scenarios were considered. The focus was on the extreme wind speed values, performing comparisons between the past and future expected extreme winds. Finally, the third analysis is related to the wave conditions. Thus, using as a forcing factor each of the wind fields that was previously analyzed, simulations employing a spectral wave model were carried out. The wave modeling system was focused using three different computational domains with increasing resolution towards the target area, and the nearshore wave conditions were evaluated. The results show that both the extreme wind and wave conditions are expected to slightly increase in the future. Especially in the wintertime, strong wind fields are often expected in this area, with wind gusts exceeding more than 70% of the hourly average wind velocity. With regard to the waves, due to the complex nearshore phenomena, considerable enhancements in terms of significant wave heights are induced, and there is also an elevated risk of the occurrence of rogue waves. This work is still ongoing, and taking into account the high navigation risks highlighted, the next step would be to elaborate the risk assessment of severe shipping conditions, particularly related to the likelihood or probability of adverse conditions with the potential of generating hazardous situations in this coastal environment.

The changes in the Earth’s climate have become more obvious in the last few decades, and research in recent years has indicated more severe impacts than initially expected [...]

The aim of the present work is to provide a general picture of the adverse weather conditions corresponding to the sites from the European coastal environment where various offshore projects are developed. In the first part of the work, the ERA5 wind and wave data (24 values per day) are processed in order to obtain the time series that cover the 10-year time interval from January 2011 to December 2020. By using some particular criteria that define the operability limit of several installation equipment (as for example the floating barges) it was possible to define several case studies. From the preliminary analysis of the wind conditions (at 10 m height above the sea level) it was noticed that the sites located in the northern regions (ocean environment) indicate higher values of the wind speeds, that can go up to 8.3 m/s compared to the value of 6 m/s indicated for the Gloria drilling platform in the Black Sea. As expected, the adverse weather patterns are directly related to the local marine conditions, being required restrictions higher than 80% in the case of the operations that are limited by the occurrences of the waves with significant wave heights higher than 1.25 m, compared to only 3.3% that define the north-western part of the Mediterranean Sea (Mistral project). The number of available windows requiring a much longer time interval (ex: 96 h) is higher in the case of Mistral and Gloria sites, being counted at least 48 opportunity events for the waves with significant wave heights below 0.5 m. Finally, it is important to mention that the analysis of the adverse weather conditions represents an important element for the marine renewable energy sector, especially as regards the enclosed basins, such as the Mediterranean or the Black seas, where offshore wind projects are expected to be implemented.

The objective of this work is to provide a comprehensive picture of the benefits that may occur from the implementation of some offshore wind projects in the island environments from the Mediterranean Sea. This takes into account the fact that in the Mediterranean Sea there are many relatively densely populated islands As a first step, the wind speed fields (at 100 m height) provided by the ERA5 dataset is processed to obtain a general image of the wind energy potential in the entire area. Some significant island environments are targeted, as for example Sardinia, Cyprus, or Malta, for which a more detailed analysis is carried out. Considering the Exclusive Economic Zones, the most promising areas in terms of the wind conditions are highlighted. This is the case of the areas located near Sardinia or Cyprus, where the average wind speed is close to 9 m/s. The results of the study also show that the best performances of a wind turbine are expected in the north-western part of this basin, where a generator can operate on a full capacity for at least 6% of the time.

In order to obtain the most efficient solution in harvesting offshore wind energy, the converting devices must be located in places where the wind provides enough power, according to the used device specifications and, as possible, with constant value during turbine lifetime. On the other hand, the device must be chosen for a specific place — imposed by other reasons, like water depth, shore distance etc. The paper presents an analysis and prediction methodology for the wind speed based on the artificial neural networks modeling. The proposed approach uses as input data the previous recorded and forecasted wind speed values and the GPS coordinates for several places in Black Sea allowing the identification of the location with less wind speed modification during analyzed period of time. Also, the model provides useful information about inputs importance on output evolution. The obtained results are used for the identification of optimal placement of wind energy converting devices, leading to an improved efficiency.

The main target of this work is to carry out an analysis of the most credible scenarios concerning the expected dynamics of the wind climate along the 21st century in the Black Sea basin. The data provided by the RCA4 climate wind model were processed and analysed. Three different Representative Concentration Pathway (RCP) scenarios are considered. These are RCP2.6, RCP4.5, and RCP8.5. The study is structured considering two 40-year time intervals. These are the near future (2021–2060), and the next 40=year time interval (2061–2100), denoted as the distant future. Moreover, in order to have a mean of comparison, the 40-year time interval (1980–2019) denoted as the recent past was also analysed. Two different parameters are processed and analysed in this study. These are the average wind power density and the maximum wind speed. The results indicate a moderate enhancement of the average wind power in the western part of the sea (of about10–20%). The coastal areas from the western and north-western parts of the sea have been identified as the most energetic and they are more appropriate for harvesting wind energy. At the same time, the results of this work indicate that in the basin of the Black Sea an increase of the maximum wind speed values is expected in the future. From this perspective, the future high storms in this basin are expected to have quite similar features with the hurricanes from the Atlantic Ocean.

Floating wind is becoming an essential part of renewable energy, and so highlighting perspectives of developing floating wind platforms is very important. In this paper, we focus on floating wind concepts and projects around the world, which will show the reader what is going on with the projects globally, and will also provide insight into the concepts and their corresponding related aspects. The main aim of this work is to classify floating wind concepts in terms of their number and manufacturing material, and to classify the floating wind projects in terms of their power capacity, their number, character (if they are installed or planned) and the corresponding continents and countries where they are based. We will classify the corresponding additional available data that corresponds to some of these projects, with reference to their costs, wind speeds, water depths, and distances to shore. In addition, the floating wind global situation and its corresponding aspects of relevance will be also covered in detail throughout the paper.

Shallow water bathymetry is a topic of significant interest in various fields, including civil construction, port monitoring, and military operations. This study presents several methods for assessing shallow water bathymetry using maritime uncrewed systems (MUSs) integrated with advanced and innovative sensors such as Light Detection and Ranging (LiDAR) and multibeam echosounder (MBES). Furthermore, this study comprehensively describes satellite-derived bathymetry (SDB) techniques within the same geographical area. Each technique is thoroughly outlined with respect to its implementation and resultant data, followed by an analytical comparison encompassing their accuracy, precision, rapidness, and operational efficiency. The accuracy and precision of the methods were evaluated using a bathymetric reference survey conducted with traditional means, prior to the MUS survey and with cross-comparisons between all the approaches. In each assessment of the survey methodologies, a comprehensive evaluation is conducted, explaining both the advantages and limitations for each approach, thereby enabling an inclusive understanding for the reader regarding the efficacy and applicability of these methods. The experiments were conducted as part of the Robotic Experimentation and Prototyping using Maritime Unmanned Systems 23 (REPMUS23) multinational exercise, which was part of the Rapid Environmental Assessment (REA) experimentations.

The aim of this work is to provide some details regarding the energy potential of the local wind and solar resources near the Galati area (south-east of Romania) by considering the performances of a few recent technologies. Based on 22 years of ERA5 data (2001–2022), a picture concerning the renewable energy resources in the Brates Lake area is provided. Comparing the wind and solar resources with in situ and satellite data, a relatively good agreement was found, especially in regards to the average values. In terms of wind speed conditions at a hub height of 100 m, we can expect a maximum value of 19.28 m/s during the winter time, while for the solar irradiance the energy level can reach up to 932 W/m2 during the summer season. Several generators of 2 MW were considered for evaluation, for which a state-of-the-art system of 6.2 MW was also added. The expected capacity factor of the turbines is in the range of (11.71–21.23)%, with better performances being expected from the Gamesa G90 generator. As a next step, several floating solar units were considered in order to simulate large-scale solar projects that may cover between 10 and 40% of the Brates Lake surface. The amount of the evaporated water saved by these solar panels was also considered, being estimated that the water demand of at least 3.42 km2 of the agricultural areas can be covered on an annual scale.

The objective of this present work is to provide a more comprehensive picture of the wind conditions corresponding to some important European marine energy sites by considering both historical (1979–2020) and climatological data (2021–2100). As a first step, the wind energy profile of each site is assessed using some statistical methods (e.g., Weibull parameters) and some relevant indicators for the wind sector, such as the downtime period (

Overcome by the increasing energy demands nowadays and the limited traditional resources, the foremost objective of the proposed study is to evaluate the efficiency of a floating wind farm operating in the coastal environment of the western Black Sea. Since coastal erosion has become a matter of urgent concern during the last decades and many states in the EU (European Union) consider the issue of coastal protection to be of utmost national importance, this study aims to reveal the positive effects such project might provide to the coastal area of Romania. Due to significant decrease of sediments from the Danube basin to the coast in the north along with the extensive development of tourist resorts, especially in the southern part, the erosion process has become more explicit, posing a severe threat primarily on the population living within an area of tens of kilometres from the coast. To provide a better overview of the principal wave patterns in the targeted area, the ERA5 dataset has been considered for the evaluation of the wave power for the 40-year period (1979–2018) for two reference points located in the proximity of the target area. Four scenarios for the simulations were carried out with a computational structure that combines a circulation model with a wave model. A generic wind farm was defined in the computational domain, taking into consideration steadily increasing distances from the shoreline: 4, 6 and 8 km. Firstly, taking into account the local wave patterns, and three-wave parameters — the significant wave height, the mean wave height and direction, the down-wave effect of the farm was evaluated. Secondly, the influence of the generic farm on the longshore currents was also assessed. The concluding results suggest that if such a project is to be taken into consideration, it would not only provide valuable renewable energy, but it would also guarantee adequate coastal protection by reducing the impact of waves and intensify resilience to terrible weather.

The objective of the present work is to assess the wave power in the North Sea in the vicinity of the most relevant wind farms that are operating there. At this moment, the coastal environment of the North Sea is among the most significant areas in the world from the point of view of harvesting marine renewable energy. Furthermore, this area is also very relevant for offshore activities related to oil and gas extraction. From this perspective, its coastal environment would be a perfect candidate for the implementation of the wave projects, which would benefit from existing infrastructure. The ERA5 dataset has been considered for the evaluation of the wave power for the 30-year period (1989–2018). 10 reference points have been defined in the coastal environment of the sea covering the most relevant locations and for them, the mean wave power has been first assessed. After this, the seasonal and monthly variability of the wave power have been also evaluated together with some statistical parameters. The results show that the northern part of the sea has relatively significant wave energy resources and it can be a viable candidate for implementation of the future wave projects. However, the linear trends indicate a slight tendency of decrease of the wave power, but on the other hand, the coefficient of resource variation has small values. Finally, a comparison with the satellite data provided by the European Space Agency is also carried out for the 27-year period 1992-2018. While in general there is a very good concordance between the two datasets, for the reference points located in the north-eastern part of the sea, which are the most resourceful locations, the satellite data indicate higher values.

According with the new European Regulations the supply chain sustainability became more and more challenging for the shipping companies. They must adapt their ships to respect the new regulations, but this means economic investment for environmental and social scopes? Or replacement of traditional fuel with a green one, will make the companies more competitive, will reduce costs and will improve the operational performance? It can be difficult for the top management to take and assume a decision like this. In this paper we will use the analytic hierarchy process (AHP), like a management instrument, based on Multi-Criteria Decision Making (MCDM) to see what solution brings more advantages for the ship owners and for the community. An illustrative case with two alternative marine fuels, liquified natural gas (LNG) and oil gas, was presented and analyzed in this paper using the proposed method. The most sustainable scenario being the one in which is used natural liquefied gas like marine fuel. The results obtained demonstrate that the method used to prioritize alternative marine fuels is feasible and helps decision makers.

This study is a first attempt at bridging functional data of five different wind turbines whose performances were recently researched in our studies with the framework of Burloiu, Rusu (Pre-planning for Black Sea offshore wind farms: a wind speed dataset for three Romanian coastal locations), while maintaining the overall goal of exploring the possibility of wind farms implementation along the Black Sea coast.Therefore, we intend to create a visual data narrative based on some of the pivotal elements of the studies mentioned above, using only the best of the three potential hotspots researched based on archived information provided by GFS, NCEP, US NATIONAL SERVICE and gradual cross-reading of the technical and cost related findings of Raileanu, Onea and Rusu.

Municipal solid wastes (MSW) are, through the amount generated and energy content, one of the energy resources that can successfully contribute to covering energy consumption at local or regional level. The integration of this resource in modern energy systems can increase the penetration of renewable energy resources in energy supply. One of the most promising technologies for converting waste into energy is gasification. As conventional district heating and cooling systems require decarbonization, one solution is the use of waste gasification and solar energy conversion equipment. This paper analysis from an energetic and economic point of view the possibility of using the fuel produced by the gasification of refuse derived fuel (RDF) and solar thermal energy in a gas engine based combined cooling, heating and power generation (CCHP) system to be integrated into a district heating and cooling system. The proposed system can generate 27295685 Nm3/year of producer gas, 14.57 GWh/year of electricity, 32.11 GWh/year of heat and 1.55 GWh/year of chilled water with a solar thermal energy input of 1.15 GWh/year. The capital cost of the CCHP system can be recovered in 9.62 years when solar collector are not used and in 6.19 years when solar collectors are used. By using RDF and solar thermal energy are saved 3567778 Nm3 of natural gas in a year.

The paper presents an analysis of the wind energy availability on long-term basis in the Republic of Moldova. This is motivated by the necessity of increasing the renewable energy sources in the global energy portfolio of the Republic of Moldova. Although there are some studies on this subject, concluding that there is a satisfactory wind energy potential, there are no references on the future evolution of the wind energy. Starting from the analysis of the historical wind speed data corresponding to the 31-year period 1990–2020 and taking into account the most significant geographic and civil requirements, several locations were chosen as possible targets for the future wind farms placement. An analysis of the predicted wind data for the 31-year period 2020–2050 based on RCP4.5 scenario, allowed to identify the optimal areas for the wind energy extraction in the republic of Moldova.

The aim of this paper is to provide a comprehensive overview of how electricity is produced from different sources and the electricity needs of the consumer. According to the Green Deal pact, the objective is to gradually reduce polluting emissions in the energy sector by 2050. In the meantime, the CO2 intensive thermal power plants (those using coal and heavy oil) will be closed and strategic investments in green energy sources will be pursued. This paper presents a detailed analysis of the profile of the Romanian electricity producer over a period of one year. Furthermore, this paper explores the possibility for the energy producer to adapt to consumer demand to reduce electricity imports, strategic locations for the installation of farms using renewable energy, and the current capacity of the national distribution system. This paper analyses electricity only quantitatively and not qualitatively, as well as the way the supplier follows consumers’ need. The paper concludes on possible problems that may arise from the case of green energy.

Renewable and distributed energy generation includes wind turbines, fuel cells, solar cells, and batteries. These distributed energy sources need special power converters in order to connect them to the grid and make the generated power available for public use. Solar energy is the most readily available energy source; hence, if utilized properly, it can power up both domestic and industrial loads. Solar cells produce DC power, and this should be converted to an AC source with the help of inverters. A multi-level inverter for an application is selected based on a trade-off between cost, complexity, losses, and total harmonic distortion (THD). A packed U-cell (PUC) topology is composed of power switches and voltage sources connected in a series-parallel fashion. This basic unit can be extended to a greater number of output voltage levels. The significance of this design is the reduced use of power switches, gate drivers, protection circuits, and capacitors. The converter presented in this paper is a 31-level topology switched by a variable switching frequency-based model predictive controller that helps in achieving optimal output with reduced harmonics to a great extent. The gate driver circuit is also optimized in terms of power consumption and size complexity. A comparison of the 9-level and the 31-level PUC inverters is carried out to study the impact of the number of levels on the total harmonic distortion. The simulation results depict that the total harmonic distortion (THD) for a nominal modulation index of 0.8 is 11.54% and 3.27% for the 9-level multi-level inverter (MLI) and the 31-level modified packed U-cell multi-level inverter (MPUC-MLI), respectively. The reduction in THD is attributed to the increased number of steps in the output when using the model predictive controller.

This editorial note is dedicated to the 10th Scientific Conference which was held on June 2022 in Galati, Romania, and was organized by the Council of Doctoral Schools of the “Dunărea de Jos” University of Galati (SCDS-UDJG) [...]

The world is targeting fully sustainable electricity by 2050. Energy storage systems have the biggest role to play in the 100% renewable energy scenario. This paper presents an optimal method for energy storage sizing and allocation in a power system including a share of wind farms. The power system, which is used as a test system, is a modified version of the IEEE 39 bus system. The optimization is applied using novel pharmacophore modeling (PM), which is compared to state-of-the-art techniques. The objective of the optimization is to minimize the costs of power losses, peak demand and voltage deviation. The PM optimization is applied using two methods, namely, weighting factor and normalization. The optimization and simulation are applied in the DIgSILENT power factory software application. The results show that normalization of PM optimization drives the power system to less cost in terms of total power losses by up to 29% and voltage deviation by up to 4% and better covers peak demand than state-of-the-art optimization techniques.

Maritime unmanned systems (MUS) have gained widespread usage in a diverse range of hydrographic survey activities, including harbor/port surveys, beach and coastline monitoring, environmental assessment, and military operations. The present article explains a validated, rapid, and reliable technique for processing hydrographic data that was obtained via an autonomous hydrographic survey, and which was executed by a prototype unmanned surface vessel (USV) belonging to the Unmanned Survey Solutions (USS) corporation. The experimentation was part of the annual Multinational Exercise Robotic Experimentation and Prototyping that was augmented by Maritime Unmanned Systems 22 (REPMUS22), which was held in the national waters of Portugal. The main objective of this experimentation was to assess the underwater environment over an ocean beach for an amphibious landing exercise. Moreover, the integration of the multibeam system with the autonomous prototype vessel was assessed. A short comparison between the USV survey and a traditional vessel multibeam survey is presented, whereby the advantages of performing an autonomous survey operation near the coastline is emphasized. A correlation between a known multibeam processing technique and the dissemination of a rapid but consistent product for operational use is described, highlighting the applicability of the technique for the data collected from small experimental platforms. Moreover, this study outlines the relationship between the particular errors observed in autonomous small vehicles and in conventional data processing methods. The resultant cartographic outputs from the hydrographic survey are presented, emphasizing the specific inaccuracies within the raw data and the suitability of distinct hydrographic products for various user domains.

The increased availability of solar energy potential, especially in southern latitudes as in the Mediterranean Sea and the Aegean Sea regions, constitutes a strong motivation for the design and development of floating offshore solar energy platforms suitable for deployment and operation in the sea environment. In this work, a boundary element method is applied to the hydrodynamic analysis of pontoon-type floating structures carrying photovoltaic panels on the deck. Results are used to estimate the responses of the above floating structures, which are then exploited to calculate the effects of waves and motions on the energy performance of photovoltaics arranged on deck (FPVs). Using as an example a 100 kWp floating module located in the nearshore area of the Pagasitikos Gulf and Evia Island in the central Greece region, the time series of environmental parameters concerning wave, wind and solar data are used, in conjunction with the hydrodynamic responses of the floating structure, to illustrate the effects of waves on the floating PV performance. The results indicate significant variations in energy production due to the dynamic angle of solar incidence generated from the floating module’s responses depending on the sea state that should be taken into account in the design process. Additionally, it is shown that the particular concept could be a promising and economically viable alternative of marine renewables contributing to the European Green Deal policies.

The present study aims to outline a general overview of the wind energy potential along the Romanian coast of the Black Sea, using the weather data provided by the Maritime Hydrographic Directorate covering a 13-year time interval (2009–2021). The data obtained from seven automatic weather coastal stations distributed along the Romanian perimeter were used to evaluate the wind regime, highlighting the Black Sea’s complex marine environment. The analysis based on the evaluation of the wind parameters per each station registered on the total period revealed that the overall wind characteristics are similar, resulting in no significant variations depending on the station’s location. Moreover, the climatic picture of the Black Sea can be interpreted as two seasons, winter and summer, a conclusion based on the analysis made of the seasonal and monthly variation of the wind aspects. Subsequently, the outcomes obtained in this research imply that the Romanian Black Sea coast has the potential to be a good location for wind energy development due to the strong winds that blow in the region.

The purpose of this study is to provide an overview of the development of the modern low-speed marine two-stroke diesel engine from the point of view of the technical water cooling plant, taking into account and starting from the market requirements for power and speed, with information and design options relevant to the entire shipping industry. Thus, through the ideas of this project, we analyze notions and relevant aspects of systems related to marine slow turning engines, including the basic thermodynamic structure of the technical water system designed for a marine engine. This study also presents the design criteria that define the size and design concept of the engine structure components, with a focus on the technical water cooling installation. The concepts for the main engine hot parts served by the technical water cooling installation play a vital role in the marine technical water generator. The choices the engine designer must make regarding basic auxiliary systems, such as fuel injection and exhaust valve actuation, are important factors to keep in mind when installing a technical water generator onboard a ship. The automation and control systems that govern the modern electronic engine, which drive the supply pump of the technical water cooling system can provide a simplified view of the engine development process. In order to point out the contributions of this study, it is important to focus on the calculations used to determine the main parameters of a technical water generator especially designed for a midsized container ship.

The Portuguese nearshore represents a suitable environment for the development of marine energy farms, with recent progress being related to the implementation of the first commercial wave farm or a large scale floating wind project. At the same time, there is also high solar power in this area that can be extracted; in the near future, the rapid development of floating solar projects all over the world is expected. In this context, the aim of the present work is to identify the complementarity between solar, wind and wave resources based on 10 years of ERA5 data (from 2012 to 2021). The results are provided mainly in terms of spatial maps. The analysis shows that solar and wind power are more significant in the southern part of this region, indicating for each resource an average value of 223 W/m2 for solar and 660 W/m2 for wind. On the other hand, the wave power gradually decreases from north to south, with an average value of 10 kW/m being expected at a distance of 50 km from the shoreline. In terms of complementarity, two scenarios were considered (mild and restrictive), the difference between them being estimated to be around 10%. Several dimensionless indices were defined in order to highlight the correlation between solar, wind and wave conditions, which may be considered as an element of novelty for the target area. In general, higher values (0.5) were noted in the case of the wind-wave and wave-solar combinations, excepting the southern part of Portugal (Algarve) where particular conditions were noted. Finally, the expected power outputs from some relevant technologies were also estimated, including a new concept of the wave energy generator designed for the WindFloat platform. Compared to the solar and wind systems, the performance of the selected wave generation system was quite low, suggesting that other types of wave energy converters would be more appropriate at this moment in the coastal area targeted. Finally, we need to mention that the idea of using multiple resources from a single marine site is an attractive one, while the methodology dedicated to this topic will continuously improve as new technological solutions emerge.

Execution time is an important topic when using metaheuristic-based optimization algorithms within control structures. This is the case with Receding Horizon Control, whose controller makes predictions based on a metaheuristic algorithm. Because the closed loop’s main time constraint is that the controller’s run time must be smaller than the sampling period, this paper joins the authors’ previous work in investigating decreasing execution time. In this context, good results have been obtained by introducing the “reference control profile” concept that leads to the idea of adapting the control variables’ domains for each sampling period. This paper continues to address this concept, which is adjusted to harmonize with the Particle Swarm Optimization algorithm. Moreover, besides adapting the control variables’ domains, the proposed controller’s algorithm tunes these domains to avoid losing convergence. A simulation study validates the new techniques using a nontrivial process model and considering three modes in which the controller works. The results showed that the proposed techniques have practical relevance and significantly decrease execution time.

In spite of the tremendous advances in computing power and continuous improvements in simulation software made in recent decades, the accurate estimation of wind turbine performance using numerical methods remains challenging. Wind turbine aerodynamics, especially when operating outside of the design envelope, is highly complex: blade stall, laminar-to-turbulent boundary layer transition, rotational effects (lift augmentation near blade root), and tip losses are present. The scope of this research is to show that the classic Reynolds-Averaged Navier–Stokes (RANS) modeling approach, although extensively tried and tested, is not yet exhausted. The NREL Phase VI rotor was used as a basis for numerical methodology development, verification and validation. The numerical model results are compared in detail with the available measured data, both globally (turbine torque and thrust, and blade bending moment) and locally (pressure coefficient distributions and aerodynamic force coefficients at several locations on the blade) over the entire experimental wind speed range. Stall initiation and spread over the blade span are well captured by the model, and rotor performance is predicted with good accuracy. RANS still presents significant value for wind turbine engineering, with a great balance between accuracy and computational cost. The present work brings potential impact on all applications of wind turbines, especially targeting offshore wind energy extraction for which great development is expected in the near future.

In the context of the European Green Deal implementation, it is expected that there will be an increase in number of the wind farms located near the coastal areas in order to support this initiative. The Black Sea represents an important source of wind energy, and as a consequence, in the present work the regional wind resources (onshore and offshore) are evaluated by considering a total of 20 years of ERA5 wind data covering the 20-year time interval from January 2002 to December 2021. From a general perspective, it is clear that the offshore areas (100 km from the shoreline) are defined by much higher wind speed values than in the onshore, reaching an average of 8.75 m/s for the points located on the western sector. During the winter, these values can go up to 8.75 m/s, with the mention that the northern sectors from Ukraine and Russia may easily exceed 8 m/s. In terms of the wind turbines’ selection, for the offshore areas defined by consistent wind resources, generators will be considered that are defined by a rated wind speed of 11 m/s. Finally, we can mention that a theoretical offshore wind turbine of 20 MW can reach a capacity factor located between 20.9 and 48.3%, while a maximum annual electricity production of 84.6 GWh may be obtained from the sites located near the Romanian and Ukrainian sectors, respectively.

In recent decades, it has become quite clear that the dynamics of the environmental matrix have been subjected to notable changes [...]

This article introduces a three-phase capacitor clamped inverter with inherent boost capability by relocating the filter components from the AC side to the configuration’s midpoint. This topology has several distinguishing characteristics, including: (a) low component count; (b) high DC-AC gain; (c) decreased capacitor voltage stresses; (d) improved power quality (extremely low voltage and current THDs) without the use of an AC-side filter; and (e) decreased voltage stresses on power semiconductor devices. Simulations were carried out on the MATLAB Simulink platform, and results under steady-state conditions, load and reference change conditions, and phase sequence change conditions, along with THD profiles, are presented. This inverter’s performance was compared to that of similar converters with intrinsic gain. A 1200 W experimental prototype was built to demonstrate the system’s feasibility and benefits. When compared to existing topologies, simulation and experimental results indicate that the proposed inverter provides superior high gain, smooth control, low stress, and a long life time.

This Editorial is dedicated to the 9th edition of the Scientific Conference organized by the Doctoral Schools of “Dunărea de Jos” University of Galati (SCDS-UDJG), which was organized in June 2021 in Galati (Romania) [...]

In these post COVID times, the world is going through a massive restructuring which India can use to its benefit by attracting foreign industrial investment. The major requirement is a reliable and ecofriendly electrical power source. Of late, renewable energy sources have increasingly become popular as alternative source of electricity. They can provide immense aid in improving the reliability of the power system, when placed properly. The alternative integrated energy sources along with FACTS devices can provide a promising future for reliable power systems. In this paper, an effective location for the solar power unit and Interline Power Flow Controller using Line Severity Index is proposed in order to avoid contingencies. An Indian 62 bus system and IEEE 57 bus system are considered for the study. The Firefly algorithm is used to tune the IPFC in the Integrated Energy Systems scenario, for a dual objective function. The effect of placement of the solar unit and the optimized IPFC is analyzed and studied in detail in this paper.

In the present research, an overview of the wind climate on the northwestern coast of the Black Sea basin is assessed, using a total of 6 years of data (2015–2020) provided by the National Institute of Marine Geology and Geoecology (GeoEcoMar). It is well known that the enclosed/semi-enclosed basins are complex environments and to accurately represent the features of wind and wave are necessary high resolution spatial fields. For the Black Sea, which is an enclosed basin with complicated regional geography, the main weather parameters reported (wind direction, wind speed, air temperature, air pressure) give a more comprehensive picture of how energetic the area of interest is, and represent the features of the Black Sea’s diversified marine environment. Finally, the results obtained in this paper cover a broad range of applications in marine studies, being useful for future research in the area of wind climate in the Black Sea.

The metal tower, or the pylon, is one of the most important elements in the construction of a wind turbine. It has the role of supporting the entire wind turbine, and it also allows access for inspection and conducting planned maintenance and repairs. Moreover, the tower ensures support for the structure and strengthens the whole assembly. It has a particularly important role, as it has to face very severe weather conditions. The present study aims to analyze the forces and moments resulting from the action of the wind on the tower of a wind turbine. Two important load cases are considered, namely, the load under operating conditions and the ultimate load under 50 year wind conditions. For this purpose, cylindrical and conical geometric shapes of the tower were chosen. These were analyzed under the action of both normal and extreme wind speeds. Then, the behavior of the two towers under the action of the wind speed for a location in the Black Sea was analyzed. Finally, in an attempt to make the structure more economical, the thickness of the shell was reduced.

Living Labs are an innovative concept that combines research, governance, and citizens, using technology and knowledge. Using design thinking techniques as a method of approach, this innovative idea builds a bridge between decision makers and stakeholders, promoting a shared vision of growth and innovation at the community level. The coastal zone is an extremely dynamic area in terms of human and natural activities. This is a particularly sensitive area to climate change, necessitating ongoing adaptation and mitigating action. This paper aims to introduce the application of the Living lab concept in the management of the coastal area of Constanta (Romania). The concept of the Living Lab means involving citizens along with public bodies and research structures. This new coastal management model will use the design thinking approach and will consider the pressures that exist between the activities that occur in the examined coastal zone. In the study, “Multi-Criteria Analysis of the Mass Tourism Management Model Related to the Impact on the Local Community in Constanța (Romania)”, published in MDPI Inventions on 28 June 2021, a coastal management model was built that took into consideration only the data given by the government. In this paper, the authors aim to expand their research by including data from independent sources, using the concept of a Living Lab.

The Blue Economy is a comprehensive model, which combines the marine and coastal ecosystems with the management of the human activities. This uses tools and mechanisms as the integrated conservation, the sustainable and efficient resource use, ICZM (Integrated Coastal Zone Management) or spatial planning. In this paper, an integrative approach has been proposed for the achievement of a sustainable development. The concept of blue economy is expected to offer efficiency and optimization of the resource use by creating opportunities for a sustainable growth in a number of the traditional and emerging economic sectors, which are considered as Blue Economy key sectors, such as: shipping/port activities, fisheries and aquaculture, coastal tourism, „Blue” energy, biotechnology, submarine mining. Under this approach, we will discuss about the Blue Economy method applied to the Romanian nearshore, by exploring the concepts of the sustainable development, conceptualising the Black Sea as a “developing space” and providing an opening opportunity for the incorporation of the real value of the natural capital.

This article briefs about a smart multifunctional single-phase inverter control for a domestic solar photo voltaic (PV)-based distributed generation that can work in both a grid-connected mode and an islanded mode by making the inverter mimic the operation of a synchronous generator. The control objectives were threefold: to provide the required active and reactive power for normal operating conditions and under varying operating conditions, to maintain the rated voltage and the rated frequency for the islanded mode, and to switch between the two modes of operation with the least amount of disturbance for the system while behaving as a virtual synchronous generator (VSG). The control structure is divided into three major loops: the outermost loop responsible for power control, the middle loop responsible for voltage control, and the innermost loop responsible for current control. The proposed control methodology incorporates the functionalities of the grid-connected and the islanded-mode control into a single complex structure and thus provides support to the grid under abnormal conditions while providing good-quality power to consumers under grid failure. The efficacy of the system is good. The operation under various modes were simulated in MATLAB Simulink, and the proportional integral (PI) controllers used for current controllers were tuned using particle swarm optimization (PSO). It can be concluded that the control structure becoming complex is benefitted by the added advantages of the smart PV system. The smart domestic PV system helps the prosumer to actively provide frequency support and voltage support, adding frequency support to the existing multifunctional PV systems.

In variable speed applications, the cycloconverter-based AC to AC power conversion technique has gained more attention among researchers and academics than the traditional rectifier-inverter-based AC to AC power conversion process. The conventional rectifier-inverter-based AC to AC power conversion process has several disadvantages. It uses multi-power stages that increase the converter power conversion losses and increase the cost, volume, and weight of power losses. Besides high conduction and switching losses, the electromagnetic interference problems also accompany the above issues. In this regard, this paper proposes a novel step-down Triac based cycloconverter for variable speed control applications. The proposed topology uses only five Triac devices for one-third and one-fourth frequency conversion of 50 Hz with reduced total harmonics distortion without using any pulse width modulation techniques. The proposed model is designed in the MATLAB/SIMULINK environment. The simulation results show that around 18.85% and 23.67% of total harmonics distortions are reduced in the proposed converter for one-third and one-fourth frequency conversion of 50 Hz, respectively. Two physical experiments are carried out to prove the validity of the simulation results.

In this paper, a novel model based on the boundary element method (BEM) is presented for the hydrodynamic analysis of floating twin-hull structures carrying photovoltaic panels, supporting the study of wave responses and their effects on power performance in variable bathymetry regions. The analysis is restricted to two spatial dimensions for simplicity. The method is free of any mild-slope assumptions. A boundary integral representation is applied for the near field in the vicinity of the floating body, which involved simple (Rankine) sources, while the far field is modeled using complete (normal-mode) series expansions that are derived using separation of variables in the constant depth half-strips on either side of the middle, non-uniform domain, where the depth exhibited a general variation, overcoming a mild bottom-slope assumption. The numerical solution is obtained by means of a low-order panel method. Numerical results are presented concerning twin-hull floating bodies of simple geometry lying over uniform and sloping seabeds. With the aid of systematic comparisons, the effects of the bottom slope and curvature on the hydrodynamic characteristics (hydrodynamic coefficients and responses) of the floating bodies are illustrated and discussed. Finally, the effects of waves on the floating PV performance are presented, indicating significant variations of the performance index ranging from 0 to 15% depending on the sea state.

When an optimal control problem requires an important computational effort, a metaheuristic algorithm (MA) can be a useful approach. An MA is conceived to solve a specific optimal control problem having a characteristic objective function. This algorithm solely yields only an optimal offline solution. The desideratum to have a closed-loop implementation can be fulfilled through a supplementary “tool”, the Receding Horizon Control (RHC) structure. This paper addresses a particular case and integrates Evolutionary Algorithms into the RHC structure. The main objective is to propose a general harmonization between the Controller of the closed loop and the Evolutionary Algorithm. Some details concerning the implementation of the closed loop and Controller are described. The impact of the RHC’s prediction technique upon the control sequences’ encoding is also analyzed. Two general structure Controllers are proposed, one of them conceived to cope with restrictive time constraints. Practical ideas have been illustrated through a case study: the well-known optimal control of a fed-batch reactor for ethanol production. This time, our implementation achieves a closed-loop solution. The results from the programs and simulation series validate the Controllers, EAs, and the closed-loop structure. Generally speaking, the association between RHC and EA can be a realistic solution to optimal process control.

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

The present work aims to provide a comprehensive picture of the wind energy potential that characterizes the Romanian coastal environment using in situ measurements and reanalysis of wind data (ERA5) that cover a 42–year time interval (1979–2020). A total of 16 reference points (both land and offshore) equally distributed along the Romanian sector are used to evaluate the local wind energy potential, targeting in this way several sites where a renewable wind project could be established. Compared to the in situ measurements (land points), the ERA5 dataset underestimates the wind speed by at least 11.57%, this value increasing as we approach the coastline. From the analysis of the spatial maps, it is likely that the wind speed steadily increases from onshore to offshore, with a sharp variation near the coastline being reported. Furthermore, the assessment of some state-of-the-art offshore wind turbines was conducted using 12 systems defined by rated capacity ranging from 2 to 10 MW. Some scenarios were proposed to identify sustainable offshore wind projects to be implemented in the Romanian coastal zone based on these results.

Traditionally and socially, the tourism in Constanta is considered to be important to the local economy. Sun and beach locations are both a draw for locals and tourists to the city, on the Black Sea. However, vacation-oriented activities in the city only have a seasonal cycle. In this paper, we proposed to analyze the mass tourist activity in Constanta, taking into account economic, social, and environmental conditions. Additionally, we attempted to build a model based on the data available. The model was developed using a PESTEL analysis to determine the supportability factor of the indicators identified. We also set out to create a projection of the activities proposed for analysis by 2050. To create a model for coastal areas, the data used in this research must be accurate and consistent. Furthermore, correctly identifying indicators and their relationships is a critical step in conducting a thorough study. Last but not least, finding the calculation coefficient for the activity in question is critical, as collecting data from various activities might be challenging when trying to find a feasible model.

The European offshore wind market is continuously expanding. This means that, together with significant technological developments, new coastal environments should be considered for the implementation of the wind farms, as is the case of the Black Sea, which is targeted in the present work. From this perspective, an overview of the wind energy potential in the Romanian exclusive economic zone (EEZ) in the Black Sea is presented in this work. This is made by analyzing a total of 20 years of wind data (corresponding to the time interval 2000–2019) coming from different sources, which include ERA5 reanalysis data and satellite measurements. Furthermore, a direct comparison between these datasets was also carried out. Finally, the results of the present work indicate that the Romanian offshore areas can replicate the success reported by the onshore wind projects, of which we can mention the Fantanele-Cogealac wind farm with an operating capacity of 600 MW.

A particularity of island areas is that they are subjected to strong sea state conditions that can have a severe impact on the beach stability, while on the other hand, they rely mainly on diesel combustion for electricity production which in the long run is not a sustainable solution. The aim of this work is to tackle these two issues, by assessing the impact of a hybrid marine energy farm that may operate near the north-western part of Giglio Island in the Mediterranean Sea. As a first step, the most relevant environmental conditions (wind and waves) over a 27-year time interval (January 1992–December 2018) were identified considering data coming from both ERA5 and the European Space Agency Climate Change Initiative for Sea State. An overview of the electricity production was made by considering some offshore wind turbines, the results showing that even during the summertime when there is a peak demand (but low wind resources), the demand can be fully covered by five wind turbines defined each by a rated power of 6 MW. The main objective of this work is to assess the coastal impact induced by a marine energy farm, and for this reason, various layouts obtained by varying the number of lines (one or two) and the distance between the devices were proposed. The modelling system considered has been already calibrated in the target area for this type of study while the selected device is defined by a relatively low absorption property. The dynamics of various wave parameters has been analysed, including significant wave height, but also parameters related to the breaking mechanics, and longshore currents. It was noticed that although the target area is naturally protected by the dominant waves that are coming from the south-western sector, it is possible to occur extreme waves coming from the north-west during the wintertime that can be efficiently attenuated by the presence of the marine energy farm.

Identifying a modeling procedure of biomass thermal decomposition that is not only simple enough to implement and use, and computationally efficient, but also sufficiently accurate for engineering design activities, and with a spectrum of applications as broad as possible is a very difficult task. The authors propose a procedure which consists of two main stages: (a) the static modeling phase with the purpose of generating the algorithm (macro functions) that supplies a Computational Fluid Dynamics (CFD) model with specific input data (source/sink terms and local material properties) and (b) the dynamic modeling phase, where the CFD model is bi-directionally coupled to the external biomass decomposition model in the form of a User-Defined Function (UDF). The modeling approach was successfully validated against data obtained from single particle decomposition experiments, demonstrating its applicability even to large biomass particles, under high heating rates and combusting conditions.

The ultraviolet water disinfection process has numerous advantages in comparison with other water treatments. This study deals with this process’s optimal control and presents all its stages, from problem statement to analysis of results. We consider a typical disinfection water system and data presented in the literature. In this case, the control inputs are the water flow rate and the UV light intensity. A nonlinear dynamic model for the UV disinfection system is constructed and generates a method to calculate the bacterial reduction. An optimal control problem (OCP) is stated using the dynamic model and two optimal criteria: the disinfection and energy criterion. The optimal solutions are yielded by a metaheuristic algorithm based on hybrid topology particle swarm optimization. The algorithm determines the optimal flow rate and light intensity for an imposed bacterial reduction. The implemented program was carried out for a wide range of input values for comprehensive analysis. The analysis of the results establishes when an optimal solution exists and the extent to which the disinfection or energy criterion is fulfilled. The method to calculate the bacterial reduction, OCP statement, optimization algorithm, and results’ analysis may be considered findings of this work.

The aim of the present work is to identify the expected nearshore and offshore impact of a marine energy farm that would be implemented in the coastal environment of Portugal. Several layouts of Wave Dragon devices were considered, the distance between each system being gradually adjusted. By processing 27–years of combined wave data coming from the European Space Agency and ERA5, the most relevant conditions have been identified. The centre of each farm layout was set to approximately 3.5 km from the coast, where a more significant attenuation of wave heights in the middle of the target area was noticed, which can go up to 16% in the case of extreme events. From the analysis of the longshore currents, it was noticed that even an arrow farm layout defined by five systems may have a significant impact, by changing the peak or by smoothing the currents profile. Wave energy is an emerging renewable sector that can also contribute tocoastal protection and, therefore, the Portuguese coast represents a suitable candidate for this type of project.

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.

The present work is focused on the analysis of flood scenarios for the settlements near the Danube discharge area into the Black Sea. From this perspective, the aim of the research is the development of flood extension maps for localities in the Danube Delta. The emphasis is on collecting the data and information needed for the entire analysis process, such as hydrological data on Danube flows and water levels (which were analyzed for 51 years), topo-bathymetric data (where 1685 cross sections were processed, measured on an 87-km section of the Danube), a digital terrain model (DTM), and others. Two methods of flood scenario analysis for the localities targeted were used in this paper. The first method was an analysis of the flood scenarios by modeling a real scenario, where it was supposed that a 20 m breach appeared in the dam which protects the localities and remained present for 24 h. The second method consisted of a Geographic Information System (GIS) analysis (static from a hydraulic point of view), where the maximum water level was superimposed over the DTM. This corresponded to a scenario in which the breach in the flood-control levee remains present for a longer period. The validated results show that the dynamic method is more efficient than the static method, both in terms of estimated flooded surfaces and in terms of simulation accuracy (taking into account more input parameters than the static method). Thus, from the obtained simulations it was observed that applying the dynamic method resulted in smaller flooded surfaces in the settlements analyzed than when considering the static method. In some cases, the differences between the flooded surfaces reached up to about 22%. This information is important and of general interest since it can be used in various fields of work, such as flood defense strategies, and investment promotion activities in the Danube discharge area or similar locations.