The current work is focused on investigating the potential of data-driven post-processing techniques, including proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD) for flame dynamics. Large-eddy simulation (LES) of a V-gutter premixed flame was performed with two Reynolds numbers. The flame transfer function (FTF) was calculated. The POD and DMD were used for the analysis of the flame structures, wake shedding frequency, etc. The results acquired by different methods were also compared. The FTF results indicate that the flames have proportional, inertial, and delay components. The POD method could capture the shedding wake motion and shear layer motion. The excited DMD modes corresponded to the shear layer flames’ swing and convect motions in certain directions. Both POD and DMD could help to identify the wake shedding frequency. However, this large-scale flame oscillation is not presented in the FTF results. The negative growth rates of the decomposed mode confi... [more]

The recursive discrete Fourier transformation (RDFT) method can be used for grid voltage phase-locking and harmonic current detection in a shunt active power filter (SAPF). However, in weak power grids such as microgrids, significant errors might occur in the amplitude and phase detection due to grid frequency deviation. In this study, to resolve this problem, a directly modified RDFT (DMRDFT) method is proposed for SAPF weak grid application. Through theoretical analysis, the errors of phase and amplitude detection were found to consist of fixed error and fluctuating error. The fixed error is only determined by frequency deviation, whereas the fluctuating error is also related to the recursive pointer and the initial phase. The DMRDFT algorithm can obtain the real grid frequency through the calculation of the phase angle difference for two consecutive periods. Then it can employ the grid frequency deviation and the recursive pointer value to directly correct the detection results gath... [more]

In this paper the magnetic nanoparticle aggregation procedure in a microchannel in the presence of external magnetic field is investigated. The main goal of the work was to establish a numerical model, capable of predicting the shape of the nanoparticle aggregate in a magnetic field without extreme computational demands. To that end, a specialized two-phase CFD model and solver has been created with the open source CFD software OpenFOAM. The model relies on the supposed microstucture of the aggregate consisting of particle chains parallel to the magnetic field. First, the microstructure was investigated with a micro-domain model. Based on the theoretical model of the particle chain and the results of the micro-domain model, a two-phase CFD model and solver were created. After this, the nanoparticle aggregation in a microchannel in the field of a magnet was modeled with the solver at different flow rates. Measurements with a microfluidic device were performed to verify the simulation re... [more]

Recently, virtual synchronous generators (VSGS) are a hot topic in the area of microgrid control. However, the traditional fixed-parameter-based VSG control methods have an obvious disadvantage. Namely, if the damping value is set to be small, the amplitude of frequency deviations under external power disturbances is large, meaning that the frequency suppression capacity is insufficient, but if the damping value is large, the dynamics of the system will be greatly sacrificed. To solve the problem, taking the dynamic characteristics and the maximum allowable frequency deviation (MAFD) into account, in this paper an improved fuzzy adaptive damping-based VSG control strategy is proposed to simultaneously attenuate the microgrid frequency fluctuations and guarantee the system dynamics. Firstly, in order to address the necessity of using an adaptive damping-based VSG, the structure of a fixed-parameter VSG method that incorporates the f-p/Q-V droop controllers is introduced, based on which... [more]

DC-DC isolated converters allowing a bidirectional flow of energy between High-Voltage DC and Low-Voltage DC networks have been proposed to be integrated in future on board power distribution systems. These converters must meet the specially stringent efficiency and power density requirements that are typical of the aeronautic industry. This makes it specially challenging to determine which converter topology is best suited for each particular application. This work presents a thorough review of several topologies of bidirectional DC-DC power converters that are considered good candidates to meet certain important aeronautic requirements, as those related with high efficiency and high power density. We perform simulations on virtual prototypes, constructed by using detailed component models, and optimized following design criteria that are in accordance with those typically imposed by aeronautic requirements. This comparative analysis is aimed to clearly identify the advantages and dra... [more]

The economic development of the EU’s countries depends on stable and permanent access to various energy sources. The integration of European energy markets is a long-term process. Each member country has a different energy balance, energy resources and electricity generation technologies. Therefore, comparing Member States with one another is a complex task. The article deals with organizing the set of objects in multidimensional spaces of variables from the point of view of a certain characteristics that cannot be measured in a simple way, i.e., the relative level of the development of energy markets. The following diagnostic variables were adopted for the analysis: consumption of electric energy generated from renewables per capita (TWH/person), hard coal consumption (million tons/person), greenhouse gas emissions per capita, available for final consumption gigawatt-hour per person, final energy consumption thousand tons of oil equivalent (TOE) per person, petroleum available for fin... [more]

In this paper, the proposed methodology minimizes the electricity cost of a laundry room by means of load shifting. The laundry room is equipped with washing machines, dryers, and irons. Additionally, the optimization model handles demand response signals, respecting user preferences while providing the required demand reduction. The sequence of devices operation is also modeled, ensuring correct operation cycles of different types of devices which are not allowed to overlap or have sequence rules. The implemented demand response program specifies a power consumption limit in each period and offers discounts for energy prices as incentives. In addition, users can define the required number of operations for each device in specific periods, and the preferences regarding the operation of consecutive days. In the case study, results have been obtained regarding six scenarios that have been defined to survey about effects of different energy tariffs, power limitations, and incentives, in a... [more]

Today’s spread of power distribution networks, with the installation of a significant number of renewable generators that depend on environmental conditions and on users’ consumption profiles, requires sophisticated models for monitoring the power flow, regulating the electricity market, and assessing the reliability of power grids. Such models cannot avoid taking into account the variability that is inherent to the electrical system and users’ behavior. In this paper, we present a solution for the generation of a compressed surrogate model of the electrical state of a realistic power network that is subject to a large number (on the order of a few hundreds) of uncertain parameters representing the power injected by distributed renewable sources or absorbed by users with different consumption profiles. Specifically, principal component analysis is combined with two state-of-the-art surrogate modeling strategies for uncertainty quantification, namely, the least-squares support vector ma... [more]

Anaerobic digestate supernatant can be used as a nutrient source for microalgae cultivation, thus integrating phytoremediation processes with high value products storage in microalgae biomass. Microalgae are able to use nitrogen and phosphorous from digestate, but high nutrient concentration can cause growth inhibition. In this study, two microalgae strains (C. vulgaris and S. obliquus) were cultivated on the anaerobic co-digestion supernatant (obtained from the organic fraction of municipal solid waste (OFMSW) and waste activated sludge (WAS)) in a preliminary Petri plate screening at different dilutions (1:10 and 1:5) using a synthetic medium (ISO) and tap water (TW). Direct Nile red screening was applied on colonies to preliminarily identify hydrophobic compound storage and then a batch test was performed (without air insufflation). Results show that C. vulgaris was able to grow on digestate supernatant 1:5 diluted, while Nile red screening allowed the preliminary detection of hydro... [more]

The growing penetrations of rooftop photovoltaics (PVs) into low-voltage (LV) distribution networks are challenging voltage regulation. Developing an effective volt-var (VV) control has been the focus of many researchers with various approaches proposed so far. However, assuming a single voltage level and balanced network model, widely adopted in existing literatures, tends to cause inaccurate and even infeasible control solutions. Besides, existing distribution VV control studies are usually based on the day-ahead predictions of PV generations and loads, introducing inevitable and non-negligible errors. To address the challenges above, this paper proposes a VV co-optimization across unbalanced medium-voltage (MV) and LV networks, by traditional and emerging techniques, to ensure the network operation with the required power quality. Specifically, the operation of MV delta-connected switched capacitors and LV distributed PV inverters is coordinated, under a three-stage strategy that su... [more]

Lost circulation occurs when the returned fluid is less than what is pumped into the well due to loss of fluid to pores or fractures. A lost-circulation event is a common occurrence in a geothermal well. Typical geothermal reservoirs are often under-pressured and have larger fracture apertures. A severe lost-circulation event is costly and may lead to stuck pipe, well instability, and well abandonment. One typical treatment is adding lost-circulation materials (LCMs) to seal fractures. Conventional LCMs fail to properly seal fractures because their mechanical limit is exceeded at elevated temperatures. In this paper, parametric studies in numerical simulations are conducted to better understand different thermal effects on the sealing mechanisms of LCMs. The computational fluid dynamics (CFDs) and the discrete element method (DEM) are coupled to accurately capture the true physics of sealing by granular materials. Due to computational limits, the traditional Eulerian−Eulerian approach... [more]

A preliminary experimental work on a centrifugal pump model specifically designed to transport slurry and multiphase flows is presented. The impeller design corresponds to the so-called “Tesla Bladed Pump” adapted from an existing DiscflowTM pump design for the petroleum deep-sea application. The overall performance results of such a specific pump design are presented for different rotational speeds and discussed in relation to affinity laws coefficients. The results show that the performance of the tested disc pump strongly differs from the conventional centrifugal bladed pump. A one-dimensional approach using complete Euler relation is used to explain the differences in the present case. Moreover, it has been found that available results in open literatures do not correspond to the real optimum conditions, more detailed research work must be performed to get a better understanding on this kind of bladed disc pump.

Solar radiation data is essential for the development of many solar energy applications ranging from thermal collectors to building simulation tools, but its availability is limited, especially the diffuse radiation component. There are several studies aimed at predicting this value, but very few studies cover the generalizability of such models on varying climates. Our study investigates how well these models generalize and also show how to enhance their generalizability on different climates. Since machine learning approaches are known to generalize well, we apply them to truly understand how well they perform on different climates than they are originally trained. Therefore, we trained them on datasets from the U.S. and tested on several European climates. The machine learning model that is developed for U.S. climates not only showed low mean absolute error (MAE) of 23 W/m2, but also generalized very well on European climates with MAE in the range of 20 to 27 W/m2. Further investiga... [more]

The paper assumes that, at the end of the operational period of a Spanish nuclear power plant, an Independent Spent Fuel Storage Installation will be used for long-term storage. Spent fuel assemblies are selected and transferred to casks for dry storage, with a series of imposed restrictions (e.g., limiting the thermal load). In this context, we present a variant of the problem of spent nuclear fuel cask loading in one stage (i.e., the fuel is completely transferred from the spent fuel pool to the casks at once), offering a multi-start metaheuristic of three phases. (1) A mixed integer linear programming (MILP-1) model is used to minimize the cost of the casks required. (2) A deterministic algorithm (A1) assigns the spent fuel assemblies to a specific region of a specific cask based on an MILP-1 solution. (3) Starting from the A1 solutions, a local search algorithm (A2) minimizes the standard deviation of the thermal load among casks. Instances with 1200 fuel assemblies (and six interv... [more]

In today’s world, renewable energy sources are increasingly integrated with nonrenewable energy sources into electric grids and pose new challenges because of their intermittent and variable nature. Energy prediction using soft-computing techniques plays a vital role in addressing these challenges. As electricity consumption is closely linked to other energy sources such as natural gas and oil, forecasting electricity consumption is essential for making national energy policies. In this paper, we utilize various data mining techniques, including preprocessing historical load data and the load time series’s characteristics. We analyzed the power consumption trends from renewable energy sources and nonrenewable energy sources and combined them. A novel machine learning-based hybrid approach, combining multilayer perceptron (MLP), support vector regression (SVR), and CatBoost, is proposed in this paper for power forecasting. A thorough comparison is made, taking into account the results o... [more]

As the heating demands of buildings drop considerably, the use of solar walls makes increasing sense. One of the obstacles to the development of such walls is their need for on-site implementation by specialized companies. On the other hand, a storage wall is generally composed of heavy materials with high inertia, which prevents prefabrication of the solar component. To avoid this problem and allow for solar walls to be prefabricated in the factory, a novel approach to replacing this heavy wall with a lighter storage wall incorporating phase change materials (PCM) has been proposed. This paper aims to demonstrate the impact of PCM on the thermal energy performance once they have been integrated into the storage wall of the composite Trombe wall. Addressed herein will be the heat transfer exchange inside a house located in the northern part of France, where a composite Trombe wall has been fitted without PCM. Three configurations will be investigated—(1) the model house without the sol... [more]

This paper proposes a novel approach to optimize the main energy consumptions of heavy oil refining industries (ORI) in response to electricity price uncertainties. The whole industrial sub-processes of the ORI are modeled mathematically to investigate the joint power-heat flexibility potentials of the industry. To model the refinery processes, an input/output flow-based model is proposed for five main refining units. Moreover, the role of storage tanks capacity in the power system flexibility is investigated. To hedge against the electricity price uncertainty, an uncertain bound for the wholesale electricity price is addressed. To optimize the industrial processes, a dual robust mixed-integer quadratic program (R-MIQP) is adopted; therefore, the ORI’s operational strategies are determined under the worst-case realization of the electricity price uncertainty. Finally, the suggested approach is implemented in the south-west sector of the Iran Energy Market that suffers from a lack of el... [more]

Ultra-short-term electrical load forecasting is an important guarantee for the safety and efficiency of energy system operation. Temperature is also an important factor affecting the changes in electric load. However, in different cases, the impact of temperature on load forecasting will vary greatly, and sometimes even lead to the decrease of forecasting accuracy. This often brings great difficulties to researchers’ work. In order to make more scientific use of temperature factor for ultra-short-term electrical load forecasting, especially to avoid the negative influence of temperature on load forecasting, in this paper we propose an ultra-short-term electrical load forecasting method based on temperature factor weight and long short-term memory model. The proposed method evaluates the importance of the current prediction task’s temperature based on the change magnitude of the recent load and the correlation between temperature and load, and therefore the negative impacts of the tempe... [more]

Various types of support structures for offshore wind turbine have been developed, and concrete structures have attracted attention due to many advantages. Although many studies have been conducted on the design of the existing steel structures, information and research on the design of concrete support structures are insufficient. Therefore, in this paper, a structural analysis model of conical concrete support structure (CCSS) is established and design optimization is presented. A detailed performance evaluation and the design of prestressed concrete were performed under the marine conditions of Phase 1 test site of southwest offshore wind project in Korea. The fluid−soil−structure interaction (FSI) was applied using the added mass method and soil spring model to represent the effects of water and soil. With the result of quasi-static analysis, a post-tensioning design was implemented by applying prestressing steel, and CCSS showed sufficient rigidity. From the natural frequency anal... [more]

Graphene is a new generation material, which finds potential and practical applications in a vast range of research areas. It has unrivalled characteristics, chiefly in terms of electronic conductivity, mechanical robustness and large surface area, which allow the attainment of outstanding performances in the material science field. Some unneglectable issues, such as the high cost of production at high quality and corresponding scarce availability in large amounts necessary for mass scale distribution, slow down graphene widespread utilization; however, in the last decade both basic academic and applied industrial materials research have achieved remarkable breakthroughs thanks to the implementation of graphene and related 1D derivatives. In this work, after briefly recalling the main characteristics of graphene, we present an extensive overview of the most recent advances in the development of the Li-ion battery anodes granted by the use of neat and engineered graphene and related 1D... [more]

Molasses is a highly dense and refined byproduct produced in the sugarcane industry, and it contains high amounts of degradable compounds. Through bioconversion, these compounds can be transformed into renewable products. However, the involved biological process is negatively influenced by the high chemical oxygen demand (COD) of molasses and ion concentration. The co-digestion of molasses with rice-alcohol wastewater (RAW) was compared with its mono-digestion at an increasing organic loading rate (OLR). Both processes were assessed by detecting the COD removal rate, the methane contents of biogas, and the structure and composition of microbial communities at different stages. Results showed that the co-digestion is stable up to a maximum OLR of 16 g COD L−1 d−1, whereas after the acclimatization phase, the mono-digestion process was disturbed two times, which occurred at a maximum OLR of 9 and 10 g COD L−1 d−1. The volatile fatty acids (VFAs) observed were 2059.66 mg/L and 1896.9 mg/L... [more]

Parameter estimation based on the measurement data of the phasor measurement unit (PMU) is an important approach for identifying the Thévenin equivalent parameters (TEPs) of power systems. However, in the process of acquiring or transmitting data in PMU, measurement errors due to external interference or internal system faults will affect the accuracy of parameter estimation. In this paper, a TEP estimation algorithm based on local PMU measurement is proposed. The algorithm considers the errors of the PMU and introduces Huber function and projection statistics (PS) to eliminate the effects of outliers and leverage measurements, respectively. Additionally, a variable forgetting factor (VFF) is used to quickly eliminate the historical data with measurement deviation and track the changes of the system. The regularization technique is used to solve the divergence problem in the inverse process of the ill-conditioned matrix, thereby improving the stability and generalization performance of... [more]

Lignin is a natural polymer, one that has an abundant and renewable resource in biomass. Due to a tendency towards the use of biochemicals, the efficient utilization of lignin has gained wide attention. The delignification of lignocellulosic biomass makes its fractions (cellulose, hemicellulose, and lignin) susceptible to easier transformation to many different commodities like energy, chemicals, and materials that could be produced using the biorefinery concept. This review gives an overview of the field of lignin separation from lignocellulosic biomass and changes that occur in the biomass during this process, as well as taking a detailed look at the influence of parameters that lead the process of dissolution. According to recent studies, a number of ionic liquids (ILs) have shown a level of potential for industrial scale production in terms of the pretreatment of biomass. ILs are perspective green solvents for pretreatment of lignocellulosic biomass. These properties in ILs enable... [more]

This research involved studying the physico-chemical parameters of fly ash derived from the combustion of 100% biomass in bubbling and circulating fluidized bed boilers of two large energy plants in Poland. Chemical composition revealed that ash contains substantial amounts of CaO (12.86−26.5%); K2O (6.2−8.25%); MgO (2.97−4.06%); P2O5 (2−4.63%); S (1.6−1.83%); and micronutrients such as Mn, Zn, Cu, and Co. The ash from the bubbling fluidized bed (BFB) was richer in potassium, phosphorus, CaO, and micronutrients than the ash from the circulating fluidized bed (CFB) and contained cumulatively less contaminants. However, the BFB ash exceeded the threshold values of Cd to be considered as a liming amendment. Additionally, according to our European Community Bureau of Reference (BCR) study Pb and Cd were more mobile in the BFB than in the CFB ash. Except for a low nitrogen content, the ash met the minimum requirements for mineral fertilizers. Acute phytotoxicity revealed no inhibition of th... [more]

Biological desulfurization of biogas from a field-scale anaerobic digester in Peru was tested using air injection (microaeration) in separate duplicate vessels and chemical desulfurization using duplicate iron filters to compare hydrogen sulfide (H2S) reduction, feasibility, and cost. Microaeration was tested after biogas retention times of 2 and 4 h after a single injection of ambient air at 2 L/min. The microaeration vessels contained digester sludge to seed sulfur-oxidizing bacteria and facilitate H2S removal. The average H2S removal efficiency using iron filters was 32.91%, with a maximum of 70.21%. The average H2S removal efficiency by iron filters was significantly lower than microaeration after 2 and 4 h retention times (91.5% and 99.8%, respectively). The longer retention time (4 h) resulted in a higher average removal efficiency (99.8%) compared to 2 h (91.5%). The sulfur concentration in the microaeration treatment vessel was 493% higher after 50 days of treatments, indicatin... [more]