The importance of simulation calculations in developing railway vehicles and their subsystems is consistently growing compared to physical experiments and track tests [...]

Research on the state of charge (SOC) prediction of lead−acid batteries is of great importance to the use and management of batteries. Due to this reason, this paper proposes a method for predicting the SOC of lead−acid batteries based on the improved AdaBoost model. By using the online sequence extreme learning machine (OSELM) as its weak learning machine, this model can achieve incremental learning of the model, which has a high computational efficiency, and does not require repeated training of old samples. Through improvement of the AdaBoost algorithm, the local prediction accuracy of the algorithm for the sample is enhanced, the scores of the proposed model in the maximum absolute error (AEmax) and maximum absolute percent error (APEmax) indicators are 6.8% and 8.8% lower, and the accuracy of the model is further improved. According to the verification with experimental data, when there are a large number of prediction samples, the improved AdaBoost model can reduce the prediction... [more]

With conventional droop control, the droop relationship between the voltage and reactive power is not purely linear because of the filter reactance. This paper focuses on the theoretical analysis to account for this characteristic and presents a precise power flow method for conventional droop control. The proposed method is universal, which can handle not only conventional droop control, but also other control strategies, such as robust droop control, constant power control, and constant voltage−frequency control. It can also handle frequency-dependent active and reactive power loads and is adapted for islanded and grid-connected systems. The proposed method extends the applicability of conventional power flow methods to microgrids so that the framework of the method is generic; any conventional power flow algorithm can be adapted to this framework. Compared with the time-domain simulation method, the proposed method is accurate, simple, and easy to implement for industrial applicatio... [more]

The structure of premixed turbulent flames and governing physical mechanisms of the influence of turbulence on premixed burning are often discussed by invoking combustion regime diagrams. In the majority of such diagrams, boundaries of three combustion regimes associated with (i) flame preheat zones broadened locally by turbulent eddies, (ii) reaction zones broadened locally by turbulent eddies, and (iii) local extinction are based on a Karlovitz number Ka, with differently defined Ka being used to demarcate different combustion regimes. The present paper aims to overview different definitions of Ka, comparing them, and suggesting the most appropriate choice of Ka for each combustion regime boundary. Moreover, since certain Karlovitz numbers involve a laminar flame thickness, the influence of complex combustion chemistry on the thickness and, hence, on various Ka and relations between them is explored based on results of complex-chemistry simulations of unperturbed (stationary, planar,... [more]

In this article, the analysis of mechanical energy changes in a gas medium flow with stable and variable density was presented. To determine the energy losses, the various sources of momentum and mass were used, which had an influence on air flow through the conduit in the system without heat exchange with the environment. The occurrence of varying density gas flow in the conduit (caused by local inflow of mass and momentum) in inclined pipes generates a natural depression−internal mechanical energy. The local momentum sources can facilitate or hinder the gas flow through the conduit. This phenomenon often appears in the network of underground mine workings and in ventilation and air conditioning installations. The characteristic for gas flow through a pipe or mining excavation is the equivalent aerodynamic resistance, the value of which is influenced by the mass and momentum of local sources. This value determines the facilitation or difficulty in gas transport through a section of co... [more]

The pore space of autoclaved aerated concretes (ACCs), regardless of their apparent density, is represented by large pores formed as a result of gas formation and fine capillary pores. With the free absorption of liquid moisture, only the capillary pores are filled. Large pores contain vapor-air mixture. Considering such a bimodal pore size distribution, it is proposed to determine the thermal conductivity of moist ACC in two stages. First, an inhomogeneous ternary system that consists of a solid skeleton with a fine porous structure containing gas and liquid moisture should be considered. Then a binary system is taken into account, the first component of which is the mentioned ternary system, and the other component of which consists of isolated gas inclusions in large pores. To determine the thermal conductivity of the ternary system, the dependences constructed using the theory of generalized conductivity were used. The thermal conductivity of the binary system was calculated using... [more]

Developing control methods that have the ability to preserve the stability and optimum operation of a wind energy generation unit connected to power systems constitutes an essential area of recent research in power systems control. The present work investigates a novel control of a wind energy system connected to a power system through a static VAR compensator (SVC). This advanced control is constructed via integration between the model predictive control (MPC) and an artificial neural network (ANN) to collect all of their advantages. The conventional MPC needs a high computational effort, or it can cause difficulties in implementation. These difficulties can be eliminated by using Laguerre-based MPC (LMPC). The ANN has high performance in optimization and modeling, but it is limited in improving dynamic performance. Conversely, MPC operation improves dynamic performance. The integration between ANN and LMPC increases the ability of the Neuro-MPC (LMPC-ANN) control system to conduct sm... [more]

In general, studies on short-term hourly electricity load modeling and forecasting do not investigate in detail the sources of uncertainty in forecasting. This study aims to evaluate the impact and benefits of applying bootstrap aggregation in overcoming the uncertainty in time series forecasting, thereby increasing the accuracy of multistep ahead point forecasts. We implemented the existing and proposed clustering-based bootstrapping methods to generate new electricity load time series. In the proposed method, we use singular spectrum analysis to decompose the series between signal and noise to reduce the variance of the bootstrapped series. The noise is then bootstrapped by K-means clustering-based generation of Gaussian normal distribution (KM.N) before adding it back to the signal, resulting in the bootstrapped series. We apply the benchmark models for electricity load forecasting, SARIMA, NNAR, TBATS, and DSHW, to model all new bootstrapped series and determine the multistep ahead... [more]

This paper presents the results of a numerical analysis of the impact of rock mass geomechanical parameters on the stability of preparatory headings located within the Legnica-Glogow Copper District. The paper shows the results of numerical calculations prepared for headings driven in two rock mass types with different strength and deformation parameters, which allow illustrating their influence on the safety of mining performed in underground copper ore mines. Numerical modeling was performed using the Examine2D 7.0 software, in the plane strain state. Numerical simulations were performed for an isotropic and for a homogenous medium. The rock medium was described with an elastic model. The parameters of the rock mass for numerical modeling were calculated using the Hoek−Brown classification. The Coulomb−Mohr strength criterion was adopted as a measure for assessing the rock mass effort. Numerical simulations confirmed the dependance between the stability of the analyzed excavations an... [more]

Cellulose particles are among the aging products of the insulating paper that are used in power transformers. Too many cellulose particles can cause transformer accidents. Traditional research and detection methods that are used for this problem generally focus on the number and length information of cellulose particles, and it is usually difficult to quantitatively describe the spatial shape of cellulose particles. However, the shape of cellulose particles is also one of the factors affecting the safety of transformer insulation. In this paper, we successfully extracted quantitative information of the spatial shape of cellulose particles in transformer oil using an image processing technique and the transport of intensity equation, providing a new novel approach for the study and detection of the shape of cellulose particles in transformer oil.

A new approach is proposed for estimating the power efficiency of an on-field solar photovoltaics (PV) system using data from thermal imaging and weather instruments obtained using an unmanned aerial vehicle (UAV). This method is specifically designed for the non-intrusive detection of the performance of the PV system in a large-scale solar power plant that could be efficient, manpower saving, operationally safe and comprehensive. In this study, a drone instrumented with a radiometer, a thermometer and an anemometer flew at a height of 1.5 m with a maximum lateral flight speed of 3.6 m/s above the PV modules (60 cells each) with hotspots or with aging but without hotspots. The average temperatures of the PV modules were then calculated through the measured radiation intensity, ambient temperature and wind speed based on the published correlation formula. The experimental correlations were obtained by measuring over 60 aging PV modules without hot-spot damage, and the uncertainties of t... [more]

Power grids play an important role in modern societies by providing an uninterrupted energy supply and have become a key driving force behind the growth of the world’s economies [...]

The state of charge (SOC) of the battery is an important basis for the battery management system to perform state monitoring and control decisions. In this paper, by identifying the internal parameters of the battery model at different temperatures and SOCs of the lithium-ion battery, the specific factors that affect the change of the parameters are analyzed, the segmentation basis of the model and the fitting method of related parameters are discussed, the second-order equivalent circuit model of the lithium-ion battery whose parameters vary with SOC and temperature is established, the unscented Kalman filter (UKF) is used to estimate the SOC of the lithium-ion battery, and an improved SOC estimation method based on optimized equivalent circuit model is proposed. Simulation and experimental results show that the improved SOC estimation strategy can obtain high estimation accuracy in a wide temperature range.

Borehole cataloguing is an important task in geological drilling. Traditional manual cataloguing provides the stratification of underground boreholes based on changes in core lithology. This paper proposes a novel borehole cataloguing method using a drilling process monitoring (DPM) system. This DPM cataloguing method stratifies a borehole according to the drilling speed through the rock. A 102 m borehole was drilled and cored in Baota district, Yan’an city, Shaanxi Province, China. The rock-breaking response parameters of the drill bit displacement, drill rod rotation speed and inlet pipe and outlet pipe oil pressures were monitored throughout the drilling process, and the drilling depth-penetration rate curve during the net drilling process was obtained. The changes in drilling speed show that the DPM cataloguing can identify the depths of the layer interfaces of the borehole and describe the stratification. The interface depth values obtained by DPM have little difference from the i... [more]

During the 20th century, the global energy system was mainly based on the use of fossil fuels, such as oil, natural gas, and coal [...]

Biological methanation is the production of CH4 from CO2 and H2. While this approach to carbon capture utilization have been widely researched in the recent years, there is a gap in the technology. The gap is towards the flexibility in biomethanation, utilizing biological trickling filters (BTF). With the current intermittent energy system, electricity is not a given surplus energy which will interfere with a continuous operation of biomethanation and will result in periods of operational downtime. This study investigated the effect of temperature and H2 supply during downtimes, to optimize the time needed to regain initial performance. Short (6 h), medium (24 h) and long (72 h) downtimes were investigated with combinations of three different temperatures and three different flow rates. The results from these 27 experiments showed that with the optimized parameters, it would take 60 min to reach 98.4% CH4 in the product gas for a short downtime, whereas longer downtimes needed 180 min... [more]

Diode-based HVDC link technology is considered an alternative to reduce the cost and complexity of offshore HVDC platforms. When this technology is used, the AC grid of the wind farm must be created artificially. This paper proposes an advanced frequency control method that permits forming an AC grid voltage system to connect offshore wind turbines to a diode-based HVDC link rectifier. The proposed algorithm can be easily implemented in the wind farm’s overall Power Plant Controller (PPC) without any change in the commercial wind turbine firmware. All wind turbines receive reactive power targets from the PPC to maintain the frequency and amplitude of the offshore AC line, delivering the maximum active power generated by the wind. A novel black start method is proposed to establish the wind farm’s local AC grid voltage system. The control method has been implemented and proved in an experimental setting. The black start has been successfully verified, and the frequency control algorithm... [more]

An advanced break or a vast region of pressurisation may occur when the working face passes through an abandoned roadway, resulting in a roof falling or water inrush. The stress evolution of the working face passing through an abandoned roadway in a coal mine was comprehensively discussed using theoretical analysis, numerical simulation, and field monitoring. In this study, the calculated critical width of the abandoned roadway where the main roof was bound to an advanced break was 5.4 m. Reducing the suspended length of the main roof is beneficial to the stability of the working face’s passage across the abandoned roadway. The maximum abutment stress on the roof occurred at the working face through a semi-abandoned roadway, reaching 44.3 MPa. Subsequently, it decreased sharply until the working face completely passed and returned to the normal level. The damage depths of the floor strata from the field monitoring were 15 and 20 m, which showed that the use of hydraulic fracturing tech... [more]

This article describes an approach for comparing material intensity values for residential buildings with different construction types. Based on the working drawings of the different construction types (wood and mineral), material intensities are calculated at the building level. Material intensities describe the materials used in a building in mass (tonnes (t)) in relation to the square meters (m2) of gross floor area (GFA) or the cubic meters (m3) of gross volume (GV). The method for determining material intensities at the building level is demonstrated. The results show that material intensities range from 0.61 t/m2 GFA to 1.95 t/m2 GFA for single-family residential buildings and from 1.36 t/m2 GFA to 1.54 t/m2 GFA for multi-storey residential buildings. The average material intensity for mineral buildings is twice as high as that for wood buildings, which means that there is a beneficial resource efficiency in building with wood instead of mineral materials. Therefore, benchmarks f... [more]

Greenhouse gases (GHG) concentration (CO2, CH4, and NOx mainly) in the Earth’s atmosphere has dramatically increased since 1960; in particular, the atmospheric CO2 levels have increased from 320 ppm to 412 ppm from 1960 to 2019 [...]

Transportation and portable applications already use hydrogen as fuel, but it is essential to use highly-efficient hydrogen storage methods to increase its usage in the future. The compressed form is the most utilized for transportation applications, but mechanical compressors have low efficiency when compressing low quantities of gas to high pressure. The most suitable device for hydrogen compression is the Electrochemical Hydrogen Compressor (EHC). It has the same structure as a Proton Exchange Membrane Fuel Cell (PEM-FC), but it works at very high-pressure ( 700 bar). The present work analyses the monopolar plate of an Electrochemical Hydrogen Compressor prone to hydrogen embrittlement. Irregular shape variations generate peaks of stress magnitude and triaxiality, further contributing to decreasing metal ductility at the local scale. The calculation of the stress field in such components is essential due to the possibility of failure due to the material embrittlement caused by hydro... [more]

Jevons Paradox has fundamental implications on sustainable development and the UN Sustainable Development Goals (SDGs). The paradox states that technological improvements aiming to increase the energy efficiency risk causing a rebound effect, and an increase in demand, production, and resource exploitation. Third world countries undergoing early-stage technological development may be particularly vulnerable, but it is also relevant in complex economic systems, where policymaking on climate and energy building on insufficient knowledge and attention to rebound effects can impair the desired outcome in terms of climate change mitigation, resource use and sustainable development.

Electricity has a crucial function in contemporary civilization. The power grid must be stable to ensure the efficiency and dependability of electrical equipment. This implies that the high-voltage equipment at the substation must be reliably operated. As a result, the appropriate and dependable use of systems to monitor the operating status of high-voltage electrical equipment has recently gained attention. Partial discharge (PD) analysis is one of the most promising solutions for monitoring and diagnosing potential problems in insulation systems. Noise is a major challenge in diagnosing and detecting defects when using this measurement. This study aims to denoise PD signals using a data decomposition method, improved complete ensemble empirical mode decomposition with adaptive noise algorithm, combined with statistical significance test to increase noise reduction efficiency and to derive and visualize the Hilbert spectrum of the input signal in time-frequency domain after filtering... [more]

Terrestrial tight oil has extremely strong diagenesis heterogeneity, so a large number of rock thin slices are needed to reveal the real microscopic pore-throat structure characteristics. In addition, difficult identification, high cost, long time, strong subjectivity and other problems exist in the identification of tight oil rock thin slices, and it is difficult to meet the needs of fine description and quantitative characterization of the reservoir. In this paper, a method for identifying the characteristics of rock thin slices in tight oil reservoirs based on the deep learning technique was proposed. The present work has the following steps: first, the image preprocessing technique was studied. The original image noise was removed by filtering, and the image pixel size was unified by a normalization technique to ensure the quality of samples; second, the self-labeling image data augmentation technique was constructed to solve the problem of sparse samples; third, the Mask R-CNN alg... [more]

Carbonate reservoirs commonly have significant heterogeneity and complex pore systems due to the multi-scale characteristic. Therefore, it is quite challenging to predict the petrophysical properties of such reservoirs based on restricted experimental data. In order to study the heterogeneity and size of the representative elementary volume (REV) of vuggy dolostones, a total of 26 samples with pore sizes ranging from micrometers to centimeters were collected from the Cambrian Xiaoerbulake Formation at the Kalping uplift in the Tarim Basin of northwestern China. In terms of the distribution of pore size and contribution of pores to porosity obtained by medical computed tomography testing, four types of pore systems (Types I−IV) were identified. The heterogeneity of carbonate reservoirs was further quantitatively evaluated by calculating the parameters of pore structure, heterogeneity, and porosity cyclicity. The results indicate that different pore systems yield variable porosities, por... [more]