This paper devises an output-feedback multi-loop positioning technique adopting the speed observer and multi-motor synchronizer, targeting the dual (master and slave) motor elevator system applications, providing the three contributions. First, the order-reduction observer continuously extracts the speed information from the motor position measurement, independent of the system model information. Second, the order-reduction stabilizer accomplishes the speed synchronization tasks for both the master and slave motors. Third, the resultant feedback system guarantees to exponentially recover the desired first-order transfer function from the reference to the actual motor position despite the model-plant mismatches. The prototype elevator system adopting the dual motor experimentally validates the practical advantages of the proposed technique.

In this paper, the theoretical properties of transients in three-phase networks, including the fourth wire and unbalanced source, are systematically investigated by resorting to several analytical tools. First, a Cartesian space vector is introduced to provide the geometrical three-dimensional representation of a three-phase voltage/current transient. It is shown that a voltage/current transient can be always represented as a three-dimensional trajectory leaving one plane (corresponding to the previous steady state) towards another plane (corresponding to the new steady state at the end of the transient). The quantity driving the trajectory from one plane to another is the Park/Clarke zero component. Second, the Clarke transformation is used to study the original three-phase circuit as a superposition of two independent transients: the transient of the Clarke space vectors and the transient of the Clarke zero components. Third, the Park transformation is used to evaluate the dq0 compon... [more]

As a new and unconventional reservoir, Quaternary mudstone biogas reservoirs in the Qaidam Basin are widely distributed and thick. They have great potential for biogas exploration. However, the mudstone biogas reservoirs in this area characterized by weak cementation, high clay content, and easy hydrolysis. Using existing methods, it is difficult to obtain the rock electrical parameters and evaluate the saturation. This greatly affects the evaluation of oil and gas reserves. This study selected core samples from the Quaternary mudstone biogas reservoir in Qaidam Basin, prepared the samples through core conformation pretreatment, and conducted rock electrical experiments using the self-absorption water augmentation method to obtain the rock electrical parameters of the mudstone biogas reservoirs for the first time. Then, the factors influencing the rock electrical parameters of the mudstone biogas reservoir were analyzed. The results showed that: (1) the porosity of the mudstone core sa... [more]

In this study, we propose the use of a short-distance and fixed-type wireless power transmission transformer via a half-bridge LLC resonant converter. A ceramic insulating layer was used instead of an air gap, meaning that the heat generated from the transformer core and the PCB winding was quickly transferred to the external metal case, with the ceramic insulating layer acting as a heat pipe. In order to stabilize the output voltage, we proposed the use of IR photo tunnel technology, and it was applied to two ceramic insulating layers so that the voltage error signal of the secondary output voltage could be transmitted as light to the primary side. As a result, it was possible to physically separate the primary and secondary sides of the power circuit centering on the ceramic insulating layer. The experiment was carried out with the input voltage of 400 V, the output voltage of 54 V, the maximum output power of 1 kW, and the switching frequency of 1.3 MHz or higher. As a result, the m... [more]

The increase in heterogeneous data in the building energy domain creates a difficult challenge for data integration. Schema matching, which maps the raw data from the building energy domain to a generic data model, is the necessary step in data integration and provides a unique representation. Only a small amount of labeled data for schema matching exists and it is time-consuming and labor-intensive to manually label data. This paper applies semantic-similarity methods to the automatic schema-mapping process by combining knowledge from natural language processing, which reduces the manual effort in heterogeneous data integration. The active-learning method is applied to solve the lack-of-labeled-data problem in schema matching. The results of the schema matching with building-energy-domain data show the pre-trained language model provides a massive improvement in the accuracy of schema matching and the active-learning method greatly reduces the amount of labeled data required.

The IT infrastructure is the basis for the efficient and effective flow of logistic information between the individual elements of the logistical system. Therefore, the aim of this research was to assess the diversification of equipment in IT infrastructure in enterprises in Central Pomerania in Poland. The research was conducted in 2021 using the CAWI method. The research covers five categories of IT infrastructure: IT equipment, software/applications, means of communication, devices cooperating in the smart internet network and other devices. The study was conducted on a sample of 353 enterprises located in the area of Central Pomerania. The results of the conducted research indicate that the degree of use of the IT infrastructure in the analyzed enterprises varies. Taking into account the size of the enterprise, IT infrastructure is much more often used by large and medium enterprises than by small and micro enterprises. In addition, the results also show the diversification of the... [more]

The issue of shifting loads from road to rail is always vivid when it comes to reducing CO2 emissions from transport. Practically not every load transported by road vehicles over a long distance can be transferred to rail. Additionally, the potential of the railway lines is limited, which means that the network is not able to accept huge amounts of loads from road transport. In the article, attention was paid to the typology of cargo susceptible to changing the means of transport. The article discusses the factors influencing the real possibility of CO2 reduction by changing the mode of transport. The analysis and calculation example of the selected region in Poland is presented.

This paper presents the results of detonation and explosion characteristics for ammonium nitrate, aluminium, and aluminium-magnesium alloy powder mixtures. The following parameters were determined: detonation velocities, blast waves overpressure and their specific impulses. The emission of radiation was recorded, and the history of temperature of the detonation products cloud was established. It was shown that addition of aluminium-magnesium alloy powder increases blast waves’ characteristics. Moreover, it increases the time of the afterburning reaction after detonation and increases the temperature of detonation products.

In the high-speed rail industry, the overhead contact line erected along the railroad is used to supply the electricity to the high-speed train via a pantograph on the carbody’s roof. This work attempts to explore the effect of contact line pre-sag on the contact quality between the pantograph and the contact line. A nonlinear finite element approach is implemented to build the overhead contact line system with accurate description of the pre-sag of the contact line. Through a nonlinear solution, the effect of contact line pre-sag on the contact force is analysed with different train speeds and tension classes. The analysis result indicates the feasibility of tuning the pre-sag to improve the interaction performance at a given speed and tension class. In the low-speed range, the change of pre-sag does not have a significant effect on the interaction performance. However, when the speed increases up to a certain value, the effect of pre-sag on the contact force is nonnegligible. The inc... [more]

We report a quantitative study of the effect of low-concentration methanol (MeOH) on the formation and dissociation of hydrates based on CH4 and CO2/N2 guest molecules. The kinetic promotion and dissociation ability of MeOH is also compared with the anionic surfactant sodium dodecyl sulfate (SDS, 100 ppm, 50 ppm). The effects of concentration changes (1 wt% and 5 wt%), pressure (p = 80−120 bar), guest molecules (CH4 and CO2), and temperature (1 °C and below 0 °C) are investigated using slow constant ramp (SCR) and isothermal (IT) temperature schemes. The results show that the kinetics are affected by the guest molecule and MeOH concentration. For CH4 gas, 5 wt% MeOH shows better promotion, while for CO2/N2 gas mixtures, 1 wt% MeOH gives better promotion. This conclusion agrees well with our previous results demonstrating optimal CH4 recovery and CO2 storage in the presence of 5 wt% MeOH. The promoting and inhibiting properties of MeOH could be beneficial in CH4 production from gas hydr... [more]

From a global perspective, carbon emissions are a global problem that needs to be solved urgently. At present, 61% of countries have committed to achieving net zero emissions. Compared with industry and construction, the transportation sector has become the focus and challenge for countries to achieve carbon neutrality due to the characteristics of strong mobility, scattered emission sources, and complex social behaviors. Therefore, the issue of carbon emissions in the transportation industry has become the focus of academic attention. This paper first calculates the carbon emission efficiency (CEE) of the regional transportation industry through the super-efficiency SBM model and then evaluates its regional differentiation characteristics through the Theil index, which has important practical significance for reducing regional carbon emissions. The results show that the national transportation CEE average value is 0.612, a relatively low level. The spatial distribution of China’s tran... [more]

Disclosure of non-financial information, especially regarding corporate governance (CG), is an important element of companies’ communication with their stakeholders. This paper sets out to define—from a theoretical and practical perspective—the scope of CG reporting in Polish fuel, gas, and energy (“energy”) companies required under EU directives and national regulations. The paper presents the results of a study investigating whether and to what extent annual corporate governance statements (CGSs) prepared by energy companies, compared with other companies listed on the Warsaw Stock Exchange (WSE-LCs), are consistent with “Best Practices for WSE-LCs 2016” (BPs for WSE-LCs). The study group consisted of energy companies submitting their 2017−2020 reports, as well as other companies listed on the WSE, as a comparative group (i.e., a total of 179 reports). We used a monographic method to study theoretical problems and annual CGSs and performed a critical review of the literature, as well... [more]

In this paper, qualitative theoretical derivations, finite element analysis (FEA) and experiments are used to investigate the electromagnetic force (EF) and vibration characteristics of end windings. In contrast to previous studies, this study focuses not only on end winding EF/vibration under normal and radial static air gap eccentricity (RSAGE) conditions, but also for the cases of radial dynamic air gap eccentricity (RDAGE) and radial dynamic static hybrid air gap eccentricity (RHAGE). Firstly, the magnetic flux density (MFD) is derived for normal and radial air gap eccentricity (RAGE) faults, and detailed EF expressions are obtained before and after the RAGE fault. The finite element analysis (FEA) and experimental studies were performed on a four-pole DFIG at a speed of 1500 rpm to verify the proposed theoretical analysis. It is shown that RSAGE only enlarges the EF/end winding vibration and does not introduce new frequency components. RDAGE not only increases EF/end winding vibra... [more]

In order to improve the adaptability of low-salinity waterflooding technology in some areas where freshwater resources are scarce, we aimed at implementing the low-salinity effect (LSE) in carbonate reservoirs through tuning injection seawater composition. LSE of ion tuning water (ITW) was verified by the results of core flooding tests, obtaining a water-free recovery factor of 50.7% and cumulative oil recovery of 77.2%. The micro mechanisms behind it were revealed via direct force-measuring and Zeta parameter (Zetap) measuring. Our results are expected to provide a new LSW strategy via tuning injection seawater composition in the case of carbonate reservoirs.

The imbibition phenomenon widely exists in nature and industrial applications. It is of great significance to study the mechanism of imbibition and the influence laws of related factors. In this paper, based on the assumption of interacting capillaries, a capillary bundle model of counter-current imbibition is established. In addition, the characteristics of imbibition and the influences of capillary size and fluid viscosity are analyzed. The results show that water is imbibed into the smaller capillaries and expelled from the larger capillaries. The rate of the meniscus in water-imbibition capillaries is proportional to the square root of time. In the interacting capillaries, oil production by counter-current imbibition decreases and then increases gradually with the increase of the capillary diameter difference. When the total cross-sectional area of the capillary remains unchanged, the cross-sectional area of the total water-imbibition capillaries is affected by the size distributio... [more]

Capillary trapping of gas in porous media is important for many processes such as oil recovery and gas geo-sequestration. Foam can mitigate gravity override and viscous fingering of gas by reducing its relative permeability through gas trapping. However, there are limited studies dedicated to understanding how foam assists in gas trapping, the best mode of foam injection for trapping, and its application in geo-sequestration. This paper uses an initial−residual saturation analysis to investigate foam-assisted capillary trapping during the surfactant alternating gas (SAG) injection process in saline aquifers. More specifically, we studied the effects of pore geometric properties, in situ generated foam, and surfactant concentration on gas trapping efficiency and final residual gas saturation, Sgr. First, NMR surface relaxometry measurements were carried out on the rock samples to indicate the mean pore sizes of the rocks. A series of core flooding tests, equipped with resistivity measur... [more]

Hydrogen as an energy carrier is a promising alternative to fossil fuels, and it becomes more and more popular in developed countries as a carbon-free fuel. The low boiling temperature of hydrogen (20 K or −253.15 °C) provides a unique opportunity to implement superconductors with a critical temperature above 20 K such as MgB2 or high-temperature superconductors. Superconductors increase efficiency and reduce the loss of energy, which could compensate for the high price of LH2 to some extent. Norway is one of the pioneer countries with adequate infrastructure for using liquid hydrogen in the industry, especially in marine technology where a superconducting propulsion system can make a remarkable impact on its economy. Using superconductors in the motor of a propulsion system can increase its efficiency from 95% to 98% when the motor operates at full power. The difference in efficiency is even greater when the motor does not work at full power. Here, we survey the applications of liquid... [more]

Threshold pressure gradient (TPG) is a key parameter determining the pore-scale fluid dynamics. In tight gas reservoirs, both gas and water exist in the porous rock, and the existing water can be divided into irreducible and movable water. However, how movable water saturation will influence TPG has not yet been investigated. Therefore herein, nuclear magnetic resonance (NMR) and high-pressure mercury intrusion (HPMI) experiments were performed to determine pore-scale water distribution, movable water saturation, and pore throat distribution in the core plugs. Subsequently, the air bubble method was used to measure TPG as a function of movable water saturation and permeability inside tight gas core plugs, finding that TPG increased from 0.01 MPa/m to 0.25 MPa/m with the movable saturation increased from 2% to 35%. Finally, a semi-empirical model was derived to describe the correlation between TPG, movable water saturation, and permeability, which performed better than previous models i... [more]

This work presents a comparative analysis among four power MOSFET technologies: conventional Silicon (Si), Superjunction (SJ), Silicon Carbide (SiC) and Gallium Nitride (GaN), indicating the voltage, current and frequency ranges of the best performance for each technology. For this, a database with 91 power MOSFETs from different manufacturers was built. MOSFET losses are related to individual characteristics of the technology: drain-source on-state resistance, input capacitance, Miller capacitance and internal gate resistance. The total losses are evaluated considering a drain-source voltage of 400 V, power levels from 1 kW to 16 kW (1 A−40 A) and frequencies from 1 kHz to 500 kHz. A methodology for selecting power MOSFETs in power electronics applications is also presented.

Transverse vibration of drillpipe in coring drilling is undesirable. Here, the influence of the core on drillpipe vibration is considered for the first time. Attention is focused on the vibrations of the coring drillpipe as these vibrations lead to contact and collision between drillpipe and core. A reduced-order model of drill string motion is established considering fluid load and core constraints. This model considers fluid action as distributed load and drillpipe as beam structure. The constraint of the core on lateral vibration of the drillpipe is simplified as a nonlinear force. The method of multiple scales is used to analyze the disturbance of the drillpipe’s primary resonance and harmonic resonance, and the influence law of different parameters on the drillpipe resonance is obtained. The results show that damping inhibits resonance vibration, and external excitation determines the resonance type. The existence of the core will aggravate the resonance vibration of the drillpipe... [more]

Baikouquan oil field is composed of multiple interbedded, thin, low-permeability layers, which are required to vertically fracture multiple layers and to create complex fractures for economic development. However, conventional fracture technologies create a single, simple fracture, having poor feasibility for this field. Therefore, we conducted research on fracturing technology by spontaneously selecting geologic sweet spots based on diversion. This technology can vertically fracture the thin layers one by one and horizontally divert the fracture to non-depleted areas. Firstly, a triaxial diverted fracturing experiment approach was setup, and then diverted fracturing experiments were carried out to verify the feasibility of diverted fracturing and to study the fracture geometry and the law of diversion. Next, experiments were carried out to evaluate the performance of the diversion agents. The valuated properties comprise the diversion pressure, stability time, and degradation based on... [more]

Credit default prediction for the energy industry is essential to promoting the healthy development of the energy industry in China. While previous studies have constructed various credit default prediction models with brilliant performance, the class-imbalance problem in the credit default dataset cannot be ignored, where the numbers of credit default cases are usually much smaller than the number of non-default ones. To address the class-imbalance problem, we proposed a novel CT-XGBoost model, which adds to XGBoost with two algorithm-level methods for class imbalance, including the cost-sensitive strategy and threshold method. Based on the credit default dataset consisting of energy corporates in western China, which suffers from the class-imbalance problem, the CT-XGBoost model achieves better performance than the conventional models. The results indicate that the proposed model can efficiently alleviate the inherent class-imbalance problem in the credit default dataset. Moreover, w... [more]

In recent years, connected automated vehicles (CAVs) have attracted much attention, and the coordination strategy of CAVs in isolated intersections has been widely discussed. However, these algorithms for isolated intersections cannot be directly applied in a multi-intersection road network (MiRN). The coordination strategy in the MiRN requires further investigation. This paper proposes a two-tier strategy for CAV coordination in the MiRN. First, we analyze the coordination problem in isolated intersections and formulate it as a mixed-integer programming problem. Then, for the MiRN, we propose a consensus prediction method to estimate the travel time for CAVs with different paths. Finally, a novel coordination approach is given, showing how to determine the optimal path for CAVs. The experimental results demonstrate the efficiency of the proposed strategy under various traffic flow rates. Compared with the fixed signal time assignment method and the actuated signal time assignment meth... [more]

It is critical to address energy issues as we move through the first half of the twenty-first century, as societies become firmly aware of the consequences of resource scarcity and the disastrous consequences of climate change from human activity (especially heavy industry) [...]

Aiming to solve the problems of poor CO2 displacement efficiency and serious gas-channeling and low well-opening rates in ultra-low permeability reservoirs, we carry out CO2 displacement experiments under different permeability reservoirs by using different development methods, water drive to gas drive procedures, and different fracture positions to clarify the effects of physical formation properties, injection methods, and fracture parameters on CO2 displacement efficiency in C8 ultra-low permeability reservoirs. The experimental results show that the recovery degree of CO2 miscible drive increases with an increase in permeability. When the gas−oil ratio is greater than 2000 m3/m3, serious gas channeling can be observed in both the miscible drive and immiscible drive. In addition, when the water drive is altered to be a gas drive, the water cut of 0.45 mD and 0.98 mD cores decreased, and the recovery degree increased by 13.4% and 16.57%, respectively. A long fracture length will dete... [more]