This paper investigates magnet demagnetization characteristics of the modular permanent magnet machine. The influence of flux gaps on magnet flux density, losses distribution, torque and demagnetization are analyzed for different operating conditions. The magnet demagnetizations caused by three sources, such as the PM field, the armature field, and the magnet temperature rise, are individually investigated using the frozen permeability method. Furthermore, coupled electromagnetic (EM)-thermal modelling is also adopted in this paper to fully reveal the advantages of the modular machine in improving machine EM performances. This is essential due to the temperature-dependent properties of the machines, such as the magnet remanence, coercivity, and copper resistivity. For comparison propose, the EM performances with a particular focus on the demagnetization withstand capability for both the modular and non-modular machines are investigated based on the EM-thermal coupling. It is found that... [more]

The key to ensuring the economic feasibility of EGS mainly includes two points. On the one hand, it is necessary to ensure the connectivity of the artificial fracture network; on the other hand, it is necessary to determine the most efficient geothermal energy exploitation mode. Most previous studies have only focused on one of the points. To restitute the entire geothermal energy development process, the two parts should be combined to conduct research. In this study, a random fractured medium model was established based on the TOUGH2-BIOT simulation program and the whole process of reservoir stimulation was analyzed. According to the results of reservoir stimulation, different geothermal energy exploitation schemes are set up, and the heat transfer efficiency of the conventional double vertical wells, the horizontal wells, and the double-pipe heat exchange system are comparatively analyzed. The results show that reservoir reconstruction is mainly divided into three stages: In the fir... [more]

With the increasing constraints on energy and resource markets and the non-decreasing trend in energy demand, the need for relevant clean energy generation and storage solutions is growing and is gradually reaching the individual home. However, small-scale energy storage is still an expensive investment in 2022 and the risk/reward ratio is not yet attractive enough for individual homeowners. One solution is for homeowners not to store excess clean energy individually but to produce hydrogen for mutual use. In this paper, a collective production of hydrogen for a daily filling of a bus is considered. Following our previous work on the subject, the investigation consists of finding an optimal buy/sell rule to the grid, and the use of the energy with an additional objective: mobility. The dominant technique in the energy community is reinforcement learning, which however is difficult to use when the learning data is limited, as in our study. We chose a less data-intensive and yet technica... [more]

The performance degradation issue caused by carbon deposition has limited the commercial application of natural-gas-fueled solid oxide fuel cells. Most previous corresponding studies are based on thermodynamic equilibrium analyses, while long-term transient evaluation work is lacking. Therefore, a transient multi-physics numerical model is developed in present work. The corresponding long-term performance degradation evaluation is then conducted. The results show that, for a direct internal reforming solid oxide fuel cell, the increase in carbon deposition and deterioration of performance degradation were concentrated in the first 180 days of steady−state operation and slowed down at the later stage. The electrode inlet rapidly developed a high concentration of carbon deposition after 180 days of steady−state operation. The deposited carbon deteriorated the gas transport and decayed reaction activity within the porous electrode, eventually inducing a deactivation zone with 0 current de... [more]

Gas hydrates have been considered as a new energy that could replace conventional fossil resources in the future because of their high energy density, environmental friendliness, and enormous reserves. To further analyze the potential distribution of gas hydrate stability zones (GHSZ) and the formation of a gas hydrate system in the Shenhu area of the South China Sea (SCS), a 3D petroleum simulation model (PSM) was built from 3D seismic interpretations and all available geological data. Based on the thermal calibration of the 3D model, the evolution of the GHSZ, hydrocarbon generation and migration, and the formation and accumulation of gas hydrates were simulated for the first time in the area. Thermal simulation shows that the methane source of gas hydrate originated from shallow biogenic gas and deep thermogenic gas. Most areas are dominated by shallow biogenic gas, while, only about 3% of the deep thermogenic gas derived from Enping Formation source rock and contributed to the gas... [more]

CO2 geological storage, which is an effective way to reduce CO2 emissions, is of great significance to mitigate the current greenhouse effect. In long-term CO2 storage, although the chemical reaction rate of CO2−brine−rock is slow, it can significantly change the mineral composition of rock and the structure and properties of pores and joints, and then change the transport process and distribution state of CO2 in porous media. Therefore, a simplified 2D geological model is established based on the geological data of the Shihezi Formation in the Ordos Basin, China. The mechanism of the CO2−brine−rock reaction and its effect on mineral transformation and pore permeability are studied. In the early stage of CO2 geological sequestration, the rate of CO2 intrusion into the caprock is fast, the CO2−brine−rock reaction in the early stage is mainly a dissolution reaction, and the porosity and permeability of the caprock show an increasing trend. During the period from 100 to 1000 years of CO2... [more]

Numerical reservoir simulation, which includes the construction and operation of a model that performs similarly to a real-world reservoir, is an effective method for exploring complex reservoir issues. Due to the complexity of constructing reservoir environments for experiments, numerical simulation is a vital method for studying flow behavior under reservoir conditions. In this study, a black-oil modeling simulator was used to construct, simulate, and evaluate a conceptual hydrocarbon reservoir model. The model evolved by drilling two production wells and one injection well in two cases. The first case consisted of two horizontal production wells and one injection well, while the second consisted of two vertical production wells and an injection well. In total, 25 simulation runs were performed, and the results showed that horizontal wells perform better than vertical wells in terms of productivity, with a field oil production total of 1,930,000 m3. This is significantly higher than... [more]

Spatiotemporal evolution and fluctuation characteristics of a centrifugal compressor are investigated by numerical simulation under near-stall conditions and with a high mass-flow rate. The large-eddy simulation (LES) for unsteady computations is implemented in the numerical simulation of unsteady flow. The internal flow physical mechanism of the centrifugal compressor is presented at a high mass-flow rate (1.1 Qn) and low mass-flow rate (0.8 Qn, near-stall). The spatiotemporal evolution of the velocity and streamline for the internal flow of the centrifugal compressor demonstrates that a lot of large-scale eddies near the tongue are transformed into small-scale ones at high mass-flow rates. High mass-flow rate resulted in excessive fluid velocity in the impeller. A large amount of impact loss massive backflow appears near the tip clearance, and boundary layer separation of the suction surface emerges firstly and at a low mass-flow rate. Considerable flow loss occurs in the centrifugal... [more]

A deep understanding of the pore-scale fluid flow mechanism during the CO2 flooding process is essential to enhanced oil recovery (EOR) and subsurface CO2 sequestration. Two-phase flow simulations were performed to simulate the CO2 flooding process based on the phase-field method in this study. Two-dimensional models with random positions and sizes of grains of circular shape were constructed to reproduce the topology of porous media with heterogeneous pore size distributions in the reservoir rock. A multiple-parameter analysis was performed to investigate the effects of capillary number, viscosity ratio, wettability, density, gravity, interfacial tension, and absolute permeability on the two-phase fluid flow characteristics. The results indicated that when the capillary number and viscosity ratio were large enough, i.e., log Ca = −3.62 and log M = −1.00, the fingering phenomenon was not obvious, which could be regarded as a stable displacement process. CO2 saturation increased with th... [more]

This paper presents a novel design approach of a Petri-net-based cyber-physical system (CPS). The idea is oriented toward implementation in a field-programmable gate array (FPGA). The proposed technique permits error detection in the system at the early specification stage in order to reduce the time and prototyping cost of the CPS. Due to the state explosion problem, the traditional verification methods have exponential computational complexity. In contrast, we show that under certain assumptions, the proposed algorithm is able to detect possible errors in the system even in cubic O(|T|2|P|) time. Furthermore, all the required steps of the proposed design method are presented and discussed. The idea is illustrated by a real-life case study example of a traffic light crossroad. The system was modelled, analysed, implemented, and finally validated within the FPGA device (Virtex-5 family).

The continuum theory-based models, which include solid stress models and gas-solid drag models, are required for the modeling of gas-solid flows in the framework of the Eulerian−Eulerian method. The interactions among particles are characterized by their diverse behaviors at different flow regimes, including kinetic motion, particle−particle collision and enduring friction. It is difficult to describe the particle behaviors at various regimes by mathematical methods accurately. Therefore, it is very important to develop proper solid stress models that can capture the inherent characteristics of the flow behaviors. In addition, the gas-solid fluidization system is a typical heterogeneous system, which exhibits locally inhomogeneous structures such as bubbles or particle clusters with different shapes and sizes. Due to these inhomogeneous characteristics, the gas-solid drag model has become one of the key challenges in the simulation of gas-solid flows. Various forms of constitutive rela... [more]

In this paper, a competing risks model with dependent causes of failure is considered under left-truncated and right-censoring scenario. When the dependent failure causes follow a Marshall−Olkin bivariate exponential distribution, estimation of model parameters and reliability indices are proposed from classic and Bayesian approaches, respectively. Maximum likelihood estimators and approximate confidence intervals are constructed, and conventional Bayesian point and interval estimations are discussed as well. In addition, E-Bayesian estimators are proposed and their asymptotic behaviors have been investigated. Further, another objective-Bayesian analysis is also proposed when a noninformative probability matching prior is used. Finally, extensive simulation studies are carried out to investigate the performance of different methods. Two real data examples are presented to illustrate the applicability.

The formation shear-wave (S-wave)’s velocity information around a borehole is of great importance in evaluating borehole stability, reflecting fluid invasion, and selecting perforation positions. Dipole acoustic logging is an effective method for determining a formation S-wave’s velocity radial profile around the borehole. Currently, the formation S-wave’s radial-profile inversion methods are mainly based on the impacts of radial velocity changes of formations outside the borehole on the dispersion characteristics of dipole waveforms, without considering the impacts of an acoustic tool on the dispersion curves in the inversion methods. Accordingly, the inversion accuracy is greatly impacted in practical data-processing applications. In this paper, a novel inversion algorithm, which introduces equivalent-tool theory into the shear-velocity radial profile constrained-inversion method, is proposed to obtain the S-wave’s slowness radial profile. Based on the equivalent-tool theory, the aco... [more]

This paper presents the comparisons between two types of switched reluctance machines (SRMs) and SRM converters. An SRM with a segmental rotor is compared with a conventional SRM (CSRM), and an SRM converter containing a passive boost circuit is compared with a conventional asymmetric half-bridge (AHB) converter. The segmental SRM has an asymmetric rotor with a segmented structure. The four rotor segments are made of steel laminations. Two segments are misaligned with the other two by 15 degrees. The torque ripple of the SRM with this structure is decreased, and the static torque is increased compared to a conventional SRM. The boost converter comprises a front-end circuit and a conventional AHB converter. The front-end circuit boosts the voltage level. The boosted voltage accelerates the rising and falling progress of the phase current. In this way, the SRM can obtain a greater speed and a smaller torque ripple. The comparison is conducted in simulation and validated through the exper... [more]

With the advancement of data-acquisition systems, information technology, and network technologies, the energy and power system has entered the deep integration of the cyber and physical sides as known as cyber-physical energy and power system (CPEPS) leading to more attention from researchers and practitioners in industry. The feedback loops in which physical processes affect cyber parts and vice versa, therefore, can gain greater efficiency, resilience, and intelligence through the data exchange process between two layers. The concept of CPEPS has been existed for a long time and its applications are gradually increasing in the real world, however, there has been still many potential risks and challenges in the research and development process. Simulation method is a common and simple approach for the purpose of analyzing, evaluating, and considering solutions before actual implementation. For this purpose, this paper provides first the framework of CPEPS, and current applications an... [more]

Liquid hydrogen has been studied for use in vehicles. However, during the charging process, liquid hydrogen is lost as gas. Therefore, it is necessary to estimate and reduce this loss and simulate the charging process. In this study, the initial charging process of a vehicle liquid hydrogen tank under room temperature and atmospheric pressure conditions was numerically investigated. A transient thermal-fluid simulation with a phase-change model was performed to analyze variations in the volume, pressure, mass flow rate, and temperature. The results showed that the process could be divided into three stages. In the first stage, liquid hydrogen was actively vaporized at the inner wall surface of the storage tank. The pressure increased rapidly, and liquid droplets were discharged into the vent pipe during the second stage. In the third stage, the mass flow rates of liquid and hydrogen gas at the outlet showed significant fluctuations, owing to complex momentum generated by the evaporatio... [more]

Polyvinylidene fluoride and its copolymers can be used as active materials for energy harvesting and environmental sensing. Energy harvesting is one of the most recent research techniques for producing stable electrical energy from mechanical sources. Polyvinylidene fluoride−trifluoroethylene (PVDF-TrFE) is applicable for sensors and self-powered devices such as medical implants and wearable electronic devices. The preparation of electrospun P(VDF-TrFE) nanofibers is of great interest for the fabrication of sensors and self-powered devices, nanogenerators, and sensors. In this regard, it is necessary to investigate the effects of various parameters on the morphology and piezoelectric output voltage of such nanofibers. In this study, we have examined the effect of concentration and feed rate on the nanofiber diameter. It has been found that by increasing the concentration and feed rate of the polymer solution, the diameter of the nanofibers increases. The experimental results and the fi... [more]

Currently, thermal power plants operating on hydrocarbon fuels (gas, fuel oil, peat, shale, etc.) are one of the main sources of electricity. An effective and promising method for suppressing harmful emissions (NOx, carbon oxides, soot) from the combustion of fossil fuels is the injection of steam into the combustion chamber. The influence of various mathematical submodels was studied on the accuracy of the numerical simulation of the process of n-heptane combustion in a laboratory burner with steam additive to the reaction zone as a promising chemical engineering method for the disposal of substandard liquid fuels and combustible waste with the production of thermal energy. The problem was solved in a three-dimensional stationary formulation. Systematic verification of these submodels, and a comparison of the results of the calculation with the experimental data obtained were carried out. The comparison with the experimental data was carried out for gas components and temperature dist... [more]

Real-time battery SOX estimation including the state of charge (SOC), state of energy (SOE), and state of health (SOH) is the crucial evaluation indicator to assess the performance of automotive battery management systems (BMSs). Recently, intelligent models in terms of deep learning (DL) have received massive attention in electric vehicle (EV) BMS applications due to their improved generalization performance and strong computation capability to work under different conditions. However, estimation of accurate and robust SOC, SOH, and SOE in real-time is challenging since they are internal battery parameters and depend on the battery’s materials, chemical reactions, and aging as well as environmental temperature settings. Therefore, the goal of this review is to present a comprehensive explanation of various DL approaches for battery SOX estimation, highlighting features, configurations, datasets, battery chemistries, targets, results, and contributions. Various DL methods are criticall... [more]

Supercritical CO2 fracturing has unique advantages for improving unconventional reservoir recovery. Supercritical CO2 can penetrate deep into the reservoir and increase reservoir reform volume, and it is less damaging to reservoir and easy to flow back. However, when the supercritical CO2 flows as the sand-carrying fluid in the fracture, the settlement of the proppant is still worth studying. Based on the study of supercritical CO2 density and viscosity properties, assuming that the reservoir has been pressed out of the vertical crack by injecting prepad fluid, the proppant characteristics in sand-carrying fluid under different conditions were studied by numerical simulation. After the analysis, the proppant accumulation and backflow will occur at the end of the crack. Large sand diameters, high fluid flow rates, high sand concentrations, high reservoir temperatures, and low reservoir pressures can help to shorten deposition time, and the small particle size, high fluid flow rate, low... [more]

Research into condensate gas reservoirs in the oil and gas industry has been paid much attention and has great research value. There are also many deep condensate gas reservoirs, which is of great significance for exploitation. In this paper, the seepage performance of deep condensate gas reservoirs with natural fractures was studied. Considering that the composition of condensate gas changes during the production process, the component model was used to describe the condensate gas seepage in the fractured reservoir, modeled using the discrete fracture method, and the finite element method was used to conduct numerical simulation to analyze the seepage dynamic. The results show that the advancing speed of the moving pressure boundary can be reduced by 55% due to the existence of threshold pressure gradient. Due to the high-speed flow effect in the near wellbore area, as well as the high mobility of oil, the condensate oil saturation near the wellbore can be reduced by 42.8%. The existe... [more]

Internal combustion engine (ICE) exhaust gases provide a high amount of energy which is partially lost to the environment. Such energy can be recovered with a turbocharger turbine or other after-treatment device. As the engine exhaust flow varies not only with the engine load but also with the opening and closing of the exhaust valves, a proper matching between the engine and the turbine should be established to maximize the recovery of waste energy. That is why a twin-scroll or dual turbocharging system is implemented, especially in multi-cylinder engines. Such systems require a very complex pipeline to eliminate the interference of the exhaust pulses between the adjacent cylinder ignitions. In this study, the two-stage, multi-channel turbine system was investigated for two different rotor geometries: the old, high-performance rotor A and the smaller but more modern rotor B, which was scaled to match rotor A. Both geometries were compared at three different turbine speeds and variable... [more]

An increase in consumption and inefficiency, fluctuating trends in demand and supply, and a lack of critical analytics for successful management are just some of the problems that the energy business throughout the world is currently facing. This study set out to assess the potential contributions that AI and ML technologies could make to the expansion of energy production in developing countries, where these issues are more pronounced because of the prevalence of numerous unauthorized connections to the electricity grid, where a large amount of energy is not being measured or paid for. This study primarily aims to address issues that arise due to frequent power outages and widespread lack of access to energy in a wide range of developing countries. Findings suggest that AI and ML have the potential to make major contributions to the fields of predictive turbine maintenance, energy consumption optimization, grid management, energy price prediction, and residential building energy deman... [more]

Energy consumption calculations and thermal comfort conditions assessment are crucial issues in building simulations when using Building Energy Performance Simulation (BEPS) tools. The available software has been separately validated under different boundaries and operating conditions. Consequently, the predicted output of the same building simulated with two separate software can disagree. This issue is relevant not only for research purposes but also for professionals who need to compare the energy performance of the same building with different simulation engines. This work aims at contributing to the field in two ways. Above all, it clarifies the preparation of the building model and the correct definition of input data and boundary conditions when different software are used (IDA ICE and Design Builder/Energy Plus). In addition, it compares the output (energy and indoor temperatures) of two BEPS for the same building (in different configurations) exposed to the same weather condit... [more]

This paper presents the design and modeling procedure of a wireless power transfer (WPT) system applied to In-wheel-motor (IWM). The system is designed to transmit over 10 kW of power following the physical constraints faced by the IWM applications. The issues of coil misalignment and load change are discussed as particular scenarios in IWM. The finite element model is built for circular, rectangular, and double-D coils, finding that the rectangular coil has the best performance considering the transmission interval and misalignment resistance. The circuit design procedure is presented, and the analysis of the influence of load and mutual inductance change on the WPT system is addressed. Finally, the performance of the design is verified with experiments on a full-scale prototype. It is proved that the WPT system successfully transmits 10 kW of power with a DC−DC efficiency of over 90% under a transmission interval of 140 mm. The output voltage is stable under 40 mm coil misalignment s... [more]