Characteristics Of System Research Articles

Application and analysis of superconducting magnetic eddy current heater used in wind thermal power generation system

AbstractIn order to cope with the grid fluctuation caused by large‐scale wind power connected to the grid, the wind thermal power generation system has been proposed and extensively studied. The wind thermal power generation system uses a wind turbine to drive a heat generation device to heat the heat storage medium, which is further exchanged to drive a turbine to generate electricity. A superconducting magnetic eddy current heater (SMH) is proposed for the characteristics of wind thermal power generation system, which uses non‐resistive, large current‐carrying superconducting coils for excitation, and has high output efficiency and power density. The working principle of magnetic eddy current heating is analysed, and the structure of SMH with no ferromagnetic material and two heating screens inside and outside is proposed according to the characteristics of SMH. An analytical model of the SMH is established, and the influence of the structure and materials of the SMH on the magnetic field distribution is analysed. Based on this, a 22‐pole SMH was designed and analysed for output power at 10–20 rpm. A three‐dimensional magnetism‐stress combined analysis model of SMH is established, and the strain and stress characteristics of SMH are simulated under the condition of maximum output power, which verifies the feasibility of the mechanical properties of existing superconducting materials for application in SMH.

Experimental investigation on the characteristics of a controllable separate heat pipe-based cold storage temperature control system

PCM cold storage systems have been widely employed in household refrigerators due to their economy and efficiency. However, the PCM heat transfer process is out of effective control, limiting the accurate temperature control ability of the system. Herein, a controllable separated heat pipe that can regulate heat transfer is introduced into the PCM cold storage system to resolve its issues. A novel controllable separate heat pipe-based cold storage temperature control system is proposed. The dynamic temperature control ability and cold storage characteristics of the system under various operating conditions are revealed through experiments. As a result, the spatial inhomogeneity of the temperature field of the PCM is discovered which is related to the unsteady heat transfer between the PCMs in different regions and to the on–off state of the controllable separate heat pipe. In the discharging mode, the stable temperature control time of the compartment decreases by 53% when the temperature decreases from 7 °C to 1 °C. In addition, a lower inlet temperature of the ethylene glycol solution results in faster cold storage rates and greater temperature differences of the PCMs in different regions (the maximum temperature difference is 3.47 °C when the inlet temperature is −26 °C). Moreover, the results of door opening experiments show that the temperature can be controlled within an accuracy of 2.5 °C when the door opening time is 60 s, demonstrating the temperature regulation ability of the system. The results verify the feasibility of the technical route and provide a valuable reference for the optimization of precise temperature control systems.

Analysis and experimental research of transient temperature rise characteristics of high-speed cylindrical roller bearing

In this paper, on one hand, the time-varying characteristics of the heat source and thermal boundary conditions of the high-speed spindle system were analyzed considering the thermal-structural coupling effect. And a transient bearing temperature field prediction method combining the thermal network method and finite element method was proposed. Furthermore, the relationships between time step, calculation efficiency and calculation results were analyzed. On the other hand, a online real-time monitoring system of the transient temperature of the cylindrical roller bearing inner ring for maximum speed of 13,000 r/min was designed and implemented using fibre optic sensing technology. Comparing with the conventional static thermal analysis results, it is verified that the simulation method proposed in this paper has higher accuracy. This paper provides a new approach for analysing and testing the thermal characteristics of high-speed spindle system.

Vibration behavior and power transmission of coupled plate structures with embedded acoustic black holes joined at an arbitrary angle

The Acoustic Black Hole (ABH) technology is widely recognized for its passive vibration and noise attenuation capabilities, characterized by lightweight and high efficiency. Exploring the dynamic behavior and energy transmission characteristics of the ABH coupled-plate system is a novel endeavor that provides a theoretical foundation for applying ABH structures in complex coupled systems. In this work, a semi-analytical dynamic model for the ABH coupled-plate system (comprising an ABH plate and a uniform plate) with an arbitrary connection angle is proposed by using the Rayleigh-Ritz framework. To ensure the continuity of high-order spatial derivatives at the edges, the modified version of the Fourier series is employed to describe the vibration displacement fields for transverse and in-plane vibration components. This enables the proposed model to determine the necessary derivatives of relevant quantities, namely the structural intensity and power flow, which facilitates the description of energy transmission behaviors in the ABH coupled-plate structure. Firstly, the convergence characteristics of the model are studied and the accuracy of modal information and dynamic response is verified through the comparison of those calculated from the finite element method (FEM), additionally, the experiment is carried out to verify the proposed model. Subsequently, several numerical examples are presented to study the vibrational characteristics of the ABH coupled-plate system and the good vibration attenuation of the ABH coupled-plate is observed as well. Finally, the vibrational energy transmission results are obtained and the influence of some important system parameters such as coupling angles on energy transmission characteristics in such systems are investigated. This work can shed some new light on ABH structures with potential application to such complex coupled-plate structures.

Construction of power load control and management terminal operation system based on machine learning technology

With the increasing Power Load (PL), the operation of the power system is facing increasingly severe challenges. PL control is an important means to ensure the stability of power system operation and power supply quality. However, traditional PL control methods have limitations and cannot meet the requirements of load control in the new era of power systems. This is because with the development of modern industry and commerce, the demand for electricity is gradually increasing. This article constructed a PL control and management terminal operating system based on machine learning technology to achieve intelligent management of PL, so as to improve the operational efficiency and power supply quality of the power system. This article identified the design concept of a PL control management terminal operating system based on machine learning technology by reviewing the current research status of PL control technology. Based on the operational characteristics and data characteristics of the power system, this article selected suitable machine learning algorithms to process and analyze load data, and established a prototype of a PL control and management terminal operating system based on machine learning technology, so as to realize intelligent processing and analysis of load data and conduct experimental verification. The experimental results show that through the comparative study of 6 sets of data in the tertiary level, the difference between the system and the real tertiary level is 0.079 kw, 0.005 kw and 0.189 kw respectively. Therefore, therefore, the average difference between the predicted value and the measured value of the PL system is about 0.091 kw. This indicated that the system had high accuracy and real-time performance in predicting PL, which could effectively improve the load control efficiency and power supply quality of the power system. The PL control management terminal operating system based on machine learning technology constructed in this article provided new ideas and methods for the development of PL control technology. In the future, system algorithms can be further optimized and a more intelligent PL control and management terminal operating system can be constructed to cope with the growing PL and increasingly complex power system operating environment.

Simulation Experiment Design and Control Strategy Analysis in Teaching of Hydrogen-Electric Coupling System

Hydrogen energy, as a clean and green energy medium, is characterized by large capacity, extended lifespan, convenient storage, and seamless transmission. On the one hand, in the power system, hydrogen can be prepared by the electrolysis of water using the surplus power from intermittent new energy generation, such as photovoltaic and wind power, to increase the space for new energy consumption. On the other hand, it can be used to generate electricity from the chemical reaction between hydrogen and oxygen through the fuel cell and be used as a backup power source when there is a shortage of power supply. In this paper, based on the teaching practice, the conversion mechanism and coupling relationship between various forms of energy, such as photovoltaic energy, hydrogen energy, and electric energy, were deeply analyzed. Further, a hydrogen-electricity coupling digital simulation experimental system, including photovoltaic power generation, fuel cell, and electrolysis hydrogen system, was formed. Simultaneously, considering the synergy between hydrogen production and electricity generation businesses, as well as the demand for the efficient utilization and flexible regulation of multiple energy sources, eight sets of simulation experimental scenarios were designed. A cooperative control strategy for the hydrogen-electric coupling system was proposed and validated through simulation on the MATLAB/SIMULINK-R2023a platform. This study shows that the simulation system has rich experimental scenarios and control strategies, and can comprehensively and accurately demonstrate the multi-energy complementary and cooperative control characteristics of the hydrogen-electric coupling system.

Two-stage optimization of hydrogen and storage coordination for a multi-region flexible intermodal multi-energy port system

To address the issue of imbalanced electricity and hydrogen supply and demand in the flexible multi-energy port area system, a multi-regional operational optimization and energy storage capacity allocation strategy considering the working status of flexible multi-status switches is proposed. Firstly, based on the characteristics of the port area system, models for system operating costs, generation equipment, energy storage devices, flexible multi-status switches, and others are established. Secondly, the system is subjected to a first-stage optimization, where different regions are optimized individually. The working periods of flexible multi-status switches are determined based on the results of this first-stage optimization, targeting the minimization of the overall daily operating costs while ensuring 100% integration of renewable energy in periods with electricity supply-demand imbalances. Subsequently, additional constraints are imposed based on the results of the first-stage optimization to optimize the entire system, obtaining power allocation during system operation as well as power and capacity requirements for energy storage devices and flexible multi-status switches. Finally, the proposed approach is validated through simulation examples, demonstrating its advantages in terms of economic efficiency, reduced power and capacity requirements for energy storage devices, and carbon reduction.

CFD simulation for comparative of hydrodynamic effects in biochemical reactors using population balance model with varied inlet gas distribution profiles

Abstract The operational efficiency of the airlift reactors relies significantly on the aeration and mixing provided by the inlet system. The diffused aeration system is the most energy-intensive component affecting the operation of the bioreactor, accounting for 45–75 % of the energy costs. This study presents a coupled CFD-PBM to investigate the collective impacts of multiple bubble diameters, variations in inlet gas distribution types, and flow rates on the hydrodynamic characteristics of bubble columns. The simulation results were validated through comprehensive comparisons with experimental data. The experimental data and simulations of the single bubble size model (SBSM) and multi-bubble size model (MBSM) were compared, proposing an enhanced inlet gas distribution type. The results indicate a close resemblance between the MBSM data and the experimental results, with an error margin not exceeding 5 %. Moreover, different flow rates were found to cause varying sensitivities in the bubble size distribution (BSD) within the column. Furthermore, the simulation results validate the similarity between lift coefficients and critical diameters to experiments and shed light on favorable conditions for reactor design. The key findings of this study encompass: (1) the use of MBSM can accurately predict the tower system characteristics; (2) the column circulation is intensified with small inlet bubble size and high gas velocity, which is favorable for chemical reactions and microbial aggregation to proceed; and (3) the BSD is not sensitive to the inlet gas distribution type at high flow rates.

Family planning service disruptions in the first two years of the COVID-19 pandemic: Evidence from health facilities in seven low- and middle-income countries.

Many speculated that COVID-19 would severely restrict the delivery of essential health services, including family planning (FP), but evidence of this impact is limited, partly due to data limitations. We use cross-sectional data collected from regional and national samples of health facilities (n = 2,610) offering FP across seven low- and middle-income countries (LMICs) between 2019 and 2021, with longitudinal data from four geographies, to examine reported disruptions to the FP service environment during COVID-19, assess how these disruptions varied according to health system characteristics, and evaluate how disruptions evolved throughout the first two years of the pandemic, relative to a pre-pandemic period. Findings show significant variation in the impact of COVID-19 on facility-based FP services across LMICs, with the largest disruptions to services occurring in Rajasthan, India, where COVID-19 cases were highest among geographies sampled, while in most sub-Saharan African settings there were limited disruptions impacting FP service availability, method provision, and contraceptive supplies. Facility-reported disruptions to care were not reflected in observed changes to the number of FP clients or types of stockouts experienced in the first two years of the pandemic. Public and higher-level facilities were generally less likely to experience COVID-19-related disruptions to FP services, suggesting policy mitigation measures-particularly those implemented among government-operated health facilities-may have been critical to ensuring sustained delivery of reproductive healthcare during the pandemic.

Optimization of characteristic parameters of rectangular solar chimney adapted to agricultural greenhouses

In order to build a composite application scenario for the synergistic development of clean energy generation and agricultural production, this research designs a solar chimney equipped with a rectangular collection system according to the structural characteristics of agricultural greenhouses. With collector efficiency as the primary objective and theoretical power as the secondary objective, the infusion angle is designed for the connecting section between the collection system and the chimney from the perspective of reducing the local resistance loss, and the transition factor ζ is introduced to define it accurately. Response surface methodology was then used to analyze the effect of the level of key system characteristics on collector efficiency and static pressure, and a regression model was developed to determine the best combination within the target optimization range. Results show that the infusion angle prevents too much solar energy from being lost in the vortex by reducing the local resistance loss, which increases the collector efficiency of the system. And when the transition factor is 0, the divergence angle is 2.86°, and the inlet height is 0.05 m, the collector efficiency and static pressure reach 48.75 % and −6.1 pa, respectively, which are 213 % and 563 % higher than the original model.

Study on long-term operation characteristics of the medium-deep ground source heat pump system with solar heat storage

Long-term heating operation of the medium-deep ground source heat pump (MGSHP) system will cause the underground temperature around the mid-deep borehole heat exchanger (MBHE) significantly lower than its initial value, which will reduce the operating efficiency of the MGSHP system. In some cases, the temperature of the circulating water in MBHE even is lower than the lowest value required by the heat pump unit, which will lead to operation failure of the unit. Attenuating the ground temperature decrease by storing heat underground during non-heating seasons is an effect way to maintain the heat extraction capacity of the MBHE. In this paper, the influence of storing solar energy underground during non-heating seasons on the long-term operating characteristics of the MGSHP system is studied. The MBHE heat transfer model which considers the heat storage process is developed and embedded in the software of TRNSYS. Based on the numerical simulation model of solar assisted mid-deep ground source heat pump (SAMGSHP) system built by TRNSYS, the long-term characteristics including the variations of the fluid temperature of the MBHE, the ground temperature distribution and the COP of the heat pump unit of the MGSHP system with heat storage during non-heating seasons are analyzed and compared with the case without heat storage. The results show that storing solar energy underground during non-heating seasons can effectively improve the ground temperature, significantly slow down the decline of the circulating water temperature of the MBHE in heating seasons and apparently increase the COP of the heat pump unit. The results can serve as a reference for engineering applications of MGSHP systems, especially those cannot completely meet the original design heating load.

Risk, sensitive analysis, and optimization of a new multi-generation system activated by solar and biomass energies

In recent years, the use of clean energies has become much more important due to the increase of environmental pollutants and the reduction of fossil fuel resources. Another important parameter in the establishment of energy systems is the assessment of the risks caused by the construction of the system and the provision of operational solutions to manage and reduce these risks. In this research, a new multi-generation system that is activated using solar and biomass energies has been evaluated thermodynamically and thermo-risky. This system consists of a Brayton cycle, a steam Rankine cycle, a transcritical CO2 cycle, a proton membrane electrolyzer (PEME) unit, and an internal combustion engine (ICE). A notable characteristic of the proposed system is its capability to recover waste heat from the gas turbine cycle, which is subsequently utilized to drive both a steam Rankine cycle and a transcritical CO2 cycle. The sensitivity analysis has been performed to investigate the effects of the input parameters on the system performance and finally, an optimization for the effective parameters of the system has been conducted. The results of the calculations show that the proposed system has energy and exergy efficiencies of 22.05 % and 15.93 %, respectively. The risk analysis was conducted by considering the potential hazards such as jet fires, jet of combusted gases, and system overpressure. The analysis indicates that the system poses a low level of risk. The overall risk, along with the risk per unit of system exergy, has been estimated at 4.247 × 10–8 injuries/year and 3.73 × 10–11 injuries/year.kW, respectively. In optimal conditions, the energy and exergy efficiency of the system reaches 25.79 % and 19.08 %.

Enhancing melting and solidification characteristics of a triple-pipe latent heat energy storage system via a wavy central wall with a sinusoidal fixed wavelength

This study aims to improve the melting and solidification characteristics of a triple-pipe heat storage unit by introducing a wavy middle plate with a sinusoidal fixed wavelength. The inner and outer tubes facilitate the flow of heat transfer fluids (HTFs), while the middle tube houses the phase change material (PCM). Various scenarios are examined to gauge the impact of the wavy central wall on the PCM's phase change performance, comparing liquid fraction and mean temperatures with cases featuring a straight middle plate. The primary goal is to pinpoint the optimal scenario with the shortest discharging/charging times and the highest rates of heat release/storage. The investigation commences by assessing the effects of middle wall thickness (2, 4, 6, and 8 mm) on the PCM's phase change characteristics, comparing liquid fraction and mean temperature with a straight middle plate. Subsequently, the influence of various sinusoidal wavelengths (250, 125, 50, and 25 mm) on both melting and solidification performances of the PCM is numerically examined to identify the optimum case. The research also delves into the effects of various sinusoidal amplitudes (2.5, 5.0, 7.5, and 10 mm) on the PCM's phase change process. In the final step, the capability of the wavy middle plate, with various phase shifts (0°, 90°, 180°, and 270°), in improving the PCM's phase change characteristics is analyzed. Numerical results highlight that, among the tested scenarios, the configuration with a 5 mm amplitude and a 25 mm wavelength (A5λ250) exhibits outstanding performance during both melting and solidification phases. A5λ250 showcases a 19.92 % reduction in melting time and a 2.44 % reduction in solidification time compared to other cases, coupled with a 22.55 % improvement in heat storage and a 3.48 % enhancement in heat release. However, introducing a phase shift in the melting process adversely affects system performance. Conversely, adjusting the phase shift of A5λ25 to 270° leads to enhancements in both solidification time and heat release rate. Specifically, solidification time improves by 0.86 %, and the rate of heat release increases by 0.66 W compared to A5λ25–0.

The CRISPR-Cas system in clinical strains of Acinetobacter baumannii: an in-silico analysis.

Acinetobacter baumannii is a relevant bacterium due to its high-resistance profile. It is well known that antimicrobial resistance is primarily linked to mutations and the acquisition of external genomic material, such as plasmids or phages, to which the Clustered Regularly Interspaced Short Palindromic Repeats associated with Cas proteins, or CRISPR-Cas, system is related. It is known that the system can influence the acquisition of foreign genetic material and play a role in various physiological pathways. In this study, we conducted an in-silico analysis using 91 fully assembled genomes of clinical strains obtained from the NCBI database. Among the analyzed genomes, the I-F1 subtype of the CRISPR-Cas system was detected showcasing variations in architecture and phylogeny. Using bioinformatic tools, we determined the presence, distribution, and specific characteristics of the CRISPR-Cas system. We found a possible association of the system with resistance genes but not with virulence determinants. Analysis of the system's components, including spacer sequences, suggests its potential role in protecting against phage infections, highlighting its protective function.

The determinants of school performance in selected MENA countries: what role of the education system’s characteristics?

Based on data from the 2011 TIMSS international survey related to the 2nd year of secondary school of eleven MENA countries, this work aims to identify the characteristics of the educational system that influence the students' academic performance in mathematics in these countries, while highlighting the case of Morocco. The estimation of an empty three-level model, to explain the probability of achieving a score of 400 points or more in mathematics, showed that a significant and non-negligible part (8.04%) of the total variance is due to the differences between the characteristics of the countries. The results of this study showed that, particularly in Morocco, students' academic performance could be improved by providing autonomy to schools to choose the syllabus, by making preschool a obligatory educational cycle and by increasing the volume of time reserved for teaching mathematics.

Research on improving low-frequency oscillation characteristics of wind power grid-connected power system with doubly-fed wind generator based on virtual impedance power system stabilizer

Research on improving low-frequency oscillation characteristics of wind power grid-connected power system with doubly-fed wind generator based on virtual impedance power system stabilizer

Incommensurate fractional-order analysis of a chaotic system based on interaction between dark matter and dark energy with engineering applications

Chaotic systems, characterized by their sensitivity to initial conditions and the presence of deterministic unpredictability, have garnered significant attention in various fields of science and engineering. Researchers have demonstrated a growing interest in recent years in identifying various physical systems as chaotic system, including but not limited to fluid dynamics, electrical circuits, and biological oscillators. In this study, a cosmological chaotic system that portrays the interaction between dark matter and dark energy is examined using incommensurate fractional-order analysis. The effects of incommensurate fractional orders are evaluated by means of phase portraits, bifurcation diagrams and Lyapunov exponents spectra. It is dedicated that wider chaotic regions are observed once the values of these incommensurate fractional orders are changed. Meanwhile, a hidden attractor is found based on the stability analysis and basin of attraction in the incommensurate fractional-order dark matter and dark energy (IFODMDE) chaotic system. These findings highlight the richer dynamic characteristics of the IFODMDE chaotic system. Furthermore, the identified hidden attractor is effectively employed in this study for various engineering applications, including chaos control, random number generator (RNG) design, and image encryption. The analytical results offer a more accurate description of real-world physical phenomena, thanks to the inclusion of incommensurate fractional orders. The application results prove the good randomness of the IFODMDE chaotic system.

Connecting the Dots: The Cerebral Lymphatic System as a Bridge Between the Central Nervous System and Peripheral System in Health and Disease.

As a recently discovered waste removal system in the brain, cerebral lymphatic system is thought to play an important role in regulating the homeostasis of the central nervous system. Currently, more and more attention is being focused on the cerebral lymphatic system. Further understanding of the structural and functional characteristics of cerebral lymphatic system is essential to better understand the pathogenesis of diseases and to explore therapeutic approaches. In this review, we summarize the structural components and functional characteristics of cerebral lymphatic system. More importantly, it is closely associated with peripheral system diseases in the gastrointestinal tract, liver, and kidney. However, there is still a gap in the study of the cerebral lymphatic system. However, we believe that it is a critical mediator of the interactions between the central nervous system and the peripheral system.

Substantiation of the range of changes in the elastic-damping and inertial characteristics of the oscillatory system of agricultural MES with mounted technological equipment

This article discusses the issue of substantiating the range of changes in the elastic-damping and mass-inertial characteristics of agricultural mobile power equipment (MES) with mounted technological equipment. Substantiation of the range of changes in the elastic-damping and inertial characteristics of an oscillatory system is an important stage in the design process of various mechanical systems and equipment. In this article, the authors present experimental data necessary for further studies of the springing system and present a study aimed at ensuring optimal operating conditions of the system, minimizing the level of vibrations and vibrations, predicting the behavior of the system in various operating conditions and modes. The article describes the research methods used, presents the results and draws conclusions. The research plays an important role in the design of agricultural MEAS aggregated with various technological equipment.

Wireless Power Transfer-Based Voltage Equalizer for Scalable Cell-String Charging

Wireless power transfer (WPT)-based voltage equalizer (VE) shows unique advantages due to its physical isolation. Meanwhile, the markets of high-power fast charging have imposed significant needs for high-voltage wireless charging systems. However, a WPT-based charging equalizer cannot support a large-scale cell-string. This paper proposes a wireless charging VE with modularity to balance cascaded cell-strings automatically using multiple coils. The WPT system's intrinsic high-frequency power is used to power the voltage multiplier (VM). Only two diodes and one capacitor are required for an extra cell, which enables fewer components and a simple structure. Circuit analysis and a one-transmitter-two-receiver charging equalization experiment validate the system's operating principles. The voltage gaps among eight ultra-capacitor (UC) cells are equalized from 1.1 V to 0.01 V, with an overall efficiency of 76.5% under a 35.2 V output. Non-ideal conditions with coupling mismatch and frequency shifts are also analyzed to reveal the system's characteristics. It contributes several ways to providing general modular wireless charging equalization solutions for large-scale cell-string with lower cost and higher scalability.