最新刊期
卷 55 ， 期 4 ， 2023
- 摘要：With the accelerated construction of the new power system and the continual improvement of intelligent power equipment, low-carbon and digital construction of electric power equipment have become an important trend. Among them, the accurate measurement of the magnetic field distribution of electrical equipment in power systems is the key of its health status evaluation, energy losses calculation and structural design optimization. A passive optical fiber magnetic field sensor was designed in this paper to meet the measurement requirements of the magnetic field generated from the electrical equipment and to solve the bottleneck problems of the environmentally friendly power equipment. This sensor realized the high-precision passive measurement of the external magnetic field, which was based on the coupling structure between the magnetic-mechanical conversion functional dielectric and fabry-perot (F–P) optical interference cavity. First of all, the extrinsic F–P interference structure was designed according to the F–P interference principle. Besides, the influence of different packaging materials on the sensitivity of the sensor was discussed by measuring the magnetic sensing properties of sensors with various materials. The sensing performance of the sensor under DC magnetic field was tested, and influence factors of the measurement range was studied to obtain a wide measurement range. Finally, the dynamic performance of the sensor was tested under the AC magnetic field according to the measurement requirements in the power system. The results showed that this sensor can realize real-time detections of the AC/DC magnetic field. The measurement range, sensitivity and resolution of the sensor were 0～120 mT, 447 pm/mT and 17 μT respectively. Meanwhile, it had excellent tracking properties for the AC magnetic field below 50 Hz, which proved the feasibility for its application in the passive magnetic field measurement of the new power system. Hence, the optical fiber magnetic field sensor proposed in this paper has the advantages of a wide measurement range and passive measurement characteristics, without the need of the battery replacement or the power supply from the induction, which meets the development requirements of low carbon power systems.关键词：magnetic field sensors;F–P interference;optical fiber;magneto-mechanical conversion functional dielectric
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发布时间：2024-01-10 - 摘要：Contact resistance of an electrical connection structure (ECR) is an important indicator to evaluate the reliability of the electrical contact system. The strap contact is an important electrical connection component in eco-friendly insulating gas GIS equipment. Its ECR will affect the total resistance of the equipment. Factors such as the excessive current flow, the conductor vibration, and the improper installation can also leads to poor electrical contact, local overheating of the strap contacts, insulation discharge and other failures, which is directly related to the operation stability of environmental protection gas GIS equipment. To study the mechanism and regularity of ECR, MATLAB and laser confocal microscope were used to capture the grayscale image of the contact area in this paper. The nominal contact area Aa and fractal dimension D of the contact area were obtained. Using the fractal theoretical model, the contact resistance of the strap contact was numerically calculated. The rationality and accuracy of applying the fractal theoretical model to analytically calculate the contact resistance of the electrical connection structure was verified through ECR test measurements. Since ECR is closely related to the actual contact area, the elastic deformation, the first elastic-plastic deformation, the second elastic-plastic deformation and the plastic deformation during the electrical contact process of the strap contact were studied. What's more, the effect of different fractal dimensions on the actual contact area of the electrical contact was studied. The research found that the fractal theoretical model can be used for the theoretical calculation of ECR for the strap contact of the GIS equipment. It was obtained that the larger the fractal dimension of the electrical contact surface, the earlier the contact deformation enters the elastic-plastic stage, and the easier it is to enter the second elastic stage. In the plastic deformation stage, the more complex the surface morphology, the smaller the actual contact area required to achieve the same bearing capacity. The research results are helpful for the optimal design of the eco-friendly insulating gas GIS electrical connection structure, and can provide a theoretical basis for the multi-physics calculation of the eco-friendly insulating gas GIS equipment electrical connection structure and the state evaluation of the electrical contact performance.关键词：fractal model;strap contact;contact resistance;elastic-plastic deformation;actual contact area
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发布时间：2024-01-10 - 摘要：The sag of the transmission line is an important index for its safe operation. Focusing on the calculation deviation of conductor sag caused by the non-uniform temperature distribution of transmission lines and the creep, the influence degree of the radial temperature and the creep on the sag calculation model was studied in this paper. Firstly, the finite element model of the conductor was established based on its physical composition and structural characteristics. Considering different operating conditions of the transmission line, the radial temperature was analyzed through the finite element simulation. Secondly, considering the radial temperature difference of stress, the radial thermal expansion and the creep, the sag calculation model was built. Based on the force balance principle, the relationship among the radial thermal expansion considering the radial temperature difference, the stress and the strain of the conductor was studied and the relationship between creep and strain was analyzed. Then the conductor sag was calculated through the function of the strain and the sag. Finally, in order to verify the accuracy and practicability of the sag calculation model, the model was verified by a 110 kV transmission line in Shaanxi Province. The results show that the influence on the accuracy of the sag calculation from largest to smallest are the creep, the radial temperature difference and the radial thermal expansion based on the 110 kV transmission line in Shaanxi Province. Without taking into account the radial temperature difference, the radial thermal expansion and creep, the error of sag was in the range from –45.2% to –30.0%. And the maximum error was 45.2%. The error range under the optimization model of sag in this paper was less than 1.1%. When the influence of the radial temperature difference and the radial thermal expansion on the sag is ignored, the error of sag is existed and the error becomes greater with the increase of the radial temperature difference.关键词：transmission line;radial temperature;creep;sag;finite element simulation
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发布时间：2024-01-10 - 摘要：With the gradual development of power equipment towards high voltage, large capacity, and high integration, higher requirements have been put forward for the insulation materials of its thermal conductivity. This article drew inspiration from the biomimetic structure of the natural pearl. The composite insulation paper was constructed by using the one-dimensional aramid nanofibers (ANF) with high-temperature resistance as the skeleton network, and the two-dimensional boron nitride nanosheets (BNNS) with high thermal conductivity as the functional units. Firstly, the lithium citrate was used as a surfactant to peel hexagonal boron nitride (h-BN) into BNNS through a combination of ultrasound and hydrothermal reaction. Its microstructure and dispersion characteristics were also studied. Then, the concentrated alkali deprotonation method was used to peel the Kevlar fiber (AF) into ANF. Using ANF and BNNS as nanocomposites, the BNNS/ANF composite insulation paper was prepared through the vacuum assisted filtration technology. Its microstructure, thermal conductivity, mechanical properties, and breakdown performance were further analyzed. The results show that the thin layer BNNS prepared by peeling has a high aspect ratio, and the uniform accumulation between BNNS and ANF forms a dense brick mud structure. This brick mud structure helps to improve the breakdown performance and mechanical properties of the composite insulation paper. When the filling mass fraction of BNNS is 20%, the standard breakdown field strength of the BNNS/ANF composite insulation paper reaches 313.04 kV/mm, and its tensile strength reaches 216.64 MPa, which are 166.47% and 126.38% of the corresponding parameters of the pure ANF insulation paper, respectively. In addition, the directional distribution of BNNS in the ANF network forms a continuous thermal conductivity bridge, which significantly improving the thermal conductivity of the composite insulation paper. When the filling mass fraction of BNNS is 30%, the thermal conductivity of the composite insulation paper reaches 5.31 W/(m·K), which is 211.55% of that of the pure ANF insulation paper. Thus, the composite insulation paper has high thermal conductivity, good mechanical properties and excellent electrical insulation, which can effectively solve the problem of equipment insulation and heat dissipation. It is expected to be widely used in electrical equipment.关键词：boron nitride nanosheets;aramid nanofibers;composite insulating paper;brick and mortar structure;thermal conductivity
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发布时间：2024-01-10 -
Simulation of the Discharges in Millimetre Gap Driven by Radio-frequency and Kilohertz AC Voltages AI导读
摘要：Atmospheric pressure short-gap discharge is an effective means to generate cold plasma. Common AC driving power sources include the RF power supply and the kHz AC power supply, but the comparison of the air gap discharge characteristics caused by these two different frequency power sources has been rarely studied. In this paper, the non-uniform field structure of an 1mm needle-plate gap was taken as the discharge structure, which was approximated as a one-dimensional model in the spherical coordinate system. A classical plasma fluid model based on multicomponent and local energy approximation under the drift-diffusion approximation was established. The discharge process of 1 mm helium (mixed with 0.1% nitrogen) gap driven by a 13.56 MHz radio frequency (RF) or 50 kHz AC (LF) power supply was simulated. The discharge characteristics under the 1 mW and 1 W deposition energies were studied. The results showed that the RF discharge mode was corona discharge at 1mW. The charged particles in the gap had a low density and mainly concentrated near the power electrode. When the deposition power increased to 1W, the gap discharge showed obvious glow-discharge characteristics, the sheath appeared near the electrode, and there was a quasi-electrically neutral plasma region in the middle of the gap. The igniting voltage amplitude of LF discharge was higher than that of RF, and LF discharge would transition from the corona discharge mode to the glow discharge mode smoothly without any obvious conversion process when increasing the voltage. For these two kinds of discharge, penning ionization was the main ionization path under the corona discharge mode. While the direct electron impact ionization became the dominant ionization channel under the glow discharge mode. In addition, under the same deposition power, the maximum electron density, the electron temperature and the positive ion temperature of the LF discharge were higher than those of RF discharge, but the temporal uniformity was poorer, showing obvious pulse discharge characteristics.关键词：atmospheric pressure low temperature plasma;gas discharge;gap breakdown;simulation of plasmas- 255
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发布时间：2024-01-10 - 摘要：There is a small number of bubbles in the oil of oil-immersed power transformers with long-term operation. The complex electric field environment inside the equipment can change the motion state of these bubbles, which leads to the electric field distortion and ultimately causing the insulation deterioration. In this paper, an automatic bubble generation device was designed to simulate the formation of bubbles in oil, and their motion trajectories were captured using a high-speed camera. Then a gas-liquid two-phase flow model was established through the finite element simulation software in order to obtain the electric field distribution surrounding the bubbles. Finally, this study discussed the gyration phenomenon that occurs when bubbles rise from a mechanical perspective using simulation models. Furthermore, an image processing software was employed to analyze the effects of the bubble size and the electric field intensity on the motion trajectories of the bubbles in this study. Results revealed that an increase in the bubble size and the electric field intensity can alter the force acting on the bubble itself, which leads to larger deviations in its movement. Based on the simulation calculation and analysis, it can be found that the existence of the extremely inhomogeneous electric field causes variations in the electric field intensity at different regions of the bubble surface. The bubble surface was divided into different regions and simulation results were used to calculate the force acting on the regions. The results showed that the force acting on these regions were not uniform. Based on the final analysis, it can be concluded that the presence of the extremely inhomogeneous electric field led to uneven surface forces. It is the main cause for the displacement and deformation of bubbles, ultimately resulting in the multi bubble gyration. Moreover, the process causes the temporary accumulation of multiple bubbles between the two electrodes, intensifying the distortion of the electric field and resulting in a significant degradation of the insulation performance. The study can be applied to the operational condition assessment of oil-immersed power equipment with long-term operation.关键词：bubbles;transformer oil;bubble gyration;extremely inhomogeneous electric field
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发布时间：2024-01-10 - 摘要：At present, the environmentally friendly insulating medium C6F12O has been applied in the gas switch cabinet. Selecting suitable porous materials to adsorb the decomposition products of C6F12O mixtures can not only ensure the stable operation of the switch cabinet, but also provide the safety protection for the promotion of C6F12O environmental protection gas switch cabinet applications. In this paper, the adsorption performance of the ZSM-5 molecular sieve on the thermal decomposition products of C6F12O/CO2 mixtures and the effect on the concentration of C6F12O and CO2 were investigated by adsorption experiments. At the same time, the adsorption process was simulated based on the molecular dynamic simulation, and kinetic parameters such as the concentration distribution function, the radial distribution function, and the diffusion coefficient were calculated to clarify the adsorption mechanism. The experimental results showed that the main decomposition products of the the C6F12O/CO2 mixtures are C2F6, C3F8, C4F10, C3F6, C3F7H, C5F12 and C6F14 under the overheating fault.The ZSM-5 molecular sieve has adsorption effect on most decomposition products except C5F12 and C6F14. It has excellent adsorption performance for C3F8, C4F10, and C3F7H, and the adsorption rate is over 80%. It has a certain adsorption capacity for C2F6 and C3F6, but the adsorption effect is not obvious. Before the experiment, the main insulating medium C6F12O and CO2 have higher concentrations, the ZSM-5 molecular sieve has little effect on its concentration. The adsorption rate after the experiment is 1.77% and 0.25% respectively after the experiment. The simulation results showed that the ZSM-5 molecular sieve can well adsorb gas molecules (C2F6, C3F8, C4F10, C3F6, C3F7H) with kinetic diameters equivalent to its own pore size. The adsorption effect of gas molecules (CO2, CF4, C5F12, C6F12O, C6F14) with too small or too large molecular volumes is not obvious. In conclusion, the ZSM-5 molecular sieve can be used for the adsorption and treatment of decomposition products in C6F12O gas switch cabinets, to ensure the safe and stable operation of the equipment. It also provides a reference for the selection of filter materials in related power protection equipment.关键词：C6F12O/CO2 mixtures;thermal decomposition products;ZSM-5 molecular sieve;adsorption experiment;molecular dynamics simulation
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发布时间：2024-01-10 - 摘要：The loss and the amount of metal conductors are the key factors to be considered in the optimization design of the dry-core reactor. In order to effectively reduce the loss and cost, this paper proposed a multi-objective optimization method for the dry-core reactor based on the multi-physical field simulation and the VIKOR decision. Firstly, the dry-core reactor was taken as the research object, and the magnetic field-flow field-temperature field model was established. The loss density of the core and the coil obtained from the magnetic field calculation was used as the heat source, and the reactor temperature distribution was obtained through the fluid-thermal coupling calculation; Then the magnetic field-structure field model was established. Taken the electromagnetic force calculated based on the magnetic field as the stress item, the vibration displacement distribution of the core and coil were calculated. The temperature rise and vibration displacement results of the core reactor under different structural parameters were obtained by combining the finite element simulation and the Latin hypercube test design. In order to further simplify the optimization process, the sensitivity analysis method was used to reduce the dimension of parameters. The agent model among the design parameter, the temperature rise and the vibration was established considering key parameters. The multi-objective genetic algorithm was used to obtain the Pareto frontier solution set that meets the performance requirements of the reactor. Considering the conflict between the amount of metal conductor and the loss of the reactor, the VIKOR comprehensive decision method was introduced. On the basis of determining the weight of the optimization objective, the benefit ratio of the Pareto solution set was calculated. The optimal design parameter combination was determined by the minimum benefit ratio. The correctness of the optimization design method was verified by simulation. Compared with that before optimization, the consumption of iron core and coil metal conductors of the optimized iron core reactor decreases by 3.0% and 16.6% respectively with the loss increased by 4.4%. At the same time, the temperature rise and vibration decreases by 7.4% and 16.7% respectively on the basis of meeting the design requirements. The proposed method can effectively improve the performance and provide guidance for the optimization design of reactors.关键词：core reactor;finite element modeling;agent model;multi-objective optimization;VIKOR decision
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发布时间：2024-01-10 - 摘要：The increasing voltage level and complex operating environment of power systems have placed more and higher demands on cable insulation materials. The insulation materials should have superior electrical, thermal and mechanical properties when working in extreme environments with moisture and strong electric fields. The polymer-based nanocomposite dielectric has gained much attention for its unique structure and excellent electrical, mechanical and chemical properties. The performance of nanocomposites depends on the stability of the microstructure morphology formed by nanoparticles and crosslinking. In order to investigate the effect of crosslinking degree on the water-tree aging characteristics of nanocomposites from the microstructure aspect, two kinds of crosslinked polyethylene/montmorillonite (XLPE/OMMT) nanocomposites with different crosslinking degrees were prepared in this paper by regulating the crosslinking time, and the accelerated water-tree aging experiment was conducted. Firstly, the water-tree morphology was observed by the polarized light microscopy. The length and initiation probability of water trees were calculated, and the gel content was tested to characterize the crosslinking degree of the nanocomposites. Secondly, the changes of the chemical composition of the specimens before and after aging were analyzed by the Fourier Infrared Spectroscopy (FTIR). The carbonyl index and methylene index that characterize the aging degree of the nanocomposite specimens were calculated. Finally, the scanning electron microscope (SEM) was used to compare the changes of the crystal morphology in the water-tree area and the nonwater-tree area before and after aging. The damage of the water-tree growth to the crystal structure was also studied. The experimental results show that the crosslinking degree of nanocomposites affects the initiation probability of water trees. The water-tree morphology of the specimens in the positive crosslinking state is sparse, whose fractal dimension and duty cycle is small. The electrochemical degradation phenomenon exists during the aging process of the specimens, and the carbonyl group increases. An appropriate crosslinking degree can produce a more perfect three-dimensional mesh structure, with smaller variability of the crystal size of the specimens, more uniform crystal distribution, and lower degree of the crystal damage after aging. The organic montmorillonite (OMMT) forms a solid interfacial force between the layers and the matrix, which enhances the molecular chain toughness. The barrier effect of OMMT and the perfect crosslinked network work together to hinder the diffusion and aggregation of water molecules, inhibit the generation of microscopic water gaps, and improve the water trees resistance of nanocomposites.关键词：crosslinking degree;nanocomposite material;crosslinked polyethylene;organic montmorillonite;water-tree aging
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发布时间：2024-01-10
ENVIRONMENTALLY FRIENDLY POWER EQUIPMENT FOR CARBON PEAKING AND CARBON NEUTRALITY GOALS
- 摘要：Total dissolved gas (TDG) supersaturation caused by dam spills may lead to gas bubble disease and even fish mortality, resulting in serious negative impacts on the aquatic ecosystem. With more and more high dams put into operation in recent years, the problem of total dissolved gas supersaturation has become an important ecological risk restricting the safe operation of high dam discharge in China. By combining literature analyses and the authors' research experience in the field, the problem of dissolved gas supersaturation, its effect on fish and the mitigation measures were retrospected. First, for the protection needs of endemic fish in the upper reaches of the Yangtze River, the negative effect of TDG supersaturation and the tolerance ability of fishes to TDG supersaturation were reviewed. The mechanism of TDG supersaturation and its simulation technology was revealed from the perspective of the generation and dissipation process. The mitigation technology and its engineering application were described from the engineering measures, dispatching measures, and ecological function utilization measures. According to the ecological safety demand of high dam discharge in China, the research trend at home and abroad was analyzed. It was proposed that the current key problems and challenges mainly include further revealing the mechanism of TDG supersaturation, improving the accurate and advanced prediction methods, strengthening the engineering feasibility study of TDG mitigation technology, implementing the cascade muti-object optimal dispatching based on TDG supersaturation mitigation, and promoting the establishment of fish tolerance standards to TDG supersaturation. The effort of this paper aims at providing scientific reference and guide for the solution of TDG supersaturation and guarantee the ecological safety of high dam operation.关键词：dam spill;total dissolved gas;supersaturation;fish;tolerance;mitigation measure
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发布时间：2024-01-10 -
Experimental Study on Characteristics of Bouder Bars Evolution in Mountainous Sediment-laden River AI导读
摘要：The water and sediment conditions influence the channel evolution around the river boulder regions in mountainous sediment-laden rivers, which significantly changes the characteristics of water and sediment movement and riverbed deformation. Through field investigation of Baisha River and Longxi River, the tributaries of Minjiang River in Dujiangyan City, the bed sand composition, and morphological characteristics of the typical boulder reaches were analyzed. Field investigations found that due to the torrential rains and floods of mountain rivers and the sediment carried by them, as well as the changing terrain of the river, a large amount of upstream sand was silted in the section of the boulder river, resulting in the development of many beaches in the riverbed. Based on the field investigation of typical riverbed and physical model experiments, the effects of the boulder and sediment supply on hydrodynamic characteristics and beach development in river reach were analyzed. According to the experimental results, it can be concluded that the heavy rain and flash floods produced abundant sediment supply including boulders, resulting in the large average particle size of the Baisha River and the Longxi River, and forming a large number of boulder reaches. The hydraulic factors around the boulder abruptly, lead to considerable changes in the water level and riverbed forms. Under the sediment supply, the upstream sediment is mainly lateral banded source deposition, while the downstream sediment deposition is prominent on both sides, which is easy to form a drift stone beach. The development of boulder beaches can increase the local riverbed gradient and slow down the river channel cutting. While the non-uniformity of the upstream sediment supply changes the local water level and sediment deposition scale around the boulder. Therefore, the morphological characteristics of the boulder riverbed under the condition of water and sediment are revealed. It shows that the sediment and boulders from the upper reaches of the mountainous rivers jointly affect the development process of the beach, and the boulders have a prominent impact on the movement of water and sediment in the mountainous sediment-laden river.关键词：mountainous sediment-laden river;water and sediment movement;boulder beach;riverbed form- 348
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发布时间：2024-01-10 - 摘要：Earthquakes, landslides, mountain torrents can occur frequently in mountainous areas. During these events, a large number of particles can enter the river channel, causing abrupt changes of sediment supply. Due to varied sediment transportation capacity at different river reaches, sediments may be deposited and accumulated at some locations along the river, which leads to sharp increases of riverbed and water level. This poses a great threat to the prevention and control of water and sediment disasters in mountainous rivers. According to the field investigation of Baisha River and the Longxi River, boulder distribution can increase the river scouring and reduce the sediment deposition along the river banks. It can be seen that boulders can regulate the sediment supply in downstream river effectively. In this study, the characteristics of sediment transportation in a typical mountainous river under the influence of boulders have been analyzed via the CFD-DEM coupling method. In particular, the influences of sediment mass, flow rate and boulder spacing on the granular dynamics, sediment supply and water level along the mountainous river have been discussed. The numerical results show that boulders on the riverbanks can change the sediment transportation path. The debris particles typically move downstream along the middle of the river, which reduces the amount of sediment deposited on both sides of the river. Boulders can regulate the sediment supply in the lower reaches of the mountainous river by prolonging the time and reducing the flux of sediment transportation. As the boulders spacing and flow rate decrease and the debris mass from gully increases, the ‘catching’ efficiency of boulders will gradually increase. This effect can reduce the overall sediment deposition area in the mountainous river and keep the deposition location reasonably far away from the protected reach. Thus, a significant decrease of the water level along the protected reach can be achieved.关键词：sediment supply;flow-sediment transport;riverbed deformation;boulders;numerical simulation
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发布时间：2024-01-10 - 摘要：The floating objects on water surfaces seriously damage river landscapes and water ecological environments. However, due to the complex and diverse river environments, there are many noise problems such as water wave disturbance, dynamic light and shadow, and strong light reflection that may reduce the accuracy of image-based object detection. To solve the problem of floating object detection and tracking in complex environments, a deep learning-based intelligent detection and tracking method for floating object targets on the water surface is proposed by combining single-frame detection and multi-frame filtering. In single-frame detection, low-resolution feature maps of 5×5 and below are removed, and high-resolution feature maps of 76×76 are enhanced by feature-added technique to improve the detection accuracy of the SSD detection algorithm for small-scale floating objects. In multi-frame filtering, an adaptive filtering algorithm framework is constructed based on spatial-temporal correlation and motion information to calculate the correlation between frames in a video frame and adaptively remove the detection results of floater targets that deviate from the motion trajectory according to the magnitude of change in the spatial position of the floater target to reduce floater tracking drift. In the information fusion stage, the detection and filter information are fused by feature comparison to achieve dynamic complementarity between detection and tracking information and are trained and validated with different detection and tracking scene datasets. The results show that the method achieves 100% detection and tracking accuracy, 0.94 success rate area, 17.27 fps average speed, and 7.18×109 computational complexities in simple water scenes with a center location error of 8 pixels. The tracking accuracy and success rate area for a center location error of 10 pixels in complex water scenes are 93.24% and 0.81 respectively, and the average speed and computational complexity are 15.02 fps and 8.76×109 respectively, balancing detection and tracking accuracy and efficiency in complex environments.关键词：deep learning;floating objects on the water surface;detection and tracking;feature fusion
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发布时间：2024-01-10 - 摘要：Bank erosion and accretion often occurred in the Lower Yellow River (LYR), which led to several negative effects such as channel migration, safety of flood control, and land loss. Therefore, it is essential to take the modules of bank erosion and bank accretion into account when calculating flow-sediment transport and channel evolution. A coupled one-dimensional model was proposed to simulate both bed evolution and bank deformation, including three modules of flow-sediment transport, bed deformation, and bank erosion and accretion. The proposed model was applied to simulate the longitudinal and lateral channel deformations in the LYR with a length of 755 km, with the years 2018 and 2020 being selected as the calibration and verification years to evaluate the model. The results indicate that the proposed model can accurately simulate the processes of bank erosion and accretion, and the absolute errors between the calculated and measured post-flood reach-scale channel widths in the braided reach, transitional reach, and meandering reach of the LYR were respectively 4 m, 5 m and 1 m in 2018 and 12 m, 14 m and 4 m in 2020. It was also found that the one-dimensional model could accurately simulate deformations, bank erosion and accretion, and riverbed evolution at section scale in different reach types. The bank deformation characteristics of the three reaches in the LYR were diverse from each other, with the deformation amplitude of the braided reach being much greater than that of the transitional reach and the meandering reach, and the deformation amplitude of the transitional reach and the meandering reach being almost the same. However, the amplitude of bank erosion in the three reaches was greater than that of the bank accretion, which reflected the trend of the channel widening in the LYR. The amounts of bank erosion and accretion were large in the LYR, and bank erosion and accretion had an important influence on channel evolution, among which bank deformation in the braided reach had an obvious contribution to channel evolution, whereas channel evolution in the transitional reach and meandering reach mainly came from the flow and sediment transport.关键词：bank erosion;bank accretion;riverbed evolution;coupled model;Lower Yellow River
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发布时间：2024-01-10
RIVER PROTECTION AND REGULATION
- 摘要：As an important construction auxiliary method, tunnel pre-supporting technology not only effectively strengthens the surrounding rock, but also has good bearing and restraining deformation. To better simulate the real stress of the tunnel pre-supporting arch shed, firstly, the orthogonal curve coordinate system was established based on the shell characteristics of the grouting pipe shed and the horizontal jet grouting arch shed, and the control equation was solved by the displacement function. Then, the Pasternak foundation model was introduced, and the mechanical shell model of the arch shed on the Pasternak two-parameter foundation was established. Finally, the analytical solution expressions of the deflection, internal force, and foundation reaction force of the arch shed were derived. The proposed model was subjected to case calculation and numerical verification, and then the deformation, transverse and longitudinal forces, and foundation contact reaction force of the pre-supporting arch shed were analyzed. The influence of arch shed design parameters on the deformation of the jet grouting arch shed was discussed. Compared with the analysis methods in the existing literature, the proposed model considers the continuity of rock-soil mass and the integrity of the grouting reinforcement area, which is closer to the real stress state of arch shed pre-support in theory compared with the traditional method. The overall deflection curves obtained by the analytical method and the numerical method are all ‘spoon-shaped’ distributions, and the results are in good agreement. The mechanical analysis shows that in the longitudinal direction, the arch shed can adjust the pressure distribution well to a certain extent, and the internal surrounding rock is in a pressure-free state. Taking the excavation face as the boundary, the influence range of the longitudinal bending moment and shear force of the arch shed is about 5 times the excavation footage. Transversely, the shear stress at the arch foot plays a leading role, and the vault is mainly dominated by normal stress and prone to material damage. Different parameters have different effects on the deformation of the arch shed structure, and the impact degree decreases in the following order: initial deflection > excavation footage > pile diameter > excavation height.关键词：tunnel engineering;pre-supporting arch shed;shell model;two-parameter foundation;analytical solution;force deformation
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发布时间：2024-01-10 - 摘要：Based on the traditional planar grid, the lateral resistance between transverse ribs and soil is enhanced by the vertical grid, which is helpful to enhance the interface interaction between reinforcement and soil, and improve the anti-deformation ability and overall stability of the reinforced soil structure. To analyze the effect of mesh size and particle size on the shear characteristics of the three-dimensional geogrid-quartz sand interface, a series of monotonic direct shear tests were carried out with three-dimensional geogrids with different mesh sizes fabricated by 3D printing technology. The effects of particle size, normal stresses, the percent open area of geogrid on the friction angle, dilatancy angle, and interface shear strength coefficient were analyzed. The interface dilatancy coefficient model was established, and the effects of the average particle size and the percent open area of geogrid were quantitatively analyzed on the three-dimensional geogrid-sand interface dilatancy. The results show that with the increase of particle size, the maximum apparent cohesive force increases by 65.53% and the maximum friction angle increases by 7.85%, indicating that particle size has a more obvious effect on the apparent cohesive force of geogrid-sand interface, but has little effect on the friction angle. With the increase of normal stress from 20 kPa to 60 kPa, the maximum dilatancy angle decreases by 38.1%~60.8%, respectively, indicating that the maximum dilatancy angle decreases gradually with the increase of the normal stress. It is found that, as the increase of particle size, or decrease of the percent open area of geogrid, the shear dilatancy increases obviously. The shear strength coefficient is with the increasing of particle size, the increase was as high as 8.76%, indicating that the coarse particle has a better reinforcement effect with three-dimensional geogrid.关键词：particle sizes;three-dimensional geogrid;reinforced soil interface;shear properties;mesh size;dilatancy coefficient
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发布时间：2024-01-10 - 摘要：The coefficient of earth pressure at rest, K0, of soil is one of its important mechanical parameters, and it is of important theoretical significance and practical value to accurately determine the coefficient K0. However, it is difficult to measure this coefficient, and much more difficult for coarse-grained soils. There are few apparatuses that can be used for studying K0 of coarse-grained soils so far, and there is almost no research on the variation law of K0 of coarse-grained soils under different initial void ratios. To investigate the variation law of the at-rest earth pressure coefficient of coarse-grained soil under different initial void ratios, a new type of apparatus K0 for the test was developed. This apparatus can be used to determine the K0of coarse-grained soil, as well as clay or sand, and can work under high-stress conditions. Several K0 tests were carried out on coarse-grained soil with different initial void ratios using this new apparatus. The parent rock of the tested coarse-grained soil was a porphyritic granite, and the particle size was less than 20 mm. The sample was 8 cm in height and 10 cm in diameter with initial void ratios of 0.3, 0.4, 0.5 and 0.6. The maximum vertical pressure was 3.7 MPa. The test results showed that when the soil was loaded under the K0 state, there was a good linear relationship between lateral stress and vertical stress, and thus K0 could be taken as a constant. With the initial void ratios of 0.3, 0.4, 0.5 and 0.6, the K0 ranged roughly from 0.30 to 0.45, and the effect of the void ratio on the K0 coefficient was evident. The at-rest earth pressure coefficient of the coarse-grained soil increased with the increase of the initial void ratio, and there was an approximately linear relationship between the two parameters. A power function could be fitted between the volumetric strain and the average normal stress (or vertical stress) of the samples under different initial void ratio conditions, and an empirical formula that could reflect the stress-strain relationship of coarse-grained soil under K0 conditions with different initial void ratios was proposed.关键词：coefficient of at-rest earth pressure;coarse-grained soil;initial void ratio;volumetric strain;average normal stress
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发布时间：2024-01-10 - 摘要：Concrete structures often fail under multiple impacts in their service life. Therefore, the repeated impacts test was conducted by split Hopkinson pressure bar (SHPB) to investigated the dynamic behavior of RSCC under the repeated impacts. RSCC with three different rubber content, respectively 10%, 20%, and 30%, was prepared to investigate the effects of rubber content and high temperature. A group of NSCC was prepared as the control group. The experimental results demonstrate that the thermal treatment of 150 ℃ has a little effect on the repeated impacts behavior. A similar behavior of RSCC to NSCC is noted. The incorporation of rubber modifies the brittleness of NSCC. It decreases the peak stress generated in the specimen. With the increase of rubber content, an increasing trend in the repeated impact number is observed. RSCC shows better resistance to the repeated impacts than NSCC. After the thermal treatment of 300 ℃, the peak stress of NSCC increases, but NSCC still shows a brittle failure mode. However, the peak stress and the total repeated impact number of RSCC decreases. RSCC shows a deteriorating resistance to the repeated impacts with the increase of the temperature and deteriorates a lot with the increase of rubber content. Furthermore, at room temperature and the temperature of 150 ℃, RSCC shows a higher total specific energy absorption (SEA) than NSCC, but NSCC shows a higher total SEA than RSCC at 300 ℃.关键词：RSCC;thermal treatment;repeated impacts;energy absorption
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发布时间：2024-01-10 - 摘要：Since the single-layer reticulated shell structure is mainly composed of circular steel tubes, the constitutive model for circular steel tube is more suitable to study the mechanical behavior of single-layer reticulated shell structures. In this study, the constitutive model of circular steel pipe considering damage accumulation was analyzed with yield criteria, elastic stiffness matrix, elastic-plastic stiffness matrix, loading criterion, flow rule, and stress-drop, and it was compared to the constitutive model of Prandtl-Reuss material to explore the mechanical performance. By providing the format of the numerical integration, this study also explored the influence of material damage accumulation on the dynamic response of single-layer reticulated shell structure. Besides, a user-defined material subroutine considering damage accumulation was incorporated into ANSYS to investigate the dynamic response of single-layer latticed shell under earthquake action. The results show that seismic performance of single-layer reticulated shell was overestimated in Prandtl-Reuss material model. The dynamic ultimate load of structure was reduced by 12.24% compared with the Prandtl–Reuss model, and most of the members yield in the whole section, forming a large number of plastic zones, when considering the structural failure of material damage accumulation. On the other hand, the cumulative damage had the influence on reducing the dynamic limit load of the structure, expanding the damage distribution, deepening the damage degree and accelerating the process of structural failure, which also caused the failure mode of the structure to change from dynamic instability to strength failure. Moreover, the numerical integration scheme was proposed in this study showing better rationality and efficiency, and the calculation accuracy of the user-defined material subroutine is reliable to provide more accurate analysis and engineering design for the seismic performance of single-layer reticulated shell structures.关键词：circular steel pipe;damage accumulation;mechanical performance;numerical integration scheme;stress-drop;user-defined material subroutine
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发布时间：2024-01-10 - 摘要：Real-time high-precision displacement measurement is important for the safety and life-cycle assessment of engineering structures. To improve the accuracy and stability of displacement measurement based on Global Navigation Satellite System (GNSS) technology, an adaptive multi-rate Kalman filter is proposed to fuse the acceleration and displacement data. Due to unreasonable settings of noise parameters, the accuracy of displacement estimation can be seriously degraded. By utilizing the characteristics of acceleration and displacement measurement noises, the adaptive estimation is realized through estimating the variance of their corresponding noises separately. Considering the noise characteristics of accelerometer and GNSS device, the estimation of noise parameters in the adaptive filter is simplified to estimate only the variance of displacement noise. The Sage-Husa estimator is used to realize the adaptive estimation of displacement noise variance so that the filter can reach a stable real-time displacement estimation under inaccurate noise parameters. First, the settings of initial noise parameters in the proposed adaptive filter are discussed to determine its rule. Then the displacement estimation performance of the filter at different signal frequencies is discussed through the harmonic displacement under time-invariant noise and time-varying noise. Finally, the effectiveness of the proposed technique is demonstrated by using a numerical simulation response from a 1.5 MW wind turbine tower under wind-earthquake coupling. The results show that even if the initial noise parameters are inaccurate and the displacement measurement noise is time-varying, the proposed technique still has satisfactory performance and robustness in real-time estimation. This research can provide a reference for real-time and high-precision displacement monitoring of structures.关键词：Kalman filters;adaptive filtering;displacement measurement;data fusion;structural health monitoring
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发布时间：2024-01-10
CIVIL ENGINEERING
- 摘要：Cemented sand-gravel dam (CSG dam) is a new type of dam, and has the advantages of low overall stress level, rapid construction, and saving engineering investment. Aiming at the difference in failure form between the CSG dam and gravity dam on complex foundations and the stability of deep sliding, the method of the geomechanical model test was adopted, selecting the Shoukoubao dam as the prototype of the CSG dam, and comparing it with the Wudu gravity dam 19# dam. The complex foundation of the dam site area was combined to form a new dam section, to simulate the operation of the CSG dam under the complex foundation, and the deformation characteristics of the dam body and the damage of the fault layer and the interlayer dislocation zone of the complex foundation were obtained through the model loading tests. From the model test data of the 19# dam section of the CSG dam and the Wudu gravity dam, and the comparative analysis of the failure modes, the results can be obtained: 1) Under the same overload multiple, the dam body of the gravity dam has a larger displacement than the dam body of the CSG dam; 2) In the final failure stage, both the CSG dam and the gravity dam body are slightly twisted, the gravity dam body rotates slightly clockwise, and the CSG dam body rotates slightly counterclockwise; 3) the faults occur to varying degrees. The relative displacement of the fault layers 10f2 and f115 occurs due to the slippage; 4) The overall downstream displacement of the gravity dam is more obvious than that of the CSG dam, and the crushing damage is more serious; 5) The safety degree of the CSG dam is 6.4 in the model test, the safety degree of gravity dam is 3.0, the safety degree of CSG dam is 5.9 obtained by using the rigid body limit equilibrium analysis, the safety degree of gravity dam is 2.5. The model test results and the theoretical analysis results have been verified by each other. Therefore, from the data results of the two, it can be concluded that the ultimate bearing capacity of the CSG dam is stronger than that of the gravity dam, the overload coefficient is larger, and the safety degree is higher than that of the gravity dam, indicating that the CSG dam is a kind of high-safety dam type.关键词：CSG dam;gravity dam;complex foundation;geomechanical model test;overload method
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发布时间：2024-01-10 - 摘要：PIV-based pressure field measurement technique enables a non-intrusive, high spatial and temporal resolution and full-field measurement of the instantaneous pressure of flows. The pressure field measurement technique was realized by reconstructing the pressure-gradient field from time-resolved velocity fields with an Eulerian approach and integrating the pressure-gradient field with an omnidirectional integration algorithm under given boundary conditions. To accurately measure the pressure field in open channel flows using PIV-based pressure field measurement technology, the accuracy, error sources, and major influencing factors on the measurement accuracy of the technique were analyzed with time-resolved direct numerical simulation data and PIV measured velocity fields of open channel flows. Based on the data, the measured pressure fields had a negligible mean bias error and a root mean square error of about 25%. By analyzing the measurement errors in the two stages of the pressure gradient field reconstruction from the velocity field and the pressure field integration from the pressure gradient field, the error was mainly introduced in the stage of reconstructing the pressure gradient field from the velocity fields and was affected by the measurement parameters of the velocity field and the method of setting boundary conditions. The influence rule of the above main influencing factors on the pressure measurement error was further analyzed. It was found that the error increased monotonously with the increase of the sampling interval of velocity fields. However, it decreased first and then increased with the increase of the measurement point spacing of velocity fields, with an optimal inner-scaled point spacing of about 7. However, the universality of the optimal value of measuring point spacing needed more data to support it. The measurement error was significantly reduced when the pressure boundary was given at the four corners of the rectangular measurement region. The PIV-based pressure field measurement technique was applied in a uniform open channel flow. The measured time-averaged pressure showed satisfactory accuracy, and the measured turbulent intensity of pressure had a reasonable vertical distribution but a relatively larger error. The results provided a theoretical and practical reference for measuring pressure fields in open channel flows.关键词：pressure measurement;open-channel turbulence;PIV;measurement accuracy;error sources
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发布时间：2024-01-10
HYDRAULIC ENGINEERING
- 摘要：Non-intrusive load monitoring (NILM) is one of the important development directions of power grid construction in China in the future. In order to overcome the problems of large amount of calculation data and low identification accuracy of traditional NILM methods, a non-intrusive load monitoring method based on CFSFDP (clustering by fast search and find of density peaks) graph Laplace algorithm was proposed in this paper. Firstly, the power threshold vector and the prior graph structure were constructed using the active power data adopting the CFSFDP algorithm. Then, the graph Laplacian quadratic optimal function was constructed by combining the total power signal and graph signal smoothness, and the optimal solution was obtained iteratively by Tikhonov regularization method, so as to realize the reconstruction of graph signal of appliance. Finally, the graph signals were converted into power signals according to the power threshold vector, which enabled non-intrusive load monitoring. The following results were obtained from the simulation analysis of two days of measured electricity consumption data of a real household, including the load monitoring results within two days and the impact of sampling frequency on the algorithm performance. 1) The proposed method can identify all the equipments running within the first day, and the calculated proportion of electricity consumed by each electric equipment is close to the actual situation. 2) The load identification accuracy of the proposed method for the next day is 90.1%, which is superior to four comparison methods. The decomposition accuracy of a single appliance is more than 91%, and the vast majority of devices have lower power consumption error than the comparison methods. 3) When the data sampling interval is increased to 2 min, although the precision, identification accuracy and single appliance decomposition accuracy of the proposed method are all reduced, its calculation results gains superior performance and time complexity than the comparison methods. The simulation results verify the effectiveness of the proposed non-intrusive load monitoring method and its superiority for solving practical low-frequency NILM problems.关键词：NILM(non-intrusive load monitoring);CFSFDP clustering algorithm;graph Laplace quadratic;Tikhonov regularization
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发布时间：2024-01-10
ELECTRICAL ENGINEERING
- 摘要：The drive axle is one of the core components of the micro-vehicle transmission system, which bears complex loads and affects the safety, comfort and power of the vehicle. The performance of drive axle has a significant effect on vehicle NVH (noise vibration and harshness). In order to obtain the influence laws of drive axle vibration response and further implementthe active control of the dynamic characteristics, a multi-factor coupling vibration model is established based on lumped mass method considering the key excitations of the hypoid gear transmission system in drive axle, including time-varying mesh stiffness, damping, transmission error and impact. The differential equations of the nonlinear vibration model were derived on the basis of Newton’s Law, which are further solved by the Runge-Kutta method. After performing the optimization of the hypoid gears, the influence laws of input speed and load torque changes on the vibration characteristics are discussed considering the numerical solutions on the verticality, torsion and axial directions for both the driving and driven gears. Computational results indicate that the proposed solution can reduce the gear vibration, and a nearly chaotic phenomenon is caused by the complicated vibration laws of the vertical and axial dimensions for the driving gear and driven gear, while a quasi-periodic state is for the torsional dimension. In addition, the changes in input speed and loading torque have the largest impacts on the axial vibration, followed by the vertical dimension, and the smallest in the torsional dimension. The results of the vibration test and data analysis for the gear transmission system also demonstrate that higher dynamic performance can be obtained for optimized samples, which also supports the theoretical analysis of the drive axle. The proposed approach is expected to be applied to improve dynamic performance of certain products by analyzing the key excitation factors and predicting the vibration response of the drive axle.关键词：hypoid gear;lumped mass method;vibration characteristics;chaotic motion;dynamic performance
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发布时间：2024-01-10
MECHANICAL ENGINEERING
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