最新刊期
卷 55 ， 期 3 ， 2023
- 摘要：The high dam is an important strategic infrastructure that supports the efficient development of hydropower and the comprehensive utilization of water resources. It continuously and stably provides energy supply and flood control guarantees for economic and social development, generating huge social and economic benefits. There are numerous high dam hubs in the southwest region, including several large and super-large high dam hubs such as the Baihetan, Xiluodu, Jinping First-stage, and Dagangshan. Large unit power generation, large flow flood discharge, and high-speed water flow energy dissipation have become the norm, and the destruction of flood discharge and energy dissipation buildings has become a common key threat to dam safety in high dam hub projects. Regular inspection of the overflow surface damage of flood discharge and energy dissipation structures during the operation period of hydropower hubs has become an important means to grasp their working performance and evaluate the safety status of the structure. With the innovation and development of equipment technology and information technology, relying on underwater robots to carry out intelligent damage detection of hydraulic structures in high dam hubs has become a trend. However, due to the complex and harsh detection conditions such as sandy water bodies and underwater sediment deposition in southwestern rivers, the coupling mechanism between high-speed water flow and flow surface damage is still unclear, and there is a lack of theoretical and technical methods for damage detection and evaluation. The contradiction between the large inspection scope, low inspection efficiency, and poor environmental adaptability also needs to be solved, and the efficiency of damage perception and identification still needs to be improved. There are still many difficulties in efficient and precise inspection and scientific comprehensive evaluation. In response to the significant demand for structural safety during the operation of flood discharge and energy dissipation buildings in the high dam hub, it is necessary to focus on solving three key scientific problems: 1) Damage formation mechanism and evolution law under the coupling effect of high-speed water flow and flow surface; 2) Adaptive inspection theory and methods suitable for complex environments; 3) Mechanism analysis and data-driven fusion of structural safety risk analysis and evaluation theory. The four important research aspects that need to be paid attention to in proposing the intelligent inspection and safety evaluation theory and method for flood discharge and energy dissipation buildings in high dam hubs are as follows: 1) Evolution mechanism of coupled damage on the flow surface under the action of high-speed water flow; 2) Multi-information cognitive mechanism and adaptive inspection methods in complex environments; 3) Intelligent identification and quantification methods for damage characteristics of flood discharge and energy dissipation structures; 4) Structural security analysis and evaluation system for multiple information fusion. Through in-depth research on the theory and methods of intelligent inspection and safety evaluation, this study reveals the formation mechanism and evolution law of damage to the overflow surface of flood discharge and energy dissipation buildings in the southwest mountainous and canyon areas. It breaks through the autonomous intelligent inspection method of flood discharge outlets and water cushion pond structures with strong adaptability in complex environments, develops key technologies for intelligent classification and quantification of damage based on multi-dimensional perception information, and constructs a structural safety analysis and evaluation model that integrates multiple data of "inspection monitoring simulation". Taking the Dagangshan Hydropower Station on the Dadu River as a typical case, the application verification of intelligent inspection methods and evaluation models was carried out to support the safe operation, maintenance, and intelligent control of key flood discharge and energy dissipation buildings in the Dagangshan Hydropower Station on the Dadu River Basin. The aim is to provide theoretical and technical methods for the operation safety, damage prevention, and control of high dams. The research results have significant scientific value and guiding significance in ensuring the safety of power generation in cascade hydropower stations and improving the refined management level of hydropower operation and maintenance.关键词：high dams;flood fischarge and energy dissipation;hydraulic simulation;engineering safety;intelligent inspection
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发布时间：2024-01-10
INVITED CONTRIBUTION
- 摘要：Sulfur hexafluoride (SF6) is a potent greenhouse gas with a global warming potential index (GWP) of 23 900 times that of carbon dioxide and an atmospheric lifespan of 3 200 years. It is widely used in high-voltage switchgear. The widespread use of SF6 poses a huge potential threat to the greenhouse effect problem, and limiting its use in power switchgear is an effective way to promote the development of the green power industry. The current situation, trends, and critical technologies of environmentally friendly switchgear at home and abroad in recent years were reviewed in this article. The development of environmentally friendly switchgear switches is based on the development of SF6 removal technology-environmentally friendly alternative gas-insulated switching and vacuum breaking + environmentally friendly gas-insulated switching. The insulation performance, breaking performance, and decomposition characteristics of SF6-alternative gas C4F7N, C5F10O, perfluorocarbons (c-C4F8, C3F8, CF4), CF3I, and HFO were summarized and compared. The current status and development trend of existing environmentally friendly gas-insulated switchgear products was introduced. Through comparative analysis, it was recognized that C4F7N, C5F10O are promising alternative gas solutions. The critical technology of vacuum breaking + environmentally friendly gas-insulated was described. The results indicated that solid particles generated after multiple discharges of CF3I and c-C4F8 in environmentally friendly gases affect their insulation performance. The weak dielectric strength of perfluorocarbon gas restricts its research progress. Comparative analysis showed that C4F7N and C5F10O promise gas alternatives, and the insulation and breaking performance of C4F7N and C5F10O mixed gases meet the equipment requirements. However, their insulation performance is sensitive to the uniformity of the internal electric field in the equipment, and the irreversible decomposition process produces complex products. At present, high-voltage gas environmentally friendly insulated switchgear has developed to 170 kV/50 kA, using three types of environmentally friendly mixed gases: C5F10O/O2/CO2, C4F7N/O2/CO2, and C4F7N/CO2. The critical technology of vacuum breaking + environmentally friendly gas-insulated was described. The current research status of high current vacuum arc magnetic field control technology, vacuum arc extinguishing indoor and outdoor insulation technology, vacuum interrupter X-ray leakage and temperature rise characteristics was summarized. Based on this, the current situation and future development trend of vacuum-breaking type environmentally friendly electric switching equipment were summarized. The results indicated that longitudinal magnetic control is an effective method of arc control. However, research on vacuum arcs under longitudinal magnetic fields mainly focuses on small gaps. Analysis suggested that a significant challenge will be developing longitudinal magnetic control for vacuum switches to higher voltage levels. By optimizing the opening curve of vacuum circuit breakers, the efficiency of longitudinal magnetic control can be effectively improved; The development of vacuum switches towards higher voltage levels poses a considerable challenge to vacuum interrupters’ indoor and outdoor insulation. Increasing the contact gap and adopting multiple breaks are currently the main ways to improve the insulation capacity of the arc extinguishing chamber. However, there are problems with vacuum insulation saturation and difficulty in voltage sharing. Environmental friendly gas pressurization and insulation coating can effectively improve the outdoor insulation capacity of vacuum arc extinguishing, which puts forward higher requirements for the airtightness and vacuum bellows of switchgear. The development of vacuum switches towards higher voltage levels and the increased rated current have put forward higher requirements for heat dissipation and X-ray shielding in vacuum interrupters. Previous studies have shown horseshoe-type longitudinal magnetic contacts have good thermal flow capacity. The commercial single break vacuum arc extinguishing chamber has developed to 145 kV/40 kA, and the development trend of vacuum breaking environmentally friendly power switchgear has been summarized based on existing products. Based on the current research status, further research focuses on the development of environmentally friendly high-voltage power switchgear towards higher voltage levels were summarized, including the decomposition characteristics of environmentally friendly gases under different fault conditions and the relationship between their decomposition products and insulation arc extinguishing performance, magnetic control technology for large diameter and large distance vacuum arcs, optimization design of insulation coordination for vacuum breaking environmentally friendly power switchgear, and control of vacuum arc extinguishing room temperature rise under high current, intended to provide a reference for the future development of SF6-free eco-friendly power switchgear.关键词：SF6-alternative gas;vacuum interrupter;environment-friendly high-voltage power switchgear
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发布时间：2024-01-10 - 摘要：Polyimide (PI) dielectric materials have excellent electrical and mechanical properties as well as high thermal and chemical stability. They are widely used in the production of electric and electronic equipment, and are an important part of insulation materials. In recent years, with the demand of green energy and sustainable development, social development increasingly requires materials to be self-healing and recycling after damage. However, due to the super stability of the molecular structure of PI itself, the molecular chain is not easy to move in low temperature conditions, and it is difficult to achieve active self-healing and recycling after damage. Therefore, it is necessary to design and develop new reversible molecular structures suitable for PI from the perspective of intrinsic molecular structure to realize the dynamic properties of the materials. Based on this, the paper reviewed recent researches on dynamic issues such as recycling and self-healing using PI as a matrix, focusing on the current preparation methods of dynamic PI, the conditions under which dynamic reactions occur, and the evaluation of the relationship between various forms of damage. Firstly, we summarized the self-healing PI dielectric materials, including the process means such as blending, copolymerization and design and preparation of new structural monomers to achieve the self-healing properties of the materials. Systematically, we summarized the current development status of self-healable PI and the difficulties and challenges faced. Secondly, we outlined the design and preparation of degradable and recyclable PI materials, as well as the recycling methods of PI dielectrics though dynamic covalent bond and dynamic cross-linking network. Finally, the problems and development prospects were summarized and prospected in the current dynamic PI system: A new dynamic crosslinking agent can be used in combination with the addition of trace organic or inorganic materials to realize the synergistic improvement of the dynamic characteristics and comprehensive properties of PI materials; by improving the process or selecting dynamic cross-linking agents, PI monomer and cross-linking agent powder level recycling can be achieved, effectively avoiding the impact of degradation catalysts; new functional monomers need to be further designed to achieve reversibility from the molecular structure level to solve the problems of PI self-healing, degradation and recycling.关键词：polyimide;electrical/mechanical damage;dynamic reaction;sustainable development
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发布时间：2024-01-10 - 摘要：The DC vacuum circuit breaker adopts the artificial zero crossing commutation mode to interrupt the DC fault current, which is one of the control and protection methods that combines economy and reliability in DC system. The post-arc dielectric recovery characteristic of vacuum circuit breaker is the key to determine the fault breaking capability. To explore the influencing factors of dielectric recovery under the coupling effect of electromagnetic and electromechanical parameters in DC vacuum circuit breakers, based on continuous transition model, the law of conservation of energy and the law of conservation of electric charge, a calculation model of charged particle number density in the current zero zone was established to study the distribution of the charged particle number density under contact contour parameters and pre-zero current drop rate. Then, by constructing a motion characteristic testing experimental platform for a 12 kV DC vacuum circuit breaker equipped with permanent magnet repulsion mechanism to measure the curve of stroke-time, the distribution of the gap length of current zero zone under the fault current, pre-zero current drop rate, and commutation input instant was obtained. Moreover, based on the drift diffusion equation, Maxwell–Stefan equation and Poisson equation, a post-arc sheath development model was established to obtain the maximum electric field intensity under the influence ofelectromagnetic and electromechanical parameters. The maximum cathode electric field intensity and critical electric field strength under the influence of zero zone metal vapor pressure and short-circuit breaking current were compared to evaluate the post-arc dielectric recovery strength with different commutation input instant, pre-zero current drop rate, transient voltage rise rate, and contact diameter. Furthermore, the limit values of the pre-zero current drop rate and commutation input instant, as well as the minimum safety gap and the breaking current limit were obtained. On this basis, a solution was provided for designing the structural parameters and commutation parameter groups of the DC vacuum circuit breaker that meet the reliable breaking requirements.关键词：DC vacuum circuit breaker;commutation circuit;current drop rate;dielectric recovery
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发布时间：2024-01-10 - 摘要：Due to the greenhouse effect of SF6 gas, new environmentally friendly substitute gases represented by C4F7N, C5F10O, C6F12O, and HFO-1234ze(E) have received widespread attention. However, there is still a lack of research on the decomposition mechanism of these gas molecules when the internal temperature of the equipment increases due to local overheating or discharge conditions. To further investigate the feasibility of using new environmentally friendly gases to replace SF6 gas, more researches are needed. This article takes HFO-1234ze(E) molecules as an example and uses the ReaxFF reactive molecular dynamics method and density functional theory to simulate and study the decomposition of HFO-1234ze(E) molecules and 20%HFO-1234ze(E)/80%CO2 mixture gases at different temperatures from a microscopic perspective. The results show that HFO-1234ze(E) molecules have seven different decomposition pathways, and the C=O bond in CO2 decomposes first. The C—F and C=C bonds in HFO-1234ze(E) have higher enthalpy values, making them difficult to break. As the temperature increases, the time of decomposition occurs earlier. When the temperature is below 2 000 K, HFO-1234ze(E)/CO2 mixture gas will hardly decompose. However, when the temperature reaches 2 000 K, HFO-1234ze(E) molecule remains stable, while CO2 molecule rapidly decomposes. At temperatures above 2 600 K, for every 2 000 K increase in temperature, about 5 more HFO-1234ze(E) molecules decompose, and about 35 more CO2 molecules decompose, until complete decomposition is reached. The mixture gas mainly decomposes into various free radicals such as CO, O2, C2O2, HF, CF4, C2F6, C3F6, and C3H3F3, among which CO is a toxic gas and HF molecules are strongly corrosive. Measures should be taken to monitor their content. The chemical properties of other decomposition products are relatively stable and environmentally friendly, and still have a certain insulating capacity. This indicates that the mixture of 20%HFO-1234ze(E) and 80%CO2 can completely replace SF6 gas to a certain extent, providing a theoretical basis and engineering guidance for further research on other new environmentally friendly mixed gases.关键词：environment-friendly mixed gas;density functional theory;HFO-1234ze (E)/CO2 mixture gas;decomposition mechanism
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发布时间：2024-01-10
ENVIRONMENTALLY FRIENDLY POWER EQUIPMENT FOR CARBON PEAKING AND CARBON NEUTRALITY GOALS
- 摘要：A high-rise ancient wooden pagoda plays an important role in architectural cultural heritage worldwide and is a representative example of Chinese ancient wooden architecture. External wind load is a harmful factor affecting the structural safety of ancient wooden pagodas. Artificial forestry can change the wind field environment of the ancient wooden pagoda to reduce wind loads and mitigate wind-induced structural damage. In this study, the wind tunnel experiments on the wooden pagoda are conducted to verify the feasibility of reducing the wind loads for the high-rise ancient wooden pagoda. A large-scale rigid model with 1∶50 was made based on a Yingxian wooden pagoda in Shanxi Province, China. The wind tunnel tests of the wooden pagoda with artificial forestry were conducted and the wind pressure distributions of the pagoda were investigated. Furthermore, the wind story forces and overturning moments of the wooden pagoda with various tree heights, distances between the forest and pagoda, and tree widths were calculated. The base shear forces and overturning moments were also discussed. The test results show that artificial forest planting can reduce the wind pressure of the pagoda surfaces in the height range of the forest shelter and on the crossward and leeward out of the height range of the forest shelter. Moreover, the tree height is a critical condition for reducing the pagoda wind loads by artificial forest planting, and taller trees make better effects. The analysis reveals that tall and large trees should be used in forest planting. The planted forest should be close to the pagoda and also be arranged as wide as possible. This study verifies the feasibility of reducing the wind pressures and loads for the high-rise ancient wooden pagoda via wind tunnel tests. It also provides a new idea for wind load reduction and wind-induced damage control of high-rise ancient wooden pagodas and can be a technical option for structural protection.关键词：wooden buildings;artificial forestry;wind effects;wind tunnels test;wind pressure
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发布时间：2024-01-10 - 摘要：With the gradual transfer of energy resources mining from shallow to deep in China, the current situation of using shallow parameters to solve deep problems and static parameters to solve dynamic problems results in the lack of scientific basis in engineering design. The initial stress state of clay has a significant influence on its dynamic properties. The long-term, graded, high-pressure consolidation method was utilized to simulate the original stress environment of clay, and the SHPB experimental device was employed to perform impact compression on the high-pressure consolidated clay under lateral restriction conditions with a strain rate ranging from 200 to 800 s–1. The stress memory effect, strain rate effect, and dynamic compression process of clay were studied. The experimental results show that the stress history of clay affects its dynamic compression process. The sample goes through the compaction section-linear elastic loading section-linear unloading section in turn. The average stress of switching point between the compaction section and linear elastic loading section under dynamic load is 3.8 MPa, which is correlated with the pre-consolidation stress of 4.2 MPa; the strain of compaction section is about 33% of the soil failure strain as well. The soil exhibits an elastic loading and linear unloading section without being a stable plastic section under the experimental strain rate, as the bullet is 200 mm or 300 mm long. It is found from the stress–strain rate relationship that the compaction section absorbs lots of the compaction energy, resulting in an unstable plastic deformation or even sudden unloading in the soil sample. The modulus of the loading and unloading section increases simultaneously with the strain rate, but the ratio of the two remains stable, which means higher impact velocity does not lead to far more damage. It can also be seen from the phenomenon of damage after impaction as well as the plastic flow analysis. At last, the high-pressure consolidation method provides an approach to studying the dynamic properties of weak and loose granular materials.关键词：soil dynamics;SHPB;dynamic mechanical property;lateral restriction condition;high consolidation stress;initial stress state
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发布时间：2024-01-10 - 摘要：This study aims to reduce the cost of high ductility cementitious composites (HDCC) and enhance the utilization of waste rice husks as building materials. The possibility of domestic oiled PVA fiber and natural river sand for HDCC production based on the orthogonal test was investigated; moreover, the workability, compression strength, tensile, and bending performance of HDCC with the substitution of cement by rice husk ash (10%, 30%, 50%, mass ratio) were systematically researched. Moreover, X-ray diffraction (XRD) was also employed to analyze the hydration products of cementitious materials. The results showed that HDCC possessed the ultimate tensile strain of 1.44% and the compressive strength of C30 could be obtained using domestic oiled PVA fiber and natural river sand; meanwhile, the water-binder ratio and PVA fiber were the main influence on the compressive and tensile strength of HDCC, respectively. Compared with the reference group, as the increment of rice husk ash, the slump of mortar tended to decrease, while the substitution of cement by 10% rice husk ash decreased the slump by 10%. Moreover, the compressive strength tended to first increase slightly and then gradually decreased, while the tensile strength showed a negative correlation; however, the tensile strain of HDCC increased significantly. The bending strength of HDCC increased with the increase of rice husk ash content, while the addition of 10% rice husk ash increased the bending strength by 37.1%; meanwhile, all the crack widths were gradually decreased and under 100 μm. Hence, the optimum substitution of cement by rice husk ash at 10% was conducive to improving the ultimate tensile strain, compressive, and bending properties of HDCC, while showing no obvious influence on the slurry mobility. The microstructure analysis revealed that rice husk ash could react with cement hydration products, thus resulting in reducing the Ca(OH)2 content and enhancing the strength of HDCC.关键词：high ductility cementitous composites;rice husk ash;mechanical properties;waste utilization
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发布时间：2024-01-10 - 摘要：Silt is often selected as the filling soil in the northwest and north China. “Pot cover effect” or rainfall infiltration are easy to cause localized wetting during the service period of airport. The wetting of silt has a significant impact on the stress response derived from the action of aircraft loading in subgrade with different structural parameters of runway. Accordingly, the stress response characteristics of silt subgrade with different degrees of wetting were investigated through the self-developed model test system, and the numerical model was then established and verified based on the laboratory tests. The interaction mechanisms of pavement slabs and the influence of wetting on stress response characteristics in the sensitive area of subgrade were analyzed via the numerical simulation under different structural parameters (e.g., the thickness and module of pavement and basement layers) of runways. The results showed that the load transfer capacity of joints had little influence on the stress response in the subgrade. The wetting of silt promoted the stress superposition effect in the subgrade, and it also increased the sensitivity of stress response in the subgrade derived from different runway parameters, while it decreased the sensitivity of the loading response depth. Under the center of the larger loading pavement, the stress response of subgrade was little affected by the stiffness of cement pavement, but largely affected by the elastic modulus of the base layer under the wetting condition. The thickness of the surface layer and base layer are the main influencing factors under the outer corner of the loading pavement, and the suitable parameters of the base layer can effectively reduce the influence of wetting on the stress state of subgrade. The research results could provide a technical basis for runway structure design, optimization, and disease treatment of subgrade in airport engineering.关键词：runway structural parameters;silt subgrade;wetting;stress response;influencing region
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发布时间：2024-01-10 -
Deformation Analysis of Shield Tunnel Undercrossing Existing Pipeline Considering Shear Deformation AI导读
摘要：The deformation of pipeline can be induced by adjacent tunneling, in turn, the safety of pipeline will be affected. Most of the theoretical studies in this regard simplify the existing pipelines as Euler–Bernoulli beams lying on the Winkler and Pasternak foundation models, without considering the shear effect of pipelines and the influence of the three-parameter Kerr foundation model on the pipeline-soil interaction. Based on this, an analytical method for predicting the longitudinal deformation of pipelines was proposed. Firstly, the vertical soil-free settlement around the tunnel induced by tunneling was calculated by the Loganathan function, then the soil-free settlement was put upon the centerline of an existing pipeline, to simplify the tunnel as the Timoshenko beam and the three-type Kerr foundation model was selected to simulate the pipeline-soil interaction, a bending moment assumption of the shear layer was proposed and the response of existing pipeline could be solved by considering with the boundary conditions at the ends of the pipeline. The results of the engineering case study show that compared with the theoretical analysis method in the existing literature, the theoretical analysis calculated by the method in this paper is closer to the existing measured data. Compared with the calculation results of the Euler–Bernoulli beam, the Timoshenko beam calculation results are more advantageous. Further parameter studies show that with the increment of the shear stiffness of the existing pipeline, the ability of pipeline to resist deformation gradually increases, which will lead to the gradual decrease of pipeline deformation but will cause the reverse increment of pipeline internal force. With the increment of volume loss rate, the external force on the existing pipeline gradually increases, which results in the increase of pipeline deformation and internal force. With the gradual increment of the diameter of the pipeline, the pipeline-soil interaction force caused by the tunneling underneath is gradually increased, which eventually leads to the stress and strain of the existing pipeline.关键词：shield tunneling;existing pipeline;Timoshenko beam;Kerr foundation model;analytical solution- 506
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发布时间：2024-01-10 - 摘要：Aiming at the problem of deformation control of subway station crossing fault construction in heterogeneous soft and hard composite stratum, the mechanical response of surrounding rock during the excavation stage was studied. And the deformation evolution law of surrounding rock under different reinforcement schemes was discussed. The result can provide theoretical guidance for the construction of subway station crossing faults, etc. Taking a subway station crossing the water-rich fault fracture zone as the background, the physical and mechanical properties and failure characteristics of surrounding rock in a special stratum were determined by laboratory experiments, and then the surrounding rock grade was determined by the BQ method. On this basis, the finite difference numerical simulation software was utilized to study the distribution characteristics of stress and deformation of surrounding rock. Combined with the control variable method, the influence of temporary support and grouting reinforcement on the overall stability of surrounding rock was studied, to determine a reasonable construction control scheme. The results show that the presence or absence of groundwater has an obvious influence on the physical and mechanical properties of surrounding rock in heterogeneous soft and hard cross strata. Diabase is particularly affected under construction disturbance; it is easy to produce shear slip failure along the joint surface. The maximum settlement value of the station vault under the influence of groundwater is 6.5 mm, which is 30% higher than that without groundwater. The maximum tensile stress of diabase (the right part of the station) is 1.62 MPa, far greater than its ultimate tensile strength of 1.25 MPa. So, the diabase side may produce a large range of failures without grouting reinforcement. Full-section grouting has a significant effect on reducing the influence of groundwater and excavation disturbance on the deformation of surrounding rock. With a 65° fault as the boundary, the smaller the dip angle of the fault, the larger the width of full-section grouting. Based on the analysis results, a safety construction scheme of full section grouting + temporary support + small footage is proposed. The monitoring results prove the research result to be effective in practice.关键词：large-span station;heterogeneous soft and hard cross-stratum;fault;diabase intrusion;control technology
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发布时间：2024-01-10 - 摘要：Due to the complexity of reliability analysis of subgrade slopes, establishing a fast estimation method of reliability index β is of great help for the promotion of probability theory in engineering practice. Using the Fellenius limit equilibrium method and Monte Carlo simulation, the reliability analysis of simple soil slopes with typical slope gradients was carried out, and the change laws of β with slope height h and the coefficient of variation of strength parameters, i.e., δc and
$\delta_\varphi $ $\overline c $ $\overline \varphi $ $\overline c $ $\overline \varphi $ $ {F}_{\mathrm{s}} $ $\; \beta _{\text{d}}^{\text{u}}$ $ a_{\text{d}}^{\text{u}} $ $ F_{\text{s}}^{{{ - }}b_{\text{d}}^{\text{u}}} $ $ a_{\text{d}}^{\text{u}} $ $ b_{\text{d}}^{\text{u}} $ $\overline \varphi $ $\overline c $ ${\overline c ^2}$ 关键词：subgrade slope;reliability index;safety factor;coefficient of variation;estimation bias- 327
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发布时间：2024-01-10 - 摘要：With the development of resources entering the stage of deep mining, the problem of dynamic disasters in the mining process of deep buried mines has become increasingly prominent. When dealing with these problems, the limitations of traditional static stability analysis methods are shown, and it is of great significance to study the design method of pillar size suitable for deep mines. Based on the area bearing theory and the method of estimating pillar strength in metal mines, the characteristics of the pillar strain energy accumulation and transformation under the instantaneous mining method were mainly discussed through the dynamic functional transformation relationship. The process of staged stratified mining of underground ore bodies was simplified, and a design method of pillar size parameters based on the theory of releasable energy was proposed to adapt to different stratified drilling and blasting methods. Relying on an engineering example, the energy method was applied and compared with the traditional strength theory method. Then, five groups of pillar size parameter schemes were proposed, which were further optimized by finite difference software (FLAC3D) to finally determined the reasonable pillar size design value. The research results show that a certain degree of dynamic response occurs inside the mine pillar under the action of dynamic excavation, while the dynamic stress and dynamic deformation that can be twice as high as that of the static analysis were also generated, and a large amount of energy was accumulated at the same time. Compared with the traditional strength calculation theory, by applying the energy method, the possibility of dynamic instability of the pillar in the case of rapid mining can be effectively avoided, and more conservative pillar size parameters were designed. As the number of excavation layers increases, the energy check method gradually tends to be equivalent to the strength static method. After optimization and comparison through numerical simulation, a plan of mining in three times, the width of the mining pillar is 22 m, and the height of 70 m was proposed, which can basically meet the needs of safety, stability and economic benefits during the mining process, and it is in good agreement with the actual engineering.关键词：underground mine;stope stability;pillar size;dynamic response;energy method
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发布时间：2024-01-10 - 摘要：Among the materials used in outlet structures of hydraulic engineering, elastic materials have a very broad application as anti-cavitation materials. It has clear practical significance and theoretical value to study the interaction between cavitation bubbles and different material surfaces and explore the anti-cavitation mechanism of elastic materials. By carrying out ultrasonic cavitation erosion experiments of materials with different elasticity, we analyze the cavitation erosion characteristics of different elastic materials from the macro and micro perspectives, and investigate the factors affecting the anti-cavitation properties of materials. The elastic materials used in this study include 216–1 silica gel, 216–2 silica gel, 218–1 silica gel, 218–2 silica gel, polyurethane, soft polyvinyl chloride, rigid polyvinyl chloride, phenolic laminate, low-density polyethylene, high-density polyethylene, polyamide and other materials, and the corresponding tensile elastic modulus ranges from 1 to 4 660 MPa. The main conclusions are as follows: 1) The materials with an elastic modulus of 1～11 MPa have no erosion mass loss under ultrasonic cavitation. In addition, the surface of the elastic material has only small texture changes and no crack or hole on the morphologies, which demonstrates their good anti-cavitation characteristics. 2) With the increase of elastic modulus, the cavitation erosion characteristics of different elastic materials have shown obvious differences, indicating that the correlation between the anti-cavitation properties of materials and their elastic modulus decreases, rather the anti-cavitation properties of materials are related to the material density, structure, etc. The larger density and densely structured materials have less erosion mass loss and change of surface roughness, while lower densely structured materials have more erosion mass loss and increased surface roughness, and the cavitation erosion is more likely to occur at the defects on the surface of the materials.关键词：elastic material;ultrasonic cavitation;cavitation bubble;cavitation erosion
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发布时间：2024-01-10 - 摘要：The riparian vegetation can change the characteristics of the river flow, thereby affecting the bank erosion, bank stability and the river evolution trends. In order to clarify the influence of riparian vegetation on the hydrodynamic characteristics, the method treating the vegetation as a solid wall boundary was proposed. Using the Reynolds stress model to close the turbulence equation, a three-dimensional hydrodynamic numerical model for the compound channel flows was constructed. The flow characteristics model of the compound channel under the condition of no vegetation was verified first. The model was then applied to the study of the water flow characteristics of a compound river with vegetation on the bank slope. The differences in the distribution of velocity, flow, river bed shear stress, Reynolds stress, and turbulence kinetic energy under emerged rigid vegetation, submerged rigid vegetation, alternating emerged and submerged rigid vegetation, and no vegetation were compared. The results show that vegetation intensifies the momentum exchange between the floodplain and the main channel, causing the increase in the number, the intensity and the range of secondary current vortexes. At the same time, the cross-sectional flow velocity, flow, river bed shear stress, Reynolds stress and turbulence kinetic energy are significantly reduced in the beach-trough junction area, and the turbulence exchange was significantly increased in the area around the vegetation. The effect is most significant when emerging rigid vegetation is planted on the bank slope. Compared with the case of no vegetation, the number of secondary flow vortices increases by one pair, and the velocity, flow distribution, river bed shear stress, Reynolds stress and turbulence kinetic energy of the bank slope vegetation area are greatly reduced and even close to zero. The turbulence exchange in the surrounding area near the vegetation is intense, and the dimensionless turbulence kinetic energy value can be increased to 20. In addition, as the riparian slope ratio decreases, the momentum exchange between the floodplain and the main channel without vegetation gradually decreases. However, when non-submerged rigid vegetation is planted on slope, the attenuation degree of momentum exchange will be weakened.关键词：riparian vegetation;flow characteristics;compound channel;Reynolds stress model;numerical simulation
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发布时间：2024-01-10 - 摘要：Rainfall intensity and duration are crucial meteorological factors to result in torrents. Intensive rainfall in short duration is very likely to cause torrent disaster. Analyzing the factors of precipitation is the key for torrent disaster prevention and warning. To investigate potential links between multiscale rainfall and localized torrent, by using hourly rainfall observation data from meteorological automatic weather station from 2010 to 2018, this paper statistically analyzed the multiscale rainfall features in hilly region centers around Magui River basin, especially focusing on possible precipitation factors causing local torrent in terms of short duration heavy rainfall (hourly rainfall over 20 mm), and concluded classified conceptual synoptic models on typical short duration heavy rainfall. The main conclusions are as follow: The maximum frequency of annual rainfall or heavy rainfall in South China is not centered on Magui River basin, however, the short duration heavy rainfall in Magui River basin is frequent and intensive. Frequent torrent disaster has closer relationship with short duration heavy rainfall in shorter time scale rather than with heavy rainfall in general concern. Short duration heavy rainfall in this region presented as bimodal peaks. The frequency and intensity of short duration heavy rainfall in pre-summer rainy season (i.e., from April to June) were higher than those in post-summer rainy season (i.e., from July to September). However, the short duration heavy rainfall is mainly concentrated in the afternoon in post-summer rainy season. The short duration heavy rainfall commonly occurs in four basic background types related to cold shear line, low-level vortex, southerly jet, and tropical cyclone, in which the differences were presented in both atmospheric system patterns and environmental conditions. These results help us to better understand the relationships between short duration heavy rainfall and torrent over hilly region in South China, and can be reference for prediction and warning on local short duration heavy rainfall and torrents.关键词：flash flood induced by rainstorm;multiscale rainfall;conceptual model;hills in South China
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发布时间：2024-01-10 - 摘要：Floating objects are important sources of apparent pollution in a river. Strengthening the detection of floating objects is an important step to improve the ecological quality of the water environment, and it is also a technical means to actively implement the “river chief system” policy. Because floating objects on the water have the characteristics of high scene complexity, irregular shapes, and multi-scale morphological changes, it is challenging to use traditional image recognition methods to detect targets quickly and effectively. In this paper we propose a real-time and robust intelligent detection method for floating objects on the water surface based on deep learning. First, the low-quality floating objects image is denoised and enhanced based on the sparse decomposition idea, which reduces the impact of the complex water surface environment on the image quality of the floating objects. Secondly, lightweight MobileNetV2 is selected as the backbone of a single shot multi-box detector (SSD), and standard convolution is replaced by depthwise separable convolution in the prediction layers. A dynamic feature pyramid network (DyFPN) is adopted at extra low cost to improve the detection precision of multi-scale objects and to make up for the deficiency of SSD to force different network layers to learn the same features. More significantly, the unified quantized convolutional neural network (Quantized-CNN) framework is applied to quantifying the error correction of the improved detector for further accelerating the computation of convolutional layers and compressing the parameters of fully connected layers to reduce the computational complexity and memory cost of the SSD algorithm. The experimental results conducted in this paper on the constructed water surface floating objects data set show that: Compared with the existing image recognition algorithm, the improved SSD detection algorithm has an average accuracy (AP) and comprehensive evaluation index (F1) score of 95.86% and 94.74%. The detection speed under the hardware GPU reaches 64.23 FPS. The parameter calculation of the detection algorithm is reduced to only 0.75×109, and the size of the model is compressed into 6.27 MB. The improved SSD algorithm achieves high accuracy and efficiency in the detection of floating objects on the water surface.关键词：intelligent detection of floating objects;deep learning;SSD algorithm;dynamic feature pyramid network;model quantification
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发布时间：2024-01-10 - 摘要：The advantages and disadvantages of dam deformation monitoring model are mainly reflected in the generalization ability of the model. Model generalization ability refers to the prediction ability of the model for samples outside the training set, and under-fitting and over-fitting are the main reasons for the low generalization ability of the model. Akaike Information Criterion (AIC) and Bayesian Information Criterion (BIC) are two commonly used model identification methods at present, but they cannot quantitatively compare and evaluate the over-fitting degree of the model. In this paper, the over-fitting degree of the model is quantified by defining the over-fitting coefficient (OC). At the same time, the complex correlation coefficient (R) is used to quantitatively judge whether the model is under-fitting, and the R–OC model recognition criterion is established. Firstly, the dam deformation monitoring sequence is divided into fitting data and verification data, and the fitting data are fitted by the total regression method to construct a variety of deformation monitoring models. Then, according to the estimation value of the monitoring model and the probability distribution of the estimation error, the early-warning limits of the abnormal monitoring data is determined. The False Alarm Rate (FAR) of each monitoring model is then calculated. Finally, according to the evaluation indexes (root mean square error (RMSE), mean absolute error (MAE), mean absolute percentage error (MAPE)) of fitting and prediction errors of fitting period and verification period of different monitoring models, the OC was determined. The two-dimensional scatter plot was drawn with the use ofR, and the generalization ability of each monitoring model was evaluated. The results show that the OC has a good correlation with the FAR of the model. When the OC is less than 1, the monitoring model does not over-fit and will not issue error warning, and the FAR of the model is 0. When OC is greater than 1, the model FAR is positively correlated with OC. On the one hand, the R–OC model identification criterion describes the fitting accuracy of the model by theR. On the other hand, the over-fitting degree of the model is quantitatively evaluated by the OC. For different number of models to be selected, R–OC criteria can identify models with high fitting and prediction accuracy.关键词：dam;deformation monitoring;model identification;over-fitting
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发布时间：2024-01-10
HYDRAULIC & CIVIL ENGINEERING
- 摘要：Pulse flow as a special flow pattern occurring in sieve plate-packed towers has attracted more and more attention because of its high heat and mass transfer efficiency. This paper proposed the corrugated sieve plate packing in order to strengthen the gas-liquid interaction, extend the pulse flow region, and increased the intensity of the pulse flow and experimentally investigated the two-phase flow pressure drop and pulse flow behaviors in three sizes of corrugated plate packing. The pulse flow operation range of corrugated stacked sieve plate packing and ordinary stacked sieve plate packing was compared, and the correlation between the pressure drop of corrugated sieve plate packing and the pulse flow operation range is put forward, and the correlation equations for the two-phase flow pressure drop and the upper and lower limits of gas and fluid flow rate for the pulse flow region in corrugated plate packing were proposed based on the experimental data analysis. The results showed that the effects of operating parameters and geometry parameters such as aperture diameter and opening rate on the pressure drop of two-phase flow in corrugated plate packing demonstrated similar trends to that in ordinary sieve packing, but the pressure drop was higher under the same conditions because of the enhanced irregular flow in the corrugated plate. The operating region for pulse flow in corrugated plate packing was significantly extended and the intensity of pulse flow was also enhanced compared with ordinary sieve packing. For the corrugated plate packing with a relatively large aperture, the onset flow rate of liquid that the pulse flow appeared was significantly reduced, and the upper limit of gas flow rate for the pulse flow region was significantly enhanced. The deviations of the correlation predictions for the correlation equations for the two-phase flow pressure drop and the upper and lower limits of gas flow rate for the pulse flow region in corrugated plate packing were 15% or less from the experimental values, which can be used for the design of corrugated plate packing tower.关键词：sieve plane plate packing;corrugated plate packing;gas-liquid downward flow;pulse flow
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发布时间：2024-01-10 - 摘要：The formation of manganese dithionate is the key scientific issue limiting the extensive industry application of flue gas desulfurization with pyrolusite. So far, the formation mechanism of manganese dithionate has not been clarified, which is difficult to provide effective theoretical guides for controlling manganese dithionate formation. The rate-controlling steps and dynamic process of manganese dithionate formation for pyrolusite leaching process with sulfur dioxide waste gas has been clarified in this paper based on the combination of theoretical analysis and experimental verification. Firstly, the reaction system was analyzed theoretically through literature studies, based on the free radical production mechanism of SO2 oxidation and the reduction leaching kinetics model derived from surface complexation and electrochemical model were proposed. The formation mechanism of manganese dithionate can be proposed based on HSO3 free radical formation mechanism, which has manifested that the formation rate of manganese dithionate was depended on the production rate of HSO3 free radical in microscopic scales, and can be determined by H+ and
$\text{HS}{\text{O}}_{\text{3}}^{{-}} $ ${{R}}_{\text{Mn}{\text{S}}_{\text{2}}{\text{O}}_{{6}}}{=}{k}\cdot{[}{\text{H}}^{{+}}]\cdot[{\text{HSO}}_{\text{3}}^{{-}}] $ $\text{HS}{\text{O}}_{\text{3}}^{{-}} $ $\text{HS}{\text{O}}_{\text{3}}^{{-}} $ 关键词：sulfur dioxide;pyrolusite;manganese dithionate;formation mechanism;dynamic- 527
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发布时间：2024-01-10 - 摘要：Fatigue crack is the main failure course of wheel steels, but its relationship with microstructure, texture, welding process and deformation remains unclear. Herein, a laser confocal microscope integrated with a tensile testing apparatus was adopted to in situ investigate the crack initiation and propagation of a 590 MPa strength wheel steel during hot-rolled, cold-deformed, and welded states based on the complex fabrication and welding processes. Further, by utilizing Electron Backscattered Diffraction (EBSD) technology, the relationship between the crack initiation and propagation process and the structure type, crystal orientation and texture strength were analyzed to reveal the underlying mechanism of the fatigue failure. It was found that the earliest crack initiation occurred in the 10% cold-deformed plate, followed by the hot-rolled plate, while the welded joint had the latest cracking onset. The crack propagation speed was highest in the cold-deformed sample, intermediate in the welded one, and lowest in the hot-rolled one. The crack propagation rate increased gradually in hot-rolled state. At the beginning stage, the crack propagation rate was low, and then increased slowly. With the extension of crack length, the stress intensity factor increased, accelerating the crack propagation. The EBSD results confirmed that the crack initiation was closely related to the dislocation slip process and the initiation in ferrite depended on the strength of {001} <110> texture. Accordingly, it was concluded that the resistance of wheel steels to fatigue crack initiation can be improved by reducing the cold-deformed structure or deformation degree during the fabrication process, as well as lowering {001}<110> texture strength of the hot-rolled one.关键词：fatigue crack;wheel steels;in situ analysis;hot-rolling;welding
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发布时间：2024-01-10 - 摘要：Given unsatisfactory heat transfer performance of the metal hydride reactors, a more compact and efficient single inlet-outlet heat exchanger tube with double helix structure was proposed. A three-dimensional model was established for the metal hydride reactors incorporating helical-coiled tubes, and was solved utilizing the commercial software package COMSOL Multiphysics 5.2a. Firstly, the thermal resistance analysis showed that for the helical-coiled tube with a 15 mm helical pitch, the percentage of the convection heat resistance inside the tube to the total thermal resistance is between 8.5% and 45.2% under different inlet flow velocities of the heat transfer fluid (0.5～3.0 m/s). The result indicated that the convection heat resistance inside the tube had a great influence on the heat transfer performance for the reactor. Then, the influences of the inlet flow velocity of the heat transfer fluid on the heat transfer performance of the reactors were investigated, and the range of the inlet flow velocity of the heat transfer fluid in the simulation was determined. Furthermore, the effects of the single and double helix structures were analyzed. The results show that when the inlet flow velocity of the heat transfer fluid is greater than 0.5 m/s, the heat transfer performance reaches a desirable level, and the average true temperature boost of the heat transfer fluid tends to stabilize. Besides, the average true temperature boost of the heat transfer fluid and the heat transfer and output performance of the reactors are significantly improved by reducing the helical pitch. For the single and double helix tubes with a 60 mm helical pitch, the time for reducing the average bed temperature to 300 K is shortened from 7 000 s to 3 000 s. In addition, the double helix tube with a 30 mm helical pitch has the higher gravimetric exergy-output rate than the single helix tube with a 15 mm helical pitch. These results suggest that the reactor with double helix tube has better heat transfer and output performance than the reactor with single helix tube. The double helix tube has a larger heat transfer area and a more uniform distribution in the metal hydride beds, thus improving the heat transfer and output performance of the reactors.关键词：metal hydride;reactor;helical-coiled tube;double helix structure;heat transfer performance
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发布时间：2024-01-10 - 摘要：Ionic liquid analogues are new solvents developed in recent years, which not only have the unique physicochemical properties of ionic liquids, but also have the advantages of simple synthesis and low price, offering great prospects for application in electrodeposition aluminum technology. However, the relevant mechanisms remain to be clarified, and these in turn are crucial for the development of new processes for the ionic liquid analogues electrolytic refining of aluminum. In the present work, AlCl3/urea ionic liquid analogues as an electrolyte, its physicochemical properties, the electrochemical behaviors of aluminum in the electrolyte, the morphology and phase structure of the deposited aluminum were investigated using such tests as conductivity meter, viscometer, linear sweep voltammetry, field emission scanning electron microscope (FE–SEM) and X-ray diffractometer (XRD). The effects of AlCl3/urea molar ratio and temperature on electrical conductivity and viscosity were systematically analyzed. The effects of temperature on the precipitation potential of aluminum ion, the kinetics of the reduction process of aluminum ion, the morphology and structure of the deposited aluminum were investigated. The results showed that the AlCl3/urea electrolyte with a molar ratio of 1.3∶1.0 had better physicochemical properties because of the highest conductivity and the lowest viscosity under the same conditions, and its conductive activation energy was 19.82 kJ·mol–1. It was found that the increase of temperature promoted the charge migration reaction, resulting in a positive shift in the precipitation potential of aluminum and an increase in the exchange current density. This trend was reinforced by the increase in temperature, indicating that the higher temperature facilitated the faster reduction of Al (Ⅲ) ions on the copper substrate. FE−SEM results showed that changes in temperature had little effect on the apparent morphology of aluminum deposition products, but had some influence on particle size and denseness. XRD analysis indicated that the grain growth pattern was also influenced by temperature, but all with (111) preferential orientation of the crystal plane.关键词：aluminum;AlCl3/urea;conductivity;viscosity;electrochemistry;electrodeposition;ionic liquid analogues
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发布时间：2024-01-10
CHEMICAL ENGINEERING & MATERIAL ENGINEERING
- 摘要：Nighttime image dehazing provides significant industrial contributions to unmanned driving and traffic security. To address the inability of the dark channel prior algorithm facing the foggy night scenes, a night image dehazing algorithm is proposed based on adaptive atmospheric light and weighted guided filtering. The distribution map of the atmospheric light is estimated using the guided filter based on the channel map obtained by image brightness and saturation. Bright channel prior is introduced to correct the transmittance of the bright region to solve the problem of dark channel failure in the bright region. To enhance the fusion of the light and dark channels, a weighted fusion method is used to calculate the weight of the bright region based on piecewise gamma correction, which is further applied to infer the initial transmittance of the raw image. A weighted aggregation guided filtering is proposed to refine the initial transmittance, focusing on addressing the edge blurring caused by the weakened tiny texture of the guided filtering. After converting the intermediate restored image into the HSV domain, image equalization is performed on the V (Value) component to further enhance the image. Finally, the linear weighting algorithm is applied to fuse the enhanced image and the intermediate restored image, to obtain the final recovered image. Experimental results demonstrate that the proposed algorithm is able to properly estimate the atmospheric light distribution map, which can effectively reflect the atmospheric light distribution for the multi-light source in a nighttime scene. The transmittance of both the bright and dark image regions can be accurately calculated to completely recover the raw image with clear texture. In addition, the proposed approach outperforms other comparative baselines, harvesting 49.4%, 18.3%, 172.3%, and 115.0% relative performance improvement on the peak signal-to-noise ratio, information entropy, average gradient, and variance of the restoration results, respectively.关键词：nighttime dehazing;atmospheric light;weighted aggregation;bright channel
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发布时间：2024-01-10 - 摘要：Cryptanalysts now can effectively find the collisions of MD5, SHA1 and other international hash algorithms in a short time. Increasing entropy to enhance the randomness of hash value is an effective way to improve the anti-collision performance of hash algorithm. Therefore, an improved scheme combining the iterative structure of error-correcting code and SM3 algorithm was proposed. Firstly, based on the linear properties of error-correcting codes and the maximization principle of minimum Hamming distance, the binary linear block codes constructed by matroid theory were selected to calculate their systematic form of generation matrix, the rules between bits were eliminated by cyclic shift, and the effective code words were calculated. Secondly, in the linear block code, an optimal code word was selected to construct the initial constant value according to the periodicity principle, and its value was assigned to the initial register. At the same time, a compression function of the initial register formation algorithm was introduced into the iterative structure to complete the second construction of the iterative structure of the hash algorithm. Finally, considering the evaluation ability of hash value information entropy on chaos degree of the algorithm, the proposed scheme was compared with existing international hash algorithms, and avalanche effect, the algorithm efficiency and memory loss were tested and comprehensively evaluated. Experimental results showed that the proposed scheme has stable avalanche effects without changing the computational efficiency, the memory loss during operation is 0.01~0.07 MB lower than that of SM3 algorithm, and the information entropy of the hash value is higher than that of other comparison algorithms. The improved scheme based on error correction code can prove that the randomness between hash bits is higher through entropy increase, which can better achieve the purpose of hiding statistical information between plaintext and hash, value, and improve the security of hash algorithm.关键词：hash algorithm;information entropy;error-correcting code;avalanche effect
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发布时间：2024-01-10 - 摘要：Smart grid, the intelligent system for the power grid, can be defined as a communication and information support platform based on the coordinated development of transmission networks and distributed power grid. It is also a highly integrated system characterized by informatization, automation, and interaction of all voltage levels, including power transmission, transformation, distribution, and dispatch. However, the smart grid is facing the following technical challenges, including the data transmission protocol for power grid monitoring, computing/processing efficiency, as well as detections for information, network attacks, and data anomalies. To this end, a novel data tag-based intelligent power grid monitoring architecture and anomaly detection algorithm is proposed using the Internet of Things and data-tagging technologies. The monitoring framework and anomaly detection are firstly designed based on data tagging for the intelligent power grid, including data labeling method, and task categories for monitoring-related big data. Subsequently, the anomaly detection paradigm is designed to support the monitoring framework, in which the sparsification/simplification and detection algorithms are proposed based on data labels. To validate the proposed framework, the experimental and simulation configurations are provided to conduct the result comparison over selective baselines, in terms of the accuracy and recall under different sequential data dimensions, anomaly data amounts, as well as running time for different test data amounts. Experimental results demonstrate that, compared to the baselines, the proposed approach achieves over 80% accuracy and 82% recall with the increase of the sequential data dimensions. In addition, a similar performance improvement in terms of accuracy and recall can also be obtained for different anomaly data amounts. As to the running time, the proposed approach also harvests a reduction of 2.0～3.0 seconds for different test data amounts.关键词：outlier data detection;monitoring;smart electric grid;data-tag
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发布时间：2024-01-10
INFORMATION ENGINEERING
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