最新刊期
卷 55 ， 期 1 ， 2023
- 摘要：Load redistribution (LR) attacks are common false data injection attacks in cyber-physical power systems. Under the background of close coupling between a natural gas network and a power system, the LR attack on the integrated electricity natural gas system (IEGS) may have a more serious impact on the safe operation of the system. Therefore, LR attacks were deeply studied under IEGS in this paper. First, based on the analysis of the mechanism of bilateral coordinated LR attack under IEGS, the implementation strategy of LR attack was studied. Second, considering the impact of cascading failures on the power system and taking the maximum economic loss of the IEGS as the objective function, the loss assessment model of LR attacks under IEGS was established. Meanwhile, the losses of different energy subsystems were measured uniformly, the risks of LR attacks on system security and economic operation under different scenarios were quantified, a new node comprehensive vulnerability evaluation index were defined, and the high vulnerability nodes in the IEGS were assessed comprehensively. Third, the nonlinear constraints in the natural gas pipe flow were linearized. The IEGS scheduling model was converted and added into the attack model as Karush–Kuhn–Tucher (KKT) optimality conditions, thus the whole model is transformed into a mix-integer linear programming. Finally, three LR attack scenarios were simulated on the IEEE 39-bus and the improved Belgium 20-bus system. During the simulation process, the attack effects of the three attacks under different attack resources were verified. Besides, the distribution and change of high vulnerability nodes of the system were analyzed, and the comprehensive protection strategies for different LR attacks were proposed. The experimental results showed that the system suffered more serious losses under bilateral coordinated LR attack. However, after adopting the comprehensive protection strategy based on the evaluation and analysis methods proposed in this paper, the system loss is significantly reduced.关键词：integrated electricity natural gas system;bilateral coordinated LR attack;node vulnerability transfer;cascading failure
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发布时间：2024-01-18 - 摘要：In order to solve the problem that the traditional electricity market mechanism can’t fully reflect the characteristics differences between renewable energy generations and conventional generations, a spot market trading model of the electricity market with high renewable energy proportion was proposed in this paper. Firstly, the renewable energy generation attributes were divided into resource attributes and load attributes, and the difference of the settlement between the real-time market and the day-ahead market caused by renewable energy generations was defined as the system balance cost. By analyzing the impact mechanism of renewable energy attributes on the system balance cost, the accuracy index and correlation index were used to describe those attributes. The renewable energy power quality index was further presented using the improved cross-entropy method. Combining this index and the system balance cost, the renewable energy power quality price was obtained for quantifying the power quality of the renewable energy. Secondly, the clearing model of the PJM market in the U.S. was improved. Renewable energy generations were added with the power quality price and cleared together with conventional generations. A market trading environment with competition on the same platform was established and the incentive-compatible settlement rule was proposed. Finally, an improved IEEE 30-nodes system example was used to verify the effectiveness of the proposed model. The case results showed that the proposed clearing method can achieve a priority consumption of high-quality renewable energy, reduce amounts of power deviation between the day-ahead market and the real-time market, decrease the system balance cost and the market average electricity price. Moreover, conventional generations can get extra income during the peak load period and the strategic bidding of renewable energy will increase its loss by an average of 9%. The research reflected that the proposed model is in favor of the improvement of renewable energy quality and fair competitions. The proposed model provides a solution to the fixed cost recovery of long-term marginal units, guides future capacity investment of conventional units and provides capacity guarantee for the construction of new power systems.关键词：power quality index;quality price;renewable energy market;spot market;market model
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发布时间：2024-01-18 - 摘要：In order to minimize the impact of coal-fired units (CFUs) decommissioning and large-scale non-synchronous generation installation on the secure and stable operation of receiving-end grids, a coordinated strategy for the decommissioning of CFUs and the configuration of synchronous condensers (SynCons) considering the support capability of power systems was proposed in this paper. Firstly, the index of the DC reactive power support factor was established, the decommissioning priority order of CFUs in the receiving-end grid was determined by the service life, the pollutant emissions, the coal consumption rate, and other general factors. Secondly, the maximum decommissioning capacity of CFUs was calculated by the post-contingency maximum rate-of-change of frequency and the frequency nadir constraints. Thus, the corresponding decommissioning strategy for CFUs has been formed. Then, a configuration strategy of SynCons based on the bisection algorithm was proposed to meet the voltage support capacity requirements of the receiving-end grid with the decommissioning of CFUs, which can achieve the optimal configuration capacity and location of SynCons. Finally, after the configuration strategy of SynCons was set, the maximum decommissioning capacity of CFUs was updated synchronously. The decommissioning strategy of CFUs was adjusted, so as to realize the mutual coordination between the decommissioning strategy of CFUs and the configuration strategy of SynCons. Simulations on a modified IEEE 39 system and the power system in Henan province were conducted to verify the effectiveness of the proposed coordinated strategy. According to the transient simulation results under multi-infeed short-circuit ratios and faults, the obtained results determined by the proposed strategy can effectively reduce the influence of CFUs decommissioning on the static voltage stability of the power system under the same decommissioning capacity. Furthermore, the transient simulation results also show that the proposed strategy can reduce the influence of large disturbances on the transient voltage stability of the receiving-end grid.关键词：decommissioning of coal-fired units;synchronous condenser;support capability;receiving-end grid;voltage;frequency
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发布时间：2024-01-18 - 摘要：Modular multilevel converter based high voltage direct current technology (MMC–MTDC) using overhead lines is an effective solution to solve the grid connected consumption of high proportion and long-distance renewable energy. However, the fault rate of overhead lines is high, and the DC fault ride through problem needs to be studied urgently. A coordinated control using the existing decentralized energy storage in the wind farm was proposed in this paper to realize the DC fault ride through of wind power generations in the MMC–MTDC. Firstly, the topology and basic working principle of MMC and energy storage systems of wind farms in the multi-terminal HVDC based on MMC were studied. Secondly, for the DC fault in the MMC–MTDC system with large-scale wind power integrated, the non-fault pole power margin was analyzed quantitatively. The unbalanced power during the fault period was absorbed by controlling the existing parallel energy storage system and the full-power converter of wind turbines. For different power consumption schemes, a fault ride through method was proposed which combining the energy storage system, converter stations, DC circuit breakers and wind farms. According to the action signal of DC circuit breakers, the fault classification was carried out and the control mode of converter station and the output of wind farm were adjusted. Thus a rapid recovery of different faults can be realized. The proposed strategy can maintain the wind power system connected to the power system during the fault period without locking, overload and other problems, and improve the system stability. Finally, the simulation model was built on the PSCAD/EMTDC platform, and the DC fault ride through strategy of the wind farm through the MMC–MTDC grid connected system was studied in detail. It was verified that the proposed DC fault ride through strategy based on the energy storage system can maintain the power balance during the fault, realize rapid fault recovery, and achieve DC fault ride through smoothly. The proposed fault ride through strategy is expected to provide the necessary basis and reference for the renewable energy in the MMC–MTDC grid connected system.关键词：MMC–MTDC;wind power generation;energy storage system;DC fault ride-through
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发布时间：2024-01-18 - 摘要：As one of the main power customers of the power system, rail transit consumes a large amount of electricity for electric locomotive traction every year. Therefore, reducing the traction energy consumption and improving the resilience and efficiency of the energy supply system are of great practical significance to promote carbon peaking and carbon neutrality. On the basis of the traditional traction power supply structure, the rail transit “grid-source-storage-vehicle” collaborative energy supply system introduces the energy storage system (ESS) and the renewable energy generation system. However, self-consistency of the three (load, the ESS and the renewable energy generation) and reducing the influence of two-way volatility and uncertainty on the energy management systems have become new issues. In order to achieve the above goals, reduce the power impact of the traction load on the traction network, and prolong the service life of the ESS, a “grid-source-storage-vehicle” dynamic threshold energy management strategy based on the fuzzy Petri networks (FPN) was proposed in this paper. Based on the basic power distribution framework of “grid-source-storage-vehicle”, a dynamic energy interaction rules were set in this strategy between the traction power supply system, the ESS and the renewable energy generation system under multiple operating conditions, which could be applied to the “grid-source-storage-vehicle” collaborative energy supply system with different structures. On this basis, the power of electric locomotive and the life of the ESS were taken as the input parameters of the FPN. After that, the adaptive dynamic adjustment of the discharge threshold was realized after the operations of fuzzification, Petri networks reasoning, and de-fuzzification. In this paper, the measured data of a traction substation was taken as a test case. The simulation results showed that, compared with the energy management strategy based on fixed thresholds, the energy feedback efficiency and regenerative braking energy storage efficiency could be effectively improved by the dynamic threshold management strategy based on FPN. At the same time, the utilization of photovoltaic power generation system is increased. The average energy taken by electric locomotives from the power system and the average discharge depth of the ESS are reduced as well, which could prolong the expected life of the ESS and improve the energy utilization of the collaborative energy supply system. To sum up, this strategy has positive significance for extending the expected life of the ESS and improving the energy utilization efficiency and operating economy of the collaborative energy supply system.关键词：rail transit;energy storage system (ESS);fuzzy Petri nets;dynamic threshold
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发布时间：2024-01-18 - 摘要：The design and analysis of modular multilevel converter (MMC) is usually carried out under the condition of power grid balance, but the AC power grid is unbalanced in actual operation. The imbalance of the power grid will cause the DC components of the circulating current of the MMC bridge arm to be no longer equal, including the positive sequence, negative sequence, and zero sequence components of the double frequency, which will increase the system loss and affect the system performance. In this paper, based on the mathematical model of MMC and the instantaneous power of phase units, the generation mechanism of circulating current was analyzed, and the equivalent circuit of each component of circulating current was obtained when the power grid is unbalanced. Then, a circulating current suppression strategy based on second order generalized integrator (SOGI) was proposed under unbalanced power grid. This strategy can suppress the second harmonic component of three-phase circulating current and the unequal DC component separately. Based on SOGI, the proposed strategy uses proportional integral (PI) control to extract the positive sequence and negative sequence second harmonic components of bridge arm circulating current. Meanwhile, quasi proportional resonance (PR) is applied to control the zero sequence second harmonic component of the circulation. Finally, a 217 level MMC system model was built in PSCAD/EMTDC platform, and through simulation experiments, the circulation suppression strategy proposed in this paper was compared with three typical strategies, i.e. the traditional circulation suppression strategy, the circulation strategy controlled by quasi proportional resonator and the circulation suppression strategy controlled by proportional integral resonator (PIR) . The experimental results showed that in the case of single-phase non-metallic ground fault, compared with the other three circulating current suppression strategies, the proposed strategy can suppress the second harmonic component of circulating current to 0.000 6 kA and reduce the harmonic distortion rate to 0.03%, which verifies its superiority. Furthermore, in the case of two-phase non-metallic ground fault, the proposed strategy can suppress the second harmonic component of the circulating current to 0.003 9 kA and reduce the harmonic distortion rate to 0.22%. The simulation results verify the effectiveness of this method.关键词：unbalanced grid;modular multilevel converter;second order generalized integrator;circulating current suppression strategy
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发布时间：2024-01-18 - 摘要：Hybrid DC, as a new direction of DC transmission technology, combines the advantages of traditional and flexible HVDC systems and plays an important role in the power grid black start. To clarify the technical conditions and control methods of hybrid DC participating in black start, a black start method based on hybrid DC and a coordinated recovery strategy of the DC receiving-end power grid were proposed in the case of major power outage for LCC-MMC hybrid DC transmission system. According to the characteristics of different recovery stages of black start, firstly, the start-up method of the hybrid DC transmission system under the condition that the receiving-end system is completely black in the initial stage were investigated, including the start-up and control methods of the sending LCC converter and the receiving MMC converter. Then, for the weak AC system at the early stage of black start, a virtual synchronization coordination recovery strategy of hybrid DC were adopted to enhance the system stability. Furthermore, after the system reaches a certain strength, corresponding control strategies and smooth switching methods between different control modes were proposed. Finally, the simulation verification were carried out in PSCAD/EMDTC software. The results show that with the energy consuming resistor at the initial stage of black start, LCC converter can effectively meet the minimum starting current limit. The MMC converter can establish the AC voltage at the passive end by using passive network control and maintain the system voltage and frequency within a stable range. After the non-black start power unit and load are connected to the grid, although the AC system strength changes, the proposed three-stage control switching strategy can effectively achieve smooth transition of each stage, and in the weak AC system stage, virtual synchronous control can ensure the system stability in the weak AC system stage. The three-stage control strategy has significant advantages over the two-stage recovery strategy, thus, the effectiveness of the proposed black start method and coordinated recovery strategy are verified.关键词：hybrid DC;black start;recovery stages;virtual synchronous;coordinated control
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发布时间：2024-01-18 - 摘要：In recent years, under the background of multi energy complementation and integrated energy systems, the gas–electricity distribution network has been developed rapidly. However, the frequently occurrence of extreme disasters around the world has brought serious challenges to the security of the energy system. In order to reduce the impact of load shed caused by extreme disasters on the system, a distributionally robust expansion planning model of integrated gas–electricity distribution considering system resilience constraints under extreme disasters was proposed. First, taking the minimum planning cost and annual operating cost as the objective function, an expansion planning model of the integrated gas–electricity distribution system considering electric vehicle charging stations, distributed gas units and energy storage equipment was established. Secondly, considering the role of extreme disasters, a distributionally robust expansion planning model of the integrated gas–electricity distribution system considering resilience constraints was put forward. The model included the base scenario and the worst scenario for extreme disasters. Among them, the economy of the system was considered in the basic scenario, the minimum planning cost and the minimum operating cost of the basic scenario were taken as the objective function, the worst scenario for extreme disasters were realized through resilience constraints to ensure the resilience of the system. And the proposed model was finally solved by the structural iterative solution model of the main problem–sub-problem. Finally, the case simulation results showed that, by increasing the planning and construction of electric vehicle charging stations, distributed gas-fired units and energy storage equipment, the economy of the system could be effectively improved. In the face of extreme disasters, the system loss could be reduced through the discharge of electric vehicle charging stations, distributed gas-fired units and energy storage equipment, but the unit planning costs required will increase significantly as the system resilience increases. The paper provides an effective and practical plan for improving system resilience at the planning level, and provides a certain reference to reduce the impact of extreme disasters on the system in the future.关键词：electric vehicle charging station;distributed gas-fired units;energy storage equipment;extreme disaster;resilience;distributionally robust optimization
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发布时间：2024-01-18 - 摘要：In order to solve the increasingly serious phenomenon of wind and solar curtailment under the large-scale development of new energy, many cities and parks in China have begun to widely electrolyze water to produce hydrogen as an effective way for new energy accommodation, resulting in more and more electricity–hydrogen coupling systems. Taking the chemical industry park as an example, a collaborative optimization dispatch method for typical park-level electricity–hydrogen coupling systems considering hydrogen load response was proposed. Firstly, based on the actual industrial park, a typical park-level electricity–hydrogen coupling system architecture was proposed. The electricity–hydrogen coupling system model of the chemical industry park including hydrogen production by coal, hydrogen production by water electrolysis, hydrogen storage tank, ammonia production by hydrogen, hydrogen fuel generator and hydrogen transmission pipeline network was further established from the perspective of source–network–load–storage. Secondly, the maximum overall benefit of the park was set as the objective function with the penalty term of wind and solar curtailment. The demand side response of the hydrogen load was considered so that the ammonia production by hydrogen can be used as a flexible resource in the park. On this basis, the coordinated optimization dispatch of the electricity–hydrogen coupling system in the chemical industry park was carried out. In order to verify the superiority of the optimal dispatch method proposed in this paper, the optimal scheduling results of three different operation scenarios were compared. The results showed that the electrolytic cell and hydrogen fuel generators could adjust their output power by tracking the changes of power supply and electrical load, reduce the power transaction and the cost of purchasing electricity under the premise of ensuring the power balance in the park. At the same time, considering the demand side response of hydrogen ammonia productions could further reduce the wind and solar curtailment and decrease the overall operation cost of the park under the premise of ensuring economic benefits.关键词：electricity–hydrogen coupling system;hydrogen production by water electrolysis;hydrogen load
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发布时间：2024-01-18 - 摘要：With the development of the electricity spot market and the “double carbon” goal in China, the participation of the wind-photovoltaic-energy storage power station (WPS) has become a mainstream trend. In order to consider the influence of the market price fluctuation and the renewable energy uncertainty on the output allocation of the WPS, a output allocation method of the WPS participating in the day-ahead, day-time and real-time markets was put forward in this paper. The portfolio theory from economics was taken as a trade-off tool for the profit and risk so that the WPS can maximize the benefits while taking the least risks. Firstly, considering the uncertainty of the wind power and photovoltaic output, a multi-time-scale revenue model was constructed based on the electricity price in the day-ahead, day-time and real-time markets. Secondly, the variance and covariance of electricity prices were used to describe the market risk and its correlation. The optimization model of output allocation was then constructed with the maximum profit and minimum risk as the objective function, considering the collaborative regulation of the internal energy of the WPS. Finally, the problem was solved by the augmented Lagrange method to get the optimal output allocation of the WPS in the electricity spot market over daily operation time. The market risk, the optimal output allocation of the WPS, the sensitivity and the calculation efficiency of risk aversion index were analyzed in this paper. The results showed that there is a strong correlation between the electricity price and risk. Compared with participating in a single market, the profit of WPS increased by 13.3% under the proposed method, the risk decreased by 84.1%. With the increase of risk aversion index, the WPS reduced its participation in high-risk markets. Moreover, this algorithm has high computational efficiency. Therefore, through the optimization method, the WPS can selectively participate in the market according to the risks and expected profits of different markets, and realize the maximization of profits and the minimization of risks according to its own risk aversion degree.关键词：portfolio theory;wind-photovoltaic-energy storage power station;outputallocation;risk aversion
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发布时间：2024-01-18
NEW TYPE POWER SYSTEM
- 摘要：With the continuous development of hydropower clean energy in China, many large hydropower projects have been built and put into operation. However, high dams and large reservoirs have led to frequent geological disasters in the reservoir area. Among them, reservoir landslide hazards are a major threat to the stability of project operation and the safety of life and property in the reservoir area, and it has become a major national demand to improve its comprehensive prevention and control capability. A reservoir landslide is a complex geological integration, which is influenced by intrinsic factors such as regional geological and topographical conditions and external hydrodynamic factors such as rainfall and reservoir water level changes. From the beginning of deformation to final instability, reservoir landslides generally take a long period of time and are an accumulating development process, involving not only the spatial and temporal superposition of rainfall infiltration and reservoir water level fluctuation but also the progressive cumulative effect of multi-factor coupling. Therefore, the mechanism of landslides in reservoir areas is very complex, and the difficulty of prevention and control is extremely high. Based on many field investigations, indoor and outdoor tests, and numerical simulations, the influence of geological and hydrological conditions on landslide susceptibility and spatial distribution was summarized, and the cumulative catastrophic instability mechanism of landslides in the reservoir area was revealed. The landslide surge simulation technology coupled with the discrete element model and the fluid mechanics model (DEM–SPH) was established, which could better reveal the strong collision between the high-speed landslide mass and the water flow and the nonlinear propagation process of the surge, and could provide a scientific basis for the landslide disaster affected area and the formulation of emergency risk avoidance plan. The monitoring technology of the 3D deformation evolution of reservoir landslides based on UAV and terrestrial laser scanning data fusion was constructed, and the comprehensive treatment technology of reservoir landslides was summarized. In addition, in view of the lack and limitation of research on the complex disaster-causing mechanism and prevention and control technology of landslides in the reservoir area driven by multiple factors, the future development direction of landslides in the reservoir area in terms of cumulative instability and stability evaluation of disasters, multi-source fusion monitoring and intelligent early warning, landslide surge fluid-solid coupling simulation and disaster impact assessment, and ecological measures support structure joint governance technology was expected to provide a reference for the research on landslide disaster prevention, control, and reduction in the reservoir area.关键词：reservoir landslides;failure mechanism;disaster assessment;monitoring and warning;prevention and mitigation
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发布时间：2024-01-18 - 摘要：Landslide dams are natural dams formed by river blockages with high speeds caused by landslides, collapses, and so on. Dam failures pose great threats to people and infrastructure upstream and downstream. A deep understanding of the influence of heterogeneous structures on dam breaching can provide an important scientific basis for the risk assessment and emergency treatments of landslide dams. In this study, laboratory physical modeling tests were conducted to investigate the effects of homogeneous, vertical heterogeneous, and horizontal heterogeneous structures on the breaching process. The experimental results showed that: 1) The erosion process of landslide dams was significantly affected by the material properties of the local location. 2) For the homogeneous dams, when the median diameter of materials increased, the breaching characteristics would change from laminar scouring to scarp erosion, then to multistage scarp erosion, the peak discharge would decrease, and the peak arrival time would be delayed. 3) For the vertical heterogeneous dams, the upper material mainly affected the duration and the upstream water level of the breach initiation stage; the middle material mainly affected the vertical erosion rate in the breach development stage; the bottom material mainly affected the stability of the downstream slope and the geometry of residual dam. The material distribution of the middle and bottom layers had the most significant effect on the peak discharge, because of the positive interaction between the breach deepening and the outflow accelerating. 4) For the horizontal heterogeneous dams, the upper material on the overflow side affected the initial vertical erosion rate; the bottom material on the overflow side and the upper material on the opposite side affected the subsequent vertical and lateral erosion rates, respectively; the influence of the bottom material on the opposite side was minimum. When designing the discharge channel, the influence of heterogeneous structures should be considered. Engineering measures should be adopted to restrict the breach deepening and promote the breach widening to minimize the peak discharge.关键词：landslide dam;physical modeling test;breaching erosion;outflow discharge;heterogeneous structure
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发布时间：2024-01-18 - 摘要：The intrusion of landslides into a river can block the river and induce surge waves. The evolution of the landslide–river blockage–surge wave disaster chain involves complex landslide–river interactions. To reproduce it realistically, an extended coupled discrete element method (DEM) and computational fluid dynamics (CFD) numerical method is proposed in this research: the VOF model is introduced to track the evolution of river free surface; a virtual sphere model is proposed to overcome the limitation of the critical size ratio of the mesh and particle; and the model is verified by several typical cases. Based on this, the simulation of the landslide–river blockage–surge wave disaster chain was carried out to reproduce the formation process of the Baige landslide-induced river damming, and the dynamic evolution process and interaction mechanism of landslide–river dynamics are investigated comprehensively. The results show that the proposed method can accurately simulate the landslide–river interaction during the evolution of landslide–river blockage–surge wave disaster chain; the landslide mass drives the propagation of surge waves, while the river significantly increases the kinetic energy dissipation of the landslide mass and has opposites effect on the deposition of the landslide along the flow directions; the simulated migration path, deposit morphology and wave erosion area of the Baige landslide are in good agreement with the field survey results, and the method successfully reproduces the October 11th, 2018 Baige landslide. The extended coupled DEM–CFD method proposed in this research provides a robust numerical tool for the understanding of the river blockage and impulse wave evolution mechanism, as well as the prediction of the disaster evolution process, which is of reference value for the of disaster emergency response and disaster mitigation strategies.关键词：landslide-induced river blockage;landslide-induced impulse wave;disaster chain;DEM–CFD coupling method;lanslide–river interaction;Baige landslide
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发布时间：2024-01-18 - 摘要：In view of the continuous incoming flow, barrier lakes in the large rivers are quite easy to be overtopped within dozens of days or even just several days and result in an extraordinary flood, seriously threatening the lives and property of people on both sides. Due to the rapid collapse deformation of the barrier body and high observation difficulty, it’s quite hard to accurately observe the breach morphology changes and hydraulic parameters at the emergency disposal site, thus obtaining no real data on the breach morphology development so far. Aimed at the huge outburst flow peak threat and ambiguous outburst mechanism, the historical barrier lake cases were investigated and revealed that it was the barrier body shape, particle gradation, reservoir capacity, and the incoming flow that determined the danger degree of the barrier lake. Moreover, referring to the Baige Barrier Lake, the large scaled 1∶80 indoor and 1∶20 outdoor physical models were both carried out to find out the breach morphology, which followed the principle of outburst flow velocity drive and outburst flow rate control. The main dynamic mechanisms of the breach development were the shear scour of sand-carrying flow, the vortex scours at the retrospective step, longitudinal scour by the high-speed outburst flow, and lateral slope collapse by gravity. The whole breach development process could be successively divided into four stages: Tail downcutting, retrospectively scouring, full section downcutting, and upstream scouring and downstream silting. Correspondingly, the horizontal breach morphology successively presented the four features of linear, inverted trumpet, hyperboloid, and approximately equal width. The retrospective step was the most efficient and determines whether the barrier body would break down. The large-scale physical model can promote the development of emergency drainage design and barrier body outburst control, providing a reference for the emergency disposal of the high-risk barrier lake.关键词：barrier lake;break mechanism;physical model;breach development;flow rate driving
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发布时间：2024-01-18 - 摘要：Landslide surge is a common geological disaster phenomenon. Due to the complex fluid-solid interaction between landslides and water, the traditional single-medium model cannot be solved accurately. Therefore, based on a coupling model of computational fluid dynamics (CFD) and discrete element method (DEM), the CFD method was used to simulate the water flow, and the DEM was used to simulate the motion of a granular landslide. Taking full advantage of the advantages of different computational models, the evolution process of landslide and surge was numerically simulated and analyzed. Firstly, this method was used to numerically simulate the particle accumulation collapse-surge experiment carried out by Robbe-Saule under the same working conditions. The particle motion process and the surge propagation process showed that the simulation results were in good agreement with the experimental results, which verified the effectiveness of the CFD–DEM fluid-solid coupling model. Then, the method was applied to analyze the evolution process of Seyu landslide-surge disaster in Houziyan reservoir of Sichuan Province, and the whole process of landslide movement, surge generation and propagation, surge climbing on the opposite bank and surge backflow was reproduced. The calculated surge height at the inlet of the power station was close to the measured data. The calculation results showed that the duration from unstable movement to static accumulation of Seyu landslide was about 20 s, and the maximum average particle velocity reached 16.12 m/s. The surge caused by the landslide spread to the opposite bank after about 10 s and then began to climb along the slope, with the maximum climbing height reaching 27.32 m. The research showed that the CFD–DEM fluid-solid coupling model could be well applied to the simulation of large-scale landslide and surge disasters in mountainous valleys, which could provide efficient technical support for disaster prevention and mitigation in the reservoir area.关键词：landslide–surge;computational fluid dynamics (CFD);discrete element method (DEM);coupled model;numerical simulation
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发布时间：2024-01-18 - 摘要：Hidden landslide hazard is the most common geological hazard in the lower reaches of the Jinshajiang River, which has the characteristics of strong concealment, and sudden and high-distance movement. In recent years, hidden landslide disasters occurred frequently in large mountainous areas, which posed a great threat to people's life and property. How to break through the limitation and lag of traditional geological disaster investigation means, identify hidden landslide hidden dangers and explore their development characteristics in advance is of great scientific significance for guiding disaster prevention and mitigation and engineering planning and construction in southwest China. The Yongshan section of the lower Jinsha River was selected, which was highly prone to geological disasters, and proposed the lifting rail time series INSAR–optical remote sensing comprehensive identification method. By using this method, we can identify the optical remote sensing information of regional time series surface deformation and hidden landslide hidden danger and explore the development characteristics of hidden landslide hidden danger through field investigation. Research showed that: 1) 26 hidden landslide hazards were identified by rail ascending sequence InSAR technology, 28 by rail descending sequence InSAR technology, and 48 by optical remote sensing (10 overlaps). A total of 92 hidden landslide hazards were identified, and a 100% field investigation was conducted on the identification results. The InSAR and optical remote sensing recognition results of lifting orbit were divided into four types: Completely consistent, partially consistent, only optical remote sensing recognition results, and only InSAR deformation recognition results. The recognition accuracy was 82.86%, 80.77%, 75.00% and 63.64%, respectively, and the overall recognition accuracy reached 78.26%. It was slightly higher than the average level of the identification of landslide hidden danger in China, which verified the reliability and effectiveness of the identification of landslide hidden danger. 2) Through comparative analysis of comprehensive remote sensing identification results, it was found that the identification results of InSAR technology and optical remote sensing were closely related to their identification methods, imaging conditions, and landslide activity, and the two could not be checked by each other directly. 3) According to the analysis of landslide development characteristics, the development law of hidden landslide hidden danger changes with the change of landform and geological conditions. The hidden landslide hidden danger identified by the lifting rail InSAR technology and optical remote sensing has certain differences in geomorphic spatial distribution and formation lithology. The results showed that the complementarity of the two methods was fully utilized to solve the problem of the invisible, unclear, and inaccurate hidden danger of hidden landslides, and improved the accuracy of landslide identification.关键词：Yongshan section of lower Jinsha River;sequential InSAR;optical remote sensing;comprehensive remote sensing identification technology;hidden landslide
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发布时间：2024-01-18 -
Slope Unit Extraction and Landslide Susceptibility Prediction Using Multi-scale Segmentation Method AI导读
摘要：Landslide susceptibility assessment can help us to effectively predict the spatial location of potential landslides, which is the basis of landslide hazard and risk assessment. Slope units are commonly employed to predict landslide susceptibility because they are extracted based on actual landforms and geomorphology with visible geological features. However, one of the key constraints limiting the applicability of slope units and the challenge in current research is how to efficiently and accurately extract slope units and take into account the heterogeneity of conditioning factors within slope units. The Chongyi County was selected as the case study. First, the aspect and shaded relief images were extracted as the initial fundamental data. The multi-scale segmentation (MSS) method was used to extract slope units and the optimal parameter combination including scale, shape weight and compactness weight was determined by combining the trial-and-error method with recorded landslide features. Then, a total of 15 conditioning factors such as elevation, slope and profile curvature were extracted based on slope units and were imported into the support vector machine (SVM) and logistic regression (LR) models to construct Slope–SVM/LR models. Furthermore, the range and standard deviation values were used to represent the heterogeneity of conditioning factors within slope units to construct the Variant Slope–SVM/LR models. Finally, the receiver operating characteristic (ROC) curves and frequency ratio (FR) accuracy were used to evaluate the predicted performance of landslide susceptibility models. The results show that: 1) when the parameters of scale, shape weight and compactness weight were set to 20, 0.8 and 0.8, respectively, slope units extracted by the MSS method in the study area were at their best. 2) The ROC accuracy of the Slope–SVM, Variant slope–SVM, Slope–LR and Variant slope–LR models was 0.812, 0.876, 0.818 and 0.839, respectively. The FR accuracy of those models was 0.780, 0.866, 0.792 and 0.865, respectively, indicating that the predicted accuracy of Variant slope–SVM/LR models was better than that of Slope–SVM/LR models. Therefore, it can be inferred that the MSS method is an effective method to accurately and automatically extract slope units, and the predicted performance of landslide susceptibility models can be significantly improved by considering the heterogeneity of conditioning factors within slope units.关键词：multi-scale segmentation method;slope unit;landslide susceptibility prediction;heterogeneity- 759
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发布时间：2024-01-18
MECHANISM OF LANDSLIDE–DAMMED LAKE AND ITS CONTROL
- 摘要：A prefabricated lightweight steel composite frames–perlite insulation reinforced with steel wire mesh composite wall (PSW) structure suitable for low-rise buildings in villages was proposed. The lightweight steel composite frame was composed of square CFST columns, H-shaped steel beams, double L-shaped joints, and concrete floors. The perlite insulation reinforced with steel wire mesh composite wall was composed of steel wire mesh reinforced mortar surface, perlite board, and EPS board. The lightweight steel composite frame was enclosed by PSW. The lightweight steel composite frame and PSW were assembled through the new connection of “packaging and gripping”. The wall units were connected through the “tongue-and-groove” connection. A full-scale two-story prefabricated lightweight steel composite frames-perlite insulation reinforced with steel wire mesh composite wall structure was subjected to seismic loading under 57 working conditions including white noise (PGA: 0.07g~1.50g). The damage evolution process, stiffness degradation, displacement response, and strain characteristics were discussed and analyzed. The results showed that: The PSW worked together with a lightweight steel composite frame and the PSW improved the lateral stiffness of the lightweight steel composite frame; With the increase of the input peak ground acceleration (PGA), the natural frequency of the structure decreased and the damping ratio increased; Under the action of 8-degree fortification earthquake (0.20g), the maximum story displacement angle was 1/361, and the structure was in the elastic stage; There was no significant damage to the structure under the action of 8-degree rare earthquake (0.51g); Under the action of an extremely rare earthquake, the damage of exterior wall was obvious, and the lightweight steel composite frame was basically intact. The flexible connection of “packaging and gripping” weakened the seismic response of the wall and improves the energy dissipation between the PSW and the lightweight steel composite frame.关键词：prefabricated structure;lightweight steel composite frame;perlite insulation reinforced with steel wire mesh composite wall;seismic performance;shaking table test
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发布时间：2024-01-18 - 摘要：To increase the applicability of the precast composite structure in low multiple-story buildings, the boundary connection of wall-slab based on monolithic precast composite structure was optimized, and a new total precast composite structure was proposed. Through the quasi-static tests of the total precast composite walls with horizontal joints using box connection, the seismic performance such as the failure mode, bearing capacity, behavior degradation law, and energy dissipation capacity of this kind of wall was studied, and the effects of different box connection details (wall shoes, integrated reinforcement, and distributed reinforcement) on the basic mechanical properties of the wall were compared and analyzed. The results showed that the total precast composite wall was a kind of structural member with lightweight, high strength, energy saving, and good seismic performance. All the specimens followed the failure path of three anti-seismic lines of “infills, middle rib-frame, and side rib column”, which highlighted the three-stage stress characteristics of the wall; Compared with the yield load and peak load of the DPC specimen (distributed reinforcement type), IPC (integrated reinforcement type) increased by 6% and 10% respectively, and WPC (wall shoes) increased by 2% and 5% respectively; The displacement ductility coefficient of all specimens was greater than 3.3, which met the seismic design requirements of reinforced concrete structures; The stiffness degradation law of all specimens was basically the same, and the stiffness degradation rate of DPC was the fastest; The cumulative energy consumption of all specimens showed a cumulative growth trend, and the cumulative energy consumption of IPC was 1.08 times that of WPC and 1.13 times that of DPC. The three different types of box connections had reliable connection performance, and the integrated reinforcement box connection had the best seismic performance. Its production and installation mode was also simpler and more efficient, which was more suitable for practical projects.关键词：precast concrete;total precast composite walls;horizontal joint;box connection;seismic performance;pseudo-static test
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发布时间：2024-01-18 - 摘要：The connections of cross-laminated timber (CLT) walls make up most of the lateral resisting mechanism and play a crucial role in the ductility and energy dissipation of the CLT wall system. An annular dissipative connector formed by U-shaped dampers was proposed to connect the CLT wall and the steel beam foundation. The aim was to shift the damage of the wall to the energy-consuming components to dissipate the seismic energy and protect the CLT wall. And the bearing load can be predicted easier, and the connections can be replaced after damage. Static shear cyclic tests were performed on seven annular dissipative connectors to investigate the main shear performance such as hysteretic curves, failure mechanisms, bearing capacities, stiffness degradation, and energy dissipation were studied. The effects of different widths and thicknesses of steel plates on the shear properties of the connections were compared. The shear bearing capacity of the anchored steel-CLT end with screws was theoretically estimated mainly based on Eurocode 5, and the calculation formula of the main mechanical parameters of the annular dissipative connectors was proposed. And the numerical simulation of energy-consuming nodes’ shear performance was carried out based on the finite element Abaqus software. The results showed that based on the experimental research, the proposed calculation formula for shear resistance of the CLT anchorage end, the calculation formula for the mechanical index of the annular Q235 damper, and the finite element analysis carried out could provide a basis for the design of dissipative connectors of CLT wall. Except for specimen D8–S86, the connections shifted the damage of wood to the energy-dissipating components. The calculation formula of the main mechanical performance index of the annular damper could accurately predict the yield force, initial stiffness, and yield displacement of the dissipative connectors. The established finite element model could predict the shear behavior of the dissipative connectors. An excellent dissipative connector (specimen D8–S55) for shear direction in load capacity and energy-dissipating capacity was presented after a series of analyses. The study can provide technical support for the engineering application of CLT structures in seismic areas.关键词：cross-laminated timber;annular dissipative connector;hysteresis curve;energy dissipation;shear resistance;finite element analysis
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发布时间：2024-01-18 - 摘要：At present, due to the cracking and falling off of the decorative layer of the building envelope, the problem of building energy consumption caused by the decline of building thermal insulation performance has been widely concerned. It is difficult to ensure that the wall has the same life as the building in the existing thermal insulation practices for exterior walls. The double shear test was carried out on a proposed sandwich composite wallboard with engineering cement-based composite (ECC) as the decorative layer and structural layer as well as extruded polystyrene (XPS) insulation board as the thermal insulation layer. On this basis, the failure modes of various specimens as well as the effects of the fabrication method, insulation layer thickness, connection, and the angle of basalt fiber reinforced polymer (BFRP) connection on the interface bond performance of ECC–XPS sandwich composite wallboard were studied. The results showed that the prefabricated specimens were of the worst bond performance, which was about 1/3 of that of the cast-in-place specimens. With the increase of insulation thickness, the shear strength and ductility of specimens decreased, and the decreased amplitude increased with the increase of thickness. The existence of connectors caused the improvement of the shear capacity and ductility of the specimen, as well as the change of the failure mode; Reducing the embedding angle of the connectors resulted in the improvement of the shear bearing capacity of the specimen, the reduction of ductility, and the change of failure mode. Toughness analysis was carried out on various specimens to evaluate the energy dissipation capacity of ECC–XPS sandwich insulation wall panels after reaching peak load. It was found that it could effectively improve the energy dissipation capacity of the specimen by setting a certain connector in the wall panel, and the specimens with 90° connector were of the most obvious improvement on the energy dissipation capacity, while the prefabricated specimens were of the worst energy dissipation capacity. In addition, based on the test results, the calculation formula of shear capacity proposed previously was revised. This study lays a foundation for the application of ECC–XPS sandwich composite wallboard in engineering practice.关键词：sandwich composite wall board;engineering cement-based composite;basalt fiber reinforced polymer;interfacial bond behavior;toughness index
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发布时间：2024-01-18
PRECAST RURAL RESIDENCES
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Development and Contribution of Natural Gas Industry Under the Goal of Carbon Neutrality in China AI导读
摘要：Achieving carbon neutrality has become a national strategy for China. Under this goal, China’s energy supply and demand structure will undergo profound changes. As a clean and efficient low-carbon fossil energy source, natural gas plays an essential role in the transition of energy consumption from high to low carbon. It is practical and worthwhile to analyze and study the contributions of natural gas to realize China’s carbon neutral goal and its perspective in the industry. In this work, the investigation of the carbon neutral concept and the implementation methods was conducted first. According to the data from research institutions, enterprises, and scholars, the prospects of China’s natural gas industry were summarized. Three scenarios were constructed based on the judgment of China’s economic development: baseline scenario, low-speed scenario, and high-speed scenario. Through the fixed base energy consumption elasticity coefficient method, the total primary energy, and natural gas consumption in the period of China’s carbon target were predicted. This study also summarizes the industry's development prospects from the supply and demand aspects of natural gas in China. The suggestions for the coupled development of natural gas and other green energy in the carbon neutral era were also made. It is found that: 1) Due to the cleanness and convenience, the consumption and proportion of natural gas in the energy system should be rapidly increased to replace coal, and it should be jointly constructed with renewable energy. 2) Based on the assumptions of the existing research, it is estimated that the total primary energy consumption of China in 2030 is 55.14×108 t~60.78×108 t (ton standard coal), and the natural gas consumption is 5 449×108 m3~6 006×108 m3; The total primary energy consumption in 2060 is 53.4108 t~68.20×108 t, and the natural gas consumption is expected to reach 5 280×108 m3~6 740×108 m3, thus the natural gas industry has huge development potential. Based on these findings, the suggestions are put forward for developing China’s natural gas industry: 1) While increasing the exploration and development of conventional natural gas at the supply side, China should actively promote the development of unconventional natural gas such as shale gas, coalbed methane, and natural gas hydrate. Moreover, boosting trade in LNG and pipeline gas to consolidate energy supply security; Gas-fired power generation and industrial heat will become the main ways of using natural gas on the consumer side. Especially in the new power system with new energy as the main source, gas power will take advantage of rapid response to bear the role of power system peak regulation and frequency regulation; The industrial sector needs to promote the replacement of coal with gas proactively, particularly in energy-intensive industries; 2) Combined with the current situation of the renewable energy industry, the roadmap of deep coupling development of the natural gas industry and green renewable energy systems such as wind, solar, and hydrogen is proposed from the three aspects: production, storage and transportation, and utilization, respectively. Firstly, increasing electric equipment in natural gas development process and developing CO2-enhanced shale gas extraction, CCUS or other negative emission technologies aggressively; Giving priority to infrastructure such as natural gas pipeline networks and underground gas storage, particularly emergency peak-shaving capacity construction to realize the deep integration of technologies such as power-to-gas, hydrogen storage, and carbon storage; Additionally, combined with the new power systems, through digital and intelligent technology to transform the management and control mode, realizing the intelligentization of natural gas storage, transportation and consumption, promoting the high-quality coordinated development of natural gas and new energy to ensure the realization of the “Dual Carbon” goals.关键词：carbon neutrality;energy transition;natural gas;renewable energy;coupled development- 661
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发布时间：2024-01-18 - 摘要：With the structural transformation of energy cleanliness for the reduction of the proportion of fossil energy and the increase of the proportion of “carbon-free” energy in China, the number of abandoned underground mines has increased. At the same time, wind and solar energy (WS) have been developed rapidly, but the utilization rate of resources is very low. In order to improve resource utilization and upgrading of transformation, a hybrid compressed air energy storage (CAES) system combining wind power and solar energy is proposed, and the abandoned underground mines are used as energy storage space of compressed air. Firstly, according to the solar power, wind energy, underground space resources of abandoned coal mine and distribution characteristics of power grid, the potential area for the establishment of WS–CAES hybrid system are obtained, which are mainly distributed in the “three north” zones. Then, the mathematical model of system parameters such as compressor, expander, heat exchanger and air storage chamber are established. The operating variables of system include heat exchanger effectiveness, ambient temperature, mass flow rate, total pressure ratio and compressor/turbine stages. The performance effect of these operating variables on the system performance and total efficiency was evaluated. Finally, in view of the feasibility of storing high-pressure gas in the roadway of the abandoned coal mine, the numerical calculation and analysis with the Comsol software is carried out from the aspects of the depth of the roadway, the permeability of the lining and the surrounding rock. The results show that the depth of the roadway has no obvious effect on the leakage of the stored gas in the system, and the roadway lining mainly plays an important role in the stability of the system, while the permeability of the surrounding rock is the key factor determining the air tightness of the system. The smaller the permeability of surrounding rock, the smaller the gas leakage and the better the air tightness, and the underground main ventilation lane and the transportation lane have the ability to store compressed air.关键词：compressed air energy storage;gas storage;air tightness;surrounding rock permeability;thermodynamic analysis;numerical simulation
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发布时间：2024-01-18 - 摘要：As the most effective strategy to reduce CO2 emission, carbon capture, utilization and storage (CCUS) technology has become the focus of global attention under the background of “carbon emission peak, carbon neutrality”. For the centrifugal compressor dry gas seal applied in CCUS technology, the spiral groove dry gas seal was taken as the object, and CO2 with impurities was used as the lubricating medium. Based on the equation of state for combustion gases and combustion gas–like mixtures（EOS–CG）, the density, enthalpy, sound speed and Joule–Thomson coefficient of CO2 mixture were studied. With the consideration of the real gas effect, viscosity–temperature–pressure effect, choked flow effect, centrifugal inertia effect and convective heat transfer between lubricating gas and sealing face, based on the solution of the Reynolds equation, energy equation and heat conduction equation of sealing rings by the finite difference method, the pressure field, temperature field, opening force and leakage rate of the CO2 with impurities dry gas seal was analyzed. The results showed that the density of CO2 with impurities increases with the increase of the pressure, and the enthalpy, Joule–Thomson coefficient increases with the decrease of the pressure when temperature is constant. The density decreases with the increase of the temperature when pressure keeps constant while an opposite trend is obtained for enthalpy. The sound speed increases as temperature increases while Joule–Thomson coefficient reduces under the same pressure within a lower pressure condition. In addition, when entrance pressure is 12 MPa, inlet temperature is 380 K, rotating speed is 15000 r/min, outlet pressure is 1.9 MPa, the temperature difference between the inlet and outlet of gas film is about 23 K, and it is about 10 K for sealing ring end face. When the rotating speed, inlet pressure and inlet temperature are regarded as variables, the temperature of gas film and sealing rings increases with the increase of the rotating speed and the inlet temperature, respectively, but decreases with the increase of the inlet pressure. The opening force increases with the increasing of the rotating speed, inlet pressure and inlet temperature. The leakage rate decreases with the increase of the rotating speed and inlet temperature, and increases with the increase of the inlet pressure.关键词：CCUS;CO2 with impurities;physical parameters;dry gas seal;temperature field
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发布时间：2024-01-18
CARBON NEUTRALITY AND GREEN ENERGY
- 摘要：After dam impoundment, the downstream reach will suffer from cumulative erosion for a long period of time. Due to different boundary conditions, the erosion adjustment characteristics of cross sections in different river patterns are different. Based on the measured date of cross sections in the Jingjiang Reach of the Yangtze River which is downstream of the Three Gorges Reservoir (TGR) from 2003 to 2018, in this paper we selected the typical cross sections of straight reaches, bifurcated reaches and meandering reaches, calculated the cross section characteristic parameters such as width, average depth and width-to-depth ratio, analyzed the similarities and differences of erosion adjustment of cross sections from different river patterns, and discussed its causes. The main findings include: 1) There are similarities and differences in morphological adjustments of cross sections in different river patterns. Under bankfull water level, the cross sections of different river patterns generally develop in the direction of narrowing and deepening. The width-to-depth ratio of straight and bifurcated cross sections under low water level is generally reducing, the cross sections develop in the direction of narrowing and deepening, while the width-to-depth ratio of meandering cross sections under low water level is mostly increasing, i.e., the cross sections develop at the direction of widening and shallowing. 2) The difference in the adjustment of the width-to-depth ratio between the bankfull channel and the low water channel is mainly controlled by the difference in the swinging range of the hydrodynamic axis. The swinging range of the hydrodynamic axis of the straight and bifurcated reaches cover both bankfull channel and low water channel, thus, the erosion is concentrated in the bankfull channel and low water channel, and they both show the characteristics of narrowing and deepening. As for the meandering reaches, the swinging range of the hydrodynamic axis lies in the bankfull channel, but exceeds the range of low water channel. During the flood season, it swings to the convex bank and washes the convex bank beach, thus the low water channel widens significantly, and the deep pool in the concave bank is deposited, the cross section develops in the direction of widening and shallowing. It is also found that the greater the width of the initial convex bank beach, the greater the rate of change of the width-to-depth ratio. 3) The lateral swinging range of the hydrodynamic axis reduced after impoundment, leading to a more concentrated scouring power, and this effect is more significant in wide and shallow reaches during the erosion process. In addition, the relative fine bed materials in wide and shallow reaches lead to low anti-scouring capacity, and thus a greater amplitude of the change in width-to-depth ratio after impoundment in cross sections that have larger width-to-depth ratio before impoundment.关键词：Jingjiang reach;river patterns;bankfull channel;low water channel;cross section geometry
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发布时间：2024-01-18 - 摘要：In recent years, scholars all over the world have realized that subsurface storm flow mechanism is one of the important runoff generation mechanisms in small watersheds in humid mountainous area. It is crucial to further explore the subsurface storm flow mechanism for flash flood simulation. This paper divides the discharge process of subsurface storm flow into three stages: water storage stage, rapid discharge stage and surface discharge stage. In the water storage stage, the precipitation needs to supplement the depression on the bedrock or the relative impermeable layer first. The phenomenon of “large rainfall but small runoff” often occurs in this stage. In the rapid discharge stage, the depression on the bedrock or the relative impermeable layer has filled, the transient saturation area gradually expands, and the pre-event water discharges rapidly. The phenomenon of “small rainfall but large runoff” often occurs in this stage. In the surface discharge stage, the transient saturation area further extends to the ground surface and discharges in the form of surface runoff. Based on this, the water storage and discharge formula is proposed to quantitatively describe the three stages, and the subsurface storm flow-based mountain hydrological model (SSFM) is constructed. Taking Guanshan River basin in Danjiangkou City, Hubei Province as the study area, 12 measured flood processes are selected and simulated by SSFM. Comparing the simulation results with those of TOPMODEL, the distributed time-varying gain model and Xin’anjiang model, it can be seen that: 1) the average peak flow errors of the time-varying gain model (TVGM), Xin’anjiang model, TOPMODEL and SSFM are –29.61%, –51.74%, –29.08%, –24.82%, respectively, and the average runoff depth errors are –30.83%, –26.87%, –18.43%, –9.67%, respectively. 2) The “water storage stage” and “rapid discharge stage” can explain the variation characteristics of “large rainfall but small runoff” and “small rainfall but large runoff” in flash flood process of Guanshan River basin. The results show that due to the introduction of three-stage subsurface storm flow mechanism, the simulation effect of SSFM is obviously improved compared to other models. SSFM is more suitable for flash flood simulation in small watersheds in humid mountain area, and it has potential application to flash flood forecasting and early warning.关键词：Guanshan River basin;subsurface storm flow mechanism;three-stage water storage and discharge formula;SSFM model;flood simulation
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发布时间：2024-01-18 - 摘要：Compared with conventional concrete structures, cracking of underwater concrete structures have a worse effect on structural safety. Accurate and timely monitoring of cracks in the process of occurrence and development is of great significance to ensure the safety of wading engineering and prevent accidents. Based on the coupling effects among fluid, heat source, and crack, a temperature tracer method for crack monitoring in underwater concrete structures was proposed and three crack monitoring schemes were designed. These three monitoring schemes realize the conversion between cracked information and thermodynamic information of cracked position using assemblies with monitoring tube and microporous casing, monitoring tube and hollow casing, and monitoring tube and irrigation tube, respectively. Among them, the first two monitoring schemes mainly use the principle of heat conduction to change the thermodynamic parameters of the medium around the cracks after cracking, so as to change the heat transfer law of the heat source. The third scheme mainly uses the principle of convective heat transfer and makes the crack section produce a convective heat transfer effect through irrigation, so as to improve the heat transfer speed. Concrete beam specimens were made according to the above three monitoring schemes, respectively. The transient heat transfer model tests were carried out by using the sensing heating element composed of a fiber bragg grating temperature sensor and a ceramic heating tube. A discriminant index reflecting the cooling rate was defined to identify crack information according to the subsection characteristics of the heat source cooling curve, and the identification effects were analyzed and compared. The results showed that these three monitoring schemes could well judge whether there were cracks. In terms of crack location, the third scheme had a better effect. In terms of quantitative identification of crack width, the first scheme could not identify the crack width quantitatively, the second scheme could only identify the crack width in the flowing water environment, and the third scheme could identify the crack width according to the leakage flow.关键词：structural health monitoring;crack detection;point heat source;fiber bragg grating;temperature tracer method
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发布时间：2024-01-18 - 摘要：To reduce the construction cost, improve the construction efficiency and simplify the analysis process of system transformation of a self-anchored suspension bridge, the influencing parameters of the main cable sag were derived based on the parabola theory, and by adjusting the cable saddle pushing and suspender cable tensioning strategies, a three-stage and two-round system transformation theme of non-extension suspender cables in combination with the controllability and sensitivity of each parameter was proposed. To simulate the construction status of the main and splay cable saddles in the scheme in the finite element calculation, the center point of the cable saddle and the tower top point or the center point of the splay cable saddle base were used to establish two boundaries, namely, the rigid arm and the principal and subordinate constraints. The temporary fixing and sliding status of the cable saddle were simulated by activating and deactivating the rigid arm, and the over-pushing status of the cable saddle was simulated by setting the forced displacement of the cable saddle center point. Taking two examples with a two-tower-three-span bridge and a single-tower-two-span bridge, according to the actual situation of the site, two sets of system transformation schemes of non-extension suspender cables were formulated respectively, and the FEM was established to simulate and analyze the system transformation process of the two bridges. The results of parameter analysis showed that the main span of the self-anchored suspension bridge was the key span to avoid the extension suspender cables, and the main cable span and main cable length were the key controllable parameters that affect the sag of main cables and avoid the extension suspender cables. The extension suspender cables can be effectively avoided by increasing the initial deformation of the main cable. The construction scheme was to change the span of the main cable by tensioning suspender cables to the main span longer segments to make the cable saddles reach the designated position in advance, and to increase the elastic elongation of the main cable by pouring the part of the secondary dead load and tensioning suspender cables in the first round to make the stiffening beam leave from the scaffold. The analysis results of two bridge examples showed that in the early stage of the system transformation, the main cable saddles were in the controllable slip state and the designated position in advance, and in the later period, the suspender cables on both sides of the tower were tensioned symmetrically, so that the anti-slip safety factor and the bridge tower stress changed steadily, and the establishing process of the scheme was simplified. The proposed scheme cable saddle simulation method has achieved the expected purpose, which can provide a reference for the system transformation of self-anchored suspension bridges of the same type.关键词：self-anchored suspension bridge;system transformation;main cable shape;suspender cable tension;cable saddle pushing
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发布时间：2024-01-18 - 摘要：Compared with the shield construction on straight lines, the settlement of existing tunnel caused by undercrossing construction of a curved metro shield tunnel is more complex and less studied. The settlement of the existing tunnel was analyzed using a two-stage analysis method. In the first stage, considering the effects of the over-excavation gap and the unbalanced construction parameters during the undercrossing, a three-dimensional solution of the tunnel-induced free ground settlement caused by the construction of a new curved shield was established using the mirror image method, modified Loganathan method and Mindlin solution. In the second stage, the tunnel-induced free ground settlement was considered as the displacement load imposed on the existing tunnel, and based on the Pasternak foundation and Timoshenko beam theory, a governing equation that can consider both soil and tunnel shear effects was established, and the finite difference method was used to reduce the order of the equation and solve it. The effectiveness of the governing equation was verified by engineering monitoring data, and the key parameters affecting the settlement of existing tunnels were analyzed. The results showed that the settlement groove of existing tunnels caused by the undercrossing construction of the new curved shield tunnel was asymmetrically distributed, and the maximum settlement position was located at 1～2 m inside the curve, which was different from the calculation results without considering the influence of the curve. The settlement of existing tunnels increased with the decrease of the radius of shield curve R0, and the settlement growth rate inside the curve was greater than that outside the curve, the general requirement was not less than 300 m. When R0 was greater than 600 m, it could be regarded as a straight tunnel. The settlement of existing tunnels also increased with the increase of the shield blade diametersD′, and the variational trend was presented obviously, but the impact on the settlement groove was small. The settlement of existing tunnels decreased with the increase of the vertical distance between the new tunnel and the existing tunnel Zc.关键词：curved shield tunnel;new tunnel;existing tunnel;mirror method
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发布时间：2024-01-18
HYDRAULIC & CIVIL ENGINEERING
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