最新刊期
卷 50 ， 期 4 ， 2018
- 摘要：Digital virtual assets have become an important social wealth. However, the research on digital virtual asset protection is still at the exploratory stage at home and abroad, and the systematic basic theory research needs to be solved, especially the systematic research on basic mathematical model, security management and transaction, security threat management mechanism and so on. All these have become the trend and hotspot in the field of cyberspace digital virtual asset protection. In order to effectively deal with the severe challenge of digital virtual assets protection, the basic theory system of digital virtual assets protection, which includes the crypto-currency, digital copyright, network games and other network space digital virtual assets, is studied. The mathematical models of virtual assets, security management, threat perception and risk control are used to establish the basic theory and method for the protection of cyberspace digital virtual assets. Three key scientific problems of digital virtual assets protection, such as the mathematical representation of digital virtual assets, the safety and controllability of the application about digital virtual assets, and the research on the threat management and control of digital virtual assets are considered, and 1 basic mathematical model, 3 key technologies, and 1 set of prototype systems are proposed, which can be briefly described as the 1-3-1 plan. Through the research of digital virtual asset basic mathematical model, digital virtual asset security management and transaction technology, digital virtual asset security threat perception method and digital virtual asset dynamic risk control mechanism, the basic theory and method of digital virtual asset protection are given. Finally, a digital virtual asset security management and transaction prototype system is built to verify the correctness and reliability of the research results. The following five aspects of innovation are realized, which are the mathematical model of digital virtual assets based on algebraic theory, statistical analysis, non-distinguishable confusion, information hiding, all homomorphism encryption, lattice theory signature; the digital virtual asset safety management and transaction method based on new block chain, workload proof and swarm intelligence; the adaptive discovery method for security threats of digital virtual assets based on Immune Theory; the real-time quantitative calculation method of digital virtual assets security threat based on human body temperature risk warning mechanism; the dynamic risk control method for digital virtual assets based on the threat of network environment. Based on the above content, a theoretical research system of cyberspace digital virtual assets protection is constructed to solve the technical problems of the mathematical characterization of digital virtual assets, the safety and control ability of the application of digital virtual assets, and the threat management and control of digital virtual assets. This study is of great theoretical significance and wide application prospects for the protection of digital virtual assets in cyberspace, and the results have great significance to protect the national cyberspace security, to develop independent intellectual property rights and self-control rights of cyberspace digital virtual asset protection technology, and to break the technical blockade and monopoly against our country.关键词：cyberspace security;digital virtual assets;virtual asset protection;electronic money;cryptocurrency;digital copyright
- 33
- |
- 2
- |
- 0
发布时间：2024-04-08 - 摘要：Air transport plays an important role in promoting the world economy and social development. The statistics of international civil aviation organization show that global air traffic is approximately doubled every fifteen years, and the existing air traffic navigation system is close to saturation. The existing air traffic management (ATM) systems automatically acquire and process air traffic control information for air traffic controller, through surveillance data fusion, flight data processing, meteorology and aeronautical information processing and safety nets processing. However, the limited decision-making support ability leads to the low intelligent degree of ATM system, which can’t meet the need of the future development of ATM. In order to adapt to the rapid development of aviation industry in the future, some countries and organizations are committed to carrying out new technologies to solve the problems of air traffic safety, airspace congestion and flight delays. In 2004, the EU proposed the "Single European Sky ATM Research(SESAR)" program and proposed tore-plan European airspace to meet air traffic demand and improve the efficiency of ATM system. The key technologies of the program include four key areas of ATM: efficient airport operations, advanced air traffic services, optimized air traffic network services and reliable ATC infrastructure. In 2005, the United States proposed the next generation air transportation system(NEXTGEN), including ADS-B, data communication, en route automation modernization, terminal automation modernization and replacement, NAS voice system and system wide information management. In 2012, ICAO launched the aviation system block upgrade plan (ASBU). The ASBU involved four aviation performance improvement areas, including airport operations, globally interoperable systems and data, optimum capacity and flexible flights and efficient flight path. Each area consists of multiple threads and distributed in four blocks according to the implementation stage. CAAC is also implementing or planning a large number of ASBU modules to cope with the rapid development of Chinese civil aviation. The existing ATM system and its future planning mainly focus on the infrastructure construction, without enough intelligent applications. In recent years, with the support of deep learning, high performance computing and big data, artificial intelligence technology has been rapidly used in various fields. Especially, technologies of computer vision, speech recognition and natural language processing have made breakthrough and rapid industrialization. Artificial intelligence, represented by deep learning, emphasizes that judgment and decision-making based on a large number of prior knowledge, which is consistent with the decision-making process of ATM. Therefore, artificial intelligence technology can promote the development of air traffic control key technologies, improve safety and the efficiency of air traffic control and reduce the workload of air traffic controller. The great benefit of the rapid development of artificial intelligence makes the intellectualized ATM a necessity. In this paper, the concept of intellectualized ATM and the overall framework of intellectualized ATM system were presented. The overall framework of intellectualized ATM includes the perception layer, network layer, platform layer, application layer and visual layer. All kinds of communication, navigation, surveillance, weather, wireless, video capture, radio frequency identification and other facilities of the perception layer offer the infrastructures for ATM. The network layer transmits information by using special line network, satellite communication network, Internet, mobile network and so on. The platform layer achieves information storage, sharing and mining by using of SWIM, cloud computing, intelligent big data mining. Application layer studies the application of artificial intelligence technology in air traffic control, airspace management, air traffic flow management, flight service, general aviation and unmanned aerial vehicle. The visual layer provides efficient and intelligent interaction through the portal, virtual visualization, intelligent UI and mobile applications. The research direction of intellectualized ATM includes intelligent ATM data processing, intelligent decision-making, air traffic control speech recognition and air traffic control robot. The intelligent ATM data processing involves various kinds of ATM data acquisition, processing, transmission, interaction and intelligent mining. Intelligent decision-making focuses on intelligent conflict management, intelligent air traffic flow management, intelligent planning and management, intelligent AMAN and DMAN, intelligent airport operation, etc. In view of the important role of ground-to-air communication in air traffic control, the intelligent simulation pilot and air traffic control safety monitoring based on automatic speech recognition should be studied. The intellectualized ATM system has the capabilities of air traffic control perception, planning, reasoning and action based on artificial intelligence. Thus, the overall framework and key technologies provide the theoretical basis and technical support for the development of intellectualized ATM system.关键词：air traffic management;artificial intelligence;deep learning;reinforcement learning;ATM robot
- 34
- |
- 1
- |
- 4
发布时间：2024-04-08 - 摘要：The strong rockburst disaster in deep tunnels is a difficult issue for the safety of excavation and the efficient application. The design of scientific blasting excavation has become an important technical means for the effective control of strong rockburst disasters. This paper conducts a aseries of numerical simulation and field tests involving the efficiency of the destressing blasting control on the strong rockburst disasters, based on the prevention and the control of frequent strong rockburst disasters with the increase of buried depth and in-situ stresses at diversion tunnels at Jinping Ⅱ hydropower station. The two destressing blasting schemes are demonstrated by numerical simulation. The one is to use twin-row inclined radial drillings in rock walls and the other is to apply vertical advance boreholes on tunnel faces. The results indicate that the relaxation zones appear at the left side wall blasting holes, the central part of the vault, the right side haunch and the spandrel blasting holes, after performing the scheme one. As for the method two, the extended range of relaxation zones occur in front of the tunnel faces by means of destressing blasting and release concentrated stress on tunnel faces. Based on the comparison of the Russenses Rockburst Discrimination Law, the two methods play an important role in the rockburst prevention and control effect. The intensity of rockburst after destressing blasting is reduced and occurs a strong rockburst, such as the left side of the wall between the bottom to the haunch, the right side of the wall ranging from the lower haunch to the vault, the left side of the spandrel and the right side of the bottom wall . Furthermore, the possibility of the rockburst occurrence on the face is also significantly reduced. Field test verification further demonstrates the feasibility and effectiveness of the rapidly released stress based on blasting pressure relief theory to prevent and control rockburst. In addition, the field tests analyze the advantages of the two schemes on blasting relief for preventing and controlling strong rockburst. Based on the comprehensive research and the field application, this paper proposes several rockburst prevention and control measures at diversion tunnels in Jinping Ⅱ hydropower station, which is benefit for the design and construction of blasting excavation in strong rockburst.关键词：blasting relieving pressure;deep tunnels;rapid stress release;strong rockburst prevention and mitigation;numerical simulation;field tests
- 27
- |
- 2
- |
- 3
发布时间：2024-04-08 - 摘要：The gas-liquid flow in the porous medium of coal is the foundation for understanding the theoretical expression of permeability, and it is also play a vital role in revealing the mechanism of low-permeability. Based on the fractal structure of capillary in micro and nano scales, a fractal tortuosity model established in the longitudinal direction and a fractal cross-section model established in the transverse direction were employed to quantitatively analyze the pore structure of low permeability coal. The differences in the definition of the tortuosity based on the Hagen–Poiseuille equation and the capillary pressure formula are analyzed. The latter one combined with the mercury intrusion experiments is more suitable for the seepage of coal pores below the micro scale. Based on the relationship of fractal scales, the effects of the aspect ratio and the fractal dimension of tortuosity on the fractal coefficient were theoretically analyzed. The mercury intrusion tests in coal were also carried out, and the average tortuosity and fractal dimensions were calculated; the product of the two was defined as the fractal coefficient. Based on the Carman-Kozeny equation, the fractal equation of cross-section can be deduced, including the theoretical expressions on the fractal dimension of perimeter and area. A gas-liquid displacement model was established based on Washburn dynamic equations; the fractal equations of the interface position and velocity were obtained. The nano-micro pore structure of low-permeability coal was reconstructed based on Nano–CT and the pore size and volume distribution were obtained. The fractal dimension of the perimeter and area was calculated based on the experimental data. Finally, a two-phase of N2–H2O displacement experiment was carried out based on NMR. Moreover, the distance and velocity distribution of the interface were obtained. The results show that the fractal structure of capillary model can be used as a geometric bridge to explain the mechanism of low permeability. The defined fractal coefficient can effectively reflect the influence of tortuosity and fractal dimension, as well as the linear relationship with permeability. The reliability of the fractal cross-section model was verified, and the low-permeability mechanism of coal should still consider the influence of fractal cross-section roughness. The validity of the fractal dynamic equation was confirmed by the distribution of water flooding signals by NMR.关键词：low-permeability;fractal structure;fractal tortuosity model;fractal cross-section model;fractal dynamic equation
- 2747
- |
- 1743
- |
- 4
发布时间：2024-01-10 - 摘要：Mixed-mode fracture is of concern in rock mechanics. To better understand the failure behavior of rocks under mixed-mode loading, several groups of mixed-mode fracture tests were conducted on sandstone using notched deep beam (NDB) specimens. In this study, the fracture loads and corresponding fracture surfaces under different mixed-mode loadings were obtained, and the relation between mixed-mode fracture strength of the sandstone specimens and loading mixity was discussed. Using three widely accepted fracture criteria (i.e., the MTS, MSED and MERR criterions), the fracture loads were theoretically estimated, and our results show that the IR-criterion and the MERR criterion agreed well with the experimental data, whereas the MTS and MSED criterions significantly over-predicted the fracture strength of the sandstone specimens for mode-II-dominated loadings. Finally, a surface topography measurement for each rough fracture surface was conducted using a laser profilometer, and the fracture surfaces were experimentally obtained and numerically reconstructed. Using the fractal method, the mixed-mode fracture surface topography properties of these surfaces were then theoretically investigated. In our study, no obvious relationship between the fractal dimension and the initial loading mixity was observed. Therefore, the investigated surfaces were almost statistically identical. Such results emphasized that the failure mode of rocks induced by mixed-mode loading is essentially the tensile mode.关键词：mixed-mode fracture;fracture strength;fracture toughness;rough surface;fractal dimension
- 2596
- |
- 1629
- |
- 0
发布时间：2024-01-10 - 摘要：The drilling and blasting method is the major excavation method for large underground caverns. Except for the load from in-situ stresses (static), the cavern rock mass will also bear the dynamic load frequently from blasting during excavation. The coupling effect of the in-situ stress and the blasting-induced disturbance is more significant at depth where in-situ stresses are much higher. So the study on the rock behavior, especially its fracture characteristics under the coupling loads may provide a theoretical basis for the prediction and control of the specific problems of rock engineering at a great depth. In this paper, the cracked chevron notched Brazilian disc (CCNBD) specimens of granite were tested to investigate their fracture toughness and failure characteristics under coupled pre-static and cyclic load by MTS815 Flex Test GT testing system. The static strength or fracture toughness is first acquired, and then the pre-static load of the 50%, 85% and 90% of the static strength is set respectively and the other 50%, 15% and 10% of the static strength is further applied as cyclic disturbance load, thus to obtain the fracture toughness under coupled loading. All the acoustic emission (AE) signals are recorded in the tests, and Felicity ratio and b-value are analyzed. Results indicate that: 1) The crack opening displacement (COD) of the specimens under coupled load is larger than that under static load, but it decreases with the increase of pre-static load. 2) The plastic deformation ratio and corrected fracture toughness increases gradually with the increase of pre-static load. 3) Granite has better capability to withstand the cyclic disturbance load under lower pre-static load. When the pre-static load reaches 90%, the capability drops greatly and the failure is progressive.关键词：coupled loading;granite;fracture toughness;Felicity ratio;b value of AE
- 2405
- |
- 1478
- |
- 0
发布时间：2024-01-10 - 摘要：The creep of coal rock has an effect on the gas permeability during methane extraction, coal bed gas exploitation and coal and gas outburst in mines. It is important to study the evolution of gas-filled coal creep-seepage and to obtain the coupling relationship between creep and seepage. In this paper, the evolution of gas-filled coal creep-seepage at different gas pressures was tested under conventional triaxial compression. The results showed that the axial strain grew by degrees as the stress increased step by step, until the destruction of coal samples. On the other hand, the gas permeability of coal was declined first and then raised, which can be concluded that micropores and microcraks within the coal body went through two changes. When the stress was less than the long-term strength of coal, the micropores and microcraks were closed; the gas seepage channels were blocked and then the gas permeability was on the decline. While the stress was greater than the long-term strength or the strain was greater than the strain-threshold of coal, the gas seepage was raised. The micropores and microcraks were adjoined and the gas seepage channels were expanded. Therefore, it is suggested that the stress exceeding long-term strength and the strain reaching a threshold are the prerequisites for the instability of coal and rock, which indicates a new way to study coal rock failure. Based on Kozeny-Carman formula, reasonable hypothesis and deduction, the coupling formula between strain and permeability was obtained. Moreover, this coupling formula was validated by the test data. The above findings would play an important role in the development of the stress field, fracture field and seepage field coupling theory.关键词：gas-filled coal;creep-seepage coupling;strain threshold;strain-permeability formula
- 2376
- |
- 1599
- |
- 4
发布时间：2024-01-10 - 摘要：The shift of plant water sources occurs seasonally. During the dry seasons, plants would progressively use deep soil water or groundwater when shallow soil water was depleted. During the wet seasons, when shallow soil water was adequate, plants would mainly use shallow soil water. Few hydrological, land surface and atmospheric models have addressed this phenomenon. This paper aimed to improve the performance of the distributed, land surface-hydrological model ParFlow.CLM. A new simulation method of plant root water uptake based on potential difference was coupled into ParFlow.CLM to analyze the impact of the shift of plant water sources on the regional ET simulation. The improved model was able to simulate the changes of regional ET and soil moisture, and was capable to capture the dynamics of plant groundwater use. The results from the modified model showed that the plants mainly relied on groundwater during the dry seasons. Plant groundwater use was one of the most important plant water-use strategies to mitigate the impacts of droughts. Comparing the results in dry year 2008 with those in normal year 2009, the duration and the amount of plant groundwater use were 53 days longer, 36% higher in 2008, respectively. The comparison between the modified and original model performances showed that, when ET was energy-limited, the results of two models coincided with each other. However, when ET was water-limited, the two models had significant difference in the simulations of plant transpiration and deep soil moisture dynamics.The impacts of the shift of plant water sources on the regional ET and the influences of groundwater level changes on the plant water use were considered in the modified model. As a result, the plant transpiration result from the modified model was 71 mm/a (43% of annual transpiration) higher than the results ofthe original model. If the shift of plant water sources was ignored in the numerical models, it would lead to considerable bias in regional ET and deep soil water simulation. Such bias would become more significant in the simulations during dry seasons or in the arid and semi-arid regions.关键词：evapotranspiration;plant water sources;root water uptake;distributed land surface-hydrological model
- 3336
- |
- 1808
- |
- 1
发布时间：2024-01-10 - 摘要：The floodplain domain is a base of living and development of local communities in the Lower Yellow River (LYR), and it is also an important site for flood routing, flood retention, and sediment deposition. The farm dikes constructed along the main channel in the LYR can withstand small and median floods, and protect farmland and villages from flooding. However, when a great flood occurs, it is very easy to cause farm dike to breach, and the dike-break induced floods usually cause catastrophic loss of human life and property. In this study, a laboratory model was constructed to study the routing of farm dike-break induced floods, and the characteristics of water level variation in the main channel as well as the propagation process of flood wave on the floodplain were analyzed based on the measured data. A two-dimensional numerical model based on the finite volume method with unstructured triangular mesh was then employed to study dike-break floods, and the model was then validated by the measurements, and close agreement was obtained between the model predictions and the experimental data. Finally, the validated model was used to simulate the dike-break floods using different roughness values in floodplain area, and the effects of floodplain roughness on water level, flow velocity and arrival times of wavefront routing were investigated. The results show that: 1) after the farm dike breached, water levels in the main channel decreased first, and then kept stable, and then rose to another stable level, and water levels on the floodplain generally kept rising firstly and finally tended to be stable. The flow velocities on the floodplain generally kept increasing firstly and then decreased to zero. The breach discharge decreased first, and then kept stable, and then decreased to zero; and 2) the floodplain roughness degrees have no significant effects on the breach discharge and overbank flood routing, but have a great influence on the arrival times of wavefront routing. The arrival times of wavefront routing on the floodplain increased gradually with an increase in floodplain roughness degrees, which decreased gradually with an increase in inflow discharge. The flow velocity on the floodplain decreased gradually with an increase in floodplain roughness degrees.The results could deepen the understanding of dike-break floods routing, and be applied as reference for the subsequent relevant researches.关键词：farm dike-break floods;physical experiment;numerical modelling;flood routing;floodplain roughness
- 2051
- |
- 1967
- |
- 6
发布时间：2024-01-10 - 摘要：At high Froude number (Fr) by large flow velocity, the water level along the concave bank of a curved smooth spillway is extremely high, and the bed of the convex bank will be exposed, and the flow status in the basin pool is poor.These poor hydraulic characteristics pose a serious threat to the project. A new curved spillway was proposedto improve the flow regimein a bend. The multistage steps werearranged in the spillway, and the bottom bed elevation of each step along the concave bank was higher than that along the convex bank.The design was verified by the hydraulic model test, and the hydraulic characteristics were studied in detail based on the three-dimensional numerical simulation .The hydraulic model test was based on a realspillway project of a reservoir,and the three-dimensional numerical model employed the RNG "k-ε" turbulence model and the VOF method.The simulationwas compared with the experimental measurement to verify the reliability and accuracy of the numerical model.The position of the mainstream zone was analyzed by using the water surface line and velocity distribution at three representative cross sections. For Section Ⅱ, the velocity vector and pressure distribution were analyzed for understanding of flow patterns and cavitation erosion in the spillway. The energy dissipation effect was analyzed according to the energy dissipation standard. The results show that the flow velocity and water depth of the cross section tend to be uniform, and the negative pressure zone is mainly located in the small triangle area formed by the wall, the vertical plane and the step surface. In addition, the energy dissipation of the flow is obviously strengthened along the path, and the deflected flow near the bank is greatly reduced, and the water flows smoothly into the pool. Combined with the pre-aerator, the problems of aerial drainage and energy dissipation of curved spillway under the flow condition of large flow velocity and high Froude number are solved.关键词：high Froude number Fr;large flow velocity;curved spillway;local elevated steps;hydraulic characteristics
- 1962
- |
- 1552
- |
- 1
发布时间：2024-01-10 - 摘要：The characteristic motion of the traction load in typical fluctuating backwater area, including the plane conformation, the promotion track of the sedimentation during the drawdown process of the reservoir, and the increasing process of the upstream flow, were studied based on the physical model tests. The results indicated that due to the large specific drop in the reach, the upstream and downstream flow patterns of the reservoir pinch-out point were different, and the sediment transport capacity would drop sharply in the course of the water flow changing from a jet to a slow flow. During the drawdown process of the reservoir, keeping the upstream water at a constant level until sediment transport distance was similar to the advancing distance of reservoir pinch-out point and the downstream level fell to 875 m, the siltation near the top of river bay would be cut into the upper and lower parts separately. The difference of sediment gradation between two grades of silt was more obvious, reflecting the separation effect of water flow. Comparatively, increasing the upstream flow while keeping sediment supply and the downstream level unchanged, the bed-load sediment of the downstream propulsion was relatively small, which showed that the bedload transport in the area of fluctuant backwater was greatly influenced by the backwater action in the lower reaches of the river. Under the premise that the total amount of the upstream sediment was given, the promoting of the frontier sedimentation was mainly affected by the decreasing water level of the reservoir, and the effect by the upstream flow was relatively small.关键词：fluctuating backwater area;bed-load;generalized model
- 1930
- |
- 1469
- |
- 1
发布时间：2024-01-10 - 摘要：In the mountainous region, the geometrical shape of a navigation channel is often changed from narrow-deep to wide-shallow, yielding the longitudinal change of motions of flow and sediment. By performing model experiments, this study investigated the variation of flow and sediment motions in the longitudinal direction, and explained the mechanism. With different upstream flow conditions, the water depth and the velocity in the main channel and foodplains were measured to explore the pattern of their changes in the longitudinal direction. Based on the measurements of bed shear stresses and bedload experiments, the threshold for estimating the movement of bedload had been proposed. The experimental result indicated that the geometrical shape of navigation channel significantly affected flow and sediment motions; The largest change of flow depth was observed at the interface of the narrow-deep channel and the wide-shallow channel; The difference of flow depth in two channels increased as flow depth increased; The mean channel velocity increased from the end of narrow-deep channel, achieved the maximum (about 1.5 times greater than the mean channel velocity in the upstream channel) at the interface of two channels, and finally reached to a steady value (about 0.8 of the mean channel velocity in the upstream channel). The bedload experiment indicated that the motion of bedload could be evaluated from the comparison between the bed shear velocity and the critical shear velocity for the initiation of bedload . Most bedload stops moving and deposits when the condition for bedload deposition is satisfied. In the mountainous navigation channel with an intact bed armor layer that did not break, the proposed threshold can be employed directly to estimate whether the bedload from upstream will move to downstream or not.关键词：widening navigation channel;water depth;velocity distribution;friction shear velocity;sediment deposition;estimation criteria
- 2288
- |
- 1342
- |
- 4
发布时间：2024-01-10 - 摘要：Flight trajectory prediction is the basis of air traffic management and simulation. Aiming at the problems of insufficient accuracy and instability of existing prediction methods, a trajectory prediction algorithm based on historical radar data and machine learning was proposed in this paper. The positional offsets between adjacent update moments were regarded as the model object and Gaussian mixture model (GMM) was applied to model the distribution of data. Then the historical flight trajectory was used to optimize the model parameters by expectation maximization (EM) algorithm. The probabilistic statistical model can precisely describe the randomicity of flight operation by learning the moving pattern of the same flight with collected trajectory. Based on the learned model, the sequential Monte Carlo (SMC) approach was used to sample the relative position offsets sequence at each update time during flight operation. For a given flight, the position and elevation of the runway at the departure airport are the initialization of trajectory. Combined with sequence of positional offsets, the position of the flight was predicted, which further generates a complete flight trajectory. The model parameters were updated based on the collected trajectories in the database when the prediction errors exceed the preset threshold, or over a regular period of time. The proposed method has been applied to a real air traffic flow management system. The results showed that the prediction results are more accurate than that of kinematic model and regression model. Moreover, during the climb and descent phase of the flight, the prediction results are more stable than that of the existing methods, which is a fatal bottleneck of these methods.关键词：trajectory prediction;historical radar data;Gaussian mixture model;relative position excursion;machine learning
- 2698
- |
- 1786
- |
- 3
发布时间：2024-01-10 - 摘要：Rerouting is an important strategy to deal with bad weather, military activities, traffic flow control and other emergency situations in the process of flight operation. An improved rerouting algorithm based on mining features of historical radar data is proposed. Firstly, reroutingconstraints are established by taking the economy, security, route features, and the impact of traffic flow and capacity into consideration. A rough process is made to select the optimal rerouting zone and possible key-point sequences which meet those constraints for rerouting.The routes duringhistorical flight operations are analyzed by the positions of historical flights. Combining with the flights whose plan path contain the given route, a utilization representation is proposed to select the preferred key point. Then, the optimal key-point sequence is obtained by analyzing its utilization from historical radar data. Taking the velocity vector as the modeling object, the machine learning algorithm is used to mine the flight pattern of the route segment. Gaussian Mixture Model is applied to model the distribution of velocity, and Markov chain Monte Carlo is used to predict the velocity sequence during rerouting. Finally, the whole rerouting path is planned by kinematics equation with constant acceleration rules. The application of a large-scale traffic management system demonstrates the high practicability ofthe proposed algorithm with considering the actual operating conditions of flight. The proposed approach can also predict the trajectory of rerouting flights, which provides the data supportfor the air traffic flow management in the rerouting path areas. Therefore, the rerouting issue of flight can be solvedreasonably and efficiently.关键词：reroute;constraints;historical radar data;key point sequence;machine learning
- 2221
- |
- 1420
- |
- 2
发布时间：2024-01-10 - 摘要：In order to solve the problem of conformance monitoring during turns in which the disturbances, inherent uncertainties and variabilities, such as navigation errors,monitoring system errors, and differences of turning point and turning radius, make it difficult to determine whether an aircraft conforms to the assigned flight plan or the issued command, an approach based on the comparison between the expected state values and the measured state values was proposed. The interval of expected state values was calculated through modeling the conforming flights using Gaussian Processes. The deviation term was introduced to enable the model to describe the reasonable change of state values at different time points during turns. The calculation was completed under the framework of Bayesian inference in Gaussian Processes, and stochastic sampling was used to compute the posterior distribution which is analytically intractable after introducing deviation term. The proposed model for conforming flights was trained by the historical flight data. It can avoid common problems when the expected state values were inferred directly from flight plan or control command, mainly including the failure to account for the influences caused by various factors in practical situations. The experiments using flight data from realistic surveillance system showed that the calculated interval of expected state values in the proposed model reflects the reasonable range of state values and therefore is capable of monitoring conforming flights. Furthermore, compared with the conformance monitoring based on threshold value of trajectory deviation, this proposed approach achieved better false alarm rate and detection time and avoid the performance issues caused by improper settings of threshold value. The results also showed that this proposed approach has extensibility and can improve the performance of conformance monitoring by using more state values in addition to position information.关键词：trajectories;Gaussian distribution;sampling;covariance matrix
- 2621
- |
- 1461
- |
- 0
发布时间：2024-01-10 - 摘要：In order to solve the problems that the existing DNS traffic analysis is limited by large data in complex large-scale networks, and the current visual analysis is not yet applied to DNS traffic analysis, a DNS traffic analysis model based on trend to domain and request information(TDRI) is proposed. The combined with network security and visual analysis method of big data, a multi view association DNS traffic visual analysis system based on TDRI DNS traffic analysis model is designed and implemented. First, the long-term and massive DNS traffic data of complex large-scale real networks are observed and analyzed. Then, a DNS traffic analysis model that includes DNS traffic eigenvalue time-series trend, request domain, and domain request information is abstracted and presented from three perspectives of requester, domain and request. Finally, based on the proposed DNS flow analysis model, the DNS traffic visual analysis system, which includes data selection and interrelated interactive view, is designed to support the analysis process of DNS traffic data driven by the problem analysis. The multi-view associated DNS traffic visual analysis system based on TDRI is applied to the real environment of campus network, which helps analysts find malicious access behavior in the network from DNS traffic and maliciousbehavior for DNS.The experimental results show that the proposed analysis method can improve the efficiency of DNS traffic analysis in the large-scale network environment and analyze the malicious behavior in the DNS traffic, which provides a guarantee for the safe and stable operation of the campus network DNS.关键词：DNS;visual analytics;model of DNS traffic analysis;big data
- 3095
- |
- 1537
- |
- 2
发布时间：2024-01-10 - 摘要：In order to solve the problem of illegal member’s tracking attack, which caused by the vehicle units’ privacy disclosure in vehicular ad hoc networks (VANETs), a vehicle identity authentication protocol based on lightweight group signature was proposed by analysis of topology and communication characteristics of VANETs in this paper, which can authenticate the vehicles anonymously in a fast and efficient way. The protocol has five stages. In the initialization phase, the public/private key pairs and system parameters of the group were generated by the VANETs system, then the group public key and system parameters were distributed to the on-board units by the roadside auxiliary facilities. The group private key was kept by the group manager. When a vehicle unit entered VANETs, the unit’s own identity was submitted to the group manager by the blind signature. A group certificate would be distributed to the vehicle unit by the group manager when authentication passed. In the cooperative communication stage, the vehicle member who owned the group certificates signed the state information with the valid certificate and group public key, then sent it to the nearby vehicle units by the car sensors, and achieved cooperative driving with surrounding vehicles. In the message verification stage, only can the legal vehicle members open the received status information by using group public key, but couldn’t know the true identity of the message sender. In this way, the anonymous communication among vehicles was realized. In the stage of signature verification, when a vehicle unit broadcasted a false message for the purpose of exclusively using road resource and caused traffic accident, the group manager can open the signature of the message by using the group private key, and traversed the corresponding vehicle members to carry on the accountability. The innovation of the paper was the usage of improved lightweight group signature technology, which could ensure that the length of group public key and group signature didn’t depend on the number of group members. Zero knowledge proof was also used as a means of membership authentication which improved the speed of authentication among the members. The security of the protocol was analyzed and proved mathematically in this paper, and a LAN simulation platform composed of 100 PC machines was built to simulate the cooperative communication among vehicle units in VANETs. The experimental results showed that authentication time of the protocol was about 7 ms among 100 vehicle users. The performance of the proposed protocol is superior to the contrasted schemes. It greatly reduced the storage and calculation burden of the vehicle units during the process of identity authentication.关键词：VANETs;privacy protection;group signature;identity authentication
- 2607
- |
- 1870
- |
- 3
发布时间：2024-01-10 - 摘要：In the current way of generating block data, the scenarios of micro trading are easy to encounter the efficiency bottleneck. In order to solve the problem of long waiting time for micro trading in blockchain, a novel strategy called real-time micro trading strategy with blockchain (RMTSB) was proposed in this paper. Firstly, a delay control Petri net model(DCPN) was constructed to describe, analyze and control the system that has delay information. Secondly, in order to record and evaluate the transaction process, a transaction data block structure with personal credit index and a personal credit evaluation method for micro trading were proposed. Then, on the basis of credit analysis and DCPN model, the paper presented the RMTSB strategy. Finally, the real-time micro trading strategy with blockchain is established from both the full node and SPV. To verify the validity of the proposed strategy, three kinds of transaction process were simulated, namely the conventional blockchain transaction process, the trading process under RMTSB strategy and the trading process under RMTSB strategy with network delay variables. The contingency of a single experiment was eliminated by the delay accumulation of multi-round transactions. The simulation results demonstrated that, compared with the conventional blockchain trading models, the RMTSB strategy improved the efficiency of transaction verification,Specifically, the transaction delay can be reduced by 50%~75%. Therefore, this strategy can simplify the certification process to a certain extent, and thus improve the payment speed of micro trading in blockchain, making blockchain really become a supporting technology in micro trading application scenarios.关键词：blockchain;micro trading;delay control Petri net;credit
- 2859
- |
- 1678
- |
- 0
发布时间：2024-01-10 - 摘要：In order to solve the problems of long classification time and large storage space incurrent packet classification algorithms, a fast packet classification approach (Uscuts) based on unit space partition was proposed. The method mainly includes rule preprocessing, rule space partition and decision tree construction stage. First, based on the multidimensional matrix design model, the original rules were mapped in reverse order to the multidimensional matrix, and the target rules which have the same semantics with the original rules and mutually independent rule spaces were obtained. Then, the corresponding space of the target rules was divided and a classification decision tree was constructed. Each branch of the decision tree corresponds to an independent multidimensional rule subspace, which means each leaf node of the decision tree just relates only one rule. Therefore, when the packet was matched to the leaf node, the classification decision of the packet can be directly determined to be accept. Unlike the traditional packet classification methods, the sequence matching should be continued within the rule group associated with the leaf nodes, which significantly raised the speed of packet classification. In addition, when dividing the rules space, Uscuts used the division method based on the unit space boundary. Compared with the current classification algorithms, the number of the rule subspace was effectively reduced and the storage space was saved. To further validate the efficiency and effectiveness of the proposed algorithm, different sizes of rules and packets were generated to test the time required for packet classification. The test results showed that the time complexity of Uscuts could reach
$O$ $k$ $n$ $O$ $k$ $n$ $n$ $k$ 关键词：packet classification;firewall;unit space;decision tree algorithms- 2340
- |
- 1494
- |
- 0
发布时间：2024-01-10 - 摘要：In order to achieve a matching cost which involves the local feature information of pixels, a stereo matching system with the adaptive weight AD-Census was presented. The system improved upright cross support region construction by imposing the threshold of the absolute difference (AD) in gray between the adjacent pixels. An exponential function was used to adaptively set a pair of appropriate weights AD and the census matching costs based on the shortest arm of each pixel. Because the shortest arm of each pixel could reflect the local feature of pixels, the weights adaptively set was related to the local information of pixels. The weight of AD was larger than the weight of the census matching if the pixel was in regions nearby image edges. The weight of the census matching was larger than the weight of AD if the pixel was in textureless region. The experimental Results on the Middlebury stereo benchmark v3 showed that the performance of the system with the adaptive weight AD-Census is better than that of the system with AD-Census. The average disparity errors of all pixels are reduced by 25% and the average disparity errors of non-occlusion pixels are reduced by 20%. Moreover the matching results of some image libraries including Adir image library showed that the stereo matching system with the adaptive weight AD-Census is especially superior for the texture-rich images and the images comprising repetitive textures.关键词：stereo matching;adaptive weight;AD-Census;upright cross support region;matching cost
- 2386
- |
- 1866
- |
- 13
发布时间：2024-01-10 - 摘要：In order to achieve both link prediction and sign prediction in signed networks, a new algorithm PSNBS was proposed on the basis of the similarity and structural balance theory, aiming to address the following two problems, namely, the imbalance between accuracy and complexity of link prediction algorithms based on the similarity in traditional social networks, and its incapability to be applied to signed networks directly. Firstly, combining with topology characteristics of signed networks and the choice of optimal step length, the 2-step and 3-step similarity scores of the two nodes based on structural balance theory were defined by effectively integrating attribute similarity and path similarity. Secondly, considering the different similarity contributions of paths of different step lengths, the adjustable influence factor of step length was introduced. Then, the total prediction score of the two nodes on the basis of the structural balance theory was defined. The absolute value of the score measures the similarity of the two nodes, i.e. the probability of the establishment of the future link, and the sign of the score is the sign prediction result of the future link. Thirdly, for the special case that the prediction score is 0, the concept of negative density of the node was introduced so as to predict the sign using the degree attribute of the node. Finally, link and sign prediction were completed according to the total prediction score of the two nodes and their negative density. Experiments were carried out on several data sets by using AUC, AUCBS and PrecisionBS as the evaluation index. Results showed that the algorithm proposed can achieve higher accuracy in the prediction of future links and the sign prediction of known edges, which verified its effectiveness and robustness. Furthermore, PSNBS algorithm had higher prediction accuracy in sign prediction compared with two classical sign prediction algorithms CN and ICN.关键词：link prediction;signed networks;similarity;structural balance theory
- 2646
- |
- 1438
- |
- 3
发布时间：2024-01-10 - 摘要：In order to solve the problem of insufficient hit rates of voice activity detection (VAD) in complex background noise environments, an environment-aware VAD algorithm is proposed. Aiming at the poor noise immunity of the single fixed threshold method used in conventional algorithms, different thresholds are adopted during the mutual conversion processes of voice and noise frames, and the thresholds are updated adaptively. And a method of feature combination is proposed to overcome the defect that a single feature cannot cope with the complex noise environments, which combines the likelihood ratio, energy entropy characteristic, and mean harmonic number value characteristic. Then, the idea of environmental noise classification is introduced, which classifies the noise environments using supported vector machine and selects optimal feature combination according to the type of noise environments, so as to improve the performance of the algorithm further. Finally, simulation experiments are conducted to evaluate the performance of the proposed algorithm, in which the NOIZEUS speech database is utilized, and five kinds of noises such as babble, pink, white, f16 and volvo are selected as background noise. And the hit rates of various feature combinations are compared to verify the effectiveness of the algorithm. Experimental results show that the proposed algorithm outperforms existing algorithms and can achieve about 80% overall hit rate in various noise environments, and it can balance the voice hit rate and the false alarm rate as well.关键词：voice activity detection;double adaptive threshold;noise classification;feature conjunction
- 2343
- |
- 1803
- |
- 1
发布时间：2024-01-10 - 摘要：In order to further explore the effect of multiple parameters weighted fractional Fourier transform (MP-WRFRT) on the higher order baseband modulations, the quantitative and qualitative research on 8PSK constellation splitting in WFRFT-based systems were carried out. The constellation splitting function was defined, and the corresponding geometry model was also established. Based on the vector composition method, the 8PSK constellation splitting criteria was obtained in MP-WFRFT-based systems. By analyzing the relationship between combined vector and constellation superposition, it was deduced that there was one-to-one correspondence between the magnitude ratio of different MP-WFRFT’s time-domain coefficients and the number of constellation points. The constellation splitting system based on MP-WFRFT was proposed, then the number of constellation splitting points and blurring factors were used to properly decide the MP-WFRFT’s parameters. The corresponding mixed integer program was also built and the Genetic Algorithm (GA) was adopted to solve the optimal program. Simulation results demonstrated that the basic splitting patterns, the number of splitting points and the blurring rule were all in accord with the basic 8PSK constellation splitting criteria in MP-WFRFT-based systems. Besides, the bit error rate (BER) performance comparisons also showed that the unauthorized receiver’s performance was degraded while the authorized receiver’s communication quality was maintained well in the MP-WFRFT-based systems. MP-WFRFT can make the original baseband signals achieve a good performance on the anti-energy detection and anti-constellation recognition, which can further improve the system’s anti-interception ability, and can be implemented in the secure communications.关键词：multiple parameters weighted fractional Fourier transform (MP-WFRFT);8PSK;constellation splitting;mixed integer optimization;anti-interception
- 2461
- |
- 1534
- |
- 1
发布时间：2024-01-10 -
Modeling and Application of Admittance Parameters of Nanometer MOSFET Under Millimeter Wave Band AI导读
摘要：In order to describe the bias dependence of nanometer MOSFET from the strong inversion to weak inversion regimes under millimeter wave band, the modeling of the high frequency equivalent circuit of MOSFET and its technology of parameter extraction were studied. A simple and accurate method for obtaining the parameters of the small signal model was proposed. Based on the physical structure of device of 45 nm MOSFET, a millimeter wave equivalent circuit model of MOSFET suitable for parameter extraction was described by taking into account the intrinsic physical characteristics of the devices, the electromagnetic characteristics of the pin and the parasitic characteristics of the test pad and test interconnects. By analyzing the two port network parameters of the presented millimeter wave small signal equivalent circuit of 45 nm MOSFET, the first order simplified mathematical model of admittance (Y) parameter of quasi-static approximate millimeter wave equivalent circuit was developed. Then, the proposed Y parameter model was applied to extract the component of equivalent circuit of nanometer MOSFET in order to offer the excellent continuity and smoothness of the extracted results under different bias conditions. Using the radio frequency multi-finger NMOSFET with the number of fingers Nf=10, the gate width W=2 μm and the gate length L=45 nm, the simulation accuracy of the presented Y parameter model from 1 to 50 GHz was verified under different bias points. The experimental results also showed the bias dependence of 45 nm MOSFET. The practicability and accuracy of proposed model and the parameters extract algorithm derived from it were also verified by the consistency comparison of the simulated results by using ADS2013 tool and the measured data. Therefore, the proposed Y parameter model can be transplanted to the automatic simulation design tool easily and accurately. The different characterizations of monotonic features of the intrinsic element parameters of the equivalent circuits is of great significance to the optimization design of the millimeter wave integrated circuit from the strong inversion to weak inversion regime.关键词：nanometer MOSFET;admittance parameter;small signal equivalent circuit;millimeter wave- 2050
- |
- 1770
- |
- 0
发布时间：2024-01-10 -
Multi-objective Optimal Operation Scheme Based on CS-PSO Algorithm of Battery Energy Storage System AI导读
摘要：In order to make full use of the battery energy storage systems (BESS) in the smart distribution network (SDN), a multi-objective optimization model (MOPM) for BESS optimal operation was established, whose objective was to minimize the electricity purchase cost, energy loss fee and voltage regulation cost of the SDN by controlling the charging or discharging power of BESS. And the energy conservation and capacity limits of BESS were included in these constraint conditions of the MOPM. Then an analytic hierarchy process was applied for calculating the weight of each sub-objective function so as to transform the multi-objective function into a single comprehensive objective. To efficiently solve the optimal model, an improved particle swarm optimization algorithm — crisscross and particle swarm optimization algorithm (CS-PSO) was presented by introducing the vertical and horizontal crossover operator into the PSO algorithm and using the method of cross searching to maintain the diversity of the population. Meanwhile, the states of charge of BESS were selected as the elements of particle position vector for solving the model. Finally, the IEEE34-bus system with distributed generations (DGs) and BESS was simulated to demonstrate the effectiveness of the proposed optimal model and algorithm. Compared with the solutions of three single-objective optimal modes, the results showed that the multi-objective optimization was able to make good use of the energy storage system and provide a variety of services for SDN to obtain the maximum comprehensive benefit. Meanwhile, the calculation performances of three intelligent optimization algorithms were compared, which showed that the CS-PSO algorithm had good convergence and computational efficiency in solving the nonlinear programming problems. Furthermore, the influence of the optimal operation of BESS on the system voltage profile was also analyzed, which showed that the multi-objective optimal operation of BESS could improve the voltage quality.关键词：BESS;multi-objective optimal operation;analytic hierarchy process;crisscross and particle swarm optimization algorithm- 2370
- |
- 1581
- |
- 4
发布时间：2024-01-10 - 摘要：A flame-retardant tris (3-nitrophenyl) phosphine (NPPh3) containing nitro group was synthesized from triphenyl phosphine (PPh3). Its chemical structure, thermal stability, thermal degradation behavior, charring ability, and thermal degradation products were characterized by Fourier transform infrared spectra (FTIR), nuclear magnetic resonance (1HNMR), thermogravimetric analysis (TG), and thermogravimetric analysis/infrared spectrometry(TG-FTIR). The results showed that the initial thermal decomposition temperature of NPPh3 was 291.2 ℃. The carbon residue at 800 ℃ (under N2 atmosphere) reached 28.16%, which demonstrated that the thermal stability and charring ability of PPh3 after nitrification was improved. In addition, TG-FTIR results indicated that its thermal degradation products were H2O, CO2, CO, and aromatic ring. In order to achieve a good flame retardant effect under less flame retardant, NPPh3 was used together with 9,10–dihydro–9–oxa–10–phosphaphenanthrene–10–oxide (DOPO) to prepare a flame-retardant system for epoxy resins(EP) with 4,4–diaminodiphenylmethane (DDM) as curing agent, and the synergistic effect between them was studied.LOI and UL–94 results showed that when the flame retardant content was 4.7%, the ratio of NPPh3/DOPO was at 1∶2, flame retardant epoxy resin acquired aLOI value of 33.8% and UL-94 vertical burning successfully passed V-0 flammability rating. The TG test showed that there was an obvious synergistic effect between NPPh3 and DOPO. The introduction of NPPh3/DOPO lowered the initial decomposition temperature and increased the amount of residue mass at high temperature compared with EP. Additionally, the structure and morphology of the residue chars were studied by FTIR and scanning electron microscopy(SEM). The results illustrated that NPPh3/DOPO stimulated the formation of compact and strong char layer which contained –P and –NO 2 groups, and provided a good barrier to hamper the transfer of heat and oxygen into the combustion layer. Consequently, the underlying epoxy resins were protected from further degradation and combustion, and led to an efficient flame retardant in condensed phase.关键词：nitrification;phosphorous flame retardant;epoxy resins;synergistic effect
- 2080
- |
- 1378
- |
- 0
发布时间：2024-01-10 - 摘要：High entropy alloy has broken through the design idea of traditional alloy with one or two main elements, and has a simple solid solution structure formed by various of alloying elements (≥5) with the nearly equal mole ratio. Owing to its excellent performance, high entropy alloy may open the door of the performance limit of traditional metal materials and meet higher demand for materials in the development of industrial technology. AlCoCrCuFe high-entropy alloy was fabricated by non-consumable arc remelter, and the mechanism of phase formation among the multi principal alloy element and the effect of its microstructure on the friction and wear properties were studied.The microstructure, phase structure and wear resistance of AlCoCrCuFe were investigated by XRD, SEM, EDS, microhardness tester and friction-wear tester. The results showed that AlCoCrCuFe alloy has typical dendrite structure and BCC+FCC dual phase having broaden diffraction peaks. The friction coefficient of AlCoCrCuFe/GCr15 increases at first and then decreases and stabilize with the increase of friction time, and the wear mechanism changes from delamination wear to oxidative wear under the condition of dry friction. The average friction coefficient is 0.55, and the mass loss rate is 1.44%. The reason of Cu-rich intergranular region is due to the difference of mixing enthalpy, binding capacity, solubility and melting point between Cu and other elements. The layered grid structure of spinodal decomposition is owing to the influence of coherent stress and elastic interaction caused by atomic size in dendrite region. The precipitation of nanoparticles near the dendritic boundary is determined by hysteresis diffusion effect, metal heredity and process. The difference of each component in atomic radius, mole ratio and mixing enthalpy, large residual stress and small crystalline grain results in the broaden diffraction peaks of BCC phase and FCC phase.关键词：high-entropy alloy;AlCoCrCuFe;microstructure;wear resistance
- 2556
- |
- 1801
- |
- 5
发布时间：2024-01-10 - 摘要：With the increasing prominence of energy and environment, the recycling of heavy metals is of great significance. To realize heavy metal recycling and resource utilization, The heavy metal-ions were recycled using strong acidic cation resin, and carbon-based metal composites (C–X, X= Co, Fe, Mn, Ni) were successfully prepared by an anaerobic carbonized method at 600℃. Catalytic performance of C–X composite was investigated by the activation of peroxymonosulfate(PMS) for removal of contaminants. The effect of diverse catalysts, oxidants and catalyst dosage were studied, and the main free radicals were also identified. The microscopic morphology and other characteristics of C–Co sample were characterized by SEM, TEM, EDS and XPS. The results showes that C–Co composite has a higher catalytic efficiency than others, and contaminations degradation is fitting well with the pseudo-first order kinetics model. C–Co composite also showed a different catalytic ability of PMS, PS and H2O2, and the order of catalytic efficiency was C–Co/PMS>C–Co/PS>C–Co/H2O2. In addition, with the increase of catalyst dosage , the degradation rate of target could be improved due to the increase of the catalytic activity sites. The results of the catalyst recovery experiment showed that the catalytic activity of C–Co composite remains above 85%. The quenching study showed that main free radicals in C–Co/PMS system are •OH and •SO4–. SEM and TEM characterization analysis showed that C–Co composite is composed of piece-like and needle-like structure, and Co disperses on the catalyst interior and surface. EDS analysis showed that the main elements in C–Co sample are C, O, S, Co and Na. The results of XPS characterization showed that the cobalt in the compounds presentes a high-spin Co2+ state, which was a key factor for PMS activation.关键词：heavy metal;ion resin;carbonation;peroxymonosulfate;organic contaminates;degradation
- 2818
- |
- 1311
- |
- 0
发布时间：2024-01-10 - 摘要：Classifications of welding defects are a multi-classification problem of unbalanced samples and the feature distribution of unbalanced samples also vary. Feature selection is needed to acquire more discriminating features and improve the recognition rate of rare samples. In order to complete the parameter optimization and selection of feature subset at the same time, the support vector machine was selected as the classifier to evaluate feature subset, and the artificial immune system algorithm was used to search reliable features and optimize the parameters of support vector machine. This algorithm was applied to classify and identify common welding defects such as pore, slag inclusion, crack, incomplete fusion, the lack of penetration and pseudo-defect on eight types of weld defect dataset, including mild steel butt welding, mild steel fillet welding, mild steel T-shape welding, mild steel lap welding, stainless steel butt welding, stainless steel fillet welding, stainless steel T-shape welding, and stainless steel lap welding, and was compared with direct classification result with no feature selection and under different feature selections and classification algorithms. Results indicated that the average classification accuracy rate of welding defects of pore, slag inclusion, crack, incomplete fusion, lack of penetration and pseudo-defect was （96.21±0.67）%, average sensitive value was （85.43±1.65）%, and had an obvious increase compared with traditional algorithms of correlation-based feature selection algorithm (CFS), minimum redundancy maximum relevance algorithm (mRMR), rough condition mutual information algorithm (RCMI), and the combination of Bayes and classification and regression tree (CART) on the basis of pertinence. Therefore, the proposed algorithm is superior to traditional classification methods.关键词：welding joints defects;support vector machine;artificial immune system;feature selection;classification
- 2126
- |
- 1211
- |
- 0
发布时间：2024-01-10 -
Thermo-fluid-solid Coupling Model and Numerical Simulation of Supercritical CO2 Antireflection Coal AI导读
摘要：In view of the situation that the permeability of the most high gas coal seam is poor and the effect of coalbed methane extraction is not ideal by strengthening extraction in low permeability coal seam, which combines the strong diffusion, dissolution-increasing-permeability on pore medium and other unique advantages of super-critical carbon dioxide. According to the evolution features of coal pore fissure after the action of supercritical carbon dioxide, the micro porosity and permeability evolution equation was gained, the damage variable was ascertained according to the change of the porosity. Thermo-fluid-solid coupling model of coal was built after the action of supercritical carbon dioxide, which considered the effects of volume stress, temperature, pore pressure and the dissolution-increasing-permeability action of supercritical carbon dioxide, field variable subroutine supplied by ABAQUS was used, the PYTHON script and the two development function of subprogram were combined, the increasing-permeability law of numerical simulation is realized in the low permeability coal seam injected by supercritical carbon dioxide. The results showed that after the injection of supercritical carbon dioxide, the volume stress, temperature and pore pressure around the injection-gas hole changed obviously, with the increase of the distance from the injection hole, the influence degree gradually weakened and tended to be stable. New pore fissures sprouted constantly and interconnected with the original hole fissures in the coal around the injection hole, the crevice at all levels evolved constantly to the depth of coal, the micro-porosity was increased by two orders of magnitude than that before injecting the gas. The fracturing and increasing permeability action of supercritical CO2, the coal was damaged with different degrees, the closer the injection-gas hole is, the greater the degree of damage is and the faster the damage increases, the longer the gas injection, the greater the increase in damage. Effective development of micro pore and fissure of coal, more transport channels were provided for the diffusion and seepage of coal bed methane, the permeability coefficient of coal was increased by three orders of magnitude than before gas injection.关键词：supercritical CO2;permeability coefficient;porosity;increasing permeability action- 1939
- |
- 1487
- |
- 1
发布时间：2024-01-10 -
Optimization Method of Annular Flow Electromagnetic Measurement System with One Pair of Electrodes AI导读
摘要：With the continuous drilling of petroleum, especially in the area of narrow mud weight window, the lack of downhole flow information may lead to the overflow and blowout arose on account of. Using the drilling technique of downhole micro-flux control could effectively solve problems of overflow and blowout which appeared in the narrow mud weight window. And the information of downhole annular flow, which was obtained through using the technology of downhole annular flow measurements, was the core part and assurance to implement the downhole micro-flux control. Based on the digital optimization technology, the system of downhole annular flow measurement was optimized . Firstly, the basic theoretical model and optimization principle of annular flow electromagnetic measurement system with one pair of electrodes were proposed. Also based on Bevir’s vector weight function theory, the solution of virtual current potential and virtual current density for annular flow channel electromagnetic flow measurement system was realized. Weigh function was closely related to magnetic and virtual current density. When virtual density remained unchanged, which meant that virtual current density was a constant value,weigh function could be close to constant by optimizing the excitation structure. Secondly, the optimum design of the downhole annular electromagnetic flow system was realized, based on the Multiphysics COMSOL simulation of the factor of key structure for annular electromagnetic measurement system . According to different boundaries, virtual current potential and virtual current density for annular flow channel electromagnetic flow measurement system were solved, the distribution of virtual current density was mastered. By analyzing the COMSOL simulation data of single-pair coils excitation structure and synthetically balancing the evaluation index of vector weight function, the optimum parameter of excitation structure was obtained. Through modeling, optimizing and analyzing the evaluation index, the optimum parameter of excitation for downhole annular flow measurement system was solved to improve the measurement accuracy.关键词：annular flow;optimal design;simulation optimization;weigh function;COMSOL;electromagnetic measurement- 2122
- |
- 1418
- |
- 1
发布时间：2024-01-10 - 摘要：Field signature method (FSM) is a common monitoring technology for metal pipeline corrosion. However, there are a lot of shortcomings in FSM Technology such as the measurement results are easily disturbed by the drift and the temperature difference between the reference plate and the measured pipe will lead to a large measurement errors. Multi-frequency alternative current field signature method (MACFSM) is introduced to assess the wall thickness of metal pipeline based on finite element simulation. Multi-excitation current with a series of frequency from high to low is injected into the measured metal pipe, and penetration depth will increase with decreasing frequency while voltage between electrodes will decrease. When penetration depth reach to the inner wall of measured pipe, voltage between electrodes will remain the same. Therefore, all of the recorded voltages can be fitted into a function, then take the derivative of this function, while the penetration depth of the first zero of derivative is equal to the wall thickness of the measured pipe. Then, the experiment was applied to verify the simulation. 0.1 A multi frequency exciting current was injected into the metal pipeline with a defect depth of 3.5 mm, and the defect depth was solved accurately by the derivative extreme value. The simulation and experiment showed that multi-frequency alternative current Field signature method (MACFSM) does not need reference voltage, and the measured voltage also does not need to be compared with original voltage; especially this method can overcome the adverse effect caused by baseline drift of electric circuit system and change in temperature, therefore the reliability of long term on-line monitoring technology can be greatly improved.关键词：multi frequency alternating current;field signature method (FMS);potential drop;skin effect;drift
- 2058
- |
- 1453
- |
- 2
发布时间：2024-01-10 - 摘要：The variable ratio tooth profile is the key to realize “variable transmission ration” for recirculating ball variable ratio steering gear, and it is a kind of envelope surface formed by the envelope process of involute tooth profile in accordance with the variable ratio transmission relationship.This special envelope process leads to difficulties in modeling and Computer Numerical Control ( CNC) machining of the variable ratio tooth profile. Focused on the digital design method and CNC machining method for variable ratio tooth profile of recirculating ball variable ratio steering gear, the gear sector of variable ratio gear pair was taken as a set of intersection lines obtained by using countless planes perpendicular to the axis of the gear sector to cut the gear sector. Assuming that there was a line through a point on the variable ratio tooth profile and parallel to the variable ratio rack would generate a series of interactions between this line and the corresponding intersection lines in gear transmission, and the point that the length coordinate value was the extremum of all intersections was a variable ratio tooth profile point. The mathematical models used to solve the variable ratio tooth profile points were established and the corresponding solution algorithm was developed. Tooth profile point cloud of a variable ratio rack was obtained based on this method. Using the tooth profile point cloud, planning of the tool path, size selection of the finishing tool and calculation of the cutter bar vector at cutter-contact point were completed, and CNC end milling of the variable ratio tooth profile was achieved. The relevant tests of transmission ratio and transmission stability on the sample were performed, and the experimental results verified the correctness of the proposed method. This method could overcome some disadvantages of designing variable ratio tooth profile with meshing principle, and realize the digital modeling and CNC end milling of variable ratio tooth profile .关键词：recirculating ball variable ratio steering gear;variable ratio tooth profile;digital modeling;end milling;transmission stability
- 2232
- |
- 1470
- |
- 1
发布时间：2024-01-10 - 摘要：The aero blade is an important part of the aero engine. Its machining accuracy directly affects the performance and life of the aero engine. 3D contour measurement is usually use to value the machining accuracy. As a typical free surface, the blade has complex surface structure which leads to processing difficulties, also exacerbates the measurement difficulty. Coordinate measuring machine is the highest accuracy contour measuring method, but limited to the blade surface complexity and the current CMM contact measurement technology, it has to collect a large number of surface data points in order to fully show the surface characteristics of the blade and make the measurement efficiency very low. Based on the 3D blade model, a sampling method was proposed based on improved firefly algorithm. Firstly, the curves of the blade sections were extracted, and then the points obtained by equal arc-length method of the cross-section were collected. The initial point position data were used to simulate a small firefly community. Calculating the curvature relationship between the points in the community and determining the moving direction and the step length of the target point were helpful to the automatic updating of the distribution points’ positions. Finally, all the sampling points of the blade surface were obtained. The algorithm could achieve the free number configuration of the measurement points so that the purpose of adjusting the measurement efficiency was achieved. And then the algorithm was useful for improving the precision of the sampling points. By comparing the contour deviation, the maximum position deviation and the average position deviation of the fitting curve and the original curve with equal arc-length sampling algorithm and the equal parameters sampling algorithm, the proposed sampling algorithm showed its better sampling quality than the other two algorithms. It laid a technical foundation for the high efficiency measurement of the blade.关键词：blade;contour measurement;coordinate measurement machine;cross-section;sampling;improved firefly algorithm
- 1913
- |
- 1806
- |
- 1
发布时间：2024-01-10
- Technical support is provided by Beijing Founder electronics co., LTD 京ICP备09064830号-19
京公网安备11010802024621 - It is recommended to read the content of this site in Chrome&IE9+. Please switch to extreme mode in browser 360.
- Cookies We use cookies to help provide and enhance our service and tailor content. By continuing, you agree to the use of cookies.
0