最新刊期
卷 52 ， 期 3 ， 2020
- 摘要：As the scale of lunar exploration projects continues to expand, it is difficult to provide sufficient and sustainable energy supply for all activities on the moon just relying on the solar cells or small radioisotope power sources. The development of lunar in-situ energy supply technology is the key foundation of various lunar-based activities. The temperature difference between the day and night on the lunar surface is extremely large, while the temperature of the lunar rock layer is basically constant with a depth of more than 1 m. Based on the characteristics of the huge temperature difference between the lunar soil and rock constant temperature layer and the lunar surface, a conceptualization of lunar-based in-situ energy support technology that can use the temperature difference to generate electricity was proposed. The design and implementation of lunar thermoelectric materials thermovoltaic power generation technology and lunar magnetic levitation power generation technology were developed. The lunar thermoelectric material thermovoltaic power generation system directly used the thermoelectric materials to realize the thermoelectric conversion. The device was designed with three layers of soaking plates connected by heat pipes, which solved the problem of insufficient heat transfer caused by the poor thermal conductivity of the lunar regolith or rock. The lunar surface radiant energy (daytime) and lunar soil heat energy (night) were continuously converted into electrical energy. The lunar magnetic levitation power generation system and technology used the heat pipe to transfer heat in the lunar regolith to the generator, in which the circulating working fluid was heated and evaporated, then the magnetic levitation turbine generator worked to generate electricity. After that, the circulating working fluid was condensed by radiative heat exchange between the surface heat exchanger and space. Working fluid would be pressurized back to the generator by the pump, and it absorbed the heat pipe heat again to cycle power generation. Based on this methodology, the lunar magnetic levitation power generation system converted the temperature difference between the lunar surface and the lunar moon rock constant temperature layer into electrical energy. Those two types of power generation technologies have the advantages of no mechanical friction, high efficiency, long life and light weight, which can provide technical supports for the in-situ energy supply of lunar exploration activities.关键词：moon;in-situ energy supply;huge difference in temperature;thermovoltaic power generation;magnetic levitation power generation
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发布时间：2024-01-08 - 摘要：Due to the good corrosion resistance and high bearing capacity, the concrete-filled stainless steel tube has an excellent application prospect in the offshore platform, bridge and underground engineering. However, there is no relevant specification for calculating the capacity of concrete-filled stainless steel tube. In order to investigate the bearing capacity of circular concrete-filled stainless steel stub columns (CSSSC), the uniaxial compression experiments of seamless CSSSC with different diameter thickness ratios were conducted. As a result of the experiment, the failure modes of CSSSC under uniaxial compression, the load-axial strain curve, the load-hoop strain curve, the load-longitudinal strain curve, the relationship between bearing capacity and stainless steel tube constraint coefficient, and the relationship between the ductility of specimens and the constraint coefficient of stainless steel tube were all obtained. Meanwhile, based on the results in this study and existing literatures, a regression formula for predicting the axial bearing capacity was obtained, which was compared with the results calculated according to standards of different countries. Finally, the compressive bearing capacity model of circular stainless steel tube concrete was derived from the fitting formula and compared with some existing models, such as Mander’s model, Li’s model, Xiao’s model and Teng’s model. The results show that the typical failure mode of CSSSC under uniaxial compression was outward local buckling failure. The ductility and bearing capacity of specimens increased with the increase of the restraint effect coefficient of stainless steel tube. The calculation method of bearing capacity of concrete-filled steel tubular used in the calculation of bearing capacity of short circular stainless steel tubular concrete columns was relatively small, and the calculation result of the fitting formula in this study was closer to the test results. The results of the bearing capacity model presented here, Xiao’s model and Teng’s model were close to the test results, but the standard deviation of the calculation results of the model in this study was the smallest and the bearing capacity of the circular stainless steel tube concrete short column was slightly larger than that of Xiao’s model and Teng’s model.关键词：concrete-filled stainless steel tube stub column;bearing capacity model;axial loading capacity;ductility;failure modes
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发布时间：2024-01-08 - 摘要：The mechanism of fissure water pressure is highly complicated in the process of changing in situ stresses. To elucidate the influence of water pressure on crack propagation law, based on discrete element theory and laboratory test, the evolution mechanism of a single flaw in cement mortar specimens under uniaxial compression and internal water pressure is studied. According to the characteristics of low permeability of rock particles, a more suitable model of fluid-solid coupling for rock is proposed by correcting the calculation rules of interaction between fluid and particles and improving the calculation of the parameters of the convective area. The results show that when the crack angle is 450 and the internal water pressure reaches 1 MPa, the wing crack will propagate along the maximum stress drop in the initial stage, and the tensile stress near the flaw will be dissipated because of the crack propagation. After the specimens reach the peak stress, a large number of secondary cracks are initiated and propagate, and the number of micro-cracks increases exponentially with the increasing axial strain, which cause the compressive stress field at the tip of the pre-existing flaw to release. Unlike the traditional hydraulic fracturing mechanism, the water pressure does not penetrate along newly generated cracks. Under the constant internal water pressure, the water pressure will only spread along the wing cracks rather than the already existing secondary cracks owing to the existence of partial compressive stress field at the crack tip. The pore size between the particles is dynamically changing due to the constant variation of axial stress, which in turn affects the variation law of water pressure, thus forming three different types of water pressure changes as follows: Type Ⅰ: the water pressure decreases rapidly when the axial strain reaches the peak value, while the decrease is not significant, and then the water pressure increases with increasing axial strain; Type Ⅱ: the water pressure increases with the increase of axial strain; Type Ⅲ: the water pressure drops rapidly to 0 MPa when axial strain reaches the peak value, and finally the water pressure dissipates.关键词：crack propagation;discrete element;hydraulic coupling;measuring circle
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发布时间：2024-01-08 - 摘要：The hydro-wind-solar complementary system is an important innovation to improve the overall utilization benefits of renewable energy in China. With the higher penetration of renewable generation resources such as wind power and solar power, the uncertainty after integrating wind and solar is the core problem of multi-energy complementary system research. The risks and benefits of multi-energy system considering the uncertainty of one-day ahead wind and solar output forecasts was discussed. Specifically, the risk and benefit evaluation indices are proposed from three aspects of reliability, stability and economy. The short-term optimal operation model of multi-energy system is established, and the one-day ahead power generation plan is proposed using output predictions of diverse power plants. Then, the actual operation process of hydropower station is simulated and updated according to the actual output of wind and solar power plants following the one-day ahead power generation plan. Finally, the planed and actual operation process of each power station are compared to evaluate the comprehensive impacts of output forecast uncertainty on the risks and benefits of the multi-energy system. The multi-energy complementary system of Jinping Ⅰ in Yalong River Basin, which takes in 2.09 million kW solar power and 1.05 million kW wind power, is used as the study case. The results show that the power generation benefits of the multi-energy system have increased by 37.13% compared with each power plant running independently, with more stable total output process. The multi-energy system shows good reliability at the annual scale. During the low water level period of the reservoir, the frequency of load loss condition increases significantly, accounting for more than 96% in the annual cycle, the system reliability is correspondingly undermined. During the flood season, the maximum release of the reservoir increased by 47.06% after multi-energy integration, which brings certain risks to the power generation and flood control of the basin.关键词：multi-energy integration;hydropower operation;power generation plan;hydro-wind-solar;risk analysis
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发布时间：2024-01-08 -
Riverbed Armoring Processes in a Sand-gravel Bed River After the Three Gorges Project Operation AI导读
摘要：Upstream damming can greatly alter the flow and sediment conditions entering downstream reaches in the middle reaches of the Yangtze River, with the bed material continuously coarsened, which has a significant influence on the sediment transport and bed evolution in the downstream of the Three Gorges Project (TGP). In order to study the riverbed armoring and sediment exchange processes among bed material, bed load, and suspended load layer in the Yizhi Reach and Zhijiang Reach, the model with three-state transition probability (Markov Chain) and hiding-exposure effects of non-uniform sediment are introduced. The equilibrium equation of sediment quality in active layer is proposed for calculating grain size distribution. In this model, the influences of flow and sediment regimes, riverbed erosion and deposition on SEP are discussed. The results show that, the composition of surface bed material at Zhicheng station was obviously coarsening, and the grain size distribution curves shifted to the left. The grain size range of surface bed material in 2003 was 0.002～41.000 mm, and changed to 0.031～86.000 mm in 2017. In addition, the median grain size of surface bed material at Zhicheng station showed an upward trend and fluctuated after 2010, but the fluctuation range was relatively small. The monthly change process of the median grain size can be divided into three categories according to the time node of flood periods. The probabilistic model developed in this study is verified against the field measures with both bed load and suspended load particles, and the modeling results show a reasonable agreement with the measured data at Zhicheng station from 2003～2009. Accordingly, the probabilistic model can be used to predict the riverbed armoring and annual process of sediment exchange in sand-gravel bed in the Yizhi Reach and Zhijiang Reach. The model can be used to reveal the mechanism of sediment motion and non-equilibrium sediment transport in sand-gravel bed rivers.关键词：sediment exchange;riverbed armoring;Markov stochastic process;sand-gravel bed;the Three Gorges Project- 2478
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发布时间：2024-01-08 - 摘要：The spatial positioning of temperature-measuring optical fibers is of great significance for accurately grasping the real temperature distribution of a concrete dam. To solve the difficult positioning problem of a single optical fiber in the process of continuous monitoring temperature in a concrete dam, a mathematical model of data symmetry analysis based on mirroring and shifting and curve fitting of data was established and proposed to confirm the symmetry center of original data monitored by bifilar embedded optical fiber through combining with temperature measuring principle of distributed temperature sensing (DTS) system, bifilar embedded construction technology of optical fiber and characteristics of optical fiber temperature measuring data in a concrete dam. On that basis, the number of measuring points of valid temperature-measuring optical fibers and the corresponding relationship between monitoring length and embedded optical fiber meter identification can be confirmed. Then a space-location method of valid temperature-measuring fiber for new pouring block was proposed. The engineering application result indicated that the temperature-measuring section of valid temperature-measuring optical fiber and space position corresponding to each measurement points could be accurately determined by using the space-location method. The comparative analysis results indicated that the differences of monitoring temperature value between three temperature measuring points of optical fiber and thermometers were mostly within 0.8 ℃, and the space-location result was accurate and reliable. Up to now, the method has been successfully applied to more than 160 warehouses of 5 typical dam monoliths for Baihetan arch dam. The proposed precise localization method provided the accurate and reliable original data for the research work of temperature state analysis and safety evaluation of Baihetan arch dam.关键词：concrete dam;VTMOF;bifilar embedded;data symmetry analysis;accurate space-location
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发布时间：2024-01-08 - 摘要：The applicability of a hydrological model is an important issue for its application. On the basis of Clark linear distributed unit hydrograph model, the urban road network confluence in the North region of Future Science & Technology Park located in Beijing was selected for case study, in order to comprehensively validate the linear effect of road network confluence and applicability of Clark unit hydrograph model. The model performance was tested out by using determination coefficient ( R2), Nash–Sutcliffe efficiency (NSE) and relative error of total runoff (RE). The results showed that the average value of determination coefficient is 0.73 which varies from 0.4 to 0.89, the average value of Nash–Sutcliffe efficiency is 0.26 which varies from –0.77 to 0.87, the average value of relative error of total runoff is –0.18 which varies from –0.77 to 0.36. The variation rules of different indexes are closely related to the rainfall intensity for individual rainfall, in which with the increase of rainfall intensity, the determination coefficient and Nash–Sutcliffe efficiency increase toward 1.0, with the relative error of total runoff approaches zer. This indicated that the simulation effect of Clark unit hydrograph model tends to be optimal as the linear effect of road network confluence process increases continuously with the increase of rainfall intensity.关键词：hydrological model;urban road network;confluence;Clark unit hydrograph;linear effect
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发布时间：2024-01-08 - 摘要：In order to solve the problem that the displacement response of isolation layer is too large in the case of the isolated structure under the super intensity, the strategy of optimizing the passive viscous damper based on the active control algorithm was proposed. The passive viscous damper was installed in the foundation isolation structure to form the passive hybrid control structure, and the passive hybrid control basically achieved the control effect of active hybrid control, so as to solve the problem that the displacement response of isolation layer was too large under the super intensity. First set the active control device in the isolation layer to form active hybrid vibration isolation control system, the active control method for isolation layer of active control and speed characteristic, secondly, using the active control force and velocity curve, fitting by the least squares method of passive viscous dampers optimal damping coefficient and the speed index, finally designing a passive viscous dampers installed in isolation layer, forming a passive hybrid vibration isolation control system. Taking a seven-story foundation isolation structure as the controlled model, and conducting the simulation analysis of the active hybrid isolation control system and the passive hybrid isolation control system, it could be seen that the active hybrid isolation control could reduce the displacement of the isolation layer by 39.41%, 45.04% and 55.54%, respectively. The shock absorption rates of passive hybrid isolation control on the displacement of isolation layer were 36.40%, 44.30% and 52.51%, respectively. Passive hybrid vibration isolation control for displacement of isolation layer damping rate could reach more than 90% of the active hybrid vibration isolation control effect, passive hybrid vibration isolation control for the acceleration response of the isolation layer damping rate could reach more than 60% of the active hybrid vibration isolation control, passive hybrid control was also achieved at the same time reduce the earthquake response of the isolation layer not to increase the response of the upper structure, based on the active control algorithm design of passive viscous damper passive hybrid control structures basically achieved the effect of the active control. The feasibility of designing passive viscous damper based on active control was illustrated.关键词：foundation isolation structure;active control algorithm;passive viscous damper;hybrid control system
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发布时间：2024-01-08 - 摘要：In order to better revealed the shear characteristics and mechanical behavior of soil-rock mixture, three samples of indoor mixtures with different rock contents were selected for the studied of the core wall material of a soil-rock dam in Bole District, Xinjiang, by importing the random polyhedron templates to build real block particles, and the different content of rock under different confining pressure of large direct shear test simulation of soil-rock-mixture PFC3D stone content in the sample shear strength was studied, the influence of soil-rock-mixture was analyzed in the process of shearing force of soil-rock-mixture volume change and chain distribution network. The results show that the fitting degree between simulation results and laboratory tests was good, they had good consistency. The higher content of rock, the greater the shear strength of soil-rock mixture. Under the same normal stress, the dilatancy of the sample increases with the increase of the rock content, the low rock content is the softening characteristic, and the high rock content is the hardening characteristic. With the increase of rock content, the number of strong chains increases, the distribution becomed more concentrated, and the overall stability is relatively stable. The soil-rock mixture shows higher shear strength macroscopically. This studied could better understand the micromechanical mechanism of soil-rock mixture and provided reference for the relevant rock-soil mechanical simulation.关键词：discrete element method;direct shear test;soil-rock mixture;numerical simulation;particle flow code
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发布时间：2024-01-08 - 摘要：Mechanical properties of aeolian sand concrete, are important indicators to characterize the performance of aeolian sand concrete. Domestic and foreign scholars have extensively studied the cubic compressive strength, splitting tensile strength and microscopic mechanism of aeolian sand concrete, but there are few researches on the mechanical properties of concrete under axial compression, while the compression of concrete prism is closer to the engineering practice. Therefore, 10 groups of aeolian sand–fly ash concrete were prepared by mixing aeolian sand (replacement rate was 0～40%) and fly ash (replacement rate was 10%～20%) with river sand and cement of equivalent quality. The 60-day-old aeolian sand–fly ash concrete axial compression test was carried out, and the axial compression failure morphology, microstructure, stress–strain relationship, axial compressive strength, peak strain, elastic modulus and Poisson’s ratio of the aeolian sand–fly ash concrete were tested. It was found that the stress–strain curves of aeolian sand concrete with different amounts of aeolian sand in the elastic stage are basically consistent. After entering the elastic-plastic stage, the stress of aeolian sand concrete increases faster than that of the reference concrete, and the brittleness of concrete increases. The axial compressive strength, elastic modulus and Poisson’s ratio showed a trend of increasing first and then decreasing with the increase of aeolian sand content, and decreased with the increase of fly ash content. Finally, the constitutive parameter A of the rising section of Guo Zhenhai’s classic model was subjected to secondary evolution, and an evolution model between the constitutive parameter and axial compressive strength and aeolian sand content was established. The constitutive equation of the stress–strain rising section of aeolian sand concrete was obtained. The calculation model had certain reference for the research and application of aeolian sand concrete.关键词：aeolian sand–fly ash concrete;axial compression;constitutive parameters
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发布时间：2024-01-08 - 摘要：The geological conditions and geotechnical engineering problems are complex and changeable in China. As the construction of engineering projects, deep non-uniform settlement conditions (such as underground coal mining, foundation pit excavation and groundwater level change) can lead to serious deformation and failure of the slopes and foundations overlying them. Pile foundation is a common method of slope reinforcement in engineering projects. Therefore, it is necessary to figure out the failure behaviors of pile foundations under deep non-uniform settlement conditions. Centrifuge model tests were conducted to investigate the deformation and failure behavior of pile foundations under the condition of deep non-uniform settlement which was simulated by the hydraulic system in different ranges. The influence mechanism of deep non-uniform settlement and the failure mechanism of pile foundation were investigated. The observation results are as follows: 1) under the condition of deep non-uniform settlement, there were three main slip surfaces in the slopes, among which the slip surfaces near the deep non-uniform settlement area were obvious sliding failure and the sliding surface near the foundation was mainly tensile failure; 2) the deep non-uniform settlement first led to the slip failure inside the soil from bottom to top, and then led to the instability of the pile foundations, and finally led to the slip surface near the foundation from top to bottom; 3) the range of deep non-uniform settlement changed the location and shape of the slip surfaces of the slopes by influencing the spatial and temporal distribution of the deformation localization; 4) there was an influence range of deep non-uniform settlement condition, and the boundary of the influence range was distributed around piles.关键词：deep non-uniform settlement;pile foundation;slope;failure;centrifuge model test
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发布时间：2024-01-08 - 摘要：To investigate the suction effect on the stress and strain of soil around cylindrical cavity, the analytical solution of effective stress in unsaturated soils was derived. In the elastic and plastic regions, the Hooke’s law and the modified Cam–Clay model were respectively employed. Taking suction as a hardening parameter, the governing equations about stress-strain around the cylindrical cavity were established. By introducing the auxiliary variable, the equilibrium differential equation in Eulerian system was transformed into Lagrangian system. The cylindrical cavity expansion in unsaturated soils was analyzed by solving the first-order ordinary differential equations where the elastic-plastic boundary was the initial conditions. Taking the values of stress and specific volume at the elastic-plastic boundary as initial values, the effects of suction and initial specific volume on the distributions of stress and strain were calculated and analyzed. The results showed that the soil around the cylindrical cavity changed from elastic state to plastic state due to the cavity expansion, and the suction had a significant effect on the stress state of plastic region. With the suction increase, three stress components, as well as the ultimate cavity pressures increased. For loose soils with larger void ratio, the ranges of plastic region reduced with the suction increasing. The specific volume decreased monotonously along the radial direction, which tended to be obvious as the suction increasing. However, for dense soils with smaller void ratio, the effect of suction on the ranges of plastic region was so small that could be ignored. The specific volume near the elastic-plastic boundary increased due to the dilatancy occurring. The larger the suction were, the more obvious of the dilatancy appeared. Finally, the reliability of the proposed method was verified by comparing with the data from lateral pressure test and calculation by the finite element method.关键词：unsaturated soil;suction;cylindrical cavity expansion;modified Cam–Clay model;pressuremeter test
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发布时间：2024-01-08 - 摘要：Affected by the cyclic injection and production loads of stored energy, the surrounding rock of underground salt cavern gas storage will produce tensile cyclic fatigue damage or even damage. To investigate the fracture mechanical behavior and damage evolution law of salt rock with impurities under tensile cyclic loads, three-point bending loading and unloading tests and rock damage acoustic emission monitoring tests of pure salt rock, halogen bearing salt rock and salt rock with impurities were carried out, using the MTS815 rock mechanics testing system and three-dimensional acoustic emission monitoring system. The results showed that: 1) the toughness of salt rocks was enhanced by the bonding of heterogenite and shale. The mean fracture toughness of pure salt rocks under three-point bending and unloading was 6.36 MPa·mm0.5. The fracture toughness of heterogenite salt rocks was 43.08% higher than that of pure salt rocks, and the fracture toughness of impurity salt rocks was 3.18 times higher than that of pure salt rocks. 2) Impurities led to the improvement of brittleness of salt rock, the area covered by the acoustic emission events of pure salt rock was larger than that of heterogenite salt rock and rock salt with impurities. Under three-point bending loading and unloading, acoustic emission events in the rock gradually spread from the groove tip to the load point until the rock was completely fractured. 3) The degree of salt rock damage increased gradually with the increase of cycle times, while the growth rate gradually decreased. The damage variable and groove opening had an exponential function relationship. The inflection point of the curve of damage variable-opening degree had a prediction effect on the study of rock instability tendency. 4) The rc value of AE parameter reflected the evolution trend of main cracks and microcracks in the whole failure process of salt rock bending loading and unloading. In the residual stage after peak, the rc curve of pure salt rock and heterogenite salt rock continued to rise, and the microcracks developed steadily. The impurity salt rocks showed stronger brittleness, and the rc curve of the residual post-peak stage showed the opposite changing trend to that of the pure salt rocks and the hetero halite salt rocks.关键词：salt rock;bending loading and unloading;fracture toughness;acoustic emission technology;rock instability
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发布时间：2024-01-08 - 摘要：The rock damage evolution is directly related to the safety control of major underground engineering. As the threshold stress in the process of rock deformation and failure, whether the characteristic stress can be accurately identified directly affects the effect of damage assessment. Based on the RMTTS stress test system and the MISTRAS acoustic emission test system, the related research on the crack stress identification and damage quantitative evaluation of limestone was carried out. The characteristics of acoustic emission (AE) signals corresponding to each stage of the stress–strain curve were analyzed by AE test under uniaxial compression of limestone, and the AE signals had a large increase in frequency and energy level when the crack propagation developed from stable stage to unstable stage. Based on the variation law of Felicity effect ratio FR during uniaxial cyclic loading of limestone, a crack damage stress identification method independent of strain measurement was proposed. The recognition results for 3 sets of limestone cores were in the range of 0.70
${\sigma _{\rm{c}}} $ $ {\sigma _{\rm{c}}}$ ${\sigma _{\rm{c}}} $ 关键词：rock mechanics;acoustic emission;crack damage stress;damage evolution- 1971
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发布时间：2024-01-08 -
Influence Line Analysis and Damage Detection of Railway Bridge Deflection with Non-ideal Boundaries AI导读
摘要：It is difficult to achieve the influence line analysis accurately and damage detection exactly of assembled railway bridge girder because the boundary conditions are somewhere between the rigid and articulation connections. The non-ideal supporting conditions were considered in the assembled girder structure, a girder model of the elastic supported boundary with rotational restraint was established to simulate the actual prefabricated assembled beam. The initial uncertainty parameters of the girder section were introduced based on the lognormal distribution. The analytical expression of the deflection influence line of arbitrary beam section was deduced by the force-method, and the damage identification method of the assembled girder structure based on the influence line of deflection was proposed. A three-span continuous composite steel girder bridge was established as a simulation example to verify the proposed method. The positions of measuring points of deflection influence line, location and degree of regional damage and testing noise were studied to provide theoretical basis for the analysis of deflection influence line and damage identification of assembled girder structures. The results show that the proposed indicator can locate and quantify the local damage of the span and its adjacent span of a precast assembly railway bridge with non-ideal boundary. The proposed indicator had a superior noise resistance and it is susceptible to damage of the middle span of the girder and longitudinal girders. Based on the influence lines measuring, the continuity of the supports in the assembled girder bridge can be evaluated. The method in this paper can provide theoretical reference for the deflection influence lines analysis and damage identification of the actual railway bridges.关键词：railway bridge;non-ideal supporting;deflection influence line;uncertainty;damage identification;test noise- 2306
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发布时间：2024-01-08 - 摘要：The slope runoff is a hydrodynamic condition in which particles are transported and rolled on a loose medium slope. In order to study the effect of slope runoff on the stability of slope granular particles, an indoor flume flush test was carried out. Three types of particle sizes and four kinds of slope angles were set in the experiment. The high-speed camera was used to record the slope granular particles being washed by the water flow to obtain the critical runoff depth hcr of the particle scouring under different conditions. The experimental results showed that the hcr decreased with the increase of slope angle under the same particle size, and when the slope angle was 20° and 22°, the hcr increased first and then decreased. However, when the slope angle was 24° and 26°, the hcr increased with the increase of the particle size. The reason for the phenomenon is that when the change in the permeability of the slope caused by the increase of the particle size is the main controlling factor affecting the stability of the particles, the particles are more likely to be migrated by the infiltration of water. In order to explain the experimental phenomenon, a mathematical model coupling slope runoff and seepage was established to analyze the stability of particles under runoff conditions. The theoretical expression of the hcr was given by combining the flow velocity characteristics of the water flow with the force-starting characteristics of the particles, indicating that hcr is controlled by particle size, particle specific gravity, porosity, slope permeability, slop angle and so on. By comparing the experimental data with the calculated results, it was found that the measured value and the theoretical value of the hcr decreases, but the relative errors which are all controlled within 35% between them increases with the increase of the slope angle in the same particle size interval. In order to correct the error between the measured value and the calculated value, the neural network module of MATLAB was used to fit the data, and the critical water depth hcr correction equation with two neural network structures was established with high precision.关键词：slope granule;flume test;critical water depth;runoff-seepage model;data fitting
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发布时间：2024-01-08 - 摘要：In order to avoid the legal risks of using foreign countries’ cryptographic algorithms and address the compliance requirements of the regulations on commercial cryptographic management of China, the support of Chinese commercial cryptographic algorithms (national cryptographic algorithms) was added into the virtual trusted platform module (vTPM); simultaneously, to respond to the autonomous and controllable requirements of cybersecurity and promote the large-scale application of virtual trusted computing technology in the domestic cloud computing business the related components of the virtual trusted chain were transformed. Firstly, the interfaces of the Hash cryptographic algorithm SM3 and the symmetric cryptographic algorithm SM4 in the cryptographic toolkit GmSSL (GM/T secure socket layer) were added to vTPM, and the asymmetric cryptographic algorithm SM2 was implemented by the big number arithmetic module of GmSSL, which provides the trusted computing functions based on the national cryptographic algorithms for upper-layer applications. Secondly, the implementation for the SM3 algorithm was added into the related components so that the virtual trusted chain based on the national cryptographic algorithm can be established. Finally, the correctness of the interfaces and the effectiveness of the virtual trusted chain were verified, and the boot time of the virtual machine based on the SM3-algorithm and SHA–1-algorithm virtual trusted chain were compared. The experiments show that the interfaces added are correct and effective, and compared with the virtual machine based on the SHA–1-algorithm virtual trusted chain, the boot time of the one based on the SM3-algorithm virtual trusted chain only increases by 3%, of which the security is improved while its performance consumption is acceptable.关键词：cloud computing;trusted computing;virtual trusted platform module;virtual trusted chain
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发布时间：2024-01-08 - 摘要：In order to solve the problems of the limited devices resources in the edge computing environment and the negligence of computing load as well as the redundant trust path in the existing trust models, a trust evaluation optimization model of the edge computing was proposed based on the graph theory. First, an architecture of trust model based on edge computing was built, of which the complex and huge trust relationship between edge devices was abstracted into a directed weighted graph, and the trust relationship between devices was defined and explained. Then, an adaptive aggregation method based on the information entropy theory was used to aggregate the trust value, which could correct the difference between multi-source trust. Secondly, the constraints of trust threshold, path length restriction and sliding window were added. With these multiple constraints, the nodes and trust edges that obviously do not meet the trust requirements were filtered in advance, which reduces unnecessary computing consumption. Finally, an improved depth first search algorithm was used to filter redundant trust edges, which could avoid loop and node detour problems in the trust path search process. The recursive function Combine was further used to aggregate the feedback trust value. The MATLAB simulation software was used to determine the experiment parameters, and verified the model’s ability of distinguishing malicious nodes from normal nodes. The proposed model was compared with PSM model, RFSN model and random selection model in interaction success rate, time cost and energy cost. The experimental results show that compared with other models, the proposed model could achieve stable state quickly in network environments with different honesty degrees, and the time and energy costs are lower than that of other models. The proposed model can reduce the resource overhead of edge devices and improve the network life cycle while ensuring the effectiveness.关键词：edge computing;trust model;trust path;redundancy optimization
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发布时间：2024-01-08 -
Assessment Model of Cloud Service Security Level Based on Standardized Security Metric Hierarchy AI导读
摘要：In order to cope with the issues existing in the traditional literature that assessment metrics are coarse-grained and non-quantitative as well as assessment methods are subjective and low efficiency, an assessment model of could service security level based on the standardized security metric hierarchy was proposed. First, a fine-grained, quantifiable and standardized cloud service security metric hierarchy was structured according to the principle of evaluation metric system. The content of cloud service security metric hierarchy was composed of both domestic and foreign standards related to the cloud service security. Second, a cloud service security level evaluation model was proposed based on the metric hierarchy. Considering the difference of metric’ types and impact of attributes on the security features of cloud services, a security level assessment method was designed based on the objective weights assignment of the metrics to evaluate the security level of cloud services. Finally, a case study and a performance comparison experiment were respectively conducted to validate effectiveness of the proposed assessment model and efficiency of its evaluation method. Experimental results show that the proposed assessment method is efficient and accurate in the cloud service security level assessment, and the evaluation method outperforms the traditional cloud service security assessment methods.关键词：cloud service;security metric;security level assessment;objective weight assignment;TOPSIS- 2716
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发布时间：2024-01-08 - 摘要：In wireless sensor network (WSN), the user authentication protocol (UAP) is an important scheme to guarantee the legality of admitted-users and access security of sensing information for sensor node. These are various security flaws in many proposed UAPs (i.e. Fan protocol), which are vulnerable to diverse cyber security attacks. In particular, they could not effectively defend against the node compromised attack, the password guessing attack, the privileged-insider attack, and so forth. In addition, the user’s anonymity is not supported so that the user privacy cannot be preserved. To tackle these security challenges, an anonymous two-factor user authentication protocol (AT–UAP) for hierarchical WSN was proposed. In the registration phase of AT–UAP, the password was transmitted via hiding Hash to enhance the transmission security, and the correlation between the secret parameters of gateway node and the users was increased to achieve the uniqueness of the secret parameter. Furthermore, in the authentication phase of AT–UAP, the association between the session key, system time and the user identity was enhanced to achieve the uniqueness and the dynamicity of the session key. Then a password update scheme was introduced to change the password freely and to guarantee the freshness of the password without contacting the cluster head. The logic analysis and the simulation results show that, compared with Fan protocol, AT–UAP can not only defend against the node compromised attack, the password guessing attack, and the privileged-insider attack, but also achieve the anonymity of user authentication on the basis of only adding a small amount of computational overhead. Moreover, compared with Nam protocol, He–Kumar protocol, and Mir protocol, AT–UAP utilizes the lightweight security operations such as hash function, cascade operation, and XOR operation to reduce the computation overhead of sensor node, also optimizes the registration process of sensor nodes to gateway nodes. Its comprehensive performance was better than that of three UAPs mentioned above. Hence, AT–UAP is suitable for the resource-constrained sensor nodes. Meantime, it could significantly improve the security of the wireless sensor network.关键词：wireless sensor network (WSN);user authentication protocol (UAP);two-factors;anonymity
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发布时间：2024-01-08 - 摘要：In order to solve the problem of inaccurate audio comparison caused by noise and delay in broadcast audio, an audio comparison algorithm with delay-adaptive-aware was proposed. To tackle the poor noise immunity of audio feature distance measurement in conventional algorithms, cepstrum was used to analyze the mixed signal of two audio to estimate delay adaptively and comparison, which has a strong ability to resolve equidistant frequency components in the power spectrum. Then, a method of short delay was proposed to obtain accurate similarity between two audios in different situations, which is added short delay in one of the audio. Afterwards, the optimal short delay was selected according to the effect of adding different short delay, so as to improve the performance of the algorithm further. Finally, the simulation experiments were conducted to evaluate the performance of the proposed algorithm, in which multiple audio clips of different broadcast programs were utilized under the condition of different SNR and additive white Gaussian noise. And the delay estimation results and audio similarity under different SNR are compared to verify the effectiveness of the algorithm. Experimental results show that the proposed algorithm outperforms existing algorithms and can achieve 90.36% audio comparison matching accuracy at a low SNR (2 dB), and the calculation speed can meet the requirement of real-time comparison.关键词：audio comparison;delay estimation;cepstrum analysis;real-time broadcast audio
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发布时间：2024-01-08 - 摘要：Volatile organic compounds (VOCs) are the main precursors for the formation of haze and ozone, and most of them are toxic and cause great harm to the human body, so it is necessary to control their pollution emissions. Catalytic combustion is an effective way to deal with VOCs. The effects of preparation methods on the catalytic combustion of toluene by CeO2 and CeOx/CeO2 were studied, and the reasons for the differences in performance were analyzed. CeO2 was prepared by thermal decomposition method, chemical precipitation method and hydrothermal method, then 15% CoOx was supported on CeO2 by dipping-roasting. Toluene was used as the target pollutant to catalyze CeO2 and CoOx/CeO2. The performance of catalytic oxidation was evaluated, and the physical and chemical properties of the catalyst were characterized by XRD, BET, SEM, H2–TPR and Raman. The results showed that: under the test conditions of toluene concentration of 1 000 μL/L and space velocity of 20 000 h–1, CeO2–P prepared by chemical precipitation method had the best catalytic activity, reaching a toluene removal rate of 80% at 375 ℃. After the Co species were recombined, Co/CeO2–P could reach 90% removal rate at 255 ℃. At 300 ℃, Co/CeO2–P still maintained 100% toluene removal rate after a long period of experiment for 78 h. CeO2–P prepared by the chemical precipitation method had a smaller grain size, a larger specific surface area, and better surface redox properties, so it Showed better catalytic activity. After the combination of CeO2 and Co species, due to the large specific surface area and excellent redox performance of CeO2, more Co3+ was formed, and cerium oxide could provide rich surface active oxygen species, making CoOx/CeO2–P the best catalytic activity and stability. CeO2 prepared by different methods had different specific surface areas and surface redox properties, which were the main factors affecting its catalytic activity.关键词：catalytic combustion;volatile organic compounds;preparation methods;ceria
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发布时间：2024-01-08 - 摘要：The numerical simulation is mostly employed in the existing studies of micro-texture. Compared with the numerical solution, the analytical solution describes more clearly the influence of main factors on the lubrication performances and the potential relationship between various physical variables in the piston ring with dimples. And it can also improve the designers understanding. Firstly, the cavitation zone, the pressure distribution and the load capacity of one dimensional oil film between the cylinder liner and piston ring with equispaced dimples, are analyzed with the analytical method based on the inlet suction mechanism and flow continuity condition. Secondly, the analytical solution for load capacity of one oil film period is obtained by integrating one-dimensional analytical solution. The analytical solutions show that the pressure distributions of the first n–1 dimples are similar and the maximum pressures of the firstn–1 dimples is equal, which is decided by the inlet pressure, the distance between dimples and the cavitation pressure, while the pressure distribution and maximum pressure of dimplen are decided by the outlet pressure besides these three factors. When the dimples are equispaced, the maximum pressure is about double inlet pressure in the first n–1 dimples and about the sum of the inlet and outlet pressures in the dimplen. They also show the influences of dimple depth on the cavitation distribution and the load capacity. When the dimple depth is more than half of the oil film thickness, the area of cavitation zone decreases with the increase of dimple depth. At last, the Fluent software is employed to simulate the oil film with four equispaced dimples. The results of analytical calculation and numerical calculation are consistent. The analytical solutions can explain the cavitation, the pressure distribution and the trend of load capacity in numerical simulation. The same optimal geometric size at the maximum load capacity is obtained with the numerical and the analytical solution, and the difference of load capacity between two solutions is below 10%.关键词：analytical solution;load capacity;simulation validation;cylindrical dimples;piston ring
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发布时间：2024-01-08 - 摘要：Distance measurement based on digital image is non-contact measurement. Among them, the convergent binocular vision system has a large measurement field and has no specific requirements for the camera’s spatial layout. It is one of the current research hotspots of distance measurement based on digital image technology. The mathematical model of distance measurement based on digital image is established according to the principles of camera pinhole imaging. A binocular camera is used to acquire planar image information (pixel coordinates) of a measured object in the space coordinate system, and these information are then used to calibrate the internal parameters and external parameters rotation matrix , translation vector . A methodology is presented to determine the relationship among the pixel coordinate system, the image coordinate system, the camera coordinate system and the world coordinate system as well as calculate the spatial distance between two points of a measured object by using their pixel coordinates on the planar image. A distance measurement instrument was developed based on digital images with the goal of optimized portability, power consumption and compatibility. the RK3288 is used as the core processor, and IMX–179 is selected as the image sensor, the Linux system is selected as developed system.This paper discusses the approaches to image acquisition, data transmission, data exchange, and data processing modules of the instrument. The instrument of distance measurement algorithm based on digital image has the advantages of good real-time performance, high measurement efficiency, simple system structure, and low cost. Experiments showed that the distance measurement instrument show digital images has a measurement error of less than 1% at a distance of 10 cm when the object is located at 50 cm to 100 cm in front of the camera. The measurement instrument based on this algorithm has a wide range of applications in robot vision, non-contact engineering measurement, intelligent manufacturing and other fields.关键词：digital image processing;machine vision;distance measurement;instrument design
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发布时间：2024-01-08 - 摘要：In the process of oil and gas exploitation, with the increase of drilling depth, the rock hardness is increased, and the downhole friction resistance is larger, the drill string system is prone to stick-slip vibration, which may lead to premature component failure and low drilling efficiency. Therefore it is of great significance for the study of stick-slip control technology. Combined with the actual working conditions in the drilling process, a new torsional vibration tool is proposed, and the torsional vibration model and nonlinear dynamic model of the drill string system based on the tool are established. To study the stick-slip reduction effect of the tool, the case study and experimental test are carried out respectively. The control variable method is used in the case study. Firstly, given the specific values of the rotation speed of the turntable and the weight on bit (WOB), the angular velocity of each component of the drill string system with and without the tool are compared and analyzed. Secondly, both the case of “the same WOB, different turntable speeds” and the case of “the same turntable speed, different WOBs” are considered, and the angular velocity of the drill bit with and without tools in the drill string system are calculated respectively. During the experimental test, the test with and without tools are carried out at the same well, and combined with the logging data of adjacent well which did not use the tool, the viscosity reduction effect of the tool is analyzed. The results show that under the same parameters, sticky-slip vibrations can be clearly eliminated or suppressed using the new torsional vibration tool. Meanwhile, increasing the rotational speed of the turntable, and appropriately reducing the drilling pressure can inhibit the stick-slip vibration of the drill string to a certain extent. And within the allowable range of error, the theoretical calculation results are consistent with the test results, which verifies the correctness of the theoretical model, the solution method and the analysis of the examples. The proposed new torsional vibration tool, established dynamic model and research results have important reference significance for reducing the stick-slip vibration and improving the rock-breaking efficiency.关键词：drilling;torsional vibration tool;stick-slip;torsional vibration;dynamics
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发布时间：2024-01-08 -
Numerical Simulation on the SK Type Static Mixing Process for In-situ Injection Molding Resin System AI导读
摘要：Aiming at the problem of on-line mixing of in-situ injection molding for low molecular thermoplastic resin system in molten state, based on the independent in-situ injection molding system platform, and combined with simulation and experimental research, the SK static mixing of a new type of low molecular thermoplastic resin system CBT500/DBTL was studid. COV in statistical theory was uesd for quantitative characterization of mixing quality. In the process, the influence mechanism and law of the number of elements, length-diameter ratio and the helix angle of the core of the SK type static mixing head on the mixing quality were obtained. The results showed that the mixing quality increases as the number of mixing core units increases. When the number of mixing core units increases from 3 to 10, the value of COV reduces from 0.90 to 0.05.The smaller the length-diameter ratio, the shorter the distance through which the same mixing quality is reached.When the length-diameter ratio is reduced from 1.5 to 1.0, the length of the mixing head required for the COV value of 0.05 is reduced from 116 mm to 80 mm. The larger the helix angle, and the better the mixing ability.After passing through 10 mixing cores, the COV increases from 0.05 to 0.08 when the helix angle increases from 120° to 180°.The experimental results are consistent with the simulation results, which verifies the reliability of the simulation results. The research results provide a reference for the development of resin system on-line mixing device of in-situ injection molding.关键词：in-situ injection molding;mixing head;low molecular thermoplastic resin;thermoplastic composit- 2266
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发布时间：2024-01-08 - 摘要：In order to evaluate the reliability of the cylindrical worm drive mechanism, the Taylor series expansion is used to expand the state function of the worm gear mechanism and the first four-order center moments of the structural state function are obtained. Regarding this as a constraint condition, the probability density functions of the worm gear tooth surface contact strength and tooth root bending strength structural state function are obtained by combining the maximum entropy principle. On the basis of the probability density functions, the reliability of the two failure modes of the worm gear is analyzed. On the other hand, considering the correlation between the two failure modes of worm gear tooth surface contact and tooth root bending, the reliability model under failure-related conditions is established, and the correlation coefficient between the two failure modes and the overall reliability of worm gear are given. Taking the worm gear of a reducer as an example, the proposed method is verified by Monte Carlo simulation. The results show that the reliability method based on the fourth moment and the maximum entropy principle has higher precision, and there is a certain correlation between the two failure modes of the worm wheel. Therefore, the failure-related worm wheel reliability assessment method is of great significance for the comprehensive reliability assessment of worm drive.关键词：cylindrical worm drive;reliability;failure correlation;fourth-order moment method;maximum entropy theory
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发布时间：2024-01-08
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