最新刊期
卷 51 ， 期 4 ， 2019
- 摘要：The mountain area accounts for 30% of the land area globally, with more than 5 000 people dying each year from flash floods. China’s flash flood disaster control zone covers 48% of the land area, with the living population accounting for 44.2% of the country’s population. Since 2 000, about 1 000 people in China have died each year as a result of flash floods, and the number of deaths from flash floods accounts for about 70% of the death toll from flood disasters. A mountain area often shows the characteristics of steep terrain, broken surface, thick soil layer and frequent rainstorm, and thus, the mountain flood and sediment movement coupling causes the disaster to be prominent because of the steep rise and fall of the flood and the dramatic changes of riverbeds. The prevention and control of flash flood disaster has become a prominent problem to China’s major infrastructure constructions such as agriculture, energy, transportation and national defense security, regional social and economic development and the safety of people’s lives and property. The study of rainstorm and flash flood disaster is still the focus of flood control and disaster reduction in China. Facing the severe disaster risk situation of flood and sediment transport, it is difficult to solve the problem of disaster prevention using the traditional theory and technology of sediment movement, which do not consider the actual coupling process of flood and sediment. In fact, there is not enough understanding of the catastrophic effect of sediment supply mutation on major flash flood disaster. Nowadays, the mechanism between flood and sediment transport coupled into the disaster area identification is unclear, and the prevention and control technology of flood and sediment disaster is not perfect in mountain area. Therefore, it is urgent to systematically sort out the law of flood and sediment transport in rainstorm mountain, by realizing the theoretical innovation of the coupling disaster of flood and sediment movement, putting forward the effective measures of source control and regional comprehensive prevention of major flood and sediment disasters, and significantly improving the technical level of flood and sediment disaster prevention and control in China. It will provide theoretical basis and technical support for safeguarding the safety of major projects in the country and the safety of people’s lives and property. The research on early warning theory and prevention and control technology of rainstorm and flash flood disaster has been studied mainly by rainfall–runoff–water level analysis, taking the critical rainfall/water level threshold condition as the criterion, and less involving the severe adjustment mechanism of riverbed caused by the mutation of sediment supply. But a large number of rainstorm flash flood disaster scene shows that the coupling between sediment supply and flood is the key source power of major flash flood disaster. The project " Research on flash flood disaster under the mutation of sediment supply” is based on the field investigation of rainstorm and flood disaster in mountainous areas and the inversion simulation of disaster experiment. Through the theoretical analysis of hydrology, soil mechanics, hydraulics and river dynamics, in combined with the numerical simulation, the applicants will investigate the coupling disaster process of storm flood in typical small watersheds, sediment from landslide, gravel and pebble transport with a large range of size distribution and the excess sediment supply in a gully. The characteristics of storm flood and sediment in mountain regions, the complex transport power of the riverbed, the water and sediment motion and channel response patterns with excessive sediment supply will be systematically investigated. The response disaster mechanism of rainstorm flood process in the mountain region and the mutation of sediment supply will be clarified. The forgoing researches will provide theoretical and technical support for the early warning and prevention of flood disaster in the mountain region, and will enrich and perfect the hydrological sediment motion and the disaster prevention method during the flood disaster.关键词：mountainous area;storm flood;sediment supply;flash flood disaster;disaster mechanism
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发布时间：2024-01-05 - 摘要：Earthquake changes the structure and physical-mechanical properties of the rock-soil mass in gravel soil slope, which increase the number and magnitude of rainfall landslides post earthquake. The existing researches on the effect of earthquake and rainfall on the gravel soil slope stability are mainly theoretical analysis and numerical analysis, but lack of validation. The coupling mechanism between earthquake and rainfall on landslide is extremely complex, therefore it is difficult to quantitatively analyze the effect of earthquake and rainfall on slope stability. Taking rainfall-induced gravel landslides post earthquake in Wenchuan earthquake stricken area as objects,a series of shaking table model tests, rainfall model tests and slope crest loading tests were carried out to analyze the stability of gravel landslide. The test results showed that the seismic loading induces fissures developing in slope crest and slope body, the upper slope becomes looser and the lower slope become more compressible. The rainfall seepage speed increase, the stability of rock-soil body decrease, the weight of landslide increase and the seepage force increase, thus the stability is obviously decreasing. The stability of rainfall-induced gravel landslide post earthquake is lower than rainfall or earthquake landslide. As the increasing of seismic intensity or rainfall intensity, the stability is obviously decreasing. As the seismic intensity is 0 or 0.1g and subsequent rainfall intensity is 100 mm/h, the drop rate of ultimate bearing capacity is relative large than the seismic intensity is 0.2g or 0.4g. It means that the effect of subsequent rainfall on slope stability post earthquake is more significant when the seismic intensity is relative low. Based on physical modelling experiments, the effect of earthquake and rainfall on slope stability was quantitatively analyzed, which can provide reference for the prediction and early warning of rainfall-induced gravel landslide post earthquake.关键词：earthquake;rainfall;gravel soil slope;slope crest loading;ultimate bearing capacity;stability
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发布时间：2024-01-05 - 摘要：Field observations show that loose soils are common deposit in gullies after an earthquake which provides ideal sources of material for debris flows and landslides. During rainfall infiltration process, pore structure provided by coarse soil skeleton provids a natural flow channel inside soil for fine particles to migrate, thus degrading the stability of soil structure and causing further slope failure. Pervious study of fine particle migration in soil mainly focused on seepage experiments, mid-scale flume test with rainfall as a boundary condition, and other macro-scale methods. However, these methods could not directly obtain the parameters such as pore structure, velocity of fine particles, and pore pressure inside soil sample to quantify the internal erosion process. In the current study, a series of one-dimensional cylinder microscopic seepage tests were designed, the coarse to fine particle size ratio was chosen as a controlling parameter, the three-dimensional computed tomography technology in Shanghai Synchrotron Radiation Facility (SSRF) was then used to quantify the characteristics of fine particle migration during seepage process. The numerical simulation using discrete element method (DEM) coupled with Darcy’s flow was then used to back analysis the physical test. The results of CT and numerical calculations revealed that there existed preferential erosion in the inflow and outflow region of the soil sample. When the numerical simulation is calculated to 2.5s, 37.05% and 31.95% of the fine particles had been eroded in above two regions, respectively, while the erosion at other locations is relatively low. The form of fine particle erosion inside the soil in the direction of seepage includs the loss balance of loss and supply and gradual erosion. The average kinetic energy of the fine particles tends to increase along the seepage path. On the one hand, the forming of long-term clogging to flow channels is reflected by the decreasing of average kinetic energy and quantity of fine particles with time; On the other hand, the temporary clogging to flow channels is reflected by the rate of increase of the number of fine particles in the measurement region larger than the rate of increase of average kinetic energy. The fine particle migration characteristics in the soil on the microscopic scale are mainly affected by the fluid state and pore characteristics, and its research is of great value for understanding the mechanism of loose soil slope failure.关键词：loose soils;fine particle migration;CT scan;imaging analysis;fluid-solid coupling
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发布时间：2024-01-05 - 摘要：Based on the single hole dilution mathematical model, the mathematical relationship model between fluorescence photocurrent and seepage velocity of landslide slopes was established, and the fluorescence photoelectric monitoring probe and measuring system for seepage velocity of slope observation hole were designed and developed. Through laboratory experiments, the characteristics of photoelectric current of fluorescent solution with different concentration and the influence of groundwater environmental factors such as water temperature, turbidity, acidity and alkalinity on the intensity of fluorescent photoelectric current were studied, and the suitability of fluorescent photoelectric method in monitoring underground seepage of reservoir bank landslide was demonstrated. The results showed that the photocurrent intensity increases with the increase of fluorescent solution concentration in the temperature range of 5～25 ℃ and there is a significant linear relationship between the low concentration range of 0～0.006 5%, which meets the theoretical requirements of the application of fluorescent photoelectric velocimetry to the monitoring of seepage velocity in landslide slopes. At the same time, when the concentration of fluorescent solution is constant, the photocurrent intensity decreases gradually with the increase of temperature, and the linear law is obvious, and the fitting lines of different concentrations are approximately parallel distribution, with little slope. The influence of temperature on light current intensity is much lower than that of concentration change, but in practical application, the initial temperature and the end temperature are basically the same, and the influence of temperature on the monitoring results of seepage velocity can be neglected. Under strong acidic conditions, the molecular activity of fluorescent agent will be reduced, and the photocurrent intensity will be decreased obviously. However, the activity of fluorescent solution will be restored after alkali neutralization. The selected Luyor–6200 fluorescent reagent can satisfy the monitoring of seepage velocity in conventional acidic and alkaline groundwater environment. The turbidity has a great influence on the photocurrent, but the photocurrent intensity of the turbid fluorescent solution can be restored to that of the normal fluorescent solution after a long time of stationary. Therefore, it takes at least 4 days for the hole to be stationary for field application. Finally, the implementation scheme of on-site monitoring of seepage velocity of landslides by fluorescence photoelectric velocimetry was given关键词：landslide;rock and soil;groundwater;seepage velocity;single hole dilution;fluorescence photoelectric method
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发布时间：2024-01-05 - 摘要：Valuating breach flood of landslide dam is usually through analyzing the breach process caused by hydraulically driven breaking-sliding process.The traditional analytical method does not use the limit equilibrium method, or the slope angle of the slip surface is not changed during the collapse process, or the pore water pressure is not considered. In fact, the hydraulically driven breaking-sliding process is a problem that needs to be solved by the limit equilibrium. An approach to determine the critical slip surface by analytical method with circular slip surfaces, the effective and total stress methods dealing with different dam materials, and a procedure to model the stepped failures of the breaking-sliding process due to continuous toe cutting were proposed. A spreadsheet entitled DBS–IWHR was developed to the breaking-sliding process analysis. This spreadsheet was incorporated into another spreadsheet entitled DB–IWHR for the calculation of flood hydrograph caused by hydraulically driven breaking-sliding. Research indicated that DBS–IWHR proposed a simulation step to determine the hydraulically driven breaking-sliding process of the dam, which included finding the factor of safety for a specific circular slip surfaceFS; among a variety of possible slip surfaces, determining the critical one associated with the minimum factor of safety Fm; determining the critical depth of toe cutting associated with Fm = 1; modeling the stepped breaking-sliding process. The simulation of the collapse process could be performed in four steps manually. The spreadsheets are transparent and self-explanatory, easy for practitioners to understand and check for secondary development through the web. The developed approach was tested by back analysis of the Tangjiashan landslide dam breached in 2008 with a flood peak of 6 500 m3/s, breach width of 150 m. The predicted flood peak is 7 610 m3/s and the breach width is 139.6 m. The calculated results of the final breach base level and the peak discharge were in good agreement with the field data. Further, the results were shown to verify the reliability of the improved hydraulically driven breaking-sliding process simulation method.关键词：landslide dam;slip surface;the effective versus total stress analysis;breaking-sliding process
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发布时间：2024-01-05 - 摘要：Rainfall intensity has a significant influence on the rainfall infiltration process of landslide slope, and thus plays an important role in the deformation stability of landslide. To reveal the relationship between rainfall infiltration process and the failure mode of landslide deformation and instability, the response law and deformation and failure mode of pore water pressure and soil pressure of landslide accumulation body under different rainfall intensity were deeply studied based on the indoor large-scale landslide model test of artificial rainfall simulation, and the deformation and failure mechanism of rainfall-induced landslide was revealed. Results showed that rainfall infiltration caused the increase of pore water pressure and soil pressure in landslide accumulation, and the growth rate of pore water pressure and soil pressure increased with the increase of rainfall intensity. The deformation and failure of deposit landslide was closely related to the pore water pressure changes, the pore water pressure of the deposit landslide increased along with the increase of rainfall duration grows, and the matrix suction decreased continuously, landslide damage zone will produce cracks, upper side due to squeezing effect under the heaving of soil, slope toe would be partial flow phenomenon such as soil. The rainfall intensity was closely related to the deformation and failure mode of the accumulation landslide when the rain strength was 0.44 mm/min. A wide range of sliding failure occured along the slope along the most dangerous shear plane, and eventually plastic flow was formed when the rain strength is 0.57 mm/min.关键词：rainfall infiltration;landslide physical simulation test;rainfall intensity;pore water pressure;landslide accumulation
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发布时间：2024-01-05 - 摘要：The at-rest earth pressure coefficient is an important mechanical parameter of soil, so the study of the at-rest earth pressure coefficient of coarse grained soil has important theoretical value and practical significance. The relevant research about the influence of initial relative density on at-rest earth pressure coefficient of coarse grained soil is almost blank. To study the at-rest earth pressure coefficient behavior of coarse grained soil with different initial relative density, by changing initial relative density of a sandy gravel and a rockfill with the same gradation, a number of tests to obtain the at-rest earth pressure coefficient behavior of these test specimens were performed using a new-developed large-size apparatus. The test data showed that the at-rest earth pressure coefficient decreases with increasing effective vertical stress, and the tendency of decreasing at-rest earth pressure coefficient trends to weaken with increasing effective vertical stress. There exists a linear negative correlation between the values of at-rest earth pressure coefficient and initial relative density for coarse grained soil. The at-rest earth pressure coefficient is influenced by soil type. During the loading the at-rest earth pressure coefficient of sandy gravel is 4.0%~7.5% greater than that of rockfill, and during the unloading the at-rest earth pressure coefficient of sandy gravel is 0~12.4% greater than that of rockfill. The analysis of the test data of rockfill showed that the relation between at-rest earth pressure coefficient and effective vertical stress, developed by the authors, is appropriate for coarse grained soil with initial relative density that is not zero. Based on the relation, an empirical formula, which can describe well the relationship of effective vertical stress and initial relative density to at-rest earth pressure coefficient for coarse grained soil, was obtained. Furthermore, this empirical formula was verified by test data of sandy gravel.关键词：at-rest earth pressure coefficient;coarse grained soil;initial relative density;effective vertical stress;soil type
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发布时间：2024-01-05 - 摘要：Cable structures are more and more widely used in railway bridges, however there is no rating requirement for the cable structures in the current code for rating existing railway bridges yet. Most of the rating methods are based on were based on the adjustment factor for the cable force or frequency in the existing bridge standards or theories, while few of them are paid attention to the studies or requirements about the cable force increment adjustment factor were carried out in current literatures or specifications. In addition, further study and validation should be firmly confirmed on how to reasonably select the cable length and how to determine the finite element model for the theoretical calculation of cable force in calculating the adjustment coefficient. Based on the above, the rating method of cable force increment adjustment coefficient was proposed, and the reasonable calculation method of cable length and theoretical calculation model for cable force were determined by the comparison of case study. The cable force calculation formula under different boundary conditions was accurately derived based on the string theory and energy method, and the simplified calculation model of cable force loaded was suggested considering vibration frequency ratio, and the increment adjustment factor of cable force was derived on the basis of the simplified model. Experimental cases demonstrated that the results by the accurate methods of cable force is in good agreement with the result of finite element calculation and the simplified method. By comparing with the cable force, the cable force variation and the basic frequency, the cable length should be reasonably selected for the measured cable force calculation during the transition from the measured frequency to the cable force. The theoretical cable force can be determined according to the finite element model of overall bridge, and the vibration frequency of the cable can be determined according to the local cable model equivalent to the cable force of the finite element model of overall bridge. Compared with the adjustment coefficient of vibration frequency, cable force deviation rate and cable force adjustment factor, the increment adjustment factor of cable force can remarkably reflect the variation amplitude of the cable force and evaluate the technical status of cable structure, which can be used as the rating standard of cable structures and suitable for evaluating the medium length hangers with the bending stiffness affecting parameter
$\mu$ 关键词：cable force increment;adjustment factor;accurate solution method;simplified solution method;case study- 2451
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发布时间：2024-01-05 - 摘要：The fluctuating velocity structure of open channel turbulence has a significant influence on the momentum transfer and energy dissipation. Based on the instantaneous velocity data obtained by Particle Image Velocimetry (PIV) measurements in longitudinal sections for open-channel flows over smooth and rough beds, the probability distribution of the fluctuating velocity in the inner region was discussed. The vertical distribution characteristics of the probability of turbulence events (PTE) were analyzed, and the quadrant distribution of Reynolds stress (RS) and turbulent kinetic energy (TKE), as well as the relationship between RS, TKE and PTE were studied. The results showed that after bed roughness increased, the probability distribution and organization structure of the fluctuating velocity in the inner region would change. While the probability distribution of longitudinal fluctuating velocity became sharp and presented a high narrow peak, the probability distribution of vertical fluctuating velocity gradually flattened and came close to normal distribution. Meanwhile, the strip structure of the longitudinal fluctuating velocity clearly exhibited in the inner region of the smooth bed gradually became irregular or even disappeared. The predominance of turbulence events of the 2nd quadrant and the 4th quadrant would not change with bed roughness, but the distribution characteristics of PTE would vary. When bed roughness increased, PTE of the 2nd quadrant increased in general along the total water depth, while PTE of the 4th quadrant increased only in the inner region. The bed roughness had a greater impact on the 2nd quadrant turbulence event than the 4th quadrant turbulence event. Furthermore, the predominance of the 2nd quadrant turbulence events were relatively enhanced, while the difference of PTE between the 2nd quadrant and the 4th quadrant were reduced, and the turbulence anisotropy decreased. For open channel flow with smooth bed or rough bed, the RS and TKE of the 2nd, 4th quadrant were larger than that of the 1st, 3rd quadrant, especially the values of the 2nd quadrant were at their maximum, and the quadrant TKE could account for 39.3% of the total TKE. With the increase of bed roughness, the absolute values of RS and TKE of the 2nd, 4th quadrant were increased, the increase of RS in the inner region was particularly obvious, and the increase of TKE in the inner and outer regions was close. At the same time, the change of PTE, RS and TKE in the 2nd, 4th quadrant had strong relevance.关键词：fluctuating velocity;quadrant analysis;probability of turbulent events;reynolds stress;turbulent kinetic energy
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发布时间：2024-01-05 - 摘要：Flash floods in mountainous watersheds are often caused by the rainstorm. They are different from regular floods by having a smaller timescale and a faster flowing front of water and debris. The storm flood in mountainous watersheds presents strong nonlinearity, and the related hydrological calculation remains one of the critical challenges for accurate flash flood forecasting, which is further constrained by the availability of local datasets. In this paper, we present the empirical formulas derived from the distributed unit hydrographs which are subtracted from the rainfall intensity and the spatial variation of terrain, land use and soil type within each watershed. By selecting 26 774 small mountainous watersheds in Gansu province as study sites, we utilize variable fuzzy clustering method to capture the variation of unit hydrographs, and the empirical formulas between the watershed characteristics and the peak discharge of unit hydrographs are obtained in each cluster. The results show that variable fuzzy clustering method performs well in the classification of the distributed unit hydrographs, the derived empirical formulas can produce reliable results on the calculation of flood peak discharge in small mountainous watersheds. Meanwhile, flood peak discharge is mainly affected by drainage area, main channel network length and corresponding longitudinal gradient, and the derived empirical formulas show wide application potential in the hydrological calculation of rainstorm in small mountainous watersheds, especially in ungauged basins.关键词：small mountainous watersheds;distributed unit hydrographs;confluence process;variable fuzzy clustering method;empirical formula
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发布时间：2024-01-05 - 摘要：In order to accurately analyze the stability of soil-rock-mixture slopes, a method which considers the random distribution, proportion of rock blocks, and the dip angles of bedrock is put forward. Based on the rock block proportion and gradation of soil-rock-mixture slope, the slope model is randomly generated under the rock block proportion from 10% to 60%. The slope model is also randomly generated under the dip angle of bedrock from 0° to 20°. Each rock block proportion and dip angle of bedrock model takes into account eight different rock distribution locations. Finally, the generated model is imported into Optum G2 to establish the model of soil-rock- mixture slopes. The stability of soil-rock-mixture slopes are analyzed by finite element limit analysis method, and the calculated results are compared with those obtained by equivalent strength parameter model of Kalender. The results show that the maximum and minimum lower and upper limit safety factors of soil-rock-mixture slopes with the same rock block proportion and dip angle of bedrock vary greatly due to the difference of the spatial distribution of rock blocks. The shear zone in the soil-rock-mixture slopes is no longer circular, but shows three typical expansion modes. They are "around stone", "distributary" and "inclusion". The safety factors of soil-rock-mixture slopes obtained by equivalent strength parameter model of Kalender and random rock block model are quite different. The results show that the safety factor obtained by the method of random rock block model is feasible. The research results can provide reference for the design and construction of soil-rock-mixture slopes.关键词：soil-rock-mixture slope;stability;limit analysis;rock block proportion;dip angle of bedrock
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发布时间：2024-01-05 - 摘要：Since the uneven construction quality and the inherent heterogeneity of concrete, the material properties of the gravity dam have spatial variability. The spatial variability of the concrete strength parameters will affect the seismic performance of dams, while it is rarely considered in the current seismic dynamic analysis of gravity dams. The random field theory was employed to generate the spatial variation random field of concrete tensile strength. The Midpoint method was used to discretize the random field and then Cholesky decomposition and linear transformation were performed on the generated correlation coefficient matrix. A series of independent standard normal distribution sample matrices were utilized to generate corresponding correlation lognormal distribution sample matrices to simulate the spatial variability of tensile strength. Considering the spatial variability of concrete tensile strength, the seismic nonlinear dynamic analysis of Koyna gravity dam was carried out by using Concrete Damaged Plasticity model. Based on the statistical significance, the dynamic response characteristics of the dam, such as the number of cracks, the depth of cracks, the distribution range of cracks on the upstream surface and the displacement of the dam crest were studied. The results showed that, after considering the spatial variability of tensile strength, the dynamic response of the Koyna gravity dam has obvious dispersion, and the additional cracks on the upstream causes the horizontal displacement of the dam crest to be downstream, the vertical displacement to be uplifted, and the residual displacement to be increased. Meanwhile, the mean depth of crack is larger than that of homogeneous assumption, and the extent of dam damage is generally aggravated. The actual observed cracks in the Koyna gravity dam are within the calculated crack distribution. The parameter sensitivity analysis showed that the mean value and variability of the dynamic response of the dam increases with the increase of the coefficient of variation of tensile strength, while they are not sensitive to the horizontal autocorrelation distance of tensile strength.关键词：gravity dam;spatial variability;seismic cracking;dynamic analysis
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发布时间：2024-01-05 - 摘要：In order to address the problems that the features and information is limited in short text, the short text features are not fully expressed by traditional convolutional neural network (CNN) and recurrent neural network (RNN), a text classification model named convolutional gated recurrent neural network was proposed to represent sentence feature vector and classify short texts. The pooling operation was removed in convolution layerof the model to retain sequential structure and location information in text data. Series–parallel convolution structure was used to extract multi-feature combination of words and local context information as the input of RNN. Then, the gated recurrent unit (GRU) was used as the structure of RNN to represent the sentence features based on the sequential information of text. The features were input to the classifier with additive margin to guide network to learn distinguishing features and realize short text classification. The short text classification data set TREC, MR, and Subj were applied for testing. The influence of network hyper-parameters selection and convolution layer structures on classification accuracy were simulated and analyzed, and common text classification models were compared in experiments. Experimental results demonstrated that the classification accuracy of text data was improved by removing the pooling operation and using smaller convolution kernels for series–parallel convolution in the multi-feature representation. Compared with the GRU with the same number of parameters, the classification accuracy of the proposed model was increased by 2.00%, 1.23% and 1.08% in three datasets respectively. Compared with the CNN with the same number of parameters, the classification accuracy of the proposed model was increased by 1.60%, 1.57% and 0.80% in three datasets respectively. Compared with Text–CNN, G–Dropout, F–Dropout and other common models, the classification results also kept best. Therefore, experiments showed that the classification accuracy was effectively improved by the proposed model, which could be applied to short text classification scenarios.关键词：feature representation;short text classification;recurrent neural network;gated recurrent unit
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发布时间：2024-01-05 - 摘要：In order to solve the problem that traditional identity-based fully homomorphic encryption schemes can only perform homomorphic operations and access control on ciphertexts under the same identity, a multi-identity fully homomorphic encryption scheme was proposed based on LWE problem. Firstly, the identity-based fully homomorphic encryption scheme was optimized by using a gadget matrix and a new form of encryption and decryption was obtained, which reduced noise, and changed the dimension of the underlying lattice basis in the identity-based encryption. Secondly, by using the multi-key fully homomorphic transformation mechanism, the masking system was constructed to generate auxiliary ciphertext. Finally, the multi-identity fully homomorphic encryption scheme was constructed to handle ciphertexts under different identities in which the multi-key scenario was extended to the multi-identity scenario. The results showed that the proposed scheme combined identity-based encryption with multi-key fully homomorphic encryption, and was proved to be IND–CPA security under the selected identity. Compared with other schemes, the ciphertext size and noise expansion were reduced when encrypting a single-bit message and evaluating ciphertexts, and more PKGs were allowed to participate in the generation and distribution of private key. Meanwhile, a 2-round multi-party computation protocol could be constructed by the given threshold decryption scheme.关键词：identity-based encryption;fully homomorphic encryption;multi-identity;threshold decryption
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发布时间：2024-01-05 - 摘要：In order to generate high quality soft shadows with low time cost, a fast rendering algorithm of percentage closer soft shadows was proposed. Based on the technology of percentage closer soft shadows, a multi-scale shadow map was used to preprocess the shadow map. By removing those pixels that contributed less to queries about shadow map, the cost of preprocessing was reduced. Based on the fast traversal algorithm, an effective sampling mode was used to sample search area thus improved the accuracy of traversal results by utilizing sampling information. And then, a reuse scheme was exploited. In the scheme, only one representative pixel was calculated for a group of similar pixels, and the other pixels in the group reused the calculation result of the representative pixel, which reduced the amount of calculation and thus improved the performance of algorithm. Finally, soft shadows were blurred to get more smooth edges. In addition, to determine appropriate parameters, a series of experiments were conducted. In order to verify the validity and versatility of the algorithm, several randomly generated scenarios were used for test and the comparisons with the mainstream algorithms were conducted. The comparison indexes were the quality of soft shadows and the running time of algorithms. The experimental results showed that the proposed algorithm has higher performance while ensuring the quality of soft shadows. Furthermore, the larger proportion of shadows virtual scenes has, the greater performance improvement the proposed algorithm gains.关键词：soft shadows;percentage closer soft shadows (PCSS);multi-scale shadow map;fast traversal;pixel reuse
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发布时间：2024-01-05 - 摘要：In order to solve the problems of energy storage location and capacity in transmission network with high percentage of renewable energy, an optimal method considering N–1 security constraints based on chance constraints was proposed. It can calculate the location, rated capacity and power of energy storage. On the premise of ensuring the security of the transmission network, the economic benefits of the transmission network and the proportion of new energy consumption should be improved. In this paper, the benefits of power plants, renewable plants and energy storage owners were considered. An object function was established to minimize the generating cost, wind-solar energy abandoning cost and maximize energy storage benefits. To acquire the optimal location, rated capacity and power of energy storage, many constraints were introduced, such as conventional generators on-off and power output, charge-discharge state and power of energy storage,N and N–1 security constraints of transmission network. According to the predicted data of typical daily load, wind power and photovoltaic, a simulation example was established for the reliability test system of generation and transmission IEEE RTS–96. The problem was solved by the improved generalized Benders decomposition method. Then, the sensitivity analysis method was used to compare and analyze the optimization results. The analysis results showed that the branch power flow overstepping could effectively eliminated whenN–1 fault occurred. The security of the transmission network underN–1 state could be ensured. Compared with the method without consideringN–1 security constraints, although slightly lower in economy, the maximum capacity of online units and load rate balance safety indicators are significantly improved, which accordingly improves the security of transmission network after energy storage integration. The proposed method can be used to guide energy storage planning with higher security requirements, and is worth to apply in engineering projects.关键词：energy storage optimization;chance constraints;unit commitment;N–1 security constraints;Benders decomposition
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发布时间：2024-01-05 - 摘要：Hydraulic drilling rigs play an important role in modern tunneling construction. Existing hydraulic drilling rigs need to control 6 hydraulic cylinders and 2 hydraulic motors separately when searching for holes. The electro-hydraulic proportional valve controls the position control system of the hydraulic cylinder. Taking the position control of the arm cylinder by the electro-hydraulic proportional valve as an example, the other joint control systems can be deduced by analogy. The position control system of the hydraulic cylinder controlled by the electro-hydraulic proportional valve is actually a system that corrects the displacement of the hydraulic cylinder in real time during the drilling operation. This system can control the deviation between the desired displacement and the actual displacement of the hydraulic cylinder, which requires adding a controller to the control section. The structure of the fuzzy control system was designed, and the method and process of Fuzzy PID parameter tuning were discussed. Then the fuzzy controller of the electro-hydraulic proportional valve control hydraulic cylinder was designed and simulated by MATLAB’s Fuzzy toolbox and SIMULINK module. The simulation results showed that in this valve-controlled hydraulic cylinder control system, the Fuzzy PID controller has strong anti-interference ability, fast response and stable performance.关键词：hydraulic drilling jumbo;electro-hydraulic proportional valve;controller;Fuzzy PID
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发布时间：2024-01-05 - 摘要：Dynamic transmission error is an important indicator of the quality of harmonic gear transmission. It can also provide a basis for further improving the design and processing of harmonic reducer. Therefore, the research on transmission error has important theoretical significance and engineering value. In order to verify the factors affecting the accuracy of harmonic gear transmission, the motion accuracy of the harmonic gear transmission was analyzed and studied through experimental methods. Starting from the error source of harmonic gear transmission, the cause of the error was analyzed firstly, then the transmission error curve of the reducer under different loads and speeds was tested. The measured data was interpolated and filtered to eliminate the " noise spike” and then discrete. The Fourier transform and the Hilbert transform was used to deal with the error signal. Comparing with the performance in the time-frequency domain, the effects of speed and load on the transmission error of the harmonic reducer were studied. The variation of transmission error and frequency component of transmission error with speed and load was analyzed. The experimental results of the Japanese SHF–25/120–2UH reducer showed that the transmission accuracy of the harmonic reducer under rated load is better than that of the no-load or light load. The transmission error curve of the harmonic reducer changes with the change of the load, but due to the coupling effect of different error components, the total transmission error does not change significantly. At the same time, the transmission error is almost the same at different speeds.The main errors of the dynamic transmission error of the harmonic drive are the double frequency, the multiple meshing accumulative errors of the 1/3 frequency, and the accumulative errors generated by the rotation of the circular spline. The cumulative error of 1//3 frequency make the biggest influence to the transmission error.关键词：harmonic reducer;gear;transmission error;transmission accuracy;spectrum analysis
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发布时间：2024-01-05 - 摘要：In order to explore the change rule of piston thermal state, a turbocharged intercooled diesel engine was treated as the research object. The temperature at designated point at the top surface of piston was measured by thin film thermocouple temperature measurement method and lead transmission system under transient operating process and the temperature values at different locations of the piston top surface at the calibrated power operating point and the maximum torque operating point are obtained by calculating the test data. The research results show that the temperature field of the piston changes dramatically during transient condition of the engine. The temperature of each measuring point at the top surface of piston rises sharply during the early stage of the cold start and rapid acceleration situations. The piston temperature variation is the largest up to 180 ℃ during the cold start process, and then its up to 140 ℃ during the rapid acceleration process. At the early stage of the rapid deceleration, the temperature of each measuring point of the piston rises rapidly, reaches the maximum at about 20 s. The maximum temperature of the four measuring points is 346,341,314,343 ℃ respectively, and then slowly decreases to a stable value. At the rated power point, the maximum stable temperature of the top surface of the piston is 331 ℃, and the temperature difference of the top surface is 31 ℃. At the maximum torque operating point, the maximum stable temperature of the piston top is 336 ℃, and the temperature difference of the top surface is 29 ℃.关键词：diesel engine;piston;thermal state;transient condition;transient temperature field
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发布时间：2024-01-05 - 摘要：Centrifugal compressors will be reverse during shutdown due to failure in actual application, so the dry gas seal applied in compressors should possess some ability to the reverse rotation. The double-row spiral groove dry gas seal was taken as an example and the CO2 gas was used as the sealing medium. The opening force, leakage rate, gas film stiffness and ratio of opening force to leakage rate etc were calculated at the rotation of forward, stop and reverse. The speed of reverse rotation at which the gas film stiffness equals to zero is an important indicator to show the anti-reversal capability of dry gas seal. The results showed that the opening force and leakage rate of CO2 real gas are greater than those of ideal gas, but the ratio of opening force to leakage rate less than those of ideal gas. When the dry gas seal performance of double-spiral groove lubricated by CO2 gas is analyzed, it is necessary to consider the real gas effects of CO2 gas. Double-spiral groove dry gas seals have some reverse rotation capability and the seals will normally operate when the reversal speed is less than that of the gas film zero stiffness. The gas film zero stiffness rotational speed reaches a maximum of 2 524 r/min as to the calculated example.关键词：dry gas seal;spiral groove;real gas effect;reverse rotation capability;analytical method
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发布时间：2024-01-05 - 摘要：Maximum output displacement and resolution are two contradictory performance indexes of micro positioning system. Usually, the two important indexes cannot be satisfied simultaneously by flexibility-targeting structure optimization method. A final optimal model was established considering both output displacement and resolution. And the corresponding solution was established for the special model with two non-linear contradictory objectives. Firstly, the parameters with a greater effect on the whole performance of the system were found out and the optimization variables were obtained. Constrained condition was built up according to the design requirements and relationship among these variables. Secondly, by the usage of these optimization variables, two expressions for the maximum output displacement and the resolution were built up and defined as objective function and constrained function respectively. At last, a synthetic algorithm was adopted to solve this kind of optimization model by integrating three methods, that’s the branch and bound method, interior point method and exterior point method. The optimization model was obtained by interior point method. The synthetic algorithm took any one of the possible solutions of this optimization model as the starting point. The branch and bound method were applied to narrow searching scope. Then the final optimized solution could be obtained based on the solution of exterior point method. The method was applied to a micro-griper system. Results showed that the constrained effect on the maximum output displacement was different when the resolution requirement changed within different scopes. During the process of parameter optimization for the micro-griper system, the global optimization was realized by taking into account of two contradictory objectives.关键词：resolution;maximum output displacement;micro-gripper system;parameter optimization;optimization algorithm
- 2045
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- 1149
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发布时间：2024-01-05 -
Preparation and Characterization of Hydrophobic Tubular Ceramic Membrane for Membrane Distillation AI导读
摘要：An experimental study was conducted on the problem of low salt rejection of tubular hydrophobic ceramic membranes for membrane distillation. First, the both ends of a ceramic membrane support were uniformly coated with mixture of self-made oxide AB and deionized water in the given ratio and sintered at a high temperature, and the ends were vitrified and sealed in order to solve the problem of the short circuit flow from the end face. Then, at room temperature, hydrophobic modification of the tubular support was carried out by using the isopropanol solution of 1H,1H,2H,2H–perfluorodecyltriethyloxysilane (C16H19F17O3Si, FAS) with the solution volume of 50 mL and a concentration of 0.01 mol/L to prepare a hydrophobic FAS–ZrO2–Al2O3 composite membrane. By increasing the number of grafting modification times (3 days per time), the hydrophobic properties of the membrane tubes were investigated by using the pure water penetrating pressure of the hydrophobic tubular ceramic membrane as the index. And the modified membrane tubes were used to carry out AGMD experiments. The analysis of SEM, IR and water contact angle test were used to observe and determine the hydrophobic nature of the inner surface of the tubular membranes. The results showed that under the conditions of NaCl thermal solution temperature of 75 ℃, bulk flow rate of 25 L/h, concentration of 2%, cooling water temperature of 15 ℃ and flow rate of 50 L/h, the best comprehensive performance was 3# membrane tube whose membrane distillation flux reached 4.29 kg/(m2·h) and rejection rate was 99.83%. The two hydrophobic groups CxF2x+1 and Si—CH2CH2·CxF2x+1 in the fluorosilane were successfully grafted on the inner surface of the tubular ZrO2–Al2O3 ceramic membrane by using 1H,1H,2H,2H–perfluorodecyltriethoxysilane to modify the ceramic membrane tube. The inner surface of the tube formed a very good hydrophobic layer and the water contact angle was of 142°. Therefore, the FAS-ZrO2–Al2O3 composite membrane met the requirements for membrane distillation, which makes it possible to desalinate high-salt brackish water by AGMD in order to obtain high-purity water.关键词：membrane distillation;tubular ceramic membrane;FAS;hydrophobic modification;desalination- 2119
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发布时间：2024-01-05 - 摘要：The scandium-contained red mud ore in Yunnan contains TFe of 25.68 %, Sc2O3 of 70.66 g/t, scandium is dispersed mainly in rutile, pyroxene, feldspar, Muscovite, minerals such as calcite. In order to solve the problem of the separation of iron and scandium, the sodium chloride roasting–low intensity magnetic separation–hydrochloric acid leaching of segregation joint mineral smelting and processing was put forward to processing the scandium-contained red mud. Making the iron from hematite to metallic iron and magnetite in the new phase, scandium mineral crystal structure was destructed and conditions were favorable created for the separation of iron and scandium. Test results showed that iron concentrate of iron grade of 73.99%, scandium contained of 5.22 g/t, iron recovery of 88.99% and the scandium leaching rate of 96.78%, scandium contained of 6.37 g/t in the leaching residue could be obtained under the comprehensive conditions of segregation roasting temperature of 950 ℃, segregation roasting time of 60 min, sodium chloride dosage of 10%, the coke dosage of 15%, the coke size of –0.5～0.25 mm, low intensity magnetic separation, magnetic field intensity H = 0.12 T, low intensity magnetic grinding fineness of <0.045 mm occupying 95%, the hydrochloric acid dosage of 30%, leaching time of 120 min, leaching temperature of 55 ℃, leaching liquid-solid ratio of R=2∶3. The results of MLA, SEM and EPMA analysis showed that after scandium red mud was decomposed and roasting with sodium chloride, hematite (Fe2O3) was transformed into new ferrite phase dominated by metal iron (Fe) and magnetite (Fe3O4) and a small amount of ferric oxide (FeO) and ferrosilite(Fe2SiO4).The main compositions of leaching residue were SiO2, CaO and Al2O3. CaO and Al2O3 were significantly decreased compared with those before leaching, Leaching residue in no obvious Sc spectrum peak, which indicated that low intensity magnetic separation tailings after hydrochloric acid leaching, most scandium was dissolved into the leaching liquid, and the dissolution of scandium is relatively complete.It is reasonable to the separation of iron and scandium by sodium chloride segregation roasting-low intensity magnetic separation-hydrochloric acid leaching, and the separation of iron and scandium is obviously.关键词：scandium;scandium-contained red mud;segregation roasting;low intensity magnetic separation;leaching
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发布时间：2024-01-05 - 摘要：Process safety analysis is important and necessary in the chemical process industries. However, a lack of a systemic methodology for inherent safety studies in an unsteady state, which causes more hazards and accidents. In order to analyze the inherent safety of the F22 vaporization unsteady state process of the steam dilution pyrolysis, the lumped parameter mathematic model for the F22 vaporization was established by using the thermal equilibrium equation. The model was numerically calculated to obtain the unsteady state time course profiles of operating temperature, pressure and F22 gas outlet mass flow rate, which were consistent with the field data. Then, the factors influencing the inherent safety of the TFE production process were systematically analyzed. The inherent safety index system of the TFE production process was established from three aspects of chemical, process, and equipment. The indices were graded according to relevant standards,and literature and membership functions were established. Index values and calculated data were input into the MATLAB Fuzzy logic toolbox. The IF-THEN rules were used to establish the Fuzzy inference rules, and the inherent safety degree of each index was defuzzified by the method of center of area (COA). The initial weight and variable weight of each index were calculated using the combination of analytic hierarchy process and variable weight method. Finally, the inherent safety degree of the F22 vaporization node was calculated. The results showed that the steady state time is nearly 1 000 s. The temperature, pressure, and outlet gas volume in the first 500 s increase rapidly. The steady state values are 268.55 K、432.405 kPa and 1.085 kg/s respectively. The inherent safety degree decreases with time. The initially inherent safety 0.576 4 dropped to 0.574 2 at steady state. The results showed that the unsteady state (a start-up process) appears a higher risk. The method and results provide a theoretical basis for the safe design, monitoring, and management of the F22 vaporization node in the process.关键词：TFE pyrolysis process;F22 vaporization;inherent safety;unsteady state;Fuzzy logic
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发布时间：2024-01-05 - 摘要：It is one of the research focuses to study the aging performance degradation modeling and life prediction methods in the field of corrosion and protection for rubber and other polymer materials. Theoretical basis and reference would be provided for performance monitoring, maintenance and replacement of rubber parts through exploring the application of newly developed reliability theory, such as accelerated aging method. The traditional aging modeling method of polymer materials contains the disadvantages of strong model dependence, high difficulty in parameter identification and insufficient precision. In order to accurately predict and evaluate the aging degradation law of rubber at room temperature, the interpolation method was used to calculate the pseudo-failure life at different acceleration temperatures through analyzing indoor high temperature accelerated aging data. The performance degradation shift factors of each acceleration temperature relative to the minimum acceleration temperature were calculated according to the data set. It was found in further research that the shift factors satisfies the Arrhenius equation, and the data of accelerated aging at each high temperature could be converted to the reference temperature according to the shift factors. The principle of temperature superposition was applied by the established acceleration model, and the shift factor at room temperature was obtained by the linear extrapolation of the high temperature shift factors, thus the prediction equation for the aging performance degradation of rubber at normal temperature was developed, with which the accuracy was verified through the comparison with measured data. The results showed that the rubber accelerated aging data would be quickly processed by the proposed integrated method, and the normal temperature performance degradation result obtained by the proposed method is distributed in the two times dispersion line compared to measurement data, which meet the engineering requirements. This paper can provide reference for accelerated aging data processing and life prediction of related polymer materials.关键词：rubber;performance degradation;accelerated aging;time-temperature superposition;life prediction
- 1982
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发布时间：2024-01-05
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Slope Stability Analyses of Outang Landslide Based on the Peak and Residual Shear Strength Behavior AI导读
摘要：Most of the natural and compacted fine-grained soil slopes that are in saturated or unsaturated condition undergo a large deformation prior to reaching failure conditions. Such slopes should be designed taking account of their strain-softening behavior using the residual shear strength (RSS) parameters. In this paper, the slope stability of a recently reactivated Outang landslide near the Three Gorges Dam in China is analyzed based on the RSS parameters of unsaturated soils. In addition, comparisons are provided in the FOS values of slope using both the peak shear strength (PSS) and RSS parameters. Firstly, a series of site investigations of the hydrologic and geologic conditions, ground surface displacements and cracks were described. The PSS and RSS behaviors of the sliding soils derived from a series of direct shear test results performed on saturated and unsaturated soil specimens are summarized. Secondly, a series of slope stability analysis were conducted considering the precipitation and Yangtze River water level variation within a representative period of 7 months, based on thePSS and the RSS properties. In this study, three different scenarios were considered, which include: i) considering only the precipitation with a constant water level; ii) considering only the decrease in water level without rainfall; iii) considering the combination of precipitation and decrease in water level. In each scenario, four steps were included to calculate the values of factor of safety (FOS) at different times. 1) A steady-state seepage analysis was conducted with a constant total head at 525 m on the left boundary and 175 m on the slope surface below the Yangtze River water level. The initial pore water pressures were simulated in the slope under no precipitation and variation of water level. 2) A specific boundary condition was applied on the slope surface to model the precipitation and Yangtze River water level variation. A transient seepage analysis was conducted to calculate pore water pressures at different times based on the initial pore water pressures. 3) The FOS values at different times were calculated by the Morgenstern-Price method taking account of the variation of pore water pressures at different times, using the peak shear strength (PSS) parameters. 4) The last step was repeated replacing PSS parameters with RSS parameters. The RSS parameters were lower than the peak values from laboratory’s direct shear test results for the soils in the sliding zones. The reduction in shear strength from peak to residual state under unsaturated soil condition was greater than that for a saturated soil. The FOS decreased almost linearly with time for the scenario in which only the influence of rainfall infiltration was considered. However, the total reduction in the FOS was relatively small. The FOS decreased rapidly at a linear rate with respect to time with a decrease in water level for the scenario in which Yangtze River water level decrease was considered. The FOS reached to a relatively constant value after Yangtze River water level reached the lowest value. The decrease in Yangtze River water level was the dominant factor that contributed to a reduction in the FOS. The FOS was strongly dependent on the development of the phreatic line after the Yangtze River water level reached the lowest value. The FOS calculated by RSS (i.e. FOSR) is less than unity; they were approximately 16% lower in comparison to that calculated by PSS (FOSP). If PSS parameters were used, the slope would still be stable even under the combined influence of precipitation and Yangtze River water level decrease. These results are inconsistent with the field observations. For this reason, the RSS parameters should be taken into account to evaluate reliably the slope stability of the Outang landslide.关键词：unsaturated soil;landslide reactivation;residual shear strength;slope stability analysis- 2602
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发布时间：2024-01-05
水动力型滑坡灾害机理与防控
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