最新刊期
卷 54 ， 期 3 ， 2022
- 摘要：There are abundant moraine soil sources distributed in the Qinghai–Tibet Plateau of China, with complex historical causes, changeable material structure, and large differences in mechanical properties. Moraine landslide often occurs under the action of rainfall and ice and snow melting. The debris of landslide enters the gully and mixes with water flow, which is very easy to produce the moraine landslide—debris flow—dammed lake disaster chain, which is the key and difficult point of disaster prevention and reduction in the plateau. In recent years, the Sichuan—Tibet railway project and major hydropower development in Tibet have faced a great threat from the moraine landslide—debris flow—dammed lake disaster chain. It is a major national demand to improve the capacity of disaster prevention, reduction and relief. Moraine landslide—debris flow—dammed lake—dam-breaking flood is a chain disaster process of cascade amplification, which involves complex dynamic evolution mechanisms such as landslide initiation, movement behavior transformation, erosion amplification along the process, multi-stage river blocking superposition, and dam break water–sediment coupling. Especially under complex meteorological conditions, there are some problems such as unclear mechanism, inaccurate model, and lack of simulation technology. It is urgent to carry out the research on the complex dynamic mechanism, control theoretical model, and whole process numerical simulation of moraine landslide—debris flow—dammed lake disaster chain process. Combined with the research status at home and abroad, five research contents are further proposed: 1) Evolution of mechanical properties of moraine soil under complex meteorological conditions. 2) Dynamic disaster process and migration model of moraine landslide—debris flow. 3) Formation mechanism and simulation of moraine landslide—debris flow—dammed lake. 4) Mechanism of erosion and outburst of moraine dam and the process of flow channel expansion. 5) Mechanism of water-sediment interaction in the downstream channel and the simulation of flood evolution. Many preliminary explorations and research work have been carried out to preliminarily reveal the migration of moraine landslide debris flow and multi-stage river blocking mechanism, a dam break evolution model that can consider water erosion and intermittent collapse of the broken slope has been built, and the simulation method of moraine landslide—debris flow—dammed lake disaster chain evolution process has been discussed. The results lay a foundation for further understanding of the complex dynamic mechanism of the moraine landslide—debris flow—dammed lake disaster chain process, constructing the control theoretical model and developing the whole process numerical simulation system. And the results are expected to provide a theoretical basis for the mechanism of moraine landslide—debris flow—dammed lake disaster chain and technical support for non-engineering risk reduction and emergency disposal decision-making.关键词：moraine soil;landslide—debris flow—dammed lake;disaster chain mechanism;landslide dam break evolution model;numerical simulation of disaster chain process
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发布时间：2024-01-10 - 摘要：Laboratory experiments are one of useful approaches for investigating landslide dam breaching. However, due to the small size of the dam and limited storage volume of the landslide lake, the dam breaching process in the existing experiments differ much from that of the natural landslide dam. A large-scale landslide dam breaching experiment system was built with the lake volume up to 380 m3. Series of large-scale tests were conducted to investigate influence of the downstream surface slope of the landslide dam comprising of non-cohesive wide-graded sand-gravel material. It was found that the breaching process of landslide dam can be divided into four stages: longitudinal erosion, back-ward erosion, rapid development and nearly stabilization stage. The erosion characteristics in different stages were quite different. During the breaching process, it is found that head-cut and the collapse of soil on both sides of the breach are the main mechanisms of the rapid breach development. The erosion characteristics are quite similar in the longitudinal erosion stage for cases with different downstream surface slope, while it differs much at both the back-ward erosion and rapid development stages. Larger downstream surface slope means easier for forming water fall at the breach, which further leads rapid vertical and lateral development. This is the reason for the formation of bed-fall of the breach. The breaching duration varies greatly under different downstream surface slope conditions: With a higher downstream surface slope of the landslide dam, the breach duration was shorter, head-cut erosion formed easier, the breach developed faster and the peak of outburst flood appeared earlier and with a larger value. Moreover, the post-flood bed morphology at the downstream channel and formation mechanism of the deposition area on both sides of the downstream channel were primarily analyzed.关键词：landslide dam;large-scale laboratory experiment;erosion process;downstream slope;deposition mechanism
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发布时间：2024-01-10 - 摘要：For the landslide susceptibility prediction (LSP) based on machine learning (ML) models, the reasonable selection of negative samples has an important influence on the LSP performance. Generally, the main selection methods include randomly selecting from the whole study area or from the specific attribute areas such as low slopes. The negative samples selected by the above methods are often inaccurate or biased, resulting in low accuracy and low reliability of LSP. To solve this problem, the coupling model of ML and information value (IV) method was proposed for LSP. Taking Ruijin City as the study area, the attribute values of the environmental factors were transformed into the IV values of the contribution to the landslide to obtain the very low and low susceptibility areas. The negative samples were randomly selected in the above areas for the training and validation of machine learning models. The new coupling models of IV–SVM and IV–RF were constructed for the LSP of Ruijin. Further, IV–SVM and IV–RF models were compared with the single SVM and RF model with negative samples randomly selected from the whole study area, as well as the low-slope SVM and RF model with negative samples randomly selected from specific attribute areas with a slope less than 2°. Finally, Kappa coefficient (KC) and receiver operating characteristic (ROC) curve were used to verify and compare the modeling results. The AUC values of the ROC curve and KC of IV–SVM and IV–RF models were 0.828, 0.920 and 0.876, 0.988, which were higher than those of single SVM, RF model and low-slope SVM, RF model, respectively. Meanwhile, IV–SVM and IV–RF models have a smaller mean value and larger standard deviation of a susceptibility probability distribution. Results showed that: 1) IV–SVM and IV–RF models had the higher LSP accuracies than those of the single SVM, RF model and low-slope SVM, RF model, respectively; 2) RF model had higher LSP accuracy compared to the SVM model; 3) The coupling model such as IV–RF could address the inaccuracy of negative sample sampling existing in the single model and the shortcomings of the low slope model in the selection of slope interval, thus improving the LSP accuracy. In conclusion, this study provided a new idea for the negative sample sampling method for LSP using ML models.关键词：landslide susceptibility prediction;negative samples selection;information value;random forest;support vector machine
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发布时间：2024-01-10 - 摘要：The landslide—blocking river—dammed lake disaster chain is a typical disaster in mountain and gorge areas. The interaction between landslides and rivers, as the linking process in this disaster chain, often determines the scale of continuation of subsequent disasters in time and space. It is critical to reproduce the complex fluid-solid coupling process in the assessment of the landslide-blocking river disasters. By using the Drucker–Prager model to simulate the sliding of the landslide body, along with an artificial equation of state to model the flow of water, the two-phase double-point material point method (TPDP–MPM) program was developed. The simulation of the landslide-water body interaction process on an experimental scale was conducted and verified the reliability of TPDP–MPM in multiphase coupling problems. On this basis, a landslide—dammed lake disaster chain, namely the Pingdu River being blocked by the Erhuang Village landslide, Shiyan City, Hubei in 2011, was reproduced by the TPDP–MPM program. According to the TPDP–MPM simulation results, this disaster could be divided into four stages: unstable initiation, high-speed sliding, river braking, and accumulation. Based on the velocity field of the landslide mass and the evolution of the kinetic energy, the sliding pattern of the Erhuang Village landslide and the mechanism of river braking were revealed. The research results provided a theory and method for the whole process analysis and risk assessment of the landslide—dammed lake disaster chain.关键词：disaster chain;dammed lake;material point method;fluid–soil coupling;kinematic analysis
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发布时间：2024-01-10 - 摘要：The reliability of three-dimensional discrete element numerical simulation of granular materials depends on the reasonable calibration of mesoscopic parameters. At present, systematic research on the calibration method of mesoscopic parameters is lacking. Based on the comparative analysis of indoor direct shear test and numerical simulation, the correlation between the macroscopic mechanical parameters of granular materials and the mesoscopic parameters of particles was revealed. Besides, the calibration method of the meso parameters of the numerical simulation of granular materials was proposed, and the rationality of the calibration method was verified. The research result showed that: in the linear model, the macro elastic constant of the sample was positively correlated with the normal contact stiffness of the particles, but not sensitive to the change of the tangential contact stiffness. Based on this, the calibration method of contact stiffness (normal and tangential) of particles was proposed. The shear stress-shear displacement curve of the numerical direct shear test was well agreed with the experimental value, so the reliability and rationality of the calibration method were verified; Through the numerical test of the direct shear of gravel, it was found that the internal force chain network of the particles deflected from the vertical direction to the diagonal direction of the shear box with the increase of shear displacement, and the shear shrinkage and expansion occurred with the change of the overall velocity field of the particles during the shear process. The meso parameter calibration method proposed was used to conduct a numerical simulation of an indoor landslide motion test. The morphology of landslide gravel accumulation in the numerical simulation was consistent with the indoor test result, which verified the applicability of the calibration method in the simulation analysis of accumulated gravel landslide.关键词：accumulated debris;particle discrete element;direct shear test;mesoscopic parameter calibration;landslide simulation
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发布时间：2024-01-10
MECHANISM OF LANDSLIDE–DAMMED LAKE AND ITS CONTROL
- 摘要：The hybrid fuzzing technique leverages the symbolic execution techniques and the fuzz testing techniques to achieve complementary goals. The synchronization of testcase is the key to collaborate between modules. However, the testcase synchronization was implemented with an exchange and integration approach in existing hybrid fuzzing techniques, which ignores runtime information when the symbolic execution module was exploring the program state. To solve the above problem, a testcase synchronization method for hybrid fuzzing based on keypoints, namely Sol-QSYM, was proposed. Sol-QSYM aims to analyze the execution process of symbolic execution, locate and identify the code coverage oriented program keypoints, and then guide the testcase scheduling and mutation process of fuzz testing to achieve a finer-grained testcase synchronization. First, a set of variables corresponding to the hard-to-reach branches of the fuzz testing module was identified in the symbolic execution and extracted as the keypoints of the program. Secondly, to fully utilize the results of the symbolic solution, the keypoints of the single solution were further combined to help the symbolic execution module to additionally generate more testcases that can be imported by the fuzz testing module. Finally, in the fuzz testing module, the testcases containing keypoints in the seed selection step were preferentially selected to guide the testing process in exploring specific areas of the program, and the keypoint locations were highlighted in the mutation step to guide the generation of testcases that would cover new branches of code. A prototype system was implemented based on the hybrid vulnerability mining tool QSYM, and 12 real programs were selected for experimental evaluation. The results of experiments showed that compared to QSYM, Sol-QSYM improved the import rate of test cases by 12.73%, code coverage rate by 9.07%. Meanwhile, it found more program crashes. All these results indicated that the enhanced test case synchronization method can improve the utilization of program state exploration results in symbolic execution by hybrid vulnerability mining.关键词：fuzz testing;symbolic execution;testcase synchronization;hybrid fuzzing
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发布时间：2024-01-10 - 摘要：In the real world, many problems have the need to conduct relevant operations at a specific time. Timed-release encryption (TRE) is a cryptographic primitive in which the sender specifies the decryption time of the receiver, which can meet the above requirement. To address the problem that the current TRE schemes based on the periodic broadcast time trapdoor of the non-interactive time server cannot meet the user’s arbitrary specified decryption time, and the interactive time server mode meets the arbitrary decryption time but cannot guarantee the user’s identity privacy, a TRE scheme using onion routing network was proposed. In the scheme, when the decryption time approaches, the time trapdoor request was taken as the innermost onion, and the layer by layer encrypted onion was constructed and transmitted to the time server. The time server generates the corresponding time trapdoor and returns it to the receiver according to the original route, so that the user can hide the identity information when making a trapdoor query at any time. Meanwhile, for the node failure problem in the process of onion routing delivery, a method for constructing each layer of onion based on broadcast encryption was proposed, so that each layer of onion node can decrypt that layer of onion. The scheme achieves the trapdoor of successfully querying arbitrary time to the time server while ensuring the anonymity of user’s identity. Security analysis showed that the scheme is secure and robust against possible single-point speculation, monitoring attacks, replay attacks, and collusion attacks. Efficiency analysis showed that compared with the pairing-based onion routing scheme, the proposed scheme reduces the time consumption of solving the node failure problem by about 59%, thus realizing efficient anonymous query.关键词：timed-release encryption;anonymous query;time trapdoor;onion routing;broadcast encryption
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发布时间：2024-01-10 - 摘要：In order to solve the problem of low audit efficiency due to the use of power exponent, bilinear mapping, point hash mapping and other expensive operations in the existing certificateless cloud auditing scheme, an efficient certificateless cloud auditing scheme was designed in this paper. In the key generation stage, combined with the certificateless signature technology, the user’s public and private keys were generated by the key generating center (KGC) in cooperation with the user, so that the strong dependence of auditing system security on KGC security was avoided. Consequently, the shortcomings of complex public key certificate management under the public key infrastructure (PKI) system and the inherent key escrow issues under the identity-based cloud audit scheme were solved. In the data preprocessing stage, the data was encrypted and divided into blocks. Therefore, the data content privacy was protected and the calculation and communication overhead of the scheme was reduced. In the data dynamic update stage, the virtual index data structure was used to realize the insertion, deletion and modification of data blocks. As a result, the extra computational overhead caused by label recalculation was avoided. In the data auditing stage, the task of users to verify the integrity evidence was replaced by a third party auditor (TPA), which reduces the user’s computational burden. In the section of security analysis, it was proved that the substitution attack from the cloud was resisted, the privacy protection was achieved, and the forgery attacks by two types of adversaries were resisted. In the performance analysis part, numerical analysis and comparison of the proposed scheme with the existing schemes were carried out on the JPBC library. The experiments show that the proposed scheme significantly reduces the computational cost.关键词：cloud storage;data integrity;data possession proof;no bilinear pair;certificateless signature
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发布时间：2024-01-10 - 摘要：Recommender systems can effectively alleviate the problem of information overload caused by the rapid development of the Internet. However, the occurrence of shilling attacks restricts the healthy development of recommender systems. Therefore, how to detect shilling attacks accurately and efficiently is an important problem in the field of recommender systems security. The existing detection methods usually design hand-crafted detection features based on expert knowledge or automatically learn features from a single perspective using deep learning, then the attack users are identified according to the extracted features by hard classification, resulting in the poor detection performance. By automatically learning features from multiple perspectives and introducing a hesitant fuzzy decision, a novel detection method based on CNN and hesitant fuzzy set was proposed and named CNN-HFS. Firstly, for each user, three behavior matrices were extracted from the perspectives of rating, preference and rating time, respectively. To reduce the influence of data sparse, these matrices were scaled by bicubic interpolation to correspondingly obtain a dense rating matrix, a dense preference matrix and a dense time matrix. Next, each scaling matrix of users was regarded as an image, and three different CNN classifiers were trained based on these scaling matrices in three different views respectively. For each user, three membership degrees to the classifier of attack users were calculated. Finally, a fuzzy hesitant set was introduced to make a comprehensive decision, and the attack users were identified according to the decision results. To validate the effectiveness of the proposed CNN-HFS, the extensive experiments were conducted on the MovieLens 1M and Amazon datasets. The evaluation metrics of precision, recall and F1-measure were used to compare the proposed method with SVM-TIA, CoDetector, CNN-SAD, SDAEs-PCA, CNN-R, CNN-P and CNN-T. The experimental results showed that the proposed method is superior to seven baseline methods in terms of three detection metrics and achieves an excellent detection performance under various attacks.关键词：recommender system;attack detection;convolution neural network;hesitant fuzzy sets
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发布时间：2024-01-10 - 摘要：In order to relieve the alarm fatigue of security analysts and improve the security operation efficiency, an attacker IP analysis system based on the Ensemble-based Local Outlier Factor algorithm (EBLOF) was proposed in this paper. Firstly, normalized network security alarm logs were extracted and merged, and then the feature engineering was constructed from the attribute dimension and attack behavior dimension of attacker IP. Secondly, inspired by the idea of ensemble learning and traditional LOF anomaly detection algorithm, a robust EBLOF algorithm of finding high-threat attacker IP was constructed in the system. Thirdly, a set of online learning architecture was built by the system, aiming to solve the problem that the machine learning model was difficultly updated online. Through the batch real-time learning technology, the learning architectures ensure that the learning model can be updated online from the system architecture level rather than the algorithm level. Finally, the EBLOF algorithm of this paper was trained on the public anomaly detection data set ODD. The experimental results showed a fact that the algorithm has better robustness than the naive LOF algorithm under different data distributions. The system proposed in the paper was applied in real attack and defense scenarios. Its effectiveness and feasibility were verified by comparing with security operation analysts.关键词：cyber space situation awareness;attacker analysis;local abnormal factors;ensemble learning
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发布时间：2024-01-10
CYBERSPACE SECURITY
- 摘要：The bolted prefabricated concrete wall is widely used in construction due to its simple connection and rapid construction. The quasi-static tests of seven full-scale dry-type bolted prefabricated concrete walls (including four steel-plate-type bolted walls and three through-connection-type bolted walls) were conducted. The test results indicated that the bolted prefabricated wall would spread out at horizontal connection firstly and then the wall had rigid rotation, resulting in a lower lateral stiffness than the cast-in-place wall panel. Based on the elastic theoretical researches and finite numerical analyse, the horizontal deformation feature of the bolted prefabricated concrete wall was revealed, and the effect factors of lateral stiffness were analyzed. Moreover, the calculation formula of initial lateral stiffness of bolted prefabricated concrete wall was derived and its reliability was verified by numerical analyse and test results. In addition, through parameter analyse, a simplified calculation formula for initial lateral stiffness reducing the coefficient of bolted prefabricated concrete wall considering four effect factors (steel ratio of connection, height-width ratio of wall, axial compression ratio, and relative position of connection) was proposed. The error between the results by simplified formula and numerical analysis results is within 20%, indicating that the predicated results by the proposed simplified formula have high precision.关键词：prefabricated concrete wall panel;bolted connection;lateral stiffness;numerical analysis
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发布时间：2024-01-10 - 摘要：It is of great significance to explore the evolution law of shrinkage cracks in soil sample structure for the rational protection of earthen ruins. In order to study the dry shrinkage deformation characteristics of Zhouqiao earthen soil, an indoor dry shrinkage test was carried out. In order to further reveal the internal mechanism of soil shrinkage cracking and surface tension change, the surface tension gradient parameter is introduced. Based on SEM images, the microscopic model of Zhouqiao earthen soil was established in ABAQUS software, and the fracture evolution was simulated. The results show that the fracture evolution process of soil sample can be summarized as: tensile stress field, single main fracture, secondary horizontal and tertiary deep fractures, and the formation of fracture network. The duration of tensile stress field and single main fracture is long, while the duration of secondary horizontal and tertiary deep fractures is short. The mechanism of crack types can be summarized as follows: local shear, local tension and local mixed tension shear. With the development of crack, it gradually develops from tensile force to mixed tensile shear force, and the main crack extends outward perpendicular to the stress surface. Due to different length of water molecule migration path, the upper soil sample is more likely to produce large shrinkage deformation than the deeper soil sample, and causes the development of deep cracks. With the stability of water migration path, horizontal cracks become the main factor for the development of soil cracks. By analyzing the rose chart of fracture rate, it is found that the fracture rate of the soil sample in the upper part is generally lower than that in the lower part, and the fractures are mostly concentrated in the direction of 90° and 270°, indicating that the micro capillary pores and excessive internal shrinkage of the soil sample are the reasons for the cracks. The normalization results show that the model can better reflect the generation, evolution and development of soil micro damage in Zhouqiao site. The research results have reference value for the repair and protection of soil fissures in Zhouqiao site.关键词：earthen ruins;micromodel;shrinkage deterioration;rose chart
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发布时间：2024-01-10 - 摘要：In order to improve the quality of the porous asphalt pavement in seasonal freezing areas and reduce the freeze-thaw damage of the pavement, the modified porous asphalt mixture with glass fiber, diatomite and old asphalt pavement materials are employed to improve the performance. The changes in compressive strength, porosity, and strain of porous asphalt mixtures with different material contents after freeze-thaw cycles are analyzed by considering the influence of different materials and different material contents on the water stability of porous asphalt mixtures. Based on the theory of damage mechanics, the compressive strength is used as an index to represent damage variables, and the evolution of freeze-thaw damage of modified porous asphalt mixtures is also studied. Based on the CT non-destructive testing and digital image processing technology, the changes in the number of air voids and air void area of the glass fiber porous asphalt mixture before and after freezing-thawing are analyzed. The test results show that the compressive strength of the mixture decreases with the increase of the number of freeze-thaw cycles, and the void ratio and strain show an increasing trend. Four porous asphalt mixtures with 0.7% glass fiber content, 15% old asphalt pavement material content, 25% diatomite content and 15% old asphalt pavement material and 20% diatomite content present the best water stability. The modification effect of glass fiber is the best. Mixing glass fiber, 15% diatomite and 15% old asphalt pavement material may reduce the freeze-thaw damage of porous asphalt mixtures. However the recycled porous asphalt mixtures containing diatomite have more serious damage and have higher strength in the early stage of damage, which are more suitable for short-term frozen soil areas. Compared with recycled porous asphalt mixtures containing diatomite, the porous asphalt mixture containing glass fiber, recycled porous asphalt mixture and porous asphalt mixture containing diatomite have a longer rapid damage period, a shorter damage stability period and a shorter damage evolving period. The number of air voids in the sample increases and the average single air void area decreases with a lower glass fiber content, while the sample with a higher glass fiber content has the opposite effect.关键词：road engineering;porous asphalt mixture;modification;moisture stability;freeze-thaw damage;mesoscopic characteristics
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发布时间：2024-01-10 - 摘要：To scientifically and reasonably analyze the bending vibration frequency of the new type composite box girder bridge with corrugated steel webs, taking into account the shear deformation effect of corrugated steel webs and the shear lag effect of box girder, the Galerkin method and the Hamilton principle were used to deduce the free vibration control differential equation and natural boundary conditions of the bridge type. According to the natural boundary conditions, the calculation formula of the bending vibration frequency of the new type composite box girder bridge with corrugated steel webs under the influence of shear deformation effect and shear lag effect was solved. The results were compared with the measured results and ANSYS finite element results, and the influencing factors of the bending vibration frequency were analyzed. The results showed that the calculation results of the bending vibration frequency were in good agreement with the measured results and the ANSYS finite element results, which verified the correctness of the derived frequency calculation formula. The bending vibration frequency increased with the increase of the high-span ratio. When it was less than 0.05, the increase of the bending vibration frequency was relatively gentle. When the height-span ratio was greater than 0.05, the increase of the bending vibration frequency was more significant. The bending vibration frequency increased with the increase of the width-span ratio, but the overall increase was not obvious. The frequency increased with the increase of the thickness of the corrugated steel web, and the higher the order, the more significant the increase. The shear lag effect of the box girder had little effect on the bending vibration frequency, and the maximum error of the first 5 orders was only 6.73%. The shear deformation of the corrugated steel webs had a great influence on the bending vibration frequency, and the maximum error of the first five orders was as high as 51.18%.关键词：composite box girder;corrugated steel webs;bending vibration frequency;shear deformation;shear lag;Galerkin method
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发布时间：2024-01-10 - 摘要：To evaluate the reinforcement effect of steel-UHPC (Ultra-High Performance Concrete) composite deck for a long-span steel box girder cable-stayed bridge, an in-situ test was carried out under random traffic flow. The fatigue performance of orthotropic steel decks with steel–UHPC composite deck and ERE (epoxy bond chips layer, resin asphalt, epoxy bond chips layer) deck were evaluated by Specifications for Design of Highway Steel Bridge (JTG D64—2015), based on the in-situ strain monitoring data. The residual fatigue life of fatigue-prone details was calculated by Miner’s linear cumulative damage rule. To check the crack resistance of the UHPC layer of the steel–UHPC composite deck and calculate the steel deck maximum deflection and the asphalt pavement maximum tensile stress, a finite element model was established. The results showed that there were large stresses in the rib side of the rib-to-deck welded joint, the floor beam cutout, and the rib splice welded joint. These areas’ residual fatigue life is 214, 186, and 61 years, respectively. The rib splice welded joint had the risk of fatigue failure in the design reference period. The maximum stresses amplitude of each fatigue-prone detail decreased below the constant amplitude fatigue limit, and the residual fatigue life increased to infinity after the orthotropic steel deck was strengthened with a steel–UHPC composite deck. The maximum tensile stress of the UHPC layer of the steel–UHPC composite deck was 4.68 MPa, and the crack resistance met the design requirements. After the orthotropic steel deck was strengthened with a steel–UHPC composite deck, the stiffness of the orthotropic steel deck was improved obviously, the steel deck’s maximum deflection was 0.69 mm with a reduction of 34%. The maximum tensile stress of asphalt pavement was 0.42 MPa with the reduction of 59%. The fatigue performance of each fatigue-prone detail met the design requirement after the orthotropic steel deck was strengthened with a steel–UHPC composite deck, and the crack resistance of the deck pavement was improved.关键词：steel bridges;ultra-high performance concrete;reinforcement;fatigue;pavements
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发布时间：2024-01-10 - 摘要：The stability of coastal soft soil stratum is dramatically affected by external construction. To clarify the disturbance mechanism of the shallow shield tunnel engineering to the stratum, a refined numerical model for simulation of shield dynamic excavation was established based on the finite difference scheme, and the disturbance effect of every construction factor on the stratum was studied according to the modeling results. In the model, the combined effects of four factors on surrounding soil, including cutter head friction, excavation supporting force, grouting pressure, and shield friction, were considered. Referring to the behavior change of the grouting layer in the practical project, the relationship between pressure dissipation and slurry solidification during the shield tail grouting was divided into three stages to simulate the flowing state, the initial setting state and the final setting state of the slurry, respectively, and the corresponding parameters were sectionally assigned to the grouting layer of the newly-built tunnel and adjusted in real-time along with the excavation process. This model can realistically reflect the whole process of shield tunneling and realize the refined simulation of the construction. The numerical model was verified by comparison with the results from the field monitoring of the shield tunnel project with 1.0D (D is the outer diameter of the tunnel) burial depth in Xiamen Metro, and the influence of the above four construction factors on the soft soil stratum disturbance during the shallow excavation process was calculated and compared, and the effect of the factors on the disturbance deformation was summarized. The results show that the cutter head pushing causes the radial expansion of the forward soil. In the grouting process, a settlement groove is formed within 1.0D on both sides of the excavation space, and the near-field rebound and far-field expansion occur to the soil lateral displacements on two sides of the tunnel during the solidification of the grouting layer. The increase of the cutter head friction and shield friction will further aggravate the stratum disturbance deformation, and with the increase of the excavation supporting force and grouting pressure, the surface settlement slightly slows down and the stratum lateral displacement significantly increases. The results are of guiding significance for disturbance prediction and parameter selection in shallow shield excavation.关键词：shield tunnel;shallow buried;soft soil stratum;refined simulation;field monitoring
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发布时间：2024-01-10 - 摘要：When a water-rich karst cavity exists in front of the tunnel face, the thickness of the anti-inrushing rock mass between the tunnel face and the water-rich karst cavity will gradually decrease as the excavation of the tunnel progresses. Once the thickness of the anti-inrushing rock mass reaches the limit, the water inrush disaster will occur. An accurate prediction of the minimum safe thickness of the anti-inrushing structure can effectively avoid the occurrence of water inrush disaster in karst area. For the shear failure and bending failure modes of the anti-inrushing structure caused by water pressure, the corresponding mechanical models of anti-inrushing structure are established. The minimum safe thicknesses of anti-inrushing structure for the two models are calculated by using the shear strength criteria, the bending strength criteria, and the elastic thin-plate theory. The results calculated by present models are in good agreement with those calculated on the basis of the bending theory of fixed beam, the shear theory of rock column, and catastrophe theory. The results of parameter sensitivity analysis show that: 1) The water-insulating rock mass of deep-buried tunnel is prone to the bending failure, and the water-insulating rock mass of shallow tunnel is prone to the shear failure. 2) The minimum safe thickness of anti-inrushing structure is positively correlated with tunnel excavation radius, karst water pressure and Poisson’s ratio, and the order of influence degree from large to small is tunnel excavation radius, karst water pressure and Poisson’s ratio of surrounding rock. 3) The boundary conditions of the model will affect the minimum safe thickness of the anti-inrushing structure. When the excavation radius R<6 m and the karst water pressurePw<0.35 MPa, the minimum safe thickness can be calculated based on the boundary simply supported condition. WhenR≥6 m and Pw≥0.35 MPa, the minimum safe thickness need to be calculated based on the fixed boundary conditions. This method provides a new way for the calculation of water gushing of circular tunnel in water-rich karst area. Finally, combined with a karst tunnel with water inrush, the corresponding parameters are substituted into the bending type Ⅰ expression, and the minimum safe thickness is generally consistent with the thickness reserved in the project, which shows that the analytical solution of the minimum safe thickness in this paper is reasonable.关键词：circular tunnel;anti-inrushing structure;minimum safe thickness;theory of thin plates;water inrush
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发布时间：2024-01-10 - 摘要：With the development of seismic isolation technology, the service environment of the isolated bridge is becoming increasingly complicated, and the effect of ambient temperature on the seismic performance of isolated bridge should be considered urgently. To reduce the maximum response and residual deformation of the bridge under the action of an earthquake, combining the advantages of the lead rubber bearing (LRB) and shape memory alloy (SMA), a self-resetting SMA–LRB bearing was formed. In view of the temperature sensitivity of rubber and SMA materials, based on a 4–span SMA–LRB seismic isolation continuous girder bridge, the nonlinear dynamic time history analysis of isolated continuous girder bridges under different ambient temperatures was performed to obtain the dynamic response of the key parts of the structure, while the mechanical properties of SMA–LRB bearings at different ambient temperatures were considered. The results showed that the addition of SMA to LRB increased the horizontal rigidity and effectively controls the displacement response of the bearing. At the same time, the self-reset characteristic of SMA made the residual displacement control effective. As the ambient temperature decreases, the peak displacement and residual displacement of the LRB and SMA–LRB bearings would decrease, but the displacement control ability and self-reset ability of the SMA–LRB bearing would decrease compared with normal temperature. The stiffness of the bearing increased with the decrease of the ambient temperature, which caused an increment in the displacement of the top of the pier and the shear force at the bottom of the pier, and the shear force at the bottom of the lower pier was more sensitive to temperature changes. The qualitative evaluation of the influence of ambient temperature on the seismic performance of SMA–LRB isolated bridge can provide reference for the analysis and design of such bridges.关键词：isolated bridge;shape memory alloy (SMA);lead-rubber bearing (LRB);ambient temperature;seismic response
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发布时间：2024-01-10 - 摘要：A circular carbon steel tube was added to the core concrete inside square stainless-steel tubes, the constraint effect coefficient to the core concrete and the ductility of the composite CFST sections could be improved remarkably, as a result, the anti-corrosion protection and fire protection of traditional steel structures could be reduced, furthermore, the disadvantageous influence of the demolished concrete lumps (DCLs) in new concrete could also be improved. Sixteen composite-sectioned concrete-filled stainless steel tubular (CS–CFSST) stub columns filled with high-strength demolished concrete lumps (DCLs) were tested. The influence of factors such as the replacement ratio of the demolished concrete lumps, confinement factor, and different concrete strength of new or demolished concrete on the mechanical performance was investigated. According to the testing results, the axial bearing capacity of the CS–CFSST stub columns decreased with the increase of the mix ratio of DCLs, the maximum decreasing amplitude of the bearing capacity was 6.8% with the replacement ratio of 20%. The failure modes of the CS–CFSST stub columns were quite familiar with those of normal CS–CFSST stub columns filled with normal fresh concrete. Two types of failure modes, drum-shaped and shear failure modes were found in the inner circular CFST stub columns, and excellent ductility and residual bearing capacity were also found as the load-deformation curves kept horizontally or ascended slowly, the residual bearing capacity of all the specimens were higher than 63% of its bearing capacity. The simplified method of constraint effect coefficient in the CS–CFSST stub column was proposed, and four calculation methods of the bearing capacity of the CS–CFSST stub columns infilling with DCLs were compared, coincident results were obtained using the calculation method considering the ultimate bearing capacity reduction of the circular CFST section.关键词：composite-sectioned stainless concrete-filled steel tubular column;stainless steel;demolished concrete lump;axial compressive behavior
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发布时间：2024-01-10 - 摘要：To verify the applicability of wave theory in studying the free vibration characteristics and impact response of the cable–beam structure, and to preliminarily explore the behaviors of elastic wave propagation through the structure under moving load, the dynamic response function was derived from the transverse vibration differential equation of Timoshenko beam and the longitudinal wave equation of cables. The reverberation-ray matrix was used to obtain the waveform solution of the structural response. Based on the idea of discrete Fourier transform (DFT), the series solution of structural transient response was derived to solve the inverse problem of the traditional reverberation-ray matrix (MRRM). The improved MRRM was verified by experiment and finite element method (FEM). The results showed that at the speed of 30 km/h, the deviation between the theoretical maximum strain and FEM results was 5% and that between theoretical and experimental results was 8%. When the vehicle speed was 40 km/h, the deviation between the theoretical maximum strain and FEM results was 4.0%, which was 9.8% between theoretical and experimental results. Taking the beam-cable system as the research object, the maximum deviation between the first five natural frequencies calculated by improved MRRM and FEM was 0.29%, and the deviation between the first two natural frequencies was 0. The wave response characteristics of the cable-stayed beam under moving load were analyzed and the theoretical results were in good agreement with the FEM results. It could be inferred that the improved MRRM had high reliability in calculating the transient wave response of bridge structure under moving load. Based on the analyses of the frequency domain response, it was found that the flexural waves in the Timoshenko beam under moving load were mainly low-frequency responses whose frequencies were lower than 2 times the fundamental frequency of the structure. Furthermore, the reasonable selection criteria of frequency range were explored in the process of finding the wave response, to further improve the calculation efficiency of MRRM.关键词：beam-cable structural system;elastic waves;moving load;method of reverberation-ray matrix
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发布时间：2024-01-10 - 摘要：River flow is affected by boundary shear stress, and too large boundary shear stress will lead to erosion and reduce the stability of river banks, and cause river morphology changes by affecting sediment deposition and transport. To study the shear stress of river boundary is equivalent to the study of flow characteristics in river. Because there are too many complex factors affecting the boundary shear stress in rivers, a two-dimensional rectangular straight open channel flow model was established by numerical software after removing all factors, and the laboratory experiments were carried out on the rectangular straight open channel model by using similarity theory. Firstly, numerical simulation was carried out for flows in uniform straight channels of 5 different scales. Since the stage-discharge relation obtained from the simulation results is highly consistent with the stage-discharge relation deduced by Manning formula, it can be considered that the parameters simulated by the model are true and reliable. In the case of non-uniform flow, through the concepts of under-uniform flow and super-uniform flow, 9 cases of straight open channels under different discharges were simulated in this paper. The momentum theorem was used to analyze the force at 101 points with the same spacing in the center of the non-uniform straight path. The average value of shear stress was taken between every two points, and then the resistance of all points was summed up to approximate the integral of the river bed resistance, which will greatly reduce the influence of the error caused by uncertain factors such as stage fluctuation. A general formula of bed shear stress was derived, which showed that the bed shear stress could be calculated by the water depth h, flow velocity u and Manning roughness coefficient n, regardless of whether the flow of rectangular open channel is uniform or not. To verify the new formula, the new formula was compared to four existing formulas, and the results showed that the new formula conformed to the momentum theorem and had physical significance. The research result is simpler than the traditional methods and can provide a faster algorithm in required calculations.关键词：hydraulics;rectangular open channel;shear stress;numerical simulation
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发布时间：2024-01-10
HYDRAULIC & CIVIL ENGINEERING
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Inter-class Repulsive Slack Discriminant Transfer Learning Based on Rolling Bearing Fault Diagnosis AI导读
摘要：In view of the problem that it is difficult or even impossible to obtain the class labels of new working condition samples under actual variable working conditions, which leads to the low fault diagnosis accuracy, a novel fault diagnosis method based on inter-class repulsive slack discriminant transfer learning (IRSDTL) is proposed. In the proposed IRSDTL, a nonnegative extended slack matrix is constructed to transform the strict binary label matrix into an extended slack label matrix for increasing the distance between different class label vectors in source domain and making the common subspace dimension no longer limited to the number of class labels. As a result, the classification error in source domain is reduced, and the generalization ability of IRSDTL is improved. Moreover, the joint distribution difference is introduced to reduce the difference between auxiliary and target domains, which can better realize the cross-domain transfer learning between two domains; the inter-class repulsive force term is constructed to promote the discriminative learning effect by increasing the distance between one class subdomain samples and the other class subdomains in the two domains. Finally, the whole framework of IRSDTL is optimized by the alternating direction multiplier (ADM) method to easily obtain the optimal parameter values of IRSDTL. The labeled samples under historical working conditions can be used by IRFDTL to perform high-precision class discrimination on the testing samples under new working conditions when there are no class labels of testing samples. Thus, precise fault diagnosis of the testing samples under new working conditions can be achieved by the proposed IRSDTL-based fault diagnosis method. The experimental results of rolling bearing fault diagnosis show that the diagnosis accuracy of the proposed method is higher than that of the other four transfer learning-based methods, and its misdiagnosis rates of misdiagnosing the three types of faults as normal state and the normal state as three types of faults are low, and the effectiveness and practicability of the proposed method are verified.关键词：rolling bearing;fault diagnosis;variable working conditions;inter-class repulsive slack discriminant transfer learning;inter-class repulsive force term- 775
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发布时间：2024-01-10 - 摘要：Due to the complex geometric structure of screw thread, it is difficult to mesh the internal and external screw surfaces of screw thread parts in the finite element analysis of screw thread parts, which often leads to difficulties in finite element modeling of screw thread structure and poor convergence of numerical calculation. In this paper, based on the fact that the geometry of any cross section of the thread perpendicular to its axis is the same, the standard helix formula formulated by the International Organization for Standardization (ISO) is selected, and the three-dimensional eight node element is used to accurately establish the finite element model of the threaded connector. The model not only considers the influence of screw thread elevation angle on itself, but also arranges the element layers of each pitch in order, the node numbers on each layer are orderly distributed, and the nodes on the internal and external screw thread surfaces are close to each other. These characteristics enable the model to accurately map the mechanical properties of threaded connection structures in engineering, optimize the convergence state of numerical calculation of the model, and facilitate the mechanical profile analysis of the calculated results. To verify the validity of the established finite element modeling method of threaded connection structure , the relationship between tightening angle and preload force in screw structure, the distribution of axial force in screw structure are deduced and theoretically analyzed, and the axial force distribution of M12 standard bolt is calculated as an example. The results of numerical experiments show that the relationship between the tightening angle and the preload of the screw connection structure is consistent with the theoretical analysis results, the axial force distribution of M12 bolt is consistent with the theoretical calculation results, the stress concentration coefficient at the root of the thread is consistent with the experimental results, the stress distribution and plastic strain distribution are consistent with the actual engineering measurement. A parametric modeling software for bolt and nut is developed base on proposed the finite element modeling scheme of threaded connection structures. The software can quickly view and generate three-dimensional finite element models of different types of bolts and nuts according to the input thread diameter, pitch number and other parameters. In the engineering analysis and optimization design, it not only avoids the tedious repetitive work of designers, but also improves the design accuracy and work efficiency, which can better meet the actual engineering needs.关键词：threaded connector;finite element method;parametric modeling;validity analysis
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发布时间：2024-01-10
MECHANICAL ENGINEERING
- 摘要：In order to solve three problems of traditional recommendation models, i.e., data sparsity, low robustness and the lack of deep-level semantics among heterogeneous features, a novel correlation visual adversarial Bayesian personalized ranking (CVABPR) recommendation model was proposed. First, based on the movie titles in the original MovieLens datasets, the corresponding movie posters were downloaded from Internet movie database (IMDB) to construct two multimodal datasets named MovieLens−100k−WMI and MovieLens−1M−WMI, respectively. Second, a group of heterogeneous but complementary image features were extracted using the SENet model to describe movie posters accurately. Then, the cluster canonical correlation analysis model was improved to mine the implicit cluster canonical correlation between the heterogeneous features. Afterwards, the correlation was used to optimize the visual Bayesian personalized ranking (VBPR) model to better depict the movies to be recommended. Finally, a perturbation factor was absorbed into the recommendation model to enhance the robustness of the CVABPR model through adversarial learning, making the recommendation model more stable and generating high-quality recommendation results. To verify the proposed CVABPR model, a set of experiments were carried out on two multimodal datasets. Evident performance improvements of the CVABPR model were observed on the two datasets. Specifically, a 3.802% performance improvement of the mean average precision (MAP) metric was obtained on the MovieLens−100k−WMI dataset, and a 4.609% performance improvement of the MAP metric was observed on the MovieLens−1M−WMI dataset. The mainstream baseline was defeated by the CVABPR model. Based on ablative analysis experiments, a more important role of the adversarial learning strategy was found compared with the cluster canonical correlation. Additionally, larger performance improvements were observed on the MovieLens−1M−WMI dataset with higher data sparsity. The key challenges of data sparsity and the lack of deep semantic among heterogeneous features were solved to a certain degree. Meanwhile, the CVABPR model has strong robustness.关键词：data sparsity;recommendation model;Bayesian personalized ranking;adversarial learning;cluster canonical correlation
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发布时间：2024-01-10
INFORMATION ENGINEERING
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