最新刊期
卷 53 ， 期 6 ， 2021
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Research Progress on Rapid Hazard Assessment of Landslide Dams Caused by Landslides and Avalanches AI导读
摘要：Landslide dams usually formed by river blockages with massive amounts of materials from avalanches, landslides caused by earthquake, rainfall, and volcanic eruption. The formation and breaching of landslide dams caused by landslides or avalanche normally have characteristics of sudden occurrence, sudden breach and high risks, posing great threats to people and infrastructure upstream and downstream. The study of rapid hazard assessment of landslide dams is of great significance for emergency risks management. At present, rapid hazard assessment of landslide dams mainly focuses on four aspects, i.e., the possibility of dam formation, stability, longevity, and breaching flood. This paper first reviewed the influencing factors and efficient discriminant formula study of landslide dam formation. Then, the definition, affecting factors and rapid evaluation model of the stability and longevity of landslide dams were specifically summarized. Finally, the failure modes, affecting factors and quick prediction models of dam breaching flood were analyzed in detail. The present research showed that the formation of landslide dams was mainly affected by the topographic conditions, solid material sources and water sources, and the stability, longevity, and breaching parameters were mainly influenced by the geometrical characteristics, materials, structures, and hydrological characteristics of landslide dams. The evaluation models based on the influencing factors can estimate the formation, stability, longevity, and breaching parameters quickly, but the accuracy of results still needs to be improved. On this basis, five directions are proposed for further research: 1) large-scale model tests on the occurrence and migration process of landslides or avalanches under different factors (e.g., earthquake, rainfall) should be carried out, so as to establish the rapid assessment model of dam formation; 2) new methods to obtain the dam materials and internal structural quickly should be studied; 3) prediction research on breaching degree of landslide dam should be carried out to analyze the risk of residual landslide dam; 4) quick assessment model of dam breaching flood should be established from the perspective of watershed to guide water dispatching and engineering construction; 5) dynamic risk assessment of the impact of disaster chain on the whole river basin should be carried out to provide important reference for disaster prediction and emergency treatment.关键词：landslide dam;rapid hazard assessment;dam formation;stability;longevity;dam breaching flood- 1394
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发布时间：2024-01-10 -
Research Framework of the State-dependent Dilatancy Theory and Breach Evolution Law of Landslide Dam AI导读
摘要：Landslide dams are usually formed instantaneously by natural forces, the accumulation bodies have the characteristics of complex space structure, wide gradation of dam materials, poor dam stability, and they are easy to fail under the flow erosion. As a major natural disaster of flood and drought, safety evaluation and disaster prediction of landslide dams have been the focus of attention by the scholars around the world, but many questions remain unanswered, which are mainly manifested in: 1) Accumulation bodies are composed of natural wide-graded rockfill materials with significant state-dependent correlation, there is a lack of the state-dependent dilatancy theory and constitutive model of wide-graded rockfill materials. 2) After the formation of landslide dams, they would be affected by external loads, such as the rise of upstream water level of dammed lake, continuous unsteady seepage, landslide surge in the dammed lake, and earthquake, there is also a lack of standards and methods for stability evaluation. 3) Due to the lack of necessary flood relief facilities, the landslide dams are prone to fail; under the action of outburst flow, obvious nonlinear characteristics are manifested during the breach development, as well as strong unsteady flow characteristics of the hydraulic elements; there is a lack of numerical models for landslide dam breaching which can reflect the erosion mechanisms of wide graded materials. Therefore, it is necessary to conduct integrated scientific measures, such as field explorations, multi-scale physical model tests, and numerical simulation methods, so as to reveal the physical description, internal structure, macroscopic mechanical properties of the landslide dams and their spatial and temporal variations; and then, a state-dependent (i.e., gradation, pore ratio, and stress level) dilatancy equation for wide-graded landslide deposit will be presented, and a generalized elastic-plastic constitutive model that can adapt to complex stress paths and the limit equilibrium analysis method of landslide dam body will be established. Large-scale hydraulic model tests and centrifugal model tests of dam breaching will be conducted to reveal the dynamic erosion characteristics of landslide dam materials and the evolution law of breaches under the action of unsteady flow. Subsequently, the erosion equation of sand-laden flow under the dynamic boundary condition by the action of unsteady flow will be established, and the numerical model for dam breach process considering the fluid-solid interaction will be put forward to realize the numerical simulation of the characteristics of water flow movement, the law of dam material transport, the evolution process of breaches, and the structural instability of landslide dam in the whole process of overtopping and seepage failure. Integrating the reliability theory and numerical simulation method of dam breach process, an integrated numerical simulation platform for seepage, deformation, stability, and failure process of landslide dams considering fluid-solid will be developed; consequently, the theoretical system and method of safety evaluation and disaster prediction of the full-life cycle of the landslide dams will be established. The expected results achieved in the project will provide scientific theory and key technological support for improving the decision-making level of disaster prevention and reduction of landslide dams in China.关键词：landslide dam;dilatancy theory;constitutive model;erosion characteristics;breach mechanism;multi-filed coupling;breach model;stability evaluation- 1276
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发布时间：2024-01-10 - 摘要：On October 10 and November 3, 2018, the Baige landslide blocked the Jinsha River twice, causing huge damage to the downstream. There are still three large-scale residual deformation bodies K1, K2, and K3 around the previous sliding source area, which may be slide and block the river again. Restricted by the natural geological conditions of the landslide area, there is little research work on the residual Baige landslide, which cannot provide support for the risk management of the Jinsha River hydropower project construction. Based on the topographic survey, deformation measurement, and deep structure detection in the deformation area, the volume, destabilization mode, and possible sliding combinations of the three residual bodies were analyzed. The scale of the unstable body entering the river was evaluated on the basis of scraping effect, motion trajectory, loose factor, etc. Based on the current valley topographic data, the previous barrier body morphology analysis and PFC3D software simulation, the future barrier body parameters were predicted for different sliding modes. The results showed that the volume of three unstable areas reached 159.3×104 m3, 460×104 m3, and 142×104 m3 respectively; there were three types of destabilization in the residual body of Baige landslide, namely, the small-scale collapse, the large-scale unloading deformation, and the sliding; the possible and the most dangerous combination was that the four sub-zones 1–4, 2–1, 3–1, and 3–2 slide at the same time with the volume of 271×104 m3; under different sliding conditions of the deformable rock, the maximum height of barrier body was 47.5 m with the ground elevation 2 937.5 m when sliding along the main chute into the river, and 28.7 m with the ground elevation 2 923.7 m when sliding along the upstream slope of the Baige landslide groove.关键词：Baige landslide;residual unstable masses;river blockage;risk analysis
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发布时间：2024-01-10 - 摘要：China is one of the countries with the most serious disasters of dammed lakes, where the dammed lakes pose a great threat to the safety of people’s lives and properties among the upstream inundated area and the downstream outburst flood routing area. A deep understanding of the scouring and breaching processes of landslide dam can provide important scientific and technological basis for the design of emergency discharge channel and the formulation of downstream emergency measures. According to the event of 2018 Baige landslide-dammed lake in the Jinsha River, the scouring and breaching processes of landslide dam were systematically studied by conducting the laboratory physical modeling tests. Test results showed that the erosion and breaching processes of landslide dam could be divided into four stages, i.e., flow incubation stage, retrogressive scouring stage, dam break development stage, and riverbed rebalancing stage. When the retrogressive erosion scarp was traced back to the upstream slope top and the inlet section of the discharge channel was eroded, the discharge channel would connect to form a ramp with the bottom slope i>0. Then the flow velocity and flow rate increase suddenly, and the dam break developed rapidly. The results also showed that when the excavation width of the chute remained constant and the depth increased, the peak flow would decrease, the peak time would be delayed and the process of the burst flow became smoother; when the depth of the chute was fixed, the peak time would be delayed as the width increased. Finally, according to the testing results, some suggestions were put forward for the optimal design of the discharge channel: The location of the discharge channel should be arranged in the pass with the lowest crest elevation to reduce the peak flow and shorten the breaching time; when excavating the spillway, priority should be given to increasing its depth to minimize the water level of the dammed lake during dam breaching.关键词：landslide-dammed lake;physical modeling test;scouring and breaching;discharge of breaching;discharge channel
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发布时间：2024-01-10
MECHANISM OF LANDSLIDE–DAMMED LAKE AND ITS CONTROL
- 摘要：A deep understanding of the loading and unloading rate effect of rock mass mechanical response under mining stress path is an important basis for defining the optimal advancing rate of actual working face. Based on the initial crustal stress environment of Pingdingshan mining area, the evolution law of stress under the condition of protective layer mining with the depth of kilometer was analyzed quantitatively. The research on the mechanical behavior of coal and rock mass under different unloading rates was carried out, which was more in line with the real stress state. At the same time, the comparative analysis with the results of tests without considering the mining was carried out. The results showed that: 1) In the conventional triaxial compression test, the strength of the sample was less affected by the unloading rate, and there was no obvious change at 1～4 MPa/min, and only when it reached 5 MPa/min, the strength increased significantly to about 115 MPa. 2) With the increase of unloading rate, the strength of coal and rock mass showed a trend of decreasing, rising and falling again. The strength of coal and rock mass reached the maximum under the unloading rate of 1 MPa/min and 4 MPa/min, and its peak stress was about 64 MPa, which was 12% higher than that of 3 MPa/min sample. 3) The micro cracks could be fully developed and expanded under low unloading rate, and the fracture density of the specimen decreased with the increase of unloading rate, and it was 1.61 times for 1 MPa/min and 5 MPa/min, respectively, and thus the gas drainage efficiency could be improved by properly reducing the mining speed. 4) The volume strain of coal and rock in the whole mining process at different mining speeds not only had the volume compression in the relative initial state, but also had the volume expansion in the failure stage, which could be regarded as the mining characteristics. This was obviously different from that in the relative initial state without considering the mining test, which was always volume compression under mining. The strength of coal and rock was obviously smaller, and the damage degree was greater. The research results can lay a theoretical foundation for similar geological conditions to carry out protective layer mining design.关键词：protected coal seam;stress response;mining mechanics;unloading rate
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发布时间：2024-01-10 - 摘要：With the rise of development and utilization of marine resources, inclined pile foundation with good horizontal bearing capacity has been widely used as marine structures such as cross-sea bridge, offshore platform and high pile wharf. Under the action of strong nonlinear superposition of wave and current, severe local scour will occur around the inclined pile, which will reduce the safety of the structure and even lead to structural damage. In order to understand the influence of inclination angle on the scour characteristics of downstream inclined piles under different wave heights and flow velocities, and the difference from that of vertical piles, local scour tests under combined waves and current and pure current were carried out in the wave-current flume. By conducting tests on α=0°, 10°, 20° and 30° downstream inclined piles, the influence of inclination angle on scour duration, relative time scale and scour hole morphology was studied. The influence of dimensionless parameters Fr, KC and Ucw on maximum scour depth of downstream inclined pile was analyzed, and detailed comparison was made with previous vertical pile data. The results showed that when the pile was inclined to downstream, inclination angle had an important influence on the scouring characteristics of pile under combined waves and current. Compared with the vertical pile, with the increase of inclination angle, development rate of scour depth, scale and depth of scour hole gradually decreased, while ralative time scale increased gradually. For the 20° downstream inclined pile, when d50=0.403 mm, Uc=0.206 m/s, H=7 cm, the time for maximum scour depth point to be transferred from lateral front to front was about 60 min, which was much longer than that of a vertical pile. The dune of downstream inclined pile was distributed symmetrically along the central axis and had a bimodal structure, and the scour hole shape was obviously different from that of a vertical pile. Under the condition of moveable bed, regular sand waves were formed on the bed surface, the scour hole scale was further reduced, and the double peaks were more obvious. The relative scour depth of downstream inclined pile was the function of dimensionless parameters Fr, KC and Ucw, which was consistent with the trend for a vertical pile’s fitting curve.关键词：inclined pile;inclination angle;local scour;combined waves and current
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发布时间：2024-01-10 - 摘要：Three kinds of magnesium-based foamed concrete with dry density grade A05 were prepared by chemical foaming with magnesium oxychloride cement, magnesium oxysulfide cement and magnesium phosphate cement as cementing materials respectively. By designing orthogonal tests, the influences of water/cement ratio, magnesium cement component ratio, retarder content, fly ash content and polypropylene fiber content on the compressive strength of three kinds of magnesia-based foamed concrete were determined, the action mechanisms of the important influencing factors were compared and analyzed, and the functional relationships between the specific strength of magnesium-based foamed concrete and the component ratio parameters of magnesium-based foamed concrete were established. The results showed that the primary and secondary factors affecting the compressive strength of magnesium oxychloride foamed concrete were the ratio of magnesium cement components>water/cement ratio>fly ash content>polypropylene fiber content>retarder content. The influence of various factors on compressive strength of magnesium oxysulfide foam concrete was the same as that of magnesium oxychloride foam concrete.The relationship between the factors influencing the compressive strength of magnesium phosphate foamed concrete was as follows: the ratio of magnesium cement components>retarder content>water/cement ratio>fly ash content>polypropylene fiber content. Different from magnesium oxychloride foam concrete and magnesium oxysulfide foam concrete, the content of retarder had a higher degree of influence. The component ratio of magnesium cement was an important index affecting the strength of magnesia-based foamed concrete. The compressive strength of magnesium oxychloride foamed concrete and magnesium sulfide foamed concrete had the same change trend with the increase of the component ratio of magnesium cement, both of which first decreased and then increased, while magnesium phosphate foamed concrete showed the trend of first increased and then decreased with the increase of the component ratio of magnesium cement. There was a power function relationship between the specific strength of three kinds of magnesium-based foamed concrete and the component ratio of magnesium-based foamed concrete.关键词：magnesia-based foamed concrete;mixture ratio;orthogonal test;compressive strength;specific strength
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发布时间：2024-01-10 - 摘要：Due to the weak integrity of the damaged masonry pagodas, it is easily to be destroyed heavily for the pagodas affected by earthquake again, even are collapsed. Using rigid hoops to restrain and strengthen the masonry can improve the mechanical properties of ancient masonry pagodas. To study the seismic performance of damaged masonry pagoda reinforced with rigid hoop, three sub-structure models of the masonry pagoda were designed and constructed, and the pseudo-static tests were carried out. The failure phenomena of seismic damaged specimens and the specimens restrained by angle steel hoops were observed, and the load-displacement curves of the restrained specimens were obtained. The numerical models were established to calculate the stress, strain and deformation of the ancient pagoda substructure, and the seismic performance indexes of the reinforced ancient pagoda substructure were obtained through comparative analysis with the test results. As results, the hoop device can effectively confine the horizontal deformation and the expansion of diagonal cracks, improve the ability of the ancient pagoda substructure to resist horizontal deformation, and delay the degradation of structural rigidity. The numerical model can reflect well to the damage of the structure and reinforcement device the characteristics of collaborative work with the structure of the pagoda, and the research results can provide references for the seismic reinforcement of ancient masonry pagoda.关键词：masonry pagoda;hoop reinforcement;pseudo-static test;seismic performance
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发布时间：2024-01-10 - 摘要：Microwave-assisted concrete aggregate recycling is a new green technology, with little pollution and low energy generated during the heating process. The influence of moisture content on the microwave heating effect and concrete strength weakening was explored, and the separation effect of aggregate and mortar in concrete after microwave heating was analysed. Different heating paths were utilized to heat the concrete test blocks to obtain their temperature rise characteristics, and the compressive strength of the test blocks with different moisture content after heating was obtained by conducting uniaxial compression tests. The testing results showed that microwave power and moisture content were two important factors affecting the concrete breaking. When the water content of the test block was relatively high, the test block would break under a short irradiation time and low temperature under higher microwave power input. The aggregate-mortar interface debonding occurred, which could reduce the adhesion of mortar on aggregate, and more complete aggregates with low mortar adhesion could be selected from the crushed concrete. The testing results may provide a reference for further development of microwave-assisted concrete recycling technology.关键词：microwave irradiation;concrete;moisture content;heating effect;strength weakening
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发布时间：2024-01-10 - 摘要：Exploring the fluid flow mechanism in rock masses is of great significance for preventing water inrush during excavation of underground constructions such as tunnels. Quantitative descriptions of the hydraulic properties of single rock fracture subject to normal stresses and shear displacement are the basis for understanding the coupled hydro-mechanical processes in fractured rock masses; however, the quantitative relationships among stress, deformation, aperture, inertial coefficients have not been developed in previous works. Granite specimens with single fracture were prepared and flow tests with variable water heads were carried out, in which incremental normal stresses were applied at each fixed shear displacement to characterize the evolution of permeability. The surface morphology of fractures was digitalized using a three-dimensional high-resolution scanning system. A self-designed numerical code was employed to calculate the deformation of fractures under normal stresses based on the framework of variational principles in contact mechanics. The fracture deformation and void space variation under different shear displacements and normal stresses were investigated. By extracting the aperture data and solving Navier–Stokes equations using COMSOL software, a series of numerical simulations were performed to investigate the nonlinear flow behavior of fluids within fractures under different shear displacements and normal stresses. The relationships among shear displacement, normal stress, void space distributions and parameters describing the nonlinear flow were quantitatively analyzed. The results showed that the fracture surface damage areas obtained from the experiment agreed well with the numerical simulation results, which verified the reliability of the deformation calculation code. The normal stress and the shear displacement exhibited a decreasing power function and an increasing exponential function with the fracture aperture, respectively. The increase in the shear displacement resulted in the concentration of contact areas. The inertia coefficientB in the Forchheimer equation and the critical hydraulic gradient Jc could quantitatively characterize the nonlinear flow behavior. B and Jc exhibited decreasing power functions with the shear displacement. The increasing rates and ranges of Jc and B decreased gradually as shear advances. When the shear displacement increased from 2 to 8 mm, the range of Jc decreased from 6.10×10–3 to 1.20×10–3 by a rate of 80.32%. The range of B decreased sharply from 2.97×1014 Pa·s2·m–7 to 2.43×1013 Pa·s2·m–7 by a rate of 91.28%. A similar power function relationship existed between RSD～B and between RSD～Jc. Finally, a predictive function was proposed to quantify the onset of nonlinear fluid flow through fractures.关键词：single fracture;normal stress;shear displacement;fracture deformation;nonlinear flow
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发布时间：2024-01-10 - 摘要：As the controlling reservoir that possesses a large storage capacity in Yellow River, the operation of Xiaolangdi Reservoir (XLD) is of great importance to the reservoir maintenance and the downstream channel shaping. Considering the integrated economical profit of power generation and sediment discharge, an operation model of XLD was established by coupling the calculations of water-sediment balances with the calculation of power generation. There were two types of optimization objectives: the maximum of power generation and the maximum of integrated profits. The hydrographs of water level, discharge and turbine output were constrained according to the regulation rules during the late sediment-retaining period of the XLD Reservoir. The model was solved by the dynamic programming, and was adopted to obtain different operation schemes under different optimization objectives in a typical dry year of 2015 and a typical high flood year of 2012. The results showed that: 1) with the power generation as the optimization objective, the operation scheme could to energy outputs of 7.130×109 kW·h in 2015 and 10.215×109 kW·h in 2012; 2) with the integrated profits as the optimization objective, an annual power outputs of 7.017×109 kW·h and 9.524×109 kW·h could be achieved in 2015 and 2012 respectively, along with sediment discharges of 31×106 t and 166×106 t; 3) when comparing these two schemes with different optimization objectives, it could be found that both schemes would finally achieve an increase in the integrated profits, whereas the latter would result in a larger increase by sacrificing part of the power generation in exchange for a silting reduction in the reservoir; 4) optimization schemes in both typical years would produce an increase in power generation and integrated profits, with a larger increase being obtained for the typical high flow year. Furthermore, some suggestions were also proposed for improving the current operation schemes in some typical years.关键词：flow–sediment transport and power generation;reservoir regulation;integrated profits;dynamic programming;Xiaolangdi Reservoir
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发布时间：2024-01-10 - 摘要：The mechanical properties of the interface between soil and structure have always been a hot topic in geotechnical engineering. In order to explore the interfacial shear characteristics of non-water reaction polymer and concrete, the effects of vertical stress and shear rate on shear strength and shear modulus of polymer concrete interface were studied based on monotonic direct shear test. The experimental results showed that: under the given vertical stress and shear rate, with the increase of shear displacement, the polymer concrete interface presented shear softening phenomenon. The shear rate had little effect on the interfacial shear strength, cohesion and friction angle, but had a significant impact on the interfacial shear modulus, and the shear modulus value decreased with the increase of shear rate, and the decrease amplitude was obvious; the vertical stress had a significant impact on the shear strength and shear modulus of polymer concrete interface, and the shear strength and shear modulus of polymer concrete interface changed with the increase of shear rate. The vertical stress increased continuously. At the same time, the hyperbolic constitutive model formula of polymer concrete interface was systematically deduced, and the validity of the model was preliminarily verified according to the relevant experimental results.关键词：polymer;interface shear characteristics;shear strength;shear modulus;constitutive model
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发布时间：2024-01-10 - 摘要：Coral islands is mainly composed of calcareous sand with characteristics of irregular shape, multi porosity, high compressibility and friability. During the ecological development and construction of coral island, due to the particularity of calcareous sand, it is necessary to study the constitutive model of calcareous sand considering the particle breakage, to provide references for the design and construction of coral island engineering. To obtain the stress-strain and grading curves of calcareous sand, the triaxial tests with different confining pressures were carried out and the particles were screened. The test results showed that the calcareous sand with the same gradation and density had different degrees of strain softening and dilatancy under different confining pressures, especially under the lower confining pressures. In the range of confining pressure with strain softening and dilatancy, with the increase of confining pressure, the axial strain corresponding to the peak point of deviatoric stress and the critical expansion point increases. Calcareous sand had different degrees of particle breakage under different confining pressures. The higher confining pressure is, the higher degree of particle breakage is, and the more content of fine particles is. At the same time, to accurately describe the stress-strain relationship of calcareous sand, the tangent deformation modulus and tangent volume ratio of Nanjing Hydraulic Research Institute (NHRI) double yield surface model were modified. Based on the fractal theory and Mohr–Coulomb theory, the index considering particle breakage was established to modify the internal friction angle. Finally, the constitutive model of calcareous sand considering particle breakage was established, and the significance of each material constant was clarified. Fortran language was used to simulate the modified constitutive model, and the results were compared with the experimental results, which were in good agreement. Combined with the relevant experimental data in the references, the established constitutive model of calcareous sand considering particle breakage was extended and verified. The results showed that the model could accurately reflect the strain softening and dilatancy of calcareous sand under different confining pressures.关键词：calcareous sand;constitutive model;particle breakage;fractal theory;strain softening;dilatancy
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发布时间：2024-01-10 - 摘要：To effectively evaluate the loss of axial force for the bolts in cable clamp of suspension bridge, the influence factors analyses and application of ultrasonic identification method for cable clamp blot axial force in suspension bridge were carried out. Firstly, the axial force calculation formula was established based on the acoustic elastic effect, and the accuracy of this formula was verified by experiments. Then, effects of the non-stress acoustic time difference and stress coefficient difference on the recognition accuracy was analyzed. Finally, this method was utilized to identify the tension efficiency and the axial force loss during the lifting process. The results show that: 1) The acoustoelastic effect of bolts is obvious and the recognition error of screw axial force is less than 1.1%. 2) Identification errors caused by the coupling state of sensors and the blot geometry and material parameters are 47.7 kN and 43.1 kN, respectively. 3) The stress coefficients of different bolts are different. Identification deviation caused by the difference of stress coefficients between calibrated bolts and tested bolts is 4.75%. 4) With the increase of screw nut tightening degree, the tension efficiency can reach more than 94%, which is 95.93% higher than that before the tightening degree of nut is not controlled. The bolt axial force is seriously lost with the increase of beam weight. The measured minimum average axial force of cable clamps is 424.32 kN, which is only 56.58% of the designed axial force. In the process of beam section hoisting, the cable clamp bolts should be tensioned in time to ensure construction safety.关键词：suspension bridge;cable clamp;bolt;axial force identification;acoustoelastic effect;influence factor analysis
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发布时间：2024-01-10 - 摘要：Flash floods propagating in mountain rivers deliver massive sediment, resulting in significant change of riverbed topography. Particularly in the diverging-converging sections, the significant topographical change and associated flow stage rise can easily lead to high risk in flood inundation. The understanding of the characteristics of flow, sediment transport and riverbed morphological evolution is important to flood disaster prevention and mitigation. This study employed a two-dimensional hydro-morphological model to simulate the processes of flow, sediment transport and riverbed morphological evolution at diverging-converging sections in a mountain river under the change of sediment supply. The modeling results showed that when the sediment supply was sufficient, sediment tended to deposit in the widening section and be scoured in the narrowing section. This led to the overall aggradation of riverbed. Without sediment supply, the riverbed, however, showed a degradation trend. As a result of sediment supply, the water stage grew in response to bed aggradation, leading to the increase in surface gradient. This mechanism in turn maintains the capacity of sediment transport of the river by increasing the bed shear stress because of the upstream sediment supply. The present study offers significant insights that upstream sufficient sediment supply can cause the water level to rise through reshaping the bed topography of the mountain river with width variation, thus inducing the flood inundation risk in the upstream reach.关键词：mountainous river;diverging-converging sections;flash flood related to sediment transport;stage rise;numerical simulation
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发布时间：2024-01-10 - 摘要：The flow scour around bridge piers is the result of the interaction among the flow, sediment and the pier. The complex relationship between water and sediment movement around bridge piers is an important cause of bridge water damage. Quantitative analysis of scour topographic characteristics of bridge piers and its interaction with the flow is an important breakthrough in deeply understanding the mechanism of the flow and sediment interaction around bridge piers and its practical engineering application. In this paper, the flow scour experiment around bridge piers of uniform sediment moving bed was carried out with different inclination angles under two kinds of slope conditions, and four model inclination angles of 0°, 5°, 10° and 15° were set along the downstream direction. The PIV (particle image velocimetry) system was employed to measure the two-dimensional flow field around bridge piers, and the SFM (structure from motion) method was used to achieve the three-dimensional reconstruction of scour topography. Based on this, the characteristics of three-dimensional topography structure of bed surface scour and flow field were analyzed, which are used to build up the coupling relationship between the two. The results show that: 1) The SFM method can be applied to reconstruct the three-dimensional structure of scour topography. As the scour experiment reaches its equilibrium stage, the scour depth in front and on both sides of the model is deeper, and the rear is of convex shape, rising to the bed surface along the flow direction. 2) The size, area and volume of the scour hole increase with the increase of the flow intensity, and decrease with the increase of the inclination angle. As the depth of scour hole increases, the cross-sectional area and three-dimensional morphology increase in parabola with opening upward. 3) As the inclination angle of the bridge pier model increases, the disturbance region of the rear streamwise velocity decreases and the influence region on the spanwise velocity increases. 4) As the model inclination angle increases, influence regions of swirling-strength and shear stress decrease. The deep scour hole around bridge piers can be easily formed by the flow shear stress, and the large-scale streamwise vorticity on both sides of the bridge pier extends downstream, which leads to the formation of shallow long grooves on the back two sides of the bridge pier.关键词：inclination angle;three-dimensional reconstruction;two-dimensional flow field;swirling-strength;shear stress;coupling relationship
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发布时间：2024-01-10 - 摘要：Deflection is the basic data of bridge health monitoring. It can provide quantitative information for both structural safety evaluations and maintenance purposes. By analyzing the relationship between the displacement and its first and second derivatives (inclination and curvature), a method to detect the local stiffness damage of the structure by using the area difference of curvature of the deflection curve before and after the damage was proposed. The area enclosed by the curvature curves before and after damage was divided into several elements, and the ratio of the square of each element area to the sum of the square of all elements area was used as the damage location parameter
$\Delta {A_\kappa } $ $\Delta {A_\kappa } $ $\Delta {A_\kappa } $ $\Delta {A_\kappa } $ $\Delta {A_\kappa } $ 关键词：bridge health monitoring;damage detection;curvature area difference;local stiffness- 1218
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发布时间：2024-01-10 -
Water Retaining Effect of a Slit Dam and Prediction Method for Flow Depth in Steep Slope Rivers AI导读
摘要：Slit dam is an engineering measure for debris flow prevention and control. For a steep slope river with low sediment supply, slit dams mainly exhibit the effects on water retaining. A series of experiments were performed to investigate the water retaining effect of a slit dam in steep slope rivers. With different dam permeability and upstream discharges, the water depth in the free flow section upstream of the dam, the backwater section in front of the dam and the fully developed flow section downstream of the dam were measured. The prediction model for the water depth in the free flow section upstream of slit dam and in the fully developed flow section downstream of the dam had been established. The computational model for predicting water depth at different longitudinal positions in the backwater section and the method for predicting the length of backwater section had been proposed. The result indicated that flow depth and backwater length were affected primarily by the upstream discharge and dam permeability. As the permeability decreased or/and the upstream discharge increased, the water depth in front of the dam and the backwater region both increased. However, the water depth in the fully developed flow section downstream of the dam was primarily relevant to discharge flow and channel condition. The proposed method for predicting water depth in the free flow section upstream of the dam, the fully developed flow section downstream of the dam, the backwater section in front of the dam and backwater length were verified by using 30 groups of experimental data. The prediction had a good agreement with measurements, indicating that the proposed methods were capable of predicting the flow depth in the above sections and the length of backwater section. This study had achieved the accurate prediction of the flow depth at different longitudinal positions and the length of backwater section, which provided a theoretical basis for the structural design of the slit dam in the steep slope rivers with low sediment supply.关键词：slit dam;water retaining effect;dam permeability;backwater length;computational methods- 1259
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发布时间：2024-01-10
HYDRAULIC & CIVIL ENGINEERING
- 摘要：Surface quenching of the rail steel using the laminar plasma jet can increase its service life, but the treatment parameters can only be determined by the experimental methods currently, which is time-consuming and laborious. If a simulation model for the surface quenching process can be established to quickly predict the variation of the temperature field in the surface quenching process and the hardness distribution within the hardened zone, the optimal treatment parameters can then be obtained rapidly. A numerical simulation model was firstly established by the finite element method to obtain the temperature distribution. Then the limit value of the carbon diffusion was determined by the hardness distribution obtained from the surface quenching experiment. After that, the Austenite transformation rate at each heating rate was determined using JMATPRO. Finally, a model for predicting the metallographic structure was proposed. With the numerical simulation model, the variation of the temperature field during the surface quenching process could be obtained. By selecting the nodes greater than the phase transition temperature (for example, 745 ℃ for the U75V rail steel), the width and depth of the hardened zone could be predicted. The prediction error was found to be within 8% errors compared with experimental results. By extracting the temperature change curve of the nodes in the hardening zone and substituting into the metallographic structure prediction model, the transformation of the austenite and martensite at each node position in the hardening zone could be calculated, and the hardness at the hardening zone could be predicted. A series of surface quenching experiments with different surface quenching parameters, e.g. including arc current, anode diameter, scanning speed, etc., were carried out. It was found that the hardness predicted by the proposed simulation model was in good agreement with the actual hardness, which verified the effectiveness of the proposed simulation model for the laminar plasma jet surface quenching of rail steel.关键词：U75V steel;laminar plasma jet;numerical simulation;surface quenching;Austenite formation
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发布时间：2024-01-10 - 摘要：Thermal error prediction and compensation of CNC machine tools is an important technology to improve the machining accuracy and reliability of CNC machine tools. The thermal error of machine tool is time-varying and nonlinear. To improve the accuracy and robustness of thermal error prediction, a numerical control machine tool thermal error prediction model based on attention mechanism and deep learning network was proposed. Using the data conversion strategy, the original temperature data of CNC machine tool was transformed into temperature image, which could be directly used as the input of deep learning network. The complete information of the temperature field of the machine tool was retained by converting the temperature field data into the temperature image points. At the same time, the nonlinear and coupling problems between the temperature measuring points were avoided by using the deep learning modeling method. A recognition network of temperature sensitive points based on attention mechanism was proposed. According to the correlation degree between temperature measuring points and thermal error, different weights were given to each temperature measuring point to avoid the disadvantages of artificial selection of temperature measuring points. A 12–layer deep CNN learning prediction network was established to mine the nonlinear mapping relationship between temperature image and thermal error by using its powerful image feature learning ability. This method does not need to preselect the key temperature points, retained more relationship between thermal error and machine temperature characteristics, and can significantly improve the prediction accuracy of the model. In order to improve the accuracy and generalization ability of thermal error model, dropout regularization method and Adam optimization algorithm were introduced to optimize the structure and parameters of deep convolution neural network. The method shows high prediction accuracy in the thermal error verification of G460L CNC lathe. Compared with the thermal error models based on BP neural network, multiple regression and CNN network, the proposed method performs better in generalization performance.关键词：temperature measuring points;convolutional neural network;thermal error of machine tool;deep learning
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发布时间：2024-01-10
MECHANICAL ENGINEERING
- 摘要：High entropy alloys break through the traditional alloy design concept with one or two elements as basic elements, and have a simple phase structure and excellent comprehensive performance prepared by equimolar ratio or near equimolar ratio, which is expected to further expand the performance limit and application of metal materials. In order to study the effect of element doping on phase structure, microstructure and wear resistance, CoCrCuFeMn and CoCrCuFeMnZr high entropy alloys with equal molar ratio were prepared by vacuum melting method. The phase structure, microstructure, hardness and wear resistance of CoCrCuFeMn alloy before and after Zr addition were investigated by XRD, OM, SEM, EDS, microhardness tester and friction-wear tester. It was found that after Zr addition, the phase structure of CoCrCuFeMnZr alloy was changed from the original two FCC phases to two HCP phases, and the microstructure was obviously refined. The two alloys were typical dendrite structure. The friction curves of the two alloys showed a trend of first increasing, then decreasing, and then stabilizing. After Zr addition, the friction coefficient and mass loss rate decreased from 0.57 and 4.14% to 0.47 and 0.49% respectively, and the microhardness increased from 219.6 HV to 983.5 HV. The results showed that the HCP transformation of alloy phase structure was mainly related to the formation of a rough solid-liquid interface rich in Zr with large atomic radius and Z-shaped HCP orientation. The reason why Cu is enriched in the interdendrite region is that its melting point is the lowest, its electronegativity is the largest, its atomic radius is second only to Zr, and it has the corresponding largest positive mixing enthalpy with all alloy elements except Zr, so it is enriched in the interdendrite region with the latest solidification. Due to the fact that the melting point of Mn is only higher than that of Cu, Mn has the largest electronegativity difference except Zr, and there is a negative mixing enthalpy between Mn and Co or Zr and the largest positive mixing enthalpy between Mn and Cu, which is not conducive to its long-range diffusion and entering into the lattice site of the leading phase, the segregation coefficient of Mn is the smallest. The increase of hardness and wear resistance of the alloy with Zr element is due to fine grain strengthening, solid solution strengthening and phase structure transformation.关键词：high-entropy alloy;microstructure;wear properties
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发布时间：2024-01-10 - 摘要：Transition metal Fe2+ is the most economical, effective and environmentally friendly PS activation substance, but Fe2+ is prone to be oxidized and loses its activation ability, resulting in poor continuous effect of the Fe2+/PS system. In order to improve the efficiency of the Fe2+/PS system in oxidizing and degrading organic pollutants, iohexol, a commonly used iodinated X–ray contrast media in medical field, was taken as the target pollutant, and its degradation in four advanced oxidation proeesses such as UV/PS, Fe(C2O4)3 3–/PS, UV/Fe(C2O4)3 3–/PS and Fe2+/PS was studid. The effects of Fe(C2O4)3 3– concentration, ultraviolet light intensity and pH on the degradation of iohexol and PS decomposition in UV/Fe(C2O4)3 3–/PS system were examined, and then the Fe2+ concentration change and its conversion rate in the system were analyzed. The results verified that the oxidation decomposition rates of iohexol in the four advanced oxidation systems were 83.8%, 7.0%, 98.8%, and 69.9% respectively, among which the UV/Fe(C2O4)3 3–/PS system could promote the reduction of ferrous irons through ultraviolet light, Fe2+ that activates PS in the solution was gradually released, and the degradation of iohexol was the most efficient and complete. As the concentration of Fe(C2O4)3 3– increased, the decomposition rate of PS in the UV/Fe(C2O4)3 3–/PS system increased, while the degradation rate of iohexol first increases and then decreases. Under four different initial Fe(C2O4)3 3– concentrations (20, 50, 100, 200 μmol/L), the degradation rate of iohexol is in the order of 100>200>50>20 μmol/L. In the UV/Fe(C2O4)3 3–/PS system, the Fe2+ concentration first increases rapidly and then slowly decreases, the degradation rate of iohexol, the decomposition rate of PS and the highest conversion rate of Fe2+ are all positively correlated with ultraviolet light intensity and negatively correlated with pH. Therefore, the use of ultraviolet light to reduce iron ions can greatly improve the Fe2+ activation efficiency, and the system has strong adaptability to influencing factors such as light intensity and pH, and has great application prospects in the field of advanced oxidation in water treatment.关键词：ultraviolet light;ferrous;photoreduction;persulfate;iohexol
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发布时间：2024-01-10 - 摘要：The secondary fly ash problem in the application process of fly ash of municipal solid waste incineration (shorter form: fly ash) melting treatment technology has become a constraint. It is beneficial to the development of harmless and resource utilization technology of secondary fly ash by mastering the distribution law of salt in the gas phase product of fly ash melting, and it can be used as a reference for the design of tail gas purification equipment and operation. The fly ash released from one municipal solid wastes incineration plant in Jiangsu Province was adopted. The fly ash melting experiments were performed in a self-designed high-temperature pilot-scale plasma arc furnace system. The weight subtraction method, X–ray fluorescence spectroscopy, atomic absorption spectrometry and electrochemical process were used to analyze melting fly ash and slag during melting and to abtain gaseous phase migration rate of Na, K, Ca, Mg and Fe. The thermodynamic model was used to simulate the distribution rules of gaseous phase salts at 1000～1600 ℃, with 0～50% auxiliary material, at different atmosphere (without gas, nitrogen or air) and 0～12% water content of fly ash. The simulation results showed that NaCl, (NaCl)2, KCl, (KCl)2, CaCl2, KCaCl3, KMgCl3, FeCl2 etc. were main compositions of gaseous phase salts during fly ash melting. These compositions distribution was greatly effected by melting temperature and was little effected by melting atmosphere, auxiliary material amount and water content of fly ash. At atmosphere, there were new product Na2SO4 in gaseous phase salts. The simulation values and the experimental values of gaseous phase migration ratio of Na and K fitted well, and the simulation values were largely smaller than the experimental ones of Ca, Mg and Fe. It is suggested that the distribution law of gaseous product salt should be used to develop the technology of salt separation or chloride salt utilization, so as to realize the comprehensive utilization of secondary fly ash, change the current situation that the secondary fly ash is mainly landfill, and thoroughly realize the harmless and resource utilization of fly ash.关键词：fly ash;thermodynamic analysis;gaseous phase salt;melting
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发布时间：2024-01-10
CHEMICAL ENGINEERING & MATERIAL ENGINEERING
- 摘要：Frequency diverse array (FDA) radar applies a small frequency offset between the adjacent elements to synthesize a range-angle-dependent beampattern. It is difficult to control the beam steering for the coupled time-variant beampattern. For this problem, the time-variant characteristic and point beam forming of FDA radar were mainly studied in the paper. Firstly, the characteristic of transmit beampattern of FDA using linearly increasing frequency increment was analyzed. Secondly, two signal models of FDA using logarithmically frequency increments (log–FDA) and multicarrier frequency increments (multi-FDA) were constructed, where the multi-FDA transmit beampattern has lower sidelobes. Then, the relationship between the time variable of the frequency increase term and the time variable of the propagation term in the two time modulated signal models was studied in detail. If both of them are the same, the time-varying characteristics of the transmit beampattern can be eliminated by the two time variables offset. However, they have different physical meanings. When the electromagnetic signal is generated and propagated in space, the time variable in the frequency increase term will not change, whereas the time variable of the propagation term in the propagation process is related to the propagation characteristics of the electromagnetic wave, which is a variable quantity, so the two time variables cannot offset each other. Finally, the simulation results verify the correctness of the transmit beampattern analysis of time modulated FDA radar, and demonstrate that the spot transmit beampattern with dynamic forward propagation can be synthesized using log–FDA and multi-FDA, where the beampattern of the multi-FDA has lower sidelobes.关键词：frequency diverse array;nonlinear frequency increment;time varying characteristic;point beam forming
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发布时间：2024-01-10
INFORMATION ENGINEERING
- 摘要：In order to alleviate the burden of continuous increasing energy consumption falling on the power system and solve the complex calculation problem in the joint dispatching of large-scale electrical equipment, a hybrid decentralized optimization of dispatching the large-scale controllable appliances and energy storage equipment considering demand side response was proposed in this paper. Firstly, two mathematical models of controllable electrical equipment load and energy storage equipment were established. On this basis, a mixed integer non-linear centralized optimization model was mathematically formulated under the constraints of the operation characteristics of the system and equipment, with the objective of minimizing the sum of electricity purchase cost, users’ dissatisfaction cost and energy storage equipment loss cost. Secondly, for tackling the difficult nonlinear centralized optimization problems of high dimensionality, multi objectives and multiple constraints, the Lagrange relaxation method was used to decompose the problem into two sub-problems, namely, optimally scheduling the controllable electrical equipment load and optimizing the dispatch of the energy storage equipment. Then, the former was further decomposed into optimizing dispatch of each controllable electrical equipment and solved by the interior point method, while the latter was decomposed into a set of mixed integer linear optimization sub-problems of scheduling each energy storage equipment and solved in parallel by the Benders decomposition method. Thirdly, a series of numerical simulations together with comparison analysis were performed to verify the effectiveness and superiority of the proposed dispatch optimization method. For example, the optimization objective value and the optimal dispatch solution corresponding to the proposed method were illustrated and compared with those of the centralized method to demonstrate the effectiveness of the hybrid decentralized optimization method. And the influence of different numbers of dispatching equipment on the computation efficiency was investigated on the centralized and decentralized optimization method to show the superiority of the proposed hybrid decentralized optimization method. According to the numerical simulation results, the optimization objective value of the proposed method is basically consistent with that of the centralized. Moreover, the identified dispatch solution enables to efficiently respond to the time-of-use and results in good effect of peak-shaving and valley-filly. Besides, the calculation efficiency of the proposed hybrid decentralized optimization method is of high computation efficiency and not affected by the increasing number of the schedulable electrical equipments.关键词：demand response;mixed integer nonlinear programming;decentralized optimization;Lagrangian relaxation method;interior point method;Benders decomposition
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发布时间：2024-01-10
ELECTRICAL ENGINEERING
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