最新刊期
卷 53 ， 期 1 ， 2021
- 摘要：Based on the analysis of large deformation cases of tunnel surrounding rock both at home and abroad, the present study found that the factors such as in-situ stress, geological structure and formation lithology are the basic conditions for the occurrence of large deformation of tunnel surrounding rock. Then, a concept of tectonic-induced large deformation of soft rock was proposed. According to the concept and mechanism of tectonic-controlled large deformation of tunnel surrounding rock mass, the classification of large deformation of soft rock in tunnel was redefined (fault type, fragmentation type and small angle type). Based on the ratio of rock strength and in situ stress, emphasizing the influence of structural movement, and considering five factors including stratum age, occurrence of dominant structural plane, rock strength, rock strata thickness and rock mass integrity, a new grading method for large deformation of tunnel surrounding rock in different geological exploration stages was proposed. The new grading method for tectonic-induced large deformation of tunnel surrounding rock mass proposed in this paper was systematically verified by employing 18 large deformation cases of Yakou tunnel, Yanbian tunnel, Xinlin tunnel and so on. Results demonstrated that the grading method proposed in the present study is reliable. The research results are of great importance for the understanding of the large deformation mechanism as well as the identification and control of large deformation disasters of tunnel surrounding rock mass.关键词：large deformation of surrounding rock;large deformation of structural soft rock;patterns of large deformation;classification of large deformation
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发布时间：2024-01-10 - 摘要：Flood risk is a very important subject in hydrology. Firstly, the exact meaning of flood risk has been discussed, and two concepts of flood risk in the current situation, time risk and annual risk, have been pointed out. In the former, Both risks resulting from annual maximum flood and submajor flood are considered simultaneously in the design. In the latter, only risk resulting from annual maximum flood is considered in the design. Secondly, frequency or probability is defined as flood risk degree in this paper. While time frequency corresponds to time flood risk degree, annual frequency corresponds to annual flood risk degree. Lastly, the analysis and calculation show that the standards for flood control of annual flood risk degree and time flood risk degree are different from each other. The difference between annual flood risk degree based on annual maximum flood value and that based on annual maximum and submajor flood value has been discussed. The former accords with current standard for flood control of water-related engineering, whereas the latter is not consistent fully with the current standard for flood control.关键词：flood risk;flood risk degree;standard for flood control;annual maximum sample selection;super quantitative sampling
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发布时间：2024-01-10 - 摘要：In order to improve the local buckling resistance of thin-walled concrete filled-steel tube column, a type of restraint namely spiral stiffener was proposed. Through the axial compression experiments of the six kinds of the concrete filled-steel tube composite columns, i.e., the common steel pipe, straight rib, built-in opening straight rib, inner spiral rib, spiral rib and external spiral rib-reinforced, the failure process, ultimate load, displacement and strain were compared and analyzed, and the failure mode and mechanism of the spiral stiffened thin-walled concrete-filled steel tube column were obtained. The results show that, the bearing capacity of the thin-walled concrete-filled steel tubular can be effectively improved by setting straight rib, opening straight rib and internal spiral rib. However, their constraint mechanisms were quite different. The vertical stiffener played a significant role in improving the bearing capacity, while the spiral rib played a major role by restraining the transverse deformation of the steel tube, and its contribution to the vertical stiffness was small. For the spiral rib external form, due to the lack of restrictions on the external concrete deformation, the cracking of spiral rib was serious and the spiral rib quitted service in advance. When the vertical steel bar was set, the steel bar and spiral rib formed “block” constraints on the concrete, which delayed the development of cracks, worked well with the core members, and improved the bearing capacity and deformation capacity. The spiral stiffener proposed in this paper can better solve the problem of poor deformation capacity of traditional thin-walled concrete filled steel tube. When the spiral rib was placed outside, the steel pipe can be protected by external concrete, avoiding fire prevention and anticorrosion treatment, thus reducing the maintenance cost in the later stage. The new composite members have good mechanical performance, and the research work can provide technical support for the engineering application.关键词：thin-walled concrete filled-steel tubular;spiral stiffener;axial compression experiment;failure mode;ultimate bearing capacity
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发布时间：2024-01-10 - 摘要：Flash flood disaster, especially affected by the coupling of flood and sediment, is categorized into at least three forms: water flood disaster, water-sediment flow disaster and debris flow disaster. There are significant differences in characteristics, scale and warning threshold of different disaster forms. The traditional research ideas of prevention and early warning techniques for flash flood disaster mainly depend on the “rainfall–runoff–stage” relationship, but lack of system consideration of interactions among “rainfall–runoff–sediment” and characteristics of flash flood disaster resulted from coupling of flow and sediment movement, and then an early warning of the disaster with “sediment deposition–water level sudden increase” due to excessive sediment supply is very easy to miss. According to the analysis and investigation, loose particles formed by landslides are the important source of sediment supply for water-sediment flow disaster in Zhongdu River basin and Baisha River basin, which are the tributaries of Jinsha River and Min River, the results indicate that the water-sediment flow disaster and debris flow disaster could be occurred, respectively. For this reason, the TRIGRS model (transient rainfall infiltration and grid based regional slope-stability model) was utilized to analyze the landslide susceptibility of basins, in that the low risk areas were divided into water flood disaster warning zones, the higher-risk areas with rich solid source into water-sediment and debris flow disaster warning zones according to riverbed morphology. Water flood disaster warning index can be calculated through four methods: rising rate of flood level, real-time accumulated precipitation, inversion on water level/flow and broadcast warning of simple precipitation station, in Zhongdu River basin. The method of rising rate of flood level based on riverbed deformation was used in the calculation of critical flood level for water-sediment flow disaster in Baisha River basin. The results indicated that landslide risk was low in the Zhongdu River and downstream of Baisha River, so its villages could be divided into water flood disaster warning zone. The middle and upper reaches of Baisha River were higher-risk area of landslide in which steep and gentle slope join area could be divided into warning zone of water-sediment disaster, and steep slope area could be debris flow disaster warning zone. The warning results in Zhongdu River basin showed that the methods of inversion on water level/flow and broadcast warning had limited early-warning effect, the warning reliability based on the methods of flood rising rate and real-time accumulated precipitation were higher, and could assist in catching the causing moment of flood disaster in advance. In addition, the method of rising rate of flood level on the basis of river-bed deformation had an expected warning effect for water-sediment flow disaster in Baisha River basin. Overall, this division warning method had high reliability and could provide technical support for flash flood disaster prevention.关键词：flash flood disaster;flood coupled sediment disaster;division warning;early warning index
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发布时间：2024-01-10 - 摘要：Due to the variation of the water level and the water diversion demand, many sluices can satisfy the requirement for both forward and reverse operation. Because of the complicate loading situation when retaining the water inversely, the lifting force will significantly increase, leading to the seriously insufficient lifting force of the hoist. Therefore, a predicting method of the gate lifting force based on CFD (computational fluid dynamics) using the homogenous model was proposed, with one control sluice in Jiangsu Province being the benchmark case. The analysis was performed for the gate lifting force at different opening height of the gate when the sluice retained the water inversely. The reason for increase of the required gate lifting force was also analyzed. The results indicate that the numerical gate lifting force with CFD agrees well with the experiment and the proposed method can effectively predicate the gate lifting force and its tendency as the gate opening height increases. The opening force of the flat steel gate when the gate retains the water inversely is greatly increased compared to the case where the gate operates in the opposite direction. During the lifting process, the vertical force induced by water is the key reason for the lifting force incensement. The force results in the pressure difference between both sides of the bottom main beam (higher pressure on the upper side and lower pressure on the other side). The pressure difference is first increased, then decreased, and then increased and then decreased, which results in the same tendency of the opening force. The research results of this paper are of great significance to improve the accuracy of numerical simulation of the flow field through the gate, improve gate design, and optimize the opening force of plane steel gate.关键词：vertical-lifting plane steel gate;retaining water inversely;gate lifting force;CFD;main beam
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发布时间：2024-01-10 -
Stability Analysis of the Soil–Rock Slope Considering Long Axis Inclination and Soil–Rock Interface AI导读
摘要：In order to accurately analyze the stability of soil–rock slopes, based on the original rock shape library, a random soil–rock slope model establishing method was proposed. This method could consider the shape and distribution characteristics of rocks very well. Using this method, finite element limit analysis software Optum G2, combined with physical models, the stability of soil–rock slope considering different rock contents (0～50%), long axis inclinations (0°～180°) and soil–rock contacting surface (0.01～1.40) were studied. The results showed that the influence of rocks on the shear zone of the slope included three development modes: “bypass”, “diversion” and “include”, which lead to the change of bending point, length and developing direction of the shear zone. Through the study on the stability of slope with different rock contents, it was found that when rock content was more than 20%, the influence of rock distribution on the stability of slope was greater, and the slope with high rock content was prone to “local” or “disintegrating” failure. At the same rock content, the minimum (or maximum) safety factor was obtained when the long axial inclinations of rock blocks were parallel (or vertical) to the shear zone of the slope. When the rock long axis was vertical to the shear zone of the slope, the slope was prone to “disintegration” failure, which was mainly related to the “induced” effect of the rock long axis on the shear zone of the slope. Under the same rock distribution model, the slope safety factor decreased with the decrease of the soil–rock contacting surface coefficient, and when soil–rock contacting surface strength was lower than that of the soil, the “attraction” effect of rocks to development of the shear zone would appeared. The research results could provide a reference for the stability analysis and treatment of soil–rock slopes.关键词：soil–rock slope;limit analysis;stochastic rock models;rock content;long-axis inclination;soil–rock contesting surface- 2785
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发布时间：2024-01-10 - 摘要：In order to explore the temperature field distribution characteristics and thermal effect of corrugated steel web (CSW) box girder in dry cold region, and to make up for the lack of the definition of temperature gradient mode of CSW box girder in the current standard, a new-pattern composite box girder bridge with CSWs in dry cold region of Northwest China was taken as the research object. Based on the field thermal observation data, the temperature distribution law of the new composite structure under the action of sunshine was analyzed, and the 2D temperature gradient model was proposed by least square fitting. By establishing the refined FEM of the new-pattern composite box girder with CSWs, the temperature response of the bridge was calculated based on the measured temperature gradient function, and the influence of profiled steel plate on the thermal stress of the composite box girder was analyzed. The results showed that the 2D temperature gradient of CSW box girder of vertical piecewise polynomial and transverse exponential function based on field measured data was in good agreement with the calculated value of measured temperature field, which could provide necessary reference for the calculation of similar engineering temperature load in this climate area. Under the action of solar temperature, there was a significant temperature gradient at the interface between the top plate and the web plate of the new-pattern CSW composite box girder. Transverse tensile stresses up to 2.42, 1.83 and 1.26 MPa appeared at the upper edge of the flange plate, the top plate web interface and the central axis of each box chamber, respectively, which might induce cracks in the deck and attention should be paid in the design. Under the measured temperature gradient, the transverse tensile stress of the upper edge of the central axis of each box chamber roof could be reduced by more than 0.5 MPa by the closed profiled steel sheet, which was beneficial to the crack resistance of the bridge deck. While the open profiled steel plate could increase the transverse tensile stress of the upper edge of the flange plate of each box chamber by 15%～18%, which was unfavorable to the crack resistance of the bridge deck.关键词：composite beam;profiled steel sheet;thermal field;thermal effect;thermal stress
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发布时间：2024-01-10 - 摘要：Determination of the dynamic strength characteristics and stress evolution law of rock mass after blasting is the key to study the rock mass failure characteristics near the blasthole, and utilization of a reasonable dynamic strength model directly determines the correctness of the calculated results of the gunhole failure zone. The calculation formula of hole damage zone related to rock mass ratio has been studied with both theoretical and site experimental analyses. Based on the displacement compatibility equation of cylindrical wave, the formula for calculating the strain rate of rock mass near the blasthole was derived and applied to the rate-dependent dynamic compression and tensile strength criteria related to rock mass. The calculation model of the failure area of blasthole was also established. So that the error of the calculation result brought by selecting parameters according to experience was effectively avoided. At the same time, based on the measured result of bench blasting in practical engineering, the destruction characteristics at the bottom of the residual hole under different borehole diameters and charge conditions were recorded. Furthermore, the failure characteristics of residual holes in rock bottom were analyzed. The theoretical calculation results of fracture zone were close to the experimental statistical results under different borehole diameters and charge conditions. It verified the accuracy of the calculation formula through comparisons between measured and calculated values, which had important reference significance for the actual prediction and numerical simulation of blasting damage area of practical engineering.关键词：rock mass blasting failure characteristic;dynamic action;strain rate correlation;dynamic strength of rock mass
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发布时间：2024-01-10 - 摘要：The baffle-drop shaft is widely used in deep tunnel drainage system due to its fine applicability and high energy dissipation. To fully reveal the high speed water–air two-phase flow characteristics in baffle-drop shaft during discharge process, a scale of 1∶25 physical model test and the numerical simulation based on the Realizable k–ε model and volume of fluid (VOF) method were carried out. The distribution law of water and air in the baffle-drop shaft was studied under different flow conditions. The formation mechanism of cavity area in wet side and the variation process of air pressure in dry side were expounded. And the distribution law of shaft wall pressure and hydrodynamic loadings on different baffles were analyzed. The results showed that the formation of “cavity area” in the baffle-drop shaft was caused by the internal air compressed to the limit, and another reason came down to the negative pressure caused by the entrainment of the water flow in wet side. At large inflow, the distribution law of flow velocity in drop shaft was low velocity on central baffles and high velocity on upper and lower baffles. But when the inflow was small, the flow velocity decreased gradually along the direction of the shaft depth. The air pressure varied from –0.96 to 2.46 kPa under the top-sealed condition, and the air pressure on the dry side did not change over time when the relative vent diameter of shaft cover is greater than 0.105. The wall pressure of the drop shaft increased with the decrease of the shaft height, and the maximum wall pressure of the upper, central and lower baffles of the shaft were 42.25 kPa, 21.5 kPa and 16.75 kPa, respectively. The research results provided a scientific basis for the design theory and safe running of the baffle-drop shaft of deep tunnel drainage system.关键词：deep tunnel drainage system;baffle-drop shaft;hydraulic characteristics;numerical simulation;physical model
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发布时间：2024-01-10 - 摘要：The low-velocity circulation pattern in groyne fields could promote the sediment deposition and lengthen the mean residence time of nutrients, thus creating a favorable growth environment for aquatic plants. Although flow hydrodynamics in cavity zones had been well studied, vegetation effects on the recirculating flow were rarely considered. Laboratory experiments were adopted to investigate the flow structure and sediment deposition in groyne fields with emerging vegetation, where the PIV (particle image velocimetry) was employed to measure the velocity vector in clean water and the combined method of photo, weighing and particle size analysis was used to investigate the sediment phenomenon in muddy water. The results revealed that the presence of vegetation reduced the circulation velocity and rearranged the circulation systems inside the cavity, i.e. from the double gyres to a sing one. In addition, the plants suppressed the evolution of coherent eddies in the mixing layer, with a distinct decrease in the eddy scale. Due to the deflecting effect of consecutive groyne on the main-stream, sand in the main channel was transported into the groyne field in a form of fine suspended load through two ways, i.e., by the circulation structure and by the turbulent vortex at the interface. As the sediment transport was subject to hydraulic characteristics, different flow structures between the non-vegetated and the vegetated cases could lead to the difference of sediment deposition. Under the same diachronic condition, the deposition with the coarse particle size and the relative large weight was mostly concentrated in the primary circulation area in the non-vegetated case; but for the vegetated condition, as the restriction effect of vegetation community could reduce the oscillation intensity of Kelvin−Helmholtz shear layer and the water exchange coefficient between the cavity and the main channel, the deposition with the fine size and the small weight was almost evenly distributed in the whole groyne filed. Such differences were particularly evident in the upstream groyne fields (i.e., the transitional stage of of hydraulic characteristics).关键词：groyne fields;vegetation;model experiment;flow structure;sediment deposition
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发布时间：2024-01-10 - 摘要：In the construction of water conservancy, hydropower, underwater tunnels and other geotechnical engineering, rock materials with initial damage are under the coupling action of axial compression and hydraulic pressure for a long time, which seriously affects the long-term stability of geotechnical engineering. The fractured sandstone specimens obtained by preloading were taken as the research object in order to ensure the long-term stability of geotechnical engineering under the coupling of axial compression and hydraulic pressure. The single-stage loading creep tests on the fractured sandstone under the coupling action between axial compression and hydraulic pressure and its creep model were investigated by using a multi-channel rock rheological system. The effects of both the hydraulic pressure and the initial load on creep properties were mainly analyzed. The accuracy and rationality of the constructed creep model were discussed. The results showed that the axial creep of fractured sandstone decreased with the increase of hydraulic pressure. The maximum creep strain rate in the acceleration phase of creep increased with hydraulic pressure increasing. The maximum axial creep strain rate in the initial and the failure stage increased with the initial load increasing. Based on the damage theory, the nonlinear equation of the basic components of the creep model considering initial damage was established. According to the power function equation, a new accelerated creep viscoplastic model was proposed. According to the creep properties of fractured sandstone under the coupling of axial compression and hydraulic pressure, a one-dimensional nonlinear creep model considering aging damage was established. Based on the increment theory, a three-dimensional nonlinear creep model considering aging damage under axial compression was constructed. The creep curves predicted by the new creep models were highly correlated with creep experimental results, which indicated that the established creep model considering the aging damage can well describe the creep change characteristics of fractured rock under the coupling of axial presume and hydraulic pressure. It can provide a theoretical basis for evaluating the long-term stability of geotechnical engineering under the coupling of the in-situ stress and hydraulic pressure.关键词：hydraulic pressure;fractured sandstone;aging damage;creep characteristics;creep model
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发布时间：2024-01-10 - 摘要：In order to better study the creep properties of rocks under different conditions, the rock triaxial creep tests were conducted using the MTS812.02 test system. Based on the rock rheological mechanics, damage theory and the characteristic analysis of the creep curves, the viscoelastic-plastic damage element was introduced into the creep model, and a new method for determining the creep parameters was proposed. The whole process description of rock creep curve was realized. The results showed that the viscoelastic-plastic damage element provided a new idea for describing the whole process of rock creep curve. The improved model can consider the dual effects of over-stress difference and time, and then obtain the relationship between creep parameters and over-stress difference and time. The damage degradation characteristics of the creep property parameters of rock during the creep process with time and over-stress difference were all reflected. This further revealed the internal mechanism of creep deformation damage, and also predicted the variation of rock creep parameters with time and stress. The creep parameter fitting formula was substituted into the original creep damage model, and the damage creep model considering the dual influences of stress and time on the creep parameters was established. At the same time, by improving the damage evolution equation of the viscoelastic-plastic damage component, the damage degree of the rock during the creep process can be better reflected. The relationships between creep parameters and stress and time were analyzed. A new method for determining creep parameters was proposed. The degradation characteristics of creep parameters were obtained, and the physical meanings of creep parameters were more clearly defined. By comparing the experimental results with the model calculation results, it was concluded that the model curve had a good agreement with the test curve under high stress state. The correctness of the improved creep model and the rationality of the creep parameter determination method were also verified.关键词：triaxial creep;overstress;damage creep model;creep parameters
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发布时间：2024-01-10 - 摘要：In view of the short durability life of concrete structure in Western saline soil area, the reinforced concrete specimens were buried on site in the saline soil area of Golmud, and non-destructive degradation indexes such as ultrasonic velocity, quality and steel resistance of specimens were periodically collected every 150 d. Damage and deterioration evaluation was analyzed from both macro and micro aspects through the evaluation parameters of dynamic elastic modulus ξa, quality evaluation parameters ξb, evaluation parameters of steel bars without corrosion ξc and SEM images. Wiener random process was selected for modeling and life prediction. The results showed that under the combined actions of corrosive ions and climate, the ξa and ξb values of concrete fluctuated with a slight increase in the early stage and an accelerated decline in the middle and late stages. The value of ξa was more sensitive to the change of concrete performance, and the value of ξc of the steel bar decreased linearly. The Cl–, SO4 2–, CO3 2– and other corrosive anions in the saline soil enter the concrete through diffusion and capillary adsorption, and form Friedel’s salt, silica fume gypsum, ettringite, gypsum, calcium carbonate and other corrosive expansion crystals with concrete hydration products. From a microscopic point of view, it was observed that the corrosion products in the concrete were distributed in sticks, rods, fibers, and needles. On the other hand, the corrosion products of steel bar were accumulated in granular and cluster shape, and there were corrosion pits on the surface of steel bar. The Wiener stochastic process model could well predict the life of reinforced concrete in saline soil environment, and the life curves of concrete and steel bar changed in three stages. The concrete life value obtained by the quality and dynamic elastic modulus degradation index was higher than the steel bar life obtained by the resistance degradation index, and the life value obtained by the concrete relative dynamic elastic modulus was lower than the life value obtained by the relative quality degradation index. Service life of C35, C40 and C45 reinforced concrete in Golmud saline soil environment was approximately 4500 d, 5000 d and 5800 d, respectively.关键词：reinforced concrete;saline soil;Wiener random process;durability;life prediction
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发布时间：2024-01-10 - 摘要：By applying the method of unidirectional freezing, a series of laboratory tests were carried out to study the anti-frost jacking ability of belled piles in seasonal frozen soil regions. The tests were conducted on piles with different bell angles (non-bell, 45º, 60º and 70º), different embedded depths (240 mm, 290 mm and 340 mm), and different bell diameters (74 mm, 98 mm and 114 mm). Based on the test and calculated results, the ultimate freezing depths of the three test groups were 19.51 cm, 14.36 cm and 14.80 cm, respectively. The ultimate frost jacking displacements of belled piles with different bell angles were almost the same, which were merely 28.3% of the straight pile. The ultimate frost jacking displacements of belled piles didn’t decrease in proportion with the increase of embedded depth, but it decreased in proportion with the increase of enlarged base diameter. With the increase of freezing depth, the frost jacking amount amplitude of the piles increased first and then decreased, and it was negatively correlated with the soil freezing rate. The frost jacking rate of straight pile increased first and then decreased rapidly with the increase of freezing depth, while the frost jacking rate of belled pile increased first and then decreased steadily with the increase of freezing depth. The frost heave of soil had a funnel shape under the constraint of pile. Further, the constraint effect of belled pile was stronger than that of straight pile, which indirectly indicated that the anti-frost jacking ability of belled pile was better than that of straight pile. Considering the freezing rate of soil and frost jacking amount of pile in the freezing process, the concept of anti-frost jacking factor of pile was proposed as the criterion of anti-frost jacking ability of pile, and anti-frost jacking effects of belled piles were also analyzed under different influencing factors. The analysis showed that the anti-frost jacking ability of pile was less affected by bell angle, but it could be improved by increasing the embedded depth and diameter of enlarged base. Comprehensive comparison showed that the diameter of enlarged base was the most important factor affecting the anti-frost jacking ability of pile, followed by the buried depth of the pile, and the smallest influence was the bell angle. The test results and analyses can provide references for designing and theoretical calculation of belled piles in seasonal frozen soil regions.关键词：seasonal frozen regions;belled piles;anti-frost jacking ability;frost jacking amount;frost jacking rate;constraint frost heave;anti-frost jacking factor
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发布时间：2024-01-10 - 摘要：The complicated topographical conditions and rainstorms frequently lead to mountain flash flood disasters, which severely restrict the social and economic development in southwest China. It is very important to scientifically understand the process of flash flood, reveal the disaster mechanism, and construct the early warning system of flash flood considering the regional characteristics. Based on the field investigation and analysis of “8·16” flash flood disaster occurred in the zhongdu River basin. Pingshan County, Sichuan Province, this study systematically analyzed the catastrophic response of flash flood from three aspects of regional rainfall characteristics, flood steeply rising phases and human activities. This study took two methods including a water level discharge relationship and rising of flood level into account early warning values, respectively. The results showed that the heavy rainfall from the upstream Mabian County resulted in this flood disaster event, and the rising of flood level greatly shortened the transfer time duration of residents along the zhongdu riverbank. On the other hand, residents made cultivated land through floodplain, which reduced the flood discharge capacity and increased the disaster risk. It belongs to a typical sudden flash flood disaster under the comprehensive interactions among regional heavy rainfall, topographical conditions and human activities. In short, the traditional early-warning method of inversions on water level/flow missed several alarms in selected sections, and has slightly poor accuracy. However, the water level rising rate early-warning method is a more reliable from the escape time. That is to say, it is useful to adopt the coupling methods such as rising of flood level and traditional ways in the basin to establish a Mabian County-to-Pingshan County joint flash flood early-warning system.关键词：flash flood;disaster mechanism;rising rate of flood level;critical rainfall;early warning system
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发布时间：2024-01-10 - 摘要：The discharge from high dams will lead to the supersaturation of total dissolved gas (TDG) in water. Its adverse effects will last for a long distance, which will cause the downstream fish get gas bubble disease and even die. With the construction and operation of a large number of high dams, this ecological environmental problem has attracted more attentions. Based on the three-year prototype observation sets of supersaturated TDG at dam A in Dadu river, it was analyzed about the influencing factors and rules of the generation and dissipation of supersaturated TDG, and an optimal discharge pattern for dam A was discussed. It is shown that the levels of supersaturated TDG generated by the discharge of different spillway buildings are significantly different. The saturation level generated by deep hole is higher than that generated by spillway tunnel. There is a good positive correlation between the generated value of saturation and the discharge. But the correlation between the generated TDG and the downstream water elevation is not significant. The level of initial saturation affects the decrease of TDG saturation per unit distance. Water depth is an important factor affecting the dissipation of supersaturated TDG. The shallower the water depth is, the greater the dissipation coefficient is. Based on the analysis results of three-year prototype observation data, a predictive model of TDG generation downstream of dam A was proposed. Optimal operation to mitigate the negative impact of TDG was discussed. A suggestion is that, when the flow is less than the discharge capacity of the spillway tunnel (1 384 m3/s), the spillway tunnel is recommended to discharge the flood, and when the flow is greater than the discharge capacity of the spillway tunnel and less than 2 600 m3/s, the combined discharge of a single deep hole and the spillway tunnel is suggested. In this way, the generated TDG saturation can be controlled below 129%. The multi-year prototype observation study enriches the prototype observation results of the supersaturated TDG of high dam discharge, which provide important field data and technical support for the further exploration of the mechanism of supersaturated TDG and mitigation measures. It is of significance for the water ecological protection of hydropower developed rivers.关键词：total dissolved gas;supersaturation;prototype observation;model;mitigation measure
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发布时间：2024-01-10
HYDRAULIC & CIVIL ENGINEERING
- 摘要：A novel 2–UPR&2–RPU parallel mechanism with redundance structure was proposed, which has two rotations and one movement (2R1T) degree of freedom. Based on the screw theory, the degrees of freedom and motion characteristics of the mechanism were analyzed, and the correctness of the analysis was verified by the modified G–K formula. By analyzing the constraints of each branch, the reverse solutions of position was solved by establishing the closed-loop vector equations of each branch. The velocity and acceleration of the mechanism were analyzed by the differential transformation method based on symbolic operation, then the velocity Jacobian matrix and the second order influence coefficient matrixes were obtained. On the basis of this, the Jacobian matrix of each branch was also figured out. The dynamics model of the mechanism was constructed by using the virtual work principle based on the kinematics. For the character that the distribution of the active joints’ drive forces was not unique due to the redundant actuation, the driving force and driving power equation were obtained by the method of 2-norm of driving force. Based on this, a calculation program was written for the constructed mathematical model by using MATLAB, and the constructed kinematics and dynamics model were simulated through specific numerical examples. Finally, in order to verify the correctness of the mathematical model constructed, a virtual prototype of the mechanism was established in ADAMS and simulated under the same conditions. The results were compared with those of MATLAB. The simulation results of both were basically consistent, indicating the correctness of the established mathematical model and showing the max errors of driving force of each rod with 0.091%, 1.83%, 1.04%, 1.40%, respectively. The results showed that under the given motion law, the mechanism does not produce rigid impact. At the beginning and the end of the motion, a certain flexible impact will occur. The driving force of each driving rod changes smoothly during the entire movement, and the total work by the method of 2-norm of the driving force is 1 143.2 J.关键词：redundant parallel mechanism;kinematics;dynamics;power consumption
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发布时间：2024-01-10 - 摘要：In order to overcome the disadvantage of conventional precise point methods, optimization approaches and numerical atlas, and further improve the accuracy of continuous path synthesis of planar six-bar linkage, a novel analytical approach with Flourier series was presented to solve path synthesis problem for planar six-bar linkage. Firstly, the planar Stephenson-Ⅲ six-bar linkage was decomposed into a four-bar linkage and a two-bar group for the purpose of decoupling the design parameters of linkage. Then, on the basis of obtaining the design parameters of the four-bar linkage on the left by the established comprehensive method, a closed vector equation containing the design variables of the two-bar group on the right was established based on the complex vector theory. The linkage rotation angle function was formulated according to the Fourier series, and substituted into a vector loop equation. Through eliminating and substituting, the vector loop equation was changed into a complex number equation that contain the design variables of mechanism, the harmonic parameters of the linkage rotation angle function and the input angle. With regard to the properties of the complex exponent, the mathematic expression containing the design variables of mechanism and the harmonic parameters of the linkage rotation angle function was obtained. Accordingly, the relationship between the design variables and the synthetic design harmonic parameters of rotation angle function was obtained. According to this function relation, the synthetic design equation was established. Through the elimination Groebner base algebra approach, the comprehensive design equation was simplified into a unary quartic equation containing the design parameters of the mechanism and the harmonic parameters of the linkage rotation angle function, the analytical solutions for the two-bar group on the right was derived and the general formula for calculating the design variables of the right two-bar group was established. Using the method of connecting rod mechanism path synthesis, 12 groups of design parameters of the four-bar linkage on the left and 4 groups of design parameters of the two-bar linkage on the right can be obtained. By combining the results, 48 sets of integrated design parameters of planar Stephenson-Ⅲ six-bar linkage path synthesis can be obtained. Through the dynamic simulation program, the comprehensive results were verified to check whether there were cranks, branching problems and order problems. And the design parameter value which met the requirements can be finally obtained according to comprehensive error. Based on the aforementioned theory, the procedure of solving path synthesis problem by the proposed method can be obtained. The computer programs have been developed for the proposed method by MATLAB for solving the problem. An example was provided to verify the validity and feasibility of the proposed method. Verification results showed that the proposed approach can overcome the shortage of multi-point path synthesis method and to solve path synthesis problems for planar Stephenson-Ⅲ six-bar linkage with no limitations on the number of precision points. Compared with numerical atlas and optimization approaches, the proposed method avoided the use of extensive numerical atlas databases and optimal initial solutions, and obtained the results by solving the equation. Therefore, this approach has the characteristics of high accuracy, fast solution velocity and high repeatability, and is suitable for computer programming. The research of this approach provided the theory basis for development of synthesis software.关键词：planar Stephenson-Ⅲ six-bar linkage;path synthesis;Fourier series;analytical approach
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发布时间：2024-01-10
ECHANICAL ENGINEERING
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Salient Object Detection Based on Multi-scale Feature Extraction and Multi-level Feature Fusion AI导读
摘要：Salient object detection has been widely used in image retrieval, image segmentation, pedestrian recognition and other fields. Current mainstream detection methods fuse multi-level feature information through short connection to add feature maps, which cannot accurately and effectively control the transmission of information flow. In addition, existing salient detection methods usually use single feature detection, which results in discontinuous and fuzzy boundary between the saliency object region and the background. A new salient object detection method based on multi-scale feature extraction and multi-level feature fusion was proposed in this paper. Firstly, the multi-scale context information was obtained by using the dilated convolution of different expansion rates to make up for the deficiencies caused by single feature detection. Secondly, a multi-level feature fusion module was designed, which fuses low-level feature, high-level feature and global context feature information for different distribution characteristics of them. It can not only restrain the transmission of noise, but also restore the spatial detail structure information of the saliency object effectively. At the same time, a concise attention module was constructed, which can effectively retain the channel information after feature map fusion. The F-score, mean absolute error, structural measurement, precision–recall rate curve and F-measure curve have been evaluated experimentally. Experiments on five public datasets show that compared with other thirteen mainstream detection methods, the proposed method in this paper achieves significant improvements in different evaluation indicators, of which the F-score, and structural measurement on four datasets are better than other methods. Meanwhile, the saliency map predicted by the proposed method in this paper has better continuity of edge contours and clearer details of spatial structure details.关键词：salient object detection;multi-scale feature extraction;multi-level feature fusion;saliency map;deep learning- 2367
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发布时间：2024-01-10 - 摘要：In order to solve the problem of authority deception or lacking of trust in the incentive mechanisms, the blockchain technology is used due to its decentralization, openness, immutable and anonymity. However, existing incentive mechanisms based on blockchain has design defects or lack of evaluation. To solve the above problems, a distributed incentive architecture based on blockchain was proposed, which can provide guidance and evaluation basis for the design of incentive mechanism. In this architecture, an incentive mechanism was considered as a transaction in the blockchain, and the basic and additional requirements of the incentive mechanisms based on blockchain were formulated from the three aspects of payment flow, payment method and payment amount of the transaction, including the entire process of incentive transactions. Then, a three-stage blockchain-based incentive mechanism framework for scene adaptation, payment strategy, and effect evaluation was designed. In the scene adaptation stage, the interests of the participants were extracted by analyzing the role relationship of the scenario to apply to the difference of transaction verification and payment flow in different scenarios. The payment strategy stage provided the characteristics and functions of various cryptocurrencies, pricing strategies and payment methods to guide the selection of cryptocurrency, the design of pricing strategy and the determination of payment method. The effect evaluation stage was used to analyze the effect of the incentive mechanism from the aspects of security and credibility, privacy protection, scalability, etc., so as to give a more comprehensive evaluation. Finally, the architecture was used to design and evaluate the incentive mechanism of the crowdsensing application. The evaluation results show the optimization effect of the incentive design scheme in terms of security and truthfulness, privacy protection, and efficiency improvement, thereby verifying the effectiveness of the architecture.关键词：incentive mechanism;blockchain;cryptocurrency;payment strategy;incentive effect
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发布时间：2024-01-10
INTERNET OF THINGS
- 摘要：The gas–liquid cross-flow array (GLCA) system captures particles from industrial tail gas by forming arrays of liquid columns through distribution plates and the particle removal efficiency can be improved by increasing the number of unit rows of liquid columns arrays. However, the system has high operation energy consumption which mainly composed of water recycle. To reduce the energy consumption of GLCA system, non-uniform falling film at windward side which plays a major role in particle capture was utilized to supersede previous liquid columns technology. Large eddy simulation (LES) and discrete phase model (DPM) were employed in the numerical simulation of flow field and particle motion respectively for non-uniform falling film GLCA system with different liquid film angles. The model of liquid falling film angle of 360° was regarded as that of liquid-columns GLCA system and compared with the experiment under the same conditions for verification, which proves a good agreement between simulation result and experiment data. The numerical simulation results of different liquid film angles indicated that particle removal efficiency of one unit row decreases gradually with the reduction of the angles, but the water consumption also decreases. There is an optimal angle of film to minimize water consumption in the system for a specific particle removal task. The removal efficiency of large particles is relatively small, indicating that inertial impact is the main removal mechanism. Using the evaluation criteria of specific power consumption as a baseline, the windward film angle of falling film channel was optimized with the numerical simulation model based on the exhausted gas data of a certain compound fertilizer production by ammonia-acid process. The results showed that the optimal angle with the lowest operation energy consumption of the non-uniform falling film GLCA system is 70°, 634 rows of units required in the system and the corresponding specific power consumption could be as low as 1.83×10–4 kW·h·m–3 when the quality dust removal efficiency of exhaust gas reaches 80%. The specific power consumption could be equivalent to Grade 1 comparing to the energy efficiency grades of the electrostatic precipitator in coal-fired power plants.关键词：gas–liquid cross-flow array;falling film flow;numerical simulation;specific power consumption;operating energy consumption
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发布时间：2024-01-10 - 摘要：As a halogen-free flame retardant, Octaphenylcyclotetrasiloxane (P4) was synthesized by using Diphenyldimethoxysilane, was extruded with polycarbonate (PC) in proportion to gain the halogen-free flame retardant PC. The flame retardant PC samples were evaluated through limit oxygen index (LOI) test, UL–94 vertical combustion test (VBT), scanning electron microscope (SEM), thermogravimetic analysis (TGA), melt index (MI) test and mechanical property test. The results showed that P4 has an obvious flame retardancy effect on the PC and the flame retardancy level increased gradually. P4 is dispersed uniformly in PC and PC degraded to some extent wile char layer residues of PC became denser as the content of P4 increased. Besides, the thermal stability of PC increased to some extent and its carbon yield rose obviously in air when the content of P4 reached to a high level. The MFR of PC increased a little indicating the molecular weight declined to some extent. Furthermore, its tensile strength and impact strength declined obviously when added low content of octaphenylcyclotetrasiloxane while the two strength changed little when content of octaphenylcyclotetrasiloxane reached 4%. Meanwhile, the bending strength declined little as the content of octaphenylcyclotetrasiloxane increased.关键词：octaphenylcyclotetrasiloxane;polycarbonate;flame retardancy;mechanical property
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发布时间：2024-01-10 -
Experimental Study on Grouting Material of Red Mud–blast Furnace Slag–steel Slag Ternary System AI导读
摘要：In order to solve the problems of environmental pollution and high cost caused by a large amount of cement consumed in the treatment of underground engineering disasters, this paper prepared the red mud–blast furnace slag–steel slag based ternary system solid waste grouting materials based on the synergetic theory, and systematically studied the effect of steel slag on the working performance and mechanical strength of the red mud- blast furnace slag binary system, combined with X-ray diffraction and Fourier transform infrared light. The mechanism was analyzed by means of spectrum, SEM and mercury porosimetry. The results showed that the steel slag can enhance the mechanical strength of the binary system of red mud–blast furnace slag. When the content of steel slag is 10%, the compressive strength can reach 12.78 MPa in 28 days, with an increase of 59.84%. After mechanical grinding and high temperature activation, the synergistic effect of steel slag can be further improved. With the decrease of steel slag particle size, the physical strength of slurry paste matrix gradually increases, and with the increase of activation temperature, the physical strength of stone first increases and then decreases. When the activation temperature is 700 ℃ and the particle size is 200 mesh, the mechanical strength of the stone body of red mud blast furnace slag steel slag based grouting material is the best, and the strength reaches 15.1 MPa in 28 days. In addition, the addition of steel slag can also promote the setting of red mud blast furnace slag based slurry, shorten the setting time and reduce the fluidity of slurry. The micro analysis showed that the steel slag can participate in the hydration reaction of red mud- blast furnace slag system, and the steel slag particles have filling effect in the slurry paste matrix, making the paste matrix more dense, thus improving the physical strength of the paste matrix. In addition, under high temperature conditions, glauberite, dicalcium silicate, tricalcium silicate and calcium aluminate cementitious minerals are formed in the steel slag, which can promote the formation of ettringite and calcium aluminate hydrate and enhance the strength.关键词：geopolymer;grouting material;red mud;activation mechanism;synergetic effect- 1749
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发布时间：2024-01-10 - 摘要：Fluorescent polyurethane has attracted more and more attention in recent years in the field of fluorescent polymer research. A novel multifunctional polyurethane (MFU) with solid and acid-base response fluorescence emission was synthesized using 1, 5-dihydroxynaphthalene as fluorescent functional monomer. The structure was confirmed by characterization with 1H NMR, FTIR and UV−vis. The fluorescence luminescence properties of the solid and solution samples were studied by fluorescence spectrophotometer. The acid-base response fluorescence properties of MFU solution samples were also studied by dropwise adding experiment. The results showed that the proton absorption peak of naphthene group appeared in the range of 7.20 to 7.54 in1H NMR, which corresponds to the vibration peak of naphthene group skeleton in the vicinity of 1 630 ,1 548 ,1 483 cm–1 in FTIR spectrum, and the conjugated absorption band at 226 nm and in the range of 260 to 340 nm in the UV−vis spectrum. In addition, the peak at 226 nm in the UV−vis spectrum was selected as the reference, and the standard curve method was used for quantitative analysis according to the lambert-bill law. The results of analysis indicated that the content of fluorescent groups in the MFU molecular chain was consistent with the theoretical calculation within the error allowed. Structural characterizations revealed that fluorescent polyurethane containing functional groups 1,5−dihydroxynaphthalene in the molecular chain was successfully prepared. Fluorescence spectra showed that MFU samples had strong fluorescence emission at a wide range of 460 nm in either solution or solid state, while the pure polyurethane samples had no significant fluorescence emission in either state. Interestingly, the solution samples had different luminous wavelengths in the acid (490 nm, blue-green light) and base (460 nm, blue light) environments, with a maximum displacement of over 30 nm. The fluorescence intensity in the strongly alkaline (pH=11) environment decreased by 89% compared to the strongly acidic (pH=3) environment. Based on the dual-characteristic response behavior of MFU solution samples in acid-base environment, the novel fluorescent polyurethane MFU is expected to be used in dual-signal detection for strong acid and strong base. Therefore, a novel multifunctional polyurethane with solid state and acid-base response fluorescence emission was successfully prepared by introducing fluorescent functional monomer through chemical bond.关键词：fluorescent polyurethane;1,5–dihydroxynaphthalene;solid-state fluorescence;acid-base response fluorescence
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发布时间：2024-01-10
CHEMICAL ENGINEERING & MATERIAL ENGINEERING
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