最新刊期
卷 54 ， 期 5 ， 2022
- 摘要：The rapid development of new energy has brought opportunities and challenges to the electric power and chemical industry. On the one hand, the consumption of renewable energy leads to a large amount of waste of energy such as water and light. On the other hand, replacing carbon-based fossil energy ammonia with green hydrogen as raw material can greatly reduce the carbon emissions of the chemical industry. Therefore, the use of hydropower, photovoltaics, and other renewable energy sources to electrolyze water to produce hydrogen can provide green raw materials for ammonia synthesis, which can significantly improve the capacity of renewable energy consumption, reduce energy consumption, and carbon emissions, and serve the national goal of “carbon peaking and carbon neutrality”. However, the fluctuation of renewable energy power is difficult to meet the stability requirements of the traditional synthetic ammonia production process, and there are still many challenges in the design and operation of large-scale renewable energy electrolysis of water to produce hydrogen and synthetic ammonia. There is an urgent need to carry out systematic research and breakthroughs in key technologies for the integration and regulation of large-scale electrolysis of water for hydrogen production to ammonia synthesis systems that adapt to the fluctuating characteristics of renewable energy. In this regard, the process and its topology structure of the renewable energy electrolysis water and the synthesis ammonia process are firstly introduced, including the electrolysis water hydrogen production section, the compression buffer section, and the chemical ammonia synthesis section. Furthermore, the key technical system for the construction of the system was proposed, including the synthetic ammonia process multi-stable optimization and flexible control technology under the fluctuating conditions of renewable energy, the modular integration and cluster dynamic control technology for large-scale hydrogen production system by electrolytic water with “electricity–heat–mass” coupling, “source—grid—hydrogen—ammonia” system-wide coordinated control technology for the volatility of renewable energy and multi-stable characteristics of the chemical industry, comprehensive security protection and market operation for electricity, hydrogen, ammonia, and other elements mechanism. Contents include: Aiming at the optimization of the synthetic ammonia process and multi-stage cooperative regulation technology suitable for flexible production, a high-fidelity proxy model for synthetic ammonia is developed by integrating the subsystems of the synthetic tower, compressor, gas separation, and heat transfer network, considering the hydrogen storage and supply quantity and the performance of the catalyst. The adaptation scheme and collaborative control technology of each subsystem of water electrolysis for hydrogen production and ammonia synthesis under the fluctuation of renewable energy supply and market demand are studied. Aiming at the modular integration and cluster dynamic control technology of large-scale water electrolysis and hydrogen production system, the multi-time-scale time-domain simulation method of the cluster system is studied based on singular perturbation and surrogate model technology, and the multi-physical coupling state space model of the electrolytic cluster system is established. Considering the module startup-shutdown unit commitment scheduling, scheduling and power allocation between the modules, and safe operation of the interval constraint and electro-thermal interface features, to improve the hydrogen yield, improve energy efficiency, improve the power tracking and grid load frequency control as the goal, to build the multi-objective hierarchical cluster system scheduling and control model. Aiming at the whole system cooperative control technology of hydrogen energy participating in the power grid, the flexible operation method of multiple sections with steady-state operation characteristics of hydro-solar complementary power generation, power-to-hydrogen production, hydrogen storage, ammonia synthesis, and ammonia storage is studied, and the flexible dynamic cooperative control method of electric hydrogen production and ammonia synthesis system is also studied. The simulation model of electric hydrogen production and ammonia synthesis system with static equivalent and parameter aggregation methods is integrated. The optimal control method and technical index of the system with hydrogen and ammonia in the source grid are studied. Combined with the characteristics of frequency modulation and peak regulation, the strategy of power-to-hydrogen production and ammonia synthesis system participating in power system auxiliary service is studied. It has significant social benefits and strategic significance to improve the local consumption rate of renewable energy and the friendliness of grid-connected scheduling and reduce chemical carbon emissions and reduce chemical carbon emissions by building a large-scale water electrolysis system for hydrogen production and ammonia synthesis with renewable energy.关键词：hydrogen energy;ammonia synthesis;green hydrogen;green ammonia;renewable energy;volatility
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发布时间：2024-01-10
FOCUS ON STATE KEY RESEARCH DEVELOPMENT PROGRAM OF CHINA
- 摘要：Vegetation restoration is one of the important reasons for the decrease of sediment yield in the Loess Plateau. To explore the effect of vegetation coverage on sediment transport, the relationship between vegetation coverage and sediment transport rate was analyzed by combining the theoretical analysis and the field plot experiment. Based on the Einstein’s theory of sediment movement, the movement process of sediment particles on slope surface was analyzed theoretically from the perspective of sediment movement, and the relationship between slope relative sediment transport rate and vegetation coverage was established. The field runoff scour experiments were carried out to verify the formula. Six flow levels (flow range 0.14～1.40 L·s–1, including 0.14, 0.28, 0.56, 0.83, 1.11 and 1.40 L·s–1) and eight vegetation coverage levels (0, 20%, 30%, 40%, 50%, 60%, 80%, 100%) were set for 48 groups of experiments. The results showed that the calculated value was larger than the measured value; under the condition of large flow, the calculated value was in good agreement with the measured value; there was a certain deviation between the calculated value and the measured value under the condition of small flow. Based on the analyses of theory and test, the influence of vegetation on sediment transport capacity was related to vegetation coverage, plant diameter and sediment particle size. Under the same slope topography and vegetation coverage, the vegetation with smaller plant diameter was more beneficial to sediment reduction than the vegetation with larger plant diameter. In the area with coarser sediment particle size, the effect of slope vegetation on sediment reduction was more obvious, and the same planting only needed to reach a small coverage, then it could start to play an effective effect on sediment reduction. When the vegetation coverage was low, the coverage threshold for the effective effect of sediment reduction was determined by the particle size of sediment and the plant diameter of vegetation.关键词：Loess Plateau;vegetation coverage;overland flow;sediment transport rate;effective sediment reduction threshold
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发布时间：2024-01-10 - 摘要：Deep geotechnical engineering often faces complex variable temperature environments. The thermal cycle effect of rock mechanical properties is important for the stability evaluation of reservoir and surrounding rock and the rational utilization of rock materials. For fine grained dense granite geothermal reservoir, its mechanical properties are related to energy-efficient exploitation and engineering safety. Therefore, thermal cycling experiment, uniaxial compression experiment, and optical microscope observation experiment were carried out to study the failure characteristics, the changes in mechanical parameters, and the influence mechanism of fine grained dense structure on the mechanical properties of granite. The results showed that the changing trend of rock failure characteristics and mechanical properties with the temperature and times of thermal cycle was closely related to the structure. For the fine grained dense granite, the uniaxial compressive strength and elastic modulus gradually decreased with the increase of upper limit temperature and times of thermal cycle, and the reduction rate of compressive strength became slow after more than 10 thermal cycles. The increase of the upper limit temperature of the thermal cycle can improve the sensitivity of the mechanical properties of granite to the deterioration of the thermal cycle. Internal thermal cycling at 300 ℃ would not change the brittle failure characteristics of fine grained dense granite. The microscopic observation and analysis show that the thermal cycle could significantly promote the crack propagation of granite. After 20 thermal cycles at 20～300 ℃, the linear crack density was 1.69 mm–1, which was 1.5 times that of one thermal cycle. Due to the fine and dense structure, the expansion and compaction effect of granite mineral particles was constrained, resulting in the predominance of crack initiation and propagation evolution induced by thermal stress, and then the macro mechanical parameters decreased nonlinearly with the corresponding linear crack density. This study had a certain reference value for the exploration of deep geotechnical engineering mechanics problems in variable temperature environments.关键词：deep rock mechanics;fine grained dense granite;geothermal development;microcrack;thermal cycle
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发布时间：2024-01-10 - 摘要：The true triaxial apparatus is an ideal instrument to study the mechanical properties of soil under complex stress state, but how to keep the loading structure and soil without friction and independent loading in three directions is the technical bottleneck of the development of true triaxial apparatus. Aiming at the problem of bidirectional friction between rigid loading plate and specimen in rigid-flexible compound true triaxial apparatus, based on a new friction reduction method in which the contact between soil and loading plate is changed from whole contact to distributed contact and sliding friction to rolling friction, a bidirectional micro-friction load transfer plate for true triaxial test is developed. The structure principle and detail structure of the device are introduced in detail. The effect of the friction-reducing measures of the distributed contact instead of the integral contact and sliding friction into rolling friction is demonstrated by large-scale direct shear test and numerical calculation. The results show that: 1) The friction coefficient between the specimen and the loading plate is tested by large-scale direct shear test, and the value is as low as 0.023. Compared with the traditional friction reduction method, the friction coefficient can be reduced by more than 90%. 2) Compared with the integral contact, the distributed contact can make the stress and deformation of the sample in three directions more uniform, and reduce the friction between the sample and the loading plate to a great extent. 3) The distributed sliding blocks are overlapped with each other and the gap is reserved to meet the synchronous deformation with the sample, and the three-dimensional non-interference independent loading of true triaxial test under the condition of large deformation (the maximum vertical deformation is 90 mm, and the strain is up to 15%) is realized. The successful development of the bi-directional micro friction load transfer plate for geotechnical true triaxial test effectively eliminates the interfacial friction between the specimen and the loading plate, so that the specimen can deform freely in both directions in the tangent direction of the contact surface, and ensure that the three-dimensional loading does not interfere with each other under the condition of large deformation, solving the key technical problems in the development of true triaxial apparatus.关键词：bidirectional micro-friction load transfer plate;true triaxial test;friction coefficient;three-dimensional loading without interference
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发布时间：2024-01-10 - 摘要：To investigate the damage mechanism of the thick coating in the steel frames under earthquake, one small-scale experiment was conducted. The failure modes and positions of the thick coating in the steel beam and columns were observed in detail. The inter-story displacement angle, beam, and column strain of steel frame structure under earthquake were obtained, and the relationship between inter-story displacement angle, strain, and the failure of the coating was analyzed. Based on the software ABAQUS, the elastoplastic damage model was used to predict the damage and fell-off behavior of the coating. In addition, the fell off and the failure mechanism of the thick coating in one steel column reported by the literature and the beam, column, and connection of the present steel frame were analyzed, and a comparison between the theoretical and experimental results was conducted. Results showed that the coating fell off on the web of the beam and the column did not occur, and it easily occurred on the beam-column connection, particularly near the connection region and the top flange of the beam. According to the strains of beam and column under earthquake, it was found that the position beyond the steel yield strain was corresponding to the part where the coating falls off. The Numerical results showed that the steel strain exceeded the yield strain or the inter-story drift ratio exceeded 1/150, and the coating fell off often occurred. Therefore, the elastoplastic damage model can reasonably predict the thick coating falling off. Meanwhile, the coating equivalent plastic strain distribution, the fell off position and the steel equivalent plastic strain conformed to the Mises stress distribution. In other words, larger steel equivalent strain and the Mises stress easily led to the coating fell off. It was found that the coating equivalent strain has an important effect on its fell off, and the thick coating effective plastic failure strain 0.002 could be used in the numerical analysis. In all, the presented results can be used in the coating design of the large-span steel frame, and thus it has a larger engineering application value.关键词：steel frame structure;earthquake;scale model;coating;damage mechanism
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发布时间：2024-01-10 - 摘要：For the complexity of deformation mechanism of the concrete arch dam and the highly non-linearity of measured value, the explanatory performance of prediction model for dam deformation is important. A combined forecasting model for concrete arch dam deformation was proposed, which combined the residual effective components. In view of the fact that the statistical model can not effectively relate the influence of material property evolution on dam deformation, the hybrid model was constructed by calculating hydraulic components with the finite element method. At the same time, considering the chaos and periodicity of the mixed model residual sequence, the high-frequency and low-frequency signals were modeled and predicted one by one by using the limit learning machine (ELM) model and the seasonal difference autoregressive integration sliding average model (SARIMA). Considering the influence of ELM model parameters on model predictive performance, an optimized ELM model for high-frequency signal processing was constructed by combining particle swarm optimization (PSO) with good global search ability to optimize its parameters. Finally, the combined forecasting model of concrete arch dam deformation was built by superimposing the forecasting results of high and low frequency signals with the modeling results of the hybrid model. Taking a concrete arch dam as an example, by establishing the three-dimensional finite element numerical model of the dam, the water pressure components of typical measuring points PLA1 and PLA2 on the displacement arch crown beam were calculated. Based on the construction of the mixed model, the residual sequence variation regularity of typical measuring points was analyzed and predicted by the combination model. The analysis results showed that the forecasting results of the combined model were better than those of the statistical model, hybrid model and EEMD–PSO–ELM model, which validated the rationality and feasibility of the model. At the same time, the combined model had an excellent capability of non-linear information mining, modeling and prediction, and could provide new technical support for the analysis and prediction of dam deformation monitoring data.关键词：concrete arch dam;deformation monitoring;hybrid model;combined model
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发布时间：2024-01-10 - 摘要：The comprehensive assessment of severity degree of dam failure impact is an important part of dam risk evaluation and management. There are two major problems identified in the traditional comprehensive evaluation of dam break consequences: Constant weight set subjectively determined by human beings, and incompatibility between evaluation index value and evaluation grade standard. In order to solve the above-mentioned drawbacks, based on existing laws and regulations and industry norms, the life loss, economic loss, social impact and environmental impact are selected as comprehensive evaluation indexes of dam break consequences, considering the characteristics that the set pair analysis deals with the uncertainty of the system effectively and the advantage of extenics in dealing with the incompatibility problem, the variable weight set pair–extenics coupling model is established, in which the variable weight theory is used to modify the constant weight. In this model, the connection membership degree of extenics is determined according to the domain of extenics set divided by identity, difference and opposite of set pair analysis. Furthermore, the integrated connection membership degree of extenics is calculated combined with the variable weight, and is used to determine the evaluation grade according to the principle of the maximum membership. The application to the comprehensive evaluation of dam break consequences of five reservoirs in Jiangxi Province. The results show that: 1) In the comprehensive evaluation of the consequences of dam break of five reservoirs, the exponential excitation state variable weight vector motivates the poor evaluation indexes to a certain extent and increases their weight values, highlighting the status of the poor indexes in the comprehensive evaluation, avoiding the negative effects of the poor indexes being covered by the good indexes, and emphasizing their seriousness; 2) The comprehensive evaluation grades of dam break consequences of the five reservoirs are basically consistent with the evaluation grades calculated by other evaluation models, with the highest degree of dispersion and better discrimination, which shows good practicability and provides a new method for comprehensive evaluation of dam break consequences.关键词：dam break consequences;comprehensive evaluation;variable weight;set pair–extenics coupling
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发布时间：2024-01-10 - 摘要：The rapids abating hydraulic index generally refers to the combination of the maximum route flow velocity and gradient of a ship which can sail through the rapids by itself under the condition of rated load and rated main engine power. It is the critical flow condition to determine whether the ship can sail through the rapids by itself, and it is the reference basis for analyzing the effect of rapids regulation. This paper analyzes the defects of the existing methods to determine the rapids abating hydraulic index, and points out the shortcomings of the existing expressions of comprehensive rapids abating hydraulic index, such as unreasonable selection of key parameters, unclear relationship between influencing factors and main variables, etc. Based on the basic relationship between flow resistance and flow velocity, gradient resistance and gradient, and according to the basic principle of the balance between ship thrust and navigation resistance, from the perspective of overcoming the existing shortcomings of the calculation and expression of the rapids abating hydraulic index, a traditional expression and pre-estimation formula of dimensionless rapids abating hydraulic index were derived. Applying the test results of 500-ton ship at hydrostatic speed in Lancang River, the variation law between the ratio of actual propeller speed to the rated propeller speed with the advancing coefficient was obtained. When calculating the rapids abating hydraulic index, the propeller speed should not be taken as the rated speed. The results show that there is an obvious deviation between the flow resistance calculated by the Zvankov formula and the ship thrust. The correction curve of the resistance correction coefficient with the ship Froude number was plotted. It is pointed out that the calculation formula of Zvankov flow resistance needs to be properly modified according to the results of full-scale ship test. The rapids abating hydraulic indexes of various types of motor ships in Lancang River were analyzed and calculated, and the rationality of the traditional expression of dimensionless rapids abating hydraulic index were verified. It is proved that the dimensionless parabola is more appropriate to describe the relationship between flow velocity and gradient in the rapids abating hydraulic index. Based on the principle of dimensional analysis and through the numerical regression analysis of the rapids abating hydraulic indexes of various motor ships in Lancang River, the pre-estimation formula of dimensionless rapids abating hydraulic index was established, which can significantly improve the calculation efficiency of the rapids abating hydraulic index.关键词：rapids abating hydraulic index;dimensionless power-load ratio;full-scale ship test;propeller speed ratio;modified function;motor ship;pre-estimation formula
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发布时间：2024-01-10 - 摘要：Alkali-resistant glass fiber has good mechanical performance, economy and durability. By adding alkali-resistant glass fiber, cement-based composites can be well strengthened, which has a wide range of engineering application prospects. To study the compressive properties and the stress–strain relationship of alkali-resistant glass fiber engineered cementitious composites (ECC), 33 groups of high-performance cement-based material specimens were tested under axial load. The effects of fiber content, fiber length, and water-cement ratio on the compressive properties and stress–strain relationship of alkali-resistant glass fiber ECC were emphatically analyzed, and the calculation model for the stress–strain relationship of alkali-resistant glass fiber ECC was proposed. The results show that the crack resistance, mechanical property, and deformation capacity of cement-based materials can be significantly improved by adding alkali-resistant glass fiber under uniaxial compression. The improvement of compressive strength and deformation capacity of the alkali-resistant glass fiber ECC is related to the fiber content, fiber length, and water-cement ratio. The compressive strength and deformation capacity of alkali-resistant glass fiber ECC specimens roughly tend to increase with the increase of fiber content and length, but the compressive strength of specimens decreases due to the obvious “agglomeration” phenomenon when the fiber content is too much. The compressive strength of specimens is mainly affected by the water-cement ratio, and it exhibits smaller with a larger water-cement ratio. When the fiber mass content is 6.5%, the fiber length is 18 mm and the water-cement ratio is 0.32, the comprehensive mechanical properties of alkali-resistant glass fiber ECC are relatively better, and compared with the comparison specimens, the compressive strength and deformation capacity can be increased by 25.6% and 88.0%, respectively. The calculation results of the proposed stress–strain relationship model are in good agreement with the experimental values, which can be used to describe the whole process of compression failure of alkali-resistant glass fiber ECC.关键词：alkali-resistant glass fiber;engineered cementitious composite;stress-strain relationship;compressive strength
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发布时间：2024-01-10 -
Mechanical Properties and Modified Duncan–Chang Model of Ferronickel Slag–Clay–Cement Modified Soil AI导读
摘要：To study the mechanical properties of ferronickel slag–clay–cement (FNSCC) modified soil, the undrained triaxial compression tests of FNSCC modified soil under different ferronickel slag mixing ratios, moisture content and curing times were carried out. The stress-strain curve and secant elastic modulus of FNSCC modified soil samples under different working conditions were obtained, and the influence mechanism and failure mode of mechanical properties were analyzed. Based on the experimental results, the modified Duncan–Chang constitutive model suitable for FNSCC modified soil was established. The results show that the stress-strain curve of FNSCC modified soil has obvious strain softening characteristics. The peak strength first increases and then decreases with the increase of water content. The swelling failure of the sample with a water content of approximately 15 % is particularly obvious. The peak strength of FNSCC modified soil increases with the decrease of the ferronickel slag incorporation ratio. With the increase of the ferronickel slag incorporation ratio, the failure mode of specimens changed from bulging failure to shear failure. With the increase of curing time, the failure mode changes from a plastic failure such as bulging deformation to a brittle failure such as local tension crack. The secant elastic modulus of FNSCC modified soil decreases with the increase of axial strain. When the axial strain is less than 2%, the addition ratio of ferronickel slag, water content, and curing time have a great influence on the secant elastic modulus. When the axial strain is greater than 2%, each factor has little effect on the secant elastic modulus. The modified Duncan–Chang model can better reflect the strain softening phenomenon of FNSCC modified soil. The model parameters m, nand l are approximately linear with confining pressure. The model parameter m is most affected by the ratio of FNSCC modified soil, followed by the curing time, and the moisture content is the smallest. The curve calculated by the modified Duncan–Chang model is in good agreement with the measured curve, which verifies the rationality of the fitting parameters.关键词：ferronickel slag;triaxial test;strain softening;failure mode;modified Duncan–Chang model- 412
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发布时间：2024-01-10 -
Effects of Normal Loading and Unloading on the Post-grouting Sand–Concrete Interface Shear Behavior AI导读
摘要：The mechanical properties of the soil-structure interface have always been one of the key and hot issues in the field of geotechnical engineering, and revealing its mechanism is helpful to promote the understanding of the bearing characteristic of structures such as pile foundations and retaining walls. A total of 28 groups of large direct shear tests with the post-grouting sand–concrete interface were conducted under three different grout volumes and four kinds of loading and unloading conditions to analyze the interface mechanical properties and the distribution of shearing influence range. The test results show that grouting can gradually eliminate the difference between the interface’s initial shear modulus and shear stress due to the loading and unloading of the interface. The softening phenomenon doesn’t exist in the un-grouted interface, while the post-grouting interface exhibits softening and the softening occurs in the unloading interface shearing process with low applied normal stress. The grout cement improves the mechanical properties of the interface by increasing the equivalent cohesive force of the interface but has no significant effect on the equivalent internal friction angle of the interface. The improvement of the interface equivalent cohesive force on the loading interface is better than the unloading interface under the same grout volume. The distribution of interface shearing influence range under unloading conditions is slightly larger than that under the loading conditions. Regardless of the loading, unloading, and grouting conditions, the distribution of interface shearing influence range is positively correlated with the interface peak shear stress. Under the same applied normal stress, the mechanical properties of the unloading post-grouting interface were improved due to the formation of the grout bulb by compaction grouting to increase the roughness of the concrete plate, while the mechanical properties of the loading post-grouting interface were improved by penetration grouting to form the soil-cement mixture. The research results can provide guidance for the post-grouting of pile foundations in practical projects.关键词：interface;unloading;shear bands;mechanical properties;grouting- 407
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发布时间：2024-01-10 - 摘要：To avoid the brittle failure of welds at the intersection of the beam and column flanges under the action of earthquakes, a honeycomb replaceable plastic hinged beam-column joint was designed. The ABAQUS finite element simulations of low-cycle reciprocating loading and low-cycle reciprocating loading test were carried out on four frame specimen models of different honeycomb energy dissipation ring sizes based on this node. The finite element model of each frame specimen and the hysteresis curve, skeleton curve, stiffness degradation curve, ductility performance of each frame specimen were fully analyzed, and the normal thickness and radial thickness of the honeycomb energy dissipation ring were discussed. The results showed that the hysteretic curve of the honeycomb replaceable plastic hinge node frame was relatively full and had a good energy consumption capacity. Increasing the radial thickness of the honeycomb energy-consuming ring array in equal intervals could improve the energy consumption capacity and deformation ability of the honeycomb beam-column node frame after yield; When the normal thickness of the honeycomb energy-consuming ring array was increased from the thickness of the H-type steel beam web to 3 times the thickness of the H-type steel beam web, the energy consumption capacity of the honeycomb beam and column frame specimen was significantly improved. The failure position of the honeycomb energy-consuming unit in the honeycomb beam and column frame specimen test was almost completely consistent with the position with large stress distribution in the finite element model of the honeycomb beam and column frame specimen, which was in line with the actual situation. Compared with the seismic node of the traditional steel structure beam and column, the honeycomb replaceable plastic hinge beam and column node converted the brittle damage at the beam and column weld into the damage at a specific location on the beam, fully transferring the stress at the beam and column node weld, and the honeycomb replaceable plastic hinge node protects the beam and column node weld, which could effectively realize the plastic hinge outward transfer. The honeycomb replaceable plastic hinge beam and column node can effectively reduce the weld cracking phenomenon of the beam and column nodes, reduce the probability of weld cracking and collapse of steel structures under large earthquakes, easy modular factory processing, significantly improve construction efficiency, and facilitate the steering and threading of fire pipes, cables and other facilities.关键词：frame beam-column joints;plastic hinge;honeycomb energy consumption ring;energy dissipation capacity
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发布时间：2024-01-10 - 摘要：Dynamic disturbance promotes the development of internal cracks in the underground rock mass, and changes the effective stress, permeability, and porosity of rock mass. Therefore, the evolution law and mechanism of porosity, permeability, and effective stress coefficient (Biot’s coefficient) of tight granite under dynamic cyclic loading were studied. Firstly, a dynamic cyclic loading test considering different disturbance factors (axial static stress, force amplitude, frequency, and cycle number) was carried out for granite. Then, the porosity and permeability measurements were performed for the disturbed granite, and the cross-plotting method was used to calculate the Biot’s coefficient of the disturbed granite. The experimental results indicate that: 1) Dynamic cyclic loading promotes internal crack propagation in granite, leading to increases in pore volume and seepage channels, and degradations of effective stress. Thus, an increase in the Biot’s coefficient, permeability, and porosity was exhibited for the disturbed granite. 2) With the increase of the stress level, the changes in Biot’s coefficient, permeability, and porosity of the disturbed granite have obvious stress thresholds, i.e., 65%UCS~70%UCS, where their increasing rate increases rapidly after the threshold value are exceeded. As the frequency increases, the Biot’s coefficient, permeability, and porosity gradually decrease due to the decrease of creep cumulative damage, whilst an approximately linearly increasing change is presented with the increase of the number of cycles. 3) Prediction models for Biot’s coefficient and permeability are established based on the correlation analysis. The predictions are in good agreement with the experimental observations. The testing results in this context are likely to be helpful for understanding the effect of dynamic disturbance on the parameters such as porosity, permeability, and Biot’s coefficient of granite and could provide a reference for determining Biot’s coefficient and permeability of the granite stratum after dynamic disturbance.关键词：dynamic cycle loading;Biot’s coefficient;permeability;porosity;prediction model
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发布时间：2024-01-10 - 摘要：Under the action of wind, snow particles will drift and deposit, which will adversely affect the surrounding area of the structures. For adjacent opening structures, the distribution of wind-induced snow around the structure is more complicated, and is not explicitly included in any design code. This problem is addressed herein by performing wind tunnel tests. Taking the single roof structure with opening and the double opening roof structures as the research object, the wind tunnel tests on the distribution of wind-induced snow were carried out; the influence of the orientation of openings on the distribution of snow on the surface and the surrounding area of the single arched structure was analysed; the influence of structures spacing and relative angle on snow distribution between two models was also analysed. Based on wind tunnel test data, through the comparison of the fractal characteristics of particles in the whole area, the wind-induced snow drift was analyzed quantitatively, which is of random fluctuation in external chaotic motion. The following results have been obtained. The structure opening has a significant effect on the distribution of snow around the roof structure. The snow at the corners of the windward edge of the roof structure is completely eroded, resulting in a horseshoe-shaped vortex. The snow on the leeward side of the structure creeps into the form of ripples. The snow distribution is favorable when the hole is located on the other vertical sides of the test specimen. The wind-induced snow between two structures is not a simple superposition of the individual models. As the spacing between the buildings is reduced, the snow deposition between the two structures is increased. When the opening angle of the two models is 30°, the structural stability is less favorable. Through the analysis of the fractal characteristics of the particle coverage area, the following results are obtained. The structure opening has a significant effect on the distribution of snow around the arch structure than relative angle. The roughness of snow on the central axis and the longitudinal axis is the smallest when hole is located on the other vertical sides of the structure. When the opening angle is 60°, the particle roughness is the largest, whereas the local maximum snow depth coefficient of 60° is lower than 30°. Therefore, the above arrangement should be avoided in the design.关键词：opening arch structure;snow distribution;wind tunnel test;snow depth coefficient;fractal dimension
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发布时间：2024-01-10 - 摘要：Real-time reservoirs operation can be combined with effective hydrological forecast information, which is of significant guide for the trade-offs between the flood control and utilizable benefit. However, the use of hydrological forecast information faces unavoidable uncertainties. Therefore, the flood risk control analysis should be considered in the field of the real-time reservoir operation. A dynamic control model of multi-reservoir flood limited water levels (FLWLs) during flood seasons based on the two-stage flood risk analysis method is proposed to solve the problem that the length and accuracy of forecast period among reservoirs in the system do not match with each other. First, the two-stage flood risk analysis method evaluates the uncertainty of the flood forecasting by dividing the operation horizon into the forecast lead-time and the beyond-forecast time period. The risk within the forecast lead-time induced by the streamflow uncertainty is estimated by counting the frequency of failure numbers among all scenarios with the help of the scenario-based forecasts. The risk beyond the forecast time period caused by the possible high-water level at the end of the forecast period is determined using reservoir flood routing with the design flood hydrographs. A real-time model of multi-reservoir systems is then established by considering the two-stage flood risk analysis method, and the objective of this model is to maximize the hydropower benefit. The results show that: 1) the proposed two-stage flood risk analysis method can take into account the potential risks within and beyond the forecast time period; 2) the proposed dynamic control of the FLWLs in multi-reservoir systems can increase the total hydropower generation in summer flood season for the five-reservoir system of the Hanjiang River Basin by 0.23 billion kW·h in 2010 year without increasing the flood risk, and the dynamic optimal decision-making process of the multi-reservoir system’s flood storage can be obtained.关键词：two-stage analysis method;multi-reservoir;flood limited water level during flood seasons;flood risk;Hanjiang River basin
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发布时间：2024-01-10 - 摘要：In the western regions of China with high seismic risks, many pre-stressed concrete continuous rigid-frame bridges with high piers and long spans have been constructed. Generally, cantilever construction technology is used, but the construction period is long. The bridge may suffer earthquakes during construction. The possible seismic damage to the main beam and pier of the rigid-frame bridges in the cantilever construction stage was explored under the strong earthquake. Based on the Miaoziping bridge, which had undergone the Wenchuan earthquake, three structural systems, i.e. maximum cantilever T-frame, asymmetric single cantilever T-frame of side-span-closure, and continuous rigid-frame of the completed bridge, were established to simulate the transition process of cantilever construction from statically indeterminate to once statically indeterminate to multiple statically indeterminate. The strong motion records near the bridge site during the Wenchuan earthquake were selected as the inputs for time history analysis. Combined with the actual earthquake damage of Miaoziping bridge in the completion state, the main beam stress, and piers internal force of the three system structures were analyzed under the strong earthquake. Compared with the bridge completion stage, the top plate and web at the consolidation of piers and girder were also prone to cracking in the maximum cantilever stage under strong earthquakes, but it was not easy to crack in most other positions; In the side-closure-stage, the (principal) tension stress and (principal) compressive stress were also relatively larger in the top plates and bottom plates near the closing section of side-span, the web near the 1/5 to 2/5 area of the side span, and the top plates and bottom plates near consolidation pier-beam, which were also prone to cracking, but the mid-span was not easy cracking. In the two construction phases, although the longitudinal bending moment at the middle-high position of piers was more than twice that of the completed bridge stage, it was not easy to crack; the top and bottom of the main pier were easy to crack, which was consistent with the response of the completed bridge. It is recommended that the seismic importance coefficients of class A continuous rigid frame bridges be 0.76 during the construction period. The research results provide a reference for the construction of high pier and long-span rigid frame bridges with cantilever construction technology meeting earthquakes.关键词：large-span rigid-frame bridge with high piers;seismic response;box girder cracking;maximum cantilever construction state;piers cracking
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发布时间：2024-01-10 - 摘要：The dynamic characteristics of water and sediment in a meandering channel are more complex than that in a straight channel. The bed evolution and the characteristics of overbank floods in bend are affected by the changes of flood and sediment discharge. The laboratory experiment was carried out in a curved flume under several flow discharges and sediment supplies in this paper. The water surface elevation, bed topography, water level of bend and longitudinal velocities along the main channel and the floodplain were measured in detail, and the effects of flow discharges and sediment supplies on bed evolution and overbank floods in the meandering channel were discussed. The calculation results of Lan Yunchang formula, Zhang Hongwu formula and Mao Peiyu formula for the water surface superelevation of the curved channel were compared, Lanyunchang formula could better predict the water surface elevation of the curved reaches with stable bedform under different flow and sediment discharges. The sediment supply had little effect on bed evolution in bend with inbank flows, for that most of the sediment supply was deposited in the upstream straight reach or transported to the downstream reach and only a small amount of recharge sediment was deposited in the bend reach. More upstream sediment was transported to the curved reach and deposited by overbank flows. With the increase of sediment supply, the sediment deposition in the curved main channel increased, which however had little effect on the water level and flow velocity in bend. When the flood discharge increased, the water level in the bend and the flow velocity in the concave bank increased significantly. The results indicated that the flood discharge was the key factor affecting the water level in the bend and the flow velocity in floodplain, and the upstream sediment supply was the secondary influencing factor. The flow velocity in floodplain in the 30-60° of 90° bend reach was higher than that in the main channel and upstream reach. The maximum flow velocity in the floodplain occurred in section 50°, which could reach 1.3 times of the upstream flow velocity. The above results are of great significance for flood control and disaster reduction of meandering rivers.关键词：meandering channels;water surface superelevation;overbank floods;bed evolution
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发布时间：2024-01-10
HYDRAULIC & CIVIL ENGINEERING
- 摘要：To solve the problems of low penetration, serious wear and low rock-breaking efficiency during traditional disc cutter rock breaking under the geological conditions of hard rock, many new auxiliary rock breaking methods have been proposed, such as creating pre-cutting grooves on the rock through laser, water jet, and other non-contact rock-breaking methods to assist disc cutter rock breaking. To clarify the rock breaking mechanism of the disc cutter under the condition of the pre-cutting grooves, the particle discrete element method is used to establish two auxiliary rock breaking simulation models for the pre-cutting grooves at the side of the disc cutter (side-type) and in front of the disc cutter (front-type). The influences of the depth of the pre-cutting grooves and the cutter spacing on the propagation of rock-breaking cracks by the disc cutter are explored. The research results show that: 1) The pre-cutting grooves in the side-type auxiliary rock-breaking model mainly affect the expansion of cracks, and the lateral cracks propagate to the bottom of the pre-cutting grooves during the process of inducing rock breaking. The pre-cutting grooves in the front-type auxiliary rock-breaking model mainly affect the initiation of cracks, and only lateral cracks are generated at the early stage of penetration, and the lateral cracks are promoted to propagate to both sides; 2) The vertical force of the disc cutter and the number of cracks decreases with the increase of the depth of the pre-cutting grooves, while the vertical force of the disc cutter increases with the increase of the cutter spacing, and the number of cracks first increases and then decrease with the increase of the cutter spacing; 3) Under the same condition, the side-type auxiliary rock-breaking model is higher than that of the front-type auxiliary rock-breaking model, but the vertical force of the disc cutter in the front-type auxiliary rock-breaking model is much smaller than the vertical force of the disc cutter in the side-type auxiliary rock-breaking model. The auxiliary effect of the pre-cutting grooves can be fully utilized by further increasing the penetration of the disc cutter in the front-type auxiliary rock-breaking model; 4) When the penetration of the disc cutter is constant, the side-type auxiliary rock-breaking model is suitable for the case where the depth of the pre-cutting grooves is greater than the penetration of the disc cutter, and the front-type auxiliary rock-breaking model is suitable for the case where the depth of the pre-cutting grooves is less than the penetration of the disc cutter.关键词：pre-cutting grooves;crack extension;disc cutter;particle discrete element;rock fragmentation
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发布时间：2024-01-10 - 摘要：As an efficient, accurate and convenient flow measurement instrument, electromagnetic flowmeter is widely used in the measurement of conductive fluids such as industrial fluid measurement, oilfield drilling fluid measurement and blood measurement. Due to the influence of external disturbance and flow velocity distribution, the electromagnetic flowmeter still has the problem of low measurement accuracy in the process of flow measurement. Improving the structure of the electromagnetic flowmeter excitation coil is one of the important means to improve accuracy. In this paper, based on a new type of positive eight sides, the accuracy of electromagnetic flow measurement was improved with magnetic field coil. Firstly, based on the study of the optimization principle of the weight function, the theoretical model of the magnetic field of the regular octagonal coil was analyzed to obtain the optimization idea of the electromagnetic flowmeter based on the uniform magnetic field theory. Secondly, based on the finite element analysis software, a simulation model of the regular octagonal excitation coil electromagnetic flowmeter was established, and the optimal structural parameters of the regular octagonal excitation coil magnetic field distribution were determined. By comparing the weight function distribution of the circular and square coils under the same conditions, the advantages of the uniformity of the weight function distribution of the regular octagonal coil were proved. Finally, an experimental platform was built to verify the magnetic field test experiment and the fluid test experiment. The magnetic field test results showed that the magnetic induction intensity of the regular octagonal coil electromagnetic flowmeter can be maintained at the central area of the pipeline. About 2.063 mT, the overall magnetic induction intensity fluctuation range is within 0.11 mT, indicating that the regular octagonal coil magnetic field has good uniformity. The fluid test result showed that when the flow rate is 0.743~2.582 m/s, the single-point relative indication value The maximum error is only 0.950%, and the system repeatability error is below 1.034%. The optimized system improves the measurement accuracy, which has guiding significance for the subsequent design of the excitation coil of the electromagnetic flow meter.关键词：electromagnetic flowmeter;coil optimization;uniform magnetic field;weight function;finite element analysis
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发布时间：2024-01-10
MECHANICAL ENGINEERING
- 摘要：The coal dust disaster is serious in deep mining of coal mine. The use of nonionic surfactant can effectively improve the wettability of coal dust and inhibit the generation and diffusion of coal dust. In order to explore the wetting process and mechanism of different surfactants on coal dust surface, the effects of nonionic surfactants lauryl glucoside (APG) and Triton X–100 on the wettability of coal dust surface were studied by molecular dynamics simulation and experiment. Three coal–water interface adsorption system models were established based on benzene ring carbon skeleton structure. Analysis the adsorption equilibrium configurations and spatial distribution of the surfactant on surface of coal were calculated on the basis of the interaction energy between coal/surfactant/water and energy changes, looked at the two kinds of surfactants and the ability of water molecules to form hydrogen bond. The coal samples from three groups of coal seams in Pingdingshan mining area in Henan Province were tested, the experiments of sedimentation and contact angle were carried out, and the surface free energy composition of the coal samples was calculated. The simulation results were verified, the characteristics of aromatic hydrocarbon groups in the coal samples and the interaction mechanism between Triton X–100 and coal molecules were tested by Fourier infrared spectroscopy (FT–IR). The results showed that when the adsorption equilibrium state is reached, the non-ionic surfactant molecules are connected with each other through alkyl chains to form an aggregation state, which is distributed at the coal water interface and the water gas interface. Triton X–100 can promote the adsorption of water molecules on the coal surface by enhancing the interaction with water molecules, which has a great impact on the wettability of the coal surface. The indoor test results showed that the wetting effect of Triton X–100 on the coal surface is better than APG, and the effect is the best at the critical micelle concentration. The higher the content of aromatic hydrocarbons in coal dust, the better the adsorption of Triton X–100. The research results provided a theoretical support and guidance for scientific and efficient dust suppression in deep mining.关键词：nonionic surfactant;coal dust;wettability;molecular dynamics
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发布时间：2024-01-10 - 摘要：Sillenite bismuth ferrite (S-BFO) was prepared by a co-precipitation-low temperature hydrothermal technique. The catalytic performance of S-BFO was evaluated by activating peroxymonosulfate (PMS) to remove ciprofloxacin (CIP). The results showed that adding 0.675 mmol/L PMS and 1000 mg/L of catalyst at the condition of initial pH value (6.5±0.1) and reaction temperature (25±1)℃, the removal rate of CIP (5.0 mg/L) was reached 84.8%. Under the same reaction conditions, the degradation efficiency of S-BFO activated PMS for CIP was higher than persulfate (PS). The morphology and crystal structure of S-BFO were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The effects of PMS concentration and initial pH value on the degradation of CIP in S-BFO/PMS system were investigated. The application potential of S-BFO/PMS system in the treatment of pollutants under real water conditions was evaluated. The results of ROS quenching experiments indicated that 1O2 is the main ROS in the S-BFO/PMS system, rather than
$\cdot \mathrm{SO}_4^{-} $ 关键词：sillenite bismuth ferrite;peroxymonosulfate;ciprofloxacin;mechanism;products- 380
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发布时间：2024-01-10 - 摘要：Saccharin (SAC) is the earliest artificial sweetener applied as additive in food, beverage, medicine and forage. SAC is hardly digested by human body and other organisms, and discharged into the water environment mostly. Characterized with high detection frequency and concentration, outstanding persistence and toxicity risk, SAC has been recognized as an emerging organic contaminant. Focused on UV/H2O2 process, the degradation of SAC by pre-chlorine, ozonation and UV/H2O2 was compared from the aspect of degradation efficiency and kinetics. The influencing factors including oxidant dosage, UV radiation intensity, initial SAC concentration, the pH value of solution, water temperature, and common anions (
$\mathrm{Cl}^{-}, \mathrm{CO}_3^{2-}, \mathrm{NO}_3^{-}, \mathrm{SO}_4^{2-} $ $\mathrm{NO}_3^{-}>\mathrm{SO}_4^{2-}>\mathrm{CO}_3^{2-}>\mathrm{Cl}^{-} $ 关键词：UV/H2O2 combined progress;saccharin;drinking water treatment;oxidation degradation;water quality safety- 503
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发布时间：2024-01-10 - 摘要：To study the properties of Qtech T26 blast-mitigation polyurea (T26 polyurea) and the protective properties and fracture mechanism of T26 polyurea-protected reinforced concrete slabs under contact blast action, dynamic thermomechanical analysis and 10 kg trinitrotoluene (TNT) contact blast tests were carried out. The polymer master curve was fitted based on the Williams, Landel, Ferry equation and a scanning electron microscope was used to analyze the microscopic fracture morphology of typical areas on the blast face and back face of the coated reinforced concrete slab. The results showed that T26 polyurea is significantly influenced by frequency, confirming the strain rate sensitivity of T26 polyurea in terms of its thermomechanical properties. The loss factor of T26 polyurea remains above 0.24 when the external load frequency is greater than or equal to 1000 Hz, resulting in high energy absorption efficiency. The reinforced concrete slab with a 10 mm T26 polyurea coating was damaged by 10 kg TNT contact blast with the back blast surface coating intact and no fragments flying out. T26 polyurea on the blast face was not detached from the concrete, and the adhesion between T26 polyurea and concrete interface was quite good after surface treatment, which means that there was still favorable adhesion between the coating and concrete under the tensile wave generated by the explosion.The fracture mechanism of T26 polyurea under blast loading is characterized by high temperature mechanical property failure mechanism, coupled high temperature and impact loading fracture mechanism, high speed loading brittle fracture mechanism and tensile fracture mechanism. The area of maximum deformation of the backblast surface is the circular area on the outside of the longitudinal deformation area, the central area of the backblast surface is subjected to high strain rate loads during protection and a small amount of brittle damage occurs. T26 polyurea has achieved contact explosion with zero fragmentation protection, showing a great value for structural blast fragmentation protection in practical engineering.关键词：polyurea;blast-mitigation protection;time-temperature superposition;fracture mechanism
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发布时间：2024-01-10
CHEMICAL ENGINEERING & MATERIAL ENGINEERING
- 摘要：Aiming at the problems of low brightness and blurred details in images captured under low light, an image enhancement algorithm based on gradient sparsity and multi-scale variational constraint was proposed by analyzing the defects of traditional Retinex theory. Firstly, the input image was transformed from RGB space to HSV space, and the luminance component was extracted to decouple three channels. Then, according to the gradient global significance of zero norm, a new relative total variation regular term was defined. After that, the luminance component was punished in HSV space, and a variational model with gradient sparsity was constructed to constrain the brightness channel. By expanding the control factors to multiple scales, a multi-scale variational constraint was formed, which improves the accuracy of illumination estimation and makes it more in line with the illumination distribution characteristics. According to the Retinex theory, areflection map corresponding to brightness channel was obtained. Then, the rough details, medium details and fine details of the image were extracted by using different illumination results corresponding to constraints in different scales of brightness channel, and the details of the reflection map was enhanced by multi-scale detail weighting. Finally, the illumination map after Gamma correction was recombined with the enhanced reflection ma, and the color space conversion was carried out to obtain the output enhanced image. Experimental comparisons show that the enhanced images of the proposed algorithm visually have richer colors richness and lower color difference level, and keep the naturalness well. Compared with the original images, the performance of mean value, average gradient and information entropy have been greatly improved. Compared with the existing advanced algorithms, the average quantitative index of the proposed algorithm achieves a better effect on the enhanced images of different types of low-light images with higher computational efficiency.关键词：image enhancement;HSV space;sparse gradient;multi-scale variational model;luminance constraints
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发布时间：2024-01-10 - 摘要：In order to effectively solve the defects of boundary distortion, artifacts and training instability when repairing complex background and high-resolution images, an image inpainting algorithm based on dual-generation adversarial network and multi-scale arbiter was proposed. Firstly, the damaged image was inputted to the content prediction network based on the dilated convolution layer, in which the reconstruction loss and the global judge based on the generated confrontation loss were adopted as the standard to perform the rough repair. Subsequently, the rough result was fed into the detail restoration network containing a hollow convolution layer and a contextual attention layer, whose outputs were decoded, deconvolved and sent to a three-scale discriminator. The proposed algorithm was trained and tested on the public image data sets. Finally, the network parameters were optimized by using three different scales of anti-loss functions to capture the multi-scale edge information of damaged area and generate reasonable and realistic texture details. The proposed algorithm was evaluated by the restoration experiments, dual network restoration comparison, high-resolution restoration comparison, target removal experiment, ablation experiment and objective experiment. The experimental results show that the proposed algorithm can generate reasonable structure and clear texture details when repairing images with complex backgrounds. The dual network structure is superior over single network structure. When repairing high-resolution images, the texture granularity obtained is better than that of the comparison algorithms. When the proposed algorithm is applied to high-resolution target removal, the results with clear and reasonable structure and fine texture can be obtained. Ablation experiments verify the effectiveness of the proposed modules. The indicators obtained by the proposed algorithm, i.e. peak signal-to-noise ratio, structural similarity, average error and average error are better than that of the state-of-the-art methods. In summary, the proposed algorithm can combine the overall semantics of the image, enhance the repair accuracy of image details, and effectively avoid structural texture disorder, pixel overlap, boundary distortion.关键词：image inpainting;dual-generation adversarial network;multi-scale discriminator;reconstruction loss;generation adversarial loss
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发布时间：2024-01-10 - 摘要：A segmentation network of Tiny cracks (TCS-Net) is proposed to solve the problems of small cracks with few pixels, low contrast between cracks and background, much interferences from similar textures, and uneven illumination. TCS-Net has a coding-decoding structure similar to that of U-Net network. The soft Pooling was used in down-sampling process to preserve the basic features of original images while maintaining the amplification of high-response features, thus reducing information loss and preserving the details and location of crack edges. In the up-sampling process, a semantic compensation module combining channel attention and spatial attention was added at the decoding end to fuse the features of each layer at the coding end, which could enhance the multi-scale details of cracks. In view of the classification problem of unbalanced data in crack segmentation task, in order to avoid the training process being dominated by most classes (background pixels),the binary cross entropy loss and Dice coefficient were combined by TCS-Net model as the objective loss function to solve the problem of training instability caused by attention tendency of single loss. It can also optimize performance indicators such as accuracy, crossover ratio and recall rate. The proposed fracture segmentation model was tested on a real containment image. Experimental results show that, compared with the existing mainstream semantic segmentation models, TCS-Net fracture segmentation model improves the intersection over union ratio index by 5%~9% and recall ratio index by 9%~13%, which demonstrates that the model achieves higher detection rate and detection accuracy. The proposed TCS-Net can be effectively applied to the fine crack segmentation task under the conditions of serious imbalance between target and background, complex background with many disturbances.关键词：crack segmentation;attention mechanism;fully convolution neural networks
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发布时间：2024-01-10 - 摘要：In recent years, deep learning-based methods have shown excellent performance in the field of image restoration. However, most deep networks are structured based on experience, and less consideration is given to fusion with existing traditional algorithms, therefore these networks arepoorly interpretable. To address this problem, an image restoration algorithm based on wavelet domain ADMM deep networkwasproposed. Firstly, a wavelet transform is introduced to the data term as well as the prior term simultaneously, an image recovery model under wavelet domain was proposed. Consequently the image recovery problem was transformed from spatial domain into wavelet domain, and a new image degradation model and recovery cost function were constructed. Then, in order to effectively reduce the difficulty of the optimal solution, the ADMM algorithm was introduced to further decompose it into a more manageable restoration subproblem and a denoising subproblem, and obtain the best estimate of the wavelet domain image through continuous optimization. Finally, the specific form of the solution based on the above optimization process guides the construction of a deep convolutional neural network to achieve end-to-end image recovery. The perceptual field and spatial feature mappingsizeof this networkis increased and decreased respectivelysince the image processing was executed in the wavelet domain. Not only does it achieve better performance, but also significantly reduces the complexity of operations and increases the processing speed. The proposed network was applied to image deblurring and image denoising tasks to verify the recovery performance on Set10, BSD68 and Urban100 datasets. The relevant experimental results show that the proposed algorithm achieves better recovery results for both deblurring and denoising tasks, with an increase of 0.08~0.18 dB in PSNR values while the resultant images retain more detailed information, thus outperforming the comparison methods in both quantitative and qualitative results.关键词：image restoration;wavelet transform;ADMM;convolutional neural network
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发布时间：2024-01-10
INFORMATION ENGINEERING
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