Abstract: Among heavy metals which contaminate soil, mercury has caused the attention of environmentalists because of its properties of wide spreading and high toxicity. Moreover, along with the development of modern industry, a great amount of mercury has been discharged into soil. This not only poses great threat on environmental security, but also puts forward urgent requirements for soil remediation. In combination with the research status of soil remediation, the origin and main species of mercury in contaminated soil are introduced. Remediation methods such as soil washing, soil stabilization/solidification, heat treatment, electrokinetic remediation, nanotechnology and biological techniques are systematically reviewed. The development prospect is put forward as a result, providing effective reference for environmentalists.
Abstract: In top coal caving mining, the state of top coal and overburden strata changes from continuous media to discontinuous and loose aggregate media. It is difficult to theoretically describe the transition and action of mining induced pressure in discrete top coal and fractured overlaying strata. Based on the photoelastic experiment principle, the network structure and the evolution characteristics of force chains in discrete top coal and discontinuous overlaying key strata are investigated during fully mechanized top coal caving mining by employing photoelastic test equipment that allows biaxial loading and bilateral particle flowing. The study shows that overburden load in discontinuous strata displays a complicated network composed by weak and strong force chains. Top coal caving mining destroys the equilibrium of the initial force chain network structure, and a composed beam-arch force chain structure forms in top coal and overlaying strata, where the overburden load is transformed into the front coal seam in the form of strong force chains. With mining face advancing and top coal caving, the beam-arch force chain network in overlaying strata develops, and a larger force chain arch structure forms. Bending, breaking and instable movement of the key strata give rise to an inverse moving of the force chain arching foot and a compaction process of the strong force chain network. The distribution density and intensity of force chains evidently increase, resulting in strong pressure phenomena taking place in the mining face. Under the biaxial loading condition, the effect of the beam-arch force chain structure becomes much evident in the earth. The entire structure of the force chain arch displays perfectly, the structure of the strong force chain network becomes denser, and due to breaking and instability of the key stratum, the pressure phenomenon of the force chain arch in front of the mining face and coal seam manifests much pronounced.
Abstract: Drawing scheduling is the most important process in block cave mining. The traditional analysis process of drawing scheduling is random and inefficient without system scientific analysis. A mixed integer programming method was proposed in this paper to solve the optimization problem of drawing scheduling. Taking the ore reserve quantity, ore grade, drawing index and production scheduling index as the constraints and the grade fluctuation as the objective function, a drawing scheduling optimization model was built based on the mixed integer programming method. It was solved with the CPLEX solver invoked by model language that was programmed with YALMIP in MATLAB for a certain copper mine. Finally, the optimal arrangement scheme of drawing scheduling was obtained. It is proved that this model is scientific and feasible, the grade fluctuation reduces by 18%, and compared with the traditional, this drawing scheduling saves costs by meeting the desired production quantity more closely and reducing the employee time spent on preparing schedules.
Abstract: It is a universal phenomenon for all the mines that paste-filling material arrives at stope at different initial temperatures. The strength properties and stress-strain relation of paste at different initial temperatures have effect on the mining-filling cycle and the dilution of adjacent stope mining. A series of uniaxial compressive strength tests were performed on hardened paste with initial temperatures of 2, 20, 35 and 50℃ to obtain the stress-strain evolution curves at different initial temperatures. The damage constitutive models of paste at different initial temperatures were established on the basis of theoretical derivation and experimental results. A temperature-time coupling damage constitutive model was further proposed according to parameter regression of the established models. Finally, the temperature-time coupling damage constitutive model was embed into the solid mechanics module of Comsol software, which is for uniaxial compressive experiment simulation. The simulation results show good accordance with the experimental stress-strain curves, verifying the reliability of the proposed constitutive model.
Abstract: Aiming at the requirement of high speed and precision in blast furnace fault diagnosis systems, a new strategy based on global optimization least-squares support vector machines (LS-SVM) was proposed to solve this problem. Firstly, the variable metric discrete particle swarm optimization algorithm was employed to optimize the feature selection and LS-SVM parameters. Secondly, the feature vector was compressed by kernel principal component analysis. Finally, the heuristic error correcting output codes were constructed on the basis of Fisher linear discriminate rate. In the fault diagnosis scheme, fewer LS-SVM classifiers were applied through meaningful partitions and recombination of fault training samples. Simulation results show that the proposed fault diagnosis method can not only improve the fault detection accurate rate, but also enhance the timeliness of the entire system.
Abstract: The viscosity of solid-containing slags can be calculated using the Roscoe equation combined with the calculation functions of multi-component & multi-phase equilibria and pure-liquid slag's viscosity in FactSage software. An FeO-SiO2-Fe3O4-CaO-Al2O3-MgO system used in copper smelting was studied in this paper. Firstly, the parameters of the Roscoe equation were fitted using the measured viscosities of analogous slag in the literature, and the accuracy of viscosity calculated by the method for this slag system was verified additionally. Then, the effect of slag components' contents on the equilibrium phase-composition and viscosity was investigated based on the calculation model. Accordingly, the reasonable proportions of components in the slag were obtained. When the mass fractions of slag components are FeO 40%~60%, SiO2 25%~40%, Fe3O4 0%~15%, CaO 0%~10%, Al2O3 0%~8%, and MgO 0%~4%, the molten slag with good liquidity and fewer solids can be obtained in the smelting process.
Abstract: The suspension and mixing characteristics of high-content solid particles were experimentally studied in a tank stirred with an Intermig impeller.An optical fiber technology was adopted to measure the bottom and axial solid concentration under different conditions of impeller diameter,rotational speed and impeller-bottom distance,and the critical suspension speed and power consumption were also investigated at the same time.The results show that the Intermig impeller has good axial mixing performance in the solid-liquid stirred system with high solid content.High impeller diameter and low impeller-bottom distance could improve the solid suspension and uniform distribution with low power consumption.By analyzing and fitting the experimental results,the bottom solid uniformity is calculated by Froude number with the equation of Q=0.58Fr-0.35 and the power number is calculated by Reynolds number with the equation of NP=2.1Re-0.2.
Abstract: Three kinds of primary carbonitrides were classified in H13 hot work die steel through experiment,including (Vx,Mo1-x)(Cy,N1-y) rich in V and C,(Tix,V1-x)(Cy,N1-y) rich in Ti and N,and (Tix,V1-x)(Cy,N1-y) rich in V and C,some having a core in the center.The element variation and Gibbs energy of the carbonitrides during H13 solidification were analyzed based on the solidification segregation model and the two-sublattice model,taking the interaction between components into account as well as the alloying element content and C/N ratio of the three types of primary carbonitrides.It is found that Tiand N-rich (Tix,V1-x)(Cy,N1-y) forms when the solid fraction reaches 0.9,while the other Vand C-rich (Tix,V1-x)(Cy,N1-y) generates when the solid fraction is greater than 0.96 during solidification.The critical solid fraction for the formation of these two (Tix,V1-x)(Cy,N1-y) decreases with increasing Ti and N contents soluted in the carbonitrides.The formation of (Vx,Mo1-x)(Cy,N1-y) during solidification can be affected by the x value.The critical solid fraction decreases as less vanadium is soluted in (Vx,Mo1-x)(Cy,N1-y),leading to larger size carbonitrides demonstrated by the models,which fit well with experimental data.The influence of oxides and carbonitrides on heterogeneous nucleation for the carbonitrides was also researched through lattice misfitting analysis.
Abstract: Microstructure transformation of Fe-13Cr-5Ni martensitic stainless steel during continuous heating was investigated by optical microscopy, transmission electronic microscopy, X-ray diffraction, and microhardness testing. Experimental results show that at the heating rate of 10℃·s-1,there is an austenite memory phenomenon after heating to the austenite phase region and quenching to room temperature. Austenite tends to nucleate and grow at lath boundaries in an acicular shape, which has Kurdjumov-Sachs (K-S) orientation relationships with the parent phase. Furthermore, heating to different temperatures in the dual-phase region and quenching to room temperature, the amount of retained austenite in samples firstly increases, gets to the peak at 650℃, and then decreases with the increasing of annealing temperature. This trend is coincident with the trend of micro-hardness of the same samples.
Abstract: As a part of heat treatment processes, solution treatment and aging treatment have a great influence on the mechanical properties of 6016 aluminum alloy. In this article, solution temperature, solution time, aging temperature and aging time were taken as parameters to design a heat treatment scheme by central composite design (CCD). At room temperature, the yield strength, elongation, and Vickers hardness of specimens were measured by mechanical testing. The second-generation non-dominated sorting genetic algorithm (NSGA-Ⅱ) solves the shortcomings of the first-generation algorithm, such as the difficulty in parameter selection and low efficiency. In this study, the response surface model derived was used as the objective function to perform the multi-objective optimization by means of NSGA-Ⅱ. After calculation, the Pareto solutions were obtained to filtrate out the solution with comprehensive performance, and then, to acquire the corresponding parameters of the solution and aging process.
Abstract: SiC-carbon/carbon (C/C) composites were prepared by doping nano-SiC, and the influence of nano-SiC on the graphitization degree of carbon material was investigated by X-ray diffraction and high-resolution transmission electron microscopy (HRTEM). The nano-SiC can promote the graphitization degree of carbon material. An apparent graphitization structure around the nano SiC was observed by HRTEM, and the carbon material has a higher graphitization degree when it is closer to the nano-SiC. The oxidation resistance of SiC-C/C composites was also studied through static oxidation experiment. It is found that the anti-oxidation performance of C/C composites increases with increasing nano-SiC content, and the nano-SiC forms a uniform SiO2 protective layer at high temperature, which could cover the carbon material surface to prevent the material from oxidation. In addition, the SiO2 protective layer is thicker and has a higher oxidation resistance property when the matrix material contains more nano-SiC.
Abstract: Contact strain measurement is a tool for studying the high temperature mechanical behavior of components and materials. The measurement precision is the key point of the high temperature strain measurement field, where creep is the main factor that affects the measurement precision at high temperature. In this paper, the creep characteristics of strain gauges were analyzed according to the material mechanism of creep by a high temperature strain measurement system. A grating creep model was obtained from the creep rule and experiment measurement results. Based on the grating creep model, the influence factors of strain gauge creep output were studied by the finite element model. Finally, a compensation model of high temperature strain creep was established to improve this high temperature strain measurement precision, and it was validated by experimental data.
Abstract: The combustion experiment of an existing double P type radiant tube and the corresponding CFD simulation were performed in this paper. By contrast, the maximum error of NOx concentration between numerical calculation and experimental data is 3.6%, and the deviation of the other parameters is less than 1%. Then the concept of air classification was applied to the double P type radiation tube to design a belt pipe nozzle hierarchical gas-fired radiant tube. The flow and heat transfer characteristics were studied. The results show that when air into the branch pipe accounts for 25% of the total amount of air, the radiant tube wall temperature and thermal efficiency are the highest. When the content of gas into the branch is 20%, the radiation tube wall temperature realizes the minimization and the uniformity of wall temperature is the best. When both air and gas at the same air-fuel ratio are introduced into the branch pipe, and the volume of air and fuel gas is 25% of the total amount of gas, the gas temperature distribution in the radiant tube is the most uniform. When the volume of air and fuel gas into the branch pipe increases from 5% to 35%, the wall surface temperature decreases first and then increases slowly; when it is 20%, the radiation tube wall temperature reaches a minimum.
Abstract: The consistency of five different 18650 cells used in electric vehicles both at the initial and aged states was evaluated by electrochemical test and statistical analysis. The effects of current, temperature and voltage on the cell consistency were examined. The results show that, to ensure a reasonable level of the cell consistency, the current rates during the charging and discharging processes should be less than 0.3C and 0.5C, respectively, and the operating temperature should be higher than 0℃. In addition, the cell sorting process is crucial to control the cell consistency. An additional descriptor, the k value, representing the decreasing rate of open circuit voltage during calendar test, should be involved in the cell sorting.
Abstract: Iron and steel enterprises are facing difficult problems such as increasing inventory, excess capacity, and poor profitability. It is urgent to solve them through the development of green and intelligent manufacturing technology for iron and steel enterprises to address the current critical situation. Based on the analysis of the characteristics of manufacturing processes in iron and steel enterprises, the materials flow (with a core of iron element flow) and its corresponding energy flow network, as well as the deficiencies of the synergy between materials flow and energy flow in existing enterprise information systems, synergetic optimization methods between materials flow and energy flow in the iron and steel manufacturing process were investigated in this paper. It revealed that the coupling between materials flow and energy flow should be planned, designed and implemented for both the unit manufacturing equipment and the overall manufacturing process. The synergetic optimization can be achieved by three approaches, including perfecting information monitoring, synergizing planning and synergizing scheduling. Based on the analysis, a schematic resolution on top of the existing information system architecture was proposed towards the optimization of production, resource and energy. The synergetic optimization between materials flow and energy flow in the iron and steel manufacturing process can be realized by improving the corresponding functions of the existing manufacturing execution system, enterprise resource planning and energy management system, facilitated by a newly proposed information subsystem handling the synergetic optimization with the support of digitization and modelling of the relevant information in materials flow and energy flow.
Abstract: The particle swarm algorithm is often trapped in a local optimum due to poor diversity, resulting in a premature stagnation phenomenon. In order to overcome this shortcoming, an immune particle swarm optimization algorithm based on the adaptive search strategy was proposed in this paper. Firstly, the concentration mechanism was improved. Secondly, in order to make full use of the resources of the particle population, the number of particles of sub-populations was controlled by the maximum concentration of particles. Finally, the inferior sub-populations were vaccinated, and the maximum concentration of particles was used to control the search range of the vaccine, so the population degradation was avoided, and the convergence accuracy and the global search ability of the algorithm were improved. Simulation results show the effectiveness and superiority of the proposed algorithm in solving the complex function optimization problems.
Abstract: In order to research the effect of cycling loading and unloading rates on the deformation and permeability of sandstone, cycling loading and unloading tests were performed with a self-made thermal-hydrological-mechanical coupling test system for gas-infiltrated coal and rock. The results show that the axial deformation of sandstone 駐著 1 is larger in the initial cycle and tends to be stable with cycling, but the influence of unloading rate is minimal. The loading deformation modulus and unloading deformation modulus both increase and the rising speed becomes slow with the increase of the number of cycles. In the same cycle, the unloading deformation modulus is bigger than the loading deformation modulus, and their difference gradually decreases with the test proceeding. Meanwhile, the difference of permeability variations in loading and unloading phases decreases with the increasing of unloading rate. Starting from the fifth cycle, the shape of permeability curves is "∞". The evolution rule of permeability can be characterized by using the change regularity of axial strain. The variation of axial strain △ε1i is influenced by unloading rate v2i and loading stress σmaxi, which both promote the development of strain. The relationship of them can be characterized with a power function.
Abstract: Rock-block collapse has been a hot issue in the study of geological hazards for many years, and it is difficult to prevent because of its sudden disintegration, which is a serious threaten to human life and property safety. Rock-block collapse is caused by dynamic failure derived from system instability, so it can be more effective to apply vibration characteristic parameters in damage assessment and early warning. By using a laser Doppler vibrometer, the cohesion damage of control fissure was analyzed by natural vibration frequency in the paper. Based on the modified limit equilibrium model, the safety factor of the block with a deteriorating structural plane was calculated by the frequency, which decreased from 1.17 to 1.04, in accordance with the reality. The results show that the natural vibration frequency can effectively identify the unstable rock cumulative damage and provide objective data for reasonable determination of the cohesion. The laser Doppler vibrometer technology based on natural vibration frequency can satisfy cumulative damage evaluation of unstable rocks. It will play a significant role in engineering applications in the future.
Abstract: Since traditional instruments cannot apply stress in soil-water characteristic curve tests, we develop a suction controlled triaxial apparatus, by which soil-water characteristic curve tests are performed under different stress states. Further, the influence of stress state on the pore characteristics is discussed. The results show that both consolidation pressure and matrix suction can lead to the irreversible contraction deformation of soil. The soil under a larger consolidation pressure has a denser structure and a less void, leading to a smaller pore size and quantity. So it results in a worse permeability. Accordingly, it shows a better water retentivity. Air can hardly enter and water can hardly drain out, which give rise to a larger air entry value and a smaller slope of the soil-water characteristic curve. The soil-water characteristic curve of a compacted soil mainly depends upon current void ratio, not directly upon stress state. The influence of consolidation pressure on the soil-water characteristic curve is embodied in pore distribution properties. For similar pore distribution properties, the soil-water characteristic curve should be similar regardless of stress state. A larger consolidation pressure causes a less hysteresis.
Abstract: Open System for Earthquake Engineering Simulation (Abbrev. OpenSees) was used to do some exploratory numerical research on the cross laminated timber (CLT) infill wall-steel frame system. Numerical analysis was performed including the mechanical performance of the CLT infill wall-steel frame under monotonic and cyclic loading, cooperative working performance between the CLT panel and steel frame, and the influence of the number of bracket connections on the mechanical performance of the structure. The results are presented as follows:the lateral stiffness and bearing capacity of the steel frame can be strengthened by the CLT infill wall; flexible connections show a better performance of energy dissipation; the gap setting is not only used to postpone the cracking time of the wall, but also beneficial to develop the energy dissipation and deformation of connections; the number of connections has great effect on the lateral resistance of the structure, and furthermore, various stiffness and energy dissipation capacities of the structure can be designed by adjusting the number and space of connections.
Monthly, started in 1955 Supervising institution：Ministry of Education Sponsoring Institution：University of Science and Technology Beijing Editorial office：Editorial Department of Chinese Journal of Engineering Publisher：Science Press Chairperson：Ren-shu Yang Editor-in-Chief：Ai-xiang Wu ISSN 2095-9389CN 2095-9389
