Abstract: Multi-robot formation control is one of the most important research directions in the field of robotics. In this paper, the definition and characteristics of multi-robot formation control were given and several traditional formation control methods were introduced, such as leader-follower method, behavior-based method, artificial potential method, and virtual structure method, and their advantages and disadvantages were stated. The era in which these traditional control methods are applied is termed as "Former Formation Control Era" (FFCE). Following the development of multi-agent theory, the multi-agent technology has become popular and is considered as an efficient solution to the multi-robot system formation control problem, and it has generated several favorable results. The era in which this technology is adopted is termed the "Post Formation Control Era" (PFCE). In this era, the multi-agent theory has gained much attention following the developments in the communication technology, computation technology, and artificial intelligence technology. The FFCE emphasizes that multiple robots are able to accomplish complex tasks that are unachievable by a single robot, while forming a desired formation, which improves the efficiency of a required task as well as shorten the completion time of the task. However, the PFCE emphasizes much more cost-effectiveness, synchronization, and coordination than the FFCE. Meanwhile, the PFCE does not pay much attention to the task assignment for each individual, but assigns each sub-task autonomously to each individual on the basis of simple rules, and there exists no "irreplaceable" individual. Finally, this paper presented the basic steps for solving the formation control problem using multi-agent technologies.
Abstract: Lithium-ion batteries, now widely used in many fields, have a long cycle life, low self-discharge rate, high capacity and energy efficiency, no memory effect, and are environment-friendly. While enhancing everyday life, this new energy source comes with a number of serious safety risks. Due to the wide variety of battery materials used, the performance and safety features of these batteries also vary greatly. Capacity degradation and thermal runaway occur under extreme conditions such as high temperatures and over-charging, thus limiting their further promotion and use. With the large-scale application of the lithium-ion battery, the number of safety-related incidents have shown an increasing trend each year. To date, research on the safety of this battery has made great progress, especially with respect to thermal decomposition of the electrolyte and electrode materials. This paper reviews the factors influencing the thermal stability of the electrolyte, the thermal runaway process as it relates to the product composition, and the monomer and battery-pack safety and fire-extinguishing measures. It is found that the thermal stability of the electrolyte is affected by both the lithium salt and the organic solvent. When the internal temperature of the battery reaches about 120℃, an exothermic reaction begins to appear. Thermal runaway will spontaneously proceed with the continuous accumulation of heat, and at the same time, hydrogen and alkane gas products are produced that have combustion and explosion risks. Compared with carbon dioxide and dry powder fire extinguishing agents, the fire-extinguishing effect of heptafluoropropane and water is better. Lastly, the paper considers the application prospects of the lithium-ion battery and describes the directions of future research, including the thermal runaway process under the different abuse conditions, the product formation mechanism of the thermal runaway, the development of a new electrolyte, and the search for a high-efficiency fire-extinguishing medium.
Abstract: Ore particle segregation commonly occurs during dump leaching because of the differences of particle size, surface roughness, and relative density. The presence of a fine interlayer is key factor of the uneven erosion of the ore surface during leaching, which seriously limits the bioleaching efficiency of copper extraction. To explore the interaction effects of fine interlayers on leaching behavior, the surface morphology and passivation occurrence during the leaching process was studied, where coarse ore particles (4 mm < d < 6 mm) and fine ore particles (2 mm < d < 4 mm) were selected, and a bioleaching experiment of secondary copper sulfide with fine interlayers located at different positions was carried out. Analysis were carried out using computed tomography (CT) scanning technology and field-emission scanning electron microscopy-energy dispersive spectrometry (FE SEM-EDS) technology in the macro, meso, and micro scales. As a result, the macro leaching dynamics, meso-scale ore particle agglomeration, and micro surface morphology characteristics as well as passivation were studied. The results show that fine interlayer leads to a lower copper extraction rate, which is lower than when the fine interlayers are mixed with homogeneous coarse granular medium. The effects of fine interlayers on ore extraction depend on their location. In the experiment, the fine interlayers located at the top results in the highest copper extraction rate (71.3%) after leaching for 60 days; the degrees of evolution of the ore surface pore structure are different at different heights inside the same fine interlayers. The copper extraction rate reaches its peak after leaching for 60 days. The ore particle agglomerations and passivation phenomenon are significant. Passivation layers, such as of jarosite, polysulfide, extracellular polymeric substances, sulfur film, are formed on the ore surface.
Abstract: Paste backfilling technology, by which tailings paste is transported into underground stopes, does not only relieve the environmental pressure caused by increasing volumes of tailings ponds, but also averts the potential dangers of underground goaf. However, because of the complex characteristics of some mine tailings, it is challenging to adopt the paste backfilling technology for tailings disposal, as the pipeline transportation of highly muddy pastes is difficult because of the poor flowability caused by high yield stress. To improve the flowability of tailings pastes, a rheological experimental setup have been designed to investigate the mechanism of how pumping agents affect the rheological properties of a highly muddy paste. The results show that a significant linear relationship exists between the tailings paste concentration and corresponding yield stress, with different pumping agent dosages. Further analysis reveals a significant exponential relationship between pumping agent dosage and slope (or intercept) of the linear function. Finally, the prediction function for the yield stress is proposed, considering the pumping agent dosage and tailings paste concentration. This can characterize how the pumping agent influences the rheological properties of a highly muddy paste and enable precise forecasting of the pumping agent dosage and management of slurry flowability. Based on the prediction model, the effect mechanism of pumping agent on a highly muddy tailings paste rheology is proposed. Based on the analysis of the images observed from an environmental scanning electron microscope (ESEM), it is found that the presence of pumping agent causes the destruction of flocs in tailings pastes. Meanwhile, the optimal dosage of pumping agent suggested by experiments is about 1%. Furthermore, the pumping agent accounts for floc size shrinkage and consequently yield stress reduction. Moreover, increasing the distance between broken flocs weakens their interactions and slows down the flocs destruction rate. The observations agree with the theoretical analysis results.
Abstract: Low winter temperatures are a widespread concern for mines in China that use cemented paste backfill (CPB). A low environmental temperature has a significant effect on the CPB temperature, which can affect its hydration rate and early strength. Using paste material from the Jiashi Copper Mine (JCM) in winter, this paper prepared a total of 129 specimens and investigated the effect on these specimens of different amounts of water and cement, the method for adding cement, the dosage of the pumping agent, and the amount of aggregate used. The prepared specimens had a temperature range of 8-12℃ and were cured in a standard curing box with a temperature of 20℃ and humidity of 95%. After curing periods of 3, 7, and 28 d, the paper performed uniaxial compressive strength (UCS) tests on the specimens. The test results show that the UCS values of the 7 d and 28 d specimens are 1.44-fold and 2.4-fold those of the 3 d specimens, respectively. The 7 d UCS evolution accords with a 2℃ hydration progress, which leads to gradual strength development. However, the 28 d UCS evolution accords with a 20℃ hydration progress. This indicates that the temperature of the paste has a slight effect on its long-term strength. Based on the effect of low temperature on the strength of the 7 d paste, the paper proposed the addition of high-temperature water to the paste backfill system. Using a practical paste ratio at the JCM, the paper calculated a theoretical high-temperature water flow of 6-8 m3·h-1. When the water temperature ranges between 70-100℃, the temperature of the paste can be improved from 6℃ to 15-19℃. The paper recommends the use of an industrial water heater for providing the hot water, with a conservative power output of 400 kW. The use of this water heater will yield a cost improvement of 2.9 RMB per cube of filling material.
Abstract: There are abundant manganese mineral resources in Chengkou and Xiushang County, Chongqing City, as well as a phosphorus content that is over the national standard; thus, the mass percent of phosphorous in Si-Mn alloys produced from manganese ores is over 1%. This can easily result in "cold brittleness" and reduce the steel quality when the alloys are used for deoxidation and alloying in steelmaking. Therefore, it is important to research on the dephosphorization of Si-Mn alloy. Dephosphorization of a high-phosphorus Si-Mn alloy was studied under dephosphorizing agents of Si-Ca alloy, rare earth silicon, and Al-based dephosphorizer in a silicon molybdenum furnace of 1400℃. In the experiment, CaO-CaF2 (mass ratio of 25:75) was used as a covering slag, and the ratio of slag-metal is 0.2:1. The phosphorous content in the Si-Mn alloy after dephosphorizatoin was detected by an inductively coupled plasma (ICP) spectrometer, and the phase composition of the slag was analyzed by X-ray diffractometry (XRD). The effects of different dephosphorizing agents and their dephosphorization rates were analyzed. The results show that the dephosphorization rate increases with dephosphorizer content. For Al-based dephosphorizer, the dephosphorization effect is optimum at 8% dephosphorizer content, whereby the phosphorus content in the Si-Mn alloy is reduced to 0.21%, which meets the national standard (≤ 0.25%), and the dephosphorization rate reaches 78%. The efficiency of Si-Ca alloy is lower; the dephosphorization rate is 47% even when the alloy content reaches 10%. The effect of rare earth silicon is the least; the dephosphorization rate is 22% when the content reaches 10%. Thus, the Al-based dephosphorizer is the best dephosphorization agent under the present experimental conditions.
Abstract: The micro nonmetallic inclusion and oxygen content in steel significantly affect its performance, and removing the inclusion involves a difficult process. A nitrogen absorption and release method has been developed with which nonmetallic inclusions and T[O] were efficiently removed from bearing steel. However, the inclusions in bearing steel are highly different from those in Si-Mn deoxidized steel, and the effect of the nitrogen absorption and release method on the Si-Mn deoxidized steel remains unclear. Based on this, a thermal experiment was carried out in this study to investigate the removal of nonmetallic inclusions from Si-Mn deoxidized steel by nitrogen absorption and release method, where SWRH82B hot rolled wire coil was used as the experimental steel, and five groups of increasing nitrogen pressure (0.02, 0.035, 0.05, 0.065 and 0.08 MPa) were set up. The results show that for all groups, the T[O] and T[N] in the steel reduce to below 1×10-5 and 5×10-6, respectively, after the molten steel is subjected to 20 min of increasing nitrogen and 30 min of vacuum treatment. The lowest T[O] and T[N] in the steel is 4×10-6 and 2×10-6, respectively, and the inclusion removal rates for all the groups are more than 40%. The T[O] removal rates for all the groups are more than 78%.This result proves that nitrogen absorption and release method is efficient in removing inclusions and T[O] in Si-Mn deoxidized steel. Furthermore, the removal rate of inclusion and T[O] in the steel increases with the nitrogen pressure. When the nitrogen pressure is 0.08 MPa, the removal rates of T[O] and the inclusions are 89.2% and 87.4%, respectively. Theoretical analysis shows that the nucleation rate, number, and density of bubble in molten steel increase with pressure, the efficiency of the inclusions removal can be promoted.
Abstract: High-angle grain boundaries and martensite/austenite (M/A) constituents are two critical factors that contribute to low impact toughness in metals. The generation mechanism of the high-angle grain boundaries is closely related to the crystallography of the transformed products, which are transformed by prior austenite. Austenite undergoes phase transformation when cooled to ambient temperature and cannot be retained. During coherent phase transformation, variant pairs, from which the high-angle grain boundaries originate, are transformed. Variant selection is a common phenomenon in coherent phase transformation. The properties of the prior austenite grain, such as its shape, size, orientation, texture, and particularity of formation, will affect the subsequent phase transformation dramatically, and the variant pairs are accordingly introduced. However, it is impossible to evaluate this effect when the prior austenite orientation is unclear. Hence, the orientation needs to be reconstructed. In this article, a simple method of reconstructing the prior austenite orientation during coherent phase transformation is proposed by employing the {110}α stereographic projection on the basis of electron backscatter diffraction (EBSD) measurements. Retained austenite is not necessary when applying this methodology. The results show that the prior austenite orientation is well reconstructed with superior precision of below 2°. This is especially applicable when strong variant selection occurs or when reconstructing a tiny part of the prior austenite grain. The specific unknown orientation relationship (OR) between prior austenite and ferrite has a little effect on the reconstruction process, averting complicated calculations of this specific unknown OR. It is still possible to reconstruct the austenite orientation when the actual OR is not accessible. Moreover, it can be employed to all the coherently transformed products that maintain an OR from K-S OR to N-W OR to the prior austenite grain. A specific example in which this method is adopted is given, and the austenizing behavior is studied. At higher austenization temperatures, a special type of austenite grain, i.e, an austenite twin, is transformed. This is difficult to occur at lower austenization temperatures, implying that the austenite twin formation is closely correlated to the austenization temperature. The formation mechanism of austenite twin and its effect on the following phase transformation remains unclear; thus, much emphasis should be placed on it.
Abstract: The shape of a hot rolled strip is a main indicator of its quality, and camber is a significant defect arising from problems in shape quality. Differences in the bearing clearance of the two sides of a rough mill can cause a crossed roller, which leads an imbalance in the rolling force and, thereby, camber. A camber defect adversely affects product quality and the stability of the subsequent finish-rolling production process. The simulation and control of asymmetric shapes is one of the hottest topics in the field of modern strip rolling. To solve this problem and enhance the quality and precision of the strips produced, exploring and analyzing the problem of camber in hot rough rolling is necessary. This study investigated the generation of camber in the 1580 mm roughing mill R2 of a steel plant during the hot-continuous-rolling process. This paper established a three-dimensional elastic-plastic dynamic coupling model of the rolls and slab using the finite element (FE) analysis software ABAQUS/Explicit. In addition, the paper used a data analysis method based on the node-set coordinate output. By balancing the relationship between computational precision and efficiency, the study found the FE model to run stably. Using the proposed model, the paper systematically investigated the influence of cross position and angle on the camber, slab wedge, and amount of rolling force under different conditions. Based on the FE results, the paper then characterized the influence law for the occurrence of a cross roll with respect to bearing clearance and slab camber. Numerical examples demonstrate that the relationship between the camber and cross-angle position is linear, and that between the slab camber and clearance is a quadratic curve.
Abstract: In the harsh marine environment, the traditional aluminum alloy coating has difficulty meeting the requirements of use, which can affect equipment performance. The traditional coating and a modified graphene composite were prepared with a base of 7A52 aluminum alloy, which has excellent anticorrosive properties. Then, the electrochemical noise was recorded to monitor the initial corrosion process of the modified graphene coating in 3.5% NaCl solution. By time-domain, statistical time-domain, Fourier transform, and frequency-domain analyses, the corrosion process was studied in coatings with different graphene-composite contents. Based on the change in the electrochemical noise parameters of the coating corrosion conditions, the graphene content that exhibited the best anti-corrosion performance was determined. The results reveal that for different levels of modified graphene, the electrochemical noise of the coatings differs at certain times. When the graphene coating is corroded, the current potential change process experiences a fluctuation range from small to large and the fluctuation range decreases. It is found that the AC impedance of the coating in the high-frequency region increases with increased modified graphene content. After adding modified graphene to the coating, the corrosion potential of the coating shifts significantly, the corrosion current density decreases, and the corrosion resistance of the coating is significantly increased. After immersion in 3.5% NaCl solution, pits of various severities appear on the aluminum alloy surface, whereas only a small number of pits appear on a 1% graphene coating. By combining the AC impedance results, the polarization curves, and the corrosion morphology of the aluminum alloy surface, the best coating corrosion resistance was observed to occur when the graphene content was 1%.
Abstract: The basic challenges in the preparation and application of particle-reinforced metal matrix composites are the difficulty in achieving a uniform and stable mixing and the weak bonds between the particles and matrix. At present, these challenges are mainly tackled by making the particles into precursor beforehand and adopting the wetting treatment technologies, respectively. However, these measures can result in lower production efficiency and higher preparation costs. Based on the molten metal die forging process, an innovation technology termed "mixing by the molten metal and cohering by high pressures" was proposed to prepare the metal matrix composites reinforced with ceramic particles without a precursor or wetting them beforehand. Using this technique, a kind of ZTA particles-reinforced KmTBCr26 cast iron wear resistant composite with a good compound effect had been prepared, and the microstructure, hardness, and impact property of the ZTA/KmTBCr26 composite was studied. The study reveals that the particle distribution in the ZTA/KmTBCr26 composite is generally uniform, and the interfacial bonding between ceramic particle and KmTBCr26 matrix is of micromechanical interlocking. The results of impact tests show that the impact toughness of the composites is significantly lower than that of the single metal, and the fracture morphology indicates that the fracture of the composites extends through the ceramic particle instead of the matrix. No particle detachment is observed, which indicates a high bonding strength between the particles and matrix. Furthermore, the dry friction and wear properties of the ZTA/KmTBCr26 composite and KmTBCr26 cast iron were investigated. The results show that the wear resistance of the composite is 1.82 times that of the KmTBCr26 cast iron when the load is lower, while the wear resistance of the composite increased by 3.3 times under the higher load.
Abstract: Based on the requirements of blast furnace burden surface monitoring imaging, this study investigated the measurement of the radar cross section (RCS) of the blast furnace radar target. For the first time, a highly precise automatic measurement of the RCS of a blast furnace stock line in a microwave anechoic chamber was realized. Based on this, the characteristics of the blast furnace radar target were studied. The RCS typical distribution of coke and sinter particles and the scattering directivity pattern of the blast furnace stock line at 10 GHz were measured based on a comparative method, and the measured dynamic range was -10-15 dB. Problems such as the intensity difference of radar echo signals between the coke and sinter distribution in the industrial field were explored and analyzed by the RCS measurement and imaging diagnosis. The stock line shape of coke and sinter on the industrial site, known as platform plus funnel type, was simulated, and bulk materials were placed and scaled down. Synthetic aperture radar (SAR) imaging verification was performed on the shrinkage ratio model of the typical stock line, and the reasons for imaging loss and error were deeply analyzed. At a low frequency, the imaging of the funnel section is not satisfactory; hence the test frequency band should be improved. A blast furnace stock line made of standard balls was used to analyze the imaging errors. The absolute errors in the azimuth and range directions are 1.2% and 5.8%, respectively, and the azimuth measurement error in the anechoic chamber does not exceed ±0.01 m.
Abstract: In industrial production, bearings are widely used in rotating machinery. Bearing fault diagnosis plays an important role in preventing disasters and protecting lives and properties. Because weak bearing fault characteristics are often submerged in a noise background, the difficulty of extracting the bearing fault feature information is increased. Therefore, this paper proposed a method which combined the general scale transformation theory with the adaptive stochastic resonance in a periodical potential system. This method was used to detect the fault characteristics of the bearing rolling element in the noise background. In the proposed method, general scale transformation was first used to satisfy the condition of small parameters in the stochastic resonance. Then the random particle swarm optimization algorithm was applied to choose the optimal system parameters to affect the adaptive stochastic resonance. Meanwhile, an improved signal-to-noise ratio (ISNR) was set as the evaluation index in the adaptive stochastic resonance. After being processed and optimized by the adaptive stochastic resonance based on the general scale transformation method, the experimental weak signal with a rolling element bearing failure under the noise background could be effectively extracted. In addition, the effect of processing fault signals by the adaptive stochastic resonance in the periodical potential system was compared with the adaptive stochastic resonance method in a bistable system based on the general scale transformation. The results show that the adaptive stochastic resonance in the periodical potential system increases the signal-to-noise ratio better than the adaptive stochastic resonance in the bistable system. Moreover, the adaptive stochastic resonance in the periodical potential system involves fewer iterations, and the computation time is shorter than that of the adaptive stochastic resonance in the bistable system. This indicates that the proposed method of diagnosing bearing element fault based on the general scale transformation and the adaptive stochastic resonance in a periodical potential system is superior. Especially in engineering systems, a large amount of data and extensive computation time is required for fault diagnosis. Because of the early fault warning system achieved by the proposed method, fault diagnosis is more efficient and unnecessary losses are reduced. Therefore, the proposed method can serve as a reference in improving the efficiency of mechanical equipment fault diagnosis in engineering systems.
Abstract: Before digital images become available to consumers, they usually undergo several stages of processing, which include acquisition, compression, transmission, and presentation. Unfortunately, each stage introduces certain types of distortion, such as white noise, Gaussian blur, and compression distortion, which may degrade the perceptual quality of the final image. Therefore, it is important to design an effective and robust image quality assessment method to automatically evaluate distortions in image quality. Image quality assessment is widely used in image compression, image deblur, image enhancement, and other image processing domains. In general, no-reference image quality assessment methods have profound practical significance and broad application value; hence, it remains the main focus of many researchers. At present, many image quality assessment methods extract features and predict image quality using single edge detection operations such as gradient or local binary pattern. However, it is difficult for a single edge detection operation to represent the whole perceptual quality of distorted images, and hence, their predictions may not be satisfactory. To eliminate the limitations of single edge detection operation, this paper proposes a new no-reference image quality assessment method based on a multiple edge detection operation. The paper considers first-order and second-order derivative information and utilize their similarity to predict image quality. The proposed method first converted color images to grayscale images, and calculated the gradient magnitude (GM), relative gradient magnitude (RM), relative gradient orientation (RO), and Laplacian of Gaussian (LOG) of the grayscale images. The feature vectors extracted from the maps were divided into two parts, where one part was the standard deviation of RO, and the second part utilized conditional entropy to quantify the similarity and relationship of GM, RM, and LOG. The images were naturally multiscale, and distortions affected the image structures across scales. Hence, all features at two scales were extracted:the original image scale and at a reduced resolution (low-pass filtered and down sampled by a factor of 2). Lastly, an AdaBoost back-propagation network was used to train and establish a regression model to predict the image quality. The experiment of the proposed method was performed on two public databases, LIVE and TID2008, and the results show that the score predicted by this new method has a good correlation with the subjective quality score. Moreover, this method can reflect perceptual quality properly using only ten-dimensional feature vectors, and the performance of correlation coefficient can exceed some state-of-the-art no-reference image quality assessment algorithms.
Abstract: Beam-to-column connection plays a key role in structure designs, especially for steel structures, as the seismic performance the connection directly affects the safety, reliability, utilization, and economic indicators of steel structures. During the Northbridge earthquake in the USA and Hyogoken Nanbu (Kobe) earthquake in Japan, several steel structures collapsed because of unexpected brittle fractures around the beam-to-column connections. The economic loss encountered in the Kobe earthquake is estimated to be about 10 trillion JPY (approximately 580 billion RMB). Moreover, it caused approximately 6500 civilian fatalities and destroyed tens of thousands of houses in Kobe and the surrounding cities. The corner beam-to-column connection suffered from complicated seismic loadings during the earthquakes. Corner beam-to-column connections are the weak points in an aseismic design, and under biaxial lateral loadings, they induce large torsional deformations. In this study, five specimens were tested under pseudo-static loadings to investigate the influence of loading paths on the seismic behavior of corner or side beam-to-column connections. The main experimental parameters were the loading paths (uniaxial loading, biaxial symmetrical loading, and biaxial center symmetrical loading) and width-to-thickness ratio of the steel column (D/t=22 and 33). The main seismic characteristics of specimens were studied, such as the hysteretic behavior, stiffness degradation, and energy dissipation. The results indicate that the loading paths affect the stiffness and bearing capacities of the specimens. The bearing capacities of the specimens under the biaxial center symmetrical loading are 20% lower than those under the uniaxial loading, while the bearing capacities of the specimens under the biaxial symmetrical loading are equal to those under the uniaxial loading. The width-to-thickness ratio of the square steel column is one of the key factors that affect the bearing capacities of the specimens. The bearing capacities gradually decrease with an increase in the width-to-thickness ratio. All the specimens exhibit a good energy dissipation capacity, and the hysteretic curves are stable and numerous. The equivalent viscous damping coefficients of all the specimens are around 0.2.
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
