Abstract: The cemented paste backfill (CPB), a current research hotspot, is a safe, green, and efficient technical means to reduce cost and meet the requirements of solid waste treatment. The paste slurry is prepared from a variety of filling materials and later transported to the underground mining area through a pipeline; thus, it must meet the flow and transportation requirements. Additionally, the rheological properties of CPB significantly affect the flowability and transportability of the filling slurry, a key index to evaluate the performance of the filling slurry. However, due to the multiscale and high concentration of CPB, its rheological behavior is highly complex, and the existing rheological model is insufficient in describing the rheological behavior of the paste under shearing. The paste slurry will show a solid–fluid transition phenomenon at an ultralow shear rate, shear thinning at a steady-state shear, and shear thickening at a considerably high shear rate; the common rheological model can only be applied to the range of action of steady-state shear. Thus, the mechanism of the rheological behavior must be studied to identify the causes of the rheological model failure and discuss the fine mechanical mechanism between particles during shear. Conclusively, the interaction between the tailing particles and the tailing sand particles and water varying the overall friction coefficient of the paste with the application of shear rate is the root cause of the complex rheological behavior exhibited by CPB. By analyzing the limitations of the traditional paste rheological model, the domestic and international literature studies are reviewed based on the surface properties of particles and the interaction between the particles and water. First, the reasons for the formation of the hydrogen bond network structure on the surface of tailing particles and their influencing factors were analyzed. Next, the origin and variation of the microscopic friction force between particles under shearing influenced by the hydrogen bond network structure were described. The internal mechanisms of the rheological behaviors, including shear banding, shear thinning, and shear thickening, were analyzed, and the friction dissipation law of the paste rheological behavior with the changing shear rate was summarized. It is proposed that the accurate measurement of macroscopic friction is the key to analyzing its rheological behavior in the paste system, and clarification of the fine mechanical mechanism of complex rheological behavior promotes the development of metal ore paste rheology from macroscopic rheology to mesoscopic causation.
Abstract: This study explores the full-field strain and dynamic fracture characteristics of a linear shaped charge under different initiation positions. The explosion dynamic caustic line experiment system is employed to examine the characteristics of the blast crack propagation of the linear shaped charge at different initiation positions and capture the dynamic information of the crack tip propagation speed and stress intensity factor. Furthermore, the digital image correlation method was used to show the strain evolution law of the linear shaped charge at different initiation positions, as well as the medium strain response of the charge near the explosion zone caused due to detonation transmission. The results show that in end-initiation, the wing crack length at the initiation point is the smallest, and the wing crack propagation length increases with the detonation propagation of the explosive. Conversely, in center-initiation, the propagation length of the wing cracks at the center is less than those at both ends. The propagation length of the wing cracks in the noninitiation end is the longest for end-initiation, where the velocities of the wing crack initiation and propagation are minimum. For center-initiation, the wing crack initiation and propagation velocities are the smallest, i.e., irrespective of the initiation position, the wing crack initiation and propagation velocities at the initiation point are lower than that at other locations. Based on the dynamic stress intensity factor analysis, irrespective of the initiation position, the center wing cracks are type Ⅰ cracks with the largest crack toughness, the stress intensity factor value is the maximum, and the wing cracks at the ends are type Ⅰ?Ⅱ composite cracks dominated by type Ⅱ. Based on the full-field strain analysis of the linear shaped charge, at end-initiation, the range of tension and strain action is mainly along the direction of explosive transmission, and the tension and strain action area at the noninitiation end is larger than that at the initiation end. The corresponding position of the maximum compressive strain is 0.67–0.83 times the charge length from the initiation point. When the center detonates, the action process of tension and compression strain propagates symmetrically from the center to both ends of the initiation, and the strain at the center is the largest. The compressive stress concentration at the end occurs under both initiation modes because the explosive transmission is the process of energy accumulation; thus, the effect of the explosive explosion on the medium grows increasingly stronger along the direction of explosive transmission.
Abstract: To investigate the acoustic emission (AE) characteristics of tensile fracture in the rock, an AE experiment of granite, marble, and red sandstone using an expanding agent for fracture generation was designed. Characteristic parameters of AE signals and the P-wave first-motion polarity were analyzed in detail. Results show that the cumulative count and energy of the AE signal increase exponentially when a macroscopic failure occurs in all three kinds of rock samples. The centroid frequency of AE signals of granite, marble, and red sandstone samples mainly concentrates in the range of 100–300 kHz, 200–400 kHz, and 200–500 kHz, respectively, and the proportion of high centroid frequency events in the red sandstone test is the highest, followed by marble and granite. As the AE signal’s centroid frequency in all three kinds of rocks changed with the time of expander action, more AE signals with a low centroid frequency appeared in the late loading period, indicating the increase of large-scale fracture in the late loading period. Meanwhile, RA values of AE signals of the three rock samples mainly concentrate between 0 and 1.9. AF values of marble and red sandstone mainly concentrate between 50 kHz and 100 kHz, and AF values of granite mainly concentrate between 200 kHz and 250 kHz. Distribution characteristics of the RA?AF indicate that the tensile failure dominates the cracking process in such an experiment. The P-wave first-motion polarity analysis method was used to obtain the first-motion polarity of AE signals of each rock sample. Results showed that there are 77.82%, 79.5%, and 87.42% T-type crackles in granite, marble, and red sandstone, respectively. Moreover, granite and marble exhibit almost no S-type crackle, while red sandstone samples have 9.93% S-type crackles. Both RA?AF distribution and P-wave first-motion polarity analyses are statistical analysis methods, which can qualitatively analyze the type of rock fracture.
Abstract: The vacuum degassing process plays an important role in the production of high cleanliness steel, so it is extremely urgent to determine the different reaction sites of liquid steel under reduced pressure and how to reflect the overall degassing efficiency through reasonable parameters. Based on a similar kinetic mechanism, this paper experimentally simulated the vacuum degassing process of molten steel using the release process of dissolved oxygen (DO) in water. Under a vacuum pressure condition, a large number of small bubbles were observed to precipitate from the vessel’s internal wall or the surface of the oxygen probe. This phenomenon corresponds well to the internal degassing reaction assumption made in previous degassing mathematical models. To verify the existence of internal degassing sites, mechanical stirring was introduced to analyze and calculate the degassing rate at the bath surface and internal site. Results showed that the degassing rate at the bath surface is very low throughout the whole process and the bubbles that precipitated from internal degassing sites greatly improve the DO removal rate. Especially at a pressure of 25 kPa, the degassing rate is about ten times that at the bath surface. It was also confirmed that the internal degassing reaction mainly occurs in the initial stage of degassing, particularly in the range of high DO concentration. Moreover, the removal of DO is a first-order reaction process, and its volumetric mass transfer coefficient k · A · V?1 is constant. Therefore, the removal process of DO can be used to simulate the degassing behavior of molten steel. To describe the effect of vacuum pressure and argon flow rate on k · A · V?1, the correlation between log (k · A · V?1) and log ε was determined by introducing the concept of stirring power density ε. Finally, the correlation was compared with the results from previous simulation studies.
Abstract: In combination with the digital and green development needs of the foundry industry, this article proposes a digital patternless freezing casting method. In this method, mixed water green sand particles are frozen and transformed to a certain strength in a low-temperature environment, which are then directly cut through a sand mold CAD three-dimensional model. Pouring to obtain castings with dimensional accuracy that meets the requirements, this is a new technology, new process, and new method in the field of casting. With the fast development of the rapid and sub-rapid solidification technology of metals, the nonequilibrium solidification theory of liquid–solid transformation during the preparation of metals and alloy materials has been developed by leaps and bounds. Using some special nonequilibrium solidification techniques to prepare metal parts, and to make metal parts with a special structure that traditional casting does not have, can improve the materials’ properties and structures. The nonequilibrium solidification mechanism based on the freezing casting technology is not yet clear. Based on the nonequilibrium solidification process of the freezing casting principle, a higher cooling rate will considerably affect the heat transfer and mass transfer behavior of casting during solidification, which will then considerably affect the alloy micro component distribution and fracture morphology, ultimately affecting the service performance of the alloy material. Based on the digital precision forming technology of patternless frozen casting, this paper realized the rapid forming of the frozen sand mold. Frozen casting flat castings were obtained by pouring the A356 high-temperature aluminum alloy. The distribution of trace elements in frozen and resin sand castings was characterized by electron probe microanalysis, and the fracture morphology of frozen and resin sand castings was analyzed. Results show that the solubility of the Si element in the aluminum matrix phase of freeze casting is significantly higher than that of resin sand casting. In addition, the distribution of the Mg element in freeze casting is more uniform than that in resin sand casting, and there are more segregation areas of the Mg element composition in resin sand casting specimens. The fracture morphology of freeze-cast specimens is a mixed fracture mode of toughness and brittleness. Meanwhile, the fracture morphology of resin sand casting specimens has a cleavage step failure morphology and rectangular tear structure morphology, and the alloy tends to exhibit a brittle fracture.
Abstract: The water beam mark is a common problem in slab heating, which causes quality defects on strip steel. In hot strip rolling, the heating quality of the slab considerably influences the rolling stability and quality of the finished strip. The water beam mark caused by the heating process and equipment is a common defect in the slab heating. A slab water beam imprint has a great influence on the control precision of the rolling force and thickness of the finished strip. Presently, recognizing the water beam mark is difficult and the workload in the industry is heavy. To solve these problems, this study proposed a recognition algorithm of a hot-rolled strip steel water beam mark based on a semisupervised learning model of an improved denoising autoencoder (DAE). Based on the DAE, random noise was added to each layer of the coding layer, a classification layer was added after a hidden layer, and fake labels were added to the training data. Decoding and classification training are conducted simultaneously. These methods result in the model becoming semisupervised. In this study, we extract the temperature difference of the strip temperature data at the outlet of the roughing mill and use it to train the model. Experimental results showed that the algorithm can accurately recognize the water beam mark of strip steel. The classification accuracy of the proposed model is 5.0%–10.0% higher than other mainstream models when the number of tag proportions is small. When the number of tag proportions is large, the accuracy of the proposed model reaches up to 93.8%. According to the result, the production efficiency can be improved using this model.
Abstract: Chemical resistance sensors stand out among many gas sensing methods because of their simple structure, low-cost fabrication, facile integration with various electronic devices, and quick analysis; therefore, presently, they are widely used for gas sensing. Chemical resistance sensing is achieved by changing the electronic distribution of the sensing material. Among these chemical resistance sensors, the selective adsorption of gases and the corresponding detection of sensitive materials in the resistance sensor used for detecting volatile organic compounds (VOCs) are very important. In addition, measures to ensure the selectivity of detection are necessary. Therefore, the specific surface area, pore size and functional groups of sensing materials, and some auxiliary materials determine the response and sensitivity of the sensor. Metal-organic framework materials (MOFs) are a new class of organic-inorganic hybrid materials. It is characterized by rich porosity, high specific surface area, structural diversity, and chemical stability, making it exhibit good potential in the gas storage and separation field, catalysis field, and chemical sensing field. Some MOF derivatives, in addition to their properties, such as good electrical conductivity, have characteristics of MOF, such as high specific surface area. Therefore, MOF and its derivatives have been widely studied and applied as sensitive materials and filter media in gas sensors. Some MOF and MOF derivatives can be used as sensitive materials for chemical resistance sensors to improve the response to VOCs, and MOF membranes can also be used for their selective adsorption as a filter layer to improve the selectivity of sensors to the target gas. In this paper, the basic principle of chemical resistance sensors, the role, principle, and application of MOF and MOF derivatives in the detection of volatile organic compounds by resistance sensors are summarized, and the development prospect and challenges are discussed.
Abstract: Graphene oxide/titanium dioxide (GO–TiO2) composites were prepared via a one-step hydrothermal synthesis method using graphene oxide and tetrabutyl titanate as raw materials. The effects of different mass ratios of tetrabutyl titanate on the microstructure and properties of the GO–TiO2 composites were studied. The microscopic morphology of these composites was observed through a scanning electron microscope, and the phase composition and structure were analyzed using X-ray diffraction, infrared spectroscopy, and Raman spectroscopy. The light absorption performance and thermal stability of the composites were analyzed via ultraviolet–visible spectroscopy and a thermal gravimetric analyzer. As the content of tetrabutyl titanate increases, the TiO2 generation increases; material surface area climbs up and then declines; surface defects decline and then climb up; absorption peak in the visible light range strengthens and then weakens; and degree of recombination climbs up and then weakens. When the content of tetrabutyl titanate exceeded 100 mL, the dispersibility of TiO2 in the GO–TiO2 composites became poor, thereby reducing the light absorption performance and thermal stability of the composites. When the GO was 320 mg and tetrabutyl titanate was 100 mL in the precursor solution, the obtained composite material exhibited superior surface properties, optical properties, and thermal stability. TiO2 was uniformly dispersed on the surface of the composite material. The composite material exhibited a high absorption intensity of visible light, high recombination, few surface defects, and an ID/IG ratio of 0.91. Characteristic peaks at 1573 and 1428 cm?1 were the strongest. The absorption edge of TiO2 in the composite was bathochromic shifted to the visible light range, and the absorption peak was significantly enhanced in the visible light range of 440–800 nm. The composite material exhibited good anticorrosion and antifouling abilities. The thermal stability of the composite was 84.89% higher than that of GO at 800°C. These composites have great prospects for development in the fields of anticorrosion and antifouling.
Abstract: Reinforcement corrosion is one of the most serious problems limiting the durability of concrete structures. Corrosion inhibitors are used as admixtures in the fresh concrete to prolong the service life of the concrete structure, and calcium nitrite is the most extensively tested admixed inhibitor. However, the premature deactivation and overdose of conventional inhibitors limit their application, and one strategy to solve this problem is to use smart inhibitors with controlled release, long-term effects, and targeting performance. In this paper, a smart inhibitor of LDH-NO2 was prepared based on the Zn?Al layered double hydroxide as a shell and the nitrite ions as a core. The first principles calculation, physical detection techniques, immersion test, and electrochemical methods were performed to study the micro- and macro-controlled release mechanism and inhibition property of LDH-NO2. The results show that: (1) The nitrites in LDH-NO2 can release spontaneously in the chloride-contaminated or/and carbonated concrete. The release process reaches equilibrium in 1 h, repairing the corrosion damage of steel reinforcement in time. (2) The LDH-NO2 is much more sensitive in the carbonated concrete than chloride-included concrete, reflected in the greater energy of ion-exchange reaction and the more stable product with thinner interlayer with stronger interlayer force. (3) In the simulated pore solution of chloride-contaminated and carbonated concrete, the corrosion inhibition efficiency of 5 g·L?1 LDH-NO2 on carbon steel reinforcement exceeds 99%, reducing the corrosion rate of carbon steel by one order of magnitude. (4) Compared with the conventional NaNO2 inhibitor, LDH-NO2 effectively prolongs the corrosion initiation time while decreasing the corrosion area of carbon steel reinforcement. (5) The corrosion inhibition performance of LDH-NO2 is mainly due to the release of $ {\text{NO}}_2^ - $from LDH rather than the corrosive ion adsorption on LDH. Therefore, the smart inhibitor of LDH-NO2 shows excellent corrosion inhibition and a long-term effect in the reinforced concrete environment.
Abstract: One of the most aggressive organic acids for stainless steel is formic acid. In particular, the corrosion of 316L stainless steel in aqueous formic acid solutions at high temperatures is directly related to its safe operation and production efficiency. To better understand the passivation-activation transition behavior of 316L stainless steel in aqueous formic acid solutions, an investigation was conducted at the formic acid mass fractions of 0.5%, 5%, 15%, and 30% at 90 ℃. Laboratory immersion tests with a period of 1200 hours were performed at each formic acid mass fraction to document the corrosion rates and the corrosion morphologies of 316L stainless steel, and electrochemical tests, including open circuit potentials and anodic polarization curves, were conducted in the presence of dissolved oxygen using conventionally divided glass cells with three electrodes. The influences of formic acid mass fraction on corrosion rate, corrosion morphology, open circuit potential, primary passivation potential, critical current density, passive current density, and passive film breakdown potential were analyzed. In addition, the effects of H+ and HCOO? ions on anodic reactions occurring in the active region, the active-passive transition region, and the passive region were discussed. Due to the stability of the passive state, the laboratory immersion tests showed that at the formic acid mass fractions of 0.5%, 5%, and 15%, 316L stainless steel suffered from slight corrosion, and thus no measurable weight losses could be acquired. However, in the 30% aqueous formic acid solution, the corrosion rate of 316L stainless steel reached 1.2 × 10?3 mm·a?1, which indicated that 316L stainless steel was in the active state and the passivation-activation transition had occurred. The corrosion of 316L stainless steel in aqueous formic acid solutions is characteristic of non-uniform generalized corrosion. According to the results of electrochemical tests, with an increasing mass fraction of formic acid, the open circuit potentials and the primary passivation potentials became nobler, the critical current densities and the passive current densities increased, and the passive film breakdown potentials shifted to negative values. It is suggested that the passivation-activation transition of 316L stainless steel in aqueous formic acid solutions may be due to the competitive adsorption between HCOO? and OH? ions. Therefore, formic acid mass fraction increased, anodic dissolution accelerated, the formation of passive film was delayed, and corrosion susceptibility increased. In short, the concentration of formic acid significantly influences the corrosion behavior of 316L stainless steel from passivation to activation.
Abstract: In related work, such as human ear shape clustering, three-dimensional human ear modeling, and personal customized headphones, the key physiological curves of the human ear and the accurate positions of key points need to be determined. Moreover, as an important biological feature, the morphological analysis and classification of the human ear are of considerable value for medical work related to the human ear. However, because of the complex morphological structure of the human ear, the generation of a general standard for the morphological structure of the human ear is difficult. This study divided the morphological structure of the human ear into three regions, namely, helix, antihelix, and concha, for instance segmentation and key physiological curve extraction. Traditional edge extraction methods are sensitive to illumination and posture variations. Moreover, the color distribution of one human ear image is relatively consistent. Thus, the transition among the three regions may not be obvious, which will cause poor adaptability for traditional edge extraction methods when extracting the key physiological curves of the human ear. To address this problem, this study proposed an improved YOLACT（You Only Look At CoefficienTs） instance segmentation model based on the ResNeSt backbone and the “screening mask” strategy, which improves the original YOLACT model from two aspects, namely, localization and segmentation. Our ResNeSt-based YOLACT model was trained with labeled ear images from the USTB-Helloear image set. In the prediction stage, the original cropping mask strategy was discarded and replaced with our proposed screening mask strategy to ensure the integrity of the edges of the segmentation area. These improvements enhance the accuracy of curve detection and extraction and can accurately segment different regions of the human ear and extract key physiological curves. Compared with other methods, our proposed method shows better segmentation accuracy on the test image set and is more robust to posture variations of the human ear.
Abstract: With the gradual establishment of regional cooperative air defense systems by the world’s military powers, the success rate of a single-aircraft penetration operation is greatly reduced, and the concept of many-to-one cooperative operation has been widely valued. As a new type of lethal aerial weapon, suicide unmanned aerial vehicles (UAVs) have played an important role in many local wars recently. Compared with traditional missiles, suicide UAVs can hover in a combat area for a long time, waiting for potential targets. Moreover, a suicide UAV cannot be easily detected via an early warning system and can approach targets covertly. Further, the manufacturing cost of a suicide UAV is low, and it can form a large-scale swarm for a surprise attack. Therefore, in the foreseeable future, a multi-UAV cooperative attack is likely to subvert existing combat styles. According to the operational characteristics and requirements of multi-UAV cooperative attacks, a general guidance scheme for the cooperative attack of multi-UAVs is proposed. Based on the theory that proportional navigation law has trajectory uniqueness under specific variable constraints, the guidance phase is divided into coordination and terminal phases by selecting coordinated variables. The improved Dubins method is used in the track control of the coordination phase to realize the space–time synchronous convergence of coordination variables. The 3D space guidance is decoupled into longitudinal- and lateral-plane guidance in the terminal phase, and the impact time of the swarm is consistent based on the proportional guidance with the same coefficient. A track segment control realizes the space–time cooperation of the swarm considering the target defense range constraint. Numerical simulation and actual flight test results show that the scheme has real-time online planning ability, can realize an omnidirectional saturation attack under the space–time cooperation of a large-scale UAV swarm, and has high impact time and space precision.
Abstract: In 1954, Felix Wankel became the first in the world to successfully develop a rotary engine with the cooperation of the NSU. The invention of the rotary engine is a revolution in the structure of the internal combustion engine. The rotary engine exhibits advantages of simple structure, small and light, stable operation, and better high-speed performance. However, the development of the rotary engine is seriously restricted by its poor sealing problem. The apex seal is provided on each apex of the rotor to keep each working chamber gas-tight. Since it is directly exposed to high-pressure combustion gas and subjected to various kinds of restraint involved in the planetary motion, most efforts have been concentrated on the study of its performance and durability. The apex seal has three key problems: vibration, gas leakage, and wear. These problems will lead to the emergence of chatter marks that are called the nail marks of the devil. These problems directly affect the working performance and service life of the rotary engine. Mazda and NSU have made great contributions to the improvement of apex seals. Many types of apex seals have been developed, such as solid-type, split-type, cross-hollow, and three-piece. Many materials have been used as apex seals, such as alumetizing carbon, special cast iron, and fiber-reinforced ceramics. With the development of material technology, some new materials and treatment processing technology could be applied to the apex seal, e.g., laser surface treatment and new coatings. Carbon fibers, graphene, and nanometer materials could improve the wear resistance and mechanical property. This paper summarized the achievements of Mazda, NSU, and Curtiss-Wright. Finally, according to the new materials and treatment processing technology, the new structures and new materials for the apex seals were given in this paper. The trumpet-shaped notch structure, roller pin structure, cantilever flexure structure and multi apex sealing system can be used to improve the sealing performance of apex seals. Laser surface textured and new materials such as nano-ceramic and graphene are the breakthrough point to solve the sealing and wear problem of apex seals. This paper puts forward some suggestions for the future development of apex seals.
Abstract: In the combination of source rock and reservoir separated by the caprock of a petroliferous basin, the scale of oil and gas accumulation is controlled by the relative length of the effective period of oil and gas transported by the oil source fault. The accurate determination of the effective period of oil and gas transported by the oil source fault in the combination of source rock and reservoir separated by caprock plays an essential role in identifying the oil and gas distributions and guiding oil and gas exploration. Based on a study of the oil–gas transport mechanism and the effective period by the oil source fault of reservoir separated by caprock, a set of determination methods of the effective period for transporting oil and gas by the oil source fault of the reservoir separated by caprock was established herein by coupling the period for transporting oil and gas by the oil source fault and that when the source rocks expelled hydrocarbon. The period for transporting oil and gas by the oil source fault was determined by determining the period when the faults started to destroy the sealing capacity of the mudstone caprock, the period when the faults stopped their activity, and the period when the fault fillers began sealing. The geochemical characteristics of the source rock were used to determine the period when the source rocks expelled hydrocarbon. The application results show that at line L2, the effective period for transporting oil and gas from the F1 oil source fault to the reservoir of the 1st member of Dongying Formation (E3d1) is relatively long (i.e., time: 5.3 Ma). This is conducive to transporting the oil and gas generated by the source rocks of the 1st member of Shahejie Formation (E3s1) to the 3rd member of Dongying Formation (E3d3) through the mudstone caprock of the 2nd member of Dongying Formation (E3d2) to accumulate in the reservoir of E3d1 (the upper part of the structure has not been drilled yet). At line L8, the effective period for transporting oil and gas from the F1 oil source fault to the reservoir of E3d1 is relatively short (i.e., time: 2.4 Ma). Oil and gas are mainly transported by fault fillers, which is not conducive to transporting the oil and gas generated by the source rocks of E3s1 to the E3d1 through the mudstone caprock of E3d2 to accumulate in the reservoir of E3d1. The results are coincident with the fact that small-scale oil and gas have been found near line L8 of the F1 oil source fault in E3d1 of the Nanpu 5th structure, suggesting that the method is feasible for application in the determination of the effective period for transporting oil and gas by the oil source fault of a reservoir separated by caprock.
Abstract: China’s deep space exploration program is a complex and systematic project involving many fields and having great technical difficulties and funding requirements. The current program optimization method was developed in response to the demonstration group’s demonstration and the expert evaluation of the intermediary agency. This method requires a long demonstration period and makes rapid scientific decisions difficult. The Analytic Hierarchy Process (AHP) and the Fuzzy Analytic Hierarchy Process (FAHP) are both practical multi-factor and multi-objective decision-making methods that are widely used in many fields. To solve the problem of AHP being difficult to verify and judge for consistency, the concept of a fuzzy, consistent matrix was introduced, followed by the establishment of the FAHP. The introduction of the FAHP into the optimization of the overall scheme for deep space exploration benefits both the selection of the optimal overall scheme at the national level, which enables all relevant parties to reach consensus as soon as possible, and the national scientific decision-making process. This study established a systematic index evaluation model based on the FAHP model, considering the multi-index and multi-level structure of technology, science, and funding, among other things. By combining expert judgment and theoretical analysis, a judgment matrix of indicators at various levels was established and weight coefficients were derived for the Chang’e-4 mission plan in China’s lunar exploration project. Then, the overall plan was evaluated for optimal applicability. The results show that the three factors of technology, science, and funding are more important than time and benefit. Advancement and reliability are the primary control factors under the technical criteria. Scientific value is the major controlling factor when it comes to scientific criteria. The development cost is the primary constraint on the funding criterion. Planning compliance and planning feasibility are the primary controlling factors under the cycle criterion. Scientific output and technological promotion are the major controlling factors under the criterion of benefit. Among the four alternatives, the one in which the relay satellite is launched by the Long March 4C and the lander and rover are launched by the Long March 3B has the largest sorting weight. As a result, this solution is the optimal solution that is also consistent with the current situation. This research can help China provide rapid and scientifically sound support for various deep space exploration programs.
Abstract: With the continuous development of urban underground space in China, safety problems between urban underground pipelines and underground engineering construction that are in active service are constantly emerging. As an important way of excavating engineering rock and soil mass, blasting has a particularly prominent impact on pressure pipelines due to its harmful seismic effect. It is of great significance to study the vibration damage effect of the pressure pipeline under the excavation blasting earthquake to guide the safety production of the adjacent pipeline blasting construction and the safety design of the pressure pipeline under the influence of adverse factors such as blasting vibration. Based on the above research requirements, the stress characteristics of a thin-walled pipe with uniform internal pressure under an incident P-wave caused by blasting are first analyzed. The stress analytical calculation model under the seismic wave of pressure pipeline blasting is then established by quasi-static analysis and superposition principle. Based on the yield characteristics of pressure pipeline materials and the Tresca yield theory, a safety criterion calculation model for the vibration velocity of pressure pipeline under P-wave blasting is established. Combined with two engineering cases of a directly buried pressure thin-walled pipeline under explosion, the calculation model is verified. Results show that before the application of blasting load, the pipeline is only subjected to uniform internal pressure with initial axial and tangential stresses. After blasting, the pipeline is subjected to both internal pressure and blasting seismic P-wave load. Results reveal that the peak stress of the pipeline decreases with the increase of the incident angle. Moreover, the tensile failure mainly occurs at normal incidence, and the tangential failure mainly occurs at the total reflection. The vibration velocity of the safety control of the pressure pipeline increases with the increase of the incident angle. In the actual project, according to the actual situation of the internal pressure of the pipeline, the smaller value is selected as the safety control value.
Abstract: Clean and efficient fire extinguishing technology has been a hot research topic in fire science. The research of acoustic extinguishing technology originates from the discovery that the different acoustic modes of combustion noise can lead to an unstable oscillation of the flame and local flame extinction. Recently, acoustic extinguishing technology has gradually entered the research field of scholars because it is clean and exhibits no secondary pollution. To study the fire extinguishing mechanism and analyze the specific control behavior of the acoustic wave on an unclosed flame, the flame shapes and the combustion characteristics of the pool flame with 3, 4, and 5 cm diameters under a 30–90 Hz acoustic force were analyzed. The experimental system includes a high-speed camera, signal generator, power amplifier, loudspeaker, and acoustic signal analysis device. The flame image analysis shows that the transverse sound wave intensifies the unsteady flow of the vortex, and the flame shape under an acoustic force could be divided into three types of state: intermittent, deflective, and stable. The numerical analysis of the flame geometry shows that the flame surface is highly twisted and wrinkled under the intermittent and deflective states with a higher fractal dimension. The frequency-domain signal analysis of the flame area, height, and width shows that the flame signal is very unstable in the intermittent state, and the peak frequency domain is concentrated in the range of 0–10 Hz. The acoustic frequency is always prominent in the frequency distribution of the flame width signal. Based on the relationship between the flame inclination angle and Richardson number, the form of the latter under the action of the acoustic wave was proposed. In the 50–70 Hz range, the response of the flame to the acoustic frequency was particularly considerable, and there may be a marginal effect when the acoustic frequency is higher or lower than the said range. The critical Ria?1 of the intermittent and deflective states are 10.32 and 2.92, respectively.
Abstract: Volatile organic compounds (VOCs) have a wide variety and large emissions. VOCs are precursors of ozone and photochemical smog. Some VOCs, such as benzene, toluene, and xylene (BTX), are carcinogenic, teratogenetic, and mutagenic, which can greatly harm the skin, viscera, and nervous system. Researchers estimated in 2013 that 5.5 million people died from air pollution worldwide, thus becoming a serious threat to our daily lives. In the context of massive VOC emissions, the dramatic decline of the regional air quality, and the frequent occurrence of environmental problems, more attention has been paid to the control of VOCs. Governments have formulated a series of regulations and policies to limit the emissions of man-made VOCs. Under the guidance of strict policies, scholars have conducted extensive research on the governance technology of VOCs. Taking the catalytic oxidation of VOCs as the topic in this study, 4654 papers were processed by the Web of Science database, and the development tendency and research status of the topic were analyzed by way of bibliometrics. Results show that the VOC catalytic oxidation has abundant research depth in the past 25 years. The research prospect is found to be admirable and the number of published papers shows an exponential growth trend. China is the largest contributor of publications in the world, accounting for 34% of the total research. The biggest producing institution and journal are the University of Chinese Academy of Sciences (6.66%) and the Applied Catalysis B-Environmental (11.68%), respectively. Chemistry and Engineering are the most popular subjects. In addition, the hot word analysis in recent years shows that the most popular element in the catalyst is Mn, while toluene is the most common substrate of VOCs in the experiment. At the same time, this paper summarizes common catalyst substances and VOC substrates, which consequently reflects the current main research direction and provides guidance for future research.
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
