最新刊期
卷 52 ， 期 1 ， 2020
- 摘要：The exploration of lunar resources and the utilization of lunar underground spaces are important steps for human beings to explore the moon and incorporate the moon into the scope of human activities. Based on the geological features of the moon and the temperature characteristics of lunar surface, integrated considering the factors such as the lunar latitude, the thermal conductivity of lunar soil/rock, the temperature characteristics of the lunar thermostatic layer and the latitude-dependent temperature range, the schemes of lunar underground human bases, lunar underground rail transit, lunar organism storage, and lunar thermal energy storage in the lunar thermostatic layer were proposed. Aiming at the proposed use scheme of the lunar thermostatic layer, technical implementation schemes for the space support and construction of the lunar underground human base, the lunar underground rail transit based on electromagnetic technology, the temperature-adjustable lunar strategic reserve, and thermal storage in situ based on the difference in thermal conductivity between lunar rock and soil were designed. Based on the above-mentioned schemes and technologies, this paper systematically summarized the technical challenges and key scientific problems facing in the underground space utilization of the lunar thermostatic layer. The researches provide technical solutions for the future establishment of lunar human bases and lunar underground space utilization.关键词：lunar thermostatic layer;underground space;lunar base;rail transport;thermal energy storage
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发布时间：2024-01-08 - 摘要：With the rapid development of portable electronic products and electric vehicles, the performance of lithium ion batteries has been put forward higher requirements. Compared with traditional lithium cobalt oxide cathode materials, nickel-rich layered metal oxides have higher energy density and lower raw material cost, and are considered as ideal cathode materials for lithium-ion batteries. However, its structural defects and unstable surface chemical properties will deteriorate the electrochemical properties, thermodynamic stability and safety performance. This paper reviews the research progress of modification of nickel-rich ternary cathode materials in recent years, aiming at providing important ideas for future design of nickel-rich ternary cathode materials and realizing their industrial application. Firstly, the inherent defects of nickel-rich cathode materials and the degradation mechanism of electrochemical performanceare introduced. Then, the modification strategies to improve the properties of nickel-rich materials by adjusting the interface structure are discussed, including coating electrochemical inert substances, designing element concentration gradient and core-shell structure, constructing core-shell heterostructure and controlling the thickness of the coating materials. After that, the strategies to improve the performance of nickel-rich cathode materials by bulk doping of elements are also summarized, including alkali metal-sites doping, transition metal sites doping, oxygen sites doping and synergy co-doping. Finally, the future development in this field is summarized and prospected,expecting to inspire more innovative ideas and strategies to promote the practical application of nickel-rich cathode materials.关键词：lithium-ion battery;ternary cathode;nickel-rich;surface coating;element doping
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发布时间：2024-01-08 - 摘要：There are many bending branched shoals, which are the main obstacles of navigation, in the upper reaches of the Yangtze River, and the reaches are also the main breeding areas of endangering fish Acipenser sinensis. Currently, waterway regulation projects in this region seldom consider the impact on aquatic habitats. In addition, existing habitat assessment methods are mainly based on the weighted usable area (WUA) of habitats in the instream flow incremental methodology (IFIM). In this study, we took the bending branched shoal in the upper reaches of the Yangtze River as a case study, considering the zoning characteristics of the spawning grounds of Acipenser sinensis with different functions. On the basis of patch area ratios of habitat, fragmentation index and habitat connectivity index, a comprehensive evaluation model of fish habitat were constructed, and the effects of submerged spur dikes on the habitat of Acipenser sinensis were studied. Results indicated that appropriate layout of submerged dike could improve the environmental quality of the habitat of Acipenser sinensis obviously. In addition, the number of patches was proportional to the length of submerged dikes, and the area ratio of patches and the fragmentation index of habitat were inversely related with the number of dams, while the connectivity index of habitat was mainly affected by the number of dams. From the point of protecting endangered species, the number and length of regulation projects for the bending braided shoals hindering the navigation should be controlled properly. In addition, the comprehensive evaluation model of fish habitat based on the reproduction and life habits of endangering species proposed in this study can overcome the problems currently existing in the habitat evaluation only according to the WUA, and it is more suitable for the environmental quality evaluation of fish habitat.关键词：bending branched channels;submerged spur dikes;Acipenser sinensis;functional zones of spawning grounds;comprehensive evaluation model of habitats
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发布时间：2024-01-08 -
Optimized Water Distribution Model of Irrigation District Based on the Backtracking Search Algorithm AI导读
摘要：With the increasing contradiction between water resources supply and demand in large irrigation areas in northwest China, grain production security gradually faces a serious threat. The traditional optimal irrigation water distribution models are mainly based on the objective function to optimize the allocation of crop water requirement, but the parameters and constraints of the objective function are more complex, which makes it nearly impossible to achieve the global optimal water distribution. This paper took the Xijun irrigation area of Heihe River basin as an example, on the basis of the principle of “based on constant flow discharge to control sluice gate” to study. It is possible to propose a backtracking search algorithm (BSA) to optimize water distribution model of irrigation district. BSA aims to choose different groups of branch canals under the constant flow rate of the main canal to ensure all branch canals can satisfy irrigation requirements. The irrigation water distribution time diagram of the branch canals was solved by backtracking search method, and the skewness coefficient of the sluice gate control time point was further obtained. In addition, the results of vector evaluation genetic algorithm (VEGA) and particle swarm optimization (PSO) were used to compare with BSA, and the adaptability of BSA was evaluated by analyzing the canal system of Xiaohe station. This study showed that the irrigation water distribution time of BSA, VEGA and PSO was 12.70 days, 14.38 days and 15.50 days respectively, the minimum deviation coefficient of BSA valve opening time point was 0.093, so BSA water distribution model had obvious superiority and stability. Besides, Xidong canal system, the water utilization rate of 0.651, had zero abandoned water, while Xiaohe station, with a high water utilization rate, had serious abandoned water, so BSA was generally applicable to areas with a lower water utilization rate of canal system. Under the reasonable application conditions, using BSA to optimize water distribution in irrigation area is able to not only guarantee better irrigation time to meet the requirements of canal system irrigation system, but also maintain the relative stability of fluid transportation to achieve the purpose of irrigation water distribution optimization.关键词：irrigation water distribution;backtracking search algorithm;vector evaluation genetic algorithm;particle swarm optimization- 2397
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发布时间：2024-01-08 - 摘要：In order to solve the modeling problems of saturated porous media, the engineering mixture theory was used to formulate the bulk constitutive theoretical framework of saturated porous media. Firstly, Supposing that the bulk deformation works of porous solid and fluid matrix were mutually independent and using Terzaghi’s effective spherical stress and pore pressure and fluid matrix pressure as stress state variables of constitutive model, the bulk stains expressions of solid phase and solid matrix and fluid matrix were obtained in the complementary energy. Secondly, the solid and fluid bulk constitutive equations of saturated porous cubes of balsawood in the loading and unloading stages were founded on the basis of the measuring data of model test conducted by Lade and de Boer. The calculating formulae of mechanical parameters were deduced such as solid bulk tangent modulus, Biot’s tangent coefficient and fluid Biot’s tangent modulus and so on. The change rules of mechanical parameters along with Terzaghi’s effective spherical stress and pore pressure were analyzed in the loading stage for solid bulk tangent modulus, Biot’s tangent coefficient and fluid Biot’s tangent modulus and so on. Finally, the one-dimensional consolidation equation of saturated porous media was derived from the bulk constitutive models of the paper and static balance equation. The consolidation behaviors of saturated porous cubes of balsawood were numerically analyzed and the change curves of consolidation degree and settlement with time were obtained. The researches show that, the solid bulk tangent modulus increased along with Terzaghi’s effective spherical stress and decreased along with pore pressure. The Biot’s tangent coefficient was between 0.42～0.95 and decreased along with Terzaghi’s effective spherical stress and pore pressure. The fluid Biot’s tangent modulus decreased firstly and then increased with Terzaghi’s effective spherical stress, and decreased with the increase of pore pressure. The tangent coefficient of pore pressure was less than 1.0 in most cases. The initial pore pressure was not equal to the external load in saturated porous media considering the compressibility of solid matrix. Thus the immediate settlement exists in saturated porous media after external load was applied. The modeling method in the paper can be used to model and numerically analyze nonlinear saturated porous media.关键词：engineering mixture theory;saturated porous media;solid bulk strain;solid matrical bulk strain;fluid seepage amount
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发布时间：2024-01-08 - 摘要：The flooding of the Yellow River results in lower water level and higher salt content in Kaifeng area. Under capillary effect, the bottom of Kaifeng city wall, which is mainly composed of soil, is in a state of wet and dry alternation. Under the action of salinity and frost heaving, the deterioration of city walls constantly occur. How to control the occurrence of capillarity is the key problem in the protection of historic buildings. In this paper, the imitation site soils of 4 types and 16 samples are tested, which contain 0, 1%, 3% and 5% mass ratio by the water repellent SHP–60. In order to explore the protection and repair methods of the wall soil, the capillary water absorption and water immersion disintegration test of the imitation site soil was improved by the water repellent SHP–60. By exploring the improvement effect of soil water properties of imitation sites under different SHP–60 content, and taking SEM picture by scanning electron microscopy and observing the microstructures of soil samples, it was found that the surface of SHP–60 adsorbed soil particles was birdnesting and connected, and the internal pore was reduced to form a waterproof film, which increased the water resistance of soil samples. The results showed that the SHP–60 coating around the pores of the soil particles can generate a large hydrophobic force and effectively enhance the hydrophobic properties of the soil particles. With the increase of SHP–60 content, the improvement effect of water properties is better. The imitation site soil with SHP–60 content of 5% can reduce the capillary water absorption quality by 92.34%. The immersion test found that a small amount of SHP–60 can effectively improve the disintegration performance of the imitation site soil. The 3%～5% of silicone water repellent can change the micro-structure of imitation site soil, reduce internal porosity and increase soil compactness. The formed waterproof film can improve the hydrophobic property of surface tension, and then effectively improve the water resistance of imitated site soil and prevent the erosion of site soil by underground capillary water. The research results provide a new idea for the restoration of soil sites.关键词：imitation ruins;improvement;capillary water absorption;submerging test
- 2020
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发布时间：2024-01-08 - 摘要：The load-bearing body theory is proposed to analyze the full-range spatial load-bearing characteristics of four-pillar chock-shield support top beam, as the traditional load-bearing area theory based on the plane force system fails in this case. The spatial force system expression is obtained and the analytical expression of the load-bearing surface is also derived by constructing the spatial mechanics model of the four-pillar support top beam separation body. The load-bearing body is the ultimate load-bearing body when the support is at the maximum support height via the curved surface judgment principle. The shape is similar to that of the “triangular curved cone” body, which is characterized by low circumference and high center. The vertical and horizontal sections of the ultimate load-bearing body of the four-pillar support are employed to obtain the longitudinal and transverse load-bearing area and the load-bearing capacity contour surface. The above analysis shows that the support resultant force and the area of the longitudinal load-bearing section in the middle of the top beam are the largest, and attenuated along both sides of the area, which is the same as the theoretical results for the plane load-bearing area. The morphological characteristics of different positions in the transverse load-bearing area are significantly distinct with the limit load-bearing point m0 as the boundary. The area of the load-bearing area is the largest at m0 point, and decreases from front to back. Moreover, the shape of the load-bearing capacity contour surface is of triangular distribution, and the larger the load-bearing capacity is, the smaller the triangle will be. A volume calculation method for quantifying the support load-bearing capacity is proposed; the key factors affecting the ultimate load-bearing body volume are the working resistance of the single support pillar and the positioning dimensions of the pillars. The results show that the abnormal decrease of the working resistance of single pillar will affect the rated working resistance of the support. The overall load-bearing capacity of the support is affected and the adaptability of support to the roof is also weakened, while the load capacity is reduced. Increasing the spacing of the pillars appropriately can increase the load-bearing capacity of the support, expand the effective support area, enhance the adaptability of the support to the change of roof load, and improve the roof control effect, but the overall support efficiency of the support does not change.关键词：four-pillar chock-shield support;ultimate load-bearing body;longitudinal and transverse area;load capacity
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发布时间：2024-01-08 - 摘要：The deformation of reservoir landslide is mainly resulted from fluid-solid coupling. It is not occurred immediately, but gone through a long-term development and exhibiting typical rheological characteristics. In this study, the extended Burgers creep model (M–2K) was derived and extended into the three-dimensional form. The creep testing results of the landslide soil were fitted by the derived M–2K creep model and the creep model parameters were obtained. A time-dependent relationship was introduced in to the traditional fluid-solid coupling analyses, and a mathematical model of the seepage–creep coupling was derived and solved by finite element method. Taking the Baijiabao landslide in the Three Gorges Reservoir Area as an example, the numerical calculations considering the seepage–creep coupling or non-coupling were completed using this program. The results demonstrate that the three-dimensional M–2K creep model had a high fitting degree and could reflect the creep properties of the landslide soil. The finite element calculation results show that the pore pressure reduction value under the seepage–creep coupling condition was greater than that under the non-coupling condition. The displacement calculation results of the key points under seepage–creep coupling or non-coupling conditions were compared with the actual GPS displacement measurements. The evolution trend of calculated results were basically consistent with the actual monitoring results, and the displacement values of two monitoring points considering the seepage–creep coupling were larger than those without considering the coupling process and more closer to the actual value. The results show that the established mathematical model of seepage–creep coupling is reasonable and the finite element numerical solution procedure is correct. The research provides a more reasonable and accurate new way for reservoir landslide prediction.关键词：landslide;fluid–solid coupling;creep model;seepage
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发布时间：2024-01-08 - 摘要：The complex water and sediment conditions and river form in mountainous rivers result in abundant vegetation covering the beach, which significantly changes the water and sediment movement and bed deformation characteristics. The experiments were conducted in a physical model with natural vegetation for studying the effects of vegetation and sediment supply on the river deformation and flow structure in the channel. According to the experimental results, it can be concluded that vegetation leaves increase the disturbance of water flow and reduce the flow velocity. When the upstream supply sediment occurs, the sediment is wavily transport in the vegetated beach, and form some small sand dunes around the vegetation zone, and most of the sediment is deposited at the head and tail of the beach. When the submerged vegetation withered, the stems and leaves are washed away, the flow washes the foot bases of the beach more intensely. Vegetation and sediment supply can adjust the flow division ratio of the branch. Sediment supply and vegetation reduce the diversion ratio of left branch. As a summary, vegetation and sediment supply significantly reduce velocity and thus have an important influence on the water-sediment movement, which accelerates the beach development and adjusts the flow division of branch.关键词：mountainous rivers;vegetation;sediment supply;branch diversion;beach development
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发布时间：2024-01-08 - 摘要：With the increasing number of projects such as water conservancy, railway, highway and urban construction, more and more blasting projects are being carried out in neighboring populated areas. The seismic effect created by blasting operations vibrates adjacent buildings and disturbs residents living in these buildings, and the resulting residents’ annoyance effect, disturb effect and worrying about the damage of the building, often lead to disputes and complaints. Annoyance rate used in psychophysics is applied in quantitative evaluation of blasting vibration comfort. In view of the fact that the blasting particle vibration velocity is mostly monitored rather than accelerated in practice, the vibration acceleration was calculated using the wavelet denoising-based four-point forward difference method based on the measured blasting vibration velocities. According to the sensitivity of human body to blasting vibration in different directions, different frequency ranges and vibration duration, the weighted RMS acceleration was obtained by weighting the vibration acceleration, and then the conversion total weighted RMS acceleration in three directions was applied to the annoyance rate model. Combined the site blasting vibration monitoring data in a hydropower project and the results of field survey, thirty-nine groups of monitoring data and comfort investigation data were obtained. Through comparative analysis, 23 of the 39 surveys the residents showed no obvious response, and the corresponding maximum annoyance rate was about 0.06. A total of 11 surveys the residents showed obvious response, and the corresponding annoyance rate ranged from 0.077 to 0.164. A total of 5 surveys the residents reacted intensely, and the annoyance rate reached about 0.17～0.31. Considering the characteristics of blasting vibration, it is suggested that the annoyance rate should be less than 0.07 as the basis for choosing blasting design scheme and the upper limit of control, which can effectively reduce the complaints of residents about blasting vibration.关键词：hydroelectric project;blasting vibration;annoyance rate;acceleration;annoyance rate;evaluation method
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发布时间：2024-01-08 - 摘要：Due to the widely use of Rayleigh damping model in structural seismic response and the significant influence of the calculation method for RDC on structural response, it is necessary to develop a rational calculation method for Rayleigh damping coefficients (RDC). With the necessity and reality that the multi-dimensional earthquakes along different directions act on structures simultaneously and the strain energy response can well reflect the structural mechanical behavior, the calculation method of RDC based on strain energy response under multi-dimensional excitation was established. The rational pseudo excitation formula was constructed and used to calculate the strain energy response based on the calculation formula for the response under one direction seismic excitation. By applying the pseudo excitation formula to the system under multi-dimensional excitation, the pseudo excitation method for the strain energy of the system was proposed. Based on the pseudo excitation method, the novel weight coefficient for the error square of the mode damping ratio and the corresponding calculation method for RDC were obtained. Taking three kinds of large-span spatial structures without slab and three kinds of tower structures for examples. The large-span spatial structures included the symmetric structure, the eccentric structure in one direction and the eccentric structure in two directions, while the tower structures included the symmetric double towers building, the eccentric double towers building in one direction and the eccentric three towers building in two directions. The proposed calculation method for RDC and the existed calculation method considering the influence of only two modes were put into the application with four strong ground motions. The results showed that the errors of the structural response of the symmetric large-span spatial structure from both the method for RDC were both small, but for the other spatial structures, the minimum value and the maximum value of the errors of the response from the existed calculation method were 5.89% and 19.64%, while that values from the proposed calculation method were 0 and 6.10%, and for all the tower structures, that values from the existed calculation method were 5.76% and 51.17%, while that values from the proposed calculation method were 0.07% and 4.48%, respectively. The comparison showed the proposed calculation method was rational.关键词：Rayleigh damping coefficients;strain energy;multi-dimensional excitation;pseudo excitation method;calculation method
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发布时间：2024-01-08 -
Application of Digital Image Correlation Method Based on Stereo Vision in Blasting Throwing Effect AI导读
摘要：Whether the blasting throwing object can move in accordance with design directly determines the success or failure of the blasting project. For further investigating the motion process of blasting throwing object, a new quantitative motion measurement system for blasting throwing effect based on digital image correlation and stereo vision was established in this paper. This system was used in several concrete model blasting tests for blasting throwing object tracking and observing. The throwing fragments were tracked by using digital image correlation matching algorithm and their special coordinates were calculated with stereo vison principle. Then, the trajectory and velocity of each fragment were obtained. The result showed that the motion process of blasting throwing object can be divided into two stages: The integral accelerating stage and dispersive decelerating stage. In the first stage, the thrust from explosion gas accelerated the integral throwing object with a maximum velocity of 16.63～19.65 m/s. The termination of this stage was about 9 ms and the throwing object detached from the concrete model within 6.5 ms. In the second stage, the throwing object falled into fragments which decelerate separately. The motion process of each fragment varied from each other because of its location and shape. Fragments on the surface were the potential blasting flyrocks as they had the largest velocity up to 26.24 m/s. These fragments decelerated under gravity and air resistance. Fragments in the middle or lower place decelerated under gravity, air resistance and thrust from the residual explosion gas with a lower deceleration. And the velocity of these fragments was 9～16 m/s. The flaky shaped fragments had the lowest velocity with 5～6 m/s as they were spinning constantly during the motion process which consumed their kinetic energy. The integral motion was simple and the dispersive motion was complicated. In addition to the blasting parameters and characters of the medium itself, the shape and location of the throwing fragment will also influence its motion process. Fragments on the surface had the largest velocity and were easier to form blasting flyrocks. An effective new method for blasting throwing effect research and flyrock prediction was provided in this paper.关键词：digital image correlation;throwing effect;stereo vision;blasting flyrock- 2115
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发布时间：2024-01-08 - 摘要：The permeability characteristics of iron tailings are one of the important factors affecting the stability of the dam. The permeability coefficient is an important indicator of its permeability. Many formulas for calculating permeability coefficient have been proposed by scholars at home and abroad. However, these formulas are mostly applicable to coarse-grained soil, and its applicability to iron tailings is not clear. Therefor it is necessary to verify the accuracy of these formula and establish a calculation model for the permeability coefficient of iron tailings. The permeability properties of iron tailings sand were analyzed from various angles such as FC value, gradation, particle size, specific surface area and inter-particle void ratio with water head test in laboratory. The results showed that the permeability coefficient of iron tailings sand is affected by the fine content. The threshold of fine content is about 40%. The traditional formula for calculating the permeability coefficient was applied, but the results are inaccurate. The relationship among permeability coefficient of the iron tailings sand and the non-uniform coefficient Cu, the curvature coefficient Cc, the average particle size, the weighted average particle size, the volume ratio surface and the interparticle void ratio es is nonlinear. It is difficult to characterize the change of permeability coefficient when the fine content is large. However, the relationship between permeability coefficient of the iron tailings sand and the effective particle size and inter-particle void ratio is linear. A formula was developed for the determination of permeability coefficient of iron tailings sand by analyzing the effective particle size and inter-particle void ratio data. It is significant for the seepage field analysis and stability calculation of the Chenkeng tailings dam. This can be used to calculate the permeability coefficient of magnetite tailings.关键词：iron tailings sand;fines content;permeability coefficient;effective particle size;void ratio of inter-fines
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发布时间：2024-01-08 - 摘要：In the construction of infrastructures such as the large-scale water conservancy, hydropower, energy and transportation, it is important to find out the bad geological characteristics in rock mass structure to ensure the smooth construction of the project. However, conventional geophysical prospecting methods are difficult to detect the fine characteristics of the borehole surrounding rock structure, such as the range and trend of the abnormal area. Therefore, a new method was proposed based on the laboratory rock sample defect detection method. The method based on directional acoustic scanning of detecting borehole surrounding rock structure was realized by combining directional acoustic probe, rotating parts and positioning device in order to be suitable for detecting borehole surrounding rock structure characteristics. Firstly, the annular scanning matrix was established according to the scanning detection data, and the data processing method for constructing the annular scanning map was put forward. Then, the mapping relationship between the acoustic data and the annular scanning matrix was constructed, and the corresponding acoustic processing data were matched according to the mapping relationship, thus forming the structural sectional map of the surrounding rock of the borehole. After superimposing the depth information, the structure of the surrounding rock of the borehole was realized. Finally, aiming at the difficulty of determining the parameters of rock sound velocity and defect location in the defect area of borehole surrounding rocks, two-dimensional scanning vectors of sound velocity and distance dimension were constructed by using the phase characteristics of different frequency acoustic wave transmission in rocks, and numerical analysis method was used to solve the acoustic velocity of rock and the location of abnormal area, thus realizing the structural characteristics of borehole surrounding rocks. Signature stereo rendering and parameter extraction were applied to practical engineering, and the feasibility and accuracy of the method were verified.关键词：borehole detection;surrounding rock structure;acoustic scanning;surrounding rock defects;surrounding rock sound velocity
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发布时间：2024-01-08 - 摘要：In order to accurately calculate the contact stiffness of the fractal surface of cycloid needle wheel, a fractal model considering friction coefficient was proposed. Based on the modified Weierstrass–Mandelbrot function and differential geometry, a two-dimensional rough surface model of cycloidal gear tooth modified by second order parabola method and needle tooth was established. The model showed the morphological characteristics of the complete conjugate tooth profile and the needle tooth in particularly form in the macro and micro field of view, the cycloidal pin wheel was in the elastic deformation stage under meshing load, and the friction force correction factor was introduced. The contact stiffness of two rough contact surfaces at the micro level was calculated. The results showed that the contact stiffness Kn of fractal surface of cycloid needle wheel keeps steady at first and then increases rapidly with the increase of the meshing force F on the contour, finally the contact stiffness is inclined down. The increase of surface roughness Ra and friction factor μ led to the decrease of contact stiffness Kn, and the increase of modification coefficient a1 will slow down the increase of contact stiffness Kn. Compared with the Hertz contact stiffness established by the LTCA model, the correctness of the cycloid pin wheel fractal model was verified, and the advantage of transforming the contact stiffness Kn from static to dynamic process and from oneness to continuity was demonstrated.关键词：cycloid wheel;fractal theory;surface roughness;friction coefficient;contact stiffness
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发布时间：2024-01-08 -
Influence of Critical Process Parameters on the Thermal Physical Process in Selective Laser Melting AI导读
摘要：Selective laser melting (SLM) is of vital value in the manufacturing industry which melt powder material, such as metal powder, layer-by-layer by using laser beam. Nevertheless, the thermal physical phenomena and the influence of process parameters on the thermal physical process need to be further studied. A multi-track numerical model, considering the phase change and irreversible powder-to-solid transition, was established to simulate the SLM of 316L stainless steel. The effects of laser power, scan speed and effective laser beam diameter on the temperature field, melting time, cooling rate and melt pool dimension was studied. Experiment was conducted to verify the reliability of numerical simulation results. The results indicated that the melting time is easily affected by laser power and scan speed, while the maximum cooling rate is more sensitive to effective laser beam diameter. With relative low laser power or high scan speed, the melt pool dimension is comparatively small, and easy to form cave like defects. The effective laser beam diameter has a small effect on the melt pool dimension. The stability of melt pool firstly has no certain change tendency and then increases with the increasing laser power. With the increase of scan speed, the stability of melt pool decreases continuously. The effect of effective laser beam diameter on the stability of melt pool is uncertain. The numerical simulation results are approximately in accordance with the experimental results and provide guides to tuning and optimizing the process parameters in SLM.关键词：selective laser melting;process parameter;numerical simulation;temperature distribution;melt pool characteristics- 2694
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发布时间：2024-01-08 - 摘要：In order to improve the cutting speed control performance of the ball screw sub-laser cutting platform, based on the principle of double power reaching law and fuzzy control, a controller of gain fuzzy adaptive double power reaching law was designed. The Lagrangian dynamic model of the ball screw pair motion system was established by lumped parameter method for considering the various axial and torsional vibrations of ball screw pair. Meanwhile, the Stribeck friction model was introduced to estimate the friction that high-precision control systems were greatly affected by the high nonlinearity of friction. Due to the chattering of the traditional double power reaching law, the saturation function was introduced instead of the symbol function, which inhibited the chattering of control system to some extent. The fuzzy relationship between the laser cutting depth, velocity and gain was analyzed and established.The fixed gain was difficult to ensure the optimal dynamic control effect of the laser cutting, based on the laser cutting depth as the adaptive reference, the fuzzy controller based on the fuzzy rule table adaptively adjusted the control gain, which enhanced the robustness and adaptability of the system. Simulation and experimental results showed that it was not only solved the overshoot problem of the control system, but also improved the response speed and robustness of the system, effectively weakened the chattering of the system compared with the PI controller and the traditional double power reaching law controller. Meanwhile, the laser cutting laboratory platform was built. It was found that the best laser cutting depth range was 1/2～2/3 the thickness of the cell, and the best laser cutting speed was 200 m/s by the laser cutting experiment on the ball screw sub-laser cutting platform. On this basis, the PI controller, the traditional double power reaching law controller and the control method proposed in this paper were used for laser cutting. By comparing and analyzing the slit image of battery obtained by the metallographic microscope, it was showed that the slit of the cell obtained by the control method proposed in this paper is flat, which verifies the superiority of the control method proposed in the laser cutting speed control performance.关键词：PI controller;sliding mode control;gain;double power reaching law;fuzzy control;laser cutting
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发布时间：2024-01-08 - 摘要：In order to further improve the sealing performance of bidirectional dry gas seal, a fir tree-groove dry gas seal with radial orderly micro-structure at the bottom of hydrodynamic groove was designed. Based on the theory of gas lubrication, a 3D gas film model was established and Fluent software was used to simulate the steady flow of gas film. The performance parameters (opening force, Fo, and ratio of opening force to leakage, Fo/Q) of fir tree-groove dry gas seal with or without micro-structure were compared and analyzed under different structures and working conditions. The results showed that the orderly micro-structure design can enhance Fo at low speed, which is helpful to solve the problem that dry gas seals are prone to wear during start-up and shut-down, and the improvement effect is more significant when the groove depth is small; The existence of the micro-structure can reduce air flow oscillation and improve operation stability; The performance is the best when the width of micro-structure equals to the space, Bm/Cm=1. When film thickness, δ is 2 μm, the depth of micro-structure, ε of 1.0～1.3 μm can makes Fo/Q good and the laser processing efficient; when the pressure difference between inlet and outlet (∆P) is large, the Fo and Fo/Q can be enhanced more effectively; The existence of micro-structure hardly affects the general rules of the effect of δ, hg, N and ∆P on of the fir tree-groove dry gas seal.关键词：orderly micro-structure;laser processing;dry gas seal;numerical simulation
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发布时间：2024-01-08 - 摘要：With the wide use of helical planetary gears in the case of high-speed and heavy loads, the study of dynamic loads characteristics become great significance for reduction vibration and noises. Firstly, correctly describing meshing stiffness and meshing error of planetary gear was the top priority of dynamic analysis, so an approach of loaded tooth contact analysis for planetary gears (PLTCA) combining gear geometry analysis and mechanical analysis of tooth was proposed to calculate meshing stiffness of gears and corner meshing impact, which was prepared for further analysis of planetary gear dynamics. Secondly,considering time-varying meshing stiffness and corner meshing impact excitation, a lumped-parameter planetary gear model was established and forces responses were got by solving the dynamic equations with numerical method.The results showed that the dynamical meshing forces increase remarkably with the speed increase except resonance speed. Besides, installation error, especially the center distance error, is responsible for the difference in value of meshing stiffness, and lead to the more resonance speeds, furthermore. With floating planetary gear , the dynamic forces are reduced at the resonant speeds, and the dynamic meshing force of some gears are obviously reduced with increasing speeds due to the differences in value of meshing stiffness.关键词：helical planetary gear;dynamical force;loaded tooth contact analysis;corner meshing impact;meshing stiffness;load sharing coefficient
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发布时间：2024-01-08 - 摘要：Nowadays, there is an interest in fully applying on the reaction solution, such as desulfurization by pyrolusite or leaching pyrolusite with sulfur dioxide, for the purpose of controlling air pollution and the recovery of manganese salt. However, some researchers aimed at studying on the technological problem that there was a byproduct of S2O6 2– ,which debase the main product of MnSO4 from the desulfurization solution. In the present work, a large amount of Na2SO4 was prepared by the low temperature pyrolysis of Na2S2O6, which was acquired as the precursor by MnS2O6 that was carbonated by the carbonization reagent (NaHCO3). During the thermal decomposition process of Na2S2O6·2H2O, the reaction products and the temperatures of the key steps of reaction processes were investigated and both of the reaction mechanisms and the kinetic parameters were deduced. The thermal decomposition experiments showed that 255 ℃ was the optimum temperature for the preparation of Na2SO4 by the thermal decomposition of Na2S2O6, which underwent two steps including dehydration and desulfurization. The characterization results of X-ray diffraction (XRD) and Ion chromatography (IC) showed that the decomposition product was the pure and single phase cubic sodium sulfate. The thermal decomposition process of Na2S2O6 was characterized by thermo-gravimetric analysis and differential scanning calorimetry analysis (TG–DSC), in which the activation energies (Ea) of dehydration and desulfurization were calculated by the combining Kissinger differential method and the Coats–Redfern integral method, respectively. The processes of dehydration and desulfurization of Na2S2O6·2H2O were controlled by phase boundary reaction model fitting shrinking sphere equation with the Ea of 14.75～18.11 kJ/mol for dehydration and 132.61～137.18 kJ/mol for desulfurization. SO2 was observed as the main decomposition gas. Finally, the reaction equations were demonstrated combined with the chemical analysis method. Based on realizing the resource recovery, this technology of the thermal decomposition of Na2S2O6·2H2O is feasible and used to avoid the acidic wastewater problem within the liquid–phase method, from which decomposition gas could reacted with sodium bicarbonate again during the process of thermal decomposition.关键词：manganese dithionate;sodium sulfate;carbonization;thermodynamics process;recovery
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- 1084
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发布时间：2024-01-08 - 摘要：The fluorescence quenching mechanism, association constant, binding mode and the activity and conformation of pepsin (PEP) between two enantiomers of nicotine (NIC) and PEP were investigated through fluorescence spectroscopy, UV–vis spectroscopy and molecular docking techniques. S–NIC and R–NIC quenched the intrinsic fluorescence of PEP through dynamic quenching mode because of the increase in the Stern–Volmer quenching constant (Ksv) values with the increase in the temperature. The quenching ability of R–NIC was significantly stronger than S-NIC, as evidenced by UV–Vis spectroscopy. The effective association constant (Ka) showed that at the same temperature decreased in the order of R–NIC > S–NIC. The activation energy ( Ea) was calculated to be 12.67 kJ/mol and 2.65 kJ/mol for the binding of S–NIC and R–NIC to PEP, respectively. This difference implied an unequal participation of the two enantiomers and R–NIC was more intimate to bind with PEP, and the binding of S–NIC and R–NIC with PEP were both primarily controlled by hydrophobic forces. Synchronous and three-dimensional fluorescence spectroscopy showed that the micro-environmental and conformational of PEP were changed along with the interaction between two enantiomers and PEP. In addition, the activity experiments in vitro indicated that the activity of pepsin was inhibited with increased S–NIC and R–NIC concentration, and the R–NIC was much greater than S–NIC on the activity suppression. Molecular docking study provided the same binding sites, the two enantiomers were located the groove between the N– and C–terminal domains.关键词：nicotine enantiomer;pepsin;interaction mechanism;molecular spectroscopy;molecular docking
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- 777
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发布时间：2024-01-08 - 摘要：Stand-off free layer damping is a vibration reduction treatment established on the traditional free layer damping structure. Based on the theory of stand-off free layer damping, polyurethane-rubber stand-off layer damping material was prepared by using rigid polyurethane foam as stand-off layer and rubber as damping layer for suppressing structural vibration. With considering the shear deformation of damping layer, the equation of motion for cantilever beam treated with the composite material was derived by the principle of modal superposition and Lagrange equation. The composite damping material with the thickness ratio of 1 to 3 and segmented stand-off layer was applied to the cantilever steel beam. The amplitude-frequency curves, loss factors, and mode frequencies were analyzed by the hammering test. The results showed that when the thickness ratio of the stand-off layer to the damping layer is increased from 1 to 3, the vibration response peaks of the model are reduced by 13%～62% and the loss factors are also increased obviously. When the ratio exceeds 1.5, the damping performance of the material on the low-order mode of the beams continues to increase, while the damping effect of the higher-order mode tends to be stable. As the results of the segmented stand-off layer, its bending stiffness is reduced and the processing area of the damping layer gets larger. The vibration response peaks of the models are reduced by more than 16%, while the additional mass of damping treatment is not significantly increased. It is concluded that the vibration reduction performance of the composite damping material could be better by increasing the thickness ratio of the stand-off layer to the damping layer, especially at low frequency. The design of segmental stand-off layer is helpful to further improve the damping performance based on composite materials.关键词：stand-off layer damping;segmented stand-off layer;free damping;vibration reduction
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发布时间：2024-01-08 - 摘要：In order to solve the problem of low efficiency for manual configuration parameter tuning of Spark jobs caused by the large number of parameters, large parameter search space and mutual influence among parameters, a smart configuration parameter tuning method was proposed. Firstly, a set of core configuration parameters of Spark that had great effort to jobs’ performance were selected, then the performance prediction model was built based on the selected configuration parameters and the corresponding jobs’ performance information using support vector regression algorithm. By changing the size of the data set, the predicted value of the model was compared with the real running time of the job, and the evaluation index proved the effectiveness and accuracy of the jobs’ performance prediction model. Secondly, several optimization algorithms of configuration parameters based on hill climbing, simulated annealing, recursive random search and particle swarm were designed and implemented. The solution quality of these algorithms was analyzed by experiments. The experiment results showed unique advantage of recursive random search against other algorithms on both convergence result and convergence variance, which indicate recursive random search had both good stability and adaptability to different types of jobs. Compared with experienced optimization configuration, the experiment results showed that the smart optimization configuration can bring 4%, 15% and 22% average performance improvement to typical Spark jobs, which demonstrate that smart optimization configuration can obtain more suitable parameters for given jobs efficiently and improve running performance of jobs.关键词：Spark;configuration parameters;performance prediction;smart optimization
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发布时间：2024-01-08 -
Research on Improvement of Collaborative Filtering Recommendation Algorithm Based on Data Sparseness AI导读
摘要：According to the users’ activity-behaviors, the collaborative filtering recommendation algorithms recommend the interest items to users. However, as the number of users and items increase, the activity of users on a single item decreases, resulting in poor recommendation quality. To solve this problem, an optimization algorithm to improve the recommendation quality in the case of sparse data was proposed in this paper, which combines the item-based and user-based recommendation algorithm. Firstly, the score of the items was predicted according to the similarity between users preliminary; secondly, the recommendations are got based on similarities between items. The average value was combined with the predicted value when filling unrated vacancy values. The weight of the items that commonly scored by users and the weight of users that commonly scored the same items were considered. In experiment, the recommended effects of several basic recommendations algorithms were firstly compared to select a better basic for deep research. Secondly, the proposed algorithm was compared with other algorithms. Finally, for further comparison the data sparsity to several extents was increased. The experiment results showed that the optimization algorithm proposed in this paper had better recommendation. The experiment of data sparsity changes showed that as the data sparsity increases, the optimization algorithm proposed in this paper has obvious advantages.关键词：sparsity;recommendation algorithm;similarity;optimization- 2269
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- 1101
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发布时间：2024-01-08
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