Abstract:The flying car is one of the new vehicles orienting the future aerospace transportation, and its performance is partially determined by gear transmission reliability. In this paper, the test speed changer with offset compound gear (OCG) transmission on a tilting wing flying car was studied for the fatigue reliability estimation and structure optimization. Firstly, the input load spectrum of the OCG speed changer was simulated based on the mission profile. Then the fatigue reliabilities of gear stages and the gear transmission system were estimated based on the stress strength interference theory. During the optimization process, the system fatigue reliability was the objective function, while the number of gear teeth, normal module, face width, pressure angle and shift coefficient were design variables. With the constraints of basic structure, strength and weight, the genetic algorithm was utilized to obtain an optimized solution. The comparison between the optimized structure and the initial one shows that the fatigue reliability of speed changer improves by 3.83% and the mass decreases by 2.4%. This work provides a design method for the development of such systems.

Abstract:On the basis of the multi-segment function construction method, the reproduction design of non-circular gear pairs with preset time-varying transmission ratio is proposed. Combined with the practical application of non-circular gear pairs in industry, a new continuously variable transmission mechanism with non-circular gear pair is presented. The influence of basic parameters of non-circular gear on output transmission ratio is discussed. By using software, such as SolidWorks and Adams, the simulation model of this continuously variable transmission mechanism is established. The simulation results show that a variable output speed ratio can be obtained by changing the relative phase angle of non-circular gear pair, and the influence of the relative phase angle on the output speed ratio is revealed. A non-circular gear pair experimental platform is built, and the experimental results show that the change trend of the experimental transmission ratio is consistent with that of the theoretical transmission ratio, with the maximum experimental error of 6.8%, demonstrating the feasibility and correctness of the theoretical analysis of this variable transmission mechanism.

Abstract:Micro gear is the key element of micro-electro-mechanical system(MEMS). The tooth surface wear is one of the main factors affecting its service performance and failure mode. In order to study the wear mechanisms of micro gear, the UMESHMOTION subroutine in ABAQUS is developed based on the Archard wear theory, and a finite element analysis model of the wear in micro gear is established combining with ALE adaptive mesh technology. Then, the tooth surface wear distribution under different meshing periods is obtained and verified. Based on the constructed finite element model, considering the interaction of the master and slave tooth surface wear, the influence of different material properties (modulus of elasticity) and material pairing on the tooth surface wear distribution are analyzed. The results show that the most serious wear of the micro gear tooth surface occurs at the base circle near the tooth root, and the wear near the tooth tip is lighter; compared with the material properties, different material pairing has a more significant effect on the wear of the micro gear.

Abstract:The previous dynamic analyses of the concrete pump truck mainly focus on a single subsystem of concrete pump truck, ignoring the coupling effect of its subsystems. In this work, a dynamic analysis method of the whole concrete pump truck under the real load condition was developed. The finite element model of the concrete pump truck was established, and two kinds of impact loads were loaded to simulate the dynamic impact of the concrete pump truck in working condition. The concrete flow velocity model was established, and then the impact load caused by the friction of concrete flow on the pipe wall was deduced. Based on the working principle of the concrete pump hydraulic system, the pumping impact load caused by concrete pumping was calculated. HyperMesh and the MSC. Nastran solver were used to perform the pre-processing and solving of the finite element dynamic simulation of the concrete pump truck. Finally, the simulation and experimental results under three typical working conditions were compared. The results of the simulation and experiment is consistent, verifying the rationality of the impact load model and the reliability of the simulation results.

Abstract:In order to guide the fatigue test of small samples and find the best fitting method of S-N curve under small samples, an improved classical sample information aggregation method is proposed. Based on the consistency of the fatigue life probability quantiles of the specimens under different stress levels, data sharing and fusion methods are adopted to realize the application of sample data information aggregation under different stress levels. According to the linear relationship between stress and fatigue life, the improved sample information aggregation method is used to parameterize and gradually search the average fatigue life under each stress level in the small sample data to obtain the optimal value of fatigue life under different stress levels. The least squares method is used to fit the S-N curve. The fatigue characteristics of the S-N curve are compared and analyzed with different stress levels as the benchmark. The comparison and analysis results show that the maximum relative error of the curves fitted with the improved method and the traditional group method is less than 5%, and the range of predicted fatigue life error is the smallest, which shows that the improved method promotes the reliability of fatigue analysis of small samples.

Abstract:Multi-resource constrained flexible job shop scheduling problem (MRC-FJSP) is a kind of complex combinatorial optimization problem. A multi-population particle swarm optimization algorithm with random network (MPSO-RDnet) was proposed for solving MRC-FJSP with the objective to minimize makespan. First, a new decoding method which combines semi-active decoding and heuristic rule decoding was designed. The original solution space was cut out effectively. Second, two neighborhood structures based on the critical path were designed to improve the local search ability of the population, and a multi-population strategy based on the random network structure graph was added to improve the global search ability of the algorithm. A reinitialization strategy for the algorithm search stagnation was proposed to enhance the robustness of the algorithm. Numerical experiments verified the effectiveness and efficiency of proposed algorithm.

Abstract:The metal-rubber composite-cycloid gear pair with a small tooth difference has small volume and compact structure. Metal rubber has a strong deformation compensation ability and can help realize high precision transmission. The structure and principle of the composite-cycloid gear pair were introduced, and a three-dimensional model of the gear pair was established to explore the influences of structural parameters of rigid and rigid-flexible gear pairs on their dynamic characteristics. After a rigid flexible mixed model of the metal-rubber gear pair was established in ADAMS, the dynamic simulation of the metal-rubber gear pair with a small tooth difference was carried out. The influences of the changes of elastic modulus, the clearance of the double gear, and the distance between the centers of the two pairs of gears on the angular velocity, the angular acceleration, the meshing force, and the transmission error of the metal-rubber gear pair were analyzed. At the same time, the differences of the angular velocity and the transmission error between the rigid and rigid-flexible composite gear pairs were analyzed. The results show that the vibration fluctuation can be reduced by increasing the distance between the centers of the gear pair with a small tooth difference, and increasing the elastic modulus of metal rubber and the clearance of double gear. The angular velocity and the transmission error of rigid-flexible composite cycloid gears are smaller than those of rigid gears, indicating that the metal rubber plays a role in reducing vibration in the new NN gear pair with a small teeth difference.

Abstract:An online measurement system is developed for the contour error measurement of large cylindrical parts. The system is controlled by single-chip microprocessor + PC. The rotation of the measured parts is driven by two synchronously rotating rollers, and their surface profile is measured through a non-contact sensor. The companion algorithms for evaluating the roundness error are programmed to extract the contour error value of each equinox of the workpiece surface, and the contour error curve is plotted. Theoretical analyses and experimental results show that the system is feasible to carry out the online measurements of large cylinders, and may be of value for various engineering applications.

Abstract:Ti-6Al-4V titanium alloy has the characteristics of low density, stable structure and high strength at high temperature. It is widely used in the manufacturing of key parts of aviation industry, such as wing beam, landing gear support rib. The wire arc additive manufacturing technology began in 1980s, which has the advantages of high forming efficiency, high utilization rate of raw materials and simple equipment. At present, the wire arc additive manufacturing technology of Ti-6Al-4V alloy has been widely studied and some progresses have been achieved. This paper reviews the development history and research hotspots of wire arc additive manufacturing technology, and summarizes its latest research and application at home and abroad. The microstructure, mechanical properties and control technology Ti-6Al-4V alloy produced by wire arc additive manufacturing are summarized and prospected.

Abstract:With the consumption of high-quality iron ore resources, the grade of iron ore available to iron and steel enterprises gradually decreases. Therefore, high alumina iron ore resources have attracted more and more attention. However, high alumina materials in the smelting process in the blast furnace will bring a series of problems, such as viscous slag iron, low furnace temperature, and smelting safety issues. From the perspective of blast furnace slag, this paper analyzes the effects of Al₂O₃ mass fraction on equilibrium phase, melting temperature and phase precipitation temperature of blast furnace slag, as well as the changes of liquid phase zone and viscosity of high alumina slag by using FactSage thermodynamic software. The results show that 1) when the slag is of low alumina (5% to 10%), with the increase of Al₂O₃ content, the melting temperature of slag increases, and the precipitates are feldspar phase and pure material phase. The viscosity of blast furnace slag increases slowly. The content of SiO₂ in slag is large, and the viscosity of slag is too high, which is not suitable for blast furnace smelting. 2) When the slag is of medium alumina (10% to 15%), with the increase of Al₂O₃ content, the melting temperature of the slag increases, and the precipitates are spinel phase, feldspar phase and pure material phase. The viscosity of the blast furnace slag increases slightly when the content of alumina is low. The Al₂O₃ content has little effect on the properties of the blast furnace slag, and the increase of the binary basicity of the slag has an obvious effect on the decrease of the viscosity of the blast furnace slag. 3) When the slag contains high alumina (15% to 30%), with the increase of Al₂O₃ content, the melting temperature of the slag increases, the precipitated phases are spinel phase, feldspar phase and pure material phase. The viscosity of the blast furnace slag increases at a rate of 0.011 Pa·s/%. In order to ensure that the solid phase precipitation temperature and viscosity of the slag meet the normal blast furnace smelting requirements, it is suggested that MgO/Al₂O₃ should be in the range from 0.4 to 0.5, the binary alkalinity R₂ range should be between 1.1 and 1.3, and the mass fraction of TiO₂ can be appropriately increased to about 5% in neutral atmosphere.

Abstract:The tuning of the weight parameters on the input and output variables can significantly affect the performance of a model predictive controller (MPC) to achieve a good closed-loop dynamic response. However, the currently available approaches based on the bi-layer multi-objective optimization (MOO) for tuning MPC weight parameters are computation-consuming. In this study, a new tuning algorithm is proposed, which converts the bi-layer MOO-based approach into a single-layer nonlinear programming (NLP) problem by treating the sub-optimization problem of MPC in the lower layer as the optimal KKT (Karush-Kuhn-Tucker) condition of the optimization in the upper layer, so as to reduce the computational cost. The simulation results demonstrate that the MPC tuned by NLP method shows similar or even better performance than the MPC tuned by MOO-based method. Moreover, by using the NLP tuning method, the computational time of the MPC tuning can be significantly reduced from a range of 1.0 h to 1.5 h for the MOO-based tuning method to a range of 5 s to 90 s.

Abstract:Automotive manufacturing industry in Chongqing faces the problem of large emission of volatile organic compounds (VOCs) and unclear characteristics of pollutant emission during painting procedure. In this work, the site investigations of twenty-eight automotive manufacturing enterprises’ basic situation and 9 representative enterprises’ VOCs characteristic components of coating were carried out. Among these enterprises, VOCs source spectrum of 3 typical enterprises was monitored to analyze featured pollutants. The maximum incremental reactive activity method was used to estimate the contribution of VOCs components to ozone production. The results of survey and monitoring reveal that the paint spraying and drying were the major points where VOCs were produced and emitted in the painting procedure of automotive manufacturing. Aromatic hydrocarbons were the main species of VOCs, accounting for 34.66% to 88.47%. Aromatic hydrocarbons and oxygenated volatile organic compounds (OVOCs), such as trimethyl benzene, xylene, ethyl toluene, methyl isobutyl ketone and ethyl acetate were VOCs characteristic components, especially 1,2,4-trimethyl benzene accounting for 12.82% to 28.65%. VOCs characteristic components were affected by raw materials and waste gas treatment facilities, such as composition and content of solvent, operating parameters of waste gas treatment facilities and adsorption materials. The 1,2,4-trimethyl benzene was the most active component for ozone generation.

Abstract:The coagulation effect and floc characteristics of M. aeruginosa, Synedra and Anabaena were studied, separately, by using ferric chloride and aluminum sulfate coagulants. The results show that the ferric salt has better coagulation and removal effect on the three algae species than aluminum salt does, and the three algae species achieves best coagulation effect when the ratio of coagulant is ferric salt coagulant > aluminum salt coagulant. The M. aeruginosa has the worst coagulation effect, and Synedra has the best under different dosages of ferric and aluminum salts. Compared with the use of aluminum salt, the three algae flocs coagulated by iron salt have larger fractal dimension. The fractal dimension value of Synedra is the largest(the maximum value:1.72) and that of M. aeruginosa is the smallest(the maximum value:1.17), indicating the effect of algae morphology on the flocs structure. The particle size(d₅₀) of the flocs of the three algae species when coagulated with ferric salt is larger than that of the flocs using aluminum salt, and the strength and recovery factor of the ferric salt flocs are smaller than those of the aluminum salt flocs. The maximum value of d₅₀ of M. aeruginosa floc (632 μm) is smaller than that of Synedra floc (765 μm) and Anabaena floc (777 μm) when using ferric salt. Synedra has the largest recovery factor of 26.54%, and Anabaena has the smallest recovery factor of 11.04% when using ferric salt. When the three algal flocs reach the isoelectric point, the dosage of ferric salt is greater than that of aluminum salt. The zeta potential of algal floc can be used to analyze the dosage corresponding to the optimal removal rate of algae coagulation. The M. aeruginosa flocculation is mainly electroneutralized, while the adsorption bridge and netting may play a more important role in the flocculation of Anabaena and Synedra.

Abstract:With the development of digital cities and smart cities, urban simulation has developed from two-dimensional to three-dimensional. Urban three-dimensional real-world modeling becomes more and more challenging. Due to the high density and rapid change of urban features, traditional manual 3D modeling methods are inefficient and cannot adapt to the rapidly changing urban environment. Therefore, UAV tilt photography technology is often used for fast 3D modeling. However, UAV tilt photography method cannot solve the problems of urban object occlusion, canopy occlusion, eaves occlusion, glass light transmission, etc., resulting in defects in the 3D model, such as local texture distortion, object pulling, and object voids. To dealing with these issues, taking the campus of University of Chinese Academy of Sciences as the research area, a fusion modeling method was proposed by combining the UAV tilt photography technology with ground LIDAR technology. In the experiment, a drone image acquisition strategy of "regular route mainly automatic shooting-based, supplemented by interest area with manual shooting" was used in the field; in interior work, "manual coarse registration and ICP algorithm fine registration" was used. The experimental results show that the method of multi-source data fusion can not only ensure the efficiency of 3D modeling, but also solve the problems of ground distortion and holes in the UAV alone modeling method, improving the accuracy of the model, and optimizing the 3D model of the city.