Abstract:

Abstract: Aiming to solve the position tracking problem of permanent magnet synchronous motor driven manipulator system,a robust control strategy combining active disturbance rejection control and Hamiltonian control was proposed.Firstly,the electrical subsystem and mechanical subsystem model considering uncertainty were established,and the model was transformed into a single-motor-driven single-joint port Hamiltonian structure according to the independent joint control idea.Then,the cascaded extended state observer was designed to estimate the total disturbance of the mechanical subsystem,and the designed control law achieved robust tracking of the desired position while simply and efficiently obtaining the desired q-axis current.Finally,a robust Hamiltonian controller which could combine the interconnections and damping assignment Hamiltonian controller with the H∞ controller based on the system Hamiltonian structure was designed to achieve high precision robust current tracking,and improves the problem of large initial control input by improving the timing of introducing H∞. Compared with modelless active disturbance rejection control of the electrically driven robot manipulators,the simulation results verified the effectiveness of the proposed control scheme.Compared with traditional ESO,the joint position tracking accuracy of the cascaded ESO could be improved by 0.003 rad.Compared with the Hamiltonian controller,the joint position tracking accuracy of the improved robust Hamiltonian controller was improved by 0.005 rad,the current tracking accuracy was significantly improved,and the initial control input of the improved H∞ introduction timing was significantly reduced.

Abstract: Standing stake seems simple but actually profound.In order to interpret the internal law of standing stake process and assist students in standing stake training,combined with experiments and data analysis,based on the human pose estimation technology,the dynamic characteristic parameters of standing stake process were extracted,and the digital expression and evaluation system of standing stake posture was constructed.Firstly,the human pose estimation algorithm OpenPose was used to extract the human keypoints from the video of standing stake.Secondly,the key characteristic parameters of digital expression were determined according to the essentials of standing stake.Then,the dynamic time warping algorithm and discriminant analysis method were used to calculate the evaluation indexes of each characteristic parameter.Finally,based on the long-term standing stake data,the coefficient of variation method was used to assign different weights to each evaluation index,to discuss the importance of each characteristic parameter and to comprehensively evaluate standing stake performance.The specific implementation included:designing an experiment to collect standing stake video from the front and side,six Tai Chi professional experts and twenty-two students participated in this research,and the students were divided into experimental and control groups.Through the analysis of standing stake parameters of the expert group,it was found that standing stake was actually a dynamic process,and the experimental data expressed the dynamic characteristic parameters of different parts from the front and side.At the same time,the long-term standing stake data of students in the experimental group was tracked for eight months.Through the comparative evaluation with the expert data,it revealed that the trunk,thigh,knee and hip were the more important body parts in standing stake process.In addition,after digital evaluation and guidance,standing stake quality of students in the experimental group was significantly improved,which could verify the effectiveness of digital expression and evaluation system for auxiliary training.

Abstract: The mask wearing detection in natural scenes is often affected by various factors such as the style and color of the mask,the skin color of the wearer,and the weather.In this study,based on the original YOLOv4,the coordinate attention mechanism was introduced to improve the utilization of the backbone network for spatial information of shallow feature maps and better capture small objects-masks.At the same time,it could enrich the semantic information of shallow feature maps and strengthen the long-distance dependencies to more accurately locate and identify object regions.This paper improved the network structure of YOLOv4 to enhance the capacity and depth of the overall network,so as to expand the receptive fields and improved the robustness of the algorithm.The introduction of DIoU-NMS could alleviate the phenomenon that the object was blocked and incorrectly suppressed.DIoU-NMS could perform NMS from the two aspects of IoU and center point distance of bounding boxes,so that the selection of the IoU threshold was not so harsh.The experimental results showed that the average precision of the improved YOLOv4 was 95.81%,which was 4.62% higher than the average precision of the original YOLOv4.The improved YOLOv4 had exciting performance and could complete the task of comprehensive and accurate mask wearing detection in natural scenarios.

Abstract: At the demands of digital,networked and intelligent transformation and upgrading of manufacturing enterprises,automated guided vehicle (AGV) is widely used in the logistics transportation of production operation.On the basis of workpiece process route planning,it is urgent to plan the transportation in each process to meet the requirements of actual production.Aiming to solve the flexible job shop scheduling problem with limited AGV,a multi-objective scheduling model was established with the optimization functions of maximum completion time,AGV quantity and resource imbalance rate.An improved whale algorithm based on production Gantt chart was proposed to solve the above model.Firstly,the basic principle of whale algorithm was introduced.Secondly,a three-stage real number coding method including AGV quantity,process sequence and AGV number was designed to transform the discrete data into continuous positions in whale individuals.Then the algorithm was improved from three aspects.During initialization,a better initial population was obtained by reverse learning strategy;in the iterative process,adaptive weight and mutation factor were added separately to improve the convergence accuracy and global search ability of the algorithm.Finally,the improved whale algorithm,the basic whale algorithm and the NSGA-II were used separately to solve the scheduling model.The simulation results showed that the improved whale algorithm had higher solution quality and the running time was 21.6% shorter than NSGA-II.The algorithm proposed in the paper had certain practical value in solving the intelligent job shop scheduling problem with limited AGV resources.

Abstract: The influence of thermal layout of thermoelectric coolers on the actual performance of thermoelectric cooling module was investigated by finite element simulation of six groups of thermoelectric coolers with the same dimensions and theoretical performance parameters,but different quantity,type and arrangement.The results showed that the thermal layout of thermoelectric coolers could affect the actual performance of thermoelectric cooling module.In the six groups studied,“center single piece”,“center double pieces”and “center four pieces” with the same arrangement showed nearly the same actual performance.In the optimal arrangement mode “uniform distribution four pieces” condition,compared with the previous three,when the heat source heating power was 30 W and 50 W and the working current was the maximum current Imax,the refrigeration effect increased by 13.88% and 9.17%,respectively,and the refrigeration efficiency increased by 12.24% and 12.12%,respectively.

Abstract: Because of the complexity of working conditions,it is difficult to extract fault features from vibration signal of the rolling bears.In order to address this problem,a fault feature extraction method based on fast iterative filter decomposition (FIF) and maximum second-order cyclostationarity blind deconvolution (CYCBD) method was proposed.Firstly,the fault signal of the rolling bearing was decomposed by FIF to obtain a series of intrinsic mode function.The components with the correlation coefficient of the source signal greater than 0.6 were reconstructed,and the appropriate cycle frequency was set according to the decomposition result obtained by FIF.Then the CYCBD method was used to unmix and denoise the reconstructed signal.Finally,the processed signal was envelope demodulated to successfully extract the fault features.Compared with the prominent noise component in the signal,the amplitude of fault characteristic frequency obtained by processing was higher than that of noise.Therefore,the method proposed in this paper could effectively realize the extraction of bearing fault frequency and its frequency doubling characteristics.

Abstract: According to the application demand of low CO content in fuel cell hydrogen source,the thermodynamic analysis of bio-oil steam reforming process for hydrogen production was carried out,and the process conditions of high hydrogen and low CO were optimized and obtained by response surface method.Firstly,the thermodynamic analysis of hydrogen production by bio-oil steam reforming was carried out in the range of temperature 300-1 500 K,pressure 0.1-0.7 MPa and water to carbon ratio 1.0-7.0.The results showed that high temperature,low pressure and high water to carbon ratio were favorable for hydrogen production,while low temperature,higher pressure and high water to carbon ratio could inhibit the formation of CO.Then,reaction temperature,pressure and water to carbon ratio were determined as the analysis variables,and the high hydrogen yield and low CO dry basis molar concentration were taken as the optimization objectives.The response surface method was used for prediction and analysis,and the low CO process conditions of hydrogen production by bio-oil steam reforming suitable for fuel cell application were obtained.The optimized results were compared with the experimental results under similar reaction conditions,and the values were close.Comparing the hydrogen yield and CO dry basis molar concentration of response surface prediction optimization results with those of Aspen Plus thermodynamic simulation results,the parameter error was less than 5%.The thermodynamic optimal conditions for hydrogen production by bio-oil steam reforming with the effect of high hydrogen and low CO were obtained as follows：temperature 814.98 K,pressure 0.10 MPa and water carbon ratio 6.00.In these conditions,the yield of hydrogen was 88.74% and the dry basis molar concentration of CO was 3.07%.

Abstract: In order to explore the droplet detection chip with short detection instrument time,small continuous phase reagent consumption and small single column spacing,the micro-channel simulation geometric model was established,and the model validity verification experiment was carried out.Using Fluent simulation software,and simulating 16 kinds of droplet detection chips with different structural sizes in the orthogonal experiment,the subjective weighting method and the objective weighting method were combined to form a combination weighting method to weight the evaluation indicators.TOPSIS and RSR were used to jointly evaluate the numerical simulation results,and the order of superiority and inferiority of 16 kinds of structures were obtained.The evaluation results showed that a droplet detection chip with the optimal size structure could be obtained in the conditions of the continuous phase channel size of 80 μm,the discrete phase channel size of 90 μm,the cross exit channel size of 100 μm and the channel depth of 50 μm.The droplet detection chip with that structure consumed less continuous phase reagent per unit time and could produce the performance with smaller droplet sequence spacing and short detection interval time of single droplet.

Abstract: In order to study the influence of the operating parameter of thermal management system on the cooling effect of proton exchange membrane fuel cell (PEMFC),a dynamic model of the PEMFC thermal management system was established based on the MATLAB/Simulink simulation platform and the correctness of the system model was verified.The model included voltage model and temperature model of stack and cooling circuit model.Bypass valve opening,coolant flow,and air flow were regarded as independent variables and the change rule and influence of independent variables on coolant temperature at inlet and outlet and coolant temperature difference between inlet and outlet were studied through established system model.The results showed that when the air flow increased from the minimum to the maximum,the air flow had the greatest impact on the coolant temperature at inlet and outlet which droped by 27.9-29.0 ℃ and 26.6-28.4 ℃,respectively.Both bypass valve opening and coolant flow had an effect on the coolant temperature at inlet and outlet,meanwhile the former had a stronger effect than the latter and the effect of bypass valve opening was more prominent when it less than 0.7.Although the coolant flow had the smallest influence on the temperature of the coolant inlet and outlet,it had a dominant effect on the coolant temperature difference between the coolant inlet and outlet which droped by about 9 ℃ when the air flow increased from the minimum to the maximum.

Abstract: A mesoscopic topology optimization for viscoelastic damping layer of constrained layer damping (CLD) plates was proposed to solve the problem of vibration reduction optimization of CLD structures.The viscoelastic damping layer consisted of 3D unit cells.Representative volume element (RVE) was used to analyze the equivalent material properties of 3D unit cells.The imposed boundary conditions on the 3D unit cells of the viscoelastic layer were considering rigid skin effects.A mesoscopic topology optimization model for viscoelastic damping layer of CLD structure was established to maximize the modal loss factor of macrostructure.The sensitivities of the objective function with respect to the design variables were analyzed and the design variables were updated by optimality criteria (OC) method.The modal analysis of finite element model of periodic perforated CLD plate was carried out.Campared with fined-mesh method,the maximum errors of natural frequency and modal loss factor calculated by RVE considering rigid skin effects were 0.09% and 3.60%,respectively.However,the maximum errors of natural frequency and modal loss factor calculated by the traditional homogenization method were 1.18% and 6.59%,respectively.It could be seen that the calculation accuracy of RVE considering rigid skin effects was higher than that of the traditional homogenization method.With the volume fraction of viscoelastic damping material being 0.4 as the constraint,the meso-configuration of viscoelastic damping material of CLD plate was optimized with the first,second and third order modal loss factor maximization as the optimization objective.The results showed that the meso-configuration of viscoelastic damping layer was related to the modal shape of the target order and the direction of modal shear stress.Although the consumption of viscoelastic damping material was reduced by 60%,the first three modal loss factors of the optimized structure increased by 3.70%,14.86% and 10.22%,respectively.The resonant peaks decreased by 9.71%,10% and 13.33%,respectively.The correctness and effectiveness of the proposed optimization method were verified.

Abstract: In order to explore the mechanical properties of the main structures of the three-core fiber composite submarine cable during torsion,220 kV three-core fiber composite submarine cable was taken as the sample.Based on the finite element software ABAQUS,a 3D numerical simulation model of 220 kV three-core fiber composite submarine cable was established.On the premise of guaranteeing the authenticity of mechanical structure,the calculation model was simplified and the surface-surface contact control was set up to simulate the relative motion of each layer when the outermost structure was torsionally driven by external force.The yield sequence and effect of torsion angle on stress of the steel armor,copper conductor and optical fiber were mainly studied by numerical simulation experiments.The results showed that the stress of the steel armor,copper conductor and optical fiber at the same section increased initially and then decreased due to the axial stress diffusion,while the stress at both ends was lower,and greater compared to the yield stress of the material itself at 0.2-0.5 times model length away from the fixed end during the torsion of the cable.The torsion angle along the axial direction had a good synchronicity and a linear downtrend.With the increase of torsion angle,the stress concentration appeared at 0.1 times model length away from the both ends of the steel armor and the optical fiber,and the copper conductor kept a higher level along the axial direction.During the torsion process,copper conductor,the steel armor and optical fiber yielded successively,and the safety margin had obvious non-synchronicity.

Abstract: In order to study the longitudinal reinforcement bonding performance of crumb rubber concrete beam-column joints,four beam-column joints specimens were designed and fabricated,including one full-scale joint of ordinary concrete and three full-scale joints of rubber concrete.The rubber replacement rate was 15%.Low cyclic loading tests were carried out on each specimen to obtain the failure modes,load-displacement hysteresis curves and bond stress hysteresis curves of longitudinal bars under different materials and axial compression ratios,and the average bond stress of longitudinal bars was analyzed.The results show that under low cyclic loading,the failure mode of each node specimen is the shear failure of the core area.The average bond stress increases linearly with load.After entering the yield stage,the average bond stress reaches the peak and gradually degenerates,resulting in bond slip.At the same concrete strength grade,the bond strength of longitudinal reinforcement in beam-column joints is reduced by 5% by adding rubber.With the increase of axial compression ratio,the bond stress and relative bond strength of longitudinal reinforcement increase,and the bonding performance is improved.The bond strength of longitudinal bars at high axial pressure ratio (0.59) is 5% and 13% higher than that at medium (0.37) and low (0.15) axial pressure ratios,respectively.Under the rubber replacement rate,the effect of high axial pressure ratio (0.59) on the bond performance of longitudinal reinforcement is greater than that of adding rubber.

Abstract: To study seismic response of high-speed railway bridge under near-fault earthquake,this study took a high-speed railway rigid frame bridge as the sample of study,the whole bridge model was established by OpenSees and seismic fragility curves were established by reliability theory,bridge fragility under near-fault and far-field earthquakes were compared and analyzed.The influence of near-fault ground motion velocity pulse effect on seismic response of bridge structure was studied.The results showed that under the action of a near-fault earthquake with velocity impulse,the fragility of bridge members and systems in each damage state was significantly higher than that of far-field seismic motion.The fragility of bridge systems in near-fault and far-field seismic action was higher than that of a single component.The seismic fragility evaluation system using a single component could overestimate the seismic performance of the bridge.Compared with the first-order boundary method,the second-order boundary method took into account the correlation between bridge members.The upper and lower bounds of the fragility curves were smaller and the seismic fragility of the bridge was more accurate.In rare earthquakes,the system′s fragility under near-fault earthquakes increased by percent point of 3,13,23,3,respectively,compared with that under far-field earthquake.The influence of velocity pulse effect on seismic response of bridge structure should be considered in the evaluation of the seismic performance of bridge structure near fault area.

Abstract: Studying the influence of multi-walled carbon nanotubes (MWCNTs) contents on mechanical properties of modified saturated clay is of great significance for its design and application in refuse landfill clay liner materials.Triaxial compression tests and scanning electron microscope (SEM) tests were performed to analyze the influence of different MWCNTs contents on the shear strength and the mechanism of mechanical properties was revealed from the microstructure evolution.The triaxial tests results showed that the shear strength increased first and then decreased with the increasing MWCNTs content,and the maximum value was detected at 0.5% MWCNTs content.The shear strength of samples doped with MWCNTs was greater than that without content.The cohesion strength showed similar change tend with the shear strength and the maximum value existed between 0.5% and 1.0%.The internal friction angle first decreased and then increased with the increasing MWCNTs content,and the minimum value appeared at 1.0% content.The results indicated that the shear strength of clay could be significantly improved by mixing MWCNTs with 0.5%-1.0% content.The MWCNTs altered the microstructure of the clay,which was the main cause of the change in the soil macroscopic mechanical properties.SEM results indicated that the contact between clay particles was relatively close and the large and small pores showed a uniform distribution in the specimen without MWCNTs content.The number and size of pores in the soil sample changed significantly after adding MWCNTs.It increased the compactness of the specimen with lower content,in which the threshold was determined to be 0.5% content,leading to the increase in shear strength.It could be observed that the number of pores increased but was less than the specimen without content with the increasing MWCNTs contents (1% and 2%).It could be attributed to the reason that the adsorption and cementation of MWCNTs on soil particles were weakened due to lubricating effect,resulting in a decrease in shear strength.

Abstract: In order to investigate the comprehensive effects of pH value,coagulant and coagulant aid dosage,stirring strength,and flocculation time on the coagulation process,aluminum sulfate was used as coagulant and PAM as coagulant aid to treat kaolin raw water.Turbidity,average particle size and dimension of flocs were used as response values.The response surface method was used to optimize the coagulation conditions and analyze the coagulation mechanism.Finally,the regression model equation including all parameters was established.The results showed that when the turbidity of raw water was 95.47 NTU,the turbidity removal rate was 87.42% under the conditions of pH value of 8.00,aluminum sulfate dosage of 21.47 mg/L,PAM dosage of 5.75 mg/L,stirring intensity of 31.41 r/min and flocculation time of 19.37 min.It is found that the dosage (coagulant and coagulant aid) and pH value had the most significant influence on the coagulation effect,and played a decisive role in the morphology and structure of flocs.The stirring strength and flocculation time affected the formation rate and final morphology of flocs,whose influence was less than the former.Three parallel experiments were carried out under the optimal conditions,and the relative error between the actual turbidity and the predicted value is 2.66%,which indicated that the model had guiding significance for optimizing the working conditions and enhancing the coagulation effect in practical engineering.

Abstract: Formation of olefins directly from CO2 hydrogenation is one of the effective and valuable routs for utilization.Formation of high value-added products directly from CO2-H2 mixtures may occur via a combination of reverse water-gas-shift (RWGS) reaction and Fisher-Tropsch (FT) synthesis over Fe based catalysts.This route produces by-products,which leads to a complex reaction system and low olefins selectivity.In this stu-dy,a series of Fe-Zn catalysts with Na were synthesized to get a deep insight into the effects of Na on the catalytic hydrogenation of CO2 and the structures of Fe-Zn catalyst at working state,by steady-state rate measurements,In-situ X-ray diffraction (In-situ XRD),In-situ X-ray photoelectron spectroscopy (In-situ XPS),In-situ diffuse reflectance infrared Fourier transform spectroscopy (In-situ DRIFTS).Decorating with Na facilitated the formation of Fe5C2.Electron transfer occured between Na and Fe5C2,resulting in the increase of electron density of Fe sites,which was not conducive to the secondary hydrogenation of olefin and improved the ratio of olefin to alkane.Decorating with Na facilitated C-C coupling by regulating the proportion of surface CH* species.The results showed that the Na exhibited the best catalytic performance for CO2 hydrogenation to olefins at 593 K and 1.5 MPa.the selectivity of olefins in hydrocarbons was as high as 65%,the O/P ratio was up to 6,and the CO selectivity was below 18%.

Abstract: In order to solve the problem that the nano-TiO2 sensor had a fast response to H2,but the recovery was too slow at room temperature,commercial nano-In2O3 was introduced to modify it.In2O3/TiO2 nanocomposite pressed films and In2O3/TiO2 nanotube arrays were prepared by pressing method and anodic oxidation-deposition method,respectively.They were applied to hydrogen sensors,and their hydrogen sensitivity were studied at room temperature.The samples were characterized by scanning electron microscopy,X-ray diffraction and specific surface area measurement.And the effects of different electrodes (Ag,Pt,Pd),different heat treatment temperatures and different In2O3/TiO2 mass fractions on the hydrogen sensitivity of the sensors at room temperature were studied.It was found that compared with the pure TiO2 sensor,the composite sensor expanded the detection range of hydrogen,and could detect 1×10-6-1×10-3 hydrogen at room temperature,and the recovery time was greatly shortened.Among them,the In2O3/TiO2 composite sensor with a mass fraction of 20% and annealed at 600 ℃ with Pt as the electrode exhibited the best hydrogen sensitivity.At room temperature,the response time to 1×10-6 H2 was 7 s,and the recovery time is 32 s.