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RSS2018 Vol. 37, No. 2
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2018, 37(2): 165-171.
doi: 10.13433/j.cnki.1003-8728.2018.0201
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Abstract:
The wind turbines in the wind farm are easy to be affected by wakes of upstream wind turbines. In this study, a FSI model based on nonlinear geometrically exact beam (GEB) and a free-vortex wake (FVW) model are applied to study coupled responses under wake effect. As a result, to the downstream wind turbine, the rotor power will decrease and while the load fluctuation of rotor blades will increase, even when the distance between upstream and downstream wind turbines is 6 rotor diameters. After one rotor diameter offset, the load fluctuation cannot decrease significantly.
The wind turbines in the wind farm are easy to be affected by wakes of upstream wind turbines. In this study, a FSI model based on nonlinear geometrically exact beam (GEB) and a free-vortex wake (FVW) model are applied to study coupled responses under wake effect. As a result, to the downstream wind turbine, the rotor power will decrease and while the load fluctuation of rotor blades will increase, even when the distance between upstream and downstream wind turbines is 6 rotor diameters. After one rotor diameter offset, the load fluctuation cannot decrease significantly.
2018, 37(2): 172-179.
doi: 10.13433/j.cnki.1003-8728.2018.0202
Abstract:
Based on the dynamic theory of rolling bearings, the dynamic differential equations of cylindrical roller bearing with the large acceleration were established and solved by Hilbert-Hughes-Taylor(HHT) integer algorithm with the variable steps. The collision force and angular speed of cage and roller at stop stage were used as the boundary conditions of finite element contact model. The influences of material of cage, working conditions and structural parameters of bearing on cage stress were investigated. The results are as following:cage stress is produced mostly by centrifugal force when bearing is working at a constant speed, but at stop stage, cage stress is caused mostly by collision force between rollers and cage and reaches several times of that at a constant speed; When bearing is working under the same condition, the safety factor of steel cage is greater than that of copper cage; The cage stress decrease firstly and then increase with the supply oil temperature increasing, and there is a reasonable supply oil temperature to get a relative lower cage stress; Reasonable radial clearance, load and supply oil temperature can significantly reduce cage stress level at stop stage.
Based on the dynamic theory of rolling bearings, the dynamic differential equations of cylindrical roller bearing with the large acceleration were established and solved by Hilbert-Hughes-Taylor(HHT) integer algorithm with the variable steps. The collision force and angular speed of cage and roller at stop stage were used as the boundary conditions of finite element contact model. The influences of material of cage, working conditions and structural parameters of bearing on cage stress were investigated. The results are as following:cage stress is produced mostly by centrifugal force when bearing is working at a constant speed, but at stop stage, cage stress is caused mostly by collision force between rollers and cage and reaches several times of that at a constant speed; When bearing is working under the same condition, the safety factor of steel cage is greater than that of copper cage; The cage stress decrease firstly and then increase with the supply oil temperature increasing, and there is a reasonable supply oil temperature to get a relative lower cage stress; Reasonable radial clearance, load and supply oil temperature can significantly reduce cage stress level at stop stage.
2018, 37(2): 180-186.
doi: 10.13433/j.cnki.1003-8728.2018.0203
Abstract:
A small module face gear with curved tooth and an involute cylindrical worm transmission system have been studied with the finite element analysis. The calculation models of time-varying mesh stiffness and stress of face gear with curved tooth are established. Firstly, some existing mesh stiffness calculation methods are introduced, and their disadvantages are analyzed. Based on the gear geometry and the gear formation theory, this paper derives the mathematical models for the involute cylindrical worm and the face gear with curved tooth and obtains the discrete coordinates on the tooth surface. On this basis, the paper establishes the geometrical model and the assembly model and then develops the model of face gear with five teeth. Then it elaborates the time-varying mesh stiffness calculation method based on the finite element analysis. The accuracy of this method is verified with an example of straight tooth column gear. Through the contrast with available literatures, the calculation method in this paper is checked. Finally, the finite element model of the face gear with curved tooth is created with the ANSYS software. Then the paper applies the finite element model to analyzing the gears in several different meshing positions during the transmission.
A small module face gear with curved tooth and an involute cylindrical worm transmission system have been studied with the finite element analysis. The calculation models of time-varying mesh stiffness and stress of face gear with curved tooth are established. Firstly, some existing mesh stiffness calculation methods are introduced, and their disadvantages are analyzed. Based on the gear geometry and the gear formation theory, this paper derives the mathematical models for the involute cylindrical worm and the face gear with curved tooth and obtains the discrete coordinates on the tooth surface. On this basis, the paper establishes the geometrical model and the assembly model and then develops the model of face gear with five teeth. Then it elaborates the time-varying mesh stiffness calculation method based on the finite element analysis. The accuracy of this method is verified with an example of straight tooth column gear. Through the contrast with available literatures, the calculation method in this paper is checked. Finally, the finite element model of the face gear with curved tooth is created with the ANSYS software. Then the paper applies the finite element model to analyzing the gears in several different meshing positions during the transmission.
2018, 37(2): 187-192.
doi: 10.13433/j.cnki.1003-8728.2018.0204
Abstract:
Firstly, the equilibrium bifurcation analysis of the piezoelectric system proves its nonlinear bistable characteristics, and also obtains the equations of motion. Then, the harmonic balance method is applied to derive relationship of the excitation amplitude, excitation frequency, response amplitude and output power. It could predict dynamic responses of the intrawell and interwell oscillations of the bistable piezoelectric energy harvester. The effects of the parameters, such as damping, impedance, excitation amplitude and excitation frequency on the response amplitude and output power, are analyzed. The results show that the damping and impedance have a great influence on the width and the amplitude of the energy harvester. There exist the high and low energy states for intrawell and interwell oscillations. The maximum power could be got by adjusting impedance under the excitation with different amplitudes and frequencies.
Firstly, the equilibrium bifurcation analysis of the piezoelectric system proves its nonlinear bistable characteristics, and also obtains the equations of motion. Then, the harmonic balance method is applied to derive relationship of the excitation amplitude, excitation frequency, response amplitude and output power. It could predict dynamic responses of the intrawell and interwell oscillations of the bistable piezoelectric energy harvester. The effects of the parameters, such as damping, impedance, excitation amplitude and excitation frequency on the response amplitude and output power, are analyzed. The results show that the damping and impedance have a great influence on the width and the amplitude of the energy harvester. There exist the high and low energy states for intrawell and interwell oscillations. The maximum power could be got by adjusting impedance under the excitation with different amplitudes and frequencies.
2018, 37(2): 193-198.
doi: 10.13433/j.cnki.1003-8728.2018.0205
Abstract:
Based on the multiphase flow pattern and pressure loss mechanism of vertical pipe lifting, the pressure loss compensation coefficient of pipe diameter is proposed according to the pressure loss compensation method. The physical model of the air lift device was established based on the theory of simulated air lift. The new type air lift pipeline structure was designed. The influence of pressure loss compensation coefficient on mass flow rate of air lift under different air flow rate and immersion rate was calculated. Based on this analysis, the water flow rate and lifting efficiency of the gas lift equipment under different compensation coefficients were analyzed. The results show that the diameter of the pipeline has influence on the pressure loss, and the larger the pipe diameter is, the smaller the pressure loss is. The reasonable pressure compensation coefficient can reduce the pressure loss of the pipeline by changing the shape of the pipeline structure, and reduce the pressure loss of the pipeline during the lifting process, thus changing the position of the phase change point of the multiphase flow pattern and improving the efficiency of air lift device. Mass flow rate is the very parameter to measure the ability of air lift device, when the pressure compensation coefficient is positive, the pressure loss of the multiphase flow pattern is reduced and the water flow rate of the air lift device is improved. When the pressure compensation coefficient is increasing from 0 to 4°, the water flow rate of air lift starts to improve and tends to stabilize. When the air flow rate is 4.2 kg/h and 2.5 kg/h, the water flow rate increases to a higher value when the pressure compensation coefficient is 2.5°~3° and 0.7°~1°, and the maximum efficiency of air lift increases by 14.6% and 9.5%.
Based on the multiphase flow pattern and pressure loss mechanism of vertical pipe lifting, the pressure loss compensation coefficient of pipe diameter is proposed according to the pressure loss compensation method. The physical model of the air lift device was established based on the theory of simulated air lift. The new type air lift pipeline structure was designed. The influence of pressure loss compensation coefficient on mass flow rate of air lift under different air flow rate and immersion rate was calculated. Based on this analysis, the water flow rate and lifting efficiency of the gas lift equipment under different compensation coefficients were analyzed. The results show that the diameter of the pipeline has influence on the pressure loss, and the larger the pipe diameter is, the smaller the pressure loss is. The reasonable pressure compensation coefficient can reduce the pressure loss of the pipeline by changing the shape of the pipeline structure, and reduce the pressure loss of the pipeline during the lifting process, thus changing the position of the phase change point of the multiphase flow pattern and improving the efficiency of air lift device. Mass flow rate is the very parameter to measure the ability of air lift device, when the pressure compensation coefficient is positive, the pressure loss of the multiphase flow pattern is reduced and the water flow rate of the air lift device is improved. When the pressure compensation coefficient is increasing from 0 to 4°, the water flow rate of air lift starts to improve and tends to stabilize. When the air flow rate is 4.2 kg/h and 2.5 kg/h, the water flow rate increases to a higher value when the pressure compensation coefficient is 2.5°~3° and 0.7°~1°, and the maximum efficiency of air lift increases by 14.6% and 9.5%.
2018, 37(2): 199-205.
doi: 10.13433/j.cnki.1003-8728.2018.0206
Abstract:
To solve evaluation and decision making problems on module division in modular product design, an evaluation method was presented based on uncertain linguistic multiple attribute decision making. Different module partition methods and criteria may result in different module partition options, calling for proper evaluation to make an appropriate decision. According to the multi-attribute cost evaluation system, and with the help of DULOWG (dependent uncertain linguistic ordered weighted geometric) operator, give evaluation on module division. Attributes of module division options were reckoned, a multi-attribute evaluation matrix was proposed, by using uncertain linguistic variables to adjust the weight, in order to reduce subjectivity and improve its objectivity and validity. Eventually, an optimal solution was arrived with the comprehensive influence of multi-attribute costs by assessing different options. A switch-gear was taken as an example to demonstrate the feasibility and effectiveness of the method. At the same time, this method was compared with the fuzzy analytic hierarchy process, and the advantages of the method were presented.
To solve evaluation and decision making problems on module division in modular product design, an evaluation method was presented based on uncertain linguistic multiple attribute decision making. Different module partition methods and criteria may result in different module partition options, calling for proper evaluation to make an appropriate decision. According to the multi-attribute cost evaluation system, and with the help of DULOWG (dependent uncertain linguistic ordered weighted geometric) operator, give evaluation on module division. Attributes of module division options were reckoned, a multi-attribute evaluation matrix was proposed, by using uncertain linguistic variables to adjust the weight, in order to reduce subjectivity and improve its objectivity and validity. Eventually, an optimal solution was arrived with the comprehensive influence of multi-attribute costs by assessing different options. A switch-gear was taken as an example to demonstrate the feasibility and effectiveness of the method. At the same time, this method was compared with the fuzzy analytic hierarchy process, and the advantages of the method were presented.
2018, 37(2): 206-210.
doi: 10.13433/j.cnki.1003-8728.2018.0207
Abstract:
In this paper, by analyzing and improving the existing spatial linkage mechanism, a kind of 6R symmetric spatial flapping mechanism with two degrees of freedom is proposed for flapping-wing air vehicle. Firstly, through the theoretical calculation and simulation analysis of 6R spatial flapping-wing mechanism, the effect of different pole lengths on the "8" shape trajectory of wingtip is obtained. Then, a design method is proposed to improve the flight stability by adjusting the average dihedral angle of flapping-wing. The proposed mechanism is simulated by Adams software and the results show that the design of spatial flapping-wing mechanism is robust and steady, and the requirement of 90° phase difference between flapping angle and torsion angle is met.
In this paper, by analyzing and improving the existing spatial linkage mechanism, a kind of 6R symmetric spatial flapping mechanism with two degrees of freedom is proposed for flapping-wing air vehicle. Firstly, through the theoretical calculation and simulation analysis of 6R spatial flapping-wing mechanism, the effect of different pole lengths on the "8" shape trajectory of wingtip is obtained. Then, a design method is proposed to improve the flight stability by adjusting the average dihedral angle of flapping-wing. The proposed mechanism is simulated by Adams software and the results show that the design of spatial flapping-wing mechanism is robust and steady, and the requirement of 90° phase difference between flapping angle and torsion angle is met.
2018, 37(2): 211-219.
doi: 10.13433/j.cnki.1003-8728.2018.0208
Abstract:
For the case of the clearance between the male and female rotors and the clearance between the rotors and the cylinder is fewer than tens of microns actually, overcoming the shortcomings that it enlarged the model gap to the millimetre level in order to draw a high quality body grid when Fluent moving grid computing so as to avoid the phenomenon of negative volume grid in the process of calculation, a new method to replace the moving grid technology is explored, for the use of CFD calculation and analysis of twin screw compressor. With which, the clearance of the fluid domains for CFD simulation is reduced, and the gap between the model is processed to millimeter level or even zero, meanwhile, the simulation accuracy and reliability of the analysis results are effectively improved. For the new CFD simulation method, the surface meshes of screw compressor fluid domains are generated in ANSA and the grids of the domains are generated with polyhedral meshes and trimmed meshes in STAR-CCM+, and the CFD simulation of screw compressors is carried out by Morphing in STAR-CCM+ solver, whose analysis results are consist with theory and the actual situation,and can be used to guide the screw rotor profiles design and optimization after analysis.
For the case of the clearance between the male and female rotors and the clearance between the rotors and the cylinder is fewer than tens of microns actually, overcoming the shortcomings that it enlarged the model gap to the millimetre level in order to draw a high quality body grid when Fluent moving grid computing so as to avoid the phenomenon of negative volume grid in the process of calculation, a new method to replace the moving grid technology is explored, for the use of CFD calculation and analysis of twin screw compressor. With which, the clearance of the fluid domains for CFD simulation is reduced, and the gap between the model is processed to millimeter level or even zero, meanwhile, the simulation accuracy and reliability of the analysis results are effectively improved. For the new CFD simulation method, the surface meshes of screw compressor fluid domains are generated in ANSA and the grids of the domains are generated with polyhedral meshes and trimmed meshes in STAR-CCM+, and the CFD simulation of screw compressors is carried out by Morphing in STAR-CCM+ solver, whose analysis results are consist with theory and the actual situation,and can be used to guide the screw rotor profiles design and optimization after analysis.
2018, 37(2): 220-225.
doi: 10.13433/j.cnki.1003-8728.2018.0209
Abstract:
The kinematic and dynamic constraints of under-actuated mechanism is incomplete and its movement is uncertain. The elastic reaction of flexible joint involved in an under-actuated mechanism can compensate for the incompleteness of dynamic constraints to some extent, but the certainty of the motion still related to the initial state of the mechanism and the stiffness of the flexible joint. To solve this problem, taking a planar 2-DOF under-actuated mechanism with a flexible joint as an example, a numerical iterative algorithm is proposed to solve the kinematics and dynamics of the mechanism, the deterministic motion was obtained by solving the kinematics and dynamics equations. First, the kinematics model and dynamics model are established, then using MATLAB programming, the optimal stiffness range under different initial state are obtained. Finally, the fitted curve between optimal driving torque and spring stiffness are also obtained by analyzing multiple sets of data.
The kinematic and dynamic constraints of under-actuated mechanism is incomplete and its movement is uncertain. The elastic reaction of flexible joint involved in an under-actuated mechanism can compensate for the incompleteness of dynamic constraints to some extent, but the certainty of the motion still related to the initial state of the mechanism and the stiffness of the flexible joint. To solve this problem, taking a planar 2-DOF under-actuated mechanism with a flexible joint as an example, a numerical iterative algorithm is proposed to solve the kinematics and dynamics of the mechanism, the deterministic motion was obtained by solving the kinematics and dynamics equations. First, the kinematics model and dynamics model are established, then using MATLAB programming, the optimal stiffness range under different initial state are obtained. Finally, the fitted curve between optimal driving torque and spring stiffness are also obtained by analyzing multiple sets of data.
2018, 37(2): 226-231.
doi: 10.13433/j.cnki.1003-8728.2018.0210
Abstract:
Insufficient braking torque of magneto-rheological fluid(MRF)brake is always a key factor restricting the application of MRF brake. In this paper, by adding semicircular grooves and ridges on the surface of the conventional brake disc, the working area of the brake disc is increased and the braking torque of the MRF brake is increased. The model of the braking torque with the combination of the ridge and the groove is established, and the parameters influencing the torque are obtained. The location of the center of the ridge is obtained by the mathematical derivation method. The magnetic field of the working gap of the circular groove brake disc is analyzed by ANSYS electromagnetic module to determine the size of the ridge. The research results show that the brake torque of the circular groove disc-type MRF brake is improved by 33% compared with that of the conventional disc-type MRF brake.
Insufficient braking torque of magneto-rheological fluid(MRF)brake is always a key factor restricting the application of MRF brake. In this paper, by adding semicircular grooves and ridges on the surface of the conventional brake disc, the working area of the brake disc is increased and the braking torque of the MRF brake is increased. The model of the braking torque with the combination of the ridge and the groove is established, and the parameters influencing the torque are obtained. The location of the center of the ridge is obtained by the mathematical derivation method. The magnetic field of the working gap of the circular groove brake disc is analyzed by ANSYS electromagnetic module to determine the size of the ridge. The research results show that the brake torque of the circular groove disc-type MRF brake is improved by 33% compared with that of the conventional disc-type MRF brake.
2018, 37(2): 232-236.
doi: 10.13433/j.cnki.1003-8728.2018.0211
Abstract:
Considering the impact of joint-torque variation of robot on the working quality, and aiming at the force control problem during the complex trajectory planning, an optimized algorithm for dynamics problems based on direct collocation method was proposed. With the analysis of robot's dynamical model, the direct collocation method was used to turn the robot's dynamic optimization problem into multi-objective optimization problem of nonlinear equations, and the sequential quadratic programming was used to solve the equations.For the initial value sensitivity problem which exists in the highly non-convex function extreme value solving process of the equations, the linear quadratic regulator was used to provide iterative initial values for sequential quadratic programming. Theoretical analysis and numerical simulation results indicated that the proposed method can guarantee smooth variation of robot's torque, angle and angular velocity during complex trajectory operation, stabilize working quality, and it can control energy consumption during working process more reasonably.
Considering the impact of joint-torque variation of robot on the working quality, and aiming at the force control problem during the complex trajectory planning, an optimized algorithm for dynamics problems based on direct collocation method was proposed. With the analysis of robot's dynamical model, the direct collocation method was used to turn the robot's dynamic optimization problem into multi-objective optimization problem of nonlinear equations, and the sequential quadratic programming was used to solve the equations.For the initial value sensitivity problem which exists in the highly non-convex function extreme value solving process of the equations, the linear quadratic regulator was used to provide iterative initial values for sequential quadratic programming. Theoretical analysis and numerical simulation results indicated that the proposed method can guarantee smooth variation of robot's torque, angle and angular velocity during complex trajectory operation, stabilize working quality, and it can control energy consumption during working process more reasonably.
2018, 37(2): 237-243.
doi: 10.13433/j.cnki.1003-8728.2018.0212
Abstract:
Aiming at the early fault features of roller bearings are too weak so that it is difficult to get effective identification, an early fault diagnosis method based on Adaboost_SVM integrated learning model for rolling bearing early fault diagnosis is proposed in this paper. Firstly, those sensitive feature parameters are selected through analyzing the feature parameters developing trend based on the rolling bearing vibration data in whole life process acquired by the university of Cincinnati. Then, the ensemble learning model with Adaboost_SVM is constructed, and applied to the rolling bearing early fault identification. Adaboost can adaptively improve the classification performance of conventional SVM. Compared with the traditional single SVM classifier, Adaboost_SVM has the best stability and the highest early fault diagnosis accuracy. The experimental results show that the Adaboost_SVM can effectively diagnose rolling bearing early failure modes with those sensitive feature parameters.
Aiming at the early fault features of roller bearings are too weak so that it is difficult to get effective identification, an early fault diagnosis method based on Adaboost_SVM integrated learning model for rolling bearing early fault diagnosis is proposed in this paper. Firstly, those sensitive feature parameters are selected through analyzing the feature parameters developing trend based on the rolling bearing vibration data in whole life process acquired by the university of Cincinnati. Then, the ensemble learning model with Adaboost_SVM is constructed, and applied to the rolling bearing early fault identification. Adaboost can adaptively improve the classification performance of conventional SVM. Compared with the traditional single SVM classifier, Adaboost_SVM has the best stability and the highest early fault diagnosis accuracy. The experimental results show that the Adaboost_SVM can effectively diagnose rolling bearing early failure modes with those sensitive feature parameters.
2018, 37(2): 244-249.
doi: 10.13433/j.cnki.1003-8728.2018.0213
Abstract:
When using competitive behavior dynamics coordination methods to mobile robot path planning in unknown environment, the robot motion velocity parameters are difficult determined and it is easy to generate parameter oscillation in behavior competition, leading to the path of planning not optimization. A new path planning method based on particle swarm optimization for behavior dynamics algorithm is proposed. In this method, the particle swarm optimization algorithm is used to integrate the basic behaviors in path planning process based on the behavior dynamics model, which instead of the behavior parameter coordination of the competitive behavior dynamics. So that the robot can automatically obtain the weight of each basic behavior according to the real-time environment information collected by the vision senor. By comparing the proposed method with the competitive behavior dynamic coordination methods, the experiment results verify the feasibility and superiority of the proposed method.
When using competitive behavior dynamics coordination methods to mobile robot path planning in unknown environment, the robot motion velocity parameters are difficult determined and it is easy to generate parameter oscillation in behavior competition, leading to the path of planning not optimization. A new path planning method based on particle swarm optimization for behavior dynamics algorithm is proposed. In this method, the particle swarm optimization algorithm is used to integrate the basic behaviors in path planning process based on the behavior dynamics model, which instead of the behavior parameter coordination of the competitive behavior dynamics. So that the robot can automatically obtain the weight of each basic behavior according to the real-time environment information collected by the vision senor. By comparing the proposed method with the competitive behavior dynamic coordination methods, the experiment results verify the feasibility and superiority of the proposed method.
2018, 37(2): 250-257.
doi: 10.13433/j.cnki.1003-8728.2018.0214
Abstract:
In the process of borehole hydraulic jet mining, the effect of chip hold-down produced at the bottom of the well on debris easily leads to poor transport capacity of an airlift system. To solve this problem, a new particle feeding method similar to the real situation was proposed, and the water jet nozzles were introduced to investigate the airlift performance and its critical points. The results are found as follows:The chip hold-down could be eliminated in the case of N=3, in turn, this makes the mass flow rate of solids and lifting efficiency increase greatly and then have a slight variations with increasing N; The appropriate inhomogeneity of spatial distribution of the water jet nozzles are also given to promote the airlift performance. Moreover, the mass flow rate of solids and lifting efficiency are especially improved by using water jet nozzles in the case of HQG,L for conveying water. However, the critical air flow rate QG,S and the critical volumetric flux JL,cri corresponding to lifting river sand are significantly decreased due to the disappearance of chip hold-down and then have a slight decrease with the increase of N. The JL,cri is very close to the computational value of theoretical model uLcri when H=0. But as H rises, their differences increase gradually.
In the process of borehole hydraulic jet mining, the effect of chip hold-down produced at the bottom of the well on debris easily leads to poor transport capacity of an airlift system. To solve this problem, a new particle feeding method similar to the real situation was proposed, and the water jet nozzles were introduced to investigate the airlift performance and its critical points. The results are found as follows:The chip hold-down could be eliminated in the case of N=3, in turn, this makes the mass flow rate of solids and lifting efficiency increase greatly and then have a slight variations with increasing N; The appropriate inhomogeneity of spatial distribution of the water jet nozzles are also given to promote the airlift performance. Moreover, the mass flow rate of solids and lifting efficiency are especially improved by using water jet nozzles in the case of HQG,L for conveying water. However, the critical air flow rate QG,S and the critical volumetric flux JL,cri corresponding to lifting river sand are significantly decreased due to the disappearance of chip hold-down and then have a slight decrease with the increase of N. The JL,cri is very close to the computational value of theoretical model uLcri when H=0. But as H rises, their differences increase gradually.
2018, 37(2): 258-262.
doi: 10.13433/j.cnki.1003-8728.2018.0215
Abstract:
Spline parts are widely used in power transmission mechanism with large carrying capacity, good guide,high centering precision. The traditional processing method is mainly cutting process and extrusion, rolling of non cutting process. Limited by the process, the thin-walled workpieces are extremely easy to wrongly deform in the spline machining and the accuracy cannot meet the requirement of process. Because the machining process of high temperature alloy material is poor and the cutting force is big, it is difficult to deform the thin wall and slender shaft of aeronautical material. In the process of axial vibration extrusion of spline with frequency and amplitude modulation, the additional vibration can effectively reduce the deformation resistance and improve the precision. Study onthe extrusion process parameters, compared with the traditional process, can find out the qualitative relations of parameters, on which optimization of vibration extrusion process parameters and adjustment of the machine is based. Thus, there is much guiding significance for processing design of spline vibration extrusion of thin wall and slender shaft in the measure and analysis of FM modulation extrusion process parameters.
Spline parts are widely used in power transmission mechanism with large carrying capacity, good guide,high centering precision. The traditional processing method is mainly cutting process and extrusion, rolling of non cutting process. Limited by the process, the thin-walled workpieces are extremely easy to wrongly deform in the spline machining and the accuracy cannot meet the requirement of process. Because the machining process of high temperature alloy material is poor and the cutting force is big, it is difficult to deform the thin wall and slender shaft of aeronautical material. In the process of axial vibration extrusion of spline with frequency and amplitude modulation, the additional vibration can effectively reduce the deformation resistance and improve the precision. Study onthe extrusion process parameters, compared with the traditional process, can find out the qualitative relations of parameters, on which optimization of vibration extrusion process parameters and adjustment of the machine is based. Thus, there is much guiding significance for processing design of spline vibration extrusion of thin wall and slender shaft in the measure and analysis of FM modulation extrusion process parameters.
2018, 37(2): 263-269.
doi: 10.13433/j.cnki.1003-8728.2018.0216
Abstract:
In this paper, the influence of the material constitutive parameters on the serrated chip is analyzed based on the orthogonal cutting model in high speed machining. The results show that the cutting force and cutting temperature change linearly with the constitutive parameters A, B, C and n; The parameters A and n have great influence on the chip morphology, while the parameters B, C and m influence the curvature radius of serrated chip; However, the effects of the parameters C and m on the chip morphology, cutting force and cutting temperature can be ignored at C below 0.01 and m above 5. The value of A increases with the increasing of hardness value and decreasing of n of workpiece. For materials depending on strain rate, value of C is larger; And for workpiece vulnerable to temperature, value of m is smaller. It can provide a guidance for predicting the variation of the material parameters under different hardness, inferring the material hardness value according to the material constitutive parameters and the comparison of material property difference.
In this paper, the influence of the material constitutive parameters on the serrated chip is analyzed based on the orthogonal cutting model in high speed machining. The results show that the cutting force and cutting temperature change linearly with the constitutive parameters A, B, C and n; The parameters A and n have great influence on the chip morphology, while the parameters B, C and m influence the curvature radius of serrated chip; However, the effects of the parameters C and m on the chip morphology, cutting force and cutting temperature can be ignored at C below 0.01 and m above 5. The value of A increases with the increasing of hardness value and decreasing of n of workpiece. For materials depending on strain rate, value of C is larger; And for workpiece vulnerable to temperature, value of m is smaller. It can provide a guidance for predicting the variation of the material parameters under different hardness, inferring the material hardness value according to the material constitutive parameters and the comparison of material property difference.
2018, 37(2): 270-275.
doi: 10.13433/j.cnki.1003-8728.2018.0217
Abstract:
In the single point incremental forming process, the different process conditions and forming force will largely change the contact stress and strain state, sheet rupture, accumulation and wrinkling defects, finally inducing the lower forming quality and precision. An ultrasonic vibration single point incremental forming method was proposed in this paper based on the numerical control technology. This method will give rise to a lower force and a higher quality by changing the momentary contact state, lubrication condition and defromation mechanism between the tool head and the workpiece. The ultrasonic vibration spindle and sheet clamping system were designed based on the experiment platform of Hass numerical control machine and the test forming force system of Kistler was also designed. Through a large number of experiments, the forming force variation regularities under different vibration process were obtained.
In the single point incremental forming process, the different process conditions and forming force will largely change the contact stress and strain state, sheet rupture, accumulation and wrinkling defects, finally inducing the lower forming quality and precision. An ultrasonic vibration single point incremental forming method was proposed in this paper based on the numerical control technology. This method will give rise to a lower force and a higher quality by changing the momentary contact state, lubrication condition and defromation mechanism between the tool head and the workpiece. The ultrasonic vibration spindle and sheet clamping system were designed based on the experiment platform of Hass numerical control machine and the test forming force system of Kistler was also designed. Through a large number of experiments, the forming force variation regularities under different vibration process were obtained.
2018, 37(2): 276-279.
doi: 10.13433/j.cnki.1003-8728.2018.0218
Abstract:
In order to improve the accuracy of tool wear area detection, a new method for tool wear detection based on the characteristics of tool wear area is proposed. Firstly, the tool image is filtered by using Gauss filter to eliminate the noise information and gain a filter image. Then, the background texture information is extracted by using the difference of Gaussian filter to get a difference image. On the basis, the center-surround operation is used to obtain the saliency map between the filter image and the difference image, by which can eliminate high frequency noise and uneven illumination of low frequency background information, and improve saliency of the tool wear area. Finally, the tool wear region is segmented and filtered according to the characteristics of tool wear area. The experimental results show that the method can accurately detect the tool wear area and has higher detection accuracy.
In order to improve the accuracy of tool wear area detection, a new method for tool wear detection based on the characteristics of tool wear area is proposed. Firstly, the tool image is filtered by using Gauss filter to eliminate the noise information and gain a filter image. Then, the background texture information is extracted by using the difference of Gaussian filter to get a difference image. On the basis, the center-surround operation is used to obtain the saliency map between the filter image and the difference image, by which can eliminate high frequency noise and uneven illumination of low frequency background information, and improve saliency of the tool wear area. Finally, the tool wear region is segmented and filtered according to the characteristics of tool wear area. The experimental results show that the method can accurately detect the tool wear area and has higher detection accuracy.
2018, 37(2): 280-286.
doi: 10.13433/j.cnki.1003-8728.2018.0219
Abstract:
An interval optimization method is suggested based on the dimension tolerancewhich are described by using the interval analysis. In this method, the basic dimensions and their tolerances are both taken as the design variables. And the maximum of the weight factor that indicated the level of manufacturability is selected as the design object, which is constrained by the original strictest limits and the dominated demand of policymakers. Furthermore, the model is converted into a deterministic optimization problem because of the uncertainty of the design parameters in object and constrains have been considered and handled by interval center and right boundary. The method has settled a type of practical engineering problems such as how to maximize the allowance set under given nominal design and the most severe constrains. At last, the method is applied to a numerical calculation example and a vehicle crashworthiness design. The results of these applications demonstrate the efficiency and the engineering practicability of the presented approach.
An interval optimization method is suggested based on the dimension tolerancewhich are described by using the interval analysis. In this method, the basic dimensions and their tolerances are both taken as the design variables. And the maximum of the weight factor that indicated the level of manufacturability is selected as the design object, which is constrained by the original strictest limits and the dominated demand of policymakers. Furthermore, the model is converted into a deterministic optimization problem because of the uncertainty of the design parameters in object and constrains have been considered and handled by interval center and right boundary. The method has settled a type of practical engineering problems such as how to maximize the allowance set under given nominal design and the most severe constrains. At last, the method is applied to a numerical calculation example and a vehicle crashworthiness design. The results of these applications demonstrate the efficiency and the engineering practicability of the presented approach.
2018, 37(2): 287-292.
doi: 10.13433/j.cnki.1003-8728.2018.0220
Abstract:
After measuring the thickness for normal pole piece of lithium battery after the process of rolling, the author has discovered that the thickness of pole piece is not uniform. By setting up mechanical mathematic model for the initiative roller of roller press, the non-uniformity mechanism of pole piece thickness has been figured out. To correct this disadvantage and promote the quality of the lithium battery, the proposal to improve the structure of traditional roller press has beendesigned, where the bearing seats and two sets of hydraulic cylinders with different forces will be installed at both sides of roller. a model and analysis for the optimized roller press via computer software Solidworkshave studied, from which we can work out the force applied on the hydraulic cylinder to ensure the minimum bending stress of the roller. Then set up design platform for pole piece of roller based on computer programming languages software to increase the speed to obtain related working parameters for optimized roller press. The experiment results have shown that the optimized roller press can make the thickness of lithium battery pole piece more uniform and greatly improve the automation level for the production of lithium battery.
After measuring the thickness for normal pole piece of lithium battery after the process of rolling, the author has discovered that the thickness of pole piece is not uniform. By setting up mechanical mathematic model for the initiative roller of roller press, the non-uniformity mechanism of pole piece thickness has been figured out. To correct this disadvantage and promote the quality of the lithium battery, the proposal to improve the structure of traditional roller press has beendesigned, where the bearing seats and two sets of hydraulic cylinders with different forces will be installed at both sides of roller. a model and analysis for the optimized roller press via computer software Solidworkshave studied, from which we can work out the force applied on the hydraulic cylinder to ensure the minimum bending stress of the roller. Then set up design platform for pole piece of roller based on computer programming languages software to increase the speed to obtain related working parameters for optimized roller press. The experiment results have shown that the optimized roller press can make the thickness of lithium battery pole piece more uniform and greatly improve the automation level for the production of lithium battery.
2018, 37(2): 293-299.
doi: 10.13433/j.cnki.1003-8728.2018.0221
Abstract:
The fault detection method based on random compression of frequency domain and sparse representation classification for rotation machinery is proposed. The random compression of frequency domain is a way to achieve feature extraction. Fourier Transform converts vibration signal to get the amplitude sequence. And then, the compressive measurement of amplitude sequence is implemented with random matrix as fault feature vector. In sparse representation classification, the fault feature library is composed of fault feature vectors of which fault pattern is known. The classification of test feature vector is converted to a sparse optimization problem. The sparse representation coefficient of test feature vector under fault feature library is obtained using Orthogonal Matching Pursuit. With the sparse representation coefficient, the reconstruction residual of test feature vector under each fault pattern is obtained and the fault detection is done. The effectiveness of the proposed fault detection method is verified through the experiment of gear and bearing vibration.
The fault detection method based on random compression of frequency domain and sparse representation classification for rotation machinery is proposed. The random compression of frequency domain is a way to achieve feature extraction. Fourier Transform converts vibration signal to get the amplitude sequence. And then, the compressive measurement of amplitude sequence is implemented with random matrix as fault feature vector. In sparse representation classification, the fault feature library is composed of fault feature vectors of which fault pattern is known. The classification of test feature vector is converted to a sparse optimization problem. The sparse representation coefficient of test feature vector under fault feature library is obtained using Orthogonal Matching Pursuit. With the sparse representation coefficient, the reconstruction residual of test feature vector under each fault pattern is obtained and the fault detection is done. The effectiveness of the proposed fault detection method is verified through the experiment of gear and bearing vibration.
2018, 37(2): 300-305.
doi: 10.13433/j.cnki.1003-8728.2018.0222
Abstract:
In the process industry, stiction nonlinearity existing in pneumatic control valve will lead to performance deterioration even oscillation in the control loops. Since the existing methods using fuzzy clustering algorithm may easily make wrong diagnosis in the detection, an improved method was proposed in this paper, which can effectively recognize the external disturbance and valve stiction. Firstly, the routine operating data were clustered using fuzzy clustering algorithm to obtain cluster centers and the goodness-of-fit was evaluated according to the distribution characteristic of sticky valve input-output data. The convex-concave property recognition of the quadrilateral formed by cluster centers was taken. On basis of the distribution of cluster centers, a new stiction index was defined. The simulations and two flow control loops of chemical industry were used to verify the validity and veracity of the improved method.
In the process industry, stiction nonlinearity existing in pneumatic control valve will lead to performance deterioration even oscillation in the control loops. Since the existing methods using fuzzy clustering algorithm may easily make wrong diagnosis in the detection, an improved method was proposed in this paper, which can effectively recognize the external disturbance and valve stiction. Firstly, the routine operating data were clustered using fuzzy clustering algorithm to obtain cluster centers and the goodness-of-fit was evaluated according to the distribution characteristic of sticky valve input-output data. The convex-concave property recognition of the quadrilateral formed by cluster centers was taken. On basis of the distribution of cluster centers, a new stiction index was defined. The simulations and two flow control loops of chemical industry were used to verify the validity and veracity of the improved method.
2018, 37(2): 306-312.
doi: 10.13433/j.cnki.1003-8728.2018.0223
Abstract:
This article integrates a driver with a controller and improves kinematic mathematical model of a Delta robot to achieve the drive and control integration in the Delta robot. The drive and control integrated technology uses the architecture of ARM + DSP, the ARM core in the master subsystem mainly achieves the trajectory generation, peripheral control and communication. The DSP C28 core in the control subsystem mainly achieves the control of a servo motor and the motion control of the Delta robot. Meanwhile, an improved method which ueses the geometric vector method is presented to desolve the kinematic mathematical model of the Delta robot which makes the software design more convenient. Finally, the application results obtained with the Delta robot system-duplicated robot body shows that the robot's positioning accuracy error is ±0.01 mm, the error for each axis is stable and reliable, and the overall performance of the robot system fulfills the functional requirements of the motion control system.
This article integrates a driver with a controller and improves kinematic mathematical model of a Delta robot to achieve the drive and control integration in the Delta robot. The drive and control integrated technology uses the architecture of ARM + DSP, the ARM core in the master subsystem mainly achieves the trajectory generation, peripheral control and communication. The DSP C28 core in the control subsystem mainly achieves the control of a servo motor and the motion control of the Delta robot. Meanwhile, an improved method which ueses the geometric vector method is presented to desolve the kinematic mathematical model of the Delta robot which makes the software design more convenient. Finally, the application results obtained with the Delta robot system-duplicated robot body shows that the robot's positioning accuracy error is ±0.01 mm, the error for each axis is stable and reliable, and the overall performance of the robot system fulfills the functional requirements of the motion control system.
2018, 37(2): 313-317.
doi: 10.13433/j.cnki.1003-8728.2018.0224
Abstract:
The surface exposure prototype was a high-speed technology in the field of stereo lithography, and the exposure time was a key parameters in the processing process:if the exposure time was too short, the deformation of parts would be high that the resin layer would fall into the next layer; on the contrary, if the exposure time was too long, the object couldn't be manufactured that the vacuum force caused by the curing layer and the resin tank made the print the metal platform generated when an increase in tension increases. Firstly, by comparing the different exposure time samples of the gel content and the double bond conversion rate, it shown that the curing degree increased with the increasing of exposure time, and cured degree in 10~20 s could reach 90%; by comparingthe different samples of storage tensile modulus, it shown the mechanical properties increased with the increasinbgof exposure time. Through the comprehensive comparison of the degree of curing, molding mechanical properties, molding precision three factors, the best exposure time was of 15 s. Finally, the rationality of the above best exposure time was verified by two ACME-DLP layered experiments.
The surface exposure prototype was a high-speed technology in the field of stereo lithography, and the exposure time was a key parameters in the processing process:if the exposure time was too short, the deformation of parts would be high that the resin layer would fall into the next layer; on the contrary, if the exposure time was too long, the object couldn't be manufactured that the vacuum force caused by the curing layer and the resin tank made the print the metal platform generated when an increase in tension increases. Firstly, by comparing the different exposure time samples of the gel content and the double bond conversion rate, it shown that the curing degree increased with the increasing of exposure time, and cured degree in 10~20 s could reach 90%; by comparingthe different samples of storage tensile modulus, it shown the mechanical properties increased with the increasinbgof exposure time. Through the comprehensive comparison of the degree of curing, molding mechanical properties, molding precision three factors, the best exposure time was of 15 s. Finally, the rationality of the above best exposure time was verified by two ACME-DLP layered experiments.
2018, 37(2): 318-323.
doi: 10.13433/j.cnki.1003-8728.2018.0225
Abstract:
In order to explore the failure mechanism of an aircraft engine's crankshaft torsional vibration damper, the finite element modal analysis and experimental verification of the engine shafting are carried out. Then, axial vibration displacement amplitude of the shaft is calculated based on coupled torsional-axial vibration theory and harmonic response analysis. On the basis of calculation results, the failure analysis of the torsional vibration damper is completed. The research results show that the aircraft engine often works in the transition condition, which causes torsional resonance and coupled torsional-axial vibration. The axial vibration makes the shafting axial displacement larger. The coupled axial force is the main cause of torsional vibration damper failure.
In order to explore the failure mechanism of an aircraft engine's crankshaft torsional vibration damper, the finite element modal analysis and experimental verification of the engine shafting are carried out. Then, axial vibration displacement amplitude of the shaft is calculated based on coupled torsional-axial vibration theory and harmonic response analysis. On the basis of calculation results, the failure analysis of the torsional vibration damper is completed. The research results show that the aircraft engine often works in the transition condition, which causes torsional resonance and coupled torsional-axial vibration. The axial vibration makes the shafting axial displacement larger. The coupled axial force is the main cause of torsional vibration damper failure.
2018, 37(2): 324-328.
doi: 10.13433/j.cnki.1003-8728.2018.0226
Abstract:
A new intelligent method of transmission scheme for aero-engine accessory drive system with parallel shafts system is investigated, Considering the influence of both attachment interference and the design criterion of transmission, the drive system of attachments is regarded as a single-input and multi-output black box. By using the knowledge of graph theory, the adjacency matrix is defined, then referring to TSP (Traveling Salesman Problem), the weight of the attachment node path can be determined except the possibility of forming a transmission chain between attachment units that contrary to the criterion. The feasible layout schemes of the parallel shafts transmission system for aero-engine accessory are obtained by using Breadth First Search. The different degree of any units is connected with various driving modes. The optimal scheme is obtained automatically from feasible schemes under the target of smallest drive chain volume. The validity of the intelligent scheme design method is verified by the example of six-shafts attachments transmission scheme design.
A new intelligent method of transmission scheme for aero-engine accessory drive system with parallel shafts system is investigated, Considering the influence of both attachment interference and the design criterion of transmission, the drive system of attachments is regarded as a single-input and multi-output black box. By using the knowledge of graph theory, the adjacency matrix is defined, then referring to TSP (Traveling Salesman Problem), the weight of the attachment node path can be determined except the possibility of forming a transmission chain between attachment units that contrary to the criterion. The feasible layout schemes of the parallel shafts transmission system for aero-engine accessory are obtained by using Breadth First Search. The different degree of any units is connected with various driving modes. The optimal scheme is obtained automatically from feasible schemes under the target of smallest drive chain volume. The validity of the intelligent scheme design method is verified by the example of six-shafts attachments transmission scheme design.
