Author Center
Editor Work
Peer Review
Editorial Entry
Email Alert
RSS2021 Vol. 40, No. 3
Display Method:
2021, 40(3): 329-336.
doi: 10.13433/j.cnki.1003-8728.20200073
PDF 2835KB
Abstract:
In order to improve the limitation of the traditional multiple linear fitting transfer function methods, to analyze and predict combustion noise of internal combustion engines more accurately, the improved genetic algorithm was used to optimize the combustion noise transfer functions and mechanical noise. Firstly, the combustion noise transfer functions were calculated by changing oil injection strategies under the same working condition, and the consistency rule of the combustion noise transfer functions under different loads was verified by experiments. According to this rule, combustion noise transfer functions were calculated under load characteristics, and overall noises were predicted under different oil injection strategies with cylinder pressure data. The results showed that the improved genetic algorithm had more advantages in calculating the combustion noise transfer function; the combustion noise transfer function and mechanical noise can be accurately obtained by calculating the load characteristic data, and predicted deviations of overall noise were less than 2%.
In order to improve the limitation of the traditional multiple linear fitting transfer function methods, to analyze and predict combustion noise of internal combustion engines more accurately, the improved genetic algorithm was used to optimize the combustion noise transfer functions and mechanical noise. Firstly, the combustion noise transfer functions were calculated by changing oil injection strategies under the same working condition, and the consistency rule of the combustion noise transfer functions under different loads was verified by experiments. According to this rule, combustion noise transfer functions were calculated under load characteristics, and overall noises were predicted under different oil injection strategies with cylinder pressure data. The results showed that the improved genetic algorithm had more advantages in calculating the combustion noise transfer function; the combustion noise transfer function and mechanical noise can be accurately obtained by calculating the load characteristic data, and predicted deviations of overall noise were less than 2%.
2021, 40(3): 337-343.
doi: 10.13433/j.cnki.1003-8728.20200065
Abstract:
Aiming at the contradiction between the mobility and the adsorption of the wall-climbing robot with permanent magnet adsorption, an electromagnet power on-off mechanism is proposed, and a wall-climbing robot based on this mechanism is designed. The mechanical design of the robot is carried out. In order to prevent the robot from slipping, overturning and flipping, the mechanics of the robot is analyzed and the magnetic field of the electromagnet is simulated with COMSOL software, and then the design of the electromagnet and the manufacture of the robot is completed. The experimental results show that the robot can crawl flexibly on different angle walls in any posture, which verifies the reliability of the electromagnet power on-off mechanism. The robot has wide application in the inspection of large steel structures.
Aiming at the contradiction between the mobility and the adsorption of the wall-climbing robot with permanent magnet adsorption, an electromagnet power on-off mechanism is proposed, and a wall-climbing robot based on this mechanism is designed. The mechanical design of the robot is carried out. In order to prevent the robot from slipping, overturning and flipping, the mechanics of the robot is analyzed and the magnetic field of the electromagnet is simulated with COMSOL software, and then the design of the electromagnet and the manufacture of the robot is completed. The experimental results show that the robot can crawl flexibly on different angle walls in any posture, which verifies the reliability of the electromagnet power on-off mechanism. The robot has wide application in the inspection of large steel structures.
2021, 40(3): 344-349.
doi: 10.13433/j.cnki.1003-8728.20200061
Abstract:
An improved quadratic programming method is proposed to deal with the problem of tension distribution for redundantly constrained cable-driven parallel robots. The kinematics model of the general redundantly constrained cable-driven parallel robot is established, and the dynamic equations of the general redundantly constrained cable-driven parallel robot are obtained after the force analysis of the mechanism. Combined with the idea of closed-form force, the concept of reference force is introduced, and the traditional quadratic programming method is improved to obtain the optimization model of cable tension distribution suitable for redundantly constrained cable-driven parallel robots. Taken a 6-DOF cable-driven parallel robot with eight cables as an example, MATLAB/Simulink/xPC tool is used for real-time simulation experiments to achieve dynamic operation of the parallel robot under two typical spatial motion trajectories. The improved quadratic programming algorithm, the traditional quadratic programming algorithm and the closed-form algorithm are used to solve the problem of tension distribution respectively. Comparing the simulation results of these three tension distribution algorithms, it is verified that the improved quadratic programming algorithm for solving the problem of tension distribution is reasonable.
An improved quadratic programming method is proposed to deal with the problem of tension distribution for redundantly constrained cable-driven parallel robots. The kinematics model of the general redundantly constrained cable-driven parallel robot is established, and the dynamic equations of the general redundantly constrained cable-driven parallel robot are obtained after the force analysis of the mechanism. Combined with the idea of closed-form force, the concept of reference force is introduced, and the traditional quadratic programming method is improved to obtain the optimization model of cable tension distribution suitable for redundantly constrained cable-driven parallel robots. Taken a 6-DOF cable-driven parallel robot with eight cables as an example, MATLAB/Simulink/xPC tool is used for real-time simulation experiments to achieve dynamic operation of the parallel robot under two typical spatial motion trajectories. The improved quadratic programming algorithm, the traditional quadratic programming algorithm and the closed-form algorithm are used to solve the problem of tension distribution respectively. Comparing the simulation results of these three tension distribution algorithms, it is verified that the improved quadratic programming algorithm for solving the problem of tension distribution is reasonable.
2021, 40(3): 350-355.
doi: 10.13433/j.cnki.1003-8728.20200077
Abstract:
Topological optimization is an effective means to improve structural performance and achieve totally novel designs. With the Heaviside projection function, this article presents a topological optimization method based on constraining the density design variables. The method adopts a linear material interpolation model without penalization, which is quite different from the solid isotropic material with penalization (SIMP) method. Its basic idea is, firstly, to find the optimal structural ″thickness″ (material density) distribution with the optimality criterion method. Secondly, sequential constraints are applied to the material density distribution through a floating projection function to push it towards a 0/1 distribution step by step. In this topological optimization method, the material density directly represents the material ″thickness″ distribution in the structure. Therefore the solutions of the proposed topological optimization method are fundamentally different from the SIMP method. Numerical examples demonstrate that the proposed method can obtain clearer and smoother structural topologies and avoid the difficulties in selecting artificial material interpolation schemes.
Topological optimization is an effective means to improve structural performance and achieve totally novel designs. With the Heaviside projection function, this article presents a topological optimization method based on constraining the density design variables. The method adopts a linear material interpolation model without penalization, which is quite different from the solid isotropic material with penalization (SIMP) method. Its basic idea is, firstly, to find the optimal structural ″thickness″ (material density) distribution with the optimality criterion method. Secondly, sequential constraints are applied to the material density distribution through a floating projection function to push it towards a 0/1 distribution step by step. In this topological optimization method, the material density directly represents the material ″thickness″ distribution in the structure. Therefore the solutions of the proposed topological optimization method are fundamentally different from the SIMP method. Numerical examples demonstrate that the proposed method can obtain clearer and smoother structural topologies and avoid the difficulties in selecting artificial material interpolation schemes.
2021, 40(3): 356-363.
doi: 10.13433/j.cnki.1003-8728.20200072
Abstract:
Aiming at the problem of quantifying the severity of vibrating mechanical rolling bearing fault, by analyzing the fault characteristics of rolling bearings, the influence of local single fault size on contact deformation is considered by Hertz contact theory; and by introducing load distribution area, a dynamic model of double impact phenomenon of a single local damage fault in the outer ring of rolling bearings is established. According to this model, two groups of bearings with different defect sizes are simulated and test on a circular vibrating screen. The results show that the rolling element produces double shock signal through defects. The rolling bearing fault size is quantified according to the time interval of double shock signal, and the average accuracy is over 96%, which verifies the correctness of the model and the feasibility of applying this method to the fault quantification of rolling bearings in vibrating machine.
Aiming at the problem of quantifying the severity of vibrating mechanical rolling bearing fault, by analyzing the fault characteristics of rolling bearings, the influence of local single fault size on contact deformation is considered by Hertz contact theory; and by introducing load distribution area, a dynamic model of double impact phenomenon of a single local damage fault in the outer ring of rolling bearings is established. According to this model, two groups of bearings with different defect sizes are simulated and test on a circular vibrating screen. The results show that the rolling element produces double shock signal through defects. The rolling bearing fault size is quantified according to the time interval of double shock signal, and the average accuracy is over 96%, which verifies the correctness of the model and the feasibility of applying this method to the fault quantification of rolling bearings in vibrating machine.
2021, 40(3): 364-370.
doi: 10.13433/j.cnki.1003-8728.20200076
Abstract:
Aiming at the problem of the path search of the lunar probe in complex terrain environment, a multi-constrained grid map model was established, and an improved ant colony optimization algorithm was used for global path planning. The parameter adaptive adjustment and two-way search parallel strategy were added to the ant colony algorithm to improve the success of the ant search path, and the corners of the path were processed to make the planned global path smoother and safer, making the detector effective in large avoid obstacles on the scale map. Simulation test results show that this path planning method combines the characteristics of global planning, so that the detector can reach the target point quickly and safely along an optimal path that is as short and smooth as possible.
Aiming at the problem of the path search of the lunar probe in complex terrain environment, a multi-constrained grid map model was established, and an improved ant colony optimization algorithm was used for global path planning. The parameter adaptive adjustment and two-way search parallel strategy were added to the ant colony algorithm to improve the success of the ant search path, and the corners of the path were processed to make the planned global path smoother and safer, making the detector effective in large avoid obstacles on the scale map. Simulation test results show that this path planning method combines the characteristics of global planning, so that the detector can reach the target point quickly and safely along an optimal path that is as short and smooth as possible.
2021, 40(3): 371-376.
doi: 10.13433/j.cnki.1003-8728.20200067
Abstract:
Climbing robot is a typical rootless multi-body system. It was difficult to establish its dynamical equation with traditional Lagrange equation by means of Lagrange multiplier. A simple dynamics modeling method was presented to covert climbing robot into the multi-body system with fixed base through adding the dynamic nominal mechanism between the robot and the ground reference frame. The dynamical equation without constraint condition was firstly established using traditional Lagrange equation and screw theory. Then dynamical equation of climbing robot subject to some desired trajectory was acquired based on the Udwadia-Kalaba theory, which overcomed the disadvantage of obtaining dynamical equation from traditional Lagrange equation by Lagrange multiplier. The stimulation results of the motion trajectory of climbing robot proved that the dynamical equation established by this method conforms to the matter of fact.
Climbing robot is a typical rootless multi-body system. It was difficult to establish its dynamical equation with traditional Lagrange equation by means of Lagrange multiplier. A simple dynamics modeling method was presented to covert climbing robot into the multi-body system with fixed base through adding the dynamic nominal mechanism between the robot and the ground reference frame. The dynamical equation without constraint condition was firstly established using traditional Lagrange equation and screw theory. Then dynamical equation of climbing robot subject to some desired trajectory was acquired based on the Udwadia-Kalaba theory, which overcomed the disadvantage of obtaining dynamical equation from traditional Lagrange equation by Lagrange multiplier. The stimulation results of the motion trajectory of climbing robot proved that the dynamical equation established by this method conforms to the matter of fact.
2021, 40(3): 377-381.
doi: 10.13433/j.cnki.1003-8728.20200018
Abstract:
Taking the pressure hull of a seabed observer at 1 000 m depth as the study object, this paper compared and analyzed the calculation results of classical formulas and the limitations of empirical formulas based on the finite element method. Through linear buckling and non-linear post-buckling analysis, the rule of critical bearing load, ultimate strength and post-buckling behavior characteristics of models with different aspect ratios can be obtained. Moreover, the critical instability load formula of stiffened cylindrical shells can be deduced through the finite element calculation and analysis under multiple working conditions, thus obtaining the stiffened cylindrical shell structure with 14.8% of weight reduction.
Taking the pressure hull of a seabed observer at 1 000 m depth as the study object, this paper compared and analyzed the calculation results of classical formulas and the limitations of empirical formulas based on the finite element method. Through linear buckling and non-linear post-buckling analysis, the rule of critical bearing load, ultimate strength and post-buckling behavior characteristics of models with different aspect ratios can be obtained. Moreover, the critical instability load formula of stiffened cylindrical shells can be deduced through the finite element calculation and analysis under multiple working conditions, thus obtaining the stiffened cylindrical shell structure with 14.8% of weight reduction.
2021, 40(3): 382-387.
doi: 10.13433/j.cnki.1003-8728.20200026
Abstract:
There are many factors affecting the grinding quality, which make it difficult to control the material removal. Based on the existing material removal models, a new material removal model is established which mainly aimed at cylindrical grinding tool. In the model, the half power of contact force, reciprocal of contact velocity and spindle speed are directly proportional to material removal per unit area. The other uncontrollable factors are modeled as a material removal coefficient. A series of single factor experiments are carried out on the cylinder bar which considering the effect of grinding process parameters on material removal per unit area. Then the material removal coefficient is calibrated according to the experimental data. Finally, the material removal model is also validated by a series of multi-factor experiments. The results show that the proposed material removal model is accurate and reliable.
There are many factors affecting the grinding quality, which make it difficult to control the material removal. Based on the existing material removal models, a new material removal model is established which mainly aimed at cylindrical grinding tool. In the model, the half power of contact force, reciprocal of contact velocity and spindle speed are directly proportional to material removal per unit area. The other uncontrollable factors are modeled as a material removal coefficient. A series of single factor experiments are carried out on the cylinder bar which considering the effect of grinding process parameters on material removal per unit area. Then the material removal coefficient is calibrated according to the experimental data. Finally, the material removal model is also validated by a series of multi-factor experiments. The results show that the proposed material removal model is accurate and reliable.
2021, 40(3): 388-393.
doi: 10.13433/j.cnki.1003-8728.20200060
Abstract:
Different concentrations of grinding fluids were prepared for rolling finishing of 7075 aluminum alloy specimens. When the grinding fluid is only deionized water, after finishing for 50 min, the surface brightness of the specimen was the worst, the surface scratches were more, the change rate of surface roughness value and the material removal rate were the smallest, the roughness value Ra decreased from 1.233 μm to 0.406 μm, and the material rate of surface roughness value was the greatest. The roughness value Ra decreased from 1.290 μm to 0.169 μm. Under the action of grinding fluid with chemical additives, the grain refinement occurred in the specimen surfaces, and the average grain size decreased and the number increased. Grinding fluid plays an important role in the surface brightness, surface roughness and material removal rate of 7075 aluminum alloy specimens in rolling finishing, which improves the surface quality of specimens. When the ratio of Na2SiO3·9H2O and CH4N2S is 1∶1, the surface quality is the best, and the composition of grinding fluid has a certain relationship with the surface grain refinement of specimens.
Different concentrations of grinding fluids were prepared for rolling finishing of 7075 aluminum alloy specimens. When the grinding fluid is only deionized water, after finishing for 50 min, the surface brightness of the specimen was the worst, the surface scratches were more, the change rate of surface roughness value and the material removal rate were the smallest, the roughness value Ra decreased from 1.233 μm to 0.406 μm, and the material rate of surface roughness value was the greatest. The roughness value Ra decreased from 1.290 μm to 0.169 μm. Under the action of grinding fluid with chemical additives, the grain refinement occurred in the specimen surfaces, and the average grain size decreased and the number increased. Grinding fluid plays an important role in the surface brightness, surface roughness and material removal rate of 7075 aluminum alloy specimens in rolling finishing, which improves the surface quality of specimens. When the ratio of Na2SiO3·9H2O and CH4N2S is 1∶1, the surface quality is the best, and the composition of grinding fluid has a certain relationship with the surface grain refinement of specimens.
2021, 40(3): 394-402.
doi: 10.13433/j.cnki.1003-8728.20200062
Abstract:
As the basis component of CNC machine tools, the performance of the machine tools is mainly determined by the supporting structure. However, the structure optimization of machine tools manufactured by the traditional materials is nearly to the extreme value. So, a composite structure manufactured by the concrete which is used for the machine tools′ supporting parts is presented. As an example, the sandwich structure is used for the machine tools′ bed, with the steel is used as shell and concrete as core, and the navigation is embedded and further optimal designed for improving the stability. Firstly, the machine tool bed manufactured by the traditional material and the new bed manufactured by the concrete are analyzed for the dynamics and static properties respectively via finite element method, and the results are compared further. Secondly, with the static deformation of the guider as constraint, the supporting structure of the guider is designed to improve the performance. Then, the thermal property of the composite structure bed was verified by the steady-state and transient thermal analysis. Lastly, the presented method is used to redesign and optimize the structure of a horizontal machine center bed. The results show that although the static-stiffness of the concrete composite structure bed is almost equal to the prototyping bed which with traditional material, but the dynamic and thermal properties are improved greatly with the optimization design, and the cost reduction. So the feasibility of the structure and the design method is further proved.
As the basis component of CNC machine tools, the performance of the machine tools is mainly determined by the supporting structure. However, the structure optimization of machine tools manufactured by the traditional materials is nearly to the extreme value. So, a composite structure manufactured by the concrete which is used for the machine tools′ supporting parts is presented. As an example, the sandwich structure is used for the machine tools′ bed, with the steel is used as shell and concrete as core, and the navigation is embedded and further optimal designed for improving the stability. Firstly, the machine tool bed manufactured by the traditional material and the new bed manufactured by the concrete are analyzed for the dynamics and static properties respectively via finite element method, and the results are compared further. Secondly, with the static deformation of the guider as constraint, the supporting structure of the guider is designed to improve the performance. Then, the thermal property of the composite structure bed was verified by the steady-state and transient thermal analysis. Lastly, the presented method is used to redesign and optimize the structure of a horizontal machine center bed. The results show that although the static-stiffness of the concrete composite structure bed is almost equal to the prototyping bed which with traditional material, but the dynamic and thermal properties are improved greatly with the optimization design, and the cost reduction. So the feasibility of the structure and the design method is further proved.
2021, 40(3): 403-409.
doi: 10.13433/j.cnki.1003-8728.20200031
Abstract:
The four-bit double pass electrothermal pneumatic microvalve is proposed based on the traditional pneumatic microvalve in this research, in which its valve channel structure and control method are innovatively designed: it adopts the way of setting electric heating sheets in the closed air cavity, and controls the electric heating Whether or not and the current intensity, the four-position bidirectional control effect is realized, and the pressure threshold can be adjusted according to needs. The COMSOL software is used to numerically analyze the heat transfer process, flow field characteristics and the force of the valve diaphragm. The current-pressure characteristics inside the air cavity, the stress-strain characteristics of the diaphragm, the velocity in the fluid channel, the pressure distribution, and various aspects of the electrothermal pneumatic microvalve were simulated. The study found that the stress of the diaphragm in the four-bit double pass electrothermal pneumatic microvalve is mainly concentrated in the position where the diaphragm contacts the air chamber and the position of the obstruction obstacle; the speed and pressure changes in the fluid channel are mainly concentrated in the obstruction obstacle and the diaphragm. When the electric heater passes the corresponding current intensity, the temperature can reach about 85 ℃ in 1 s.
The four-bit double pass electrothermal pneumatic microvalve is proposed based on the traditional pneumatic microvalve in this research, in which its valve channel structure and control method are innovatively designed: it adopts the way of setting electric heating sheets in the closed air cavity, and controls the electric heating Whether or not and the current intensity, the four-position bidirectional control effect is realized, and the pressure threshold can be adjusted according to needs. The COMSOL software is used to numerically analyze the heat transfer process, flow field characteristics and the force of the valve diaphragm. The current-pressure characteristics inside the air cavity, the stress-strain characteristics of the diaphragm, the velocity in the fluid channel, the pressure distribution, and various aspects of the electrothermal pneumatic microvalve were simulated. The study found that the stress of the diaphragm in the four-bit double pass electrothermal pneumatic microvalve is mainly concentrated in the position where the diaphragm contacts the air chamber and the position of the obstruction obstacle; the speed and pressure changes in the fluid channel are mainly concentrated in the obstruction obstacle and the diaphragm. When the electric heater passes the corresponding current intensity, the temperature can reach about 85 ℃ in 1 s.
2021, 40(3): 410-416.
doi: 10.13433/j.cnki.1003-8728.20200028
Abstract:
On the basis of the theory of electrochemistry, a mathematical model for the formation of oxide film in the ELID grinding of sapphire was established, and the process of oxide film formation was qualitatively analyzed. A series of sapphire ELID grinding experiments were carried out on a MGK71206X/F NC surface grinder, to further reveal the effects of the processing parameters such as interelectrode gap and voltage on the pre-dressing time as well as the variation of the oxide film thickness and growth rate. According to the experimental results, an evaluation method of oxide film state based on thickness, adhesion, porosity, and pre-dressing time was proposed to optimize the parameters such as the interelectrode gap, pulse frequency, voltage, and grinding wheel speed. The results showed that the optimal combination of parameters was at an interelectrode gap of 0.5 mm, a pulse frequency of 90 kHz, voltage of 120 V and grinding wheel speed of 1 500 r/min.
On the basis of the theory of electrochemistry, a mathematical model for the formation of oxide film in the ELID grinding of sapphire was established, and the process of oxide film formation was qualitatively analyzed. A series of sapphire ELID grinding experiments were carried out on a MGK71206X/F NC surface grinder, to further reveal the effects of the processing parameters such as interelectrode gap and voltage on the pre-dressing time as well as the variation of the oxide film thickness and growth rate. According to the experimental results, an evaluation method of oxide film state based on thickness, adhesion, porosity, and pre-dressing time was proposed to optimize the parameters such as the interelectrode gap, pulse frequency, voltage, and grinding wheel speed. The results showed that the optimal combination of parameters was at an interelectrode gap of 0.5 mm, a pulse frequency of 90 kHz, voltage of 120 V and grinding wheel speed of 1 500 r/min.
2021, 40(3): 417-422.
doi: 10.13433/j.cnki.1003-8728.20200059
Abstract:
The heat generation and heat conduction of a grounding resistor in the plateau environment are quite different from those in the plain, lead to frequent faults in the grounding resistor and cannot guarantee the normal operation of the distribution network. In this paper, the heat generation and heat conduction of the grounding resistor are analyzed, and the convection and heat transfer coefficient model between the grounding resistor and the surrounding environment is established. The finite element analysis of the temperature rise of the grounding resistor at different altitudes from 0 to 5 km is carried out, and the linear relationship between the temperature rise of the grounding resistor and its altitude is obtained, providing reference for the normal operation of the distribution network in the plateau environment and reducing the accidents of the grounding resistor burning.
The heat generation and heat conduction of a grounding resistor in the plateau environment are quite different from those in the plain, lead to frequent faults in the grounding resistor and cannot guarantee the normal operation of the distribution network. In this paper, the heat generation and heat conduction of the grounding resistor are analyzed, and the convection and heat transfer coefficient model between the grounding resistor and the surrounding environment is established. The finite element analysis of the temperature rise of the grounding resistor at different altitudes from 0 to 5 km is carried out, and the linear relationship between the temperature rise of the grounding resistor and its altitude is obtained, providing reference for the normal operation of the distribution network in the plateau environment and reducing the accidents of the grounding resistor burning.
2021, 40(3): 423-427.
doi: 10.13433/j.cnki.1003-8728.20200276
Abstract:
In order to solve the problem that it is difficult to train an accurate deep learning model with small sample data set in the industrial field, a deep learning target detection method based on transfer learning was proposed to detect the endpoint of the flexible end-effector under small sample data set. Firstly, the target detection network is constructed using the ResNet; Then the domain adaptive transfer method is used to construct the adaptive network, and the pre-trained ResNet-50 network parameters are transferred to the training process of the endpoint detection model of the flexible end-effector, so as to r educe the training difficulty of the deep learning model. The experimental results show that the model has a good detection effect under the training of 500 images, in which the positioning accuracy of the endpoint is not more than 1.675 mm.
In order to solve the problem that it is difficult to train an accurate deep learning model with small sample data set in the industrial field, a deep learning target detection method based on transfer learning was proposed to detect the endpoint of the flexible end-effector under small sample data set. Firstly, the target detection network is constructed using the ResNet; Then the domain adaptive transfer method is used to construct the adaptive network, and the pre-trained ResNet-50 network parameters are transferred to the training process of the endpoint detection model of the flexible end-effector, so as to r educe the training difficulty of the deep learning model. The experimental results show that the model has a good detection effect under the training of 500 images, in which the positioning accuracy of the endpoint is not more than 1.675 mm.
2021, 40(3): 428-434.
doi: 10.13433/j.cnki.1003-8728.20200064
Abstract:
The existing pneumatic gauges have unstable measurement values and workpiece measurement wear. This article analyzes the measuring principles of the pneumatic gauges, performs numerical calculation and experimental measurement of its internal flow field, and finds that the existing probes of a connecting rod do not form an effective support. Air film and disordered airflow in the exhaust tank result in poor measurement stability; local high pressure zones are generated at the edge of the exhaust tank, leading to the increased air resistance coefficient, which affects the measurement accuracy. The dual E-type exhaust groove-structured probe with better measurement stability and reliability is proposed. By analyzing the internal flow characteristics of the dual E-type probe, its pressure and flow field distribution is more uniform. The air flow fluctuation converges to a stable value, and the measurement fluctuation amplitude is 1/5 of the existing probe, which effectively improves the measurement accuracy and stability.
The existing pneumatic gauges have unstable measurement values and workpiece measurement wear. This article analyzes the measuring principles of the pneumatic gauges, performs numerical calculation and experimental measurement of its internal flow field, and finds that the existing probes of a connecting rod do not form an effective support. Air film and disordered airflow in the exhaust tank result in poor measurement stability; local high pressure zones are generated at the edge of the exhaust tank, leading to the increased air resistance coefficient, which affects the measurement accuracy. The dual E-type exhaust groove-structured probe with better measurement stability and reliability is proposed. By analyzing the internal flow characteristics of the dual E-type probe, its pressure and flow field distribution is more uniform. The air flow fluctuation converges to a stable value, and the measurement fluctuation amplitude is 1/5 of the existing probe, which effectively improves the measurement accuracy and stability.
2021, 40(3): 435-441.
doi: 10.13433/j.cnki.1003-8728.20200066
Abstract:
In the paper, an improved LQR lateral motion control method with feedforward control is proposed to solve the lateral motion control problem of self-driving vehicle. Firstly, the path tracking error dynamics model is built by using a 2-DOF vehicle dynamics model, and the LQR controller and the feedforward controller are designed based on the path tracking error dynamics model. Secondly, based on the analysis of LQR controller parameters, a parameter calculation method based on path tracking error and a parameter adjustment rule based on vehicle-road position relation are proposed to improve the adaptability and control accuracy of LQR controller. Finally, the designed controller is tested by Matlab/Carsim co-simulation. The simulation results show that the improved LQR controller can track the target path well, and can control the lateral deviation and heading deviation of unmanned vehicle in a small range, whether in double or continuous lane changing conditions.
In the paper, an improved LQR lateral motion control method with feedforward control is proposed to solve the lateral motion control problem of self-driving vehicle. Firstly, the path tracking error dynamics model is built by using a 2-DOF vehicle dynamics model, and the LQR controller and the feedforward controller are designed based on the path tracking error dynamics model. Secondly, based on the analysis of LQR controller parameters, a parameter calculation method based on path tracking error and a parameter adjustment rule based on vehicle-road position relation are proposed to improve the adaptability and control accuracy of LQR controller. Finally, the designed controller is tested by Matlab/Carsim co-simulation. The simulation results show that the improved LQR controller can track the target path well, and can control the lateral deviation and heading deviation of unmanned vehicle in a small range, whether in double or continuous lane changing conditions.
2021, 40(3): 442-447.
doi: 10.13433/j.cnki.1003-8728.20200074
Abstract:
A sliding mode control method of yaw moment based on the combined control of yaw rate and side slip angle was proposed to solve the problem of vehicle yaw stability for a type of multi-wheel independent electric vehicles. The controller was designed in a hierarchical structure. Firstly, based on the sliding mode control theory, the upper controllers controlled the yaw rate and side slip angle respectively, and the target value of the additional yaw-moment was obtained. Then, we used weighted summation of out-up of two parts to get the final target of the additional yaw-moment. Finally, the lower controller adopted motor output constraint and ground adhesion constraint to optimize torque distribution. The simulation test results showed that the sliding mode control method can effectively improve the yaw stability of the vehicle compared with the classical PID control method.
A sliding mode control method of yaw moment based on the combined control of yaw rate and side slip angle was proposed to solve the problem of vehicle yaw stability for a type of multi-wheel independent electric vehicles. The controller was designed in a hierarchical structure. Firstly, based on the sliding mode control theory, the upper controllers controlled the yaw rate and side slip angle respectively, and the target value of the additional yaw-moment was obtained. Then, we used weighted summation of out-up of two parts to get the final target of the additional yaw-moment. Finally, the lower controller adopted motor output constraint and ground adhesion constraint to optimize torque distribution. The simulation test results showed that the sliding mode control method can effectively improve the yaw stability of the vehicle compared with the classical PID control method.
2021, 40(3): 448-455.
doi: 10.13433/j.cnki.1003-8728.20200027
Abstract:
Due to the excessive energy consumption of the typical radial flow magnetorheological valve power supply, different soft magnetic materials are used to split the valve core, and the structure of the magnetic flux type radial flow magnetic rheological valve is designed. Because of their different magnetic permeability, the soft magnetic materials are arranged and combined so that the magnetic energy loss at the valve core is reduced, and the magnetic field is induced to enter the annular axial gap, thereby increasing the area of action of the magnetic field on the magnetorheological fluid. The Lagrangian multiplier method together with the quasi-Newton method is used to search for the basic structural optimization of the valve body. The optimized magnetic flux type radial flow magnetorheological valve is simulated with the Maxwell software. The simulation results are in close agreement with the theoretical results, thus proving the reliability of the optimization results. The simulation results show that the energy utilization of the magnetic flux type radial flow magneto-rheological valve is 33.3% higher than that of the typical radial flow magneto-rheological valve and that its volume is reduced by 37.7% when the maximum pressure drops by 1.8 MPa.
Due to the excessive energy consumption of the typical radial flow magnetorheological valve power supply, different soft magnetic materials are used to split the valve core, and the structure of the magnetic flux type radial flow magnetic rheological valve is designed. Because of their different magnetic permeability, the soft magnetic materials are arranged and combined so that the magnetic energy loss at the valve core is reduced, and the magnetic field is induced to enter the annular axial gap, thereby increasing the area of action of the magnetic field on the magnetorheological fluid. The Lagrangian multiplier method together with the quasi-Newton method is used to search for the basic structural optimization of the valve body. The optimized magnetic flux type radial flow magnetorheological valve is simulated with the Maxwell software. The simulation results are in close agreement with the theoretical results, thus proving the reliability of the optimization results. The simulation results show that the energy utilization of the magnetic flux type radial flow magneto-rheological valve is 33.3% higher than that of the typical radial flow magneto-rheological valve and that its volume is reduced by 37.7% when the maximum pressure drops by 1.8 MPa.
2021, 40(3): 456-462.
doi: 10.13433/j.cnki.1003-8728.20200075
Abstract:
In order to obtain the influence rule of the marginal microcosmic damage to stress concentration effect of 7B04 aluminum alloy which caused by corrosion pits, ANASYS finite element method was adopted to erect two corrosion pits model, which respectively were semi-ellipsoid corrosion pit model and semi-ellipsoid corrosion pit model that including a marginal microcosmic damage, based on linear elastic fracture mechanics, stress concentration effect of two models was calculated and analyzed. Results show that marginal microcosmic damage has direct influence to stress concentration effect of corrosion pits through value of Kt and influence zone and influence zone size. Firstly, Kt, max value of two model was respectively 3.359 and 2.24. Secondly, obvious area of stress concentration effect of emi-ellipsoid corrosion pit model that including a marginal microcosmic damage located at the intersection region between marginal damage and ellipsoidal corrosion pit. Thirdly, the influence of marginal microcosmic damage to corrosion pit stress concentration effect was influenced by size and orientation of marginal microcosmic damage itself, Kt increased with h/l value increase, and usually Kt, θ=45°>Kt, θ=0 at the same size condition of marginal microcosmic damage.
In order to obtain the influence rule of the marginal microcosmic damage to stress concentration effect of 7B04 aluminum alloy which caused by corrosion pits, ANASYS finite element method was adopted to erect two corrosion pits model, which respectively were semi-ellipsoid corrosion pit model and semi-ellipsoid corrosion pit model that including a marginal microcosmic damage, based on linear elastic fracture mechanics, stress concentration effect of two models was calculated and analyzed. Results show that marginal microcosmic damage has direct influence to stress concentration effect of corrosion pits through value of Kt and influence zone and influence zone size. Firstly, Kt, max value of two model was respectively 3.359 and 2.24. Secondly, obvious area of stress concentration effect of emi-ellipsoid corrosion pit model that including a marginal microcosmic damage located at the intersection region between marginal damage and ellipsoidal corrosion pit. Thirdly, the influence of marginal microcosmic damage to corrosion pit stress concentration effect was influenced by size and orientation of marginal microcosmic damage itself, Kt increased with h/l value increase, and usually Kt, θ=45°>Kt, θ=0 at the same size condition of marginal microcosmic damage.
2021, 40(3): 463-469.
doi: 10.13433/j.cnki.1003-8728.20200030
Abstract:
For 5083 aluminum alloy friction stir welded(FSW) butt joints, the effect of the kissing bonding defect depth on the fatigue strength of friction stir welded joints was studied. The Vickers hardness distribution on the joint cross-section was measured via Microhardness tester, the test results showed that the hardness value distribution is almost "W" shape. The nominal stress-fatigue life relationship of specimens with different kissing bond depths were obtained under the constant amplitude fatigue loading on MTS809 fatigue testing machine. The tensile fatigue fractures were observed via scanning electron microscope(SEM)and measured the kissing bond depth, the results showed that the cracks all originated from the kissing bonding defect area. The finite element model for stress and strain calculation was established via ABAQUS software, with the results from finite element analysis, the fatigue lives of specimens were predicted with the notch stress method and local stress-strain method. The results showed that notch stress method is more effective for the low cycle fatigue life prediction.
For 5083 aluminum alloy friction stir welded(FSW) butt joints, the effect of the kissing bonding defect depth on the fatigue strength of friction stir welded joints was studied. The Vickers hardness distribution on the joint cross-section was measured via Microhardness tester, the test results showed that the hardness value distribution is almost "W" shape. The nominal stress-fatigue life relationship of specimens with different kissing bond depths were obtained under the constant amplitude fatigue loading on MTS809 fatigue testing machine. The tensile fatigue fractures were observed via scanning electron microscope(SEM)and measured the kissing bond depth, the results showed that the cracks all originated from the kissing bonding defect area. The finite element model for stress and strain calculation was established via ABAQUS software, with the results from finite element analysis, the fatigue lives of specimens were predicted with the notch stress method and local stress-strain method. The results showed that notch stress method is more effective for the low cycle fatigue life prediction.
2021, 40(3): 470-474.
doi: 10.13433/j.cnki.1003-8728.20200063
Abstract:
Ultrasonic strengthening technology can be used to improve the surface integrity of materials in order to increase the fatigue life. The effect of the ultrasonic rolling strengthening on the fatigue property of high-strength steel was studied. Metallographic microscope, microhardness tester and scanning electron microscope were utilized to analyze microstructure and microhardness of the strengthened specimens, and the results showed that the strengthened layer can be obtained after ultrasonic strengthening treatment, and the microstructure become finer, the microhardness can be improved by 9.8% as well. At the same time, the fatigue life of the 30CrMnSiNi2A high-strength steel can be increased by 38.4% comparing with the polished specimens at a test stress of 1 400 MPa.
Ultrasonic strengthening technology can be used to improve the surface integrity of materials in order to increase the fatigue life. The effect of the ultrasonic rolling strengthening on the fatigue property of high-strength steel was studied. Metallographic microscope, microhardness tester and scanning electron microscope were utilized to analyze microstructure and microhardness of the strengthened specimens, and the results showed that the strengthened layer can be obtained after ultrasonic strengthening treatment, and the microstructure become finer, the microhardness can be improved by 9.8% as well. At the same time, the fatigue life of the 30CrMnSiNi2A high-strength steel can be increased by 38.4% comparing with the polished specimens at a test stress of 1 400 MPa.
2021, 40(3): 475-480.
doi: 10.13433/j.cnki.1003-8728.20200011
Abstract:
This paper studies the additive manufacturing technology based on droplet ejection. The numerical calculation of the droplet ejection process was carried out with the level set method. After analyzing the flow field distribution of droplet ejection, the response surface method (RSM) is used to establish and then correct the fitting model. The fitting relations between the distance of droplets that form a ball and the fracture height under different parameters are put forward. According to the fitting relations, the morphology of the ejected droplets under different inlet pressure pulse conditions is predicted, and the reliability of the fitting relations is verified by comparing the prediction results with the simulation results. The simulation results show that the amplitude and pulse width of the pressure pulse at the nozzle inlet and the droplet morphology during the droplet ejection are closely related. There exists a critical relationship between the pressure amplitude and the pulse width. When this relationship is not satisfied, the droplet cannot be ejected from the nozzle. Only when the pressure amplitude and pulse width satisfy this critical relationship can droplets be ejected smoothly to overcome the surface tension. In the case of meeting the ejection conditions, the greater the amplitude and pulse width of the pressure pulse is, the farther the droplet is formed into a ball. The smaller the amplitude and pulse width of the pressure pulse is, the closer the droplets are to the ball.
This paper studies the additive manufacturing technology based on droplet ejection. The numerical calculation of the droplet ejection process was carried out with the level set method. After analyzing the flow field distribution of droplet ejection, the response surface method (RSM) is used to establish and then correct the fitting model. The fitting relations between the distance of droplets that form a ball and the fracture height under different parameters are put forward. According to the fitting relations, the morphology of the ejected droplets under different inlet pressure pulse conditions is predicted, and the reliability of the fitting relations is verified by comparing the prediction results with the simulation results. The simulation results show that the amplitude and pulse width of the pressure pulse at the nozzle inlet and the droplet morphology during the droplet ejection are closely related. There exists a critical relationship between the pressure amplitude and the pulse width. When this relationship is not satisfied, the droplet cannot be ejected from the nozzle. Only when the pressure amplitude and pulse width satisfy this critical relationship can droplets be ejected smoothly to overcome the surface tension. In the case of meeting the ejection conditions, the greater the amplitude and pulse width of the pressure pulse is, the farther the droplet is formed into a ball. The smaller the amplitude and pulse width of the pressure pulse is, the closer the droplets are to the ball.
2021, 40(3): 481-486.
doi: 10.13433/j.cnki.1003-8728.20200294
Abstract:
In this paper, morphology and microstructure analysis, micro-area composition analysis, metallographic structure examination, hardness test, determination of hydrogen content and inclusion of the same batch bolt as well as field inspection of bolt socket of the fractured bolts and cracked bolts for X Aircraft were carried out. Combined with the objective evidences, such as fracture oxidation corrosion, no periodic extend crack or shear lips (crescent area), a new explanation of the intergranular characteristics of the fracture source region is given, and finally it is concluded that the bolt is overload cracking under the action of the three-dimensional stress.
In this paper, morphology and microstructure analysis, micro-area composition analysis, metallographic structure examination, hardness test, determination of hydrogen content and inclusion of the same batch bolt as well as field inspection of bolt socket of the fractured bolts and cracked bolts for X Aircraft were carried out. Combined with the objective evidences, such as fracture oxidation corrosion, no periodic extend crack or shear lips (crescent area), a new explanation of the intergranular characteristics of the fracture source region is given, and finally it is concluded that the bolt is overload cracking under the action of the three-dimensional stress.
2021, 40(3): 487-492.
doi: 10.13433/j.cnki.1003-8728.20200180
Abstract:
Based on the refined finite element model constructed by using the virtual test, the study on the optimization design of large scale wing is carried out. A unified optimization model is constructed by transforming the loads of different working condition models. Using the spar and rib positions, the main wing box is automatically divided into the different design regions, and the optimization variables and design constraints are defined according to the characteristics of each design region. The wing size is optimized by using the full stress optimization algorithm to achieve a weight reduction rate of 13.3%. A numerical example shows that the optimization of the wing size by using the refined finite element model is feasible, and the modeling problems can be solved by dealing the related model.
Based on the refined finite element model constructed by using the virtual test, the study on the optimization design of large scale wing is carried out. A unified optimization model is constructed by transforming the loads of different working condition models. Using the spar and rib positions, the main wing box is automatically divided into the different design regions, and the optimization variables and design constraints are defined according to the characteristics of each design region. The wing size is optimized by using the full stress optimization algorithm to achieve a weight reduction rate of 13.3%. A numerical example shows that the optimization of the wing size by using the refined finite element model is feasible, and the modeling problems can be solved by dealing the related model.
