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RSS2019 Vol. 38, No. 9
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2019, 38(9): 1313-1318.
doi: 10.13433/j.cnki.1003-8728.20190009
PDF 1037KB
Abstract:
The fault diagnosis of bearing is an important mean to ensure the safe operation of the equipment. The key of fault diagnosis is the method of vibration signal demodulation. Adaptive noise complete set empirical mode decomposition (CEEMDAN) is an adaptive signal processing method, which has good demodulation performance in nonlinear and non-stationary signals. In this paper, an improved CEEMDAN fault diagnosis algorithm based on kurtosis criterion was proposed. First, using the improved CEEMDAN method based on kurtosis criteria to extract useful modal component signals. After that, the selected modal signals are superimposed and the output energy signals are obtained through the Teager operator. Finally, the fault feature frequency is extracted from the envelope spectrum analysis, and the fault diagnosis is realized. The improved method has a certain practical value in practical application through the test of simulation and processing equipment parts.
The fault diagnosis of bearing is an important mean to ensure the safe operation of the equipment. The key of fault diagnosis is the method of vibration signal demodulation. Adaptive noise complete set empirical mode decomposition (CEEMDAN) is an adaptive signal processing method, which has good demodulation performance in nonlinear and non-stationary signals. In this paper, an improved CEEMDAN fault diagnosis algorithm based on kurtosis criterion was proposed. First, using the improved CEEMDAN method based on kurtosis criteria to extract useful modal component signals. After that, the selected modal signals are superimposed and the output energy signals are obtained through the Teager operator. Finally, the fault feature frequency is extracted from the envelope spectrum analysis, and the fault diagnosis is realized. The improved method has a certain practical value in practical application through the test of simulation and processing equipment parts.
2019, 38(9): 1319-1326.
doi: 10.13433/j.cnki.1003-8728.20180317
Abstract:
In designing the rod-fastened rotors in terms of the similarity principle, there is a significant size effect due to dimensional changes and the mechanism of the scaling law of the rotors with crack defects is not clear. Based on the dimensional analysis method, the mechanism of size effect of crack propagation has been analyzed. The distribution law of the stress intensity factor and the change in stiffness was analyzed for the different size cracked rods during crack propagation. The sensitivity of natural frequencies drifting in cracked rotors of different size models was compared. Finally, a method which can simulate the crack propagation process by using the pre-tightening force reduction of rod-fastened rotors has been proposed. The phenomenon in natural frequencies drifting under different cracked rod distribution forms has also been compared with the experimental. The conclusions provide a theoretical basis for the serial design and equipment maintenance of the rod-fastened rotors.
In designing the rod-fastened rotors in terms of the similarity principle, there is a significant size effect due to dimensional changes and the mechanism of the scaling law of the rotors with crack defects is not clear. Based on the dimensional analysis method, the mechanism of size effect of crack propagation has been analyzed. The distribution law of the stress intensity factor and the change in stiffness was analyzed for the different size cracked rods during crack propagation. The sensitivity of natural frequencies drifting in cracked rotors of different size models was compared. Finally, a method which can simulate the crack propagation process by using the pre-tightening force reduction of rod-fastened rotors has been proposed. The phenomenon in natural frequencies drifting under different cracked rod distribution forms has also been compared with the experimental. The conclusions provide a theoretical basis for the serial design and equipment maintenance of the rod-fastened rotors.
2019, 38(9): 1327-1334.
doi: 10.13433/j.cnki.1003-8728.20180315
Abstract:
The main reducer is an important part for the unmanned helicopter transmission system. In order to avoid the high temperature to affect its working performance, a three-dimensional model for the main reducer cabin is established. The flow field and temperature field in the main reducer cabin in the front flight state is simulated via CFD (Computational fluid dynamics), the method to improve the heat dissipation performance in the main reducer cabin is obtained. The results show that to increase the size of the side vent can effectively suppress the eddy current near the side vent, and to adjust the distance of the fan from the main reducer, to change the circular air deflector to the square air deflector with the wind guide ring, to adjuste the distance between the fan and the radiator can reduce the non uniformity of the heat dissipation of the radiator and improve the heat dissipation performance.
The main reducer is an important part for the unmanned helicopter transmission system. In order to avoid the high temperature to affect its working performance, a three-dimensional model for the main reducer cabin is established. The flow field and temperature field in the main reducer cabin in the front flight state is simulated via CFD (Computational fluid dynamics), the method to improve the heat dissipation performance in the main reducer cabin is obtained. The results show that to increase the size of the side vent can effectively suppress the eddy current near the side vent, and to adjust the distance of the fan from the main reducer, to change the circular air deflector to the square air deflector with the wind guide ring, to adjuste the distance between the fan and the radiator can reduce the non uniformity of the heat dissipation of the radiator and improve the heat dissipation performance.
2019, 38(9): 1335-1342.
doi: 10.13433/j.cnki.1003-8728.20180321
Abstract:
In order to meet the transportation requirements of downhole tools in horizontal wells, a new hydraulic telescopic downhole tractor with high traction and anti-jamming is presented in this paper. Whether the supporting mechanism of the tractor can be maintained and locked up with the pipe wall is the key for the retractable tractor to crawl forward. Therefore, the mechanical model of the traction locking of the tractor under the action of loads is established, and the conditions of the traction locking are analyzed. With the smaller supporting cylinder pressure as the evaluation standard, the traction locking conditions under different layout modes of the supporting mechanism are analyzed, and the optimal layout of the hydraulic telescopic downhole tractor is obtained. Finally, the correctness of the traction lock-up condition of the tractor is verified by simulation analysis. This paper has certain guiding significance for the design of hydraulic telescopic tractor.
In order to meet the transportation requirements of downhole tools in horizontal wells, a new hydraulic telescopic downhole tractor with high traction and anti-jamming is presented in this paper. Whether the supporting mechanism of the tractor can be maintained and locked up with the pipe wall is the key for the retractable tractor to crawl forward. Therefore, the mechanical model of the traction locking of the tractor under the action of loads is established, and the conditions of the traction locking are analyzed. With the smaller supporting cylinder pressure as the evaluation standard, the traction locking conditions under different layout modes of the supporting mechanism are analyzed, and the optimal layout of the hydraulic telescopic downhole tractor is obtained. Finally, the correctness of the traction lock-up condition of the tractor is verified by simulation analysis. This paper has certain guiding significance for the design of hydraulic telescopic tractor.
2019, 38(9): 1343-1349.
doi: 10.13433/j.cnki.1003-8728.20180312
Abstract:
Structural lightweight is the key of design for advanced humanoid robots. Based on the bionics theory, a bionic robots thigh is designed according to the CT scanning surface of human femur. An non-periodic structure tetrahedron grid along the vertical stress line is built in the inner thigh to achieve its lightweight, and then the spatial grid is optimized at different positions according to the simulation results of actual working condition via static finite element method. Finally, the selective laser melting technology was used to 3D printing the extremitas inferior of the robots thigh without supports on the inner grid to verify the manufacturability of the solid and spatial grid chimera structure. The optimal thigh weight is much less than the solid body, and the stress peak of the internal optimal grid structure is significantly lower than that of the pre-optimal structure. The 3D printing parts are complete and well designed. It provides a new idea for designing and manufacturing the humanoid robots.
Structural lightweight is the key of design for advanced humanoid robots. Based on the bionics theory, a bionic robots thigh is designed according to the CT scanning surface of human femur. An non-periodic structure tetrahedron grid along the vertical stress line is built in the inner thigh to achieve its lightweight, and then the spatial grid is optimized at different positions according to the simulation results of actual working condition via static finite element method. Finally, the selective laser melting technology was used to 3D printing the extremitas inferior of the robots thigh without supports on the inner grid to verify the manufacturability of the solid and spatial grid chimera structure. The optimal thigh weight is much less than the solid body, and the stress peak of the internal optimal grid structure is significantly lower than that of the pre-optimal structure. The 3D printing parts are complete and well designed. It provides a new idea for designing and manufacturing the humanoid robots.
2019, 38(9): 1350-1356.
doi: 10.13433/j.cnki.1003-8728.20190007
Abstract:
For the problem of misalignment of a dual-rotor system, which affects the vibration characteristics of the system, the dynamic simulation and vibration analysis of the dual-rotor system with coupling misalignment in inner rotor are carried out. Taking a certain aero-engine as the structural object, the dynamic finite element model of the dual-rotor system with coupling misalignment in inner rotor is established by applying additional load caused by misalignment. The vibration spectrum characteristics and the shaft centerline orbits are compared with the increase of the misalignment of rotors. The results show that the vibration can be transferred via intershaft bearing that the vibration response caused by inner rotor coupling misalignment can be monitored both in the support position of the outer rotor and the corresponding position of the inter-bearing; the rotating frequency is not sensitive to coupling misalignment, while the second harmonic frequency is sensitive to coupling misalignment, whose amplitude increases with the increase of the coupling misalignment, and the closer the support position to the coupling, the more sensitive to the misalignment; the shaft centerline orbits are transformed from "ellipse" to the "inner eight" shape with the increase of the coupling misalignment.
For the problem of misalignment of a dual-rotor system, which affects the vibration characteristics of the system, the dynamic simulation and vibration analysis of the dual-rotor system with coupling misalignment in inner rotor are carried out. Taking a certain aero-engine as the structural object, the dynamic finite element model of the dual-rotor system with coupling misalignment in inner rotor is established by applying additional load caused by misalignment. The vibration spectrum characteristics and the shaft centerline orbits are compared with the increase of the misalignment of rotors. The results show that the vibration can be transferred via intershaft bearing that the vibration response caused by inner rotor coupling misalignment can be monitored both in the support position of the outer rotor and the corresponding position of the inter-bearing; the rotating frequency is not sensitive to coupling misalignment, while the second harmonic frequency is sensitive to coupling misalignment, whose amplitude increases with the increase of the coupling misalignment, and the closer the support position to the coupling, the more sensitive to the misalignment; the shaft centerline orbits are transformed from "ellipse" to the "inner eight" shape with the increase of the coupling misalignment.
2019, 38(9): 1357-1365.
doi: 10.13433/j.cnki.1003-8728.20180318
Abstract:
The paper puts forward a new speed bump energy harvester based on bi-stable vibration (SBEHBV). Its mechanical model and dynamic equations are established. The four kinds of a commonly used speed bump are selected through simulation. The dynamic response and output power of the SBEHBV system excited by one wheel impact pattern, i.e., the front (or rear) wheel or by two wheel impact pattern, i.e., the front wheel followed by rear wheel, are studied with the parameters of different speed bumps respectively. The simulation results show that the numbers of crossing potential barriers of the SBEHBV system with the parameters of the class Ⅱ speed bump are much more than those of the system with other class speed bumps. The time of large-amplitude motion occurrence and the average output power are more than those of others. Therefore, the output power of the SBEHBV system with the class Ⅱ speed bump under the excitation of a different vehicle weight is studied further. The simulation results also show that the weight of the vehicle is heavier and that its output power is greater. Furthermore, the optimum resistance is obtained by studying the effect of different external load resistance on the output power.
The paper puts forward a new speed bump energy harvester based on bi-stable vibration (SBEHBV). Its mechanical model and dynamic equations are established. The four kinds of a commonly used speed bump are selected through simulation. The dynamic response and output power of the SBEHBV system excited by one wheel impact pattern, i.e., the front (or rear) wheel or by two wheel impact pattern, i.e., the front wheel followed by rear wheel, are studied with the parameters of different speed bumps respectively. The simulation results show that the numbers of crossing potential barriers of the SBEHBV system with the parameters of the class Ⅱ speed bump are much more than those of the system with other class speed bumps. The time of large-amplitude motion occurrence and the average output power are more than those of others. Therefore, the output power of the SBEHBV system with the class Ⅱ speed bump under the excitation of a different vehicle weight is studied further. The simulation results also show that the weight of the vehicle is heavier and that its output power is greater. Furthermore, the optimum resistance is obtained by studying the effect of different external load resistance on the output power.
2019, 38(9): 1366-1372.
doi: 10.13433/j.cnki.1003-8728.20180311
Abstract:
In order to improve the jet performance of self-excited pulse nozzles, the flow field of self-excited pulse nozzle was numerically analyzed by computation fluid dynamics (CFD), and the structure of the nozzle was optimized globally using the response surface method. A mathematic optimization model with nozzle inlet diameter d1, outlet diameter d2, cavity length Lc, cavity diameter Dc as design variables and the impact force F as objective function was established. Through analyzing the mathematical model established, the parameters' optimal values of the nozzle structure are obtained. Finally, the optimized nozzle structure was analyzed and compared with the original, and it was found that the jet performance of the optimized nozzle was significantly improved, and the impact force was increased by about 20%. By analyzing the interaction diagram, the influence of each structural parameter on the jet performance was obtained.
In order to improve the jet performance of self-excited pulse nozzles, the flow field of self-excited pulse nozzle was numerically analyzed by computation fluid dynamics (CFD), and the structure of the nozzle was optimized globally using the response surface method. A mathematic optimization model with nozzle inlet diameter d1, outlet diameter d2, cavity length Lc, cavity diameter Dc as design variables and the impact force F as objective function was established. Through analyzing the mathematical model established, the parameters' optimal values of the nozzle structure are obtained. Finally, the optimized nozzle structure was analyzed and compared with the original, and it was found that the jet performance of the optimized nozzle was significantly improved, and the impact force was increased by about 20%. By analyzing the interaction diagram, the influence of each structural parameter on the jet performance was obtained.
2019, 38(9): 1373-1379.
doi: 10.13433/j.cnki.1003-8728.20180319
Abstract:
This paper proposes an axial modulating permanent magnetic gear (PMG) which has a high output torque. With the overall size of the axial modulating PMG kept still, the permanent magnets (PMs) on the input rotor and the output rotor are installed with Halbach magnet arrays to increase the intensity of a coupled magnetic field in an airgap. The proposed PMG was investigated with the finite element method. The simulation results show that the output torque of the PMG with Halbach magnet arrays is significantly larger than that of the PMG with the conventional magnet arrays. The harmonic analysis of waves of magnetic flux in airgaps indicates that the trends of magnetic flux produced by the PM on the PMG with Halbach magnet arrays and those on the PMG with conventional magnet arrays are similar, thus having the same transmission mechanisms. The sector angle of the PM on the PMG with Halbach magnet arrays can be optimized to further increase its output torque.
This paper proposes an axial modulating permanent magnetic gear (PMG) which has a high output torque. With the overall size of the axial modulating PMG kept still, the permanent magnets (PMs) on the input rotor and the output rotor are installed with Halbach magnet arrays to increase the intensity of a coupled magnetic field in an airgap. The proposed PMG was investigated with the finite element method. The simulation results show that the output torque of the PMG with Halbach magnet arrays is significantly larger than that of the PMG with the conventional magnet arrays. The harmonic analysis of waves of magnetic flux in airgaps indicates that the trends of magnetic flux produced by the PM on the PMG with Halbach magnet arrays and those on the PMG with conventional magnet arrays are similar, thus having the same transmission mechanisms. The sector angle of the PM on the PMG with Halbach magnet arrays can be optimized to further increase its output torque.
2019, 38(9): 1380-1385.
doi: 10.13433/j.cnki.1003-8728.20180320
Abstract:
Considering the non-stationary and nonlinear characteristics of the gearbox vibration signal, it is difficult in signal processing and fault detection. A fault feature extraction method based on complementary ensemble empirical mode decomposition (CEEMD), multi-scale permutation entropy (MPE) and sample entropy (SE) is proposed in this paper. Firstly, the gearbox vibration signal is subjected to complementary ensemble empirical mode decomposition, and the modal components are filtered and reconstructed according to the correlation coefficient principle. Then, the multi-scale permutation entropy is used to extract the modal components and extract the features. Simultaneously the sample entropy of reconstructed signals is extracted as the features. Finally, the extracted fault features are merged into the Gaussian process classifier for experimental verification. The experimental results show that the method can effectively extract the fault characteristics of the gearbox vibration signal, and Gaussian classifiers can perform fault detection accurately and quickly.
Considering the non-stationary and nonlinear characteristics of the gearbox vibration signal, it is difficult in signal processing and fault detection. A fault feature extraction method based on complementary ensemble empirical mode decomposition (CEEMD), multi-scale permutation entropy (MPE) and sample entropy (SE) is proposed in this paper. Firstly, the gearbox vibration signal is subjected to complementary ensemble empirical mode decomposition, and the modal components are filtered and reconstructed according to the correlation coefficient principle. Then, the multi-scale permutation entropy is used to extract the modal components and extract the features. Simultaneously the sample entropy of reconstructed signals is extracted as the features. Finally, the extracted fault features are merged into the Gaussian process classifier for experimental verification. The experimental results show that the method can effectively extract the fault characteristics of the gearbox vibration signal, and Gaussian classifiers can perform fault detection accurately and quickly.
2019, 38(9): 1386-1392.
doi: 10.13433/j.cnki.1003-8728.20190005
Abstract:
For the static strength requirement, an approach for topology optimization design of thermoelastic structures with global stress constrains is proposed. The minimization of the structure volume is developed as the objective function under the combined action of thermal and mechanical loads. The stress relaxation method is adopted to avoid the singularity phenomena for the stress based topology optimization problem. All elemental stresses are aggregated into a global stress using the modified P-norm method. The global stress is approximately equal to the maximum stress and used as the constraint. The model for topology optimization of the thermoelastic structures with the global stress constraints is established. The method of moving asymptotes is performed to solve the optimization problems. The results of numerical examples show that the proposed method is effective. As the thermal load increases, optimal structure obtained by the stress-constrained topology optimization is different and leads to more materials used.
For the static strength requirement, an approach for topology optimization design of thermoelastic structures with global stress constrains is proposed. The minimization of the structure volume is developed as the objective function under the combined action of thermal and mechanical loads. The stress relaxation method is adopted to avoid the singularity phenomena for the stress based topology optimization problem. All elemental stresses are aggregated into a global stress using the modified P-norm method. The global stress is approximately equal to the maximum stress and used as the constraint. The model for topology optimization of the thermoelastic structures with the global stress constraints is established. The method of moving asymptotes is performed to solve the optimization problems. The results of numerical examples show that the proposed method is effective. As the thermal load increases, optimal structure obtained by the stress-constrained topology optimization is different and leads to more materials used.
2019, 38(9): 1393-1400.
doi: 10.13433/j.cnki.1003-8728.20190144
Abstract:
A new parallel drive bidirectional deflection platform is proposed. The movable platform is connected to the base with the two cross-branched and concentric two-branch structures in the space, and the platform can realize the large-angle deflection in both X and Y directions. The kinematics equation of the platform was established and the Jacobian matrix was obtained. The kinematics simulation analysis of the platform was carried out, and the simulation results and calculation results were compared so as to verify the feasibility of the platform design and the accuracy of the motion. All the source errors of the platform are given. According to the error independent action principle, Monte Carlo method, the instantaneous arm method and the total differential method are used to analyze and calculate the error of different types of source errors respectively. The local errors are obtained. According to the average method of the error synthesis method, the error of each local error is integrated, and the maximum motion error of the platform around the X and Y axes is obtained.
A new parallel drive bidirectional deflection platform is proposed. The movable platform is connected to the base with the two cross-branched and concentric two-branch structures in the space, and the platform can realize the large-angle deflection in both X and Y directions. The kinematics equation of the platform was established and the Jacobian matrix was obtained. The kinematics simulation analysis of the platform was carried out, and the simulation results and calculation results were compared so as to verify the feasibility of the platform design and the accuracy of the motion. All the source errors of the platform are given. According to the error independent action principle, Monte Carlo method, the instantaneous arm method and the total differential method are used to analyze and calculate the error of different types of source errors respectively. The local errors are obtained. According to the average method of the error synthesis method, the error of each local error is integrated, and the maximum motion error of the platform around the X and Y axes is obtained.
2019, 38(9): 1401-1405.
doi: 10.13433/j.cnki.1003-8728.20190032
Abstract:
In order to determine the vibration fatigue limit of the typical bolt connectors with different connection types and different nominal thicknesses, and compare the vibration fatigue characteristics of them, the vibration fatigue tests were carried out. According to the special requirements of the testing, a simply-supported fixture was designed, which was then verified and optimized by the finite element software and modal testing. This simply-supported fixture was proved meeting the design requirements. Furthermore, the strain values of the large-magnitude vibration were obtained by the curve-fitting method from the strain values of the small-magnitude vibration. By making the curve fitting, the strain-life curves of the four type connections were depicted. At last, the testing was completed successfully, and it can be concluded that:1) the simply-supported fixture dose apply to the vibration testing of the bolt connections and can be used in the same kind testing later; 2) in the situation of the same strain level, the double-row-screw bolt connection has the longest vibration fatigue life, that is to say it has the best vibration fatigue characteristic; 3) the failure part of all connections is the metal part, so in the next step of designing, the metal type should be substituted and the dynamic strength of it should be reinforced.
In order to determine the vibration fatigue limit of the typical bolt connectors with different connection types and different nominal thicknesses, and compare the vibration fatigue characteristics of them, the vibration fatigue tests were carried out. According to the special requirements of the testing, a simply-supported fixture was designed, which was then verified and optimized by the finite element software and modal testing. This simply-supported fixture was proved meeting the design requirements. Furthermore, the strain values of the large-magnitude vibration were obtained by the curve-fitting method from the strain values of the small-magnitude vibration. By making the curve fitting, the strain-life curves of the four type connections were depicted. At last, the testing was completed successfully, and it can be concluded that:1) the simply-supported fixture dose apply to the vibration testing of the bolt connections and can be used in the same kind testing later; 2) in the situation of the same strain level, the double-row-screw bolt connection has the longest vibration fatigue life, that is to say it has the best vibration fatigue characteristic; 3) the failure part of all connections is the metal part, so in the next step of designing, the metal type should be substituted and the dynamic strength of it should be reinforced.
2019, 38(9): 1406-1413.
doi: 10.13433/j.cnki.1003-8728.20190004
Abstract:
With the increasing proportion of titanium alloys and carbon fiber reinforced plastics (CFRP) in aerospace manufacturing, the cutting of laminated components has become a research hotspot. Since the cutting temperature not only affects the wear and durability of the tool, but also directly affects the machining accuracy of the workpieces and the quality of the machined surface. Based on the principle of helical milling, the mechanism of interface heat transfer in drilling titanium alloy/composite is studied. The interface model for titanium alloy/composite stacks is established. The model is calculated with computer simulation. The titanium alloy/composite experiment was carried out, and the heat transfer coefficient between the tool and the workpiece and interface heat transfer coefficient were corrected and verified via experimental data. By comparing the thermal theory and the experimental results in helical milling of titanium alloy/CFRP stacks, the analysis results and experimental data presented in this paper high consistency, which can provide a theoretical basis for studying helical milling cutting heat in titanium alloy/composite materials stacks.
With the increasing proportion of titanium alloys and carbon fiber reinforced plastics (CFRP) in aerospace manufacturing, the cutting of laminated components has become a research hotspot. Since the cutting temperature not only affects the wear and durability of the tool, but also directly affects the machining accuracy of the workpieces and the quality of the machined surface. Based on the principle of helical milling, the mechanism of interface heat transfer in drilling titanium alloy/composite is studied. The interface model for titanium alloy/composite stacks is established. The model is calculated with computer simulation. The titanium alloy/composite experiment was carried out, and the heat transfer coefficient between the tool and the workpiece and interface heat transfer coefficient were corrected and verified via experimental data. By comparing the thermal theory and the experimental results in helical milling of titanium alloy/CFRP stacks, the analysis results and experimental data presented in this paper high consistency, which can provide a theoretical basis for studying helical milling cutting heat in titanium alloy/composite materials stacks.
2019, 38(9): 1414-1419.
doi: 10.13433/j.cnki.1003-8728.20190006
Abstract:
To improve the quality of a laser communication terminal, the paper studies the optimization of its primary mirror. Based on the multi-objective topological optimization theory and the compromise programming method, it establishes the mathematical model of multi-objective topological optimization, with the multiple stiffness conditions and the weight minimization considered. The Optistruct software is used to optimize the primary mirror and its new model is obtained, which is reconstructed and analyzed with the finite element analysis. The deformation of the mirror surface is analyzed in the horizontal and vertical conditions of the primary mirror. The results show that the lightweight ratio of the primary mirror reaches 55.3% and that its surface figure in the vertical condition is larger than the original model, satisfying requirements for the primary mirror for laser communication. Compared with different structures of the lightweight primary mirror, the surface figure of the multi-objective topological optimized primary mirror is larger, thus verifying the feasibility of the optimization method.
To improve the quality of a laser communication terminal, the paper studies the optimization of its primary mirror. Based on the multi-objective topological optimization theory and the compromise programming method, it establishes the mathematical model of multi-objective topological optimization, with the multiple stiffness conditions and the weight minimization considered. The Optistruct software is used to optimize the primary mirror and its new model is obtained, which is reconstructed and analyzed with the finite element analysis. The deformation of the mirror surface is analyzed in the horizontal and vertical conditions of the primary mirror. The results show that the lightweight ratio of the primary mirror reaches 55.3% and that its surface figure in the vertical condition is larger than the original model, satisfying requirements for the primary mirror for laser communication. Compared with different structures of the lightweight primary mirror, the surface figure of the multi-objective topological optimized primary mirror is larger, thus verifying the feasibility of the optimization method.
2019, 38(9): 1420-1428.
doi: 10.13433/j.cnki.1003-8728.20190002
Abstract:
The high-speed precision surface grinding experiment of surface-hardened ductile iron QT700-2 for automotive engine crankshaft was carried out with CBN grinding wheel. The relationship between the grinding parameters, material removal rate, maximum undeformed chip thickness and the grinding force, specific grinding energy was studied. The empirical formula of grinding force and specific grinding energy is established. According to the requirements of crankshaft grinding, the high-speed precision grinding parameters of QT700-2 are optimized, which lays a foundation for high-speed precision grinding of automobile crankshaft.
The high-speed precision surface grinding experiment of surface-hardened ductile iron QT700-2 for automotive engine crankshaft was carried out with CBN grinding wheel. The relationship between the grinding parameters, material removal rate, maximum undeformed chip thickness and the grinding force, specific grinding energy was studied. The empirical formula of grinding force and specific grinding energy is established. According to the requirements of crankshaft grinding, the high-speed precision grinding parameters of QT700-2 are optimized, which lays a foundation for high-speed precision grinding of automobile crankshaft.
2019, 38(9): 1429-1436.
doi: 10.13433/j.cnki.1003-8728.20180308
Abstract:
In order to increase the practicability of magnetorheological damper (MRD), its structure with embedded permanent magnets is proposed. According to the internal structure parameters of SG-MRD60, all design schemes are obtained through discretizing structural parameters. Taking the improvement of the comprehensive performance of a composite MRD as optimization objective, this paper establishes a performance evaluation system. Based on the equivalent model of magnetic circuit, the function of the performance is obtained. By integrating this objective function with the fuzzy comprehensive evaluation method, the optimal design scheme is screened out. The simulation results show that the average mechanical properties of the new comprehensive structure of the MRD are improved by 9.6% under the condition of 2 A current and no magnetic field of the permanent magnet. The magnetic flux density of damping gap is 0.296 T under the condition of 0 current. The adjustment range is from -58.4% to 59.1% under the ±2 A current condition and meets the needs of engineering application.
In order to increase the practicability of magnetorheological damper (MRD), its structure with embedded permanent magnets is proposed. According to the internal structure parameters of SG-MRD60, all design schemes are obtained through discretizing structural parameters. Taking the improvement of the comprehensive performance of a composite MRD as optimization objective, this paper establishes a performance evaluation system. Based on the equivalent model of magnetic circuit, the function of the performance is obtained. By integrating this objective function with the fuzzy comprehensive evaluation method, the optimal design scheme is screened out. The simulation results show that the average mechanical properties of the new comprehensive structure of the MRD are improved by 9.6% under the condition of 2 A current and no magnetic field of the permanent magnet. The magnetic flux density of damping gap is 0.296 T under the condition of 0 current. The adjustment range is from -58.4% to 59.1% under the ±2 A current condition and meets the needs of engineering application.
2019, 38(9): 1437-1442.
doi: 10.13433/j.cnki.1003-8728.20190008
Abstract:
The profile bending parts of Titanium alloy gradually become the main load-bearing components of advanced civil composite material fuselage due to their excellent properties. The forming quality is directly related to the assembly accuracy of aircraft. Here, a study on the stretch bending process of L-section profile of OT4M titanium alloy was conducted. Firstly, a model for stretch bending process was developed. Then, multiple groups of thermal uniaxial tension under different conditions were performed to determine the deformation behavior of profiles. Lastly, the electrically assisted stretch bending were carried out with insulation mold. The results indicate that the plastic deformation capacity of material is significant affected by the temperature and velocity, the application of insulation mold in the stretch bending process can reduce springback by keeping profiles forming at a temperature of 490℃.
The profile bending parts of Titanium alloy gradually become the main load-bearing components of advanced civil composite material fuselage due to their excellent properties. The forming quality is directly related to the assembly accuracy of aircraft. Here, a study on the stretch bending process of L-section profile of OT4M titanium alloy was conducted. Firstly, a model for stretch bending process was developed. Then, multiple groups of thermal uniaxial tension under different conditions were performed to determine the deformation behavior of profiles. Lastly, the electrically assisted stretch bending were carried out with insulation mold. The results indicate that the plastic deformation capacity of material is significant affected by the temperature and velocity, the application of insulation mold in the stretch bending process can reduce springback by keeping profiles forming at a temperature of 490℃.
2019, 38(9): 1443-1450.
doi: 10.13433/j.cnki.1003-8728.20180309
Abstract:
It is an important way to improve the intelligent degree of hobbing machine by grasping the intelligent state and improving the weak link of intelligent hobbing machine. To describe the smart development process of hobbing machine, a maturity model for smart hobbing machine was built by referring capability maturity model integration technology. On the other hand, a smart hobbing machine maturity comprehensive evaluation index system was established to describe the characteristics of intelligent hobbing machine. In order to evaluate the maturity of smart hobbing machines, a method combined with interval analytic hierarchy process and fuzzy comprehensive evaluation was proposed. The quantitative evaluation results can reasonably assess the maturity of smart hobbing machines and point out the improvement direction for smarter. An example with a smart hobbing machine in a business verified the present effectiveness.
It is an important way to improve the intelligent degree of hobbing machine by grasping the intelligent state and improving the weak link of intelligent hobbing machine. To describe the smart development process of hobbing machine, a maturity model for smart hobbing machine was built by referring capability maturity model integration technology. On the other hand, a smart hobbing machine maturity comprehensive evaluation index system was established to describe the characteristics of intelligent hobbing machine. In order to evaluate the maturity of smart hobbing machines, a method combined with interval analytic hierarchy process and fuzzy comprehensive evaluation was proposed. The quantitative evaluation results can reasonably assess the maturity of smart hobbing machines and point out the improvement direction for smarter. An example with a smart hobbing machine in a business verified the present effectiveness.
2019, 38(9): 1451-1456.
doi: 10.13433/j.cnki.1003-8728.20180314
Abstract:
The roughness data sequence generated in machining process will contain a variety of features, and a single prediction model cannot simultaneously capture multiple data features, and it is difficult to improve the prediction accuracy. Therefore, a combined prediction model based on support vector machine (SVM) and BP neural network algorithm (BP) considering the complexity of data features in machining process is proposed, which can simultaneously capture the linear characteristics and nonlinearity of data features. In order to full play the two prediction algorithms, particle swarm optimization (PSO) is used to optimize the parameters of the support vector machine and the weights in the BP neural network. Through milling experiments, and comparing with PSO-SVM, PSO-BP algorithm and the model for surface roughness, the superiority of the combined model (PSO-SVM+PSO-BP) is verified.
The roughness data sequence generated in machining process will contain a variety of features, and a single prediction model cannot simultaneously capture multiple data features, and it is difficult to improve the prediction accuracy. Therefore, a combined prediction model based on support vector machine (SVM) and BP neural network algorithm (BP) considering the complexity of data features in machining process is proposed, which can simultaneously capture the linear characteristics and nonlinearity of data features. In order to full play the two prediction algorithms, particle swarm optimization (PSO) is used to optimize the parameters of the support vector machine and the weights in the BP neural network. Through milling experiments, and comparing with PSO-SVM, PSO-BP algorithm and the model for surface roughness, the superiority of the combined model (PSO-SVM+PSO-BP) is verified.
2019, 38(9): 1457-1464.
doi: 10.13433/j.cnki.1003-8728.20190136
Abstract:
Based on the high-speed train pantograph, a single-arm single-slide pantograph model was established. The numerical simulation method was used to study the unsteady aerodynamic characteristics of the pantograph under different working conditions with crosswind conditions. The vortices, streamline, pressure and the variation law of the aerodynamic power and moment coefficients, and the frequency domain characteristics of the three-dimensional flow field were analyzed. The difference of flow characteristics between single-arm single-slide pantographs at high speed and super-high speed was discussed. The results show that due to the super-high speed running, the average and amplitude of the aerodynamic load of the pantograph increase, the oscillation period decreases, and the corresponding spectrum becomes wider. The effects of pitching moment and side moment caused by unsteady lift and crosswind were significant. The vibration of the pantograph in the vertical direction was intensified, so the single-arm pantograph with relatively compact structure is beneficial to reduce longitudinal vibration. However, the height of the underframe was larger and the angle of the pantograph was smaller, these result in:a large-scale low-speed wake occurs at the junction of the upper arm and the lower arm, and the structure and distribution of the small-scale separation vortex are relatively complicated. The research results have important significance and value for the study and application of unsteady aerodynamic characteristics of pantograph with cross-wind.
Based on the high-speed train pantograph, a single-arm single-slide pantograph model was established. The numerical simulation method was used to study the unsteady aerodynamic characteristics of the pantograph under different working conditions with crosswind conditions. The vortices, streamline, pressure and the variation law of the aerodynamic power and moment coefficients, and the frequency domain characteristics of the three-dimensional flow field were analyzed. The difference of flow characteristics between single-arm single-slide pantographs at high speed and super-high speed was discussed. The results show that due to the super-high speed running, the average and amplitude of the aerodynamic load of the pantograph increase, the oscillation period decreases, and the corresponding spectrum becomes wider. The effects of pitching moment and side moment caused by unsteady lift and crosswind were significant. The vibration of the pantograph in the vertical direction was intensified, so the single-arm pantograph with relatively compact structure is beneficial to reduce longitudinal vibration. However, the height of the underframe was larger and the angle of the pantograph was smaller, these result in:a large-scale low-speed wake occurs at the junction of the upper arm and the lower arm, and the structure and distribution of the small-scale separation vortex are relatively complicated. The research results have important significance and value for the study and application of unsteady aerodynamic characteristics of pantograph with cross-wind.
2019, 38(9): 1465-1469.
doi: 10.13433/j.cnki.1003-8728.20190001
Abstract:
The wear conditions of cutting tools can be studied with finite element method. This method can not only obtain various parameters in cutting process, but also has advantages in low cost and high efficiency. The key technologies in cutting tool wear with finite element technique was studied. These technologies include the constitutive model, contact type and friction model, wear model and wear calculation, ALE grid technology, separation criterion and fracture criterion. In addition, the existing problems in the current researches were analyzed and the future development were proposed. This paper has guiding the significance for promoting the use of finite element techniques in cutting tool wear.
The wear conditions of cutting tools can be studied with finite element method. This method can not only obtain various parameters in cutting process, but also has advantages in low cost and high efficiency. The key technologies in cutting tool wear with finite element technique was studied. These technologies include the constitutive model, contact type and friction model, wear model and wear calculation, ALE grid technology, separation criterion and fracture criterion. In addition, the existing problems in the current researches were analyzed and the future development were proposed. This paper has guiding the significance for promoting the use of finite element techniques in cutting tool wear.
2019, 38(9): 1470-1476.
doi: 10.13433/j.cnki.1003-8728.20190071
Abstract:
The maintenance costs of wind turbines remain high, one of the primary causes of which is the selection of maintenance strategy. Currently, wind farms generally take the preventive replacement maintenance strategy at regular intervals. This strategy is inflexible, not enough to take full advantage of the economic dependence between components. This study applies an opportunistic group replacement maintenance (OGRM) strategy on wind turbines. At first, Weibull distribution is utilized to describe reliability of main components. A uniform formula is proposed to express and subdivide maintenance costs. Then, according to principles of the OGRM strategy, maintenance schedules are obtained by simulation. Finally, combined with historical failure data and maintenance cost data from a certain wind farm, a specific case of implementing the strategy at a component level is given. The results show that, compared with the traditional preventive replacement maintenance strategy, the OGRM strategy reduces total maintenance times and costs, which verifies the effectiveness of applying the strategy on wind turbines.
The maintenance costs of wind turbines remain high, one of the primary causes of which is the selection of maintenance strategy. Currently, wind farms generally take the preventive replacement maintenance strategy at regular intervals. This strategy is inflexible, not enough to take full advantage of the economic dependence between components. This study applies an opportunistic group replacement maintenance (OGRM) strategy on wind turbines. At first, Weibull distribution is utilized to describe reliability of main components. A uniform formula is proposed to express and subdivide maintenance costs. Then, according to principles of the OGRM strategy, maintenance schedules are obtained by simulation. Finally, combined with historical failure data and maintenance cost data from a certain wind farm, a specific case of implementing the strategy at a component level is given. The results show that, compared with the traditional preventive replacement maintenance strategy, the OGRM strategy reduces total maintenance times and costs, which verifies the effectiveness of applying the strategy on wind turbines.
