Transactions of Nanjing University of Aeronautics & Astronautics
Volume 35,Issue 3,2018 Table of Contents
2018, 35(3):395-402.
DOI: 10.16356/j.1005-1120.2018.03.395
Abstract:
It is well known that Tikhonov regularization in standard form may determine approximate solutions that are too smooth for ill-posed problems, so fractional Tikhonov methods have been introduced to remedy this shortcoming. And Tikhonov regularization for large-scale linear ill-posed problems is commonly implemented by determining a partial Arnoldi decomposition of the given matrix. In this paper, we propose a new method to compute an approximate solution of large scale linear discrete ill-posed problems which applies projection fractional Tikhonov regularization in Krylov subspace via Arnoldi process. The projection fractional Tikhonov regularization combines the fractional matrices and orthogonal projection operators. A suitable value of the regularization parameter is determined by the discrepancy principle. Numerical examples with application to image restoration are carried out to examine that the performance of the method.
It is well known that Tikhonov regularization in standard form may determine approximate solutions that are too smooth for ill-posed problems, so fractional Tikhonov methods have been introduced to remedy this shortcoming. And Tikhonov regularization for large-scale linear ill-posed problems is commonly implemented by determining a partial Arnoldi decomposition of the given matrix. In this paper, we propose a new method to compute an approximate solution of large scale linear discrete ill-posed problems which applies projection fractional Tikhonov regularization in Krylov subspace via Arnoldi process. The projection fractional Tikhonov regularization combines the fractional matrices and orthogonal projection operators. A suitable value of the regularization parameter is determined by the discrepancy principle. Numerical examples with application to image restoration are carried out to examine that the performance of the method.
2018, 35(3):403-412.
DOI: 10.16356/j.1005-1120.2018.03.403
Abstract:
For wired local area networks (LANs), their effectiveness and invulnerability are very critical. It is extraordinarily significant to evaluate the network performance effectively in the design of a reasonable network topology and the performance improvement of the networks. However, there are many factors affecting the performance of the networks, and the relation among them is also complicated. How to evaluate the performance of the wired LANs more accurately has been a heavy challenge in the network research. In order to solve the problem, this paper presents a performance evaluation method that evaluates the effectiveness and invulnerability of the wired LANs. Compared to traditional statistical methods, it has the distinct advantage of being able to handle several dependent variables simultaneously and tolerates the measurement errors among these independent variables and dependent variables. Finally, the rationality and validity of this method are verified by the extensive experimental simulation.
For wired local area networks (LANs), their effectiveness and invulnerability are very critical. It is extraordinarily significant to evaluate the network performance effectively in the design of a reasonable network topology and the performance improvement of the networks. However, there are many factors affecting the performance of the networks, and the relation among them is also complicated. How to evaluate the performance of the wired LANs more accurately has been a heavy challenge in the network research. In order to solve the problem, this paper presents a performance evaluation method that evaluates the effectiveness and invulnerability of the wired LANs. Compared to traditional statistical methods, it has the distinct advantage of being able to handle several dependent variables simultaneously and tolerates the measurement errors among these independent variables and dependent variables. Finally, the rationality and validity of this method are verified by the extensive experimental simulation.
2018, 35(3):413-422.
DOI: 10.16356/j.1005-1120.2018.03.413
Abstract:
A discontinuous Galerkin (DG)-based lattice Boltzmann method is employed to solve the Euler and Navier-Stokes equations. Instead of adopting the widely used local Lax-Friedrichs flux and Roe Flux etc., a hybrid lattice Boltzmann flux solver (LBFS) is employed to evaluate the inviscid flux across the cell interfaces. The main advantage of the hybrid LBFS is its flexibility for capturing both strong shocks and thin boundary layers through introducing a function which varies from zero to one to control the artificial viscosity. Numerical results indicate that the hybrid lattice Boltzmann flux solver behaves very well combining with the high-order DG method when simulating both inviscid and viscous flows.
A discontinuous Galerkin (DG)-based lattice Boltzmann method is employed to solve the Euler and Navier-Stokes equations. Instead of adopting the widely used local Lax-Friedrichs flux and Roe Flux etc., a hybrid lattice Boltzmann flux solver (LBFS) is employed to evaluate the inviscid flux across the cell interfaces. The main advantage of the hybrid LBFS is its flexibility for capturing both strong shocks and thin boundary layers through introducing a function which varies from zero to one to control the artificial viscosity. Numerical results indicate that the hybrid lattice Boltzmann flux solver behaves very well combining with the high-order DG method when simulating both inviscid and viscous flows.
2018, 35(3):423-431.
DOI: 10.16356/j.1005-1120.2018.03.423
Abstract:
A novel double-foot piezoelectric linear motor is proposed. The kinematic model of the motor under stepping motion is presented. The motor mainly consists of a stator with four piezoelectric stacks, a mover, a holding mechanism, and a preloading mechanism to achieve large stroke with high resolution. Finite element simulations are carried out to analyze the motion characteristics of the motor. A prototype is fabricated and a serial experiments are conducted to validate the feasibility of the motor principle. Experimental results indicate that the motor can move at a speed of 670.22 μm/s with a driving frequency of 120 Hz and a voltage of 120 V. The resolution of the proposed motor is 3.6 μm while the resolution of the single-step motion is 0.1 μm.
A novel double-foot piezoelectric linear motor is proposed. The kinematic model of the motor under stepping motion is presented. The motor mainly consists of a stator with four piezoelectric stacks, a mover, a holding mechanism, and a preloading mechanism to achieve large stroke with high resolution. Finite element simulations are carried out to analyze the motion characteristics of the motor. A prototype is fabricated and a serial experiments are conducted to validate the feasibility of the motor principle. Experimental results indicate that the motor can move at a speed of 670.22 μm/s with a driving frequency of 120 Hz and a voltage of 120 V. The resolution of the proposed motor is 3.6 μm while the resolution of the single-step motion is 0.1 μm.
2018, 35(3):432-436.
DOI: 10.16356/j.1005-1120.2018.03.432
Abstract:
Sr0.6Ba0.4Nb2O6 micro-rods are prepared by the molten-salt method with K2SO4, KCl-K2SO4, and KCl as fluxes. It reveals that the Sr0.6Ba0.4Nb2O6 synthesized with KCl as a flux exhibits a single phase with tetragonal tungsten bronze structure. The measurement of X-ray diffraction indicates that the Sr0.6Ba0.4Nb2O6 micro-rods synthesized at 1 300℃ are anisotropic. The morphology of the powers is examined by transmission electron microscope. It reveals that the length-diameter ratio of Sr0.6Ba0.4Nb2O6 micro-rods increases with increasing annealing temperature from 900℃ to 1 300℃. At 1 300℃, the rod possesses a large length-diameter ratio of 8:1. Moreover, the analysis of the piezoelectric properties of single micro-rods using a piezo-response force microscope indicates that the domains of the material are arranged along its radial direction.
Sr0.6Ba0.4Nb2O6 micro-rods are prepared by the molten-salt method with K2SO4, KCl-K2SO4, and KCl as fluxes. It reveals that the Sr0.6Ba0.4Nb2O6 synthesized with KCl as a flux exhibits a single phase with tetragonal tungsten bronze structure. The measurement of X-ray diffraction indicates that the Sr0.6Ba0.4Nb2O6 micro-rods synthesized at 1 300℃ are anisotropic. The morphology of the powers is examined by transmission electron microscope. It reveals that the length-diameter ratio of Sr0.6Ba0.4Nb2O6 micro-rods increases with increasing annealing temperature from 900℃ to 1 300℃. At 1 300℃, the rod possesses a large length-diameter ratio of 8:1. Moreover, the analysis of the piezoelectric properties of single micro-rods using a piezo-response force microscope indicates that the domains of the material are arranged along its radial direction.
2018, 35(3):437-448.
DOI: 10.16356/j.1005-1120.2018.03.437
Abstract:
The problem of two-dimensional (2D) direction of arrival (DOA) estimation for double parallel uniform linear arrays is investigated in this paper. A real-valued DOA estimation algorithm of noncircular (NC) signal is proposed, which combines the Euler transformation and rotational invariance (RI) property between subarrays. In this work, the effective array aperture is doubled by exploiting the noncircularity of signals. The complex arithmetic is converted to real arithmetic via Euler transformation. The main contribution of this work is not only extending the NC-Euler-ESPRIT algorithm from uniform linear array to double parallel uniform linear arrays, but also constructing a new 2D rotational invariance property between subarrays, which is more complex than that in NC-Euler-ESPRIT algorithm. The proposed 2D NC-Euler-RI algorithm has much lower computational complexity than 2D NC-ESPRIT algorithm. The proposed algorithm has better angle estimation performance than 2D ESPRIT algorithm and 2D NC-PM algorithm for double parallel uniform linear arrays, and is very close to that of 2D NC-ESPRIT algorithm. The elevation angles and azimuth angles can be obtained with automatically pairing. The proposed algorithm can estimate up to 2(M-1) sources, which is two times that of 2D ESPRIT algorithm. Cramer-Rao bound (CRB) of noncircular signal is derived for the proposed algorithm. Computational complexity comparison is also analyzed. Finally, simulation results are presented to illustrate the effectiveness and usefulness of the proposed algorithm.
The problem of two-dimensional (2D) direction of arrival (DOA) estimation for double parallel uniform linear arrays is investigated in this paper. A real-valued DOA estimation algorithm of noncircular (NC) signal is proposed, which combines the Euler transformation and rotational invariance (RI) property between subarrays. In this work, the effective array aperture is doubled by exploiting the noncircularity of signals. The complex arithmetic is converted to real arithmetic via Euler transformation. The main contribution of this work is not only extending the NC-Euler-ESPRIT algorithm from uniform linear array to double parallel uniform linear arrays, but also constructing a new 2D rotational invariance property between subarrays, which is more complex than that in NC-Euler-ESPRIT algorithm. The proposed 2D NC-Euler-RI algorithm has much lower computational complexity than 2D NC-ESPRIT algorithm. The proposed algorithm has better angle estimation performance than 2D ESPRIT algorithm and 2D NC-PM algorithm for double parallel uniform linear arrays, and is very close to that of 2D NC-ESPRIT algorithm. The elevation angles and azimuth angles can be obtained with automatically pairing. The proposed algorithm can estimate up to 2(M-1) sources, which is two times that of 2D ESPRIT algorithm. Cramer-Rao bound (CRB) of noncircular signal is derived for the proposed algorithm. Computational complexity comparison is also analyzed. Finally, simulation results are presented to illustrate the effectiveness and usefulness of the proposed algorithm.
2018, 35(3):449-454.
DOI: 10.16356/j.1005-1120.2018.03.449
Abstract:
The multilevel characteristic basis function method (MLCBFM) with the adaptive cross approximation (ACA) algorithm for accelerated solution of electrically large scattering problems is studied in this paper. In the conventional MLCBFM based on Foldy-Lax multiple scattering equations, the improvement is only made in the generation of characteristic basis functions (CBFs). However, it does not provide a change in impedance matrix filling and reducing matrix calculation procedure, which is time-consuming. In reality, all the impedance and reduced matrix of each level of the MLCBFM have low-rank property and can be calculated efficiently. Therefore, ACA is used for the efficient generation of two-level CBFs and the fast calculation of reduced matrix in this study. Numerical results are given to demonstrate the accuracy and efficiency of the method.
The multilevel characteristic basis function method (MLCBFM) with the adaptive cross approximation (ACA) algorithm for accelerated solution of electrically large scattering problems is studied in this paper. In the conventional MLCBFM based on Foldy-Lax multiple scattering equations, the improvement is only made in the generation of characteristic basis functions (CBFs). However, it does not provide a change in impedance matrix filling and reducing matrix calculation procedure, which is time-consuming. In reality, all the impedance and reduced matrix of each level of the MLCBFM have low-rank property and can be calculated efficiently. Therefore, ACA is used for the efficient generation of two-level CBFs and the fast calculation of reduced matrix in this study. Numerical results are given to demonstrate the accuracy and efficiency of the method.
2018, 35(3):455-463.
DOI: 10.16356/j.1005-1120.2018.03.455
Abstract:
Because of the inevitable debugging lag, imperfect debugging process is used to replace perfect debugging process in the analysis of software reliability growth model. Considering neither testing-effort nor testing coverage can describe software reliability for imperfect debugging completely, by hybridizing testing-effort with testing coverage under imperfect debugging, this paper proposes a new model named GMW-LO-ID. Under the assumption that the number of faults is proportional to the current number of detected faults, this model combines generalized modified Weibull (GMW) testing-effort function with logistic (LO) testing coverage function, and inherits GMW's amazing flexibility and LO's high fitting precision. Furthermore, the fitting accuracy and predictive power are verified by two series of experiments and we can draw a conclusion that our model fits the actual failure data better and predicts the software future behavior better than other ten traditional models, which only consider one or two points of testing-effort, testing coverage and imperfect debugging.
Because of the inevitable debugging lag, imperfect debugging process is used to replace perfect debugging process in the analysis of software reliability growth model. Considering neither testing-effort nor testing coverage can describe software reliability for imperfect debugging completely, by hybridizing testing-effort with testing coverage under imperfect debugging, this paper proposes a new model named GMW-LO-ID. Under the assumption that the number of faults is proportional to the current number of detected faults, this model combines generalized modified Weibull (GMW) testing-effort function with logistic (LO) testing coverage function, and inherits GMW's amazing flexibility and LO's high fitting precision. Furthermore, the fitting accuracy and predictive power are verified by two series of experiments and we can draw a conclusion that our model fits the actual failure data better and predicts the software future behavior better than other ten traditional models, which only consider one or two points of testing-effort, testing coverage and imperfect debugging.
2018, 35(3):464-471.
DOI: 10.16356/j.1005-1120.2018.03.464
Abstract:
A linear parameter varying (LPV) flight dynamics model (FDM) is proposed to cater for atmospheric disturbance analysis in special flight conditions. A novel FDM which is capable of addressing the influence of turbulent wind is derived under the wind frame. An affine parameter dependent LPV model with wind effects is built based on function substitution method. The optimal solution for the decomposing function of the LPV FDM is obtained by genetic algorithm (GA). The analysis of dynamic response indicates that the genetic-optimized LPV FDM approximates the nonlinear FDM evidently, since it identifies the instantaneous dynamics and flight states varying in a wide range. The simulations of approach and landing against wind shear show that the genetic-optimized LPV FDM captures the instantaneous dynamic response when flying through turbulent wind, indicating that the LPV model can be further applied to turbulent wind special flight analysis and control law design.
A linear parameter varying (LPV) flight dynamics model (FDM) is proposed to cater for atmospheric disturbance analysis in special flight conditions. A novel FDM which is capable of addressing the influence of turbulent wind is derived under the wind frame. An affine parameter dependent LPV model with wind effects is built based on function substitution method. The optimal solution for the decomposing function of the LPV FDM is obtained by genetic algorithm (GA). The analysis of dynamic response indicates that the genetic-optimized LPV FDM approximates the nonlinear FDM evidently, since it identifies the instantaneous dynamics and flight states varying in a wide range. The simulations of approach and landing against wind shear show that the genetic-optimized LPV FDM captures the instantaneous dynamic response when flying through turbulent wind, indicating that the LPV model can be further applied to turbulent wind special flight analysis and control law design.
2018, 35(3):472-482.
DOI: 10.16356/j.1005-1120.2018.03.472
Abstract:
The two line elements (TLEs), released by the North American Aerospace Defense Command (NORAD), are chosen for CubeSats' mission operators. Unfortunately, they have errors and other accompanied problems, which cause large deviations in the in-track component. When a TLE value is available at a certain epoch, the dominant error is the angular error. It is proposed to correct the angular error by solving-for the mean argument of latitude at the desired epoch. A batch least squares technique and range rate measurements are used for the correction process. With the assistance of satellite tool kit (STK) software and Matlab, a simulation to verify the orbit determination (OD) technique is implemented. This paper provides an angular correction low cost OD method and presents a complete analysis for various test cases. This approach maintains high accuracy in cross-track and radial and makes great improvement in in-track at the same time, but it is exclusive for circular orbits. When it is applied to an elliptical orbit, the error will be unacceptable. Therefore, the angular error is corrected using the longitude of periapsis which totally mitigates the error at the epoch under consideration. For inclinations less than 20o, the mean longitude is preferred for the angular correction as it provides more accuracy compared with the mean argument of latitude.
The two line elements (TLEs), released by the North American Aerospace Defense Command (NORAD), are chosen for CubeSats' mission operators. Unfortunately, they have errors and other accompanied problems, which cause large deviations in the in-track component. When a TLE value is available at a certain epoch, the dominant error is the angular error. It is proposed to correct the angular error by solving-for the mean argument of latitude at the desired epoch. A batch least squares technique and range rate measurements are used for the correction process. With the assistance of satellite tool kit (STK) software and Matlab, a simulation to verify the orbit determination (OD) technique is implemented. This paper provides an angular correction low cost OD method and presents a complete analysis for various test cases. This approach maintains high accuracy in cross-track and radial and makes great improvement in in-track at the same time, but it is exclusive for circular orbits. When it is applied to an elliptical orbit, the error will be unacceptable. Therefore, the angular error is corrected using the longitude of periapsis which totally mitigates the error at the epoch under consideration. For inclinations less than 20o, the mean longitude is preferred for the angular correction as it provides more accuracy compared with the mean argument of latitude.
2018, 35(3):483-493.
DOI: 10.16356/j.1005-1120.2018.03.483
Abstract:
Nonlinear dynamic inversion (NDI) has been applied to the control law design of quad-rotors mainly thanks to its good robustness and simplicity of parameter tuning. However, the weakness of relying on accurate model greatly restrains its application on quad-rotors, especially nano quad-rotors (NQRs).NQRs are easy to be influenced by uncertainties such as model uncertainties (mainly from complicated aerodynamic interferences, strong coupling in roll-pitch-yaw channels and inaccurate aerodynamic prediction of rotors) and external uncertainties (mainly from winds or gusts), particularly persistent ones.Therefore, developing accurate model for altitude and attitude control of NQRs is difficult. To solve this problem, in this paper, an improved nonlinear dynamic inversion (INDI)method is developed,which can reject the above-mentioned uncertainties by estimating them and then counteracting in real time using linear extended state observer (LESO). Comparison with the traditional NDI(TNDI) method was carried out numerically, and the results show that, in coping with persistent uncertainties, the INDI-based method presents significant superiority.
Nonlinear dynamic inversion (NDI) has been applied to the control law design of quad-rotors mainly thanks to its good robustness and simplicity of parameter tuning. However, the weakness of relying on accurate model greatly restrains its application on quad-rotors, especially nano quad-rotors (NQRs).NQRs are easy to be influenced by uncertainties such as model uncertainties (mainly from complicated aerodynamic interferences, strong coupling in roll-pitch-yaw channels and inaccurate aerodynamic prediction of rotors) and external uncertainties (mainly from winds or gusts), particularly persistent ones.Therefore, developing accurate model for altitude and attitude control of NQRs is difficult. To solve this problem, in this paper, an improved nonlinear dynamic inversion (INDI)method is developed,which can reject the above-mentioned uncertainties by estimating them and then counteracting in real time using linear extended state observer (LESO). Comparison with the traditional NDI(TNDI) method was carried out numerically, and the results show that, in coping with persistent uncertainties, the INDI-based method presents significant superiority.
2018, 35(3):494-506.
DOI: 10.16356/j.1005-1120.2018.03.494
Abstract:
Vibration fatigue is one of the main failure modes of blade. The vibration fatigue life of blade is scattered caused by manufacture error, material property dispersion and external excitation randomness. A new vibration fatigue probabilistic life prediction model (VFPLPM) and a prediction method are proposed in this paper. Firstly, as one-dimensional volumetric method (ODVM) only considers the principle calculation direction, a three-dimensional space vector volumetric method (TSVVM) is proposed to improve fatigue life prediction accuracy for actual three-dimensional engineering structure. Secondly, based on the two volumetric methods (ODVM and TSVVM), the material C-P-S-N fatigue curve model (CFCM) and the maximum entropy quantile function model (MEQFM), VFPLPM is established to predict the vibration fatigue probabilistic life of blade. The VFPLPM is combined with maximum stress method (MSM), ODVM and TSVVM to estimate vibration fatigue probabilistic life of blade simulator by finite element simulation, and is verified by vibration fatigue test. The results show that all of the three methods can predict the vibration fatigue probabilistic life of blade simulator well. VFPLPM &TSVVM method has the highest computational accuracy for considering stress gradient effect not only in the principle calculation direction but also in other space vector directions.
Vibration fatigue is one of the main failure modes of blade. The vibration fatigue life of blade is scattered caused by manufacture error, material property dispersion and external excitation randomness. A new vibration fatigue probabilistic life prediction model (VFPLPM) and a prediction method are proposed in this paper. Firstly, as one-dimensional volumetric method (ODVM) only considers the principle calculation direction, a three-dimensional space vector volumetric method (TSVVM) is proposed to improve fatigue life prediction accuracy for actual three-dimensional engineering structure. Secondly, based on the two volumetric methods (ODVM and TSVVM), the material C-P-S-N fatigue curve model (CFCM) and the maximum entropy quantile function model (MEQFM), VFPLPM is established to predict the vibration fatigue probabilistic life of blade. The VFPLPM is combined with maximum stress method (MSM), ODVM and TSVVM to estimate vibration fatigue probabilistic life of blade simulator by finite element simulation, and is verified by vibration fatigue test. The results show that all of the three methods can predict the vibration fatigue probabilistic life of blade simulator well. VFPLPM &TSVVM method has the highest computational accuracy for considering stress gradient effect not only in the principle calculation direction but also in other space vector directions.
2018, 35(3):507-515.
DOI: 10.16356/j.1005-1120.2018.03.507
Abstract:
The Noether symmetries and the conserved quantities for generalized Birkhoffian systems with time delay are studied. Firstly, the generalized Pfaff-Birkhoff principle with time delay is proposed, and the generalized Birkhoff's equations with time delay are obtained. Secondly, the generalized Noether quasi-symmetric transformations of the system are defined, and the criterion of the Noether symmetries is established. Then the Noether theorem for generalized Birkhoffian systems with time delay is established. Finally, by imposing restrictions of constraints on the infinitesimal transformations, the Noether theorem of constrained Birkhoffian systems with time delay is established. One example is given to illustrate the application of the results.
The Noether symmetries and the conserved quantities for generalized Birkhoffian systems with time delay are studied. Firstly, the generalized Pfaff-Birkhoff principle with time delay is proposed, and the generalized Birkhoff's equations with time delay are obtained. Secondly, the generalized Noether quasi-symmetric transformations of the system are defined, and the criterion of the Noether symmetries is established. Then the Noether theorem for generalized Birkhoffian systems with time delay is established. Finally, by imposing restrictions of constraints on the infinitesimal transformations, the Noether theorem of constrained Birkhoffian systems with time delay is established. One example is given to illustrate the application of the results.
2018, 35(3):516-521.
DOI: 10.16356/j.1005-1120.2018.03.516
Abstract:
By taking a 2.3 MW double-fed asynchronous generator as an example, a new method for fast simulation analysis of ventilation cooling system inside generator is proposed based on the one-dimensional simulation software FLOWMASTER. The thermal-fluid coupling simulation model of ventilation cooling system inside generator is established. Under the stable running state of the generator, the flow velocity distribution and temperature rise of the key parts of the generator are analyzed. The results prove that the ventilation structure design of the generator meets the temperature rise limit. The simulation results are compared with the theoretical calculation results and the experimental results, which verify the correctness of the thermal-fluid coupling simulation method proposed in this paper.
By taking a 2.3 MW double-fed asynchronous generator as an example, a new method for fast simulation analysis of ventilation cooling system inside generator is proposed based on the one-dimensional simulation software FLOWMASTER. The thermal-fluid coupling simulation model of ventilation cooling system inside generator is established. Under the stable running state of the generator, the flow velocity distribution and temperature rise of the key parts of the generator are analyzed. The results prove that the ventilation structure design of the generator meets the temperature rise limit. The simulation results are compared with the theoretical calculation results and the experimental results, which verify the correctness of the thermal-fluid coupling simulation method proposed in this paper.
2018, 35(3):522-528.
DOI: 10.16356/j.1005-1120.2018.03.522
Abstract:
High volume fraction SiCp/Al aluminum matrix composite possesses a variety of outstanding properties, such as high thermal conductivity and low coefficient of thermal expansion. It is widely applied in many fields, especially in automotive and aerospace. An orthogonal experiment is conducted to study the effects of relevant parameters on the mechanical properties by CO2 laser. Then the micro-hardness in different regions is measured. The effects of such parameters as laser power, middle layer thickness and welding speed on the tensile strength of the welded joints are discussed. The experimental results indicate that the maximum of the tensile strength of the welded joints is attained at the laser power of 1 200 W, the welding speed of 1.5 m/min and the middle layer thickness of 0.3 mm. In addition, the mechanism of the improvement of micro-hardness on the weld bead is also analyzed.
High volume fraction SiCp/Al aluminum matrix composite possesses a variety of outstanding properties, such as high thermal conductivity and low coefficient of thermal expansion. It is widely applied in many fields, especially in automotive and aerospace. An orthogonal experiment is conducted to study the effects of relevant parameters on the mechanical properties by CO2 laser. Then the micro-hardness in different regions is measured. The effects of such parameters as laser power, middle layer thickness and welding speed on the tensile strength of the welded joints are discussed. The experimental results indicate that the maximum of the tensile strength of the welded joints is attained at the laser power of 1 200 W, the welding speed of 1.5 m/min and the middle layer thickness of 0.3 mm. In addition, the mechanism of the improvement of micro-hardness on the weld bead is also analyzed.
2018, 35(3):529-538.
DOI: 10.16356/j.1005-1120.2018.03.529
Abstract:
To fulfill the demands for higher quality, efficiency and flexibility in aviation industry, a multi-functional end effector is designed to automate the drilling and riveting processes in assembling carbon fiber reinforced polymer (CFRP) and aluminum components for a robotic aircraft assembly system. To meet the specific functional requirements for blind rivet installation on CFRP and aluminum materials, additional modules are incorporated on the end effector aside of the basic processing modules for drilling. And all of these processing modules allow for a one-step-drilling-countersinking process, hole inspection, automatic rivet feed, rivet geometry check, sealant application, rivet insertion and installation. Besides, to guarantee the better quality of the hole drilled and joints riveted, several online detection and adjustment measures are applied to this end effector, including the reference detection and perpendicular calibration, which could effectively ensure the positioning precision and perpendicular accuracy as demanded. Finally, the test result shows that this end effector is capable of producing each hole to a positioning precision within ±0.5 mm, a perpendicular accuracy within 0.3°, a diameter tolerance of H8, and a countersink depth tolerance of ±0.01 mm. Moreover, it could drill and rivet up to three joints per minute, with acceptable shearing and tensile strength.
To fulfill the demands for higher quality, efficiency and flexibility in aviation industry, a multi-functional end effector is designed to automate the drilling and riveting processes in assembling carbon fiber reinforced polymer (CFRP) and aluminum components for a robotic aircraft assembly system. To meet the specific functional requirements for blind rivet installation on CFRP and aluminum materials, additional modules are incorporated on the end effector aside of the basic processing modules for drilling. And all of these processing modules allow for a one-step-drilling-countersinking process, hole inspection, automatic rivet feed, rivet geometry check, sealant application, rivet insertion and installation. Besides, to guarantee the better quality of the hole drilled and joints riveted, several online detection and adjustment measures are applied to this end effector, including the reference detection and perpendicular calibration, which could effectively ensure the positioning precision and perpendicular accuracy as demanded. Finally, the test result shows that this end effector is capable of producing each hole to a positioning precision within ±0.5 mm, a perpendicular accuracy within 0.3°, a diameter tolerance of H8, and a countersink depth tolerance of ±0.01 mm. Moreover, it could drill and rivet up to three joints per minute, with acceptable shearing and tensile strength.
2018, 35(3):539-546.
DOI: 10.16356/j.1005-1120.2018.03.539
Abstract:
A global energy fairing method, applied to automated fiber placement (AFP) tool path, was proposed. The main purpose was to improve the adaptability of AFP path towards part with sharp curvature variation as well as product quality. The relation between path geometric property and manufacturing property was discussed and a series of experiments were carried out. Based on cubic B-Spline global fairing method, the AFP tool path was faired which decreased the tool path curvature and curvature changing rate. Compared with initial ones, the path faired by the proposed method was relatively flat and smooth, which contributed to layup efficiency and reducing bulking defects. The method was demonstrated potentials in application for AFP manufacturing, especially for aeronautic and aerospace industry practice.
A global energy fairing method, applied to automated fiber placement (AFP) tool path, was proposed. The main purpose was to improve the adaptability of AFP path towards part with sharp curvature variation as well as product quality. The relation between path geometric property and manufacturing property was discussed and a series of experiments were carried out. Based on cubic B-Spline global fairing method, the AFP tool path was faired which decreased the tool path curvature and curvature changing rate. Compared with initial ones, the path faired by the proposed method was relatively flat and smooth, which contributed to layup efficiency and reducing bulking defects. The method was demonstrated potentials in application for AFP manufacturing, especially for aeronautic and aerospace industry practice.
2018, 35(3):547-555.
DOI: 10.16356/j.1005-1120.2018.03.547
Abstract:
With the growing needs of prepreg tapes for the automated fiber placement (AFP), the deviation-rectifying of prepreg in slitting process was investigated on a self-developed 16-tow prepreg slitting and winding machine. The process of slitting and rewinding of prepreg tape was introduced, and the reason of prepreg tape deviation in slitting process was analyzed. In order to ensure the quality of the narrow prepreg slits, the application of the fuzzy PID algorithm in a closed-loop control system was discussed. A fuzzy PID algorithm was designed by combining fuzzy rules and PID controller. By applying it to precise deviation-rectifying control strategy, the automatic control of rectification could be achieved with accuracy of 0.1 mm, which satisfies the requirement of the prepreg tape both in slitting quality and layup quality for AFP.
With the growing needs of prepreg tapes for the automated fiber placement (AFP), the deviation-rectifying of prepreg in slitting process was investigated on a self-developed 16-tow prepreg slitting and winding machine. The process of slitting and rewinding of prepreg tape was introduced, and the reason of prepreg tape deviation in slitting process was analyzed. In order to ensure the quality of the narrow prepreg slits, the application of the fuzzy PID algorithm in a closed-loop control system was discussed. A fuzzy PID algorithm was designed by combining fuzzy rules and PID controller. By applying it to precise deviation-rectifying control strategy, the automatic control of rectification could be achieved with accuracy of 0.1 mm, which satisfies the requirement of the prepreg tape both in slitting quality and layup quality for AFP.
2018, 35(3):556-564.
DOI: 10.16356/j.1005-1120.2018.03.556
Abstract:
The effect of dry density, water-cement ratio, the addition of fly ash, and sand content on the porosity and pore distribution of foamed concrete is investigated. Digital microscopy and Image J software are employed to examine the landscape of pores with different sizes. Based on the Balshin empirical formula, a mathematical model is established to quantitatively predict the relationship between the pore structures and the compressive strength of foamed concrete. The results well demonstrate that there is a significant correlation between the modified formula and empirical parameters.
The effect of dry density, water-cement ratio, the addition of fly ash, and sand content on the porosity and pore distribution of foamed concrete is investigated. Digital microscopy and Image J software are employed to examine the landscape of pores with different sizes. Based on the Balshin empirical formula, a mathematical model is established to quantitatively predict the relationship between the pore structures and the compressive strength of foamed concrete. The results well demonstrate that there is a significant correlation between the modified formula and empirical parameters.
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