Transactions of Nanjing University of Aeronautics & Astronautics
Volume 37,Issue 5,2020 Table of Contents
2020, 37(5):663-675.
DOI: 10.16356/j.1005-1120.2020.05.001
Abstract:
This paper introduces the Chinese “Dove”—A practical application system of bird-mimetic air vehicles developed for more than a decade by the Institute of Flight Vehicle Innovation of Northwest Polytechnic University （NWPU） in China. Firstly， the main components， flight capability and flight verification of the Chinese “Dove” are presented. Then， the methods for the aerodynamic simulation and wind tunnel experiments are put forward. Secondly， the design of high-lift and high-thrust flexible flapping wings， a series of flapping mechanisms， gust-resistance layout and micro flight control/navigation system are presented. Some future studies on the application system of bionic micro air vehicles are given， including observation of natural flight creatures， aerodynamics in flight， mechanical and new material driving systems， structural mechanics， flight mechanics， and the information perception and intelligent decision-making control， which are related to research of flight bioinformatic perception and brain science. Finally， some application examples of complex flapping movements， active/passive deformation of bird wings， new low-energy motion-driven system， bionic intelligent decision-making and control/navigation are discussed.
This paper introduces the Chinese “Dove”—A practical application system of bird-mimetic air vehicles developed for more than a decade by the Institute of Flight Vehicle Innovation of Northwest Polytechnic University （NWPU） in China. Firstly， the main components， flight capability and flight verification of the Chinese “Dove” are presented. Then， the methods for the aerodynamic simulation and wind tunnel experiments are put forward. Secondly， the design of high-lift and high-thrust flexible flapping wings， a series of flapping mechanisms， gust-resistance layout and micro flight control/navigation system are presented. Some future studies on the application system of bionic micro air vehicles are given， including observation of natural flight creatures， aerodynamics in flight， mechanical and new material driving systems， structural mechanics， flight mechanics， and the information perception and intelligent decision-making control， which are related to research of flight bioinformatic perception and brain science. Finally， some application examples of complex flapping movements， active/passive deformation of bird wings， new low-energy motion-driven system， bionic intelligent decision-making and control/navigation are discussed.
2020, 37(5):676-681.
DOI: 10.16356/j.1005-1120.2020.05.002
Abstract:
The simplification of fatigue load spectrum， which can effectively reduce experimental cost， is of great importance for structural fatigue tests. By introducing random variables， the probabilistic tolerance method of removing small amplitude cycles proposed in this paper takes into account the randomness of both load and fatigue limit. The probability of the damage occurrence caused by the removed small loads is calculated to ensure that it cannot exceed the given probabilistic tolerance. Accordingly， the omission level is obtained and the truncated spectrum is formed. The unnotched aluminum sheet specimens are used to perform the fatigue test on the original fatigue spectrum and truncated fatigue spectrum of a transporter. The test results show that there is no statistical difference between the test life of the truncated spectrum and that of the original spectrum， which demonstrates the validity of the small-load-omitting method that considers randomness.
The simplification of fatigue load spectrum， which can effectively reduce experimental cost， is of great importance for structural fatigue tests. By introducing random variables， the probabilistic tolerance method of removing small amplitude cycles proposed in this paper takes into account the randomness of both load and fatigue limit. The probability of the damage occurrence caused by the removed small loads is calculated to ensure that it cannot exceed the given probabilistic tolerance. Accordingly， the omission level is obtained and the truncated spectrum is formed. The unnotched aluminum sheet specimens are used to perform the fatigue test on the original fatigue spectrum and truncated fatigue spectrum of a transporter. The test results show that there is no statistical difference between the test life of the truncated spectrum and that of the original spectrum， which demonstrates the validity of the small-load-omitting method that considers randomness.
2020, 37(5):682-693.
DOI: 10.16356/j.1005-1120.2020.05.003
Abstract:
Shaftless ducted rotor （SDR） is a new type of ducted rotor system designed with ducted-rotor-motor integration， which is quite different from traditional ducted rotor （DR） in aerodynamic characteristics. The sliding mesh based on unstructured grid is used to simulate the aerodynamic characteristics of SDR and DR. Then， the effects of five key parameters， namely， the rotor disk height， the number of blades， the spread angle of the duct， the central hole radius and the ducted lip radius on the aerodynamic characteristics of the SDR are investigated. It is found that the same-sized SDR produces a larger total lift than the DR in hovering， but the lift proportion of its duct is reduced. In the forward flight， a large low-speed region is generated behind the SDR duct， and the reflux vortex in blade root above the advancing blade has the trend for inward diffusion. The rotor disk height has similar effects on SDR and DR. Increasing the number of blades can effectively increase the total lift of SDR， which also increases the lift proportion of duct. Increasing the spread angle of the duct will lead to the rotor lift coefficient decrease， reducing the central hole radius can increase the total lift， but the component lift coefficient decreases. Appropriately increasing the ducted lip radius can increase the total lift， which begins to decrease after reaching a certain value.
Shaftless ducted rotor （SDR） is a new type of ducted rotor system designed with ducted-rotor-motor integration， which is quite different from traditional ducted rotor （DR） in aerodynamic characteristics. The sliding mesh based on unstructured grid is used to simulate the aerodynamic characteristics of SDR and DR. Then， the effects of five key parameters， namely， the rotor disk height， the number of blades， the spread angle of the duct， the central hole radius and the ducted lip radius on the aerodynamic characteristics of the SDR are investigated. It is found that the same-sized SDR produces a larger total lift than the DR in hovering， but the lift proportion of its duct is reduced. In the forward flight， a large low-speed region is generated behind the SDR duct， and the reflux vortex in blade root above the advancing blade has the trend for inward diffusion. The rotor disk height has similar effects on SDR and DR. Increasing the number of blades can effectively increase the total lift of SDR， which also increases the lift proportion of duct. Increasing the spread angle of the duct will lead to the rotor lift coefficient decrease， reducing the central hole radius can increase the total lift， but the component lift coefficient decreases. Appropriately increasing the ducted lip radius can increase the total lift， which begins to decrease after reaching a certain value.
2020, 37(5):694-701.
DOI: 10.16356/j.1005-1120.2020.05.004
Abstract:
Through taking uncertain mechanical parameters of composites into consideration， this paper carries out uncertain modal analysis for an unmanned aircraft landing gear. By describing correlated multi-dimensional mechanical parameters as a convex polyhedral model， the modal analysis problem of a composite landing gear is transferred into a linear fractional programming（LFR） eigenvalue solution problem. As a consequent， the extreme-point algorithm is proposed to estimate lower and upper bounds of eigenvalues， namely the exact results of eigenvalues can be easily obtained at the extreme-point locations of the convex polyhedral model. The simulation results show that the proposed model and algorithm can play an important role in the eigenvalue solution problem and possess valuable engineering significance. It will be a powerful and effective tool for further vibration analysis for the landing gear.
Through taking uncertain mechanical parameters of composites into consideration， this paper carries out uncertain modal analysis for an unmanned aircraft landing gear. By describing correlated multi-dimensional mechanical parameters as a convex polyhedral model， the modal analysis problem of a composite landing gear is transferred into a linear fractional programming（LFR） eigenvalue solution problem. As a consequent， the extreme-point algorithm is proposed to estimate lower and upper bounds of eigenvalues， namely the exact results of eigenvalues can be easily obtained at the extreme-point locations of the convex polyhedral model. The simulation results show that the proposed model and algorithm can play an important role in the eigenvalue solution problem and possess valuable engineering significance. It will be a powerful and effective tool for further vibration analysis for the landing gear.
2020, 37(5):702-712.
DOI: 10.16356/j.1005-1120.2020.05.005
Abstract:
For the numerical simulation of compressible flows， normally different mesh sizes are expected in different regions. For example， smaller mesh sizes are required to improve the local numerical resolution in the regions where the physical variables vary violently （for example， near the shock waves or in the boundary layers） and larger elements are expected for the regions where the solution is smooth. h-adaptive mesh has been widely used for complex flows. However， there are two difficulties when employing h-adaptivity for high-order discontinuous Galerkin （DG） methods. First， locally curved elements are required to precisely match the solid boundary， which significantly increases the difficulty to conduct the “refining” and “coarsening” operations since the curved information has to be maintained. Second， h-adaptivity could break the partition balancing， which would significantly affect the efficiency of parallel computing. In this paper， a robust and automatic h-adaptive method is developed for high-order DG methods on locally curved tetrahedral mesh， for which the curved geometries are maintained during the h-adaptivity. Furthermore， the reallocating and rebalancing of the computational loads on parallel clusters are conducted to maintain the parallel efficiency. Numerical results indicate that the introduced h-adaptive method is able to generate more reasonable mesh according to the structure of flow-fields.
For the numerical simulation of compressible flows， normally different mesh sizes are expected in different regions. For example， smaller mesh sizes are required to improve the local numerical resolution in the regions where the physical variables vary violently （for example， near the shock waves or in the boundary layers） and larger elements are expected for the regions where the solution is smooth. h-adaptive mesh has been widely used for complex flows. However， there are two difficulties when employing h-adaptivity for high-order discontinuous Galerkin （DG） methods. First， locally curved elements are required to precisely match the solid boundary， which significantly increases the difficulty to conduct the “refining” and “coarsening” operations since the curved information has to be maintained. Second， h-adaptivity could break the partition balancing， which would significantly affect the efficiency of parallel computing. In this paper， a robust and automatic h-adaptive method is developed for high-order DG methods on locally curved tetrahedral mesh， for which the curved geometries are maintained during the h-adaptivity. Furthermore， the reallocating and rebalancing of the computational loads on parallel clusters are conducted to maintain the parallel efficiency. Numerical results indicate that the introduced h-adaptive method is able to generate more reasonable mesh according to the structure of flow-fields.
2020, 37(5):713-725.
DOI: 10.16356/j.1005-1120.2020.05.006
Abstract:
It is widely acknowledged that the performance of a piezoelectric stack would decline with the temperature decreasing， which will exert negative influence on its application in low-temperature environment. Therefore， a convenient and efficient warming structure for the piezoelectric stack is proposed in this paper to solve this problem. Based on the theoretical analysis of heat transfer， two heating modes， namely， overall heating and local heating are analyzed and compared. Moreover， experimental tests are conducted to evaluate the effectiveness of the structure. Based on the results， it can be concluded that the theoretical results are confirmed with experimental results. Besides， the temperature and performance of the piezoelectric stack are kept stable as temperature varies from 10 ℃ to -70 ℃， which manifests the feasibility of the structure. Therefore， this paper could be an available reference for those engaged in cryogenic investigation of smart materials and structures.
It is widely acknowledged that the performance of a piezoelectric stack would decline with the temperature decreasing， which will exert negative influence on its application in low-temperature environment. Therefore， a convenient and efficient warming structure for the piezoelectric stack is proposed in this paper to solve this problem. Based on the theoretical analysis of heat transfer， two heating modes， namely， overall heating and local heating are analyzed and compared. Moreover， experimental tests are conducted to evaluate the effectiveness of the structure. Based on the results， it can be concluded that the theoretical results are confirmed with experimental results. Besides， the temperature and performance of the piezoelectric stack are kept stable as temperature varies from 10 ℃ to -70 ℃， which manifests the feasibility of the structure. Therefore， this paper could be an available reference for those engaged in cryogenic investigation of smart materials and structures.
2020, 37(5):726-738.
DOI: 10.16356/j.1005-1120.2020.05.007
Abstract:
An algorithm integrating reduced order model （ROM）， equivalent linearization （EL）， and finite element method （FEM） is proposed to carry out geometrically nonlinear random vibration analysis of stiffened plates under acoustic pressure loading. Based on large deflection finite element formulation， the nonlinear equations of motion of stiffened plates are obtained. To reduce the computation， a reduced order model of the structures is established. Then the EL technique is incorporated into FE software NASTRAN by the direct matrix abstraction program （DMAP）. For the stiffened plates， a finite element model of beam and plate assembly is established， in which the nodes of beam elements are shared with shell elements， and the offset and section properties of the beam are set. The presented method can capture the root-mean-square （RMS） of the stress responses of shell and beam elements of stiffened plates， and analyze the stress distribution of the stiffened surface and the unstiffened surface， respectively. Finally， the statistical dynamic response results obtained by linear and EL methods are compared. It is shown that the proposed method can be used to analyze the geometrically nonlinear random responses of stiffened plates. The geometric nonlinearity plays an important role in the vibration response of stiffened plates， particularly at high acoustic pressure loading.
An algorithm integrating reduced order model （ROM）， equivalent linearization （EL）， and finite element method （FEM） is proposed to carry out geometrically nonlinear random vibration analysis of stiffened plates under acoustic pressure loading. Based on large deflection finite element formulation， the nonlinear equations of motion of stiffened plates are obtained. To reduce the computation， a reduced order model of the structures is established. Then the EL technique is incorporated into FE software NASTRAN by the direct matrix abstraction program （DMAP）. For the stiffened plates， a finite element model of beam and plate assembly is established， in which the nodes of beam elements are shared with shell elements， and the offset and section properties of the beam are set. The presented method can capture the root-mean-square （RMS） of the stress responses of shell and beam elements of stiffened plates， and analyze the stress distribution of the stiffened surface and the unstiffened surface， respectively. Finally， the statistical dynamic response results obtained by linear and EL methods are compared. It is shown that the proposed method can be used to analyze the geometrically nonlinear random responses of stiffened plates. The geometric nonlinearity plays an important role in the vibration response of stiffened plates， particularly at high acoustic pressure loading.
2020, 37(5):739-749.
DOI: 10.16356/j.1005-1120.2020.05.008
Abstract:
In view of the engineering background that CK drone aircraft needs modification and upgrading to improve its maneuvering performance， numerical research and analysis of air inlet aerodynamic performance are carried out. Firstly， based on the introduction of the theoretical knowledge involved in aircraft maneuvering flight， parameters such as aircraft attitude and engine mass flow etc. required for the aerodynamic performance calculation of CK drone aircraft air inlet are determined. By analyzing the test data of WP6 engine inlet distortion simulation board， the typical indexes are extracted as the basis for evaluating the air inlet performance of CK drone aircraft. Then， the aerodynamic characteristics of the inlet of CK drone aircraft under different maneuvering conditions are numerically studied， and the total pressure recovery coefficient and pressure distortion index of the outlet section are obtained. Several conclusions and suggestions are formed after the study. When CK drone aircraft flies at positive angle of attack， the inlet has good aerodynamic characteristics， which can meet the requirements of engine intake during high maneuverable flight. In the flight of negative angle of attack， the total pressure loss and pressure distortion at the outlet section of air inlet increase sharply， which cannot guarantee the stable working of the engine. On the premise that the aircraft attitude is satisfied， CK drone aircraft can use three engine thrust states of “Rated”， “Modified rated” and “Maximum” for high maneuverable flight.
In view of the engineering background that CK drone aircraft needs modification and upgrading to improve its maneuvering performance， numerical research and analysis of air inlet aerodynamic performance are carried out. Firstly， based on the introduction of the theoretical knowledge involved in aircraft maneuvering flight， parameters such as aircraft attitude and engine mass flow etc. required for the aerodynamic performance calculation of CK drone aircraft air inlet are determined. By analyzing the test data of WP6 engine inlet distortion simulation board， the typical indexes are extracted as the basis for evaluating the air inlet performance of CK drone aircraft. Then， the aerodynamic characteristics of the inlet of CK drone aircraft under different maneuvering conditions are numerically studied， and the total pressure recovery coefficient and pressure distortion index of the outlet section are obtained. Several conclusions and suggestions are formed after the study. When CK drone aircraft flies at positive angle of attack， the inlet has good aerodynamic characteristics， which can meet the requirements of engine intake during high maneuverable flight. In the flight of negative angle of attack， the total pressure loss and pressure distortion at the outlet section of air inlet increase sharply， which cannot guarantee the stable working of the engine. On the premise that the aircraft attitude is satisfied， CK drone aircraft can use three engine thrust states of “Rated”， “Modified rated” and “Maximum” for high maneuverable flight.
2020, 37(5):750-757.
DOI: 10.16356/j.1005-1120.2020.05.009
Abstract:
The health status of aero engines is very important to the flight safety. However， it is difficult for aero engines to make an effective fault diagnosis due to its complex structure and poor working environment. Therefore， an effective fault diagnosis method for aero engines based on the gravitational search algorithm and the stack autoencoder （GSA-SAE） is proposed， and the fault diagnosis technology of a turbofan engine is studied. Firstly， the data of 17 parameters， including total inlet air temperature， high-pressure rotor speed， low-pressure rotor speed， turbine pressure ratio， total inlet air temperature of high-pressure compressor and outlet air pressure of high-pressure compressor and so on， are preprocessed， and the fault diagnosis model architecture of SAE is constructed. In order to solve the problem that the best diagnosis effect cannot be obtained due to manually setting the number of neurons in each hidden layer of SAE network， a GSA optimization algorithm for the SAE network is proposed to find and obtain the optimal number of neurons in each hidden layer of SAE network. Furthermore， an optimal fault diagnosis model based on GSA-SAE is established for aero engines. Finally， the effectiveness of the optimal GSA-SAE fault diagnosis model is demonstrated using the practical data of aero engines. The results illustrate that the proposed fault diagnosis method effectively solves the problem of the poor fault diagnosis result because of manually setting the number of neurons in each hidden layer of SAE network， and has good fault diagnosis efficiency. The fault diagnosis accuracy of the GSA-SAE model reaches 98.222%， which is significantly higher than that of SAE， the general regression neural network （GRNN） and the back propagation （BP） network fault diagnosis models.
The health status of aero engines is very important to the flight safety. However， it is difficult for aero engines to make an effective fault diagnosis due to its complex structure and poor working environment. Therefore， an effective fault diagnosis method for aero engines based on the gravitational search algorithm and the stack autoencoder （GSA-SAE） is proposed， and the fault diagnosis technology of a turbofan engine is studied. Firstly， the data of 17 parameters， including total inlet air temperature， high-pressure rotor speed， low-pressure rotor speed， turbine pressure ratio， total inlet air temperature of high-pressure compressor and outlet air pressure of high-pressure compressor and so on， are preprocessed， and the fault diagnosis model architecture of SAE is constructed. In order to solve the problem that the best diagnosis effect cannot be obtained due to manually setting the number of neurons in each hidden layer of SAE network， a GSA optimization algorithm for the SAE network is proposed to find and obtain the optimal number of neurons in each hidden layer of SAE network. Furthermore， an optimal fault diagnosis model based on GSA-SAE is established for aero engines. Finally， the effectiveness of the optimal GSA-SAE fault diagnosis model is demonstrated using the practical data of aero engines. The results illustrate that the proposed fault diagnosis method effectively solves the problem of the poor fault diagnosis result because of manually setting the number of neurons in each hidden layer of SAE network， and has good fault diagnosis efficiency. The fault diagnosis accuracy of the GSA-SAE model reaches 98.222%， which is significantly higher than that of SAE， the general regression neural network （GRNN） and the back propagation （BP） network fault diagnosis models.
2020, 37(5):758-767.
DOI: 10.16356/j.1005-1120.2020.05.010
Abstract:
Based on feature modeling and mathematical analysis methods， a process-oriented and modular parametric design system for advanced turbine cooling blade is developed with UG API， aiming at the structural complexity and high design difficulty of aero-engine cooling turbine blade. The relationship between the external and internal body features， the body attached feature is analyzed as viewed from the feature and parameter terms. The parametric design processes and design examples of the external body shape， tenon， platform and internal body shape， ribs， pin fins are introduced. The system improves the design efficiency of cooling turbine blade and establishes the foundation of multidisciplinary design optimization procedure for it.
Based on feature modeling and mathematical analysis methods， a process-oriented and modular parametric design system for advanced turbine cooling blade is developed with UG API， aiming at the structural complexity and high design difficulty of aero-engine cooling turbine blade. The relationship between the external and internal body features， the body attached feature is analyzed as viewed from the feature and parameter terms. The parametric design processes and design examples of the external body shape， tenon， platform and internal body shape， ribs， pin fins are introduced. The system improves the design efficiency of cooling turbine blade and establishes the foundation of multidisciplinary design optimization procedure for it.
2020, 37(5):768-777.
DOI: 10.16356/j.1005-1120.2020.05.011
Abstract:
Taking the typical face gear connection structure of the combined rotor as the research object， this paper studies the distribution rules of the contact state， contact stress and slip distance of the contact tooth surface of face gear under different centrifugal force and temperature conditions by using the finite element method， in order to improve the reliability of face gear connection structure. And the influence of centrifugal force and temperature on the maximum wear depth of the tooth surface is studied based on the fretting wear model proposed by McColl. Results show that： （1） The external diameter has an opening phenomenon on the contact surface of the face gear under the centrifugal effect， which reduces the load-bearing area； （2） The contact stress at the inner root of the face gear is the largest and the wear is the most serious； （3） The temperature field causes the contact surface to be thermally expanded， resulting in the large uneven deformation， and the tooth surface appears drum-shape； （4） The maximum contact stress and the maximum wear depth occur in the middle of the tooth root； （5） As the temperature increases， the maximum wear depth of the tooth surface increases significantly. Consequently， reducing temperature of the combined rotor plays an important role in effectively reducing the wear of the face gear and improving the connection life of face gear connection structure.
Taking the typical face gear connection structure of the combined rotor as the research object， this paper studies the distribution rules of the contact state， contact stress and slip distance of the contact tooth surface of face gear under different centrifugal force and temperature conditions by using the finite element method， in order to improve the reliability of face gear connection structure. And the influence of centrifugal force and temperature on the maximum wear depth of the tooth surface is studied based on the fretting wear model proposed by McColl. Results show that： （1） The external diameter has an opening phenomenon on the contact surface of the face gear under the centrifugal effect， which reduces the load-bearing area； （2） The contact stress at the inner root of the face gear is the largest and the wear is the most serious； （3） The temperature field causes the contact surface to be thermally expanded， resulting in the large uneven deformation， and the tooth surface appears drum-shape； （4） The maximum contact stress and the maximum wear depth occur in the middle of the tooth root； （5） As the temperature increases， the maximum wear depth of the tooth surface increases significantly. Consequently， reducing temperature of the combined rotor plays an important role in effectively reducing the wear of the face gear and improving the connection life of face gear connection structure.
2020, 37(5):778-786.
DOI: 10.16356/j.1005-1120.2020.05.012
Abstract:
The problem of joint direction of arrival （DOA） and polarization estimation for polarization sensitive coprime planar arrays （PS-CPAs） is investigated， and a fast-convergence quadrilinear decomposition approach is proposed. Specifically， we first decompose the PS-CPA into two sparse polarization sensitive uniform planar subarrays and employ propagator method （PM） to construct the initial steering matrices separately. Then we arrange the received signals into two quadrilinear models so that the potential DOA and polarization estimates can be attained via quadrilinear alternating least square （QALS）. Subsequently， we distinguish the true DOA estimates from the approximate intersecting estimations of the two subarrays in view of the coprime feature. Finally， the polarization estimates paired with DOA can be obtained. In contrast to the conventional QALS algorithm， the proposed approach can remarkably reduce the computational complexity without degrading the estimation performance. Simulations demonstrate the superiority of the proposed fast-convergence approach for PS-CPAs.
The problem of joint direction of arrival （DOA） and polarization estimation for polarization sensitive coprime planar arrays （PS-CPAs） is investigated， and a fast-convergence quadrilinear decomposition approach is proposed. Specifically， we first decompose the PS-CPA into two sparse polarization sensitive uniform planar subarrays and employ propagator method （PM） to construct the initial steering matrices separately. Then we arrange the received signals into two quadrilinear models so that the potential DOA and polarization estimates can be attained via quadrilinear alternating least square （QALS）. Subsequently， we distinguish the true DOA estimates from the approximate intersecting estimations of the two subarrays in view of the coprime feature. Finally， the polarization estimates paired with DOA can be obtained. In contrast to the conventional QALS algorithm， the proposed approach can remarkably reduce the computational complexity without degrading the estimation performance. Simulations demonstrate the superiority of the proposed fast-convergence approach for PS-CPAs.
2020, 37(5):787-795.
DOI: 10.16356/j.1005-1120.2020.05.013
Abstract:
Tikhonov regularization is a powerful tool for solving linear discrete ill-posed problems. However， effective methods for dealing with large-scale ill-posed problems are still lacking. The Kaczmarz method is an effective iterative projection algorithm for solving large linear equations due to its simplicity. We propose a regularized randomized extended Kaczmarz （RREK）algorithm for solving large discrete ill-posed problems via combining the Tikhonov regularization and the randomized Kaczmarz method. The convergence of the algorithm is proved. Numerical experiments illustrate that the proposed algorithm has higher accuracy and better image restoration quality compared with the existing randomized extended Kaczmarz （REK） method.
Tikhonov regularization is a powerful tool for solving linear discrete ill-posed problems. However， effective methods for dealing with large-scale ill-posed problems are still lacking. The Kaczmarz method is an effective iterative projection algorithm for solving large linear equations due to its simplicity. We propose a regularized randomized extended Kaczmarz （RREK）algorithm for solving large discrete ill-posed problems via combining the Tikhonov regularization and the randomized Kaczmarz method. The convergence of the algorithm is proved. Numerical experiments illustrate that the proposed algorithm has higher accuracy and better image restoration quality compared with the existing randomized extended Kaczmarz （REK） method.
2020, 37(5):796-803.
DOI: 10.16356/j.1005-1120.2020.05.014
Abstract:
For the advantages of easy realization and rapidly intelligent response， the one-cycle control was applied in five-phase six-leg switching power amplifier for magnetic bearing. This paper improves the one-cycle control considering resistance voltage drop and derives its mathematical models. The improved algorithm is compared with the former one. The simulation and experimental results show that the improved algorithm can effectively reduce the output current ripple， achieve good tracking of the given current， improve the control accuracy， and verify the effectiveness and superiority of the method.
For the advantages of easy realization and rapidly intelligent response， the one-cycle control was applied in five-phase six-leg switching power amplifier for magnetic bearing. This paper improves the one-cycle control considering resistance voltage drop and derives its mathematical models. The improved algorithm is compared with the former one. The simulation and experimental results show that the improved algorithm can effectively reduce the output current ripple， achieve good tracking of the given current， improve the control accuracy， and verify the effectiveness and superiority of the method.
2020, 37(5):804-815.
DOI: 10.16356/j.1005-1120.2020.05.015
Abstract:
Deep dielectric charging/discharging， caused by high energy electrons， is an important consideration in electronic devices used in space environments because it can lead to spacecraft anomalies and failures. The Jovian planets， including Saturn， Uranus， Neptune and Jupiter’s moons， are believed to have robust electron radiation belts at relativistic energies. In particular， Jupiter is thought to have caused at least 42 internal electrostatic discharge events during the Voyager 1 flyby. With the development of deep space exploration， there is an increased focus on the deep dielectric charging effects in the orbits of Jovian planets. In this paper， GEANT4， a Monte Carlo toolkit， and radiation-induced conductivity （RIC） are used to calculate deep dielectric charging effects for Jovian planets. The results are compared with the criteria for preventing deep dielectric charging effects in Earth orbit. The findings show that effective criteria used in Earth orbit are not always appropriate for preventing deep dielectric charging effects in Jovian orbits. Generally， Io， Europa， Saturn （RS=6）， Uranus （L=4.73） and Ganymede missions should have a thicker shield or higher dielectric conductivity， while Neptune （L=7.4） and Callisto missions can have a thinner shield thickness or a lower dielectric conductivity. Moreover， dielectrics grounded with double metal layers and thinner dielectrics can also decrease the likelihood of discharges.
Deep dielectric charging/discharging， caused by high energy electrons， is an important consideration in electronic devices used in space environments because it can lead to spacecraft anomalies and failures. The Jovian planets， including Saturn， Uranus， Neptune and Jupiter’s moons， are believed to have robust electron radiation belts at relativistic energies. In particular， Jupiter is thought to have caused at least 42 internal electrostatic discharge events during the Voyager 1 flyby. With the development of deep space exploration， there is an increased focus on the deep dielectric charging effects in the orbits of Jovian planets. In this paper， GEANT4， a Monte Carlo toolkit， and radiation-induced conductivity （RIC） are used to calculate deep dielectric charging effects for Jovian planets. The results are compared with the criteria for preventing deep dielectric charging effects in Earth orbit. The findings show that effective criteria used in Earth orbit are not always appropriate for preventing deep dielectric charging effects in Jovian orbits. Generally， Io， Europa， Saturn （RS=6）， Uranus （L=4.73） and Ganymede missions should have a thicker shield or higher dielectric conductivity， while Neptune （L=7.4） and Callisto missions can have a thinner shield thickness or a lower dielectric conductivity. Moreover， dielectrics grounded with double metal layers and thinner dielectrics can also decrease the likelihood of discharges.
2020, 37(5):816-830.
DOI: 10.16356/j.1005-1120.2020.05.016
Abstract:
Using the traditional swarm intelligence algorithm to solve the cooperative path planning problem for multi-UAVs is easy to incur the problems of local optimization and a slow convergence rate. A cooperative path planning method for multi-UAVs based on the improved sheep optimization is proposed to tackle these. Firstly， based on the three-dimensional planning space， a multi-UAV cooperative cost function model is established according to the path planning requirements， and an initial track set is constructed by combining multiple-population ideas. Then an improved sheep optimization is proposed and used to solve the path planning problem and obtain multiple cooperative paths. The simulation results show that the sheep optimization can meet the requirements of path planning and realize the cooperative path planning of multi-UAVs. Compared with grey wolf optimizer （GWO）， improved gray wolf optimizer（IGWO）， chaotic gray wolf optimizer（CGWO）， differential evolution （DE） algorithm， and particle swam optimization （PSO）， the convergence speed and search accuracy of the improved sheep optimization are significantly improved.
Using the traditional swarm intelligence algorithm to solve the cooperative path planning problem for multi-UAVs is easy to incur the problems of local optimization and a slow convergence rate. A cooperative path planning method for multi-UAVs based on the improved sheep optimization is proposed to tackle these. Firstly， based on the three-dimensional planning space， a multi-UAV cooperative cost function model is established according to the path planning requirements， and an initial track set is constructed by combining multiple-population ideas. Then an improved sheep optimization is proposed and used to solve the path planning problem and obtain multiple cooperative paths. The simulation results show that the sheep optimization can meet the requirements of path planning and realize the cooperative path planning of multi-UAVs. Compared with grey wolf optimizer （GWO）， improved gray wolf optimizer（IGWO）， chaotic gray wolf optimizer（CGWO）， differential evolution （DE） algorithm， and particle swam optimization （PSO）， the convergence speed and search accuracy of the improved sheep optimization are significantly improved.
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