Transactions of Nanjing University of Aeronautics & Astronautics
Volume 0,Issue 3,2024 Table of Contents
2024(3):263-277.
DOI: 10.16356/j.1005-1120.2024.03.001
Abstract:
The tail-sitter vertical takeoff / landing （VTOL） unmanned aerial vehicle （UAV） exhibits poor stability and limited compatibility with traditional landing gears. To address the aforementioned issues， a novel landing gear incorporating free-tail technology is proposed. The landing gear adopts a tandem multi-stage structure， which can ensure the length of the tail force arm in cruise condition while lowering the fuselage altitude. Furthermore， the dynamic landing process is regulated through the employment of virtual centroid force distribution techniques， streamlining the control process and facilitating seamless trajectory optimization during mode transition. Based on the single-point dataset of the cat center point， a neural network is used to train the landing gear control， which makes the landing gear adaptive takeoff and landing speed and accuracy effectively improved. Subsequently， multi-objective optimization and similarity conversion are executed in conjunction with parameter requirements of different modes of the UAV， effectively enhancing landing adaptability and stability of the tail-sitter VTOL UAV.
The tail-sitter vertical takeoff / landing （VTOL） unmanned aerial vehicle （UAV） exhibits poor stability and limited compatibility with traditional landing gears. To address the aforementioned issues， a novel landing gear incorporating free-tail technology is proposed. The landing gear adopts a tandem multi-stage structure， which can ensure the length of the tail force arm in cruise condition while lowering the fuselage altitude. Furthermore， the dynamic landing process is regulated through the employment of virtual centroid force distribution techniques， streamlining the control process and facilitating seamless trajectory optimization during mode transition. Based on the single-point dataset of the cat center point， a neural network is used to train the landing gear control， which makes the landing gear adaptive takeoff and landing speed and accuracy effectively improved. Subsequently， multi-objective optimization and similarity conversion are executed in conjunction with parameter requirements of different modes of the UAV， effectively enhancing landing adaptability and stability of the tail-sitter VTOL UAV.
2024(3):278-288.
DOI: 10.16356/j.1005-1120.2024.03.002
Abstract:
Piecewise linear blade twist is studied as a method for reducing the rotor vibratory loads. A rotor model based on an elastic beam concept is used to predict the loads. A four-bladed rotor with a shape similar to the UH-60 rotor is used as a baseline for comparisons. The blade is divided into three segments， which are inner， middle and outer segments respectively. Effect of the twist at different segments on the loads is discussed. The twists at all the segments can reduce the 4/rev （revolution） vertical hub force at low speeds. The 4/rev force can be reduced by 99.5% with a -24°/R （R is the blade radius） twist at the middle segment at 80 km/h. The twist at the inner segment is not helpful for reducing the 4/rev rolling and pitching moments， while the twists at other segments can control both the moments at most speeds. A parameter sweep is conducted to minimize these loads. To reduce the 4/rev force， all the segments need to be twisted at low speeds， while untwisted blades perform better at high speeds. For controlling the 4/rev moments， the outer segment should be highly twisted at low speeds， while high twists at the middle segment are essential at medium to high speeds.
Piecewise linear blade twist is studied as a method for reducing the rotor vibratory loads. A rotor model based on an elastic beam concept is used to predict the loads. A four-bladed rotor with a shape similar to the UH-60 rotor is used as a baseline for comparisons. The blade is divided into three segments， which are inner， middle and outer segments respectively. Effect of the twist at different segments on the loads is discussed. The twists at all the segments can reduce the 4/rev （revolution） vertical hub force at low speeds. The 4/rev force can be reduced by 99.5% with a -24°/R （R is the blade radius） twist at the middle segment at 80 km/h. The twist at the inner segment is not helpful for reducing the 4/rev rolling and pitching moments， while the twists at other segments can control both the moments at most speeds. A parameter sweep is conducted to minimize these loads. To reduce the 4/rev force， all the segments need to be twisted at low speeds， while untwisted blades perform better at high speeds. For controlling the 4/rev moments， the outer segment should be highly twisted at low speeds， while high twists at the middle segment are essential at medium to high speeds.
2024(3):289-299.
DOI: 10.16356/j.1005-1120.2024.03.003
Abstract:
Rotor displacement control of a bearingless switched reluctance motor （BLSRM） with single-winding stator is proposed. First， the structure and working principle of BLSRM are briefly introduced. The equivalent magnetic circuit method is used to establish a mathematical model of suspension force and stiffness. In addition， a rotor-dynamic model is established to attain the relation between force and rotor displacement. Finally， a prototype motor is designed and the suspension control of the motor is implemented. The validity of the proposed method is verified by experimental results.
Rotor displacement control of a bearingless switched reluctance motor （BLSRM） with single-winding stator is proposed. First， the structure and working principle of BLSRM are briefly introduced. The equivalent magnetic circuit method is used to establish a mathematical model of suspension force and stiffness. In addition， a rotor-dynamic model is established to attain the relation between force and rotor displacement. Finally， a prototype motor is designed and the suspension control of the motor is implemented. The validity of the proposed method is verified by experimental results.
2024(3):300-310.
DOI: 10.16356/j.1005-1120.2024.03.004
Abstract:
Currently， the axial motion of linear-rotary switched reluctance motor （LRSRM） can only achieve axial positioning， and the two-degree-of-freedom motion is simple. A linear-velocity control method is proposed in the paper to improve the axial control performance. The axial displacement and velocity of rotor are controlled by linear position/velocity observer. The torque winding current and axial-force winding current are calculated by the mathematical model of torque and axial force， and then distributed to the corresponding conducted region for current hysteresis. It can effectively regulate the axial velocity and displacement of the rotor during the rotation process. The effectiveness and accuracy of the proposed method are verified by simulation and experiments.
Currently， the axial motion of linear-rotary switched reluctance motor （LRSRM） can only achieve axial positioning， and the two-degree-of-freedom motion is simple. A linear-velocity control method is proposed in the paper to improve the axial control performance. The axial displacement and velocity of rotor are controlled by linear position/velocity observer. The torque winding current and axial-force winding current are calculated by the mathematical model of torque and axial force， and then distributed to the corresponding conducted region for current hysteresis. It can effectively regulate the axial velocity and displacement of the rotor during the rotation process. The effectiveness and accuracy of the proposed method are verified by simulation and experiments.
2024(3):311-324.
DOI: 10.16356/j.1005-1120.2024.03.005
Abstract:
Relevant to thermoacoustic combustion instability in engines， the pressure oscillations in gas-solid two-phase turbulent flow have long been a topic of great concerns. To understand the pressure oscillation characteristics in gas-solid two-phase flow， three-dimensional unsteady numerical calculations are conducted for typical two-phase gas-solid backstep flow using the combined self-adaptive turbulence eddy simulation （SATES） and discrete phase model （DPM） method. The accuracy and reliability of the numerical method is firstly validated by comparisons with the experimental data. Then， the unsteady pressure signal of the two-phase gas-solid flow is compared with that of the pure gas phase flow， and it is found that with the addition of solid particles， the dominant frequency of pressure oscillation is slightly changed， and the oscillation amplitude significantly decreases. Finally， the effects of diameter and mass fraction of solid particles on the pressure oscillation are investigated. It is found that with increasing the solid particle diameter， the amplitude of pressure oscillation firstly decreases and then increases， and the amplitude exhibits the smallest with the diameter of 10 μm； with increasing the mass fraction of solid particle， the pressure oscillation amplitude shows a decreasing trend. The results demonstrate that the properties of solid particles in two-phase flow have a small impact on the dominant frequency of pressure oscillation， while a significant impact on the oscillation amplitude.
Relevant to thermoacoustic combustion instability in engines， the pressure oscillations in gas-solid two-phase turbulent flow have long been a topic of great concerns. To understand the pressure oscillation characteristics in gas-solid two-phase flow， three-dimensional unsteady numerical calculations are conducted for typical two-phase gas-solid backstep flow using the combined self-adaptive turbulence eddy simulation （SATES） and discrete phase model （DPM） method. The accuracy and reliability of the numerical method is firstly validated by comparisons with the experimental data. Then， the unsteady pressure signal of the two-phase gas-solid flow is compared with that of the pure gas phase flow， and it is found that with the addition of solid particles， the dominant frequency of pressure oscillation is slightly changed， and the oscillation amplitude significantly decreases. Finally， the effects of diameter and mass fraction of solid particles on the pressure oscillation are investigated. It is found that with increasing the solid particle diameter， the amplitude of pressure oscillation firstly decreases and then increases， and the amplitude exhibits the smallest with the diameter of 10 μm； with increasing the mass fraction of solid particle， the pressure oscillation amplitude shows a decreasing trend. The results demonstrate that the properties of solid particles in two-phase flow have a small impact on the dominant frequency of pressure oscillation， while a significant impact on the oscillation amplitude.
2024(3):325-343.
DOI: 10.16356/j.1005-1120.2024.03.006
Abstract:
A dynamic model of a stabilized drogue with four control surfaces is developed to mitigate the aerodynamic disturbances caused by the bow wave effect and wind turbulence during the docking stage of hose-drogue systems. Numerical simulations are used to identify the aerodynamic characteristics of the drogue， and the data is simplified using linear and polynomial functions. The aerodynamic model is used to design a linear quadratic regulator （LQR） controller. MATLAB/Simulink is used to construct a hose-drogue model and verify the effectiveness of the actively controllable stabilized drogue in reducing the effect of disturbances. The study also investigates the effects of control surface deflection angles on hose catenary curves using a static model. Numerical simulations show that the actively controllable stabilized drogue reduces the effects of the bow wave and wind turbulence， which maintains the stability of the hose-drogue system and improves the success rate of aerial refueling.
A dynamic model of a stabilized drogue with four control surfaces is developed to mitigate the aerodynamic disturbances caused by the bow wave effect and wind turbulence during the docking stage of hose-drogue systems. Numerical simulations are used to identify the aerodynamic characteristics of the drogue， and the data is simplified using linear and polynomial functions. The aerodynamic model is used to design a linear quadratic regulator （LQR） controller. MATLAB/Simulink is used to construct a hose-drogue model and verify the effectiveness of the actively controllable stabilized drogue in reducing the effect of disturbances. The study also investigates the effects of control surface deflection angles on hose catenary curves using a static model. Numerical simulations show that the actively controllable stabilized drogue reduces the effects of the bow wave and wind turbulence， which maintains the stability of the hose-drogue system and improves the success rate of aerial refueling.
2024(3):344-358.
DOI: 10.16356/j.1005-1120.2024.03.007
Abstract:
Ingestion of the ice crystals in aircraft engines can lead to the thrust loss or even blade damage， posing a potential threat to flight safety. To investigate the impact characteristics of the ice crystals in the compressor cascade， a method is established to calculate the trajectories of ice crystal particles impacting the blade pressure surface and suction surface separately which can avoid the intersections of the particle trajectories. Based on this method， the effect of the particle size and shape on the ice crystal impact characteristics are numerically studied in details. Results show that the total collection coefficient increases with the increase of the particle equivalent diameter and aspect ratio. For the particles with the same shape， the total collection coefficient increases by 44.1% when the particle diameter increases from 20 μm to 50 μm； for the particles with the same size， the total collection coefficient increases by 39% when the particle aspect ratio increases from 0.1 to 10. The increase of the collection coefficient of the blade pressure surface is the main reason for the increase of the total collection coefficient. The blade leading edge is mainly characterized by the fragmentation of ice crystals and the blade surface is mainly characterized by the rebound of the ice crystals. In most parts of the blade surface， the ice crystal particles have a non-elastic rebound. In terms of the particle size， the distribution trend of the collection coefficient after the secondary impact is very similar to that of the primary impact， with a notable difference being a reduction of about 70% of the maximum value of the collection coefficient. However， in terms of the particle aspect ratio， the trend of the secondary impact collection coefficient at the leading edge of the blade is opposite to that of the primary impact， with elongated ice crystal particles exhibiting a lower secondary collection coefficient.
Ingestion of the ice crystals in aircraft engines can lead to the thrust loss or even blade damage， posing a potential threat to flight safety. To investigate the impact characteristics of the ice crystals in the compressor cascade， a method is established to calculate the trajectories of ice crystal particles impacting the blade pressure surface and suction surface separately which can avoid the intersections of the particle trajectories. Based on this method， the effect of the particle size and shape on the ice crystal impact characteristics are numerically studied in details. Results show that the total collection coefficient increases with the increase of the particle equivalent diameter and aspect ratio. For the particles with the same shape， the total collection coefficient increases by 44.1% when the particle diameter increases from 20 μm to 50 μm； for the particles with the same size， the total collection coefficient increases by 39% when the particle aspect ratio increases from 0.1 to 10. The increase of the collection coefficient of the blade pressure surface is the main reason for the increase of the total collection coefficient. The blade leading edge is mainly characterized by the fragmentation of ice crystals and the blade surface is mainly characterized by the rebound of the ice crystals. In most parts of the blade surface， the ice crystal particles have a non-elastic rebound. In terms of the particle size， the distribution trend of the collection coefficient after the secondary impact is very similar to that of the primary impact， with a notable difference being a reduction of about 70% of the maximum value of the collection coefficient. However， in terms of the particle aspect ratio， the trend of the secondary impact collection coefficient at the leading edge of the blade is opposite to that of the primary impact， with elongated ice crystal particles exhibiting a lower secondary collection coefficient.
2024(3):359-371.
DOI: 10.16356/j.1005-1120.2024.03.008
Abstract:
The cabin structure of amphibious aircraft needs to withstand the impact force in the process of water-entry， which will affect the performance of amphibious aircraft significantly. A baseline cabin structure for an amphibious aircraft is established. According to the cabin geometry， the pressure distribution on the cabin during the water-entry process is obtained by numerical simulation. A finite element model of the cabin structure is established and the parametric study is carried out to obtain the effects of different design parameters on the cabin structure. Then， a framework is built to optimize the cabin structure， with the structural deformation and stress distribution during the water-entry process taken into account. In the optimization， the strain and stress are regarded as the constraints and the structure mass is the objective. After the optimization， the optimized design is further verified using the one-way coupling analysis method. The results show that the distribution of internal stringers and the thickness of the bottom skin have a significant influence on the maximum von Mises stress. By optimizing the design parameters of the cabin structure， the structure mass can be significantly reduced while the structural strength and stiffness can satisfy the constraints simultaneously.
The cabin structure of amphibious aircraft needs to withstand the impact force in the process of water-entry， which will affect the performance of amphibious aircraft significantly. A baseline cabin structure for an amphibious aircraft is established. According to the cabin geometry， the pressure distribution on the cabin during the water-entry process is obtained by numerical simulation. A finite element model of the cabin structure is established and the parametric study is carried out to obtain the effects of different design parameters on the cabin structure. Then， a framework is built to optimize the cabin structure， with the structural deformation and stress distribution during the water-entry process taken into account. In the optimization， the strain and stress are regarded as the constraints and the structure mass is the objective. After the optimization， the optimized design is further verified using the one-way coupling analysis method. The results show that the distribution of internal stringers and the thickness of the bottom skin have a significant influence on the maximum von Mises stress. By optimizing the design parameters of the cabin structure， the structure mass can be significantly reduced while the structural strength and stiffness can satisfy the constraints simultaneously.
2024(3):372-386.
DOI: 10.16356/j.1005-1120.2024.03.009
Abstract:
To facilitate collaborative decision making in future air traffic management systems under the trajectory based operation framework， a collaborative conflict-free four-dimensional （4D） trajectory planning method is proposed. Firstly， a multi-objective integer linear optimization model is developed to improve flight efficiency and inter-airline equity under conflict-free constraint. Secondly， a Gini coefficient-based metric is formulated to quantify the inter-airline equity of operation cost allocation. Thirdly， to improve the problem-solving efficiency， a grid-based conflict detection method is employed to accelerate conflict detection and a multi-objective hybrid-metaheuristic optimization algorithm （MHMOA） is designed to approximate the optimal non-dominated solutions by combining the simulated annealing （SA） and hill-climbing local search algorithms. Finally， the optimization results of the MHMOA， SA and two conventional multi-objective optimization algorithms are compared and analyzed using the actual flight plan and route network data. The results indicate that MHMOA can obtain higher-quality non-dominated solutions with lower delays， flight level shifts and better equity than other three algorithms， and outperform in terms of three multi-objective optimization performance metrics. The obtained solution can provide more detailed decision support for air traffic managers.
To facilitate collaborative decision making in future air traffic management systems under the trajectory based operation framework， a collaborative conflict-free four-dimensional （4D） trajectory planning method is proposed. Firstly， a multi-objective integer linear optimization model is developed to improve flight efficiency and inter-airline equity under conflict-free constraint. Secondly， a Gini coefficient-based metric is formulated to quantify the inter-airline equity of operation cost allocation. Thirdly， to improve the problem-solving efficiency， a grid-based conflict detection method is employed to accelerate conflict detection and a multi-objective hybrid-metaheuristic optimization algorithm （MHMOA） is designed to approximate the optimal non-dominated solutions by combining the simulated annealing （SA） and hill-climbing local search algorithms. Finally， the optimization results of the MHMOA， SA and two conventional multi-objective optimization algorithms are compared and analyzed using the actual flight plan and route network data. The results indicate that MHMOA can obtain higher-quality non-dominated solutions with lower delays， flight level shifts and better equity than other three algorithms， and outperform in terms of three multi-objective optimization performance metrics. The obtained solution can provide more detailed decision support for air traffic managers.
2024(3):387-402.
DOI: 10.16356/j.1005-1120.2024.03.010
Abstract:
Tracking registration is a critical technology of augmented reality （AR）. Marker-based and image-based registration methods have been widely used in augmented assembly systems. However， the space station encounters distinctive challenges due to weak product texture， symmetrical structure， limited data， and difficulty in attaching markers. This paper presents a novel 3D object tracking method specifically designed for induced maintenance applications in the Chinese space station， aiming to replace traditional paper manuals with the AR technology to provide astronauts with more intuitive operational guidance. We propose a marker-less approach for intelligent maintenance of the Chinese space station. A point pair feature method that combines curvature information for improving efficiency is employed to estimate the initial frame pose， obviating the need for manual adjustment to achieve the corresponding pose. This is crucial for astronauts， as precise movement in the microgravity environment is a significant challenge. Precise restrictions on the position of astronauts are eliminated， and the tracking robustness of space symmetric products is further enhanced by incorporating both texture and region information. The method utilizes both point cloud and 2D image. It leverages point cloud matching to estimate the initial pose of the first frame and recalculates the pose after loss of tracking. Once the pose of the previous frame is obtained， the tracking is calculated solely according to the region and texture information of the 2D image to obtain real-time tracking. The experimental results show that our method has the same pose trend as the marked-based method. And the error difference between the measurements based on electronic vernier calipers is in the millimeter level. The successful replacement of filters using specialized tools designed specifically for space products demonstrates the practicality and potential of implementing induced maintenance procedures on space station.
Tracking registration is a critical technology of augmented reality （AR）. Marker-based and image-based registration methods have been widely used in augmented assembly systems. However， the space station encounters distinctive challenges due to weak product texture， symmetrical structure， limited data， and difficulty in attaching markers. This paper presents a novel 3D object tracking method specifically designed for induced maintenance applications in the Chinese space station， aiming to replace traditional paper manuals with the AR technology to provide astronauts with more intuitive operational guidance. We propose a marker-less approach for intelligent maintenance of the Chinese space station. A point pair feature method that combines curvature information for improving efficiency is employed to estimate the initial frame pose， obviating the need for manual adjustment to achieve the corresponding pose. This is crucial for astronauts， as precise movement in the microgravity environment is a significant challenge. Precise restrictions on the position of astronauts are eliminated， and the tracking robustness of space symmetric products is further enhanced by incorporating both texture and region information. The method utilizes both point cloud and 2D image. It leverages point cloud matching to estimate the initial pose of the first frame and recalculates the pose after loss of tracking. Once the pose of the previous frame is obtained， the tracking is calculated solely according to the region and texture information of the 2D image to obtain real-time tracking. The experimental results show that our method has the same pose trend as the marked-based method. And the error difference between the measurements based on electronic vernier calipers is in the millimeter level. The successful replacement of filters using specialized tools designed specifically for space products demonstrates the practicality and potential of implementing induced maintenance procedures on space station.
Mobile website
Website Copyright © Transactions of Nanjing University of Aeronautics & Astronautics