Transactions of Nanjing University of Aeronautics & Astronautics
Issue 4,2023 Table of Contents
1 Effects of Finite Length Wedge on the Initiation Structure of Oblique Detonation Waves in Combustor
2023(4):367-381.
DOI: 10.16356/j.1005-1120.2023.04.001
Abstract:
The oblique detonation engine （ODE） uses the oblique detonation wave （ODW） generated by a wedge in supersonic combustible mixtures to achieve fast and efficient combustion， which is more applicable to air-breathing hypersonic aircraft with higher flight Mach numbers than a conventional scramjet. Prior to the practical application of ODE， it is first necessary to clarify the initiation structure characteristics of ODWs in the combustor under flight conditions. However， previous studies usually used the infinite length wedge hypothesis which cannot really reflect the flow and combustion characteristics of finite length induced ODW in the actual combustor. Two key design parameters， i.e.， the wedge length and end inclination angle， are used to investigate the effects of finite length wedge on the initiation structure of ODW in an ODE at different flight Mach numbers. Results show that there is a critical wedge length for different ODW initiation structures corresponding to different flight conditions. Only when the wedge length is shortened to the critical length， the ODW initiation structure will change significantly. When the wedge length is equal to or less than this critical length， both the wedge length and end inclination angle will affect the structure. On the contrary， the expansion wave generated at the end of the wedge cannot affect the heat release and compression wave convergence on the wedge， so it will not affect the ODW initiation process and structure. By analyzing the heat release process on the wedge， a theoretical method for predicting the critical wedge length is proposed to contribute to the combustor design. The calculated results under different flight conditions are in good agreement with the simulation results.
The oblique detonation engine （ODE） uses the oblique detonation wave （ODW） generated by a wedge in supersonic combustible mixtures to achieve fast and efficient combustion， which is more applicable to air-breathing hypersonic aircraft with higher flight Mach numbers than a conventional scramjet. Prior to the practical application of ODE， it is first necessary to clarify the initiation structure characteristics of ODWs in the combustor under flight conditions. However， previous studies usually used the infinite length wedge hypothesis which cannot really reflect the flow and combustion characteristics of finite length induced ODW in the actual combustor. Two key design parameters， i.e.， the wedge length and end inclination angle， are used to investigate the effects of finite length wedge on the initiation structure of ODW in an ODE at different flight Mach numbers. Results show that there is a critical wedge length for different ODW initiation structures corresponding to different flight conditions. Only when the wedge length is shortened to the critical length， the ODW initiation structure will change significantly. When the wedge length is equal to or less than this critical length， both the wedge length and end inclination angle will affect the structure. On the contrary， the expansion wave generated at the end of the wedge cannot affect the heat release and compression wave convergence on the wedge， so it will not affect the ODW initiation process and structure. By analyzing the heat release process on the wedge， a theoretical method for predicting the critical wedge length is proposed to contribute to the combustor design. The calculated results under different flight conditions are in good agreement with the simulation results.
2023(4):382-400.
DOI: 10.16356/j.1005-1120.2023.04.002
Abstract:
To study the change of aerodynamic characteristics of the spanwise adaptive wing with the folding angle， a kind of folding wing tip morphing aircraft， the modified Cessna 550 aircraft with shape memory alloys as hinge actuators， is considered. A novel modeling scheme is proposed based on the variable aerodynamic parameters about the folding angles. This kind of modeling scheme can explicitly account for changes in aerodynamic properties resulting from folding motion of symmetrical tip of the wing. To explore how folding motion will influence the aerodynamic performances of the aircraft， the computational fluid dynamics （CFD） is employed to build aircraft models and obtain aerodynamic coefficients under different folding angles of the wing tip. The aerodynamic parameters about the folding angles are specified through the curve fitting for obtaining the numeric nonlinear models. The taking-off， maneuvering and landing performances under different folding angles are analyzed to select the best morphing strategy and obtain the best aerodynamic performance. Longitudinal steady stability analysis is presented to validate the feasibility of the proposed morphing strategy.
To study the change of aerodynamic characteristics of the spanwise adaptive wing with the folding angle， a kind of folding wing tip morphing aircraft， the modified Cessna 550 aircraft with shape memory alloys as hinge actuators， is considered. A novel modeling scheme is proposed based on the variable aerodynamic parameters about the folding angles. This kind of modeling scheme can explicitly account for changes in aerodynamic properties resulting from folding motion of symmetrical tip of the wing. To explore how folding motion will influence the aerodynamic performances of the aircraft， the computational fluid dynamics （CFD） is employed to build aircraft models and obtain aerodynamic coefficients under different folding angles of the wing tip. The aerodynamic parameters about the folding angles are specified through the curve fitting for obtaining the numeric nonlinear models. The taking-off， maneuvering and landing performances under different folding angles are analyzed to select the best morphing strategy and obtain the best aerodynamic performance. Longitudinal steady stability analysis is presented to validate the feasibility of the proposed morphing strategy.
2023(4):401-419.
DOI: 10.16356/j.1005-1120.2023.04.003
Abstract:
As the helicopters in a multi-lift system fly in a close formation， there is severe aerodynamic interference between the wake of the rotors， bringing complex aeromechanics coupling. So it is necessary to investigate interference and resulting performance changes before studying performance optimization and advanced formation control. A baseline configuration of four tandem helicopters carrying a load cooperatively in a “2-lead” formation is performed to explore the interference and performance. A vortex-panel approach based on the viscous vortex particle method is employed to investigate the performances and flow fields in a steady-flight state. The steady-flight state is obtained by a hierarchical trimming method， and the vortex-panel approach is validated by wind tunnel experiments. On this basis， aerodynamic interferences and performances at different flight speeds and variant relative positions are investigated. Computational results indicate that for the baseline configuration， there exists serious interference between helicopters in the front-and-rear arrangement， especially at forward flight. At the advance ratio of 0.1， there exists a 20% thrust loss and a 15% power increase for the front rotor of the tandem helicopter behind the formation. The aerodynamic interference will be reduced significantly if the distance between the front and the rear helicopter meets any of the three conditions below： more than 3.5D（D represents the rotor diameter） in the longitudinal direction， more than 0.75D in the lateral direction， or more than 0.5D in the vertical direction.
As the helicopters in a multi-lift system fly in a close formation， there is severe aerodynamic interference between the wake of the rotors， bringing complex aeromechanics coupling. So it is necessary to investigate interference and resulting performance changes before studying performance optimization and advanced formation control. A baseline configuration of four tandem helicopters carrying a load cooperatively in a “2-lead” formation is performed to explore the interference and performance. A vortex-panel approach based on the viscous vortex particle method is employed to investigate the performances and flow fields in a steady-flight state. The steady-flight state is obtained by a hierarchical trimming method， and the vortex-panel approach is validated by wind tunnel experiments. On this basis， aerodynamic interferences and performances at different flight speeds and variant relative positions are investigated. Computational results indicate that for the baseline configuration， there exists serious interference between helicopters in the front-and-rear arrangement， especially at forward flight. At the advance ratio of 0.1， there exists a 20% thrust loss and a 15% power increase for the front rotor of the tandem helicopter behind the formation. The aerodynamic interference will be reduced significantly if the distance between the front and the rear helicopter meets any of the three conditions below： more than 3.5D（D represents the rotor diameter） in the longitudinal direction， more than 0.75D in the lateral direction， or more than 0.5D in the vertical direction.
2023(4):420-433.
DOI: 10.16356/j.1005-1120.2023.04.004
Abstract:
The phenomenon of supercooled large droplets （SLD） icing poses a severe threat to the safe operation of aircraft. The Sobol sequence sampling method， radial basis function（RBF） method， and Sobol’s sensitivity index analysis method are used to conduct a multiparameter sensitivity analysis of SLD icing. The influence of four parameters， including icing surface roughness， presence or absence of evaporation， droplet size distribution， and the number of shots， on the shape and amount of icing formation is analyzed. The first-order sensitivity index is used to determine the degree of influence of each parameter on the ice shape parameters， and the total sensitivity index is used to compare the influence of parameter interactions on the ice shape or amount of icing formation. It is found that there is a consistent sensitivity law of the ice shape characteristic parameters of the leading edge of the airfoil to the four parameters， all of which are most affected by the roughness of the icing surface， with a total sensitivity index of more than 0.476 1. The number of shots has the least effect， with a total sensitivity index of about 0.2， while the remaining parameters are affected by evaporation， droplet size distribution， in the descending order.
The phenomenon of supercooled large droplets （SLD） icing poses a severe threat to the safe operation of aircraft. The Sobol sequence sampling method， radial basis function（RBF） method， and Sobol’s sensitivity index analysis method are used to conduct a multiparameter sensitivity analysis of SLD icing. The influence of four parameters， including icing surface roughness， presence or absence of evaporation， droplet size distribution， and the number of shots， on the shape and amount of icing formation is analyzed. The first-order sensitivity index is used to determine the degree of influence of each parameter on the ice shape parameters， and the total sensitivity index is used to compare the influence of parameter interactions on the ice shape or amount of icing formation. It is found that there is a consistent sensitivity law of the ice shape characteristic parameters of the leading edge of the airfoil to the four parameters， all of which are most affected by the roughness of the icing surface， with a total sensitivity index of more than 0.476 1. The number of shots has the least effect， with a total sensitivity index of about 0.2， while the remaining parameters are affected by evaporation， droplet size distribution， in the descending order.
2023(4):434-446.
DOI: 10.16356/j.1005-1120.2023.04.005
Abstract:
This paper takes the high-speed permanent magnet synchronous motor （HSPMSM） control system for electric environment control as the research object. Considering that researches on sensorless control of HSPMSM mainly focuses on algorithm realization and rotor estimation error elimination， we proposes a global stability analysis and parameter design method based on small-signal analysis for sensorless control in full-speed. This method designs the parameters of the position estimation loop based on extended back electromotive force （EMF） method， and studies the influence of the parameters of position estimation loop and speed loop on system stability. Then we uses the root locus to design the upper frequency of I/f control and the lower frequency of extended back EMF method to determine the stable domain of switching. Also， the sensitivity of motor parameters under high temperature are analyzed. Finally， full-speed experiment is carried out on the 45 kW， 40 000 r/min surface mounted HSPMSM for electric environment control. The result shows that the designed loop parameters and switching speed achieve better dynamic and steady-state performance， and the sensitivity of parameter is consistent with the theoretical analysis. It provides a feasible idea for global parameter design and sensitivity analysis of HSPMSM in the full-speed.
This paper takes the high-speed permanent magnet synchronous motor （HSPMSM） control system for electric environment control as the research object. Considering that researches on sensorless control of HSPMSM mainly focuses on algorithm realization and rotor estimation error elimination， we proposes a global stability analysis and parameter design method based on small-signal analysis for sensorless control in full-speed. This method designs the parameters of the position estimation loop based on extended back electromotive force （EMF） method， and studies the influence of the parameters of position estimation loop and speed loop on system stability. Then we uses the root locus to design the upper frequency of I/f control and the lower frequency of extended back EMF method to determine the stable domain of switching. Also， the sensitivity of motor parameters under high temperature are analyzed. Finally， full-speed experiment is carried out on the 45 kW， 40 000 r/min surface mounted HSPMSM for electric environment control. The result shows that the designed loop parameters and switching speed achieve better dynamic and steady-state performance， and the sensitivity of parameter is consistent with the theoretical analysis. It provides a feasible idea for global parameter design and sensitivity analysis of HSPMSM in the full-speed.
2023(4):447-459.
DOI: 10.16356/j.1005-1120.2023.04.006
Abstract:
Efficient information transmission is crucial for the development of space-ground integrated network（SGIN）， especially with the growing complexity of low Earth orbit （LEO） satellite architectures. This study aims to optimize the handover process between terrestrial users and satellites by considering metrics such as handover times， elevation angle， and available channels. The proposed mathematical model divides the Earth into multiple regions， and the optimization objective is a weighted sum of the number of handovers and load balance， which determines the weighted coefficients based on different scenarios. The elevation angle can be optimized by setting a threshold that indicates the quality of information transmission. The study transforms the SGIN handover problem into an integer linear programming （ILP） problem and solves it by using mathematical tools to provide an optimal solution. However， due to the high algorithmic complexity of the ILP-based strategy in practical engineering applications， a heuristic handover strategy based on bipartite graphs is also proposed. Simulations on a typical LEO satellite constellation （Globalstar） validate the effectiveness of the proposed handover strategies.
Efficient information transmission is crucial for the development of space-ground integrated network（SGIN）， especially with the growing complexity of low Earth orbit （LEO） satellite architectures. This study aims to optimize the handover process between terrestrial users and satellites by considering metrics such as handover times， elevation angle， and available channels. The proposed mathematical model divides the Earth into multiple regions， and the optimization objective is a weighted sum of the number of handovers and load balance， which determines the weighted coefficients based on different scenarios. The elevation angle can be optimized by setting a threshold that indicates the quality of information transmission. The study transforms the SGIN handover problem into an integer linear programming （ILP） problem and solves it by using mathematical tools to provide an optimal solution. However， due to the high algorithmic complexity of the ILP-based strategy in practical engineering applications， a heuristic handover strategy based on bipartite graphs is also proposed. Simulations on a typical LEO satellite constellation （Globalstar） validate the effectiveness of the proposed handover strategies.
2023(4):460-471.
DOI: 10.16356/j.1005-1120.2023.04.007
Abstract:
The complexity of the modern space environment is increasing dramatically under the condition of informatization. Thus， it is difficult for ground operators to process a large amount of information and recognize the approaching intention of unknown objects in a short time. A dynamic Bayesian network model combined with fuzzy theory and experts’ experience is designed to help operators recognize the approaching intention quickly and systemically. Compared with the static Bayesian network （SBN）， the dynamic Bayesian network is more practical in recognizing the intention of multiple time slices and predicting the future trends through successive probabilities calculation， which is suitable for rapidly changing environment in space. Numerical examples show that the proposed method of intention prediction is feasible and effective.
The complexity of the modern space environment is increasing dramatically under the condition of informatization. Thus， it is difficult for ground operators to process a large amount of information and recognize the approaching intention of unknown objects in a short time. A dynamic Bayesian network model combined with fuzzy theory and experts’ experience is designed to help operators recognize the approaching intention quickly and systemically. Compared with the static Bayesian network （SBN）， the dynamic Bayesian network is more practical in recognizing the intention of multiple time slices and predicting the future trends through successive probabilities calculation， which is suitable for rapidly changing environment in space. Numerical examples show that the proposed method of intention prediction is feasible and effective.
2023(4):472-486.
DOI: 10.16356/j.1005-1120.2023.04.008
Abstract:
This paper proposes a super-resolution inversion and reconstruction algorithm for remote sensing images of unknown bands of interest. The proposed method utilizes a built-in spectral reflectance database and the existing multi-spectral image to achieve the accurate classification of substances through the implementation of a Gaussian hybrid clustering algorithm and correlation distance method after radiation calibration and atmospheric correction. The image mixing algorithm based on the manifold space constraint obtains the distribution of ground substances， based on which the spectral reflectance image of the unknown band of interest is reconstructed. By employing the single-window algorithm， the temperature field of low-resolution ground substances is inverted through the far-infrared image， and the Shepard interpolation algorithm is used to interpolate the low-resolution temperature field to obtain a high-resolution ground temperature field. According to the spectral reflectance and the temperature field of the ground substances， using the remote sensing link imaging model， the high-resolution remote-sensing image of unknown infrared band of interest is super-resolution inversion reconstructed. Experimental results show that the reconstructed infrared image of various scenes has a high similarity with the original scene image， which has great benefits for improving the ability of target detection and recognition.
This paper proposes a super-resolution inversion and reconstruction algorithm for remote sensing images of unknown bands of interest. The proposed method utilizes a built-in spectral reflectance database and the existing multi-spectral image to achieve the accurate classification of substances through the implementation of a Gaussian hybrid clustering algorithm and correlation distance method after radiation calibration and atmospheric correction. The image mixing algorithm based on the manifold space constraint obtains the distribution of ground substances， based on which the spectral reflectance image of the unknown band of interest is reconstructed. By employing the single-window algorithm， the temperature field of low-resolution ground substances is inverted through the far-infrared image， and the Shepard interpolation algorithm is used to interpolate the low-resolution temperature field to obtain a high-resolution ground temperature field. According to the spectral reflectance and the temperature field of the ground substances， using the remote sensing link imaging model， the high-resolution remote-sensing image of unknown infrared band of interest is super-resolution inversion reconstructed. Experimental results show that the reconstructed infrared image of various scenes has a high similarity with the original scene image， which has great benefits for improving the ability of target detection and recognition.
2023(4):487-499.
DOI: 10.16356/j.1005-1120.2023.04.009
Abstract:
With the development tendency of energy saving and weight reduction of aerospace materials， high-performance composite materials have been widely used in aircraft skins. However， the surface quality detections of composite skin parts are mostly carried out manually， leading to low detection efficiency and low accuracy. Visual detection has gained more and more attention in recent years， mainly because of its non-destructive detecting characteristics with high precision and flexibility. In view of the visual detection requirements of surface defects of composite skin parts， a robot-based detection platform was constructed， which innovatively integrated manipulator module， image acquisition module， laser ranging module， the deep learning module， and the complementary upper computer software. In order to ensure the efficiency and accuracy of detection， the detection algorithm of the system was developed based on YOLOv5. In addition， on account of the lack of raw composite skin parts， the dataset for training was expanded by employing the following three methods： Mirroring and rotating， translating， and adding noise. Experiments validate that the system can realize online， automatic， and accurate detections of various types of composite skin parts. The proposed system can complete detection of an image with a size of 5 496 pixel× 3 672 pixel in 0.744 s， and the detection accuracy reaches 96.35%， which meets the requirements for composite surface quality detection.
With the development tendency of energy saving and weight reduction of aerospace materials， high-performance composite materials have been widely used in aircraft skins. However， the surface quality detections of composite skin parts are mostly carried out manually， leading to low detection efficiency and low accuracy. Visual detection has gained more and more attention in recent years， mainly because of its non-destructive detecting characteristics with high precision and flexibility. In view of the visual detection requirements of surface defects of composite skin parts， a robot-based detection platform was constructed， which innovatively integrated manipulator module， image acquisition module， laser ranging module， the deep learning module， and the complementary upper computer software. In order to ensure the efficiency and accuracy of detection， the detection algorithm of the system was developed based on YOLOv5. In addition， on account of the lack of raw composite skin parts， the dataset for training was expanded by employing the following three methods： Mirroring and rotating， translating， and adding noise. Experiments validate that the system can realize online， automatic， and accurate detections of various types of composite skin parts. The proposed system can complete detection of an image with a size of 5 496 pixel× 3 672 pixel in 0.744 s， and the detection accuracy reaches 96.35%， which meets the requirements for composite surface quality detection.
2023(4):500-510.
DOI: 10.16356/j.1005-1120.2023.04.010
Abstract:
It is necessary to evaluate man-hour （MH） before receiving the order to guide the quotation and forecast the delivery date for a manufacturing contractor. As an important part of assembled MH， it has important practical significance. Aiming at the characteristics of multi-specification and small-batch production， an assembly MH estimation model based on support vector machine （SVM） is proposed. Apart from single component attributes， assembly process， and historical MH data， we also consider the average of shortest path length （ASPL）， which quantifies the complexity of an assembly， as influencing factors of assembly MH. Furthermore， the auto calculating methods of these factors based on 3D models with Creo JLink are proposed. Through the comparison of several algorithms， SVM is chosen as the optimal algorithm for assembly MH modeling. Genetic algorithm （GA） is used to avoid the local solution and accelerate convergence when searching for the optimal parameters of SVM （c and g）. Finally， the proposed GA-SVM model is trained and applied to predict the assembly MH of the bionic leg for the radar device. Experimental results show that GA-SVM has higher prediction accuracy than other methods in this paper and the whole predicting process only takes about 3 min.
It is necessary to evaluate man-hour （MH） before receiving the order to guide the quotation and forecast the delivery date for a manufacturing contractor. As an important part of assembled MH， it has important practical significance. Aiming at the characteristics of multi-specification and small-batch production， an assembly MH estimation model based on support vector machine （SVM） is proposed. Apart from single component attributes， assembly process， and historical MH data， we also consider the average of shortest path length （ASPL）， which quantifies the complexity of an assembly， as influencing factors of assembly MH. Furthermore， the auto calculating methods of these factors based on 3D models with Creo JLink are proposed. Through the comparison of several algorithms， SVM is chosen as the optimal algorithm for assembly MH modeling. Genetic algorithm （GA） is used to avoid the local solution and accelerate convergence when searching for the optimal parameters of SVM （c and g）. Finally， the proposed GA-SVM model is trained and applied to predict the assembly MH of the bionic leg for the radar device. Experimental results show that GA-SVM has higher prediction accuracy than other methods in this paper and the whole predicting process only takes about 3 min.
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