Transactions of Nanjing University of Aeronautics & Astronautics
Volume 0,Issue 3,2023 Table of Contents
2023(3):239-252.
DOI: 10.16356/j.1005-1120.2023.03.001
Abstract:
When robotic systems are used to perform the in-situ machining of the large spacecraft cabin， there is a dual-objective optimization issue concerning the numbers of cabin’s rotation and the overall machining performance of robots. An optimization method of cabins rotation scheme is proposed based on the robots’ stiffness characteristic and the non-dominated sorting genetic algorithm （NSGA）-Ⅱ. First， a quality evaluation index for all machining features is proposed based on the Cartesian stiffness of robots， and the process of machining is analyzed and modeled. Second， to utilize the NSGA-Ⅱ， a double chromosome coding method is proposed to encode the machining process， corresponding crossover and mutation operator is also designed. Third， to solve the frequent appearing of illegal codes， a repair operator that ensures the population’s evolutionary efficiency is specially designed based on the problem structure. Finally， the result of a case study shows that increasing the number of rotation postures to a certain extent can effectively improve the robots’ machining performance， and achieve a comprehensive optimization of the mission’s time efficiency and machining quality.
When robotic systems are used to perform the in-situ machining of the large spacecraft cabin， there is a dual-objective optimization issue concerning the numbers of cabin’s rotation and the overall machining performance of robots. An optimization method of cabins rotation scheme is proposed based on the robots’ stiffness characteristic and the non-dominated sorting genetic algorithm （NSGA）-Ⅱ. First， a quality evaluation index for all machining features is proposed based on the Cartesian stiffness of robots， and the process of machining is analyzed and modeled. Second， to utilize the NSGA-Ⅱ， a double chromosome coding method is proposed to encode the machining process， corresponding crossover and mutation operator is also designed. Third， to solve the frequent appearing of illegal codes， a repair operator that ensures the population’s evolutionary efficiency is specially designed based on the problem structure. Finally， the result of a case study shows that increasing the number of rotation postures to a certain extent can effectively improve the robots’ machining performance， and achieve a comprehensive optimization of the mission’s time efficiency and machining quality.
2023(3):253-263.
DOI: 10.16356/j.1005-1120.2023.03.002
Abstract:
Carbon fiber reinforced silicon carbide （Cf/SiC） composite materials possess high strength， wear resistance， and anisotropy， thus their machining is very difficult and demands extra precautions. In this research， finite element analysis （FEA） simulations and experiments of the slot milling process have been carried out to analyze the cutting performance of Cf/SiC with a polycrystalline diamond （PCD） tool. Effects of machining parameters on cutting forces are studied and material removal mechanisms at different fiber cutting angles have been investigated. The finite element model has been generated in ABAQUS/CAE software and the machining is performed. by using user-defined material subroutine. Effects of machining parameters on cutting forces are calculated through FEA simulations and compared with experimental results to authenticate the finite element model. Cutting forces in x-axis and y-axis directions obtained from experiments and simulations have been analyzed and a good agreement is found between them. The resultant cutting forces decrease with the increase in cutting speed. However， with the increase of feed per tooth the resultant cutting forces increase. When the machining is performed along the fiber direction， stresses generated near the tool edge are minimum. The stresses rise with the increase of the fiber cutting angle. This research provides an efficient way to analyze the cutting performance of Cf/SiC composite materials.
Carbon fiber reinforced silicon carbide （Cf/SiC） composite materials possess high strength， wear resistance， and anisotropy， thus their machining is very difficult and demands extra precautions. In this research， finite element analysis （FEA） simulations and experiments of the slot milling process have been carried out to analyze the cutting performance of Cf/SiC with a polycrystalline diamond （PCD） tool. Effects of machining parameters on cutting forces are studied and material removal mechanisms at different fiber cutting angles have been investigated. The finite element model has been generated in ABAQUS/CAE software and the machining is performed. by using user-defined material subroutine. Effects of machining parameters on cutting forces are calculated through FEA simulations and compared with experimental results to authenticate the finite element model. Cutting forces in x-axis and y-axis directions obtained from experiments and simulations have been analyzed and a good agreement is found between them. The resultant cutting forces decrease with the increase in cutting speed. However， with the increase of feed per tooth the resultant cutting forces increase. When the machining is performed along the fiber direction， stresses generated near the tool edge are minimum. The stresses rise with the increase of the fiber cutting angle. This research provides an efficient way to analyze the cutting performance of Cf/SiC composite materials.
2023(3):264-272.
DOI: 10.16356/j.1005-1120.2023.03.003
Abstract:
Generally， a one-way clutch uses coil springs to push and energize the rollers. However， clutches with coil springs are hard to assemble. Moreover， using coil springs， the rollers are prone to bear eccentric load during operation， which decreases the reliability of the clutch. In order to increase the manufacturability and durability of the one-way clutch， an accordion spring is proposed. First， the equivalent spring constant is derived using energy method. After that， a rigid-flexible coupling finite element model is established to analyze and discuss the piecewise linear property of the spring’s stiffness characteristic. Based on the equal stiffness assumption， a parametric design method that uses length as constraints and load as boundary conditions is further proposed to design the spring. Finally， several accordion springs are made to carry out an experiment， which validates the accuracy of the theoretical model， the finite element analysis （FEA） model and the parametric design method.
Generally， a one-way clutch uses coil springs to push and energize the rollers. However， clutches with coil springs are hard to assemble. Moreover， using coil springs， the rollers are prone to bear eccentric load during operation， which decreases the reliability of the clutch. In order to increase the manufacturability and durability of the one-way clutch， an accordion spring is proposed. First， the equivalent spring constant is derived using energy method. After that， a rigid-flexible coupling finite element model is established to analyze and discuss the piecewise linear property of the spring’s stiffness characteristic. Based on the equal stiffness assumption， a parametric design method that uses length as constraints and load as boundary conditions is further proposed to design the spring. Finally， several accordion springs are made to carry out an experiment， which validates the accuracy of the theoretical model， the finite element analysis （FEA） model and the parametric design method.
2023(3):273-284.
DOI: 10.16356/j.1005-1120.2023.03.004
Abstract:
Annular plate structure is widely used in the engineering field. A unified method is proposed to predict the free vibration behavior of the annular plates in the steady-state thermal environment. Based on the spectral geometry method （SGM）， the displacement of the annular plate is expanded by the improved Fourier series. The potential energy and the maximum kinetic energy of the annular plate are obtained based on the first-order shear deformation theory （FSDT）. Three sets of linear springs and one set of rotating springs are used to simulate the arbitrary boundary of the annular plate. The continuity of the circumferential boundary of the annular plate with subtended angle of 360° is realized by using circumferential coupling spring. The Rayleigh-Ritz method is used to construct the theoretical model of the annular plate， and the vibration characteristics of the annular plate are solved. The accuracy of this method is verified by comparing with the finite element calculation results. The method used in this paper is a meshless method， which is more computationally efficient than current mainstream methods， such as the finite element method （FEM）. The relationships between the modal numerical solution and boundary condition and the ratio of inner and outer radius in the thermal environment are studied. This paper provides a reference for the application of annular plates in engineering practice.
Annular plate structure is widely used in the engineering field. A unified method is proposed to predict the free vibration behavior of the annular plates in the steady-state thermal environment. Based on the spectral geometry method （SGM）， the displacement of the annular plate is expanded by the improved Fourier series. The potential energy and the maximum kinetic energy of the annular plate are obtained based on the first-order shear deformation theory （FSDT）. Three sets of linear springs and one set of rotating springs are used to simulate the arbitrary boundary of the annular plate. The continuity of the circumferential boundary of the annular plate with subtended angle of 360° is realized by using circumferential coupling spring. The Rayleigh-Ritz method is used to construct the theoretical model of the annular plate， and the vibration characteristics of the annular plate are solved. The accuracy of this method is verified by comparing with the finite element calculation results. The method used in this paper is a meshless method， which is more computationally efficient than current mainstream methods， such as the finite element method （FEM）. The relationships between the modal numerical solution and boundary condition and the ratio of inner and outer radius in the thermal environment are studied. This paper provides a reference for the application of annular plates in engineering practice.
2023(3):285-292.
DOI: 10.16356/j.1005-1120.2023.03.005
Abstract:
This paper proposes a self-deploying membrane sunshield structure to satisfy the requirements of lightweight， easy unfolding with high expansion ratio， and not requiring the driving power. Four equal length tape springs are used to unfold the Kapton membrane folded with leaf-in and circumferential and the folding ratio is calculated. In order to prevent the problems of hook and damage during the unfolding process， stress and trajectories of the membrane as well as the tape spring modal distribution of the skeleton are analyzed. Finally， a test prototype completes to verify the feasibility of the designment. The results show that by applying the tape springs as the driving method， the membrane unfolding process is smooth， and the membrane will not be damaged. The maximum stress at the membrane crease is about 42.3 MPa which is lower than the allowable stress of the material and the folding ratio reaches 69.4.
This paper proposes a self-deploying membrane sunshield structure to satisfy the requirements of lightweight， easy unfolding with high expansion ratio， and not requiring the driving power. Four equal length tape springs are used to unfold the Kapton membrane folded with leaf-in and circumferential and the folding ratio is calculated. In order to prevent the problems of hook and damage during the unfolding process， stress and trajectories of the membrane as well as the tape spring modal distribution of the skeleton are analyzed. Finally， a test prototype completes to verify the feasibility of the designment. The results show that by applying the tape springs as the driving method， the membrane unfolding process is smooth， and the membrane will not be damaged. The maximum stress at the membrane crease is about 42.3 MPa which is lower than the allowable stress of the material and the folding ratio reaches 69.4.
2023(3):293-306.
DOI: 10.16356/j.1005-1120.2023.03.006
Abstract:
In order to increase the rate of Cu2ZnSnS4 （CZTS） photocatalytic degradation of Rhodamine B （RhB）， type-Ⅰ heterojunction of the CZTS/g-C3N4 composite structure was successfully prepared by a hydrothermal method in this work. CZTS/g-C3N4 is applied in photocatalytic degradation of the colored dye RhB. The results showed that g-C3N4 was attached to the surface of flower-like CZTS， and the two formed a type-Ⅰ heterojunction. CZTS acted as an electron trap for g-C3N4， which improved the separation efficiency of carriers. The results of photocatalytic degradation of RhB showed that CZTS/g-C3N4 composite structure could improve the photocatalytic degradation effect of RhB. The best photocatalytic efficiency of RhB was 98.63% within 60 min.
In order to increase the rate of Cu2ZnSnS4 （CZTS） photocatalytic degradation of Rhodamine B （RhB）， type-Ⅰ heterojunction of the CZTS/g-C3N4 composite structure was successfully prepared by a hydrothermal method in this work. CZTS/g-C3N4 is applied in photocatalytic degradation of the colored dye RhB. The results showed that g-C3N4 was attached to the surface of flower-like CZTS， and the two formed a type-Ⅰ heterojunction. CZTS acted as an electron trap for g-C3N4， which improved the separation efficiency of carriers. The results of photocatalytic degradation of RhB showed that CZTS/g-C3N4 composite structure could improve the photocatalytic degradation effect of RhB. The best photocatalytic efficiency of RhB was 98.63% within 60 min.
2023(3):307-322.
DOI: 10.16356/j.1005-1120.2023.03.007
Abstract:
When the observation requirement from users exceeds the satellite’s observation capability， astronomy satellite task scheduling becomes an oversubscription problem. For the oversubscribed task scheduling of astronomical satellites， a framework with a clustering phase and a short-term task scheduling phase is designed. First， a task clustering model is established to reduce the size of the oversubscribed task. Second， using the clustered results as input， we develop a mathematical model of short-term scheduling for the tasks. Finally， we propose an improved artificial bee colony algorithm with adaptive hybrid search strategies （DirectABC）. It introduces an adaptive elite global-local search strategy and an adaptive variable neighborhood optimal search strategy to the basic artificial bee colony algorithm （BasicABC）. The proposed algorithm demonstrates superior optimum-searching capability and a faster convergence speed in the simulation. In addition， it effectively reduces the number of tasks in the clustering phase and improves task completion in the short-term task scheduling phase.
When the observation requirement from users exceeds the satellite’s observation capability， astronomy satellite task scheduling becomes an oversubscription problem. For the oversubscribed task scheduling of astronomical satellites， a framework with a clustering phase and a short-term task scheduling phase is designed. First， a task clustering model is established to reduce the size of the oversubscribed task. Second， using the clustered results as input， we develop a mathematical model of short-term scheduling for the tasks. Finally， we propose an improved artificial bee colony algorithm with adaptive hybrid search strategies （DirectABC）. It introduces an adaptive elite global-local search strategy and an adaptive variable neighborhood optimal search strategy to the basic artificial bee colony algorithm （BasicABC）. The proposed algorithm demonstrates superior optimum-searching capability and a faster convergence speed in the simulation. In addition， it effectively reduces the number of tasks in the clustering phase and improves task completion in the short-term task scheduling phase.
2023(3):323-335.
DOI: 10.16356/j.1005-1120.2023.03.008
Abstract:
Vibration spectrum extraction is essential for fault diagnosis of rotating machinery. Environmental diversification and the presence of noise limit the performance of traditional single-modal vibration extraction methods. Since visual and audio signals have different sampling frequencies， noise and environmental constraints， audio-visual fusion can effectively solve the problem caused by single modality. Based on this， this paper proposes a wideband spectrum extraction method based on an audio-visual fusion deep convolutional neural network， which fully fuses the effective information of different modalities to complement each other. The proposed model uses a dual-stream encoder to extract features from different modalities， and a deep residual fusion module extracts high-level fusion features and feeds them to the decoder. The experimental results show that the performance of this model is superior to the latest vibration extraction methods， and the proposed model outperforms other state-of-the-art models such as RegNet， MFCNN， and L2L， which improves the accuracy of vibration spectrum extraction by 15% in noisy environment.
Vibration spectrum extraction is essential for fault diagnosis of rotating machinery. Environmental diversification and the presence of noise limit the performance of traditional single-modal vibration extraction methods. Since visual and audio signals have different sampling frequencies， noise and environmental constraints， audio-visual fusion can effectively solve the problem caused by single modality. Based on this， this paper proposes a wideband spectrum extraction method based on an audio-visual fusion deep convolutional neural network， which fully fuses the effective information of different modalities to complement each other. The proposed model uses a dual-stream encoder to extract features from different modalities， and a deep residual fusion module extracts high-level fusion features and feeds them to the decoder. The experimental results show that the performance of this model is superior to the latest vibration extraction methods， and the proposed model outperforms other state-of-the-art models such as RegNet， MFCNN， and L2L， which improves the accuracy of vibration spectrum extraction by 15% in noisy environment.
2023(3):336-353.
DOI: 10.16356/j.1005-1120.2023.03.009
Abstract:
In order to solve the problem of increasing tracking error of flexible joint system caused by model uncertainty and external unknown disturbance， a prescribed performance backstepping control method based on unknown state estimator and tracking differentiator is proposed. An unknown state estimator based on low-pass filter is designed， which can estimate the lumped disturbance only depending on the nominal value of the model. A novel finite-time convergence prescribed performance function is constructed. Based on this function， a backstepping controller is designed to ensure that all signals in the closed-loop system are bounded， and the joint tracking error converges to any given small area within the given time. To avoid the differential explosion of the backstepping controller， a tracking differentiator based on the improved Sigmoid function is designed to estimate the differential signal of virtual control law. The simulation results show that the proposed method can guarantee the joint tracking error converges to any given range within the finite time under the disturbance of unmodeled dynamics and unknown input， and can effectively improve the transient and steady-state performance of flexible joints.
In order to solve the problem of increasing tracking error of flexible joint system caused by model uncertainty and external unknown disturbance， a prescribed performance backstepping control method based on unknown state estimator and tracking differentiator is proposed. An unknown state estimator based on low-pass filter is designed， which can estimate the lumped disturbance only depending on the nominal value of the model. A novel finite-time convergence prescribed performance function is constructed. Based on this function， a backstepping controller is designed to ensure that all signals in the closed-loop system are bounded， and the joint tracking error converges to any given small area within the given time. To avoid the differential explosion of the backstepping controller， a tracking differentiator based on the improved Sigmoid function is designed to estimate the differential signal of virtual control law. The simulation results show that the proposed method can guarantee the joint tracking error converges to any given range within the finite time under the disturbance of unmodeled dynamics and unknown input， and can effectively improve the transient and steady-state performance of flexible joints.
2023(3):354-366.
DOI: 10.16356/j.1005-1120.2023.03.010
Abstract:
The stress and strain of the components composed of prefabricated grooves， warheads， foam titanium， foam aluminum and the detector are calculated when they rush to the moon surface rocks at a speed of 130 m/s and under 1/6 gravity of earth. The foam metal in the component can bear the force of the detector and provide the recoil force. The stress of preformed groove and warhead is 1 200—2 000 MPa， while the stress of foam titanium and foam aluminum is 10 MPa and 1 MPa， respectively， with significant reduction. The stress of foam titanium is reduced to 1%， and that of foam aluminum is reduced to 1 ‰. The component has also undergone a series of different angle collision tests at low temperatures （-182.85 ℃） and high temperatures （127.15 ℃）， and the detector can still operate normally.
The stress and strain of the components composed of prefabricated grooves， warheads， foam titanium， foam aluminum and the detector are calculated when they rush to the moon surface rocks at a speed of 130 m/s and under 1/6 gravity of earth. The foam metal in the component can bear the force of the detector and provide the recoil force. The stress of preformed groove and warhead is 1 200—2 000 MPa， while the stress of foam titanium and foam aluminum is 10 MPa and 1 MPa， respectively， with significant reduction. The stress of foam titanium is reduced to 1%， and that of foam aluminum is reduced to 1 ‰. The component has also undergone a series of different angle collision tests at low temperatures （-182.85 ℃） and high temperatures （127.15 ℃）， and the detector can still operate normally.
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