Transactions of Nanjing University of Aeronautics & Astronautics
Volume 38,Issue S1,2021 Table of Contents
2021, 38(S1):1-9.
DOI: 10.16356/j.1005-1120.2021.S.001
Abstract:
Under the absolute coordinate system， the unsteady Reynolds averaged Navier-Stokes （URANS）equations and the k-ω SST turbulence model are solved using the finite volume method to simulate the aerodynamic characteristics of large seaplane flying with the ground-effect above wavy surface. The velocity inlet wave-making method and the volume of fluid model are used to accurately simulate the linear regular waves and to precisely capture the free surface. This paper studies the influence of the sideslip angle on the aerodynamic characteristics of large seaplane when it is cruising above wavy water. The results show that the wave surface mainly affects the pressure distribution on the lower surface of the wing. When the sideslip angle varies from 0° to 8°， the varying of frequency of aerodynamic forces is consistent with the wave encounter frequency， and both periods are 0.6 s. With the increase of the sideslip angle， the lift coefficient and the pitching moment coefficient decrease. However， when the sideslip angle is smaller than 4°， the decrease amplitude is small， and the significant decrease occurs above 4° and during the whole process of the change of sideslip angle， the aerodynamic fluctuation amplitude is almost unchanged. As the drag coefficient increases with the increase of sideslip angle， significant increase also occurs when the value is greater than 4°， and the fluctuation amplitude does not show any correlations. The rolling moment coefficient and yaw moment coefficient increase with the increase of the sideslip angle， and the fluctuation amplitudes of both increase linearly with the increase of the sideslip angle.
Under the absolute coordinate system， the unsteady Reynolds averaged Navier-Stokes （URANS）
2021, 38(S1):10-16.
DOI: 10.16356/j.1005-1120.2021.S.002
Abstract:
In view of the reduction of hovering efficiency near high tension when a helicopter rotor hovers， a numerical simulation method of lifting rotor hovering aerodynamic characteristics based on leading edge droop is established in this paper. It is dominated by Reynolds average N-S equation in integral form. Firstly， VR-12 airfoil is taken as the research object， and the influence of leading edge droop angle on the aerodynamic characteristics of two-dimensional airfoil is studied. Secondly， the modified 7A rotor is taken as the research object， and the effects of different leading edge droop angles at the position of blade r/R=0.75—1 on the aerodynamic characteristics in hover are explored. It is found that the leading edge droop can significantly improve the aerodynamic characteristics of two-dimensional airfoil and three-dimensional hovering rotor near high angle of attack， and can effectively inhibit the generation of stall vortex.
In view of the reduction of hovering efficiency near high tension when a helicopter rotor hovers， a numerical simulation method of lifting rotor hovering aerodynamic characteristics based on leading edge droop is established in this paper. It is dominated by Reynolds average N-S equation in integral form. Firstly， VR-12 airfoil is taken as the research object， and the influence of leading edge droop angle on the aerodynamic characteristics of two-dimensional airfoil is studied. Secondly， the modified 7A rotor is taken as the research object， and the effects of different leading edge droop angles at the position of blade r/R=0.75—1 on the aerodynamic characteristics in hover are explored. It is found that the leading edge droop can significantly improve the aerodynamic characteristics of two-dimensional airfoil and three-dimensional hovering rotor near high angle of attack， and can effectively inhibit the generation of stall vortex.
2021, 38(S1):17-23.
DOI: 10.16356/j.1005-1120.2021.S.003
Abstract:
This paper discusses the temperature field distribution of piezoelectric stack with heating and thermal insulation device in cryogenic temperature environment. Firstly， the model of the piezoelectric damper is simplified and established by using partial-differential heat conduction equation. Secondly， the two-dimensional Du Fort-Frankel finite difference scheme is used to discretize the thermal conduction equation， and the numerical solution of the transient temperature field of piezoelectric stack driven by heating film at different positions is obtained by programming iteration. Then， the cryogenic temperature cabinet is used to simulate the low temperature environment to verify the numerical analysis results of the temperature field. Finally， the finite difference results are compared with the finite results and the experimental data in steady state and transient state， respectively. Comparison shows that the results of the finite difference method are basically consistent with the finite element and the experimental results， but the calculation time is shorter. The temperature field distribution results obtained by the finite difference method can verify the thermal insulation performance of the heating system and provide data basis for the temperature control of piezoelectric stack.
This paper discusses the temperature field distribution of piezoelectric stack with heating and thermal insulation device in cryogenic temperature environment. Firstly， the model of the piezoelectric damper is simplified and established by using partial-differential heat conduction equation. Secondly， the two-dimensional Du Fort-Frankel finite difference scheme is used to discretize the thermal conduction equation， and the numerical solution of the transient temperature field of piezoelectric stack driven by heating film at different positions is obtained by programming iteration. Then， the cryogenic temperature cabinet is used to simulate the low temperature environment to verify the numerical analysis results of the temperature field. Finally， the finite difference results are compared with the finite results and the experimental data in steady state and transient state， respectively. Comparison shows that the results of the finite difference method are basically consistent with the finite element and the experimental results， but the calculation time is shorter. The temperature field distribution results obtained by the finite difference method can verify the thermal insulation performance of the heating system and provide data basis for the temperature control of piezoelectric stack.
2021, 38(S1):24-31.
DOI: 10.16356/j.1005-1120.2021.S.004
Abstract:
The influences of the internal and external outlet angles on separation performance and flow field are compared and analyzed. Two arc functions are employed for controlling the internal and external angles. The separation process in the cyclone tube is calculated by using two-fluid model based on the Eulerian-Eulerian method. The results show that the structure with the internal outlet angle smaller than the external one is more beneficial to the separation performance. It is found that the small internal angle can help increase the swirl number， while the small external angle can help increase the friction coefficient. Several groups of numerical simulations are conducted for the air intake unit of the gas turbine in practice. When the internal outlet angle is 35° and the external outlet angle is 40°， the blade has sufficient cyclone strength and the separation rate of particles with diameters of 10—100 μm is between 70%—98%. The small blade angle is more conducive to the separation of fine particles， leading to violent collision of large particles on the outer wall and reduction of separation efficiency. In addition， reducing the external angle is conducive to the discharge of large particles.
The influences of the internal and external outlet angles on separation performance and flow field are compared and analyzed. Two arc functions are employed for controlling the internal and external angles. The separation process in the cyclone tube is calculated by using two-fluid model based on the Eulerian-Eulerian method. The results show that the structure with the internal outlet angle smaller than the external one is more beneficial to the separation performance. It is found that the small internal angle can help increase the swirl number， while the small external angle can help increase the friction coefficient. Several groups of numerical simulations are conducted for the air intake unit of the gas turbine in practice. When the internal outlet angle is 35° and the external outlet angle is 40°， the blade has sufficient cyclone strength and the separation rate of particles with diameters of 10—100 μm is between 70%—98%. The small blade angle is more conducive to the separation of fine particles， leading to violent collision of large particles on the outer wall and reduction of separation efficiency. In addition， reducing the external angle is conducive to the discharge of large particles.
2021, 38(S1):32-39.
DOI: 10.16356/j.1005-1120.2021.S.005
Abstract:
In order to alleviate noise pollution and improve the sustainability of airport operation， it is of great significance to develop an effective method to predict airport aviation noise. A three-layer neural network is constructed to gain computational simplicity and execution economy. With the preferred node number and transfer functions obtained in comparative tests， the constructed network is further optimized through the genetic algorithm for performance improvements in prediction. Results show that the proposed model in this paper is superior in accuracy and stability for airport aviation noise prediction， contributing to the assessment of future environmental impact and further improvement of operational sustainability for civil airports.
In order to alleviate noise pollution and improve the sustainability of airport operation， it is of great significance to develop an effective method to predict airport aviation noise. A three-layer neural network is constructed to gain computational simplicity and execution economy. With the preferred node number and transfer functions obtained in comparative tests， the constructed network is further optimized through the genetic algorithm for performance improvements in prediction. Results show that the proposed model in this paper is superior in accuracy and stability for airport aviation noise prediction， contributing to the assessment of future environmental impact and further improvement of operational sustainability for civil airports.
2021, 38(S1):40-48.
DOI: 10.16356/j.1005-1120.2021.S.006
Abstract:
The problem of abnormal flight recovery has always been the focus and difficulty in the field of civil aviation， and has important research significance. According to the recovery strategy， characteristics， and constraints of aircraft， aircrews and flights， this paper is based on the column generation algorithms. A mathematical optimization model for the integrated recovery of aircraft and aircrew in the case of temporary aircraft failures was established， and the corresponding solution algorithm was designed. At the same time， the influence of aircraft and aircrew on route selection was taken into account. Finally， the method of calling Cplex by Java was used. Part of the flight plan data actually operated by the company verifies the feasibility， accuracy and timeliness of the model and algorithm.
The problem of abnormal flight recovery has always been the focus and difficulty in the field of civil aviation， and has important research significance. According to the recovery strategy， characteristics， and constraints of aircraft， aircrews and flights， this paper is based on the column generation algorithms. A mathematical optimization model for the integrated recovery of aircraft and aircrew in the case of temporary aircraft failures was established， and the corresponding solution algorithm was designed. At the same time， the influence of aircraft and aircrew on route selection was taken into account. Finally， the method of calling Cplex by Java was used. Part of the flight plan data actually operated by the company verifies the feasibility， accuracy and timeliness of the model and algorithm.
7 Delay Compensation Observer with Sliding Mode Controller for Rotary Electro-hydraulic Servo System
2021, 38(S1):49-56.
DOI: 10.16356/j.1005-1120.2021.S.007
Abstract:
The hip’s lower limb exoskeleton essential and most important function is to support human’s payload as well as to enhance and assist human’s motion. It utilizes an electro-hydraulic servo manipulator which is required to achieve precise trajectory tracking and positioning operations. Nevertheless， these tasks require precise and robust control， which is very difficult to attain due to the inherent nonlinear dynamic behavior of the electro-hydraulic system caused by flow-pressure characteristics and fluid volume control variations of the servo valve. The sliding mode controller （SMC） is a widely used nonlinear robust controller， yet uncertainties and delay in the output degrade the closed-loop system performance and cause system instability. This work proposes a robust controller scheme that counts for the output delay and the inherent parameter uncertainties. Namely， a sliding mode controller enhanced by time-delay compensating observer for a typical electro-hydraulic servo system is adapted. SMC is utilized for its robustness against servo system parameters’ uncertainty whereas a time-delay observer estimates the variable states of the controller （velocity and acceleration）. The main contribution of this paper is improving on the closed loop performance of the electro hydraulic servo system and mitigating the delay time effects. Simulation results prove the robustness of this controller， which forces the position to track the desired path regardless of the changes of the amount of transport delay of the system’s states. The performance of the proposed controller is validated by repeating the simulation analysis while varying the amount of delay time.
The hip’s lower limb exoskeleton essential and most important function is to support human’s payload as well as to enhance and assist human’s motion. It utilizes an electro-hydraulic servo manipulator which is required to achieve precise trajectory tracking and positioning operations. Nevertheless， these tasks require precise and robust control， which is very difficult to attain due to the inherent nonlinear dynamic behavior of the electro-hydraulic system caused by flow-pressure characteristics and fluid volume control variations of the servo valve. The sliding mode controller （SMC） is a widely used nonlinear robust controller， yet uncertainties and delay in the output degrade the closed-loop system performance and cause system instability. This work proposes a robust controller scheme that counts for the output delay and the inherent parameter uncertainties. Namely， a sliding mode controller enhanced by time-delay compensating observer for a typical electro-hydraulic servo system is adapted. SMC is utilized for its robustness against servo system parameters’ uncertainty whereas a time-delay observer estimates the variable states of the controller （velocity and acceleration）. The main contribution of this paper is improving on the closed loop performance of the electro hydraulic servo system and mitigating the delay time effects. Simulation results prove the robustness of this controller， which forces the position to track the desired path regardless of the changes of the amount of transport delay of the system’s states. The performance of the proposed controller is validated by repeating the simulation analysis while varying the amount of delay time.
2021, 38(S1):57-68.
DOI: 10.16356/j.1005-1120.2021.S.008
Abstract:
The lorentz force-type magnetic bearing （LFTMB） with good linearity is suitable for the high-precision deflection control of the magnetically suspended gyrowheel （MSGW）. Two kinds of novel implicit LFTMBs are proposed in allusion to the poor magnetic flux density uniformity of the existing explicit LFTMB. The improvement of uniformity is realized under the paramagnetic contribution of magnetic ring. Their structures are introduced， the mathematical models are established based on the equivalent magnetic circuit method and the magnetic fields are analyzed by the finite element method based on the design parameters. Simulation results indicate that the magnetic flux density uniformity of implicit LFTMBs is superior to the traditional explicit LFTMB. Furthermore， the implicit trapezoid LFTMB with double magnetic circuits is better than that of those with single magnetic circuit， in terms of the magnetic flux density uniformity and the magnetic flux density. The magnetic flux density of implicit trapezoid double magnetic circuits LFTMB is verified by the experiment. The error between the experimental results and the simulation results is within 5%， which shows that the implicit trapezoid double magnetic circuits LFTMB is promising to meet the high-precision agile maneuver requirement of the magnetically suspended gyrowheel.
The lorentz force-type magnetic bearing （LFTMB） with good linearity is suitable for the high-precision deflection control of the magnetically suspended gyrowheel （MSGW）. Two kinds of novel implicit LFTMBs are proposed in allusion to the poor magnetic flux density uniformity of the existing explicit LFTMB. The improvement of uniformity is realized under the paramagnetic contribution of magnetic ring. Their structures are introduced， the mathematical models are established based on the equivalent magnetic circuit method and the magnetic fields are analyzed by the finite element method based on the design parameters. Simulation results indicate that the magnetic flux density uniformity of implicit LFTMBs is superior to the traditional explicit LFTMB. Furthermore， the implicit trapezoid LFTMB with double magnetic circuits is better than that of those with single magnetic circuit， in terms of the magnetic flux density uniformity and the magnetic flux density. The magnetic flux density of implicit trapezoid double magnetic circuits LFTMB is verified by the experiment. The error between the experimental results and the simulation results is within 5%， which shows that the implicit trapezoid double magnetic circuits LFTMB is promising to meet the high-precision agile maneuver requirement of the magnetically suspended gyrowheel.
2021, 38(S1):69-75.
DOI: 10.16356/j.1005-1120.2021.S.009
Abstract:
Due to the influence of the groundwater level， the internal humidity of the subgrade changes and the stability of the subgrade is affected. The main purpose of this paper is to obtain a reliable model of subgrade soil water content variation under the action of dry-wet cycle through sensor readings. Thus， an indoor soil column model test system is designed， and the readings of the sensors are used to determine the changing law of moisture field in the subgrade soil. The sensor readings indicate that the water content gradually decreases along the height of the soil column， and the water in the upper part of the soil column continuously loses， while the water in the lower part migrates upward to supplement. With the increase of dry-wet cycle index， the water holding capacity of soil decreases， and the soil surface gradually cracks and tends to rupture.
Due to the influence of the groundwater level， the internal humidity of the subgrade changes and the stability of the subgrade is affected. The main purpose of this paper is to obtain a reliable model of subgrade soil water content variation under the action of dry-wet cycle through sensor readings. Thus， an indoor soil column model test system is designed， and the readings of the sensors are used to determine the changing law of moisture field in the subgrade soil. The sensor readings indicate that the water content gradually decreases along the height of the soil column， and the water in the upper part of the soil column continuously loses， while the water in the lower part migrates upward to supplement. With the increase of dry-wet cycle index， the water holding capacity of soil decreases， and the soil surface gradually cracks and tends to rupture.
2021, 38(S1):76-83.
DOI: 10.16356/j.1005-1120.2021.S.010
Abstract:
In the current study， an effort has been taken to manufacture and compare the characteristics of functionally graded tubes. Two samples have been produced with a commercially pure aluminium matrix reinforced by 10%（in weight） SiC and Al2O3 with a 16 μm average size via horizontal centrifugal casting. In addition to microstructure analysis， the mechanical and wear characteristics have been investigated across the thickness of the produced tubes. The results showed that the addition of SiC and Al2O3 particles relative to the unreinforced matrix （pure Al） significantly enhance the mechanical properties and wear resistance of the produced tubes. Thus， these tubes are the best choice for automobile applications.
In the current study， an effort has been taken to manufacture and compare the characteristics of functionally graded tubes. Two samples have been produced with a commercially pure aluminium matrix reinforced by 10%（in weight） SiC and Al2O3 with a 16 μm average size via horizontal centrifugal casting. In addition to microstructure analysis， the mechanical and wear characteristics have been investigated across the thickness of the produced tubes. The results showed that the addition of SiC and Al2O3 particles relative to the unreinforced matrix （pure Al） significantly enhance the mechanical properties and wear resistance of the produced tubes. Thus， these tubes are the best choice for automobile applications.
2021, 38(S1):84-92.
DOI: 10.16356/j.1005-1120.2021.S.011
Abstract:
Based on the new modified couple stress theory and considering the flexoelectric effect of the piezoelectric layers， the Euler Bernoulli nano-beam model of composite laminated materials driven by electrostatically fixed supports at both ends is established. The nonlinear differential governing equations and boundary conditions are derived by the Hamilton principle. The generalized differential quadrature method （GDQM） and the Newton Raphson method are used to numerically solve the differential governing equations. The influence of flexoelectric effect on the static and the dynamic pull-in characteristics of laminated nano-beams is analyzed. The results of the numerical calculation are in a good agreement with those in the literature when the model degenerated into a nano-beam model without flexoelectric effect. The stacking sequence， length scale parameter l and piezoelectric layer applied voltage Vp of the composite will affect the pull-in voltage， frequency and time-domain response of the structure. Given that the flexoelectric effect will reduce the pull-in voltage and dimensionless natural frequency of the structure， the maximum dimensionless displacement at the midpoint of the beam and the period of time-domain response should be increased.
Based on the new modified couple stress theory and considering the flexoelectric effect of the piezoelectric layers， the Euler Bernoulli nano-beam model of composite laminated materials driven by electrostatically fixed supports at both ends is established. The nonlinear differential governing equations and boundary conditions are derived by the Hamilton principle. The generalized differential quadrature method （GDQM） and the Newton Raphson method are used to numerically solve the differential governing equations. The influence of flexoelectric effect on the static and the dynamic pull-in characteristics of laminated nano-beams is analyzed. The results of the numerical calculation are in a good agreement with those in the literature when the model degenerated into a nano-beam model without flexoelectric effect. The stacking sequence， length scale parameter l and piezoelectric layer applied voltage Vp of the composite will affect the pull-in voltage， frequency and time-domain response of the structure. Given that the flexoelectric effect will reduce the pull-in voltage and dimensionless natural frequency of the structure， the maximum dimensionless displacement at the midpoint of the beam and the period of time-domain response should be increased.
2021, 38(S1):93-101.
DOI: 10.16356/j.1005-1120.2021.S.012
Abstract:
When the machine tool is in the start- and stop-stages， the stick-slip phenomenon will be observed and high-precision positioning， machining accuracy and fretting feed will not be guaranteed. The most critical reason is that there is the difference between the dynamic and the static friction coefficients. Textures with different area ratios are fabricated on the surfaces of the upper PTFE-based composite and the friction tests are carried out on a reciprocating tribotester under the boundary lubrication and flat-on-flat contact conditions. The results show that there exists an optimal textured area ratio of 19.6% that can minimize the difference between the dynamic and the static friction coefficients.
When the machine tool is in the start- and stop-stages， the stick-slip phenomenon will be observed and high-precision positioning， machining accuracy and fretting feed will not be guaranteed. The most critical reason is that there is the difference between the dynamic and the static friction coefficients. Textures with different area ratios are fabricated on the surfaces of the upper PTFE-based composite and the friction tests are carried out on a reciprocating tribotester under the boundary lubrication and flat-on-flat contact conditions. The results show that there exists an optimal textured area ratio of 19.6% that can minimize the difference between the dynamic and the static friction coefficients.
2021, 38(S1):102-114.
DOI: 10.16356/j.1005-1120.2021.S.013
Abstract:
This study combines the three-dimensional model of the high-temperature proton exchange membrane fuel cell（HT-PEMFC） with theoretical analysis， by optimizing the structure of the fuel cell， adding a semicircular baffle in the gas channel and implementing novelly arranged obstacles to improve the PEMFC performance. The effects of velocity distribution， interface reactant concentration and pressure drop on performance are studied. The results show that adding obstacles in the gas channel will produce vertical velocity and can improve output performance， especially in the case of high current density and higher baffle radius. The superiority of the optimized structure in mass transfer capacity is proved， and a mechanism explanation is given for the improvement of performance.
This study combines the three-dimensional model of the high-temperature proton exchange membrane fuel cell（HT-PEMFC） with theoretical analysis， by optimizing the structure of the fuel cell， adding a semicircular baffle in the gas channel and implementing novelly arranged obstacles to improve the PEMFC performance. The effects of velocity distribution， interface reactant concentration and pressure drop on performance are studied. The results show that adding obstacles in the gas channel will produce vertical velocity and can improve output performance， especially in the case of high current density and higher baffle radius. The superiority of the optimized structure in mass transfer capacity is proved， and a mechanism explanation is given for the improvement of performance.
2021, 38(S1):115-121.
DOI: 10.16356/j.1005-1120.2021.S.014
Abstract:
The joint power allocation （PA） and beamforming （BF） design problem is studied to maximize the energy efficiency of a two-user downlink millimeter-wave system with non-orthogonal multiple access under imperfect channel state information （CSI）. By means of block coordinate descent， convex-concave procedure， and successive convex approximate， we propose a suboptimal joint PA and BF design scheme to address this non-convex problem. Simulation results verify that the proposed joint PA and BF design scheme is more effective when compared to some existing schemes.
The joint power allocation （PA） and beamforming （BF） design problem is studied to maximize the energy efficiency of a two-user downlink millimeter-wave system with non-orthogonal multiple access under imperfect channel state information （CSI）. By means of block coordinate descent， convex-concave procedure， and successive convex approximate， we propose a suboptimal joint PA and BF design scheme to address this non-convex problem. Simulation results verify that the proposed joint PA and BF design scheme is more effective when compared to some existing schemes.
2021, 38(S1):122-128.
DOI: 10.16356/j.1005-1120.2021.S.015
Abstract:
Technological advances in computer science and their application in our daily life allow us to improve our understanding of problems and solve them effectively. A system design to detect people with fever and determine high-risk areas using infrared thermography and big data is presented. In order to detect people with fever， face detection algorithms of Viola-Jones and Kanade-Lucas are investigated， and comparison between them is presented using a training set of 406 thermal images and a test set of 2 072 thermal images. Thermography analysis is performed on detected faces to obtain the temperature level on Celsius scale. With this information a sample database is created. To perform big data experimental analysis， Power Bi tool is used to determine the high-risk area. The experimental results show that Viola-Jones algorithm has a higher performance recognizing faces of thermal images than Kanade-Lucas， having a high detection rate， less false-positives rate and false-negatives rate.
Technological advances in computer science and their application in our daily life allow us to improve our understanding of problems and solve them effectively. A system design to detect people with fever and determine high-risk areas using infrared thermography and big data is presented. In order to detect people with fever， face detection algorithms of Viola-Jones and Kanade-Lucas are investigated， and comparison between them is presented using a training set of 406 thermal images and a test set of 2 072 thermal images. Thermography analysis is performed on detected faces to obtain the temperature level on Celsius scale. With this information a sample database is created. To perform big data experimental analysis， Power Bi tool is used to determine the high-risk area. The experimental results show that Viola-Jones algorithm has a higher performance recognizing faces of thermal images than Kanade-Lucas， having a high detection rate， less false-positives rate and false-negatives rate.
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