Transactions of Nanjing University of Aeronautics & Astronautics
Volume 0,Issue 6,2022 Table of Contents
2022(6):637-650.
DOI: 10.16356/j.1005-1120.2022.06.001
Abstract:
The air-turbo-rocket （ATR） engine is a promising propulsion plant for achieving numerous surface and air launched missile missions. The application of lobed mixer in the ATR combustor can promote the mixing of the fuel-rich gas and the air， thus improving the engine performance significantly. The numerical simulation method was conducted to explore the effects of lobe peak-to-trough width ratio on mixing and combustion performance in ATR combustors. Results show that： For a given peak lobe width b1， the combustion efficiency and total pressure loss decrease with the increase of trough lobe width b2； For a given b2， the combustion efficiency and total pressure loss decrease with the increase of b1； The fan-type lobed mixer with smaller b2 has a better effect on promoting the combustion efficiency in the region near the ATR combustor center line than that with a pair of parallel side walls. The total pressure recovery coefficient reaches more than 0.99 at the exit of combustor in nonreactive combustion while the total pressure loss reaches more than 4% in the reacting combustion. Compared with the mixing process， more than 80% of the total pressure loss is caused during combustion.
The air-turbo-rocket （ATR） engine is a promising propulsion plant for achieving numerous surface and air launched missile missions. The application of lobed mixer in the ATR combustor can promote the mixing of the fuel-rich gas and the air， thus improving the engine performance significantly. The numerical simulation method was conducted to explore the effects of lobe peak-to-trough width ratio on mixing and combustion performance in ATR combustors. Results show that： For a given peak lobe width b1， the combustion efficiency and total pressure loss decrease with the increase of trough lobe width b2； For a given b2， the combustion efficiency and total pressure loss decrease with the increase of b1； The fan-type lobed mixer with smaller b2 has a better effect on promoting the combustion efficiency in the region near the ATR combustor center line than that with a pair of parallel side walls. The total pressure recovery coefficient reaches more than 0.99 at the exit of combustor in nonreactive combustion while the total pressure loss reaches more than 4% in the reacting combustion. Compared with the mixing process， more than 80% of the total pressure loss is caused during combustion.
2022(6):651-662.
DOI: 10.16356/j.1005-1120.2022.06.002
Abstract:
A flow control method based on an active jet is developed to restart hypersonic inlets. The dynamic restarting process is numerically reproduced by unsteady Reynolds averaged Navier-Stokes（RANS） modeling to verify the effectiveness and reveal the influence of jet conditions. The active jet improves the inlet unstart status by drawing the high-pressure separation bubble from the internal compression duct and performing a full expansion to alleviate the adverse pressure gradient. Moreover， the favorable pressure gradient in the inlet caused by jet expansion allows for a successful restart after turning off the jet. The influence of the jet momentum ratio is then analyzed to guide the design of the active jet control method and choose the proper momentum ratios. A low jet momentum does not eliminate the high-pressure separation bubble， whereas an excessive jet momentum causes severe momentum loss due to the induced shock. The general rule in restarting the inlet using an active jet is to allow a full jet expansion downstream of the jet slot while avoiding excessive momentum loss upstream and preventing the thick low-speed layer.
A flow control method based on an active jet is developed to restart hypersonic inlets. The dynamic restarting process is numerically reproduced by unsteady Reynolds averaged Navier-Stokes（RANS） modeling to verify the effectiveness and reveal the influence of jet conditions. The active jet improves the inlet unstart status by drawing the high-pressure separation bubble from the internal compression duct and performing a full expansion to alleviate the adverse pressure gradient. Moreover， the favorable pressure gradient in the inlet caused by jet expansion allows for a successful restart after turning off the jet. The influence of the jet momentum ratio is then analyzed to guide the design of the active jet control method and choose the proper momentum ratios. A low jet momentum does not eliminate the high-pressure separation bubble， whereas an excessive jet momentum causes severe momentum loss due to the induced shock. The general rule in restarting the inlet using an active jet is to allow a full jet expansion downstream of the jet slot while avoiding excessive momentum loss upstream and preventing the thick low-speed layer.
2022(6):663-671.
DOI: 10.16356/j.1005-1120.2022.06.003
Abstract:
When the variable geometry hypersonic inlet is sealed with ceramic wafers， the cavity flows inside the sealing chamber can be affected by the boundary layer near the side wall. To study the influence of the boundary layer thickness near the side wall on the flow and leakage characteristics in sealing chamber， the numerical calculation of the cavity flow in the sealing chamber under different inflow boundary layer thicknesses is carried out. The results show that three-dimensional cavity flow structures are close to being asymmetric， and the entrance pressure of the leakage path can also be affected by asymmetry； with the increase of the thickness of the boundary layer， the pressure at the cavity floor and the seal entrance decreases. Finally， the existing leakage prediction model is modified according to the distribution rule of the cavity floor and the flow properties in the leakage path.
When the variable geometry hypersonic inlet is sealed with ceramic wafers， the cavity flows inside the sealing chamber can be affected by the boundary layer near the side wall. To study the influence of the boundary layer thickness near the side wall on the flow and leakage characteristics in sealing chamber， the numerical calculation of the cavity flow in the sealing chamber under different inflow boundary layer thicknesses is carried out. The results show that three-dimensional cavity flow structures are close to being asymmetric， and the entrance pressure of the leakage path can also be affected by asymmetry； with the increase of the thickness of the boundary layer， the pressure at the cavity floor and the seal entrance decreases. Finally， the existing leakage prediction model is modified according to the distribution rule of the cavity floor and the flow properties in the leakage path.
2022(6):672-683.
DOI: 10.16356/j.1005-1120.2022.06.004
Abstract:
In the real-world situation， the lunar missions’ scale and terrain are different according to various operational regions or worksheets， which requests a more flexible and efficient algorithm to generate task paths. A multi-scale ant colony planning method for the lunar robot is designed to meet the requirements of large scale and complex terrain in lunar space. In the algorithm， the actual lunar surface image is meshed into a gird map， the path planning algorithm is modeled on it， and then the actual path is projected to the original lunar surface and mission. The classical ant colony planning algorithm is rewritten utilizing a multi-scale method to address the diverse task problem. Moreover， the path smoothness is also considered to reduce the magnitude of the steering angle. Finally， several typical conditions to verify the efficiency and feasibility of the proposed algorithm are presented.
In the real-world situation， the lunar missions’ scale and terrain are different according to various operational regions or worksheets， which requests a more flexible and efficient algorithm to generate task paths. A multi-scale ant colony planning method for the lunar robot is designed to meet the requirements of large scale and complex terrain in lunar space. In the algorithm， the actual lunar surface image is meshed into a gird map， the path planning algorithm is modeled on it， and then the actual path is projected to the original lunar surface and mission. The classical ant colony planning algorithm is rewritten utilizing a multi-scale method to address the diverse task problem. Moreover， the path smoothness is also considered to reduce the magnitude of the steering angle. Finally， several typical conditions to verify the efficiency and feasibility of the proposed algorithm are presented.
2022(6):684-695.
DOI: 10.16356/j.1005-1120.2022.06.005
Abstract:
The dynamic parameter identification of the robot is the basis for the design of the controller based on the dynamic model. Currently， the primary method for solving angular velocity and angular acceleration is to filter and smooth the position sequence and then form a differential signal. However， if the noise and the original signal overlap in the frequency domain， filtering the noise will also filter out the valuable information in the frequency band. This paper proposes an excitation trajectory based on Logistic function， which fully uses the information in the original signal and can accurately solve the angular velocity and angular acceleration without filtering and smoothing the position sequence. The joint angle of the excitation trajectory is mapped to the joint angular velocity and angular acceleration one by one so that the joint angular velocity and joint angular acceleration can be obtained directly according to the position. The genetic algorithm is used to optimize the excitation trajectory parameters to minimize the observation matrix’s condition number and further improve the identification accuracy. By using the strategy of iterative identification， the dynamic parameters identified in each iteration are substituted into the robot controller according to the previous position sequence until the tracking trajectory approaches the desired trajectory， and the actual joint angular velocity and angular acceleration converge to the expected value. The simulation results show that using the step-by-step strategy， the joint angular velocity and joint angular acceleration of the tracking trajectory quickly converge to the expected value， and the identification error of inertia parameters is less than 0.01 in three iterations. With the increase of the number of iterations， the identification error of inertial parameters can be further reduced.
The dynamic parameter identification of the robot is the basis for the design of the controller based on the dynamic model. Currently， the primary method for solving angular velocity and angular acceleration is to filter and smooth the position sequence and then form a differential signal. However， if the noise and the original signal overlap in the frequency domain， filtering the noise will also filter out the valuable information in the frequency band. This paper proposes an excitation trajectory based on Logistic function， which fully uses the information in the original signal and can accurately solve the angular velocity and angular acceleration without filtering and smoothing the position sequence. The joint angle of the excitation trajectory is mapped to the joint angular velocity and angular acceleration one by one so that the joint angular velocity and joint angular acceleration can be obtained directly according to the position. The genetic algorithm is used to optimize the excitation trajectory parameters to minimize the observation matrix’s condition number and further improve the identification accuracy. By using the strategy of iterative identification， the dynamic parameters identified in each iteration are substituted into the robot controller according to the previous position sequence until the tracking trajectory approaches the desired trajectory， and the actual joint angular velocity and angular acceleration converge to the expected value. The simulation results show that using the step-by-step strategy， the joint angular velocity and joint angular acceleration of the tracking trajectory quickly converge to the expected value， and the identification error of inertia parameters is less than 0.01 in three iterations. With the increase of the number of iterations， the identification error of inertial parameters can be further reduced.
2022(6):696-706.
DOI: 10.16356/j.1005-1120.2022.06.006
Abstract:
A nonlinear sliding mode adaptive controller for a thin-film diffractive imaging system is designed to achieve accurate pointing direction over the attitude of subarrays in large-diameter mirror arrays. The kinematics and dynamics equations based on error quaternion and angular velocity are derived， and a diffractive thin-film sub-mirror array controller is designed to point precisely. Moreover， the global stability of the controller is proved by the Lyapunov method. Since the controller can adaptively identify the inertia matrix of each sub-mirror system， it is robust to bounded disturbances and changes in inertia parameters. At the same time， the continuous arctangent function is introduced， which is effectively anti-chattering. The simulation results show that the designed controller can ensure the accurate tracking of the diffractive film in each sub-mirror in the presence of rotational inertia matrix uncertainty and various disturbances.
A nonlinear sliding mode adaptive controller for a thin-film diffractive imaging system is designed to achieve accurate pointing direction over the attitude of subarrays in large-diameter mirror arrays. The kinematics and dynamics equations based on error quaternion and angular velocity are derived， and a diffractive thin-film sub-mirror array controller is designed to point precisely. Moreover， the global stability of the controller is proved by the Lyapunov method. Since the controller can adaptively identify the inertia matrix of each sub-mirror system， it is robust to bounded disturbances and changes in inertia parameters. At the same time， the continuous arctangent function is introduced， which is effectively anti-chattering. The simulation results show that the designed controller can ensure the accurate tracking of the diffractive film in each sub-mirror in the presence of rotational inertia matrix uncertainty and various disturbances.
2022(6):707-720.
DOI: 10.16356/j.1005-1120.2022.06.007
Abstract:
A dynamic programming-sequential quadratic programming （DP-SQP） combined algorithm is proposed to address the problem that the traditional continuous control method has high computational complexity and is easy to fall into local optimal solution. To solve the globally optimal control law sequence， we use the dynamic programming algorithm to discretize the separation control decision-making process into a series of sub-stages based on the time characteristics of the separation allocation model， and recursion from the end stage to the initial stage. The sequential quadratic programming algorithm is then used to solve the optimal return function and the optimal control law for each sub-stage. Comparative simulations of the combined algorithm and the traditional algorithm are designed to validate the superiority of the combined algorithm. Aircraft-following and cross-conflict simulation examples are created to demonstrate the combined algorithm’s adaptability to various conflict scenarios. The simulation results demonstrate the separation deploy strategy’s effectiveness， efficiency， and adaptability.
A dynamic programming-sequential quadratic programming （DP-SQP） combined algorithm is proposed to address the problem that the traditional continuous control method has high computational complexity and is easy to fall into local optimal solution. To solve the globally optimal control law sequence， we use the dynamic programming algorithm to discretize the separation control decision-making process into a series of sub-stages based on the time characteristics of the separation allocation model， and recursion from the end stage to the initial stage. The sequential quadratic programming algorithm is then used to solve the optimal return function and the optimal control law for each sub-stage. Comparative simulations of the combined algorithm and the traditional algorithm are designed to validate the superiority of the combined algorithm. Aircraft-following and cross-conflict simulation examples are created to demonstrate the combined algorithm’s adaptability to various conflict scenarios. The simulation results demonstrate the separation deploy strategy’s effectiveness， efficiency， and adaptability.
2022(6):721-734.
DOI: 10.16356/j.1005-1120.2022.06.008
Abstract:
As one of the most important steps in the design of bearing-less rotor systems， the design of flexible beam has received much research attention. Because of the very complex working environment of helicopter， the flexible beam should satisfy both the strength and dynamic requirements. However， traditional optimization research focused only on either the strength or dynamical characteristics. To sufficiently improve the performance of the flexible beam， both aspects must be considered. This paper proposes a two-stage optimization method based on the Hamilton variational principle： Variational asymptotic beam section analysis （VABS） program and genetic algorithm （GA）. Consequently， a two-part analysis model based on the Hamilton variational principle and VABS is established to calculate section characteristics and structural dynamics characteristics， respectively. Subsequently， the two parts are combined to establish a two-stage optimization process and search with GA to obtain the best dynamic characteristics combinations. Based on the primary optimization results， the section characteristics of the flexible beam are further optimized using GA. The optimization results show that the torsional stiffness decreases by 36.1% compared with the full 0° laying scheme without optimization and the dynamic requirements are achieved. The natural frequencies of flapping and torsion meet the requirements （0.5 away from the passing frequencies of the blade， 0.25 away from the excitation force frequency， and the flapping and torsion frequencies keep a corresponding distance）. The results indicate that the optimization method can significantly improve the performance of the flexible beam.
As one of the most important steps in the design of bearing-less rotor systems， the design of flexible beam has received much research attention. Because of the very complex working environment of helicopter， the flexible beam should satisfy both the strength and dynamic requirements. However， traditional optimization research focused only on either the strength or dynamical characteristics. To sufficiently improve the performance of the flexible beam， both aspects must be considered. This paper proposes a two-stage optimization method based on the Hamilton variational principle： Variational asymptotic beam section analysis （VABS） program and genetic algorithm （GA）. Consequently， a two-part analysis model based on the Hamilton variational principle and VABS is established to calculate section characteristics and structural dynamics characteristics， respectively. Subsequently， the two parts are combined to establish a two-stage optimization process and search with GA to obtain the best dynamic characteristics combinations. Based on the primary optimization results， the section characteristics of the flexible beam are further optimized using GA. The optimization results show that the torsional stiffness decreases by 36.1% compared with the full 0° laying scheme without optimization and the dynamic requirements are achieved. The natural frequencies of flapping and torsion meet the requirements （0.5 away from the passing frequencies of the blade， 0.25 away from the excitation force frequency， and the flapping and torsion frequencies keep a corresponding distance）. The results indicate that the optimization method can significantly improve the performance of the flexible beam.
2022(6):735-749.
DOI: 10.16356/j.1005-1120.2022.06.009
Abstract:
The conventional dynamic control devices， such as fluid viscous damper （VFD） and isolating bearings， are unsuitable for the double-deck cable-stayed bridge due to a lack of sustainability， so it is necessary to introduce some high-tech dynamic control devices to reduce dynamic response for double-deck cable-stayed bridges under earthquakes. A （90+128） m-span double-deck cable-stayed bridge with a steel truss beam is taken as the prototype bridge. A 3D finite element model is built to conduct the nonlinear time-history analysis of different site categories in fortification intensity Ⅸ （0.40 g） degree area. Two new types of dynamic control devices-cable sliding friction aseismic bearings （CSFABs） and elasticity fluid viscous dampers composite devices （EVFDs） are introduced to reduce the dynamic responses of double-deck cable-stayed bridges with steel truss beam. The parametric optimization design for the damping coefficient C and the elastic stiffness of spring K of EVFDs is conducted. The following conclusions are drawn：（1） The hybrid support system by EVFDs and CSFABs play a good function under both seismic and regular work， especially in eliminating the expansion joints damage； （2） The hybrid support system can reduce the beam-end displacement by 75% and the tower-bottom bending moment by 60% under the longitudinal seismic excitation. In addition， it can reduce the pier-bottom bending moment by at least 45% under transverse seismic and control the relative displacement between the pier and beam within 0.3 m. （3） Assuming the velocity index α=0.3， the parametric optimization suggests the damping coefficient C as 2 000 kN·s·m-1 in site Ⅰ0， 4 000 kN·s·m-1 in site Ⅱ， 6 000 kN·s·m-1 in site Ⅳ， and the elastic stiffness of spring K as 10 000 kN/m in site Ⅰ0， 50 000 kN/m in site Ⅱ， and 100 000 kN/m in site Ⅳ.
The conventional dynamic control devices， such as fluid viscous damper （VFD） and isolating bearings， are unsuitable for the double-deck cable-stayed bridge due to a lack of sustainability， so it is necessary to introduce some high-tech dynamic control devices to reduce dynamic response for double-deck cable-stayed bridges under earthquakes. A （90+128） m-span double-deck cable-stayed bridge with a steel truss beam is taken as the prototype bridge. A 3D finite element model is built to conduct the nonlinear time-history analysis of different site categories in fortification intensity Ⅸ （0.40 g） degree area. Two new types of dynamic control devices-cable sliding friction aseismic bearings （CSFABs） and elasticity fluid viscous dampers composite devices （EVFDs） are introduced to reduce the dynamic responses of double-deck cable-stayed bridges with steel truss beam. The parametric optimization design for the damping coefficient C and the elastic stiffness of spring K of EVFDs is conducted. The following conclusions are drawn：（1） The hybrid support system by EVFDs and CSFABs play a good function under both seismic and regular work， especially in eliminating the expansion joints damage； （2） The hybrid support system can reduce the beam-end displacement by 75% and the tower-bottom bending moment by 60% under the longitudinal seismic excitation. In addition， it can reduce the pier-bottom bending moment by at least 45% under transverse seismic and control the relative displacement between the pier and beam within 0.3 m. （3） Assuming the velocity index α=0.3， the parametric optimization suggests the damping coefficient C as 2 000 kN·s·m-1 in site Ⅰ0， 4 000 kN·s·m-1 in site Ⅱ， 6 000 kN·s·m-1 in site Ⅳ， and the elastic stiffness of spring K as 10 000 kN/m in site Ⅰ0， 50 000 kN/m in site Ⅱ， and 100 000 kN/m in site Ⅳ.
2022(6):750-758.
DOI: 10.16356/j.1005-1120.2022.06.010
Abstract:
Due to the paramagnetic property of liquid oxygen， the Kelvin force can be induced in liquid oxygen under non-uniform magnetic field. Based on the volume of fluid （VOF） model， the positioning effect of the force in liquid oxygen tanks is analyzed under various Bond numbers （Bo） and magnetic Bond numbers （Bom）. The results show that the magnetic field has the effect of repositioning the liquid oxygen in the tank when the gravity field is not enough or absent. Additionally， the gas-liquid interface has a periodic fluctuation during the process due to the inhomogeneous Kelvin force distribution， and more effective suppression of fluctuation can be achieved under the condition of a larger Bom. The new method of controlling gas-liquid interface of liquid oxygen tank under micro gravity condition is hoped to be developed in the future.
Due to the paramagnetic property of liquid oxygen， the Kelvin force can be induced in liquid oxygen under non-uniform magnetic field. Based on the volume of fluid （VOF） model， the positioning effect of the force in liquid oxygen tanks is analyzed under various Bond numbers （Bo） and magnetic Bond numbers （Bom）. The results show that the magnetic field has the effect of repositioning the liquid oxygen in the tank when the gravity field is not enough or absent. Additionally， the gas-liquid interface has a periodic fluctuation during the process due to the inhomogeneous Kelvin force distribution， and more effective suppression of fluctuation can be achieved under the condition of a larger Bom. The new method of controlling gas-liquid interface of liquid oxygen tank under micro gravity condition is hoped to be developed in the future.
2022(6):759-762.
DOI: 10.16356/j.1005-1120.2022.06.011
Abstract:
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