Transactions of Nanjing University of Aeronautics & Astronautics
Volume 32,Issue 4,2015 Table of Contents
1 Experimental Research on the Performance of an Open Loop Cycle Carbon Dioxide Refrigeration System
2015, 32(4).
Abstract:
Carbon dioxide is an ideal natural refrigerant because of its advantageous characteristics. In this study, an open loop cycle carbon dioxide (CO2) refrigeration system is established, and the cooling performances of high-pressure CO2 at different storage conditions (25°C, 30°C, and 35°C) are investigated. Moreover, the experimental mass flow rates of CO2 are compared with the theoretical values at different conditions and refrigeration capacities. The results indicate that the storage condition of CO2 has a significant impact on the refrigeration performance and the mass flow rate of CO2 increases with increasing storage temperature at a given refrigeration capacity.
Carbon dioxide is an ideal natural refrigerant because of its advantageous characteristics. In this study, an open loop cycle carbon dioxide (CO2) refrigeration system is established, and the cooling performances of high-pressure CO2 at different storage conditions (25°C, 30°C, and 35°C) are investigated. Moreover, the experimental mass flow rates of CO2 are compared with the theoretical values at different conditions and refrigeration capacities. The results indicate that the storage condition of CO2 has a significant impact on the refrigeration performance and the mass flow rate of CO2 increases with increasing storage temperature at a given refrigeration capacity.
2015, 32(4).
Abstract:
In order to analyze the attitude errors of the vertical docking test system of small satellite, the static error and kinematic error of test system are taken into account. The working principle of test system and coordinate of actuator are introduced. The model of friction torque on the joints and torque on the docking mechanism are built. Dynamics equation of actuator is built by Lagrange equation and Nielsen equation. Under the condition of 24 different angle groups, the calculation of dynamics equation is completed by using MATLAB/SIMULINK platform and kinematic errors of actuator are obtained. The attitude error models of docking mechanism are built. Results shows that the main angle error sources of yaw, row, pitch are not identical. The attitude error of yaw angle can be decreased by compensating the angle error around axis-x. The attitude error of row angle mainly originates in system error, which can be eliminated by adjusting non-orthogonal degree.
In order to analyze the attitude errors of the vertical docking test system of small satellite, the static error and kinematic error of test system are taken into account. The working principle of test system and coordinate of actuator are introduced. The model of friction torque on the joints and torque on the docking mechanism are built. Dynamics equation of actuator is built by Lagrange equation and Nielsen equation. Under the condition of 24 different angle groups, the calculation of dynamics equation is completed by using MATLAB/SIMULINK platform and kinematic errors of actuator are obtained. The attitude error models of docking mechanism are built. Results shows that the main angle error sources of yaw, row, pitch are not identical. The attitude error of yaw angle can be decreased by compensating the angle error around axis-x. The attitude error of row angle mainly originates in system error, which can be eliminated by adjusting non-orthogonal degree.
2015, 32(4).
Abstract:
In the present study, the influence of the chemical nonequilibrium on the thermal characteristics is explored by using 2D hybrid grid direct simulation Monte Carlo(DSMC) parallel method. An improved molecule search algorithm is proposed, which can preserve the high efficiency of area search algorithm. This method can not only overcome the defects of area search algorithm, but also give all information about molecules hitting surface. The heat flux calculation method of rarefied hypersonic flow is established, testing methods of chemical reaction probability for five species of mixed gas with limited speed chemical reactions are also selected. To validate the effectiveness of the present method, hypersonic flow around cylinder is firstly simulated, and subsequently numerical simulations of the heat flux and flow field characteristics around the blunt body at different heights are carried out in the paper under two different cases: thermal nonequilibrium condition and thermochemical nonequilibrium condition. Numerical results demonstrate the validity and reliability of methods developed in this paper.
In the present study, the influence of the chemical nonequilibrium on the thermal characteristics is explored by using 2D hybrid grid direct simulation Monte Carlo(DSMC) parallel method. An improved molecule search algorithm is proposed, which can preserve the high efficiency of area search algorithm. This method can not only overcome the defects of area search algorithm, but also give all information about molecules hitting surface. The heat flux calculation method of rarefied hypersonic flow is established, testing methods of chemical reaction probability for five species of mixed gas with limited speed chemical reactions are also selected. To validate the effectiveness of the present method, hypersonic flow around cylinder is firstly simulated, and subsequently numerical simulations of the heat flux and flow field characteristics around the blunt body at different heights are carried out in the paper under two different cases: thermal nonequilibrium condition and thermochemical nonequilibrium condition. Numerical results demonstrate the validity and reliability of methods developed in this paper.
2015, 32(4).
Abstract:
According to the principle of heat transfer in limited space, the thickness formula of heat-insulating layer is deduced through the conduction analysis in this paper. Polishing experiments are conducted with the same technological parameters. Compared with polishing experiments, the heat transfer model is proved to be right. According to the result of experiments, Polyurethane heat-insulating layer can effectively increase the service life of the ice fixed abrasive pad, and smooth melting rate in the process of polishing to improve the quality of polishing. Theoretical basis for research of temperature field of ice fixed abrasive polishing can be provided by the heat transfer model.
According to the principle of heat transfer in limited space, the thickness formula of heat-insulating layer is deduced through the conduction analysis in this paper. Polishing experiments are conducted with the same technological parameters. Compared with polishing experiments, the heat transfer model is proved to be right. According to the result of experiments, Polyurethane heat-insulating layer can effectively increase the service life of the ice fixed abrasive pad, and smooth melting rate in the process of polishing to improve the quality of polishing. Theoretical basis for research of temperature field of ice fixed abrasive polishing can be provided by the heat transfer model.
2015, 32(4).
Abstract:
A new robust control method of a nonlinear flight dynamic system with aerodynamic coefficients and external disturbance has been proposed. The proposed control system is a combination of the dynamic surface control (DSC) and the nonlinear disturbance observer (NDO). DSC technique provides the ability to overcome the “explosion of complexity” problem in backstepping control. NDO is adopted to observe the uncertainties in nonlinear flight dynamic system. It has been proved that the proposed design method can guarantee uniformly ultimately boundedness of all the signals in the closed-loop system by Lyapunov stability theorem. Finally, simulation results show that the proposed controller provides better performance than the traditional nonlinear controller.
A new robust control method of a nonlinear flight dynamic system with aerodynamic coefficients and external disturbance has been proposed. The proposed control system is a combination of the dynamic surface control (DSC) and the nonlinear disturbance observer (NDO). DSC technique provides the ability to overcome the “explosion of complexity” problem in backstepping control. NDO is adopted to observe the uncertainties in nonlinear flight dynamic system. It has been proved that the proposed design method can guarantee uniformly ultimately boundedness of all the signals in the closed-loop system by Lyapunov stability theorem. Finally, simulation results show that the proposed controller provides better performance than the traditional nonlinear controller.
2015, 32(4).
Abstract:
The multi-resolution adaptive grids method is proposed to solve the problems of inefficiency in the previous grid-based methods, and it can be used in clouds simulation and the interactive simulation between objects and clouds. OBB(Oriented Bounding Box) hierarchical trees of objects are established, and the resolutions of global and local grids can be selected automatically. The motion equations of fluid dynamics are simplified. Upwind difference is applied to ensure the stability of the simulation process during the discrete process of partial differential equations. To solve the speed problem of existed phase functions, the improved phase function is applied to illumination calculation of clouds. Experimental results show that the proposed methods can promote the simulation efficiency and meet the need for the simulation of large-scale clouds scene. Real-time rendering of clouds and the interaction between clouds and objects have been realized without preprocessing stage.
The multi-resolution adaptive grids method is proposed to solve the problems of inefficiency in the previous grid-based methods, and it can be used in clouds simulation and the interactive simulation between objects and clouds. OBB(Oriented Bounding Box) hierarchical trees of objects are established, and the resolutions of global and local grids can be selected automatically. The motion equations of fluid dynamics are simplified. Upwind difference is applied to ensure the stability of the simulation process during the discrete process of partial differential equations. To solve the speed problem of existed phase functions, the improved phase function is applied to illumination calculation of clouds. Experimental results show that the proposed methods can promote the simulation efficiency and meet the need for the simulation of large-scale clouds scene. Real-time rendering of clouds and the interaction between clouds and objects have been realized without preprocessing stage.
2015, 32(4).
Abstract:
Joint clearance as an important stochastic factor, can significantly deteriorate positioning and repeatability accuracies and lower assembly quality of a 6-dof docking mechanism. Considering pose accuracy with traditional error model that possesses inherent imprecision, both probabilistic and deterministic approaches based on forward kinematics are presented in this paper, to analyze comprehensive pose error (CPE) in simulation. Results indicate an identical trend emerges for each CPE with both approaches, and both CPEs perform opposite variations as the moving platform upgrades. The findings provide theoretical reference for refinement of assembly quality evaluation of this mechanism.
Joint clearance as an important stochastic factor, can significantly deteriorate positioning and repeatability accuracies and lower assembly quality of a 6-dof docking mechanism. Considering pose accuracy with traditional error model that possesses inherent imprecision, both probabilistic and deterministic approaches based on forward kinematics are presented in this paper, to analyze comprehensive pose error (CPE) in simulation. Results indicate an identical trend emerges for each CPE with both approaches, and both CPEs perform opposite variations as the moving platform upgrades. The findings provide theoretical reference for refinement of assembly quality evaluation of this mechanism.
2015, 32(4).
Abstract:
The mechanical gas seal of aero engine have to face the problems of high wear rate and short lifetime. Surface texture has shown beneficial effects over the tribological characteristics. In the present study, a hydrodynamic model for dimpled annular area of mechanical gas seal considering the “interaction effect” between neighboring two dimples is developed based on Reynolds equation. Different multi-row columns are chosen and the dimensionless pressure in radial and circumferential directions is calculated. The results indicate that the “interaction effect” is more obvious in circumferential direction than in radial direction even the area and depth of the dimples are same. It has also been found that, for 5×5column, the dimensionless average pressure value considering the “interaction effect” increased by 45.41% compared with 1×5column. Further analysis demonstrates the model with 5×5column can be more reasonable based on the consideration on both computing time and accuracy to investigate the hydrodynamic effect for dimpled mechanical gas seal.
The mechanical gas seal of aero engine have to face the problems of high wear rate and short lifetime. Surface texture has shown beneficial effects over the tribological characteristics. In the present study, a hydrodynamic model for dimpled annular area of mechanical gas seal considering the “interaction effect” between neighboring two dimples is developed based on Reynolds equation. Different multi-row columns are chosen and the dimensionless pressure in radial and circumferential directions is calculated. The results indicate that the “interaction effect” is more obvious in circumferential direction than in radial direction even the area and depth of the dimples are same. It has also been found that, for 5×5column, the dimensionless average pressure value considering the “interaction effect” increased by 45.41% compared with 1×5column. Further analysis demonstrates the model with 5×5column can be more reasonable based on the consideration on both computing time and accuracy to investigate the hydrodynamic effect for dimpled mechanical gas seal.
2015, 32(4).
Abstract:
Flight delays are increasingly becoming an important factor restricting the quality of aviation services and sustainable development besides weather and other uncontrollable reasons. The reasonable queue of departure flight and arrival flight is one of the important means of reducing flight delays on busy airports. This article focuses on the Pareto optimization problem of flight departure sequencing, the runway takeoff sequencing is seen as a single machine scheduling problem with two objective functions: the total weighted minimum number of departure flights failed to take off and the longest delay time at least. So the integer programming model is established and solved by multi-objective genetic algorithm for it. The simulation results show, this method not only can obtain the goal of better results, but also can provide a variety of options for dispatchers combining with the scene of trade-offs, which improves the flight departure plan flexibility and effectiveness.
Flight delays are increasingly becoming an important factor restricting the quality of aviation services and sustainable development besides weather and other uncontrollable reasons. The reasonable queue of departure flight and arrival flight is one of the important means of reducing flight delays on busy airports. This article focuses on the Pareto optimization problem of flight departure sequencing, the runway takeoff sequencing is seen as a single machine scheduling problem with two objective functions: the total weighted minimum number of departure flights failed to take off and the longest delay time at least. So the integer programming model is established and solved by multi-objective genetic algorithm for it. The simulation results show, this method not only can obtain the goal of better results, but also can provide a variety of options for dispatchers combining with the scene of trade-offs, which improves the flight departure plan flexibility and effectiveness.
2015, 32(4).
Abstract:
In this paper a preconditioned gridless method is developed for solving Euler equations at low mach numbers. The preconditioned system in conservation form is obtained by multiplying a preconditioning matrix of the type of Weiss and Smith to the time derivative of the Euler equations, which are discretized using a gridless techniques wherein the physical domain is distributed by clouds of points. The implementation of the preconditioned gridless method is mainly based on the frame of the traditional gridless method without preconditioning, which may fail to have convergence for low Mach number simulations, therefore the modifications corresponding to the affect terms of preconditioning are mainly addressed in the paper. The numerical results show that the preconditioned gridless method still functions for compressible transonic flow simulations and additionally, for nearly incompressible flow simulations at low Mach numbers as well. The paper ends with nearly incompressible flow over a multi-element airfoil, which demonstrates the ability of the method presented for treating flows over complicated geometries.
In this paper a preconditioned gridless method is developed for solving Euler equations at low mach numbers. The preconditioned system in conservation form is obtained by multiplying a preconditioning matrix of the type of Weiss and Smith to the time derivative of the Euler equations, which are discretized using a gridless techniques wherein the physical domain is distributed by clouds of points. The implementation of the preconditioned gridless method is mainly based on the frame of the traditional gridless method without preconditioning, which may fail to have convergence for low Mach number simulations, therefore the modifications corresponding to the affect terms of preconditioning are mainly addressed in the paper. The numerical results show that the preconditioned gridless method still functions for compressible transonic flow simulations and additionally, for nearly incompressible flow simulations at low Mach numbers as well. The paper ends with nearly incompressible flow over a multi-element airfoil, which demonstrates the ability of the method presented for treating flows over complicated geometries.
2015, 32(4).
Abstract:
For an in-depth study on the symmetric properties for nonholonomic non-conservative mechanical systems, the fractional action-like Noether symmetries and conserved quantities for nonholonomic mechanical systems are studied, which are based on the fractional action-like approach for dynamics modeling proposed by El-Nabulsi. Firstly, the fractional action-like variational problem is established, and the fractional action-like Lagrange equations of holonomic system and the fractional action-like differential equations of motion with multiplier for nonholonomic system are given; secondly, according to the invariance of fractional action-like Hamilton action under infinitesimal transformations of group, the definitions and criteria of fractional action-like Noether symmetric transformations and quasi-symmetric transformations are put forward; finally, the fractional action-like Noether theorems for both holonomic system and nonholonomic system are established, and the relationship between the fractional action-like Noether symmetry and the conserved quantity is given.
For an in-depth study on the symmetric properties for nonholonomic non-conservative mechanical systems, the fractional action-like Noether symmetries and conserved quantities for nonholonomic mechanical systems are studied, which are based on the fractional action-like approach for dynamics modeling proposed by El-Nabulsi. Firstly, the fractional action-like variational problem is established, and the fractional action-like Lagrange equations of holonomic system and the fractional action-like differential equations of motion with multiplier for nonholonomic system are given; secondly, according to the invariance of fractional action-like Hamilton action under infinitesimal transformations of group, the definitions and criteria of fractional action-like Noether symmetric transformations and quasi-symmetric transformations are put forward; finally, the fractional action-like Noether theorems for both holonomic system and nonholonomic system are established, and the relationship between the fractional action-like Noether symmetry and the conserved quantity is given.
2015, 32(4).
Abstract:
With the action of small perturbation on generalized El-Nabulsi-Birkhoff fractional equations, the perturbation to Noether symmetries and adiabatic invariants are studied under the framework of El-Nabulsi’s fractional model. Firstly, based on the invariance of El-Nabulsi-Pfaff action under the infinitesimal transformations of group, the exact invariants are given. Secondly, on the basis of the definition of higher order adiabatic invariants of a dynamical system, the adiabatic invariants of the Noether symmetric perturbation for disturbed generalized El-Nabulsi’s fractional Birkhoff system are presented under some conditions, and some special cases are discussed. Finally, an example known as Hojman-Urrutia problem is given to illustrate the application of the results.
With the action of small perturbation on generalized El-Nabulsi-Birkhoff fractional equations, the perturbation to Noether symmetries and adiabatic invariants are studied under the framework of El-Nabulsi’s fractional model. Firstly, based on the invariance of El-Nabulsi-Pfaff action under the infinitesimal transformations of group, the exact invariants are given. Secondly, on the basis of the definition of higher order adiabatic invariants of a dynamical system, the adiabatic invariants of the Noether symmetric perturbation for disturbed generalized El-Nabulsi’s fractional Birkhoff system are presented under some conditions, and some special cases are discussed. Finally, an example known as Hojman-Urrutia problem is given to illustrate the application of the results.
2015, 32(4).
Abstract:
Based on laser diffraction and Shifrin-transform, the measurement method of particle size distribution has been improved extensively. While, in real measurements, some noise peaks exist in the data of inversion and are misread as particle distribution peaks. On the other hand, the improved method used a truncation function as a filter is hard to distinguish adjacent peaks. In this paper, by introducing bimodal resolution criterion, the filter function is optimized. And a quasi truncation function with the optimized filter function is studied to achieve optimal bimodal resolution and remove noise peaks. This new quasi truncation function fits multimode distribution very well. By combining the quasi truncation function with Shifrin-transform, noise peaks are removed well and the adjacent peaks are distinguished clearly. Finally, laser diffraction experiments are applied and the particle size distribution is analyzed by applying this method. The results show that the quasi truncation function has better bimodal resolution than the truncation function. Generally, by combining the quasi truncation function with Shifrin-transform, in particle size distribution measurements with laser diffraction, the bimodal resolution is greatly increased and the noise is removed well. And our results can restore perfectly the original distribution. Therefore, the new method by combining the quasi truncation function with Shifrin-transform provides a feasible and effective way to measure the multimode particle size distribution by laser diffraction.
Based on laser diffraction and Shifrin-transform, the measurement method of particle size distribution has been improved extensively. While, in real measurements, some noise peaks exist in the data of inversion and are misread as particle distribution peaks. On the other hand, the improved method used a truncation function as a filter is hard to distinguish adjacent peaks. In this paper, by introducing bimodal resolution criterion, the filter function is optimized. And a quasi truncation function with the optimized filter function is studied to achieve optimal bimodal resolution and remove noise peaks. This new quasi truncation function fits multimode distribution very well. By combining the quasi truncation function with Shifrin-transform, noise peaks are removed well and the adjacent peaks are distinguished clearly. Finally, laser diffraction experiments are applied and the particle size distribution is analyzed by applying this method. The results show that the quasi truncation function has better bimodal resolution than the truncation function. Generally, by combining the quasi truncation function with Shifrin-transform, in particle size distribution measurements with laser diffraction, the bimodal resolution is greatly increased and the noise is removed well. And our results can restore perfectly the original distribution. Therefore, the new method by combining the quasi truncation function with Shifrin-transform provides a feasible and effective way to measure the multimode particle size distribution by laser diffraction.
2015, 32(4).
Abstract:
An iterative free-wake computational method has been developed for the prediction of aerodynamic interaction characteristics between the twin rotors of a tandem helicopter. In this method, the mutual interaction effects between twin rotors as well as the rotor and wake have been included, and a rotor wake model, blade aerodynamic model and rotor trim model have been coupled during the process of solution. A new dual-rotor trim method has been presented to be suitable for the aerodynamic interaction calculations between tandem twin rotors. By the present method, the blade aerodynamic loads and rotor performance on a tandem twin-rotor in the conditions of interactions have been calculated, and the comparisons with the available experimental data have been also made to show the capability of the present method. Then, the effects of such parameters as the longitudinal separation and axial separation between twin rotors on the aerodynamic interaction characteristics have been systematically analyzed. As a result, the conclusions which can be meaningful for guiding on structure layout of the tandem rotors have been obtained. Furthermore, the rotor performance between the tandem rotors and a single rotor has been compared, and the calculated results indicate that the strongest interaction state does not appear in the hovering state, but in low-speed forward flight state.
An iterative free-wake computational method has been developed for the prediction of aerodynamic interaction characteristics between the twin rotors of a tandem helicopter. In this method, the mutual interaction effects between twin rotors as well as the rotor and wake have been included, and a rotor wake model, blade aerodynamic model and rotor trim model have been coupled during the process of solution. A new dual-rotor trim method has been presented to be suitable for the aerodynamic interaction calculations between tandem twin rotors. By the present method, the blade aerodynamic loads and rotor performance on a tandem twin-rotor in the conditions of interactions have been calculated, and the comparisons with the available experimental data have been also made to show the capability of the present method. Then, the effects of such parameters as the longitudinal separation and axial separation between twin rotors on the aerodynamic interaction characteristics have been systematically analyzed. As a result, the conclusions which can be meaningful for guiding on structure layout of the tandem rotors have been obtained. Furthermore, the rotor performance between the tandem rotors and a single rotor has been compared, and the calculated results indicate that the strongest interaction state does not appear in the hovering state, but in low-speed forward flight state.
2015, 32(4).
Abstract:
Active front steering(AFS) can improve dynamic steering characteristic of the vehicle, but the model nonlinear and parameter decoupling control process are complex in traditional control methods. Therefore, a control method of AFS based on active disturbance rejection technique is proposed. In control method of active disturbance rejection, extended state observer (ESO) among of active disturbance rejection controller(ADRC) dynamically estimates internal and external disturbance of system according to the input and output of system, which can easily realize the model nonlinear and parameter decoupling control. The AFS controller consists of the proportional
Active front steering(AFS) can improve dynamic steering characteristic of the vehicle, but the model nonlinear and parameter decoupling control process are complex in traditional control methods. Therefore, a control method of AFS based on active disturbance rejection technique is proposed. In control method of active disturbance rejection, extended state observer (ESO) among of active disturbance rejection controller(ADRC) dynamically estimates internal and external disturbance of system according to the input and output of system, which can easily realize the model nonlinear and parameter decoupling control. The AFS controller consists of the proportional
2015, 32(4).
Abstract:
To overcome the shortcoming that the traditional minimum error threshold method can obtain satisfactory segmentation results only when the object and background of the image strictly obey a certain type of probability distribution, we propose the regularized minimum error threshold method and treat the traditional minimum error threshold method as its special case. Then we construct the discrete probability distribution by using the separation between segmentation threshold and the average gray-scale values of the object and background of the image so as to compute the information energy of the probability distribution. We investigate the impact of the regularized parameter selection on the optimal segmentation threshold of the regularized minimum error threshold method. To verify the effectiveness of our regularized minimum error threshold method, we select typical grey-scale images and perform their segmentation tests and compare the segmentation results obtained with our regularized minimum error threshold method with those obtained with the traditional minimum error threshold method respectively. The segmentation results, given in Figs. 2 through 4 and Table 1, and their analysis show that our regularized minimum error threshold method is feasible and produces more satisfactory segmentation results than the minimum error threshold method and does not exert much impact on object acquisition in case of the addition of a certain noise to an image. Therefore, our method can meet the requirements for extracting a real object in the noisy environment.
To overcome the shortcoming that the traditional minimum error threshold method can obtain satisfactory segmentation results only when the object and background of the image strictly obey a certain type of probability distribution, we propose the regularized minimum error threshold method and treat the traditional minimum error threshold method as its special case. Then we construct the discrete probability distribution by using the separation between segmentation threshold and the average gray-scale values of the object and background of the image so as to compute the information energy of the probability distribution. We investigate the impact of the regularized parameter selection on the optimal segmentation threshold of the regularized minimum error threshold method. To verify the effectiveness of our regularized minimum error threshold method, we select typical grey-scale images and perform their segmentation tests and compare the segmentation results obtained with our regularized minimum error threshold method with those obtained with the traditional minimum error threshold method respectively. The segmentation results, given in Figs. 2 through 4 and Table 1, and their analysis show that our regularized minimum error threshold method is feasible and produces more satisfactory segmentation results than the minimum error threshold method and does not exert much impact on object acquisition in case of the addition of a certain noise to an image. Therefore, our method can meet the requirements for extracting a real object in the noisy environment.
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