Transactions of Nanjing University of Aeronautics & Astronautics
Volume 34,Issue 5,2017 Table of Contents
2017, 34(5).
Abstract:
To do research on helicopter/ship dynamic interface, the method of combining steady flow and stochastic flow employed is adopted to establish a flow field model that is applicable to shipborne helicopter flight dynamics analysis. The steady flow is calculated by computational fluid dynamics (CFD) method, while the stochastic flow consists of the compensation velocity derived from ship motion and turbulence above the deck. The helicopter’s response to flow field of the article is calculated, which is compared with the calculation results of US army’s Military Specifications (MIL) model commonly used in engineering, verifying the accuracy of the proposed flow field model. Meanwhile, it also shows the flow field model established in this article is more appliable to flight dynamics analysis of shipborne helicopter. Based on the basis, simulate ship deck flow field in different sea conditions by adjusting the wind speed on the deck, mother ship movement and shipboard turbulence, etc. and calculate helicopter angular rate response. The results show that the difference of dynamic stability between helicopter’s roll and pitch results in that the influence on the helicopter’s roll angular rate response is greater than pitch angular rate; The frequency and amplitude of mother ship roll motion is much greater than those of pitch motion and the disturbance caused by roll motion on the air has greater influence on the helicopter response. The shipboard turbulence is the main disturbance factor that influences helicopter flight stability and its intensity determines the amplitudes of angular rate response.
To do research on helicopter/ship dynamic interface, the method of combining steady flow and stochastic flow employed is adopted to establish a flow field model that is applicable to shipborne helicopter flight dynamics analysis. The steady flow is calculated by computational fluid dynamics (CFD) method, while the stochastic flow consists of the compensation velocity derived from ship motion and turbulence above the deck. The helicopter’s response to flow field of the article is calculated, which is compared with the calculation results of US army’s Military Specifications (MIL) model commonly used in engineering, verifying the accuracy of the proposed flow field model. Meanwhile, it also shows the flow field model established in this article is more appliable to flight dynamics analysis of shipborne helicopter. Based on the basis, simulate ship deck flow field in different sea conditions by adjusting the wind speed on the deck, mother ship movement and shipboard turbulence, etc. and calculate helicopter angular rate response. The results show that the difference of dynamic stability between helicopter’s roll and pitch results in that the influence on the helicopter’s roll angular rate response is greater than pitch angular rate; The frequency and amplitude of mother ship roll motion is much greater than those of pitch motion and the disturbance caused by roll motion on the air has greater influence on the helicopter response. The shipboard turbulence is the main disturbance factor that influences helicopter flight stability and its intensity determines the amplitudes of angular rate response.
2017, 34(5).
Abstract:
In order to simulate and analysis the dynamic characteristics of the parachute from Advanced Tactical Parachute System (ATPS), the nonlinear finite element algorithm and preconditioning finite volume method are employed and coded to construct three dimensional parachute fluid-structure interaction (FSI) model. Parachute fabric material are represented by membrane-cable elements, geometrical nonlinear algorithm is employed with wrinkling technique embedded to simulate large deformations of parachute structure by applying Newton-Raphson iteration method. On the other hand, the time-dependent flow surrounding parachute canopy is simulated by using preconditioned Lower-Upper Symmetric Gauss-Seidel (LU-SGS) method. The pseudo solid dynamic mesh algorithm is coded to update the flow field mesh based on the complex and arbitrary motion of parachute canopy. Due to the large amount of computation during FSI simulation, MPI parallel computation technique has been developed for all those three modules to improve the performance of this FSI code. The FSI code has been tested to simulate one kind of ATPS parachutes to predict the parachute configuration and anticipate the parachute descent speeds. The comparison of results between this code and former literature demonstrated this code to be a useful tool for parachute designers.
In order to simulate and analysis the dynamic characteristics of the parachute from Advanced Tactical Parachute System (ATPS), the nonlinear finite element algorithm and preconditioning finite volume method are employed and coded to construct three dimensional parachute fluid-structure interaction (FSI) model. Parachute fabric material are represented by membrane-cable elements, geometrical nonlinear algorithm is employed with wrinkling technique embedded to simulate large deformations of parachute structure by applying Newton-Raphson iteration method. On the other hand, the time-dependent flow surrounding parachute canopy is simulated by using preconditioned Lower-Upper Symmetric Gauss-Seidel (LU-SGS) method. The pseudo solid dynamic mesh algorithm is coded to update the flow field mesh based on the complex and arbitrary motion of parachute canopy. Due to the large amount of computation during FSI simulation, MPI parallel computation technique has been developed for all those three modules to improve the performance of this FSI code. The FSI code has been tested to simulate one kind of ATPS parachutes to predict the parachute configuration and anticipate the parachute descent speeds. The comparison of results between this code and former literature demonstrated this code to be a useful tool for parachute designers.
2017, 34(5).
Abstract:
In this paper, numerical simulations are presented about the effects of gas rarefaction on hypersonic flow field. Due to the extremely difficult experiment, limited wind-tunnel conditions and high costs, most problems in rarefied flow regime are investigated through numerical methods, in which the Direct Simulation Monte Carlo method (DSMC) is widely used. And the unstructured DSMC method is employed here. Flows around a 2D vertical plate at a given velocity 7500m/s are simulated. For gas rarefaction is judged by the free-stream Knudsen number Kn, two vital factors are considered: molecular number density and the plate’s length. Cases in which Kn varies from 0.035 to 13.36 are simulated. Flow characters in the whole rarefied regime are described, and flow field structure affected by Kn is anaylyzed. Then, the dimensionless position D* of a certain velocity in the stagnation line is chosen as the marker of flow field to measure its variation. Through flow field tracing and least-square numerical method analyzing, it is proved that hypersonic rarefied flow field expands outward linearly with the increase of the square of Kn. At last, an empirical method is established, which can be used for the prediction of the hypersonic flow field structure at a given inflow velocity, especially the shock wave position.
In this paper, numerical simulations are presented about the effects of gas rarefaction on hypersonic flow field. Due to the extremely difficult experiment, limited wind-tunnel conditions and high costs, most problems in rarefied flow regime are investigated through numerical methods, in which the Direct Simulation Monte Carlo method (DSMC) is widely used. And the unstructured DSMC method is employed here. Flows around a 2D vertical plate at a given velocity 7500m/s are simulated. For gas rarefaction is judged by the free-stream Knudsen number Kn, two vital factors are considered: molecular number density and the plate’s length. Cases in which Kn varies from 0.035 to 13.36 are simulated. Flow characters in the whole rarefied regime are described, and flow field structure affected by Kn is anaylyzed. Then, the dimensionless position D* of a certain velocity in the stagnation line is chosen as the marker of flow field to measure its variation. Through flow field tracing and least-square numerical method analyzing, it is proved that hypersonic rarefied flow field expands outward linearly with the increase of the square of Kn. At last, an empirical method is established, which can be used for the prediction of the hypersonic flow field structure at a given inflow velocity, especially the shock wave position.
2017, 34(5).
Abstract:
Mathematical model of cross type multi-stream plate-fin heat exchanger was established. Meanwhile mean square error of accumulative heat load was normalized by dimensionless, and the equations of temperature-difference uniformity factor were improved. Evaluation factors above and performance of heat exchanger were compared and analyzed by taking aircraft three-stream condenser as an example. The results demonstrate that the mean square error of accumulative heat load is common result of total heat load and excess heat load between passages. So it can be influenced by passage arrangement, flow inlet parameters as well as flow patterns. Dimensionless parameter of mean square error of accumulative heat load can reflect the influence of passage arrangement to heat exchange performance and will not change dramatically with the variation of flow inlet parameters and flow patterns. Temperature-difference uniformity factor is influenced by passage arrangement and flow patterns. It remains basically unchanged under a certain range of flow inlet parameters.
Mathematical model of cross type multi-stream plate-fin heat exchanger was established. Meanwhile mean square error of accumulative heat load was normalized by dimensionless, and the equations of temperature-difference uniformity factor were improved. Evaluation factors above and performance of heat exchanger were compared and analyzed by taking aircraft three-stream condenser as an example. The results demonstrate that the mean square error of accumulative heat load is common result of total heat load and excess heat load between passages. So it can be influenced by passage arrangement, flow inlet parameters as well as flow patterns. Dimensionless parameter of mean square error of accumulative heat load can reflect the influence of passage arrangement to heat exchange performance and will not change dramatically with the variation of flow inlet parameters and flow patterns. Temperature-difference uniformity factor is influenced by passage arrangement and flow patterns. It remains basically unchanged under a certain range of flow inlet parameters.
2017, 34(5).
Abstract:
A rotor dynamic model is built up for investigating the effects of tightening torque on dynamic characteristics of low pressure rotors connected by a spline coupling. The experimental rotor system is established using a fluted disk and a speed sensor which is applied in an actual aero engine for speed measurement. Through simulating calculation and experiments, the effects of tightening torque on the dynamic characteristics of the rotor system connected by a spline coupling including critical speeds, vibration modes and unbalance responses are analyzed. The results suggest that when increasing the tightening torque, the first two critical speeds and the amplitudes of unbalance response gradually increase in varying degrees while the vibration modes are essentially unchanged. In addition, changing axial and circumferential positions of the mass unbalance can lead to various amplitudes of unbalance response and even the rates of change.
A rotor dynamic model is built up for investigating the effects of tightening torque on dynamic characteristics of low pressure rotors connected by a spline coupling. The experimental rotor system is established using a fluted disk and a speed sensor which is applied in an actual aero engine for speed measurement. Through simulating calculation and experiments, the effects of tightening torque on the dynamic characteristics of the rotor system connected by a spline coupling including critical speeds, vibration modes and unbalance responses are analyzed. The results suggest that when increasing the tightening torque, the first two critical speeds and the amplitudes of unbalance response gradually increase in varying degrees while the vibration modes are essentially unchanged. In addition, changing axial and circumferential positions of the mass unbalance can lead to various amplitudes of unbalance response and even the rates of change.
2017, 34(5).
Abstract:
ME-wheel is a new type of non-inflatable safety tyre, and the structure is significantly different from traditional pneumatic tyre. In order to investigate cornering properties of mechanical elastic wheel (ME-wheel), experimental research on mechanics characteristics of ME-wheel under steady-state cornering conditions were carried out. The test of steady-state cornering properties of ME-wheel at different experimental parameters conditions was conducted by test bench about dynamic mechanical properties of tyre. Cornering properties curves were used to analyze the steady-state cornering properties of ME-wheel, namely the variation tendency of lateral force or aligning torque with the increase of side-slip angle. Moreover, evaluation indexes for cornering properties of ME-wheel were picked up and effect of different experimental parameters (including vertical load, friction coefficient, and speed) on cornering properties of ME-wheel was contrastively analyzed. The research in this paper could provide certain reference to facilitate structure parameters and cornering properties optimizing process of ME-wheel.
ME-wheel is a new type of non-inflatable safety tyre, and the structure is significantly different from traditional pneumatic tyre. In order to investigate cornering properties of mechanical elastic wheel (ME-wheel), experimental research on mechanics characteristics of ME-wheel under steady-state cornering conditions were carried out. The test of steady-state cornering properties of ME-wheel at different experimental parameters conditions was conducted by test bench about dynamic mechanical properties of tyre. Cornering properties curves were used to analyze the steady-state cornering properties of ME-wheel, namely the variation tendency of lateral force or aligning torque with the increase of side-slip angle. Moreover, evaluation indexes for cornering properties of ME-wheel were picked up and effect of different experimental parameters (including vertical load, friction coefficient, and speed) on cornering properties of ME-wheel was contrastively analyzed. The research in this paper could provide certain reference to facilitate structure parameters and cornering properties optimizing process of ME-wheel.
2017, 34(5).
Abstract:
A combined arrival and departure scheduling is investigated for multi-airport system to alleviate the problem of airspace congestion and flight delay. Firstly, the scheduling problem for multi-airport system is defined through in-depth analysis of the characteristics of arrival and departure operations. Then, lots of constraints are taken into account, such as wake vortex separation, transfer separation, release separation, and operational separation in different modes of multiple runway operations. Furthermore, the scheduling model is constructed and improved simulated annealing algorithm is proposed by minimizing the total delay. Finally, Shanghai multi-airport system is chosen to conduct the simulation and validation. The simulation results indicate that the proposed method is able to effectively improve the operational efficiency of arrivals and departures for multi-airport system.
A combined arrival and departure scheduling is investigated for multi-airport system to alleviate the problem of airspace congestion and flight delay. Firstly, the scheduling problem for multi-airport system is defined through in-depth analysis of the characteristics of arrival and departure operations. Then, lots of constraints are taken into account, such as wake vortex separation, transfer separation, release separation, and operational separation in different modes of multiple runway operations. Furthermore, the scheduling model is constructed and improved simulated annealing algorithm is proposed by minimizing the total delay. Finally, Shanghai multi-airport system is chosen to conduct the simulation and validation. The simulation results indicate that the proposed method is able to effectively improve the operational efficiency of arrivals and departures for multi-airport system.
2017, 34(5).
Abstract:
Ti2AlNb intermetallic alloy is a newly developed high-temperature resistant structural material due to its excellent material and mechanical properties, which also make it to be one of the most difficult-to-cut materials. In order to investigate the machinability of Ti2AlNb alloy, a series of turning experiments of Ti2AlNb alloy with varying cutting speed and feed rate using coated carbide tools were carried out. The results associated with cutting forces, cutting temperature and tool wear are presented and discussed. Moreover, the cutting performance of Ti2AlNb alloy is evaluated in comparison with that of most commonly used Ti6Al4V and Inconel 718 alloy in terms of the cutting forces and cutting temperature. Considering material removal rate and tool life, the optimized machining parameters (cutting speed v=40-50m/min, feed rate f=0.08-0.1mm/rev)for cutting Ti2AlNb alloys using coated carbide tools are recommended.
Ti2AlNb intermetallic alloy is a newly developed high-temperature resistant structural material due to its excellent material and mechanical properties, which also make it to be one of the most difficult-to-cut materials. In order to investigate the machinability of Ti2AlNb alloy, a series of turning experiments of Ti2AlNb alloy with varying cutting speed and feed rate using coated carbide tools were carried out. The results associated with cutting forces, cutting temperature and tool wear are presented and discussed. Moreover, the cutting performance of Ti2AlNb alloy is evaluated in comparison with that of most commonly used Ti6Al4V and Inconel 718 alloy in terms of the cutting forces and cutting temperature. Considering material removal rate and tool life, the optimized machining parameters (cutting speed v=40-50m/min, feed rate f=0.08-0.1mm/rev)for cutting Ti2AlNb alloys using coated carbide tools are recommended.
2017, 34(5).
Abstract:
In this paper, a new third-order optimized symmetric weighted essentially non-oscillatory (WENO-OS3) scheme is used to simulate the hypersonic shock wave/boundary layer interactions. Firstly, the scheme is presented with the achievement of low dissipation in smooth region and robust shock-capturing capabilities in discontinuities. The Maxwell slip boundary conditions are employed to consider the rarefied effect near the surface. Next, several validating tests are given to show the good resolution of the WENO-OS3 scheme and the feasibility of the Maxwell slip boundary conditions. Finally, hypersonic flows around the hollow cylinder truncated flare and the 25o/55o sharp double cone are studied. Discussions are made on the characteristics of the hypersonic shock wave/boundary layer interactions with and without the consideration of the slip effect. The results indicate that the scheme has a good capability on predicting heat transfer and a high resolution on describing fluid structures. With the slip boundary conditions, the separation region at the corner is smaller and the prediction is more accurate than that with no-slip boundary conditions.
In this paper, a new third-order optimized symmetric weighted essentially non-oscillatory (WENO-OS3) scheme is used to simulate the hypersonic shock wave/boundary layer interactions. Firstly, the scheme is presented with the achievement of low dissipation in smooth region and robust shock-capturing capabilities in discontinuities. The Maxwell slip boundary conditions are employed to consider the rarefied effect near the surface. Next, several validating tests are given to show the good resolution of the WENO-OS3 scheme and the feasibility of the Maxwell slip boundary conditions. Finally, hypersonic flows around the hollow cylinder truncated flare and the 25o/55o sharp double cone are studied. Discussions are made on the characteristics of the hypersonic shock wave/boundary layer interactions with and without the consideration of the slip effect. The results indicate that the scheme has a good capability on predicting heat transfer and a high resolution on describing fluid structures. With the slip boundary conditions, the separation region at the corner is smaller and the prediction is more accurate than that with no-slip boundary conditions.
10 Practical Survey on Design and Testing of Flight Control Laws on Helicopter Engineering Simulators
2017, 34(5).
Abstract:
A practical survey on engineering implementation of flight control laws on helicopter engineering simulators is proposed. Advances of helicopter engineering simulators are introduced. Practical flight control technologies are reviewed，with an emphasis on discussing the corresponding engineering simulation programs. Finally, the difficulties of implementing advanced control technologies are addressed, and the future development of helicopter engineering simulators are highlighted.
A practical survey on engineering implementation of flight control laws on helicopter engineering simulators is proposed. Advances of helicopter engineering simulators are introduced. Practical flight control technologies are reviewed，with an emphasis on discussing the corresponding engineering simulation programs. Finally, the difficulties of implementing advanced control technologies are addressed, and the future development of helicopter engineering simulators are highlighted.
2017, 34(5).
Abstract:
Hot forming with synchronous cooling (HFSC) is a novel technique for heat-treatable, high-strength aluminum alloys, which allows the alloys to acquire good formability, negligible springback, rapid processing and better mechanical properties. However, the deformation behavior and microstructure evolution of the alloys during HFSC are complex and need to be studied due to the temperature effects and strain rate effects. Uniaxial tensile tests in a temperature range of 250-450℃ and a strain rate range of 0.01-1/s for AA2024-H18 aluminum alloy sheet were conducted with a Gleeble-3500 Thermal-Mechanical Simulation Tester. And based on metallography observation and analysis, AA2024-H18 aluminum alloy sheet in HSFC process exhibits hardening and dynamic recovery behaviors within the temperature range of 250-450℃. Strain rate showed different effects on ductility at different temperatures. Compared with traditional warm/hot forming methods, AA2024-H18 aluminum alloy achieved a better work-hardening result through HFSC operations, which promises an improved formability at elevated temperature and thus good mechanical properties of final part. After HSFC operations, the microstructure of the specimens is composed of elongated static recrystallization grain.
Hot forming with synchronous cooling (HFSC) is a novel technique for heat-treatable, high-strength aluminum alloys, which allows the alloys to acquire good formability, negligible springback, rapid processing and better mechanical properties. However, the deformation behavior and microstructure evolution of the alloys during HFSC are complex and need to be studied due to the temperature effects and strain rate effects. Uniaxial tensile tests in a temperature range of 250-450℃ and a strain rate range of 0.01-1/s for AA2024-H18 aluminum alloy sheet were conducted with a Gleeble-3500 Thermal-Mechanical Simulation Tester. And based on metallography observation and analysis, AA2024-H18 aluminum alloy sheet in HSFC process exhibits hardening and dynamic recovery behaviors within the temperature range of 250-450℃. Strain rate showed different effects on ductility at different temperatures. Compared with traditional warm/hot forming methods, AA2024-H18 aluminum alloy achieved a better work-hardening result through HFSC operations, which promises an improved formability at elevated temperature and thus good mechanical properties of final part. After HSFC operations, the microstructure of the specimens is composed of elongated static recrystallization grain.
2017, 34(5).
Abstract:
Wireless interrogation of rectangular micro-strip patch antenna for strain measurement was investigated by simulations. In order to analyze the antenna performance, a micro-strip line-feeding patch antenna at 10GHz was designed. Then, a patch antenna wirelessly fed by a horn was proposed to measure the strain. The direction information of strain detected by the patch antenna was also taken into consideration. Moreover, the strain can be detected both in width and length direction. It is shown that the strain can be measured wirelessly using a standard horn antenna. This kind of wireless strain sensing technique offers a significant potential for wireless structural health monitoring (SHM), especially for high-end equipment.
Wireless interrogation of rectangular micro-strip patch antenna for strain measurement was investigated by simulations. In order to analyze the antenna performance, a micro-strip line-feeding patch antenna at 10GHz was designed. Then, a patch antenna wirelessly fed by a horn was proposed to measure the strain. The direction information of strain detected by the patch antenna was also taken into consideration. Moreover, the strain can be detected both in width and length direction. It is shown that the strain can be measured wirelessly using a standard horn antenna. This kind of wireless strain sensing technique offers a significant potential for wireless structural health monitoring (SHM), especially for high-end equipment.
2017, 34(5).
Abstract:
The subsurface damage (SSD) layers of monocrystalline germanium wafers lapped by three different ways were measured and compared by the method of nanoindentation and micro morphology. Three ways such as ice-fixed abrasive, thermosetting fixed abrasive and free abrasive lapping were used to lap monocrystalline germanium wafers. The SSD depth was measured by a nanoindenter, and the subsurface morphology of SSD layer was observed by an atomic force microscope. The results show that the SSD layer of monocrystalline germanium wafer is mainly composed of soft corrosion layer and plastic scratch and crack growth layer. Compared with thermosetting fixed abrasive and free abrasive lapping, the SSD depth lapped with ice-fixed abrasive is shallower. Moreover, the SSD morphology of monocrystalline germanium wafer lapped with ice-fixed abrasive is superior to those of two other processing methods.
The subsurface damage (SSD) layers of monocrystalline germanium wafers lapped by three different ways were measured and compared by the method of nanoindentation and micro morphology. Three ways such as ice-fixed abrasive, thermosetting fixed abrasive and free abrasive lapping were used to lap monocrystalline germanium wafers. The SSD depth was measured by a nanoindenter, and the subsurface morphology of SSD layer was observed by an atomic force microscope. The results show that the SSD layer of monocrystalline germanium wafer is mainly composed of soft corrosion layer and plastic scratch and crack growth layer. Compared with thermosetting fixed abrasive and free abrasive lapping, the SSD depth lapped with ice-fixed abrasive is shallower. Moreover, the SSD morphology of monocrystalline germanium wafer lapped with ice-fixed abrasive is superior to those of two other processing methods.
2017, 34(5).
Abstract:
—Based on the current distribution on the parallel microstrip lines and emission cancellation characteristic of close equal and opposite currents, a novel balun structure for dipole antenna is proposed. In this paper, the principle of the balun structure is elaborated and verified. Then a dipole antenna with resonance at 2.45GHz constructed with the balun is fabricated and measured. The simulated and measured reaction coefficient(S11) of the antenna are in good agreement over 2~3GH. The relative bandwidth with S11 of below -10dB is more than 25%. The antenna also shows a good radiation pattern at 2.45GHz. The structure can provide a new balun design method for dipole antennas.
—Based on the current distribution on the parallel microstrip lines and emission cancellation characteristic of close equal and opposite currents, a novel balun structure for dipole antenna is proposed. In this paper, the principle of the balun structure is elaborated and verified. Then a dipole antenna with resonance at 2.45GHz constructed with the balun is fabricated and measured. The simulated and measured reaction coefficient(S11) of the antenna are in good agreement over 2~3GH. The relative bandwidth with S11 of below -10dB is more than 25%. The antenna also shows a good radiation pattern at 2.45GHz. The structure can provide a new balun design method for dipole antennas.
15 Practical Survey on Design and Testing of Flight Control Laws for Helicopter Engineering Simulators
2017, 34(5):465-476.
DOI: 10.16356/j.1005-1120.2017.05.465
Abstract:
A practical survey on engineering implementation of flight control laws on helicopter engineering simulators is proposed. Advances of helicopter engineering simulators are introduced. Practical flight control technologies are reviewed，with an emphasis on discussing the corresponding engineering simulation programs. Finally, the difficulties of implementing advanced control technologies are addressed, and the future development of helicopter engineering simulators are highlighted.
A practical survey on engineering implementation of flight control laws on helicopter engineering simulators is proposed. Advances of helicopter engineering simulators are introduced. Practical flight control technologies are reviewed，with an emphasis on discussing the corresponding engineering simulation programs. Finally, the difficulties of implementing advanced control technologies are addressed, and the future development of helicopter engineering simulators are highlighted.
2017, 34(5):477-486.
DOI: 10.16356/j.1005-1120.2017.05.477
Abstract:
Wireless interrogation of a rectangular microstrip patch antenna for strain measurement is investigated by simulations. To analyze the antenna performance, a microstrip linefeeding patch antenna at 10 GHz is designed. A patch antenna wirelessly fed by a horn is proposed to measure the strain. The direction information of strain detected by the patch antenna is also considered. The strain can be detected both in the width and length directions. It is shown that the strain can be measured wirelessly using a standard horn antenna. This kind of wireless strainsensing technique offers significant potential for wireless structural health monitoring (SHM), especially for highend equipment.
Wireless interrogation of a rectangular microstrip patch antenna for strain measurement is investigated by simulations. To analyze the antenna performance, a microstrip linefeeding patch antenna at 10 GHz is designed. A patch antenna wirelessly fed by a horn is proposed to measure the strain. The direction information of strain detected by the patch antenna is also considered. The strain can be detected both in the width and length directions. It is shown that the strain can be measured wirelessly using a standard horn antenna. This kind of wireless strainsensing technique offers significant potential for wireless structural health monitoring (SHM), especially for highend equipment.
2017, 34(5):487-495.
DOI: 10.16356/j.1005-1120.2017.05.487
Abstract:
Ti2AlNb intermetallic alloy is a newly developed hightemperature resistant structural material due to its excellent material and mechanical properties, which also make it to be one of the most difficult-to-cut materials. In order to study the machinability of Ti2AlNb alloy, a series of turning experiments of Ti2AlNb alloy with varying cutting speed and feed rate using coated carbide tools are carried out. The results associated with cutting forces, cutting temperature and tool wear are presented and discussed. Moreover, the cutting performance of Ti2AlNb alloy is evaluated in comparison with that of most commonly used Ti6Al4V and Inconel 718 alloys in terms of the cutting forces and cutting temperature. The comparison results show that there is a correlation between the machinability and the mechanical properties of work material properties. Additionally, considering mat erial removal rate and tool life, the optimized machining parameters for cutting Ti2AlNb alloys using coated carbide tools are recommended.
Ti2AlNb intermetallic alloy is a newly developed hightemperature resistant structural material due to its excellent material and mechanical properties, which also make it to be one of the most difficult-to-cut materials. In order to study the machinability of Ti2AlNb alloy, a series of turning experiments of Ti2AlNb alloy with varying cutting speed and feed rate using coated carbide tools are carried out. The results associated with cutting forces, cutting temperature and tool wear are presented and discussed. Moreover, the cutting performance of Ti2AlNb alloy is evaluated in comparison with that of most commonly used Ti6Al4V and Inconel 718 alloys in terms of the cutting forces and cutting temperature. The comparison results show that there is a correlation between the machinability and the mechanical properties of work material properties. Additionally, considering mat erial removal rate and tool life, the optimized machining parameters for cutting Ti2AlNb alloys using coated carbide tools are recommended.
2017, 34(5):496-503.
DOI: 10.16356/j.1005-1120.2017.05.496
Abstract:
The subsurface damage (SSD) layers of monocrystalline germanium wafers lapped by three different ways were measured and compared by the method of nanoindentation and micro morphology. Three ways such as icefixed abrasive,thermosetting fixed abrasive and free abrasive lappings are adopted to lap monocrystalline germanium wafers. The SSD depth was measured by a nanoindenter, and the morphology of SSD layer was observed by an atomic force microscopy(AFM). The results show that the SSD layer of monocrystalline germanium wafer is mainly composed of soft corrosion layer and plastic scratch and crack growth layer. Compared with thermosetting fixed abrasive and free abrasive lappings, the SSD depth lapped with icefixed abrasive is shallower. Moreover, the SSD morphology of monocrystalline germanium wafer lapped with ice-fixed abrasive is superior to those of two other processing ways.
The subsurface damage (SSD) layers of monocrystalline germanium wafers lapped by three different ways were measured and compared by the method of nanoindentation and micro morphology. Three ways such as icefixed abrasive,thermosetting fixed abrasive and free abrasive lappings are adopted to lap monocrystalline germanium wafers. The SSD depth was measured by a nanoindenter, and the morphology of SSD layer was observed by an atomic force microscopy(AFM). The results show that the SSD layer of monocrystalline germanium wafer is mainly composed of soft corrosion layer and plastic scratch and crack growth layer. Compared with thermosetting fixed abrasive and free abrasive lappings, the SSD depth lapped with icefixed abrasive is shallower. Moreover, the SSD morphology of monocrystalline germanium wafer lapped with ice-fixed abrasive is superior to those of two other processing ways.
2017, 34(5):504-513.
DOI: 10.16356/j.1005-1120.2017.05.504
Abstract:
Hot forming with synchronous cooling (HFSC) is a novel technique for heat-treatable, high-strength aluminum alloys, which allows the alloys to acquire good formability, negligible springback, rapid processing and better mechanical properties.However, the deformation behavior and microstructure evolution of the alloys during HFSC are complex and need to be studied due to the temperature and strain rate effects. Uniaxial tensile tests in a temperature range of 250—450 ℃ and a strain rate range of 0.01—1s for AA2024-H18 aluminum alloy sheet are conducted with a Gleeble3500 ThermalMechanical Simulation Tester. And based on metallography observation and analysis, AA2024H18 aluminum alloy sheet in HSFC process exhibits hardening and dynamic recovery behaviors within the temperature range of 250—450 ℃. Strainrate shows different effects on ductility at different temperatures. Compared with traditional warm/hot forming methods, AA2024-H18 aluminum alloy achieves a better workhardening result through HFSC operations, which promises an improved formability at elevated temperature and thus good mechanical properties of final part. After HSFC operations, the microstructure of the specimens is composed of elongated static recrystallization grain.
Hot forming with synchronous cooling (HFSC) is a novel technique for heat-treatable, high-strength aluminum alloys, which allows the alloys to acquire good formability, negligible springback, rapid processing and better mechanical properties.However, the deformation behavior and microstructure evolution of the alloys during HFSC are complex and need to be studied due to the temperature and strain rate effects. Uniaxial tensile tests in a temperature range of 250—450 ℃ and a strain rate range of 0.01—1s for AA2024-H18 aluminum alloy sheet are conducted with a Gleeble3500 ThermalMechanical Simulation Tester. And based on metallography observation and analysis, AA2024H18 aluminum alloy sheet in HSFC process exhibits hardening and dynamic recovery behaviors within the temperature range of 250—450 ℃. Strainrate shows different effects on ductility at different temperatures. Compared with traditional warm/hot forming methods, AA2024-H18 aluminum alloy achieves a better workhardening result through HFSC operations, which promises an improved formability at elevated temperature and thus good mechanical properties of final part. After HSFC operations, the microstructure of the specimens is composed of elongated static recrystallization grain.
2017, 34(5):514-523.
DOI: 10.16356/j.1005-1120.2017.05.514
Abstract:
A rotor dynamic model is built up for investigating the effects of tightening torque on dynamic characteristics of low pressure rotors connected by a spline coupling. The experimental rotor system is established using a fluted disk and a speed sensor which is applied in an actual aero engine for speed measurement. Through simulating calculation and experiments, the effects of tightening torque on the dynamic characteristics of the rotor system connected by a spline coupling including critical speeds, vibration modes and unbalance responses are analyzed. The results show that when increasing the tightening torque, the first two critical speeds and the amplitudes of unbalance response gradually increase in varying degrees while the vibration modes are essentially unchanged. In addition, changing axial and circumferential positions of the mass unbalance can lead to various amplitudes of unbalance response and even the rates of change.
A rotor dynamic model is built up for investigating the effects of tightening torque on dynamic characteristics of low pressure rotors connected by a spline coupling. The experimental rotor system is established using a fluted disk and a speed sensor which is applied in an actual aero engine for speed measurement. Through simulating calculation and experiments, the effects of tightening torque on the dynamic characteristics of the rotor system connected by a spline coupling including critical speeds, vibration modes and unbalance responses are analyzed. The results show that when increasing the tightening torque, the first two critical speeds and the amplitudes of unbalance response gradually increase in varying degrees while the vibration modes are essentially unchanged. In addition, changing axial and circumferential positions of the mass unbalance can lead to various amplitudes of unbalance response and even the rates of change.
21 Hypersonic Shock Wave/Boundary Layer Interactions by a Third-Order Optimized Symmetric WENO Scheme
2017, 34(5):524-534.
DOI: 10.16356/j.1005-1120.2017.05.524
Abstract:
A novel thirdorder optimized symmetric weighted essentially nonoscillatory (WENO-OS3) scheme is used to simulate the hypersonic shock wave/boundary layer interactions. Firstly, the scheme is presented with the achievement of low dissipation in smooth region and robust shockcapturing capabilities in discontinuities. The Maxwell slip boundary conditions are employed to consider the rarefied effect near the surface. Secondly, several validating tests are given to show the good resolution of the WENO-OS3 scheme and the feasibility of the Maxwell slip boundary conditions. Finally, hypersonic flows around the hollow cylinder truncated flare (HCTF) and the 25°/55° sharp double cone are studied. Discussions are made on the characteristics of the hypersonic shock wave/boundary layer interactions with and without the consideration of the slip effect. The results indicate that the scheme has a good capability in predicting heat transfer with a high resolution for describing fluid structures. With the slip boundary conditions, the separation region at the corner is smaller and the prediction is more accurate than that with noslip boundary conditions.
A novel thirdorder optimized symmetric weighted essentially nonoscillatory (WENO-OS3) scheme is used to simulate the hypersonic shock wave/boundary layer interactions. Firstly, the scheme is presented with the achievement of low dissipation in smooth region and robust shockcapturing capabilities in discontinuities. The Maxwell slip boundary conditions are employed to consider the rarefied effect near the surface. Secondly, several validating tests are given to show the good resolution of the WENO-OS3 scheme and the feasibility of the Maxwell slip boundary conditions. Finally, hypersonic flows around the hollow cylinder truncated flare (HCTF) and the 25°/55° sharp double cone are studied. Discussions are made on the characteristics of the hypersonic shock wave/boundary layer interactions with and without the consideration of the slip effect. The results indicate that the scheme has a good capability in predicting heat transfer with a high resolution for describing fluid structures. With the slip boundary conditions, the separation region at the corner is smaller and the prediction is more accurate than that with noslip boundary conditions.
2017, 34(5):535-542.
DOI: 10.16356/j.1005-1120.2017.05.535
Abstract:
In order to simulate and analyze the dynamic characteristics of the parachute from advanced tactical parachute system (ATPS), a nonlinear finite element algorithm and a preconditioning finite volume method are employed and developed to construct three dimensional parachute fluid-structure interaction (FSI) model. Parachute fabric material is represented by membrane-cable elements, and geometrical nonlinear algorithm is employed with wrinkling technique embedded to simulate the large deformations of parachute structure by applying the Newton-Raphson iteration method. On the other hand, the time-dependent flow surrounding parachute canopy is simulated using preconditioned lower-upper symmetric Gauss-Seidel (LU-SGS) method. The pseudo solid dynamic mesh algorithm is employed to update the flow-field mesh based on the complex and arbitrary motion of parachute canopy. Due to the large amount of computation during the FSI simulation, massage passing interface(MPI) parallel computation technique is used for all those three modules to improve the performance of the FSI code. The FSI method is tested to simulate one kind of ATPS parachutes to predict the parachute configuration and anticipate the parachute descent speeds. The comparison of results between the proposed method and those in literatures demonstrates the method to be a useful tool for parachute designers.
In order to simulate and analyze the dynamic characteristics of the parachute from advanced tactical parachute system (ATPS), a nonlinear finite element algorithm and a preconditioning finite volume method are employed and developed to construct three dimensional parachute fluid-structure interaction (FSI) model. Parachute fabric material is represented by membrane-cable elements, and geometrical nonlinear algorithm is employed with wrinkling technique embedded to simulate the large deformations of parachute structure by applying the Newton-Raphson iteration method. On the other hand, the time-dependent flow surrounding parachute canopy is simulated using preconditioned lower-upper symmetric Gauss-Seidel (LU-SGS) method. The pseudo solid dynamic mesh algorithm is employed to update the flow-field mesh based on the complex and arbitrary motion of parachute canopy. Due to the large amount of computation during the FSI simulation, massage passing interface(MPI) parallel computation technique is used for all those three modules to improve the performance of the FSI code. The FSI method is tested to simulate one kind of ATPS parachutes to predict the parachute configuration and anticipate the parachute descent speeds. The comparison of results between the proposed method and those in literatures demonstrates the method to be a useful tool for parachute designers.
2017, 34(5):543-552.
DOI: 10.16356/j.1005-1120.2017.05.543
Abstract:
Numerical simulations are presented about the effects of gas rarefaction on hypersonic flow field. Due to the extremely difficult experiment, limited wind-tunnel conditions and high cost, most problems in rarefied flow regime are investigated through numerical methods, in which the direct simulation Monte-Carlo (DSMC) method is widely adopted. And the unstructured DSMC method is employed here. Flows around a vertical plate at a given velocity 7 500 m/s are simulated. For gas rarefaction is judged by the free-stream Knudsen number (Kn), two vital factors are considered: molecular number density and the plate′s length. Cases in which Knvaries from 0.035 to 13.36 are simulated. Flow characters in the whole rarefied regime are described, and flow-field structure affected by Kn is analyzed. Then, the dimensionless position D* of a certain velocity in the stagnation line is chosen as the marker of flow field to measure its variation. Through flow-field tracing and least-square numerical method analyzing, it is proved that hypersonic rarefied flow field expands outward linearly with the increase of √Kn. An empirical method is proposed, which can be used for the prediction of the hypersonic flow-field structure at a given inflow velocity, especially the shock wave position.
Numerical simulations are presented about the effects of gas rarefaction on hypersonic flow field. Due to the extremely difficult experiment, limited wind-tunnel conditions and high cost, most problems in rarefied flow regime are investigated through numerical methods, in which the direct simulation Monte-Carlo (DSMC) method is widely adopted. And the unstructured DSMC method is employed here. Flows around a vertical plate at a given velocity 7 500 m/s are simulated. For gas rarefaction is judged by the free-stream Knudsen number (Kn), two vital factors are considered: molecular number density and the plate′s length. Cases in which Knvaries from 0.035 to 13.36 are simulated. Flow characters in the whole rarefied regime are described, and flow-field structure affected by Kn is analyzed. Then, the dimensionless position D* of a certain velocity in the stagnation line is chosen as the marker of flow field to measure its variation. Through flow-field tracing and least-square numerical method analyzing, it is proved that hypersonic rarefied flow field expands outward linearly with the increase of √Kn. An empirical method is proposed, which can be used for the prediction of the hypersonic flow-field structure at a given inflow velocity, especially the shock wave position.
2017, 34(5):553-560.
DOI: 10.16356/j.1005-1120.2017.05.553
Abstract:
Mathematical model of cross type multi-stream plate-fin heat exchanger is established. Meanwhile, mean square error of accumulative heat load is normalized by dimensionless,and the equations of temperature-difference uniformity factor are improved. Evaluation factors above and performance of heat exchanger are compared and analyzed by taking aircraft three-stream condenser as an example. The results demonstrate that the mean square error of accumulative heat load is common result of total heat load and excess heat load between passages. So it can be influenced by passage arrangement, flow inlet parameters as well as flow patterns. Dimensionless parameter of mean square error of accumulative heat load can reflect the influence of passage arrangement to heat exchange performance and will not change dramatically with the variation of flow inlet parameters and flow patterns. Temperature-difference uniformity factor is influenced by passage arrangement and flow patterns. It remains basically unchanged under a certain range of flow inlet parameters.
Mathematical model of cross type multi-stream plate-fin heat exchanger is established. Meanwhile, mean square error of accumulative heat load is normalized by dimensionless,and the equations of temperature-difference uniformity factor are improved. Evaluation factors above and performance of heat exchanger are compared and analyzed by taking aircraft three-stream condenser as an example. The results demonstrate that the mean square error of accumulative heat load is common result of total heat load and excess heat load between passages. So it can be influenced by passage arrangement, flow inlet parameters as well as flow patterns. Dimensionless parameter of mean square error of accumulative heat load can reflect the influence of passage arrangement to heat exchange performance and will not change dramatically with the variation of flow inlet parameters and flow patterns. Temperature-difference uniformity factor is influenced by passage arrangement and flow patterns. It remains basically unchanged under a certain range of flow inlet parameters.
2017, 34(5):561-566.
DOI: 10.16356/j.1005-1120.2017.05.561
Abstract:
A novel balun structure for dipole antenna, which is based on the current distribution on parallel microstrip lines and the emission cancellation characteristic of close equal and opposite currents, is proposed. The principle of the balun structure is first elaborated and verified. Then, a dipole antenna with resonance at 2.45 GHz is constructed using the balun and its radiation pattern is measured. The simulated and measured reflection coefficients (S11) of the antenna are in good agreement 2—3 GHz. The relative bandwidth with an S11of below -10 dB is more than 25%. The antenna also shows a good radiation pattern at 2.45 GHz. The proposed structure can provide a new balun design method for dipole antennas.
A novel balun structure for dipole antenna, which is based on the current distribution on parallel microstrip lines and the emission cancellation characteristic of close equal and opposite currents, is proposed. The principle of the balun structure is first elaborated and verified. Then, a dipole antenna with resonance at 2.45 GHz is constructed using the balun and its radiation pattern is measured. The simulated and measured reflection coefficients (S11) of the antenna are in good agreement 2—3 GHz. The relative bandwidth with an S11of below -10 dB is more than 25%. The antenna also shows a good radiation pattern at 2.45 GHz. The proposed structure can provide a new balun design method for dipole antennas.
2017, 34(5):567-577.
DOI: 10.16356/j.1005-1120.2017.05.567
Abstract:
For the research of helicopter/ship dynamic interface, the method of combining steady flow and stochastic flow is adopted to establish a flow field model applied to the flight dynamics analysis of shipborne helicopter. The steady flow is calculated by computational fluid dynamics (CFD) method, while the stochastic flow is composed of the compensation velocity derived from ship motion and turbulence above the deck. The accuracy of the proposed flow field model is verified by comparing the helicopter response in the proposed flow field with the results calculated by US Army′s Military Specifications (MIL) model which is commonly used in engineering. Meanwhile, it also shows the proposed flow field model is more appliable to flight dynamics analysis of shipborne helicopter. On that the basis, ship deck flow field is simulated at different sea conditions by adjusting the wind speed on the deck, mother ship movement and shipboard turbulence, etc. And helicopter angular rate response is calculated. The results show that the difference of dynamic stability between helicopter′s roll and pitch leads to the facts that the influence of above factors on the helicopter′s roll angular rate response is greater than that of pitch angular rate, that the frequency and amplitude of mother ship roll motion are much greater than those of pitch motion, and that the disturbance caused by roll motion on the air has greater influence on the helicopter response. The shipboard turbulence is the main disturbance factor that influences helicopter flight stability and its intensity determines the amplitudes of angular rate response.
For the research of helicopter/ship dynamic interface, the method of combining steady flow and stochastic flow is adopted to establish a flow field model applied to the flight dynamics analysis of shipborne helicopter. The steady flow is calculated by computational fluid dynamics (CFD) method, while the stochastic flow is composed of the compensation velocity derived from ship motion and turbulence above the deck. The accuracy of the proposed flow field model is verified by comparing the helicopter response in the proposed flow field with the results calculated by US Army′s Military Specifications (MIL) model which is commonly used in engineering. Meanwhile, it also shows the proposed flow field model is more appliable to flight dynamics analysis of shipborne helicopter. On that the basis, ship deck flow field is simulated at different sea conditions by adjusting the wind speed on the deck, mother ship movement and shipboard turbulence, etc. And helicopter angular rate response is calculated. The results show that the difference of dynamic stability between helicopter′s roll and pitch leads to the facts that the influence of above factors on the helicopter′s roll angular rate response is greater than that of pitch angular rate, that the frequency and amplitude of mother ship roll motion are much greater than those of pitch motion, and that the disturbance caused by roll motion on the air has greater influence on the helicopter response. The shipboard turbulence is the main disturbance factor that influences helicopter flight stability and its intensity determines the amplitudes of angular rate response.
2017, 34(5):578-585.
DOI: 10.16356/j.1005-1120.2017.05.578
Abstract:
A combined arrival and departure scheduling problem is investigated for multi-airport system to alleviate the problem of airspace congestion and flight delay. Firstly, the combined scheduling problem for multi-airport system is defined through in-depth analysis of the characteristics of arrival and departure operations. Then, several constraints are taken into account, such as wake vortex separation, transfer separation, release separation, and separation in different runway operational modes. Furthermore, the scheduling model is constructed and simulated annealing algorithm is proposed by minimizing the total delay. Finally, Shanghai multi-airport system is chosen to conduct the simulation and validation. And the simulation results indicate that the proposed method is able to effectively improve the efficiency of arrival and departure operations for multi-airport system.
A combined arrival and departure scheduling problem is investigated for multi-airport system to alleviate the problem of airspace congestion and flight delay. Firstly, the combined scheduling problem for multi-airport system is defined through in-depth analysis of the characteristics of arrival and departure operations. Then, several constraints are taken into account, such as wake vortex separation, transfer separation, release separation, and separation in different runway operational modes. Furthermore, the scheduling model is constructed and simulated annealing algorithm is proposed by minimizing the total delay. Finally, Shanghai multi-airport system is chosen to conduct the simulation and validation. And the simulation results indicate that the proposed method is able to effectively improve the efficiency of arrival and departure operations for multi-airport system.
2017, 34(5):586-592.
DOI: 10.16356/j.1005-1120.2017.05.586
Abstract:
Mechanical elastic wheel (ME-wheel) is a new type of non-inflatable safety tyre, and the structure is significantly different from traditional pneumatic tyre. In order to investigate cornering properties of ME-wheel, experimental research on mechanics characteristics of ME-wheel under steady-state cornering conditions are carried out. The test of steady-state cornering properties of ME-wheel at different experimental parameter conditions is conducted by test bench for dynamic mechanical properties of tyre. Cornering property curves are used to analyze the steady-state cornering properties of ME-wheel, namely the variation tendency of lateral force or aligning torque with the increase of side-slip angle. Moreover, evaluation indexes for cornering properties of ME-wheel are extracted and the effect of different experimental parameters (including vertical load, friction coefficient, and speed) on cornering properties of ME-wheel is contrastively analyzed. The proposed research can provide certain reference to facilitate structure parameters and cornering properties optimizing process of ME-wheel.
Mechanical elastic wheel (ME-wheel) is a new type of non-inflatable safety tyre, and the structure is significantly different from traditional pneumatic tyre. In order to investigate cornering properties of ME-wheel, experimental research on mechanics characteristics of ME-wheel under steady-state cornering conditions are carried out. The test of steady-state cornering properties of ME-wheel at different experimental parameter conditions is conducted by test bench for dynamic mechanical properties of tyre. Cornering property curves are used to analyze the steady-state cornering properties of ME-wheel, namely the variation tendency of lateral force or aligning torque with the increase of side-slip angle. Moreover, evaluation indexes for cornering properties of ME-wheel are extracted and the effect of different experimental parameters (including vertical load, friction coefficient, and speed) on cornering properties of ME-wheel is contrastively analyzed. The proposed research can provide certain reference to facilitate structure parameters and cornering properties optimizing process of ME-wheel.
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