Transactions of Nanjing University of Aeronautics & Astronautics
Volume 33,Issue 6,2016 Table of Contents
2016, 33(6):639-646.
Abstract:
Since an engine is seen as the ″heart″ of an airplane, the objective and scientific evaluation of it is significant to ensure normal operation of airlines. Aiming at the limitations of current studies on selecting engines, a quantitative comprehensive evaluation system of engine options was established and an optimization model based on the utility theory and analytic hierarchy process (AHP) was proposed. Considering the judgement of different customers on the balance between income and risk, the utility of each evaluation index was determined by utilizing the piecewise utility function. The AHP was use d to analyze individual demands of customers. Finally, the optimal scheme was selected through calculating the weighted utility value. According to the actual needs of a domestic airline, the utility of three engine options was calculated. The results showed that the value of risk factor can be set to determine the selection scheme based on the degree of preferences (conservative type, neutral type or adventurous type).
Since an engine is seen as the ″heart″ of an airplane, the objective and scientific evaluation of it is significant to ensure normal operation of airlines. Aiming at the limitations of current studies on selecting engines, a quantitative comprehensive evaluation system of engine options was established and an optimization model based on the utility theory and analytic hierarchy process (AHP) was proposed. Considering the judgement of different customers on the balance between income and risk, the utility of each evaluation index was determined by utilizing the piecewise utility function. The AHP was use d to analyze individual demands of customers. Finally, the optimal scheme was selected through calculating the weighted utility value. According to the actual needs of a domestic airline, the utility of three engine options was calculated. The results showed that the value of risk factor can be set to determine the selection scheme based on the degree of preferences (conservative type, neutral type or adventurous type).
2016, 33(6):647-656.
Abstract:
We review the state of the art of dynamic modeling methods for heli copter simulators. Major dynamic models, including ARMCOP, GENHEL, FLYRT, BEMAP,FB412 and UTIAS, are introduced. We address offaxis response problem by focusing on flexible blade model, PittPeters dynamic inflow model, PetersHe finite state inflow model and free wake model which are integrated with the baseline model. With the advances in computing power, efficient freevortex algorithms and parallel processing, free wake model can be used to simulate in realtime and significantly improves the ffectivene ss of solving offaxis response problem.
We review the state of the art of dynamic modeling methods for heli copter simulators. Major dynamic models, including ARMCOP, GENHEL, FLYRT, BEMAP,FB412 and UTIAS, are introduced. We address offaxis response problem by focusing on flexible blade model, PittPeters dynamic inflow model, PetersHe finite state inflow model and free wake model which are integrated with the baseline model. With the advances in computing power, efficient freevortex algorithms and parallel processing, free wake model can be used to simulate in realtime and significantly improves the ffectivene ss of solving offaxis response problem.
2016, 33(6):657-669.
Abstract:
A surface mesh movement algorithm, c ombining surface mesh mapping with Delaunay graph mapping, is proposed for surface mesh movement involving complex intersections, like wing/pylon intersections. First, surface mesh mapping is adopted for the movement of intersecting lines along the spanwise direction and the wing surface mesh, and then Delaunay graph mapping is utilized for the deformation of the pylon surface mesh, guaranteeing consistent and smooth surface meshes. Furthermore, the corresponding surface sensitivity procedure is implemented for accurate and efficient calculation of the surface sensitivities. The proposed surface mesh movement algorithm and the surface sensitivity procedure are integrated into a discrete adjointbased optimization framework to optimize the nacelle position on the DLRF6 wingbodynacelle pylon configuration for drag minimization. The results demonstrate that the stro ng shock on the initial pylon surface is nearly eliminated and the optimal nacelle position can be obtained within less than ten iterations.
A surface mesh movement algorithm, c ombining surface mesh mapping with Delaunay graph mapping, is proposed for surface mesh movement involving complex intersections, like wing/pylon intersections. First, surface mesh mapping is adopted for the movement of intersecting lines along the spanwise direction and the wing surface mesh, and then Delaunay graph mapping is utilized for the deformation of the pylon surface mesh, guaranteeing consistent and smooth surface meshes. Furthermore, the corresponding surface sensitivity procedure is implemented for accurate and efficient calculation of the surface sensitivities. The proposed surface mesh movement algorithm and the surface sensitivity procedure are integrated into a discrete adjointbased optimization framework to optimize the nacelle position on the DLRF6 wingbodynacelle pylon configuration for drag minimization. The results demonstrate that the stro ng shock on the initial pylon surface is nearly eliminated and the optimal nacelle position can be obtained within less than ten iterations.
2016, 33(6):670-677.
Abstract:
Landing gears are one of the key components for large or middle unmanned aerial vehicles, and their working performances directly affect flying security and aircraft takingoff and landing performance. Thus, it is meaningful to study the retraction system. Based on CATIA and ADAMS software platforms, a virtual model of landing gear retraction system is built for performance test, and then dynamic simulation is carried out. Afterwards, a test system for landing gear retraction is established, and the test data are compared with the results acquired from dynamics simulation. The main factors which affect the dynamic performance of retractable landing gear are analyzed emphatically. The simulation results show that aerodynamic load has an impact on retraction time, the mass force affects extension process, and the oil hole size of hydraulic actuator has an effect on both retraction time and extension time.
Landing gears are one of the key components for large or middle unmanned aerial vehicles, and their working performances directly affect flying security and aircraft takingoff and landing performance. Thus, it is meaningful to study the retraction system. Based on CATIA and ADAMS software platforms, a virtual model of landing gear retraction system is built for performance test, and then dynamic simulation is carried out. Afterwards, a test system for landing gear retraction is established, and the test data are compared with the results acquired from dynamics simulation. The main factors which affect the dynamic performance of retractable landing gear are analyzed emphatically. The simulation results show that aerodynamic load has an impact on retraction time, the mass force affects extension process, and the oil hole size of hydraulic actuator has an effect on both retraction time and extension time.
2016, 33(6):678-686.
Abstract:
For accurate aeroelastic analysis, the unsteady rotor flowfield is solved by computational fluidynamics (CFD) module based on RANS/Euler equations and movingembedded grid system, while computational structural dynamics (CSD) module is introduced to handle blade flexibility. In CFD module, dual time stepping algorithm is employed in temporal discretization, Jameson twoorder central difference (JST) scheme is adopted in spatial discretization and BL turbulent model is used to illustrate the viscous effect. The CSD module is developed based on Hamilton′s variational principles and moderat e deflection beam theory. Grid deformation is implemented using algebraic method through coordinate transformations to achieve deflections with high quality and efficiency. A CFD/CSD loose coupling strategy is developed to transfer information between rotor flowfield and blade structure. The CFD and the CSD modules are verified seperately. Then the CFD/CSD loose coupling is adopted in airloads prediction of UH60A rotor under high speed forward flight condition. The calculated results agree well with test data. Finally, effects of torsional stiffness properties on airloads of rotors with different tip swept angles (from 10° forward to 30° backward) are investigated. The results are evaluated through pressure distribution and airloads variation, and some meaningful conclusions are drawn the moderated shock wave strength and pressure gradient caused by varied tip swept angle and structural properties.
For accurate aeroelastic analysis, the unsteady rotor flowfield is solved by computational fluidynamics (CFD) module based on RANS/Euler equations and movingembedded grid system, while computational structural dynamics (CSD) module is introduced to handle blade flexibility. In CFD module, dual time stepping algorithm is employed in temporal discretization, Jameson twoorder central difference (JST) scheme is adopted in spatial discretization and BL turbulent model is used to illustrate the viscous effect. The CSD module is developed based on Hamilton′s variational principles and moderat e deflection beam theory. Grid deformation is implemented using algebraic method through coordinate transformations to achieve deflections with high quality and efficiency. A CFD/CSD loose coupling strategy is developed to transfer information between rotor flowfield and blade structure. The CFD and the CSD modules are verified seperately. Then the CFD/CSD loose coupling is adopted in airloads prediction of UH60A rotor under high speed forward flight condition. The calculated results agree well with test data. Finally, effects of torsional stiffness properties on airloads of rotors with different tip swept angles (from 10° forward to 30° backward) are investigated. The results are evaluated through pressure distribution and airloads variation, and some meaningful conclusions are drawn the moderated shock wave strength and pressure gradient caused by varied tip swept angle and structural properties.
2016, 33(6):687-695.
Abstract:
To analyze the dynamic interaction between detonation waves and coolant flow in a hydrogen fuelled detonation chamber, a hydrogen fuelled detonation chamber with a cooled liner was designed and a simulation model was established. An explicit highresolution total variation diminishing (TVD) scheme was eveloped to solve the twodimensional Euler equations implemented with an augmented reduced mechanism of the hydrogen/air mixture. A pointimplicit method was used to solve the numerical stiffness of the chemical reaction source term. The interaction between detonative was and coolant flow were presented. The interaction dynamics between detonation waves and coolant flow in a detonation chamber were investigated. The results indicated that there were some negative interaction effects between detonation waves and coolant flow.
To analyze the dynamic interaction between detonation waves and coolant flow in a hydrogen fuelled detonation chamber, a hydrogen fuelled detonation chamber with a cooled liner was designed and a simulation model was established. An explicit highresolution total variation diminishing (TVD) scheme was eveloped to solve the twodimensional Euler equations implemented with an augmented reduced mechanism of the hydrogen/air mixture. A pointimplicit method was used to solve the numerical stiffness of the chemical reaction source term. The interaction between detonative was and coolant flow were presented. The interaction dynamics between detonation waves and coolant flow in a detonation chamber were investigated. The results indicated that there were some negative interaction effects between detonation waves and coolant flow.
2016, 33(6):696-705.
Abstract:
Formation of entrance and exit defects in coarse pitch orbital drilling (CPOD) of carbon fiber reinforced plastic (CFRP) plates was investigated. Deep observation on entrance and exit morphology shows tear and burr are typical defects. Meanwhile, tear is more obvious than burr, and more entrance tears emerge than exit tears. As one of the major causes of entrance and exit defects in CPOD, cutting forces were substaintially studied by contr ast experiments. Then, the effect of cutting parameters on entrance and exit tear was qualitatively analyzed through a single factor test. Experiment results indicate that the variation of rotation speed has little influence on entrance and exit tear. Increasing tangential feed per tooth can enlarge entrance tear, but bring little effect on exit tear. By increasing axial feed pitch, the hole entrance and exit show severe tear. When revolution radius grows bigger and bigger, entrance and exit tear firstly decreases, and then increases. Finally, the models of tear and delamination during CPOD of CFRP were established, the formation mechanisms of entrance and exit defects were revealed, and the ontrol strategies were accordingly put forward.
Formation of entrance and exit defects in coarse pitch orbital drilling (CPOD) of carbon fiber reinforced plastic (CFRP) plates was investigated. Deep observation on entrance and exit morphology shows tear and burr are typical defects. Meanwhile, tear is more obvious than burr, and more entrance tears emerge than exit tears. As one of the major causes of entrance and exit defects in CPOD, cutting forces were substaintially studied by contr ast experiments. Then, the effect of cutting parameters on entrance and exit tear was qualitatively analyzed through a single factor test. Experiment results indicate that the variation of rotation speed has little influence on entrance and exit tear. Increasing tangential feed per tooth can enlarge entrance tear, but bring little effect on exit tear. By increasing axial feed pitch, the hole entrance and exit show severe tear. When revolution radius grows bigger and bigger, entrance and exit tear firstly decreases, and then increases. Finally, the models of tear and delamination during CPOD of CFRP were established, the formation mechanisms of entrance and exit defects were revealed, and the ontrol strategies were accordingly put forward.
2016, 33(6):706-713.
Abstract:
Plunge grinding experiments were carried out on CSS42L stainless steel with the white fused alumina wheel. The grinding forces were measured with variations in accumulated material removal volume. Then the morphological features of worn grinding wheel were analyzed by optical microscopy and the grinding temperatures were measured with a thermocouple. For comparison, C45 steel was ground under the same conditions. The results indicated that the grinding forces of CSS42L were at least twice that of C45 steel. When the accumulated removal volume overcame 375 mm3, strong adhesion was found between the abrasives and workpiece CSS42L. Nevertheless, adhesion was hardly found after 800 mm3 workpiece C45 steel was removed. In order to enhance the machining property of CSS42L, a brazed CBN wheel was incorporated into the grinding of CSS42L, and the grinding forces and temperatures were found significantly decreased, whose maximum decreasing amplitude was about 70% and 80%, respectively.
Plunge grinding experiments were carried out on CSS42L stainless steel with the white fused alumina wheel. The grinding forces were measured with variations in accumulated material removal volume. Then the morphological features of worn grinding wheel were analyzed by optical microscopy and the grinding temperatures were measured with a thermocouple. For comparison, C45 steel was ground under the same conditions. The results indicated that the grinding forces of CSS42L were at least twice that of C45 steel. When the accumulated removal volume overcame 375 mm3, strong adhesion was found between the abrasives and workpiece CSS42L. Nevertheless, adhesion was hardly found after 800 mm3 workpiece C45 steel was removed. In order to enhance the machining property of CSS42L, a brazed CBN wheel was incorporated into the grinding of CSS42L, and the grinding forces and temperatures were found significantly decreased, whose maximum decreasing amplitude was about 70% and 80%, respectively.
2016, 33(6):714-720.
Abstract:
Geometry of end mill cutters plays a vital role in the stability of the flexible parts milling. The present study considers helix angle and number of flutes. Multifrequency solution is established to draw stability Lobe diagram(SLD) for different helix angles and number of flutes. SLD for the two cases shows that the greater the value of helix angle, the more stable the milling process will be, and conversely increasing the number of flutes degrades the stability of flexible parts milling. A simple empirical methodology is adopted to employ the inclined plane workpiece geometry offering a gradual increase of the axial depth of cut in the feed direction. Surface roughness is used as a measure of stability. Test results corroborate the model conclusions very well.
Geometry of end mill cutters plays a vital role in the stability of the flexible parts milling. The present study considers helix angle and number of flutes. Multifrequency solution is established to draw stability Lobe diagram(SLD) for different helix angles and number of flutes. SLD for the two cases shows that the greater the value of helix angle, the more stable the milling process will be, and conversely increasing the number of flutes degrades the stability of flexible parts milling. A simple empirical methodology is adopted to employ the inclined plane workpiece geometry offering a gradual increase of the axial depth of cut in the feed direction. Surface roughness is used as a measure of stability. Test results corroborate the model conclusions very well.
2016, 33(6):721-725.
Abstract:
In recent years, unmanned air vehicles (UAVs) are widely used in many military and civilian applications. With the big amount of UAVs operation in air space, the potential security and privacy problems are arising. This can lead to consequent harm for critical infrastructure in the event of these UAVs being used for criminal or terrorist purposes. Therefore, it is crucial to promptly identify the suspicious behaviors from the surrounding UAVs for some important regions. In this paper, a novel fuzzy logic based UAV behavior detection system has been presented to detect the different levels of risky behaviors of the incoming UAVs. The heading velocity and region type are two input indicators proposed for the risk indicator output in the designed fuzzy logic based system. The simulation has shown the effective and feasible of the proposed algorithm in terms of recall and precision of the detection. Especially, the suspicious behavior detection algorithm can provide a recall of 0.89 and a precision of 0.95 for the high risk scenario in the simulation.
In recent years, unmanned air vehicles (UAVs) are widely used in many military and civilian applications. With the big amount of UAVs operation in air space, the potential security and privacy problems are arising. This can lead to consequent harm for critical infrastructure in the event of these UAVs being used for criminal or terrorist purposes. Therefore, it is crucial to promptly identify the suspicious behaviors from the surrounding UAVs for some important regions. In this paper, a novel fuzzy logic based UAV behavior detection system has been presented to detect the different levels of risky behaviors of the incoming UAVs. The heading velocity and region type are two input indicators proposed for the risk indicator output in the designed fuzzy logic based system. The simulation has shown the effective and feasible of the proposed algorithm in terms of recall and precision of the detection. Especially, the suspicious behavior detection algorithm can provide a recall of 0.89 and a precision of 0.95 for the high risk scenario in the simulation.
2016, 33(6):726-732.
Abstract:
Exploiting the sourcetorelay channel phase information at the relays can increase the rate upperbound of distributed orthogonal spacetime block codes (STBC) from 2/K to 1/2, where K is the number of relays. This technique is known as distributed orthogonal spacetime block codes with channel phase information (DOSTBCCPI). However, the decoding delay of existing DOSTBCCPIs is not optimal. Therefore, based on the rate of 1/2 balanced complex orthogonal design (COD), an algorithm is provided to construct a maximal rate DOSTBCCPI with only half the decoding delay of existing DOSTBCCPI. Simulation results show that the proposed method exhibits lower symbol error rate than the existing DOSTBCCPIs.
Exploiting the sourcetorelay channel phase information at the relays can increase the rate upperbound of distributed orthogonal spacetime block codes (STBC) from 2/K to 1/2, where K is the number of relays. This technique is known as distributed orthogonal spacetime block codes with channel phase information (DOSTBCCPI). However, the decoding delay of existing DOSTBCCPIs is not optimal. Therefore, based on the rate of 1/2 balanced complex orthogonal design (COD), an algorithm is provided to construct a maximal rate DOSTBCCPI with only half the decoding delay of existing DOSTBCCPI. Simulation results show that the proposed method exhibits lower symbol error rate than the existing DOSTBCCPIs.
2016, 33(6):733-738.
Abstract:
Considering that perfect channel state information (CSI) is hard to obtain in practice, the capacity o f downlink distributed antennas system (DAS) with imperfect CSI is analyzed over Rayleigh fading channel. Based on the performance analysis, using the probability density function and numerical calculation, an accurate closedform expression of ergodic capacity of downlink DAS under imperfect CSI is derived. It includes the one under perfect CSI as a special case. This theoretical expression can provide good performance evaluation for downlink DAS for both perfect and imperfect CSI due to its accuracy. Simulation results indicate that the theoretical analysis agrees well with the corresponding simulation, and the capacity can be increased effectively by decreasing the estimation error and /or path loss.
Considering that perfect channel state information (CSI) is hard to obtain in practice, the capacity o f downlink distributed antennas system (DAS) with imperfect CSI is analyzed over Rayleigh fading channel. Based on the performance analysis, using the probability density function and numerical calculation, an accurate closedform expression of ergodic capacity of downlink DAS under imperfect CSI is derived. It includes the one under perfect CSI as a special case. This theoretical expression can provide good performance evaluation for downlink DAS for both perfect and imperfect CSI due to its accuracy. Simulation results indicate that the theoretical analysis agrees well with the corresponding simulation, and the capacity can be increased effectively by decreasing the estimation error and /or path loss.
2016, 33(6):747-753.
Abstract:
A directional ultrawideband (UWB) antenna with improved radiation patterns is presented. The proposed sheme comprises a differentialfed microstrip antenna and a rectangular cavity. The hexagonshaped slot and four trianglecut corners on the ground plane of the planar antenna are used to improve the impedance matching within the UWB frequency range. A rectangular cavity is used as the reflector for the planar microstrip antenna, so as to achieve directed radiation. The measured results indicate that the designed antenna exhibits a stable broadside directional radiation patterns within the entire operating frequency band. Furthermore, thanks to the differentially driven technique, the crosspolarization is greatly decreased and the polariz ation purity is maintained in a high level.
A directional ultrawideband (UWB) antenna with improved radiation patterns is presented. The proposed sheme comprises a differentialfed microstrip antenna and a rectangular cavity. The hexagonshaped slot and four trianglecut corners on the ground plane of the planar antenna are used to improve the impedance matching within the UWB frequency range. A rectangular cavity is used as the reflector for the planar microstrip antenna, so as to achieve directed radiation. The measured results indicate that the designed antenna exhibits a stable broadside directional radiation patterns within the entire operating frequency band. Furthermore, thanks to the differentially driven technique, the crosspolarization is greatly decreased and the polariz ation purity is maintained in a high level.
14 Numerical Simulation of An Axial Flow Fan with Proper Aft Fins for Floating
Wind Turbines Model Test
2016, 33(6):754-760.
Abstract:
It is difficult to generate homogeneous wind in model test for floating wind turbines, especially when using array of axial fans. We design and compare proper fins behind the blades for an axial fan to produce antitwist flow based on the computational fluid dynamics (CFD). The result is promising and proves that suitable designed fins can be an effective solution.
It is difficult to generate homogeneous wind in model test for floating wind turbines, especially when using array of axial fans. We design and compare proper fins behind the blades for an axial fan to produce antitwist flow based on the computational fluid dynamics (CFD). The result is promising and proves that suitable designed fins can be an effective solution.
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