Transactions of Nanjing University of Aeronautics & Astronautics
Volume 34,Issue 2,2017 Table of Contents
2017, 34(2):105-114.
DOI: 10.16356/j.1005-1120.2017.02.105
Abstract:
In order to solve the cross-channel signal problem caused by the uniform channelized wideband digital receiver when processing wideband signal and the problem that the sensitivity of the system greatly decreases when the bandwidth of wideband digital receiver increases, which both decrease the wideband radar signal detection performance, a new wideband digital receiver based on the modulated wideband converter (MWC) discrete compressed sampling structure and an energy detection method based on the new receiver are proposed. Firstly, the proposed receiver utilizes periodic pseudo-random sequences to mix wideband signals with baseband and other sub-bands. Then the mixed signals are low-pass filtered and downsampled to obtain the baseband compressed sampling data, which can increase the sensitivity of the system. Meanwhile, the cross-channel signal will all appear in any sub-bands, so the cross-channel signal problem can be solved easily by processing the baseband compressed sampling data. Secondly, we establish the signal detection model and formulate the criterion of the energy detection method. And we directly utilize the baseband compressed sampling data to carry out signal detection without signal reconstruction, which decreases the complexity of the algorithm and reduces the computational burden. Finally, simulation experiments demonstrate the effectiveness of the proposed receiver and show that the proposed signal detection method is effective in low signal-to-noise ratio (SNR) compared with the conventional energy detection and the probability of detection increases significantly when SNR increases.
In order to solve the cross-channel signal problem caused by the uniform channelized wideband digital receiver when processing wideband signal and the problem that the sensitivity of the system greatly decreases when the bandwidth of wideband digital receiver increases, which both decrease the wideband radar signal detection performance, a new wideband digital receiver based on the modulated wideband converter (MWC) discrete compressed sampling structure and an energy detection method based on the new receiver are proposed. Firstly, the proposed receiver utilizes periodic pseudo-random sequences to mix wideband signals with baseband and other sub-bands. Then the mixed signals are low-pass filtered and downsampled to obtain the baseband compressed sampling data, which can increase the sensitivity of the system. Meanwhile, the cross-channel signal will all appear in any sub-bands, so the cross-channel signal problem can be solved easily by processing the baseband compressed sampling data. Secondly, we establish the signal detection model and formulate the criterion of the energy detection method. And we directly utilize the baseband compressed sampling data to carry out signal detection without signal reconstruction, which decreases the complexity of the algorithm and reduces the computational burden. Finally, simulation experiments demonstrate the effectiveness of the proposed receiver and show that the proposed signal detection method is effective in low signal-to-noise ratio (SNR) compared with the conventional energy detection and the probability of detection increases significantly when SNR increases.
2017, 34(2):115-124.
DOI: 10.16356/j.1005-1120.2017.02.115
Abstract:
Based on the option prioritization in graph model for conflict resolution of two decision makers(DMs), new logical and matrix representations of four stability concepts for DMs′ attitude are proposed. The logical representation of attitude is defined, and converted to the matrix form in order to develop a decision support system (DSS) efficiently. Compared with existing definitions of DMs′ attitude based on states, the proposed definitions of attitude based on options are convenient and more effective to generate preferences since that of states can be significantly larger than that of options in a large conflict. In addition, it is easier to obtain the information of the prioritization of option statements than to obtain preference of states for users. The proposed representations are applied to the process conflict during aircraft manufacturing to demonstrate the efficiency of the new approach.
Based on the option prioritization in graph model for conflict resolution of two decision makers(DMs), new logical and matrix representations of four stability concepts for DMs′ attitude are proposed. The logical representation of attitude is defined, and converted to the matrix form in order to develop a decision support system (DSS) efficiently. Compared with existing definitions of DMs′ attitude based on states, the proposed definitions of attitude based on options are convenient and more effective to generate preferences since that of states can be significantly larger than that of options in a large conflict. In addition, it is easier to obtain the information of the prioritization of option statements than to obtain preference of states for users. The proposed representations are applied to the process conflict during aircraft manufacturing to demonstrate the efficiency of the new approach.
2017, 34(2):125-133.
DOI: 10.16356/j.1005-1120.2017.02.125
Abstract:
To make full use of expanded ma neuverability and increased range, adaptive constrained on-board guidance technology is the key capability for a glide vehicle with a double-pulse rocket engine, especially under the requirements of desired target changing and on-line reconfigurable control and guidance. Based on the rapid footprint analysis, whether the new target is within the current footprint area is firstly judged. If not, the rocket engine ignites by the logic obtained from the analysis of optimal flight range by the method of hp-adaptive Gauss pseudospectral method (hp-GPM). Then, an on-board trajectory generation method based on powered quasi-equilibrium glide condition (QEGC) and linear quadratic regulator (LQR) method is used to guide the vehicle to the new target. The effectiveness of the guidance method consisted of powered on-board trajectory generation, LQR trajectory tracking, footprint calculation, and ignition time determination is indicated by some simulation examples.
To make full use of expanded ma neuverability and increased range, adaptive constrained on-board guidance technology is the key capability for a glide vehicle with a double-pulse rocket engine, especially under the requirements of desired target changing and on-line reconfigurable control and guidance. Based on the rapid footprint analysis, whether the new target is within the current footprint area is firstly judged. If not, the rocket engine ignites by the logic obtained from the analysis of optimal flight range by the method of hp-adaptive Gauss pseudospectral method (hp-GPM). Then, an on-board trajectory generation method based on powered quasi-equilibrium glide condition (QEGC) and linear quadratic regulator (LQR) method is used to guide the vehicle to the new target. The effectiveness of the guidance method consisted of powered on-board trajectory generation, LQR trajectory tracking, footprint calculation, and ignition time determination is indicated by some simulation examples.
2017, 34(2):134-142.
DOI: 10.16356/j.1005-1120.2017.02.134
Abstract:
In order to overcome the efficiency problem of the conventional gradient-based optimal design method, a highly-efficient viscous adjoint-based RANS equations method is applied to the aerodynamic optimal design of hovering rotor airfoil. The C-shaped body-fitted mesh is firstly automatically generated around the airfoil by solving the Poisson equations, and the Navier-Stokes (N-Ｓ) equations combined with Spala rt-Allmaras (S-A) one-equation turbulence model are used as the governing equations to acquire the reliable flowfield variables. Then, according to multi-constrained characteristics of the optimization of high lift/drag ratio for hovering rotor airfoil, its corresponding adjoint equations, boundary conditions and gradient expressions are newly derived. On these bases, two representative rotor airfoils, NACA0012 airfoil and SC1095 airfoil, are selected as numerical examples to optimize their synthesized aerodynamic characteristics about lift/drag ratio in hover, and better aerodynamic performance of optimal airfoils are obtained compared with the baseline. Furthermore, the new designed rotor with the optimized rotor airfo il has better hover aerodynamic characteristics compared with the baseline rotor. In contrast to the baseline airfoils optimized by the finite difference method, it is demonstrated that the adjoint optimal algorithm itself is practical and highly-efficient for the aerodynamic optimization of hover rotor airfoil.
In order to overcome the efficiency problem of the conventional gradient-based optimal design method, a highly-efficient viscous adjoint-based RANS equations method is applied to the aerodynamic optimal design of hovering rotor airfoil. The C-shaped body-fitted mesh is firstly automatically generated around the airfoil by solving the Poisson equations, and the Navier-Stokes (N-Ｓ) equations combined with Spala rt-Allmaras (S-A) one-equation turbulence model are used as the governing equations to acquire the reliable flowfield variables. Then, according to multi-constrained characteristics of the optimization of high lift/drag ratio for hovering rotor airfoil, its corresponding adjoint equations, boundary conditions and gradient expressions are newly derived. On these bases, two representative rotor airfoils, NACA0012 airfoil and SC1095 airfoil, are selected as numerical examples to optimize their synthesized aerodynamic characteristics about lift/drag ratio in hover, and better aerodynamic performance of optimal airfoils are obtained compared with the baseline. Furthermore, the new designed rotor with the optimized rotor airfo il has better hover aerodynamic characteristics compared with the baseline rotor. In contrast to the baseline airfoils optimized by the finite difference method, it is demonstrated that the adjoint optimal algorithm itself is practical and highly-efficient for the aerodynamic optimization of hover rotor airfoil.
2017, 34(2):143-151.
DOI: 10.16356/j.1005-1120.2017.02.143
Abstract:
In coupled mode, the major problem of boom refueling system is undesirable nozzle loads. An automated load alleviation system (ALAS) is needed to alleviate nozzle loads. In order to simulate dynamic of the system and to validate ALAS, dynamic model is developed. Two models are established, which are the static model and the moving model, named after the two relative states between the fixed boom and the extension boom. Kane method is employed as main method considering system′s multi-body characteristics. D′Alembert′s principle is used to calculate nozzle loads. Simulation is conducted to research the effects of position disturbance and velocity disturbance on nozzle loads. Results indicate that position disturbance plays a more significant role in inducing nozzle loads. A fuzzy control law based ALAS is validated using the formulated model. It is concluded that this model can simulate system dynamic and validate ALAS.
In coupled mode, the major problem of boom refueling system is undesirable nozzle loads. An automated load alleviation system (ALAS) is needed to alleviate nozzle loads. In order to simulate dynamic of the system and to validate ALAS, dynamic model is developed. Two models are established, which are the static model and the moving model, named after the two relative states between the fixed boom and the extension boom. Kane method is employed as main method considering system′s multi-body characteristics. D′Alembert′s principle is used to calculate nozzle loads. Simulation is conducted to research the effects of position disturbance and velocity disturbance on nozzle loads. Results indicate that position disturbance plays a more significant role in inducing nozzle loads. A fuzzy control law based ALAS is validated using the formulated model. It is concluded that this model can simulate system dynamic and validate ALAS.
2017, 34(2):152-162.
DOI: 10.16356/j.1005-1120.2017.02.152
Abstract:
For a class of aeroengine nonlinear systems, a novel nonlinear sliding mode controller(SMC) design method based on artificial bee colony (ABC) algorithm is proposed. In view of the strong nonlinearity and uncertainty of aeroengines, sliding mode control strategy is adopted to design controller for the aeroengine. On basis of exact linearization approach, the nonlinear sliding mode controller is obtained conveniently. By using ABC algorithm, the parameters in the designed controller can be tuned to achieve optimal performance, resulting in a closed loop system with satisfactory dynamic performance and high steady accuracy. Simulation on an aeroengine verifies the effectiveness of the presented method.
For a class of aeroengine nonlinear systems, a novel nonlinear sliding mode controller(SMC) design method based on artificial bee colony (ABC) algorithm is proposed. In view of the strong nonlinearity and uncertainty of aeroengines, sliding mode control strategy is adopted to design controller for the aeroengine. On basis of exact linearization approach, the nonlinear sliding mode controller is obtained conveniently. By using ABC algorithm, the parameters in the designed controller can be tuned to achieve optimal performance, resulting in a closed loop system with satisfactory dynamic performance and high steady accuracy. Simulation on an aeroengine verifies the effectiveness of the presented method.
2017, 34(2):163-168.
DOI: 10.16356/j.1005-1120.2017.02.163
Abstract:
A dynamic hysteresis model based on neural networks is proposed for piezoelectric actuator. Neural network has been widely applied to pattern recognition and system identification. However, it is unable to directly model the systems with multi-valued mapping such as hysteresis. In order to handle this problem, a novel hysteretic operator is proposed to extract the dynamic property of the hysteresis. Moreover, it can construct an expanded input space to transform the multi-valued mapping of hysteresis into one-to-one mapping. Then neural networks can directly be used to approximate the behavior of dynamic hysteresis. Finally, the experimental results are presented to illustrate the potential of the proposed modeling method.
A dynamic hysteresis model based on neural networks is proposed for piezoelectric actuator. Neural network has been widely applied to pattern recognition and system identification. However, it is unable to directly model the systems with multi-valued mapping such as hysteresis. In order to handle this problem, a novel hysteretic operator is proposed to extract the dynamic property of the hysteresis. Moreover, it can construct an expanded input space to transform the multi-valued mapping of hysteresis into one-to-one mapping. Then neural networks can directly be used to approximate the behavior of dynamic hysteresis. Finally, the experimental results are presented to illustrate the potential of the proposed modeling method.
8 Shaking Table Model Test of Isolated Structure on Soft Site and Analysis on Its Isolation Efficiency
2017, 34(2):169-176.
DOI: 10.16356/j.1005-1120.2017.02.169
Abstract:
Adopting a soft site model built on soft interlayer soil foundation , a shaking table test for soft interlayer soil-isolated structure interaction is conducted to investigate the seismic response of isolated structure on soft site, and analyze its isolation effect. Test results show that the test can reflect the earthquake response characteristics of isolated structure on soft site. It is on soft site that the dynamic characteristics of isolated structure, acceleration magnification factor (AMF) of isolated structure and isolation efficiency of the isolation layer differ from those on rigid foundation with an soil-structure interaction (SSI) effect, represented by the reduction in fundamental vibration frequency of isolated structure and the increase of damping ratio with changes of the SSI effect. SSI can either increase or decrease AMF of isolated structure on soft site, depending on the characteristics of earthquake motion input. Furthermore, the isolation efficiency of isolation layer on soft site is decreased with the SSI effect, which is related to the peak ground acceleration (PGA) and the characteristics of earthquake motion input.
Adopting a soft site model built on soft interlayer soil foundation , a shaking table test for soft interlayer soil-isolated structure interaction is conducted to investigate the seismic response of isolated structure on soft site, and analyze its isolation effect. Test results show that the test can reflect the earthquake response characteristics of isolated structure on soft site. It is on soft site that the dynamic characteristics of isolated structure, acceleration magnification factor (AMF) of isolated structure and isolation efficiency of the isolation layer differ from those on rigid foundation with an soil-structure interaction (SSI) effect, represented by the reduction in fundamental vibration frequency of isolated structure and the increase of damping ratio with changes of the SSI effect. SSI can either increase or decrease AMF of isolated structure on soft site, depending on the characteristics of earthquake motion input. Furthermore, the isolation efficiency of isolation layer on soft site is decreased with the SSI effect, which is related to the peak ground acceleration (PGA) and the characteristics of earthquake motion input.
2017, 34(2):177-187.
DOI: 10.16356/j.1005-1120.2017.02.177
Abstract:
To study the bridging effect of partly-cured Z-pin, Z-pins with different curing degrees are manufactured by controlling pultrusion parameters. A unit cell is selected to analyze the stress of Z-pinned laminates and the quantitative relationship between the maximum bridging force and Z-pin diameter, embedded length, interfacial shear strength and tensile strength is acquired. The Z-pin ″bridging law″ test and Z-pin tensile test are carried out to study the effect of Z-pin′s curing degree on bridging effect, and the bridging efficiency is defined to evaluate the reinforcement effect of Z-pin. The mode Ⅰ interlaminar fracture toughness (GⅠC) is measured by the double cantilever beam test. The experimental results show that Z-pin′s co-curing with laminate matrix can improve the bridging force significantly and the fitting results show a linear relationship between Z-pin curing degree and interfacial shear strength. The three-dimensional images of the surface of pullout Z-pins indicate that the failure mode changed from totally interfacial debonding to a mixed mode. Finally, the reinforcement by partly-cured Z-pin can be used to further enhance the interlamina r toughness. Compared with completely-cured Z-pin, ＧⅠC of Z-pin with 67.6% curing degree increases by 47.0%.
To study the bridging effect of partly-cured Z-pin, Z-pins with different curing degrees are manufactured by controlling pultrusion parameters. A unit cell is selected to analyze the stress of Z-pinned laminates and the quantitative relationship between the maximum bridging force and Z-pin diameter, embedded length, interfacial shear strength and tensile strength is acquired. The Z-pin ″bridging law″ test and Z-pin tensile test are carried out to study the effect of Z-pin′s curing degree on bridging effect, and the bridging efficiency is defined to evaluate the reinforcement effect of Z-pin. The mode Ⅰ interlaminar fracture toughness (GⅠC) is measured by the double cantilever beam test. The experimental results show that Z-pin′s co-curing with laminate matrix can improve the bridging force significantly and the fitting results show a linear relationship between Z-pin curing degree and interfacial shear strength. The three-dimensional images of the surface of pullout Z-pins indicate that the failure mode changed from totally interfacial debonding to a mixed mode. Finally, the reinforcement by partly-cured Z-pin can be used to further enhance the interlamina r toughness. Compared with completely-cured Z-pin, ＧⅠC of Z-pin with 67.6% curing degree increases by 47.0%.
2017, 34(2):188-194.
DOI: 10.16356/j.1005-1120.2017.02.188
Abstract:
The present study aims to analyze free vibration of thin skew plates made of functionally graded material (FGM) by using the weak form quadrature element method. The material properties vary continuously through the thickness according to a power-law form. A novel FGM skew plate element is formulated according to the neutral surface based plate theory and with the help of the differential quadrature rule. For verifications, Numerical results are compared with available data in literature. Results reveal that the non-dimensional frequency parameters of the FGM skew plates are independent of the power-law exponent and always proportional to those of homogeneous isotropic ones when the coupling and rotary inertias are neglected. In addition, employing the physical neutral surface based plate theory is equivalent to using the middle plane based plate theory with the reduced flexural modulus matrix.
The present study aims to analyze free vibration of thin skew plates made of functionally graded material (FGM) by using the weak form quadrature element method. The material properties vary continuously through the thickness according to a power-law form. A novel FGM skew plate element is formulated according to the neutral surface based plate theory and with the help of the differential quadrature rule. For verifications, Numerical results are compared with available data in literature. Results reveal that the non-dimensional frequency parameters of the FGM skew plates are independent of the power-law exponent and always proportional to those of homogeneous isotropic ones when the coupling and rotary inertias are neglected. In addition, employing the physical neutral surface based plate theory is equivalent to using the middle plane based plate theory with the reduced flexural modulus matrix.
2017, 34(2):195-204.
DOI: 10.16356/j.1005-1120.2017.02.195
Abstract:
Engineering practice has shown that early faults of gearboxes are a leading maintenance cost driver that can easily lower the profit from a wind turbine operation. Ａ novel oil-lubricated electrostatic monitoring of wear debris for a wind turbine gearbox is presented. The continuous wavelet transform (CWT) is used to eliminate the noises of the original electrostatic signal. The kurtosis and root mean square (RMS) values of the time domain signal are extracted as the characteristic parameters to reflect the deterioration of the gearbox. The overall tendency of electrostatic signals in accelerated life test is analyzed. In the eighth cycle, the abnormal wear in the wind turbine gearbox is detected by electrostatic monitoring. A comparison with the popular MetalScan monitoring is given to illustrate the effectiveness of the electrostatic monitoring method. The results demonstrate that the electrostatic monitoring method can detect the fault accurately.
Engineering practice has shown that early faults of gearboxes are a leading maintenance cost driver that can easily lower the profit from a wind turbine operation. Ａ novel oil-lubricated electrostatic monitoring of wear debris for a wind turbine gearbox is presented. The continuous wavelet transform (CWT) is used to eliminate the noises of the original electrostatic signal. The kurtosis and root mean square (RMS) values of the time domain signal are extracted as the characteristic parameters to reflect the deterioration of the gearbox. The overall tendency of electrostatic signals in accelerated life test is analyzed. In the eighth cycle, the abnormal wear in the wind turbine gearbox is detected by electrostatic monitoring. A comparison with the popular MetalScan monitoring is given to illustrate the effectiveness of the electrostatic monitoring method. The results demonstrate that the electrostatic monitoring method can detect the fault accurately.
2017, 34(2):205-210.
DOI: 10.16356/j.1005-1120.2017.02.205
Abstract:
Double perovskite oxide Sr2FeMoO6 powder is prepared by a solid state reaction method. The microwave absorption properties of Sr2FeMoO6 and paraffin wax composites are studied in the frequency range of 2—18 GHz at room temperature. The optimum absorption -36.7 dB is achieved at 17.7 GHz with a matching thickness of 5.0 mm, which indicates that Sr2FeMoO6/paraffin composites can be potential microwave absorbers in a relatively high frequency range. The excellent microwave absorption properties are attributed to the good electromagnetic match between dielectric loss and magnetic loss. The dielectric loss is considered to be caused by orientation polarization and interfacial polarization, while the magnetic loss is caused by natural resonance in the low frequency range, eddy current loss as well as exchange resonance in the high frequency range.
Double perovskite oxide Sr2FeMoO6 powder is prepared by a solid state reaction method. The microwave absorption properties of Sr2FeMoO6 and paraffin wax composites are studied in the frequency range of 2—18 GHz at room temperature. The optimum absorption -36.7 dB is achieved at 17.7 GHz with a matching thickness of 5.0 mm, which indicates that Sr2FeMoO6/paraffin composites can be potential microwave absorbers in a relatively high frequency range. The excellent microwave absorption properties are attributed to the good electromagnetic match between dielectric loss and magnetic loss. The dielectric loss is considered to be caused by orientation polarization and interfacial polarization, while the magnetic loss is caused by natural resonance in the low frequency range, eddy current loss as well as exchange resonance in the high frequency range.
2017, 34(2):211-219.
DOI: 10.16356/j.1005-1120.2017.02.211
Abstract:
Identifying the stiffness and damping of active magnetic bearings (AMBs) is necessary since those parameters can affect the stability and performance of the high-speed rotor AMBs system. A new identification method is proposed to identify the stiffness and damping coefficients of a rotor AMB system. This method combines the global optimization capability of the genetic algorithm(GA) and the local search ability of Nelder-Mead simplex method. The supporting parameters are obtained using the hybrid GA based on the experimental unbalance response calculated through the transfer matrix method. To verify the identified results, the experimental stiffness and damping coefficients are employed to simulate the unbalance responses for the rotor AMBs system using the finite element method. The close agreement between the simulation and experimental data indicates that the proposed identified algorithm can effectively identify the AMBs supporting parameters.
Identifying the stiffness and damping of active magnetic bearings (AMBs) is necessary since those parameters can affect the stability and performance of the high-speed rotor AMBs system. A new identification method is proposed to identify the stiffness and damping coefficients of a rotor AMB system. This method combines the global optimization capability of the genetic algorithm(GA) and the local search ability of Nelder-Mead simplex method. The supporting parameters are obtained using the hybrid GA based on the experimental unbalance response calculated through the transfer matrix method. To verify the identified results, the experimental stiffness and damping coefficients are employed to simulate the unbalance responses for the rotor AMBs system using the finite element method. The close agreement between the simulation and experimental data indicates that the proposed identified algorithm can effectively identify the AMBs supporting parameters.
2017, 34(2):220-228.
DOI: 10.16356/j.1005-1120.2017.02.220
Abstract:
The reliability and safety of the pneumatic ducts are essential for flight safety. A beam element model of the duct system is developed and the factors that impact the stress performance of the duct system are investigated, such as stress check standards, flight acceleration, internal temperature and internal pressure. The results show that the stress synthetic method as the stress check standard can obtain the more safety design results. The maximum stress of straight pipe is affected significantly by the acceleration in a plane perpendicular to straight pipe, while the maximum stress of bend pipe is greatly affected by the acceleration in the direction perpendicular to plane of the bend pipe. Meanwhile, internal pressure has little effect on the maximum stress of bend pipe and straight pipe. Temperature has little effect on the maximum stress of bend pipe while has a big impact on the maximum stress of straight pipe.
The reliability and safety of the pneumatic ducts are essential for flight safety. A beam element model of the duct system is developed and the factors that impact the stress performance of the duct system are investigated, such as stress check standards, flight acceleration, internal temperature and internal pressure. The results show that the stress synthetic method as the stress check standard can obtain the more safety design results. The maximum stress of straight pipe is affected significantly by the acceleration in a plane perpendicular to straight pipe, while the maximum stress of bend pipe is greatly affected by the acceleration in the direction perpendicular to plane of the bend pipe. Meanwhile, internal pressure has little effect on the maximum stress of bend pipe and straight pipe. Temperature has little effect on the maximum stress of bend pipe while has a big impact on the maximum stress of straight pipe.
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