Transactions of Nanjing University of Aeronautics & Astronautics
Volume 35,Issue 1,2018 Table of Contents
2018, 35(1):1-9.
DOI: 10.16356/j.1005-1120.2018.01.01
Abstract:
A parametric study of a high-power-density dual resonator for achieving low frequency broadband electromagnetic energy harvesting is reported. The dual resonator consists of a rectilinear oscillator (RLO) performing magnetic levitation and a rotary oscillator (RTO) performing electromagnetic coupling through a stator and a rotor. Both oscillators, coupled by magnetic forces generated by a set of arc permanent magnets, radially magnetized and centro-symmetrically fixed onto the RLO and the rotor of the RTO achieve the reciprocating-to-rotary motion conversion and frequency up-conversion. Specifically, the dual resonator is able to convert stochastic reciprocating motion into controllable rotation, provide intrinsic frequency up-conversion, use non-contact magnetic coupling to provide near loss-free energy transfer and be configured into specific applications to obtain and maintain high-energy orbits of multi-stable energy harvesting. While solely focusing on developing a dual resonator provides substantial benefits, its dynamic behavior is unclear, thus electromagneticdynamic governing equations are derived, and a curve fitting model of restoring torque of RTO under different repulsive magnets configurations are developed to predict key characteristics and to improve performance of the electromechanical system. Power analysis is carried out for providing a quantitative guidance of customizing the harvester to achieve an optimal power density.
A parametric study of a high-power-density dual resonator for achieving low frequency broadband electromagnetic energy harvesting is reported. The dual resonator consists of a rectilinear oscillator (RLO) performing magnetic levitation and a rotary oscillator (RTO) performing electromagnetic coupling through a stator and a rotor. Both oscillators, coupled by magnetic forces generated by a set of arc permanent magnets, radially magnetized and centro-symmetrically fixed onto the RLO and the rotor of the RTO achieve the reciprocating-to-rotary motion conversion and frequency up-conversion. Specifically, the dual resonator is able to convert stochastic reciprocating motion into controllable rotation, provide intrinsic frequency up-conversion, use non-contact magnetic coupling to provide near loss-free energy transfer and be configured into specific applications to obtain and maintain high-energy orbits of multi-stable energy harvesting. While solely focusing on developing a dual resonator provides substantial benefits, its dynamic behavior is unclear, thus electromagneticdynamic governing equations are derived, and a curve fitting model of restoring torque of RTO under different repulsive magnets configurations are developed to predict key characteristics and to improve performance of the electromechanical system. Power analysis is carried out for providing a quantitative guidance of customizing the harvester to achieve an optimal power density.
2018, 35(1):10-19.
DOI: 10.16356/j.1005-1120.2018.01.010
Abstract:
A novel extended methodology for chatter suppression in milling process by applying external forced vibrations to the workpiece in two orthogonal directions which are the feed and cross-feed directions. Both the regenerative and forced chatter suppression during the milling process of flexible workpieces are investigated. Here, the workpiece is subject to a sinusoidal periodic force in the feed direction to disrupt the regenerative effect. Additionally, to minimize the forced chatter, the workpiece is subject to the periodic excitation force in cross-feed direction. This force is proportional to the magnitude of the estimated cutting force in cross-feed direction and has a phrase opposite to the cutting force to minimize the vibration amplitudes. The effectiveness of the proposed method is evaluated numerically and experimentally, for the spindle speed located in both the local minima and local mixima of the stability lobe diagram. The numerical simulations indicate significant suppression effect in terms of vibration amplitudes, resulting in suppression of both the regenerative chatter and forced chatter. Experiments were conducted by using a workpiece-mounted active stage composed of flexure hinges and driven by piezoelectric actuators. The experimental results agree qualitatively with the numerical simulations. The proposed method indicates a remarkable vibration reduction effect for both regenerative and forced chatters.
A novel extended methodology for chatter suppression in milling process by applying external forced vibrations to the workpiece in two orthogonal directions which are the feed and cross-feed directions. Both the regenerative and forced chatter suppression during the milling process of flexible workpieces are investigated. Here, the workpiece is subject to a sinusoidal periodic force in the feed direction to disrupt the regenerative effect. Additionally, to minimize the forced chatter, the workpiece is subject to the periodic excitation force in cross-feed direction. This force is proportional to the magnitude of the estimated cutting force in cross-feed direction and has a phrase opposite to the cutting force to minimize the vibration amplitudes. The effectiveness of the proposed method is evaluated numerically and experimentally, for the spindle speed located in both the local minima and local mixima of the stability lobe diagram. The numerical simulations indicate significant suppression effect in terms of vibration amplitudes, resulting in suppression of both the regenerative chatter and forced chatter. Experiments were conducted by using a workpiece-mounted active stage composed of flexure hinges and driven by piezoelectric actuators. The experimental results agree qualitatively with the numerical simulations. The proposed method indicates a remarkable vibration reduction effect for both regenerative and forced chatters.
2018, 35(1):20-27.
DOI: 10.16356/j.1005-1120.2018.01.020
Abstract:
The mass of very small vehicles is often comparable to that of their drivers, and thus there is a greater degree of coupling between the vehicle and the driver, compared with a case for traditional vehicles. When developing small vehicles, it is necessary to give ample consideration to the dynamics of the person who ride them. Here, a model of a human body riding a small personal vehicle was constructed to investigate the dynamics of the person inside such a vehicle. Moreover, an experiment on posture maintenance by acceleration of direction of travel was conducted and the parameters for posture control were identified using a genetic algorithm. Results shows that body behavior could be successfully simulated using the proposed model, and the control parameters were effective in determining the posture maintenance characteristics of the vehicle occupant.
The mass of very small vehicles is often comparable to that of their drivers, and thus there is a greater degree of coupling between the vehicle and the driver, compared with a case for traditional vehicles. When developing small vehicles, it is necessary to give ample consideration to the dynamics of the person who ride them. Here, a model of a human body riding a small personal vehicle was constructed to investigate the dynamics of the person inside such a vehicle. Moreover, an experiment on posture maintenance by acceleration of direction of travel was conducted and the parameters for posture control were identified using a genetic algorithm. Results shows that body behavior could be successfully simulated using the proposed model, and the control parameters were effective in determining the posture maintenance characteristics of the vehicle occupant.
2018, 35(1):28-37.
DOI: 10.16356/j.1005-1120.2018.01.028
Abstract:
To reduce the collision shock and risk of injury to an infant in an in-car crib (or in a child safety bed) during a car crash, it is necessary to limit the force acting on the crib below a certain allowable value. To realize this objective, we propose a semi-active in-car crib system with the joint application of regular and inverted pendulum mechanisms. The crib is supported by arms similar to a pendulum, and the pendulum system itself is supported by arms similar to an inverted pendulum. In addition, the arm acting as a regular pendulum is joined with the arm acting as an inverted pendulum through a linking mechanism for simplicity, and the friction torque of the joint connecting the base and the latter arm is controlled using a brake mechanism, which enables the proposed in-car crib to gradually increase the deceleration of the crib and maintain it at around the target value. This system not only reduces the impulsive force but also transfers the force to the infant′s back using a spin control system, i.e., the impulse force is made to act perpendicularly on the crib. The spin control system was developed in our previous work. The present work focuses on the acceleration control system. A semi-active control law with acceleration feedback is introduced using the sliding mode control theory. Especially, a feedback system of the crib acceleration relative to the vehicle is proposed for the high-vibrational environment. Further, a control experiment using scale model is conducted to confirm the effectiveness, and some results are reported.
To reduce the collision shock and risk of injury to an infant in an in-car crib (or in a child safety bed) during a car crash, it is necessary to limit the force acting on the crib below a certain allowable value. To realize this objective, we propose a semi-active in-car crib system with the joint application of regular and inverted pendulum mechanisms. The crib is supported by arms similar to a pendulum, and the pendulum system itself is supported by arms similar to an inverted pendulum. In addition, the arm acting as a regular pendulum is joined with the arm acting as an inverted pendulum through a linking mechanism for simplicity, and the friction torque of the joint connecting the base and the latter arm is controlled using a brake mechanism, which enables the proposed in-car crib to gradually increase the deceleration of the crib and maintain it at around the target value. This system not only reduces the impulsive force but also transfers the force to the infant′s back using a spin control system, i.e., the impulse force is made to act perpendicularly on the crib. The spin control system was developed in our previous work. The present work focuses on the acceleration control system. A semi-active control law with acceleration feedback is introduced using the sliding mode control theory. Especially, a feedback system of the crib acceleration relative to the vehicle is proposed for the high-vibrational environment. Further, a control experiment using scale model is conducted to confirm the effectiveness, and some results are reported.
5 Variational Mode Decomposition for Rotating Machinery Condition Monitoring Using Vibration Signals
2018, 35(1):38-50.
DOI: 10.16356/j.1005-1120.2018.01.038
Abstract:
The failure of rotating machinery applications has major time and cost effects on the industry. Condition monitoring helps to ensure safe operation and also avoids losses. The signal processing method is essential for ensuring both the efficiency and accuracy of the monitoring process. Variational mode decomposition (VMD) is a signal processing method which decomposes a non-stationary signal into sets of variational mode functions (VMFs) adaptively and non-recursively. The VMD method offers improved performance for the condition monitoring of rotating machinery applications. However, determining an accurate number of modes for the VMD method is still considered an open research problem. Therefore, a selection method for determining the number of modes for VMD is proposed by taking advantage of the similarities in concept between the original signal and VMF. Simulated signal and online gearbox vibration signals have been used to validate the performance of the proposed method. The statistical parameters of the signals are extracted from the original signals, VMFs and intrinsic mode functions (I MFs) and have been fed into machine learning algorithms to validate the performance of the VMD method. The results show that the features extracted from VMD are both superior and accurate for the monitoring of rotating machinery. Hence the proposed method offers a new approach for the condition monitoring of rotating machinery applications.
The failure of rotating machinery applications has major time and cost effects on the industry. Condition monitoring helps to ensure safe operation and also avoids losses. The signal processing method is essential for ensuring both the efficiency and accuracy of the monitoring process. Variational mode decomposition (VMD) is a signal processing method which decomposes a non-stationary signal into sets of variational mode functions (VMFs) adaptively and non-recursively. The VMD method offers improved performance for the condition monitoring of rotating machinery applications. However, determining an accurate number of modes for the VMD method is still considered an open research problem. Therefore, a selection method for determining the number of modes for VMD is proposed by taking advantage of the similarities in concept between the original signal and VMF. Simulated signal and online gearbox vibration signals have been used to validate the performance of the proposed method. The statistical parameters of the signals are extracted from the original signals, VMFs and intrinsic mode functions (I MFs) and have been fed into machine learning algorithms to validate the performance of the VMD method. The results show that the features extracted from VMD are both superior and accurate for the monitoring of rotating machinery. Hence the proposed method offers a new approach for the condition monitoring of rotating machinery applications.
2018, 35(1):51-57.
DOI: 10.16356/j.1005-1120.2018.01.051
Abstract:
Rotation of a pair of wings was driven by the vertical harmonic motion of a pin inserted into the center hole of the wings. To elucidate the mechanism by which the rotational motion of the wings was excited, the relationship between the wings and the pin was examined by tracking their motions using both displacement measurements and high-speed photography. The motion modes occurred in this study were categorized into five types: slipping, rolling, jumping (without eccentricity), jumping (with eccentricity), and non-rotation. In the case that the hole of the wings was located at a distance from the center of the wings, referred to as ″with eccentricity,″ the slipping, jumping (with eccentricity), and non-rotation modes resulted. The experimental results showed that the mechanism of the jumping (with eccentricity) was different from that of the other modes (slipping, rolling, jumping (without eccentricity)), which are well known to be driven by the periodical reaction of the wings against the vertical vibration of the pin. It was found that the jumping (with eccentricity) was driven by the non-periodical force with the collision between the wing hole and the pin.
Rotation of a pair of wings was driven by the vertical harmonic motion of a pin inserted into the center hole of the wings. To elucidate the mechanism by which the rotational motion of the wings was excited, the relationship between the wings and the pin was examined by tracking their motions using both displacement measurements and high-speed photography. The motion modes occurred in this study were categorized into five types: slipping, rolling, jumping (without eccentricity), jumping (with eccentricity), and non-rotation. In the case that the hole of the wings was located at a distance from the center of the wings, referred to as ″with eccentricity,″ the slipping, jumping (with eccentricity), and non-rotation modes resulted. The experimental results showed that the mechanism of the jumping (with eccentricity) was different from that of the other modes (slipping, rolling, jumping (without eccentricity)), which are well known to be driven by the periodical reaction of the wings against the vertical vibration of the pin. It was found that the jumping (with eccentricity) was driven by the non-periodical force with the collision between the wing hole and the pin.
2018, 35(1):58-68.
DOI: 10.16356/j.1005-1120.2018.01.058
Abstract:
Many countries which seek to understand the acoustic performance of railway noise barriers have established standards for the conduct of in-situ experiments. However, there are no universally acknowledged receiver positions for the evaluation of the barrier performance, a fact which may be leading to uncertainty over the noise reduction capabilities of available barriers. In terms of the descriptor of the barrier performance, the general recommendation is the A-weighted sound pressure level, although the latter is considered to underestimate low frequencies for railway noise barrier. Thus, in this study, the comparison of receiver positions and the descriptors among existing Chinese, ISO and European standards were investigated. Based upon a combination of diffraction theory and standards, a rearrangement of receiver positions and one-third-octave-band analysis were proposed. In addition, in line with improved methods, an in-situ measurement of insertion loss for a 1.5 m high railway noise barrier was designed and conducted. The results of the experiment validate as effective and applicable the new receiver positions. These results also suggest that one-third-octave-band analysis is indispensable.
Many countries which seek to understand the acoustic performance of railway noise barriers have established standards for the conduct of in-situ experiments. However, there are no universally acknowledged receiver positions for the evaluation of the barrier performance, a fact which may be leading to uncertainty over the noise reduction capabilities of available barriers. In terms of the descriptor of the barrier performance, the general recommendation is the A-weighted sound pressure level, although the latter is considered to underestimate low frequencies for railway noise barrier. Thus, in this study, the comparison of receiver positions and the descriptors among existing Chinese, ISO and European standards were investigated. Based upon a combination of diffraction theory and standards, a rearrangement of receiver positions and one-third-octave-band analysis were proposed. In addition, in line with improved methods, an in-situ measurement of insertion loss for a 1.5 m high railway noise barrier was designed and conducted. The results of the experiment validate as effective and applicable the new receiver positions. These results also suggest that one-third-octave-band analysis is indispensable.
2018, 35(1):69-83.
DOI: 10.16356/j.1005-1120.2018.01.069
Abstract:
The elastic support/dry friction damper is a type of damper which is used for active vibration control in a rotor system. To establish the analytical model of this type of damper, a two-dimensional friction model-ball/plate model was proposed. By using this ball/plate model, a dynamics model of rotor with elastic support/dry friction dampers was established and experimentally verified. Moreover, the damping performance of the elastic support/dry friction damper was studied numerically with respect to some variable parameters. The numerical study shows that the damping performance of the elastic support/dry friction damper is closely related to the stiffness distribution of the rotor-support system, the damper location, the pressing force between the moving and stationary disk, the friction coefficient, the tangential contact stiffness of the contact interface, and the stiffness of the stationary disk. In general, the damper should be located on an elastic support which has a large vibration amplitude in order to achieve a better damping performance, and the more vibration energy in this elastic support concentrates, the better performance of the damper will be. The larger the tangential contact stiffness of the contact interface, and the stiffness of the stationary disk are, the better performance of the damper will be. There will be an optimal value of the friction force at which the damper performs best.
The elastic support/dry friction damper is a type of damper which is used for active vibration control in a rotor system. To establish the analytical model of this type of damper, a two-dimensional friction model-ball/plate model was proposed. By using this ball/plate model, a dynamics model of rotor with elastic support/dry friction dampers was established and experimentally verified. Moreover, the damping performance of the elastic support/dry friction damper was studied numerically with respect to some variable parameters. The numerical study shows that the damping performance of the elastic support/dry friction damper is closely related to the stiffness distribution of the rotor-support system, the damper location, the pressing force between the moving and stationary disk, the friction coefficient, the tangential contact stiffness of the contact interface, and the stiffness of the stationary disk. In general, the damper should be located on an elastic support which has a large vibration amplitude in order to achieve a better damping performance, and the more vibration energy in this elastic support concentrates, the better performance of the damper will be. The larger the tangential contact stiffness of the contact interface, and the stiffness of the stationary disk are, the better performance of the damper will be. There will be an optimal value of the friction force at which the damper performs best.
2018, 35(1):84-93.
DOI: 10.16356/j.1005-1120.2018.01.084
Abstract:
A disc-pad friction system is modelled as that two moving pads act symmetrically on an annular beam with flexible boundary condition. Simulation procedure is proposed to deal with the moving interactions and calculation is carried out by using the finite difference method, which shows that only the first-order mode vibration of the beam can be induced. Then the partial differential equation of motion of the disk is reduced to a first-order mode vibration system with time-varying stiffness. As the disk speed is decreased below the critical speeds, the relative equilibrium of the pad on the disk loses its stability and stick-slip type limit cycle vibrations are resulted in all directions′ movements. Acceleration of the disk motion on the frictional instability is also investigated. The period of stick-slip vibration with large amplitude will be shortened with higher moving deceleration.
A disc-pad friction system is modelled as that two moving pads act symmetrically on an annular beam with flexible boundary condition. Simulation procedure is proposed to deal with the moving interactions and calculation is carried out by using the finite difference method, which shows that only the first-order mode vibration of the beam can be induced. Then the partial differential equation of motion of the disk is reduced to a first-order mode vibration system with time-varying stiffness. As the disk speed is decreased below the critical speeds, the relative equilibrium of the pad on the disk loses its stability and stick-slip type limit cycle vibrations are resulted in all directions′ movements. Acceleration of the disk motion on the frictional instability is also investigated. The period of stick-slip vibration with large amplitude will be shortened with higher moving deceleration.
2018, 35(1):94-100.
DOI: 10.16356/j.1005-1120.2018.01.094
Abstract:
Stability is usually in the sense of Lyapunov′s asymptotical stability, thus the solutions starting from points close to a stable equilibrium may have a very long transient. In the applications of time-delayed feedback controls,it is important not only to determine the stable regions in the gain plane or gain space, but also to find out the abscissa that can be used as an index of stability. Based on the D-subdivision method, this paper proposes a simple algorithm for finding and labeling the stable regions in feedback gain plane with abscissa.The labeled sub-regions with smaller abscissa are better in applications. The main results are presented for the controlled pendulum or inverted pendulum under a delayed feedback, and are illustrated with two case studies.
Stability is usually in the sense of Lyapunov′s asymptotical stability, thus the solutions starting from points close to a stable equilibrium may have a very long transient. In the applications of time-delayed feedback controls,it is important not only to determine the stable regions in the gain plane or gain space, but also to find out the abscissa that can be used as an index of stability. Based on the D-subdivision method, this paper proposes a simple algorithm for finding and labeling the stable regions in feedback gain plane with abscissa.The labeled sub-regions with smaller abscissa are better in applications. The main results are presented for the controlled pendulum or inverted pendulum under a delayed feedback, and are illustrated with two case studies.
2018, 35(1):101-108.
DOI: 10.16356/j.1005-1120.2018.01.101
Abstract:
Considering gyroscopic effects caused by rotational speed, torsional vibration as well as coupling effects among inner rotor, out rotor and casing, a dynamic model of the dual-rotor-casing system is established using finite element (FE) method. By comparing the natural characteristics obtained from MATLAB and ANSYS, the developed model is verified. Then rubbing-induced vibration responses in dual-rotor-casing system are analyzed. The effects of rotational speed and speed ratio on rubbing vibration responses of the system are discussed. Results show that different combined frequency components will appear in the spectrum except two unbalanced excitation frequencies and their multiple frequency components, and these frequencies can be used as the dual-rotor aero-engine rubbing failure diagnosis frequencies when rubbing occurs. Besides, the amplitude of torsional vibration is larger than that of lateral vibration under the same working condition, and speed ratio has a great impact on the periodicity of the system rubbing-induced motion trajectory. The amplitude of rubbing-induced responses under counter-rotation is less than that under co-rotation with the same parameters.
Considering gyroscopic effects caused by rotational speed, torsional vibration as well as coupling effects among inner rotor, out rotor and casing, a dynamic model of the dual-rotor-casing system is established using finite element (FE) method. By comparing the natural characteristics obtained from MATLAB and ANSYS, the developed model is verified. Then rubbing-induced vibration responses in dual-rotor-casing system are analyzed. The effects of rotational speed and speed ratio on rubbing vibration responses of the system are discussed. Results show that different combined frequency components will appear in the spectrum except two unbalanced excitation frequencies and their multiple frequency components, and these frequencies can be used as the dual-rotor aero-engine rubbing failure diagnosis frequencies when rubbing occurs. Besides, the amplitude of torsional vibration is larger than that of lateral vibration under the same working condition, and speed ratio has a great impact on the periodicity of the system rubbing-induced motion trajectory. The amplitude of rubbing-induced responses under counter-rotation is less than that under co-rotation with the same parameters.
2018, 35(1):109-115.
DOI: 10.16356/j.1005-1120.2018.01.109
Abstract:
With the development of wireless sensor network (WSN) applications in intelligent monitoring, additional support for the low power consumption wireless nodes can be provided by piezoceramics that harvest vibrational energy. First, we describe the effects of stimulation variations on piezoceramics and the energy harvesting circuit set-up. Two types of piezoceramics were stimulated at different frequencies and amplitudes to obtain the power output characteristics. Then, the energy harvesting circuit was studied and coupled with the piezoceramics. A double peak phenomenon was found in energy harvesting using a hard piezoceramic which gave a direct proof that the nonlinearity of the piezo constant should be considered in application. Finally, energy storage and output were studied and analyzed. Electronic components for the WSN were recommended according to the output power and the application. The results will give an instruction for piezoceramic energy harvesting under various stress amplitudes on its implementation.
With the development of wireless sensor network (WSN) applications in intelligent monitoring, additional support for the low power consumption wireless nodes can be provided by piezoceramics that harvest vibrational energy. First, we describe the effects of stimulation variations on piezoceramics and the energy harvesting circuit set-up. Two types of piezoceramics were stimulated at different frequencies and amplitudes to obtain the power output characteristics. Then, the energy harvesting circuit was studied and coupled with the piezoceramics. A double peak phenomenon was found in energy harvesting using a hard piezoceramic which gave a direct proof that the nonlinearity of the piezo constant should be considered in application. Finally, energy storage and output were studied and analyzed. Electronic components for the WSN were recommended according to the output power and the application. The results will give an instruction for piezoceramic energy harvesting under various stress amplitudes on its implementation.
2018, 35(1):116-125.
DOI: 10.16356/j.1005-1120.2018.01.116
Abstract:
Considering the elastic supports, the finite element model of rotor-bladed disk-casing system is established using commercial software ANSYS/LS-DYNA. Assuming that broken blade is released from the disk, the complicate rubbing responses of unbalanced rotor-bladed disk-casing system are studied under different operational speeds. In addition, influences of both plastic deformation of blade and casing failure are analyzed. The results show that there exist some multiple even fractional frequencies in the transient and steady vibration responses of unbalanced rotor. Besides, one nodal diameter vibration of bladed disk coupling with the lateral vibration of the shaft as well as the first order bending vibration of blade can be excited under low operational speed, while the first order bending vibration of blade coupling with the lateral vibration of disk-shaft is easily excited under high operational speed. During rubbing process, three distinct contact states can be observed: broken blade-casing contact, broken blade-blade component-casing contact and broken blade-casing contact/blade component-casing contact/blade self-contact. It is worth noting that the third contact state is related to the operational speed. With the increase of operational speed, self-contact in the blade may occur.
Considering the elastic supports, the finite element model of rotor-bladed disk-casing system is established using commercial software ANSYS/LS-DYNA. Assuming that broken blade is released from the disk, the complicate rubbing responses of unbalanced rotor-bladed disk-casing system are studied under different operational speeds. In addition, influences of both plastic deformation of blade and casing failure are analyzed. The results show that there exist some multiple even fractional frequencies in the transient and steady vibration responses of unbalanced rotor. Besides, one nodal diameter vibration of bladed disk coupling with the lateral vibration of the shaft as well as the first order bending vibration of blade can be excited under low operational speed, while the first order bending vibration of blade coupling with the lateral vibration of disk-shaft is easily excited under high operational speed. During rubbing process, three distinct contact states can be observed: broken blade-casing contact, broken blade-blade component-casing contact and broken blade-casing contact/blade component-casing contact/blade self-contact. It is worth noting that the third contact state is related to the operational speed. With the increase of operational speed, self-contact in the blade may occur.
2018, 35(1):126-134.
DOI: 10.16356/j.1005-1120.2018.01.126
Abstract:
Electrostatic monitoring technology of particle charging information can facilitate online monitoring of aero- engine, which effectively enhances engine fault diagnosis and health managements. Unlike traditional engine state monitoring technologies, aircraft engine monitoring by gas path electrostatic monitoring not only covers the predicted information source itself, but also detects the information that can provide an early warnings for initial fault states through gas path charging levels. This paper establishes a non-stationary time sequence change-point model for anomaly recognition of electrostatic signals based on change-point theory combined with difference method of non-stationary time series. Finally, electrostatic induction data were utilized by the engine life test for a particular aircraft to validate the proposed algorithm. The results indicate that the activity level and the event rate were 0.5—0.8 (nc) and 50%, respectively, which were far greater than 4—12 (pc) and 0—4% under normal working conditions of the engine.
Electrostatic monitoring technology of particle charging information can facilitate online monitoring of aero- engine, which effectively enhances engine fault diagnosis and health managements. Unlike traditional engine state monitoring technologies, aircraft engine monitoring by gas path electrostatic monitoring not only covers the predicted information source itself, but also detects the information that can provide an early warnings for initial fault states through gas path charging levels. This paper establishes a non-stationary time sequence change-point model for anomaly recognition of electrostatic signals based on change-point theory combined with difference method of non-stationary time series. Finally, electrostatic induction data were utilized by the engine life test for a particular aircraft to validate the proposed algorithm. The results indicate that the activity level and the event rate were 0.5—0.8 (nc) and 50%, respectively, which were far greater than 4—12 (pc) and 0—4% under normal working conditions of the engine.
2018, 35(1):135-145.
DOI: 10.16356/j.1005-1120.2018.01.135
Abstract:
Several types of coupling methods for resolving aerothermoelastic problems associated with hypersonic wings are summarized, and the appropriate coupling methods for engineering calculations are selected. Then, the calculation and analysis methods for the subdisciplines in this field are introduced, and the time step issue is discussed. A two-way-coupling rapid static aerothermoelastic method for analyzing hypersonic wings is proposed. This method considers thermal effects and is used to conduct an aerothermoelastic response analysis for a hypersonic wing. In addition, the aerodynamic force, heat flux, structural deformation and temperature field are obtained. The following three conclusions are drawn. First, the heating effect has a significant impact on the static aeroelastic response of hypersonic wings; therefore, thermal protection shields are essential. Second, the application of thermal protection shields reduces the differences in the calculation results between the one- and two-way-coupling methods. Third, hypersonic wings exhibit large thermal deformation under high-temperature environments, and in certain cases, the thermal deformation is even larger than the deformation caused by aerodynamic force.
Several types of coupling methods for resolving aerothermoelastic problems associated with hypersonic wings are summarized, and the appropriate coupling methods for engineering calculations are selected. Then, the calculation and analysis methods for the subdisciplines in this field are introduced, and the time step issue is discussed. A two-way-coupling rapid static aerothermoelastic method for analyzing hypersonic wings is proposed. This method considers thermal effects and is used to conduct an aerothermoelastic response analysis for a hypersonic wing. In addition, the aerodynamic force, heat flux, structural deformation and temperature field are obtained. The following three conclusions are drawn. First, the heating effect has a significant impact on the static aeroelastic response of hypersonic wings; therefore, thermal protection shields are essential. Second, the application of thermal protection shields reduces the differences in the calculation results between the one- and two-way-coupling methods. Third, hypersonic wings exhibit large thermal deformation under high-temperature environments, and in certain cases, the thermal deformation is even larger than the deformation caused by aerodynamic force.
2018, 35(1):146-153.
DOI: 10.16356/j.1005-1120.2018.01.146
Abstract:
The reason for the asymmetry phenomenon of shock/boundary layer interactions (SBLI) in a completely symmetric nozzle with symmetric flow conditions is still an open question. A model for the asymmetry of nozzle flows was proposed based on the properties of fluid entrainment in the mixing layer and momentum conservation. The asymmetry model is deduced based on the nozzle flow with restricted shock separation, and is still applicable for free shock separation. Flow deflection angle at nozzle exit is deduced from this model. Steady numerical simulations are conducted to model the asymmetry of the SBLIs in a planar convergent-divergent nozzle tested by previous researchers. The obtained values of deflection angle based on the numerical results of forced symmetric nozzle flows can judge the asymmetry of flows in a nozzle at some operations. It shows that the entrainment of shear layer on the separation induced by SBLTs is one of the reasons for the asymmetry in the confined SBLIs.
The reason for the asymmetry phenomenon of shock/boundary layer interactions (SBLI) in a completely symmetric nozzle with symmetric flow conditions is still an open question. A model for the asymmetry of nozzle flows was proposed based on the properties of fluid entrainment in the mixing layer and momentum conservation. The asymmetry model is deduced based on the nozzle flow with restricted shock separation, and is still applicable for free shock separation. Flow deflection angle at nozzle exit is deduced from this model. Steady numerical simulations are conducted to model the asymmetry of the SBLIs in a planar convergent-divergent nozzle tested by previous researchers. The obtained values of deflection angle based on the numerical results of forced symmetric nozzle flows can judge the asymmetry of flows in a nozzle at some operations. It shows that the entrainment of shear layer on the separation induced by SBLTs is one of the reasons for the asymmetry in the confined SBLIs.
2018, 35(1):154-161.
DOI: 10.16356/j.1005-1120.2018.01.154
Abstract:
Numerical simulations of unsteady flow problems with moving boundaries commonly require the use of geometric conservation law (GCL). However, in cases of unidirectional large mesh deformation, the cumulative error caused by the discrete procedure in GCL can significantly increase, and a direct consequence is that the calculated cell volume may become negative. To control the cumulative error, a new discrete GCL (D-GCL ) is proposed. Unlike the original D-GCL, the proposed method uses the control volume analytically evaluated according to the grid motion at the time level n, instead of using the calculated value from the D-GCL itself. Error analysis indicates that the truncation error of the numerical scheme is guaranteed to be the same order as that obtained from the original D-GCL, while the accumulated error is greatly reduced. For validation, two challenging large deformation cases including a rotating circular cylinder case and a descending GAW-(1) two-element airfoil case are selected to be investigated. Good agreements are found between the calculated results and some other literature data, demonstrating the feasibility of the proposed D-GCL for unidirectional motions with large displacements.
Numerical simulations of unsteady flow problems with moving boundaries commonly require the use of geometric conservation law (GCL). However, in cases of unidirectional large mesh deformation, the cumulative error caused by the discrete procedure in GCL can significantly increase, and a direct consequence is that the calculated cell volume may become negative. To control the cumulative error, a new discrete GCL (D-GCL ) is proposed. Unlike the original D-GCL, the proposed method uses the control volume analytically evaluated according to the grid motion at the time level n, instead of using the calculated value from the D-GCL itself. Error analysis indicates that the truncation error of the numerical scheme is guaranteed to be the same order as that obtained from the original D-GCL, while the accumulated error is greatly reduced. For validation, two challenging large deformation cases including a rotating circular cylinder case and a descending GAW-(1) two-element airfoil case are selected to be investigated. Good agreements are found between the calculated results and some other literature data, demonstrating the feasibility of the proposed D-GCL for unidirectional motions with large displacements.
2018, 35(1):162-169.
DOI: 10.16356/j.1005-1120.2018.01.162
Abstract:
Experimental investigation on the aerodynamic performance and aeroacoustic characteristics of model rotors with different tip anhedral angles in hover are conducted in the paper. Three sets of model rotors with blade-tip anhedral angle 0°(reference rotor), 20°and 45°respectively are designed to analyze the influence of the anhedral angle on the hovering performance and aeroacoustics of rotor. In the environment of anechoic chamber, the hover experiments under the different collective pitch and blade numbers, are carried out to measure the figure of merit (FM), time history of sound pressure and sound pressure level (SPL) of the three rotor models. Based on test results, the comparison and analysis of hovering performance and aeroacoustic characteristics among the three rotor models have been done. Meanwhile, for the sake of analysis, the rotor wake and blade pressure distribution are simulated by means of computational fluid method (CFD). At last, some conclusions about the effects of blade-tip anhedral angle on the aerodynamic performance and aeroacoustic characteristics in hover are obtained. An anhedral blade tip can enhance the FM of the rotor, and decrease the rotor loads noise to some extent.
Experimental investigation on the aerodynamic performance and aeroacoustic characteristics of model rotors with different tip anhedral angles in hover are conducted in the paper. Three sets of model rotors with blade-tip anhedral angle 0°(reference rotor), 20°and 45°respectively are designed to analyze the influence of the anhedral angle on the hovering performance and aeroacoustics of rotor. In the environment of anechoic chamber, the hover experiments under the different collective pitch and blade numbers, are carried out to measure the figure of merit (FM), time history of sound pressure and sound pressure level (SPL) of the three rotor models. Based on test results, the comparison and analysis of hovering performance and aeroacoustic characteristics among the three rotor models have been done. Meanwhile, for the sake of analysis, the rotor wake and blade pressure distribution are simulated by means of computational fluid method (CFD). At last, some conclusions about the effects of blade-tip anhedral angle on the aerodynamic performance and aeroacoustic characteristics in hover are obtained. An anhedral blade tip can enhance the FM of the rotor, and decrease the rotor loads noise to some extent.
2018, 35(1):170-180.
DOI: 10.16356/j.1005-1120.2018.01.170
Abstract:
As all-electric aircraft has many advantages, an aircraft nose wheel steering system would be developed to the all-electric direction. Concerning the control demand of the nose wheel steering system, based on the basic principles of nose wheel steering system and the design technique of mechanotronics, an all-electric aircraft nose wheel steering system, composed of a nose wheel steering mechanism of two worm gear and a control servo system of fly-by-wire with both steering and anti-shimmy functions is designed to meet the demand for operation control in the nose wheel steering system. Then, based on the LMS-AMESim software, the simulation model of the system is established to simulate the dynamics for the verification of its steering function. The simulation results indicate that the nose wheel steering system is reasonable, and can meet the requirements of the general project. Furthermore, the prototypes of the steering mechanism and control system are studied to validate the design, and the steering test bench is prepared to test the designed system. The test results, such as steer angle, rotate speed of motor are analyzed in details and compared with the theoretical results. The analysis and comparison results show that the design is reasonable and the property of the prototype can achieve the design objectives.
As all-electric aircraft has many advantages, an aircraft nose wheel steering system would be developed to the all-electric direction. Concerning the control demand of the nose wheel steering system, based on the basic principles of nose wheel steering system and the design technique of mechanotronics, an all-electric aircraft nose wheel steering system, composed of a nose wheel steering mechanism of two worm gear and a control servo system of fly-by-wire with both steering and anti-shimmy functions is designed to meet the demand for operation control in the nose wheel steering system. Then, based on the LMS-AMESim software, the simulation model of the system is established to simulate the dynamics for the verification of its steering function. The simulation results indicate that the nose wheel steering system is reasonable, and can meet the requirements of the general project. Furthermore, the prototypes of the steering mechanism and control system are studied to validate the design, and the steering test bench is prepared to test the designed system. The test results, such as steer angle, rotate speed of motor are analyzed in details and compared with the theoretical results. The analysis and comparison results show that the design is reasonable and the property of the prototype can achieve the design objectives.
2018, 35(1):181-187.
DOI: 10.16356/j.1005-1120.2018.01.181
Abstract:
A decision-making problem of missile-target assignment with a novel particle swarm optimization algorithm is proposed when it comes to a multiple target collaborative combat situation. The threat function is established to describe air combat situation. Optimization function is used to find an optimal missile-target assignment. An improved particle swarm optimization algorithm is utilized to figure out the optimization function with less parameters,which is based on the adaptive random learning approach. According to the coordinated attack tactics, there are some adjustments to the assignment. Simulation example results show that it is an effective algorithm to handle with the decision-making problem of the missile-target assignment (MTA) in air combat.
A decision-making problem of missile-target assignment with a novel particle swarm optimization algorithm is proposed when it comes to a multiple target collaborative combat situation. The threat function is established to describe air combat situation. Optimization function is used to find an optimal missile-target assignment. An improved particle swarm optimization algorithm is utilized to figure out the optimization function with less parameters,which is based on the adaptive random learning approach. According to the coordinated attack tactics, there are some adjustments to the assignment. Simulation example results show that it is an effective algorithm to handle with the decision-making problem of the missile-target assignment (MTA) in air combat.
2018, 35(1):188-202.
DOI: 10.16356/j.1005-1120.2018.01.188
Abstract:
The influence of varying shim layers on the progressive damage/failure of a composite component in a bolted composite-aluminum aerospace structural assembly was investigated using a non-linear three-dimensional (3D) structural solid elements assembled model of a carbon fiber-reinforced polymer (CFRP)-aluminum single-lap joint with a titanium (Ti-6Al-4V) fastener and a washer generated with the commercial finite element (FE) software package, ABAQUS /Standard. A progressive failure algorithm written in Fortran code with a set of appropriate degradation rules was incorporated as a user subroutine in ABAQUS to simulate the non-linear damage behavior of the composite component in the composite-aluminum bolted aerospace structure. The assembled 3D FE model simulated, as well as the specimen for the experimental testing consisted of a carbon-epoxy IMS-977-2 substrate, aluminum alloy 7075-T651 substrate, liquid shim (Hysol EA 9394), solid peelable fiberglass shim, a titanium fastener, and a washer. In distinction to previous investigations, the influence of shim layers (liquid shim and solid peelable fiberglass shim) inserted in-between the faying surfaces (CFRP and aluminum alloy substrates) were investigated by both numerical simulations and experimental work. The simulated model and test specimens conformed to the standard test configurations for both civil and military standards.The numerical simulations correlated well with the experimental results and it has been found that:(1) The shimming procedure as agreed upon by the aerospace industry for the resolution of assembly gaps in bolted joints for composite materials is the same for a composite-aluminum structure; liquid shim series (0.3, 0.5 and 0.7 mm thicknesses) prolonged the service life of the composite component whereas a solid peelable fiberglass shim most definitely had a better influence on the 0.9 assembly gap compared with the liquid shim; (2) The shim layers considerably influenced the structural strength of the composite component by delaying its ultimate failure thereby increasing its service life; and (3) Increasing the shim layer′s thickness led to a significant corresponding effect on the stiffness but with minimal effect on the ultimate load.
The influence of varying shim layers on the progressive damage/failure of a composite component in a bolted composite-aluminum aerospace structural assembly was investigated using a non-linear three-dimensional (3D) structural solid elements assembled model of a carbon fiber-reinforced polymer (CFRP)-aluminum single-lap joint with a titanium (Ti-6Al-4V) fastener and a washer generated with the commercial finite element (FE) software package, ABAQUS /Standard. A progressive failure algorithm written in Fortran code with a set of appropriate degradation rules was incorporated as a user subroutine in ABAQUS to simulate the non-linear damage behavior of the composite component in the composite-aluminum bolted aerospace structure. The assembled 3D FE model simulated, as well as the specimen for the experimental testing consisted of a carbon-epoxy IMS-977-2 substrate, aluminum alloy 7075-T651 substrate, liquid shim (Hysol EA 9394), solid peelable fiberglass shim, a titanium fastener, and a washer. In distinction to previous investigations, the influence of shim layers (liquid shim and solid peelable fiberglass shim) inserted in-between the faying surfaces (CFRP and aluminum alloy substrates) were investigated by both numerical simulations and experimental work. The simulated model and test specimens conformed to the standard test configurations for both civil and military standards.The numerical simulations correlated well with the experimental results and it has been found that:(1) The shimming procedure as agreed upon by the aerospace industry for the resolution of assembly gaps in bolted joints for composite materials is the same for a composite-aluminum structure; liquid shim series (0.3, 0.5 and 0.7 mm thicknesses) prolonged the service life of the composite component whereas a solid peelable fiberglass shim most definitely had a better influence on the 0.9 assembly gap compared with the liquid shim; (2) The shim layers considerably influenced the structural strength of the composite component by delaying its ultimate failure thereby increasing its service life; and (3) Increasing the shim layer′s thickness led to a significant corresponding effect on the stiffness but with minimal effect on the ultimate load.
2018, 35(1):203-218.
DOI: 10.16356/j.1005-1120.2018.01.203
Abstract:
In many wireless sensor networks (WSNs) applications, the preservation of source-location privacy plays a critical role in concealing context information, otherwise the monitored entities or subjects may be put in danger. Many traditional solutions have been proposed based on the creation of random routes, such as random walk and fake sources approach, which will lead to serious packet delay and high energy consumption. Instead of applying the routing in a blind way, this article proposes a novel solution for source location privacy in WSNs by utilizing sensor ability of perceiving the presence a mobile attacker nearby, for patient attackers in particular to increase the safety period and decrease the data delivery delay. The proposed strategy forms an intelligent silent zone (ISZ) by sacrificing only a minority of sensor nodes to entice patient attackers away from real packet routing path. The analysis and simulation results show that the proposed scheme, besides providing source location privacy energy efficiently, can significantly reduce real event reporting latency compared with the existing approaches.
In many wireless sensor networks (WSNs) applications, the preservation of source-location privacy plays a critical role in concealing context information, otherwise the monitored entities or subjects may be put in danger. Many traditional solutions have been proposed based on the creation of random routes, such as random walk and fake sources approach, which will lead to serious packet delay and high energy consumption. Instead of applying the routing in a blind way, this article proposes a novel solution for source location privacy in WSNs by utilizing sensor ability of perceiving the presence a mobile attacker nearby, for patient attackers in particular to increase the safety period and decrease the data delivery delay. The proposed strategy forms an intelligent silent zone (ISZ) by sacrificing only a minority of sensor nodes to entice patient attackers away from real packet routing path. The analysis and simulation results show that the proposed scheme, besides providing source location privacy energy efficiently, can significantly reduce real event reporting latency compared with the existing approaches.
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