Probabilistic Fault Recoverability(FR) property reveals the capability of a system to accommodate faults under admissible input energy constraints in the sense of satisfactory probability. Motivated by the idea of pro...Probabilistic Fault Recoverability(FR) property reveals the capability of a system to accommodate faults under admissible input energy constraints in the sense of satisfactory probability. Motivated by the idea of probabilistic control methods, a class of admissible probability density functions is designed for detailed description of fault parameters, under which several probabilistic FR conditions are established. This significantly enlarges the range of recoverable faults obtained from the deterministic FR analysis. The tradeoffs between the risk of performance degradation and this increased recoverability margin are exactly achieved by allowing a small risk of FR violation. This paper analyzes the probability FR of dynamic systems with switching and interconnection characteristics, and applies the new results to several aircraft models including single longitudinal aircraft dynamic, Highly Maneuverable Technology(HiMAT) vehicle and meta aircraft. Simulation results show the efficiency of the proposed methods based on the comparison between deterministic and probabilistic cases.展开更多
The techniques widely used in ultrasonic measurements are based on the determination of the time of flight (T.o.F). A short train of waves is transmitted and same transducer is used for reception of the reflected sign...The techniques widely used in ultrasonic measurements are based on the determination of the time of flight (T.o.F). A short train of waves is transmitted and same transducer is used for reception of the reflected signal for the pulse-echo measurement applications. The amplitude of the received waveform is an envelope which starts from zero reaches to a peak and then dies out. The echoes are mostly detected by simple threshold crossing technique, which is also cause of error. In this paper digital signal processing is used to calculate the time delay in reception i.e. T.o.F, for which a maximum similarity between the reference and the delayed echo signals is obtained. To observe the effect of phase uncertainties and frequency shifts (Doppler), this processing is carried out, both directly on the actual wave shape and after extracting the envelopes of the reference and delayed echo signals. Several digital signal processing algorithms are considered and the effects of different factors such as sampling rate, resolution of digitization and S/N ratio are analyzed. Result show accuracy, computing time and cost for different techniques.展开更多
In-flight particle velocity and flux distribution were measured using CCD thermal spray monitor system during supersonic plasma spray processing with nano-structured Al_2O_3-TiO_2 feed stocks. According to the results...In-flight particle velocity and flux distribution were measured using CCD thermal spray monitor system during supersonic plasma spray processing with nano-structured Al_2O_3-TiO_2 feed stocks. According to the results of particle flux measurement, the largest radian of the divergent particle stream is about 0.2. Within the measuring range, top speed of in-flight particles reached 800m/s. Particle acceleration was accomplished within 4cm down stream of the nozzle. Average particle velocity (about 450m/s) exceeded local sound speed (340m/s) even at a mean standoff distance of 17cm. With increasing mean standoff distance, average velocity of in-flight particle decreased according to a parabolic rule approximately. Image diagnosis showed that the result of in-flight particle velocity measurement is credible.展开更多
This paper presents a theoretic implementation method of Morphing Unmanned Submersible Aerial Vehicle （MUSAV）, which can both submerge in the water and fly in the air. Two different shapes are put forward so that th...This paper presents a theoretic implementation method of Morphing Unmanned Submersible Aerial Vehicle （MUSAV）, which can both submerge in the water and fly in the air. Two different shapes are put forward so that the vehicle can suit both submergence and flight, considering the tremendous differences between hydrodynamic configuration and aerodynamic configuration of a vehicle. The transition of the two shapes can be achieved by using morphing technology. The water-to-air process, including water-exit, morphing, take-off and steady flight, is analyzed. The hydrodynamic and aerodynamic model of the vehicle exiting the water surface obliquely and then taking off into the air has been founded. The control strategy after morphing is analyzed and the control method is given. Numerical method is used to validate the motion model of the water-exit process. Results of simulations show the validity of the proposed model and the feasibility of MUSAV in theory.展开更多
This paper presents a novel onboard system called In-Flight Awareness Augmentation System (IFA<sup>2</sup>S) to improve flight safety. IFA<sup>2</sup>S is designed to semi-automatically (with h...This paper presents a novel onboard system called In-Flight Awareness Augmentation System (IFA<sup>2</sup>S) to improve flight safety. IFA<sup>2</sup>S is designed to semi-automatically (with human supervision) avoid hazards and accidents due to either internal or external causal factors. The requirements were defined in an innovative way using Systems-Theoretic Process Analysis (STPA) method and applied next to model the system. IFA<sup>2</sup>S increases aircraft awareness regarding both itself and its environment and, at the same time, recognizes platform and operational constraints to act in accordance to predefined decision algorithms. Results are presented through simulations and flight tests using state machines designed to allow the adoption of appropriate actions for the identified hazards. The different decision algorithms are evaluated over as many as possible hazard situations by simulations conducted with software Labview and XPlane flight simulator. Flight tests are performed in a small fixed wing aircraft and make use of a limited version IFA<sup>2</sup>S, partially attending identified requirements. Results support the conclusion that IFA<sup>2</sup>S is capable of improving flight safety.展开更多
基金supported by National Natural Science Foundation of China (Nos. 61773201, 62073165)the 111 Project,China (No. B20007)the Fundamental Research Funds for the Central Universities, China (No. NZ2020003)。
文摘Probabilistic Fault Recoverability(FR) property reveals the capability of a system to accommodate faults under admissible input energy constraints in the sense of satisfactory probability. Motivated by the idea of probabilistic control methods, a class of admissible probability density functions is designed for detailed description of fault parameters, under which several probabilistic FR conditions are established. This significantly enlarges the range of recoverable faults obtained from the deterministic FR analysis. The tradeoffs between the risk of performance degradation and this increased recoverability margin are exactly achieved by allowing a small risk of FR violation. This paper analyzes the probability FR of dynamic systems with switching and interconnection characteristics, and applies the new results to several aircraft models including single longitudinal aircraft dynamic, Highly Maneuverable Technology(HiMAT) vehicle and meta aircraft. Simulation results show the efficiency of the proposed methods based on the comparison between deterministic and probabilistic cases.
文摘The techniques widely used in ultrasonic measurements are based on the determination of the time of flight (T.o.F). A short train of waves is transmitted and same transducer is used for reception of the reflected signal for the pulse-echo measurement applications. The amplitude of the received waveform is an envelope which starts from zero reaches to a peak and then dies out. The echoes are mostly detected by simple threshold crossing technique, which is also cause of error. In this paper digital signal processing is used to calculate the time delay in reception i.e. T.o.F, for which a maximum similarity between the reference and the delayed echo signals is obtained. To observe the effect of phase uncertainties and frequency shifts (Doppler), this processing is carried out, both directly on the actual wave shape and after extracting the envelopes of the reference and delayed echo signals. Several digital signal processing algorithms are considered and the effects of different factors such as sampling rate, resolution of digitization and S/N ratio are analyzed. Result show accuracy, computing time and cost for different techniques.
文摘In-flight particle velocity and flux distribution were measured using CCD thermal spray monitor system during supersonic plasma spray processing with nano-structured Al_2O_3-TiO_2 feed stocks. According to the results of particle flux measurement, the largest radian of the divergent particle stream is about 0.2. Within the measuring range, top speed of in-flight particles reached 800m/s. Particle acceleration was accomplished within 4cm down stream of the nozzle. Average particle velocity (about 450m/s) exceeded local sound speed (340m/s) even at a mean standoff distance of 17cm. With increasing mean standoff distance, average velocity of in-flight particle decreased according to a parabolic rule approximately. Image diagnosis showed that the result of in-flight particle velocity measurement is credible.
基金financially supported by the National Natural Science Foundation of China(Grant No.51541905)
文摘This paper presents a theoretic implementation method of Morphing Unmanned Submersible Aerial Vehicle （MUSAV）, which can both submerge in the water and fly in the air. Two different shapes are put forward so that the vehicle can suit both submergence and flight, considering the tremendous differences between hydrodynamic configuration and aerodynamic configuration of a vehicle. The transition of the two shapes can be achieved by using morphing technology. The water-to-air process, including water-exit, morphing, take-off and steady flight, is analyzed. The hydrodynamic and aerodynamic model of the vehicle exiting the water surface obliquely and then taking off into the air has been founded. The control strategy after morphing is analyzed and the control method is given. Numerical method is used to validate the motion model of the water-exit process. Results of simulations show the validity of the proposed model and the feasibility of MUSAV in theory.
文摘This paper presents a novel onboard system called In-Flight Awareness Augmentation System (IFA<sup>2</sup>S) to improve flight safety. IFA<sup>2</sup>S is designed to semi-automatically (with human supervision) avoid hazards and accidents due to either internal or external causal factors. The requirements were defined in an innovative way using Systems-Theoretic Process Analysis (STPA) method and applied next to model the system. IFA<sup>2</sup>S increases aircraft awareness regarding both itself and its environment and, at the same time, recognizes platform and operational constraints to act in accordance to predefined decision algorithms. Results are presented through simulations and flight tests using state machines designed to allow the adoption of appropriate actions for the identified hazards. The different decision algorithms are evaluated over as many as possible hazard situations by simulations conducted with software Labview and XPlane flight simulator. Flight tests are performed in a small fixed wing aircraft and make use of a limited version IFA<sup>2</sup>S, partially attending identified requirements. Results support the conclusion that IFA<sup>2</sup>S is capable of improving flight safety.
