Damage on surfaces often compromises the efficiency of some types of energy production, the safety and reliability of components, and ultimately increases costs. The environment can degrade the structural integrity of...Damage on surfaces often compromises the efficiency of some types of energy production, the safety and reliability of components, and ultimately increases costs. The environment can degrade the structural integrity of surfaces in service by the accumulation of large numbers of small destructive events, which based on the Central Limit Theorem leads to a Gaussian distribution of pit depth. In order to develop safety envelopes relating fracture loci with topological parameters of a brittle material, scatter plots were obtained and analyzed. Starting with an engineering surface, after 6 to 9 micrometers of average degradation depth, safety envelopes could be developed using average roughness and two other proposed parameters. Interestingly, maximum pit depth showed very low correlation with the location of fracture, at the early stage of degradation studied. This is attributed to relaxation of stress concentration at a given pit location due to the assuaging effect caused by neighboring pits. Additionally, energy at fracture was obtained, and a maximum relaxation region was observed. Analytical and experimental study of this region, as well as ductility effects are currently under research.展开更多
In this paper,as for the unmanned air vehicle(UAV)under external disturbance,an attainable-equilibrium-set-based safety fight envelope(SFE)calculation method is proposed,based on which a prescribed performance protect...In this paper,as for the unmanned air vehicle(UAV)under external disturbance,an attainable-equilibrium-set-based safety fight envelope(SFE)calculation method is proposed,based on which a prescribed performance protection control scheme is presented.Firstly,the existing definition of the SFE based on attainable equilibrium set(AES)is extended to make it consistent and suitable for the UAV system under disturbance.Secondly,a higher-order disturbance observer(HODO)is developed to estimate the disturbances and the disturbance estimation is applied in the computation of the SFE.Thirdly,by using the calculated SFE,a desired safety trajectory based on the time-varying safety margin function and first-order filter is developed to prevent the states of the UAV system from exceeding the SFE.Moreover,an SFE protection controller is proposed by combining the desired safety trajectory,backstepping method,HODO design,and prescribed performance(PP)control technique.In particular,the closed-loop system is established on the basis of disturbance estimation error,filter error,and tracking error.Finally,the stability of the closed-loop system is verified by the Lyapunov stability theory,and the simulations are presented to illustrate the effectiveness of the proposed control scheme.展开更多
文摘Damage on surfaces often compromises the efficiency of some types of energy production, the safety and reliability of components, and ultimately increases costs. The environment can degrade the structural integrity of surfaces in service by the accumulation of large numbers of small destructive events, which based on the Central Limit Theorem leads to a Gaussian distribution of pit depth. In order to develop safety envelopes relating fracture loci with topological parameters of a brittle material, scatter plots were obtained and analyzed. Starting with an engineering surface, after 6 to 9 micrometers of average degradation depth, safety envelopes could be developed using average roughness and two other proposed parameters. Interestingly, maximum pit depth showed very low correlation with the location of fracture, at the early stage of degradation studied. This is attributed to relaxation of stress concentration at a given pit location due to the assuaging effect caused by neighboring pits. Additionally, energy at fracture was obtained, and a maximum relaxation region was observed. Analytical and experimental study of this region, as well as ductility effects are currently under research.
基金supported in part by the National Science Fund for Distinguished Young Scholars 61825302in part by the National Natural Science Foundation of China under Grant U2013201in part by the Key R&D projects(Social Development)in Jiangsu Province of China under Grant BE2020704.
文摘In this paper,as for the unmanned air vehicle(UAV)under external disturbance,an attainable-equilibrium-set-based safety fight envelope(SFE)calculation method is proposed,based on which a prescribed performance protection control scheme is presented.Firstly,the existing definition of the SFE based on attainable equilibrium set(AES)is extended to make it consistent and suitable for the UAV system under disturbance.Secondly,a higher-order disturbance observer(HODO)is developed to estimate the disturbances and the disturbance estimation is applied in the computation of the SFE.Thirdly,by using the calculated SFE,a desired safety trajectory based on the time-varying safety margin function and first-order filter is developed to prevent the states of the UAV system from exceeding the SFE.Moreover,an SFE protection controller is proposed by combining the desired safety trajectory,backstepping method,HODO design,and prescribed performance(PP)control technique.In particular,the closed-loop system is established on the basis of disturbance estimation error,filter error,and tracking error.Finally,the stability of the closed-loop system is verified by the Lyapunov stability theory,and the simulations are presented to illustrate the effectiveness of the proposed control scheme.
