Based on the linear parameter-varying （LPV） adaptive observer, the robust fault diagnosis for a class of LPV systems with external disturbances is studied. Since the flight control system （FCS） is nonlinear and ti...Based on the linear parameter-varying （LPV） adaptive observer, the robust fault diagnosis for a class of LPV systems with external disturbances is studied. Since the flight control system （FCS） is nonlinear and time-varying, the LPV technique is used for FCS. And then the adaptive fault estimation algorithm based on the LPV adaptive observer is proposed to estimate the fault. To minimize the effect of disturbances on the fault estimation, the H~ robust performance index is introduced to design the LPV adaptive fault diagnosis observer and the fault estimation algorithm. The result shows that the method has good estimation performance and is robust to external disturbances. The design method is presented in terms of linear matrix inequalities （LMIs）. Finally, a helicopter LPV FCS model with the actuator fault is used to illustrate the effectiveness of the proposed method.展开更多
Through taking uncertain mechanical parameters of composites into consideration,this paper carries out uncertain modal analysis for an unmanned aircraft landing gear.By describing correlated multi-dimensional mechanic...Through taking uncertain mechanical parameters of composites into consideration,this paper carries out uncertain modal analysis for an unmanned aircraft landing gear.By describing correlated multi-dimensional mechanical parameters as a convex polyhedral model,the modal analysis problem of a composite landing gear is transferred into a linear fractional programming(LFR)eigenvalue solution problem.As a consequent,the extreme-point algorithm is proposed to estimate lower and upper bounds of eigenvalues,namely the exact results of eigenvalues can be easily obtained at the extreme-point locations of the convex polyhedral model.The simulation results show that the proposed model and algorithm can play an important role in the eigenvalue solution problem and possess valuable engineering significance.It will be a powerful and effective tool for further vibration analysis for the landing gear.展开更多
This paper shows some properties of symmetry function induced by a convex body in a normal linear space. Some relationships between symmetry function induced by a convex body and Minkowski functional of the convex bod...This paper shows some properties of symmetry function induced by a convex body in a normal linear space. Some relationships between symmetry function induced by a convex body and Minkowski functional of the convex body are presented.展开更多
Without considering the influence of heat,existing fractal contact models are not applicable to analyze the contacts when the temperature changes.For this problem,the normal load model and the normal stiffness model o...Without considering the influence of heat,existing fractal contact models are not applicable to analyze the contacts when the temperature changes.For this problem,the normal load model and the normal stiffness model of thermal elasto-plastic contact of rough surfaces are developed respectively in this paper.The proposed model is based on the normal contact mechanics model of fractal theory of anisotropic and thermal elasto-plastic contact theory which can be used to characterize the rough surface thermodynamic properties.Then the validity of the model is verified.Finally,the influence of main parameters on the total normal load and the whole normal stiffness of thermal elasto-plastic contact at the interface is analyzed by contact simulation.The results show that the total normal load of thermal elasto-plastic contact increases with the increases of temperature.The whole normal stiffness of thermal elasto-plastic contact increases with increasing coefficient of linear expansion,scale factor,temperature difference or fractal dimension,but decreases with increasing fractal roughness.This model expands basic theory and applications of traditional models,and can be used to calculate and analyze the contacts when the temperature changes.展开更多
A method of verifying the viability criterion at a given point for a region with nonsmooth boundary, which is expressed by a quasidifferentiabl function, under a differential inclusion which is a convex hull of finite...A method of verifying the viability criterion at a given point for a region with nonsmooth boundary, which is expressed by a quasidifferentiabl function, under a differential inclusion which is a convex hull of finitely many functions, is proposed. By this method, determining the viability is transformed into solving a number of systems of linear inequalities, or equivalently solving a number of linear programming problems. For the other differential inclusion, called the generalized convex process, it is shown that viability condition holds for a polytope if and only if it holds at all of its vertices. This result is an extension of corresponding one for a linear control system.展开更多
and uses it imply that application In this paper the author gives a method of constructing characteristic matrices, to determine the Buchstaber invariants of all simple convex 3-polytopes, which each simple convex 3-p...and uses it imply that application In this paper the author gives a method of constructing characteristic matrices, to determine the Buchstaber invariants of all simple convex 3-polytopes, which each simple convex 3-polytope admits a characteristic function. As a further of the method, the author also gives a simple new proof of five-color theorem.展开更多
Abstract In the study of n-dimensional spherical or hyperbolic geometry, n≥3, the volume of various objects such as simplexes, convex polytopes, etc. often becomes rather difficult to deal with. In this paper, we use...Abstract In the study of n-dimensional spherical or hyperbolic geometry, n≥3, the volume of various objects such as simplexes, convex polytopes, etc. often becomes rather difficult to deal with. In this paper, we use the method of infinitesimal symmetrization to provide a systematic way of obtaining volume formulas of cones and orthogonal multiple cones in S^n（1） and H^n（-1）.展开更多
A small cover is a closed manifold M^n with a locally standard （Z2）^n-action such that its orbit space is a simple convex polytope P^n. Let A^n denote an n-simplex and P（m） an m-gon. This paper gives formulas for ...A small cover is a closed manifold M^n with a locally standard （Z2）^n-action such that its orbit space is a simple convex polytope P^n. Let A^n denote an n-simplex and P（m） an m-gon. This paper gives formulas for calculating the number of D-J equivalent classes and equivariant homeomorphism classes of orientable small covers over the product space △^n1 × △^n2 × P（m）, where n1 is odd.展开更多
The entropy of a hypersurface is given by the supremum over all F-functionals with varying centers and scales, and is invariant under rigid motions and dilations. As a consequence of Huisken's monotonicity formula...The entropy of a hypersurface is given by the supremum over all F-functionals with varying centers and scales, and is invariant under rigid motions and dilations. As a consequence of Huisken's monotonicity formula, entropy is non-increasing under mean curvature flow. We show here that a compact mean convex hypersurface with some low entropy is diffeomorphic to a round sphere. We also prove that a smooth selfshrinker with low entropy is a hyperplane.展开更多
基金Supported by the National Natural Science Foundation of China(60811120024)Aeronautical Scienceand Technology Innovation Foundation of China(08C52001)~~
文摘Based on the linear parameter-varying （LPV） adaptive observer, the robust fault diagnosis for a class of LPV systems with external disturbances is studied. Since the flight control system （FCS） is nonlinear and time-varying, the LPV technique is used for FCS. And then the adaptive fault estimation algorithm based on the LPV adaptive observer is proposed to estimate the fault. To minimize the effect of disturbances on the fault estimation, the H~ robust performance index is introduced to design the LPV adaptive fault diagnosis observer and the fault estimation algorithm. The result shows that the method has good estimation performance and is robust to external disturbances. The design method is presented in terms of linear matrix inequalities （LMIs）. Finally, a helicopter LPV FCS model with the actuator fault is used to illustrate the effectiveness of the proposed method.
基金supported by the National Nature Science Foundation of China(No.51805503)the Beijing Natural Science Foundation(No.3202035)。
文摘Through taking uncertain mechanical parameters of composites into consideration,this paper carries out uncertain modal analysis for an unmanned aircraft landing gear.By describing correlated multi-dimensional mechanical parameters as a convex polyhedral model,the modal analysis problem of a composite landing gear is transferred into a linear fractional programming(LFR)eigenvalue solution problem.As a consequent,the extreme-point algorithm is proposed to estimate lower and upper bounds of eigenvalues,namely the exact results of eigenvalues can be easily obtained at the extreme-point locations of the convex polyhedral model.The simulation results show that the proposed model and algorithm can play an important role in the eigenvalue solution problem and possess valuable engineering significance.It will be a powerful and effective tool for further vibration analysis for the landing gear.
基金Supported by the Natural Science Foundation of China（10771086） Supported by the Natural Science Foundation of Fujian Province（S0650021）
文摘This paper shows some properties of symmetry function induced by a convex body in a normal linear space. Some relationships between symmetry function induced by a convex body and Minkowski functional of the convex body are presented.
基金Project(52130501)supported by the National Natural Science Foundation of ChinaProject(LY20E050012)supported by the Natural Science Foundation of Zhejiang Province,ChinaProject(Y201942581)supported by the Scientific Research Project of Education Department of Zhejiang Province,China。
文摘Without considering the influence of heat,existing fractal contact models are not applicable to analyze the contacts when the temperature changes.For this problem,the normal load model and the normal stiffness model of thermal elasto-plastic contact of rough surfaces are developed respectively in this paper.The proposed model is based on the normal contact mechanics model of fractal theory of anisotropic and thermal elasto-plastic contact theory which can be used to characterize the rough surface thermodynamic properties.Then the validity of the model is verified.Finally,the influence of main parameters on the total normal load and the whole normal stiffness of thermal elasto-plastic contact at the interface is analyzed by contact simulation.The results show that the total normal load of thermal elasto-plastic contact increases with the increases of temperature.The whole normal stiffness of thermal elasto-plastic contact increases with increasing coefficient of linear expansion,scale factor,temperature difference or fractal dimension,but decreases with increasing fractal roughness.This model expands basic theory and applications of traditional models,and can be used to calculate and analyze the contacts when the temperature changes.
基金This research is supported by the National Natural Science Foundation of China under Grant No. 10671126 and Shanghai Leading Academic Discipline Project under Grant No. S30501.
文摘A method of verifying the viability criterion at a given point for a region with nonsmooth boundary, which is expressed by a quasidifferentiabl function, under a differential inclusion which is a convex hull of finitely many functions, is proposed. By this method, determining the viability is transformed into solving a number of systems of linear inequalities, or equivalently solving a number of linear programming problems. For the other differential inclusion, called the generalized convex process, it is shown that viability condition holds for a polytope if and only if it holds at all of its vertices. This result is an extension of corresponding one for a linear control system.
基金the National Natural Science Foundation of China(No.10931005)the Shang-hai National Natural Science Foundation(No.10ZR1403600)the Research Fund for the DoctoralProgram of Higher Education of China(No.20100071110001)
文摘and uses it imply that application In this paper the author gives a method of constructing characteristic matrices, to determine the Buchstaber invariants of all simple convex 3-polytopes, which each simple convex 3-polytope admits a characteristic function. As a further of the method, the author also gives a simple new proof of five-color theorem.
文摘Abstract In the study of n-dimensional spherical or hyperbolic geometry, n≥3, the volume of various objects such as simplexes, convex polytopes, etc. often becomes rather difficult to deal with. In this paper, we use the method of infinitesimal symmetrization to provide a systematic way of obtaining volume formulas of cones and orthogonal multiple cones in S^n（1） and H^n（-1）.
基金supported by the National Natural Science Foundation of China(No.11371118)the Specialized Research Fund for the Doctoral Program of Higher Education(No.20121303110004)the Natural Science Foundation of Hebei Province(No.A2011205075)
文摘A small cover is a closed manifold M^n with a locally standard （Z2）^n-action such that its orbit space is a simple convex polytope P^n. Let A^n denote an n-simplex and P（m） an m-gon. This paper gives formulas for calculating the number of D-J equivalent classes and equivariant homeomorphism classes of orientable small covers over the product space △^n1 × △^n2 × P（m）, where n1 is odd.
文摘The entropy of a hypersurface is given by the supremum over all F-functionals with varying centers and scales, and is invariant under rigid motions and dilations. As a consequence of Huisken's monotonicity formula, entropy is non-increasing under mean curvature flow. We show here that a compact mean convex hypersurface with some low entropy is diffeomorphic to a round sphere. We also prove that a smooth selfshrinker with low entropy is a hyperplane.
