Robust tracking control design for a flexible air-breathing hypersonic vehicle

A nonlinear robust controller was presented to improve the tracking control performance of a flexible air-breathing hypersonic vehicle(AHV) which is subjected to system parametric uncertainties and unknown additive time-varying disturbances.The longitudinal dynamic model for the flexible AHV was used for the control development.High-gain observers were designed to compensate for the system uncertainties and additive disturbances.Small gain theorem and Lyapunov based stability analysis were utilized to prove the stability of the closed loop system.Locally uniformly ultimately bounded tracking of the vehicle's velocity,altitude and attack angle were achieved under aeroelastic effects,system parametric uncertainties and unknown additive disturbances.Matlab/Simulink simulation results were provided to validate the robustness of the proposed control design.The simulation results demonstrate that the tracking errors stay in a small region around zero.

Dynamic modeling and simulation for the flexible spacecraft with dynamic stiffening

A rigid flexible coupling physical model which can represent a flexible spacecraft is investigated in this paper. By applying the mechanics theory in a non-inertial coordinate system,the rigid flexible coupling dynamic model with dynamic stiffening is established via the subsystemmodeling framework. It is clearly elucidated for the first time that,dynamic stiffening is produced by the coupling effect of the centrifugal inertial load distributed on the beamand the transverse vibration deformation of the beam. The modeling approach in this paper successfully avoids problems which are caused by other popular modeling methods nowadays： the derivation process is too complex by using only one dynamic principle; a clearly theoretical explanation for dynamic stiffening can＇t be provided. First,the continuous dynamic models of the flexible beamand the central rigid body are established via structural dynamics and angular momentumtheory respectively. Then,based on the conclusions of orthogonalization about the normal constrained modes,the finite dimensional dynamic model suitable for controller design is obtained. The numerical simulation validations showthat： dynamic stiffening is successfully incorporated into the dynamic characteristics of the first-order model established in this paper,which can indicate the dynamic responses of the rigid flexible coupling system with large overall motion accurately,and has a clear modeling mechanism,concise expressions and a good convergence.

Flexible Covalent Organic Frameworks:Design,Synthesis,and Applications

Structural flexibility is an intriguing characteristic observed in materials that endows them with dynamic properties,allowing for intelligent adaptation and deformation in response to varying conditions.Covalent organic frameworks(COFs),a promising class of crystalline porous polymers,have garnered significant attention due to their unique features,including well-ordered,predesignable,and tunable structures,as well as their light-weighted nature and high thermal/chemical stability.Integrating flexibility into COFs offers a captivating pathway for developing advanced materials with dynamic properties and versatile functionalities.The flexible COF field is currently experiencing rapid expansion,and there is a growing need for systematic review articles that offer a comprehensive overview of the developments in this domain.In this mini-review,we delve into the factors that contribute to structural flexibility in COFs from the point of structural design.We summarize and categorize various modes of achieving flexibility across different dimensions,and discuss the potential applications of flexible COFs in vapor/gas adsorption,sensing,and smart membrane separations;further,we highlight their prospects and future research advancement.

Contact-impact formulation for multi-body systems using component mode synthesis

The efficiency and accuracy are two most concerned issues in the modeling and simulation of multi-body systems involving contact and impact. This paper proposed a formulation based on the component mode synthesis method for planar contact problems of flexible multi-body systems. A flexible body is divided into two parts： a contact zone and an un-contact zone. For the un-contact zone, by using the fixed-interface substructure method as reference, a few low-order modal coordinates are used to replace the nodal coordinates of the nodes, and meanwhile, the nodal coordinates of the local impact region are kept unchanged, therefore the total degrees of freedom （DOFs） are greatly cut down and the computational cost of the simulation is significantly reduced. By using additional constraint method, the impact constraint equations and kinematic constraint equations are derived, and the Lagrange equations of the first kind of flexible multi-body system are obtained. The impact of an elastic beam with a fixed half disk is simulated to verify the efficiency and accuracy of this method.

Improved Market Mechanism for Energy Storage Based on Flexible State of Energy

In this paper,a new operational mode is proposed for energy storage,in which an improved semi-centralized mechanism is proposed for energy storage to participate in the day-ahead energy market.The new operational mode,i.e.,the flexible state-of-energy(SOE)mode,is proposed based on the previous fixed SOE mode,under which the final SOE of energy storage at the end of the last period of the scheduling horizon is not limited to a predefined value.Accordingly,the value of the SOE is introduced to quantify the deviation cost of the final SOE from the predefined value.Under the proposed market mechanism,energy storage submits to the system operator the unit charging and discharging costs and the value of the SOE.The system operator dispatches the charging and discharging power of energy storage according to the data submitted and system operations.A comparative analysis is conducted in the case studies,and results demonstrate that the proposed mechanism is efficient in further realizing the flexibility potential of energy storage and reducing the total cost of the power system.