Analysis of adaptive shell structures using a refined laminated model

This work presents the development of a shell conical panel finite element model, which has the possibility of having embedded piezoelectric actuators and/or sensors patches. A mixed laminated theory is used, which combines an equivalent single layer higher order shear deformation approach for the mechanical behavior with a layerwise representation in the thickness direction to describe the distribution of the electric potential in each of the piezoelectric layers of the finite element. The electrical potential function is represented through a linear variation across the thickness with two electric potential nodes for each piezoelectric layer. Based in this model an active damping scheme applied to laminated shell structures is presented and discussed.     

差动式磁控形状记忆合金执行器研究

磁控形状记忆合金（MSMA）是一种新型具有形状记忆功能的合金材料,特别适合于制造高精度的运动与位置控制执行器.针对传统MSMA执行器磁场励磁控制功率大、恢复弹簧压力不易调整和MSMA变形受温度影响较大等缺点,提出了一种差动式MSMA执行器,采用永磁体产生恒定偏磁磁场,励磁绕组仅提供差动可控磁场,两个MSMA元件轮流工作,其中一个元件变形产生的压力用于另一个元件恢复变形从而取消了恢复弹簧.该差动式MSMA执行器减小了控制功率,消除了温度对MSMA的影响,提高了控制精度、稳定性和动态响应速度.文中给出了样机实验结果.     

国产核电电动执行器的发展前景

本文阐述了核电执行器的试验要求、国产核电执行器的基本状况以及在国内的发展前景，为核电站用电动执行器的逐步国产化提供一定的参考。     

Dielectric Elastomers in Actuator Technology

Electroactive polymers (EAPs) are characterized by their ability to respond to external electric stimulation by displaying a significant shape or size displacement. Actuators, based on dielectric elastomers exhibiting low elastic stiffness and high dielectric constants, can produce high strain levels from 10 to 380 %. Typically, acrylic and silicone materials are used as dielectric layer in such actuators. Their potential to mimic the movement of animals, insects and even human body parts are increasingly of interest for researchers in the field of biomimetics, as well as more classical application fields like robotics. The control of the most important material properties, elastic moduli and dielectric constants of the dielectric elastomers and electrode materials, together with the control of fabrication parameters i.e. film thickness, electrode manufacturing as well as design of the actuator configuration allow the fabrication of tailor‐made actuators, which match the necessary requirements for a given application. Theoretical models contribute to a deeper understanding of EAP actuators and improve design and optimisation.     

The FEM optimization of active vibration control in structures by solving the corresponding two-point-boundary-value problem

An algorithm for solving optimal active vibration control problems by the finite element method (FEM) is presented. The optimality equations for the problem are derived from Pontryagin’s principle in the form of a set of the fourth order ordinary differential equations that, together with the initial and final boundary conditions, constitute the boundary value problem in the time domain, which in control is referred to as a two-point-boundary-value problem. These equations decouple in the modal space and can be solved by the FEM technique. An analogy between the optimality equations and the governing equations for a set of certain static beams permits obtaining numerical solutions to the optimal control problem with the help of standard ‘structural’ FEM software. The optimal action of actuators is automatically calculated by applying the independent modal space control concept. The structure’s response to actuation forces is also determined and can independently be verified for spillover effects. As an illustration, the algorithm is used for the analysis of optimal action of actuators to attenuate vibrations of an elastic fin.     

High-order tracking differentiator based adaptive neural control of a flexible air-breathing hypersonic vehicle subject to actuators constraints

In this paper, an adaptive neural controller is exploited for a constrained flexible air-breathing hypersonic vehicle (FAHV) based on high-order tracking differentiator (HTD). By utilizing functional decomposition methodology, the dynamic model is reasonably decomposed into the respective velocity subsystem and altitude subsystem. For the velocity subsystem, a dynamic inversion based neural controller is constructed. By introducing the HTD to adaptively estimate the newly defined states generated in the process of model transformation, a novel neural based altitude controller that is quite simpler than the ones derived from back-stepping is addressed based on the normal output-feedback form instead of the strict-feedback formulation. Based on minimal-learning parameter scheme, only two neural networks with two adaptive parameters are needed for neural approximation. Especially, a novel auxiliary system is explored to deal with the problem of control inputs constraints. Finally, simulation results are presented to test the effectiveness of the proposed control strategy in the presence of system uncertainties and actuators constraints.     

Multi-scale distributed parameter modeling of ionic polymer-metal composite soft actuator

This paper describes the modeling of a soft actuator called an ionic polymer-metal composite (IPMC) by using distributed port-Hamiltonian (DPH) systems on multiple spatial scales. The multi-scale IPMC structure consists of an electric double layer, an electro-stress diffusion coupling and a flexible beam. The coupling of the structure can be modeled by the DPH systems with unidirectional energy flows on connecting boundaries of the subsystems, and it is called a boundary multi-scale coupling. The boundary multi-scale couplings derived from detailed models can be used for multi-scale retaining interconnections of various reduced models, e.g. numerical models with approximations.     

Reliability enhancement in nickel-particle-dispersed alkaline niobate piezoelectric composites and actuators

Piezoceramics and related devices are naturally fragile. Here we have produced piezoelectric composites of Ni-particle-dispersed Li-doped (K,Na)NbO₃ (LKNN/Ni), and used these composites to make actuators with functionally graded microstructure (FGM). The mechanical properties of the LKNN/Ni composites were greatly enhanced by the incorporation of Ni particles. An LKNN-20%Ni composite exhibited double the fracture toughness of the monolithic LKNN ceramic. An LKNN/Ni piezoelectric FGM actuator subjected to a large number of cycles of electrical loading still maintained acceptable driven performance. The enhancement of reliability in the LKNN/Ni composites and actuators is attributed to the uniformly dispersed Ni particles in the piezoceramic matrix. Deformation of these Ni particles absorbs the energy of crack propagation and thus greatly strengthens the composites and devices. These new FGMs contribute further to the reliability enhancement of piezoelectric actuators.