Shape Control Of Structures Research Articles

Optimal shape control of a beam using piezoelectric actuators with low controlvoltage

This paper deals with the shape control of a cantilever beam structure by using laminatedpiezoelectric actuators (LPAs) with a low control voltage. The shape control equation ofthe cantilever beam partially covered with LPAs is derived based on the constitutiverelations of the elastic material and piezoelectric material and shear deformation beamtheory (Timoshenko theory). The actuating forces produced by the LPAs areformulated as well. It reveals how the actuating forces depend on the number ofpiezoelectric layers, the thickness of piezoelectric layers and the position of theactuators. The driving voltages of the LPAs are then determined by a geneticoptimization algorithm. The shape control of the cantilever beam from applying theoptimal voltage to the LPAs is simulated. The simulation results show that anLPA of large layer number is able to diminish effectively the pre-deflection of thebeam under a low control voltage. The voltage applied to the LPA of five layerswas almost five times smaller than that of one layer. In addition, increasing thenumber of LPA layers can significantly improve the control performance as theacting forces of the LPA are a quadratic function of the LPA layer number. TheL2 norm of the displacement array of all nodes is diminished about 30% after optimization.Also with the same low control voltage, the LPA can obtain a better control performancethan the conventional single layer piezoelectric actuator.

Optimal placement of piezoelectric curve beams in structural shape control

Shape control of flexible structures using piezoelectric materials has attracted much attention due to its wide applications in controllable systems such as space and aeronautical engineering. The major work in the field is to find a best control voltage or an optimal placement of the piezoelectric actuators in order to actuate the structure shape as close as possible to the desired one. The current research focus on the investigation of static shape control of intelligent shells using spatially distributed piezoelectric curve beam actuators. The finite element formulation of the piezoelectric model is briefly described. The piezoelectric curve beam element is then integrated into a collocated host shell element by using nodal displacement constraint equations. The linear least square method (LLSM) is employed to get the optimum voltage distributions in the control system so that the desired structure shape can be well matched. Furthermore, to find the optimal placement of the piezoelectric curve beam actuators, a genetic algorithm (GA) is introduced in the computation model as well as the consideration of the different objective functions. Numerical results are given to demonstrate the validity of the theoretical model and numerical algorithm developed.

Active shape control of composite structures under thermal loading

Maintaining the shape of high-precision structures such as space antennas and opticalmirrors is still a challenging issue for designers. These structures are subjected to varyingtemperature conditions which often introduce thermal distortions. The development ofsmart materials offers great potential to correct the shape and to minimize thesurface error. In this study, shape control of a composite structure under thermalloading using piezocomposites is investigated. The composite structure is made ofa foam core and two carbon–epoxy face sheets. Macro-fiber composite (MFC™)patches are bonded on one side of the structure. The structure is subjected to athrough-the-thickness temperature gradient which induces thermal distortion,essentially in the form of bending. The objective is to apply electric potential tothe MFC™ actuators such that the deflection can be minimized. Finite-elementanalyses are conducted using the commercial software ABAQUS. Experimentsare performed to study thermally induced distortion, piezoelectric actuation,and compensation of thermal distortion using MFC™ actuators. Numerical andexperimental results are compared. A control loop based on strain measurements isused to actively control the structure. The results show that MFC™ actuators cancompensate thermal distortion at all times, and that this is an efficient methodology.

LINEAR INVERSE ANALYSIS OF STRESS AND SHAPE CONTROL OF STRUCTURES WITH MEMBERS OF VARIABLE LENGTH

There are many structures that are controlled their shapes and/or stress distribution by being actively varied the length of their members. Some of the structures with vibration control system, so-called variable geometry trusses and many of the tension structures are examples of such structures. One of the difficulties in the design and realization of such structural systems is how to grasp the relationship between the member length change, and their shapes and stress distribution. In this paper a simple and effective linear inverse theory for the control of such structures is described. Then its validity is proved by showing some numerical examples and the comparison with the results of real scale tests of a tensegrity frame.

Application of SMA in Membrane Structure Shape Control

Shape memory alloy (SMA) actuators have found a wide range of applications due to their unique properties such as high force, long stroke, small size, light weight, and silent operation, etc. However, their strong nonlinear properties make them a challenge to achieve accurate actuations. A simple control strategy is presented based on the idea of adjusting the SMA wire temperature as rapidly as possible. This strategy is simple, stable, and requires no hysteresis model or thermal model. The strategy is tested first on tracking displacement outputs, and effects of updating rate and input current on control accuracy are also discussed. It is then used for active shape control of a membrane structure model by adjusting its boundary tensions. Results indicate that under the developed control strategy, SMA wire actuators can offer very good accuracy in tracking displacement outputs and tension outputs. For the membrane structure shape control, the structure shape precision is improved greatly.

Topology optimization-based distribution design of actuation voltage in static shape control of plates

This paper investigates the optimal spatial distribution of single-channel actuation voltage in static structural shape control problem. It is pointed out that single-channel actuation voltage input for shape control applications is of practical importance due to its ease of implementation. The Mindlin plate theory is used in the finite element modeling of laminates with piezoelectric layers. The optimal distribution of the single-channel actuation voltage is formulated as a discrete optimization problem with tri-level design variables, where a least-square function measuring the structural shape error is to be minimized under a constraint on the control effort. Such a problem is then transformed into a continuous one by introducing element-wise artificial design variables defining the topological feature of the control voltage distribution. A power-law function relating the design variables and the applied voltages is proposed to penalize intermediate values of the design variables. Based on the sensitivity analysis, the problem is solved effectively using the MMA algorithm tailored for constrained least-square problems. Numerical examples presented demonstrate the validity of the proposed problem formulation and numerical approaches.

Shape-dependent electrocatalytic activity of platinum nanostructures

Since many metallic nanostructures with different shapes exhibit unique chemical and physical properties, a systematic attempt to synthesize these shape-controlled structures for property–shape correlation remains an important challenge in contemporary materials chemistry. Main difficulties like poor shape selectivity, low yield, presence of impurity phases, difficulty of separation, etc., are exacerbated since metallic structures have high surface energies which favour lower surface areas, and consequently many synthesis strategies, including the use of hard and soft templates and external nucleating agents, are being employed along with theoretical guidelines from density functional calculations on simpler systems. One of the important application areas where these structures have gained profound attention is in electrocatalysis, where the kinetics of many structure-sensitive reactions of technological relevance have been experimentally observed to show drastic changes with shape especially in the nanosize domain, at least in one dimension. Considering their scientific and technological importance, this feature article provides an overview of the recent progress on the shape-controlled synthesis of metallic nanostructures with special emphasis on platinum, and their crucial role in the electrocatalysis of anodic reactions for polymer electrolyte fuel cells.

Evolutionary piezoelectric actuators design optimisation for static shape control of smart plates

This paper presents a new evolutionary algorithm to solve various structural shape control problems of smart composite plate structures with active piezoelectric actuators. The linear least square (LLS) method and the features of evolutionary strategies are employed to find the applied voltages and shapes for the active piezoelectric actuators, respectively, in order to achieve the desired structural shapes by gradually removing the active piezoelectric material part of the element based on the error function sensitivity number. In the finite element (FE) analysis, an error function sensitivity number, including electro-mechanical effect, is one derived to compute the change in error functions that are defined in terms of least square difference between calculated and desired structural shapes. The evolutionary piezoelectric actuator design optimisation (EPADO) is proposed here to optimise the active piezoelectric actuator shape at a given applied voltage. Finally, several numerical examples are presented to verify that the proposed algorithm improves structural shape control by reducing the error function.

Extensive Experiments on Genetic Algorithms for the Optimization of Piezoelectric Actuator Locations

For shape control of smart structures, we have developed a series of micro-genetic-algorithms for optimal placement of a large number of piezoelectric actuators. Here, we investigate the effect on the solution quality of 1) different random seed generators; 2) restart criteria in micro-genetic-algorithms, specifically the two parameters, the number of generations used for the inner loop and the level of diversity in the population; and 3) different numbers of actuators. We also report a comparison of our genetic algorithms with two heuristic integer programming algorithms: worst-out-best-in and exhaustive single point substitution proposed by Haftka and Adelman (Selection of Actuator Locations for Static Shape Control of Large Space Structures by Heuristic Integer Programming, Computers and Structures, Vol. 20, 1985, pp. 572-582). Using current genetic algorithms, we not only get better layouts of actuators than reported in our previous publications, but we also find that the most distinct nature of genetic algorithms is randomness and robustness. The best parameter setting of genetic algorithms is dependent on both the number of evaluations used for termination and the seed generator used. Moreover, the best parameter setting of genetic algorithms varies as the number of actuators changes. To get the highest quality of solutions, multiple runs using different random seed generators are necessary. The time of investigation can be significantly reduced using a coarse grain parallel computing. Comparison of our genetic algorithms with the worst-out-best-in and exhaustive single point substitution shows that for a group of runs our genetic algorithms usually converge faster in the first few thousand evaluations and are more likely to find better solutions than the worst-out-best-in and exhaustive single point substitution algorithms.

Experimental Studies on Active Shape Control of Composite Structures using SMA Actuators

In this article, the experimental modeling and active shape control of hybrid composite structures actuated by shape memory alloy (SMA) wires are presented and discussed. The thermomechanical properties of the SMA wires are experimentally measured. SMA actuators with residual strains are prepared by loading-unloading tensile tests. Hybrid composite structures are established by attaching the SMA actuators on the surface of a graphite/epoxy composite beam and plate by bolt-joint connectors. The first-order numerical model is used to model the response of the hybrid composite structures attached to the SMA actuators. The parameters of the first-order model are experimentally determined and the response is compared with experimental data. For faster and more accurate shape/deflection control of the hybrid composite structure, feedforward and proportional integral derivative (PID) feedback controllers are designed and applied to the hybrid composite structure. The PID feedback controller significantly improves the performance of the SMA actuators.

Testing of Membrane Space Structure Shape Control Using Genetic Algorithm

Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields.

Macroelectronics

AbstractAs revolutionary as microelectronics has been as a technology, there are functions that it does not address. Microelectronics focuses on ever-smaller integrated circuits (ICs) in ever-fewer square millimeters of space to increase clock speeds and decrease the power required for computer processing functions. However, applications requiring control, communications, computing, and sensing over a large area are difficult or costprohibitive to achieve because of the material incompatibilities of traditional ICs with structures, materials, and manufacturing technology. Macroelectronics addresses these applications with the aim of providing active control circuitry in situ over areas of many square meters for displays, solar panels, x-ray imagers, surface measurements, structural shape control, vehicle health monitoring, and other large-system applications. The materials challenges of macroelectronics integrated circuits (MEICs) reviewed in this issue include lightweight flexible substrates, thin-film transistors (TFTs) with IC or near-IC performance, modeling, and manufacturing technology. Compatible component materials, flexible substrates, processing conditions, host system composition, and functionality provide grand challenges that are just beginning to be addressed by researchers.

Adaptronic Systems for Aerospace Applications (Adaptronische Systeme für Anwendungen in der Luftfahrt)

Summary An overview of different activities related to the application of adaptronics is given, which includes structural health monitoring, shape control and active flow, damping of vibration and noise, and smart skins. Micro aerial vehicles are described as an interesting adaptronics demonstrator platform with aerospace in general being vigorously showing where adaptronics can be applied.

Shape Control of Cable-Network Structures Based on Concept of Self-Equilibrated Stresses

Shape Control of Cable-Network Structures Based on Concept of Self-Equilibrated Stresses

Dynamic shape control of subdomains of structures

In the present paper the method of shape control of structures is applied to the following problem. Given a three-dimensional elastic body with sources of self-stress acting in the background, how do we have to distribute these sources within a subdomain of the structure in order to control the deformation of this subdomain. In the first part we present a solution for given disturbances, such as body forces and surface tractions, for which an open-loop strategy is sufficient. In the second part we assume the time variation of the disturbances unknown; hence, a closed-loop strategy has to be applied. We design distributed sensors and actuators to be collocated to each other. This allows us to use a simple PD controller to ensure the stability of the closed-loop system. In the third part we discuss the application of discretely acting actuators and sensors to approximate the distributed ones. This is especially important in practical applications. Finally, numerical results for a cantilever beam are presented. Results are excellent with respect to the goal of controlling the deformation within a subsection of the beam. Copyright © 2005 John Wiley & Sons, Ltd.

Voltage and evolutionary piezoelectric actuator design optimisation for static shape control of smart plate structures

This paper presents an iterative technique for multi-criteria design problem in structural shape control applications, which consist of voltage and piezoelectric actuator criteria designs based on the linear least square (LLS) method and the evolutionary piezoelectric actuator design optimisation (EPADO), respectively. The criterion identifies the overall effects of the error function on these two components of design criteria due to removing active piezoelectric materials. Two algorithms are proposed. One is the alternative voltage and evolutionary piezoelectric actuator design optimisation (AVEPADO). Another is voltage and evolutionary piezoelectric actuator design optimisation (VEPADO). Both algorithms aim to simultaneously optimise the active piezoelectric actuator configuration and the applied voltage. Numerical results are presented to show that the proposed algorithms are capable of determining both voltage distribution and piezoelectric actuators configuration in structural shape control problems.

Static shape control of repetitive structures integrated with piezoelectric actuators

In this paper, several simplification methods are presented for shape control ofrepetitive structures such as symmetrical, rotational periodic, linear periodic,chain and axisymmetrical structures. Some special features in the differentialequations governing these repetitive structures are examined by considering the wholestructures. Based on the special properties of the governing equations, severalmethods are presented for simplifying their solution process. Finally, the static shapecontrol of a cantilever symmetrical plate with piezoelectric actuator patches isdemonstrated using the present simplification method. The result shows that presentmethods can effectively be used to find the optimal control voltage for shapecontrol.

Energy Optimization in Local Shape Control of Structures with Nonlinear Peizoelectric Actuators

Shape control of a local part of a structure rather than the entire structure is often encountered in engineering practice using as less control energy as possible. Energy optimization for local shape control of structures integrated with nonlinear piezoelectric actuators is investigated. The local shape is maintained by assigning the generalized displacements to the desired ones at some given points. The distortion of the residual shape is also limited to a given range. This optimal control voltage distribution is solved by using elimination and the Lagrange multiplier method. A unique solution scheme based on Cholesky decomposition and eigenvalue problem is given to reduce the computational load for finding the Lagrange multipliers from an algebraic equation. The final optimal control voltage distribution for the nonlinear system is obtained by an iteration procedure. Finally, an example is given to illustrate the present method, and the results show that proper relaxation of the error tolerance of the residual shape can significantly reduce the control energy requested for the local shape control of the designated area.

Path Planning and Open-Loop Shape Control of Modular Tensegrity Structures

We characterize the planned path for a shape change in a tensegrity structure as a path from one equilibrium to another. For tensegrity structures, this means that in every desired configuration the structure has to satisfy tensegrity conditions. Required trajectories are feasible, and changes in potential energy are not required to follow these trajectories. This is a benefit over normal control paths that require strain-energy changes because such energy must be supplied by the control system. For the class of modular tensegrity structures defined, configurations that satisfy tensegrity conditions can be parameterized in terms of only a few parameters that can meaningfully be related to the overall desired shape of the structures. Equilibrium rest lengths of string elements are defined first. An open-loop rest-length control is defined by slowly varying desired geometric parameters, which causes the structure to track trajectories defined by the time-dependent geometric parameters. Examples with simulation results show different reconfiguration scenarios of tensegrity plates and class-2 tensegrity towers.

Active robust shape control of flexible structures

In recent years, active control methods have been developed to improve the performance of flexible space structures, with most of them focused on the suppression of structural vibration. In this paper, an approach for active robust shape control of flexible structures is developed using piezoceramic actuators and strain sensors. Dynamic models for flexible structures with integrated actuators and sensors are derived and a controller is designed to cause the structure to maintain a specified shape and reject disturbances. The control system robustness of flexible structures with parameter perturbation uncertainty is discussed. This active robust shape control method is tested via experimental implementation.