Flexible Structural Systems Research Articles

The control of flexible structure systems by division motion method

The paper presents a new approach to the flexible structure systems synthesis on the base of using a method to dynamic compensation and a division of motion on rate within the framework of systems with large coefficients and discontinuous control, allowing to decompose a problem of large dimensionality to the independently solved a problems of smaller dimensionality (Drakunov at el. 1990).

Planar Motion of a Cable-Supported Beam with Feedback Controlled Actions

Active tendon control for slender and flexible structural systems such as guyed mast and cable-stayed bridge, is an innovative methodology to contain their oscillations. In this paper, a simple cable-supported cantilever beam is controlled by means of an imposed longitudinal displacement at the grounded end of the cable aiming to stabilize planar oscillation amplitudes of both cable and beam. The equations of motion of this system are obtained including cable elasticity through finite strain. Analytical eigensolutions of the linearized equations are used to investigate influences of mechanical characteristics on a family of structural systems and to derive a nonlinear discrete model by classical Galerkin method. A one mode model is used to design linear and nonlinear feedback control laws. Comparisons on the effectiveness of different strategies are made on the basis of both control intensity and system response amplitudes.

Modeling of a flexible beam actuated by shape memory alloy wires

A thermomechanical model is developed to predict the structural response of a flexible beam with shape memory alloy (SMA) wire actuators. A geometrically nonlinear static analysis is first carried out to investigate the deformed shape of a flexible cantilever beam caused by an externally-attached SMA wire actuated electrically. The actuation force applied by the SMA actuator to the beam is evaluated by solving a coupled problem that combines a thermodynamic constitutive model of SMAs with the heat conduction equation in the SMA and the structural model of the beam. To calculate the temperature history of the SMA actuator for given electrical current input, the heat transfer equation is solved with the electrical resistive heating being modeled as a distributed heat source along the SMA wire. The steps in the formulation are connected together through an iterative scheme that takes into account the static equilibrium of the beam and the constitutive relation of SMAs, thus translating an electrical current history input into beam strain output. The proposed model is used to simulate the experimental results, thus demonstrating the feasibility of using SMA actuators for shape control of active flexible structural systems.

Evaluation of Seismic Torsional Provisions in Uniform Building Code

The main change in the torsional provisions of the 1991 edition of the \IUniform Building Code\N (UBC) from the 1979 UBC edition is the need to amplify the accidental eccentricity for torsionally flexible structural systems. This paper evaluates the consequences of the change on the strength design requirement and the ductility demand on the edge lateral force-resisting elements in torsionally unbalanced structural systems, which are designed based on the two editions of the UBC code. The major improvement of the 1991 UBC is its ability to limit the additional ductility demand on the stiff-edge element of a torsionally unbalanced system to an acceptable level, even when the system is torsionally flexible.

Dynamic response analysis of flexible structural systems with nonlinear characteristics

Dynamic response analysis of flexible structural systems with nonlinear characteristics

Robust Observer-Based Control of Large Flexible Structures

This paper considers robust stabilization of the spillover phenomenon of large flexible structures. New frequency domain robustness measures for a large flexible structure system controlled by an observer-based compensator is derived via a state-space framework. In the present approach, control and observation spillover are viewed as parametric perturbations, and the total spillover (combination of control and observation spillover) is treated as the unmodeled dynamics. A robust observer-based output feedback control law, obtained by solving two algebraic Riccati equations, is provided. Finally, a simply supported beam example is included to illustrate the application.

Collocated Sensor/Actuator Positioning and Feedback Design in the Control of Flexible Structure System

This paper presents a new control design method for the control of flexible systems that not only guarantees closed-loop asymptotic stability but also effectively suppresses vibration. This method allows integrated determination of actuator/sensor locations and feedback gain via minimization of an energy criterion, which is chosen as the integrated total energy stored in the system. The energy criterion is determined via an efficient solution of the Lyapunov equation and minimized with a quasi-Newton or recursive quadratic programming algorithm. The prerequisite for this optimal design method is that the controlled system be asymptotically stable. This study shows that when the controller structure is a collocated direct velocity feedback design with positive definite feedback gain, the number and placement of actuators/sensors are the only factors needed to determine necessary and sufficient conditions for ensuring closed-loop asymptotic stability. The application of this method to a simple flexible structure confirms the direct relationship between our optimization criterion and effectiveness in vibration suppression.

Robust Control of Magnetic Levitation Systems by Means of H<SUP>∞</SUP> Control/μ-Synthesis

This study is concerned with an application of H∞ control and μ synthesis to magnetic levitation systems which have special flexible structures and the solution of the spillover problem. At first, we show the typical spillover phenomenon caused by the interaction between the control system and the flexible structure system using PID control. Next, applying mixed-sensitivity H∞ control to the magnetic levitation system, we design the control system for it without spillover and describe in detail how to design an H∞ controller. Finally, we analyze the structured singular value and design the μ controller using D-K iteration. In this paper, we assume the magnetic levitation system as an uncoupled system between the X and Y directions for simplicity, which is the third-order system with the exception of the guideway. As a result, it has been clarified that the H∞ controller and μ-controller have the characteristics of two kinds of filters, a low-pass filter and a notch filter. It is found that the μ controller is superior to the H∞ controller in terms of robust stability and robust performance. From experiments, we obtained good data on the magnetic levitation without spillover.

Use of Piezoelectric Films in Detecting and Monitoring Damage in Composites

The increasing emphasis over the past few years on intelligent material systems and structures has resulted in a significant research effort in the areas of embedded and bonded sensors and actuators. Of the many sensing materials available, piezoelectric sensors offer a number of ad vantages. The sensor output, proportional to changes in surface displacement over a large area, can be used to interpret variations in structural and material properties, e.g., the compliance of the material. This type of sensor has also been used as an ultrasonic transducer. It offers the advantage of having a low structural impedance, thus giving an accurate measurement of the change in area, and consequently can only be used as an actuator on flexible structural systems. The aim of this article is to demonstrate the use of piezoelectric film sensors as a structural integrity monitoring device for composite materials. Tests to date have been aimed at detecting and monitoring impact damage in composite materials, as well as detecting damage in composite-to-metal mechanically fastened joints.

Modelling and Optimum Design of the Control System based on the Identification of Spatial Matrices.

The authors propose a method to design the optimum control system toward flexible structural systems. The mechanical structural system can be modelled by identifying the spatial matrices from experimental frequency response functions. The optimum control system is easily designed by applying the optimum control theory to the identified system. However, the stability of the control system is not always guaranteed because the mechanical system is generally identified with small degrees of freedom ignoring high-order modes. This report proposes an optimization method of the control system which guarantees the stability of the actual system which is also an identified system with high degrees of freedom. The characteristics of both the identified and actual system are simultaneously optimized by the proposed method based on sensitivity analysis and nonlinear programming. An experimental example verifies the effectiveness of the proposed method.

ＭＦ（Ｍｉｓｓｉｏｎ‐Ｆｕｎｃｔｉｏｎ）制御の一般的な性質について

A feature of the Mission-Function (MF) control is studied in this paper. The MF control is a control algorithm compatible with the fundamentals of mechanics of flexible structures and employs the mission function. The mission function is a Lyapunov function which includes such mechanical information of the system as the Hamiltonian and also a generalized energy to improve the performance of the controller. This paper presents the necessary conditions for the MF control in a general form. Another purpose of the paper is to present a feature belongs to the MF control, that application of the control algorithm reduces to the design of an optimal regulator for the flexible structural system. Two examples for application of the MF control are shown through the use of the numerical simulation.

Distributed vibration control and identification of coupled elastic/piezoelectric systems: Finite element formulation and applications

Recent development of large and flexible structural systems has emphasised the importance of distributed structural identification and vibration control of these high-performance distributed parameter systems (DPSs). In this paper, distributed piezoelectric sensors and actuators are used for structural identification and vibration control of DPSs. The distributed piezoelectric layers can respond to structural oscillation and generate output voltages due to the direct piezoelectric effect; and they can also separately produce control forces/moments due to the converse piezoelectric effect. An improved piezoelectric finite element with internal degree of freedom is first formulated. Then structural identification and control using the piezoelectric finite element is derived. State variable transformation of the dynamic equation is also presented. Distributed structural identification and control of DPSs are studied using theoretical, experimental, and finite element techniques.

Distributed vibration control and identification of coupled elastic/piezoelectric shells: Theory and experiment

In the recent development toward building large and flexible aerospace structural systems, active distributed vibration control and structural identification are of importance to their high-demanding performance. In this paper, a generic distributed parameter systems—a generic layered shell made of a passive elastic material sandwiched between two piezoelectric layers—is proposed and analysed. One of the coupled piezoelectric layers monitors the structural oscillation via the direct piezoelectric effect and the other controls the oscillation via the converse effect. Theories on distributed structural identification and control are derived. System dynamic equations and state equations of the coupled shell are formulated using Hamilton's principle and Kirchhoff-Love theory. Distributed structural identification and control of elastic structures are demonstrated by laboratory experiments.

Partial eigenstructure assignment and its application to large scale systems

The notion of partial eigenstructure assignment (PEA) via linear state feedback control in linear multivariable systems is introduced. This notion is a natural extension of eigenstructure assignment and partial eigenvalue assignment. Some theoretical basis for PEA is provided, and a parametric expression for feedback gain matrices achieving PEA is derived. An effective numerical algorithm for PEA tailored to large-scale systems is presented. As an extension of the algorithm, a recursive algorithm for eigenstructure assignment is presented. These algorithms possess the following desired properties: (1) compared to existing methods, the presented algorithms significantly reduce the required computation time via transforming high-dimensional matrix computations into low-dimensional matrix computations; (2) they can be implemented in a parallel fashion. The proposed algorithm for PEA is applied to modal control of large flexible space structure systems. >

Robust control of flexible structure systems (Application of robust model matching method to a flexible spacecraft model).

This paper studies robust control of flexible structure systems such as LSS (Large space structures) theoretically and experimentally. In control of flexible structure systems, it is important to desigh the robust controller which realizes low sensitivity for parameter changes of the controlled object and robust stability in residual higher modes which cause spillover instatability. In this paper, the robust model matching (RMM) method is adopted to design the low sensitive controller, and low -pass filters are used to increase the robust stability in the high frequency range taking account of their dynamics. Then, the controller designed by the proposed method is applied to the flexible spacecraft model, and the effectiveness of the controller is demonstrated in both computer simulation and control experiments.

Modeling and control of a flexible structure system. Suppression of spillover instability.

In this paper, the modeling and control of flexible structure systems are studied by taking an elastic arm system as an example. Especially, high-speed positioning control suppressing spillover instability is examined. First of all, an equation of motion is derived using the finite element method for a controlled object, and a modal analysis is applied to the equation in order to obtain a reduced order model of the object. Subsequently, the transfer function method based on design freedom is adopted to design the controller. The effectiveness of the controller derived by this method is demonstrated in computer simulation results on time responses. Also, the results are compared with those obtained by the theory of optimal control.

Near-source Earthquakes, Base-isolated Structures And Semiactive Dampers

This paper examines the problem of protecting flexible structures from rapid, long-period motions. Recent records from near-source earthquakes have created concerns about the vulnerability of flexible structural systems such as base isolated structures. First, a comprehensive analytical study is developed which shows that the presence of friction type forces (rigid-plastic behavior) reduces substantially displacements by keeping accelerations (base shears) at low levels. However, in some cases the presence of high friction forces in the isolation system of a structure are responsible for permanent displacements of the superstructure. Electrorheological dampers and other semi-active dampers can in principle supply the friction type forces needed at the beginning of the shaking through their capability of developing rigid-viscoplastic behavior; but also, can eliminate the presence of permanent displacements since the friction forces can be removed at some point during shaking allowing the superstructure to re-center. Finally, it is shown that with the current available technology of electrorheological fluids, ER-dampers, when properly designed, can deliver the level of friction type-forces needed even for large values of design velocities such as 1 m/sec or more. ER-dampers are unique dissipative devices which can effectively protect flexible structures from near-source earthquakes.