bluuebunny/crossref_metadata_2025_split huggingface dataset:
Multiplexing Embedded Nitinol Actuators to Obtain Increased Bandwidth in Structural Control
Authors: Srinivasan A. V. , Mcfarland D. Michael , Canistraro Howard A. , Begg Eric K. 
Published: August 2009

A wide variety of applications of shape memory alloys is seen in devices where the response required of them is essentially quasi-static. At the same time, the high damping intrinsic to the alloys known as "quiet metals," such as Nitinol, have led to their use as passive distributed dampers. However, it is generally felt that the frequency response of SMA actuators is too slow to permit their use for structural control where they need to supply a time-dependent force at the natural frequency of a structure. In many applications the response time of SMA actuators is ultimately limited by heat transfer. Typically, very rapid heating can be achieved but the time needed for cooling is long compared to the vibratory period of typical mechanical or civil structures. A unique approach has been found suitable to overcome this inherent limitation. The approach is based on using several Nitinol wires as actuators in parallel and energizing subsets of these during successive cycles of structural motion, effectively trading reduced control authority for increased frequency response. Thus, with an array of actuators an effective bandwidth can be achieved that is demonstrated to be greater than the bandwidth possible with a single actuator. This technique of multiplexing several actuators was established in principle by the senior author of this paper in 1990. Most recently, upon completion of the effort reported here, the authors learned that Wilson et al. (1990) had employed a similar approach to obtain a higher frequency bandwidth. The approach has now been extended to demonstrate its validity by applying it to a robust box beam made of steel. Furthermore, successful performance of the multiplexing scheme has led to the analysis, design, fabrication and testing of a composite beam in which NiTiNOL fibers were embedded. A series of vibration tests were conducted on the composite beam along with temperature measurements using an infrared camera. With the multiplexing approach, the first two modes of the composite beam, at 23.5 Hz and 144 Hz respectively, were excited. This unique approach can now be developed further to design structural systems of interest to industry and build smart composite structures. This serves the eventual goal of controlling vibration at frequencies higher than was thought possible with this material.
Model-Independent Vibration Control of Flexible Beam-Like Structures Using a Fuzzy Based Adaptation Strategy
Authors: Cohen K. , Weller T. , Levitas J. , Abramovich H. 
Published: August 2009

The present study deals with an AFCA (Adaptive Fuzzy Control Algorithm) for an Euler-Bernoulli approximation of a two-dimensional version of a cantilever beam-like orthogonal tetrahedral space truss. Transient disturbances, modeled as a unit impulse, excite all the modes of the beam. The resulting transverse displacement at the free end of the beam and its corresponding rate are observed by sensors placed there, and active control of the beam is provided by a collocated force actuator. A design methodology for the closed-loop control algorithm that is independent of an exact mathematical model (space-state model, F.E.M., etc.) of plant dynamics and which is based on fuzzy logic is presented. First, the behavior of the open-loop system is observed. Then, the control force applied to the system emulates the behavior of a dynamic vibration absorber which is tuned to the measured fundamental frequency. This approach not only assures inherent stability associated with passive absorbers, but also circumvents the phenomenon of modal spillover. The damping and the mass ratios of the absorber adapt themselves by using a fuzzy decision-making process. This results in relatively quick settling times, low overshoots and dying out of vibration within a few seconds. When the control force is turned off after a mere 16 seconds, almost all the vibrational energy is dissipated. In addition, the performance of the AFCA is insensitive to varying initial conditions. To demonstrate the robustness of the control system to changes in the temporal dynamics of the cantilever beam, the transient response to a considerably perturbed plant is simulated. The Young's modulus of the beam was raised as well as lowered substantially, thereby significantly perturbing the natural frequencies of vibration. The mode shapes, however, remain unchanged. For these cases, too, the AFCA provides similar settling times and rates of vibrational energy dissipation.
Determination of Design of Optimal Actuator Location and Configuration Based on Actuator Power Factor
Authors: Liang C. , Sun F. P. , Rogers C. A. 
Published: August 2009

In this paper, a new design algorithm is proposed for optimization of the inducedstrain actuator location and configuration for active vibration control based on an actuator performance index, namely the actuator power factor. The concept of actuator power factor, developed recently by the authors, describes the capability of an integrated induced strain actuator, such as PZT or Terfenol, to transfer the supplied electrical energy into structural mechanical energy (kinetic or potential energy of the mechanical system). A system optimized based on the actuator power factor will guarantee the highest energy efficiency for single frequency and broad-band applications. This paper will also show that a higher energy efficiency corresponds to higher mechanical performance. The approach introduced in this paper is much more convenient to use than the conventional modal domain optimization approach. Furthermore, since the power factor approach can include the electrical parameters from the power system, it will allow a system optimization design including the power electronics and energy consumption. The basic concept of the actuator power factor will be introduced first in this paper. Its utility in the system optimization will be discussed using a PZT actuator-driven simply-supported beam. The optimization of actuator location, length, and thickness will be discussed through numerical examples. This paper will also discuss how to use the actuator energy density and actuator power factor to estimate the dynamic response of a system.
A Superelastic Shape-Memory-Alloy Beam Model
Authors: Auricchio Ferdinando , Sacco Elio 
Published: August 2009

The present paper proposes a simple shape-memory-alloy beam model, based on the classical Euler-Bernoulli beam theory. Due to restrictive kinematical assumptions, a one-dimensional constitutive equation is used. Thus, the material behavior is described through a simple l-D phenomenological model, which allows for different material responses in tension and compression as well as for different elastic properties between austenite and martensite. Two numerical procedures are developed for the determination of the cross-section response together with a time-step integration algorithm. Then, the implementation of the shape-memory-alloy beam model within a finite-element framework is addressed. Several numerical examples are investigated to assess both the performance of the beam model and the procedure developed. The complex behavior of a typical cross section is emphasized. The results obtained from the simulation of three and four-point bending tests are compared both with experimental results and with numerical solutions obtained from a three-dimensional finite-element scheme.
Static and Dynamic Testing of Large-Amplitude Rotary Induced-Strain (LARIS Mk 2) Actuator
Authors: Giurgiutiu Victor , Rogers Craig A. , Mcneil Shane 
Published: August 2009

A new concept for obtaining large-amplitude rotary displacements from small linear displacements generated by induced-strain active material stacks is considered. The concept utilizes the theory of twist-warping coupling in thin-wall open tubes. A large-displacement induced-strain rotary actuator, LARIS Mk 2, was built and tested under static and dynamic conditions. A rotary displacement of 60 was measured over a 0-50 Hz frequency range. The frequency response was found to be flat up to 40 Hz, and then increasing in the 40-50 Hz frequency range. The theoretical development of the torsional vibration response for the LARIS Mk 2 actuator is also given. The derivation is performed in a general format for a body with distributed elastic and inertia parameters, and with generic boundary conditions consisting of root stiffness and tip angular deflection. The results of this theoretical analysis are confirmed by experimental measurements. The theory presented is versatile and can be used for the analysis of other torsional vibration devices with specific root and tip boundary conditions. This LARIS concept presented in this paper can be successfully used in a series of aerospace and mechanical engineering applications, as for example in the actuation of adaptive control surfaces for aircraft wings and helicopter blades, or as rotary vane actuators in the control of turbomachinery exhaust flow for active reduction of turbulence, vibrations, and noise.
CASTOR Active Damping Experiment, Preliminary Flight Results
Authors: Bousquet P. W. , Guay P. , Mercier F. 
Published: August 2009

The experiment "'CASTOR" (French acronym for Characterization of Structures in ORbit) is dedicated to the analysis of the structural dynamic modes of the MIR station, and to the investigation of the dynamic behaviour-in zero g conditions-of a truss mock-up with various damping technologies. This project has been developed under CNES management in less than three years. The work in orbit was performed by a French cosmonaut within the frame of the CASSIOPEE mission in MIR at the end of August 1996. This paper is dedicated to the active damping systems for CASTOR's truss structure. They consist essentially of three piezoelectric members, and one reaction mass actuator. Both systems use collocated sensors and actuators. Their development and flight tests are part of CNES' general activities whose aim is to improve, demonstrate the efficiency, and prepare the application of active control techniques for future space missions. Typical applications include optical systems with high stability requirements, large antennas, sensitive microgravity payloads, spacecrafts with flexible appendages, and large orbital infrastructures. In Bonus (1995), we presented the motivations behind the test in zero g conditions, and a full description of the equipment. In this paper, we briefly recapitulate upon the design of the active systems, before summing-up the recent development activities. The operations in flight are then presented. A few zero-g measurements are shown without much interpretation considering the short time available between flight and conference. The active systems exhibited excellent performances in flight. Preliminary conclusions are drawn with respect to the CASSIOPEE mission and to further activities.
The Fractional Order Elastic-Viscoelastic Equations of Motion: Formulation and Solution Methods
Authors: Escobedo-Torres Javier , Ricles James M. 
Published: August 2009

The equations of motion of structures with elastic and viscoelastic materials in the time domain are derived. The development is consistent with the finite element formulation and leads to a system of equations where the matrices are symmetric, real, and composed of constant coefficients. A four-parameter fractional derivative model is used to model the frequency dependence of the linear viscoelastic material since experimental data can be fitted successfully over a wide frequency range. The resulting equations of motion are known as the elastic-viscoelastic equations of motion. Numerical procedures for solving the elastic-viscoelastic equations of motion in the time domain are developed, and a procedure based on the central-difference method that incorporates fractional derivatives is presented. The numerical stability of the procedure is presented, and criteria for selecting the size of the time step are given. The closed-form, steady state solution of a single degree of freedom system is obtained in the frequency domain and is utilized to validate the results obtained by using the numerical procedures. The proper selection of the stiffness for viscoelastic dampers placed in elastic structural systems is discussed in order to ensure that the damper is effective in reducing dynamic amplification of the structure. The dynamic response of a multi-degree of freedom structure, obtained by using the numerical procedures, is used to demonstrate the effectiveness of the dampers in reducing the structural response to dynamic loading.
Method for Multiple Mode Piezoelectric Shunting with Single PZT Transducer for Vibration Control
Authors: Wu Shu-Yau 
Published: August 2009

We report a method for passive piezoelectric shunt-damping of multiple vibration modes using a single piezoelectric transducer (PZT). The method, which is different from other multiple-mode shunting (Edberg et al., 1992; Hollkamp, 1994), is to employ a blocking circuit in series with each parallel resistor-inductor shunt circuit designed to control one structural mode. The blocking circuit consists of one parallel capacitor-inductor antiresonant circuit or a series of them. The number of the antiresonant circuits in each shunt circuit depends on the number of the structural modes to be controlled simultaneously. These antiresonant circuits are designed to produce infinite electrical impedance, or antiresonance, at the natural frequencies of all other shunt circuits. Each shunt circuit with the addition of the blocking circuit is functional for its own mode yet blocks or causes open circuit for all other frequency modes. Therefore, when the individual shunt circuits are all connected to the two terminals of the PZT to form a composite shunt circuit for the multiple-mode shunting, they will not interfere with each other. The method is also easier and more reliable for finetuning and damping control. We analyze first the multiple-mode shunt-damping circuit with both the generalized circuit and the modified circuit. The latter derived from the former is intended to reduce the number of the antiresonant circuits and to make the composite shunt circuit simpler to operate. Experimentally we have designed two modified shunt circuits and successfully demonstrated vibration reduction of two and three structural modes with a single PZT transducer bonded on a two-wing aluminum cantilever beam. For three-mode shunt damping, the resonant amplitudes at 206, 348.5, and 484.5 Hz are reduced for 13.28, 7.30, and 9.45 dB, respectively.
A Parallel Control System for Continuous Architecture Using Finite Element Method
Authors: Isobe Daigoro , Nakagawa Hisashi 
Published: August 2009

In this paper, a parallel control system for continuous architecture formed by bimorph piezoelectric actuators has been developed and verified. Finite Element Method (FEM) is adopted as the control scheme for it is capable of expressing the behavior of the whole system by evaluating the stiffness equations. Conventional control system requires a slight change in its state equations, depending on the shape of a system or the quantity of the linked members. Although FEM is mainly a computational tool for analyzing structures, fluids, etc., the capability of expressing the whole continuous system can be applied to parallel control schemes, and may be practical if the computational time is reduced to real-time use. An inverse theory, which is simplified by using the linearity of the electric potential distribution in a bimorph piezoelectric actuator, is applied for calculating control voltage of the actuators. The algorithm using this theory consumes less computational memory, and runs faster than the numerical schemes using generalized inverse matrices. This paper seeks the reduction of dofs and thus the computational time, by implementing noncompatible four-node element to the FEM control program. The finite element allows in-plane bending mode by considering noncompatible mode in shape functions, and can obtain practical solutions by minimum number of elements. By examining the experiments on static displacement control of connected piezoelectric actuators, the validity of the FEM parallel control system has been confirmed.
Terfenol-D Nonlinear Vibration Absorber
Authors: Pratt Jon R. , Oueini Shafic S. , Nayfeh Alu H. 
Published: August 2009

An active nonlinear vibration absorber scheme for flexible structures is demonstrated. The absorber exploits the nonlinear transduction of nonbiased Terfenol-D actuators. It uses a quadratic feedback control law and the "quadratic" strain-field characteristic of a nonbiased Terfenol-D actuator to achieve a nonlinear coupling between the absorber and the forced structure. A saturation phenomenon is induced by tuning the frequency of the underdamped second-order absorber to one-half that of the primary structure. As a result, the structural vibrations are greatly reduced. This type of control has been demonstrated previously using linear actuators; the nonlinearities have been introduced via the control algorithm. Here, we show that nonbiased Terfenol-D actuators can perform effectively the "squaring" operation, instead of the algorithm, and achieve similar results. We develop the theory and present experimental results for the control of the first and second modes of a cantilever beam. We also consider application of the strategy experimentally when the forcing is due to a rotating imbalance. In this case, the excitation source is nonideal. Our results indicate that the saturation-based control technique implemented with a Terfenol-D actuator constitutes an effective nonlinear vibration absorber.
Modeling of Nonlinear Hysteresis in Elastomers under Uniaxial Tension
Authors: Banks H. T. , Pintér Gabriella A. , Potter Laura K. , Gaitens M. J. , Yanyo L. C. 
Published: August 2009

As a fundamental component of an overall program in modeling smart material damping devices, we consider inactive host material models for moderate to highly filled rubbers undergoing uniaxial tensile deformations. Beginning from a neo-Hookean strain energy function formulation for nonlinear extension, we develop general constitutive models for both quasi-static and dynamic deformations of a viscoelastic rod. The constitutive laws are nonlinear and contain hysteresis through a Boltzmann superposition integral term. The resulting integropartial differential equations models are shown to be equivalent to the usual Lagrangian dynamic distributed parameter models coupled with linear ordinary differential equations for internal variables (internal strains). Comprehensive well-posedness results (existence, uniqueness and continuous dependence) are summarized in a discussion of theoretical aspects of the systems. The models are validated with experiments designed and carried out explicitly for this study. In particular, quasi-static Instron experimental data are used in a least squares inverse problem formulation to estimate nonlinear elastic and nonlinear viscoelastic contributions to the general stress-strain constitutive laws proposed. It is shown that the models provide an excellent prediction of nested hysteresis loops manifested in the data. These models are then used as initial estimates in determining the nonlinear hysteretic constitutive laws for the dynamic experiments. It is shown that in cases of more highly filled rubbers, multiple internal variable models lead to best fits to the data.
Monitoring of Concrete Bridges with Long-Gage Fiber Optic Sensors
Authors: Inaudi Daniele , Vurpillot Samuel 
Published: August 2009

In many bridges, the vertical displacements are the most relevant parameters to be monitored in both the short and long term. Current methods (such as triangulation, water levels or mechanical extensometers...) are often tedious to use and require the intervention of specialized operators. The resulting complexity and costs limit the temporal frequency of these traditional measurements. The spatial resolution obtained is in general low and only the presence of anomalies in the global structural behavior can be detected and warrant a deeper and more precise evaluation. To measure bridge vertical displacements at low cost and frequently in time, one solution consists of installing a network of fiber optic sensors during concrete pouring or installing them on the surface of the structure. By subdividing the whole structure into structural elements and those elements into cells that are analyzed by the sensors, it is possible to obtain information about the average cell deformation (e.g., mean curvature) that can then be combined to obtain the global structural displacement field. In 1996, a concrete highway bridge near Geneva (Switzerland) was instrumented with more than 100 low-coherence fiber optic deformation sensors. The Versoix Bridge is a classical concrete bridge consisting in two parallel pre-stressed concrete beams supporting a 30-cm concrete deck and two overhangs. To enlarge the bridge, the beams were widened and the overhang extended. In order to increase the knowledge on the interaction between the old and the new concrete, we choose low-coherence fiber optic sensors to measure the displacements of the fresh concrete during the setting phase and to monitor the long term deformations of the bridge. The aim is to retrieve the spatial displacements of the bridge in an earth-bound coordinate system by monitoring its internal deformations. The vertical and horizontal curvatures of the bridge are measured locally at multiple locations along the bridge span by installing sensors at different positions in the girder cross-section. By taking the double integral of the curvature and respecting the boundary conditions, it is then possible to retrieve the deformations of the bridge. This measurement methodology was also applied to the Lutrive Highway Bridge in Switzerland in order to measure the variation in vertical bridge displacements due to a static load test. The results obtained using the low coherence interferometric sensors of the SOFO system were then compared with the displacements obtained through an optic leveling system. In the case of this cantilever bridge of 60 meters half-span equipped with 30 fiber optic sensors, a discrepancy of less than 7% was obtained between the two measuring systems.
Embedded Quasi-Distributed Fiber-Optic Sensors for the Long-Term Monitoring of the Grouting Area of Rock Anchors in a Large Gravity Dam
Authors: Habel Wolfgang R. , Feddersen Ingo , Fitschen Carsten 
Published: August 2009

Steel anchors were installed in a gravity-dam, in order to increase the stability of the dam. Quasi-distributed fiber-optic strain sensors are centrally positioned in the complete length of these anchors to detect the long-term behavior of the tendon bonded to the rock foundation. Because the sensor rod containing the measuring lengths is directly bonded to the grout in the fixed anchor length area, it is able to measure the longitudinal strain distribution in the anchor bond area. Such sensors help to evaluate the bonding of the fixed anchor bond length in a rock or in difficult ground areas. Design of the anchors, manufacturing and on-site installations are described. The measuring principle and its characteristics are also described. Measured results given show the ability of sensorequipped anchors to monitor the tendon bond behavior over a period of years. Results four years after sensor system installation are presented.