Research Articles, Center for Intelligent Material Systems and Structures (CIMSS)
http://hdl.handle.net/10919/24824
2019-01-18T11:26:45ZActive structural acoustic control of broadband disturbances
http://hdl.handle.net/10919/52281
Baumann, William T.; Ho, Fu-Sheng; Robertshaw, Harry H.
1992-09-01T00:00:00ZA control design technique is developed to actively suppress the acoustic power radiated from a structure, with negligible fluid loading, that is persistently excited by narrow-band or broadband disturbances. The problem is constrained by the assumption that the far-field pressure cannot be measured directly. A method for estimating the total radiated power from measurements on the structure is developed. Using this estimate as a cost function and assuming knowledge of the spectrum of the disturbance, a controller is designed using the linear-quadratic-Gaussian (LQG) theory to minimize the cost. Computer simulations of a clamped-clamped beam show that there is a significant difference in the total radiated power between a system with a vibration-suppression controller and a system with an acoustic controller that accounts for the coupling of these vibrations to the surrounding fluid. In some cases, the acoustic controller increases the system vibration in order to minimize the radiated power.Active vibration and structural acoustic control of shape memory alloy hybrid composites: Experimental results
http://hdl.handle.net/10919/52280
Rogers, Craig A.
1990-12-01T00:00:00ZShape memory alloy hybrid composites have been shown both by analytical simulations and experiments to be effective adaptive materials for active vibration and structural acoustics control [Rogers and Robertshaw, Engineering Science Preprints 25, ESP25.88027, Society of Engineering Sciences (1988) and ASME Paper 88-WA/DE-9 ( 1988); Rogers et al., in Proceedings of the 30th Structures, Structural Dynamics, and Materials Conference, AIAA Paper 89-1389 (1989)]. Structural acoustics is the study of how elastic structures radiate or receive sound, and in its most fundamental form involves the simultaneous solution of the differential equations describing the structure and fluid media with appropriate boundary conditions between the two, i.e., a "fully" coupled analysis. This paper will review the state-ofthe-art of active control utilizing shape memory alloy hybrid composites and present experimental results showing active dynamic tuning by a method called active strain energy tuning (ASET), active control of sound radiation from a clamped-baffled beam, and transient vibration control of a cantilevered beam.Power consumption of piezoelectric actuators driving a simply supported beam considering fluid coupling
http://hdl.handle.net/10919/52282
Stein, Steve C.; Liang, Chen; Rogers, Craig A.
1994-09-01T00:00:00ZAn electromechanical impedance model is applied to the case of a simply supported beam in an infinite rigid baffle with a fluid medium on one side. The effects of the fluid medium are included in the impedance analysis by considering fluid-structure interaction. The use of static and impedance model for structural acoustic analysis is discussed. Various power consumptions of PZT actuator-driven underwater beam structures will be quantified. The analysis discussed in this paper will be used to determine radiated structural acoustic power without using microphones. This work is the first step toward the determination of power requirements for underwater active structural acoustic control.Dynamic analysis of piezoelectric actuator-driven circular rings using an impedance approach
http://hdl.handle.net/10919/52283
Rossi, Anna; Liang, Chen; Rogers, Craig A.
1994-09-01T00:00:00ZThis paper presents a dynamic model for the response of a circular ring excited by piezoelectric transducer (PZT) actuators bonded on the ring surface. The dynamic response is determined based on the dynamic interaction between the PZT actuators and the structure using an impedance approach. Compared with the conventional static approach, in which a statically determined ''equivalent force'' of the actuator is used as the forcing function in the dynamic analysis, the impedance approach cannot only capture the physics of the actuator/structure interaction, but also accurately predict the structural dynamic response. Experiments have also been conducted to verify the theoretical model. The predicted dynamic response using the impedance approach agrees very well with the experimental results. Comparison of the conventional static approach and the impedance model has also been presented.Modeling of distributed piezoelectric actuators integrated with thin cylindrical shells
http://hdl.handle.net/10919/52279
Zhou, Su-Wei; Liang, Chen; Rogers, Craig A.
1994-09-01T00:00:00ZThe dynamic interaction between induced strain piezoelectric (PZT) actuators and their host structures is often ignored in the modeling of intelligent structures. A more realistic investigation of intelligent material systems must account for the dynamic behaviors of integrated actuator/substrate systems. In this paper, a generic method for the dynamic modeling of distributed PZT actuator-driven thin cylindrical shells has been developed using a mechanical impedance approach. The impedance characteristics of a cylinder corresponding to the excitation of a pair of pure bending moments have been developed, from which the dynamic output moments (or forces) of PZT actuators can be accurately predicted. Direct comparisons have been made between a conventional static modeling approach and the impedance method in order to identify the critical differences between these modeling methods for thin cylindrical structures. The case studies demonstrate that the mechanical impedance matching between PZT actuators and host structures has an impact on the output performance of the actuators. The dynamic essence of integrated PZT/substrate systems has thus been revealed.Modeling of induced strain actuation of shell structures
http://hdl.handle.net/10919/52278
Chaudhry, Zaffir; Lalande, Frederic; Rogers, Craig A.
1995-05-01T00:00:00ZBased on the thin-shell Donnell theory, a model to represent the action of discrete induced strain actuator patches symmetrically bonded to the surface of a circular cylindrical shell has been developed. The model provides estimates of the bending curvatures due to the out-of-phase actuation and the in-plane strains due to the in-phase actuation of the bonded actuator patches. The magnitudes of the induced curvature and the in-plane strain are found to be identical to those of plates; however, due to the strain-displacement relations in cylindrical coordinates, the in-plane and out-of-plane displacements are coupled. Expressions for the equivalent forces and moments that represent the action of the actuator patches have been developed. Due to the curvature of the shell, the representation of the in-phase actuation with an equivalent in-plane line force applied along the edge of the actuator results in the application of erroneous rigid-body transverse forces. To avoid these rigid body forces, a method to represent the in-phase actuation with a system of self-equilibrating forces is proposed. The action of the actuator is then represented by an equivalent in-plane force and a transverse distributed pressure applied in the region of the actuator patch. Finite element verification of the proposed model is presented. The displacements due to the actual actuator actuation are compared with the proposed model, and very good agreement is found. Copyright 1995 Acoustical Society of AmericaNonlinear piezoelectricity in electroelastic energy harvesters: Modeling and experimental identification
http://hdl.handle.net/10919/52008
Stanton, Samuel C.; Erturk, Alper; Mann, Brian P.; Inman, Daniel J.
2010-10-01T00:00:00ZWe propose and experimentally validate a first-principles based model for the nonlinear piezoelectric response of an electroelastic energy harvester. The analysis herein highlights the importance of modeling inherent piezoelectric nonlinearities that are not limited to higher order elastic effects but also include nonlinear coupling to a power harvesting circuit. Furthermore, a nonlinear damping mechanism is shown to accurately restrict the amplitude and bandwidth of the frequency response. The linear piezoelectric modeling framework widely accepted for theoretical investigations is demonstrated to be a weak presumption for near-resonant excitation amplitudes as low as 0.5 g in a prefabricated bimorph whose oscillation amplitudes remain geometrically linear for the full range of experimental tests performed (never exceeding 0.25% of the cantilever overhang length). Nonlinear coefficients are identified via a nonlinear least-squares optimization algorithm that utilizes an approximate analytic solution obtained by the method of harmonic balance. For lead zirconate titanate (PZT-5H), we obtained a fourth order elastic tensor component of c(1111)(p)=-3.6673 x 10(17) N/m(2) and a fourth order electroelastic tensor value of e(3111)=1.7212 x 10(8) m/V. (C) 2010 American Institute of Physics. [doi:10.1063/1.3486519]High surface area electrodes in ionic polymer transducers: Numerical and experimental investigations of the electro-chemical behavior
http://hdl.handle.net/10919/52009
Akle, Barbar J.; Habchi, Wassim; Wallmersperger, Thomas; Akle, Etienne J.; Leo, Donald J.
2011-04-01T00:00:00ZIonomeric polymer transducer (IPT) is an electroactive polymer that has received considerable attention due to its ability to generate large bending strain (> 5%) and moderate stress at low applied voltages (+/-2 V). Ionic polymer transducers consist of an ionomer, usually Nafion, sandwiched between two electrically conductive electrodes. A novel fabrication technique denoted as the direct assembly process (DAP) enabled controlled electrode architecture in ionic polymer transducers. A DAP built transducer consists of two high surface area electrodes made of electrically conducting particles uniformly distributed in an ionomer matrix sandwiching an ionomer membrane. The purpose of this paper is to investigate and simulate the effect of these high surface area particles on the electro-chemical response of an IPT. Theoretical investigations as well as experimental verifications are performed. The model used consists of a convection-diffusion equation describing the chemical field as well as a Poisson equation describing the electrical field. The two-dimensional model incorporates highly conductive particles randomly distributed in the electrode area. Traditionally, these kinds of electrodes were simulated with boundary conditions representing flat electrodes with a large dielectric permittivity at the polymer boundary. This model enables the design of electrodes with complicated geometrical patterns. In the experimental section, several transducers are fabricated using the DAP process on Nafion 117 membranes. The architecture of the high surface area electrodes in these samples is varied. The concentration of the high surface area RuO2 particles is varied from 30 vol% up to 60 vol% at a fixed thickness of 30 mu m, while the overall thickness of the electrode is varied from 10 mu m up to 40 mu m at a fixed concentration of 45%. The flux and charge accumulation in the materials are measured experimentally and compared to the results of the numerical simulations. Trends of the experimental and numerical investigations are in agreement, while the computational capacity is limiting the ability to add sufficient amount of metal particle to the electrode in order to match the magnitudes. (C) 2011 American Institute of Physics. [ doi:10.1063/1.3556751]Computational analysis of ionic polymer cluster energetics
http://hdl.handle.net/10919/52007
Weiland, Lisa M.; Leo, Donald J.
2005-06-01T00:00:00ZIn recent years there has been considerable study of the potential mechanisms underlying the electromechanical response of ionic-polymer-metal composites. The most recent models have been based on the response of the ion-containing clusters that are formed when the material is synthesized. Most of these efforts have employed assumptions of uniform ion distribution within spherical cluster shapes. This work investigates the impact of dispensing with these assumptions in order to better understand the parameters that impact cluster shape, size, and ion transport potential. A computational micromechanics model has been developed to predict the equilibrium state of a single cluster of an ionomeric polymer with cluster morphology. No assumptions are made regarding the distribution of charge or the shape of the cluster. For a constant solvated state, the model tracks the position of individual ions within a given cluster in response to ion-ion interaction, mechanical stiffness of the pendant chain, cluster surface energy, and external electric-field loading. Expressions are developed to directly account for forces imposed on ions due to ion-cluster surface interaction. Results suggest that ion pairing is rarely complete; this in turn suggests that the classic assumptions will tend to underpredict electromechanical actuation response. (C) 2005 American Institute of Physics.Ionic polymer cluster energetics: Computational analysis of pendant chain stiffness and charge imbalance
http://hdl.handle.net/10919/52006
Weiland, Lisa M.; Leo, Donald J.
2005-06-15T00:00:00ZIn recent years there has been considerable study of the potential mechanisms underlying the electromechanical response of ionic-polymer-metal composites. The most recent models have been based on the response of the ion-containing clusters that are formed when the material is synthesized. Most of these efforts have employed assumptions of uniform ion distribution within spherical cluster shapes. This work investigates the impact of dispensing with these assumptions in order to better understand the parameters that impact cluster shape, size, and ion transport potential. A computational micromechanics model applying Monte Carlo methodology is employed to predict the equilibrium state of a single cluster of a solvated ionomeric polymer. For a constant solvated state, the model tracks the position of individual ions within a given cluster in response to ion-ion interaction, mechanical stiffness of the pendant chain, cluster surface energy, and external electric-field loading. Results suggest that cluster surface effects play a significant role in the equilibrium cluster state, including ion distribution; pendant chain stiffness also plays a role in ion distribution but to a lesser extent. Moreover, ion pairing is rarely complete even in cation-rich clusters; this in turn supports the supposition of the formation of anode and cathode boundary layers. (c) 2005 American Institute of Physics.