Free Vibration Control Research Articles

Control of free vibration with piezoelectric materials: Finite element modeling based on Timoshenko beam theory

In this study, a new smart beam finite element is proposed for the finite element modeling of beam-type smart structures that are equipped with bonded plate-type piezoelectric sensors and actuators. Constitutive equations for the direct piezoelectric effect and converse piezoelectric effect of piezoelectric materials are considered in the formulation. By using a variational principle, the equations of motion for the smart beam finite element are derived. The proposed 2-node beam finite element is an isoparametric element based on Timoshenko beam theory. The proposed smart beam finite element is applied to the free vibration control adopting a constant gain feedback scheme. The electrical force vector, which is obtained in deriving an equation of motion, is the control force equivalent to that in existing literature. Validity of the proposed element is shown through comparing the analytical results of the verification examples with those of other previous researchers. With the use of smart beam finite elements, simulation of free vibration control is demonstrated by sensing the voltage of the piezoelectric sensors and by applying the voltages to the piezoelectric actuators.

Optimization and experimental verification for the antagonistic stiffness in redundantly actuated mechanisms: a five-bar example

A closed-chain mechanism having redundancy in force domain can produce an effective spring effect by proper internal load distribution. The so-called antagonistic stiffness is provided by redundant actuation in conjunction with nonlinear geometric constraints. The objective of this study is twofold. The first one is to propose a methodology for optimal kinematic design of antagonistic stiffness and the second one is to verify the phenomenon of the antagonistic stiffness through experimentation. In this work, a five-bar mechanism that can modulate antagonistic stiffness by using redundant actuators is employed as an exemplary system. The optimal structure of the five-bar mechanism that can maximize efficiency in generation of antagonistic stiffness is evaluated and analyzed. A measure of stiffness isotropy and the gradient property of the measure are employed as the performance indices in optimization. To deal with multi-criteria based design, a composite design index based on max–min principle of fuzzy theory is used as an objective function. Two optimization results are obtained. Furthermore, a five-bar mechanism has been developed for experimental verification. The phenomenon of antagonistic stiffness has been successfully demonstrated by free vibration and indirect force control experimentation.

Development of a Self-Sensing Actuator with Laminated Piezoelectric Films Toward the Smart Vibration Control of Two-Dimensional Structures.

A self-sensing actuator constructed by four laminated piezoelectric films is developed toward the smart vibration control of two-dimensional structures. First, three kinds of mechanisms of self-sensing acutuators with two or four laminated piezoelectric films are proposed by examining the combinations of film construction and bridge circuits of analog electric controllers. And those self-sensing actuators are applied to the free vibration control of the first mode of a cantilever beam and it is ascertained that the vibration suppression effects are obtained by all the three mechanisms and the theories show good agreements with the experiments. Finally, the mechanism constructed by four laminated piezoelectric films is applied to the vibration control of a simply-supported rectangular plate as an example of two-dimensional structures and it is verified that the vibration control effect is actually obtained and the theory agrees well with the experiment.

Acoustic Power Minimization by Active Noise and Vibration Control. On Zero Control Power Output.

This paper considers an acoustic power minimization problem from the viewpoint of active noise and vibration control. It is the purpose of this paper to elucidate a common link between : actively attenuating noise in a variety of acoustic environments, using vibration or acoustic control sources. It is shown that if acoustic reciprocity holds between each point on the primary source and each point on the control source, then the acoustic power output of the control source under optimal conditions will always be zero, with the converse also being true. This concept is demonstrated for systems operating in free space, using both acoustic and vibration control sources. The physical meaning of this concept for the employment of vibration control sources, applied directly to a vibrating structure in an effort to attenuate the radiated sound field, is shown.

To absorb or not to absorb: Control source power output in active noise control systems

This paper addresses the problem of finding a common link between actively attenuating noise in a variety of acoustic environments, such as in free space or in ducts, using vibration or acoustic control sources. It is shown that if acoustic reciprocity holds between each point on the primary source and each point on the control source, then the acoustic power output of the control source under optimal conditions will always be zero, with the converse also true. This concept is demonstrated for systems operating in free space, using both acoustic and vibration control sources, and for systems operating in a semi-infinite duct with a nonrigid termination. The physical meaning of this concept for the employment of vibration control sources, applied directly to a vibrating structure in an effort to attenuate the radiated sound field, is shown.

Structural modification of simply-supported laminated plates using embedded shape memory alloy fibers

Shape memory alloy (SMA) fibers, and in particular Nitinol fibers, have been embedded in advanced composite materials to demonstrate numerous structural control/modification concepts. A large number of control concepts have been postulated, formulated and demonstrated by using the unique control parameters available from Nitinol fiber actuators. Several new paradigms for structural design and control have resulted from the unusual behavior and mechanical properties of SMA. A brief introduction to SMA, laminated composite plates with embedded SMA fibers and a description of some of the available control parameters is presented. A linear analysis for a simply-supported symmetrically laminated composite plate embedded with SMA fibers using the Rayleigh-Ritz method is presented. Results of deflection, free vibration, buckling, and structural acoustic control are discussed. Two novel structural control techniques, active strain energy tuning (ASET) and active property tuning (APT), are highlighted and the authority of each technique demonstrated.

Effectiveness of Active TMD for Buildings’ Control

This paper presents some numerical investigations obtained from studying the effectiveness of active tuned mass dampers (TMD) in suppressing the vibrations in buildings. The results of the study indicate that active TMDs are not effective for forced vibration control in buildings. However, active TMDs are very effective and economic in suppressing the free vibrations response. For typical wind excitation, it is thus recommended to use passive TMD for forced vibration control, and active TMD for free vibration control.