Active Optimum Control of Orthotropic Plates Using Piezoelectric Stiffeners

Active control of orthotropic plates subjected to an impulse loading is considered. The dynamic response is minimized using in-plane forces or bending moments induced by piezoelectric stiffeners bonded to the opposite surfaces of the plate and placed symmetrically with respect to the middle plane. The control forces and moments are activated by a piece-wise constant alternating voltage with varying switch-over time intervals. The magnitude of voltage is bounded while the switch-over time intervals are constantly adjusted to achieve an optimum control. Numerical examples presented in the paper demonstrate the effectiveness of the method and the possibility of reducing the vibrations to very small amplitudes within a short time interval which is in the order of a second.

Piezothermoelasticity and Control of Piezoelectric Laminates Exposed to a Steady-State Temperature Field

Piezothermoelastic effects of distributed piezoelectric sensors and actuators are investigated. Vibration control of piezoelectric laminates subjected to a steady-state temperature field is studied. A new 3-D piezothermoelastic finite element with three internal degrees of freedom is formulated using a variational formulation. A system equation for the piezoelectric continuum exposed to combined elastic, electric, and thermal fields is formulated. Distributed sensing and control equations are derived. All these effects are studied in a case study.

Simulated Behavior of a System With Base Excitation Using an Electrorheological Fluid Damper

The flow properties of electrorheological (ER) fluids change with the application of an electric field. Presently, these materials are a novelty with few direct applications, but they have drawn considerable interest. Proposed applications include lubricants, dampers, clutches, brakes, etc. Existing ER fluids are best described by the Bingham fluid model. The Bingham material is described by two parameters, a yield shear stress and a viscosity. When the shear stress magnitude exceeds the yield shear stress, quasi-Newtonian flow results; otherwise the material is rigid. For many ER fluids, the yield shear stress is proportional to the square of the applied electric field. In the present study, the Bingham model is applied to a rectangular flow channel. A rigid core forms midway across the film, the core thickness being proportional to the yield shear stress. The damper force is predicted as a function of a dimensionless parameter which depends on the yield shear stress, the flow rate, and channel geometry. Calculations are performed for a simple vibration isolation system. Such a system may represent a smart shock absorber to minimize vibration response to oscillation input from a bumpy road. The ER damper is shown to be effective in isolating vibration within a band of linear behavior.

Distributed Observing and Active Control of a Cantilever Plate

Structural identification and vibration control of flexible systems have drawn much attention in recent years. This article presents an analytical study on a distributed piezoelectric sensor and a distributed actuator coupled with a flexible plate. The integrated piezoelectric sensor/actuator can monitor the oscillation as well as actively control the structural vibration by the direct/converse piezoelectric effects, respectively. Based on Love assumptions, theories on distributed sensing and active vibration control of a plate using piezoelectric materials are derived. By employing the finite element technique, the integrated structure is further discretized. Applications to the dynamic measurement is demonstrated and the dynamic performance of a cantilever plate is also evaluated.

Vibration Suppression by Modulation of Elastic Modulus Using Shape Memory Alloy

A method is proposed for suppressing the resonances that occur as an item of rotating machinery is spun-up from rest to its operating speed. This proposed method invokes “stiffness scheduling” so that the resonant frequency of the system is shifted during spin-up so as to be distant from the excitation frequency. A strategy for modulating the stiffness through the use of shape memory alloy is also presented.

A “Smart” Electrorheological Fluid Dynamic Vibration Absorber

As “smart” are characterized materials which have properties that can be changed in real time by a way of an external control action. Electrorheological (ER-) fluids are such materials since their apparent viscosity can be altered substantially under a controllable electric field. ER-fluids consist of a dispersion of fine dielectric powder, usually strongly hydrophile, into a fluid lubricant. An ER-fluid is used to fill the gap between two parallel sets of circular, concentric plates assembling the “smart” vibration dynamic absorber as part of a rotor system. One set of plates is resiliently connected to a rotor but the other is rigidly attached to it. The effect of the ER-fluid activation by an external electric field on the relative motion of the plates results in a controllable damping force of viscous and friction type. Numerical simulations of the rotor vibrations are carried out for a range of speeds including resonance and for several electric field levels. Increasing the electric field in the absorber yields in rotor amplitude reduction up to a threshold electric field which sticks the plates. Substantial improvement in the absorber efficacy is obtained by active control of the electric field using a feedback control scheme which optimizes the electric field input for maximum energy dissipation.

Exploring Artificial Muscles As Actuators for Artificial Hands

This article presents a brief overview of current research and findings in developing artificial muscles. Furthermore, possibilities of applying such muscles as actuators in prosthetic hands (i.e. The Sharif Artificial Hand) have been proposed and investigated.

An Introduction to Smart Fractal Structures and Mechanisms

Fractal structures are unique in the sense that they are highly expandible or collapsible and yet they are capable of preserving their basic structural geometry in a dynamic fashion. This dynamic geometric invariance opens up a new territory in fractal solids, i.e., fractal structures, mechanisms and robot manipulators. Some of these structure are in the form of highly deployable mechanisms and possibly redundant, multi-axis, multi-arm, multi-finger robot manipulators whose kinematic structure is fractal. Thus, simple fractal structures, such as triadic cantor set, and fractal functions, such as the Weirstraus-Mandelbrot functions, govern the structural branching of such robots and essentially define their kinematic structure. These deployable fractal structures, mechanisms and robot manipulators are shown to be capable of generating unique, and yet unparalleled properties such as computer-controlled microsensing even down to molecular level (micromachining) and computer-controlled dynamics such as the creation of hypervelocity fractons with speeds in the range of hundreds of kilometers per second. A number of structures and mechanisms and their unique properties are presented in this paper and a simple kinematic model is presented and briefly discussed.

Analysis of a Piezoelectric Actuator and Receiver on an Elastic Half-Space Subjected to Harmonic Electric Excitation

Analytical solutions are formulated for the displacement, stress, and electric potential in piezoelectric actuator and receiver on an elastic half-space. The surface wave is taken into account when the piezoelectric actuator is subjected to the harmonic electric excitation. The derived analytical formulas are used to compute the output potential of piezoelectric receiver. Experiment measurements are performed and compared with numerical results in good agreement. The influence of excitation frequency, material property and dimension of the piezoelectric material is presented.

Spatial Filtering Characteristics of Distributed Piezoelectric Sensors

Distributed spatial filtering characteristics of distributed piezoelectric sensors are investigated. In general, a sensor output signal is contributed by a membrane strain and a bending strain. Depending on the sensor placement, a distributed sensor can be only sensitive to either membrane or bending modes — membrane or bending sensor. In addition, a piezoelectric sensor can be sensitive to a mode or a group of modes due to signal average of electrode surface, especially anti-symmetrical modes. Accordingly, the sensor layer can be spatially shaped such that its sensitivity can be specified. These filtering characteristics are discussed and examples demonstrated.