The purpose of this work is to investigate the application of active mode localization to discretized models of distributed parameter systems where the number of control sensors and actuators is a limiting factor. A modified eigenvector scaling technique using singular value decomposition is developed which scales the lower-mode eigenvectors, producing localization over the range of these lower natural frequencies. An example using a simply supported beam model is provided, with mode localization achieved in at least the lower 3 modes utilizing as few as two control sensor/actuator pairs.

The number of required modes to provide accurate force information in a truncated model of a flexible structure is investigated. In the context of modal truncation of a distributed parameter system, the difference in convergence rates between displacements and forces is discussed. The residual flexibility, a term from past literature, is used to recapture some of the lost force information in a truncated model. This paper presents numerical and experimental results of a study where the residual flexibility is used in conjunction with a Kalman filter so that accurate force information may be obtained from a small set of displacement measurements with a reduced-order model. The motivation for this paper is to be able to obtain accurate information about dynamic bearing loads in a rotating machine for diagnostic and control purposes.

Magnetorheological (MR) and electrorheological (ER) fluids possess rheological or flow properties that can be controllably altered by the application of electric or magnetic fields, respectively. These fluids typically consist of dispersions of micrometer-sized dielectric or soft ferro (ferri) magnetic particles that become aligned in the presence of an external electric or electrical magnetic field, respectively. Such patterns in the material, which disappear when the field is removed, cause the material to resist mechanical deformation. This controllable property of the fluids allows them to be used in adaptive-passive actuators. This paper presents the results of a preliminary experimental investigation into the performance of the MR fluids in a linear vibration damper. A squeeze-flow MR fluid damper is used to suppress vibrations of a simply supported beam. Four different MR fluids are compared.

This paper presents a numerical study in which active and hybrid vibration confinement is compared with a conventional active vibration control method. Vibration confinement is a vibration control technique that is based on reshaping structural modes to produce “quiet areas” in a structure as opposed to adding damping as in conventional active or passive methods. In this paper, active and hybrid confinement is achieved in a flexible beam with two pairs of piezoelectric actuators and sensors and with two vibration absorbers. For comparison purposes, active damping is achieved also with two pairs of piezoelectric actuators and sensors using direct velocity feedback. The results show that both approaches are effective in controlling vibrations in the targeted area of the beam, with direct velocity feedback being slightly more cost effective in terms of required power. When combined with passive confinement, however, each method is improved with a significant reduction in required power.

The ideal of controlling the vibrations of a structure by using variable stiffness members has been around for over fifteen years. Two types of mechanical springs, Type I and II, have been devised with control laws to reduce the dynamic response of structures due to disturbances. By comparing the mechanical springs and their control laws to the novel real-time piezoceramic shunt switching techniques, it is clear that piezoceramic actuators can act similar to Type I and II mechanical springs. In this paper, piezoceramic actuators are used with three different shunt circuits (capacitance ladder, switching ground circuit, and switching resistor/inductor circuit) and are compared to their mechanical spring counterparts. A new type of spring, Type III, is introduced along with a new semi-active multi-modal control scheme for piezoceramic actuators. The new multi-modal control technique is used on a simple six degree of freedom numerical example.

A new technique for measuring and actively controlling dynamic bearing loads in rotating machinery is presented. Bearing loads are estimated using the Deflection-Coefficient Method, a technique which does not rely on a full system model, and which applies commonly-used shaft-deflection measurement equipment to obtain estimates of bearing loads. The estimated bearing load is used as an error signal in an adaptive feedforward disturbance rejection controller. The result is a control system which can selectively minimize dynamic bearing loads in real time in rotating machinery systems. The method is applied to a numerical model of a typical rotating machinery system to suppress dynamic reaction forces at bearing supports.

This paper presents the development of a bimorph piezoelectric cymbal energy harvester that is particularly useful for extracting energy from the vibrating systems of relatively high compressive load. The bimorph cymbal harvester can be used to charge a capacitor or a battery through the piezoelectric layers fitted within the metal end caps under repeated compression or deformation. In this work, feasibility of a bimorph piezoelectric cymbal harvester in series operation is investigated through theoretical analysis and experimental validation. The bimorph cymbal uses a composite disc of two piezoelectric layers and a steel substrate between metal end caps. Theoretical modeling to quantify the generated energy by using bimorph cymbal design is first conducted. A parametric study is then performed to optimize generated energy with the dominant design parameters influencing energy harvesting performance for the cymbal structure. The parameters such as thickness of the end caps, radius ratio of the apex to the cavity of the end caps, cavity depth, and thickness ratio of the piezoelectric to the steel substrate are considered. Based on the optimized dimension, a cymbal harvester was fabricated and tested to validate analytically predicted open-circuit voltage on a hand jack type test rig. Experimental result indicates that the measured open-circuit voltage from the bimorph cymbal harvester is less than that of analytically predicted. However, it shows that the bimorph piezoelectric cymbal structure is an alternative cymbal design that is useful for harvesting energy from the source of relatively high load.

Rather than address morphing in the conventional way of applying forces to a fixed-compliance structure, this work addresses morphing in a structure that can exhibit variable compliance. Specifically, this work addresses the shape morphing of a simply-supported elastic beam from a forward approach perspective, that is, determining beam shape due to applied forces. The focus on this study is on the spatial distribution of the structure due to local/total modulus change in its steady state condition. The resulting morphed shapes are quantified in terms of the characteristic parameters, such as spatial distribution of the peaks of the shapes, deviation from the axis of the symmetry and, in case of flat-top shapes, the width of the flat portion.

This paper presents power generation performance of unimorph PZT (lead zirconate titanate) cymbal harvesters optimally designed for the power requirements of a specific application. Proof-of-concept work has shown that the traditional cymbal design can be adapted to a new design that is capable of sustaining higher mechanical loads by replacing the piezoelectric plate with a unimorph circular piezoelectric diaphragm between the metal end caps. The unimorph circular diaphragm is constructed by bonding PZT to a steel substrate to provide increased strength. Additional work was performed to prepare the new cymbal design for large-scale implementation in a variety of applications. The parameters that affect energy harvesting performance for the cymbal structure are first optimized by parametric studies to produce optimum generated energy from a specific range of applied cyclic forces. Key parameters in the unimorph PZT cymbal design include the material properties and the dimensions of the end caps, the ratios of the diameters of the unimorph disc and the end cap cavity, and thickness ratio of the PZT layer and the substrate. Based on the optimized unimorph PZT cymbal structure, a specimen was then fabricated and tested on the load-frame to validate analytically predicted energy generating performance. The specimen was tested under a 1 Hz cyclic load of up to 2,100 N. The measured open circuit output voltages for two different load inputs were in accordance with the analytical prediction.

Buildings are a significant source of energy consumption in the US and worldwide, and conditioning building interiors occupies a major portion of that expenditure. At the building level, a particular scenario can occur where it becomes more advantageous for a structure’s walls to be “open” to the outside, as opposed to remaining “closed”, in an insulating state. For instance, a cool night may follow a hot summer day after the sun sets, but traditional insulation captures heat built up inside a home. A clear, sunny day may also heat a building’s exterior during a cold winter day, and heat transfer to the interior would be more desirable than insulation. This paper presents a study of a concept, termed “smart insulation”, that could be used in such scenarios to take advantage of beneficial thermal gradients in order to save heating and cooling costs. Enabling heat transfer without moving air can also help control humidity within interior spaces, as well as limit noise either from moving air or through open windows. Unlike traditional insulation that maintains a specific insulating value during its useful life, smart insulation changes between an insulating and a conducting state depending on the thermal gradient. Some design concepts have been fabricated and were tested in an insulated chamber that provides a “hot side” and a “cool side”. In the test chamber, temperature measurements were taken and the insulating capacity of each design specimen was calculated. Results indicate that the designs have potential to operate between two states (with the best case ranging from 11% to 61% of a benchmark insulation case) and effectively provide sustainable heating or cooling by capitalizing on ambient outdoor conditions.

Piezoelectric micro benders are fabricated and tested to demonstrate energy generating performance. Trapezoidal and diagonal unimorph PZT benders with an interdigitated electrode pattern are utilized. The d 33 mode design is beneficial for the micro energy harvesting devices because it can generate higher voltage than that of the d 31 mode design. It can also eliminate a bottom electrode by only using an interdigitated top electrode which facilitates fabrication, as opposed to the d 31 mode design that requires both top and bottom electrodes. The MEMS benders consist of layers of SiO 2 /SiN x /ZrO 2 /PZT, and a top Au/Cr interdigitated electrode. The experimental results indicate that the fundamental frequencies of the micro benders are about 9.1 kHz for the trapezoidal bender and 18.48 kHz for the diagonal bender, respectively. The micro trapezoidal bender can generate power of approximately 1.4μW into a 680 kΩ resistive load at the resonant frequency. The diagonal bender can generate power of about 18.2 μW into a 100 kΩ resistive load at the resonant frequency.

A variety of methods have been introduced in recent years to implement morphing aircraft and other shape-changing structures, including high-force actuators that can elastically deform structural members, to stiffness-changing elements that more readily accommodate the deformations. This paper introduces a structural element of the latter type that can exist in two states: a rigid state that supports structural loads and locks the structure in place, and a soft state that enables deformation of the structure. The element itself is termed the “Smart Link” and is used in the folding mechanism of a morphing aircraft. The link is a composite made up of shape memory polymer (the softening material) and a backbone of shape memor alloy, which allows high deformation but ensures that the nominal shape is recovered upon return deformation. This paper presents the design requirements for the link in terms of the morphing aircraft application, and then presents the iterative design, fabrication, and testing process used to develop the Smart Link. Finally, results of testing of the link in the aircraft during wind tunnel tests are presented to show the pros and cons of its performance. In summary, the link met the mechanical requirements by performing multiple morphing cycles through the loads and deformation ranges (103 degrees of angle change) needed. The major drawback of the design is the response time necessary to transition the heat-activated material. Suggestions are given at the end of the paper for ways to improve the time response.

This paper presents an experimental comparison of energy generating performance between piezoelectric harvesters for use in a pressure-loaded system. The energy harvesters in this study are simply-supported, partially covered piezoelectric unimorph circular diaphragms to capture and transfer biomechanical energy into electrical power for implantable medical devices. Experimental results indicate that both PMN-PT and PZT harvesters can generate useful power that might meet requirements for specific implants under the uniform cyclic pressure loading of 40mmHg blood pressure variation, but the PMN-PT harvester demonstrates over twice the power generating performance of the PZT harvester under the same pressure loading condition.

The concept of switching the shunt circuit of a passive piezoelectric material used for vibration control has been studied by various researchers for the past decade. The technique involves connecting and disconnecting the piezoelectric actuator to and from a resistive, capacitive, or inductive shunt circuit in real time. By setting the switch timing appropriately, one can achieve significant damping in the accompanying structure. While the technique has been shown to be very effective in lab settings, the practical performance can be affected by several factors. This paper addresses some of the practical issues of switched shunts and analyzes the expected performance as various parameters vary in the system, including i) the original damping in the structure, ii) the relative stiffness of the structure and the actuator, and iii) mistiming of the shunt switching process. A simple single degree-of-freedom system with a switched resistor-inductor (RL) shunt is used in the study. The paper presents a mathematical model of the system and switched-shunt, and then presents the results of simulations that analyze the expected damping performance.

Balanced flow distribution to each cell in a fuel cell stack plays a significant role in the stack being able to operate at maximum capability and efficiency. This paper discusses the performance improvements in proton exchange membrane fuel cell stacks that can be obtained by using cell-to-cell flow distribution control. In a specially instrumented four-cell stack that employs needle valves to externally control the air and fuel flows to each cell, fuel to a single cell was reduced. The V-I curves collected under these conditions (unbalanced) are compared to curves collected when the fuel flow to each cell was equal (balanced). Reducing the fuel flow to a single cell by 30% decreased the V-I curve cutoff load by 8.5% — demonstrating the negative effect that unbalanced fuel flows can have on stack performance. Typical fuel cell stacks have no dynamic means to keep flows in the stack balanced between the cells, but this work indicates that flow balancing among cells can extend the V-I curve for a fuel cell to higher current values, allowing fuel cell stacks to operate reliably at higher loading and fuel utilizations. Plans to use novel, custom-built micro-valves to dynamically balance flow to individual cells in a fuel cell stack are being pursued as a result of this work, and the status of this development effort is provided.

This paper presents the design and analysis of a cantilever beam resonator that is driven by a piezoelectric material. The beam is a bimorph structure with Lead Zirconate Titanate (PZT) and stainless steel or aluminum layers. The PZT layer is electroded in segments to form a sensor and actuator pair for feedback to drive the resonator. An additional PZT segment is used, in conjunction with a capacitive shunt circuit, to change the vibration frequency of the resonator. The study is based on an analytical model of the beam and experimental testing.

A great amount of research has been done to determine whether piezoelectric materials can be used as power generators for a variety of portable and low power consuming devices. Among the possibilities for energy harvesters, the 31-type cantilever piezoelectric benders have been generally used. In this work a unimorph piezoelectric cantilever beam with the interdigitated electrode pattern was examined. The focus of this paper was to develop a model and propose design parameters to improve the power generating performance of the interdigitated piezoelectric power harvester.

A novel axial-flow piezoelectric microvalve for fuel cell applications has been designed and analyzed. Microvalves offer to improve flow maldistribution problems that have been identified in fuel cells. This paper will outline the design of an embeddable microvalve that has many novel features, including an axial flow characteristic, piezoelectric trimorph actuation mechanism, unlimited scalability, thermally-insensitive activation, and relative simplicity. Detailed electro-mechanical, thermal, and fluidic analyses of the design are conducted using ANSYS and MATLAB simulation packages. The valve geometry is heuristically optimized based upon the results of the analyses. Fabrication and testing of the valve is currently underway.