bluuebunny/crossref_metadata_2025 huggingface dataset:
Development and Validation of Computational Fluid Dynamics Models for Initial Stages of Cavitation
Authors: Amromin Eduard
Published: February 2014

Various computational fluid dynamics (CFD) models employed for cavitating flows are substantially based on semi-empirical assumptions about cavitation forms and liquid flows around cavitating bodies. Therefore, the model applicability must be validated with experimental data. The stages of validation of the models are analyzed here with data on cavitating hydrofoils and axisymmetric bodies in water. Results of Reynolds-averaged Navier–Stokes (RANS), large-eddy simulation (LES), detached-eddy simulation (DES), and viscous-inviscid interaction methods are compared. The necessity of simultaneous validation of several flow parameters (as cavitation inception number and location of the appearing cavity) is pointed out. Typical uncertainties in water tunnel model test data (water quality, simplified account of wall effect) and possibilities to take them into account are also discussed. The provided comparison with experimental data manifests the impossibility to describe initial stages of cavitating flows using any single model and importance of employment of a combination of models for both the cavitation zones and the flow outside of cavities.
Cauchy and Signaling Problems for the Time-Fractional Diffusion-Wave Equation
Authors: Luchko Yuri , Mainardi Francesco
Published: February 2014

In this paper, some known and novel properties of the Cauchy and signaling problems for the one-dimensional time-fractional diffusion-wave equation with the Caputo fractional derivative of order β,1≤β≤2 are investigated. In particular, their response to a localized disturbance of the initial data is studied. It is known that, whereas the diffusion equation describes a process where the disturbance spreads infinitely fast, the propagation velocity of the disturbance is a constant for the wave equation. We show that the time-fractional diffusion-wave equation interpolates between these two different responses in the sense that the propagation velocities of the maximum points, centers of gravity, and medians of the fundamental solutions to both the Cauchy and the signaling problems are all finite. On the other hand, the disturbance spreads infinitely fast and the time-fractional diffusion-wave equation is nonrelativistic like the classical diffusion equation. In this paper, the maximum locations, the centers of gravity, and the medians of the fundamental solution to the Cauchy and signaling problems and their propagation velocities are described analytically and calculated numerically. The obtained results for the Cauchy and the signaling problems are interpreted and compared to each other.
Accuracy and Reliability of Piecewise-Constant Method in Studying the Responses of Nonlinear Dynamic Systems
Authors: Dai Liming , Wang Xiaojie , Chen Changping
Published: February 2014

Accuracy and reliability of the numerical simulations for nonlinear dynamical systems are investigated with fourth-order Runge–Kutta method and a newly developed piecewise-constant (P-T) method. Nonlinear dynamic systems with external excitations are studied and compared with the two numerical approaches. Semianalytical solutions for the dynamic systems are developed by the P-T approach. With employment of a periodicity-ratio (PR) method, the regions of regular and irregular motions are determined and graphically presented corresponding to the system parameters, for the comparison of accuracy and reliability of the numerical methods considered. Central processing unit (CPU) time executed in the numerical calculations with the two numerical methods are quantitatively investigated and compared under the same computational conditions. Due to its inherent drawbacks, as found in the research, Runge–Kutta method may cause information missing and lead to incorrect conclusions in comparing with the P-T method.
Analysis of Casting Roll Temperature Distribution and Thermal Deformation in Twin-Roll Continuous Strip Casting
Authors: Zhu Guangming , Zhang Yuwen
Published: February 2014

In twin-roll continuous strip casting, casting roll is heated by molten metal, and thermal deformation is caused to change strip thickness and quality. It is imperative to understand casting roll temperature distribution and thermal deformation. In this paper, a 2D finite element (FE) model is built to analyze casting roll temperature and thermal deformation under various casting processing parameters. The influences of shrink fit of roll sleeve and shaft are taken into account and the coating was treated to be consistent to the actual situation. The results show that casting temperature fluctuates cyclically within a thin top layer in stable casting, and there is almost no temperature fluctuation near cooling water holes.
Bone Anchors—A Preliminary Finite Element Study of Some Factors Affecting Pullout
Authors: Hughes C. M. , Bordush A. , Robioneck B. , Procter P. , Brown C. J.
Published: February 2014

Bone anchors (or suture anchors) are used to provide attachment points for sutures to connect tissue such as tendons or ligaments to bone, and work by engaging a threaded portion—sometimes tapered—to the cancellous and/or cortical bone. Such repair is often needed after trauma, or as part of reconstructive surgery. This paper uses the finite element method to compare the pullout characteristics of one common type of bone anchor in different cancellous bone structures. Finite element models are created by using computed tomography (CT) scans of cancellous bone and building computer-aided design (CAD) models to define the cancellous bone geometry. Orthopedic surgeons will sometimes remove parts of the cortical shell and this paper also examines the mechanical effects of decortication. Furthermore, the importance of the connection between anchor and cortical layer is examined. One of the key outcomes from the model is that the coefficient of friction between bone and anchor determines potential mechanisms of pullout. The stiffness of anchors and the effect of the cortical layer are presented for different pullout angles to obtain the theoretical response. The results show the detailed modeling that includes the micro-architecture of the cancellous bone is necessary to capture the large variations that can exist.
Winglets for Improved Aerothermal Performance of High Pressure Turbines
Authors: Coull John D. , Atkins Nick R. , Hodson Howard P.
Published: February 2014

This paper investigates the design of winglet tips for unshrouded high pressure turbine rotors considering aerodynamic and thermal performance simultaneously. A novel parameterization method has been developed to alter the tip geometry of a rotor blade. A design survey of uncooled, flat-tipped winglets is performed using Reynolds-averaged Navier–Stokes (RANS) calculations for a single rotor at engine representative operating conditions. Compared to a plain tip, large efficiency gains can be realized by employing an overhang around the full perimeter of the blade, but the overall heat load rises significantly. By employing an overhang on only the early suction surface, significant efficiency improvements can be obtained without increasing the overall heat transfer to the blade. The flow physics are explored in detail to explain the results. For a plain tip, the leakage and passage vortices interact to create a three-dimensional impingement onto the blade suction surface, causing high heat transfer. The addition of an overhang on the early suction surface displaces the tip leakage vortex away from the blade, weakening the impingement effect and reducing the heat transfer on the blade. The winglets reduce the aerodynamic losses by unloading the tip section, reducing the leakage flow rate, turning the leakage flow in a more streamwise direction, and reducing the interaction between the leakage fluid and end wall flows. Generally, these effects are most effective close to the leading edge of the tip where the leakage flow is subsonic.
Nanoscale Fluid Mechanics and Energy Conversion
Authors: Chen Xi , Xu Baoxing , Liu Ling
Published: February 2014

Under nanoconfinement, fluid molecules and ions exhibit radically different configurations, properties, and energetics from those of their bulk counterparts. These unique characteristics of nanoconfined fluids, along with the unconventional interactions with solids at the nanoscale, have provided many opportunities for engineering innovation. With properly designed nanoconfinement, several nanofluidic systems have been devised in our group in the past several years to achieve energy conversion functions with high efficiencies. This review is dedicated to elucidating the unique characteristics of nanofluidics, introducing several novel nanofluidic systems combining nanoporous materials with functional fluids, and to unveiling their working mechanisms. In all these systems, the ultra-large surface area available in nanoporous materials provides an ideal platform for seamlessly interfacing with nanoconfined fluids, and efficiently converting energy between the mechanical, thermal, and electrical forms. These systems have been demonstrated to have great potentials for applications including energy dissipation/absorption, energy trapping, actuation, and energy harvesting. Their efficiencies can be further enhanced by designing efforts based upon improved understanding of nanofluidics, which represents an important addition to classical fluid mechanics. Through the few systems exemplified in this review, the emerging research field of nanoscale fluid mechanics may promote more exciting nanofluidic phenomena and mechanisms, with increasing applications by encompassing aspects of mechanics, materials, physics, chemistry, biology, etc.
Sectored Tube-Shaped Ionic Polymer-Metal Composite Actuator With Integrated Sensor
Authors: Tsugawa Marissa A. , Leang Kam K. , Palmre Viljar , Kim Kwang J.
Published: February 2014

This paper describes the development of a tube-shaped ionic polymer-metal composite (IPMC) actuator with sectored electrodes and an integrated resistive strain-based displacement sensor. Tube or cylindrical shaped IPMC actuators, with the ability to provide multiple degrees-of-freedom motion, can be used to create active catheter biomedical devices and novel bio-inspired propulsion mechanisms for underwater autonomous systems. An experimental tube-shaped IPMC actuator is manufactured from a 40-mm long Nafion polymer tube with inner diameter of 1.3 mm and outer diameter of 1.6 mm. The outer surface of the tube-shaped structure is plated with platinum metal via an electroless plating process. The platinum electrode on the tube’s outer surface is sectored into four isolated electrodes using a simple surface milling technique. A custom-designed strain sensor comprised of 50 AWG ni-chrome wire is developed and attached to the tube’s surface to sense the bending motion of the tube actuator. The integrated sensor is low cost and practical, and it avoids the need for bulky external sensors such as lasers for measuring deflection and feedback control. Preliminary experimental results are presented to demonstrate the performance of the IPMC tube actuator and integrated displacement sensor.
Experimental Comparison Between a Fractal-Inspired Multi-Frequency Piezoelectric Energy Converter and a Traditional Converter
Authors: Castagnetti Davide
Published: February 2014

Harvesting energy from ambient vibrations in order to power autonomous sensors is a challenging issue. The aim of this work is to compare the power output from an innovative multi-frequency fractal-inspired piezoelectric converter to that from a traditional multi-cantilever piezoelectric converter. The converters are designed in order to give the same eigenfrequencies in a given range and a prototype of both is built using commercial materials. The experimental tests investigate both the effect of the acceleration and of the resistive load applied to the converters for each of the three eigenfrequencies in the range between 0 and 120 Hz. The fractal-inspired converter exhibits a significantly higher specific output power at the first and third of the eigenfrequencies investigated.
Artificial Cochlear Hair Cells Using Active Piezoelectric Materials
Authors: Joyce Bryan S. , Tarazaga Pablo A.
Published: February 2014

The inner hair cells (IHC’s) and outer hair cells (OHC’s) in the cochlea are vital components in the process of hearing. The IHC’s are responsible for converting sound-induced vibration into electrical signals. The OHC’s produce forces that amplify these vibrations and therefore enhance the electrical signals produced by the IHC’s. The resulting “cochlear amplifier” produces a nonlinear amplification which gives the ear its ability to detect sound pressure levels ranging from 20 μPa to 20 Pa (0 to 120 dB).

This paper presents the modeling and testing of an artificial hair cell (AHC) piezoelectric sensor inspired by the hair cells found in the mammalian ear. The sensor is a bimorph cantilever beam consisting of a sensing piezoceramic element and an actuating piezoceramic element bonded to a brass substrate. The sensing element is used to detect the mechanical motion of the beam. Output feedback control can be used to send a voltage signal to the actuating element and alter the frequency response of the beam. A control law, which modifies the linear damping term of the first mode and introduces cubic damping, is used to create a closed-loop system perched at a Hopf bifurcation. The result is a system that produces a nonlinear amplification of the beam’s mechanical response in a manner which mimics the nonlinear behavior of the mammalian cochlea. This active sensor is studied under base acceleration and the initial test results are compared to a finite element model. Simulations of the closed-loop system are examined for the system with a single mode and for the system with multiple modes.
Phased Array Beamsteering in Composite Laminates for Guided Wave Structural Health Monitoring
Authors: Osterc Peter , Kim Daewon , Yoo Byungseok
Published: February 2014

In this study, a guided wave phased array beamsteering approach is applied to composite laminates. Current beamsteering algorithms derived for isotropic materials assume omnidirectional wave propagation. Due to inherent anisotropy in composites, guided wave propagation varies with direction and wavefronts no longer have perfect circular shapes.

By examining slowness, velocity and wave curves for a given composite laminate, the wavefront from a single source can be described as a function of the angle of propagation and distance from origin. Using this approach, a generic delay and sum beamforming algorithm for composite laminates is developed for any desired wave mode.

It is shown that anisotropic wave mode regions can be effectively used for beamsteering in certain directions with a linear array and performance similar or even better than isotropic case. However, the useful range of angles with a 1d linear array for anisotropic wave modes is quite small and other directions exhibit undesired grating lobes and large sidelobes.
Mass Detection via Bifurcation Sensing With Multistable Microelectromechanical System
Authors: Harne R. L. , Wang K. W.
Published: February 2014

In many applications, the detection of changing gaseous or liquid concentration within an environment is accomplished by monitoring the shift in resonance frequency of a microelectromechanical system designed to adsorb the target analyte. Recently, mass sensing using the onset and crossing of a dynamic bifurcation has been shown to reduce the mass threshold which may be detected. This approach effectively replaces detection of an analog quantity resolved by hardware capability (phase shift or resonant frequency) with a digital quantity having fundamental resolution restricted by system noise (crossing the bifurcation). While promising, successful sensing with oscillators continually excited near a system bifurcation is practically limited in performance by repeatable characteristics close to the critical crossing frequency and the passive detection ability of the sensors has not yet extended to mass quantization over a period of time. In this research, we explore an alternative method to exploit bifurcation for mass sensing by utilizing a new sensor system composed of a small bistable element within a primary linear host sensor that helps alleviate these concerns. The proposed system design provides adjustable control of the rate at which the bifurcation is crossed, helping to tailor the sensitivities of the system encountered in the transition region, introduces new bifurcations to exploit, and lends the opportunity to utilize the numerous bifurcation phenomena sequentially to denote mass accumulation quantity occurring between consecutive jump events. The conceptual underpinnings of the method are presented in detail and example operational trials are demonstrated by simulation to expound its operation and adjustability. Discussion is provided to evaluate the system in terms of existing bifurcation-based mass sensing approaches and to outline remaining goals.
Locomotion Gait Design of an Earthworm-Like Robot Based on Multi-Segment Fluidic Flexible Matrix Composite Structures
Authors: Fang Hongbin , Li Suyi , Wang K. W. , Xu Jian
Published: February 2014

In this research, a concept of earthworm-like robot with fluidic flexible matrix composite (F2MC) segments as its actuators is investigated. It explores a novel application of F2MC in the bionics field. Firstly, a general kinematics model of robot with earthworm-like locomotion is developed. Based on this model, the locomotion mechanism is analyzed in order to determine the actuation performance requirement for the F2MC segment. Then an analytical model of the F2MC segment is adopted to estimate the finite deformation under internal pressurization. By doing so, the optimal configuration of the F2MC segment that meets the requirements as an actuator is determined. A conceptual design of the earthworm-like robot based on F2MC segment is presented. After that, robotic gaits are constructed based on the kinematic locomotion mechanism with some necessary physical assumptions. Directed locomotion can be achieved based on the constructed gaits. Aiming at increasing the average velocity and motion efficiency of the robot, locomotion gaits are optimized. Optimal gaits corresponding to the maximal velocity and maximal locomotion efficiency are obtained, respectively.
Design and Implementation of Regenerative Braking System
Authors: Adhikary Debasish , Rahman Muhammad Ziaur , Nahin Md. Minal , Bin Abdullah Muhammed Soyeb
Published: February 2014

During braking an automotive, all the kinetic energy is wasted in the form of energy due to braking, energy due to air resistance and energy due to rolling resistance. In the present literature a method has been developed to recover the energy. A fly-wheel mechanism has been used for this purpose. Instead of accelerating the automobile, the recovered energy is used to drive an air compressor used in pneumatic braking systems. The recovery process and the use of the energy has been investigated through simulation using SOLIDWORKS. The system has been applied to some available driving cycles like NEDC, Artemis cycle, FTP-75 cycle, 10–15 mode Japanese driving cycle, WLTC cycle to find out the most suitable driving cycle for the developed system. The corresponding results have been presented and are found quite reasonable. It is found that about 12% of the total energy consumed in a typical vehicle is spent in driving the compressor. So by using the mechanism represented here, this energy can be saved and fuel efficiency can be increased.
Experimental Investigation of Thermoacoustic-Piezoelectric Energy Harvesters and Refrigerators With Dynamic Magnifiers
Authors: Nouh M. , Aldraihem O. , Baz A.
Published: February 2014

Conventional Thermoacoustic-Piezoelectric (TAP) energy harvesters convert thermal energy, such as solar or waste heat energy, directly into electrical energy without the need for any moving components. The input thermal energy generates a steep temperature gradient along a porous medium. At a critical threshold of the temperature gradient, self-sustained acoustic waves are developed inside an acoustic resonator. The associated pressure fluctuations impinge on a piezoelectric diaphragm, placed at the end of the resonator. The reverse phenomenon results in piezo-driven thermoacoustic refrigerators (PDTARs). A pressure wave driven by a piezo-speaker induces a temperature gradient across the porous body. In this study, the TAP harvester and the PDTAR are coupled with auxiliary elastic structures in the form of simple spring-mass systems to enhance their performance. The proposed addition is referred to as a dynamic magnifier and has been shown in different areas to amplify significantly the deflection of vibrating structures. A comprehensive model of the dynamically magnified thermoacoustic-piezoelectric (DMTAP) system has been developed earlier that includes equations of motions of the system’s mechanical components, the harvested voltage, the mechanical impedance of the coupled structure at the resonator end as well as the equations necessary to compute the self-excited frequencies of oscillations inside the acoustic resonator. Theoretical results confirmed significant amplification of the harvested power is feasible if the magnifier’s parameters are properly chosen. The performance of experimental prototypes of a DMTAP harvester and a PDTAR with a dynamic magnifier are examined here. The obtained experimental findings are validated against the theoretical results. Dynamic magnifiers serve as a novel approach to enhance the effectiveness of thermoacoustic energy harvesting and refrigeration.
Numerical Simulation and Experimental Validation of Gap Supported Tube Subjected to Fluid-Elastic Coupling Forces for Hybrid Characterization Tests
Authors: Benmalek Wissam , Collet Manuel , Foltete Emmanuel , Ouisse Morvan , Corus Mathieu
Published: February 2014

Steam Generator (SG) tubes are subjected to fluid-elastic coupling forces and impacts against support plates & anti-vibration bars. Understanding their vibrations is crucial not only at the design stage, but also to optimize the SG maintenance policy and to lengthen the SG service life. The aim of our research is to provide a better understanding of the conjugate stabilizing effects of impacts and coupling with fluid-elastic forces. Since fluid-elastic forces are difficult to simulate and expensive to reproduce experimentally, the fluid coupling forces of our numerical model are represented using velocity dependent damping and stiffness matrices, both for the fluid and the tube. Their effect is experimentally reproduced having recourse to active vibration control in the frame of specifically designed “hybrid” experimental tests. In this paper, we present a method for modeling tube vibrations in order to estimate the conjugate effects of the coupling between the fluid elastic forces and impacts. This strategy lowers the costs and avoids the difficulties associated to the case of fluid in the experiments. Our numerical model will be implemented in the active control loop in the next step of the study.
A Memory Variable Approach to Modeling the Magneto-Mechanical Behavior of Magnetic Shape Memory Alloys
Authors: LaMaster Doug , Feigenbaum Heidi , Nelson Isaac , Ciocanel Constantin
Published: February 2014

Magnetic shape memory alloys (MSMAs) have attracted interest because of their considerable recoverable strain (up to 10%) and fast response time (1 kilohertz or higher). MSMAs are comprised of martensitic variants that have tetragonal unit cells and a magnetization vector that is innately aligned with the short side of the unit cell. These variants rotate either to align the magnetization vector with an applied magnetic field or to align the short side of the unit cell with an applied compressive stress. This reorientation leads to a mechanical strain and an overall change in the material’s magnetization, allowing MSMAs to be used as actuators, sensors, and power harvesters.

This paper builds upon the work of Kiefer and Lagoudas [4,5] as well as improvements proposed by LaMaster et al. [1] to present a thermodynamic based model to predict the response of an MSMA to axial mechanical loading and transverse magnetic loading. This work is unique, however, in its use of a memory variable, which references the last stable configuration. This is similar to the approach used by Saint-Sulpice [2] in modeling SMA wires. The resulting model has zero driving force for reorientation of variants at the beginning of any load and again when the load is removed. Thus the model predicts what is seen physically, that the material is stable when no magneto-mechanical load is present. Furthermore, this model is more physical and less empirical than others in the literature, having only 2 material parameters associated with the stress-strain or stress-field response. In addition, this model includes evolution rules for the magnetic domain volume fractions and the angle of rotation of the magnetization vectors based on thermodynamic requirements.

The resulting model is calibrated and predictions are compared with both the more established Keifer and Lagoudas model as well as experimental data. Results show decent correlation with experiments. The model can be further improved by calibrating the demagnetization factor to experimentally measured changes in magnetic field.
Development and Modeling of a Highly-Adjustable Base Isolator Utilizing Magnetorheological Elastomer
Authors: Li Yancheng , Li Jianchun
Published: February 2014

This paper presents a recent research breakthrough on the development of a novel adaptive seismic isolation system as the quest for seismic protection for civil structures, utilizing the field-dependent property of the magnetorheological elastomer (MRE). A highly-adjustable MRE base isolator was developed as the key element to form smart seismic isolation system. The novel isolator contains unique laminated structure of steel and MRE layers, which enable its large-scale civil engineering applications, and a solenoid to provide sufficient and uniform magnetic field for energizing the field-dependent property of MR elastomers. With the controllable shear modulus/damping of the MR elastomer, the developed adaptive base isolator possesses a controllable lateral stiffness while maintaining adequate vertical loading capacity. Experimental results show that the prototypical MRE base isolator provides amazing increase of lateral stiffness up to 1630%. Such range of increase of the controllable stiffness of the base isolator makes it highly practical for developing new adaptive base isolation system utilizing either semi-active or smart passive controls. To facilitate the structural control development using the adaptive MRE base isolator, an analytical model was developed to stimulate its behaviors. Comparison between the analytical model and experimental data proves the effectiveness of such model in reproducing the behavior of MRE base isolator, including the observed strain stiffening effect.
Application of Preview Information to Pointing Control of Truss Structure Using Artificial Thermal Expansion on Orbit
Authors: Funakoshi Yusuke , Ishimura Kosei , Ogi Yoshiro , Iwasa Takashi
Published: February 2014

Pointing performance of the truss structure on orbit which is used for large space telescope is discussed. To achieve advanced science missions, large and precise support structures such as truss structures are needed. However, the preciseness of the structure might be lost due to various disturbances on orbit. Therefore, to realize ultra large and precise support structures, active shape control of the structures is needed. To control the shape, we use artificial thermal expansion caused by heaters instead for mechanical actuators. Control systems without mechanism have high reliability, which is very attractive to use on orbit. However, there are some constraints in the usage of heaters. To improve the control performance under such constraints, we apply “Model based Predictive Control (MPC)” as feedforward control method with preview information. In this paper, we mainly show the effectiveness of MPC compared PI control, which is one of the typical feedback control methods. We constructed structural mathematical model and thermal mathematical model in order to show performance of control system. It is confirmed that total error is decreased by MPC compared with the case of PI control through numerical simulations.
Shape Memory Actuator System for Passive Cooling Air Adjustment in Mechanical Design
Authors: Böttcher Jonas , Szwedowicz Jaroslaw , Jahn Martin , Neubauer Marcus
Published: February 2014

Passive control of cooling processes is in designs best interest. Coolant medium flow to hot components must be kept at minimum acceptable level from lifting perspective to achieve maximum process efficiency. Required cooling of the hot components depends directly on engine power setting, which in general requires a relative complex system for monitoring critical parameters and adjusting coolant’s amount with engine load. Concerning the operation reliability, pseudoplastic shape memory alloys offer a high simplicity in the design of adjustment mechanisms with large operating displacements. As the shape memory effect is induced by temperature changes, the behavior of shape memory actuators and therefore the coolant’s amount can be adjusted to the load conditions of the engine by using appropriate shape memory materials. In this paper an actuator based on a shape memory membrane using the extrinsic two-way effect is presented to vary the cross-sectional area of a cooling air channel with respect to the engine operation. The reset of the mechanism after one temperature cycle of heating and cooling is realized by using a leaf spring element, which is in varing mechanical contact with the shape memory membrane depending on the hysteresis of the entire system. Maximum displacements of the system are attained for spring forces between the force generated by the shape memory membrane in the martensitic and austenitic state. Thus, the system mechanism exhibits two non-linearities of pseudoplastic shape memory characteristic and contact mechanics with friction. For this purpose experimental investigations were carried out to acquire the fundamental force displacement behavior of the shape memory membrane to design the optimal shape of the leaf spring element. The forces required to deform the shape memory membrane in the martensitic and austenitic state were measured with respect to the membranes displacement using a load cell and a linear variable differential transformer. The displacements of the membrane were introduced using a linear bearing system. The calculations for the design of an optimal leaf spring and especially its initial shape were carried out using a discrete multi body system consisting of beam elements and torsional springs. The leaf spring with the calculated optimal shape was fabricated and incorporated into the system. The displacement behavior of the system during heating and cooling was measured using an optical distance sensor. For the analyzed temperature range up to 100 °C, the paper describes the methodological appropriacy and relevance towards the application domain for evaluated temperatures.
Layer Sequencing and Flat-Foldability of Uniformly Gridded Polygons
Authors: Xing David
Published: February 2014

Lunnon (1969) proposed a method to solve the Stamp Folding Problem which asks how many flat-foldable stack patterns there are for a given M by N rectangle grid (map). This project generalizes the original problem to include arbitrarily shaped polygons, including M by N maps. The purpose of this project is to develop a mathematical theorems that would determine whether or not a uniformly gridded polygon with a given stack pattern is flat-foldable. Furthermore, the theorems will determine the two mountain-valley assignments by which a gridded polygon with the given stack pattern can be folded flat. The results of the number of flat-foldable stack patterns for a given M by N map computed by this method is coincided by the results derived by Lunnon’s method. However, our method extends the scope of the original problem to more arbitrarily shaped polygons. This method will aide in the designing of foldable metal or paper structures.
Additive Manufacturing of Shape Memory Devices and Pseudoelastic Components
Authors: Haberland Christoph , Elahinia Mohammad , Walker Jason , Meier Horst , Frenzel Jan
Published: February 2014

Processing of Nickel-Titanium shape memory alloys (NiTi) is by no means easy because all processing steps can strongly affect the properties of the material. Hence, near-net-shaping technologies are very attractive for processing NiTi due to reduction of the processing route. Additive Manufacturing (AM) provides especially promising alternatives to conventional processing because it offers unparalleled freedom of design. In the last 5 years AM of NiTi received little attention from academics and researchers and, therefore, is far from being established for processing NiTi today. This work is to highlight the current state of the art of using the AM technique Selective Laser Melting (SLM) for processing high quality NiTi parts. For this reason, fundamentals for SLM processing of NiTi are described. It is shown in detail that a careful control of process parameters is of great importance. Furthermore, this work characterizes structural and functional properties like shape recovery, referring to the shape memory effect in Ti-rich SLM NiTi, or pseudoelasticy in Ni-rich SLM NiTi. It is shown that both types of shape memory effects can be adjusted in SLM NiTi by the choice of the raw material and processing strategy. By comparing the properties of SLM NiTi to those of conventionally processed NiTi, this work clearly shows that SLM is an attractive manufacturing method for production of high quality NiTi parts.
Towards Frequency-Independent Vibration-Based Energy Harvesting Using Frequency Up-Conversion and Power Analysis
Authors: Patel Ambrish P. , Wickenheiser Adam M.
Published: February 2014

Traditionally, vibration-based energy harvesters have been designed for specific base excitation frequencies by matching their natural frequencies. However, harvesting energy from common human motions is challenging because the low frequencies involved are incompatible with small, light-weight transducers, which have much higher natural frequencies. By using the frequency up-conversion method, a vibration-based, nonlinear, magnetically excited energy harvester exhibits efficient, broadband, frequency-independent performance.

A complete model is provided for an energy harvester utilizing the frequency up-conversion method that defines the relationship between the enclosure excitation, the base excitation and the stationary magnets, where the base of the beam is mounted elastically inside an enclosure. The average power output of a vibration-based energy harvester with frequency up-conversion is analyzed using artificial and naturally occurring base excitations such as sinusoidal and walking motions, respectively. Simulations are provided to demonstrate the broadband capabilities of vibration-based energy harvesters with frequency up-conversion, especially for driving frequencies lower than the fundamental frequency, where significant increase in power output are observed when utilizing frequency up-conversion. In addition, the advantages and limitations of approximating a range of natural base excitations with a set of orthogonal basis functions are explored, which provides motivation for Wavelets Analysis. Finally, a procedure is proposed to determine the maximum expected power output.
Development of a 2-D Interfacial Dynamic Model for Detwinning in HTSMAs
Authors: Ara Thomas , Bouby Céline , Ben Zineb Tarak , Berveiller Sophie , Patoor Etienne
Published: February 2014

This article presents the development of a 2D model for HTSMA which focus on interfaces motion in the martensitic state. We consider the topology of a 2D representative “volume” constituted of 4 martensite variants. Interfacial force is derived using Eshelby’s energy momentum tensor ans compared with a critical threshold which depends on interfacial lenght. A criterion for annihiling compatible interfaces is incorporated in this framework. The model is firtly applied to the description of detwinning mechanism in a grain. First results are presented.
Using a R-Phase SMA Methodology to Design an Energy Harvesting Unit With Tight Temperature Hysteresis
Authors: Lygin Konstantin , Czechowicz Alexander , Meier Horst
Published: February 2014

Shape memory alloys (SMA) are smart materials with the ability to remember a previous imprinted shape after plastic deformation. The shape memory actuator effect is induced by thermal energy. Its bases on crystalline transformation of NiTi-alloys from the austenitic B2 to the martensitic B19′ phase. Usually, SMA actuators show a large temperature hysteresis with high strokes and loads. A lot of technical applications are realizable with SMA-actuators, for example in automotive sector. Under special conditions an additional phase, the R-phase occurs in SMA. This transformation from the austenitic B2 phase to the R-phase is characterized by a very small temperature hysteresis. Compared to conventional transformation characteristic of B2 ⇒ B19′, the R-phase transformation has small stroke and load. Because of this the R-Phase transformation qualifies for temperature sensitive and autarkical applications in air-conditioning or heating systems. Today’s problem for engineers designing R-phase actuators is that a lot of rules and parameters need to be considered. This paper presents a methodology, which can be used as a guideline to support engineers designing R-phase actuators. The whole process from defining requirements to prototyping will be discussed for the development of an energy harvesting actuator, which uses a low thermal energy potential. This paper contribution is to fill this gap in product development methodologies for shape memory actuators.
A Miniature Three-Axis Piezoelectric Energy Harvester
Authors: Hung Chiao-Fang , Wang Chieh-Min , Ling Shin-Hung , Chung Tien-Kan
Published: February 2014

In this paper, we demonstrate a novel miniature three-axis piezoelectric energy harvester. The energy harvester consists of four piezoelectric lead zirconate titanate cantilever beams, connector, proof mass, and mechanic frame. Through the connector, a special configuration with a well-constrained mechanism of the energy harvester is achieved. Due to the configuration/mechanism of the energy harvester, the Newton’s law of inertia and piezoelectric effect are utilized to convert the in-plane (either x-axis or y-axis) and out-of-plane (z-axis) environmental vibrations into voltage responses. This achieves energy harnessing from 3-axial environmental vibration.
A Magnetic/Mechanical Approach for Optimizing a Miniature Self-Powered Current Sensor
Authors: Chung Tien-Kan , Yeh Po-Chen , Wang Chieh-Min
Published: February 2014

In this paper, we demonstrate a magnetic/mechanical approach for optimizing a miniature self-powered current sensor. The sensor consists of a piezoelectric PZT sheet, CuBe cantilever beam, NdFeB magnet, and mechanical clamp. When the sensor is placed nearby an AC-current carrying wire from a breaker, the magnet fixed on the beam of the sensor experiences an alternative magnetic attractive and repulsive force produced by an AC magnetic field generated by the wire. Due to the alternative magnetic attractive and repulsive force, the magnet fixed on the beam is oscillated. The oscillating beam deforms the PZT sheet and subsequently produces strain in the PZT sheet. Due to the piezoelectric effect, the strain is converted to a voltage response. Through the optimized approach, the voltage output of the sensor is increased from 1.27 volts to 4.01 volts when the sensor is used to detect an AC current-carrying wire of 8 ampere at 60 Hz.
Energy Harvesting From Base Excitation of a Biomimetic Fish Tail Hosting Ionic Polymer Metal Composites
Authors: Cha Youngsu , Verotti Matteo , Walcott Horace , Peterson Sean D. , Porfiri Maurizio
Published: February 2014

In this study, we seek to understand the feasibility of energy harvesting from the tail beating motion of a fish through active compliant materials. Specifically, we analyze energy harvesting from the undulations of a biomimetic fish tail hosting ionic polymer metal composites (IPMCs). The design of the biomimetic tail is specifically inspired by the morphology of the heterocercal tail of thresher sharks. We propose a modeling framework for the underwater vibration of the biomimetic tail, wherein the tail is assimilated to a cantilever beam with rectangular cross section. We focus on base excitation in the form of a superimposed rotation about a fixed axis and we consider the regime of moderately large–amplitude vibrations. In this context, the effect of the encompassing fluid is described through a nonlinear hydrodynamic function. The feasibility of harvesting energy from an IPMC attached to the vibrating structure is assessed and modeled via an electromechanical framework. Experiments are performed to validate the theoretical expectations on energy harvesting from the biomimetic tail.
Experimental Validation of a Shape Memory Alloy Constitutive Model by Heterogeneous Thermal Loading Using Infrared Thermography and Digital Image Correlation
Authors: Cornell Stephen R. , Hartl Darren J. , Lagoudas Dimitris C.
Published: February 2014

This work introduces the use of digital image correlation together with infrared thermography to study non-uniform deformations due localized heating of equiatomic NiTi. While this short paper focuses on demonstrating the mechanical response of the material to localized heating, future work will also demonstrate calibration and validation of a 3-D constitutive model of the material using the concepts presented here. A comparison is made between the behavior of the material due to localized heating and the behavior due to uniform heating and cooling. The relevant parameters used for calibration of the constitutive model are quantified using the results of an ambient heating and cooling experiment.
Multiple Patch-Based Piezoelectric Energy Harvesting From Multiple Vibration Modes of Thin Plates
Authors: Aridogan Ugur , Basdogan Ipek , Erturk Alper
Published: February 2014

Vibration-based energy harvesting using cantilevered piezoelectric beam has been extensively studied over the last decade. In this study, as an alternative to resonant piezoelectric cantilevers, we studied multiple patch-based piezoelectric energy harvesting from multiple vibration modes of thin plates. Analytical electroelastic model of the multiple patch-based piezoelectric harvesters attached on a thin plate is provided based on distributed-parameter modeling approach for series and parallel configurations of the patches. An experimental setup is built with series-configuration of double patch-based harvesters attached on the surfaces of all-four-edges clamped (CCCC) rectangular aluminum plate. Analytical simulations and experimental validations of power generation of the harvesters are performed in a case study. The experimental and analytical frequency response functions (FRF) relating voltage output and vibration response to force input are obtained. The analytical model is validated by comparing analytical and experimental FRFs for a wide range of resistive electrical boundary conditions. The harvested power output across the various resistive loads is explored with a focus on the first four modes of the aluminum plate. Experimental and analytical results are shown to be in agreement for multiple patch-based piezoelectric energy harvesting from multiple vibration modes of thin plates.
Size Effect on the Critical Stress of Nitinol Wires
Authors: Honarvar Mohammad , Konh Bardia , Datla Naresh V. , Devlin Sean , Hutapea Parsaoran
Published: February 2014

Nitinol has the best shape memory and superelasticity properties of all known polycrystalline shape memory alloys (SMAs) due to diffusionless Martensitic transformation. Due to these unique properties, Nitinol is increasingly used in different fields such as biomedical, structural and aerospace engineering. However, under certain stresses Nitinol exhibits unrecovered strain, or permanent set, that limits the applicability of Nitinol wire. This study showed that there exists a critical range of stress beyond which the permanent set is negligible. The goal of this paper is to determine range of critical stress using two different methods i.e. constant stress experiment and isothermal tensile test and to show variation of this range with changes in wire diameters.
A Vibration Energy Harvesting Structure, Tunable Over a Wide Frequency Range Using Minimal Actuation
Authors: Heit John , Christensen David , Roundy Shad
Published: February 2014

This paper introduces a novel vibration energy harvesting structure with a resonance frequency that is tunable over a large range using a simple compact mechanical adjustment that alters the structural stiffness. The frequency tuning requires minimal actuation that can be “turned off” while maintaining the new resonance frequency. Testing shows that the natural frequency can be adjusted from 32 Hz to 85 Hz. The structure is coupled with an electromagnetic transducer to generate power. Test results at varying excitation frequencies and amplitudes demonstrate tunable power generation over a very wide bandwidth. In addition to frequency tunability, the structure is a nonlinear softening spring, which provides the added benefit of a passively wider bandwidth for specific ranges of the design parameters.
Modeling and Characterization of the Effects of Field Gradients on the Behavior of Ferroelectrics With Interdigitated Electrodes
Authors: Pisani David M. , Gallagher John A. , Smith-Stewart Benjamin , Lynch Christopher S.
Published: February 2014

Macro fiber composites (MFCs) are used in applications ranging from sensing and actuation to energy harvesting and piezoelectric damping. MFCs are comprised of interdigitated electrodes (IDEs) on ferroelectric fibers that result in anisotropic in plane sensing and actuation capability. Minor hysteresis loops were measured for a MFC and the area within the minor hysteresis loops was used to assess material loss under unipolar cyclic loading. A separate set of minor hysteresis loops was run on a fully electroded plate of the same material to determine the material loss when the electric field was uniform. The MFC displayed considerably more material loss than the uniformly loaded plate. A micromechanical model implemented in a finite element code was used to model the effect of inhomogeneous fields, local stress, and polarization reorientation on the dielectric losses. The results indicate that the development of local stress in the ferroelectric material beneath the inerdigitated electrodes results in ferroelastic polarization reorientation that contributes to dielectric losses.
Numerical Evaluation of the Effect of Ni4Ti3 Precipitates on the Overall Thermo-Mechanical Response of NiTi Shape Memory Alloys
Authors: Cox Austin , Baxevanis Theocharis , Lagoudas Dimitris
Published: February 2014

The effect of precipitation on the thermo-mechanical properties of Ni-rich near-equiatomic NiTi Shape Memory Alloys (SMAs) is investigated via the finite element method. The thermo-mechanical response is simulated using a Representative Volume Element (RVE), which takes into account the structural effect of the precipitates, as well as the effect of the Ni-concentration gradient in the matrix. The Ni-distribution profile is evaluated using Fick’s law for diffusion. The obtained results reproduce several of the experimentally observed precipitation-induced changes on the transformation behavior characteristics of these materials.