bluuebunny/crossref_metadata_2025 huggingface dataset:
Flash Butt Wedge Repair of Weld Head Defects
Authors: Workman David , Kral Richard
Published: February 2012

Transverse defects in the head of rail are the cause for many repair plug insertions and can lead to potential train stoppage if not repaired in a timely manner. In 2009, 76 train derailments were attributed to transverse head defects progressing to fracture in the rail. This phenomenon has been associated with the high axle loads found in mainly North American and heavy haul markets. Market trends are for increasing axle loads which may increase the occurrence of head defects. An efficient, high-performance repair for this defect has been sought for many years. For a truly effective repair, the loss of service time must be minimized to maintain cost effectiveness and the repair must perform as close to parent metal rail as possible. In early 2009 EWI and Holland entered into a joint development program to develop a repair for transverse defects in the rail head. Gas Metal Arc Welding, Resistance Brazing and flash butt welding with a wedge geometry piece were examined as methods for the repair. The flash butt welding process appeared most viable and is already associated with high-quality rail butt joints. The benefits of flash butt wedge welding include no rail cutting or removal, rapid on track repair time within 30–45 minutes, and the ability to modify the process using the computer-controlled flash butt welding system to accommodate different rail wear conditions. Additionally, cooling rates of the weld can be controlled such that the weld and heat-affected zone (HAZ) performance closely match the base metal. Special tooling and processing parameters were developed to use flash butt welding to place a wedge-shaped piece of matching rail material into a slot cut in the rail replacing the compromised area with matching rail material. Hardness testing, bend testing, and fatigue testing of joints produced with the final process all met AREMA performance objectives. Residual stress measurements of the weld showed a tendency for residual compressive stress in the rail head, although the level of residual stress was low. Currently, the first-generation welder with automated flash-removal equipment is being deployed in the field. Results of the qualification/performance tests show these welds perform very similarly to flash butt welds currently in rail. The use of this process is expected to enable railroads to quickly repair head defects in a more efficient manner.
Development of the Finite Segment Method for Modeling Railroad Track Structures
Authors: Hamper Martin B. , Zaazaa Khaled E. , Shabana Ahmed A.
Published: February 2012

In the finite segment method, the dynamics of a deformable body is described using a set of rigid bodies that are connected by elastic force elements. This approach can be used, as demonstrated in this investigation, in the simulation of some rail movement scenarios. The purpose of this investigation is to develop a new track model that combines the absolute nodal coordinate formulation (ANCF) geometry and the finite segment method. The ANCF finite elements define the track geometry in the reference configuration as well as the change in the geometry due to the movement of the finite segments of the track. Using ANCF geometry and the finite segment kinematics, the location of the wheel/rail contact point is predicted online and used to update the creepage expressions due to the finite segment displacements and rotations. The location of the wheel/rail contact point and the updated creepage expressions are used to evaluate the creep forces. A three-dimensional elastic contact formulation (ECF-A), that allows for wheel/rail separation, is used in this investigation. The rail displacement due to the applied loads is modeled by a set of rigid finite segments that are connected by set of spring-damper elements. Each rail finite segment is assumed to have six rigid body degrees of freedom. The equations of motion of the finite segments are integrated with the railroad vehicle system equations of motion in a sparse matrix formulation. The resulting dynamic equations are solved using a predictor-corrector numerical integration method that has a variable order and variable step size. As shown in this paper, the finite segments may be used to model specific phenomena that occur in railroad vehicle applications, including rail rotations and gage widening. The procedure used in this investigation to implement the finite segment method in a general purpose multibody system (MBS) computer program is described. Four simple models are presented in order to demonstrate the implementation of the finite segment method in MBS algorithms. The limitations of using the finite segments approach for modeling the track structure and rail flexibility are also discussed.
Modeling Rail Flexibility Using Finite Element and Finite Segment Methods
Authors: Hamper Martin B. , Recuero Antonio M. , Escalona Jose´ L. , Shabana Ahmed A.
Published: February 2012

Safety requirements and optimal performance of railroad systems require the utilization of multibody System (MBS) formulations that allow for modeling flexible bodies. This investigation will present three methods suited for the study of flexible track models while conclusions about their implementations and features are made. A validated method combining Floating Frame of Reference (FFR) and Finite Element (FE) to model flexible rails is utilized for comparison. In this procedure, component mode synthesis is used to extract a number of low-frequency modes of vibration which describe the deformation of the rail. Likewise, a method that discretizes the flexible body as a finite number of rigid elements that are linked by springs and dampers is applied for railroad simulations. This method, called Finite Segment or Rigid Finite Element (FS), can in turn be combined with FFR through the extraction of mode shapes of the FS model. Convergence of the methods is analyzed. A comparison will be made between these three procedures establishing differences among them and analyzing the specific application of FS to modeling track flexibility. The three aforementioned procedures may be applied to three-dimensional track models and will be used together with three-dimensional wheel/rail contact formulation that predicts contact points online and allows for updating the creepages to account for the rail movements and deformations. Several comparisons and conclusions will be drawn in view of the results obtained in this investigation.
Comparative Study of High-Speed Passenger Rail Deployment in Megaregion Corridors: Current Experiences and Future Opportunities
Authors: Melibaeva Sevara , Sussman Joseph , Dunn Travis P.
Published: February 2012

Deployment of high-speed passenger rail services has occurred around the world in densely-populated corridors, often with the effect of either creating or enhancing a unified economic “megaregion” agglomeration. This paper will review the technical characteristics of a variety of megaregion corridors, including Japan (Tokyo-Osaka), France (Paris-Lyon), and Germany (Frankfurt-Cologne), and their economic impacts. There are many lessons to be drawn from the deployment and ongoing operation of high-speed passenger rail service in these corridors for other countries now considering similar projects, such as the US and parts of the European Union. First, we will review three international cases, describing the physical development of each corridor as well as its measured impacts on economic development. In each case, the travel time reductions of the high-speed service transformed the economic boundaries of the urban agglomerations, integrating labor and consumer markets, while often simultaneously raising concerns about the balance of growth within the region. Moreover, high-speed travel within the regions has had important implications for the modes and patterns of travel beyond the region, particularly with respect to long-distance air travel. An example is the code-shared rail-air service between DeutscheBahn and Lufthansa in the Frankfurt-Cologne corridor. Next, we will examine the implications of these international experiences for high-speed rail deployment elsewhere in the world, particularly the US and Portugal, one of the EU countries investing in high-speed rail. Issues considered include the suitability of high-speed passenger rail service in existing megaregions as well as the potential for formation of megaregions in other corridors. By understanding the impact of high-speed passenger service on economic growth, labor markets, urban form, and the regional distribution of economic activity, planners can better anticipate and prepare countermeasures for any negative effects of high-speed rail. Examples of countermeasures include complementary investments in urban and regional transit connections and cooperation with airlines and other transportation service operators. High-speed passenger rail represents a substantial investment whose implementation and ultimate success depends on a wide range of factors. Among them is the ability of planners and decision-makers to make a strong case for the sharing of benefits across a broad geography, both within and beyond the megaregion (and potential megaregion) corridors where service is most likely to be provided. This paper provides some useful lessons based on international experiences.
Energy Efficiency of Electric Traction Railways (“ELECRAIL” Project)
Authors: Marti´nez Acevedo J. C. , Mascaraque A.
Published: February 2012

With the general prospect of reducing energy consumption, the ELECRAIL project aims conduct a systematic analysis of energy consumption in metropolitan railway lines, suburban and high speed, with an assessment of the energy impact and the economic performance, including development of parameterized models and simulators for the analysis of strategies to reduce consumption through efficient design of train timetables and driving times. The project aims to systematically analyze all the ways to reduce electricity consumption in electric traction railways. The different possibilities and the study of each of the actions that are deemed most relevant have been identified: Timetabling, energy storage, supply system sizing, design and use of ancillary services, etc. Parameterized simulators and models have been developed for taking the more efficient decisions in each case, depending on existing restrictions. The project boundary is the transportation of passengers, stressing the segments where there are more traffic and investments. This presentation will be presented the main findings and conclusions of the project.
Crashworthiness Analysis of the January 26, 2005 Glendale, California Rail Collision
Authors: Parent Daniel , Tyrell David , Jacobsen Karina , Severson Kristine
Published: February 2012

In Glendale, California on January 26, 2005, impact with an SUV on the track caused a southbound commuter train to derail, impact a standing freight train, buckle laterally outward, and rake the side of a northbound commuter train. Significant deformation resulted in the front of the southbound train and the side of the northbound train. There were a total of eleven fatalities and over one hundred injuries. This incident was investigated as a part of an ongoing field study of occupant injury in passenger train collisions and derailments currently being conducted by the United States (US) Department of Transportation’s (DOT) Rail Accident Forensic Team in support of the Equipment Safety Research Program of the Federal Railroad Administration (FRA). The Forensic Team determined that the primary causal mechanism of injuries and fatalities in the Glendale incident was the loss of occupied volume of the passenger cars brought about by severe structural deformation.
Intrinsic Hydraulic Hose Condition Monitoring for Prevention of Catastrophic Failure
Authors: Smith Scott A. , Capesius Dallas J.
Published: February 2012

High-pressure hydraulic hoses are used throughout industry to transmit fluid power. The current state of the art in hose replacement consists of two strategies; these are (1) replacement upon failure and (2) time-based replacement. For the replacement upon failure method, end users inspect hoses and either replace when there is obvious physical damage or the hose has burst and allowed the release of fluid under high pressure. Hose users that employ time-based replacement cycles often collect data and either subjectively or statistically choose a replacement frequency intended to prevent unexpected failures. Engineers at Eaton Corporation worked with Purdue University to develop an alternative. A novel hose construction using two conductors with an isolating layer provides a component in an electrical circuit which can be monitored to determine the status, or health, of a hose in operation. The first step in this development was the realization that hose failure is a process and not an event. By tracking a hose’s electrical signature and characterizing the change that occurs when the internal structure begins to break down, a user is alerted prior to a catastrophic hose failure. Eaton is developing notification systems capable of both monitoring the hose’s electrical signature and alerting an equipment user prior to unexpected failure. The system requires direct electrical connection to the hose fitting for monitoring. There are currently two strategies in development, a wired system and a wireless system. The wired system uses a remote diagnostic unit with cables running to each hose assembly to query the hose and alert an equipment user directly. The wireless system employs battery-powered sensors installed on a hose assembly which communicate with a gateway located nearby. When a hose approaches its end of life a warning is issued by illuminating a warning light or issuing a remote warning through a cellular or wireless network. There are significant gains in the ability to prevent hydraulic hose failures. These unexpected incidents lead to downtime, damage to equipment, environmental damage, and serious personal injury. Additionally, using this advanced warning system allows users to use nearly a hose’s entire life. This improves asset utilization considerable when compared to the useful life sacrificed by using time-based replacement schedules. This technology will reduce operating costs and prevent downtime, environmental incidents, and the threat of personal injury present when hydraulic hose fails.
Computer-Aided Development of Shape Memory Actuators as an Approach Towards a Standardized Developing Method
Authors: Meier Horst , Czechowicz Alexander
Published: February 2012

Shape memory alloys (SMA) are thermally activated smart materials. Due to their ability to change into a previously imprinted actual shape through the means of thermal activation, they are suitable as actuators for mechatronical systems. Despite of the advantages shape memory alloy actuators provide (lightweight-actuators, lower costs…etc.) these elements are only seldom integrated by engineers into mechatronical systems. The reason for this phenomenon is the insufficiently described dynamic behavior, especially at different boundary conditions. Also the lack of empirical data (like fatigue behavior and thermal balances) is a reason why development projects with shape memory actuators lead often to failures. Therefore a need of developing methods, standardized testings of empirical properties and computer aided actuator development systems is motivated. Based on an analysis of energy fluxes into and out of the actuator, a numerical model, implemented in MATLAB/SIMULINK is presented. The numerical model includes also a configuration and design tool which allows simulating different solutions to a problem. Additionally, this paper describes a development method for SMA which is fitted to uniqueness of these smart materials. In conclusion, this paper compares the conventional developing process to the presented method applying a mechatronical SMA-device.
Design and Testing of an Enhanced Shape Memory Actuator Elastically Compensated by a Bi-Stable Rocker-Arm
Authors: Scire` Mammano Giovanni , Dragoni Eugenio
Published: February 2012

This paper presents the design, the prototype construction and the experimental testing of a shape memory actuator implementing the concept of elastic compensation put forward in a previous publication by the authors. A two-SMA actuator, compensated by a spring-assisted bistable rocker-arm, is designed theoretically to provide nearly-constant output forces, then it is built and characterized under laboratory conditions. The test results are in good agreement with the theoretical predictions and show that, for given output force, the compensated actuator produces net strokes from 2.5 to 22 times greater than an identical uncompensated actuator. The stroke improvement increases dramatically with the generated output force. Weaknesses of the compensated design are the heavier average stress sustained by the SMA springs, which could impair the fatigue life, and a higher response time.
Afterthoughts of a Founding Structural Control Theorist
Authors: Klein Richard E.
Published: February 2012

This paper reflects back on the author’s research in structural control, originating in the early 1970’s. Upon reflection, in the early 1970’s and even as far as into the 1990’s, it constituted near heresy to suggest that large civil engineering structures could be candidates for control. The previous techniques of the 1930’s of building structures with masonry and stone were then being phased out, being replaced with lighter and more cost-effective steel-framed structures. The newer designs then emerging in the late 1960’s and early 1970’s were steel-framed structures that functioned as cantilevered tubes. The characteristic designs emerging included an absence of stone or masonry especially around the steel pillars, glass or similar non-load bearing cladding. Additionally, interior walls were non-load bearing affording more spacious rooms as well as affording the occupants the ability to reposition interior walls as desired. Moreover, the newly emerging steel-framed structures with increased compliance properties were increasingly prone to wind excitations as compared to the prior generation of structures. As a consequence, a number of these newer structures exhibited increased sway and other related dynamic behaviors. My mechanical engineering servomechanisms background included groundings in observability, controllability, as well as control of spatially distributed systems. Therefore, I felt confident then that control systems theoretic methods held promise to produce favorable and cost-effective results if properly applied to problematic civil engineering structures. That confidence still remains. I also realized the critical importance of being able to design structures in advance to be controlled, as opposed to the less desirable situation of dealing with an after-the-fact retrofit of an existing problematic structure. This paper affords an opportunity for the author to provide his anecdotal recollections and afterthoughts. Because the story to be told is of personal recollections, it is presented in first person.
Fish Inspired Biomimetic Ionic Polymer Metal Composite Pectoral Fins Using Labriform Propulsion
Authors: Karthigan G. , Mukherjee Sujoy , Ganguli Ranjan
Published: February 2012

Ionic polymer metal composites (IPMC) are a new class of smart materials that have attractive characteristics such as muscle like softness, low voltage and power consumption, and good performance in aqueous environments. Thus, IPMC’s provide promising application for biomimetic fish like propulsion systems. In this paper, we design and analyze IPMC underwater propulsor inspired from swimming of Labriform fishes. Different fish species in nature are source of inspiration for different biomimetic flapping IPMC fin design. Here, three fish species with high performance flapping pectoral fin locomotion is chosen and performance analysis of each fin design is done to discover the better configurations for engineering applications. In order to describe the behavior of an active IPMC fin actuator in water, a complex hydrodynamic function is used and structural model of the IPMC fin is obtained by modifying the classical dynamic equation for a slender beam. A quasi-steady blade element model that accounts for unsteady phenomena such as added mass effects, dynamic stall, and the cumulative Wagner effect is used to estimate the hydrodynamic performance of the flapping rectangular shape fin. Dynamic characteristics of IPMC actuated flapping fins having the same size as the actual fins of three different fish species, Gomphosus varius, Scarus frenatus and Sthethojulis trilineata, are analyzed with numerical simulations. Finally, a comparative study is performed to analyze the performance of three different biomimetic IPMC flapping pectoral fins.
Field-On Versus Field-Off Characteristics of Magnetorheological Fluids With an Application in Prosthetic Devices
Authors: Gudmundsson Ketill H. , Jonsdottir Fjola , Thorsteinsson Freygardur
Published: February 2012

The study presents an experimental investigation into the trade-offs between field-on versus field-off rheological characteristics of magnetorheological (MR) fluids. This is relevant in a particular application in prosthetic devices where field-off characteristics are of equal importance to the field-on rheological characteristics. The paper introduces a biomechanical prosthetic knee joint that uses an MR fluid to actively control its rotary stiffness while an amputee walks. The knee is a synergy of artificial intelligence, advanced sensors and MR actuator technology. The knee joint is equipped with an MR rotary brake, utilizing the fluid in direct-shear mode. The MR fluid has response time in the order of milliseconds, making it possible to vary the knee’s stiffness in real-time, depending on sensors data. The field-on characteristics of the employed MR fluid define the rigidness of the knee joint while the field-off characteristics define its flexibility in the absence of a magnetic field. Five MR fluid compositions are prepared, each with a different solid loading ranging from 0.25 to 0.35, by volume. All fluids employ a commercially available carbonyl iron powder and a base fluid. The MR fluids are experimentally evaluated in a rheometer, where both field-off and field-on characteristics are measured. An MR fluid figure of merit function is introduced which is used to rate the selected MR fluids for a potential application in the MR prosthetic knee. An MR fluid composition is sought with the highest ratio between the field-on shear yield stress and the off-state viscosity. The research shows the off-state viscosity to decrease faster than the field-on shear yield stress when reducing the solid loading from 0.35 to 0.25. This suggests that an optimum solid loading exists with regards to the defined merit function. The off-state viscosity of suspensions is known to be exponentially dependent on solid loading while the field-on shear-yield stress is known to sub-quadratically dependent on solid loading. Field-on and field-off models are presented from literature. The models compared to the experimental data and used to theoretically predict the optimum solid loading with regards to field-on shear yield stress and off-state viscosity. As a result of the experimental and the theoretical analysis, a prominent MR fluid composition is selected for a potential application in the MR prosthetic knee. This has been shown to help in the development of prosthetic devices and furthering the success of an MR prosthetic knee joint.
The Effect of Scale on Fluid-Filled Flexible Composite Actuators
Authors: Peel Larry D. , Muratalla Luis , Baur Jeff , Foster Dean
Published: February 2012

Morphing aircraft and other shape-changing structures are well suited to McKibben-like flexible composite actuators. These actuators, made from fiber-reinforced elastomeric composites, are extremely efficient in converting potential energy (pressurized air) into mechanical energy. Such actuators are promising for use in micro air vehicles, prosthetics and robotics because they offer excellent force-to-weight ratios and behave similar to biological muscle. Use of an incompressible pressurizing fluid instead of compressible air may also offer higher actuator stiffness, better control, and compatibility with existing actuation systems. Using incompressible fluids also allows the actuator to serve as a variable stiffness element which can be modulated by opening and closing valves that constrain or allow fluid flow. The effect of an incompressible fluid (water) on the performance of Rubber Muscle Actuators (RMA), with varying diameters, lengths and segment lengths, was experimentally investigated in the current work. Upon pressurization with air or water, past an activation threshold, overall force and stroke increased with increasing actuation length and diameter. Actuation force when pressurized with water is slightly greater than with air. Both air and water-pressurized actuation force and strain decrease significantly when segment length is less than a minimum critical length. Closed valve actuator stiffness (modulus) of actuators at full length, when pressurized with an incompressible fluid is up to 60× greater than the open valve stiffness of the same actuator. Air-filled RMAs with equal parameters only see a 10× increase. Incompressible fluid-filled RMAs have great potential to provide needed high actuation forces within adaptive material systems. Design guidelines are given to aid additional RMA use.
Numerical Modeling of Controlled Release of Drugs From Silicone Elastomers
Authors: Jonsdottir Fjola , Gudmundsdottir Rut , Sigurdsson Sven Th. , Snorradottir Bergthora S. , Masson Mar
Published: February 2012

Silicone based medical devices, where the function is enhanced by the release of a drug or other bioactive compound, are of interest for a variety of applications. Such a device must release the drug at a given rate over a given period of time, while maintaining the shape and material properties required for the primary function of the device. Achieving these goals in an optimal fashion is challenging if one relies solely on traditional experimental work. Accurate numerical modeling compliments experimentation by allowing fast evaluation of parameters and subsequent validation of a select set of promising cases. Our ultimate goal is a numerical model which can accurately predict drug release characteristics from silicone elastomers with complicated geometry and inhomogeneous drug dispersion. In this work, we lay the foundations for such a comprehensive model. We describe a numerical model for simple geometries and carry out a parametric study for various initial and boundary conditions. We validate our modeling work by comparison with experimental trials, carried out by our own group. The work is carried out in a group composed of engineers and pharmaceutical scientists, ensuring step-by-step validation of models against experimental results.
A Morphing Wind Turbine Blade Control Surface
Authors: Daynes Stephen , Weaver Paul M.
Published: February 2012

The loads on wind turbine components are primarily from the blades. It is important to control these blade loads in order to avoid damaging the wind turbine. Rotor control technology is currently limited to controlling the rotor speed and the pitch of the blades. As blades increase in length it becomes less desirable to pitch the entire blade as a single rigid body, but instead there is a requirement to control loads more precisely along the length of the blade. This can be achieved with aerodynamic control devices such as flaps. Morphing technologies are good candidates for wind turbine flaps because they have the potential to create structures that have the conflicting abilities of being load carrying, light-weight and shape adaptive. A morphing flap design with a highly anisotropic cellular structure is presented which is able to undergo large deflections and high strains without a large actuation penalty. An aeroelastic analysis couples the work done by aerodynamic loads on the flap, the flap strain energy and the required actuation work to change shape. The morphing flap is experimentally validated with a manufactured demonstrator and shown to have reduced actuation requirements compared to a conventional hinged flap.
Tailored Fluidic Composites for Stiffness or Volume Change
Authors: Zhu Bin , Rahn Christopher D. , Bakis Charles E.
Published: February 2012

An analytical model of a composite structure consisting of an F2MC tube embedded in epoxy is used to study the impact of confining structural media on the ability of F2MC tubes to pump fluid and change stiffness. The surrounding stiff epoxy reduces the performance relative to an isolated F2MC tube, but this disadvantage can be minimized by tailoring the tube wall thickness and fiber angle. The composite can pump 250 times more fluid than a piston of the same diameter if the F2MC tube has a thick shell wall and a near-axial fiber orientation. With a moderately thick wall and low fiber angle, the closed valve axial stiffness can be increased by a factor of 2.2 relative to the open valve stiffness. The maximum pumping factor and modulus ratio, however, are 80% and 2.6% of the F2MC tube without the surrounding epoxy.
Multifunctional Micro-Mechanical Memory Devices
Authors: Merced Emmanuelle , Cabrera Rafmag , Da´vila Noraica , Sepu´lveda Nelson , Ferna´ndez Fe´lix E.
Published: February 2012

Two types of micro-mechanical memory cells are introduced in this paper. The programmable parameters are the resonant frequency of a micro-mechanical bridge and the tip deflection of a micro-mechanical cantilever. For both cases, the actuation was done by laser pulses that locally heated the vanadium dioxide (VO2) thin film coating. Due to the hysteretic behavior of the mechanical properties of the VO2 film coating across the transition, a different “memory state” was programmed with every pulse. The memory state remained programmed after the pulse ended, as long as the sample was maintained at a specific temperature (programming temperature) by using a Peltier heater. The resetting of the mechanical memory cell was accomplished by driving the temperature to regions outside the hysteretic region.
The Use of Damping to Mitigate Violent Snap-Through of Bistable Systems
Authors: Murray Gabriel Jon , Gandhi Farhan
Published: February 2012

The energy release associated with the snap-through phenomena when bistable systems transition from one stable equilibrium state to another leads to large transient oscillations which may often be unacceptable in morphing and other applications. This study, based on a bistable von-Mises truss, considers the role of damping in mitigating the transient oscillations as well as its impact on the snap-through behavior. The study also examines the energy transfer from potential to kinetic energy, and its dissipation, to understand the effect of load duration and amplitude on the behavior of bistable systems. The addition of damping was shown not to change the nature of whether or not the system will exhibit bistability. Increasing levels of damping result in the quicker decay of transient oscillations and settling of the system in the second equilibrium position, but also increase the time duration required for the system to snap-through. Damping levels in the range of 10–20% appear to result in a quick decay of the transient oscillations without causing the snap-through to become too sluggish. If the applied load is removed very quickly after snap-through there is still sufficient energy in the system to jump the energy barrier between the two equilibrium conditions and the system could settle in either position. Maintaining the load for a slightly longer duration allows the energy to dissipate (due to damping in the system), and the system is then unable to jump the energy barrier and remains in the second stable state. The applied load level determines the maximum amount of energy in the system, irrespective of how long the load is maintained. Increasing the applied load level results in additional energy in the system appearing as kinetic energy.
Design Equations for Binary Shape Memory Actuators Under Arbitrary External Forces
Authors: Spaggiari Andrea , Spinella Igor , Dragoni Eugenio
Published: February 2012

The paper presents the design equations for an on-off shape memory alloy actuator under an arbitrary system of external constant forces. A binary SMA actuator is considered where a cursor is moved against both conservative and dissipative force which may be different during the push or pull phase. Three cases are analyzed and differentiated in the way the bias force is applied to the primary SMA spring, using a constant force, a traditional spring, or a second SMA spring. Closed-form dimensionless design equations are developed, which form the basis of a step-by-step procedure for an optimal design of the whole actuator.
Modeling of Low Frequency Multi-Source Energy Harvesting Systems
Authors: Green Christopher , Erturun Ugur , Burnette Matthew , Mossi Karla
Published: February 2012

Accurate modeling of multi-source harvesters present design challenges such as the integration of mixed circuit topologies, passive versus active topologies, impedance matching, and optimization. Commercial modeling and simulation software packages offer solutions but often times are not comprehensive enough. In this work P-Spice, Simulink, and Comsol Multiphysics were used to model a multi-source energy harvesting system that incorporates the energy producing capabilities of the piezoelectric, the pyroelectric, and thermoelectric effect. A systems approach that models the material properties of the converters, the power electronics and storage was implemented. Low frequency experimental data from PZT based harvesters and thermoelectric generators were used to produce lumped parameter models. It was demonstrated that within 12% that combining effects may contribute to continuous energy harvesting operation.
Semi-Active Optimization of 2D Wave’s Dispersion Into Shunted Piezocomposite Systems for Controlling Acoustic Interaction
Authors: Collet Manuel , Ouisse Morvan , Ichchou Mohammed , Ohayon Roger
Published: February 2012

In this paper, we present an application of the Floquet-Bloch theorem in the context of electrodynamics for vibroacoustic power flow optimization by mean of distributed and shunted piezoelectric patches. The main purpose of this work is first to propose a dedicated numerical approach able to compute the multi-modal wave dispersions curves into the whole first Brillouin zone for periodically distributed 2D shunted piezomechanical systems. By using two specific indicators evaluating the evanescent part of Bloch’s waves and the induced electronic damping, we optimize the piezoelectric shunting electrical impedance for controlling energy diffusion into the proposed semi-active distributed set of cells. Sound radiation efficiency is also analyzed for showing the effects of such smart metamaterial for controlling acoustical noise.
Numerical and Experimental Investigation of an Adaptive Socket System for Leg Prosthetic
Authors: Pohl Martin , Monner Hans Peter
Published: February 2012

When amputations of limbs are necessary, prostheses are used to replace the lost functionality. Today, they are mainly made of high-tech materials as carbon fiber reinforced plastics (CFRP), titanium and aluminum. An important part of the prosthesis is the socket, connecting the patients stump with the prosthesis itself. It is in most cases made of CFRP and, by this, a more or less rigid body. This is in contradiction to the fact, that muscles and tissues within the stump are still moving while the patient is walking. To overcome this limitation, an adaptive socket system for femoral amputation is presented in this paper, which allows active deformations by piezoelectric patch actuators integrated to the structure. For design, a finite element model is created. Socket prototypes are built with optimized fabric ply setup and integrated actuators. Finally, the active deflection is tested in a laboratory set up and a passive socket with optimized ply setup is tested with a patient.
Teaching a Micro Air Vehicle How to Fly as We Teach Babies How to Walk
Authors: Han Jae-Hung , Lee Dong-Kyu , Lee Jun-Seong , Chung Sang-Joon
Published: February 2012

Micro Air Vehicles (MAVs) have become more attractive for various missions including surveillance or reconnaissance in recent years. MAVs should be capable of maintaining their attitudes through either inherent passive stability or active feedback in order to successfully perform their directives. Stability and Controllability Augmentation Systems (SCASs) are usually employed to enhance the flight performance of conventional aircrafts and Unmanned Aerial Vehicles (UAVs). However, it is no simple task to obtain an accurate numerical model for the flight dynamics of a MAV. An alternative approach for SCASs would be to incorporate reinforcement learning in order to address this numerical complexity. Such implementation has already been successful in other vehicles, such as unmanned ground vehicles (UGVs), because of their bettered stability compared to aerial vehicles. However, in order to train MAVs to learn how to fly, they must first be airborne. Similar to teaching infants how to walk, this paper presents a new method to provide an effective environment where a MAV can learn how to fly. A test setup was constructed to enable magnetic levitation of a MAV embedded with a permanent magnet. This apparatus allows for flexible experimentation: the position and the altitude of the MAV, the constraint forces, and the resulting moments are all adjustable and fixable. This ‘Pseudo Flight Environment’ was demonstrated with a fixed wing MAV model. In order for the model to maintain a constant altitude, a height hold control system was devised and implemented.
Performance of Galfenol Energy Harvester at High Temperature
Authors: Yoo Jin-Hyeong , Flatau Alison , Purekar Ashish
Published: February 2012

Recently, the development of energy harvesting devices has received considerable interest as a means of powering nodes in a wireless sensor network. Additionally, the ability to operate in a high temperature environment is a desired feature especially in the case of wireless sensor networks used in a power plant where elevated temperatures are normal. Vibration based energy harvesting is one method of scavenging energy from the environment. Traditional approaches for vibration based energy harvesting have focused primarily on piezoelectric and electromagnetic approaches. There are, however, limitations associated with high temperature applications. Iron-Gallium alloys (Galfenol) are highly magnetostrictive with magnetically induced strains as high as 400 ppm in single crystals and 280 ppm in highly textured polycrystals. Galfenol is machineable, weldable, and has tensile strength of approximately 500 MPa. These unique properties foreshadow the material’s use in conventional transducers operating in severe environments. An investigation into the magnetostriction performance at temperatures up to 225°C found magnetostriction degraded relative to that at room temperature by close to 25%. From those measurements, two important advantages of Galfenol were found. First, even though the performance degraded at 225°C, the original performance is recovered when the temperature comes back to room temperature. The second advantage is that the performance at 225°C was stable. Based on these results, it was determined that Galfenol could be utilized at temperatures of at least 225 °C. In this paper, a series of tests are conducted in a thermal chamber to evaluate the Galfenol energy harvester performances from temperatures ranging from room temperature to 200°C. A linear coupled model for a Galfenol energy harvester is developed based on fundamental properties of a tuned mass beam system. A non-linear version of the model is developed and compared to experimental evaluations. A comparison with experimental evaluations provides good correlation with results. It is shown that the Galfenol energy harvester can provide consistent power from room temperature to 200°C.
Parametrically Excited Nonlinear Piezoelectric Wind Energy Harvester
Authors: Karami M. Amin , Farmer Justin R. , Bressers Scott , Priya Shashank , Inman Daniel J.
Published: February 2012

A nonlinear piezoelectric wind energy harvester is proposed which operates at low wind speeds and is not sensitive to the speed of the gusts. The piezoelectric transduction mechanism is used instead of DC generators to eliminate the gearbox in the windmill and thus reduces the friction. The reduced friction facilitates operation of the windmill at low wind speeds. Permanent magnets have been placed in the blade part of the windmill. The magnets axially repel another set of magnets which are positioned at the tip of the piezoelectric beams. As a result, when the rotating magnets pass over the piezoelectric beams they excite the beams and affect the type of their vibrations. The nature of excitations in the proposed design is therefore both parametric excitations and ordinary excitations. The nonlinear magnetic axial force makes the vibrations of the beams nonlinear and can make the beams bi-stable. This phenomenon is utilized to enhance the power output and to improve the robustness of the power production. Two designs are presented which incorporate parametric and ordinary excitations to generate electric power. The performance of each design is examined through experimental investigations.
Energy Harvesting From Turbulence-Induced Vibration in Air Flow: Artificial Piezoelectric Grass Concept
Authors: Hobeck Jared D. , Inman Daniel J.
Published: February 2012

Turbulence-induced vibration is generally considered undesirable, and is a phenomenon that if not properly anticipated can lead to catastrophic structural failure. From an energy harvesting perspective however, these types of vibrations have been found to be quite valuable. Turbulence can greatly diminish the performance of traditional fluid flow energy harvesting devices such as turbine, or propeller type designs. Even more recently developed nontraditional harvesters that take advantage of vortex shedding, flutter, or related phenomena in fluid dynamics become extremely inefficient, and in some cases, completely fail to generate useful power in turbulent flow. Motivation for this work comes from the fact that very little research has been done on methods for harvesting energy from turbulence. The primary objective of this research is to design and develop a deploy-and-forget energy harvesting device for use in low velocity (∼0.5 m/s) highly turbulent water flow environments i.e. small rivers and streams. The work presented here focuses on a novel, lightweight, highly robust, energy harvester design referred to as “piezoelectric grass”. This biologically inspired design consists of an array of cantilevers, each constructed with piezoelectric material. When exposed to proper turbulent flow conditions, these cantilevers vibrate vigorously due to rapidly varying pressure fields along their faces. Electrical power is generated directly from these vibrations via the piezoelectric effect. Small-scale wind tunnel tests were carried out to validate the concept. Included in this paper are the results of a direct comparative study performed on two types of harvesters in air. The generating elements or “blades of grass” of one design are made of PVDF cantilevers (type-1), and those of the other design are made with PZT QuickPacks™ mounted to the base of spring steel cantilevers (type-2). Results from these tests show very clearly that optimum harvesting conditions exist. The maximum power output per cantilever was ∼1μW for the type-1 harvester, and increased up to ∼ 1mW for the type-2 harvester which is among the highest found in literature for similar harvesting methods.
Simulation-Based Optimization of a Piezoelectric Sound Generator by Combining a Finite-Element and Network Model
Authors: Starke Eric , Marschner Uwe , Pfeifer Gu¨nther , Fischer Wolf-Joachim
Published: February 2012

In this paper network methods and Finite-Element methods are combined to optimize the design of a piezoelectric sound generator. The FE-model is used to determine network parameters of the transducer model and finally the behavior of the chosen design variant. For the design optimization the network model is used. One design variant reaches a nominal sound pressure level of 93 dB at a center frequency of 497 Hz and a bandwidth of 242 Hz in the simulation. The computation of the dynamic behavior of a single design variant using the network model was approx. 600k times faster than using the FE-model.
Influence of Microstructure and UV-Conditioning on the Mechanical Response of Polymeric Foam Under Compressive Loading
Authors: Tandon G. P. , Goecke K. E. , Justice Ryan S.
Published: February 2012

The aim of this study is to evaluate the influence of microstructure, specifically, variations in foam cell size and density, on the compressive stress-strain behavior of polymeric foam material. Foams with varying densities are examined under incremental loadings to different prescribed strain levels. A comparison is made of the maximum stress level attained during deformation and residual strain on complete unloading and following recovery. Additionally, the durability of the foam material on exposure to service environment, namely, exposure to ultra-violet (UV) light and humidity, is considered. Cylindrical compression samples are exposed to Xenon Arc (63°C, 18 minutes water and light/102 minutes light only) and spectral intensity of 0.3 to 0.4 watts/m2 for 288 cycles. Parameters investigated include changes in modulus, maximum stress, residual strain and linear shape recovery due to conditioning and mechanical cycling.
Design Optimization of a Shape Memory Alloy Actuated Morphing Aerostructure
Authors: Oehler Stephen , Hartl Darren , Lagoudas Dimitris , Malak Richard
Published: February 2012

Interest in shape memory alloys (SMAs) as lightweight actuators has motivated research into finding optimal morphing structure designs to replace conventional mechanisms in aerospace control systems. Prior to the development of robust constitutive modeling tools for these alloys, application design was based on trial-and-error studies conducted using an array of physical prototypes. Using this approach, a significant amount of time and materials were expended to produce each trial design. However, constitutive models now exist, implemented within a finite element analysis (FEA) framework, that can accurately and consistently predict the thermomechanical response of SMAs. This study considers the use of ModelCenter, a tool for automating simulation processes, coupled with the Abaqus FEA suite and a constitutive model to iteratively converge upon optimal designs in an automated fashion. The engineering design problem posed involves determining the configuration of a morphing aerostructure assembly with attached SMA flexures. Design inputs include material properties and component geometries. The objective is minimization of a cost function that quantifies the deviation of the computed actuation deflection from some target deflection. This paper presents a method for constructing this optimization problem, outlines the modeling tools used to execute each analysis, and highlights the results from the optimal design solution.