bluuebunny/crossref_metadata_2025 huggingface dataset:
Transient Heat Transfer for an Actively Insulated Shape Memory Alloy Wire
Authors: Jones G. F. , Murarisetty N. R.
Published: May 2008

Certain alloys of two or more metallic elements exhibit a “shape memory effect.” These “shape memory alloys” (SMAs) have a crystalline structure that undergoes a transformation upon change in temperature in either direction. The temperature at which the change begins is referred to as the transition temperature, Tt. The most common of these alloys is nickel-titanium (referred to as Nitinol), an alloy that is approximately equal parts of each element. The transition temperature for warmup is about 72 C below which the alloy is in the martensite phase. Heating of the alloy through its transition temperature results in a martensite-to-austenite phase transition and a significant contraction of the alloy. Strains as large as 8% can be realized in this process. Upon cooling below the temperature at which the process reverses (around 38 C) the alloy expands to its original shape under the action of an externally applied load.
Conjugate Heat Transfer in a Rotor-Stator System With Through-Flow
Authors: Roy Reby , Prasad B. V. S. S. S. , Murthy S. Srinivasa
Published: May 2008

The conjugate heat transfer in a stationary cylindrical cavity with a rotating disk and fluid through-flow is analysed at various rotational speeds ranging from 10000 to 50000 rpm by using a finite volume commercial code. The numerical model and code are validated for a problem, which involves rotation and fluid through-flow. A reduction of the thermal boundary layer thickness and increase in the heat transfer coefficients are observed with increase in the rotational speed. Marked differences are noticed between the Nusselt numbers obtained from the conjugate and constant temperature analyses.
Importance of Turbulence-Radiation Interactions in Turbulent Reacting Flows
Authors: Li Genong , Modest Michael F.
Published: May 2008

Traditional modeling of radiative transfer in reacting flows has ignored turbulence-radiation interactions (TRI). Radiative fluxes, flux divergences and radiative properties have been based on mean temperature and concentration fields. However, both experimental and theoretical work have suggested that mean radiative quantities may differ significantly from those predictions based on the mean parameters because of their strongly nonlinear dependence on the temperature and concentration fields. The composition PDF method is able to consider many nonlinear interactions rigorously, and the method is used here to study turbulence-radiation interactions. This paper tries to answer two basic questions: (1) whether turbulence-radiation interactions are important in turbulent flames or not; (2) if they are important, then what correlations need to be considered in the simulation to capture them. After conducting many flame simulations, it was observed that, on average, TRI effects account for about 1/3 of the total drop in flame peak temperature caused by radiative heat losses. In addition, this study shows that consideration of the temperature self correlation alone is not sufficient to capture TRI, but that the complete absorption coefficient–Planck function correlation must be considered.
Effects of Gas Radiation on the Thermal Characteristics of Regeneratively Cooled Rocket Engines
Authors: Naraghi Mohammad H. N. , Nunes Edmundo M.
Published: May 2008

This paper studies the effects of radiative heat transfer on the thermal characteristics of regeneratively cooled rocket engines. A conjugated radiative, conductive and convective model is used to analyze the effects of radiative heat transfer in two regeneratively cooled rocket engines. One engine has liquid hydrogen and liquid oxygen as the propellant and liquid hydrogen as the coolant. The other engine has RP1 (a hydrocarbon fuel) and liquid oxygen as the propellant and liquid oxygen as the coolant. It is shown that gas radiation has some effect on the wall temperature of the LH2-LO2 engine and a small effect on its coolant flow characteristics. For the RP1-LO2 engine, however, gas radiation significantly increases the coolant pressure drop, temperature and Mach number. It is also shown that radiation effects must be addressed in cooling channel design, so that wall temperatures and cryogenic coolant flow temperature/pressure are at suitable levels.
An Efficient Method for Flow Computations for Bodies With Curved Boundaries
Authors: Lee H. , Chen M.
Published: May 2008

The difficulties of performing flow computations for bodies with arbitrary curved boundaries are well known. Many approaches have been advocated, but few have proven to be efficient, accurate, and simple to program. The earliest approach of using staircase boundaries to approximate curves is simple but crude, and would be prohibitively expensive if accurate, fine mesh results are desired. The use of meshes based on body-fitted curvilinear coordinates typically involve much more complex arithmetic and hence incur a high computational overhead. The inefficiency of curvilinear coordinates have spurred the current popularity of unstructured mesh formulations, which appear less restrictive but seem to lead to comparable overheads. The present paper describes a method based on returning to the intuitive concept of defining the boundary by placing boundary nodes on points of intersection of the boundary with the basic mesh lines. Such an arrangement creates locally acute non-uniform meshes which are well known to be ill-behaved. This is shown to be the consequence of singular behaviors in the limiting case of large “acuteness”, or the ratio of adjacent mesh increments. Differencing formulas and integration algorithms which are tolerant of such singularities, but retain the same order of accuracy as conventional nodes, are derived and used for all nodes adjacent to the boundary. In addition, algorithms for computing the normal and tangential gradients along the surface are also derived, based on vector combination of gradient components which can be easily evaluated from functions values at the nodes. Such gradients are needed for stress and pressure boundary conditions in flow computations. The method is demonstration by second order computations for the impersively started concentric cylinder Couette flow. It is shown that the method is efficient and produces accurate results.
Computational Analysis of Natural Convection in Inclined Rectangular Enclosures of Different Aspect Ratios
Authors: Rahman Mosfequr , Sharif Muhammad A. R.
Published: May 2008

Numerical investigations are conducted for free convective flow of a fluid with or without internal heat generation in rectangular enclosures of different aspect ratios and at various angles of inclination. Two principal parameters for this problem are the external Rayleigh number, RaE, which represents the effect due to the differential heating of the sidewalls and the internal Rayleigh number, RaI, which represents the strength of the internal heat generation. Results are obtained for a fixed external Rayleigh number, RaE = 2×105 with internal Rayleigh number, RaI = 0 (without internal heat generation) and also with RaI = 2×105 (with internal heat generation). Flow patterns and isotherms do not show any significant difference between the cases with and without internal heat generation other than slight shift and changes in stream function and isotherm values as long as the internal Rayleigh number RaI is less than or equal to the external Rayleigh number RaE. Local heat flux ratios along the hot and the cold wall decrease monotonically in the flow direction for a major downstream portion. At certain inclinations the local heat flux ratios increase initially and then decrease. The variation of average heat flux ratio is similar for cases with and without internal heat source situation but the corresponding amount of heat transfer is higher through the hot wall and lower through the cold wall with internal heat generation. On the other hand, the convection strength increases as the enclosure shape changes from slender through square to shallow at any particular inclination but does not vary significantly with inclination at a particular aspect ratio.
Turbulent Heat Transfer in a Backward-Facing Step Flow Using a Non-Linear k-ε Model
Authors: Assato Marcelo , de Lemos Marcelo J. S.
Published: May 2008

This work presents numerical results for heat transfer in turbulent flow past a backward-facing step. It is shown that nonlinear k-ε models perform better than their linear counterparts when simulations are compared with experimental values. Wall functions are used for simplicity of the simulations. The finite-volume technique is employed for discretizing the transport equation set on a non-orthogonal grid system. The SIMPLE method is used for correcting the pressure field. Results for the reattachment length using the non-linear model are closer to the experimental values when compared with similar calculations using the standard linear closure.
Convective-Diffusion Capacitance Finite Element Method for Heat Transfer Modeling
Authors: Rodri´guez N. J. , Davey K.
Published: May 2008

Modelling of heat transfer with bulk transport requires methods that are efficient and accurate. This is of paramount importance for the efficient simulation of many industrial processes including semi-solid forming and casting. This paper presents a new control volume capacitance method (CVCM) to cater for bulk transport. The governing equations utilised are described on a moving reference frame and are transformable into a finite element system that is similar to that used to model transient heat conduction. Any enthalpy discontinuities present are precisely accounted for with the application of an analytical integration procedure. Numerical tests on a 1-D semi-infinite problem are compared against analytical solutions; the approach is shown to be accurate, stable and computationally competitive.
Cooling Rate Studies in Aluminum Counter Gravity Lost Foam Casting
Authors: Bakhtiyarov Sayavur I. , Overfelt Ruel A. , Capps Johnathon
Published: May 2008

In this paper we present the results of the experimental study of the liquid metal front dynamics during the gravity pouring and the vacuum assisted counter-gravity lost foam casting techniques. The cooling rates of the castings produced by both techniques are compared.
Numerical Simulation and Thermometric Measurements on Mold Filling Dynamics
Authors: Bakhtiyarov Sayavur I. , Overfelt Ruel A. , Edmondson Matthew
Published: May 2008

In this paper we present the results of the CFD simulations of the mold filling dynamics in gravity and counter-gravity lost foam castings. FLOW-3D software package (Flow-Simulations, Inc.) has been used to predict flow velocity distributions and pressure losses when liquid metal flows in the step pattern. The results of simulations are compared to those obtained experimentally.
Numerical Tool for Non Newtonian Fluids Extrusion
Authors: Chambarel Andre´
Published: May 2008

The main difficulty of the numerical approach of non Newtonian fluids is its strong non linearities. For example we propose a numerical simulation of the flow of non Newtonian fluid through a capillary rheometer. This model is associated with the extrusion phenomenon.
Molecularly Self-Assembled Actuators and Devices
Authors: Claus R. , Zeng T. , Huie K. , Huie J. , Mecham J. , Arregui F. , Matias I.
Published: May 2008

Piezoelectric thin films incorporating poly(sodium 4-styrenesolfonate) (PSS) and poly(diallyldimethylammonium chloride) (PDDA) were synthesized using the electrostatic self-assembly (ESA) process. The ESA-processed PSS/PDDA film is a layer-by-layer laminated structure, which exhibits piezoelectric response directly, with a piezoelectric coefficient d33 = 6.0 pC/N and without poling treatment. It is assumed that the self-assembly process may play a very important role in molecular alignment resulting in net polarization in the layer-by-layer structured ultrathin film, a process quite different from that used to form conventional piezoelectric films. Further study concerning the principles governing the novel ESA processing of piezoelectric films and self-assembled materials, sensors and actuators is on-going.
Health Monitoring of the Steel Cables Using the Elasto-Magnetic Method
Authors: Fabo P. , Jarosevic A. , Chandoga M.
Published: May 2008

The EM method is a valuable tool for Civil Engineering for estimation of the real stress in the prestressing tendons, quality control during construction period, calculating the stress loss due to friction and relaxation, long-time monitoring of stress changes due to concrete creep, temperature changes, traffic load etc. Overview of EM technique with practical applications in the Civil Engineering is presented. The new generation of EM measuring devices is based on more than 15 years experience, including health monitoring systems for the nuclear power plant and a large span cable stayed and suspension bridges. Examples of laboratory and field tests are presented, including uncertainty of stress measurement, long-time stability, resolution and reliability.
Optimization of Plasma Spray Processing Parameters for Deposition of Nanostructured Coatings
Authors: Ahmed I. , Bergman T. L.
Published: May 2008

When nanostructured material is thermally sprayed to produce coatings, the retention of the original nanostructure that is engineered into the raw stock is a principal objective, along with production of some molten material in order to adhere the sprayed material to the surface being coated. Therefore, in contrast to spraying conventional material, complete melting of the nanostructured raw stock is to be avoided. In this study, the melting and re-solidification of sprayed material is correlated to a spray process parameter that has been introduced in the literature by others. Using computer modeling, processing of zirconia agglomerates with plasma spraying has been simulated. Transition regions of the phase change response of the material to the thermal processing conditions are identified. The retained nanostructure content and liquid fraction of the sprayed material is correlated to the particle diameters, as well as the thermal processing parameter. Finally, a novel method to produce desired coatings composed of partially molten sprayed material, by using a bimodal particle size distribution of the sprayed powder, is presented and discussed.
Advancements in Micro-Molding for Small-Scale Product Fabrication
Authors: Tom Alan M. , Coulter John P.
Published: May 2008

Globally, micro molding technology had been predicted to be a $40 billion market in 2002. Although it may seem overly optimistic, there is no doubt that micro molding will be a promising market in the near future. The ground work for micro molding technology has been initiated to enable future advancements in its technological development. Although the phrase “micro molding” has not yet become a common everyday word in the manufacturing industry, it is however prevalent and used quite extensively globally in numerous research institutes of academia and U.S. government research facilities. The development of micro molding component fabrication and its present day technology has been jump started by numerous advancements discovered and borrowed from existing electronic integrated circuit technology. Therefore, development of micro mold fabrication techniques for mass produced microstructures does not pose significant research problems. However, the same cannot be said for advancements in developing micro molding machinery and definitely not the case in the development and optimization of manufacturing processes. The following literature review is an informative attempt to concisely explain present day advancements in the development of micro scale components, focusing in particular, on micro injection molding tooling, machinery, and its accompanying processing conditions.
Multi-Scale Embedded Sensing for Damage Identification
Authors: Studer Michel , Peters Kara
Published: May 2008

This paper presents an efficient technique to uniquely identify damage through the creation of a multi-scale map of material deformations and behavior within a representative volume element (RVE) of the host structure. Optimally distributed, embedded fiber optic sensors provide strain, strain gradient, and integrated strain fields throughout the RVE. As a demonstration, an isotropic, homogeneous RVE is modeled instrumented with an evenly spaced grid of sensing elements. The multi-scale damage identification technique and an equivalent single-scale method are evaluated on the basis of damage detection and identification. A large number of induced, stochastic damage cases are analyzed, generated by introducing a crack defined by three random variables: center location, length, and orientation angle. The multi-scale sensing capability is shown to provide a higher quality strain map of the RVE from the distributed sensors, resulting in significantly improved damage identification.
Towards Characterization of Soot Morphology, Composition, and Optical Properties From Large Pool Fires
Authors: Suo-Anttila Jill , Drozda Patrick , Gritzo Louis , Choi Mun Young
Published: May 2008

The thermal hazard posed by large hydrocarbon fires is dominated by the radiative emission from high temperature soot. Since the optical and morphological properties of soot are not well known, especially in the infrared, efforts to characterize these properties are underway. Measurements of optical properties and morphology in large fires are important in heat transfer calculations, interpretation of laser-based diagnostics, and to build revised soot property models for fire field models. This research utilizes extractive measurement diagnostics to characterize soot morphology, composition, and optical properties in pool fires. The fires of interest are realistic in size, and considerably larger than recent studies, from transitionally turbulent to fully turbulent JP-8 pool fires. For measurement of the extinction coefficient, soot extracted from the flame zone is transported to a transmission cell where measurements are made using both visible and infrared lasers. Soot morphological properties are obtained by analysis via transmission electron microscopy of soot samples obtained thermophoretically within the flame zone, overfire region, and in the transmission cell. Soot composition, including carbon-to-hydrogen ration and PAH concentration, is obtained by analysis of soot collected on filters. In addition to providing insight into optical properties, soot samples obtained allow researchers to determine that the soot morphology is not affected by the transport to the transmission cell. This paper describes the diagnostics and presents some preliminary data for soot morphology, composition, and optical properties measurements within the flame zone of pool fires.
Digital Recording and Numerical Reconstruction of Holograms: A New Optical Diagnostic for Combustion
Authors: Xiao Xudong , Puri Ishwar K.
Published: May 2008

Digital holographic interferometry (DHI) is a relatively newer imaging and measurement technique that electronically records a hologram (e.g., on a CCD) and reconstructs it using a numerical method. Cumbersome chemical processing of the hologram is avoided in DHI, thereby providing greater flexibility, speed, and the potential for real time processing. In conventional holography fringes that are neither bright nor dark on a hologram cannot be accurately resolved. The DHI technique reported so far has not yet been used for combustion applications. Herein, we will evaluate its efficacy for making temperature measurements in flames and assess its applicability through a simulation. The double exposures associated with the holographic technique are each considered recorded by a hypothetical CCD sensor at separate times. We have applied the principles of Fourier optics to develop a numerical method for hologram reconstruction.
Laser Ignition and Measurement of the Fuel-to-Air Ratio of a Turbulent Jet Diffusion Flame
Authors: Phuoc Tran X. , White Frederick P.
Published: May 2008

In this work we will discuss the use of the laser-induced gas breakdown for stabilizing and measuring the fuel-to-air ratio of a turbulent jet diffusion flame. The gas breakdown was produced using a single-mode, Q-switched Nd-YAG laser which produced a 0.6-cm-diameter beam at a wavelength of 1064 nm with a 5.5 ns pulse duration. The jet flow rates ranging from 35 cm3/s (Re = 1086) to 103 cm3/s (Re = 3197) were used. The relative amounts of fuel and air concentrations at the laser focus were estimated using the late time behavior of the line radiation at the wavelength of the OI triplet near 777 nm and at the wavelength of the Hα line, 656 nm, which is emitted by electronically excited hydrogen dissociated from the methane fuel.
An Analytical Model for a Clamped Isotropic Beam Under Thermal Effects
Authors: Marques Rodrigo F. A. , Inman Daniel J.
Published: May 2008

Structures and industrial equipment often operate in environments where temperature variations take place. Although thermal effects may be negligible in some cases, they have caused the unexpected failure of mechanical systems many times. Whether or not temperature has significant effects on the dynamical behavior of such machines and structures depends upon several aspects, amongst which are geometry, material properties and boundary conditions. In this paper we investigate the dynamical behavior of a clamped beam under the influence of a uniform, quasi-statically varying temperature field. An analytical model was used, based on Euler-Bernoulli’s beam theory with the introduction of the proper boundary conditions. Temperature effects are included in terms of an axial force that shows up when the beam tends to thermally expand, but this expansion is restrained by the clamping. Preliminary results do not agree with experimental data, since perfect clamping is difficult to achieve in practice. Finally the model is updated with the inclusion of axial and torsional springs connecting the beam to the support. The spring constants were calculated through optimization procedure to minimize the differences between the natural frequencies obtained from the analytical model and the corresponding experimental ones. Agreement with experimental results is reasonable up to the 4th mode of the beam. In the future, this analytical model is to be used for design and simulation of an active controller that accounts for temperature changes in the structure.
A Time Domain Technique for Defect Identification Based on a Continuous Damage Model
Authors: Castello Daniel A. , Stutz Leonardo T. , Rochinha Fernando A.
Published: May 2008

A technique for a non-destructive detection, location and severity determination of structural defects by means of a time domain technique is presented. Since damage in a structure causes changes in the physical coefficients of elastic modulus and damping parameters, the response of an undamaged and a damaged structure to the same input excitation is different, and this can be used in a damage identification strategy. The present work uses a continuous damage model to describe the current integrity state of a structure. In order to determine this state of structural damage the minimization of an error function is desired, such a function is basically the difference between the time response of the structural model and the real structure one to the same input excitation. The effectiveness of the proposed technique is assessed on a beam like structure, where displacements, accelerations or strains may considered as being measured at a subset of the system degrees of freedom. In order to furnish realism to performed simulations, the corrupting effects of signal filtering and sampling are considered. The analysis of the results for different levels of signal-to-noise ratio is also carried on.
Micro-Control Actions of Segmented Actuators on Shallow Paraboloidal Shell Reflectors
Authors: Lih S.-S. , Hickey G. , Ding J. H. , Tzou H. S.
Published: May 2008

Shallow paraboloidal shells of revolution are common components for reflectors, mirrors, etc. This study is to investigate the micro-control actions and distributed control effectiveness of precision paraboloidal shell structures laminated with segmented actuator patches. Mathematical models and governing equations of the paraboloidal shells laminated with distributed actuator layers segmented into patches are presented first, followed by formulations of distributed control forces and micro-control actions including meridional/circumferential membrane and bending control components based on an assumed mode shape function and the Taylor series expansion. Distributed control forces, patch sizes, actuator locations, micro-control actions, and normalized control authorities of a shallow paraboloidal shell are then analyzed in a case study. Analysis indicates that 1) the control forces and membrane/bending components are mode and location dependent, 2) the meridional/circumferential membrane control actions dominate the overall control effect, 3) there are optimal actuator locations resulting in the maximal control effects at the minimal control cost for each natural mode. The analytical results provide generic design guidelines for actuator placement on precision shallow paraboloidal shell structures.
Performance Characteristics of a Smart Flexible Beam With Distributed ACLD Elements
Authors: Hau L. C. , Fung Eric H. K.
Published: May 2008

The finite element method, in conjunction with the Golla-Hughes-McTavish (GHM) viscoelastic model, is employed to model a clamped-free beam partially treated with active constrained layer damping (ACLD) elements. The governing equations of motion are converted to a state-space form for control system design. Prior to this, since the resultant finite element model has too many degrees of freedom due to the addition of dissipative coordinates, a model reduction is performed to revert the system back to its original size. Finally, optimal output feedback gains are designed based on the reduced models. Numerical simulations are performed to study the effect of different element configurations, with various spacing and locations, on the vibration control performance of a “smart” flexible ACLD treated beam. Results are presented for the damping ratios of the first two modes of vibration. It is found that improvement on the second mode damping can be achieved by splitting a single ACLD element into two and placing them at appropriate positions of the beam.
Vibration Analysis and Control of a Rotating Flexible Arm With ACLD Treatment
Authors: Fung E. H. K. , Yau D. T. W.
Published: May 2008

In this paper, the vibration behavior and control of a clamped-free rotating flexible cantilever arm with fully covered Active Constrained Layer Damping (ACLD) treatment is investigated. The arm is rotating in a horizontal plane in which the gravitational effect and rotary inertia are neglected. The stress-strain relationship for the viscoelastic material (VEM) is described by a complex shear modulus while the shear deformations in the two piezoelectric layers are neglected. Hamilton’s principle in conjunction with finite element method (FEM) is used to derive the nonlinear coupled differential equations of motion and the associated boundary conditions that describe the rigid hub angle rotation, the arm transverse displacement and the axial deformations of the three-layer composite. This refined model takes into account the effects of centrifugal stiffening due to the rotation of the beam and the potential energies of the VEM due to extension and bending. Active controllers are designed with PD for the piezo-sensor and actuator. The vibration frequencies and damping factors of the closed-loop beam/ACLD system are obtained after solving the characteristic complex eigenvalue problem numerically. The effects of different rotating speed, thickness ratio and loss factor of the VEM as well as different controller gain on the damped frequency and damping ratio are presented. The results of this study will be useful in the design of adaptive and smart structures for vibration suppression and control in rotating structures such as rotorcraft blades or robotic arms.
Thermo/Mechanical Design, Modeling, and Testing of Shape Memory Actuated Minimal and Micro Invasive Probe Systems
Authors: Wulfman David R. , Erdman Arthur G. , Strykowski Paul J.
Published: May 2008

Small scale probes implementing shape memory alloy (SMA) actuation show great promise in applications requiring remote and minimally invasive access to small environments. Such environments include physiological spaces like those located in human and animal bodies as well as cavities within mechanical systems. Probes examined here are generally snake like in appearance composed of one or multiple independent segments, which in turn are made up of one or multiple SMA actuators performing work against an elastic spine. As the actuator(s) of a given segment are activated, the spine bends causing the probe to bend in the area of that segment. When the actuator(s) are deactivated, the force generated in the bending of the spine returns the segment to its neutral position. Activation and deactivation of actuators is accomplished by heating and cooling respectively, enacting the solid phase changes that are characteristic to the shape memory effect. The gage of control over probe shape depends on the number of independent segments that are available per unit length and the degree of control an operator has over each of the segments. The work presented here discusses the constraints imposed on the design of SMA actuated probes, and how those constraints become more critical and limiting with reduced physical scale and refinement of motion control. Numerical and finite element models have been developed showing the interrelationship between mechanical design, the thermal and phase states of the SMA actuator(s), and the mechanical performance of the total system. Performance concerns examined include probe shape control and the limits of shape change as a function of physical scale. Comparative data is presented between behavior predicted by the models developed and performance observed during the testing of prototypes. It is concluded that segment length, linked to refinement of probe control, is limited by its thermal boundary conditions.
Inertially Stabilized Rifle Using Recurve Actuators
Authors: Lindner Douglas K. , Zhu Huiyu , Brei Diann , Vindlinski Jim , La Vigna Chris
Published: May 2008

This paper describes an INertially STabilized Rifle where a Recurve actuator, constructed from piezoelectric material, is used to internially stabilize the barrel assembly of a tactical rifle to compensate for the small user-induced disturbances. The requirements of this system are discussed and the actuator requirements are derived. A prototype Recurve actuator is described and the test results reported. Similarly, the power electronics needed for INSTAR are discussed. Test results for an prototype circuit are given.
Profile Sensing With an Actuated Whisker
Authors: Scholz Gregory R. , Rahn Christopher D.
Published: May 2008

Obstacle avoidance and object identification are important tasks for robots in unstructured environments. This paper develops an actuated whisker that determines contacted object profiles using a hub load cell. The shape calculation algorithm numerically integrates the elastica equations from the measured hub angle, displacement, forces, and torque until the bending moment vanishes, indicating the contact point. Sweeping the whisker across the object generates a locus of contact points that can be used for object identification. Experimental results demonstrate the ability to identify and differentiate square and curved objects at various orientations.
Design Optimization of a Piezoelectric Fiber Actuator With a Natural Curvature
Authors: Kim Cheol , Lee Dong-Yeub
Published: May 2008

Piezoelectric Fiber Composite with Interdigitated Electrodes (PFCIDE) was previously introduced as an alternative to monolithic wafers with conventional electrodes for applications of structural actuation. This paper is an investigation into the performance improvement of piezoelectric fiber composite actuators by optimizing the stacking sequence and changing the matrix material. This paper presents the numerical optimization of a piezoelectric fiber/piezoelectric matrix composite actuator with IDE (PFPMIDE). Various concepts from different backgrounds, including three-dimensional linear elastic and dielectric theories, have been incorporated into the present linear piezoelectric model. To see the structural responses of the actuator integrated with the PFPMIDE, three-dimensional finite element formulations were derived. Numerical analysis shows larger center displacement of the curved actuator with the PFPMIDE due to optimization of the piezoelectric fiber angles. This paper presents the concept of a curved actuator that occurs naturally via thermal residual stress during the curing process, as well as the optimization of the maximum curved actuator displacement, which is accomplished using the Davidon-Fletcher-Powell (DFP) method.
Lift Control Using MEMS-Based Moving Trailing-Edge Tabs
Authors: van Dam C. P. , Bauer C. , Yen Nakafuji D. T.
Published: May 2008

Micro-electro-mechanical (MEM) translational tabs are introduced for active lift control on aircraft. These tabs are mounted near the trailing edge of lifting surfaces such as aircraft wings and tails, deploy approximately normal to the surface, and have a maximum deployment height on the order of one percent of the section chord. Deployment of the tab effectively changes the sectional camber, thereby changing the aerodynamic characteristics of a lifting surface. Tabs with said deployment height generate a change in the section lift coefficient of approximately ±0.3. The microtab design and the techniques used to fabricate and test the tabs are presented.
The Role of Internal Variables on the Control of Viscoelastic Structures
Authors: Silva Luciano A. , Austin Eric M. , Inman Daniel J.
Published: May 2008

Scientists have used internal variables to model time-dependent material behavior for many years. Since the 1980s they have been employed to predict transient response of structures that include viscoelastic materials. The potentially large number of extra states introduced by the internal variables can be problematic when designing control systems, so the purpose of this paper is to explore how internal variables affect control system design. Practical designs are based on output feedback of a limited number of the physical states, but this brings up the question of whether it is advantageous to recreate the full state vector (including internal states) using a standard observer. Internal variables based on Maxwell models are used to address observability and controllability as well as full- and partial-state feedback on a single-degree-of-freedom system. Comparisons are also made between complex-modulus and internal-variable representations of viscoelastic behavior.
Inflight Deicing of Self-Actuating Aircraft Wing Structures With Piezoelectric Actuators
Authors: Lin Y. J. , Venna Suresh V.
Published: May 2008

Self-actuating aircraft wings for in-flight deicing with minimal power requirements are proposed. Lightweight piezoelectric actuators are utilized to excite the wing structure to its natural frequencies to induce shear stresses on the surface of the wing. The shears are generated in such a way that they are sufficient to break the weak bond between the ice layer and the wing surface. A laminated composite cantilever plate is used for the modeling and analysis. Analytical model is developed to predict the natural frequencies and shear stresses on the surface of the plate and finite element modal analysis is carried out to verify the results. In addition, finite element model involving the ice deposited on the underlying structure is built. The dynamic responses of the structure to harmonic excitation to its first five natural frequencies are investigated. It is observed that significant amount of ice de-bonding from the substrate occurs in the third mode, or the second symmetric mode. Moreover, the energy requirements of the piezoelectric actuators to actuate an adaptive composite structure with given weight are evaluated.
Dynamic Topology Optimization of Compliant Mechanisms and Piezoceramic Actuators
Authors: Maddisetty Hima , Frecker Mary
Published: May 2008

A topology optimization method is developed to design a piezoelectric ceramic actuator together with a compliant mechanism coupling structure for dynamic applications. The objective is to maximize the mechanical efficiency with a constraint on the capacitance of the piezoceramic actuator. Examples are presented to demonstrate the effect of considering dynamic behavior compared to static behavior, and the effect of sizing the piezoceramic actuator on the optimal topology and the capacitance of the actuator element. Comparison studies are also presented to illustrate the effect of damping, external spring stiffness, and driving frequency. The optimal topology of the compliant mechanism is shown to be dependent on the driving frequency, the external spring stiffness, and if the piezoelectric actuator element is considered as design or non-design. At high driving frequencies, it was found that the dynamically optimized structure is very near resonance.
Optimization of Relaxor Single Crystals for Bending Mode Applications
Authors: Liu T. Q. , Lynch C. S.
Published: May 2008

Rhombohedral relaxor single crystals are a class of materials that includes PZN-PT and PMN-PT in a certain range of compositions. This work presents an approach to predicting the physical properties of relaxor single crystals with an engineered domain state. A model based on properties of crystal variants and volume averaging indicates large piezoelectric coefficient d31 (690 pC/N) and d32 (−1670 pC/N) for the <110> cuts and a value over 4000 pC/N for d15 and the existence of d16 with a value as large as −2300 pC/N in <111> orientation cuts. The predictive capability of the approach results in a computational tool for the design of engineered domain states with properties optimized for specific applications. This has resulted in the identification of a crystal cut optimized for actuator and sensor applications that utilizes the transverse mode piezoelectric coupling coefficients (d31 and d32).
Orthotropy Rescaling for the Fracture Problem in Anisotropic Piezoelectric Materials
Authors: Oates William S. , Lynch Christopher S.
Published: May 2008

To date, much of the work done on ferroelectric fracture assumes the material is elastically isotropic, yet there can be considerable polarization induced anisotropy. More sophisticated solutions of the fracture problem incorporate anisotropy through the Stroh formalism generalized to the piezoelectric material. This gives equations for the stress singularity, but the characteristic equation involves solving a sixth order polynomial. In general this must be accomplished numerically for each composition. In this work it is shown that a closed form solution can be obtained using orthotropy rescaling. This technique involves rescaling the coordinate system based on certain ratios of the elastic, dielectric, and piezoelectric coefficients. The result is that the governing equations can be reduced to the biharmonic equation and solutions for the isotropic material utilized to obtain solutions for the anisotropic material. This leads to closed form solutions for the stress singularity in terms of ratios of the elastic, dielectric, and piezoelectric coefficients. The results of the two approaches are compared and the contribution of anisotropy to the stress intensity factor discussed.
Fine Particulate Formation During Biomass/Coal Cofiring
Authors: Blevins Linda G. , Cauley Thomas H.
Published: May 2008

Experiments to examine the effects of biomass/coal cofiring on fine particle formation were performed in the Sandia Multi-Fuel Combustor using fuels of pure coal, 3 combinations of switchgrass and coal, and pure switchgrass. A constant thermal input was maintained. The combustion products were cooled during passage through the 4.2 m long reactor to simulate the temperatures experienced in the convection pass of a boiler. Fine particle number densities, mass concentrations, and total number concentrations for particles between 10 nm and 1 μm at the reactor exit were determined using a Scanning Mobility Particle Sizer. The results indicate that the fine particle loading for cofiring is higher than that achieved with dedicated coal combustion but lower than that achieved with dedicated switchgrass combustion.
Dynamic Magnetomechanical Properties of Terfenol-D/Epoxy 1-3 Particulate Composites
Authors: Or Siu Wing , McKnight Geoffrey P. , Nersessian Nersesse , Carman Gregory P.
Published: May 2008

This paper describes the effect of particulate crystallographic orientation on the dynamic magnetomechanical properties of Terfenol-D/epoxy 1–3 magnetostrictive particulate composites. Two different types of composites with approximately 50% Terfenol-D volume fraction were fabricated for comparison with [112]-textured monolithic Terfenol-D. In the first type, needle-shaped, [112]-oriented particles cut from the monolithic Terfenol-D were used and in the second type, irregular-shaped, randomly oriented particles ball-milled from the monolithic material were employed. Elastic moduli (E33H and E33B), dynamic strain coefficient (d33), and magnetomechanical coupling coefficient (k33) were investigated as a function of bias field. Both composites demonstrate similar property trends with the negative-ΔE, d33, and k33 values maximizing near 30 kA/m. The maximum values achieved in the oriented type are up to 67% larger than the non-oriented type and approaches 65% of the monolithic Terfenol-D. The property improvement in the oriented type is shown to be attributed to [112] preferential particulate orientation.
Co-Firing Feedlot and Litter Biomass: Coal Blends in a Laboratory Scale Boiler Burner
Authors: Thien B. , Annamalai K. , Sweeten J.
Published: May 2008

The co-firing of animal biomass fuels with coal has the potential to solve both biomass disposal problems, and reduce net CO2 emissions. The high flame temperatures produced by coal will allow the low heating value, high ash biomass to be completely burnt. Unfortunately, the animal biomass fuels are high in nitrogen and sulfur, which could lead to greater air pollution levels in the form of NO and SO2. To determine the effect of switching to 90:10 Coal:biomass blend on combustion efficiency and emissions, the blends were fired in a 30 kW (100,000 BTU/hr) laboratory scale boiler burner. The results are presented along with the their relation to the fuel properties.
A New Self-Adjusting CVT Configuration Using Compliant Mechanisms
Authors: Christensen Myles T. , Magleby Spencer P. , Howell Larry L. , Todd Robert H. , Mortensen Clint
Published: May 2008

This paper introduces a new configuration of a Continuously Variable Transmission (CVT) that is self-adjusting and designed as a compliant mechanism. This new configuration is called the Pivot-Arm CVT. The criteria for classification as a Pivot-Arm CVT is discussed. An analytical model describing the performance of the Pivot-Arm CVT is developed. Special design considerations which may be useful in implementing Pivot-Arm CVTs are introduced and explained. The Pivot-Arm CVT model is validated through controlled testing of two Pivot-Arm CVT prototypes.
Active Stiffener Concept for Shape Control of Two Dimensional Structures
Authors: Philen Michael , Wang Kon-Well
Published: May 2008

A substantial amount of research exists concerning shape and vibration control of structures with attached piezoelectric ceramic sheet actuators. Researchers have investigated the optimal placement, size, and electrode pattern of these piezoceramic actuators to maximize the performance of the system. In many situations, the performance could be further improved with tailoring of the electromechanical properties of the actuator. For example, it was found that to avoid exciting higher order modes, the ideal actuator would be one that only actuates in one direction when controlling certain modes in a two-dimensional plate structure [1]. As known, the 31 and 32 electromechanical coupling values of a piezoelectric ceramic patch poled in the 3 direction is equal. Therefore to achieve decoupling of the actuator action in the 31 and 32 directions, a mechanism is required. In this paper, an active stiffener concept is proposed to realize such an effect where a stiffener is inserted between a host structure and the piezoelectric ceramic actuator patch. Using a solid finite element model, an analysis of a single active stiffener attached to a rigid and a flexible host structure is presented. In the analysis, the effects of various material and system parameters on the transmitted force to the structure are presented. It is seen that the active stiffener can significantly reduce the transmitted force in the selected direction. The performance of the active stiffener concept with multiple actuators is presented for controlling the shape of a large flexible circular plate structure.
An Equivalent Circuit Model for Ionic Polymer-Metal Composites and Their Performance Improvement by a Clay-Based Polymer Nano-Composite Technique
Authors: Paquette J. , Kim K. J. , Nam J.-D. , Tak Y. S.
Published: May 2008

Ionic Polymer-Metal Composite (IPMC) is a new class of polymeric material exhibiting large strain with inherent soft actuation. The observed motion characteristics of an IPMC subjected to an electric field is highly non-linear. This is believed to be due primarily to the particle electrodes on the IPMC surface, which is inherently both capacitive and resistive due to particle separation and density. Knowing that the value of resistivity and capacity can be manipulated by the number of metal platings applied to the IPMC, the force response of an IPMC when subjected to an imposed electric field is due to the interaction of an array of capacitors and resistors along with ionic migration. In this effort we attempt to incorporate a capacitive and resistive model into the previously developed linear irreversible thermodynamic model. The advantages of using such a model are i) the possible dynamic predictability of the material itself; and ii) the realization of capacitive and resistive effect arising from the particle electrodes and the base polymer, respectively. The behavior of the proposed model can explain typical experimentally obtained values well. Also, an experimental effort to improve the properties of the base polymer was carried out by a novel nanocomposite technique. The experiment results on the current/voltage (I/V) curves indicate that the starting material of ionic polymer-metal composites (IPMCs) can be optimized to create effective polymer actuators.
Manufacturing and Mechanics-Based Characterization of Macro Fiber Composite Actuators
Authors: Williams R. Brett , Grimsley Brian W. , Inman Daniel J. , Wilkie W. Keats
Published: May 2008

The use of piezoelectric ceramic materials for structural actuation is a fairly well developed practice that has found use in a wide variety of applications. However, just as advanced composites offer many benefits over traditional engineering materials for structural design, actuators that utilize the active properties of piezoelectric fibers can improve upon many of the limitations encountered with monolithic piezoceramic devices used to control structural dynamics. This paper discusses the Macro Fiber Composite (MFC) actuator, which utilizes piezoceramic fibers, for example, lead zirconate titanate (PZT), embedded in an epoxy matrix for structural actuation. An overview of the MFC assembly process is presented, followed by a cure kinetics model that describes the behavior of the thermosetting matrix. This empirical model is seen to agree closely with the experimental data. Lastly, a hybrid classical lamination theory is developed to predict the linear elastic properties of the MFC package as a function of the PZT fiber lamination angle.