bluuebunny/crossref_metadata_2025 huggingface dataset:
The Transversal Method of Lines (TMOL) Applied to Unsteady Conduction in Large Plates, Long Cylinders and Spheres With Prescribed Surface Heat Flux
Authors: Campo Antonio , Soujoudi Ramin , Davis Adelina
Published: August 2012

The Transversal Method Of Lines (TMOL) or Rothe method is a general technique for solving parabolic partial differential equations that uses a two-point backward finite-difference formulation for the time derivative and differential spatial derivatives. This hybrid approach leads to transformed ordinary differential equations where the spatial coordinate is the independent variable and the time appears as an embedded parameter. The transformed ordinary differential equations may have constant or variable coefficients depending on the coordinate system and are first-order accurate. In this work, TMOL is applied to the 1-D heat equation for large plates, long cylinders and spheres with constant thermophysical properties, uniform initial temperature and prescribed surface heat flux. The analytic solutions of the adjoint heat equations are performed with the symbolic Maple software. It is demonstrated that the approximate semi-analytic TMOL temperature distributions for the three simple bodies are much better than first-order accurate. This signifies that TMOL temperature distributions are not only valid for short times, but they are valid for the entire heating period involving short, moderate and long times.
Development and Validation of a Mathematical Model of Microfilm Formation in Atomization Cooling of Micromachining
Authors: Boughner Kyle J. , Wentz John E. , Garske Benton J.
Published: August 2012

Traditional flood cooling processes can cause problems in micromachining due to the collision force between the fluid stream and the tool being greater in magnitude than the cutting forces. The traditional processes produce insufficient cooling rates and are unable to effectively evacuate chips from the cutting zone. Atomization-based cooling addresses these issues through high evaporative cooling rates, low impact forces, and the use of a high velocity air stream to clear the cutting zone of chips. This paper presents a probabilistic model to determine the thickness of a microfilm forming on a rotating cylindrical surface, such as a microturning workpiece or a microendmill, and the relative importance of system parameters on film formation. The rate of microfilm formation is dependent upon droplet losses in the tube, at the nozzle, and the scatter of the atomized spray. Droplet diameters and Weber numbers in the tube and at the cylinder were experimentally determined and modeled as lognormally distributed. Parameters investigated in this model are fluid and mist properties (surface tension and droplet size) and system parameters (delivery tube air velocity, spray air velocity, spray geometry, cylinder diameter, and cylinder rotational velocity). A maximum film thickness effect was found for the variables of delivery tube velocity, droplet diameter, and surface tension with a value for each variable that provided a thickest film. As the variables increased or decreased from that value the film thickness decreased.
On a Decoupled Integrated Design Approach to Robotic Mechanisms
Authors: Sun Zhihong , He Dong , Zhang Bing , Zhang W. J.
Published: August 2012

In this paper, we propose a new design process which is called decoupled integrated design process for robotic mechanisms or mechanisms with consideration of their multi-functions and constraints. The example of the functions includes path generation, function generation and rigid body guidance. The example of the constraints includes minimum negative side effects to the environment the mechanism interacts. The proposed design process is a decoupled one, inspired by axiomatic design theory. In particular, the first step of the design process is to analyze the design requirement and design parameter relation, which can be represented by a correspondence matrix. When the correspondence matrix is a triangular one, the corresponding design problem is called a decoupled design problem. Subsequently, we propose a decoupled integrated design process which is applied to a decoupled problem. Throughout the paper, we take a 2-DOF five-bar mechanism as an example; yet the approach is applicable to any kind of dynamic systems.
Analysis of the Extension-Twist Coupling in Hygrothermally Stable Star Beam Composites
Authors: Muder Sean , Haynes Robert , Armanios Erian
Published: August 2012

An approximate analytical model is utilized to examine the extension-twist coupling and torsional stiffness properties of star beams constructed with a new family of hygrothermally stable optimized stacking sequences. The relationship between axial force and the twist rate is used to quantify the results. The results show that there is a decrease in torsional rigidity corresponding to an increase in extension-twist coupling. The new stacking sequences allow for the addition of more substrips while maintaining comparable levels of extension-twist coupling with beams constructed from prior benchmark layups. This results in higher levels of torsional stiffness for comparable levels of extension-twist coupling in star beams made of the new optimized stacking sequences.
Numerical Simulation of Radiation Heat Transfer of the Human Body for Determining Its Radiation Coefficient
Authors: Najjaran Ahmad , Tahavvor Ali R. , Najjaran Abdolkarim , Ahmadfard Mohammad A.
Published: August 2012

Radiation heat transfer coefficient of the human body is one of the most important factors in the field of human skin health. In this paper, the radiation coefficient of the body is calculated by considering external heat radiation of body with the infinite surrounding. At first a human body is designed, and then analysis is done on it. Two segments are assumed for human body (standing and supine). In these segments hands and feet are supposed to be totally open and stretched. In standing segment, soles and in supine segment, the entire back of the body are in contact with the ground and so don’t have heat transfer. The calculation of the results is done by weighted area average method. Radiation coefficient and radiation heat flux are calculated in various emissivity. Because of existence of air around the body in reality, the convection heat transfer is also assumed for human body. Finally two formulas are reported for these segments.
Thermal Properties of Nanotubes and Nanowires With Acoustically Stiffened Surfaces
Authors: Bifano Michael F. P. , Prakash Vikas
Published: August 2012

A core-shell elasticity model is employed to investigate the effect of a nanowire and nanotube’s increased surface moduli on specific heat, ballistic thermal conductance, and thermal conductivity as a function of temperature. Phonon confinement is analyzed using approximated phonon dispersion relations that result from solutions to the frequency equation of a vibrating rod and tube. The results indicate a maximum 10% decrease in lattice thermal conductivity and ballistic thermal conductance near 160 K for a 10 nm outer diameter nanotube with an inner diameter of 5 nm when the average Young’s Modulus of both the inner and outer free surfaces is increased by a factor of 1.53. In the presence of the acoustically stiffened surfaces, the specific heat of the nanotube is found to decrease by up to 20% at 160 K. Near room temperature, changes in thermal properties are less severe. In contrast, a 10 nm outer diameter nanowire composed of similar material exhibits up to a 12% maximum increase in thermal conductivity at 600 K, a 25% increase in ballistic thermal conductance at 400 K, and a 48% increase in specific heat at 470 K when its outer free surface is acoustically stiffened to the same degree. Our simplified model may be extended to investigate the acoustic tuning of nanowires and nanotubes by inducing surface stiffening or softening via appropriate surface chemical functionalization and coatings.
Simulation of Weld Pool Dynamics and Subsequent Thermal Stress Analysis of Welded Joint Under Gas Tungsten Arc Welding
Authors: Sen Debamoy , Ball Kenneth S. , Pierson Mark A.
Published: August 2012

Thermal stresses in the weldment influence the load carrying capacity of the welded structure and have significant practical implications. Various welding parameters (like, welding speed, current, surfactant activity, etc.) influence the weld pool dynamics, which in turn affect the thermal history of the workpiece. Hence, the complete weld pool dynamics need to be considered for predicting an accurate thermal profile in the welded structure before a thermal stress analysis is conducted. In this study, the thermal profile created due to fluid flow, heat transfer and phase change during Gas Tungsten Arc (GTA) welding is incorporated in conducting a thermal stress analysis of the welded workpiece. The effect of preheat on the developed thermal stresses is also analyzed.
Spatially Controllable Deposition of Electrospray Microparticles
Authors: Zhang Xu , Zhao Yi
Published: August 2012

Electrospray has been widely used in micro/nanotechnology which deposit micro/nanoscale particles on planar surfaces. However, in conventional electrospray approach the distribution of these particles patterned on the collecting surface is poorly controlled. This work introduces a programmable patterning method of electrospray, which microparticles are sprayed on micropatterned collecting chips. By manipulating the local electrical field using a combination of activated and floating electrodes, a good spatial contrast of microparticle patterning is obtained. In addition, the size-dependent contrast enhancement is demonstrated using a series of electrode arrays with different electrode patterns. Combined with encapsulation technique, this unique electrospray method promises potential applications in the field of functional cell/tissue engineering.
A Thermoeconomic-Artificial Intelligence Combined Approach to the Diagnosis of Energy Systems
Authors: Melli Roberto , Verda Vittorio , Vernica Sorin-Gabriel
Published: August 2012

In this paper, the combined application of two different approaches to the diagnosis of energy systems is proposed. The first approach is based on thermoeconomic analysis. It consists on the filtration of effects due the dependence of the efficiencies of components on their operating condition. This is obtained through productive models which relate resources and products. With respect to physical models, these are generally less accurate but more compact and thus more suitable to deal with the available measurements in real plants. The second approach is an artificial intelligence (AI) technique. This is based on the calculation of appropriate indicators that experience shows to be affected by possible anomalies. Malfunctions are detected and recognized through the analysis of deviations registered by the indicators during plant operation. The diagnosis methods are applied to a gas turbine plant with real anomalies. These are investigated in order to highlight possible advantages and disadvantages of the two methods and the benefits that can be reached through their combined application.
Reversible Process Structures as a Base of Sustainable Engineering
Authors: Winkler Wolfgang G. , Williams Mark C.
Published: August 2012

The analysis of exergy losses of a system is a well-known way to determine the influence of the second law on existing systems. Thermo-economics combines this methodology with economic calculations. Using this methodology engineering becomes an evolutionary process. Since system structures are virtual, reversible system structures are possible and inevitable irreversibility is only caused by its real components. They can be described by their exergetic efficiency. Thus reversible system structures can be used as general valid benchmarks for system engineering. It allows easy comparison or a trade-off between possible solutions. The use of a few basic reversible processes allows the building of larger reversible structures including an effective management of released and demanded entropy within the system, as can be shown in different applications and missions. The effective use of renewable sources can be considered as well however bioprocesses are not investigated yet.
Capacitive Readout Technique for Studies of Dissipation in GaN Nanowire Mechanical Resonators
Authors: Montague Joshua R. , Bertness Kris A. , Sanford Norman A. , Bright Victor M. , Rogers Charles T.
Published: August 2012

A variable-temperature homodyne reflectometry measurement technique for detecting nanoscale mechanical motion has recently been developed. We have extended this technique to make the first all-electrical measurements of an ensemble of as-grown, c-axis, single-crystal gallium nitride (GaN) nanowires. These nanowires are approximately 15 μm in length and 100 nm in diameter, and have fundamental resonance frequencies near 1 MHz, and mechanical quality factors, Q, (resonance frequency divided by resonance width) in excess of 104. These high-Q values are sensitive to surface conditions and offer the opportunity to study intrinsic damping mechanisms in the nanoscale resonators. The new microwave measurement technique has allowed us to study the ensemble behavior of nanowire resonances while varying extrinsic variables (e.g., temperature) and obtain statistics on nanowire resonance behavior. Our apparatus allows measurements to be made in either a two-phase lock-in mode, or in a power-spectrum mode, both of which have unique advantages. Our measurements demonstrate a position-spectral noise floor of 0.3 nm/ Hz, largely set by the dynamic range of our microwave readout system.
Effect of Humpback Whale Inspired Tubercles on Marine Tidal Turbine Blades
Authors: Gruber Timothy , Murray Mark M. , Fredriksson David W.
Published: August 2012

The addition of protuberances, inspired by the humpback whale flipper, on the leading edge of lift producing foils has been shown to improve hydrodynamic performance under a certain range of flow conditions. Specifically, finite wing models have displayed delayed stall characteristics at higher angles of attack and increased maximum lift coefficients without significant hydrodynamic penalties. The objective of this project was to investigate the impact that leading edge protuberances (i.e. tubercles) have on the effectiveness of marine tidal turbine blades, especially at lower tidal flow speeds. The experimental results obtained utilizing three different blade designs (baseline and two tubercle modified) are compared. All blades were designed with a 3-D computer aided design software package and manufactured utilizing rapid prototype techniques. The tests were conducted in the 120 ft tow tank at the U.S. Naval Academy using an experimental apparatus that measured flow speed and electrical power generated. Results for power coefficients are presented for a range of tip speed ratios. Cut-in velocity was also used to evaluated the blade designs. For all test criteria, the tubercle modified blades outperformed the smooth leading edge baseline design blades at the lower test velocities, and did not show degraded performance at the higher velocities tested.
Cradle-to-Gate Life Cycle Analysis Comparison of Stamped Aluminum and Injection Molded Polypropylene Vertical Axis Wind Turbine Blades
Authors: Riley Senta , Wentz John E. , Angeli John
Published: August 2012

Wind turbines have seen increasing use over the past decades as an alternative mode of energy production. One specific use of vertical axis wind turbines is for the powering of rural telecommunication towers. In this research a cradle-to-gate life cycle analysis is used to compare three different designs for a stackable, capped, Savonius-style vertical axis wind turbine blade capable of producing from one to three kilowatts. The analysis compares the energy consumed and carbon dioxide emissions from material production and manufacturing of two different aluminum blade designs and a polypropylene design each having the same energy generation capacity. Primary and secondary aluminum materials were included in the analysis. Life cycle inventories from two software programs were used and compared with values gleaned from published literature. The results of the analysis revealed that the least energy and carbon dioxide impact came from using a recycled aluminum design while the most was from manufacturing using primary aluminum.
An Inverse Method for Controlling the Temperature Distribution and Identification of the Conductivity of Thick Cylindrical Shells
Authors: Rastgoftar Hossein , Moslehy Faissal A.
Published: August 2012

The paper presents an inverse method for control of temperature distribution in thick cylindrical shells. Since the thickness is large enough, three-dimensional heat diffusion equations must be considered. To control the temperature distribution, the heat fluxes at the boundary surfaces of the cylindrical shell are assigned values such that the desired temperature distribution, which satisfies the steady state heat conduction equation, will be achieved. Furthermore, a Lyapunov-based method for identification of the conductivity of the cylinder is presented, and the estimated conductivity is updated such that it converges to the exact value. The numerical results are obtained by the finite element method (FEM), which include the heat flux at the surfaces of the cylinder. These results are shown to be in excellent agreement with the analytical solution.
An Examination of the Behavior of Thermodynamic Properties in the Compressed Liquid Region
Authors: Karimi Amir , Manteufel Randall D. , Mulligan Kelly
Published: August 2012

Most thermodynamic textbooks state that the specific volume, specific internal energy, and the entropy of fluids in the compressed liquid region are independent of pressure and vary only with temperatures. Therefore in the compressed liquid region, these properties at given pressures and temperatures are approximated by their saturated liquid properties at the given temperatures. Examination of property values in the compressed liquid region verifies that these assumptions are valid at low temperatures close to the triple point of the fluids. However, the data show that, with increasing temperature, the internal energy and entropy of fluids exhibit higher dependencies on pressure in the compressed liquid region. In a similar fashion, in most applications, it is assumed that the values of constant pressure specific heat (cp) and constant volume specific heat (cv) are approximately the same in the compressed liquid region. Again, examination of these properties in the compressed liquid region validates this assumption for water at low temperatures. However, with increasing temperatures away from the triple point, the deviations between the two specific heat values increase. For fluids other than water the values of cp and cv in the compressed liquid region are not very close, even at temperatures close the triple point. Thermodynamic property behavior of several common fluids in the compressed liquid region is examined in this paper. The paper presents data on the behavior of v, u, h, cp and cv in the compressed liquid region and establishes the range of pressures and temperatures in this region where it is valid to assume that the v, u, h, and s are functions of temperature only and the ranges for which the values of cp and cv can be assumed to be nearly the same.
A Modest Proposal for the Removal of Floating Rubbish From the North Pacific Central Gyre
Authors: Gerlach David W.
Published: August 2012

Floating plastic debris collects in large rotating ocean currents termed gyres. These regions of the Atlantic and Pacific Ocean have been called the “Great Garbage Patches” and received a great deal of sensational reporting in the media. The patches consist of small fragments of debris suspended in the first few meters of water. There have been several proposals and research projects on methods to catch the debris in nets or otherwise remove it from the water. The plastic must then be disposed of. This paper proposes that the captured plastic material can be incinerated on board the vessel to produce heat for driving a Rankine cycle or producing pyrolysis oil for use in a diesel engine. The resulting power could then be used propel the vessel and the waste heat to dry the incoming plastics. The energy budget of the process is analyzed showing that the energy consumed and the plastic fuel value gathered are of the same order of magnitude.
Computational Study of Pulsed Metal-Organic Chemical Vapor Deposition of Aluminum Nitride
Authors: Endres Derek , Mazumder Sandip
Published: August 2012

Particles of aluminum nitride (AlN) have been observed to form during epitaxial growth of AlN films by metal organic chemical vapor deposition (MOCVD). Particle formation is undesirable because particles do not contribute to the film growth, and are detrimental to the hydraulic system of the reactor. It is believed that particle formation is triggered by adducts that are formed when the group-III precursor, namely tri-methyl-aluminum (TMAl), and the group-V precursor, namely ammonia (NH3), come in direct contact in the gas-phase. Thus, one way to eliminate particle formation is to prevent the group-III and the group-V precursors from coming in direct contact at all in the gas-phase. In this article, pulsing of TMAl and NH3 is numerically investigated as a means to reduce AlN particle formation. The investigations are conducted using computational fluid dynamics (CFD) analysis with the inclusion of detailed chemical reaction mechanisms both in the gas-phase and at the surface. The CFD code is first validated for steady-state (non-pulsed) MOCVD of AlN against published data. Subsequently, it is exercised for pulsed MOCVD with various pulse widths, precursor gas flow rates, wafer temperature, and reactor pressure. It is found that in order to significantly reduce particle formation, the group-III and group-V precursors need to be separated by a carrier gas pulse, and the carrier gas pulse should be at least 5–6 times as long as the precursor gas pulses. The studies also reveal that with the same time-averaged precursor gas flow rates as steady injection (non-pulsed) conditions, pulsed MOCVD can result in higher film growth rates because the precursors are incorporated into the film, rather than being wasted as particles. The improvement in growth rate was noted for both horizontal and vertical reactors, and was found to be most pronounced for intermediate wafer temperature and intermediate reactor pressure.
Three-Dimensional Scouring Analysis for Open Channel Pressure Flow Scour Under Flooded Bridge Decks
Authors: Tulimilli Bhaskar Rao , Lottes Steven A. , Majumdar Pradip , Kostic Milivoje
Published: August 2012

A three-dimensional stream bed scour modeling methodology was developed using well-benchmarked commercial Computational Fluid Dynamics (CFD) software to compute the bed shear stress distribution used to calculate bed displacements and to re-mesh the computational domain as the bed is displaced. This study extends a previously developed two-dimensional iterative scouring procedure to predict the final shape and size of the scour-hole under pressure-scour flow conditions for flooded bridge decks using commercial CFD software. The current approach uses single phase flow models with an assumed flat water surface using a symmetric slip top boundary to simulate a free-surface flow condition, quasi-steady simulation to obtain the bed shear, and a moving boundary formulation based on an empirical correlation for critical shear stress to iteratively deform the bed under supercritical shear conditions until an equilibrium scour condition is obtained. The model solves the flow field using Reynolds Averaged Navier-Stokes (RANS) equations and the high Reynolds number k–epsilon turbulence model using the commercial CFD software STAR-CD. A Bash script was developed to use a Python script to compute bed displacements from the computed shear stress distribution and generate a STAR-CD processor command file to displace the bed followed by a step using the STAR-CCM+ software to remesh the domain as the bed is displaced and bed shear distribution is recomputed in an iterative procedure until the equilibrium bed contour is reached. Simulations were performed for different inundation ratios and for mean sand diameters of 1 mm and 2 mm. The model agrees reasonably well with limited experimental data for equilibrium scour shape and size with fully submerged cases compared to the cases where the bridge deck is partially submerged. This developed three-dimensional CFD scour computation procedure provides a basis for testing of additional scour related physical models while also providing an evaluation tool that can be used immediately by engineers engaged in scour risk analysis and assessment.
Drag Factors From Rollover Crash Testing for Crash Reconstructions
Authors: Arndt Mark W. , Arndt Stephen M. , Stevens Donald
Published: August 2012

A study of numerous published rollover tests was conducted by reexamination of the original works, analysis of their data, and centralized compilation of their results. Instances were identified where the original reported results for trip speed were in error, requiring revision because the analysis technique employed extrapolation versus integration and lacked correction for offset errors that develop by placing the Global Positioning System (GPS) antenna away from the vehicle Center of Gravity (CG). An analysis was performed demonstrating revised results. In total, 81 dolly rollover crash tests, 24 naturally occurring rollover crash tests, and 102 reconstructed rollovers were identified. Of the 24 naturally occurring tests, 18 were steer-induced rollover tests. Distributions of the rollover drag factors are presented. The range of drag factors for all examined dolly rollovers was 0.38 g to 0.50 g with the upper and lower 15 percent statistically trimmed. The average drag factor for dolly rollovers was 0.44 g (standard deviation = 0.064) with a reported minimum of 0.31 g and a reported maximum of 0.61 g. After revisions, the range of drag factors for the set of naturally occurring rollovers was 0.39 g to 0.50 g with the upper and lower 15 percent statistically trimmed. The average drag factor for naturally occurring rollovers was 0.44 g (standard deviation = 0.063) with a reported minimum of 0.33 g and a reported maximum of 0.57 g. These results provide a more probable range of the drag factor for use in accident reconstruction compared to the often repeated assertion that rollover drag factors range between 0.4 g and 0.65 g.
Tip-Sample Heat Transfer in Non-Contact Mode Scanning Thermal Microscopy With Wollaston Microprobes
Authors: Zhang Yanliang , Han Liang , Borca-Tasciuc Theodorian
Published: August 2012

Scanning thermal microscopy (SThM) is an attractive tool for high spatial resolution thermal characterization with minimal sample preparation.1 SThM measurements are usually performed in contact-mode, which entails multiple tip-sample heat transfer pathways, i.e. across air gap, liquid meniscus, and the solid contact. These hinder the quantification of the sample temperature or thermal properties or result in large uncertainties.2
Low Cost, Open-Loop Temperature Controller for MEMS and Modular Microfluidics Applications
Authors: Lowrey Brooks B. , Brown Christopher R. , Park Daniel S. , Murphy Michael C.
Published: August 2012

A commercially manufactured thermostat (Model C Thermostat, Portage Electronic Products Inc., North Canton, OH) was employed as a precision MEMS temperature controller for a simulated continuous flow thermal reactor, with three temperature zones to mimic a polymerase chain reaction (CFPCR) device but different temperature set points to allow use of off-the-shelf controllers and thermally-responsive fluids. The ability of the commercial thermostats to maintain the temperatures within given tolerance bands in the thermal reactor was investigated. The factory supplied and calibrated thermostats were actuated by trimetallic strips, and supplied in a normally-closed configuration. Each thermostat was arranged in series with a 28 VDC power supply, a Kapton heater, and an aluminum thermal block to establish a constant temperature boundary condition for each temperature zone. Calibration temperatures for each thermostat reflected the three temperature set points of the simulated PCR device in the testing apparatus. Temperatures were collected by fixing Type K thermocouples in the fluidic channels of the simulated PCR device, and recording the temperature over time. The commercial, off-the-shelf, open-loop controllers successfully maintained ±1°C tolerance bands within each thermal zone. The ±1°C variation in the channel temperature was caused by the chatter due to the switching of the thermostat.
The Impact of GaN/Substrate Thermal Boundary Resistance on a HEMT Device
Authors: Nochetto Horacio C. , Jankowski Nicholas R. , Bar-Cohen Avram
Published: August 2012

The present work uses finite element thermal simulations of Gallium Nitride High Electron Mobility Transistors (GaN HEMTs) to evaluate the impact of device design parameters on the junction temperature. In particular the effects of substrate thickness, substrate thermal conductivity, GaN thickness, and GaN-to-substrate thermal boundary resistance (TBR) on device temperature rise are quantified. In all cases examined, the TBR was a dominant factor in overall device temperature rise. It is shown that a TBR increase can offset any benefits offered through a more conductive substrate and that there exists a substrate thickness independent of TBR which results in a minimum junction temperature. Additionally, the decrease of GaN thickness only provides a thermal benefit at small TBRs. For TBRs on the order of 10−4 cm2K/W or greater, decreasing the GaN thickness can actually increase the temperature as the heat from the highly localized source is not sufficiently spread out before crossing the GaN-substrate boundary. The tradeoff between GaN heat spreading, substrate heat spreading, and temperature rise across the TBR results in a GaN thickness with minimum total temperature rise. For the TBR values of 10−4 cm2K/W and 10−3 cm2K/W these GaN thicknesses are 0.8 μm and 9 μm respectively.
Low Order Finite Element Modeling of Size Effects in Micro Structured Materials Based on Strain Gradient Plasticity
Authors: Park Moon Shik , Suh Yeong Sung , Song Seung
Published: August 2012

A low order finite element method using theory of strain gradient plasticity along with Taylor dislocation model was developed to evaluate size effects occurring in micro structured materials. The gradient is evaluated in the framework of nonlinear incremental analysis where plastic strains are calculated and averaged at nodes then interpolated and differentiated. The proposed method was verified by solving typical size effect problems such as micro-bending, micro-indentation, and tensile test of a particle-reinforced metal matrix composite. The predicted results show clear length scale effect and close proximity to the respective experimental results.
Monte Carlo Study of the Molecular Beam Epitaxy Process for Manufacturing Iron Oxide Nano Scale Films and Similarities With Magnesium Oxide Films
Authors: Uddin Ghulam Moeen , Sun Bing , Ziemer Katherine , Zeid Abe , Kamarthi Sagar
Published: August 2012

Functional properties of thin film metal oxides depend upon their stoichiometric and structural uniformity. Controlling the film deposition process can help tune the functionality of these films by ensuring the control over chemistry and structure of the films. The high volume manufacturing of functional devices will benefit from the development of reliable control models developed from research efforts in designing robust manufacturing processes. The use of neural networks as computer models to simulate the molecular beam epitaxy (MBE) of iron oxide thin films is presented in this work. Monte Carlo experiments are used to study the sensitivities and significances of process control variables to the stoichiometric performance indicators. Moreover, we also explore the relationship between growth dynamics of iron oxide (Fe2O3, Fe3O4, and mixed FexOy) and magnesium oxide (MgO) thin films. The common metal adsorption controlled growth mechanism of two films with different structural and stoichiometric complexities were observed and the similarities among the trends of analogous stoichiometric indicators at comparable metal arrival rates of the two films are presented. The dependence of undesirable bonding states of iron and magnesium metals with the film thicknesses was also observed in both processes. The commonalities suggest the potential to use of neural network assisted Monte Carlo analysis to link common atomic-level mechanisms to processing variables in one nano-scale system and use them to predict some level of behavior in other nanoscale processes with similar atomic-level mechanisms.
Modeling Thermal Mass of a Data Center Validated With Actual Data due to Chiller Failure
Authors: Sundaralingam Vikneshan , Isaacs Steven , Kumar Pramod , Joshi Yogendra
Published: August 2012

The task of minimizing the downtime of a data center is becoming increasingly important due to the necessity of availability and maintaining the integrity of the data being handled by the data center. Consequently, a model used to predict the thermal response of a data center would be useful information in designing mechanisms to minimize the downtime during a failure or to serve as an alternative analysis method other than CFD. This paper will focus on a thermodynamic approach of predicting the thermal response of the data center space with the use of lumped system analysis. The model will be developed and validated using actual data from a chiller failure event in the CEETHERM Data Center Laboratory. Events in sequence are: (i) Chiller failure, (ii) Data center shutdown due to critical temperatures and (iii) Chiller restored. To illustrate, the data center section of interest consists of 10 racks of servers (maximum capacity of 24kW for each rack) with a total of 3360 nodes and is chilled using chilled water from the building chiller, through which the cooling resources are distributed using a rear door heat exchanger and a cooling room air conditioning unit (CRAC). The relevant and important data that was recorded in this failure are the: (1) Server inlet temperatures, (2) CPU temperatures, (3) CRAC supply and return air temperatures, (4) Chiller supply and return water temperature, (5) Chiller flow rate, (6) Data center space temperature and humidity, (7) Server power draw and (8) CRAC fan speeds.
Effect of Supply Air Temperature on Rack Cooling in a High Density Raised Floor Data Center Facility
Authors: Kumar Pramod , Sundaralingam Vikneshan , Joshi Yogendra , Patterson Michael K. , Steinbrecher Robin , Mena Marissa
Published: August 2012

In this paper we experimentally investigate the effect of supply air temperature on rack cooling in a high density raised floor data center facility. A series of experiments are performed on a 42 U (1-U = 4.45 cm) rack populated with 1-U servers. Desired rack heat loads are achieved by managing the distribution of server compute load within the rack. During the present experiments, temperatures at various locations in the hot and cold aisle corresponding to the rack air inlet and outlet are recorded. The temperatures are measured using a grid consisting of 256 thermocouples. The temperature measurements are further complimented with the flow field at the rack inlet. Particle Image Velocimetry (PIV) technique is used to capture the flow field at the rack inlet. The temperature maps in concert with the PIV flow field help in quantifying the rack cooling effectiveness. The temperature and flow measurements are measured for various cases by altering the supply air temperatures and perforated tile flow rates. The results are analyzed and compared with the ASHRARE recommended guidelines to arrive at the optimum supply air temperature. A perceptible change in the temperature and flow distribution is observed for the six cases investigated.
Experimental Investigation on the Use of Photostrictive Optical Actuator for MEMS Devices and Verification With the FEA Modeling Results
Authors: Rahman Mosfequr , Nawaz Masud , Jackson John E.
Published: August 2012

Photostrictive materials are lanthanum-modified lead zirconate titanate (Pb, La)(Zr, Ti) O3 ceramics doped with WO3, called PLZT, exhibit large photostriction under uniform illumination of high-energy light. Photostrictive materials are ferrodielectric ceramics that have a photostrictive effect. Photostriction arises from a superposition of the photovoltaic effect, i.e. the generation of large voltage from the irradiation of light, and the converse-piezoelectric effect, i.e. expansion or contraction under the voltage applied. When non-centrosymmetric materials, such as ferroelectric single crystals or polarized ferroelectric ceramics, are uniformly illuminated, a high voltage, considerably exceeding the band gap energy, is generated. Along with this photovoltage, mechanical strain is also induced due to the converse piezoelectric effect. Photostrictive materials offer the potential for actuators with many advantages over traditional transducing electromechanical actuators made of shape memory alloys and electroceramics (piezoelectric and electrostrictive). Drawback of traditional actuators is that they require hard-wired connections to transmit the control signals which introduce electrical noise into the control signals; on the other hand PLZT actuators offer non-contact actuation, remote control, and immune from electric/magnetic disturbances. Some experimental research has been conducted on the use of PLZT materials, such as optical motor as an electromechanical device suitable for miniaturization, micro-waking machine, photo driven relay device using PLZT bimorphs and high speed (less than 10 ns), low-voltage, low power consumption optical switch. Authors have developed a computational method and implemented in an in-house finite element code which will be useful for designing systems incorporating thin film photostrictive actuators. The purpose of this current research work is to design and develop an experimental test set-up for photostriction effect measurement of PLZT thin film of different thickness, size and location on silicon wafer as smart beams, which may be useful for various MEMS device as optical actuator. The experimental results will be verified by comparing with the FEA modeling results.
Emphasizing Mechanical Feedback in Bio-Inspired Design and Education
Authors: Seipel Justin
Published: August 2012

Mechanical feedback in nature is a useful concept proposed by many researchers in different areas of biological research. The concept, at its core, is simply the idea that many mechanical processes in biology effectively act to assist in the self-stabilization of tasks, and therefore, serve functionally as a first level of feedback control. However, due to a conventional view of the nervous system as the ‘controller’ of the body, it has historically been assumed that the control of tasks does not critically depend on the self-stability properties of the mechanical (musculo-skeletal) system. More recent biological research has provided many examples that show neural feedback alone is not sufficient to control many tasks. This forces us to reframe our conventional view of feedback control in neuro-mechanical systems, and by extension, provide a more appropriate perspective when designing biologically-inspired system architectures. Here two ways of diagraming neuro-mechanical control are compared to understand whether one may be more helpful in framing neuro-mechanical control problems and biologically-inspired system design for engineering practitioners and students. This work, when developed further, is expected to provide new pedagogical frameworks for teaching neuromechanics, motor-control, and biologically-inspired methods of control.
A Variational Principle of Dislocations Kinetic in Crystals and a Toughening Mechanism of BCC or HCP Metals
Authors: Hao Su , Weertman Hans
Published: August 2012

A dislocation kinetics-based analysis has been carried out on the toughening mechanisms of alloys. It is concluded that both improved strength and toughening can be achieved through adjusting the short range interatomic interactions between embedded solute atoms, or other point defects, that affect Peierls-Nabarro energy barrier, and the long range interactions between dislocation loops and heterogeneities such coherent precipitates, second phase particles, and crystallography; the latter determines dislocation loops’ patterns such as kink-jog formation. In order to quantify the effects of lattice heterogeneities, a variation principle that defines the energy minima of dislocation line configuration has been derived, which includes the effects of three-dimensional stress states and crystallography, instead of the conventional line energy-based Eular formulation that only considers the case under shear stress. This provides an analytical means and associated numerical tool to determine the favorite dislocation loop’s patterns in an alloy. The further analysis reveals that double-kinks within single slip-plane have limited effect on toughening while the corresponding bow-out solution may lead to a lower-bound estimate of precipitate strengthening. Therefore, a proposed strategy for toughening is to create dispersed softening centers in strengthened matrix that trap accumulated dislocation loops in the form of mixed double-kinks and jog-induced climbings, for example, helices. These kinds of dislocation patterns are able to spread out localized dislocations from single or close packed parallel slipping planes to many cross-over planes in multiple slip-systems, so as to delay the formation of shear bands while maximize the magnitude of bowing-out induced strengthening.
Effects of Guide Vanes in Transition Flow From a Round Pipe to a Rectangular Chamber
Authors: Lin D. G. , Huynh B. P.
Published: August 2012

In an effort to design a rectangular-box chamber for model testing and flow visualization, to be fitted into an existing horizontal axial-flow pump circuit, shown in Fig.1[1], a computational study has been conducted into the flow of water as it expands from a 400-mm-diameter round pipe into a 3-D-rectangular-box configuration. The geometry is asymmetric; the chamber’s bottom is aligned with the pipe’s bottom, but the pipe’s top is expanded into the chamber’s top, shown in Fig. 2. A commercial Computational Fluid Dynamics (CFD) software package is used to simulate the isothermal turbulent flow, using the standard K-epsilon turbulence model. The study examines the benefits of the guide vane in reducing the transition region’s length and producing the desirable flow pattern in the test chamber.
Design, Construction and Control of a Remotely Operated Vehicle (ROV)
Authors: Marzbanrad Alireza , Sharafi Jalil , Eghtesad Mohammad , Kamali Reza
Published: August 2012

This is report of design, construction and control of “Ariana-I”, an Underwater Remotely Operated Vehicle (ROV), built in Shiraz University Robotic Lab. This ROV is equipped with roll, pitch, heading, and depth sensors which provide sufficient feedback signals to give the system six degrees-of-freedom actuation. Although its center of gravity and center of buoyancy are positioned in such a way that Ariana-I ROV is self-stabilized, but the combinations of sensors and speed controlled drivers provide more stability of the system without the operator involvement. Video vision is provided for the system with Ethernet link to the operation unit. Control commands and sensor feedbacks are transferred on RS485 bus; video signal, water leakage alarm, and battery charging wires are provided on the same multi-core cable. While simple PI controllers would improve the pitch and roll stability of the system, various control schemes can be applied for heading to track different paths. The net weight of ROV out of water is about 130kg with frame dimensions of 130×100×65cm. Ariana-I ROV is designed such that it is possible to be equipped with different tools such as mechanical arms, thanks to microprocessor based control system provided with two directional high speed communication cables for on line vision and operation unit.
Inverse Heat Conduction Errors From Temperature Bias in Thin Film Sensors: Effect of Contact Resistance
Authors: Woodbury Keith A. , Woolley Jonathan W.
Published: August 2012

Thin platinum resistance thermometers (herein called thin film sensors) are often used in applications where rapid measurements of surface temperature are required. These gages are typically vapor deposited onto a non-conducting substrate surface and electrically connected with small wires through access holes to the surface. The time response of the gage is measured in milliseconds and surface temperature data obtained with this gage is often combined with a pseudo-inverse heat conduction algorithm to provide information about the surface heat flux. However, the thermal mass of the connecting wires, though small in absolute terms, is large compared to that of the thin film, and the capacitive effect of this mass gives rise to distortions in the temperature field in the area of the gage, resulting in a small error in the sensed temperature. This temperature error, when used in the inversion for heat flux, also results in an error. In this report, a detailed model of a particular thin film gage is used to compute the response of the sensor to supposed heating conditions. The effect of contact resistance between the parent material and the lead wire connections is investigated. The response of the sensor, with and without the contact resistance, and the undisturbed surface temperature are compared to estimate the temperature error. Finally, the error in the computed heat flux is determined. A simple approximate technique based on superposition is applied to account for the sensor dynamics and correct the error in the estimated heat flux.
Analysis of Periodicity Termination in Phononic Crystals
Authors: Davis Bruce L. , Tomchek Andrew S. , Flores Edgar A. , Liu Liao , Hussein Mahmoud I.
Published: August 2012

While resonant propagation modes are non-existent within band gaps in infinite periodic structures, it is possible for anomalous band-gap resonances to appear in finite periodic structures. We establish two criteria for the characterization of band-gap resonances and propose approaches for their elimination. By considering flexural periodic beams, we show that as the number of unit-cells is increased the vibration response corresponding to band-gap resonances (1) does not shift in frequency, and (2) drops in amplitude. Both these outcomes are not exhibited by regular pass-band resonances, nor by resonances in finite homogenous beams when the length is changed. Our conclusions stem from predictions based on Timoshenko beam theory coupled with matching experimental observations.
Deployment Dynamics of a Small Carbon Fiber Tape-Spring UAV Wing
Authors: Coffin Peter , Marzocca Pier , Jha Ratan , Ahmadi Goodarz
Published: August 2012

Many mechanisms exist for folding and deploying wing surfaces on micro-scale unmanned air vehicles. A rolling tape-spring style wing offers simple construction, small mass, and compact packed volume. Deployment of the wing during flight would be advantageous for autonomous MAV launch, however the deployment process presents potential buckling issues due to the deployment dynamics and aero-structure interaction. In this study a finite element model of an example wing is developed and its deployment dynamics are compared against an experimental model. Additionally, elastic material properties are estimated using model updating, comparing predicted natural frequencies to those measured by a laser vibrometer experimentally. To better evaluate the deployment dynamics of the finite element model, in experiment a vacuum chamber is used to decouple the aero and structural dynamics. The computational results are compared with the experimental finding and good agreement was observed.