bluuebunny/crossref_metadata_2025 huggingface dataset:
Novel Fabrication Technique for 3-Dimensional Electrospun Poly(DL-Lactide-Co-Glycolide) Acid Scaffolds
Authors: Leung Linus H. , Khatounabad Elmira , Naguib Hani E.
Published: May 2012

Current tissue engineering scaffolds created by electrospinning techniques are mostly limited to a 2D membrane. In this study, a novel method to fabricate 3D fibrous scaffolds is presented, and a parametric study to identify the optimal processing parameters was performed. The fabrication technique uses a batch foaming setup to saturate the fibrous scaffolds with CO2 to lower the glass transition temperature of PLGA to allow for the sintering of the fibers. When a mechanical pressure was applied to multiple layers of the thin films in the presence of gas, the layers of PLGA scaffolds sinter to form a thick 3D fibrous structure. This study was divided into three parts. First, the effect of gas saturation on the scaffolds was examined. Three saturation pressures of 200, 300, and 400 psi and multiple saturation times of 1, 3, 5, 30, 60, and 120 minutes were used. At the lowest pressure of 200 psi, the morphology and mechanical properties of the scaffolds were not affected. As saturation pressure and time were increased, the fibers sintered, and eventually the fibrous structure was lost because the polymer was over-sintered. The second part of the study was to determine the adhesion properties of the scaffolds using gas pressure. The same processing pressures and times were used for this set of experiments, and a higher pressure was found to better adhere the layers of PLGA films together. From the first two parts of this study, the optimal combination of processing parameters was determined to be saturating the samples under 400 psi of pressure for three minutes. This set of parameters was then used in the third part of the study to fabricate 3D fibrous scaffolds. The demonstration of this ability to fabricate 3D scaffolds improves on current electrospinning techniques while maintaining a desirable fibrous structure for tissue engineering.
A Numerical Study of Non-Isothermal Peristaltic Flow of Power-Law Fluids in a Circular Tube
Authors: Yun M. S. , Huynh B. P.
Published: May 2012

Non-isothermal peristaltic flow of power-law fluids in a circular tube is investigated numerically, using a commercial Computational Fluid Dynamics (CFD) software package that employs the Finite Volume Method. Simulation is performed over the range of Reynolds-number values from 1 to 100. Temperature effect on the flow field is via fluid viscosity, which is assumed to decrease exponentially with temperature. Also, except for viscosity, other fluid properties are assumed to be constant, and are similar to those of an oil. Over a range of the power-law index covering fluid behaviour from shear-thinning, through Newtonian, to shear-thickening, it is found that allowing for temperature effects has significantly altered the flow pattern and pressure variation, even when the corresponding changes in temperature itself are small. Around the crest region, recirculation appears in non-isothermal flow at all power-law-index and Reynolds-number values considered in this work, in contrast to isothermal situations.
Matched Pair Testing of Injury Potential in Repeatable Rollover Tests With the CRIS and JRS
Authors: Mattos Garrett Anthony , Friedman Donald
Published: May 2012

The availability of repeatable dynamic rollover fixtures, like the Controlled Rollover Impact System (CRIS) and Jordan Rollover System (JRS), has changed the face of rollover structural and occupant protection development and evaluation. Tests performed with these devices have demonstrated scientific principles of occupant protection and injury potential which were previously resolvable only by expert rhetoric. Matched-pair experiments with instrumentation measuring dynamic roof crush and dummy injury metrics are now possible. The effectiveness of occupant protection features such as padding, window curtain airbags, belt pretensioners and headrests are qualitatively and quantitatively measureable. The sensitivity of rollover parameters themselves and their effect on injury potential can be determined by tests with different roll rates, pitch angles, impact angles and drop heights. Simulating injury potential to humans with ultimately biofidelic dummy musculature can also be demonstrated. This paper presents two matched pair test sets performed on the CRIS and two matched pair test sets performed on the JRS. The matched pair test sets performed on the CRIS compare the dummy injury measures in reinforced and production versions of the 1998 Ford Crown Victoria and the 1996 Chevrolet Blazer. The CRIS test of the matched pair Crown Victoria vehicles has been presented previously in a paper by Moffatt et al [1]. The matched pair tests that were performed on the JRS were conducted to study the effect of a reinforced roof on dummy injury measures. These tests, performed on production and reinforced versions of the 1998 Ford Explorer and the 1999 Hyundai Sonata, included the measurements of road loads, roof crush and crush speed, dummy upper and lower neck loads, belt loads, as well as the movement of the vehicle during the test.
Development and Testing of an Actively Adjustable Stiffness Mechanism
Authors: Marquez Eleazar , Freeman Robert A. , Vasquez Horacio
Published: May 2012

This study presents the comparison of the theoretical and experimental results of the performance of an adjustable stiffness mechanism. In particular, the use of redundant actuation is emphasized in the design of a one degree-of-freedom Watt II mechanism capable of independently controlling the effective stiffness without a change in equilibrium position. This approach is in contrast to spring mechanism designs unable to actively control the spring rate independent of deflection, and with potential applications in various types of suspension and assembly systems. Results indicate that two direct drive brush-type direct current motors are required to drive the redundantly actuated mechanism and create a system that behaves as an adjustable stiffness spring.
Effects of Position (or Location) of Non-Centrally Bonded Symmetric Double Lap Joint (or Symmetric Double Doubler Joint) on Bending Vibrations of Composite Mindlin Plates or Panels
Authors: Yuceoglu U. , Gu¨vendik O¨.
Published: May 2012

In the present study, the “Effects of Position (or Location) of Non-Centrally Bonded Symmetric Double Doubler Joint in Composite Mindlin Plates or Panels” are theoretically analyzed and are numerically solved in some detail. The “Plate Adherends” and the upper and lower “Doubler Plates” of the “Bonded Joint System” are considered as dissimilar, orthotropic “Mindlin Plates” joined through the dissimilar upper and lower very thin adhesive layers. The transverse and rotary moments of inertia are included in the analysis. The relatively very thin adhesive layers are assumed to be linearly elastic continua with transverse normal and shear stresses. The “damping effects” in the entire “Bonded Joint System” are neglected. The sets of the dynamic “Mindlin Plate” equations of the “Plate Adherends”, the “Double Doubler Plates” and the thin adhesive layers are combined together with the orthotropic stress resultant-displacement expressions in a “special form”. This system of equations, after some further manipulations, is eventually reduced to a set of the “Governing System of the First Order Ordinary Differential Equations” in terms of the “state vectors” of the problem. Hence, the final set of the aforementioned “Systems of Equations” together with the “Continuity Conditions” and the “Boundary Conditions” facilitate the present solution procedure. This is the “Modified Transfer Matrix Method (MTMM) (with Interpolation Polynomials). The present theoretical analysis and the present method of solution are applied to a typical “Non-Centrally Positioned (or Located) Symmetric Double Lap Joint (or Symmetric Double Doubler Joint) System”. The effects of the location (or position) of the “Bonded Joint System” and also of the relatively “Stiff (or “Hard”) and the relatively “Flexible” (or “Soft”) adhesive properties, on the natural frequencies and mode shapes are considered in some detail. The very interesting mode shapes with their dimensionless natural frequencies are presented for various sets of “Boundary Conditions”. From the numerical results obtained, some important conclusions are drawn for the “Bonded Joint System” studied here.
Visualization of Two-Phase Refrigerant Flow Through an Ice-Maker Evaporator
Authors: Field Brandon S.
Published: May 2012

A transparent evaporator plate has been affixed to a commercial ice-maker refrigeration system and high-speed visualization of the two-phase boiling of the R134a has been made as water is frozen on the top of the plate. The startup transient period of the freeze cycle, characterized by superheated vapor throughout the evaporator, can last up to 10 minutes as the water is pre-cooled, and the freeze cycle follows. The two-phase flow patterns have been observed as distance along the evaporator plate during the freeze cycle, and observations about the liquid phase distribution are made. The refrigerant path is a series of spiral turns, which sets up a flow pattern of the liquid phase gathering along the inner wall of the channel and being dragged by the high speed vapor. This is not an optimal flow pattern for heat transfer because the liquid is not distributed to the top of the channel.
Analysis of Local Entropy Generation via Large Eddy Simulation of Turbulent Flows
Authors: Sheikhi M. Reza H. , Safari Mehdi , Metghalchi Hameed
Published: May 2012

A novel methodology is developed for local entropy generation analysis of turbulent flows using large eddy simulation (LES). The entropy transport equation is introduced in LES. The filtered form of this equation includes the unclosed subgrid scale entropy generation effects. The closure is based on the filtered density function (FDF) methodology, extended to include the transport of entropy. An exact transport equation is derived for the FDF. The unclosed terms in this equation is modeled by considering a system of stochastic differential equations. LES/FDF is employed to simulate a turbulent shear layer involving transport of mass, energy and entropy. The local entropy generation effects are obtained from the FDF and analyzed. It is shown that the dominant contribution to entropy generation in this flow is due to the combined effects of energy transfer by heat interaction and mass diffusion.
Exact Solution of the Plane Flow and Slip Factor in Arbitrary Radial Blade Channels and Extended Design Method for Radial Impellers
Authors: Hetzer Tobias , Epple Philipp , Delgado Antonio
Published: May 2012

Since the one dimensional mean line theory, sometimes complemented with calculations of slip factors and used for design of impellers usually leads to considerable deviations from reality the plane potential theory is used to get a better insight on the flow inside the impeller and to predict characteristic curves. Investigations presented here show that it is possible to calculate the exact solution of the plane flow and slip factor in arbitrary radial blade channels. This can be used in an extended design method for radial impellers which is suggested by the authors.
Application of the PMR Topology Optimization Scheme to Dual Material Structures
Authors: Taggart David G. , Jahns Denis , Nair Arun , Dewhurst Peter
Published: May 2012

An iterative finite element based topology optimization method based on prescribed material redistribution (PMR) has recently been demonstrated to effectively identify optimal topologies for single material structures. Through the application of a family of Beta probability density and cumulative distribution functions, the method provides a gradual transition from a unimodal distribution of uniform intermediate density to a bimodal distribution of void and fully dense regions. In this paper, the PMR method is extended to dual material structures in which the tensile member strength differs from the compressive member strength. Evolution to topologies which satisfy dual material optimality criteria is ensured through the introduction of local fictitious moduli based on the local stress state. For validation, both analytically derived solutions and a numerical dual material truss optimization procedure are applied. The truss optimization procedure is based on an assumed topology for which the optimal joint coordinates and member cross-sectional areas are determined using a quasi-Newton method and fully stressed design conditions. Validation problems considered include a two-bar dual material cantilever, a dual material truss structure subjected to combined loading, and dual material shear loaded frame structures with pre-existing members. For each case, validation is provided by correlating PMR results with results obtained from the dual material truss optimization procedure. It is demonstrated that for all cases considered, the PMR method provides a reliable tool for the identification of minimum weight dual material structures.
Sustainable, Environmentally Clean Energy for Current and Future Generations
Authors: Catlow Fred
Published: May 2012

The paper compares the choices available for electricity production. Different sources are examined from the prospective of effectiveness, controllability, availability, demand, safety, climate change, environmental, social factors, economics and sustainability. This is achieved using existing and projected data. A sample survey is undertaken of different countries, specific installations and their acceptance by their communities. The paper concludes by discussing some of the political arguments and the scientific and social implications and looking at the way ahead for the future.
Differential Dielectric Sensor Model and its Applications for Water and Oil Flow
Authors: Li Hui , Mohan Ram S. , Marrelli Jack D. , Wang Shoubo
Published: May 2012

As a composition measurement tool, Differential Dielectric Sensor (DDS) developed by Chevron, has been investigated by several authors both theoretically and experimentally since 1989. The previous generation of DDS was based on empirical models which are produced time-consuming and labor-intensive. Uncertainty and repeatability are always issues limiting the application of empirical models. If parameters such as sensor geometries or properties of materials are modified in order to improve and/or optimize, the whole development process of the empirical model has to be repeated. In this paper, measurement model of DDS is developed with integrating 2 sub-models: dielectric mixture model and DD sensor model. The dielectric mixture model, taken from literature, outputs the effective dielectric permittivity of a two-component mixture. The development of DD sensor model is the main focus of this paper. Given effective permittivity provided by dielectric mixture model, DD sensor model predicts attenuation and phase shift of the transmission signal from transmitter to receiver. The measurement model is validated by experimental data and good agreement is observed.
X-Ray Particle Tracking of Dense Particle Motion in a Vibration-Excited Granular Bed
Authors: Morgan Timothy B. , Heindel Theodore J.
Published: May 2012

The Brazil nut effect is a phenomenon in which large, dense objects migrate to the top of a bed of granular media when exposed to vibration. An example of this phenomenon is finding Brazil nuts on the top of a can of mixed nuts. The same phenomenon can be observed in almost any granular system, which includes numerous industrial processes. By understanding the Brazil nut effect, knowledge can be gained to create or prevent segregation within desired industrial processes. In this project, the Brazil nut problem is examined through the use of stereoscopic X-ray imaging. The stereoscopic images are analyzed with a particle tracking algorithm to quantify large particle motion in three dimensional space. Particle motion is quantified under a variety of operating conditions to both observe the particle motion and examine the accuracy of the particle tracking algorithm.
Simulation and Experimental Research for Microparticles in Microchannels With Dielectrophoretic Field-Flow Fractionation
Authors: Song Minghao , Sun Hongwei
Published: May 2012

The Dielectrophoretic Field-flow Fractionation (DEP-FFF) is a very promising separation technique for particles and biological molecules. To further explore this technology, we conducted a computational and experimental investigation of a single particle movement in a PDMS microfluidic channel under DEP force, where both electrokinetic effects and particle hydrodynamics are considered. The model was first validated with dipole moment theory, and a polystyrene particle (∼10 μm) behavior in a non-uniform electric field created by a pair of non-symmetrical electrodes was then studied numerically. The simulation results were compared with experimental results and a good agreement was obtained. Further research is underway to study the behavior of non-spherical particles (such as nanowire, nanorod, and nanofiber) in other microfluidic systems.
Drum Cooling System for Concrete Aggregates: FEA Simulation
Authors: Ahmed Khaled I. E. , Hamouda A. M. S. , Gadala M. S.
Published: May 2012

Using hot aggregates, in concrete production, results in a drop in compressive strength of the produced concrete. Various methods have been proposed for cooling concrete aggregates. This paper proposes a modified design for a cooling drum to be used in this regard. Preliminary simulation of the heat flow during the cooling process in the drum is analyzed with the objective of optimizing the design and achieving minimum cooling time with the least possible power. A finite element model for the new design is proposed and discussed. Challenges facing numerical simulation are addressed in this paper. The results of the finite element analysis of the modified design are presented and compared with the original design.
Push-Button Discrete Event Simulation for Analysis of Factory Floor Operations
Authors: Michaloski J. , Raverdy B. , Lee B. E. , Proctor F. , Venkatesh S. , Bengtsson N. , Skoogh A.
Published: May 2012

In manufacturing, Discrete Event Simulation (DES) can be effectively used to model production and provide sustainability analysis of equipment and system operation by measuring throughput, capacity, and bottlenecks. DES allows analysis under different scenarios and conditions that can then be used to forecast more optimal system performance. For discrete parts production, DES is rarely used because of the difficulty in attaining timely and accurate statistical modeling of the equipment and process operation. In this paper we look at the use of the plant floor interoperability standard, MTConnect, as a means to improve the access to machine tool data. Given data access, we develop a Finite State Model in order to streamline Machine Tool and DES integration. A case study of a prototype Capacity Planning system using DES as a modeling back-end will be described to help in understanding resource allocation of shop floor machines to a batch of aerospace parts. Direct machine tool statistical parameterization into a Web-based DES leads to “Push-button” automated simulations.
Campus Assessment of Building Heating Energy Consumption: Informing the Climate Action Plan
Authors: Grover-Silva E. , McKahn D. A. , Weisbord D.
Published: May 2012

We present a methodology to assess the technical feasibility of building thermal energy reduction strategies from an architecturally diverse building stock that is not metered. While carbon emissions forecasting efforts are typically the domain of planning and policy, the process detailed here can inform institutional decision-making relative to investments in renewable energy, infrastructure, and offsets to further reduce carbon footprint. As a case study, we estimated the Smith College campus building thermal energy losses, an analysis which informed our Sustainability and Climate Action Plan [1]. Due to building specific physical constraints and planned renovations, different thermal envelope improvement scenarios were then considered to estimate the heating energy reduction potential of these envelope improvements. The current total heating energy consumption from 79 of our campus buildings was found to be 57,000 MMBTU/yr. Across the three building categories with minimal existing insulation and poor sealing conditions, the nominal annual thermal energy loss per square foot ranged from 27,000–37,000 BTU/ft2. Should envelope improvements be made targeting a 5 year simple payback, this annual thermal energy loss would be reduced by 40% to 34,000 MMBTU/yr. More extensive and less cost effective envelope improvements suggest further energy reductions approaching 30,000 MMBTU/yr (between 13,000–23,000 BTU/ft2/yr depending upon the building type).
Switchability and Bifurcation of Motions in a Double-Excited Fermi-Acceleration Oscillator
Authors: Luo Albert C. J. , Guo Yu
Published: May 2012

In this paper, switchability and bifurcation of motions in a double excited Fermi acceleration oscillator is discussed using the theory of discontinuous dynamical systems. The analytical conditions for motion switching in such a Fermi-oscillator are presented. Bifurcation scenario for periodic and chaotic motions is presented, and the analytical predictions of periodic motions are presented. Finally, periodic and chaotic motions in such an oscillator are illustrated.
Parametric Study of Thermal and Electrical Behavior of 3-D CNT Thin Film Networks
Authors: Ashtekar Nikhil A. , Jack David A.
Published: May 2012

Thin films composed of single-walled carbon nanotubes (SWCNTs) have been proposed as a possible multifunctional material for aerospace applications, but before these materials can experience industrial acceptance the underlying mechanisms dictating their performance must be understood. Physics-based computational tools must be developed that allow studies in the final part performance, to aid in industrial acceptance. This works presents a full 3D computational modeling approach to study the electrical and thermal behavior of a neat CNT network. The model is based on physics based stochastic distributions for the SWCNT length, diameter, and chirality, SWCNT orientation in a network, and the separation distance between two adjacent overlapping tubes. Previous models did not allow for the physically relevant distributions for nanotube geometry to serve as inputs, and results presented in the present work indicate the sensitivity of the bulk network conductivity to small deviations in the stochastic inputs. The uniqueness of this model lies in its three dimensional nature as previous attempts to predict the behavior of SWCNT thin films assume the film to be a 2D network of CNTs and results show that this is insufficient to accurately predict the thermal and electrical conductive properties. The 3D model is validated against experimental results available in the literature, and comparisons are made between the 3D and 2D network models.
The Synchronization of a Periodically Driven Pendulum With Periodic Motions in a Periodically Forced, Damped Duffing Oscillator
Authors: Luo Albert C. J. , Min Fuhong
Published: May 2012

In this paper, the analytical conditions for the controlled pendulum synchronizing with periodic motions in Duffing oscillator is developed through the theory of discontinuous dynamical systems. The conditions for the synchronization invariant domain are obtained, and the partial and full synchronizations are illustrated for the analytical conditions.
Distributed and Centralized H∞ Control of Large Segmented Telescopes
Authors: Ulutas Baris , Suleman Afzal , Park Edward J.
Published: May 2012

Next generation telescopes are to employ segmented mirrors to realize extremely large primary mirror surfaces. Most of the current ground-based telescopes has monolithic mirrors with radius upto 8 metres. Due to limitations segmentation is preferred for larger size mirrors. Segmentation of mirrors brings a challenging task of controlling the vast number of individual units. In this paper, the H∞ control of the primary mirror of the next generation telescopes are investigated. Both spatially-invariant distributed and centralized controllers are designed for simplified dynamic model of a 37 segment test unit. Firstly, the 37 segment system is modelled by adopting a nodal model. Secondly, an analytic calculation of a H∞ controller is presented. A centralized H∞ controller is, then, designed and simulated in MatLab-Simulink environment. Next, the simulation results are presented and the performance of the controller is evaluated. Thirdly, spatially-invariant distributed controller synthesis is described and a spatially-invariant distributed controller is designed for 37 segment system by controller truncation. The spatially-invariant distributed controller is simulated for the 37 segment system. The simulation results of the controller is presented and compared with the results from centralized scheme. It is shown that both centralized and spatially-invariant distributed controllers satisfy the imaging performance requirements.
A Resonant Air-Standard Heat Engine
Authors: Richards C. , Richards R. , Bardaweel H. , Anderson M.
Published: May 2012

A resonant heat engine in which the piston assembly is replaced by a sealed elastic cavity is modeled and analyzed. A linearized nondimensional lumped-parameter model is derived and used to investigate the factors that control the performance of the engine. The results show that operation at resonance is beneficial. Local maxima in efficiency are encountered at odd multiples of the resonance frequency. Efficiency is enhanced by small damping.
Light Hydrocarbon Emissions From Diesel Low Temperature Combustion
Authors: Xie Kelvin , Han Xiaoye , Reader Graham T. , Wang Meiping , Zheng Ming
Published: May 2012

A modern common-rail diesel engine was used to investigate hydrocarbon emissions under low temperature diesel combustion conditions. In this work, various EGR ratios and fuel mixing strategies were applied under a series of fixed-load conditions to progressively lower the flame temperature, which is verified by progressively reduced NOx emission. During the tests, the concentrations of total hydrocarbons, representative light hydrocarbon species (methane, acetylene, and ethylene), and hydrogen gas were measured with a set of emission analyzers, FTIR, and H2 mass-spectrometer. The trend for light hydrocarbon emissions was identified to be a function of both load and EGR ratio. Hydrogen gas can be emitted in significant quantities with the application of very high EGR. Under ultra-low NOx production conditions for medium and high load conditions, the light hydrocarbon species can account for the majority of hydrocarbon emissions.
Applying Hypoidal Gearmotors in High Cycling Queue Conveyors
Authors: Asai Jun , Robinson Robbie
Published: May 2012

The demands from Airport Baggage Handling Systems continue to expand, seemingly demanding more (faster and more security checks) with less (less people and less energy). Increased airport security drives the need for more baggage inspection points. This in turn drives the need for more automation with the benefit of fewer people screened for secured areas. In addition, airlines and airports are placing more attention to reducing carbon footprint by investigating areas for improving efficiency, but within the overall scope of reliability and flexibility. One area in this investigation is the Queue Conveyor that “meter” (space bags evenly) or “queue” (hold and release) baggage to the next station. These belt conveyors differ from normal belt conveyors due to high start/stop cycling required that can reach 1 cycle per second. Belt conveyors in Airport Baggage Handling Systems typically in the past involved helical bevel right angle or multi-stage helical mechanical speed reducers. And for high cycling start/stop applications, these are fitted with a clutch/brake assembly between the motor and mechanical speed reducer. Newer approaches involving hypoidal gearmotors operated with an AC Speed Drives (often referred to as Variable Frequency Drives or VFDs for short) are being investigated. The hypoidal gearmotor is a more compact package than the existing designs—integrating a mechanical speed reducer with a motor. This new, compact form factor driven with a VFD seems to provide more throughputs with less mechanical elements and less energy usage. This paper will review the advantages and disadvantages of the hypoidal gearmotor method in the Queue Conveyor, supported with simulated test methodology and results. Particular focus of the test will include durability, energy savings potential, and applicability of AGMA service factor in gearmotor selection. Durability will focus on the mechanical components in the high cycle application as well as the thermal capacity of the motor.
Numerical Simulation of Die Swell of Second-Order Fluids Using Smoothed Particle Hydrodynamics
Authors: Sadek Samir Hassan , Yildiz Mehmet
Published: May 2012

This work presents the development of both weakly compressible and incompressible Smoothed Particle Hydrodynamics (SPH) models for simulating two-dimensional transient viscoelastic free surface flow which has extensive applications in polymer processing industries. As an illustration with industrial significance, we have chosen to model the extrudate swell of a second-order polymeric fluid. The extrudate or die swell is a phenomenon that takes place during the extrusion of polymeric fluids. When a polymeric fluid is forced through a die to give a polymer its desired shape, due to its viscoelastic non-Newtonian nature, it shows a tendency to swell or contract at the die exit depending on its rheological parameters. The die swell phenomenon is a typical example of a free surface problem where the free surface is formed at the die exit after the polymeric fluid has been extruded. The swelling process leads to an undesired increase in the dimensions of the extrudate. To be able to obtain a near-net shape product, the flow in the extrusion process should be well-understood to shed some light on the important process parameters behind the swelling phenomenon. To this end, a systematic study has been carried out to compare constitutive models proposed in literature for second-order fluids in terms of their ability to capture the physics behind the swelling phenomenon. The effect of various process and rheological parameters on the die swell such as the extrusion velocity, normal stress coefficients, and Reynolds and Deborah numbers have also been investigated. The models developed here can predict both swelling and contraction of the extrudate successfully. The die swell problem was solved for a wide range of Deborah numbers and for two different Re numbers. The numerical model was validated through the solution of fully developed Newtonian and Non-Newtonian viscoelastic flows in a two-dimensional channel, and the results of these two benchmark problems were compared with analytic solutions, and good agreements were obtained.
A Nonlinear Model of a Slack Cable With Bending Stiffness and Moving Ends With Application to Elevator Traveling and Compensation Cables
Authors: Zhu W. D. , Ren H. , Xiao C.
Published: May 2012

A nonlinear, planar model of a slack cable with bending stiffness and arbitrarily moving ends is developed. The model uses the slope angle of the centroid line of the cable to describe the motion of the cable, and the resulting integro-partial differential equation with constraints is derived using Hamilton’s principle. A new method is developed to obtain the spatially discretized equations, and the Baumgarte stabilization procedure is used to solve the resulting differential-algebraic equations. The model can be used to calculate the equilibria and corresponding free vibration characteristics of the cable, as well as the dynamic response of the cable under arbitrarily moving ends. The results for an equilibrium and free vibration characteristics around the equilibrium are experimentally validated on a laboratory steel band. The methodology is applied to elevator traveling and compensation cables. It is found that a vertical motion of the car can introduce a horizontal vibration of a traveling or compensation cable. The results presented are verified by a commercial finite element software. The current method is shown to be more efficient than the finite element method as it uses a much smaller number of elements to reach the same accuracy. Some other interesting features include the condition for a traveling or compensation cable equilibrium to be closest to a natural loop and a direct proof that the catenary solution is unique.
Electrospun Electroactive Polymer and Metal Oxide Nanofibers for Chemical Sensor Applications
Authors: Flueckiger Jonas , Ko Frank K. , Cheung Karen C.
Published: May 2012

We present the fabrication of a polymer blend PANi/PEO nanofiber based sensor as well as a metal oxide TiO2 nanofiber based sensor. Electrospinning was used for the fabrication of the electroactive nanofibers. The conductivity of those fibers is highly sensitive to the chemical environment and is modified through the adsorption of different species. Used as a chemiresistor the nanofibers offer a higher sensitivity than thin films due to the increased surface to volume ratio. Impedance spectroscopy was used for electrical characterization of the fibers showing high sensitivity. Preliminary measurements of the sensors dynamic response when exposed to alternating chemical environments showed fast response times and good signal stability.
Computer-Aided Design of Planar Parallel Robots for Optimal Workspace and Dexterity
Authors: Huang Ming Z.
Published: May 2012

Parallel robots exhibit salient merits over their serial counterparts in applications where both accuracy and dynamic response are required. However, due to the strong dependence of geometric parameters and their performances, the corresponding design problems for the parallel robots are much more complex and the adequacy and effectiveness of the design method become more critical. In this paper, a study in the design optimization for a class of planar parallel robots is presented. The robots feature an in-parallel structure with two degrees of freedom. Dimension synthesis is performed through maximization of two key performance characteristics, addressing not only workspace but also dexterity of the robots under consideration. Optimal designs are attained using both parametric study and simplex algorithm. Results are shown by way of computer simulations aided with graphic visualizations.
Modeling of Micro Welding Process Using Electron Beam Under High Peclet Number
Authors: Gajapathi Satya S. , Mitra Sushanta K. , Mendez Patricio F.
Published: May 2012

The prospect of micro/nano technology requires the development of advanced production processes which joins them into complex systems to interact with the macro world. This has led to the evolution of micro welding. During the micro welding process, the flow of heat needs to be checked so that the essential mechanical and electrical properties of the material are not lost. Also, the amount of melting and excess evaporation has to be controlled. These can be attained by welding using localized heat sources. In the present work, electron beam micro welding process is studied and heat transfer analysis has been carried out numerically, to obtain the temperature distribution in the material. For a specified depth of melting, the effect of Peclet number on the welding process is investigated. The study shows that the high Peclet number electron beam micro welding process provides two important advantages — Control of the maximum temperature on the surface which prevents excess material loss, and limited heat transfer under the beam.
The Study of Combined Electroosmotic and Pressure Driven Flow in Wavy Nanochannels
Authors: Gunda Naga Siva Kumar , Chakraborty Suman , Mitra Sushanta Kumar
Published: May 2012

Solid surfaces of micro/nanochannels exhibit a certain degree of roughness that is incurred during fabrication and/or adsorption of macromolecules. The presence of such roughness changes the flow pattern in electroosmotic flows (EOF). The present study investigates the effect of surface waviness on combined EOF and pressure driven flow (PDF) of an electrolyte solution, in a nanochannel having charged walls. The surface profile of the top and bottom walls vary either in a varicose or in a sinuous mode. The problem is solved by using the Perturbation model, a modified linearized disturbance Navier-Stokes equations, by assuming two-dimensional combined EOF and PDF between two parallel plates as base flow. By discretizing the linearized disturbance equations using the Chebyshev collocation method in the wall normal direction and Fourier transformation in the flow direction, the perturbed velocity components are calculated. The effects of electric double layer (EDL) and amplitude of wavy surface on the flow pattern are studied. The effects of overlapped EDL are also studied as one of the limiting case. The formation of circulation regions is observed in the varicose mode channel when the EOF and PDF are flowing in the opposite direction. The decrease in the number of circulation regions is ob served for the decrease in the value of average half height of the channel to debye length ratio (κ). Serpentine or triangular type waviness in the streamline velocity is observed in sinuous mode type channel when the EOF and PDF are in opposite directions. The increase in the waviness of the streamline velocity is observed for decrease in the value of κ and increase in the amplitude a when both EOF and PDF are flowing in the same direction.
Using Team-Based Learning to Improve Learning and the Student Experience in a Mechanical Design Course
Authors: Ostafichuk Peter M. , Van der Loos H. F. Machiel , Sibley James
Published: May 2012

In 2008, a design course on mechanical components (MECH 325) at the University of British Columbia was converted from a conventional lecture-based format to a team-based learning (TBL) format. The MECH 325 course is content-rich and covers the characteristics, uses, selection, and sizing of common mechanical components (including gears, flexible drives, bearings, and so on). With the shift in course format to TBL, student performance on exams as well as responses to teaching evaluations and course surveys all indicate an improvement in the students’ perception of the course and student learning. Specifically, performance on multiple choice exam questions from different years (remaining similar in both style and difficulty) increased by 17%. Likewise, on official University teaching evaluations over a five-year period, students rated the TBL version of the course as having a reduced workload, seeming less advanced, seeming more relevant, and being more interesting. On informal course surveys, 76% of students on average indicated they felt the various elements of TBL were effective towards the course aims. Finally, from instructor observations, the shift to TBL has resulted in increased student engagement and collaboration, and an increased emphasis on higher-level learning, such as application, synthesis, and judgment.
Effect of Compression on the Effective Thermal Conductivity and Thermal Contact Resistance in PEM Fuel Cell Gas Diffusion Layers
Authors: Sadeghi Ehsan , Djilali Ned , Bahrami Majid
Published: May 2012

Heat transfer through the gas diffusion layer (GDL) of a PEM fuel cell is a key process in the design and operation a PEM fuel cell. The analysis of this process requires determination of the effective thermal conductivity as well as the thermal contact resistance between the GDL and adjacent surfaces/layers. In the present study, a guarded-hot-plate apparatus has been designed and built to measure the effective thermal conductivity and thermal contact resistance in GDLs under vacuum and atmospheric pressure. Toray carbon papers with the porosity of 78% and different thicknesses are used in the experiments under a wide range of compressive loads. Moreover, novel analytical models are developed for the effective thermal conductivity and thermal contact resistance and compared against the present experimental data. Results show good agreements between the experimental data and the analytical models. It is observed that the thermal contact resistance is the dominant component of the total thermal resistance and neglecting this phenomenon may result in enormous errors.
Determining Flow Mixing Characteristics in Low Reynolds Numbers Micro Wavy Channels by the Lattice-Boltzmann Method
Authors: Guzma´n Amador M. , Quezada Mari´a Gabriela , Sanhueza Luis E. , Di´az Andre´s J.
Published: May 2012

The Eulerian and Lagrangian flow mixing characteristics in a two-dimensional (2D) micro wavy channels for low Reynolds number have been investigated using the Lattice-Boltzmann method (LBM) for solving the governing Boltzmann Transport Equation (BTE). Numerical simulations of a Newtonian compressible flow for Reynolds number flow regimes lower than Re = 0.505 are performed using a computational model of a symmetric wavy channel with many cavities and a geometrical aspect ratio of r = a/(2L) = 0.375, where a is the amplitude of the sinusoidal wall, and L is the cavity periodic length. The Eulerian flow characteristics are determined for different Knudsen numbers with the objective of characterizing time dependent velocity and flow patterns. Then, the Lagrangian characteristics are obtained by integrating the Eulerian velocity field. Thousands of massless fluid particles are used for determining fluid particle Lagrangian trajectories, stretching fields and Lagrangian Lyapunov exponents associated to possible evidences of flow mixing enhancement in different regions of the micro channel. The numerical results demonstrate that low Reynolds number compressible flows in micro wavy channels develop Lagrangian characteristics and stretching field that can lead later to flow mixing enhancement characteristics in an electroosmotic flow in microchannels with wavy, grooved and/or any other surface pattering on the channels walls.
An Evaluation of a Modified Iosipescu Specimen for Measurement of Elastic-Plastic Properties of Solder Materials
Authors: Mukherjee Subhasis , Dasgupta Abhijit
Published: May 2012

There are various specimen configurations available in the literature for characterizing the mechanical behavior of solder interconnect materials. An ideal test specimen should use a simple geometry which produces a reasonably uniform material response throughout the gage zone and minimizes the complexity of data reduction to extract material model constants. In the thermo-mechanical micro scale (TMM) test used in this study, we use a simple, notched shear specimen, based on a concept originally proposed by Iosipescu [1967] [1], which produces a reasonably uniform shear stress field throughout the solder joint [Reinikainen et al., 1998] [2]. Our modified Iosipescu specimen comprises of two oxygen free, high conductivity (OFHC) copper platens soldered together and loaded in simple shear, as in a lap-shear specimen. The solder joint in this specimen is only 180 microns wide to capture the length scale effects of functional solder interconnects. This study examines the effects of dimensional variabilities of this modified Iosipescu test setup on the shear stress and strain distributions in the solder specimen. Variabilities encountered in these specimens include: (i) fillets at the V-notches, caused by excess solder; (ii) offset between the two copper platens along the loading direction; (iii) taper of the solder joint due to lack of parallelism of the edges of the copper platens; and (iv) misalignment between the specimen centerline and loading axis of the TMM test frame due to mounting variability. Detailed parametric studies of these four dimensional variations in the TMM specimen are conducted using a simple two-dimensional elastic-plastic finite element model. The uniformity of the shear stress field in the specimen is investigated and the variation in the extracted stress-strain curves is examined, as a function of the dimensional variabilities described above.
Application of an Optically Induced Electrokinetic Manipulation Technique on Live Bacteria
Authors: Kwon Jae-Sung , Ravindranath Sandeep , Kumar Aloke , Irudayaraj Joseph , Wereley Steven T.
Published: May 2012

In this paper, we apply a recently demonstrated rapid electrokinetic patterning (REP) technique to Shewanella oneidensis MR-1 and confirm the application possibility of the technique on bio-materials. This technique utilizes a simple microfluidic chip with two indium tin oxide (ITO) coated parallel electrodes and requires the simultaneous application of AC electric field and the hologram provided from an infrared (1064 nm) laser, in order to control and aggregate particles onto electrodes. For the experimentation in this paper, Shewanella oneidensis MR-1 are cultured by green fluorescent protein (GFP) on Luria-Bertani (LB) agar plate and through sample pretreatment process, mid-log phase samples of the bacteria finally are obtained. As a result of applying REP technique to this bacteria sample, we could collect a lot of the bacteria onto ITO electrode surfaces rapidly and the bacteria cluster could be translated with the movement of laser focus position under uniform electric field. Also it was confirmed that there exists a particular frequency range, i.e. critical frequency for REP based bacteria cluster. We could find that under the application of REP technique, the ellipsoidal bacteria are reoriented with respect to electric field lines as electrical frequency increases up. Also the change in the vertical distance between the bacteria and the electrode surface with electrical voltages could be observed. These results show that the REP technique can be used to separate, sort and manipulate bioparticles like bacteria.
Investigation of Carbon Nanofibers (CNFs) Effects on the Flexural and Thermal Behavior of E-Glass/Polyester Composites
Authors: Hossain Muhammad E. , Hossain Mohammad K. , Hosur Mahesh V. , Jeelani Shaik
Published: May 2012

Properties of polymeric composites can be enhanced tailoring with nanomaterials such as CNFs, CNTs, nanoclay etc. A high intensity ultrasonic liquid processor was used to infuse CNFs into the polyester matrix which was then mixed with catalyst using a high speed mechanical agitator. Both conventional and nanophased GRPC were fabricated by VARTM. Flexure tests were performed on the conventional, 0.1%, 0.2%, 0.3%, and 0.4 wt.% CNF-filled GRPC. The results showed 49% and 31% increase in the flexural strength and modulus, respectively, with increasing loading percentage of CNFs up to 0.2%. DMA showed 92% increase in the storage modulus, and slight increase in the Tg in the nanophased GRPC, respectively, as compared to the conventional GRPC. TGA exhibited insignificant effect of CNFs in the decomposition temperature. TMA showed less CTE in the nanophased GRPC. SEM evaluations revealed relatively less damage in fractured surfaces of the nanophased GRPC.
Performance Comparison of Frame Structures: Discrete Michell or Wolff?
Authors: Gholamirad Maryam , Epstein Marcelo
Published: May 2012

The presented work highlights parallels between natural and human designs for optimization purposes. Wolff’s law predicts that bone trabeculae orientation alterations within a dynamic environment occur in such a way as to use bone material in a structurally efficient manner; this occurs because trabeculae orientations align themselves along principal stress trajectories. Michell has also demonstrated how to optimize structures under a given a set of mechanical loads. Some researchers have recently defined a special case for optimal tensegrity structures that produces the discrete Michell truss. In this paper we have carried out a performance comparison between two different frame structures modeled based on the Wolff’s hypothesis and optimal tensegrity formulation.