bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Projectile Caliber and Speed on Bacterial Distribution in a Leg Surrogate
Authors: Krebsbach Meaghen A. , Muci-Ku¨chler Karim H. , Hinz Brandon J.
Published: May 2012

This paper examines the relationship between ballistic factors and bacterial distribution along a surrogate wound channel using ballistic gelatin cylinders with dimensions representative of the calf region of an average human leg. The ballistics factors considered were projectile caliber and speed, and Escherichia coli (E. coli) was used as the representative bacteria. In order to reduce the possibility of contamination by outside bacteria, the E. coli first underwent a transformation protocol to express Green Fluorescent Protein (GFP) and become resistant to the antibiotic ampicillin. A set volume of bacteria was pipetted onto a small piece of filter paper which was placed on the surface of a ballistic gelatin cylinder and a projectile was shot through the bacteria saturated filter paper. The ‘wound track’ was divided into slices, and the area surrounding the permanent cavity was removed with a biopsy punch, liquefied, and grown on selective LB media containing ampicillin. Examination of the bacterial colony count along the permanent cavity segments allowed comparison of how variations in projectile caliber and speed affected contamination distribution along the ‘wound track’. Initial results indicate that larger calibers may result in higher contamination distribution at the projectile entrance and exit regions and higher speeds compress the distribution and result in a drop in contamination level near the exit.
The Unsteady Fluid Dynamics of a Pair of Pitching Airfoils Using Computational Fluid Dynamics
Authors: Amiralaei M. R. , Alighanbari H. , Hashemi S. M.
Published: May 2012

The objective of the present study is to investigate the low Reynolds number (LRN) fluid dynamics of two airfoils in pitching oscillations. The airfoils are in a tandem configuration and perform in-phase oscillations. Navier-Stokes (NS) equations with Finite Volume Method (FVM) are used and the instantaneous aerodynamic force coefficients are analyzed. The effect of amplitude of pitching oscillations and Re are investigated on the fluid forces. It is found that the amplitude of pitching oscillations is of primary importance to the fluid forces, affecting them quantitatively and qualitatively. Re is found to be of secondary importance compared to the effects of the amplitude of pitching oscillations. It mainly affects the magnitude of the forces.
Experimental Investigation of Wetted Zone Due an Impinging Circular Water Jet on a Moving Surface
Authors: Seraj M. M. , Gadala M. S.
Published: May 2012

Cooling liquid jet impingement has many industrial applications such as metal manufacturing where the shape and the size of wetting area around impingement point is important in heat transfer analysis. A series of experiments on a moving surface with an impinging industrial-scale circular water jet is conducted to explore experimentally the wetting region and the hydraulic jump as the front of wetted zone. The effects of surface motion on the wetting zone and the formation and location of hydraulic jump upstream the impingement point is examined by changing systematically the surface velocity and the jet flow rates. The surface motion impacted the radial evolution of wetted zone in all direction and decreased the radius of non-circular hydraulic jump. However, higher jet flow rate suppressed its effect. Both surface velocity and jet velocity or their velocity ratio has to be considered in adjusting jet space along a jet-line in industrial cooling application.
A Parametric Study of a Three Dimensional Pitching Wing Aerodynamics
Authors: Amiralaei M. R. , Alighanbari H.
Published: May 2012

An experimental investigation is conducted to examine the effects of the amplitude of pitching oscillations and mean angle of attack on the aerodynamic behavior of a three-dimensional pitching blade. A 2D numerical simulation is also conducted based on the Unsteady Reynolds Averaged Navier-Stokes (URANS) equations and Finite Volume Method (FVM) and the results are compared with those of the experimental observations. The experimental results show that the investigated parameters affect the peaks of the lift coefficients. The hyteresis loops in the lift coefficient versus the angle of attack curves are also influenced by the variation of these parameters. However, the lift curve slopes are almost unchanged. The onset of flow separation is also dependent on the amplitude of pitching oscillations and the mean angle of attack.
Minor Losses in Rectangular Xurographic Microchannels
Authors: Torgerson Daniel , Kolekar Rahul , Gale Bruce , Ameel Tim
Published: May 2012

Xurography is a novel manufacturing process for microfluidic systems, providing rapid prototyping capability at low cost compared to traditional microfabrication technologies. An experimental study of flow characteristics in rectangular xurographic microchannels is reported. Mean microchannel depth, defined by the thickness of the double-sided adhesive kapton tape that forms the channel pattern, is 105–110 μm. The microchannels are capped with glass and mechanically reinforced to withstand the high operating pressures that accompany high Reynolds number Re flow (250–3500). Channel aspect ratios range from 0.45 to 0.074. Width and length measurements are performed using optical microscopy. Microchannel height is measured using a unique nondestructive laser interferometry technique, capable of accurate measurement of the enclosed, compressed microchannels. Data are reported for friction factor, critical Reynolds number, and minor losses in expansions, contractions, and 90° miter bends. Expansion and contraction area ratios are 2, 3, and 5. The experimental Poissuille number in laminar flow for all aspect ratios is in good agreement with theoretical values. Critical Reynolds number ranges from 1800 to 2300, and is found to be dependent on channel defects, such as adhesive droplets and edge imperfections, inherent to xurography. Expansion and contraction losses decrease gradually with increasing Re in the range 250–4000 and increase for decreasing area ratio. Loss coefficients in the 90° miter bends increase with modified aspect ratio and are nearly invariant for 1200 < Re < 2100. Loss coefficients increase nearly linearly with Re for Re < 1200 and decrease significantly for Re greater than the critical Reynolds number.
Vibration Response of Functionally Graded Rotating Disk With a Circumferential Crack
Authors: Liu Rui , Nayeb-Hashemi Hamid
Published: May 2012

In this study, the vibration characteristics of a functionally graded rotating hollow disk with the circumferential surface crack are investigated. In order to simplify the problem, the circumferential crack of the rotating hollow disk is modeled as circumferential step indentation. The Galerkin Method is used to obtain the radial and hoop stresses for disks with clamped edge at the inner radius. Finite Difference scheme is adopted to solve the partial differential equation of motion of the rotating hollow disk to obtain the mode shapes and the Campbell Diagram. The first critical speed, which is one of the important parameters limiting the performance of the rotating disk, was obtained from the Campbell Diagram. The results show that the crack will reduce the stiffness and the critical speed of the rotating disk. Critical speed increases with decreasing the distance from inner radius to the crack and decreases with increasing crack depth. Furthermore, considering the functionally graded disk, the distribution of elastic modulus does not change significantly the effects of circumferential cracks on the vibration characteristics of the rotating.
MRI-Based Three Dimensional Modeling of Blast Traumatic Brain Injury (bTBI)
Authors: Ganpule Shailesh , Gu Linxia , Chandra Namas
Published: May 2012

Blast induced traumatic brain injury (bTBI) is signature injury in recent combat scenarios involving improvised explosive devices (IEDs). The exact mechanisms of bTBI are still unclear and protective role of helmet and body armor is often questioned [1–3]. High Fidelity finite element models involving fluid structure interaction are built in order to understand effectiveness of helmet in mitigating early time blast induced mild traumatic brain injury.
Enhanced Low-Pressure Pneumatic Conveyance Using Swirl
Authors: Escandon Rodrigo , Manteufel Randall D. , Su Q. Ken
Published: May 2012

Two designs for swirl amplification have been considered for pneumatic conveyance in vertical pipes. Both designs have been experimentally evaluated in order to predict their capability. The designs have been compared to other methods of amplification or swirl generation. The motivation for the swirl in pneumatic conveyance is to minimize axial velocity by using multiple swirl amplifications to enhance the transportation for long distances. In this experimental evaluation two swirl amplifiers are considered. The evaluations are done by determining the static pressures before and after the swirl amplifier in the vertical section of an experimental system. This difference in pressure points allowed the determination of length of decay, which is the distance in which this two-phase system travels before a reduction in radial velocity. In the amplifiers, compressed air at two pressures was used for the purpose of creating a low pressure pneumatic conveying system. It is determined that when using these amplifications in the air boost, longer lengths of decay can be achieved in comparison to a no swirl system. This meant that the products transportation could be enhanced due to the addition of the swirl amplifiers. The experimental values were used to compare both designs. The more productive one was determined by its length of decay. As well as estimating the maximum obtainable distances for both swirl amplifiers at each particular amplification.
Analysis of Bloch’s Method in Structures With Energy Dissipation
Authors: Farzbod Farhad , Leamy Michael J.
Published: May 2012

Bloch analysis was originally developed to solve Schro¨dinger’s equation for the electron wave function in a periodic potential field, such as found in a pristine crystalline solid. In the context of Schro¨dinger’s equation, damping is absent and energy is conserved. More recently, Bloch analysis has found application in periodic macroscale materials, such as photonic and phononic crystals. In the vibration analysis of phononic crystals, structural damping is present together with energy dissipation. As a result, application of Bloch analysis is not straight-forward and requires additional considerations in order to obtain valid results. It is the intent of this paper to propose a general framework for applying Bloch analysis in such systems. Results are presented in which the approach is applied to example phononic crystals. These results reveal the manner in which damping affects dispersion and the presence of band gaps in periodic systems.
An Analytical Model of a Microscale Heat Exchanger: Ambient Interaction and General End-Wall Boundary Conditions
Authors: Spann Bryan , Ameel Tim
Published: May 2012

Developments in manufacturing have led to progressively smaller and more complex micro-elctro-mechanical systems (MEMS), many of which employ heat exchangers to enhance performance. Due to the size constraints on these devices, adiabatic surfaces are difficult to create, and thus, ambient thermal interaction becomes an import factor in heat exchanger performance. Similarly, end-wall boundary conditions also become a concern at this scale. A closed form mathematical solution is presented for single-pass, two-fluid, parallel and counter flow microscale heat exchangers. The model includes the effects of axial wall conduction, ambient thermal interaction at the axial exterior surface, and general end-wall boundary conditions. Heat exchanger effectiveness values above unity were found to be possible depending on the magnitude of the ambient thermal interaction and the objective of the heat exchanger. It was also found that heat flux and convection boundary conditions, can enhance heat exchanger performance. Furthermore, it was determined that the heat capacity rate ratio could be controlled to mitigate the effects of the ambient thermal interaction.
Investigation of Hole Expansion Characteristics of DP 600 With Testing and Modeling
Authors: Ram Siddharth Mohan , Kang Hong-Tae
Published: May 2012

The automotive industry utilizes stretch flanges in sheet metal components which become load carrying members providing strength to the body or they are subsequently joined with other components in vehicle structures. Failures often occur at the edge of these flanges. The Hole Expansion Test is designed specifically for characterizing the deformation of sheet steels in the flange. The test is performed for DP 600 sheet steel with the guideline of ISO standard 16630: 2009. Strains developed during the tests were measured using a non-contact strain measurement system and square grid method. This study also compared those results with finite element simulation results.
An Electromotive Force Measurement System for Alloy Fuels
Authors: Xing Changhu , Jensen Colby , Ban Heng , Mariani Robert , Kennedy J. Rory
Published: May 2012

The development of advanced nuclear fuels requires a better understanding of the transmutation and micro-structural evolution of the materials. Alloy fuels have the advantage of high thermal conductivity and improved characteristics in fuel-cladding chemical reaction. However, information on thermodynamic and thermophysical properties is limited. The objective of this project is to design and build an experimental system to measure the thermodynamic properties of solid materials from which the understanding of their phase change can be determined. The apparatus was used to measure the electromotive force (EMF) of several materials in order to calibrate and test the system. The EMF of chromel was measured from 100°C to 800°C and compared with theoretical values. Additionally, the EMF measurement of Ni-Fe alloy was performed and compared with the Ni-Fe phase diagram. The prototype system is to be modified eventually and used in a radioactive hot-cell in the future.
Underground Nuclear Energy Complexes: Technical and Economic Advantages
Authors: Kunze Jay F. , Mahar James M. , Giraud Kellen M. , Myers C. Wes
Published: May 2012

Underground nuclear power plant parks have been projected to be economically feasible compared to above ground installations. This paper includes a thorough cost analysis of the savings, compared to above ground facilities, resulting from in-place entombment (decommissioning) of facilities at the end of their life, reduced costs of security for the lifetime of the various facilities in the underground park, reduced transportation costs, and reduced costs in the operation of the waste storage complex (also underground), compared to the fair share of the costs of operating a national waste repository.
A Two-Dimensional Nonlinear Volumetric Foot Contact Model
Authors: Sandhu Sukhpreet Singh , McPhee John
Published: May 2012

This paper presents the development of a two-dimensional (2D) multibody foot contact model consisting of a volumetric model of foot pad. The volumetric model employs nonlinear springs and linear dampers to represent the complex material behavior of the foot pad, typical of a visco-hyperelastic material. The nonlinear springs of the foot contact model are motivated by an Ogden-type material that can describe the nonlinear constitutive behavior of a wide variety of biological tissues and rubbers. The geometry of the foot pad is modeled as three simplified ellipse which represent the heel, balls of the feet, and toe. The efficacy of the developed foot contact model is established by driving the simulation model with kinematics observed from walking experiments and comparing the generated ground reaction force with the experimental data.
Numerical Simulation in an Air Filled Cubical Enclosure With Protruding Heat Sinks
Authors: Botello-Arredondo Israel , Hernandez-Guerrero Abel , Pen˜a-Taveras Marino , Miranda-Razo Victor , Rubio-Arana Cuauhtemoc
Published: May 2012

The present study evaluates the effects of a protruding heat sink located on one of the vertical walls of a cubic cavity, with a free convective laminar regimen. The best of three locations for the heat sink will be determined with the analysis of the velocity and temperature fields in the cavity. An optimal operation condition is required since the cavity will contain medical products with a specific temperature range. Three different locations for the heat sink, (in the +Y direction), are to be studied: 1/3 H, 1/2 H and 2/3 H, where H is the height of the cavity, for different values of Rayleigh Number 103<Ra<106. The heat exchange occurs between the heat sink and the isothermal walls. The results obtained show that it is recommended to place the heat sink at the position H/2, as the air had the best thermal and dynamic behavior.
Variation in Size Distribution of Suspended Particulate Matters in Air With Humidity Swing Operation
Authors: Onoda Nagisa , Nakabeppu Osamu
Published: May 2012

The aim of this study is to develop a new air cleaning method being applicable to suspended particulate matters (SPM) of wide sizes. We experimentally studied about the effects of a humidity swing operation where sample air is continuously humidified with heating and dehumidified with cooling. The total of SPM concentration of sample air decreased with the humidity swing operation; however, the concentration of SPM from 0.3 to 1 μm markedly increased. Suction flow accompanying condensation, cohesion and thermophoresis were considered as the SPM reduction effects. It would appear that the nano-size SPM grew to submicron size by nuclear condensation and submicron size SPM increased. The experimental results showed that the SPM concentration of 0.3 μm or less decreased by 89% and the total of that decreased by 80%. The applicability of the humidity swing operation to removal of SPM including nano size SPM was shown by the results. Also, exponential reduction of the SPM concentration was demonstrated with applying the repeated humidity swing operation in a circulation air-cleaning apparatus. This method is expected to become effective air cleaning method applicable to wide size range of SPM.
Effects of the Properties of Dielectric Materials on the Fabrication and Operation of Digital Microfluidic Systems
Authors: Bhattacharjee Biddut , Najjaran Homayoun
Published: May 2012

Digital microfluidic systems (DMS), where liquid droplets are manipulated on a planar surface, are the recent generation of microfluidic systems. Specifically, the systems where electrowetting force is employed for the actuation of droplets on a 2-D array of electrodes are capable of performing many of the basic fluidic operations. In these systems, the actuation force on the liquid droplet is a function of the applied voltage and its frequency, dielectric properties of the liquid and the insulating material, and finally the instantaneous position of the droplet between two adjacent electrodes. At lower frequencies the applied voltage is dropped almost entirely in the insulating layer for droplets of aqueous liquids. The unit area capacitance of the insulating layer depends linearly on the dielectric constant and inversely on the thickness. Therefore, for a given voltage and frequency, stronger actuation force can be generated if a thinner layer of material with high dielectric strength is used. However, the electric-field strength of the material poses the limitation on reducing the thickness of insulating layer. Typical insulators, with high electric field strength, used in microelectromechanical systems require quite sophisticated equipment for their deposition on the substrates. On the other hand, spin-coating of polymer insulators have been adopted as an economic and faster alternative technique for the fabrication of DMS. Polymer insulators possess reasonable dielectric strength and lower thickness can be achieved from higher spin speeds. However, low electric-field strengths of these materials prohibit working with thinner layers. As a result, actuation of droplets in DMS, fabricated using these materials as insulators, requires higher voltages. Higher applied voltages are not desirable for portable systems dealing with sensitive liquid samples. This paper presents an investigation on different insulating materials in terms of the ease of fabrication and the minimum voltage requirements for operation. The results can be useful in choosing the insulating material that will result in the expected level of performance while meeting the resource constraints. As a result, this paper specifies the material, based on the comparative study, that can be used to avoid the need for a sophisticated deposition system and the fabricated DMS can be operated with much lower voltages.
Fluorescence Microscopy for the Measurement of the Surface Properties of the Gas Diffusion Layers of Fuel
Authors: Friess Brooks , Hoorfar Mina
Published: May 2012

One of the major problems of current proton exchange membrane (PEM) fuel cells is water management. The gas diffusion layer (GDL) of the fuel cell plays an important role in water management since humidification and water removal are both achieved through the GDL. Various numerical models developed to illustrate the multiphase flow and transport in the fuel cell require the accurate measurement of the GDL properties (wettability and surface energy). In a recent study, the capillary penetration technique has been used to measure indirectly the wettability of the GDL based on the experimental height penetration of the sample liquid into the porous sample. In essence, a high resolution microscope/camera was used to detect the rate of penetrated height into the sample GDL. The shortcoming of this type of visualization is that it can only be used for thin hydrophilic GDL samples with zero Teflon loadings. For the thick and high Teflon loading GDLs, there is not enough contrast to detect the height of the penetrated liquid. In the real fuel cells, the GDLs are made of the micro-porous and macro-porous layers with an optimum Teflon loading. Therefore, it is required to develop a new experimental methodology capable of detecting the rate of penetration and as a result the wettability of GDLs samples used in fuel cells. In this paper, the fluorescence microscopy technique is integrated into the experimental setup of the capillary penetration method to improve the contrast between the wetted and non-wetted area. The fluorescence setup uses a powder die, dissolved in the test fluid, which is excited by a concentrated ultraviolet light illuminated in the vertical manner. To acquire the profile images of the penetrated liquid, an optical mirror was used. This new setup has the added advantage of providing a visual representation of the different regimes of penetration (e.g., the fingering effect reported for the pathways of the liquid penetrated into the GDLs) that are defined by the capillary number and mobility ratio of each fluid. Since the GDL samples used in this study are relatively hydrophobic (e.g., with 40% Teflon loadings), the pattern of liquid penetration is not uniform. Thus, an image analysis program was developed to determine the average height of penetration based on the area under the entire wetted area. The general Washburn equation was then used to fit the extracted height data and provide the average internal contact angle for each test liquid.
Rigorous Design Process for a Groundwater Pump for Low-Yield Water Wells: A Case Study
Authors: Anderson Peter , Wonson James , Dartnall W. John
Published: May 2012

Ground-water pumping in remote areas, such as Australian farms, was for many years traditionally done by wind pumps in order to satisfy the needs of stock. Since the 1980’s solar pumps of varying designs have become popular for pumping water from farm dams and tube wells. Wind pumps, solar pumps, engine or electric motor driven pumps and even animal/human powered pumps have a future in many remote situations in the world for stock watering, irrigation and for village water supply in developing countries. In these markets there is a wide-spread view that local manufacture of the pumps is preferable, as is well documented in the literature on village water supply in developing countries. Submersible pumps that are either of the multi-stage centrifugal class or that use the progressive cavity principle have increased in popularity in the low well yield environment. However, where well yields are extremely low the efficiency of these pumps also becomes low and oversized pumps of these kinds are often inappropriately applied. Quite often in the low yield situation, tube wells are also oversized in that they are drilled to large diameters and depths so as to provide storage in order to accommodate the water demand requirements of the user. This practice leads to unnecessary deterioration of both pump and well. Designing for low production volume manufacture presents unique challenges for the designer in attempting to design a robust, versatile but cost-effective product. The design challenges include, achievement of: - high efficiency, reliability, longevity, simplicity, versatility with a minimum parts count, and all this at a low cost. A case study is presented in this paper in which the design issues are outlined. A rigorous design process has been applied in this case study.
Field Emission Efficiency of a Carbon Nanotube Array Under Parasitic Nonlinearities
Authors: Anand Sandeep V. , Roy Mahapatra D. , Sinha Niraj , Yeow J. T. W. , Melnik R. V. N.
Published: May 2012

Carbon Nanotubes (CNTs) grown on substrates are potential electron sources in field emission applications. Several studies have reported the use of CNTs in field emission devices, including field emission displays, X-ray tube, electron microscopes, cathode-ray lamps, etc. Also, in recent years, conventional cold field emission cathodes have been realized in micro-fabricated arrays for medical X-ray imaging. CNT-based field emission cathode devices have potential applications in a variety of industrial and medical applications, including cancer treatment. Field emission performance of a single isolated CNT is found to be remarkable, but the situation becomes complex when an array of CNTs is used. At the same time, use of arrays of CNTs is practical and economical. Indeed, such arrays on cathode substrates can be grown easily and their collective dynamics can be utilized in a statistical sense such that the average emission intensity is high enough and the collective dynamics lead to longer emission life. The authors in their previous publications had proposed a novel approach to obtain stabilized field emission current from a stacked CNT array of pointed height distribution. A mesoscopic modeling technique was employed, which took into account electro-mechanical forces in the CNTs, as well as transport of conduction electron coupled with electron–phonon induced heat generation from the CNT tips. The reported analysis of pointed arrangements of the array showed that the current density distribution was greatly localized in the middle of the array, the scatter due to electrodynamic force field was minimized, and the temperature transients were much smaller compared to those in an array with random height distribution. In the present paper we develop a method to compute the emission efficiency of the CNT array in terms of the amount of electrons hitting the anode surface using trajectory calculations. Effects of secondary electron emission and parasitic capacitive nonlinearity on the current-voltage signals are accounted. Field emission efficiency of a stacked CNT array with various pointed height distributions are compared to that of arrays with random and uniform height distributions. Effect of this parasitic nonlinearity on the emission switch-on voltage is estimated by model based simulation and Monte Carlo method.
Basic Numerical Assessments to Perform a Quasi-Complete LES Toward IC-Engine Applications
Authors: Brusiani Federico , Bianchi Gian Marco
Published: May 2012

Still today, the numerical representation of a fully 3D turbulent flow remains one of the most challenging task. In Computational Fluid Dynamics (CFD), turbulent flows can be numerically solved with different levels of accuracy bounded between Reynolds Averaged Navier Stokes (RANS) and Direct Numerical Simulation (DNS) methods. Today, the RANS is the standard approach to perform turbulent flow simulations. It allows a good reproduction of the mean flow conditions guaranteeing, at the same time, an acceptable computational cost for practical engineering applications. Unlike the RANS, DNS is the most complete approach that can be used to numerically solve a turbulent flow because, in this case, all the turbulent scales are directly solved. However, today the DNS approach remains inapplicable in industrial field because of the prohibitive computational power required. Between RANS and DNS, a third method can be considered for the solution of high Reynolds turbulent flows: Large Eddy Simulation (LES). LES approach allows the direct solution of the largest turbulent scales (anisotropy turbulence) while the smallest scales (isotropy turbulence) are numerically modelled by a sub-grid scale model. For this reason, with respect to RANS, LES is expected to give an improvement about turbulent flow numerical solution when the physical behaviour of the considered fluid domain is dominated by the large scales of motion. At the same time, the computational cost of a LES simulation is quite lower than for DNS simulation. Even if during the last years LES has helped to improve the comprehension of complex turbulent fluid dynamic systems, for its applications in industrial fields further insights are needed. In particular, one of the main problem linked to the LES method regards the definition of a simulation methodology by which to obtain an high solution level (i.e. high level of energy directly solved) at the lowest computational cost. To fulfill this requirement, the authors defined a new LES simulation methodology based on Adaptive Mesh Refinement (AMR). The first results obtained by its application on a backward facing step test case are here presented and discussed in detail.
Electromechanical Coupling in Ionic Polymer-Metal Composites
Authors: Davidson Jacob D. , Goulbourne N. C.
Published: May 2012

Ionic polymer-metal composites (IPMCs) are smart materials which function as soft sensors and actuators. When a small DC voltage (1–5 V) is applied to an IPMC in a cantilever configuration, ion and solvent transport through the thickness of the polymer membrane causes the transducer to bend towards the anode. For device development and use in engineering applications, actuation is often described at a higher level in terms of an electromechanical coupling between the ionic charge distribution and the stresses developed in the IPMC. In this work we derive a set of relationships describing the coupling response by starting with basic considerations of polymer microstructure and local interactions during actuation. A micromechanical modeling framework is employed in order to account for the material microstructure. Using a generalized expression for electrostatic cluster pressure which takes into account clusters recombining to form larger cluster upon expansion, we define an effective local stiffness which varies with both solvent uptake and charge density in the boundary layers. An equilibrium relationship between solvent uptake and charge density is determined by considering the free energy of the homogenized polymer as the sum of elastic, electrostatic, and chemical components. Stress developed in the boundary layers is then calculated from changes in local stiffness and solvent uptake with respect to charge density. The resulting relationship for electromechanical coupling is found to be in good agreement with previous empirical models, thus serving as a model validation and demonstrating why certain forms for electromechanical coupling can be used to explain a variety of experimental observations. Specifically, we see that stress developed in the boundary layers is well described as a quadratic polynomial in charge density due to the form of the electrostatic cluster pressures.
Study on Gas Entrainment Rate Into Liquid From Free Surface by Vortex
Authors: Koizumi Yasuo , Ito Kei , Ohshima Hiroyuki , Ohtake Hiroyasu
Published: May 2012

The gas entrainment rate into liquid by the vortex formed on the free surface was examined experimentally. Water flowed into a cylindrical vessel from a wall tangentially. Swirl flow was formed in the vessel, and then water left from the bottom outlet of the vessel. The flow state of the entrainment was visually observed by using a high speed video camera. The gas entrainment rate into water was measured. A stable vortex was formed in the test vessel. Whether the bottom of the vortex reached the bottom outlet of the vessel was dependent on the downward velocity of water; the velocity at the bottom outlet. Before the vortex tip reached the bottom of the vessel, bubbles were periodically torn off from the bottom tip of the vortex and the bubble-type gas entrainment was observed. After the bottom of the vortex reached the bottom of the vessel, the gas entrainment turned to the vortex-type gas entrainment. When the gas entrainment turned to the vortex-type gas entrainment, the flow state in the outlet pipe changed from the bubbly flow to the churn flow. After the gas entrainment varied from the bubble-type to the vortex-type, the gas entrainment rate increased drastically. The downward water velocities at the initiation of the bubble-type gas entrainment and at the transition from the bubble-type to the vortex-type gas entrainment became fast as the liquid level in the vessel became deep. The Kelvin-Helmholtz instability did not explain the bubble torn-off from the vortex tip.
Investigation of the Oscillatory Behavior of Electrostatically-Actuated Microbeams
Authors: Mojahedi Mahdi , Moghimi Zand Mahdi , Ahmadian Mohammad Taghi
Published: May 2012

Vibrations of electrostatically-actuated microbeams are investigated. Effects of electrostatic actuation, axial stress and midplane stretching are considered in the model. Galerkin’s decomposition method is utilized to convert the governing nonlinear partial differential equation to a nonlinear ordinary differential equation. Homotopy perturbation method (i.e. a special and simpler case of homotopy analysis method) is utilized to find analytic expressions for natural frequencies of predeformed microbeam. Effects of increasing the voltage, midplane stretching, axial force and higher modes contribution on natural frequency are also studied. The anayltical results are in good agreement with the numerical results in the literature.
Nonlinear Vibration and Buckling Analysis of Beams Using Homotopy Perturbation Method
Authors: Mojahedi Mahdi , Moeenfard Hamid , Ahmadian Mohammad Taghi
Published: May 2012

In this paper, homotopy perturbation and modified Lindstedt-Poincare methods are employed for nonlinear free vibrational and buckling analysis of simply supported and double-clamped beams subjected to axial loads. Mid-plane stretching effect has also been accounted in the model. Galerkin’s decomposition technique is implemented to convert the dimensionless equation of the motion to nonlinear ordinary differential equation. Homotopy and modified Lindstedt-Poincare (HPM) are applied to find analytic expressions for nonlinear natural frequencies and critical axial loads of the beams. Effects of design parameters such as axial load and slenderness ratio are investigated. The analytic expressions are valid for a wide range of vibration amplitudes. Comparing the semi-analytic solutions with numerical results, presented in the literature, indicates good agreement. The results signify the fact that HPM is a powerful tool for analyzing dynamic and vibrational behavior of structures analytically.
Design and Fabrication of a Microcantilever-Based Sensor for Nerve Gas Detection
Authors: Li Chengzhang , Miller Michele H. , Nayyar Jaspreet Singh , Bergstrom Paul L. , Velayudham Singaravelu , Liu Haiying
Published: May 2012

Surface-micromachined MEMS processes were used to fabricate this gas sensor. We fabricated a variety of designs, including those with one end fixed, two ends fixed and four ends fixed. In addition to the first bending mode, the torsional mode is being used for sensing and actuation. The placement of air venting holes as well as the placement of the sensing and actuating electrodes have been varied in the designs. A custom polymer layer (PPE-1-LBS) that absorbs the nerve gas analog DMMP is applied to the surface of gold-coated microcantilevers. The polymer coating is applied just after the cantilever is released with hydrofluoric acid but before the drying process. This paper describes the important steps in the fabrication process and compares the manufacturability of the various cantilever designs. It also compares the expected performance of four types of designs.
Natural Convection in Horizontal Fluid-Superposed Porous Layers Heated Locally From Below
Authors: Bagchi Aniruddha , Kulacki Francis A.
Published: May 2012

This paper reports numerical studies of steady two-dimensional natural convection in fluid-superposed porous layers heated locally from below. The numerical simulation is based on the Darcy-Brinkman-Forchheimer model for the porous layer and focuses on the parametric domain in which the flow is well established, i.e., the overall Rayleigh number is several orders of magnitude larger than the critical value. An emphasis is placed on revealing the effects of two dimensionless parameters on the overall Nusselt number: the porous layer-to-cavity height ratio (η = Hm/H) and the heater-to-cavity base length ratio (δ = LH/L). Calculations cover η = 0.25, 0.5, 0.75, δ = 0.25, 0.5, 1, and overall Rayleigh numbers from 103 to 106. For a fixed height ratio, overall Nusselt numbers increase with a decrease in the heater length. For a given heater length ratio, overall Nusselt number increases with an increase in the height of the overlying fluid layer. Recirculating flow is confined primarily to the overlying fluid layer with some penetration into the upper part of the porous layer. The present results represent an extension of the well studied problem of buoyant convection in superposed layers with a fully heated lower surface.
Characterization of a Liquid-Metal Micro Droplets Thermal Interface Material
Authors: Hamdan Amer M. , McLanahan Aric R. , Richards Robert F. , Richards Cecilia D.
Published: May 2012

This work presents the characterization of a thermal interface material consisting of an array of mercury micro droplets deposited on a silicon die. Three arrays were tested, a 40 × 40 array (1600 grid) and two 20 × 20 arrays (400 grid). All arrays were assembled on a 4 × 4 mm2 silicon die. An experimental facility which measures the thermal resistance across the mercury array under steady state conditions is described. The thermal interface resistance of the arrays was characterized as a function of the applied load. A thermal interface resistance as low as 0.253 mm2 K W−1 was measured. A model to predict the thermal resistance of a liquid-metal micro droplet array was developed and compared to the experimental results. The model predicts the deformation of the droplet array under an applied load and then the geometry of the deformed droplets is used to predict the thermal resistance of the array. The contact resistance of the mercury arrays was estimated based on the experimental and model data. An average contact resistance was estimated to be 0.14 mm2 K W−1.
Shape Optimization of Electrostatically Actuated Microbeams With Extended Static and Dynamic Operating Ranges
Authors: Joglekar M. M. , Pawaskar D. N.
Published: May 2012

We present a generic shape optimization methodology to maximize the static and dynamic pull–in ranges of electrostatically actuated microbeams. Energy based techniques are used to extract the static and dynamic pull–in parameters. A versatile parametric width function is used to characterize nonprismatic geometries, and the parameters of the proposed width function are optimized using the Nelder–Mead method of function minimization together with a penalty method to enforce the constraints. The constraints that we consider are encountered in typical microbeam applications. We consider matrix of several test cases in order to fully demonstrate the utility of the proposed methodology. Our results indicate that an increase in the pull–in displacement of as much as 19% can be obtained using our optimization approach. We present optimal shapes of these microbeams, that easily lend themselves to microfabrication, which exhibit the improved pull–in response in both static and dynamic regimes.
A Discrete Meshless Lagrangian Based Approach for Soft Impact Damage Modeling in Advanced Propulsion Systems
Authors: Siddens Aaron , Bayandor Javid
Published: May 2012

Soft impact on aircraft occurs in several forms, such as bird and hail strike. A discrete meshless Lagrangian based approach has been developed for modeling the fluidic behavior of soft objects during impact. This approach shows promise for developing an overall predictive methodology for accurately capturing and assessing dynamic damage in jet engines. This paper focuses on a part of this study aiming to develop a methodology capable of predicting full details of soft impact damage in turbofan engine forward sections. The initial scenario being simulated was a bird strike. Through modeling of the bird in a Lagrangian domain, the method’s suitability for simulating soft impact damage in fan section structures was evaluated. Three-dimensional explicit finite element analysis models were employed to simulate the highly nonlinear and transient response of the interactions between the non-Newtonian bird and the forward engine section resulting from impact and to capture the associated turbofan blade damage, fan assembly vibrations, and subsequent engine casing destruction. Critical features under investigation were the degradation and fracture of the turbofan blades and the engine casing. Results indicated that a meshless soft impactor model was able to produce the fluid-solid interactive behavior expected from a bird. The methodology further succeeded in effectively predicting the intricate subsequent fluid-fan assembly violent interactions. Several important considerations for crashworthiness analysis of forward sections were highlighted.
A Study of the Design and Analysis of Two Exhaust Heat Recovery Systems for Public Shower Facilities
Authors: Liu Lanbin , Fu Lin , Zhang Shigang
Published: May 2012

For large-scale public shower facilities which open up at a specified time, (such as those in schools, barracks, and natatoriums), a great deal of heat is wasted. If this exhaust heat can be recovered and recycled, it will have significant impact in saving energy and environmental protection, with significant economic benefits. In this paper, two different kinds of heat pumps, an electric and an absorption heat pump, used in heat recovery systems are proposed. Specifically, the used shower water is drained through a pipe and first collected in a gray water pool. After a period of time, as the wastewater accumulates volume, the heat pump system can begin heat recovery and recycling. The wastewater is filtered through a filter and piped to a heat exchanger to heat the tap water. Therefore, the tap water temperature can be heated from 12°C to 25°C, and the wastewater temperature will drop from 30°C to 17 °C. Afterwards, the wastewater is piped to the heat pump evaporator and the tap water piped to the condenser for additional heating. At the same time, according to the different characteristics of the electric heat pump and absorption heat pump, different heat recovery system processes and control are detailed. On this basis, the paper analyses the economic and environmental benefit of three schemes for retrofitting based on a practical example: “exhaust heat recovery using electric heat pump”, “exhaust heat recovery using electric heat pump + gas boiler” and “exhaust heat recovery using direct-fired heat pump”, then finds that direct-fired absorption heat pump heat recovery have lower energy consumption, less pollution, lower operating costs, payback period is shorter and has a promising practical application.
Study of Behavior of Two Phase Flow in Vertical Large Diameter Pipe
Authors: Kebriayi Mohammad Hassan , Karrabi Hadi , Rezasoltani Mohsen , Saidi M. H.
Published: May 2012

Knowledge of Air-water two phase flows is significant to different engineering systems such as chemical reactors and power plant and petrochemical and petroleum industry. One of the most industrial cases of two phase flow is two phase flow in vertical large pipes. In this paper in order to find two phase flow behavior along vertical large diameter pipes we simulate air inlets with different number of holes and different hole diameters in the same flow rate of air. In addition, flow characteristics such as cross-sectional void fraction and velocity and pressure were considered. To achieve this aim, main equations of flow have been developed for investigation of flow behavior in air-water two phase flows. 3-D numerical analyses were performed by a designed and written CFD package which is based on volume of fluid (VOF) approach. Geometries, which have been studied in this article, are round tubes with diameter of 5 cm and with length of 1 and 5 m. The fluid is assumed to be viscous and incompressible. The pressure-velocity coupling is obtained using the SIMPLEC algorithm. The results showed that at the entrance of the pipe the effect of air inlet geometry is significant while at the whole pipe this effect suppressed. Furthermore increasing the velocity at the inlet can increase average void fraction and decrease pressure loses along the pipe axis. Numerical results were compared with available empirical correlations and this comparison shows good agreement between this work and empirical correlations.
Optically Induced Rapid Electrokinetic Patterning of Non-Spherical Particles: Study of Colloidal Phase Transition
Authors: Thakur Raviraj Vijay , Wereley Steven
Published: May 2012

Patterning of colloidal particles on surfaces is an application that has evinced wide interest from the fluid mechanics community, due to its possible applicability in a number of engineering situations such as manufacture of photonic crystals[1], bioengineering tissues[2] and lab on chip technology[3], etc. Recently Kumar et al. had proposed the technique of rapid electrokinetic patterning (REP) [4], a hybrid opto-electric manipulation technique that can manipulate and pattern colloidal particles on an electrode surface. REP utilizes optical landscapes to create local gradients in temperature on an electrode substrate. This allows local changes in permittivity and conductivity of the fluid. Colloidal particles can then be dynamically patterned at the illuminated locations of the electrode surface. REP can be used for capturing selective group of particles and thus it serves as a sorting technique too [5].