bluuebunny/crossref_metadata_2025 huggingface dataset:
Enhanced Performance Design of Solar Desalination Device
Authors: Kowalski Gregory J. , Zenouzi Mansour
Published: May 2012

Many regions in the United States, especially in the Northeast coastal and Southern California regions, and in arid parts of the world are facing fresh water shortages while having access to salt or brackish water. At the present time, the reverse osmosis process is the most prevalent means of converting salt to fresh water. However, as energy prices continue to climb there is evidence that solar desalination may provide a more economical and sustainable means of converting salt water to fresh water. The following paper presents a design of unique modular solar distillation units that provides a mobile, flexible installation for addressing water shortages. The solar still is designed such that the condensation surface is on the shady side of the unit while the absorbing surface is designed as a series of cascading trays that significantly increases the evaporation surface area. Fresh water is produced in this device from the condensate. This design is intended to convert sea water into fresh water that is introduced into a community’s reservoir system to augment traditional water sources. The analysis of the solar distillation unit is performed for the Boston, Massachusetts, USA over a day period in the months of December and July to determine performance at the maximum and minimum ambient conditions. The performance of the proposed device is comparable with reported solar stills in the literature, without optimizing the number of trays or heat rejection surfaces.
Structural Health Monitoring of Composite Structures With Piezoelectric Wafer Active Sensors
Authors: Giurgiutiu Victor
Published: May 2012

Piezoelectric wafer active sensors (PWAS) are lightweight and inexpensive enablers for a large class of structural health monitoring (SHM) applications such as: (a) embedded guided-wave ultrasonics, i.e., pitch-catch, pulse-echo, phased arrays; (b) high-frequency modal sensing, i.e., the electro-mechanical (E/M) impedance method; (c) passive detection (acoustic emission and impact detection). The focus of this paper will be on the challenges and opportunities posed by the composite structures as different from the metallic structures on which this methodology was initially developed. After a brief introduction, the paper discusses damage modes in composites. Then, it reviews the PWAS-based SHM principles. It follows with a discussion of guided wave propagation in composites and PWAS tuning effects. Finally, the paper presents some experimental results with damage detection in composite specimens. The paper ends with conclusions and suggestions for further work.
Various Boundary Condition Implementation to Study Microfilters Using DSMC Simulation
Authors: Darbandi Masoud , Akhlaghi Hassan , Karchani Abolfazl , Vakili Soheyl
Published: May 2012

In this study, we present a vast boundary condition treatment to simulate gas flow through microfilters using direct simulation Monte Carlo (DSMC) method. We examine the effects of different boundary condition treatments on the density, pressure, and velocity distributions and suggest the best conditions to simulate gas flow through microfilters. We also refine the effects of upstream and downstream locations on the solution. The results show that uniform distributions can be achieved if we apply the inlet/outlet boundary condition at appropriate upstream and downstream distances. We also show that all the suggested boundary conditions suitably predict the pressure drop coefficient factor across the filter. To evaluate the current results they are compared with some available empirical formulations.
Pitch Stability of an Unpowered Ground Effect Vehicle
Authors: Hubbell Meagan , Hard Steven , Boots Matthew , Clarke Mary Ann , Smith James E.
Published: May 2012

The ground effect regime was first utilized in the early 1900’s with the advent of transatlantic flight. Aircraft such as the Dornier DO-X would fly close to the surface of the water in order to increase its payload and range. Since that time, research has been periodic with the largest resurgence of ground effect interest in the 1960’s. The Russian government became involved in developing aircraft designed solely for ground effect flight. The design of these aircraft was difficult due to the inherent problems that exist within ground effect. There are natural instabilities that occur, especially in the longitudinal direction that are antagonized by shifting payload weights. Past researchers have handled the unique design requirements of ground effect through the usage of high-tail devices which operate outside of ground effect and power augmented ground effect which artificially generates the lift force through the use of thrust vectoring. The Center for Industrial Research Applications (CIRA) has developed a single passenger, unpowered, subsonic aircraft that relies on gravitational forces for momentum. AirRay combines the benefits of ground effect i.e. the increased lift and decreased induced drag, with a unique approach to maintaining stability. The design of AirRay faced many challenges as a result of flying in the ground effect regime, similar to those found in the prior efforts. These include natural instabilities, primarily in the longitudinal direction, that cause the glider to want to pitch up. In addition the size requirements for a single rider to maximize maneuverability, as well as the potential for updrafts on a downhill slope are added constraints to the design of the ground effect vehicle. These issues, and others, are the subject of current study. This paper has focused on the most important aspect of the design, longitudinal stability. This research has shown positive results with respect to the effectiveness of slots, on passively controlling the movement of the center-of-pressure at varying angles of attack. The 40 degree slot located at 20% of the chord line was most advantageous in stabilizing movement. These results indicate a craft can be designed that can be stable and function in the majority of the flight conditions that have been specified.
Validation of Functional Methods for Calculating Shoulder Joint Centers Using 3D Motion Analysis
Authors: Lura Derek J. , Carey Stephanie L. , Dubey Rajiv V.
Published: May 2012

Research in upper body kinematics and kinetics requires accurate estimation of anatomical joints. Currently the use of regressive techniques using anatomical landmarks is the most common way of calculating upper limb joint centers. Research has shown that functional joint center methods can produce more accurate results than traditional regressive methods in the estimation of hip joint center. This paper investigates the use of functional methods for the estimation of the shoulder joint center using 3D motion analysis data. Three methods for calculating the functional joint center were tested: 1) a standard sphere fit regression, 2) a regression developed and tested for use finding the hip joint center (Piazza method) [1], and 3) a gradient method developed for this paper similar to the one used by Schonauer [2]. First the functional joint center methods were tested in MATLAB using data with random points rotating around a known joint center with varying amounts of noise. Using the MATLAB calculations the accuracy and repeatability of each method was analyzed. Functional joint centers were then calculated from two sets of motion analysis data. The first data set contained shoulder range of motion data, and the second set was gathered during activities of daily living (ADL). Both motion analysis sets used data collected from a healthy adult male subject using a Vicon motion analysis system. The repeatability of each method using the motion analysis data was then analyzed. The MATLAB tests show that the gradient method has the highest tolerance to noise in the data. Results from the motion analysis test show that, of the methods tested, no functional method was found to have consistent results for individual tasks. Each of the functional methods requires a range of motion not prevalent in most ADLs in order to generate a reliable joint center. Joint centers calculations improved in accuracy and reliability with a greater number of trials and larger range of motion. The functional methods are suitable for use in future studies that include a large range of motion.
Unusual Scaling Observations in the Quality Factors of Cantilevered Carbon Nanotube Resonators
Authors: Vallabhaneni Ajit K. , Rhoads Jeffrey F. , Ruan Xiulin , Murthy Jayathi Y.
Published: May 2012

This work examines the quality factors (Q factors) of resonance associated with the axial and transverse vibrations of single-wall carbon nanotube (SWCNT) resonators through the use of molecular dynamics (MD) simulation. Specifically, the work investigates the effect of device length, diameter, and chirality, as well as temperature, on the resonant frequency and quality factor of these devices, and benchmarks the results of MD simulation against classical theories of energy dissipation. Of note are the facts that the quality factors associated with transverse vibration decrease with increasing device diameter and are largely insensitive to chirality. Additionally, quality factors increase with increasing device length for transverse vibrations, but remain almost constant for axial vibrations. The predicted size dependence of the quality factors associated with axial vibration agrees well with classical theory, if the nanoscale size effect of thermal conductivity is properly accounted for. However, the size dependence of the quality factors associated with transverse vibrations deviates significantly from classical theory.
Modeling of Acoustically Augmented Electroosmotic Flows in Microchannels
Authors: Sayar Ersin , Farouk Bakhtier
Published: May 2012

Effective mixing is restricted in electrosmotically driven flows in microchannels. We investigate the effectiveness and applicability of acoustic augmentation in such flow geometries for enhanced mixing. The proposed device geometry can be exploited to integrate micropumps into complex microfluidic chips improving the portability of micro-total-analysis systems along with the capabilities of actively controlling acoustics and electrokinetics. A computational study of acoustically augmented electroosmotic flow is carried out where flexural plate waves (FPW) are considered. A transient analysis is performed for microchannels with a flexural plate wave with an applied electric field parallel to the channel walls. The nonlinear Poisson-Boltzmann and Laplace equations are used to model the induced electrical double layer (EDL) potential and the applied electric potential. The model predictions are compared with results available in the literature for electroosmotic flow, and for the flows generated by acoustic waves.
Load Balancing of Welds in Multi Station Sheet Metal Assembly Lines
Authors: Segeborn Johan , Segerdahl Daniel , Carlson Johan S. , Carlsson Anders , So¨derberg Rikard
Published: May 2012

The balancing of weld work load between executing stations and its robots has a significant influence on achievable production rate and equipment utilization. However, no automatic simulation based method for line balancing has been formulated up to this point. In practice, it is still manually conducted. Therefore in this work we propose two novel methods for load balancing of welds in multi station sheet metal assembly lines to minimize line cycle time. The methods are based on superimposition of the scenes/geometries of all line stations, with maintained robot positioning relative to the work piece, creating a “multi station”. The weld load is balanced between all multi station robots, whereupon the individual robots are combined into stations and coordinated station wise for simultaneous operation. Furthermore one of the proposed methods reduces the subsequent need for robot coordination, by introducing some restrictions on the load balancing: Firstly, for each robot, the weld load is balanced over the other station robots such that the working envelopes are maximally separated. Secondly, for each robot, the weld load is balanced over equivalently positioned robots in other line stations, based on previous station load balancing techniques. The proposed line balancing methods are applied on two industrial case studies which each involves the balancing of about 200 automotive stud welds between 3 stations, each of 4 robots. One of the proposed methods produces line cycle times close to that of the slowest uncoordinated robot, which can be considered a theoretical optimum of the line cycle time. Corresponding algorithm running time is about 30 minutes on an Intel Core 2 Quad with 8 GB RAM.
Study of Dynamic Performance of a Vehicle With Planar Suspension Systems in a Split-µ Braking-in-Turning
Authors: Zhu Jian Jun , Khajepour Amir , Esmailzadeh Ebrahim
Published: May 2012

A planar suspension system (PSS) has spring-damping struts in both the vertical and longitudinal directions so that the vibrations and shocks caused by road obstacles in any direction within the wheel plane can be effectively absorbed. Consequently, the ride comfort of a PSS vehicle can be improved considerably compared to a conventional vehicle. For a vehicle with such suspension systems, however, the wheels can move forth and back with respect to the chassis. The dynamic behaviors of a PSS vehicle under some special conditions, such as a split-μ turning combined with braking operation, may exhibit different characteristics. This paper presents the study of the transient response of a vehicle with PSS in such a case. The simulation results are also compared with those of a similar vehicle with conventional suspension under the same operational condition. The study demonstrates that the handling behavior of a PSS vehicle is generally comparable with, and in some conditions, even better than that of a conventional vehicle.
Development of Biodegradable Mg-Zn-Ca Alloys for Biomedical Applications
Authors: Chen Shuo , Smith Christopher E. , Xu Zhigang , Sankar Jagannathan
Published: May 2012

In the present study, Mg-8at.%Zn-1at.%Ca alloys were fabricated via T4 and T6 solid solution treatment technique for biomedical applications. The alloys were prepared at three different temperatures: 400 °C, 465 °C and 530°C followed by water or liquid nitrogen quenching. The microstructure of Mg-Zn-Ca alloys was characterized using X-ray diffraction (XRD) analysis, optical and electron microscopes, and energy dispersive spectroscopy, respectively. The examination of mechanical properties was conducted on micro hardness tester. The following differences can be concluded from the results: In water quenched samples, the following three phases were identified from XRD pattern: α -Mg matrix, binary Mg2Zn3 and ternary Ca2Mg6Zn3, the secondary phases are more agglomerated. At higher solution treatment temperature, the secondary phases became more dissolved to the Mg-matrix which creates better homogenized material. Higher treatment temperatures cause grains to grow and to a limited extent, samples quenched in liquid nitrogen have smaller grains than those quenched in water. The sample heat treated at the temperature of 465°C reaches a minimum hardness. While in liquid nitrogen quenched samples, the alloys consisted of four phases: α -Mg matrix, binary Mg2Zn3 and MgZn2 and ternary Ca2Mg6Zn3, the secondary phases are more distributed in a network form, at higher magnification, there are some secondary phases precipitated in rod/needle shape in the samples, the hardness of the samples decreases with the temperature increases.
Analytical, Performance and Prescriptive Measures for Life Cycle Assessment of Sustainability or Energy Efficiency Projects
Authors: Taneja Om
Published: May 2012

Sustainability goals for buildings are highly acclaimed as public and private sector’s contributions to environmental responsibility, resource efficiency, occupant comfort and well-being. All too often a building’s performance does not meet design expectations, particularly a new building’s energy savings projection that overstates achievable performance. Across the high-performing building industry, these unrealistic energy performance goals have come from, among other things, inadequate modeling and benchmarking practices, unreliable monitoring and equipment controls systems, and significant changes in space usage and tenant improvements. There is still lack of commitment to include operations staff in goal setting and provide adequate budgets for periodic benchmarking, commissioning, and tuning of buildings’ mechanical, electrical and plumbing systems. This paper provides the analytical, performance & prescriptive measures for life cycle assessment of energy efficiency projects which can help in making adaptive changes to buildings systems to suit changing uses, or other internal and external factors that directly or indirectly affect performance.
Teaching of Multimode Heat Transfer Through Laboratory Experiments
Authors: Rodgers Peter , Bojanampati Shrinivas , Eveloy Valerie , Goharzadeh Afshin , Molki Arman
Published: May 2012

Hands-on laboratory skills play a vital role in providing mechanical engineering students with a sound understanding of the scientific fundamentals and their application in solving real-life engineering problems. This paper describes a hands-on laboratory thermofluid project which is taught as part of a one-semester, junior-level mechanical engineering course titled Core Measurements Laboratory. The experiment focuses on characterization of heat transfer from a cartridge-heated, isothermal cylinder inside a circular enclosure, by conduction, natural convection and radiation. The project consists in the design and fabrication of the test facility, data acquisition and comparison of experimental results with analytical predictions, with a formal report submitted on completion. The project is undertaken by a team of four students over a five-week period. Emphasis is placed on highlighting potential discrepancies between measurement and analytical predictions, which are inherent in the test configuration considered, reflecting realistic engineering situations. Sample measurement and analysis results are reported. The teaching strategy employed to integrate fundamental theories with hands-on experiences is described. The effectiveness of the laboratory project in enhancing student learning of heat transfer, engineering analysis of discrepancies between predictions and measurements, and project management skills was demonstrated by monitoring student performance improvements over the duration of the project.
In-Plane Thermal Conduction and Conductivity Anisotropy in Ge2Sb2Te5 Films for Phase Change Memory
Authors: Li Zijian , Lee Jaeho , Reifenberg John P. , Asheghi Mehdi , Wong H.-S. Philip , Goodson Kenneth E.
Published: May 2012

Thermal conduction governs the program/erase speed and power consumption of phase change memory (PCM) devices. This work presents the in-plane thermal conductivity measurement of Ge2Sb2Te5 (GST) films suspended in a microfabricated structure for the amorphous (a-GST), face-centered cubic (f-GST) and hexagonal close packed (h-GST) phases. The unique design of free-standing GST films eliminates the out-of-plane heat loss to the substrate and achieves high sensitivity to lateral heat conduction. The measured in-plane thermal conductivities of GST thin films are 0.18 ± 0.02 Wm−1K−1 for a-GST, 0.49 ± 0.04 Wm−1K−1 for f-GST and 1.03 ± 0.06 Wm−1K−1 for h-GST. The out-of-plane thermal conductivities are measured by using the 3ω technique. We report the in-plane thermal conductivity is 81% of the out-of-plane thermal conductivity for the crystalline phases while no anisotropy is observed for the amorphous phase. The microstructure of the GST thin film is responsible for the direction-dependent thermal conductivities.
Influence of Working Fluid Properties on Internal Irreversibility of Power Systems
Authors: Dumitrascu Gheorghe , Popescu Aristotel
Published: May 2012

Thermodynamic techniques used to analyze and optimize irreversible cycles involve mainly both the exergy model, i.e. second law efficiency, and the entropy generation minimization [1]. This paper presents an appraising comprehensive direct method based on two overall numbers of irreversibility, external and internal ones. These two numbers link the first and second laws of Thermodynamics inside the first law efficiency, called in this paper the irreversible first law efficiency. The number of external irreversibility is the ratio of second law effectiveness of the cycle external heat exchanges, which were set up by relating the real heat exchange of the working fluid with external heat reservoirs, to the ideal completely reversible one, assuming both a heat transfer area tending to infinity and a heat transfer temperature difference tending to zero. The number of internal irreversibility manages the irreversible entropy production along the cycle. This paper includes selected numerical results regarding the internal irreversibility connected to the nature of the working fluid in a Joule-Brayton engine cycle.
Rolling Element Bearing Fault Diagnosis Using Complex Gaussian Wavelet
Authors: Kankar P. K. , Sharma Satish C. , Harsha S. P.
Published: May 2012

This paper is focused on fault diagnosis of bearings due to localized defects i.e. spall on the bearing components, which is essential to the design of high performance rotor bearing system. The methodology proposed in this paper for fault diagnosis of rolling element bearings, utilizes autocorrelation of raw vibration signals to reduce the dimension of vibration signals with minimal loss of significant frequency content. Dimension of vibration signal is reduced to 10% with negligible loss of information. To extract most appropriate features from auto-correlated vibration signals and for effective classification of faults, vibration signals are decomposed using complex Gaussian wavelet. Total 150 signals of healthy and defective bearings at rotor speeds 250, 500, 1000, 1500 and 2000 rpm with three loading conditions are considered. 1-D continuous wavelet coefficients of these samples are calculated at the seventh level of decomposition (27 scales for each sample). Maximum Energy to Shannon Entropy ration criterion is used to determine scale corresponding to characteristic defect frequency. Statistical features are extracted from the wavelet coefficients corresponding to selected scales. Finally, bearing faults are classified using Support Vector Machine (SVM) method. The test results show that the SVM can be used efficiently for bearing fault classification. It is also observed that classification accuracy is improved by using autocorrelation.
Effect of Geometric Parameters on the Performance of a Radial Flow Pressure Exchange Ejector
Authors: Umar Muhammad , Garris Charles A.
Published: May 2012

The “Pressure exchange” is a novel concept in turbomachinery whereby two fluids, at different energy levels, come in direct contact with each other to transfer energy and momentum between them through non-steady interface pressure forces. The rotating jets of the high pressure primary fluid, often referred to as pseudoblades, resemble solid blades on the impeller of a conventional turbomachine. The low pressure secondary fluid, ahead of the pseudoblades, is pressurized by the action of interface pressure forces. The current paper seeks to provide an insight into the complex flow phenomena occurring inside the radial flow pressure exchange ejector. This research presents the results of the first successful numerical simulation to explore the effects of spin angle, rotor cone angle and number of nozzles on the performance of a radial flow pressure exchange ejector. If this new concept is shown to be viable for gas compression at sufficiently high pressure ratios, then, in refrigeration applications, it would enable environmentally benign refrigerants to replace the harmful chlorofluorocarbons (CFC) and reduce the effluence of greenhouse gases. Applications in many other areas, where conventional ejectors are currently used, are also possible.
Piezoelectric Strain Measurement for Low Power Microsensor Applications
Authors: Amini Alborz , Bahreyni Behraad
Published: May 2012

Many transducers use mechanical strain measurements as their sensing method. We are proposing a mechanical strain measurement technique based on a change in the electrical impedance and frequency response of a piezoelectric film in a certain frequency. This piezoelectric transducer can be fabricated on top of substrate for measuring surface stress. This technique is provided with analytical and numerical models. Coupled field finite element simulations in COMSOL and Coventorwareare employed to confirm the measurable alteration in electrical impedance of the film due to applied normal and transverse stress. Piezoelectric material impedance measurement can be a precise and low power method to sense minuscule strains in micromechanical structures. To the best of our knowledge, this is the first demonstration of this technique at micro-scales.
Bubble Dynamics in a Two-Phase Bubbly Mixture
Authors: Jayaprakash Arvind , Singh Sowmitra , Chahine Georges
Published: May 2012

The dynamics of a primary relatively large bubble in a water mixture including very fine bubbles is investigated experimentally and the results are provided to several parallel on-going analytical and numerical approaches. The main/primary bubble is produced by an underwater spark discharge from two concentric electrodes placed in the bubbly medium, which is generated using electrolysis. A grid of thin perpendicular wires is used to generate bubble distributions of varying intensities. The size of the main bubble is controlled by the discharge voltage, the capacitors size, and the pressure imposed in the container. The size and concentration of the fine bubbles can be controlled by the electrolysis voltage, the length, diameter, and type of the wires, and also by the pressure imposed in the container. This enables parametric study of the factors controlling the dynamics of the primary bubble and development of relationships between the bubble characteristic quantities such as maximum bubble radius and bubble period and the characteristics of the surrounding two-phase medium: micro bubble sizes and void fraction. The dynamics of the main bubble and the mixture is observed using high speed video photography. The void fraction/density of the bubbly mixture in the fluid domain is measured as a function of time and space using image analysis of the high speed movies. The interaction between the primary bubble and the bubbly medium is analyzed using both field pressure measurements and high-speed videography. Parameters such as the primary bubble energy and the bubble mixture density (void fraction) are varied, and their effects studied. The experimental data is then compared to simple compressible equations employed for spherical bubbles including a modified Gilmore Equation. Suggestions for improvement of the modeling are then presented.
Numerical and Experimental Study of the Interaction of a Spark-Generated Bubble and a Vertical Wall
Authors: Jayaprakash Arvind , Chahine Georges , Hsiao Chao-Tsung
Published: May 2012

An understanding of the fundamental mechanisms involved in the interaction between cavitation bubbles and structures is of importance for many applications involving cavitation erosion. Generally, the final stage of bubble collapse is associated with the formation of a high-speed reentrant liquid jet directed towards the solid surface. Local forces associated with the collapse of such bubbles can be very high and can exert significant loads on the materials. This formation and impact of liquid jet is an area of intense research. Under some conditions the presence of gravity and other nearby boundaries and free surfaces alters the jet direction and need to be understood, especially that in the laboratory, small scale tests in finite containers have these effects inherently present. In this work, experiments and numerical simulations of the interaction between a vertical wall and a bubble were carried out using Dynaflow’s three-dimensional code, 3DynaFS_Bem©, which models the unsteady dynamics of a liquid flow including the presence of highly non-linear time evolving gas-liquid interfaces. The numerical predictions were validated using scaled experiments carried out using spark generated bubbles. These spark bubble tests produced high fidelity test data that properly scale the fluid dynamics as long as the geometric non-dimensional parameters, gravity and time are properly scaled. The use of high speed cameras allowing framing rates as high as 50,000 frames per second to photograph the bubbles produced high quality observations of bubble dynamics including clear visualizations of reentrant jet formation inside the bubble. Such observations were very useful in developing and validating the numerical models. The cases studied showed very good correlation between the numerical simulations and the experimental observations and allowed development of predictive rules for the re-entrant jet characteristics, including jet angle and various definitions of the jet speed.
Application of P-N Junction Actuators in the Design and Fabrication of Resonant Microdevices
Authors: Khoshaman Amir Hossein , Bahreyni Behraad , Ransley James
Published: May 2012

In this article an all-silicon resonator for integrated applications based on the recently developed p-n junction actuation method is developed. The advantages and disadvantages of using this method over other possible actuation techniques are fully illustrated. The theory of the equations governing the transduction mechanism is explained and our new simulation method is presented. The validity of this method is verified by simulation of our earlier work. The simulation results of our new work are presented as well and a fabrication method is given in order build the device.
Optimum Configuration of an Expanding-Contracting-Nozzle for Thrust Enhancement by Bubble Injection
Authors: Singh Sowmitra , Choi Jin-Keun , Chahine Georges
Published: May 2012

This paper addresses the concept of thrust augmentation through bubble injection into an expanding-contracting nozzle. Two-phase models for bubbly flow in an expanding-contracting nozzle are developed, in parallel with laboratory experiments, and used to ascertain the geometry configuration for the nozzle that would lead to maximum thrust enhancement upon bubble injection. For preliminary optimization of experimental setup’s design, a quasi 1-D approach is used. Averaged flow quantities (such as velocities, pressures, and void fractions) in a cross-section are used for the analysis. The mixture continuity and momentum equations are numerically solved simultaneously, along with equations for bubble dynamics, bubble motion, and an equation for conservation of bubble number. Various geometric parameters such as the exit and inlet areas, the area of the bubble injection section, the presence of a throat and its location, the length of the diffuser section and the length of the contraction section are varied, and their effects on thrust enhancement are studied. Investigation on the effect of the injected void fraction is also carried out. The key objective function of the optimization is the normalized thrust parameter, which is the difference between the thrust with the bubble injection and the thrust before the bubble injection, normalized by the inlet momentum. An approximate analytical expression for the normalized thrust parameter was also derived starting from the mixture continuity and momentum equations. This analytical expression involved flow variables only at three locations; inlet section, injection section, and outlet section, and the expression is simple enough to produce a quick concept design of the diffuser-nozzle thruster. The numerical and analytical approaches are verified against each other and the limitations of the analytical approach are discussed.
Characterization of Superhydrophobic Surfaces for Anti-Icing in a Low-Temperature Wind Tunnel
Authors: Swarctz Christopher , Aljallis Elias , Hunter Scott , Simpson John , Choi Chang-Hwan
Published: May 2012

In this study, a closed loop low-temperature wind tunnel was custom-built and uniquely used to investigate the anti-icing mechanism of superhydrophobic surfaces in regulated flow velocities, temperatures, humidity, and water moisture particle sizes. Silica nanoparticle-based hydrophobic coatings were tested as superhydrophobic surface models. During tests, images of ice formation were captured by a camera and used for analysis of ice morphology. Prior to and after wind tunnel testing, apparent contact angles of water sessile droplets on samples were measured by a contact angle meter to check degradation of surface superhydrophobicity. A simple peel test was also performed to estimate adhesion of ice on the surfaces. When compared to an untreated sample, superhydrophobic surfaces inhibited initial ice formation. After a period of time, random droplet strikes attached to the superhydrophobic surfaces and started to coalesce with previously deposited ice droplets. These sites appear as mounds of accreted ice across the surface. The appearance of the ice formations on the superhydrophobic samples is white rather than transparent, and is due to trapped air. These ice formations resemble soft rime ice rather than the transparent glaze ice seen on the untreated sample. Compared to untreated surfaces, the icing film formed on superhydrophobic surfaces was easy to peel off by shear flows.
Optimal Design of a Composite Scarf Repair Patch Under Tensile Loading
Authors: Breitzman T. D. , Iarve E. V. , Ripberger E. R.
Published: May 2012

Mechanics of the composite scarf repair under tensile loading with and without overlay plies was examined for nontraditional patch ply orientations. Three-dimensional nonlinear analysis was performed for repair failure prediction and good baseline comparison for open-hole scarfed panels and panels repaired by using standard ply-by-ply replacement patch composition was achieved. Multidimensional optimization was performed to calculate the repair patch ply orientations which minimize the von Mises stresses in the adhesive. These optimal stacking sequences achieved significant reduction of the stress levels and resulted in predicted up to 75% and 85% strength restoration for flush and single ply thickness over-ply repair. These results are intended to illustrate additional design variables available for efficient composite repair design, namely the composition of the repair patch.
Modeling Stress Relaxation Behaviour of a Hygrothermally Aged PC/ABS Polymer Blend
Authors: Haghighi-Yazdi Mojtaba , Lee-Sullivan Pearl
Published: May 2012

The competing effects of physical aging and moisture absorption on the relaxation behaviour of a polycarbonate/acrylonitrile-butadiene-styrene (PC/ABS) polymer blend have been investigated. Physical aging was simulated by thermal aging the blend at temperatures up to 80 °C which is below the glass transition temperature of ABS, i.e., the lower of the two components. Another set of samples was exposed to six different relative humidity and temperature combinations. Progressively aged samples in dry and hygrothermal aging conditions were then subjected to stress relaxation tests. Momentary master curves were developed by applying time/aging-time and time/moisture superposition principles for dry and hygrothermally aged specimens, respectively. The experimental data were also fitted with the Kohlrausch-Williams-Watts (KWW) model to determine the initial modulus, relaxation time constant and shape parameter. Comparisons of the first two parameters between thermally aged and hygrothermally aged conditions suggest that physical aging processes dominate absorbed moisture effects in terms of influencing viscoleastic behaviour, especially when the aging temperature approaches 80 °C.
Mechano-Kinetic Coupling Approach for Materials With Evolutionary Internal Structure
Authors: Karpov Eduard G. , Grankin Mykhailo V.
Published: May 2012

Coupled multiscale approaches for the analysis and simulation of complex multiphysics phenomena in solids have been of great interest during the last decade. These include concurrent MD/FEM models, atomistic-to-continua homogenization techniques and deterministic multiple time scale approaches. In this paper we discuss a generic approach to concurrently couple the Monte-Carlo master equation of microscopic kinetic processes, not accessible by the direct particle dynamics, with the continuum mechanics formulation. This approach can be adequate for the modeling and validation of advanced contemporary materials with dynamic internal structure, as well as evolutionary and degradation processes in materials. The approach is illustrated in application to models of interstitial and vacancy diffusion in fuel cell catalysts and binary material systems.
Numerical Simulation of the Flow and Friction in a Helically-Finned Tube
Authors: Marie Hazel , Shuster James , Pierson Kristopher C.
Published: May 2012

As the populations and the economies of the world grow, the demand for electricity rises and necessitates an increase in the supply. Moreover, the primary fuels that are used to generate electricity are finite and exhausting. This is a problem. However, an abatement of such is to increase the efficiency of the modern steam cycle, which is used to generate most of the world’s electricity. Improving the components of the steam cycle, or the boiler component in particular, can affect the efficiency of the steam cycle significantly. An integral constituent of the boiler is the boiler tube. There are several types of boiler tubes, and the helically-finned tube is one type that has proven to increase the efficiency of the boiler. However, insight of the internal flow within the helically-finned tube is still developing and incomplete. The objective of this study was to model the internal flow and measure the friction factor of a helically-finned tube for which experimental data was obtained previously. The flow was modeled numerically using Fluent, a computational fluid dynamics software package. Having solved the problem using three different modeling techniques, the percent difference between the numerical and experimental results ranged between 14% and 27%. The short tube wrapping technique, in which the exit conditions at the end of one iteration are used as the inlet conditions for the next iteration until convergence is met, proved to be the most economical in terms of computer model size and simulation time.
Development and Validation of a Three-Dimensional Finite Element Model of Cervical Spine (C3-C5)
Authors: Bahramshahi N. , Ghaemi H. , Behdinan K.
Published: May 2012

The objective of this investigation is to develop a detailed, non-linear asymmetric three-dimensional anatomically and mechanically accurate FE model of complete middle cervical spine (C3-C5) using Hypermesh and MSC.Marc software. To achieve this goal, the components of the cervical spine are modeled using 20-noded hexagonal elements. The model includes the intervertebral disc, cortical bone, cancellous bone, endplates, and ligaments. The structure and dimensions of each spinal component are compared with experimentally measured values. In addition, the soil mechanics formulation of MSC.Marc finite element software is applied to model the mechanical behaviour of vertebrae and intervertebral discs as linear isotropic two-phase (biphasic) material. The FE simulation is conducted to investigate compression, flexion\extension and right\Left lateral bending modes. The simulation results are validated and compared closely with the published experimental data and the existing FE models. In general, results show greater flexibility in flexion and less flexibility in extension. The flexion/extension curves are asymmetric with a greater magnitude in flexion than in extension. In addition, the variations of the predicted lateral C4-C5 disc bulge are investigated and the results show that the maximum disc bulge occurs at the C4-C5 anterior location.
Hybrid Liquid-Air Transpired Solar Collector: Model Development and Sensitivity Analysis
Authors: Qadir Abdul , Armstrong Peter R.
Published: May 2012

The paper develops an analytical model of a novel hybrid liquid-air transpired solar collector which could simultaneously heat air and water for applications such as regeneration of liquid desiccants. An energy balance is performed, leading to a system of ODEs which is solved to obtain the air and water outlet temperatures of the collector. Three sets of sensitivity analyses have been performed on the collector varying the total thermal capacitance rates of the air and water (m˙cp)total, ratio of air to total thermal capacitance rate (m˙cp ratio), and the usual boundary conditions of water inlet temperature Twi, ambient temperature Tamb, solar radiation G and wind speed Vw. General performance curves for the collector with increasing (Twi−Tamb)/G have been developed as a result of these analyses. It has been observed that a m˙cp ratio between 0.3 and 0.4 provides with an optimal collector performance. Moreover at low m˙cp ratios, the collector performance has been observed to be very sensitive to wind speed.
Finite Element Study of Spinal Cord Mechanics During Biomechanical Response of Middle Cervical Spine
Authors: Bahramshahi N. , Ghaemi H. , Behdinan K.
Published: May 2012

The present study is conducted to develop a detailed FE model of spinal cord and to study its behaviour under various loading conditions. To achieve the goal, a previously developed and validated FE model of the middle cervical spine (C3-C5) is utilized. The model is further modified to investigate the stresses that the spinal cord in experiences during cervical spine motion segment in compression and flexion/extension loading modes. The resulting Von Misses stress and axial strain of the anterior and posterior surfaces of the cervical spinal cord are obtained from a set of elements along the C4-C5 disc space of the dural sheath, CSF and cord. The results show that in compression, the anterior surface of spinal cord experiences larger displacement, stress, and strain than those of the posterior surface. Conversely, the analyses show that in flexion\extension, the stresses, strains, and displacements are more pronounced in posterior segment of the spinal cord. In extension, the posterior disc bulge applies pressure onto the Posterior Longitudinal Ligament and thereby, applying local pressure on the spinal cord. The FE results show a stress concentration at the point of contact between disc and spinal cord. Furthermore, the FE results of flexion test show similar stress concentration characteristic at the point of contact. However, the local stress on spinal cord is more pronounced in flexion than extension at the C4-C5 area of spinal cord. It was also determined the compressive load resulted in the highest stress concentration on the spinal cord.
Computational Modeling and Performance Evaluation of a DAX-Foam Aircraft Seat Cushion Utilizing High Loading Rate Dynamic Characteristics
Authors: Bhonge Prasannakumar S. , Thorbole Chandrashekhar K. , Lankarani Hamid M.
Published: May 2012

The aircraft seat dynamic performance standards as per CFR 14 FAR Part 23, and 25 requires the seat to demonstrate crashworthy performance as evaluated using two tests namely Test-I and Test-II conditions. Test-I dynamic test includes a combined vertical and longitudinal dynamic load to demonstrate the compliance of lumbar load requirement for a Hybrid II or an FAA Hybrid III Anthropomorphic Test Device (ATD). The purpose of this test is to evaluate the means by which the lumbar spine of the occupant in an impact landing can be reduced. This test requirement is mandatory with every change in the seat design or the cushion geometry. Experimental full-scale crash testing is expensive and time-consuming event when required to demonstrate the compliance issue. A validated computational technique in contrast provides an opportunity for the cost effective and fast certification process. This study mainly focuses on the characteristics of DAX foams, typically used as aircraft seat cushions, as obtained both at quasi-static loading rate and at high loading rate. Nonlinear finite element models of the DAX foam are developed based on the experimental test data from laboratory test results conducted at different loading rates. These cushion models are validated against sled test results to demonstrate the validity of the finite element models. The results are compared for these computational sled test simulations with each seat cushion as obtained using quasi-static and high-loading rate characteristics. The result demonstrates a better correlation of the simulation data with the full scale crash test data for the DAX foam when high loading rate data is utilized instead of quasi-static data in the dynamic finite element models. These models can be utilized in the initial design of the aircraft seats, and thus reducing the cost and time of a full-scale sled test program.
The Emergence of Compliant Foil Bearing and Seal Technologies in Support of 21st Century Compressors and Turbine Engines
Authors: Heshmat Hooshang , Ren Zhaohui , Hunsberger Andrew , Walton James , Jahanmir Said
Published: May 2012

For energy independence to become a reality, whether through the more effective use of US natural resources such as natural gas or through the continued development of the hydrogen economy, efficient and reliable large-scale compressors are needed to enhance the existing pipeline infrastructure that moves energy storing gases from production sites to end user locations. Oil-free, non-contacting seal and bearing technologies are critical to the successful development of new high efficiency and power dense compressors. Similarly with increasing emphasis on energy conservation, power and propulsion gas turbine engines will require advanced low leakage seals and may take advantage of efficiencies offered by compliant foil gas bearings. When properly applied these oil-free, non contacting technologies will have a positive impact on the operating efficiency and life of compressor and gas turbine engine systems. The overall objective of this paper is to present recent advances in compliant foil bearings and seals that make them attractive for a wide array of systems. The paper documents the design approach that includes analytical trade off studies to establish overall requirements followed by an experimental program to demonstrate the ability of the identified foil technology to meet the machine requirements. A summary of advancements in foil bearing load carrying capacity, size scaling from 6 mm to 150 mm in diameter, the ability to operate under shock loads greater than 40 g as well as under steady side loads with two different gases and finally the ability to operate at temperatures greater than 750 C will be presented. Data will also be presented showing the application of foil bearings to several different machines. Similarly, results from design, fabrication and testing of compliant foil radial and axial face seals will be discussed. Data from axial face seals testing at differential pressures, surface velocities, and normal loads greater than 675 kPa, 350 m/s, and 1100 N respectively will be presented to demonstrate non-contacting performance. Results of subcomponent testing will also be presented to demonstrate the capability of the face seal to accommodate axial excursions of up to 3.8 mm. Compliant foil radial seal testing in sizes ranging from approximately 60 to 215 mm in diameter under differential pressures to 690 kPa and surface velocities to 340 m/s will be presented and compared to prediction. The culmination of the work presented supports the application of compliant foil bearings and seals in a wide array of advanced machinery.