bluuebunny/crossref_metadata_2025 huggingface dataset:
Stability Analysis of a Rotating Stepped Shaft via Lyapunov Criterion
Authors: Abbaszadeh Chekan Jafar , Merat Kaveh , Zohoor Hassan
Published: October 2013

In this investigation, the stability analysis of a rotating elastic stepped shaft is studied and the sufficient condition for system stability in the sense of Lyapunov is derived. The model consists of an elastic stepped shaft which is clamped rigidly to a rotary device. From the model’s point of view, the entire length of shaft is partitioned into uniform segments with different characteristics. The Lyapunov direct method is applied in this survey where the Hamilton function has been chosen as the candidate Lyapunov function. Since the dynamical mode shapes of the shaft are required for the stability analysis, the shaft has been modeled by the Euler–Bernoulli beam theory and the corresponding mode shapes have been derived based on the boundary conditions and the continuity conditions between adjacent segments. In this study, the shaft is considered to have two segments with different properties. It is notable that this model can be an appropriate model for the spindle in tool machines. Our aim in this research study is determining the area of stability for the system considering the shaft characteristics. The effects of bending stiffness and mass distribution parameters of each segment are investigated on the stability margins of the system.
Controlling the Superior Reliability of Lead Free Assemblies With Short Standoff Height Through Design and Materials Selection
Authors: Arfaei B. , Wentlent L. , Joshi S. , Anselm M. , Borgesen P.
Published: October 2013

We have recently demonstrated a significantly longer life in accelerated thermal cycling for Land Grid Arrays (LGAs) assembled only with SAC305 solder paste than for the corresponding SAC305 based BGA assemblies. This superior performance was shown to be a direct effect of the solder microstructure. The final Sn solidification temperature strongly affects the initial microstructure of a SnAgCu solder joint, including the Sn grain morphology, and thus the thermomechanical behavior of the joint. Right after reflow, larger BGA joints of SnAgCu alloys, which solidify at higher temperature, reveal either a single β-Sn grain or three large grains with clearly defined boundaries formed by cyclic twinning. The orientations of the highly anisotropic Sn grains are not yet controllable in manufacturing, leading to substantial statistical scatter in the performance of the solder joints. Typical LGA solder joint dimensions, however, tend to facilitate greater undercooling and the formation of an alternative interlaced twinning microstructure.

A systematic study was undertaken to identify the parameters that control the interlaced twinning microstructure. Sn grain structures were characterized by crossed polarizer microscopy and electron backscatter diffraction (EBSD). Precipitate sizes and distributions were measured using backscattered scanning electron microscopy and quantified using image analysis software. Systematic effects of solder alloy, dimensions and pad finishes were identified. Recommendations are made as to design and materials selection. The practicality of controlling the desired microstructure, as well as potential disadvantages for certain applications is discussed.
The Early Design Reliability Prediction Method
Authors: O’Halloran Bryan M. , Hoyle Chris , Stone Robert B. , Tumer Irem Y.
Published: October 2013

The purpose of this paper is to formalize the Early Design Reliability Prediction Method (EDRPM) into a comprehensive framework, then to provide a case study using an Electrical Power System (EPS) which shows the usefulness of the methods. EDRPM has been developed to facilitate decision making in early design using quantitative reliability results [1]. Candidate components and design alternative are eliminated using justification provided by EDRPM. The output of this method is a set of design alternative that have a reliability values at or greater than a preset reliability goal. At the completion of applying EDRPM, additional metrics can be used to determine a final design. This research addresses the need for reliability methods to be moved earlier in the design process. Current methods are applicable after components have been selected. EDRPM is used during functional design, and when concepts are generated. This method also calculates functional failure rates which are applied to generate the function and component distributions. The results of the case study shows that several candidate components and design alternatives can be eliminated using EDRPM. It is demonstrated that only a subset of designs that meet the failure rate piece of the reliability goal should not be eliminated. The reliability goal is the combination of two parts; the failure rate and the probability of not exceeding the failure rate. Several of these design still have a probability of exceeding the second piece of the reliability goal given that they meet the first.
Exergy Analysis of a Solid-Oxide Fuel Cell, Gas Turbine, Steam Turbine Triple-Cycle Power Plant
Authors: Pass Rebecca Z. , Edwards Chris F.
Published: October 2013

In an effort to make higher efficiency power systems, several joint fuel cell / combustion-based cycles have been proposed and modeled. Mitsubishi Heavy Industries has recently built such a system with a solid-oxide fuel cell gas turbine plant, and is now working on a variant that includes a bottoming steam cycle. They report their double and triple cycles have LHV efficiencies greater than 52% and 70%, respectively. In order to provide insight into the thermodynamics behind such efficiencies, this study attempts to reverse engineer the Mitsubishi Heavy Industries system from publicly available data. The information learned provides the starting point for a computer model of the triple cycle. An exergy analysis is used to compare the triple cycle to its constituent sub-cycles, in particular the natural gas combined cycle. This analysis provides insights into the benefits of integrating the fuel cell and gas turbine architectures in a manner that improves the overall system performance to previously unseen efficiencies.
Thermal Transport in 3D Pillared CNT-Graphene Nanostructures
Authors: Park Jungkyu , Bifano Michael F. P. , Prakash Vikas
Published: October 2013

Thermal transport in two types of 3D pillared SWCNT-graphene nanostructures, which combine graphene floors and (6,6) armchair single-walled carbon nanotube (SWCNT) columns is studied by measuring both in-plane and out-of-plane thermal conductivity using molecular dynamics (MD) simulations with the AIREBO interatomic potential. Interpillar distance and pillar height dependency of thermal conductivity in 3D pillared SWCNT-graphene super-structure are examined at various temperatures (300K, 600K, 900K, and 1200K). It is shown that the thermal conductivity of these 3D nanostructures can be readily tuned: the in-plane thermal conductivity increases with increasing interpillar distance while the out of plane thermal conductivity increases with increasing pillar height and decreasing interpillar distance. The highest in-plane thermal conductivity obtained is 40 W/m-K for 3D super-structure with Type 1 unit cell with a 3.3 nm interpillar distance and 1.2 nm pillar height at room temperature. The highest out of plane thermal conductivity is 6.8 W/m-K for 3D super-structure with Type 1 unit cell which has 2.1 nm interpillar distance and 4.2 nm pillar height. Later, these values are compared with the thermal conductivity values of pure (6,6) SWCNT and single graphene layer, which are calculated using MD with the same interatomic potential.
Buckling Analysis of Drill Strings in Inclined Wellbores Using the Explicit Finite Element Method
Authors: Hajianmaleki Mehdi , Daily Jeremy S. , Ring Lev , Gandikota Raju
Published: October 2013

Understanding drill string buckling behavior is a significant challenge to the petroleum industry. In this paper, the explicit finite element method implemented in Abaqus software is employed to study the buckling of drill strings for inclined straight wellbores. Classic solutions for the critical buckling length of self-weighted columns as well as critical buckling load for drill pipe inside inclined wellbores are compared to explicit FEA and accurate results are provided by the finite element based predictions. The effect of different inclination angles and string effective weight due to the buoyancy effect has been studied and the results for sinusoidal and helical buckling are compared to analytical results and experimental data in the literature. The theoretical predictions for different inclination angles agree with the simulations. Theoretical buckling load of inclined drill strings approaches zero by decreasing the effective weight of a floating drill string. However, the results of finite element simulations show that significant buckling load would still exist for very low drill string effective weight. These results are confirmed by experimental results provided by other researchers. Overall, the efficacy of using explicit finite element methods to model drill string buckling behavior is demonstrated.
Effect of Surface Patterning on the Adhesive Friction
Authors: Rashwan Ola H. , Stoilov Vesselin , Alpas Ahmet T. , Guerrero Ariel R.
Published: October 2013

Tribological properties play an important role in many applications that require low adhesion or non sticking surfaces; therefore, understanding the effect of the surface morphology on adhesion can allow for improved surfaces to be created. In the last 10 years, researchers have paid attention to the impact of the surface roughness on the tribological behaviour. As a result the idea of surface pattering or texturing has emerged as a mean of controlling the friction and adhesion between contacting surfaces. In this study, the effect of the different surface patterns with specifically selected parameters, such as the pattern size, and pattern density on the adhesion force which is measured by Atomic Force Microscope (AFM) is thoroughly investigated. First, micro laser dimples of different diameters’ (D’s) of 5, 10 and 20 μm are fabricated on air hardened tool steel samples using High quality–high power CuBr vapour laser. The distance (L), between the centers of two neighbouring circular dimples, were set to different values of 5, 10, 20, 40 and 80 μm. The AFM tip is modified so that the effect of the patterning on the adhesive force can be captured. A customized micro fabricated polystyrene particle of 120 μm in diameter is used as a tip attachment to the end of calibrated silicon nitride cantilever. The pull-off force versus displacement curves are recorded and used to estimate the average adhesion force for each surface pattern. It has been observed that selected surface patterns significantly decrease the adhesive forces compared to a flat surface. The ratio D/L, which represents the pattern density or the complement of the contact area establishes a well-defined trend of decrease of the adhesion force as D/L increases.
System Evaluation and Life-Cycle Cost Analysis of a Commercial-Scale High-Temperature Electrolysis Hydrogen Production Plant
Authors: Harvego Edwin A. , O’Brien James E. , McKellar Michael G.
Published: October 2013

Results of a system evaluation and lifecycle cost analysis are presented for a commercial-scale high-temperature electrolysis (HTE) central hydrogen production plant. The plant design relies on grid electricity to power the electrolysis process and system components, and industrial natural gas to provide process heat. The HYSYS process analysis software was used to evaluate the reference central plant design capable of producing 50,000 kg/day of hydrogen. The HYSYS software performs mass and energy balances across all components to allow optimized of the design using a detailed process flow sheet and realistic operating conditions specified the analyst. The lifecycle cost analysis was performed using the H2A analysis methodology developed by the Department of Energy (DOE) Hydrogen Program. This methodology utilizes Microsoft Excel spreadsheet analysis tools that require detailed plant performance information (obtained from HYSYS), along with financial and cost information to calculate lifecycle costs. The results of the lifecycle analyses indicate that for a 10% internal rate of return, a large central commercial-scale hydrogen production plant can produce 50,000 kg/day of hydrogen at an average cost of $2.68/kg. When the cost of carbon sequestration is taken into account, the average cost of hydrogen production increases by $0.40/kg to $3.08/kg.
Experimental and Analytical Study of Sub-Watt Scale Tesla Turbine Performance
Authors: Romanin Vince D. , Krishnan Vedavalli G. , Carey Van P. , Maharbiz Michel M.
Published: October 2013

Viscous turbines, like the Tesla turbine, can be manufactured inexpensively at small scales, are robust, and are low maintenance, making them ideal for micro to watt scale energy harvesting applications. However, high efficiency turbines have not yet been demonstrated at small (sub-watt) scales. Previous studies have developed analytical models of turbine performance and analyzed parametric trends in performance for larger turbines and for air as a working fluid. In this study, the same parametric trends in performance are compared to test data for a micro-scale Tesla turbine with water as a working fluid. A Computational Fluid Dynamics (CFD) model is then compared to both the analytical and experimental turbine efficiencies. Tesla turbines were tested with 8 different nozzle configurations, 3 different rotor configurations, and several different flow rates. The test results show that several of the performance trends predicted by the analytical model match experimental results. The CFD solutions of the flow field are then used to help reconcile areas where the analytical predictions do not match experimental data. Certain trends in turbine performance are discussed, and the feasibility of further scaling down Tesla turbines (< 1 cm) is discussed.
Transient Analysis for Contained-Cold-Aisle Data Center
Authors: Alkharabsheh Sami A. , Ibrahim Mahmoud , Shrivastava Saurabh , Schmidt Roger , Sammakia Bahgat
Published: October 2013

The objective of this paper is to conduct a transient analysis for a contained-cold-aisle data center using Computational Fluid Dynamics (CFD) modeling. Containing the cold aisle reduces the inherent challenges of predictability and energy consumption of data center cooling systems by separating the hot and cold air streams. Transient analysis is crucial to further show the benefits of this methodology and investigate the potential drawbacks. In this work, we investigate the effect of variable power and flow rate in time on a raised-floor data center with specific geometry. First, a base case numerical model is established. Then, we conduct a transient analysis for the uncontained base case and the three containment configurations. The containment configurations under consideration are ceiling-only, doors-only, and fully-contained cold aisle. We hold a comparison between different geometrical configurations of the containment system under certain transient operating conditions. Computer Room Air Conditioning (CRAC) failure and change in IT-demand are chosen to represent conventional transient scenarios in a data center. The transient analysis shows overshoots of cabinet inlet air temperatures beyond the final steady state, which cannot predicted through a simple steady state analysis. In addition, the uniform temperature distribution inside the cold aisle is affected by the change in air supply and level of containment. The temperature distribution in the cold aisle changes with time. Guidelines can be recommended based on the conclusion of this study.
Molecular Simulation of the Self-Agglomeration of Carbon Nanostructures in Various Chemical Environments
Authors: Banerjee Soumik
Published: October 2013

Self-assembly of carbon nanostructures in solutions provides a cost-effective means to synthesize uniform vertically-aligned nanostructures with specific morphologies including shapes such as wires, sheets and spherical particles. In addition to facilitating the synthesis of bulk carbon nanomaterial, a complete understanding of the agglomeration mechanics also provides a means to deposit uniform layers of carbon nanostructures on top of substrates to produce molecularly-tailored composites with specific mechanical properties. Self-assembly is a complex dynamical process that involves the interaction between the nanoparticle precursors, the transport properties of the individual precursor molecules as well as the precursor-solvent interactions. Depending on the chemical nature of the solvent used during the process various nanostructures of varying shapes and morphologies can be synthesized starting from individual buckyballs and nanotubes. However, despite its wide range of applications, there is a lack of understanding of the self-assembly of carbon nanoparticles. Some of the key factors that govern the agglomeration process are the π-π interaction of the aromatic carbon nanostructures and their interaction with the solvent molecules. A predictive model for self-assembly, that relates the above parameters to the morphology, therefore needs to account for the specific molecular interactions. We present molecular simulation results that incorporate the above effects and shows that the nature of association of the nanoparticle precursors determines the shape and size of the agglomerate. Furthermore, our results show the dependency of the agglomerate size on the concentration of precursors as well as the ambient temperature.
Modeling Multi-Point Wheel/Rail Contact in the Analysis of Turnout Negotiation of Multibody Railroad Vehicles
Authors: Terao Akihiro , Sugiyama Hiroyuki
Published: October 2013

In this investigation, a numerical procedure that accounts for multipoint contact for the analysis of vehicle/turnout interactions is developed. To this end, the multiple look-up contact table approach that can be used for modeling the change in the rail cross sectional shapes on turnout along the track is generalized for multipoint contact scenarios. The numerical results are compared with those of the online constraint/elastic contact approach for the analysis of curve negotiation first, and then it is demonstrated that the numerical procedure developed in this investigation can be used for predicting the multipoint contact between the wheel and rail for the analysis of vehicle/turnout interactions.
DSMC Modeling of Dropwise Condensation With Variable Wettability
Authors: Mendoza Hector , Carey Van P.
Published: October 2013

Recent heat transfer studies on nanostructured surfaces have shown that enhanced dropwise condensation heat transfer can be attained through clusters with reduced droplet sizes. A Direct Monte Carlo Simulation (DSMC) approach is used here to investigate the limitations of dropwise condensation as droplet sizes are reduced. The model is idealized by assuming uniform droplet distribution with an effective diameter. To minimize computational time, the model further uses symmetry to focus the analysis on a quarter segment of a single droplet condensing on a cold wall. The effects of surface wettability are explored by accounting for variations in droplet conduction with contact angle, while changes of interfacial resistance with droplet curvature are also incorporated into the model. To investigate the effect of reduced droplet sizes, the simulations were run for droplets with radii between 1μm down to 5nm. The simulations were run for standard atmospheric conditions at different levels of subcooling and accommodation. In all instances, the same behavior is observed as non-continuum effects become significant at reduced diameters, causing heat transfer coefficients to reach a maximum. The predictions of the DSMC model are compared to previous work attempting to capture similar effects. The significance of the observations for current and future research in dropwise condensation is discussed in detail.
Strain Rate Effect on the Stiffness of Random Fiber Composites due to Matrix Cracking and Interfacial Debonding
Authors: Yang Wensong , Pelegri Assimina A.
Published: October 2013

Considering the wide applications of composite materials, it is necessary understand the dynamic effects of damage mechanisms, including matrix cracking and interfacial debonding, on the stiffness performance of these materials. Strain rates may have a significant effect on the dynamic behavior of composite materials subjected to dynamic loadings. In this study, a numerical approach with the finite element code ABAQUS is used to develop a failure criterion to express the effect of static and dynamic damage mechanisms on the composite’s stiffness under uniaxial tensile loading. A random epoxy/glass composite material is investigated under three strain rates: quasi-static, intermediate, and high, here 10−4, 1, and 200 s−1, respectively. The results illustrate that the interfacial debonding increases as the strain rate increases in random epoxy/glass composite materials. At the same time, the normalized stiffness components exhibit different trends with strain rate increase due to their connection to matrix cracking or interfacial debonding.
Thermal Analysis of a Modular, Microfluidic Device for the Rapid Detection of Stroke
Authors: Lowrey Brooks B. , Park Daniel S. , Murphy Michael C.
Published: October 2013

A modular, microfluidic device was designed to aid in the rapid detection and treatment of stroke. The device modules process whole blood for the detection of genes expressed in response to a stroke event using a series of assay steps including: cell capture using antibodies, thermal lysis, solid-phase reversible immobilization (SPRI) of nucleic acids, reverse transcription (RT), ligase detection reaction (LDR), and single pair fluorescence resonance energy transfer (spFRET) readout. Cell lysis, RT, and LDR require temperatures of 90°C, 37°C, 65°C and 95°C respectively, therefore strict thermal isolation constraints between thermal zones in the device modules were necessary. Thermal isolation was accomplished using 2 mm and 1 mm air gaps between the fluidic modules and heating elements in the polymer device. Finite element mathematical models (ANSYS v. 12.1, Houston, PA) were used to characterize the thermal zones in two 2D simulations. Section 1 simulation results showed ±1.5°C in cell lysis, ±1.6°C in RT, and ±1.6°C in the denaturation section of LDR. Section 2 simulation showed ±2.6°C in denaturation and ±0.4°C in the annealing/extension zone of LDR.
Multi-Functional Fullerene Soot/Alumina Composites
Authors: Robles Hernandez Francisco C. , Majkic Goran
Published: October 2013

Here are presented the results of characterization and mechanical testing of composites consisting of alumina matrix reinforced with fullerene soot. The composites were manufactured by mechanical milling, sonication, and spark plasma sintering. Small amounts of Ni and Ti were added as catalyst to in situ synthesize complex carbon structures during thermomechanical processing. Some of the carbon in the soot showed phase transformations to diamond, fullerite, graphene-like particles, etc. that act as effective reinforcement. This resulted in significant improvements in fracture toughness in fully dense samples while preserving relatively high hardness. Electrical resistivity decreases by 15 orders of magnitude. The abovementioned improvements are attributed to the formation of a homogeneous carbon coating on the alumina particles and the in situ synthesized carbon nanostructures. The type of carbon nanostructure synthesized depends on the catalyst, SPS conditions, and the amount of fullerene soot added. A small amount of ruby is present as an impurity in the alumina serving as a pressure sensor through its stress-dependent luminescence and gives additional multi-functionality to the composite.
Studying of Contact Angle Friction and Contact Angle Hysteresis (CAH) Though Force Measurements
Authors: Ni Qi , Marschke Timo , Steele Samuel , Seyed Najafi , Crane Nathan B.
Published: October 2013

A novel method of measuring contact line friction and contact angle hysteresis is described. In this method, a droplet is constrained between two surfaces while the surface of interest initiates motion. The results are compared to conventional characterization methods such as measuring the angle of inclined plane for droplet motion and measuring advancing and receding contact angles by infusing/withdrawing liquid from the substrate. At slow speeds, the proposed method provides a measure of the hysteresis but can also capture information about the contact line friction and viscous affects. Droplet force dependence on droplet size (height/width) is also investigated.
Two-Dimensional Numerical Analyses of Acoustophoresis Phenomena in Microfluidic Channel With Microparticle-Suspended, Viscous, Moving Fluid Medium
Authors: Liu Zhongzheng , Han Arum , Kim Yong-Joe
Published: October 2013

Microfluidic, acoustophoretic separation of cells and microparticles has gained significant interest since it can offer a high-throughput, high-efficient, label-free, continuous separation. However, the designs of state-of-the-art, acoustophoretic separation devices have been mainly derived from a simplistic, one-dimensional (1-D), analytical acoustic model in a “static” fluid medium. Therefore, it is not possible to consider the effects of 2-D or 3-D geometries, “moving” fluid media, and viscous boundary layers that can significantly influence cell/microparticle motions in reality. Here, a 2-D numerical modeling procedure for analyzing the acoustophoretic microparticle motion in microfluidic channels is presented to address the aforementioned deficiencies. Here, the mass and momentum conservation equations and the state equation are decomposed into zeroth-, first-, and second-order governing equations by using a perturbation method. Then, zeroth-, first-, and second-order acoustic pressures are calculated by applying a sixth-order finite difference method to the decomposed governing equations with appropriate boundary conditions under an acoustic excitation. In particular, non-reflective boundary conditions are derived for the first- and second-order governing equations and applied at the ends of a microchannel. The acoustophoretic force calculated by integrating the acoustic pressure over the surface of a rigid microparticle along with viscous drag force is then applied to the Newton’s equation of motion to analyze the acoustophoretic motion of the microparticle. By comparing numerical and 1-D analytical microparticle motions, the proposed numerical modeling procedure is validated for a 1-D plane-wave-like excitation case. It is also shown that numerically-predicted microparticle behavior is quite different from that of the 1-D analytical model for a 2-D acoustic excitation case in a realistic microchannel. Additionally, the effects of the microparticle’s size and density on its acoustophoretic motions are studied.
Interface Thermal Resistance and Length Effect on Thermal Conductivitiy of SWNT Bundles
Authors: Toprak Kasim , Bayazitoglu Yildiz
Published: October 2013

Using different calculations and measurement methods, the results for the thermal conductivity in a single wall carbon nanotube (SWNT) are compared. Then, the interface thermal resistance effects on the effective thermal conductivity of multiple SWNTs in a hexagonal packing system submerged in oil, air, and water are studied. The results show that as the interface thermal resistance increases, the effective thermal conductivity decreases. Moreover, length, length fraction, and volume fraction effects on the thermal conductivity of the system submerged in a water medium are approximated by including the interface thermal resistances of the nanotube-matrix and nanotube-nanotube. The systems’ length ranged between 500–3000 nm. The created models contain either vertically aligned or non-straight nanotubes. Non-straight nanotubes systems make one or two contact points with other nanotubes. These contact points’ location vary based on the length ratio known as the length fraction. It is found that the effective thermal conductivity of the SWNT bundle has the highest value when they are uniformly aligned and dispersed without contact. As the density and length of the SWNTs increase, the effective thermal conductivity of the bundle system also increases.
Effect of Staggered Configurations on Laminar Forced Convection Heat Transfer From Square Cylinders Inside Water/CuO Nanofluid
Authors: Jafarpur K. , Nowzari M. H. , Jayhooni S. M. H. , Abbasi Baharanchi A.
Published: October 2013

In the present article, forced convection heat transfer of steady flows pass over staggered square cylinders has been studied numerically. In the tested cases, the passing fluids are nanofluid which has water as base fluid, containing CuO as nanoparticles with different volume fractions. Besides, the flow is laminar and all cylinders are square with constant wall temperature. Recent correlations are used for viscosity and thermal conductivity of nanofluids which are functions of temperature and particle volumetric concentration. Numerical simulations have been performed for low Peclet numbers(Pe ≤ 200), since in this range the flow is steady and laminar. Four different configurations of square cylinders have been studied and the results are compared with each other. This is to investigate the effect of different staggered configurations on forced convection heat transfer inside CuO/Water nanofluids. Finally, a model which has the configuration for the highest heat transfer enhancement inside CuO/Water nanofluids with different particle volume fractions has been specified.
Optimal Sizing of Hybrid Renewable Energy Sytems Using a Hydrogen Storage System for Various Power Demand Applications
Authors: Iverson Zachariah , Achuthan Ajit , Marzocca Pier , Aidun Daryush
Published: October 2013

Hybrid systems consisting of a single or multiple renewable energy generators coupled with an environmentally-friendly storage system are used in renewable power production due to wide disparity between the intermittent power generated and the power demand. These systems also have the potential to provide 24/7 power without leaving a carbon footprint in operation. Finding the optimal size of a Hybrid Renewable Energy System (HRES) with no Loss of Power Supply (LPS) is of utmost concern when considering the Levelized Cost of Energy (LCE) of the system over its lifecycle. In this study, an optimization routine employing a search algorithm is developed to find the system configuration with a minimized LCE that meets also meets zero LPS. To this end, a system model is developed by integrating basic models of the subsystems. The system model is then used to investigate two different loading cases, 1) where the demand cannot be controlled as in the case of the power demand of a residential network, and 2) where the demand can be controlled up to certain limits, as in the case of the power demand of a data center or a data center network. Various types of controllable power demands (CoD) are studied. When compared to the power demand of a residential network, results demonstrate a significant reduction in the life cycle costs for CoD conditions.
A Mixed Damage Model for Simulating Delamination of Composite T-Joint Components
Authors: Chen J.
Published: October 2013

A mixed cohesive damage model was introduced in this paper to study the delamination of composite T-joint components under pulling load. Prediction together with part of test results was presented in this paper. Modelling prediction had a good agreement with experimental work. This study indicated that the mixed damage scale plays an important role in the progressive damage analysis of T-joint components. The mixed damage scale properly reflected the effects of interaction between different damage modes in simulating damage propagation of an object with strong coupled effects. This coupled damage effect was considered from the material softening stage to final crack. Thus a proper damage accumulation was accounted since materials begin damage. An example given in this paper shown the delamination in the deltoid region of T-joint was simulated very well. Finally, a concept of novel materials was proposed for the deltoid region of T-joint in this paper. Initial investigation by simulating delamination presented that the damage resilience of composite T-joint with novel composite materials in deltoid region significantly improved its damage resilience.
Effect of Manufacturing Process Parameters on Property Evolution of Printed Circuit Board Laminates
Authors: Lall Pradeep , Narayan Vikalp , Blanche Jim , Strickland Mark
Published: October 2013

The effect of temperature exposure encountered both during assembly and in fielded products, has a known influence on glass transition temperature of printed-circuit board (PCB) laminate materials. Printed circuit board laminates such as FR4 are composites of epoxy resin with woven fiberglass reinforcement. Interaction between manufacturing process variables that impact the changes in glass transition temperature (Tg) has been studied. The laminates studied have been broadly classified into high-Tg, and mid-Tg laminates. Different sets of reflow profiles were created by varying the process variables including, time above liquidus, peak temperature, ramp rate and cooling rate. The effect of multiple reflows encountered in normal assembly or board re-work has been studied by exposing the assemblies to multiple reflows between 2x–6x. Changes to the glass transition temperature have been classified by measurement of the glass transition temperature were measured via Thermo Mechanical Analysis (TMA). Statistical analysis of the variables has been used to determine the statistical significance of the measured changes for large populations.
Mechanical Behavior of Sn1Ag0.5Cu and Sn3Ag0.5Cu Alloys at High Strain Rates
Authors: Lall Pradeep , Shantaram Sandeep , Suhling Jeff , Locker David
Published: October 2013

Electronics may experience high strain rates when subjected to high g-loads of shock and vibration. Material and damage behavior of electronic materials at high strain rates typical of shock and vibration is scarce. Previously studies have shown that second-level interconnects have a high propensity for failure under shock and vibration loads in fine pitch electronics. Exposure to shock and vibration is common in a variety of consumer environments such as automotive and portable electronics. The low strain-rate properties of commonly used SnAgCu solders, including Sn1Ag0.5Cu and Sn3Ag0.5Cu, have been found to evolve with time after prolonged exposure to high temperatures. High strain rate properties of leadfree solder alloys in the strain-rate range of 1–100 sec−1 are scarce. Previous attempts at characterizing the high strain rates properties have focused on the use of the Split Hopkinson Pressure Bar (SHPB), which enables measurements of strain rates in the neighborhood of 1000 per sec. In this paper, a new test-technique developed by the authors has been presented for measurement of material constitutive behavior. The instrument enables attaining strain rates in the neighborhood of 1 to 100 per sec. Tests are conducted at strain rates 10, 35 and 50 per sec. High speed cameras operating at 75,000 fps have been used in conjunction with digital image correlation for the measurement of full-field strain during the test. Constancy of cross-head velocity has been demonstrated during the test from the unloaded state to the specimen failure. Solder alloy constitutive behavior has been measured for SAC105, SAC305 solders. Non-linear Ramberg-Osgood model has been used to fit the material data. The Ramberg-Osgood model available in Abaqus has been used for tensile test simulation and to correlate with DIC based experimental strain data.
Hemodynamic Abnormalities in Stented Carotid Artery: A Fluid Structure Interaction Study
Authors: Metzger Thomas A. , Chandra Santanu , Sucosky Philippe
Published: October 2013

Balloon-stented angioplasty is a common treatment for carotid arterial atherosclerosis. Clinical studies have shown that within 6 months of the initial procedure, 25% of stented-angioplasty patients develop restenosis, a postoperative narrowing of the artery due to plaque accumulation onto the stent. While hemodynamics and more specifically low oscillatory wall-shear stress have been identified as key factors promoting atherogenesis, their role in restenosis following stent implantation remains unclear. We hypothesize that the implantation of a stent generates hemodynamic abnormalities consisting of low wall shear stresses in the vicinity of arterial wall regions prone to restenosis. The objective of this study was to compare computationally the hemodynamics in normal (healthy), stenosed (atherosclerotic) and stented carotid artery bifurcation models and to investigate potential correlations between regions presenting high hemodynamic abnormalities and regions prone to postoperative stent angioplasty restenosis. Realistic, three-dimensional models of normal, stenosed and stented human carotid bifurcations consisting of the common (CCA), external (ECA) and internal (ICA) carotid arteries were developed using the computer-assisted design software Solid Edge. The characteristic dimensions of the normal and stenosed models were obtained from previously published human data. The stented model was designed by modeling the inner surface of the ICA bulb region as a rigid cylindrical surface mimicking the presence of a stent. Fluid-structure interaction (FSI) simulations were carried out using the adaptive arbitrary Lagrangian Eulerian (ALE) approach of ANSYS 14 to simulate flow and arterial wall dynamics in each model subjected to physiologic pressure and flow rate. As expected, the atherosclerotic model resulted in higher velocity and wall shear stress (WSS) levels than the normal model due to the reduced ICA lumen. In addition, while stent implantation restored the hemodynamic performance of the vessel, it generated lower WSS than in the normal model, which may contribute to restenosis. This study provides new insights into the possible hemodynamic roots of postoperative stent angioplasty restenosis.
Numerical Investigation of Multi-Scale Mixing in Microchannel T-Junction With Wavy Structure
Authors: Solehati Nita , Bae Joonsoo , Sasmito Agus Pulung
Published: October 2013

Mixing in chemical microreactors is a multi-scale processes as the transport mechanisms occur at different length scales. The small scale mixing depends mainly on molecular diffusion which causes conventional microchannel T-junction has poor mixing quality. To improve the quality, one can utilize secondary flow generated by wavy structure to enhance chaotic mixing. To gain better understanding of the interplay of transport mechanism, we develop numerical model for mixing in micro-channel T-junction with wavy structure. To ensure robust and accurate solutions, several discretization methods and mesh sizes were tested and compared. It is found that the solutions are sensitive to the Reynolds; huge amount of mesh (>107) is required to resolve small molecular diffusion and chaotic mixing especially at high Schmidt number, whilst relatively lesser mesh is found to be sufficient for conventional T-junction. Further, parallelization is found to be beneficial to expedite the computation, albeit the speed is not linear with the number of the processors. The mixing quality of T-junction with wavy structure is then compared with that of conventional T-junction counterpart. It is noted that up to 50% improvement of mixing quality is achieved with wavy structure which has potential for several applications.
Fracture Mechanics Based Life Prediction of Hollow Extrusion Dies
Authors: Qamar Sayyad Zahid
Published: October 2013

Hot metal extrusion dies, especially for hollow profiles, are quite costly. Repair or replacement of dies and affiliated tooling adds to the cost, brings down productivity, and can contribute to product defects. Reasons for the high production and maintenance cost are stringent material requirements (high-strength and high-hardness tool steels), precision manufacturing methods (spark erosion, wire EDM, etc), and a series of specialized heat treatment and surface hardening operations. Consequently, a major goal for die designers and manufacturers is longer service life. An equally important objective is a reasonably accurate prediction of time-to-failure, to help devise an optimum replacement and inventory strategy, and for good performance evaluation. Majority of hot-work extrusion dies fail by fatigue fracture. Treating the die as a flat plate with edge crack, a fracture mechanics based fatigue life prediction model was developed by the authors in an earlier work. To improve the precision of die life prediction, a hollow (tube) extrusion die is modeled in the current work as a pressurized cylinder with internal crack. Based on this new strategy, a model is developed to forecast fracture failure of extrusion dies. Stochastic nature of various fatigue related die parameters is examined. Monte Carlo simulation is used for die life prediction under a given set of operating conditions and mechanical properties. Simulated fracture life values thus obtained are quite realistic in comparison with actual extrusion die life data from the industry.
Numerical Investigation of Thermal Behavior of HV Transmission Cables in Tunnel With Water Cooling System
Authors: Wu Dicken K. H. , Lin Y. F. , Xu H. T.
Published: October 2013

In the present study, a simplified and efficient numerical simulation approach has been developed for thermal analysis for the high voltage (HV) cable tunnel with extended length. The thermal behavior analysis of different HV cable arrangements, thermal properties, as well as the amount of heat dissipating towards the water-cooled system and the surroundings was analyzed and discussed in detail. With a typical sand-filled HV cable and pipe work arrangement, the circuit water-cooling system would take up around 85% of the total heat dissipation. The remaining heat is catered by the tunnel ventilation system and the soil surrounding the tunnel. Note that an air-filled cable trough is less preferable.
Evaluation of Blister Behavior for U10Mo Mini Fuel Plates With Cold Rolled Foils
Authors: Ozaltun Hakan , Miller Samuel J.
Published: October 2013

This article aims to provide possible mechanical causes for the lowered blister temperatures of RERTR-12 and AFIP-4 fuel plates. Recent experimental investigations to determine the blister threshold temperatures have indicated lower thresholds for similar plates with comparable burn-up histories. Measured blister temperatures of roughly 100 °C lower compared to the previously tested plates may not be satisfactory for some plates. The primary differences between recent experiments and previous tests are: (1) An aggressive cold work process involving large thickness reduction ratios without normalization or full annealing (2) Subjecting the plates to a thermal cycling process prior to irradiation, and finally (3) A primarily frontal neutron flux as opposed to a transverse flux profile. It is believed that the stress field has implications to blister behavior. To investigate this claim, the stress-strain states for the fabrication procedure were evaluated. First, the residual stress profile caused by the cold rolling process was calculated. Modeling of the cold rolling process has shown confirmation of residual stresses of considerable magnitude and the existence of stress gradients with respect to foil thickness prior to the HIP process. Once calculated, these stress profiles were used as an initial condition for the fabrication process. Due to the variation in stress fields depending on location at which a foil is cut from the cold rolled plate, three representative regions were selected and implemented in the HIP simulation. Variation in stresses, depending on location of the cold rolled plate as well and variation in the through-thickness, results in a wide range of mechanical stress states. This suggests that inhomogeneous irradiation and thermal cycling behavior will result from the use of cold rolled foils. Additionally, these results suggest that there will be fundamental differences in fuel plate behavior observed between plates fabricated with cold rolled foils versus hot rolled and fully annealed foils.
Parametric Analysis of Effective Viscosity Models for Nanofluids
Authors: Meyer J. P. , Nwosu P. N. , Sharifpur M. , Ntumba T.
Published: October 2013

Viscosity is an important consideration in the application of nanofluids as heat transfer fluids. Various models have been developed to predict the viscosity of nanofluids. The accuracy of these models is of important benefit in determining the rheological performance of nanofluids, particularly in conditions which vary continuously. In this paper, a parametric analysis is undertaken to investigate the degree of variability between empirical data and model predictions. It was found that there is high variability in the compared results, which suggests that a wide range of constitutive factors need to be incorporated into the models in order to account adequately for the rheological behaviour of nanofluids.
Massively Parallel Spectral Difference Solver for Simulating Vortex-Induced Vibrations of Circular Cylinders
Authors: Liang Chunlei , DeJong Andrew S.
Published: October 2013

This paper presents high-fidelity simulations of the Vortex-Induced Vibration (VIV) phenomena using a new computational model based on the high-order spectral difference (SD) method on unstructured grids. The SD method has shown promise in the past as a highly accurate, yet sufficiently fast method for solving unsteady viscous compressible flows. A Riemann solver is used to compute the inviscid fluxes at the cell interfaces, and the viscous fluxes are computed using an averaging mechanism based on the fluxes from the two cells that share the interface. A third-order Runge-Kutta scheme is used to advance time. In this viscous, compressible flow solver, the displacement of an elastically mounted bluff body has been coupled to the lift force created by vortex shedding. The solver is validated by correlating the lift and drag coefficients with previous published results of two cases: single rigid cylinder, and single elastically mounted cylinder. The rigid cylinder case validates the accuracy of the fluid solver. The elastically mounted case validates the fluid-structure coupling. We simulate the phenomenon of wake galloping with two cylinders after the solver has been validated using single cylinder VIV phenomenon.
Electrospun Fibers Incorporated With Hydroxyapatite Nanoparticles and Graphene Nanoflakes for Bone Scaffolding
Authors: Jabbarnia A. , Patlolla V. R. , Misak H. E. , Asmatulu R.
Published: October 2013

Sol-gel driven hydroxyapatite (HA) nanoparticles and graphene nanoflakes were incorporated with polycaprolactone (PCL) at different concentrations, and then electrospun at various spinning conditions, such as distance, electrical potential, viscosity and pump speed. The HA nanoparticles were initially amorphous, so they were annealed at elevated temperature (750 °C) for two hours to make them crystalline. Scanning electron microscopy and X-ray diffraction analysis techniques were conducted on the produced nanocomposite fibers. The studies showed that the HA nanoparticles (20–50 nm) and graphene were well distributed in the PCL fibers (500 nm to 5 μm). We believed that such nanoscale biomaterials can accelerate the bone growth and bone regeneration for many patients who are seeking solutions.
Tarzan's Dilemma: A Challenging Problem for Introductory Physics Students
Authors: Rave Matthew , Sayers Marcus
Published: October 2013

The following kinematics problem was given to several students as a project in conjunction with a first-semester calculus-based physics course. The students were asked to keep a journal of all their work and were encouraged to keep even their scrap paper. The goal of the project was to expose the students to the process of doing theoretical physics, by tackling a project that is easy to pose conceptually yet surprisingly challenging in its solution.