bluuebunny/crossref_metadata_2025 huggingface dataset:
Identifying Intersections of Dispersion Curves for Phononic Crystals
Authors: Liu Kuo-Chung , Chou Yuan-Fang
Published: April 2014

Many methods have been developed to obtain the band structure of crystals. Generally, they all require numerical computation to construct the spectrum. Therefore, only discrete points instead of continuous lines provided for dispersion relations. This makes it difficult to distinguish the modes of nearby discrete points without calculating mode profiles. That is, more effort is required to determine whether two dispersion curves intersect each other or not. A new method of investigation for phononic crystals is proposed which takes advantage of finite group theory and symmetrized plane waves that can block-diagonalize secular equations. A system consisting of a periodic square array of nickel alloy cylinders and an aluminum alloy matrix is studied. Intersections between dispersion curves of different modes can be identified directly. The result contradicts that presented by Kushwaha in 1993. The method can not only distinguish different modes directly from the computed band structure but also saves computation time. Compared to plane wave expansion method, only one quarter of computation time is required for calculating the spectrum. The higher symmetry a group has, the shorter the computation time expected.
Numerical Assessment of the Aerodynamic Properties of a Solar Vehicle
Authors: Kin Warrick D. , Kruger Sunita , Janse van Rensburg Nickey , Pretorius Leon
Published: April 2014

Due to wide emphasis on climate change today, alternative fuel research is necessary. Consequently, the South African Solar Challenge has created a competitive platform for research into alternative energies, particularly solar. The University of Johannesburg (UJ) competed in the competition using their uniquely designed and built solar vehicle, Ilanga I. However, due to the constraints of the energy available, the aerodynamics of the vehicle has to be exceptionally good. Subsequently, a large proportion of the total power of the vehicle is used to overcome the aerodynamic resistance posed by the vehicle. Furthermore, much of the remaining power of the vehicle is used to overcome rolling resistance. Consequently, solar vehicles have to be as lightweight as possible in order to effectively reduce the rolling resistance. However, reducing weight of the vehicle results in the vehicle’s stability being greatly affected by side-wind effects. In order to improve on the vehicle, it is very important to test for and obtain its aerodynamic characteristics. This research article aims at obtaining the average drag coefficient felt during the majority of the race as well as the lift coefficients for side-wind cases, in order to investigate vehicle safety. Thus, through the use of Computational Fluid Dynamics (CFD), it was possible to obtain an assessment of the vehicle’s performance. Simulations were performed using the Reynold’s Averaged Navier Stokes (RANS) method with use of the k-ω SST turbulence model. This method of simulation showed reasonable predictions of the results as compared to literature.
Fabrication of Hybrid Micro-Nanofluidic Devices With Centimeter Long Ultra-Low Aspect Ratio Nanochannels
Authors: Pinti Marie , Prakash Shaurya
Published: April 2014

Hybrid microfluidic and nanofluidic devices have a variety of applications including water desalination, molecular gates and DNA sieving among several other lab-on-chip uses. Most microfluidic and nanofluidic devices currently are fabricated in glass, silicon, polydimethylsiloxane (PDMS), or with a combination of these materials. In order to impart functionality, metals, polymers or auxiliary components are often integrated with these devices. Ultra-low aspect ratio channels have several advantages including critical dimensions on the nanoscale but increased throughput compared to higher aspect ratio channels with the same critical dimension, which is important for applications where a higher volumetric flow rate is desired. Additionally, theoretical analysis is significantly easier as ultra-low aspect ratio channels can be modeled as 1-D systems. The fabrication methods for achieving low aspect ratios (< 0.005) usually require extensive facilities with several innovative fabrication and bonding schemes being previously reported. In this paper, we report on fabrication and bonding of ultra-low aspect ratio microfluidic and nanofluidic devices with aspect ratios at 0.0005 in glass/PDMS devices in contrast to the previous best reported result of 0.005 achieved in a silica device using stamp and stick PDMS bonding. The simplicity of our approach presents a new pathway to achieving the lowest aspect ratio nanochannels ever reported for channels fabricated using an interfacial layer for bonding. Centimeter long nanochannels on a borosilicate substrate were fabricated by standard UV photolithography followed by wet etching. Surface roughness of the fabricated channels is on the same order as the roughness of the initial substrate (2–3 nm) and therefore can enable fabrication of channels with critical dimensions approaching 15 nm or less. Devices were then bonded using a second borosilicate substrate with a thin PDMS adhesion layer (∼ 2 μm). The PDMS adhesion layer allows rapid, facile, and alignment-free bonding compared to traditional fusion or anodic bonds. Successful verification of device operation and functionality was determined by verifying flow in operational devices and with scanning electron microscopy to confirm bonding for the formation of nanochannels.
Growth of Patterned Micropores in Poly-Dimethylsiloxane (PDMS) Using the Thermocapillary Effect
Authors: Banait Arya , Vishwakarma Vivek , Choobineh Leila , Jain Ankur
Published: April 2014

Poly-dimethylsiloxane (PDMS) is a well-known soft polymer with applications in a wide variety of research fields. PDMS is a particularly attractive material for miniaturized bioanalytical systems because of its biocompatibility, gas permeability, chemical inertness and the ability to reproduce miniature features such as microchannels in PDMS. This paper describes a technique to obtain through-membrane pores in thin PDMS membranes. This is based on thermocapillary effect in a MEMS-based microheater device made on a glass substrate. Uncured PDMS is poured on a microheater device that has been coated with a hydrophilic substrate such as poly-ethylene oxide (PEO). Upon heating, PEO evaporates and form gas bubbles in PDMS. The gas bubbles are attracted towards the hot region of the microheater device. The bubbles eventually self-assemble along the hottest isotherm, which in this case is the microheater line. In this manner, self-assembled pores in the desired pattern are obtained. Experiments conducted at different temperatures and PDMS thicknesses throw light on the physical phenomena behind this process and demonstrate the trade-off between PDMS curing rate and bubble escape rate. Results presented in this work are expected to aid in the design of novel PDMS-based membranes for filtration, separation and concentration.
Chip Package Co-Design: Effect of Substrate Warpage on BEOL Reliability
Authors: Raghavan Sathyanarayanan , Schmadlak Ilko , Leal George , Sitaraman Suresh
Published: April 2014

Large-scale integration at lower cost has led to the usage of multi-layered organic substrates in flip-chip assemblies. However, the warpage of substrate plays an important role in the reliability of back-end-of-line (BEOL) stack on a chip. In this work, we study the effect of substrate layer configuration, and thus the warpage of the substrate at reflow temperature on BEOL reliability. A plane-strain flip-chip on substrate assembly model is utilized to study the die and solder stresses for different substrate layer configurations. Apart from studying the die stresses, fracture mechanics based approach is used to study the effect of substrate configuration on energy available for a crack present in back-end-of-line (BEOL) stack. In this paper, we describe the methodology to model the substrate with initial warpage at reflow temperature, characterize the effect of the initial warpage at reflow temperature on die stresses at room temperature and further use fracture mechanics based approach to predict the change in risk for a crack present in BEOL stack for different substrate warpage configurations at reflow temperature.
Investigating the Effect of Machining Parameters on Microdrilling of Titanium Grade 19 Alloy
Authors: Yeole Shivraj , Nunna Nagabhushana Ramesh , Banoth Balu Naik
Published: April 2014

Electrical Discharge Micro Drilling (EDMD) is considered as one of the most effective method for machining difficult to cut and hard materials like titanium alloy. However, selection of process parameters for achieving superior surface finish, higher machining rate and accuracy is a challenging task in drilling micro-holes. In this paper, an attempt is made to optimize micro-EDM process parameters for drilling micro holes on titanium grade 19 alloy. In order to verify the optimal micro-EDM process parameters settings, material removal rate (MRR), electrode wear rate (EWR) and over cut (OC) were chosen as the responses to be observed. Pulse on time, pulse off time, electrode diameter and current were selected as the governing process parameters for evaluation by Taguchi method. Nine micro holes of 300 μm, 400 μm and 500 μm were drilled using L9 orthogonal array (OA) design. Optimal combination of machining parameters were obtained through Signal-to-Noise (S/N) ratio analysis. It is seen that machining performances like material removal rate and overcut are affected by the peak current whereas electrode wear is affected by peak current and electrode diameter. Morphology of the micro holes has been studied through SEM micrographs of machined micro-hole.
Development of a Smart Computer Numerical Control System
Authors: Sang Zhiqian , Xu Xun
Published: April 2014

Traditional Computer Numerical Control (CNC) machines use ISO6983 (G/M code) for part programming. G/M code has a number of drawbacks and one of them is lack of interoperability. The Standard for the Exchange of Product for NC (STEP-NC) as a potential replacement for G/M code aims to provide a unified and interoperable data model for CNC. In a modern CNC machine tool, more and more motors, actuators and sensors are implemented and connected to the NC system, which leads to large quantity of data being transmitted. The real-time Ethernet field-bus is faster and more deterministic and can fulfill the requirement of data transmission in the high-speed and high-precision machining scenarios. It can provide more determinism on communication, openness, interoperability and reliability than a traditional field-bus. With a traditional CNC system using G/M code, when the machining is interrupted by incidents, restarting the machining process is time-consuming and highly experience-dependent. The proposed CNC controller can generate just-in-time tool paths for feature-based machining from a STEP-NC file. When machining stoppage occurs, the system can recover from stoppage incidents with minimum human intervention. This is done by generating new tool paths for the remaining machining process with or without the availability of the original cutting tool. The system uses a real-time Ethernet field-bus as the connection between the controller and the motors.
A Novel MEMS Based Immunosensor for Ebola Virus Detection
Authors: Ganesan Adarsh Venkataraman
Published: April 2014

According to WHO, “The Ebola virus can cause several viral haemorrhagic fever (VHF) outbreaks in humans with a case fatality rate of up to 90%.” On top of these physical health issues, the Ebola virus infected patients are also subjected to many psychological problems. Recently, the ebola virus had its outbreak in Uganda on May 2011. In such places, the resources are scarce and the access to hospitals is limited. Hence, there is a need for point-of-care device for the diagnosis of Ebola virus. Currently, an expensive Immunofluorescence method is used to address this need. In this paper, the authors present the design of a robust, reliable and inexpensive microfluidic patch that is capable of detecting Ebola Virus from a fingerprick sample of whole blood. The fluidic model of the device is analyzed in COMSOL Multiphysics. The analyses show that for a contact time of 1s, approximately 5.4 μL of blood can be drawn. Further, the designed micro-cantilever was analyzed and found to effectively produce 0.23557 μV for every 10 ng of the Ebola virus present.
Numerical Analysis of the Flow and Heat Transfer in the Sub-Channel of Supercritical Water Reactor
Authors: Debbarma Ajoy , Pandey K. M.
Published: April 2014

Research activities are ongoing for High performance light water reactor (HPLWR) with square double rows fuel assembly to develop nuclear power plants with the purpose to achieve a high thermal efficiency and to improve their economical competitiveness. However, there is still a big deficiency in understanding and prediction of heat transfer in supercritical fluids. This paper evaluates three-dimensional turbulent flow and convective heat transfer in a single-phase and steady-state sub-channel of HPLWR by using general computational fluid dynamics code, Ansys 14 Fluent. The major concern using supercritical water as work fluid is the heat transfer characteristics due to large variations of thermal properties of supercritical water near pseudo-critical line. In order to ensure the safety of operation in High performance light water reactor (HPLWR), heat transfer deterioration (HTD) must be avoided. Numerical results prove that the RNG k-e model with the enhanced near-wall treatment obtained the most satisfactory prediction and lead to satisfactory simulation results. The HPLWR Square fuel assembly has many square-shaped water rods, Out of four types of sub-channels; three sub-channels SC-1, SC-2 and SC-3 are investigated (adjacent to the side of the moderator flow channels (SC-1) (moderator tube and assembly gap), central sub-channels formed by four fuel rods (SC-2), adjacent to the corner of the moderator tube (SC-3). Since coolant flow distribution in the fuel assembly strongly depends on the gap width between the fuel rod and water rod, fuel rod pitch to diameter ratio 1.1–1.4 with 8mm diameter are considered for simulation. Sub-channel analysis clarifies that coolant flow distribution becomes uniform when the gap width is set to 1.0 mm. was less than 620°C. Effects of various parameters, such as boundary conditions and pitch-to-diameter ratios, on the mixing phenomenon in sub-channels and heat transfer are investigated. The effect of pitch-to-diameter ratio (P/D) on the distributions of surface temperature and heat transfer coefficient (HTC) in a sub-channel, it was found that HTC increases with P/D 1.1 first and then decreases with increasing P/D ratio. Apart from the basic geometry sub-channel, a square sub-channel with a wire-wrapped rod inside has been chosen to investigate the “wire effect”.
Study of Heat Transfer in a Thermal Barrier Coatings System Using the Dual Phase Lag Model Based on Mean Value Finite Volume Method
Authors: Akwaboa Stephen , Mensah Patrick , Dag Yusuf
Published: April 2014

This study presents a more realistic approach to evaluate in-service performance of thin layers of materials such as thermal barrier coatings (TBCs) typically found in hot sections of air, land and sea based gas turbine engines. The results of this study can also be used to analyze thermal damage to biological tissues caused by lasers in the treatment of certain diseases. The governing differential equation for the DPL model, which is second order in time and space, is reduced to a system of first order equations by the introduction of an intermediate function. The system of equations is solved numerically using a new numerical scheme codenamed the Mean Value Finite Volume Method (MVFVM). The numerical method yields minimal numerical dissipation and dispersion errors and captures discontinuities in solution domains very well. The study further showed that for thin film structures subject to short time durations, the DPL model is a better model for heat transfer as it is suitable for both microscopic and macroscopic systems.
Experimental Investigation on Pressure Drop in Corrugated Pipes
Authors: Ahn Hojin , Uslu Ibrahim
Published: April 2014

The characteristics of pressure drop in corrugated pipes were experimentally studied in both straight and helically coiled configurations. The present study employed the stainless-steel pipes with the corrugation of circular cross section, which are widely used in boilers and pipe systems between solar panels and boilers. The diameters of corrugated pipes were 20.4, 25.4, 34.5 and 40.5 mm. The corrugated pipe, approximately 10 m in length, was configured either in the straight manner or in the helical coil with the helix diameter of 0.43 or 0.64 m. Water stored in a tank was fed into a corrugated pipe by a pump while the flow rate was controlled by a control valve. The friction factors of the pipes remain constant over the range of Reynolds number from 4,000 to 50,000, indicating that the flow in the pipe was fully turbulent. When the pipe was straightly configured, the friction factors were measured to be 0.070, 0.075, 0.12 and 0.22 for the diameter of 20.4, 25.4, 34.5 and 40.5 mm, respectively. Thus the present study showed that the friction factors increased with the increasing diameter of the pipe. This result is clearly contrary to a rare experimental result available in the literature. On the other hand, as expected, the friction factor for the helically coiled configuration was higher than that of the straight configuration with the same tube diameter, and the configuration of the smaller helix diameter yielded the larger friction factor. The reason for the increasing friction factor with the increasing pipe diameter remains to be explored further.
Experimental Investigation of Vortex Structure in the Corrugated Channel
Authors: Unal Efe , Ahn Hojin , Sorguven Esra , Gul M. Zafer
Published: April 2014

Vortex structure in a corrugated channel has been studied with a PIV system measuring two-dimensional velocity fields at different locations and Reynolds numbers. The geometry of corrugation under investigation is the two-dimensional reflection of the circular cross-sectional stainless-steel flex pipe. The results show that turbulence caused by the corrugated wall affects the whole flow field in the channel even at low Reynolds number. The bulk flow field is rather chaotic in the entire channel. Moreover, the velocity vectors show significant interaction between the flow in the groove and the bulk flow. Vortex generated from the groove is very unstable and intermittent, and the vortex is not confined within the groove even at low Reynolds number. Vortex in the groove either migrates out of the groove without breaking up, or causes bursting flow from the groove to the bulk. In addition, intermittent and time-mean flow reversals are observed near the crest of the corrugation at low Reynolds number. Though the channel design is intended to be two-dimensional, flow structures in the groove appear to be three-dimensional at high Reynolds number while two-dimensional at low Reynolds number.
Modeling Control Adaptations During Recovery From Anterior Cruciate Ligament Reconstruction
Authors: DiBerardino Louis A. , Dankowicz Harry , Hsiao-Wecksler Elizabeth T.
Published: April 2014

In this paper, we aim to model a functional task affected by injury, along with the corresponding neuromuscular compensation strategy, in order to understand differences in task performance during recovery from the injury. This study is motivated by differing rates of functional task improvements during recovery from anterior cruciate ligament repair. In particular, clinical studies have shown faster recovery times for single-limb forward hopping versus single-limb crossover hopping (hopping back and forth laterally while moving forward). Modeling this hopping task will help us understand whether the main factor of the differing functional results is from the physical restrictions of the injury, the compensation strategies used to overcome these restrictions, or a combination of both. Our hypothesis is that the discrepancies in clinical functional results will be reproduced by employing a feedforward compensation strategy, where the compensation is learned and adjusted over time.
Atomistic Simulations of Fatigue Crack Growth in Single Crystal Aluminum
Authors: Lin Enqiang , Liu Yongming
Published: April 2014

The behaviors of model-I fatigue crack propagation behaviors under different strain cycles in single crystal aluminum have been systematically investigated by molecular dynamic and quasicontinuum method with embedded atom potential. Four different crack orientations: (010)[001], (111)[11-2], (110)[001] and (101)[10-1] are investigated by using the edge-crack model. Different fatigue crack growth mechanisms such as cleavage crack propagation, twinning and dislocation emission are observed. Premature crack surface contact during the unloading path is also observed for the (010)[001] crack, which is consistent with the crack closure hypothesis in the classical fatigue theory. The relationship between local deformation and crack growth kinetics are identified by using crack tip increments and crack tip opening displacement (CTOD) profiles at the selected stress cycle. The results show that crack only grows during part of the loading path and no crack growth during the unloading path, which are well in agreement with our previous in-situ SEM observations.
Development of Biomimetic and Bioactive 3D Nanocomposite Scaffolds for Osteochondral Regeneration
Authors: Castro Nathan J. , O’Brien Christopher , Zhang Lijie Grace
Published: April 2014

Osteochondral tissue is composed of ordered and random biological nanostructures and can, in principal, be classified as a nanocomposite material. Thus, the objective of this research is to develop a novel biomimetic biphasic nanocomposite scaffold via a series of 3D fabricating techniques for osteochondral tissue regeneration. For this purpose, a highly porous Poly(caprolactone) (PCL) bone layer with bone morphogenetic protein-2 (BMP-2)-encapsulated Poly(dioxanone) (PDO) nanospheres and nanocrystalline hydroxyapatite was photocrosslinked to a Poly(ethylene glycol)-diacrylate (PEG-DA) cartilage layer containing transforming growth factor-β1 (TGF-β1)-encapsulated PLGA nanospheres. Novel tissue-specific growth factor-encapsulated nanospheres were efficiently fabricated via a wet co-axial electrospraying technique. Integration and porosity of the distinct layers was achieved via co-porogen leaching and ultraviolet (UV) photocrosslinking of water soluble poly(ethylene glycol) (PEG) and <150 um sodium chloride salt particles providing greater control over pore size and increased surface area. Our in vitro results showed significantly improved human bone marrow derived mesenchymal stem cells (hMSCs) adhesion and differentiation in bone and cartilage layers, respectively. In addition, we are working on developing a novel table top stereolithography (SL) apparatus for the manufacture of custom designed 3D biomimetic scaffolds with incorporated growth factor encapsulated nanospheres for osteochondral defect repair. Our early-stage SL development has illustrated good corroboration between computer-aided design (CAD) and manufactured constructs with controlled geometry. The ultimate goal of the novel tabletop SL system is the manufacture of patient-specific implantable 3D nanocomposite scaffolds for osteochondral defect repair. The current SL system developed in our lab allows for efficient photocrosslinking of two novel nanocomposite polymeric materials for the manufacture of three-dimensional (3D) osteochondral constructs with good spatiotemporal control of growth factor release in addition to exhibiting similar mechanical properties to that of the native tissues being addressed.
Modeling Dynamic Responses of Viscoelastic Heterogeneous Soft Tissues to Step Acoustic Radiation Force
Authors: Zhao Xiaodong , Pelegri Assimina A.
Published: April 2014

The responses of soft tissue under acoustic radiation force excitations are used to image tissue mechanical properties for soft tissue discrimination and detection of breast tumors. The soft tissue viscoelasticy has been interrogated by step acoustic radiation force excitations. The corresponding induced time-dependent creep displacement is used to reconstruct soft tissue viscoelasticity or to estimate viscosity and elasticity contrast of the inclusion to background. The acoustic radiation force is highly localized in a small excitation region; and, one degree-of-freedom and homogenous assumptions are generally made to the analysis. However, these simplifying assumptions limit the accuracy of these methods. In this paper, a finite element model was built to demonstrate the effect of the dynamic response of viscoelastic heterogeneous soft tissue to step acoustic radiation force. Factors affecting the dynamic response of soft tissue were first investigated with the homogenous model, and the corresponding estimation quality based on the one degree-of-freedom model was evaluated. Then, the dynamic response of soft tissue with inclusion and different elasticity and viscocity for the tissue and the inclusion was studied. The results suggest that in order to improve the estimate of soft tissue viscoelasticity the heterogenenous nature of the tissue and its three dimensional geometry should be accounted in the model.
Efficient Heat Transfer From Non-Condensable Gas in the Process of Moist Exhaust Heat Recovery
Authors: Skop Helen , Oleynikov-White Valeriy G.
Published: April 2014

Most of the industrial waste heat is in the low temperature range. In the last few years, government agencies and equipment developers have paid attention to the advantages of heat recovery from moist industrial exhausts by cooling them to below the corresponding dew point temperature level. In case of non-aggressive and highly moisturized exhaust gas the recovery of vapor latent heat through efficient condensation can provide with significant energy savings. Indirect cooling condensers are it’s the simplest solution for such heat recovery. However, low efficiency of those condensers makes the heat recovery economically not feasible. To develop a high efficient heat and mass exchanger it is necessary to investigate the combined transfer mechanisms from exhaust vapor and non-condensable portion of the exhaust to the heat transfer surface through the condensing water vapor. This paper describes main approaches to the description of this heat and mass transfer process, operating conditions for efficient gas cooling along with interaction between non-condensable gas and condensing vapor as well as considerations of influence of heat transfer surface on efficient condensation.
Experimental Study of a Solar Thermal Desalination Unit
Authors: Abutayeh Mohammad , Humood Mohammad , Alsheghri Ammar Abdulkarim , Al Hammadi Abdullah Jamal , Farraj Abdul Rahman
Published: April 2014

Scarcity of potable water causes a serious problem in arid regions of the world where freshwater is becoming insufficient and expensive. Warm regions in the Middle East and North Africa are considered among the severest water shortage places. The objective of this project is to study the potential of using solar energy to run existing multi-stage flash (MSF) desalination units in the Arabian Gulf. One problem with MSF is the low efficiency of the system because of the bulk energy required for heating. Exploitation of solar energy in thermal desalination processes is a promising technology because of the ubiquitous nature of sun’s energy. Experimental studies were conducted on a single flash desalination unit. The pilot unit demonstrates the use of solar radiation as the thermal energy input. The process starts by preheating seawater through a vacuumed condenser. Seawater, then, flows inside a circulation tank to be indirectly heated by a heat transfer fluid. The heat transfer fluid circulates inside a flat plate solar collector facing south to absorb solar energy. After raising its temperature, seawater goes through an expansion valve and flashes in a vacuumed chamber to form brine and vapor. The vapor transfers to the condenser and condenses to form potable water by losing its latent heat of vaporization to incoming seawater. The flow rate of the working fluid is controlled via a control valve based on a set point temperature reference. The experiments were carried out using different values of the controlling variables to enhance analysis and validate results.
Large Eddy Simulation of Turbine Internal Cooling Ducts
Authors: Tyacke James , Tucker Paul
Published: April 2014

Large-Eddy Simulation and hybrid RANS-LES methods are applied to a turbine blade ribbed internal duct with a 180 degree bend containing 24 pairs of ribs. Flow and heat transfer predictions are compared with experimental data and found to be in agreement. The choice of LES model is found to be of minor importance as the flow is dominated by large geometric scale structures. The influence of inlet turbulence is also tested and has a minor impact due to the strong turbulence generated by the ribs. Large scale turbulent motions destroy any classical boundary layer reducing near wall grid requirements. The wake-type flow structure makes this and similar flows nearly Reynolds number independent, allowing a range of flows to be studied at similar cost. Hence LES is a relatively cheap method for obtaining accurate heat transfer predictions in these types of flows.
Toward Improving Fracture Toughness of Particle-Reinforced Polymer Matrix Composites
Authors: Sadeghipour Keyanoush , Wang Wenhai , Baran George
Published: April 2014

Experimental results have shown that polymer composites that have high fracture toughness tend to have high fatigue wear resistance. The work of fracture found in nacre (mother of pearl) is several orders of magnitude larger than the ceramic (aragonite) it is made of. The organic protein layers in the composite play a significant role in the mechanical response of nacre to stress. In this study, we hope to understand if an energy absorbing interphase similar to that found in nacre could have potential for toughening traditional, glass-particle-reinforced polymer composites. A multi-scale finite element model (FEM) has been developed to study the interaction between the crack and the reinforced particles. In this model, crack nucleation and propagation and the effect of particle/matrix/interphase material properties can all be characterized by the cohesive element and its traction-separation behavior. Loss of load carrying capacity begins when local deformation reaches a certain value, leading to the degradation of the material. Completely degraded elements form a traction-free crack surface. The most important advantage of this methodology for modeling fracture behavior is that macroscopic fracture criteria are not needed. 3-point bending macro-scale FEM serves to calibrate the deformation gradient of the study zone in front of the crack tip. A microscopic unit cell model was used to simulate the crack propagation. Three types of interphase were compared: (1) matrix and particle bonded without interphase, (2) matrix and particle bonded with silane interphase, and (3) matrix and particle bonded with beta-peptide (highly stretchable) interphase. Results show that the stress distribution around the filler and the bulk mechanical properties of the composite can be affected by changes in interfacial properties. Particle-reinforced polymer composites with a more compliant and stretchable interphase (e.g. beta-peptide) will help absorb local strain energy while remaining intact, allowing less damage within the matrix. This type of interphase decreases crack propagation speed and results in an increase of fracture toughness.
Finite Element Formulation for Prediction and Quantification of Stick-Slip Phenomenon in Down-Hole Tubular Expansion
Authors: Al-Abri Omar S. , Pervez Tasneem , Qamar Sayyad Z. , Khan Rashid
Published: April 2014

The challenges in exploration and development of unconventional oil and gas resources are enormous. The complex reservoir characteristics, and oil and gas flow regimes introduce difficulty in predicting the oil and gas in-place, recovery and production profiles, and wells placement, design and completion. Horizontal drilling and completion using centuries-old manufacturing process of tube forming resulted in producing oil and gas from large areas with smaller footprint on the surface. Though expensive but it optimizes the recovery. The in-situ diametral expansion of tubular using a solid mandrel causes permanent deformation in which the system experiences large frictional forces at mandrel/tubular interface resulting in stick-slip phenomenon. It results in varying tubular thickness and diametral eccentricity which causes structural instability in wells leading to premature failure.

A finite element model describing the dynamics of stick-slip phenomenon in down-hole tubular expansion was developed. Three different set of equations; one each for stick, slip and transition phases were derived using equilibrium equations, time-dependent static friction model and velocity-dependent kinetic friction model. A switch model utilizing the zero velocity interval criterion was used to define stick, slip and transition phases. The newly developed model was implemented in the finite element model by means of two user-defined subroutines namely VFRIC and VDLOAD in commercial finite element software ABAQUS. Experimental and simulation results agree well for expansion force, wall thickness reduction and tubular length shortening. It was found that the thickness variation is the most critical parameter due to its effect in lowering collapse strength of expanded tubular. Parametric study investigations showed that the effect of this phenomenon may possibly be minimized by manipulating mandrel geometry, contact conditions, and/or mandrel speed.
Fuzzy Multi-Objective Approach for Designing of Biomass Supply Chain for Polygeneration With Triple Footprint Constraints
Authors: Ubando A. T. , Aviso K. B. , Culaba A. B. , Ng D. K. S. , Tan R. R.
Published: April 2014

Polygeneration systems produce multiple energy products (i.e. electricity, heat, cooling), and other biochemical products (biofuels and syngas). Such systems offer a sustainable approach in meeting the ever-growing demand of energy, while reducing its environmental impact. The optimal design of such systems should consider the design of the supply-chain in producing the targeted energy products to reduce the resource consumption and waste generation and to maximize its economic potential. One of the important considerations in designing such a system is whether to out-source its raw materials or to produce them in-house. The criteria for such decision strategies are assessed through economics, product demand, and environmental impact. One holistic way to measure the environmental impact of such system is to consider the triple footprint: carbon, water, and land. The objective of this work is to maximize the economic potential while maintaining the footprints at acceptable levels and simultaneously meeting product demands. In this study, an adoption of fuzzy multi-objective approach is presented wherein the economic potential is introduced as a constraint. Moreover, predefined fuzzy trapezoidal-shaped limits for the product demand constraints are used which mimics the probabilistic demand scenario for each of the product streams. Lastly, the triple footprint constrains is utilized to assess the environmental impact of the polygeneration. The technique is demonstrated using a modified industrial case study of a polygeneration system.
Cooling Capacity of Metal Phase Change Material for Thermal Management of Mobile Phone Subject to Long Time Communication
Authors: Ge Haoshan , Liu Jing
Published: April 2014

Smartphone is emerging as the most popular electronic media in the last few years. With many high performance chips integrated inside, such mobile electronic system is already capable of performing a series of sophisticated computing which can only be carried out by a desktop computer before. Meanwhile, the large amount of heat released from the high flux heat generation also caused evident thermal discomfort to the users. As a remedy, the recently proposed method of using low melting point metal to absorb the transitory heat from the device opens a promising approach for keeping smartphone cool. To push forward the development of this new thermal management method, the present study is dedicated to present a comprehensive analysis on the cooling capacity of the metal phase change material for the thermal management of mobile phone subject to various running states, especially those when extremely long conversation time up to a half hour or longer occurs. A three dimensional phase change heat transfer model was established to simulate several typical continuous or transient heating cases often encountered in reality. It can be found that, through an optimum design among the geometric sizes of the cooling modular, the chip structures as well as the utilized amount of the metal phase change material, the method is highly useful for cooling the mobile phone running even under an unconventionally long communication period. Further, improvement for a better and compact thermal management through material innovation was also suggested.
Investigation of the Surge Phenomena in a Centrifugal Compressor Using Large Eddy Simulation
Authors: Semlitsch Bernhard , Jyothishkumar V. , Mihaescu Mihai , Fuchs Laszlo , Gutmark Ephraim J.
Published: April 2014

The flow through a ported shroud compressor of an automobile turbocharger is simulated using Large Eddy Simulations. Generally, the compressor is subjected to work within certain range of the mass-flow conditions. Reduction of the operation mass-flow below a certain minimum limit, leads to breakdown of the complete compressor operability. Flow reversal occurs in the compressor wheel, which results in amplification of velocity and pressure fluctuations. Consequentially, large vibratory stresses are induced into the blades under off-design condition and thereby affect the blade life duration detrimentally. The aim of this study is to understand the generation of flow-structures during extreme operable conditions (surge condition) in a centrifugal compressor. The investigation of the appearing flow-structures with the surge phenomenon is essential to explore new methods that improve the stability or the flow-operating regime of the compressor. The complete 360° compressor geometry is utilized in the computational simulations. Further, the transient sliding mesh technique is applied to account for an accurate prediction of the mesh motion and thus, the geometrical interaction between the impeller and the stationary diffuser. The numerical results are compared with available experimental measurements obtained under the same operating conditions (design and near-surge condition). The rotating stall instability is predicted using FFT data analysis. Furthermore, the numerical study captures the low frequency peak characterizing the global instability of the surge condition.
A Novel MEMS Device for Selective Surface Adsorption of Lead (II) Ions From Blood Using Carbon Aerogel
Authors: Kumar Deepan Kishore , Ganesan Adarsh Venkataraman , Swaminathan Sundaram , Sharma Niti Nipun , Mittal Ravi Kant
Published: April 2014

In this paper, we propose to design, simulate and fabricate a novel device design that would be capable of removing heavy metal ions like Lead or Arsenic from the Blood serum. The basic design of the device comprises of micro-needles at the inlet and the outlet, followed by a micro-channel where is blood is made to flow through a series of alternating constrictions. Every constriction has a coating of Carbon Aerogel to remove the Heavy metal ions like Pb. The design also eliminates the need for a valve or a micro pump as we ensure unidirectional flow by having fewer needles at the outlet as compared to the inlet and be placed in two regions of differential pressure. The present device (with surface dimensions of 100 × 150 × 75 microns) allows for blood filtration at the rate of 62.55 ml per week. Since the device has a slow filtration rate, multiple such Point-of Care device would be worn by the affected patients.
Energy Production Through Wind Using Personal Use Wind Turbines: A UAE Case Study
Authors: Zafar Sayem , Gadalla Mohamed
Published: April 2014

A model study is conducted to investigate the possible wind energy harnessing potential of a recently designed personal use wind turbine, PWT, having efficient and economical blades. The study is conducted for the conditions usually found in United Arab Emirates, UAE. The PWT has a total length of 4.5 m while the disk diameter is 3 m. The PWT dimensions make it big enough to be used to power household appliances or to charge batteries yet small enough to be installed on rooftops or buildings. The wind turbine setup uses a tail vane to keep the wind turbine aligned with the airflow. The wind turbine blades are installed at an angle of 22°, with respect to the disk plane, as it gives the highest power. For electrical power generation, a permanent magnet generator is used which is rated for 250 RPM to 100 RPM. Gears are used to increase the generator RPM to six times than that of the wind turbine. The UAE wind data is used to find the total possible power from each wind turbine. Possible number of housing units, buildings and telecommunication towers are found, in UAE, where a PWT can be installed. An analysis is conducted for the energy and exergy potential of the wind turbine rotor. The clean energy potential of the PWT is also investigated when operated by their possible users. Calculations are made at variable wind speeds to represent the average wind speed during each month. It is concluded that a country like UAE can produce on average 500 MW using PWTs. The efficiencies come out to be low for summer months while high for winter months. It is also concluded that a system like PWT would help reduce the monthly billing cost by the end user.
Analysis of Pin-Fin Heat Sinks With an Unconventional Fin Profile
Authors: Gonzalez-Hernandez Jose-Luis , Hernandez-Guerrero Abel , Rubio-Jimenez Carlos , Rubio-Arana Cuauhtemoc
Published: April 2014

In this work the performance of pin-fin heat sinks having an unconventional fin profile is compared with the use of cylindrical fins. The fin profile is a sinusoidal function and a staggered array is considered. The overall thermal resistance and total pressure drop are reported for the pin-fin heat sinks. The effect of using a wave function for the fin is studied for different number of complete waves along the height of the fins and a geometric parameter defined as the ratio of the higher to the lower radius of the fins is proposed. The study is carried out for two different inlet velocities, and for two different fin densities, corresponding to 5×5 and 7×7 arrays. An entropy generation analysis for each pin fin heat sink configuration is carried out and reported. The results of the present analysis reveal that the proposed geometry has an improvement as compared to the conventional heat sinks profiles when there is a high number of waves per fin. The effect of the geometric parameters defined in this study for the thermal and hydraulic performance is identified and discussed as well.
Use of Mobile Devices as an Interactive Learning Method in a Mechatronics Engineering Course: A Case Study
Authors: Alemohammad Hamid , Shahini Mohsen
Published: April 2014

This paper is concerned with the implementation of an innovative interactive learning tool in teaching a Mechatronics Engineering course at the University of Waterloo. The course deals with digital logic, PLC programing, and assembly language. The interactive tool, developed at Top Hat Monocle Inc., was used in teaching the assembly language part of the course. The interactive tool has two components: students’ electronic devices and a front-end website in which the instructor has control to launch demonstrations and quizzes and receive students’ responses. Students are connected through WiFi connection or their smart phones. In this study, students’ performance was evaluated using the final exam scores and the surveys. The exam results showed about 23% improvement. According to the results of the survey administered at the end of the term, students who participated on the interactive simulation and quizzes agreed that it helped the concepts “stick in their memory better”.
Optimization of Hydrofoils for Horizontal Axis Marine Current Turbines Using Genetic Algorithm
Authors: Ram Krishnil R. , Goundar Jai N. , Prasad Deepak , Lal Sunil , Ahmed Mohammed Rafiuddin
Published: April 2014

As fossil fuels near depletion and their detrimental side effects become prominent on ecosystems, the world is searching for renewable sources of energy. Tidal energy is an emerging and promising renewable energy resource. Tidal turbines can extract energy from the flowing water in a similar way as wind turbines extract energy from the wind. The upside with tidal turbines is that the density of water is approximately 800 times greater than that of air and a tidal turbine harnessing the same amount of power as a wind turbine can be considerably smaller in size. At the heart of the horizontal axis marine current turbines are carefully designed hydrofoil sections. While there is a growing need to have hydrofoils that provide good hydrodynamic and structural performances, the hydrofoils also have to avoid cavitation for safe operation. This study uses a genetic algorithm optimization code to develop hydrofoils which have the desired qualities mentioned above. The hydrofoil problem is parameterized using a composite Bezier curve with two Bezier segments and 11 control points. Appropriate curvature conditions are implemented and geometric constraints are enforced to maintain the hydrofoil thickness between 16 to 18%. XFOIL is used as the flow solver in this study. The hydrofoils are optimized at Reynolds number of 2 million and for angles between 4 to 10 degrees. The best foil from the results, named USPT4 is tested for performance with the CFD code ANSYS CFX. The CFX results are validated with experimental results in a wind tunnel at the same Reynolds number. The hydrofoil’s performance is also compared with a commonly used NACA foil.
Preparation and Characterization of Drug-Loaded Thermosensitive Hydrogels
Authors: Saeednia L. , Usta A. , Asmatulu R.
Published: April 2014

Hydrogels are the promising classes of polymeric drug delivery systems with the controlled release rates. Among them, injectable thermosensitive hydrogels with transition temperature around the body temperature have been wildly considered. Chitosan is one of the most abundant natural polymers, and its biocompatibility and biodegradability makes it a favorable thermosensitive hydrogel that has been attracted much attention in biomedical field worldwide. In this work, a thermosensitive and injectable hydrogel was prepared using chitosan and β-glycerophosphate (β-GP) incorporated with an antibacterial drug (gentamycin). This drug loaded hydrogel is liquid at room temperature, and becomes more solidified gel when heated to the body temperature. Adding β-GP into chitosan and drug molecules and heating the overall solution makes the whole homogenous liquid into gel through a 3D network formation. The gelation time was found to be a function of temperature and concentration of β-GP. This thermosensitive chitosan based hydrogel system was characterized using FTIR and visual observation to determine the chemical structure and morphology. The results confirmed that chitosan/(β-GP) hydrogels could be a promising controlled-release drug delivery system for many deadly diseases.