bluuebunny/crossref_metadata_2025 huggingface dataset:
Wavelet-Based Time-Frequency Control of a Flywheel Energy Storage System
Authors: Lewallen Colby
Published: February 2017

The objective of this paper was to implement a novel controller called “wavelet-based time-frequency control” (WFXLMS) in a computer simulation of a FES system with six degrees-of-freedom and compare its dynamic stability and active power consumption with the following conventional controllers: PID and fuzzy-logic. Specifically, all three controllers were applied to a FES system operating at 100,000 rpm, and the amplitude of vibration, rate of convergence, and current draw were compared. As of writing this paper, the PID and fuzzy-logic controllers have converged but the WFXLMS controller has not. The parameter values for the WFXLMS controller need further tweaking for a more comprehensive analysis. Despite this setback, both the fuzzy-logic and PID controllers did demonstrate convergence at 100,000 rpm. The fuzzy-logic converged immediately and the PID converged around 0.8 seconds. The PID demonstrated a periodic motion about the z axis while the fuzzy-logic settled at a constant displacement. Finally, the PID controller had a smaller maximum and average current draw over the fuzzy-logic. In conclusion, the PID controller provided sufficient control of the system with the least amount of current draw, but the fuzzy-logic controller provided the steadiest response.
Thermal Modeling of Memory Access Operations in Microprocessors
Authors: Raj Ratnesh , Sarkar Daipayan , Jain Ankur
Published: February 2017

A large fraction of energy consumed in modern microelectronic devices and systems is taken up by memory access operations, which is expected to cause significant temperature rise. Since memory access operations are very short in duration, this is expected to inherently be a transient thermal phenomenon. Despite the critical importance of thermal management in microelectronics, not much work exists on understanding the nature of thermal transport during memory access operations. In this work, a mathematical model to predict the transient temperature rise within a 3D memory chip is presented. Most heat-generating memory access processes occur over a short timescale for which the thermal penetration depth is shorter than the die thickness. This enables the modeling of such processes independent of the nature of chip cooling by treating the chip as a semi-infinite medium. A semi-infinite Green’s function model is developed for one bank of memory on a single layer of a block of the memory chip. This model is validated against finite element simulation results. Validation is also carried out by comparison of the model against the analytical solution for a limiting case. The analytical model is used to analyze transient thermal effects of various memory access processes for multiple banks. These results will help develop an understanding of optimal layouts and processes for 3D memory chips, eventually leading to co-design tools that simultaneously improve thermal and electrical performance of 3D memory chips.
Heat Transfer in Liquid-Liquid Taylor Flow in Mini-Scale Curved Tubing for Constant Wall Temperature
Authors: Adrugi W. M. , Muzychka Y. S. , Pope K.
Published: February 2017

In this paper, heat transfer enhancement using liquid-liquid Taylor flow in mini scale curved tubing for isothermal boundary conditions is examined. The copper tubing has an inner tube diameter of Di = 1.65 mm with different radii of curvature and lengths. Taylor flow is created using water and low viscosity silicone oils (0.65 cSt, 1 cSt, 3 cSt) to examine the effect of Prandtl number on heat transfer rates in curved tubing. A series of experiments are conducted using tubing with constant length and variable curvature, as well as variable length and constant curvature. The experimental results are compared with models for liquid-liquid Taylor flow in straight tubing and single-phase flow in curved tubes. The results of the research develop a new model for liquid-liquid Taylor flow in curved tubing. This research provides new insights into the effect of curvature on heat transfer enhancement for liquid-liquid Taylor flow in mini scale curved tubing, at a constant wall temperature.
Ultrasonic Communications Through a Reinforced Concrete Column
Authors: Scarton Henry A. , Wilt Kyle R. , Saulnier Gary J.
Published: February 2017

Measurements were obtained by sending high frequency acoustic waves through a reinforced concrete column. Past work involved through-wall digital communications and power delivery through metallic barriers; this paper extends that work to a reinforced concrete column. A pair of 35 mm diameter circular transducers with a thickness of 10 mm (corresponding to a resonance of 200 kHz) were epoxied to opposite sides of a 0.7 m thick reinforced concrete column. A vector network analyzer (VNA) obtained the characteristics of the acoustic channel formed between the two sensors. A voltage transfer function for this channel was found in the range of 30 kHz – 150 kHz. Although this transfer function shows a significant amount of frequency selectivity, i.e. variation with frequency, resulting from the multipath created by the acoustic energy interacting with the complex structure of column (rebar, aggregate, voids) and its surfaces, the channel is seen to be capable of supporting data transmission. The magnitude of the transfer function is seen to be highest in the region 40 kHz – 70 kHz with its theoretical capacity to be approximately 400 kbits/s for a received signal-to-noise ratio (SNR) of 60 dB. Lower SNR’s would still be able to provide data rates well in excess of 50 kbits/s, permitting the passing of low frequency data across the concrete column.
Damage Prediction for a Cervical Spine Intervertebral Disc
Authors: Motiwale Shruti , Subramani Adhitya V. , Zhou Xianlian , Kraft Reuben H.
Published: February 2017

A large part of the military population develop severe neck pain as a result of complex cyclic loading on the cervical spine. It is hypothesized that this pain is linked to accelerated intervertebral disc degeneration caused by wearing heavier head supported equipments for extended periods of time. This heavy head supported mass exerts high amplitude cyclic loads at the neck that may result in fatigue failure of the intervertebral disc. In this paper, we present a methodology to predict damage in the intervertebral disc over extended periods of time. With this model, we attempt to understand initiation and progression of damage in the disc due to loads exerted on the neck. Such an understanding can be beneficial in the development of better helmets and head mounted equipment for the soldiers.
An Enhanced Surrogate Model Based Vehicle Robust Design Method Under Materials and Manufacturing Uncertainties
Authors: Li Jie , Fang Yudong , Zhan Zhenfei , Jiang Yazhou
Published: February 2017

Robust design theories and methods have been widely implemented in automobile design. However, most of the existing studies on the robust design for vehicle merely consider the uncertainties in structural sizes of components, while those in weld and material have not been well studied in an integrated manner. This research proposes a robust design framework which can incorporate various sources of uncertainties. Several major steps are included in the proposed framework: uncertainty quantification based on test and maximum likelihood estimation, weld significance analysis and robust design based on metamodel. Uncertainties in material properties and joint strength are quantified by test and statistical approach. Weld significance analysis is employed to find out the welds which will greatly affect the interest performances. Metamodel contributes to improving the efficient of robust design. The proposed framework is successfully demonstrated through a vehicle front structure design optimization. The results show that the implementation of the proposed method which considers uncertainties of material, weld and structural size can effectively reduce the weight of vehicle while satisfying the safety constraints.
Effect of Streamwise Vortex Strength on Heat Transfer Enhancement of a Flat Plate
Authors: Raman Aditya , Chintamani Siddarth , Dennis Brian H.
Published: February 2017

This paper studies the variation of the streamwise vortex circulation resulting from a delta wing vortex generator. A delta wing vortex generator is employed in the common flow down configuration, this generates an anti-clockwise vortex over the right wing. Two different vortex generators with angle of attack 15° and 30° were considered in this study for a range of Reynolds numbers from 750 to 1500. The average Nusselt number was observed to increase with increasing Reynolds number and angle of attack. The circulation around the vortex core was calculated at different streamwise locations behind the vortex generator. The circulation of the vortex was observed to decrease in the down-stream direction. For a given Reynolds number and angle of attack, circulation at all streamwise locations was averaged in order to compare it with the trends observed by the averaged Nusselt number. The variation in averaged Circulation was identical to the Nusselt number. The vortex center locations were used to plot the trajectories by applying a least squares second order polynomial fit to the data.
Multiscale Experimental Characterization of the Delamination Resistant Mechanisms Found in the Biomineralized Exoskeleton Fish Scale Composite
Authors: Hodo Wayne , Nelms Matt , Crawford Bryan , Livi Kenneth , Rajendran A. M. “Raj”
Published: February 2017

Engineered man-made composite (inhomogeneous) materials are well known for their superior structural properties. Man-made composite materials and multilayered systems are widely used in civilian and military applications. The combined multilayered systems are attractive because they have the characteristics of being energy absorbent, lightweight, high-strength, high-stiffness, and can provide good fatigue and corrosion resistance. Although the engineered composites are promising and offer mutual exclusive material properties that are not found in other structural materials, they are prone to delamination at the glued layered interface.

In contrast to man-made composites, most superior performing materials found in nature possess a hierarchal biomineralized composite structure that tends to be delamination resistant. These delaminate resistant biocomposite structures [e.g. alligator gar’s (Atractosteus Spatula) exoskeleton fish scale] have mechanical properties that vastly exceed the properties of their relatively weak constituents. The fish scale is made up of 90 percent hard (inorganic minerals) and 10 percent soft (polymer-like organic collagen fibers) by volume. Nature integrates hard and soft materials at different length scales to form a two-layered composite that better resists delamination.

The objective of this research was to use scanning electron microscopy (SEM) and nanoindentation to investigate the delamination resistant behavior occurring at the layered interface for the alligator gar fish scale composite. The SEM imagery showed at the micron level the collagen bundles + B-Ap crystals (C/B-Ap) form a distinctive two-layered system that is connected by what is described as sawtooth geometrically structured interface. The outermost layer for the exoskeleton fish scale is called ganoine while the inner layer called bone. The layers interface seems to be mainly bonded by mechanical means using sawtooth notches, rather than the chemicals adhesives used in the man-made laminated planar interfaced composites. The notched regions for ganoine+bone materials overlap and are embedded at various depths within each layer to form periodic “repeating” bonded connections.

The indentation measurements taken at the nano-level showed that elastic moduli have property gradients occurring through the interfacial transition zone. Noticeably the ganoine layer has elastic moduli ranging from [98–67] GPa while the bone layer elastic moduli ranged from [20–13] GPa. The research findings indicate the sawtooth connections perhaps provide enhanced shear resistance at the interface and may help inhibit debonding. Additionally, the notched interlocking provides a less discrete (graded) interface, which seems to promote durability and delamination resistance.
Active Control of Viscoelastic Systems by the Method of Receptance
Authors: Singh Kumar V. , Ling Xiaoxuan
Published: February 2017

Viscoelastic materials both stores and dissipate energies and have frequency and temperature dependent properties and hence by tuning and optimizing their damping (viscous) and stiffness (elastic) properties they can be used as passive controlling devices in wide range of vibration applications. If the control of viscoelastic systems (viscoelastic structures or structures composed of viscoelastic elements) to be realized by active means, then an accurate mathematical modeling of the viscoelastic system is needed. In practice, various material models and approximation techniques such as Biot model, Golla-Hughes-McTavish (GHM) model and Anelastic Displacement Field (ADF) methods are used to model the dynamic behavior of viscoelastic systems. These models are then transformed into approximating state space models which introduces several challenges: (i) they increase the size of the related eigenvalue problems, (ii) state space realization introduces non-physical internal state variables, and, (iii) the feedback control implementation poses practical challenges such as observer and state estimator design. In this research it is shown that the active control for viscoelastic structures can be designed accurately by only utilizing the available transfer functions. These transfer functions can be obtained from dynamic experiments and the active feedback control is designed without having the knowledge of approximated state-space system matrices. The problem associated with the active control for viscoelastic system is formulated as feedback control problems in frequency domain by using the receptance method. Active control for poles and zeros assignment of the viscoelastic systems is demonstrated using numerical examples associated with the multi-degree-degree of freedom systems. It is also shown that a nested active controller can also be designed for continuous structures (beams/rods) supported by viscoelastic elements. It is highlighted that such a controller design requires modest size of transfer functions and solution of the set of linear system of equations.
Crystallinity Control of Electroplated Interconnections for Improving Their Stability and Lifetime
Authors: Liu Jiatong , Suzuki Ken , Miura Hideo
Published: February 2017

In a three-dimensional (3D) packaging systems, the interconnections which penetrate stacked silicon chips have been employed. Such interconnection structure is called TSV (Through Silicon Via) structure, and the via is recently filled by electroplated copper thin film. The electroplated copper thin films often consist of fine columnar grains and porous grain boundaries with high density of defects which don’t appear in conventional bulk material. This unique micro texture has been found to cause the wide variation of physical and chemical properties of this material. In the TSV structure, the shrinkage of the copper thin film caused by thermal deformation and recrystallization of the unique texture during high-temperature annealing is strictly constrained by surrounding rigid Si and thus, high tensile residual stress remains in the thin film after thermal annealing. High residual stress should give rise to mechanical fracture of the interconnections and the shift of electronic function of thin film devices formed in Si.

Therefore, the residual stress in the interconnections should be minimized by controlling the appearance of the porous boundaries during electroplating for assuring the longterm reliability of the interconnections. As the lattice mismatch between Cu and its barrier film (Ta) is as larger as 18%, which is the main reason for the fine columnar structures and porous grain boundaries, it is necessary to control the underlayer crystallinity to improve the crystallinity of electroplated copper thin films.

In this study, the effective method for controlling the crystallinity of the underlayer was investigated by improving the atomic configuration in the electroplated copper thin film. The result showed that by controlling the crystallinity of underlayer, crystallinity of electroplated copper thin films can be improved, the mechanical properties of thin films was improved and thus, stability and lifetime of electroplated copper interconnections can be improved.
Dehumidification Performance of Mass Exchangers Consisting of Silica Aerogel Coated Metal Foams
Authors: Nawaz Kashif , Schmidt Shelly J. , Jacobi Anthony M.
Published: February 2017

Separate sensible and latent cooling systems offer significant increases in the overall performance of cooling/dehumidification systems compared to conventional vapor-compression air-conditioning systems. Key to the energy efficiency of such systems is the performance of the heat and mass exchangers, which provide sensible cooling and dehumidification. Solid-desiccant-coated enthalpy wheels have been in use to control the moisture content of supply air for several decades. However, they have several disadvantages, including inefficient process control, relatively large volume and operational cost. In the current study, the performance of an aerogel-coated, metal-foam mass exchanger has been evaluated and compared to an enthalpy wheel for managing the latent load. Transient and steady state performance models have been developed based on the thermal-hydraulic performance of metal foams (j and f factors)1, mass diffusion coefficients (D) and adsorption/desorption isotherms. The objective of this study is to determine the feasibility of such system to replace conventional enthalpy wheels. The effect of geometry and base material of metal foam, type of silica aerogel and thickness of coating has been analyzed to determine the impact of such parameters on the overall performance of proposed dehumidification device. The study concludes that a significant amount of energy can be saved when the proposed dehumidification system is used in place of a conventional enthalpy wheel to control the moisture content of the supply stream in air conditioning systems.
Application of Iso-Strain Boundary Conditions to Deduce Orthotropic Elastic Constants of Biomineralized Fish Scale
Authors: Nelms Matt , Mohan Ram , Kelkar Ajit , Rajendran A. M. , Hodo Wayne
Published: February 2017

The Atractosteus spatulas (Alligator gar) was used as the model structure for computational analysis to estimate elastic properties. The Alligator gar possesses a flexible dermal armor consisting of overlapping ganoid scales. Each scale is a bilayer hydroxyapatite and collagen-based biocomposite and is thought to be used for protection against predators. The exoskeleton fish scale is comprised of a stiff outer ganoine layer, a characteristic “sawtooth” pattern at the interface and a compliant bone inner layer with all materials exhibiting a decreasing elastic modulus from the external to the internal layers. Scanning electron microscopy (SEM) images of the cross section of gar fish scales revealed a two-layered structure. Nanoindentation measured modulus was correlated to structural changes across the scale’s layers. Piecewise linear grading functions were used to vary the properties within and between layers as well as explicit modeling of the sawtooth interface geometry. The fish scale composite was computationally modeled using a representative volume element (RVE). The model used iso-strain boundary conditions to determine the full elastic tensor for the composite system. Using isotropic behavior for individual elements, the results show that the RVE exhibits orthotropic symmetry with slight variations due to the sawtooth interface.
Incorporating Phase Change Materials to Mitigate Extreme Temperatures in Asphalt Concrete Pavements
Authors: Athukorallage Bhagya , James Darryl
Published: February 2017

The use of Phase Change Materials (PCMs) in asphalt pavement mixtures potentially offers a solution for regulating extreme temperatures that can cause thermally-induced rutting in pavement systems. The primary objective of this study is to fundamentally understand the effect on the heat transfer and maximum surface temperature in flexible pavement systems that includes PCMs. In particular, we consider a pavement structure in which PCM is embedded in the asphalt-concrete layer with varying volume fractions.

Our simulation results show that the pavement system embedded with PCMs yield lower surface temperature values than systems without PCM (maximum temperature decrease is 1.5°C for the distributed PCM with a volume fraction of 30%). Further, we observe a higher temperature drop through the PCM-embedded asphalt layer compared to a pavement without PCM, and regions possessing temperature values less than 45°C that may help to reduce the thermally induced rutting problems. The simulation yields another interesting result: increasing PCM volume fraction beyond 60% results in higher surface temperature values. This increase in the maximum surface temperature may be explained by the fact that the PCM used in the simulation has a lower thermal conductivity than that of the asphalt-concrete that ultimately results in a lower effective thermal conductivity value for the system. Finally, we observe that an increase in the effective thermal conductivity yields lower surface temperature for the PCM embedded pavement system.
Modeling of Diffusive Behavior of Macromolecules Encapsulated in Electrospun Fibers
Authors: Yan Karen Chang , Moy Aren , Sebok Michael
Published: February 2017

Electrospun (ES) fibers made of biocompatible polymers have been used as scaffolds in tissue engineering due to the potential to mimic the fibrous environment found in the extracellular matrix of biological tissue. Bioactive macromolecules such as growth factors have also been incorporated in the electrospun fibers to promote cell growth and differentiation. Therefore, it is critical to understand and control the release rate of the bioactive molecules. This paper presents the development of a stochastic simulation method to model the diffusive behaviors of macromolecules encapsulated in electrospun fibers. Specifically, a given ES fiber sample is represented by a set of random fibers with total fiber number denoted as N. Each fiber in the set is assumed as a cylinder and has a randomly assigned diameter and length, these parameters are based on statistical distributions determined from physical fiber samples. The Fick’s diffusion equation is used to solve the concentration of encapsulated macromolecules in the fiber due to diffusion. Upon obtaining the solution of the concentration of molecules in individual fibers, one can determine the overall diffusion behavior for a given sample with random fibers distributed. A subsequent statistical characterization can be performed based on the results of a set of random generated samples. Moreover, the developed method can be applied to the diffusion of macromolecules encapsulated in microspheres. The developed method was implemented in MATHEMATICA. As an example, the ES fiber samples were generated via electrospinning alginate and poly(ethylene oxide) (PEO) blend polymer aqueous solution (1:1 ratio, 3% w/v), and FITC–dextran was mixed in the polymer solution to enable fluorescent image analysis. The fiber diameter, length and number of fibers were determined based on the fluorescent images of fiber samples. Parametric study was conducted to examine how the diffusive behavior of encapsulated macromolecules is affected by the fiber diameters, total number of fibers, diffusion constants, and boundary conditions. Furthermore, the stochastic analyses were conducted for cases of the diffusion of macromolecules encapsulated in microspheres. The model predictions agree well with the experimental data obtained from the literature.
A Novel Ultrasonic Technique for the Detection of Distributed Precursor Damages in Composites
Authors: Patra Subir , Banerjee Sourav , Habtour Ed , Haynes Robert
Published: February 2017

Detection of the initial stage of the distributed damage which we call the damage precursor in the composites namely matrix micro cracking and fiber breakage, are extremely important for diagnostic and prognostic of the material. However, existing nondestructive evaluation (NDE) and/or structural health monitoring (SHM) system are not efficient to detect such damages and often demand transformative approach over the existing techniques. Here, we present a novel ultrasonic method for identification of the distribution of the probable damage sites as an indication of the percentage of degradation of the material properties on a typical representative volume element (RVE). An American Society of Testing and Materials (ASTM) standard unidirectional (UD) carbon-fiber-reinforced-plastic (CFRP) specimen was tested under 250,000 cycles mechanical loading and 500 cycles thermal loading. Scanning Acoustic Microcopy (SAM) was used to perform Z-scan of the specimen on a particular area (6mm×6mm) of the specimen. Surface skimming ultrasonic wave velocity (SAW) profile on a representative volume element (RVE) was calculated before and after loading the specimen. A 2D map of decreased SAW regions were calculated after the loading. Statistical analysis of the SAW profile was performed to study the distributed damage evolution in the material. It is found that the damaged regions often coalesce as loading cycle increases and such sites can be predicted from the SAW profile. In addition, we also presented a nonlocal mechanics based ultrasonic technique to study damage evolution with thermomechanical loading. Nonlocal parameters were also calculated on the selected RVE by using Quasi-longitudinal wave velocity along the thickness direction. Using micro-morphic wave dispersion curve, for a selected frequency at 50 MHz. Damage Entropy (DE) was calculated from the distribution of the nonlocal parameter. We also performed optical microcopy (OM) of the selected area to investigate the development of the damages and to validate the SAW results. This work has potential to estimate the remaining useful life of the structure and provide useful information about the distributed damages states, which in turn will help Condition Based Maintenance (CBM+) of the critical locations of the structure while maintaining the aircrafts and the defense equipment.
Conceptual Design and Prototyping of an External Continuously Variable Transmission for Bicycles
Authors: Oldroyd Jordan W. , Salmon John L.
Published: February 2017

The majority of bicycle derailleur systems in use today are based on the same technology used over a century ago. This technology has made large strides in improvement over that time period, yet limitations remain. The derailleur is expensive, prone to damage, requires regular maintenance, and is a significant portion of a bike’s overall weight. Continuously Variable Transmission (CVT) technology could resolve many, if not all, of those limitations. CVT systems are commonly used in small motorized vehicles, such as go-karts or snowmobiles, and is becoming increasingly popular in the automotive industry. This research explores the application of CVT technology to a bicycle. Proto-typing and testing was conducted to understand the functionality, reliability, and feasibility of the design.
Influence of Z-Aligned Carbon Nanofibers on the Through-Thickness Thermal Conductivity of Paraffin Wax
Authors: Scruggs Alexander M. , Kirmse Sebastian , Hsiao Kuang-Ting
Published: February 2017

This research paper specifically focuses on experimentally characterizing and elaborating the effect of z-aligned carbon nanofibers (CNFs) on the through-thickness (i.e., z-direction) thermal conductivity of paraffin wax. The z-aligned CNF network present within the paraffin sample was hypothesized to provide a thermally-conductive nanostructure throughout the sample thickness, thereby increasing the thermal conductivity and the thermal energy charging/discharging capabilities of the paraffin wax. It was further hypothesized that the effectiveness of this thermally-conductive nanostructure was strongly related to both CNF alignment and CNF concentration.

To experimentally analyze the respective impact of CNF concentration (measured as a percentage of sample weight) and CNF alignment on the through-thickness thermal conductivity, z-aligned CNF-modified paraffin wax samples with various CNF concentrations were manufactured and compared with unmodified (i.e. control) paraffin wax samples and unaligned CNF-modified paraffin wax samples; the concentration of CNF-reinforcement was tested at both 0.1wt.% and 0.3wt.%. The through-thickness thermal conductivities were characterized for all samples using a steady-state parallel plate testing device and the results were compared and discussed against the experimental parameters. It was found that both CNF alignment and concentration had a strong influence on the improvement of through-thickness thermal conductivity of paraffin wax.
First-Principles Calculations and Molecular Dynamics Simulations on Effect of Hydrogen Impurity in Lead Titanate Films
Authors: Zhu Lin , You Jeong Ho , Chen Jinghong
Published: February 2017

Properties of ferroelectric films are highly influenced by inevitable defects, such as hydrogen impurity. This study is focused on theoretical and numerical studies to probe effects of hydrogen contamination on ferroelectric stability in PbTiO3 (PTO) films using the first-principles effective Hamiltonian. First-principles calculations are performed to determine the possible position, formation energy, and mobility of hydrogen impurity atom, and the calculated results are used as inputs to molecular dynamics (MD) simulations in a large system. The hydrogen atom is able to move along the polarization with small energy barriers. The energy difference between a hydrogen contaminated PTO and a pure PTO is considered as an energy penalty term induced by hydrogen contamination and has been added to the effective Hamiltonian. Then, the MD effective Hamiltonian with the energy penalty is employed in MD simulations to investigate the effects of hydrogen contamination on the ferroelectric responses of PTO films with various thicknesses and temperatures. The hysteresis loops are presented and analyzed for PTO films with various concentrations of hydrogen impurities and thicknesses. Hydrogen contamination reduces the remnant polarization, especially for thin films. As the concentration of hydrogen impurities increases, the critical thickness increases. By analyzing the vertical cross section snapshots, it has been found that the hydrogen impurity atoms near interfaces affect the polarization throughout the entire PTO films.
Modelling of a Magnetorheological Fluid Knee in a Prosthetic Leg
Authors: Nguyen The , Bapat Saurabh , Wang Xinli
Published: February 2017

The purpose of the study is to theoretically model a prosthetic knee. A knee similar to magnetorheological fluid (MRF) brake is designed and the study focuses on modelling the MRF knee, predict the torque and compare it with the experimental data. The torque generated by the MRF knee is highly dependent on the gap size, angle, and the applied current. Here, the MRF knee features a non-circular rotor which results in a variable gap size for the MR fluid, between the stator and the rotor. Therefore, the gap size varies with the angle of the knee. When the current is applied and MR knee is subjected to a magnetic field, the yield stress produces the shear friction due to which the braking torque is generated. This derives the braking torque as a function of angle and applied current. A torque equation is derived from the theoretical data to yield the predicted results. In addition to the theoretical modelling and derived torque equations, the torque for the MRF fluid is also calculated experimentally. For the validation of the theoretical model and the derived torque equations, they were compared with the experimental results.
Multi-Objective Optimization of a Data Center Modeling Using Response Surface
Authors: Phan Long , Lin Cheng-Xian
Published: February 2017

Energy consumption and thermal management have become key challenges in the design of large-scale data centers, where perforated tiles are used together with cold and hot aisles configuration to improve thermal management. Although full-field simulations using computational fluid dynamics and heat transfer (CFD/HT) tools can be applied to predict the flow and temperature fields inside data centers, their running time remain the biggest challenge to most modelers. In this paper, response surface methodology based on radial basis function is used to significantly reduce the running time for generating a large set of generations during a two-objective minimization process which uses the genetic algorithm as its main engine. Three design parameters including mass flow inlet, inlet temperature, and server heat load are investigated for a two-objective optimization. The goal is to minimize both the temperature difference and the maximum temperature inside the data center and search for a range of design parameters that satisfy both of these objectives. Numerous radial basis function models are studied and compared. Discussion on a more preferred scheme for the response surface construction is provided. Finally, a graph of Pareto font is generated showing the set of optimal designs in the objective space, and Pareto design validation is also performed.
Processing of Biodegradable Polymer Composite Using Soy Protein-Based Resin and Nanoclay
Authors: Hossain Mohammad K. , Shaily Samira N. , Harrigan Hadiya J. , Mickens Terrie
Published: February 2017

A completely biodegradable composite was fabricated from an herbal polymer, soy protein concentrate (SPC) resin. Soy protein was modified by adding 30 wt% of glycerol and 5 wt% of poly vinyl alcohol (PVA) to enhance its mechanical as well as thermal property. 3%, 5%, 10%, and 20% nanoclay (NC) were infused into the system. To evaluate its mechanical properties, crystallinity, thermal properties, bonding interaction, and morphological evaluation, tensile, X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and Fourier transform infrared spectroscopy (FTIR) tests, and optical microscopy (OM) and scanning electron microscopy (SEM) evaluation were performed. Tensile tests showed that the addition of nanoclay improved the mechanical properties of the modified resin. Soy protein is hydrophilic due to the presence of amino acids that contain various polar groups such as amine, carboxyl, and hydroxyl. As a result, polar nanoclay particles that are exfoliated can be evenly dispersed in the SPC resin. From experimental results, it is clear that adding of nanoclay with SPC resin significantly increased the stiffness of the SPC resin. A combination of 5% clay, 30% glycerol, and 5% PVA with the modified SPC resulted in the maximum stress of 18 MPa and Young modulus of 958 MPa. The modified SPC showed a reduced failure strain as well. X-ray diffraction curves showed an improvement of crystallinity of the prepared resin with increasing amount of nanoclay. Interaction among soy, glycerol, PVA, and nanoclay was clearly demonstrated from the FTIR analysis. Optical microscopy (OM) and scanning electron microscopy (SEM) micrographs revealed rougher surface in the nanoclay infused SPC samples compared to that of the neat one. SEM evaluation revealed rougher fracture surface in the NC infused samples.
Fabrication and Characterization of Bio-Based Poly Lactic Acid/Polyhydroxybutyrate-Valerate (PLA/PHBV) Blend With Nanoclay
Authors: Hossain Mohammad K. , Shaily Samira N. , Harrigan Hadiya J. , Mickens Terrie
Published: February 2017

The objective of this research is to prepare a hybrid biopolymer blend using PLA and PHBV with enhanced mechanical and thermal properties. Bio-based PLA and PHBV blends were prepared using the melt-mixing procedure. Tensile, FTIR, DSC, TGA, optical microscopy (OM), and scanning electron microscopy (SEM) tests were performed to investigate mechanical properties, bonding interaction, glass transition temperature, melting and crystalline enthalpy, thermal decomposition, and morphological analysis. Different percent (1, 2, and 3 wt%) of nanoclay was added to the system to observe the bonding interaction. It was observed that the crystallinity increases with increasing amount of nanoclay. The result showed that the tensile strength of PLA thin film and PHBV film was found to be 31.1 MPa and 14.41 MPa, respectively. Hence, PLA has better mechanical property than PHBV. On the other hand, thermal property of PHBV thin film was found to be better than that of PLA. To optimize both mechanical and thermal properties of PLA and PHBV hybrid biopolymer blend, using various combinations of PLA/PHBV including 25/75, 50/50 and 75/25 wt% a hybrid biopolymer blend was prepared. Among them, PLA-PHBV (75/25 wt%) with 2 wt% nanoclay resulted in the best outcome. The tensile strength of this prepared polymer blend was 29.34 MPa. Thermal analysis demonstrated two melting temperatures: 238.37 °C and 308.31 °C, respectively. Two glass transition temperatures were found from thermal tests which are the indication of the solution immiscibility. It had also been observed that the adding of nanoclay enhances tensile properties as well as thermal stability up to 2 wt%. It is revealed from the optical and SEM micrographs that the 2 wt% NC was dispersed uniformly throughout the resin blend.
Effects of Entrance Geometry on Solar Chimney’s Performance
Authors: Huynh B. P.
Published: February 2017

People spend most of their time indoors. A comfortable indoor environment is thus essential for the occupants’ good health and productivity. Buildings are responsible for about half of a modern society’s total energy consumption. HVAC (Heating, Ventilation and Air-Conditioning) which is often used to provide thermal comfort to the occupants, in turn accounts for a major proportion of this energy demand. Minimising HVAC energy consumption will thus result in great economic benefits. It also contributes beneficially to the issue of sustainable future and climate change, by reducing fuel burning. Natural ventilation can be used to help reduce significantly HVAC energy demand. Solar chimney (thermal chimney) is a device which absorbs solar radiation to heat the air. The heated air, becoming buoyant, rises through the chimney’s passage and induces further air currents. When fitted to a building, solar chimney can thus induce fresh outside air to flow through it for ventilation. As a very useful ventilation device, solar chimney has been the subject of many studies. However, due to the complex non-laminar, non-isothermal flow and heat transfer involved, there are still many factors affecting a solar chimney’s performance (measured by the induced flow rate of air, for instance) not yet considered, especially regarding 3-dimensional computational modelling in real-sized building settings. This work thus investigates computationally natural ventilation induced by a roof-mounted solar chimney through a real-sized 3-dimensional room, using a commercial CFD (Computational Fluid Dynamics) software package which employs the Finite Volume Method. Chien’s turbulence model of low-Reynolds-number K-ε is used in a Reynolds Averaged Navier-Stokes (RANS) formulation. Thus, the full set of Reynolds-Averaged governing equations pertaining to non-isothermal, buoyancy induced, incompressible, steady, turbulent flow of air near standard conditions at sea level, coupled with equations describing the Chien’s turbulence model, are solved, with appropriate boundary conditions. No further simplifying assumptions are made. Grid convergence tests are conducted to make sure that the grid patterns used are appropriate. Adequate numerical convergence is allowed; this often requires that relative changes in the successive iterated solutions be less than 0.0001. Accumulation errors resulting from massive or lengthy computation are also carefully monitored and minimized. 64-bits precision is used throughout. It is found that entrance geometry to the chimney’s channel affects significantly the ventilation rate, especially at higher solar heat flux, with rounded entrance resulting in higher rate. But these entrance-geometry effects also vary significantly with location of the room’s inlet-opening which in its turn affects the flow path before the chimney’s entrance.
Magnetic Resonance Thermometry Experimental Setup: A Portable Heat Transfer Experiment
Authors: Williams Elliott T. , Spirnak Jonathan R. , Samland Marc C. , Tremont Brant G. , McQuirter Alfred L. , VerHulst Claire M. , Van Poppel Bret P. , Benson Michael J. , Elkins Christopher J. , Burton Lauren S. , Eaton John K.
Published: February 2017

This work provides a detailed description of the setup and execution of an experiment employing Magnetic Resonance Thermometry (MRT) techniques for measuring the three-dimensional temperature field of a fully turbulent jet mixing with a cross flow. The proposed methodology has the flexibility of applying different thermal boundary conditions — adiabatic and conductive — by varying the materials used in the test section as well as varying the temperatures of the mixing flows. The experiment described in this paper employs a standard magnetic resonance imaging system comparable to those used in medical radiology departments worldwide. A series of MR scans with both isothermal and thermal mixing conditions were conducted and results are presented with sub-millimeter resolution across the measured 3D domain of interest within one degree Celsius. The methodology presented here holds unique advantages over conventional techniques because measurements can be acquired without introducing flow disturbances and in regions without any optical access. When coupled with other established MR-based measurement techniques, MRT provides large, robust data sets that can be used for validation, design, and insight into system thermal performance for complex, turbulent flows. The materials and components employed in this work cost approximately $13,900, and the experimental setup and data collection required approximately 48 hours.
Performance of 3-D Printed Thermoplastic Polyurethane Under Quasi-Static and High-Strain Rate Loading
Authors: Chaudhry S. , Al-Dojayli M. , Czekanski A.
Published: February 2017

As 3-D printed materials are being embraced by the manufacturing industries, understanding the response mechanism to high strain rate events becomes a concern to meet requirements for a specific application. In order to improve the mechanical performance of a 3-D printed part, it is necessary to quantify the impact of various printing parameters on the mechanical properties. Initial studies have shown that a difference in 3-D printed material is expected due to the effect of manufacturing parameters such as anisotropy relating to printing direction, infill pattern, infill percentage, layer height and orientation of the part being printed. The main focus of the study is to characterize the effect of the previously mentioned printing parameters under quasi-static and high strain rate (100–1000 /s). In this strain rate regime, the most common apparatus used is the Split Hopkinson pressure bar (also known as Kolsky bar). It consists of a cylindrical metallic bar that has a striker, input and output bar. While the specimen is fixated between the input and output bar, the striker bar is accelerated and triggers the incident bar. As a result, an elastic wave is generated which travels towards the specimen/input bar interface, where some part of it is reflected and the rest is transmitted. The Kolsky bar is adjusted by using a hollow transmitter tube and pulse shaper. Due to an impedance mismatch between the samples and bar material, the amplitude of the transmitted pulse is low. Using a hollow transmitter bar increases this amplitude due to area mismatch between the specimen and tube. Using a pulse shaper between the striker and input bar, the rise time of the elastic compressive wave increases and assists in achieving a constant rate of loading. The compressive stress strain curves were obtained under high strain rates to determine the strain rate effect. To measure the response under static testing conditions, a commercial load frame was used. A comprehensive comparison of dynamic compressive response of samples was performed to characterize the effect of printing parameters.
Single Layered Cable Under Constrained Bending: Development of New Mathematical Model and Validation
Authors: Gopalakrishnan Shibu , Dhandapani Gopinath
Published: February 2017

This paper concerns the response of a single-layered strand cable of helical wires with wires-to-core contact under free and constant curvature constrained bending. The stranded cable under static-loading conditions experiences any combination of tension, torsion and bending. A linear finite element model for helical wire strand cable for both bending cases was developed and their bending response for various load steps was analyzed. The responses thus observed were compared with the theoretical prediction reported by the present authors in the literature. The present authors have developed a theoretical model using the thin rod theory and presented a linear stiffness matrix establishing the relationship between the axial, torsional and flexural rigidities and the coupling parameters of the cable.
Fabrication and Characterization of Nanostructured Cathodes for Li-Ion Batteries
Authors: Jibhakate Piyush D. , Nelson George J.
Published: February 2017

Li-ion batteries have emerged as a leading energy storage technology for several applications including portable electronics devices and electric vehicles. Rigorous efforts are made to develop these batteries with higher energy density, higher power density, and better cycling stability while reducing cost and environmental impact. To better understand how electrode microstructure contributes to the electrode performance, the spinel LiMn2O4 (LMO) cathode material was prepared using a template-assisted sol-gel synthesis method. This method involves soaking of polycarbonate template membranes in the precursor solution followed by drying, to remove the solvent. The dried templates containing precursor materials were etched in an oxygen plasma to remove the template, and the nanostructured electrode formed was then calcined to convert these nanostructures to spinel LiMn2O4. Simultaneously, powdered LMO was prepared using the same synthesis procedure, but without the aid of a template to control electrode morphology. A series of tests were performed to study the effect of processing conditions on the structure and morphology of the nanostructured electrodes. The resulting electrodes were characterized using X-ray diffraction (XRD) and scanning electron microscope (SEM) in support of efforts to understand the effects of process parameters on the electrochemical performance of the electrode. The template assisted synthesis approach yielded an electrode of well-defined nanotubules. Extending the template soaking time was found to provide better definition of individual tubule structures. Increasing calcination temperature was found to create a better defined spinel structure for the LMO. These observations provide insight into process parameters relevant to electrode preparation and substrate selection when producing nanostructured electrodes using template-assisted methods.