bluuebunny/crossref_metadata_2025 huggingface dataset:
Organization and function of transmitter release sites at the neuromuscular junction
Authors: Meriney Stephen D. , Dittrich Markus
Published: April 2013

Abstract  The neuromuscular junction is known as a strong and reliable synapse. It is strong because it releases an excess of chemical transmitter, beyond what is required to bring the postsynaptic muscle cell to threshold. Because the synapse can sustain suprathreshold muscle activation during short trains of action potentials, it is also reliable. The presynaptic mechanisms that lead to reliability during short trains of activity have only recently been elucidated. It appears that there are relatively few calcium channels in individual active zones, that channels open with a low probability during action potential stimulation and that even if channels open the resulting calcium flux only rarely triggers vesicle fusion. Thus, each synaptic vesicle may only associate with a small number of calcium channels, forming an unreliable single vesicle release site. Strength and reliability of the neuromuscular junction emerge as a result of its assembly from thousands of these unreliable single vesicle release sites. Hence, these synapses are strong while at the same time only releasing a small subset of available docked vesicles during each action potential, thus conserving transmitter release resources. This prevents significant depression during short trains of action potential activity and confers reliability.
Information to cerebellum on spinal motor networks mediated by the dorsal spinocerebellar tract
Authors: Stecina Katinka , Fedirchuk Brent , Hultborn Hans
Published: April 2013

Abstract  The main objective of this review is to re‐examine the type of information transmitted by the dorsal and ventral spinocerebellar tracts (DSCT and VSCT respectively) during rhythmic motor actions such as locomotion. Based on experiments in the 1960s and 1970s, the DSCT was viewed as a relay of peripheral sensory input to the cerebellum in general, and during rhythmic movements such as locomotion and scratch. In contrast, the VSCT was seen as conveying a copy of the output of spinal neuronal circuitry, including those circuits generating rhythmic motor activity (the spinal central pattern generator, CPG). Emerging anatomical and electrophysiological information on the putative subpopulations of DSCT and VSCT neurons suggest differentiated functions for some of the subpopulations. Multiple lines of evidence support the notion that sensory input is not the only source driving DSCT neurons and, overall, there is a greater similarity between DSCT and VSCT activity than previously acknowledged. Indeed the majority of DSCT cells can be driven by spinal CPGs for locomotion and scratch without phasic sensory input. It thus seems natural to propose the possibility that CPG input to some of these neurons may contribute to distinguishing sensory inputs that are a consequence of the active locomotion from those resulting from perturbations in the external world.
Phase Averaged Flow Analysis in an Oscillating Water Column Wave Energy Converter
Authors: Fleming Alan , Penesis Irene , Goldsworthy Laurie , Macfarlane Gregor , Bose Neil , Denniss Tom
Published: April 2013

This paper presents the application of phase averaging to experimental data obtained during scale model testing of a forward facing bent duct oscillating water column (OWC). Phase averaging is applied to both wave probe data and a two-dimensional velocity field at the centerline plane of the OWC model obtained using particle imaging velocimetry (PIV). Results are presented for one monochromatic wave condition. The influence of varied wave frequency is briefly discussed.
Experimental Study on the Collapse Strength of Narrow Stiffened Panels
Authors: Xu Ming Cai , Guedes Soares C.
Published: April 2013

The results of five tests on narrow stiffened panels under axial compression until collapse and beyond are presented to investigate the collapse behaviors of stiffened panels. Tension tests were used to evaluate the material properties of the stiffened panels. The tests were made on panels with two half bays plus one full bay in the longitudinal direction. Initial loading cycles were used to eliminate the residual stresses of the stiffener panels. The strain gauges were set on the plates and the stiffeners to record the strain histories. The displacement load relationship was established. The collapse behavior, modes of failure and load-carrying capacity of the stiffened panels are investigated with the experiment.
Study of Gas/Liquid Behavior Within an Aeroengine Bearing Chamber
Authors: Chandra Budi , Simmons Kathy , Pickering Stephen , Collicott Steven H. , Wiedemann Nikolas
Published: April 2013

Aeroengine bearing chambers typically contain bearings, seals, shafts and static parts. Oil is introduced for lubrication and cooling and this creates a two phase flow environment that may contain droplets, mist, film, ligaments, froth or foam and liquid pools. Some regions of the chamber contain a highly rotating air flow such that there are zones where the flow is gravity dominated and zones where it is rotation dominated. The University of Nottingham Technology Centre in Gas Turbine Transmission Systems, is conducting an ongoing experimental program investigating liquid and gas flow behavior in a relevant highly rotating environment. Previously reported work by the UTC has investigated film thickness and residence volume within a simplified chamber consisting of outer cylindrical chamber, inner rotating shaft and cuboid off-take geometry (termed the generic deep sump). Recently, a more aeroengine relevant bearing chamber offtake geometry has been studied. This geometry is similar to one investigated at Purdue University and consists of a “sub-sump” region approached by curved surfaces linked to the bearing chamber. The test chamber consists of an outer, stationary cylinder with an inner rotating shaft. The rig runs at ambient pressure and the working fluid (water) is introduced either via a film generator on the chamber wall or through holes in the shaft. In addition to visual data (high speed and normal video), liquid residence volume within the chamber and film thickness were the two numerical comparators chosen. Data was obtained for a number of liquid supply rates, scavenge ratios and shaft rotation speeds. The data from the current model is compared to that from the earlier studies. The data shows that in contrast to the previously reported generic deep sump study, the residence volume of the curved wall deep sump (CWDS) designs is far less sensitive to shaft speed, liquid supply rate and scavenge ratio. The method of liquid supply only makes a significant difference at the lowest scavenge ratios. Residence volume data for the Nottingham CWDS is comparable, when appropriately scaled, to that for the Purdue design. The film thickness data shows that at the lower shaft speeds investigated the flow is gravity dominated whereas at higher shaft speeds shear dominates.
Analysis of Flow Migration in an Ultra-Compact Combustor
Authors: Bohan Brian T. , Polanka Marc D.
Published: April 2013

The ultra-compact combustor (UCC) has the potential to offer improved thrust-to-weight and overall efficiency in a turbojet engine. The thrust-to-weight improvement is due to a reduction in engine weight by shortening the combustor section through the use of the revolutionary circumferential combustor design. The improved efficiency is achieved by using an increased fuel-to-air mass ratio and allowing the fuel to fully combust prior to exiting the UCC system. Furthermore, g-loaded combustion offers increased flame speeds that can lead to smaller combustion volumes. One of the issues with the UCC is that the circumferential combustion of the fuel results in hot gases present at the outside diameter of the core flow. These hot gases need to migrate radially from the circumferential cavity and blend with the core flow to present a uniform temperature distribution to the high-pressure turbine rotor. The current research focused on correlations to control the UCC cavity velocity, control the temperature profile throughout the UCC section, analyze the exhaust species exiting the combustor, and quantify pressure losses in the system. To achieve these goals, a computational fluid dynamics (CFD) analysis was used on a UCC geometry scaled to a representative fighter-scale engine. The analysis included a study of cavity to core flow interaction characteristics, a 5- and 12-species combustion model of liquid and gaseous fuel, and determination of species exiting the combustor. Computational comparisons were also made between an engine realistic condition and an ambient pressure rig environment.
Dynamic Heat-Exchanger Model for Any Combination of Water and Steam States
Authors: Kim Eunkyeong , Yoshida Takuya , Yashiki Tatsurou
Published: April 2013

The purpose of this study is to propose a dynamic heat transfer model for predicting transient heat recovery steam generator (HRSG) behaviors involving phase changes in heat exchanger tubes. The model deals with any combination of phase states by switching the equations for heat transfer coefficient, specific volume, and friction factor corresponding to their physical characteristics. The model also constrains the change of mass flow calculated by momentum balance to satisfy thermodynamic relationships which are neglected by conventional models. The simulation results show that the proposed model predicts the transient pressure drop, outlet mass flow changes, and the reduction in heat transfer coefficient caused by dryout during heating or evaporating processes. In addition, the model improves the accuracy of mass flow transients compared to those obtained by conventional models.
Feasibility Study of an Oil-Free Turbocharger Supported on Gas Foil Bearings Via On-Road Tests of a Two-Liter Class Diesel Vehicle
Authors: Lee Yong-Bok , Bum Kwon Suk , Kim Tae Ho , Sim Kyuho
Published: April 2013

This paper presents the feasibility study of an oil-free turbocharger (TC) supported on gas foil bearings (GFBs) via on-road tests of a 2-liter class diesel vehicle. The oil-free TC is constructed using a hollow rotor with a radial turbine at one end and a compressor impeller at the other end, a center housing with journal and thrust GFBs, and turbine and compressor casings. The oil-free TC reuses parts of a commercial variable geometry turbocharger, except for the rotor-bearing system. In a test rig driven by a diesel vehicle engine (EG), the rotordynamic performance of the oil-free TC is evaluated up to the rotor speed of 130 krpm, which is measured at the compressor end. The journal GFBs are modified to enhance the rotordynamic performance by inserting three metal shims between the bump-strip layers and bearing housing. The rotordynamic performance is also measured during on-road tests by replacing the original TC of the test diesel vehicle with the constructed oil-free TC. The journal GFBs have a relatively large bearing clearance and no metal shims to generate subsynchronous motions at low TC and EG speeds. During normal vehicle driving, the TC rotor motions show steady rotordynamic operations. The oil-free TC rotates at 25 krpm ∼ 50 krpm while the vehicle runs at 20 km/h ∼ 30 km/h on the road. Subsynchronous rotor motions initiate with a frequency of ∼100 Hz at the TC speed of ∼37 krpm. As expected, the TC rotor motion also shows multiple EG-induced harmonics. Upon external shocks, produced by driving the vehicle on road-bumps, the subsynchronous motions are only excited when the rotor rotates above the initiation speed of subsynchronous motion. The excitation is nondestructive because the vehicle suspension absorbs most of the external shock. Incidentally, the external shocks appear to have no influence on the synchronous motion and engine-induced harmonics of the TC rotor.
Hybrid Model-Based Fault Detection and Diagnosis for the Axial Flow Compressor of a Combined-Cycle Power Plant
Authors: García-Matos Jesús A. , Sanz-Bobi Miguel A. , Muñoz Antonio , Sola Antonio
Published: April 2013

This technical brief is focused on the research area of fault detection and diagnosis in a complex thermodynamical system: in this case, an axial flow compressor. Its main contribution is a new approach which combines a physical model and a multilayer perceptron (MLP) model using the best advantages of both types of modeling. Fault detection is carried out by an MLP model whose residuals against the real outputs of the system determine which observations could be considered abnormal. A physical model is used to generate different fault simulations by shifting physical parameters related to faults. After these simulations are performed, the different fault profiles obtained are collected within a fault dictionary. In order to identify and diagnose a fault, the anomalous residuals observed by the MLP model are compared with the fault profiles in the dictionary and a correlation that provides a hypothesis with respect to the causes of the fault is obtained. This methodology has been applied to axial compressor operational data obtained from a real power plant. A case study based on the successful diagnosis of compressor fouling is included in order to show the potential of the proposed method.
The Influence of Reynolds Number and Roughness on the Efficiency of Axial and Centrifugal Fans—A Physically Based Scaling Method
Authors: Pelz Peter F. , Stonjek Stefan S.
Published: April 2013

There is a technical and economical need for a correction method to scale model test data, which fulfills five tasks: It should be (i) physically based, (ii) understandable and easy to apply, and (iii) universal, i.e., applicable to centrifugal as well as to axial machines of different specific speed. Moreover, the method should (iv) account for the aerodynamic quality of the machine and should (v) be reliable not only at peak efficiency, but also at off-design condition. Up to now, no method meets all five tasks. To fill that gap, a method developed at Technical University Darmstadt together with Forschungsvereinigung für Luft- und Trocknungstechnik e. V. (FLT) is introduced in this work. The method consists of three steps: Assuming the so-called master curve, scaling the efficiency itself and shifting the best efficiency point to a higher flow coefficient. For each step, a simple physical explanation is given. The validation of the method is done with test data of two axial fans with four different stagger angles and two centrifugal fans. In spite of its simplicity, the method shows a good agreement to test data compared with traditional and most recent scaling methods. A short overview about the advantages and disadvantages of compared methods and a conclusion is given at the end of this work.
Impact of Refinery Stream Gasoline Property Variation on Load Sensitivity of the HCCI Combustion
Authors: Lacey Joshua S. , Filipi Zoran S. , Sathasivam Sakthish R. , Peyla Richard J. , Cannella William , Fuentes-Afflick Peter A.
Published: April 2013

The homogeneous charge compression ignition (HCCI) combustion process is highly reliant upon a favorable in-cylinder thermal environment in an engine, for a given fuel. Commercial fuels can differ considerably in composition and autoignition chemistry; hence, strategies intended to bring HCCI to market must account for this fuel variability. To this end, a test matrix consisting of eight gasoline fuels comprised of blends made solely from refinery streams were run in an experimental, single cylinder HCCI engine. All fuels contained 10% ethanol by volume and were representative of a cross section of fuels one would expect to find at gasoline pumps across the United States. The properties of the fuels were varied according to research octane number (RON), sensitivity (S = RON-MON), and volumetric content of aromatics and olefins. For each fuel, a sweep of load (mass of fuel injected per cycle) was conducted and the intake air temperature was adjusted in order to keep the crank angle of the 50% mass fraction burned point (CA50) constant. By analyzing the amount of temperature compensation required to maintain constant combustion phasing, it was possible to determine the sensitivity of HCCI to changes in load for various fuels. In addition, the deviation of fuel properties brought about variations in important engine performance metrics like specific fuel consumption. Though the injected energy content per cycle was matched at the baseline point across the test fuel matrix, thermodynamic differences resulted in a spread of specific fuel consumption for the fuels tested.
Experimental Investigation of Tsunami Bore Forces on Vertical Walls
Authors: Robertson I. N. , Paczkowski K. , Riggs H. R. , Mohamed A.
Published: April 2013

A series of experiments have been carried out in the large wave flume (LWF) at Oregon State University to quantify tsunami bore forces on structures. These tests included “offshore” solitary waves, with heights up to 1.3 m, that traveled over a flat bottom, up a sloping beach, and breaking onto a flat reef. Standing water depths on the reef varied from 0.05 m to 0.3 m. Resulting bores on the reef measured up to approximately 0.8 m. After propagating along the reef, the bores struck a vertical wall. The resulting forces and pressures on the wall were measured. The test setup in the LWF is described, and the experimental results are reported. The results include forces and pressure distributions. Results show that the bores propagated with a Froude number of approximately 2 and that the forces follow Froude scaling. Finally, a design formula for the maximum impact force is given. The formula is shown to be an improvement over existing formulas found in the literature.
Flow and Heat Transfer Characteristics of Single Jet Impinging on Dimpled Surface
Authors: Xie Yonghui , Li Ping , Lan Jibing , Zhang Di
Published: April 2013

Based on combined particle image velocimetry (PIV) and numerical simulation, the flow and heat transfer characteristics of a single jet impinging on a dimpled surface for Dj/D = 0.318, 0.5, 1.045; δ/D = 0.1, 0.2, 0.3; Rej = 5000, 10,000, 23,000, were investigated for the first time. The distance between jet nozzle and plate was fixed and equal to H/D = 2. The results show that the flow structures of the single jet impingement with dimpled target surface can be summarized into three typical conceptual flow structures. Particularly, the third flow structure in the form of a large toroidal vortex bound up with the dimple is the result of the centrifugal force of the flow deflection at the stagnation region and spherical centrifugal force of the deep dimple surface. The heat transfer area increases when the dimple relative depth increases. For the cases of Dj/D = 0.318 and 0.5, the area increasing dominate the heat transfer process, and the average Nusselt number increases with the increasing of dimple relative depth. For the cases with Dj/D = 1.045, the local Nusselt number reduction dominate the heat transfer process, the average Nusselt number decreases with the increasing of dimple relative depth. The average Nusselt number of the Dj/D = 0.318 and 0.5 cases is larger than the baseline case, while those of the Dj/D = 1.045 cases are smaller than the baseline case. Furthermore, the correlative expressions of the local Nusselt number, stagnation points Nusselt number and average Nusselt number are obtained.
A New and Accurate Mathematical Model for Computer Numerically Controlled Programming of 4Y1 Wheels in 2½-Axis Flute Grinding of Cylindrical End-Mills
Authors: Xiao Silai , Wang Liming , Chen Zezhong C. , Wang Shequan , Tan Aiming
Published: April 2013

Solid carbide cylindrical end-mills are widely used in machining, and their helical flutes are crucial to their cutting performance. In industry, the flute is simply defined with four key parameters: the helical angle, the radial rake angle, the fluting angle, and the core radius, which are specified in an end-mill design. The flute shape is not fully defined, while it is often generated by a 1A1 or 1V1 diamond wheel in 2½-axis computer numerically controlled (CNC) grinding. Unfortunately, the two simple wheels cannot make largely different flute shapes, preventing further improvement of the end-mills. Although no research result on how the flute geometry affects the end-mill cutting attribute has come into public yet, it is now necessary to employ more complicated wheels to grind flutes with the specified parameter values but much different flute shapes. For this purpose, the 4Y1 diamond wheel is employed in this work. However, the commercial tool grinding software cannot determine the dimensions and the set-up angle for the 4Y1 wheel. To address this problem, a new mathematical model of the flute parameters in terms of the dimensions and the set-up angle of the 4Y1 wheel is formulated, thus, the 4Y1 wheel can be used in flute grinding. This work lays a foundation of using complex wheels to grind flutes with more shapes in order to improve the end-mill's cutting ability.
Keeping Smartphones Cool With Gallium Phase Change Material
Authors: Ge Haoshan , Liu Jing
Published: April 2013

With many emerging capabilities in pervasive computing, internet access, wireless communication, and data processing, the smartphone with high central processing unit (CPU) frequency is achieving extremely high running speed which also brings about discomfort to the users due to huge heat released. Here, an automatic temperature regulation strategy using low melting point metal gallium to absorb transitory heat was proposed for the first time. Experiments demonstrate that 3.4125 ml gallium would maintain the module below 45 °C for 16 min at 2.832 W. Such temperature holding time was longer than most of the conventional phase change materials (PCMs). Moreover, some interesting phase change phenomena were also discovered such that mixing SiO2 powder with gallium or just shaking the liquid metal container will help reduce the large supercooling of gallium which is beneficial for the material to quickly recover to its original service state again. The method is expected to be very useful and efficient in maintaining thermal comfort of many handheld electronics, especially for the burgeoning smartphones and panel personal computer (PPC).
Temperature-Dependent Electrical Characteristics of Ag Schottky Contacts to Differently Grown O-Polar Bulk ZnO
Authors: Kim Hogyoung , Sohn Ahrum , Cho Yunae , Kim Dong-Wook
Published: April 2013

The temperature-dependent electrical properties of Ag Schottky contacts to differently grown O-polar bulk ZnO single crystals were comparatively investigated in the temperature range of 100–300 K. Schottky contact to hydrothermal ZnO produced the higher barrier heights (lower ideality factors) than that of pressurized melt-grown ZnO. The modified Richardson plots for two samples produced the larger Richardson constant compared to the theoretical value of 32 A cm−2 K−2 for n-type ZnO, indicating that the inhomogeneous barrier height with the thermionic emission (TE) model could not explain the current transport. The conductive accumulation layers on the ZnO surfaces might not be removed effectively for two samples, which degraded the rectifying characteristics. The different electron transport characteristics between hydrothermal and pressurized melt-grown ZnO could be explained by the different degree of Ag-O formation at the interface.
Dynamic Fracture Characterization of Small Specimens: A Study of Loading Rate Effects on Acrylic and Acrylic Bone Cement
Authors: Bedsole Robert , Tippur Hareesh V.
Published: April 2013

A long-bar apparatus for subjecting relatively small samples to stress-wave loading has been devised for failure characterization. A methodology based on digital image correlation (DIC) used in conjunction with ultra high-speed photography and a long-bar impactor has been developed for determining dynamic crack initiation stress intensity factor (SIF) (KI-inid), as well as SIFs for a rapidly growing crack (KId) during high-strain rate events. By altering the material of the pulse shaper, a range of strain rates has been attained. Commercial grade PMMA was first used to calibrate the device, and then dynamic fracture characterization was performed for the first time on PMMA-based bone cement (BC). Despite several key differences, the two materials performed similarly during quasi-static fracture tests; however, under dynamic loading conditions, bone cement exhibited significantly lower crack initiation SIF (KI-inid), lower dynamic SIFs (KId), and higher crack tip velocities for three different dynamic loading rates (K·=6.5-24×104 MPam s-1).
Numerical Simulation of the Effect of the Size of Suspensions on the Solidification Process of Nanoparticle-Enhanced Phase Change Materials
Authors: El Hasadi Yousef M. F. , Khodadadi J. M.
Published: April 2013

Nanostructure-enhanced phase change materials (NePCM) have been widely studied in recent years due to their enhanced thermal conductivity and improved charge/discharge in thermal energy storage applications. In this study, the effect of the size of the nanoparticles on the morphology of the solid–liquid interface and the evolving concentration field during solidification is reported. Combining a one-fluid-mixture approach with the single-domain enthalpy-porosity model for phase change and assuming a linear dependence of the liquidus and solidus temperatures of the mushy zone on the local concentration of the nanoparticles subject to a constant value of the segregation coefficient, thermal-solutal convection as well as the Brownian and thermophoretic effects are taken into account. A square cavity containing a suspension of copper nanoparticles (diameter of 5 and 2 nm) in water was the model NePCM considered. Subject to a 5 °C temperature difference between the hot (top) and cold (bottom) sides and with an initial loading of the nanoparticles equal to 10 wt. % (1.22 vol. %), the colloid was solidified from the bottom. The solid–liquid interface for the case of NePCM with 5 nm particle size was almost planar throughout the solidification process. However, for the case of the NePCM with particle size of 2 nm, the solid–liquid interface evolved from a stable planar shape to an unstable dendritic structure. This transition was attributed to the constitutional supercooling effect, whereby the rejected particles that are pushed away from the interface into the liquid zone form regions of high concentration thus leading to a lower solidus temperature. Moreover, for the smaller particle size of 2 nm, the ensuing solutal convection at the liquid–solid interface due to the concentration gradient is affected by the increased Brownian diffusivity. Due to size-dependent rejection of nanoparticles, the frozen layer that resulted from a dendritic growth contains regions of depleted concentration. Despite the higher thermal conductivity of the colloids, the amount of frozen phase during a fixed time period diminished as the particle size decreased.
The Effect of Tear Film on Ocular Surface Temperature: A Thermodynamic Study
Authors: Tan Jen Hong , Ng E. Y. K. , Acharya U. Rajendra
Published: April 2013

The thermodynamic effect of tear film on ocular surface remains ambiguous in literature, though in general it is considered to warm the surface in blinking phase, and cool it at later stage. In this investigation, we modeled the temporal variation in ocular surface temperature (OST) on the basis of Newton's law of cooling to look into the tear film's thermodynamic effect. We assumed, the OST varied periodically and the OST just before a blink was equal to the OST observed when the surface was in equilibrium. Then, this model was incorporated into a thermodynamic equation, describing the heat exchange at the ocular surface. Simulations were subsequently performed to determine the moment when the tear film evaporated the exactly amount of energy it had just brought to the surface by blinking in an interblink period. It was found that, for tear film to possibly warm the ocular surface both in the blinking phase and the entire interblink period, its thickness had to be above 32 μm, assuming the rate of spontaneous blinking was once per 6 s. However, according to literature, tear film thickness is likely to be 3 μm, which in this case, the tear film would evaporate the tear-transferred heat just within a second, and the warming effect by tear film would be minimal; cooling should be the dominating effect.
Modeling Die Swell of Second-Order Fluids Using Smoothed Particle Hydrodynamics
Authors: Sadek Samir H. , Yildiz Mehmet
Published: April 2013

This work presents the development of a weakly compressible smoothed particle hydrodynamics (WCSPH) model for simulating two-dimensional transient viscoelastic free surface flow which has extensive applications in polymer processing industries. As an illustration for the capability of the model, the extrudate or die swell behaviors of second-order and Olyroyd-B polymeric fluids are studied. A systematic study has been carried out to compare constitutive models for second-order fluids available in literature in terms of their ability to capture the physics behind the swelling phenomenon. The effects of various process and rheological parameters on the die swell such as the extrusion velocity, normal stress coefficients, and Reynolds and Deborah numbers have also been investigated. The models developed here can predict both swelling and contraction of the extrudate successfully. The die swell of a second-order fluid was solved for a wide range of Deborah numbers and for two different Reynolds numbers. The numerical approach was validated through the solution of fully developed Newtonian and non-Newtonian viscoelastic flows in a two-dimensional channel as well as modeling the die swell of a Newtonian fluid. The results of these three benchmark problems were compared with analytic solutions and numerical results in literature when pertinent, and good agreements were obtained.
Wave Height and Wave Velocity Measurements in the Vicinity of the Break Point in Laboratory Plunging Waves
Authors: Mukaro R. , Govender K. , McCreadie H.
Published: April 2013

Results are presented of laboratory experiments undertaken to study the dynamics of wave propagation and transformation within the surf zone. The study involved measuring the external flow characteristics of regular plunging waves propagating along a 20 m long flume fitted with a 1:20 plane slope. To achieve this, monochromatic waves of frequency 0.4 Hz and a deep water wave height of 12 cm were generated by a servo-controlled piston-type wave maker. A set of calibrated parallel-wire capacitive wave gauges were employed to measure statistics of the free surface elevation along the slope in order to get an insight into the wave breaking behavior. To characterize the wave field, free surface elevation measurements were made in the vicinity of the break point. The measured time series data were analyzed at each flume position to obtain statistics of the mean water level, wave height, and wave velocity along the flume. Results show that as the wave propagates from deep water towards shallow water, there is an increase in the wave height, reaching a maximum height of about 21.5 cm at the break point, and then decreases sharply thereafter. Wave phase velocity calculations at different flume positions were made from the measured time series. Cross correlation techniques were used to determine the phase difference between the reference wave near the generator and the wave at various points along the flume. The local wave velocity was obtained by taking the phase difference between two points spaced 0.2 m apart. A comparison was made between the measured wave phase velocity, its linear shallow water ((gh)) approximation and the roller model concept wave velocity (1.3(gh)), at various points along the flume. The measured wave velocity c was found to lie in the range (gh)<c<1.3(gh) for most of the positions except near the break point. After the break point, the measured wave velocity is up to 38% higher than the theoretical value predicted using the roller model concept. Also noted is the variability of the phase speed in the breaking region. The present experiments of quantifying the mean macroscopic properties of breaking waves are a necessary prerequisite for more detailed experiments involving internal fluid velocity measurements that will follow.
The Use of Dual-Number-Automatic-Differentiation With Sensitivity Analysis to Investigate Physical Models
Authors: Andrews Malcolm J.
Published: April 2013

Local sensitivities are explored using dual-number-automatic-differentiation (DNAD) across three mathematical models of physical systems that have increasing complexity. The models are: (1) a model for the approach of a sphere to free fall; (2) the Taylor-analogy-breakup (TAB) model for liquid droplet atomization; and, (3) an evaluation of the BHR model of turbulence for the development of one-dimensional Rayleigh–Taylor driven material mixing. Sensitivity and functional shape parameters are developed that permit a relative study to be quickly performed for each model. Furthermore, compensating errors, measurement parameter sensitivity, and feature sensitivities are investigated. The test problems consider transient (initial condition effects), steady state (final functional forms), and measures of functional shape. Reduced model forms are explored and selected according to sensitivity. Aside from the local sensitivity studies of the models and associated results, DNAD is shown to be one of several useful, quickly implemented tools to investigate a variety of sensitivity effects in models and together with the present results may serve as a means to simplify a model or focus future model developments and associated experiments.
Power-Law Fluid Flow Passing Two Square Cylinders in Tandem Arrangement
Authors: Ehsan Izadpanah , Mohammad Sefid , Mohammad Reza Nazari , Ali Jafarizade , Sharifi Tashnizi Ebrahim
Published: April 2013

Two-dimensional laminar flow of a power-law fluid passing two square cylinders in a tandem arrangement is numerically investigated in the ranges of 1< Re< 200 and 1 ≤ G ≤ 9. The fluid viscosity power-law index lies in the range 0.5 ≤ n ≤ 1.8, which covers shear-thinning, Newtonian and shear-thickening fluids. A finite volume code based on the SIMPLEC algorithm with nonstaggered grid is used. In order to discretize the convective and diffusive terms, the third order QUICK and the second-order central difference scheme are used, respectively. The influence of the power-law index, Reynolds number and gap ratio on the drag coefficient, Strouhal number and streamlines are investigated, and the results are compared with other studies in the literature to validate the methodology. The effect of the time integration scheme on accuracy and computational time is also analyzed. In the ranges of Reynolds number and power-law index studied here, vortex shedding is known to occur for square cylinders in tandem. This study represents the first systematic investigation of this phenomenon for non-Newtonian fluids in the open literature. In comparison to Newtonian fluids, it is found that the onset of leading edge separation occurs at lower Reynolds number for shear-thinning fluids and is delayed to larger values for shear-thickening fluids.
An Experimental Study of Continuous and Discrete Visualization Paradigms for Interactive Trade Space Exploration
Authors: German Brian J. , Feigh Karen M. , Daskilewicz Matthew J.
Published: April 2013

Software tools that enable interactive data visualization are now commonly available for engineering design. These tools allow engineers to inspect, filter, and select promising alternatives from large multivariate design spaces based upon an examination of the tradeoffs between multiple objectives. There are two general approaches for visually representing data: (1) discretely, by plotting a sample of designs as distinct points; and (2) continuously, by plotting the functional relationships between design variables and design metrics as curves or surfaces. In this paper, we examine these two approaches through a human subjects experiment. Participants were asked to complete two design tasks with an interactive visualization tool: one by using a sample of discrete designs and one by using a continuous representation of the design space. Metrics describing the optimality of the design outcomes, the usage of different graphics, and the task workload were quantified by mouse tracking, user process descriptions, and analysis of the selected designs. The results indicate that users had more difficultly in selecting multiobjective optimal designs with common continuous graphics than with discrete graphics. The findings suggest that innovative features and additional usability studies are required in order for continuous trade space visualization tools to achieve their full potential.
2012 Freeman Scholar Lecture: Computational Fluid Dynamics on Graphics Processing Units
Authors: Vanka S. P.
Published: April 2013

This paper discusses the various issues of using graphics processing units (GPU) for computing fluid flows. GPUs, used primarily for processing graphics functions in a computer, are massively parallel multicore processors, which can also perform scientific computations in a data parallel mode. In the past ten years, GPUs have become quite powerful and have challenged the central processing units (CPUs) in their price and performance characteristics. However, in order to fully benefit from the GPUs' performance, the numerical algorithms must be made data parallel and converge rapidly. In addition, the hardware features of the GPUs require that the memory access be managed carefully in order to not suffer from the high latency. Fully explicit algorithms for Euler and Navier–Stokes equations and the lattice Boltzmann method for mesoscopic flows have been widely incorporated on the GPUs, with significant speed-up over a scalar algorithm. However, more complex algorithms with implicit formulations and unstructured grids require innovative thinking in data access and management. This article reviews the literature on linear solvers and computational fluid dynamics (CFD) algorithms on GPUs, including the author's own research on simulations of fluid flows using GPUs.
Inverse Simulation Under Uncertainty by Optimization
Authors: Du Xiaoping
Published: April 2013

Inverse simulation is an inverse process of a direct simulation. During the process, unknown simulation input variables are identified for a given set of known simulation output variables. Uncertainties such as random parameters may exist in engineering applications of inverse simulation. An optimization method is developed in this work to estimate the probability distributions of unknown input variables. The first order reliability method is employed and modified so that the inverse simulation is embedded within the reliability analysis. This treatment avoids the separate executions of reliability analysis and inverse simulation and consequently maintains high efficiency. In addition, the means and standard deviations of the unknown input variables can also be obtained. A particle impact problem is presented to demonstrate the proposed method for inverse simulation under uncertainty.
Computationally Efficient Imprecise Uncertainty Propagation
Authors: Ghosh Dipanjan D. , Olewnik Andrew
Published: April 2013

Modeling uncertainty through probabilistic representation in engineering design is common and important to decision making that considers risk. However, representations of uncertainty often ignore elements of “imprecision” that may limit the robustness of decisions. Furthermore, current approaches that incorporate imprecision suffer from computational expense and relatively high solution error. This work presents a method that allows imprecision to be incorporated into design scenarios while providing computational efficiency and low solution error for uncertainty propagation. The work draws on an existing method for representing imprecision and integrates methods for sparse grid numerical integration, resulting in the computationally efficient imprecise uncertainty propagation (CEIUP) method. This paper presents details of the method and demonstrates the effectiveness on both numerical case studies, and a thermocouple performance problem found in the literature. Results for the numerical case studies, in most cases, demonstrate improvements in both computational efficiency and solution accuracy for varying problem dimension and variable interaction when compared to optimized parameter sampling (OPS). For the thermocouple problem, similar behavior is observed when compared to OPS. The paper concludes with an overview of design problem scenarios in which CEIUP is the preferred method and offers opportunities for extending the method.
One Versus Two Implant-Retained Dentures: Comparing Biomechanics Under Oblique Mastication Forces
Authors: Żmudzki Jarosław , Chladek Grzegorz , Kasperski Jacek , Dobrzański Leszek A.
Published: April 2013

The results from clinical tests of single implant-retained dentures (SIDs) are quite promising. However, the biomechanics of SIDs are still insufficiently determined. The aim of the study was to compare the implant loads and pressures beneath one and two implant-retained dentures (TIDs) under oblique mastication forces. The finite element method was used to conduct a model analysis in order to compare loading of the denture attachment onto the implant that accompanies oblique mastication forces in the cases of SIDs and TIDs. The possibility of a denture detaching and sliding on the mucous membrane surface was simulated. The SID solution faced a more remarkable tilt in the direction of the mastication forces, a higher pressures on the mucous membrane surface, and higher implant loadings. The hingelike restraints in the TID favored utilization of the support in the posterior area. The higher pressure values for the SID can be confusing and could lead to inaccurate conclusions about the acceptability of the SID. In the TID, the same areas of the mucous membrane were persistently loaded, independent of the occlusal force direction. In contrast, in the SID the full freedom of rotational movement enhances alternating use of the mucous membrane. This finding explains the more frequent sores in the mucous membrane beneath the TID than beneath the SID.
Nonlinear Analysis of Rayleigh–Taylor Instability of Cylindrical Flow With Heat and Mass Transfer
Authors: Awasthi Mukesh Kumar
Published: April 2013

We study the nonlinear Rayleigh–Taylor instability of the interface between two viscous fluids, when the phases are enclosed between two horizontal cylindrical surfaces coaxial with the interface, and when there is mass and heat transfer across the interface. The fluids are considered to be viscous and incompressible with different kinematic viscosities. The method of multiple expansions has been used for the investigation. In the nonlinear theory, it is shown that the evolution of the amplitude is governed by a Ginzburg–Landau equation. The various stability criteria are discussed both analytically and numerically and stability diagrams are obtained. It has been observed that the heat and mass transfer has stabilizing effect on the stability of the system in the nonlinear analysis.
Thermally Actuated Microswitches: Computation of Power Requirements for Alternate Heating Configurations
Authors: Maghsoudi Elham , Martin Michael James
Published: April 2013

Steady state behavior of a thermally actuated RF MEMS switch in the open and closed positions is simulated using the governing thermal and structural equations. The switch is a bridge with a length of 250 microns, a width of 50 microns, and a thickness of 1 micron, in air with a pressure of 5 kPa. Simulations are performed for two different materials: silicon and silicon nitride. Three heating configurations are used: uniformly distributed heat, concentrated heat at the center of the top surface, and concentrated heat at the sides of the top surface. The steady state results show that the displacement at the center of the bridge is a linear function of the heat addition. This can be used to define a switch efficiency coefficient η*. In the uniformly distributed heat configuration, for a specific center displacement, a closed switch needs less heat at the top than an open switch. Adding concentrated heat at the center of the top surface yields a larger center displacement per unit heat addition than adding heat to the sides. When the heating is changed to a concentrated heat load at the center, the required heat is an order of magnitude less than heat added to the sides. Changing the contact length shows that variation in the length of the contact results in negligible changes in required heat to achieve a given displacement.
Fluorine-Doped Iron Oxide Nanomaterials by Plasma Enhanced-CVD: An XPS Study
Authors: Carraro Giorgio , Gasparotto Alberto , Maccato Chiara , Barreca Davide
Published: April 2013

In this work, we report on a single-step Plasma Enhanced-Chemical Vapor Deposition (PE-CVD) process for the synthesis of iron(III) oxide based nanomaterials. A key feature of the adopted fabrication strategy is the use of a fluorinated Fe(II) β-diketonate diamine precursor, enabling a homogeneous Fe2O3 in-situ doping and resulting in a tunable fluorine content as a function of deposition temperature. To this regard, a detailed study of the nature and amount of fluorine-containing moieties is strongly required in view of the process optimization. Specifically, X-ray Photoelectron Spectroscopy (XPS) analysis represents a strategic tool to evaluate the system chemical composition, and also to evidence the presence of fluorine in different chemical states, such as lattice fluorine (F-Fe) and traces of precursor residuals (CFx) at the system surface. In the present study, spectroscopic data are presented and discussed in detail for a representative Fe2O3 specimen.