bluuebunny/crossref_metadata_2025 huggingface dataset:
Heat Transfer Between Liquid Film Formed on the Inclined Dimpled Surface and Ambient Air
Authors: Dubrovskii Vitalii , Podvysotskii Aleksei , Shraiber Aleksandr , Chudnovsky Yaroslav , Kozlov Aleksandr
Published: August 2012

Heat transfer enhancement area attracts the close attention of the researchers and engineers worldwide for the last decades. The most popular techniques nowadays to enhance heat transfer from the surface is to extend it with the fins, studs, etc. or to profile it with the elements of artificial roughness, winglets, dimples, etc. Those types of surface enhancement allow improving the thermal efficiency of the heat transfer equipment with minimal design modification and without significant capital expenses. One of the interesting and promising techniques of the surface profiling is the formation on the surface the arrangement of spherical dimples, which generate intensive vortex structure near the surface, increase flow turbulence and, as a result, enhance heat and mass transfer between a profiled surface and a liquid (or gas) flowing over it [1–3]. In this connection, it is interesting to establish whether surface profiling will also enhance the heat transfer intensity between a liquid film on such a surface and ambient air. Unfortunately, authors were not able to find any publications on this subject in the open domain. At the same time, the investigation of this process could be of great interest for the engineering practice, in particular, for the cooling towers advancement. In the present work, the authors discuss some experimental results obtained for the different profile parameters and flow regimes.
Computer Modeling of Time History of Velocity Field and Net Momentum Output of a Synthetic Jet Actuator
Authors: Ahmadi G. , Shahrabi A. F.
Published: August 2012

Synthetic jet actuators have been used for control of flow separation in high performance airfoils for increasing lift and low drag. The synthetic jets have zero net mass flux but impart net momentum to the flow. In this study, LES simulations was used to study the time history of outlet velocity profile and net momentum imparted to the flow by a synthetic jet actuator (SJA). The SJA studied is not symmetric and operates with the aid of a piezoelectric (PZT) ceramic circular plate actuator. A three-dimensional mesh for the computational domain of the SJA and surrounding volume was developed and was used to evaluate the details of the airflow conditions inside the SJA as well as at the outlet. The vibration of the PZT ceramic actuator was used as a boundary condition in the computational model to drive the SJA. Particular attention was given to the time evolution of the SJA outlet velocity profile. The time history of the outlet velocity profile of the synthetic jet was curve-fitted to an empirical equation. The resulting outlet velocity could be used as an inlet velocity for active close loop control of airflow separation around an airfoil at high angle of attack.
Illustrating Principles of Precision Engineering Through Design and Development of a Displacement Gauge for Measuring Machines
Authors: Bosetti Paolo , Beach David W. , DeBra Daniel B. , Albonico M. , Cooper E. , Denby J. , Loh S. , Pen˜a Doll A. , Roberts M. , Ting K. , Vance W.
Published: August 2012

The paper presents a project-based course on Precision Engineering. During the course, the students have lectures and five labs in the beginning five weeks of the course, during which time they also choose a project from a set of proposals to illustrate the principles of precision engineering they are learning. Teams of 3–4 students are formed and preliminary design is carried out during this first half of the course. During the second half, they carry out the design to provide a working prototype and finally they give a final presentation. The collection of the proposals is performed with the support of internal (i.e. researchers) and external customers. The supporters are asked to suggest a high-compliance, high-sensitivity displacement gauge for measuring for example the deviation from straightness of a straight edge or deviations from roundness of a sphere or cylinder. The probe must have low force, sensitivity much smaller than typical 5 μm of a Coordinate Measuring Machine, it must be compatible with commercial A/D converters and standard electronics, and it has to be realized by a combination of mechanical amplification and using technology that lends itself to trouble-shooting by technical assistants of a variety of backgrounds. The paper illustrates the design and the development of one of the proposed projects, by discussing the design issues, the prototype manufacturing, and the testing phase. The paper then discusses how the project-based approach can strengthen and make more effective the description of physical principles behind precision engineering (flexure design, tolerance design, thermal stability, accuracy of transducers and measurement devices, etc.) and their relationship with mechanical design, part manufacturing, and assembly. It is also a very effective way of illustrating how many engineering design problems are tightly related with mechanical stiffness, how stiffness is rooted in the design engineering specifications, and how design principles like kinematic constraint impact the product conformance with requirements and specifications.
Effects of Number of Stator Blades on the Performance of a Torque Converter
Authors: Talukder Shoab Ahmed , Huynh B. Phuoc
Published: August 2012

Torque converter (TC) is a totally enclosed hydrodynamic turbomachine, used most often in automobiles for the smooth transfer of power and speed change from the engine to the transmission, and torque magnification. A typical TC has 3 major components: a pump that is attached directly to the TC cover and connected to the engine shaft, a turbine connected to the transmission shaft, and a stator connected to the transmission housing via a one-way clutch and providing guidance for the fluid flow. In this work, effects of the number of stator blades on the performance of a TC are investigated numerically, using a commercial Computational Fluid Dynamics (CFD) software package. The standard k-epsilon turbulence model was used. A Newtonian fluid whose properties correspond to industrial oil was used for the working fluid. The range of speed ratio (between turbine’s speed and pump’s) of 0.2–0.8 was considered. It was found that as the stator blades’ number increases (here from 13 to 19), the TC’s efficiency and torque ratio vary significantly, passing through minimum and generally also reaching a maximum.
Conception and Fabrication of Silicon Ring Resonator With Piezo-Resistive Detection for Force Sensing Applications
Authors: Xiong Zhuang , Walter Benjamin , Mairiaux Estelle , Faucher Marc , Buchaillot Lionel , Legrand Bernard
Published: August 2012

A new concept of Atomic Force Microscope (AFM) oscillating probes using electrostatic excitation and piezo-resistive detection is presented. The probe is characterized by electrical methods in vacuum chamber and by mechanical methods in air. The mixer measurement technique is developed to reduce the parasitic signal level. These probes resonance frequencies are in the 1MHz range and the quality factor is measured about 53,000 in vacuum and 3,000 in air. The force resolution deduced from the measurements is about 8 pN/Hz0.5.
Effect of Tip Clearance on the Performance of Forward Swept Subsonic Axial Compressor Rotors at High Stagger Angles
Authors: Ramakrishna P. V. , Govardhan M.
Published: August 2012

Tip leakage phenomenon in axial compressors is sensitive to the flow incidence, flow coefficient, tip gap height and the pressure gradients. All these geometric/flow features are considerably altered by blade stagger angle. Literature on the stagger angle effects in compressors is scarce; and indeed, such studies for various tip gap heights have not been reported yet. The present paper reports the effect of rotor stagger angle on the performance of subsonic axial compressor rotor with different forward sweep configurations and for various rotor tip clearances. The computational model for the study utilizes finest hexahedral grids. A commercial CFD package ANSYS® CFX 11.0 was used with standard k-ω turbulence model for the simulations. CFD results were well validated with experiments. The following observations were made: At higher stagger angles, flow separates from upstream suction surface locations. Little tip clearance had a positive effect for certain stagger angle increments owing to beneficial interaction of leakage flows with the local flow field. However, severe performance loss was observed at higher stagger settings with large clearances. As the stagger angle was increased, vena contracta effect was highly reduced. At high stagger angles, the flow was observed to leak in a more “axially-reversed” fashion through the tip gap. The deep lowest pressure zones near the pressure surface of the tip are due to the effect of ‘vena contracta.’ Such zones near the suction surface edge of the tip are due to flow acceleration. This particular feature is directly correlated with the tip aerofoil loading and thickness-to-tip gap ratio.
The Morphologies and Adhesion of Ceramic Films on CLAM Steel Substrates for Nuclear Fusion Applications
Authors: Song Binbin , Wu Ping , Chen Sen , Zhang Shiping
Published: August 2012

In the dual-function lithium-lead test blanket module (DFLL-TBM) thin and durable coatings with a large tritium permeation reduction factor (PRF) and high resistivity are usually used to segregate the structural wall from the liquid Li-Pb. Al2O3, Cr2O3, SiC, Er2O3, et al. are considered as the promising functional coating materials for DFLL-TBM. Due to the thermal expansion coefficients and lattice constants of ceramic and metal materials are quite different, the mechanical properties of ceramic coatings on metal substrates can be reduced by poor adhesion. In this study, Al2O3, Cr2O3, SiC, Er2O3 films were fabricated on China low activation martensitic (CLAM) steel substrates by magnetron sputtering. Atomic force microscope (AFM) was used to study the surface morphologies of ceramic films. The adhesion strength of the films, deposited on CLAM steel, was also studied by scratch test. Results indicate that the surface of SiC films is smoother than the others. While the surface morphologies of Al2O3, Cr2O3, Er2O3 films are similar. The critical load of SiC film, with a minimum value, is about 12.0 mN, while the critical load of Al2O3 reaches about 16.4 mN.
Evaluation of Human Femur Bone Radiographic Images Using AdaBoost and Support Vector Machines
Authors: Bobby Thomas Christy , Ramakrishnan Swaminathan
Published: August 2012

In this work, classification of normal and abnormal human femur bone images are carried out using Support Vector Machines (SVM) and AdaBoost classifiers. The trabecular (soft bone) regions of human femur bone images (N = 44) recorded under standard conditions are used for the study. The acquired images are subjected to auto threshold binarization algorithm to recognize the presence of mineralization and trabecular structures in the digitized images. The mechanical strength regions such as primary compressive and tensile are delineated by semi-automated image processing methods from the digitized femur bone images. The first and higher order statistical parameters are calculated from the intensity values of the delineated regions of interest and their gray level co-occurrence matrices respectively. The significant parameters are found using principal component analysis. The first two most significant parameters are used as input to the classifiers. Statistical classification tools such as SVM and AdaBoost are employed for the classification. Results show that the AdaBoost classifier performs better in terms of sensitivity and specificity for the chosen parameters for primary compressive and tensile regions compared to SVM.
Sliding Joint Constraints for the Analysis of Flexible Multibody Systems Using Intermediate Coordinates
Authors: Honda Ryo , Yamashita Hiroki , Sugiyama Hiroyuki
Published: August 2012

In this investigation, formulations of sliding joint constraints for flexible bodies modeled using the absolute nodal coordinate formulation are developed using intermediate coordinates. Since modeling of prismatic and cylindrical joints for flexible bodies requires solutions to moving boundary problems in which joint definition points are moving on flexible bodies, arc-length coordinates are introduced for defining time-variant constraint definition points on flexible bodies. While this leads to a systematic modeling procedure for sliding joints, specialized formulations and implementations are required in general multibody dynamics computer algorithms. For this reason, intermediate coordinates are introduced to derive a mapping between the generalized gradient coordinates used in the absolute nodal coordinate formulation and the intermediate rotational coordinates used for defining the orientation constraints with rigid bodies. With this mapping, existing joint constraint libraries formulated for rigid bodies can be employed for the absolute nodal coordinate formulation without significant modifications. It is also demonstrated that the intermediate coordinates and arc-length coordinates introduced for modeling sliding joint constraints can be systematically eliminated from the equations of motion and standard differential algebraic equations used in general multibody dynamics computer algorithms can be obtained. Several numerical examples are presented in order to demonstrate the use of the formulation developed in this investigation.
Vibration-Based Damage Detection in Plates Using Damage Location Vectors
Authors: Kayed Mohammed O. , Arafa Mustafa H. , Megahed Said M.
Published: August 2012

Vibration-based techniques are increasingly being recognized as effective non-destructive structural damage identification tools. One promising technique relies on combining a finite element model (FEM) of the structure under investigation with a set of experimental frequency response functions (FRFs) to construct a so-called Damage Location Vector (DLV). This paper aims to assess damage detection using DLVs both theoretically and experimentally. To this end, the method is first studied theoretically on a thin plate using simulated damage. The method is then tested experimentally on a free-free plate provided with several damage cases using impact hammer testing. The main contribution of the present work lies in attempting to improve the DLV techniques through the use of the experimental FRF data of the intact structure in addition to the theoretical FRF from a finite element. The results obtained indicate that the improved algorithm can be used to successfully detect structural damage.
Coupling Effects Between Torsion and Bending in Torsional Micromirrors Under Capillary Forces
Authors: Darvishian Ali , Moeenfard Hamid , Ahmadian Mohammad Taghi
Published: August 2012

In the current paper, a general theoretical model for the problem of micromirrors under the effect of capillary forces is presented. The presented model considers the coupling effect between torsion and bending of the torsion beams supporting the micromirror. First, the energy method, the principal of minimum potential energy is utilized for finding the equations governing the micromirror rotation and its deflection. Then using the implicit functions theorem, the equations governing the pull-in angle and pull-in displacement of the micromirror is derived. The results, shows that ignoring the bending effect in micromirrors under the effect of capillary forces, can cause a significant (up to several hundred percents) underestimation of the pull-in angle. It is observed that with increasing the ratio of the bending stiffness to the torsion stiffness, the dominant instability mode changes from bending mode to the torsion mode. It is shown that when the bending stiffness of the system is relatively low, the equilibrium point of a one degree of freedom torsion model considerably deviates from that of coupled model. The presented model in this paper can be used for safe and stable design of micromirrors under capillary force.
Fabrication of Conductive Porous Structure Loaded With Carbon Black and/or Carbon Nanotube
Authors: Li Min , Zhang Wei , Wang Chaosheng , Wang Huaping
Published: August 2012

Carbon black (CB) and/or carbon nanotube (CNT) loaded porous PP frame with enhanced conductivity was facilely fabricated via immiscible co-continuous polymer blend and subsequent dissolution process. The SEM result indicated that the agglomerated carbon additives formed continuous phase on the inner wall of the interconnected micro channel. Nitrogen gas adsorption test was carried out to characterize the nano pores resulted from these nano particles. In addition, the electrochemical performance of the material was evaluated by cyclic voltammetry and galvanostatic charge-discharge cycling. Experimental results demonstrate the effectiveness of this novel method to construct conductive material with hierarchical porous structure which integrates co-continuous porous structure with nano pores derived from deposited carbon additives.
Non-Destructive Detection of Defects in Composite Boat Hulls
Authors: Suratkar A. S. , Sajjadi A. Y. , Mitra K.
Published: August 2012

This paper demonstrates use of thermal imaging for nondestructive defect detection in a composite boat hull which covers a large area. There is a strong demand in the boat industry for a non-destructive method that can detect defects such as delamination, voids of air or fluid, cracks, acid, dry mat, and carbon fiber. These defects are always difficult to detect as they occur inside the walls of the boat. Currently, ultrasound and manual inspection methods are used to identify these defects. The manual checking technique is unscientific; furthermore the ultrasound method is not acceptable due to unsatisfactory results. Thermal imaging involves detecting infra-red radiation from a hot body; this is captured by a thermal imaging camera. A thermal heat gun is used to heat the walls of the boat hull. After heating for a specific time period, the walls of the boat start emitting radiation. Dry void attains the highest peak intensity value for short time heating followed by Acid. Other defects like carbon fiber, delamination, and dry mat took longer time to attain higher intensity value. The decay of radiations is also different for various types of defects. The maximum intensity decay occurs for dry void as compared to other defects. From the results obtained so far, it can be inferred that thermal imaging can distinctly differentiate the different kinds of defects, as well as the unaffected areas of the boat wall.
Fabrication and Characterization of a Microscale Cellular Loading Device for Cellular Biomechanical Study
Authors: Wang Qian , Kim Bongsu , Zhang Xu , Zhao Yi
Published: August 2012

Mechanical stimuli interfere with cellular behaviors under many physiological conditions. To understand the role of mechanical stimuli, engineered devices are developed to apply mechanical loads to cells in vitro. Despite of their usefulness, these devices are limited since they often lack the capacity of spatial load control, which is essential for intercellular study. Moreover, application of both compressive and tensile loads using a single loading device is challenging. Here, we fabricate and characterize a microdevice for applying programmable compressive/tensile loads to live cells. The device consists of two PDMS substrates. The top substrate consists of nine circular membranes with patterned microdots array on the top surfaces. Each membrane is connected with a microfluidic channel built in the bottom substrate. Upon actuation, the fluid in the channels deforms the membranes and applies controllable strain to cells cultured on the membranes. In this design, each membrane can be individually controlled to apply desired strain levels. The surface strain of the PDMS membranes is characterized by mapping the displacement of the dot array. The result of strain analysis shows that, the radial strain at the center of a circular membrane upon deformation ranges from about 5% compressive strain to about 20% tensile strain, validating the capacity of the device in applying both tensile and compressive stresses. Cell testing is performed using trabecular meshwork endothelial cells. Cells on different membranes are subjected to 0.5Hz of compressive or tensile stresses. The result shows that compressive and tensile stresses have different effects on the cells, indicating the device a promising solution for cellular biomechanical study.
Modelling and Simulation of a Flexible Endoscopic Surgical Instrument in a Tube
Authors: Khatait J. P. , Krijnen M. , Meijaard J. P. , Aarts R. G. K. M. , Brouwer D. M. , Herder J. L.
Published: August 2012

Flexible instruments are increasingly used to carry out complex procedures in many surgical interventions. The instrument tip is remotely controlled by the surgeon. The inherent flexibility of the instrument, coupled with the friction inside the endoscope access channel and the convoluted shape of the endoscope inside the body, makes the control of the instrument tip difficult and complicated. The objective of this paper is to model and to simulate a flexible endoscopic surgical instrument inside a tube and characterize its behaviour. The surgical instrument is modelled as a series of interconnected beam elements. The endoscope channel is modelled as a rigid tube of uniform circular cross-section. A planar model of the flexible instrument with friction is considered in this paper. Normal reaction and friction forces are calculated at the nodes. A Stribeck based continuous friction model with increased friction at low velocity is implemented in the model. Simulations are carried out both for the insertion of the flexible instrument and for fine manipulation. SPACAR, an analysis tool for flexible multibody dynamic systems, has been used for the modelling and simulation. The nodal displacement and force acting at the various nodes have been obtained depending on position and time. The simulation for the fine tip manipulation shows the stick-slip behaviour and hysteresis. The simulation results show the effect of bending rigidity and friction on motion hysteresis.
Influence of Strain Rate and Stress State on the Mechanical Behavior of Die-Casting AM60 Magnesium Alloy
Authors: Gu Gongyao , Lin Shaoting , Meng Yan , Xia Yong , Zhou Qing
Published: August 2012

This paper presents experimental study, including the test method and the test data analysis, on the die-casting AM60 magnesium alloy material. Uniaxial tension tests were carried out at various strain rates roughly from 5 × 10−4 to 1 × 102 s−1, which are of interest in vehicle crash CAE. Uniaxial compression and shear tests at strain rates from 5 × 10−4 to 5 × 10−2 s−1 were also carried out. All the specimens were cut off from die-casting plates of AM60 with thickness of 2.6 mm. The test results show that the yield stress of die-casting AM60 increases slightly with the strain rate at uniaxial tension. However, this tendency is not very significant due to the relatively large variation among the tests. There is no obvious relationship between the fracture strain and the strain rate at uniaxial tension and compression. For shear, the fracture strain decreases with higher strain rate. It is verified that this material follows the von-Mises yield criterion, with nearly symmetrical yielding behavior between uniaxial tension and compression at the same level of strain rates. And it is shown that the equivalent fracture strain or effective ultimate strength at uniaxial tension and shear states is relatively close to each other, which is significantly smaller than those at compression. According to these results, it is necessary to perform further study with additional tests at other stress states for accurately characterizing the fracture behavior of the die-casting AM60 magnesium alloy.
Analysis and Minimization Design of Force Ripples Cased by Higher Harmonics in Ironless Permanent Magnet Planar Motors
Authors: Min Wei , Zhang Ming , Zhu Yu , Liu Feng , Duan Guanghong , Hu Jinchun , Yin Wensheng
Published: August 2012

Ironless permanent magnet planar motors have significant potential for accurate positioning systems. The higher harmonics of the magnetic flux density distribution, which is ignored in the analytical model for real-time control, is usually one of the main reasons for the force ripples of the ironless permanent magnet planar motors. The force ripples cased by the higher harmonics is analyzed and minimized in this paper. An analytical model of the force ripples cased by the higher harmonics is developed first. Then it can be derived from the analytical model that the force ripples cased by some higher harmonics can cancel each other when the length of the coil is an even multiple of the pole pitch of the magnet array. Furthermore, the winding factors of the ironless permanent magnet planar motors are also derived and can be used to eliminate dominating components of the force ripples cased by the left higher harmonics. As a result, the force ripples cased by the higher harmonics can be basically eliminated with a selected coil length and winding factors. Finally, it is validated by comparison of the planar motors with finite element (FE) analysis that most of force ripples cased by higher harmonics can cancel each other when the length of the coil is an even multiple of the pole pitch of the magnet array.
The Effect of Cryogenic Cooling on White Layer Formation in Hard Machining
Authors: Umbrello D. , Caruso S. , Yang S. , Crea F. , Dillon O. W. , Jawahir I. S.
Published: August 2012

Microstructural phase transformations, commonly named as the white layer on hard turned components, have in recent times become an interesting research topic in machining. Three main theories have been proposed to justify the mechanisms of white layer formation: (i) rapid heating and quenching; (ii) severe plastic deformation; (iii) surface reaction with the environment. Furthermore, coolant application also affects the surface microstructural alterations resulting from machining operations, which have a significant influence on product performance and life. The present work aims at understanding the effects of cryogenic coolant application on machined surface alterations during orthogonal machining of hardened AISI 52100 bearing steel. Experiments were performed under dry and cryogenic cooling conditions using cubic boron nitride (CBN) tool inserts with varying initial hardness and tool shape. Several experimental techniques were used in order to analyze the machined surface. In particular, optical and scanning electron microscopes (SEM) were used for characterizing the surface topography, whereas the microstructural phase composition analysis and chemical characterization have been performed using X-ray diffraction (XRD) and energy-dispersive spectroscopy (EDS) techniques. The experimental results prove that the microstructural phase changes are partially reduced or can be totally avoided under certain cryogenic cooling conditions. Therefore, cryogenic cooling has the potential to be used for achieving enhanced surface integrity, thus contributing to improved product life and functional performance.
Influence of Pipe Roughness on the Performance of Ultrasonic Meters for Flow Rate Measurement
Authors: Orlando Alcir de Faro , Ferreira Ana Luisa , Pinheiro Jose´ Alberto
Published: August 2012

Ultrasonic flow meters have been recently used for flow rate measurement because they are a non-intrusive device and have the capability of making diagnostics of their performance and flow field distortion between two consecutive calibrations. The available completely developed flow velocity profiles in the literature is discussed in this paper and integrated along the meter ultrasonic path to simulate its performance. It was shown that for Reynolds number up to 1,000,000 and relatively roughness values smaller than ε = 0.00012 the flow is in the hydraulically smooth regime. Also, it was shown that the ratio between the area velocity and the average path velocity (kh) decreases close to centerline and increases close to the wall, when roughness increases.
Orientation Dependent Binding Energy of Graphene on Pd(111)
Authors: Kappes Branden B. , Ebnonnasir Abbas , Kodambaka Suneel , Ciobanu Cristian V.
Published: August 2012

Graphene, a two-dimensional crystalline sheet of carbon, has generated considerable attention owing to its ultra-thin geometry, high carrier mobility and tunable band gap, with potential applications in high-performance, low-power electronics and as transparent electrodes. Since graphene–based devices require metal (or metallic) contacts, knowledge of the structural and electronic properties of the metal-graphene interfaces is essential. Previous theoretical studies of graphene-metal contacts indicate that their electronic properties depend on the metal-graphene binding energies. For example, strongly interacting metals can induce a charge transfer from or to graphene, resulting in p- or n-type doping. Here, using Pd(111) as a example substrate, we focus on understanding the influence of the orientation of graphene on its binding to the substrate.
Compact Modeling of Fractal Tree-Shaped Microchannel Liquid Cooling Systems
Authors: Chen Cheng , Samadiani Emad , Sammakia Bahgat
Published: August 2012

Demands for higher computational speed and miniaturization have already resulted in extremely high heat fluxes in microprocessors. Fractal tree-shaped microchannel liquid cooling systems are novel heat transfer enhancement systems to keep the temperature of the microprocessors in a safe range. Due to the complexity of these systems, their full field numerical modeling for simulation of the flow and temperature fields is too time consuming and costly, particularly to be used within iterative optimization algorithms. In this paper, a quick but still accurate compact modeling approach based on Flow Network Modeling (FNM) is introduced for analysis of the flow filed in fractal microchannel liquid cooling systems. The compact method is applied to a representative fractal microchannel cooling system and the obtained velocity and flow rate distribution are validated against a full Computational Fluid Dynamics (CFD)-based model for three different designs. The compact model shows good agreement with the CFD results and robustness on different designs, while requiring much less computational capability and time. Afterwards, the compact model is used for optimization of the geometry of the fractal cooling system to achieve maximum flow rate and uniform flow distribution among the channels for a fixed pressure drop.
A Web Based “Virtual Racing Car Championship” to Teach Vehicle Dynamics and Multidisciplinary Design
Authors: Biral Francesco , Zendri Fabrizio , Bertolazzi Enrico , Bosetti Paolo , Galvani Marco , Trivellato Filippo , Da Lio Mauro
Published: August 2012

A web based VRCC (Virtual Racing Car Championship) application is here presented. The application is intended for educational purposes to teach students a variety of topics of the teaching course “Vehicle Dynamics and Control” in Mechatronics Master Degree Course; the present application forces students to understand the relevant parameters that govern the dynamic performance of racing cars. The application relies on an optimal control library, which is capable of calculating minimum lap times of a racing car on the basis of a comprehensive symbolic description of an open-wheel racing car dynamic model. Students are enrolled in a number of teams competing in a Championship to attain the minimum lap time (i.e., the pole position) on three circuits by choosing the appropriate setup of the racing car. The ranking is based on the best lap time obtained in the qualification session. The application stimulates students to adopt a multidisciplinary approach in a challenging and instructive environment, where they are in a position to apply a broad range of knowledges and abilities they have acquired during the Mechanotronics engineering course.
A Numerical Study to Predict the Effects of Structured Roughness Elements on Pressure Drop and Heat Transfer Enhancement in Minichannels and Microchannels
Authors: Dharaiya V. V. , Kandlikar S. G.
Published: August 2012

Better understanding of laminar flow at microscale level is gaining importance with recent interest in microfluidics devices. The surface roughness has been acknowledged to affect the laminar flow, and this feature is the focus of the current work to evaluate its potential in heat transfer enhancement. A numerical model is developed to analyze the thermal and hydrodynamic characteristics of minichannels and microchannels in presence of roughness elements. Structured roughness elements following a sinusoidal pattern are generated on two opposed rectangular channel walls with a variable gap. A detailed study is performed to check the effects of roughness height, roughness pitch, and channel separation on pressure drop and heat transfer coefficient in the presence of structured roughness elements. As expected, the structured roughness elements on channel walls result in an increase in pressure drop and heat transfer enhancement as compared to smooth channels due to the combined effects of area enhancement and flow modification. This is due to the fact that the roughness element as a small obstruction in the flow passage of narrow channels which introduces flow modifications in the flow and increases the energy transport. The improvement in global heat transfer enhancement is observed in rough channels due to velocity fluctuations. At the same time, it also causes pressure drop to increase as compared to smooth channels. The fully developed friction factor and Nusselt number results obtained from CFD simulations for smooth and rough channels are compared with the experimental data carried out in the same laboratory. The current numerical scheme is validated with the experimental data and can be used for design and estimation of transport processes in the presence of different roughness features.
Properties of Composite Cylinders Fabricated by Bladder Assisted Composite Manufacturing (BACM)
Authors: Anderson Jacob P. , Altan M. Cengiz
Published: August 2012

An innovative manufacturing method, BACM (Bladder Assisted Composite Manufacturing), to fabricate geometrically complex, hollow parts made of polymeric composite materials is presented. BACM uses an internally heated bladder to provide the consolidation pressure at the required cure temperature, and thus produces high quality components. The feasibility of this manufacturing method is demonstrated by fabricating laminated composite cylinders using multiple cure pressures and wall thicknesses. The mechanical properties, energy consumed during the curing, and void content of the composite cylinders, are investigated in detail. The curing of composite cylinders was carried out by circulating heated air inside the bladder. Using the described heating method a number of 2-, 4-, and 6-ply composite cylinders made of E-glass/epoxy prepreg (Newport 321/7781) were prepared as test samples. Cylinders were cured at 121°C (250°F) for 2 hours using bladder pressures of 207 kPa (30 psi), 345 kPa (50 psi), 483 kPa (70 psi), and 621 kPa (90 psi). The mechanical behavior of the cylinders were characterized by compressing sample rings and loading ring segments in three-point bending. The fiber volume fraction and the void content of the cylinders were determined from resin burn-off experiments and density measurements. The cylinders produced using the BACM process were found to exhibit excellent surface quality. The elastic moduli, failure strength, and void contents of the cylinders were comparable to the values obtained from flat laminates produced by hot plate molding. Compared to conventional bladder manufacturing methods, the BACM process reduced the energy required to cure the cylinder by more than 50%.
Optimized Design of Composite Materials for Heat Transport Applications
Authors: Kouchmeshky Babak , Kroll Peter , Olubanjo Ibukun
Published: August 2012

Careful design of composite materials offers a chance for engineering phonon band gaps and controlling phonon scattering. Taking advantage of this strategy, we study properties of SiC composite materials for engineering applications in which the control of thermal transport is important. In particular, knowledge of the individual contributions of phonons on thermal transport provides us the necessary information to focus on most significant phonon frequencies. In our study, we select a series of candidate model geometries and use a virtual testing method for elevated temperatures to support the design process. Integrating atomistic non-equilibrium molecular dynamics simulations to determine thermal conductivity we provide a proof-of-concept study and deliver best design scenarios of SiC composite materials with very low-thermal conductivity.
CFD Assisted Design Optimization of a Flow Distributor for Uniform Fluid Distribution
Authors: Liu Hong , Li Peiwen
Published: August 2012

This study addresses a fundamental issue of distributing a fluid flow into a number of flow channels uniformly. A basic mechanism of flow distribution is accomplished through a channel bifurcation that symmetrically split one flow channel into two downstream channels. Applying the basic mechanism, cascades flow distributions are designed to split one flow into a large number of downstream flows uniformly. Some key parameters decisive to the flow distribution uniformity in such a system have been recognized, and the flow distribution uniformity was studied for several versions of flow distributor designs using CFD analysis. The effect of the key parameters of the flow channel designs to the flow distribution uniformity was investigated. As an example of industrial application, a novel fluid packaging device was proposed and some CFD analysis results for the device were provided. The optimized flow distributor makes a very good uniform flow distribution which will significantly improve the efficiency of fluid packaging. The technology is expected to be of great significance to many industrial devices that require high uniformity of flow distribution.
Design Considerations, Performance Enhancing Techniques, and Wind Tunnel Testing for Small-Scale, Low Reynolds Number Wind Turbines
Authors: Gregg Jason R. , Burdett Timothy A. , Van Treuren Kenneth W. , McClain Stephen T.
Published: August 2012

Wind turbines have become a significant part of the world’s energy equation and are expected to become even more important in the years to come. A much-neglected area within wind turbine research is small-scale, fixed-pitch wind turbines with typical power outputs in the 1–10 kW range. This size wind system would be ideal for residential and small commercial applications. The adoption of these systems could reduce dependence on the aging U.S. power grid. It is possible to optimize a small-scale system to operate more efficiently at lower wind speeds, which will make wind generation possible in areas where current wind technology is not feasible. This investigation examines the use of the S818 airfoil, a typical blade root airfoil designed by the National Renewable Energy Laboratory (NREL), as a basis for the design of low Reynolds number (less than 200,000) systems. The literature shows that many of the airfoils proposed for wind turbine applications, including the S818, only have lift and drag data generated by numerical simulations. In previous research at Baylor, 2-D simulations published by NREL have been shown to predict an optimal design angle of attack (which is the angle at which L/D is maximized) up to 2.25° different from actual wind tunnel data. In this study, the lift and drag generated by the S818 airfoil has been measured experimentally at a Reynolds number of approximately 150,000 and compared with NREL simulation data, showing a discrepancy of 1.0°. Using the S818 airfoil, a set of wind turbine blades has been designed to collect wind turbine power data in wind tunnel testing. Design parameters investigated include the effect of design tip speed ratios (TSR) (1, 3, and 7) and the influence of the number of blades (2, 3 and 4) on power generated. At the low Reynolds numbers tested (ranging from 14,000–43,200 along the blade for a design TSR of 3 and a wind speed of 10 mph), the effect of roughness was explored as a performance enhancing technique and was seen to increase power output by delaying separation. Under these low Reynolds number conditions, separation typically occurs on smooth blades. However, the roughness acted as a passive flow control, keeping the flow attached and increasing power output. Preliminary data suggest that as much as a 50% improvement can be realized with the addition of roughness elements for a TSR of 3. Additionally, the increase in power output due to roughness is comparable with the increase in power due to adding another smooth blade.
Model Fidelity Refinement for System-Level Design of a Reusable Launch Vehicle
Authors: Smith Natasha
Published: August 2012

This paper extends research in multidisciplinary reliability-based design optimization by using model uncertainty quantification to integrate multiple levels of design. The bi-level design of a reusable launch vehicle with a component fuel tank is studied from this perspective. The system design includes a conceptual, low-fidelity weights analysis with significant model uncertainty, while the tank design provides a more rigorous analysis for the weight of one component with significantly less uncertainty. Evaluating the uncertainties of the disciplinary analysis provides two important benefits. The first is as a metric for selecting appropriate disciplinary model(s) to integrate into the system-level analysis for a desired level of reliability. The second benefit is as the basis for iterating between design levels. Rather than fully integrating the system and component analyses, this method uses model uncertainty to leverage the component design to refine the system analysis. Thus the communication between design levels is less stringent than for fully-integrated reliability based optimization.
On Nonlinear Dynamics in a Free Fluid Surface of a Tank Excited by a Non-Ideal Power Source
Authors: Navarro H. A. , Balthazar J. M. , Chavarette F. R. , Krasnopolskaya T. S. , Shvets A. Yu.
Published: August 2012

We investigate the nonlinear oscillations in a free surface of a fluid in a cylinder tank excited by non-ideal power source, an electric motor with limited power supply. We study the possibility of parametric resonance in this system, showing that the excitation mechanism can generate chaotic response. Additionally, the dynamics of parametrically excited surface waves in the tank can reveal new characteristics of the system. The fluid-dynamic system is modeled in such way as to obtain a nonlinear differential equation system. Numerical experiments are carried out to find the regions of chaotic solutions. Simulation results are presented as phase-portrait diagrams characterizing the resonant vibrations of free fluid surface and the existence of several types of regular and chaotic attractors. We also describe the energy transfer in the interaction process between the hydrodynamic system and the electric motor.
Step Ladder Failure Analysis: A Comparison of Analytical Methods
Authors: Kenner Matthew T. , Stevenson Michael E. , Knox Erick H. , Van Bree Michael P. , Wilkinson John A.
Published: August 2012

When a user falls from a step ladder, the accident can be accompanied by damage to the ladder. A common area of damage is in the vicinity of the connections between the front side rails and the lowermost step. When determining the cause of a fall, it is important to understand how this damage occurs and whether it may be causal to the accident or a result of the accident. Commonly, engineers investigating such accidents have relied on three methods of structural analysis: classic analytical methods (so-called “hand calculations”), computational methods (finite element analysis) and laboratory testing. These three methods each have strengths and weaknesses that affect how the results should be used and interpreted by the investigating engineer. Factors such as the assumptions and simplifications used as input to an analysis, the type and amount of results available as output and cost are examined. These issues are discussed in the frame work of a case study wherein all three methods are applied to the analysis of a step ladder damaged in the field. The results show that, while step ladders may, at first, appear to be relatively simple structures they are, in fact, quite complex. As a consequence, it becomes very important to understand the analysis technique being used and its inherent limitations. Without consideration of these factors, the investigating engineer can be drawn to an incorrect understanding of the damage and its cause. This, in turn, may lead to an erroneous determination of the cause of the accident.
Analytical, FEA and Experimental Methods for Computing the Resilience of Tapped Thread Joints
Authors: Amir Yosef , Reif John , Konkle Nicholas
Published: August 2012

Bolted joint behavior is based on many parameters, many of which are not well known or understood. The basic parameters describing the signature behavior of the bolted joint are the fastener and clamped joint flanges’ resilience. The level of confidence in the resilience parameter defines the confidence level of further analysis performed throughout the design phase. For general cases with simple configurations of the bolt and joint members, well-known analytical methods such as VDI 2230 satisfy the purpose of bolted joint analyses. However, in practice there are cases which deviate from the idealized joint, such as complex bolted joint geometry or dissimilar materials which cannot be simplified for an analytical model. The particular case studied here is that of a screw joint or tapped thread joint (TTJ) where the analytical model is ambiguous. In addition, for TTJs that are critical to safety a high confidence in the result is desired, so finite element analysis (FEA) or experimental methods are preferred to assess the resilience of the clamped and tapped flanges. This paper presents FEA modeling as well as analytical methods for complex joints, particularly for TTJ configurations. Resilience values for FEA and analytical approaches are presented, as well as experimental results for validation.
Kinematical Design and Simulation of a Mobile Robot With Adaptable Suspension
Authors: Medina-Rivera Vi´ctor , Cardenas Antonio , Medellin-Castillo Hugo
Published: August 2012

The kinematics design of a new mobile robot suspension for unstructured environments is presented in this paper. This design incorporates an adaptable-passive mechanism that compensates for irregularities of terrain. The new mechanism comprises two pairs of bogies joined by a crank-slider mechanism. The kinematic analysis and numerical simulations of the robot have been carried out and are presented. Two performance indexes based on the tilt angle of the payload platform and velocity of the front wheel are proposed and used as a mean of performance evaluation. From a comparative analysis of reported mobile robots in the specialized literature several advantages of the new system are identified. Moreover the results have shown that the system is able to overcome most types of obstacles with a minimum variation of the tilt angle of the payload platform.