bluuebunny/crossref_metadata_2025 huggingface dataset:
Compact Modeling of a Telecommunication Cabinet
Authors: Trivedi Aalok , Agonafer Dereje , Sivanandan Deepak , Hendrix Mark , Sahrapour Akbar
Published: August 2009

Computational Fluid Dynamics (CFD) is widely used in the telecommunication industry to validate experimental data and obtain both qualitative and quantitative results during product development. A typical outdoor telecommunications cabinet requires the modeling of a large number of components in order to perform the required air flow and thermal design. Among these components, the heat exchanger is the most critical to thermal performance. The cabinet heat exchanger and other thermal components make up a complex thermal system. This thermal system must be characterized and optimized in a short time frame to support time-to-market requirements. CFD techniques allow for completing system thermal optimization long before product test data can be available. However, the computational model of the complex thermal system leads to a large mesh count and corresponding lengthy computational times. The objective of this paper is to present an overview of techniques to minimize the computational time for complex designs such as a heat exchanger used in telecommunication cabinets. The discussion herein presents the concepts which lead to developing a compact model of the heat exchanger, reducing the mesh count and thereby the computation time, without compromising the acceptability of the results. The model can be further simplified by identifying the components significantly affecting the physics of the problem and eliminating components that will not adversely affect either the fluid mechanics or heat transfer. This will further reduce the mesh density. Compact modeling, selective meshing, and replacing sub-components with simplified equivalent models all help reduce the overall model size. The model thus developed is compared to a benchmark case without the compact model. Given that the validity of compact models is not generalized, it is expected that this methodology can address this particular class of problems in telecommunications systems. The CFD code FLOTHERM™ by Flomerics is used to carry out the analysis.
Assembly Tolerance Analysis for Injection Molded Modular, Polymer Microfluidic Devices
Authors: You Byoung Hee , Park Daniel S. , Chen P.-C. , Rani Sudheer D. , Nikitopoulos Dimitris E. , Soper Steven A. , Murphy Michael C.
Published: August 2009

Validation of a tolerance analysis for the assembly of modular, polymer microfluidic devices was performed using simulations and experiments. A set of three v-groove and hemisphere-tipped post joints was adopted as a model assembly features. An assembly function with assembly feature dimensions and locations was modeled kinematically. Monte Carlo methods were applied to the assembly function to simulate variation of the assembly. Assembly accuracy was evaluated assuming that the variations of the assembly features were randomly distributed. The estimated mismatches were 118 ± 30 μm and 19 ± 13 μm along the X- and Y-axes, respectively. The estimated vertical gap between the modules at the alignment standards along the X- and Y-axes 312 ± 37 μm and 313 ± 37 μm, compared to the designed value of 287 μm. To validate the tolerance model, two micromilled brass mold inserts containing the assembly features and alignment standards were used to double-sided injection mold polymer parts. The accuracy of the assembly of the modular microdevices was estimated by measuring the mismatch and vertical gaps between alignment standards on each axis. The measured lateral mismatches were 103 ± 6 μm and 16 ± 4 μm along the X- and Y-axes, respectively. The vertical gaps measured for the assemblies were 316 ± 4 μm and 296 ± 9 μm at the X- and Y-axes, compared to the designed distance of 287 μm. Simulation and experimental results were in accordance with each other. The models can be used to predict the assembly tolerance of polymer microfluidic devices and have significant potential for enabling the realization of cost-effective mass production of modular instruments.
Numerical Study in Wing Tip Vortex for a Modified Commercial Boeing Aircraft
Authors: Hernandez-Rivera Ricardo , Hernandez-Guerrero Abel , Rubio-Arana Cuauhtemoc , Lesso-Arroyo Raul
Published: August 2009

Recent studies have shown that the use of winglets in aircrafts wing tips have been able to reduce fuel consumption by reducing the lift-induced drag caused by wing tip vortex. This paper presents a 3-D numerical study to analyze the drag and lift forces, and the behavior of the vortexes generated in the wing tips from a modified commercial Boeing aircraft 767-300/ER. This type of aircraft does not contain winglets to control the wing tip vortex, therefore, the aerodynamic effects were analyzed adding two models of winglets to the wing tip. The first one is the vortex diffuser winglet and the second one is the tip fence winglet. The analyses were made for steady state and compressible flow, for a constant Mach number. The results show that the vortex diffuser winglet gives the best results, reducing the core velocity of the wing tip vortex up to 19%, the total drag force of the aircraft up to 3.6% and it leads to a lift increase of up to 2.4% with respect to the original aircraft without winglets.
Heat Transfer and Pressure Drop in a Converging Lattice Structure for Airfoil Trailing Edge Cooling
Authors: Saha Krishnendu , Acharya Sumanta , Nakamata Chiyuki
Published: August 2009

Lattice-matrix structures have distinct advantages in enhancing heat transfer in the cooling channels of a gas turbine blade. Lattice structures not only enhance heat transfer coefficient but also provide structural rigidity to the turbine blade. Stationary tests were performed for a 12 times scaled up model at four Reynolds numbers (4,000 < Re < 20,000) in a converging lattice structure. A narrow band liquid crystal technique is used to determine the heat transfer coefficient in the channel. The results shows very high heat transfer coefficient enhancement in the impingement regions. The average heat transfer coefficient enhancement for a channel with lattice structures is also higher (Nu/Nu0 = 1.9–3) than a pin fin cooling configuration channel (Nu/Nu0 = 1.7–2.2). The heat transfer coefficient enhancement decreases with increasing Reynolds number. Pressure data are taken at some specific points throughout the channel. High pressure drop due to the turning of the flow in the lattice structure is observed. Friction factor and overall thermal performance factor are calculated. The overall thermal performance factor lies in the range 0.64–1.
Effect of Geometric Parameters of Superhydrophobic Surface on Liquid Slip
Authors: Lee Choongyeop , Choi Chang-Hwan , Kim Chang-Jin
Published: August 2009

In this paper, we experimentally study how geometric parameters of textured hydrophobic surfaces affect a liquid slip, empowered by a custom-tuned microfabrication procedure that produces regular micro-patterns of posts and grates on an entire 4” wafer with a good size uniformity and no defect. A pitch of the patterns and a gas fraction of the structured surface are independently controlled, and the slip length over each type of patterns is measured using a rheometer system. On both grates and posts, the slip length increases linearly with a pitch but exponentially with a gas fraction. The trend of exponential increase by gas fraction appears more pronounced on posts than on grates. The defect-free surfaces allow the flows to maintain a de-wetted (Cassie) state at much higher pitches and gas fractions than previously possible, permitting flows with the maximum slip effect.
On-Track Measurement of Lateral/Vertical Wheel Loads of Running Railway Vehicles Based on the Neural Network
Authors: Younesian Davood , Javid Fahim , Esmailzadeh Ebrahim
Published: August 2009

A new approach for on-track measurement of the lateral/vertical contact forces is presented in this paper. The proposed method is based on measurement of the strain at two sides of the wheel web. Electric signals generated by the strain gauges are fed into a neural network algorithm in order to predict the lateral/vertical contact forces. Feed-forward technique is used in the neural network algorithm. A sensitivity analysis has been carried out to find the best position for the strain gauges. A dynamic model of a freight wagon is provided and a variety of numerical simulations are performed to obtain the probability distribution of the lateral and vertical contact forces. The obtained probability distribution function is then utilized to generate lateral/vertical contact forces within the practical range. In order to train the neural network system, the generated contact forces are applied to the wheel flange and the strain signals are obtained. More than 100 configurations are fed into the system in order to train it. Reliability, accuracy and sensitivity of the proposed measurement system are then investigated.
Design of Thermal Mechanical Fatigue Accelerated Life Test Criteria
Authors: Ahdad Farid , Beltrami Calogero , Bernardini Luciano
Published: August 2009

Product validation tests are essential all over the design stages of product development. In the automotive industry, laboratory fatigue testing is an accelerated test that is specifically designed to replicate fatigue damage and failure modes potentially found during field driving conditions. The work presented in this paper is mainly focused on hot components of automotive turbocharger, centered on failure due to thermal mechanical fatigue (TMF). A design of experiment (DOE) was run to define the relation between load parameters and the TMF damage. This fatigue damage model is based on the stress approach (Chaboche fatigue model), widely spread in use, to allow computing the damage under a complex duty cycle. A TMF damage transfer function was identified and it is used to select smart lab test parameters and to link that lab test damage, with customer field damage. This relation allows defining accelerated lab test criteria in order to demonstrate customer field reliability requirements. The lab test is composed of an elementary cycle repeated several times and the field duty cycle is defined via the so called “median customer”. The median customer duty cycle is defined as a combination of several elementary driving patterns (country road, city, highway, ...). For each driving sequence, an instrumented turbocharger allows measuring the relevant parameters such as gas temperature, metal temperature, rotating assembly speed... Finally, a smart lab test can be designed and a criterion defined to demonstrate, with a specific confidence level, that the customer reliability requirement is met.
Studying Dynamic Pull-In Behavior of Microbeams by Means of the Homotopy Analysis Method
Authors: Moghimi Zand Mahdi , Tajalli S. Ahmad , Ahmadian Mohammad Taghi
Published: August 2009

In this study, the homotopy analysis method (HAM) is used to study dynamic pull-in instability in microbeams considering different sources of nonlinearity. Electrostatic actuation, fringing field effect and midplane stretching causes strong nonlinearity in microbeams. In order to investigate dynamic pull-in behavior, using Galerkin’s decomposition method, the nonlinear partial differential equation of motion is reduced to a single nonlinear ordinary differential equation. The obtained equation is solved analytically in time domain using HAM. The problem is studied by two separate manners: direct use of HAM and indirect use of HAM in conjunction with He’s Modified Lindstedt-Poincare´ Method. To demonstrate the effectiveness of the solution methods, results are compared with those in literature. The comparison between obtained results and those available in literature shows good agreement.
Compliant Control of Post-Stroke Rehabilitation Robots: Using Movement-Specific Models to Improve Controller Performance
Authors: Rosati Giulio , Bobrow James E. , Reinkensmeyer David J.
Published: August 2009

Post-stroke neurorehabilitation is an emerging application field of robotics, aiming to design new treatment systems and protocols based on the use of robotic technology and virtual reality to improve patient recovery after stroke. One goal in this field is to develop robotic therapy devices that are compliant but can still assist weakened patients in making desired movements. It is hypothesized that, in this way, the interaction with the robotic system can maintain patient engagement and effort, and promote and stimulate the motor learning process of the patient. One way that has been proposed to maintain compliance while assisting weak patients is to use an adaptive controller with a forgetting term, which allows the robotic system to learn a model of the forces needed to assist the patients during exercises while encouraging patient effort. A limitation of such an approach is that the adaptive gain must be large enough to rapidly change the model for different target movements, which decreases the compliance of the robot. We show here in simulation that by building independent models for different target movements, robot compliance can be increased while still accurately achieving the target movements.
A Variant Module Division Method on Extension Logic for Assembly Process
Authors: Su Nan , Zhao Yanwei , Xing Li , Zhang Meiyan , Gui Yuankun
Published: August 2009

The paper’s focus is on the module division dynamically in the virtual assembly sequencing process for the product family, which will affect the module variant quality seriously. Most research merely divides the module on their functions, without paying the attention on which the module division is beneficial for the latter assembly process. Considered assembly relationships as a key constraint, a new variant module division measure based on Extension Logic is presented. Since the tolerances existing everywhere in the assembly process, the connection analysis is employed to build a constraint function on the tolerance. Physical constraints contain mating and combination constraints. After the dynamical position for different parts, the mating constraint is defined as the movement opposition between two mechanical elements including face alignment mating, shaft and hole mating or face against mating. Then the extension radiation model could be generated. According the average value of the relationship function to realize the module division, the product structure is divided into several sub-assemblies. As the main problem in virtual assembly is process collisions, a modified integer coded Particle Swarm Optimization Algorithm is used. Here every part is mapped to corresponding particle. The result is performed in the virtual environment of software DELMIA. At last the extension cluster method in this paper is compared with the direct dynamic cluster method. A case study is performed on virtual assembly of high power Light Emitting Diodes automatic sorting machine manufactured by a factory.
NEMS Components Design Using Intentionally Defected Dispersive Building Blocks
Authors: Hussein Mahmoud I. , Ruzzene Massimo , Leamy Michael J. , Durrie Jason J. , Davis Bruce L.
Published: August 2009

We propose a hierarchical approach for the design of NEMS components with favorable dynamical characteristics. The approach consists of two steps: (i) design of several defect-engineered crystalline materials through intentional introduction of uniformly distributed defects, and in doing so altering precisely the frequency band structure of these materials, and (ii) allocation of patches of these designed materials to various regions in the component. Through this multiscale dispersive design approach, NEMS components can be designed to act as filters forbidding the transmission of vibrations at certain frequencies or waveguides confining the flow of energy to predetermined paths. Case studies are presented for 1D and 2D nanostructures.
Wave Beaming in Nanostructured Materials With Engineered Defects
Authors: Hussein Mahmoud I. , Leamy Michael J. , Ruzzene Massimo
Published: August 2009

Recent advances in the fabrication of nanoscale material systems have made it possible to alter precisely the atomic structure in ways that enhance the properties and allow for certain functions to be realized. This work is concerned with two-dimensional periodic structures and emphasizes the effects of intentional defects on their wave propagation characteristics. In this draft paper, investigations are limited to a two-dimensional spring-mass lattice, composed of “super-cells” where mass inclusions are added to alter band-gap properties, as well as low frequency directionality. The presented results will then be extended to two-dimensional nanostructures, such as graphene nanosheets, in order to investigate their application as nanoscale acoustic waveguides, where engineered defects, uniformally distributed across the entire sheet, are introduced by design with the objective of rendering the medium anisotropic. Such anisoptropy leads to acoustic directionality, which can be exploited for waveguiding or acoustic-focusing purposes.
Design, Construction and Use of an ASTM Guarded-Hot-Plate Apparatus as an Independent Research Project
Authors: Yilmaz Emin , Pinder Edward
Published: August 2009

Thermal conductivity and/or R-value of materials may be measured using methods specified by American Society for Testing Materials (ASTM) or International Standards Organization (ISO). In general three methods are commonly used: the Hot Box, the Heat Flow Meter, and the Guarded Hot Plate. The project was assigned to a Mechanical Engineering Technology student as a research project to satisfy requirements for, senior level, “ETME-499-Independent Research in Mechanical Engineering Technology” course. Student was asked to do his own literature search for the available standard methods and select the most suitable standard method to design and construct an apparatus to measure thermal conductivity and/or R-value of insulating plane specimens. Student has decided to use the Guarded Hot Plate method since it did not require calibration and is simpler to construct. Before the standard was received, student has created some designs similar to the one described by the standard. Limited test runs indicate that polystyrene R-values were underestimated by 12–16%, and duct board R-vales were underestimated up to 22% at higher than 75 °F average specimen temperatures. Student has enjoyed designing, constructing and using the apparatus, which has real world applications. This project has forced him to use his machine design, strength of materials, thermodynamics, instrumentation, heat transfer and manufacturing processes knowledge. Paper will convey our design, construction and use experiences as well as the experience the primary author had in guiding the student towards a common goal in an “Independent Research” course.
Near-Field Radiation Calculated With an Improved Dielectric Function Model for Doped Silicon
Authors: Basu S. , Lee B. J. , Zhang Z. M.
Published: August 2009

This paper describes a theoretical investigation of near-field radiative heat transfer between doped silicon surfaces separated by a vacuum gap. Using an improved dielectric function model for heavily doped silicon, along with fluctuation-dissipation theorem, and dyadic Green’s function, the present authors calculated the energy transfer between the doped silicon surfaces near room temperature. The effects of doping level, polarization, and width of the vacuum gap on the overall radiative transfer were investigated. It was observed that increase in the doping concentration of the emitter does not necessarily enhance the energy transfer in the near field. The energy-streamline method was used to model the lateral shift of the energy pathway, which is the trace of the Poynting vectors in the vacuum gap. The analysis performed in this study may facilitate the understanding of near-field radiation for applications such as thermal management in nanoelectronics, energy conversion systems, and nanothermal manufacturing.
Simulated Enhanced Buoyancy Convection on Structure of 304 GMA Welds
Authors: Aidun Daryush K. , Lana Kyle C.
Published: August 2009

The purpose of this research project is to examine the effects of “simulated” enhanced buoyancy convection on gas-metal arc (GMA) weld bead geometry of 304 stainless steel welds at various “simulated” gravity conditions (g-levels). It was evident that gravity did have an effect on shape and geometry of the weld zone. The 4g and 8g welds had wider but shallower weld zones. The competition among the main convective forces such as Buoyancy, Lorentz, and Marangoni can significantly alter the weld zone aspect ratio as well as the shape.
Longitudinal Integration of Problem Based Learning Into Undergraduate Mechanical Engineering Courses
Authors: Chen Xiaolin
Published: August 2009

Problem-based learning (PBL) has long been recognized as an effective way to engage students in active learning. Problems are those students will finally encounter in their professional lives. Incorporating PBL into undergraduate education can motivate students to acquire knowledge and skills by tackling problems and not just to pass exams. In engineering, a common form of PBL is through course projects. Students work in teams to explore real-world problems and make presentations to share what they have learned. In practice, however, it often becomes a challenge to fully exploit the benefits of PBL in a single course because of the time constraints enforced in the curriculum. This paper describes an educational experience to longitudinally integrate PBL into several upper-division mechanical engineering courses. The goal of this PBL experimentation is to let students thoroughly research and study different aspects of a real-world problem. This is achieved by modularizing the problem and embedding the PBL modules into a series of courses. A case study will be presented to exemplify the use of modularized PBL to help cumulatively develop students’ capability in mechanical system modeling, simulation, analysis and design through several courses. The students involved are mechanical engineering undergraduates that are taking engineering analysis, dynamic systems, and computer-aided engineering courses. To conclude, student feedback and discussions on assessment strategies will be given. The modularized PBL can be a good way to mirror industrial practice in real-world engineering problem solving and to enrich students learning experience.
Effect of Electrode Shape on Droplet Actuation in Electrowetting-Based Microfluidics
Authors: Rajabi Negar , Dolatabadi Ali
Published: August 2009

This article describes the effect of electrode shape in electrowetting-based droplet actuation. A Volume of Fluid technique is applied to track the 3-D interface. The Laplace equation is solved to predict the time and space dependent electric field in the domain. The onset of actuation, contact angle distribution at the three phase line, and the droplet morphology are studied for two electrode shapes; i.e. flat and crescent. The acceleration and the velocity of the droplet are also other important parameters to show the superior performance of crescent electrode in droplet actuation.
The Configulation of the Profile of the Basic Rack for High Order of Contact
Authors: Liu Huran
Published: August 2009

After an extensive research on the fundamental theory, the theoretical basis for the Logix gearing will be presented in this paper. This includes the theory for gear meshing with high degree of contact. In comparison to previous studies, the theory of this paper is more restricted going beyond third order parameters into the fourth order, the teeth profile had one order of contact higher than that of the Logix gearing. So that further improved the contact strength of tooth profile. A large category of gearings with high order of contact was presented, while the Logix gear is only one of them, or the special example in realization of my theory. In the Logix gearing, the zigzag curvature center curve of media rank does not always lay about the pitch line and does not extend along the pitch line continuously and steadily. It goes forward and returns. So that, in terms of properties of the transverse engagement, the Logix gearing has not much improvement over the traditional Novikov gearing (in which the transverse engagement is temporally). In my gearing the curvature center of media rank extend along the pitch line continuously and steadily. The transverse engagement factor is larger than that of Logix gearing.
The Kinematical Analysis of the Hydraulic Motor With Swinging Bevel Gears
Authors: Liu Huran
Published: August 2009

A new kind of hydraulic motor suitable for the low velocity, large torque, high efficiency and mutable velocity output have been researched and developed in this paper. There are a series of creations, such as, the oil flow distribution, the principle of reducer, the output mechanics and the total structure. It features in the simple in construction, small of size, large ratio of reducer, high f ratio of torque-power, and low in energy consumption. It is suitable for all the occasions with hydraulic supply and all the fields when low velocity, large torque, high efficiency and mutable velocity output ware needed. Such as the construction mechanics, ship mechanics, heavy machine tool, heavy capstan and so on. The frequency of the hydraulic system is about 1000–2000/min, the reduced ratio of the planetary drive of swinging bevel gear is about 20–100, with 150 the maximum. This paper introduced the fundamental principle of the transmission of this mechanics, designed the basic structure of this mechanics, and analyzed the movement and forces.
Use of Combustion Modeling in the Design and Development of Coal Fired Furnaces and Boilers
Authors: Jorgensen Kris L. , Dudek Scott A. , Hopkins Mitchell W.
Published: August 2009

The design and development of industrial combustion systems often involves the use of advanced modeling tools. In pulverized coal combustion these tools must include several different effects: fluid flow, energy transport, radiation heat transfer, chemical reactions, particle transport and combustion, and the interaction between all these models. Advances in modeling the combustion of coal particles have made these tools even more useful in the design and development of coal fired combustion systems. This paper presents a comprehensive combustion model that has been developed to model the combustion processes in coal fired furnaces. This model is described in detail in the current work along with details of the individual sub-models. Examples of modeling results are presented for two applications to demonstrate the usefulness and importance of modeling coal fired furnaces and boilers.
On Exact Solutions of Switching Linear Dynamical Systems With Arbitrary Excitations
Authors: Luo Albert C. J. , Wang Yang
Published: August 2009

The exact solutions of switching linear dynamical systems with arbitrary discontinuous forcing are investigated. The switching system consists of countable prescribed linear subsystems with specified external excitations. The traditional treatments are to smoothen the discontinuity between two subsystems in such a switching system. In this paper, a method is introduced to obtain an exact solution of such a switching system. Under periodic piecewise forcing and random forcing, the exact solutions and stochastic responses of switching systems are given to help one better understand random responses in stochastic dynamical systems. For periodic forcing, the periodic responses and stability of the switching system are presented.
Dynamic Response of Ground Surface Due to External Disturbance: Analytical Solution
Authors: Hamidzadeh Hamid R.
Published: August 2009

In this investigation the propagation of a harmonic disturbance on the surface of ground is considered. The medium is assumed to be a homogeneous and isotropic, continuous and infinite which can be modeled as an elastic half space medium. Implementing elasto-dynamics analysis, the governing equation of motion for the system is developed. The developed mathematical model formulates the displacement and stresses in the medium in terms of elastic dilatation and rotations and reduces the governing equations into three wave equations in terms of elastic dilatation and rotations. These equations are solved and boundary stresses are satisfied in Fourier domain and the displacement on the surface are provided in this domain.
Heat and Mass Transfer in a Differentially Heated Enclosure Filled With Supercritical Carbon Dioxide
Authors: Prasopchingchana Uthai , Lei Zhiheng , Farouk Bakhtier
Published: August 2009

Numerical simulations of heat and mass transfer in supercritical carbon dioxide are carried out for natural convection conditions in a differentially heated square enclosure. The two vertical walls are maintained at different temperatures while the two horizontal walls are insulated. For the mass transfer studies, a heated vertical naphthalene wall is considered. Properties of supercritical carbon dioxide are evaluated from the National Institute of Standards and Technology (NIST) Standard Reference Database 12. A correlation for the mean Nusselt number along the heated wall is obtained as a function of the heat transfer Rayleigh number (for a given Prandtl number). A correlation for the temporal Sherwood number along the naphthalene surface is obtained as a function of the mass transfer Rayleigh number, and Fourier number (for a given Schmidt number). The results are compared with result available in the literature.
Evaluation of Heat Transfer Effect on a Thermal System Using Numerical Simulation
Authors: Al-Habahbeh O. M. , Aidun D. K. , Marzocca P. , Lee H.
Published: August 2009

A method that links several commercially available tools to estimate the fatigue life of thermal systems is introduced. The procedure provides an engineering tool based on existing computational packages. It is sufficiently general that it can be used for any thermal application involving fluid flow and a solid medium. A cylindrical ring model is presented to clarify the process. Computational Fluid Dynamics (CFD) and Finite Element Modeling (FEM) tools are integrated within the proposed approach. ANSYS/CFX® and Simulation® are used for such purpose. The process starts with CFD simulation to determine the convective terms necessary for the transient FEM thermal analysis. The transient FEM thermal analysis provides maximum thermal stress values. These values are employed in the fatigue life analysis to determine the fatigue life of the component.
Combustor Cooling Wiggle Strip and Geometrical Simplification
Authors: Jiang Leiyong
Published: August 2009

The flow fields of a combustor cooling wiggle strip and its corresponding simplified slot with conjugate heat transfer have been studied numerically. The effects of geometrical simplification on the flow fields have been analysed qualitatively and quantitatively. It is found that its effects on the flow velocity and temperature fields are limited to local regions near the cooling element, and are negligible in the far field. However, the simplification shows a considerable effect on the combustor liner temperature near the cooling element, about 8.5% of the average temperature across the cooling element. In short, using the simplified slot to replace the cooling wiggle strip in gas turbine combustor modeling is an acceptable practice if accurate liner temperature prediction is not required.
Atomic-Scale Three-Dimensional Phononic Crystals With a Large Thermoelectric Figure of Merit
Authors: Gillet Jean-Numa , Volz Sebastian
Published: August 2009

The design of thermoelectric materials led to extensive research on superlattices with a low thermal conductivity. Indeed, the thermoelectric figure of merit ZT varies with the inverse of the thermal conductivity but is directly proportional to the power factor. Unfortunately, as nanowires, superlattices cancel heat conduction in only one main direction. Moreover they often show dislocations owing to lattice mismatches, which reduces their electrical conductivity and avoids a ZT larger than unity. Self-assembly is a major epitaxial technology to design ultradense arrays of germanium quantum dots (QDs) in silicon for many promising electronic and photonic applications as quantum computing. Accurate positioning of the self-assembled QD can now be achieved with few dislocations. We theoretically demonstrate that high-density three-dimensional (3-D) arrays of self-assembled Ge QDs, with a size of only some nanometers, in a Si matrix can also show an ultra-low thermal conductivity in the three spatial directions. This property can be considered to design new CMOS-compatible thermoelectric devices. To obtain a realistic and computationally-manageable model of these nanomaterials, we simulate their thermal behavior with atomic-scale 3-D phononic crystals. A phononic-crystal period (supercell) consists of diamond-like Si cells. At each supercell center, we substitute Si atoms by Ge atoms to form a box-like nanoparticle. Since this phononic crystal is periodic, we compute its phonon dispersion curves by classical lattice dynamics. Non-periodicities can be introduced with statistical distributions. From the flat dispersion curves, we obtain very small group velocities; this reduces the thermal conductivity in our phononic crystal compared to bulk Si. However, owing to the wave-particle duality at very small scales in quantum mechanics, another reduction arises from multiple scattering of the particle-like phonons in nanoparticle clusters. At room temperature, the thermal conductivity in an example phononic crystal can be reduced by a factor of at least 165 compared to bulk Si or below 0.95 W/mK. This value, which is lower than the classical Einstein limit of single crystalline Si, is an upper limit of the thermal conductivity since we use an incoherent-scattering approach for the nanoparticles. Because of its very low thermal conductivity, we hope to obtain a much larger ZT than unity in our atomic-scale 3-D phononic crystal. Indeed, this silicon-based nanomaterial is crystalline with a power factor that can be optimized by doping using CMOS-compatible processes. Future research on the phononic-crystal electrical conductivity has to be performed in order to compute the full ZT with a good accuracy.
Convection and Transport in a Differentially Heated Enclosure Filled With Supercritical Carbon Dioxide: Short- and Long-Time Solutions
Authors: Lei Zhiheng , Farouk Bakhtier
Published: August 2009

Supercritical fluids are characterized by high densities, high thermal conductivities (compared to gases) and low viscosities, but low thermal diffusivities (compared to liquids). Due to the high compressibility, thermally induced acoustic waves are generated when supercritical fluids are heated/cooled along any bounding surface. In this study, we obtain both short- and long-time solutions for convective flows in a supercritical carbon dioxide filled enclosure. The NIST database 12 [1] is used to obtain the property relations for supercritical carbon dioxide. The generation and propagation of themoacoustic waves produced immediately after rapid heating of a wall are investigated by solving the fully compressible Navier-Stokes equations with an accurate equation of state, via a high-order explicit numerical scheme. For longer time solutions, when the acoustic waves damp out, an implicit solution algorithm is used to simulate the heat transfer in the above enclosure filled with supercritical carbon dioxide for longer periods time. This novel scheme allows us to investigate convective flows in an enclosure filled with supercritical fluid in a comprehensive manner.
Simulation of Swirl Combustion and NO Formation Using Various Second Order Moment Turbulent Combustion Models and DNS Verification
Authors: Wang F. , Huang Y. , Zhou L. X. , Xu C. X. , Cao J.
Published: August 2009

If the instantaneous chemistry reaction rate is taken as ws = Bρ2Y1Y2 exp(−E/RT) = ρ2Y1Y2K, here K is a contraction for the exponential term. Then, ignoring the three order fluctuation correlation term, the average reaction rate could be ws = ρ2(Y1Y2K + Y1′Y2′K + Y1K′Y2′ + Y2K′Y1′). The authors have simulated jet combustion and swirl combustion using this kind of second order moment (SOM) turbulent combustion model. The predictions are close to experimental data in most regions. In order to improve the SOM turbulent combustion model, the effect of various correlation moments in the simulation of turbulent swirl combustion and NO formation is studied by comparing different SOM turbulence-chemistry models, including the unified second-order moment (USM) model, the model accounting for only the time-averaged reaction-rate coefficient, the model accounting for only the concentration fluctuation and the model accounting for both the time-averaged reaction-rate coefficient and the concentration fluctuation. These models are incorporated into the FLUENT code for a methane-air swirling combustion and NO formation under various swirl numbers. The magnitude of various correlations and their effect on the time-averaged reaction rate are analyzed, and the simulation results are compared with the corresponding measurement results. The results showed that the USM model gives the best agreement with the experimental results and among various correlation moments the correlation of reaction-rate coefficient fluctuation with the concentration fluctuation is most important. Additionally, a direct numerical simulation (DNS) of three-dimensional channel turbulent reacting flows with consideration of buoyancy effect using a spectral method was carried out. The statistical results are shown that K′Y′ are larger than Y1′Y2′.
Designing New Cooling System for Automobiles to Get More Fuel Efficiency and Less Environment Defects
Authors: Sharifpur Mohsen
Published: August 2009

Almost all of the internal combustion engines waste a significant amount of their fuel energy from cooling system or exhaust gas. On the other hand in the warm season or regions, it needs to remove some extra heat from air conditioner radiator (condenser). This subject effects directly on global warming. Changing some part of this waste energy to shaft work (or electricity) not only has benefit in the way to find a source for hybrid automobiles but also, it has effect on global warming, fuel economy, saving natural resources and if the fuel produce CO2, less greenhouse effect and less air pollution defect could be remarkable. In this work, a new cooling system is offered that is the same as a core of boiling water (nuclear) reactors (BWR), it means a subcooled working fluid could enter to engine shell then during the heat removes from engine and exhaust gas, it will be a boiling generator (boiling heat exchange) for a smart thermodynamic cycle. In this way not only could change some parts of unused energy to work, but also it has more capability with environment. Here, it is offered this idea by using the typical engines data. The Results confirm that it can recover at least about 20% of waste heat. This new cooling system is suitable for hybrid electric vehicle (HEV) which combines a conventional propulsion system with an onboard rechargeable energy storage system. However, it can use this idea for almost the entire internal ignition engines in automobiles or somewhere that needs to remove some heat from a device, same as condensers of modified power plants or engine of ships.
Field Comparison of the Retention Properties of Pre-Fractured Heat Strengthened Laminated Glass to Tempered Glass in Factory Door Seals
Authors: Phillips Donald R.
Published: August 2009

This current study was performed to investigate the performance difference between production tempered side glazing and modern heat-strengthened laminated glass when tested with a controlled one-quarter roll where the door-mounted rearview mirror was targeted to pre-fracture the glazing. Then push out and abuse impact demonstrations were conducted on the glazing. The results of the demonstration were observed and photographed. Only unmodified, commercial glazing was used in windows that were retained in a vehicle-mounted, framed driver’s door. The testing indicates that by using laminated glass, occupant retention can be realized, significantly lowering the potential for partial or full ejection and their associated heightened injury risk.
Rapid Development of a CNC Software Within Manufacturing Automation Courses
Authors: Bosetti Paolo , Biral Francesco
Published: August 2009

A significant part of a Manufacturing Automation course is devoted to CNC machine tools, their architecture, and the part programming languages (APT, ISO G-code and so on). Nevertheless, it is not trivial to provide the students with a complete understanding of the relationships between the machine dynamics, the path planning strategy, and the control systems. For this reason, a short laboratory course has been developed aimed at the programming of a simplified CNC software with the following functionalities: to parse a part program written in a subset of the ISO G-code; to process the instruction blocks and to generate trapezoidal velocity profiles; to convert the velocity profiles reference trajectory; to interpolate the reference trajectory at the servo loop control frequency. In order to shorten the development time, the following choices have been made. The parser only implements a small subset of the ISO G-code, which is point-to-point positioning (G00), linear interpolation (G01) and full stop (M30). The velocity profiles are calculated as acceleration-limited trapezoidal profiles with zero-feed velocity boundary conditions. Finally, the system is developed in Ruby, which is an object-oriented scripting language, easy to learn and well suited for rapid prototyping of complex software systems. This is why the project has been named RNC (Ruby Numerical Control). At the course start, the overall system architecture is explained and is translated in the set of Ruby classes that have to be developed, and classes interfaces are mandatorily determined. During the laboratory activity, students work in teams, and each team is encouraged to work separately on the development of each Ruby class. At the end of the development phase, the students can interface the RNC they wrote with a machine tool simulator (developed separately) and use the whole software system to test the accuracy of the tool-tip trajectories as a function of the system parameters (servo loop gains, motors torque, masses and dynamic performance of the virtual machine tool). Moreover, thanks to the object-based architecture of RNC and to the common, pre-determined class interfaces, the students can then swap and mix different implementations of the above reported functionalities, as well as enhanced versions provided by the teacher. With respect to other similar Mathlab/Simulink based solutions, the presented laboratory activity brings a more detailed insight into a CNC software still limiting the code complexity thanks to the Ruby language and it is only based on open-source tools.
Post-Flashover Compartment Fire for Different Fire Ventilation Settings in a Medium-Sized Residential Room
Authors: Saber Hamed H. , Kashef Ahmed , Bwalya Alex
Published: August 2009

A number of fire ventilation scenarios were investigated in order to identify the proper ventilation scheme for conducting design fire tests in a medium-sized residential room of a size of 4.2 m long, 3.8 m wide and 2.4 m high. The ventilation schemes were based on using a window, door, or both with different sizes. The fuel package that was used in all scenarios consisted of a mock-up sofa made of polyurethane foam and two wood cribs underneath it. The selection of this fuel package is supported by fire statistics that many fatal residential fires begin with an item of upholstered furniture. The CFD technique was used to conduct the numerical simulations for eleven ventilation scenarios using the Fire Dynamics Simulator (FDS) version 5. The effect of window and door sizes, and fire load location on the heat release rate, burning rate, temperature during the period of fully-developed fire (post-flashover), and the onset of post-flashover and its duration were investigated.
Effect of Pressure Wave Generator Characteristics on Pulse Tube Cryocooler Performance
Authors: Jafarian A. , Saidi M. H. , Sarikhani N. , Hannani S. K.
Published: August 2009

Recent developments of superconductive industry require cryocoolers with cooling power higher than one Watt in the 70–80 K temperature range. High capacity pulse tube cryocoolers assure the cooling power required for operation of superconducting devices. The purpose of this paper is to investigate the influence of the pressure wave generator on high capacity pulse tube cryocooler performance. In this respect the hydrodynamic and thermal behavior of the cryocooler is explained by applying the mass and energy balance equations to different components of the cryocooler cycle. A linear temperature profile is assumed in the regenerator and nodal analysis technique is employed to simulate the tube section behavior numerically. Employing the proposed model the effect of pressure wave characteristics at the inlet boundary, namely, the Stirling type and G-M type pressure inlet on cryocooler performance are investigated. The influence of Pressure amplitude, frequency and swept volume is studied as well.
A Study on Evaluation of Impact Strength of Adhesive Joints Subjected to Impact Shear Loadings
Authors: Sawa Toshiyuki , Nagai Toshimasa , Iwamoto Takeshi , Kuramoto Hideaki
Published: August 2009

Adhesive joints in mechanical structures are subjected to static loading as well as impact loading. It is desired for the adhesive joints to have sufficient strength under both static and impact loadings. A lot of studies on the adhesive joints and the joint strength subjected to static loading have been carried out and examined. A few research works on the adhesive joint subjected to dynamic loading have been done, however, it has not fully elucidated for applying the joints to important sections in mechanical structures. In this study, the impact strength of adhesive joints subjected to impact shear loading is investigated using modified split Hopkinson pressure bar (SHPB) apparatus. The shear strength of adhesive joint, in which a solid cylinder is bonded to a hollow cylinder by an adhesive, is determined from maximum applied shear stress. A commercial thermosetting epoxy adhesive is used in the experiments. At the same time, the stress distributions in the joints subjected to impact shear loading are simulated by the finite-element analyses (FEA). The effect of adhesive thickness is investigated experimentally and computationally. It is shown that the strength is greatly affected by the adhesive thickness and the effect on the stress distributions in the joint is discussed.
Automotive Side Glazing Ejection Mechanisms: Part II — Review of Recent Glazing Literature
Authors: Batzer Stephen A. , Herndon G. Grant , Semones Paul T. , Thorbole Chandrashekar K. , Ziejewski Mariusz , Hooker Robert M.
Published: August 2009

In Part I of this two part series, the mechanisms of occupant ejection through automotive side glazing during rollover collisions were analyzed. It was shown that partial or complete ejection can occur through centrifugal acceleration based motion through an open portal, or due to the changes in velocity (ΔVs) developed during corner impacts. A new rollover angular velocity model was also developed and validated. In this second paper, recent literature discussing occupant retention side glazing is discussed, and the new angular rate model is applied. New dolly rollover testing of two XC90s is also presented and compared to previous testing.