bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal Assessment of Cooling System Incorporating Heat Sink and Embedded Heat Pipes for Testing High Power Microelectronics
Authors: Chiriac Victor Adrian , Lee Tien-Yu Tom
Published: April 2008

A numerical study was conducted to model the transient thermal behavior of a complex testing system including multiple fans, a mixing enclosure, copper inserts and a leaded package dissipating large amounts of power over short time durations. The system is optimized by choosing appropriate heat sink/fan structure for the efficient operation of the device under constant powering. The intent of the study is to provide a better understanding and prediction of a transient powering scenario at high powering levels, while evaluating the impact of alternative cooling fan/heat pipe designs on the thermal performance of the testing system. One design is chosen due to its effective thermal performance and assembly simplicity, with the package embedded in heat sink base with multiple (5) heat pipes. The peak temperature reached by the modified design with 4 cooling fans is ~95°C, with the corresponding Rja thermal resistance ~0.58°C/W. For the transient study (with embedded heat pipes and 4 fans), after one cycle, both peak temperature (at 45 s) and the end temperature (at 49 s) decrease as compared to the previous no heat pipe/single fan case (the end temperature reduces by ~16%). The temperature drop between peak and end for each cycle is ~80.2°C, while the average power per transient cycle is ~31.27W. With this power, the design with 5 perpendicular heat pipes, 4 fans and insert reaches a steady state peak temperature of ~98°C. Applying the superposition principle to the steady state value and 40.1°C fluctuation, the maximum transient temperature after a large number of cycles will not exceed ~138.1°C, satisfying the thermal budget under the current operating conditions. The benefit of the study is related to the possibility to extract the maximum and minimum temperatures for a real test involving a large number of heating-cooling cycles, yet maintaining the initial and peak temperatures within a certain range for the optimal operation of the device. The flow and heat transfer fields are investigated; using a combination of numerical and analytical methods, the thermal performance of the device undergoing large number of periodic thermal cycles is predicted. The comparison between measurement and simulation shows good agreement.
An Ultrasonic Based System to Measure Inter Spinous Process Distance in Humans: A Pilot Study
Authors: Medina Ariel , Gudavalli Maruti R. , Raju P. K. , Cramer Gregory D.
Published: April 2008

The objective of this research project was to develop an ultrasonic based testing system and evaluate its application on human volunteers to locate and assess the distance between adjacent lumbar vertebrae. Tests were performed on ten volunteers aged between 19 and 29 years old during two sessions. The participants were asked to lie face down on a table with lower back section uncovered while the tests were executed. A computer controlled ultrasonic system was designed for this application. A single element 3.5 MHz immersion transducer held by a customized assembly was used to propagate and receive the ultrasonic signals. The transducer was moved along the assembly to fully scan at least two contiguous spinous processes. A Lab view based program was designed to generate a two-dimensional image (B-scan) that display the shape and position of the bone tips as well as the distance between them. The standard deviation obtained from the measurements of the distance between the tips of the spinous processes of human subjects, in a given session ranged from 0.1–0.48mm. The difference between two sessions had a mean of 0.85–0.95 mm and a standard deviation of 0.87–1.03mm with reliability coefficients greater than 0.95. The study demonstrated the viability of utilizing ultrasound to precisely measure the distance between spinous processes of adjacent lumbar vertebrae.
Control System Design for Retinal Imaging Adaptive Optics Systems
Authors: Ficocelli Maurizio , Ben Amara Foued
Published: April 2008

This paper presents a solution to control system design issues for adaptive optics systems used in retinal imaging. In this paper, the control problem for adaptive optics systems is generalized to that of shape control for a flexible membrane representing a deformable membrane mirror. Due to the dynamic nature of the aberrations in the eye, the shape control problem addressed is the tracking of an unknown and time-varying shape for a distributed membrane (i.e., desired shape of the mirror). The design of a controller to achieve the shape control objective is based on a model of a distributed parameter system representing the mirror membrane. To accomplish this task, a multivariable centralized controller is utilized. Since the desired shape of the mirror is unknown and time-varying, the controller is tuned online to converge to the controller needed to achieve regulation. This is done iteratively, by taking advantage of the Q-parameterization of all stabilizing controllers, so that the controller will converge to the ideal controller. The online tuning is used to compensate for the lack of information of the desired shape for the deformable mirror.
Finite Element Formulation and Vibration Frequency Analysis of a Fluid Filled Pipe
Authors: Jia Yi , Madeira Reinaldo E. , Just-Agosto Frederick
Published: April 2008

This paper presents the formulation of a finite element model and vibration frequency analysis of a fluid filled pipe having variable cross sections. The finite element method with consideration of Coriolis force developed in [1] was adopted for frequency analysis of a pipe in this study. The stiffness matrix, the c-matrix (Coriolis force) and mass (for dynamic analysis) matrix that contain all parameters of the fluids properties and flow conditions have been developed. The numerical model was employed to simulate the dynamic performance of the piping system with the specific configurations for an application. A critical relationship between the natural frequencies and pipe geometry has been established. The results of frequencies analysis of the piping system gave us an insight whether a resonance frequency might occur.
The Design and Simulation of a High Force Low Power Actuation System for Camless Engines
Authors: Lumkes J. H. , Van Doorn W. , Donaldson J.
Published: April 2008

Camless engines require independent actuators which can provide accurate control, sufficient force, and yet only require a small percentage of engine output power. A valve actuation system that meets these requirements is designed, modeled, and simulated at engine speeds up to 6000 rpm. Based on consideration of valve actuation cycles and hydraulic power efficiency, an open-center system employing control valves in series is simulated under various operating conditions and using a range of design parameter values. The results demonstrate that the proposed system is capable of meeting the 6000 rpm engine speed requirement while using as little as 1–2% of available engine power. In addition, the system lends itself well to either open-loop or closed-loop control without requiring a separate position sensor on each engine valve [1]. This potentially reduces the cost and increases the reliability of an actuation system designed for camless engines.
Flying Height Control for a 2-DOF Tripad Slider in Hard Disk Drives With Switched Regulator
Authors: Wu Zhizheng , Ben Amara Foued
Published: April 2008

Maintaining a constant small flying height of the read/write head is an important target in the design of the ultra high storage density hard disk drives. One effective way to achieve this goal is to use a feedback regulator to suppress the flying height variations. For low flying heights, the read/write head enters into intermittent contact with the disk surface, which results in a switched system regulation problem. In this paper a new control method is proposed to maintain the flying height at its desired value based on the switched system models, despite the unknown microwaviness in the disk surface profile and the unpredictability in the switching times. First, a switched system model is constructed. Then, a Q parameterized set of switched regulators is constructed and the stability of the resulting switched closed loop system is analyzed. Online adaptive regulator tuning is then performed by adjusting the Q parameter in the controller to achieve regulation. Simulation results are presented to illustrate the effectiveness of the proposed method.
Experimental Study on Embedded-Wire Electrode for EHD-Enhanced Condensation in a Shell/Tube Bundle Heat Exchanger
Authors: Wu J. , Ohadi M. M. , Dessiatoun S. , Qi J.
Published: April 2008

In this study, EHD-enhanced external condensation heat transfer was studied experimentally using a new type of wire electrode. The tube bundle consisted of twenty-four state of the art enhanced condensation tubes, provided by a heat transfer tube manufacturer. Thin wires embedded into a plastic board at a designated spacing formed the new electrode structure. The electrode board was inserted between the tube columns of the bundle to utilize the EHD effect while also preventing flooding of the lower tubes of the bundle with the condensate from the upper tubes, thus reducing the adverse bundle effect. For the tests reported, up to 60% enhancement in the external heat transfer coefficient was achieved at an applied EHD voltage of 19 kV. When compared to the Printed Circuit Board (PCB) electrode reported in our earlier studies, the embedded wire electrode (EWE) yielded better performance.
Thermal Radiative Transport Enhancement via Surface Plasmon Polaritons in Microscale Cylindrical Regions Bounded by a Surface Active Ceramic
Authors: Hammonds James S.
Published: April 2008

A Green function approach is used with the uctuation-dissipation theorem to theoretically model radiative heat transfer in microscale cylindrical geometries. The appropriate scalar Green function is presented by employing an impedance boundary condition. While z-independent elds are produced by axial line sources, it is proposed here that the qualitative results are applicable to thermal radiation within microscale spherical domains. An application of the theoretical result demonstrates the potential importance of surface phonon polariton modes in thermal radiation transport across porous surface-active ceramics.
Kinematics and Dynamics of Nanostructured Origami™
Authors: Stellman P. , Arora W. , Takahashi S. , Demaine E. D. , Barbastathis G.
Published: April 2008

Two-dimensional (2D) nanofabrication processes such as lithography are the primary tools for building functional nanostructures. The third spatial dimension enables completely new devices to be realized, such as photonic crystals with arbitrary defect structures and materials with negative index of refraction [1]. Presently, available methods for three-dimensional (3D) nanopatterning tend to be either cost inefficient or limited to periodic structures. The Nanostructured Origami method fabricates 3D devices by first patterning nanostructures (electronic, optical, mechanical, etc) onto a 2D substrate and subsequently folding segments along predefined creases until the final design is obtained [2]. This approach allows almost arbitrary 3D nanostructured systems to be fabricated using exclusively 2D nanopatterning tools. In this paper, we present two approaches to the kinematic and dynamic modeling of folding origami structures. The first approach deals with the kinematics of unfolding single-vertex origami. This work is based on research conducted in the origami mathematics community, which is making rapid progress in understanding the geometry of origami and folding in general [3]. First, a unit positive “charge” is assigned to the creases of the structure in its folded state. Thus, each configuration of the structure as it unfolds can be assigned a value of electrostatic (Coulomb) energy. Because of repulsion between the positive charges, the structure will unfold if allowed to decrease its energy. If the energy minimization can be carried out all the way to the completely unfolded state, we are simultaneously guaranteed of the absence of collisions for the determined path. The second method deals with dynamic modeling of folding multi-segment (accordion style) origamis. The actuation method for folding the segments uses a thin, stressed metal layer that is deposited as a hinge on a relatively stress free structural layer. Through the use of robotics routines, the hinges are modeled as revolute joints, and the system dynamics are calculated.
Optical Characterization of a Bimorph Deformable Mirror
Authors: Horsley David A. , Park Hyunkyu , Chuang Chih-Wei , Laut Sophie P. , Werner John S.
Published: April 2008

This paper reports the results of interferometric characterization of a bimorph deformable mirror (DM) designed for use in an adaptive optics (AO) system. The natural frequencies of this DM were measured up to 20 kHz using both a custom stroboscopic phase-shifting interferometer as well as a commercial Laser Doppler Vibrometer (LDV). Interferometric measurements of the DM surface profile were analyzed by fitting the surface with mode-shapes predicted using classical plate theory for an elastically-supported disk. The measured natural frequencies were found to be in good agreement with the predictions of the theoretical model.
Design, Fabrication, and Characterization of Piezoresistive MEMS Shear Stress Sensors
Authors: Barlian A. Alvin , Park Sung-Jin , Mukundan Vikram , Pruitt Beth L.
Published: April 2008

This paper presents the design, fabrication, and characterization of unique piezoresistive microfabricated shear stress sensors for direct measurements of shear stress underwater. The uniqueness of this design is in its transduction scheme which uses sidewall-implanted piezoresistors to measure lateral force (and shear stress), along with traditional top-implanted piezoresistors to detect normal forces. Aside from the oblique-implant technique, the fabrication process also includes hydrogen anneal step to smooth scalloped silicon sidewalls due to Deep Reactive Ion Etch process, which was shown to reduce 1/f noise level by almost an order of magnitude for the sidewall-implanted piezoresistors. Lateral sensitivity characterization of the sensors was done using a microfabricated silicon cantilever force sensor, while out-of-plane characterization was done using Laser Doppler Vibrometry technique. In-plane sensitivity and out-of-plane crosstalk were characterized, as well as hysteresis and repeatability of the measurements. The sensors are designed to be used underwater for various applications.
Stability Analysis of a Piecewise Nonlinear Vibration Isolator
Authors: Stahl Patrick , Nakhaie Jazar G.
Published: April 2008

Many vibration isolators can be modeled with a discontinuity in the stiffness and damping coefficients. The sudden change in the values of the coefficients can be represented as a piecewise linear or nonlinear function. Soft suspensions are best for isolation; however, a nonlinear hardening suspension is required to minimize relative displacement at high amplitudes. Often, the physical design limits the relative displacement. Taking advantage of nonlinearity in the suspension is not enough in limiting the relative displacement at very high amplitude. Therefore, a secondary suspension must be involved to limit very high relative displacements. In this investigation, the averaging method was applied to the differential equation generated from the model to find the frequency response. A sensitivity analysis was performed to find regions of instability in the frequency response
Optimization of Geometrically Trimmed B-Spline Surfaces
Authors: Zhang Xinyu , Li Yaohang , Myklebust Arvid , Gelhausen Paul
Published: April 2008

Unlike the visual trimming of B-spline surfaces, which hides unwanted portions in rendering, the geometric trimming approach provides a mathematically clean representation without redundancy. However, the process may lead to significant deviation from the corresponding portion on the original surface. Optimization is required to minimize approximation errors and obtain higher accuracy. In this paper, we describe the application of a novel global optimization method, so-called hybrid Parallel Tempering (PT) and Simulated Annealing (SA) method, for the minimization of B-spline surface representation errors. The high degree of freedom within the configuration of B-spline surfaces as well as the “rugged” landscapes of objective functions complicate the error minimization process. The hybrid PT/SA method, which is an effective algorithm to overcome the slow convergence, waiting dilemma, and initial value sensitivity, is a good candidate for optimizing geometrically trimmed B-spline surfaces. Examples of application to geometrically trimmed wing components are presented and discussed. Our preliminary results confirm our expectation.
Stress Analysis of a High Temperature Heat Exchanger Used in an Advanced Nuclear Reactor
Authors: Ponyavin Valery , Subramanian Sundaresan , DeLosier Clayton Ray , Chen Yitung , Hechanova Anthony E. , Peterson Per F.
Published: April 2008

This paper presents the stress analysis of the offset strip-fin type compact high temperature heat exchanger for use in the cooling cycle of an advanced nuclear reactor for hydrogen production by the sulfur iodine thermo-chemical cycle. Three different geometry types of heat exchangers were considered: geometry with rectangular fins; geometry with rounded fins and geometry with rounded fins which include manufacturing geometrical effects (fins with roundings on their bases). The material of the heat exchanger is liquid silicon impregnated carbon composite. The two working fluids for the heat exchanger are helium gas and molten salt with maximum temperature about 1000°C. The finite element code ANSYS 9.0 was used for the simulations. The boundary conditions for temperature and pressure were obtained as results of CFD and heat transfer calculations of the heat exchanger using the finite volume code FLUENT 6.1.18 The obtained results will be used for further optimization of the high temperature heat exchanger geometry.
Simulation of Wall Pressure Fluctuations on Simplified Automobile Shapes Using a Lattice Based Method
Authors: Senthooran Sivapalan , Crouse Bernd , Balasubramanian Ganapathi , Freed David , Noelting Swen , Gleason Mark
Published: April 2008

A comparison of experimental data and CFD simulation results of wall pressure fluctuations on simplified geometries that generate flow structures similar to an automobile are presented. The numerical results have been obtained using the commercial software PowerFLOW 3.4p4a. The simulation kernel of this software is based on the numerical scheme known as the Lattice Boltzmann Method (LBM), combined with an RNG turbulence model. This scheme accurately captures time-dependent aerodynamic behavior of high Reynolds number flows over complex geometries, together with the acoustics. The geometries considered for this study represent the green house and the side mirror of a car. Spectral analysis is performed on the simulation data and the results are compared to the experimental data. This comparison provides good correlation between the simulation and experiment, and demonstrates the capability of this numerical scheme in predicting turbulent fluctuations due to complex flow phenomena.
Mathematical Modeling of Thermal Effects in Steady State Dynamics of Microresonators Using Lorentzian Function: Part 2 — Temperature Relaxation
Authors: Aagaah M. R. , Mahmoudian N. , Nakhaie Jazar G. , Mahinfalah M. , Khazaei A. , Alimi M. H.
Published: April 2008

Thermal phenomena have two distinct effects, which are called, in this report, “thermal damping” and “temperature relaxation”. In this second part of a two-part report we (only) model and investigate the temperature relaxation and its effects on microresonator dynamics. A reduced order mathematical model of the system is introduced as a mass-spring-damper system actuated by a linearized electrostatic force. Temperature relaxation is the thermal stiffness softening and is modeled as a decrease in stiffness rate, utilizing a Lorentzian function of excitation frequency. The steady state frequency-amplitude dependency of the system will be derived utilizing averaging perturbation method. Analytic equation describing the frequency response of the system near resonance which can be utilized to explain the dynamics of the system, as well as design of involved dynamic parameters is developed.
Simplifying Robust Control Designs of Parametric Uncertain Systems Using Dimensional Transformations
Authors: Hailu Haftay , Brennan Sean
Published: April 2008

Robust control techniques have become more popular in the last decade because of their ability to construct a single controller suitable for a family of plants that are represented as a nominal plant with an uncertainty bounds. A typical challenge with robust control design is that, as the size of the uncertainty block gets bigger, the complexity of the control synthesis and resulting controller exponentially increases. Using a dimensional transformation method, this work shows that some robust control problems can be recast into an equivalent representation with a much smaller size of uncertainty block. This reduction potentially reduces the conservativeness and computational complexity of both H∞/μ – synthesis methods. This method is demonstrated using the 1990 ACC benchmark problem.
A Multi-Level Multi-Integral Algorithm for the Helmholtz Equation
Authors: Dargush G. F. , Grigoriev M. M.
Published: April 2008

Previous work on the development of multi-level boundary element methods (MLBEM) has produced dramatic computational efficiencies compared to traditional methods. However, for problems involving the oscillatory kernels associated with the Helmholtz equation, the performance improvements demonstrated to date have been limited due to the presence of coarse mesh Nyquist constraints. In the present paper, we examine an extension of the original Helmholtz MLBEM to remove these limitations, based on a polar decomposition of the kernels and field variables originally proposed by Brandt. In this initial numerical implementation of these ideas, the algorithm is applied to a pair of two-dimensional half-space problems and, therefore, is limited to the fast evaluation of Rayleigh integrals. In general, excellent performance is achieved. For example, in the second problem with a non-dimensional wave number equal to 105, we obtain speed-up factors of approximately 300,000 versus a traditional BEM approach, while maintaining comparable levels of accuracy.
The Effectiveness of Transferring Multi-Agent Behaviors From a Learning Environment in the Presence of Synthetic Social Structures
Authors: Garfield Keith , Wu Annie , Onal Mehmet , Crawford Britt , Campbell Adam , Shumaker Randall
Published: April 2008

The diverse behavior representation schemes and learning paradigms being investigated within the robotics community share the common feature that successful deployment of agents requires that behaviors developed in a learning environment are successfully applied to a range of unfamiliar and potentially more complex operational environments. The intent of our research is to develop insight into the factors facilitating successful transfer of behaviors to the operational environments. We present experimental results investigating the effects of several factors for a simulated swarm of autonomous vehicles. Our primary focus is on the impact of Synthetic Social Structures, which are guidelines directing the interactions between agents, much like social behaviors direct interactions between group members in the human and animal world. The social structure implemented is a dominance hierarchy, which has been shown previously to facilitate negotiation between agents. The goal of this investigation is to investigate mechanisms adding robustness to agent behavior.
Electrolytic Microbubbler Matrices
Authors: Lee S. K. , Loth E. , Liu C.
Published: April 2008

The feasibility of generating mono-disperse micro-bubbles by electrolysis in tap water using micro-fabricated devices was investigated towards the development of a high-density bubbler matrix. The effect of electrode geometry and size, as well as artificial nucleation sites was tested using single and arrays of electrode pairs. The results indicated that circular electrode node shapes (as opposed to triangular or square nodes) nucleated bubbles from the node center and exhibited fewer instances of bubble coalescence and a higher bubble detachment frequency when operated with small anode-anode and cathode-cathode spacings. Artificial nucleation sites, produced by etching the surface of the electrodes, were shown to be able to limit nucleation to one site (though in some cases, bubbles formed underneath the dielectric layer) as well as increase current efficiency. A device with thousands of electrode pairs (a matrix of nodes) was also fabricated in order to generate a bubble cloud close to the channel wall. At a flow speed of 14 cm/s, this device demonstrated the ability to generate a bubble cloud reasonably close to the wall 20 mm from the trailing edge of the matrix of nodes, with the void fraction peaking at 1 mm from the channel wall and returning to zero at 3 mm. It yielded efficiencies greater than similar thin-wire devices, but spurious bubbles formed on the device, indicating that additional work is needed to develop this technology in a matrix format.
Controlled Separation and Trapping of Particles Using Two-frequency DEP
Authors: Loire Sophie , Zhang Yanting , Bottausci Frederic , MacDonald Noel C. , Mezic Igor
Published: April 2008

We present numerical simulations and experiments on dielectrophoretic (DEP) separation and trapping performed in a titanium-based microchannel linear electrode array. The use of electric fields and in particular dielectrophoresis (DEP) have a great potential to help miniaturize and increase the speed of biomedical analysis. Precise control and manipulation of micro/nano/bio particles inside those miniaturized devices depend greatly on our understanding of the phenomena induced by AC electric fields inside microchannels and how we take advantage of them. The studied DEP devices are composed of two parts: the inter-digitated titanium electrodes and the channel. The electrode substrate is constituted of two layers to form 4-phase traveling wave. Each electrode is 20 μm wide and separated from the other by a gap of 20 μm. The channel is 200 μm wide, 50 μm deep and 6 mm long. The device is designed to generate inhomogeneities in electric-field magnitude. This allows positive and negative DEP (p-DEP and n-DEP). Moreover, it can also produce inhomogeneities in electric-field phase, hence authorizing traveling wave DEP (twDEP). It is also capable of inducing two-frequency DEP, in contrast with most of the previous, single-frequency, designs. The advantages of two-frequency DEP were shown by theoretical work (Chang et al. 2003) and permit precise and optimal control of particles movements. We show that fluid flow effects are substantial and can affect the particle motion in a positive (enhanced trapping) and negative (trapping when separation is desired) way. We discuss the effects of AC-electroosmosis, electrothermal and dielectrophoresis combined. We discuss the advantages of two-frequency dielectrophoretic handling of bioparticles. We investigate the limits of particle size that can be accurately controlled.
Thermoeconomic Diagnosis of a Pulverized Coal-Fired Steam Generator
Authors: Rangel-Hernandez V. H. , Aguilar A. Zaleta , Valero A. , Cuadra C. Torres
Published: April 2008

An application of a novel technique to filter induced malfunctions from intrinsic ones in the field of the thermoeconomic diagnosis is presented here for the particular case of a pulverized coal-fired steam boiler. The steam boiler is part of a 350 MWe power plant located at Teruel, Spain. The thermoeconomic diagnosis developed here is underpinned by the exergy cost theory. Through application of this new technique, it is attempted to show that it allows to detect, localize and quantify more easily and precisely the causes of the malfunctions in large thermal systems, as well as the direct impact that malfunctions have on the consumption of resources. In order to do so, a hypothetical scenario of anomalies occurring in the system is proposed here. The scenario is obtained by a simulator of the steam generator which determines the operating condition corresponding to the presence of the different anomalies. The results reveal that the technique is a reliable procedure that can assist to detect more easily the causes of the malfunctions.
Vertically Aligned Multi-Walled Carbon Nanotube Arrays as Thermal Interface Materials and Measurement Technique
Authors: Tong Tao , Zhao Yang , Delzeit Lance , Kashani Ali , Majumdar Arun , Meyyappan M.
Published: April 2008

State-of-the-art thermal interface materials are briefly reviewed with an emphasis on the emerging trend of using carbon nanotubes to increase interface thermal performance. Vertically aligned multi-walled carbon nanotube (MWCNT) arrays were grown and applied as thermal interfacial enhancing materials. It is expected that the highly thermally conductive channels directly bridging the mating surfaces would significantly enhance the interface thermal conductance. We extended the all-optical pump and probe phase sensitive transient thermo-reflectance (PSTTR) method and used it to measure the interfacial properties of a three-layer sample of a vertically aligned MWCNT array grown on silicon (Si) substrate dry adhered to a glass plate. The dominant thermal resistance is identified as the dry adhered MWCNT-glass interface with a thermal conductance of ~5.9 × 104 W/m2·K, compared with MWCNT-Si interface of almost two orders of magnitude higher. Tentative explanations on the difference in the two interfaces and ways for future improvements are provided. The PSTTR measurement principle and issues are also discussed in the context.
Starting on the Right Track: Introducing Students to Mechanical Engineering With a Project-Based Machine Design Course
Authors: Dollar Aaron M. , Kerdok Amy E. , Diamond Solomon Gilbert , Novotny Paul M. , Howe Robert D.
Published: April 2008

Over the past four years, we have redesigned Harvard’s introductory mechanical engineering course to introduce the principles, practices, and pleasures of mechanical engineering in an accessible format. The main goals of the course are to provide experience in the design process, demonstrate the connection between engineering science and design early in the curriculum, and build student enthusiasm for engineering, serving to attract and retain students. Unlike most introductory mechanical engineering courses, we cover strength of materials and machine elements, material usually presented much later in the curriculum, in order to provide tools for the students to quantitatively evaluate their designs. By providing just enough of this background knowledge to allow for analysis of designs, we demonstrate the connection between engineering science and design early in curriculum and motivate in-depth coverage of these topics in later courses. The laboratories for the course build enthusiasm for engineering by incorporating exciting design projects and introducing students to some of the most attractive mechanical engineering tools. Students learn 3-D solid modeling with CAD software, create prototypes from CAD models using manual and CNC machining, and reverse engineer common consumer products. Using these tools, students build their own hardware prototypes for both a cantilever beam catapult and a model all-terrain-vehicle. These exercises, carefully chosen to reinforce the strength of materials and machine elements concepts, culminate in design contests that enhance the visibility of engineering within the larger university community and increase student interest in the field.
Simulation and Optimization of Homogeneous Decomposition of Sulfur Trioxide Gas on a Catalytic Surface
Authors: Muramalla Kiran K. , Chen Yitung , Hechanova Anthony E.
Published: April 2008

This paper deals with the development of a two-dimensional numerical model to predict the wall-catalyzed homogeneous decomposition of sulfur trioxide in a tubular component geometry for the production of hydrogen by the sulfur-iodine thermochemical water splitting cycle, a candidate cycle in the U.S. Department of Energy Nuclear Hydrogen Initiative. The reacting fluid is a mixture of sulfur trioxide gas and water vapor inside the tubes of a heat exchanger. The heat exchanger is made of Incoloy alloy 800H with ALFA-4 coated on the inner walls which acts as a catalyst. Decomposition of sulfur trioxide depends on many different parameters such as wall surface temperature, mole flow rate of the reacting mixture, diameter of the reactor tube, length of the reactor tube, operating pressure and inlet temperature of the reacting mixture. The effects of wall surface temperature, diameter of the reactor tube and mole flow rate on the decomposition of sulfur trioxide were investigated using a two-dimensional numerical model using Computational Fluid Dynamics (CFD) techniques. The preprocessor GAMBIT was used to create a computational mesh and the CFD software package FLUENT 6.2.16 [1] which is based on finite volume methods was used to simulate the problem. Both FLUENT 6.2.16 and Tecplot 10.0 are used to post process the problem.
Analysis of Dental Enamel Topography
Authors: Hilerio I. , Barron M. A.
Published: April 2008

One of the fields of active research in dentistry today is biomaterials replacing, which is expected to be increasingly more similar to human dental enamel. As these dental materials are exposed to the diverse degrading actions present in the oral environment, it is important to know its superficial topography, which is related to the existence of asperities on a smaller scale, responsible for the interaction between opposing bodies. In this work we try to characterize the superficial topography of the dental enamel and evaluating a sane tooth and another degraded by use, comparing the values of the texture SEM. The results indicate that the dental enamel presents a topographical profile with a symmetrical distribution, between peaks and valleys, relative to the parameters of amplitudes as well as to parameters of material concentrations. The values encountered for the amplitude and densities of peaks parameters are high. It was verified in the degraded tooth the existence of mechanisms of mechanical origin added to chemical reactions, producing a wear type called “chemical wear”. The existence of this phenomenon was identified by verification in the degraded tooth of the presence of more deep valleys in relation to the peaks. The abrasion mechanism, also present in this wear type, decreased significantly the amplitude of the peaks. The evaluation methodology via profilometry3D revealed potentially efficient for the characterization of superficial topography and by verification of the mechanisms of wear dental.
Effect of Clamping Pressure on PEM Fuel Cell Stack Performance
Authors: Fekrazad N. , Bergman T. L.
Published: April 2008

A two-dimensional mathematical model of a Proton Exchange Membrane fuel cell stack is developed. Taking advantage of the geometrical periodicity within the stack, the model is used to predict the detailed thermal, humidity, and electrochemical behavior of the fuel cell. Using recently-reported experimental results, the electrical and thermal contact resistances that develop within the stack, in response to the compressive force used to assemble the stack, are accounted for. The fuel cell performance, reported in terms of its power output and internal temperature distributions, is predicted to be very sensitive to the compressive load applied to the stack.
Numerical Simulation of Gas Phase Growth Environment of Carbon Nanotube Synthesis by Plasma-Enhanced Chemical Vapor Deposition
Authors: Garg R. K. , Gore J. P. , Fisher T. S.
Published: April 2008

The gas-phase growth environment of carbon nanotubes has been simulated using different published chemical reaction mechanisms for a gas mixture of methane and hydrogen. Detailed chemical analysis of the growth environment is important in identifying precursor species responsible for CNT formation and is useful in understanding fundamental mechanisms that ultimately could allow control of the CNT synthesis process. The present simulations seek to compare the roles of different gas phase reaction mechanisms and to identify precursors for CNT formation. The results show that inlet methane-hydrogen mixture converts primarily to a acetylene-hydrogen mixture, and C2H2, CH3, H2, and H are the main precursors formed in the plasma under experimentally verified CNT growth conditions in a microwave plasma reactor.
Vertical and Horizontal Academic Projects: A Novel Teaching Technique in the Faculty of Engineering of the National Autonomous University of Mexico
Authors: Espinosa Bautista A. , Garci´a del Ga´llego M. , Zepeda Sa´nchez A.
Published: April 2008

Competitiveness of the students is increasing. Students with better skills are graduating from universities all over the world. More and more efforts are being done to improve the skills of the undergraduate students. In the Faculty of Engineering of the National Autonomous University of Mexico (UNAM) many lecturers use projects to help students to better understand the concepts and to improve their teamwork skills. However many of these efforts are isolated and have been done in an empirical way. The Manufacturing and Design Center is seeking ways to get students with better skills and bring together the isolated efforts done by many lecturers. Therefore a new technique is being explored for the mechanical design area. This technique is based on the Project Based Learning method. Two main approaches are being explored: the Horizontal Projects (HP) and the Vertical Projects (VP). The basic idea for the HP is to have a Great Design Team (GDT) developing a project in one semester. Students from different subjects of the Mechanical Engineering program compose the GDT. Each of these groups have access to information related to the subject they are attending in a central database. Students work on the different issues according to their subject; e.g. Mechanics of Solids solve issues related to the stress in the different elements of the machine or product developed; the Product Design subject works on the definition of the product specifications, requirements etcetera. Periodical meetings help to evaluate the global progress of the GDT. In the VP one student works on different stages of the project as he/she moves from one semester to the next, all the time working in the same project. The expected benefit of this technique is to provide the student with a better view of the different stages involved in the development of a project. Both techniques are being explored. Each of these techniques has advantages and disadvantages. This paper describes in detail these techniques and the potential applications for other careers within the Faculty of Engineering.
Numerical Analysis of Corrosion Behavior and Oxygen Transport in the Nature Convection Lead-Bismuth Flow
Authors: Chen Huajun , Chen Yitung , Hsieh Hsuan-Tsung , Zhang Jinsuo
Published: April 2008

A two-dimensional numerical analysis of oxygen transport and corrosion behaviors in a coupled natural convection and lead bismuth eutectic (LBE) flow in a two dimensional container was carried out in detailed. In present study, it is assumed the corrosion product (iron) concentration is at its equilibrium level at the wall. The wall boundary condition for the mass transfer of corrosion production and oxygen concentration was taken based on the active oxygen control model. And also the oxygen transport in the LBE loop flow was simulated for testing and calibrating flow concentration level oxygen sensors. Both of the corrosion/precipitation rates at the wall, distribution of corrosion product and oxygen, and oxygen diffusion time are analyzed. Some useful information was obtained to understand the mechanism of corrosion behavior and oxygen transport.
Effect of Pre Oxidation on the Sliding Wear of Multi-Component Ferrous Alloys
Authors: Hilerio I. , Barron M. A.
Published: April 2008

Presence oxides on sliding surfaces can greatly influence friction and wear. Oxides have been usually considered as a friction and wear reducing agent acting as a solid lubricant. Effects of pre-oxidation, carried out at different temperatures, on the tribological behaviour of a high-speed steel and a high chromium white cast iron sliding against a ceramic material have been studied in this work. Wear was evaluated through a new methodology, which calculates the volume of removed material from topography data of the worn surface. Wear mechanisms were determined by scanning electron microscopy analysis. Results showed a large difference between wear rate of the studied materials. High speed steel had a much lower wear than high chromium white cast iron. However pre-oxidation did not cause any meaningful influence on the tribological behaviour of both material, at least in the conditions evaluated in this work.
Latchable Phase-Change Actuators for Micro Flow Control Applications
Authors: Yang Bozhi , Lin Qiao
Published: April 2008

This paper presents a novel latchable phase-change actuator that can potentially be used for flow valving and gating in portable lab-on-a-chip systems, where minimal energy consumption is required. The actuator exploits a low melting-point paraffin wax, whose solid-liquid phase changes allow the closing and opening of fluid flow through deformable microchannels. Flow switching is initiated by melting of paraffin, with an additional pneumatic pressure required for flow switching from open to closed state. After paraffin solidifies the switched state is subsequently maintained passively without further consumption of energy. The actuator can be fabricated from PDMS through the multilayer soft lithography technique. Testing results demonstrate that the actuator has a response time about 60-100 sec for flow switching, and can passively hold a microvalve closed under pressures up to 35 kPa.
Adaptive Robust Repetitive Control of Piezoelectric Actuators
Authors: Zhong Jinghua , Yao Bin
Published: April 2008

Positioning stages using piezoelectric stack actuators (PEA) possess very high theoretical bandwidth and resolution. However, their tracking performance deteriorates as nonlinear dynamics due to inherent hysteresis starts to dominate when the total length of travel increases. When tracking periodic trajectories, which is common in most industrial applications, the uncertain nonlinearity from hysteresis also becomes periodic. Having identified and separated the fast and slow dynamics of the total stage response, we adopt a simple first-order model assuming the inertial dynamics of the stage is negligible in the low tracking frequency range. By approximating the hysteresis mapping function with simple functions, the overall system model is linearly parameterized for subsequent adaptive robust controller design. Exploiting the periodicity of the uncertain hysteresis nonlinearity, it is further parameterized as finite series of harmonic functions, which eliminates the need for an exact inversion model for hysteresis while achieving high tracking accuracy. Experimental results from tracking control of sinusoidal and typical triangular trajectories show tracking error close to the sensor noise level and demonstrate the effectiveness of the approach.
Optimal Electrode Shape Design for Multi-Mode Sensors
Authors: Park Chul H. , Park Hyun C. , Lee Kimoon , So Hyun K.
Published: April 2008

This paper presents optimal electrode shape design methods for the multi-mode sensors that could detect the structural multiple modes. The structure used for this study is an isotropic cantilever beam type with a PVDF (polyvinylidene fluoride) which is bonded onto the structure as a sensor. The shape optimization problem is solved by using Genetic Algorithm (GA) and Super-position method. The performance of analytical optimal shape sensor is validated by experiment. The results show that the obtained electrode shape sensors have good performance to detect the multiple vibration modes simultaneously.
Unit Block Library of Basic Architectures for Use in Computer-Aided Tissue Engineering of Bone Replacement Scaffolds
Authors: Wettergreen M. , Bucklen B. , Starly B. , Yuksel E. , Sun W. , Liebschner M. A. K.
Published: April 2008

Guided tissue regeneration focuses on the implantation of a scaffold architecture, which acts as a conduit for stimulated tissue growth. Successful scaffolds must fulfill three basic requirements: provide architecture conducive to cell attachment, support adequate fluid perfusion, and provide mechanical stability during healing and degradation. The first two of these concerns have been addressed successfully with standard scaffold fabrication techniques. In instances where load bearing implants are required, such as in treatment of the spine and long bones, application of these normal design criteria is not always feasible. The scaffold may support tissue invasion and fluid perfusion but with insufficient mechanical stability, likely collapsing after implantation as a result of the contradictory nature of the design factors involved. Addressing mechanical stability of a resorbable implant requires specific control over the scaffold design. With design and manufacturing advancements, such as rapid prototyping and other fabrication methods, research has shifted towards the optimization of scaffolds with both global mechanical properties matching native tissue, and micro-structural dimensions tailored to a site-specific defect. While previous research has demonstrated the ability to create architectures of repetitious microstructures and characterize them, the ideal implant is one that would readily be assembled in series or parallel, each location corresponding to specific mechanical and perfusion properties. The goal of this study was to design a library of implantable micro-structures (unit blocks) which may be combined piecewise, and seamlessly integrated, according to their mechanical function. Once a library of micro-structures is created, a material may be selected through interpolation to obtain the desired mechanical properties and porosity. Our study incorporated a linear, isotropic, finite element analysis on a series of various micro-structures to determine their material properties over a wide range of porosities. Furthermore, an analysis of the stress profile throughout the unit blocks was conducted to investigate the effect of the spatial distribution of the building material. Computer Aided Design (CAD) and Finite Element Analysis (FEA) hybridized with manufacturing techniques such as Solid Freeform Fabrication (SFF), is hypothesized to allow for virtual design, characterization, and production of scaffolds optimized for tissue replacement. This procedure will allow a tissue engineering approach to focus solely on the role of architectural selection by combining symmetric scaffold micro-structures in an anti-symmetric or anisotropic manner as needed. The methodology is discussed in the sphere of bone regeneration, and examples of cataloged shapes are presented. Similar principles may apply for other organs as well.