bluuebunny/crossref_metadata_2025 huggingface dataset:
Incorporating Ethics and Lifelong Learning Into a Mechanical Engineering Technology Program
Authors: Fuehne Joseph P.
Published: April 2008

The Mechanical Engineering Technology program at Purdue University at Columbus/SE Indiana hosted ABET evaluators for the first time in the fall of 2005. Both the program objectives and outcomes of the MET program contain elements of ethical behavior and lifelong learning. These elements are simply reflective of the importance put on ethics and lifelong learning by the Accreditation Board for Engineering and Technology programs in the TC2K criteria. This work will describe the use of test cases and specific exercises that are incorporated in classes during the first semester and final semester of the two-year Associate of Science program. In-class surveys of students are also used to examine the ethical and professional behavior of students. The test cases are presented in multiple parts with students required to finish their answers to the questions from the first part before they get to see the second part. The same procedure is followed for the remaining parts of the test case. Each part of the test case also includes comments from a panel of experienced engineers who lend their expertise to the situation. These comments are shared with the students. For lifelong learning, the students are presented with a short lecture on the value of lifelong learning that includes relevant data and facts related to lifelong learning. After this, an assignment is given that asks the students to learn about how to design a container for nuclear waste storage and ship it to the proper waste disposal location. Other assignments are mentioned and can be used in a similar manner.
Modeling and Fabrication of a Micro Thermocouple Array
Authors: Cygan A. Z. , Kardak A. , Patterson D. , Podlaha-Murphy E. J. , Devireddy R. V. , Murphy M. C.
Published: April 2008

A prototype micro thermocouple array, to detect the temperature change within the neighborhood of a single cell, was produced as a proof of concept. Thermal modeling was performed to determine feasibility of the design and parametrically evaluate dimensions. The device consisted of a 3 × 3 array of type-T thermocouple junctions (copper and constantan), spaced 50 μm apart. A micro-fabricated wiring layer, intermediate post layer, and connecting junction layer were used. The intermediate post layer was designed to decrease the effect of the thermocouple wiring layer on the cell freezing response.
Integration of Computational Fluid Dynamics and Experimentation in Undergraduate Fluid Mechanics
Authors: Jokar Amir
Published: April 2008

A combination of computational and experimental analyses with the conventional lectures and problem-solving in a fundamental course such as fluid mechanics can enhance students' learning enormously. This teaching model has been examined within the mechanical engineering curriculum at WSU Vancouver, and successful results have been obtained thus far. The goal in this course was first to seed concepts and theorems of fluid mechanics in general terms, followed by numerical solutions and hands-on experimentation on selective subjects. This would allow the students to gain a deep understanding of the contents within the course timeframe. For selective fluid problems with more complications, such as the flow in the entrance region of a pipe, a computational fluid dynamic (CFD) software known as FlowLab was used to obtain numerical solutions. The assigned computational projects could open the eyes of students to the world of CFD analysis in thermal/fluid systems design. The results of the numerical analysis were then compared to the theoretical and experimental results. For experimentation, the students were divided into groups to design experimental procedures, conduct experiments, collect and interpret data, and report the results in an appropriate format. The selective experiments were relevant to the course topics including Burdon pressure gauges, manometers, flow-rate measurements, pipe flow, and flow around immersed bodies in a water tunnel. The present study addresses the details, results, and advantages of such a multi-dimensional and more interactive learning model.
Study on Positioning Accuracy of Aerostatic Lead Screw
Authors: Satomi Tadaatsu , Zhao Peng , Kobayashi Daisuke
Published: April 2008

The aerostatic lead screw is a non-contact type lead screw in which the contact surface of a male screw and a female screw is supported by a pressurized air film. It is characterized by the features that: (1) there is no degradation in accuracy due to friction wear; (2) no environmental pollution is caused by a leak and scattering of lubrication fluid; and (3) maintenance is easy and simple. However, drawbacks are that vibration is liable to occur and therefore the static rigidity is low. The aerostatic lead screw is useful for semiconductor fabrication and also effective in positioning a table on which a sample is placed in a biomicroscope. This study relates to a drunkenness analysis of the aerostatic lead screw. The drunkenness of a contact-type lead screw represented by the ball screw is generally transferred directly from the male screw to the female screw. In the aerostatic lead screw, the drunkenness based on machining accuracy error of each screw flank is not directly transferred onto the female screw and is instead averaged out by balancing of load capacities among each screw flank, so that the enhanced accuracy in positioning lead screws is expected. In this paper, a balance of the load capacity of each screw flank was computed using the aerostatic guidance theory, so as to carry out a drunkenness analysis. It is found that the balancing effect plays the vital role in improvement on drunkenness of an aerostatic lead screw used in this study.
Surface Topography Induced Ultrahydrophobic Behavior: Effect of Three-Phase Contact Line Topology
Authors: Anantharaju Neeharika , Panchagnula Mahesh , Kimsey Wayne , Neti Sudhakar , Tatic-Lucic Svetlana
Published: April 2008

The wettability of silicon surface hydrophobized using silanization reagents was studied. The advancing and receding contact angles were measured with the captive needle approach. In this approach, a drop under study was held on the hydrophobized surface with a fine needle immersed in it. The asymptotic advancing and receding angles were obtained by incrementally increasing the volume added and removed, respectively, until no change in angles was observed. The values were compared with the previously published results. Further, the wetting behavior of water droplets on periodically structured hydrophobic surfaces was investigated. The surfaces were prepared with the wet etching process and contain posts and holes of different sizes and void fractions. The surface geometry brought up a scope to study the Wenzel (filling of surface grooves) and Cassie (non filling of the surface grooves) theories and effects of surface geometry and roughness on the contact angle. Experimental data point to an anomalous behavior where the data does not obey either Wenzel or Cassie type phenomenology. This behavior is explained by an understanding of the contact line topography. The effect of contact line topography on the contact angle was thus parametrically studied. It was also inferred that, the contact angle increased with the increase in void fraction. The observations may serve as guidelines in designing surfaces with the desired wetting behavior.
Dependence of Thermal Boundary Conductance on Interfacial Mixing at the Chromium-Silicon Interface
Authors: Hopkins Patrick E. , Salaway Richard N. , Stevens Robert J. , Norris Pamela M.
Published: April 2008

The thermal conductance at solid-solid interfaces is becoming increasingly important in thermal considerations dealing with devices on nanometer length scales. Specifically, interdiffusion or mixing around the interface, which is generally ignored, must be taken into account when the characteristic lengths of the devices are on the order of the thickness of this mixing region. To study the effect of this interfacial mixing on thermal conductance, a series of Cr films are grown on Si substrates subject to various deposition conditions to control the growth around the Cr/Si boundary. The Cr/Si interfaces are characterized with auger electron spectroscopy depth profiling. The thermal boundary conductance (hBD) is measured with the transient thermoreflectance technique. Values of hBD are found to vary with both the thickness of the mixing region and the rate of compositional change in the mixing region. The effects of the varying mixing regions in each sample on hBD are discussed and the results are compared to the diffuse mismatch model.
Zero Boil-Off Cryogenic Liquid Hydrogen Storage Tank With Axial Cold-Spray System
Authors: Ho Son H. , Rahman Muhammad M.
Published: April 2008

This paper presents a steady-state analysis of fluid flow and heat transfer in a zero boil-off cryogenic storage tank for liquid hydrogen. The system includes a tank with cylindrical wall and oblate spheroidal top and bottom, and a cold-spray nozzle head whose face is set perpendicular to the axis of the tank. The nozzle head has many nozzles on its front face. The cold fluid cooled by an external cooling system enters the inlet opening at the top of the tank, follows an axial supply tube to the nozzle head and exits through the nozzles into the bulk fluid inside the tank heated by heat leak from the surroundings. The displaced fluid exits the tank through an annular outlet opening (also at the top of the tank and concentric with the inlet opening) then goes back to the external cooling system. This study considers the transport phenomena in the storage tank only with prescribed fluid flow velocity and temperature at the inlet to represent the external cooling system.
Distribution of Wheel Drive/Brake Torque Using Non-Linear Predictive Control to Enhance Vehicle Handling
Authors: Ghike Chinar , Shim Taehyun , Asgari Jahan
Published: April 2008

Wheel torque control is an effective means of improving vehicle handling and stability. Brake-based electronic stability programs which intervene in extreme situations to regulate vehicle behavior are the most common form of wheel torque control. With the advent of advanced driveline technologies, wheel torque control can also be achieved by the differential distribution of available drive torque to all four wheels. Similarly, in combined cornering and braking maneuvers, the applied brake input can be differentially distributed to regulate vehicle handling. This paper proposes an integrated scheme for wheel torque control that combines differential drive/brake torque distribution with the emergency braking control to regulate the vehicle yaw rate and side slip angle. A wheel torque controller was developed using a non-linear predictive control theory, 8 degree of freedom vehicle model, and nonlinear tires. The simulated vehicle responses show improved vehicle handling performance.
Layered Multiple Scattering Method for Analysis of Scatterer Lattice
Authors: Cai Liang-Wu
Published: April 2008

The layered multiple scattering method is derived from an approximate solution for infinite gratings. In this method, an array of regularly arranged scatterers is viewed as comprising of layers of infinite grating, and scattering of waves is treated as a multiple transmission-reflection process in a multilayer panel. The infinity nature enables the waves due to a planar incident wave to be expressed as planar waves and divided into propagating and evanescent modes. The layered multiple scattering method accounts only for the propagating modes. In this paper, this method is evaluated by comparing with exact solutions obtained by other means. The layered multiple-scattering method suggests that the only important geometric parameters for wave transmission and reflection are the grating distance and the interlayer distance. Numerical examples indicate that the method provides excellent approximate solution in general, but the errors due to evanescent modes might be significant in some aspect of wave propagation, due to interlayer interactions, such as critical frequencies of a stopband.
Modeling and Analytical Study of Scratch Drive Actuators
Authors: Honarmandi Peyman , Zu Jean W. , Behdinan Kamran
Published: April 2008

This paper presents a new analytical model of Scratch Driver Actuator (SDA) to obtain the design parameters of this device. In order to simulate working states of the SDA, three different static modes are considered: non-contact mode, transition mode, and full-contact mode. The SDA is simplified as an L-shape beam with different boundary conditions in each mode. Using beam theories in bending, the governing equation is derived and solved in each mode. The non-contact mode allows identifying the deflection and the driving voltage after which the actuator plate starts touching the substrate. From the transition mode, we calculate the primary contact length to be used for the analysis of the full-contact mode. In the full-contact mode, the SDA is completely snapped down in its working cycle. From this mode, we obtain the relationships between input voltage and design parameters such as SDA geometry, contact length, and step size. It is shown that a good agreement between theoretical results and experimental values is achieved, which verifies the validity of the new model.
Numerical Investigation of the Gas Premixing and Flow Resistance in the Micro Gas Turbine Engine Premix Chamber
Authors: Zhang Li , Yan Yunfei , Qiu Yun
Published: April 2008

Flow and diffusion in micro channel are important influence factors of premixing catalytic combustion in the micro gas turbine engine. Methane enters micro premixing chamber along axial direction, and air enters micro premixing chamber along radial direction, then methane and air mix vertically in the micro premixing chamber, passing rotational flow channels into annular chamber. The numerical investigation shows that enter flow velocity and premixing chamber structure are the dominant factors of the diffusion, and the flow resistance in premixing chamber is low. Because of the low characteristic dimension and flow velocity. For the arc-shaped and straight micro-channel, there is a method to get well mixing effections in micro premixing chamber.
Dynamic Slip Resistance at Metal-on-Metal Interfaces
Authors: Yuan Fuping , Prakash Vikas
Published: April 2008

In the present study plate-impact pressure-shear friction experiments were employed to investigate dynamic slip resistance and time-resolved growth of molten metal films during dry metal-on-metal slip under extreme interfacial conditions. By employing tribo-pairs comprising hard tool-steel against relatively low melt-point metals such as 7075-T6 aluminum alloy, interfacial friction stress of up to 300 MPa and slip speeds of approximately 250 m/s have been achieved. These relatively extreme interfacial conditions are conducive to the development of molten metal films at the tribo-pair interface. A Lagrangian finite element code is developed to understand the evolution of the thermo-mechanical fields and their relationship to the observed slip response. The code accounts for dynamic effects, heat conduction, contact with friction, and full thermo-mechanical coupling. At temperatures below the melting point the material is described as an isotropic thermally softening elastic-viscoplastic solid. For material elements with temperatures in excess of the melt temperature a purely Newtonian fluid constitutive model is employed. The results of the hybrid experimental-computational study provide new insights into the thermoelastic-plastic interactions during high speed metal-on-metal slip. During the early part of friction slip the coefficient of kinetic friction is observed to decrease with increasing slip velocity. During the later part transition in interfacial slip occurs from dry metal-on-metal sliding to the formation of molten A1 films at the tribo-pair interface. Under these conditions the interfacial resistance approaches the shear strength of the molten aluminum alloy under normal pressures of approximately 1-4.5 GPa and shear strain rates of ~ 107 s-1. It is interesting to note that the dynamic shear resistance of molten metal films decreases from ~100 MPa to ~50 MPa when the initial slip velocities increase from ~100m/s to ~250 m/s. Scanning electron microscopy of the slip surfaces reveal molten aluminum to be smeared on the tribo-pair interface. Photo-micrographs of the cross-section of the 7075-T6 A1 alloy reveals a thin region of severe shearing deformation in close vicinity of the sliding surface. The shearing deformation manifests itself as severely deformed grains in the direction of the sliding.
Simulation of Electroosmotic and Pressure Driven Flows in Microfluidic Interconnects
Authors: Rani Sudheer D. , Soper Steven A. , Nikitopoulos Dimitris E. , Murphy Michael C.
Published: April 2008

Numerical Simulations were performed to see the effect of geometrical misalignment on the progression of a sample plug in electrokinetic flows. The effect of material mismatch along with combined material and geometrical mismatch has also been investigated. A sample plug with low diffusion coefficient was introduced after the flow was fully developed. The effect of material and geometrical mismatch on the cross-sectional average of the plug concentrations were evaluated from the point of view of an optical detector. Various degrees of geometrical mismatch ranging from 0% to 75% were introduced and its effect on sample plug was evaluated. Comparison has been made with pressure driven flows to quantify the effect of geometrical mismatch.
Effective Supplier Involvement in Product Development Projects
Authors: Pakala Padmavathi K. , Allada V.
Published: April 2008

In today's scenario, many product development projects run the risk of being over budget and/or run past the scheduled deadlines. A major part of this can be attributed to the lack of effective and realistic product planning. We use the thesis that consideration of appropriate suppliers at the right time in a product development project can reduce wastes like waiting for parts to become available, unnecessary design iterations, design defects and poor design, and mitigate risks related to technology and enterprise capability. In the present paper, we present a methodology for effective supplier involvement in a product development project by blending the Design Structure Matrix (DSM) and the PERT/CPM techniques and considering supplier lead times and component interfaces of a given product architecture. We discuss the various options of supplier consolidation, postponement or early involvement of suppliers, and their effects on the product development project cost and schedule. We will demonstrate the working of the proposed methodology using a case example.
Electrostatic Capture of Airborne Nanoparticles in Swirling Flows for Bio-MEMS Applications
Authors: Jang Jaesung , Akin Demir , Lim Kwan Seop , Ladisch Michael R. , Bashir Rashid
Published: April 2008

Motivated by capture and detection of airborne biological agents in real time, we present the electrostatic capture of 100nm diameter polystyrene nanoparticles as a model system under swirling gas flows in a homemade particle collector having the forward outlet. The particle collector has five small positive electrodes on the bottom and one large grounded electrode on the top. The particles coming into the collector are slowed down during their swirling and stay in the collector before leaving. Particles captured on the center electrode of this collector were much less than those on the surrounding four electrodes and 10 - 25% of the particles with negative charges entering this collector were captured on the bottom electrodes at a flow rate of 1.1 l/min and an applied potential of 2 kV. Using a commercial CFD code FLUENT, we simulated the effects of the different types of collector outlet configurations and flow rates on the particles' trajectories, velocities, and travel times inside the collector. We also present the highest particle capture position inside the collector in those different configurations. The forward outlet configuration is the most favorable to particle capture among the tested configurations in terms of particles' minimum achievable velocities and their travel times at a flow rate of 1.1 l/min. This collector is well adaptable to integration with micro resonator devices and can be used for real-time monitoring of bioaerosols.
Effect of Grain Size and Grain Boundary on Mechanical Yielding Behavior of Fully Stabilized Zirconia
Authors: Lian Jie , Garay Javier , Wang Junlan
Published: April 2008

Mechanical properties of fully yttria stabilized zirconia (F-YSZ) with different grain sizes were investigated using instrumented indentation. While the grain size effect on the yield strength was performed on both the coarse-grained and fine-grained F-YSZ, the grain boundary effect was studied on the coarse-grained F-YSZ by performing nanoindentation within the grains and on/near the grain boundaries. Little variations were observed on mechanical properties such as hardness and reduced modulus, interesting results were obtained on the grain boundary effect on the yielding load for the course-grained F-YSZ.
Characterizing the Initial Spray From Fire Suppression Devices
Authors: Ren Ning , Blum Andrew , Wu Di , Marshall Andre´ W.
Published: April 2008

The performance of water-based fire suppression systems is governed by the dispersion of the water drops in the spray. Characterization of the spray is essential for predicting and evaluating the performance of these suppression systems. The dispersion of the spray is typically modeled using particle tracking methods. The accuracy of the spray predictions using this approach is quite sensitive to the initial spray specification. A physics based atomization model is proposed for specification of the initial spray. Inputs to the atomization model include injector geometry, injection pressure, ambient environment, and suppressant fluid properties. This modeling approach can be integrated with drop dispersion models and CFD models to characterize spray dispersion in quiescent environments or evaluate suppression performance in fire environments. In the current study, this atomization model is compared with measurements from an 'ideal' sprinkler to evaluate model performance and to support model development.
On the Dynamics of a Post-Buckled Vibrating Beam: An Experimental Study
Authors: Yogev Or , Bucher Izhak , Rubin Miles B.
Published: April 2008

A beam is clamped at one of its ends and is subjected to a shear force at its other end which causes deformation in the principal plane with stiffest resistance to bending. Above a critical value of load, bifurcation occurs, the beam twists and experiences out-of-plane deformation which tends to transfer bending to the plane of weakest resistance. Here, attention is focused on an experimental study of dynamic lateral torsional buckling. The load is exerted, by a tip mass whose inertia provides the load-levels that lead to buckling. Specifically, in the experiment, a beam is attached to the shaft of a motor at one of its ends and a large mass is attached to its other end. Rotation of the motor causes deflection of the beam in its principal plane of stiffest bending resistance. By increasing the excitation frequency and/or amplitude of oscillation of the motor's shaft, the shear force applied by the mass on the beam's end exceeds a critical value which causes dynamic lateral torsional buckling of the beam. Buckling has been observed at several operating points with different spatial and temporal motions. The deformations in the post-buckled regime are large and often complex, for this reason non-standard experimental techniques need to be employed. Only with these techniques, comparison with numerical and analytical models can take place. This work focuses on experimental investigations using several sensing elements, a laser vibration sensor, a fast video camera and a shaft encoder whose signals have be processed simultaneously to provide sufficient information about the 3D dynamics. The paper describes the experimental system, the data and signal processing methods for the non-stationary system and the unique dynamical behavior the system under dynamic buckling conditions.
Compressibility Effects in the Gas Phase for Unsteady Annular Two-Phase Flow in a Microchannel
Authors: Herescu Alexandru , Allen Jeffrey S.
Published: April 2008

High speed microscopy experiments investigating two-phase (gas-liquid) flow behavior in capillary-scale systems, that is, systems where capillary forces are important relative to gravitational forces, have revealed a unique unsteady annular flow with periodic destabilization of the gas-liquid interface. Standing waves develop on the liquid film and grow into annular lobes similar with those observed in low-speed two-phase flow. The leading face of the lobe will decelerate and suddenly become normal to the wall of the capillary, suggesting the possibility of a shock wave in the gas phase at a downstream location from the minimum gas flow section. Visualization of the naturally occurring convergent-divergent nozzle-like structures as well as a discussion on the possibility of shock wave formation are presented.
Design of a Multifunctional Aircraft Skin With Energy Harvesting via Entropy Generation Minimization
Authors: Ahlers K. , Hallinan K. P. , Sanders B. , McCarty R.
Published: April 2008

The Entropy Generation Minimization (EGM) approach is applied to the design of a new integrated radar aircraft skin, which both meets requisite aircraft structural needs and provides a pathway for the waste heat from structurally integrated power devices. Thermoelectric (TE) devices, sandwiched between a heterogeneous skin layer and the radar devices for the purpose of harvesting waste heat rejected to the ambient, are considered in the analysis. A heterogeneous skin layer is designed using the EGM approach, which is then applied to the overall mission of the aircraft to determine the optimal skin thickness and volume fractions of the matrix and inclusions in the composite skin.
Thermal Resistance of Nano Constrictions
Authors: Prasher Ravi , Tong Tao , Majumdar Arun
Published: April 2008

The advent of nanotechnology makes it possible to make constrictions of nanoscale size between contacting solids. For example devices or structures made of nanowires and nanoparticles can form a nano sized constriction. In these structures, the nanowires or nanoparticles are typically in contact with each other or another solid surface forming contact constrictions of the order of few nanometers. Understanding the thermal energy transport across the nano-constrictions is of critical importance in these applications. Our previous study derived the ballistic conductance across the constriction (Prasher, R.S., Nano Letters 5, 2155-2159 (2005)). In this paper, we further consider the wave effect of the phonons when crossing the constrictions. We show in the Rayleigh regime, where the dominant phonon wavelengths are much larger than the constriction sizes, the constriction conductance varies with temperature as T7
Computational Modelling of Fluid Flow in Radial Diffusers With Irregular Boundaries
Authors: Mariani Viviana Cocco , Prata Alvaro Toubes
Published: April 2008

Radial diffusers are the basic geometry for the automatic valves in reciprocating hermetic compressors. In the present work numerical solutions for the laminar isocoric flow in radial diffusers are performed to investigate the influence of some geometry modifications on the mass flow, rate and on the resultant force on the valve. The numerical model was able to handle irregular geometries making use of a regular mesh, and was validated through comparisons with experiments. Results are presented in terms of the effective flow and force area of valves which are important efficiency parameters for the modelling and design of reciprocating hermetic compressors. The efficiency parameters are presented and explored in terms of small modification of the valve geometry, for Reynolds numbers varying from 1000 to 2500 and two values of the gap between valve reed and valve seat. The flow was significantly affected by the geometry modifications, indicating that with little effort the performance of automatic valves can be substantialy improved. For instance, with a small chamfer of 5° at the outlet of the valve feeding orifice, the effective force area was increased by 30 percent.
Influence of Cellular Topology on Dynamic Response of Solid Foams
Authors: Alkhader Maen , Vural Murat
Published: April 2008

Current processing techniques enable the manufacture of cellular cores to prescribed cell sizes and densities. Moreover, the rapid advance in additive manufacturing techniques promises that, in the near future, the fabrication of functional cellular structures will be achieved with desired cellular topologies tailored to specific application in mind. In this perspective, it is essential to develop a detailed understanding of the relationship between mechanical response and topology in cellular structures. The present work reports the initial results of a computational investigation in this direction. The fundamental issues addressed in the present study are (i) generation of stochastic cellular structures by using Voronoi tessellations, (ii) quantitative measure of cellular topology, (iii) uniqueness of mechanical response, (iv) specimen size effect, (v) boundary effect, and (vi) high-strain-rate effects.
Heat Loss Analysis of Dross Removal in an Aluminum Furnace
Authors: Golchert Brian , Ridenour Paul , Selvarasu Naresh K. , Milovac Predrag , Zhou Chenn Q.
Published: April 2008

During the melting/production of aluminum, dross forms on the surface of the molten aluminum. Dross is a contaminant and an insulator so the aluminum industry regularly removes this dross from the aluminum surface. This is done by opening a door on the side of the furnace while the burners are still in operation and manually raking off the dross. As a result, a lot of heat is lost while the door is open. This lost heat depends upon the length of time the door is open and on the firing rate of the burners. This paper will present computational results on how much heat is lost while the door is open, the effect of this heat loss on the combustion space flow field, and the length of time needed to return to equilibrium conditions once the door is closed again.
Design of a Pneumatically Actuated Transfemoral Prosthesis
Authors: Sup Frank C. , Goldfarb Michael
Published: April 2008

This paper describes the design of an above-knee prosthesis with actively powered knee and ankle joints, both of which are actuated via pneumatic actuators. The prosthesis serves as a laboratory test-bed to validate the design and develop of control interfaces for future self-contained versions (i.e., with onboard hot-gas power and computing), and therefore includes a tether for both pneumatic power and control. The prototype prosthesis provides the full range of motion for both the knee and ankle joints while providing 100% of the knee torque required for fast cadence walking and stair climbing and 76% and 100%, respectively, of the ankle torque required for fast cadence walking and for stair climbing, based on the torques required by a healthy 75 kg subject. The device includes sensors to measure knee and ankle torque and position, in addition to a load cell that measures the interaction force and (sagittal and frontal planes) moments between the user and device.
Automation and Customization of Chip Scale Modeling for Electronic Packaging
Authors: Rebelo Nuno , Sinha Shashwat , Cadge David
Published: April 2008

Miniaturization in the electronics industry has made electronic packaging a very critical area of design and it has become crucial in gaining competitive advantage in a constantly evolving and dynamic market. One key to fast, reliable and economical electronic packaging design is quick modeling of the components and assemblies and accurate thermo-mechanical analyses. With quicker modeling there can be a greater focus on other analyses like fatigue, drop, shipping shock, moisture absorption/desorption etc. This paper presents ongoing work to automate a large part of electronic chip scale package modeling that can lead to a considerable reduction in lead time in modeling and can result in significant savings for the electronic industry. Through a host of ABAQUS scripts, modeling of multi-layered chip scale package (CSP) has been customized and has been made parameter based which can be easily manipulated by the user using ABAQUS/CAE. Solder ball modeling, which is a major component of the CSP modeling effort, is critical in analysis and consumes maximum time in chip-scale modeling due to its repetitive nature has also been automated and customized for ABAQUS/CAE. This approach can produce a big leap in chip scale modeling and analysis as the scripts can be embedded in larger automated systems that can result in a high degree of efficiency and cost saving. The paper thus discusses the methodology, scope and application of automation in CSP modeling.
Thermal Stratification and Mixing in an Open Water Pool by Submerged Mixtures of Steam and Air
Authors: Norman Timothy L. , Park Hyun-Sik , Revankar Shripad T. , Ishii Mamoru , Kelly Joseph M.
Published: April 2008

Phenomena associated with jet-plume condensation of steam-air mixtures in a large subcooled pool of water have implications in predicting global system parameters, such as the containment pressure, in light water reactors. A scaled down, reduced pressure suppression pool was designed to study condensation and mixing phenomena using scaled test conditions obtained from RELAP5 code results of a loss of coolant accident in a simplified boiling water reactor. Results from the experiments were compared with the TRACE code predictions which reveal deficiencies in the code to predict the pool thermal stratification as TRACE was not initially developed for predicting such phenomena. A dimensionless boundary map was plotted from several experimental runs of pure steam injection to determine conditions when the pool transits from being a homogeneously mixed volume to being a thermally stratified one. Steam-air mixture injection cases for single horizontal venting indicated that above a pool temperature of 40 °C with air mass flow rates below 0.1 g/s the pool can attain thermal stratification.
Synchronization of Motor Proteins Coupled Through a Shared Load
Authors: Hendricks Adam G. , Epureanu Bogdan I. , Meyho¨fer Edgar
Published: April 2008

Kinesin-1 is a processive molecular motor that converts the energy from adenosine triphosphate (ATP) hydrolysis and thermal fluctuations into motion along microtubules. This motion can be interpreted as a result of ATP-fueled nonlinear nonsmooth oscillations of coupled motor domains which interact with a microtubule to transport a cargo. This class of nano-scale motors transport cargoes for distances of several micrometers in cells. This transport can also be achieved in vitro, opening the possibility of developing robust and extremely versatile nano-scale actuators or sensors based on the machinery used by biological systems. These devices could be used in a range of nano-scale applications such as drug delivery and lab-on-a-chip. However, to design such systems, a quantitative, in-depth understanding of molecular motors is essential. Single-molecule techniques have allowed the experimental characterization of kinesin-1 in vitro at a range of loads and ATP concentrations. Existing models of kinesin movement are stochastic in nature and are not well suited to describing transient dynamics. However, kinesin-1 is expected to undergo transient dynamics when external perturbations (e.g. interaction with other kinesin molecules) cause the load to vary in time. It is thought that in the cell, several kinesin motors work cooperatively to transport a common load. Thus, a transient description is integral to capturing kinesin behavior. This paper presents a mechanistic model that describes, deterministically, the average motion of kinesin-1. The structure of the kinesin-1 molecule is approximated with a simplified geometry, explicitly describing the coupling between its two heads. The diffusion is modeled using a novel approach based on the mean first-passage time, where the potential in which the free head diffuses is time varying and updated at each instant during the motion. The mechanistic model is able to predict existing force-velocity data over a wide range of ATP concentrations (including the interval 1μM to 10 mM). More importantly, the model provides a transient description, allowing predictions of kinesin-1 pulling time-varying loads and coordinated transport involving several kinesin-1 molecules. The deterministic approach is validated by comparing results to experiments and Monte Carlo simulations of the stochastic dynamics. Furthermore, using this model, the synchronization of several kinesin-1 molecules transporting a common load is investigated. Novel methods to characterize synchronization, tailored to the particularities of these nonsmooth systems, are presented.
Analytical Solution of Turbulent Problems Using Governing Equation of Cosserat Continuum Model
Authors: Ghasvari-Jahromi H. , Atefi Gh. , Moosaie A. , Hormozi S.
Published: April 2008

In present paper the theory of the micropolar fluid based on a Cosserat continuum model has been applied for analysis of Couette flow and turbulent flow through rough pipes. The obtained results for the velocity field have been compared with known results from experiments done by Reichardt at Max Plank institute for fluids in Gottingen [1,2] and analytical solution of the problem from Gradient theory by alizadeh[3] for couette problem and with known results from experiments done by Nikuradse (1932). the boundary condition used here was the no slip one and Trostel's slip boundary condition[4].a good agreement between experimental results and the results of the problem for Reynolds near 18000 has beeen found in the couette case also in this case A new dimensionless number introduced that indicates the theoretical relation between cosserat theory and slip theory and their interaction. The solution has been performed for a Reynolds number of 106 for pipes with different values of roughness and the validity analysis approved by the results of Nikuradse's experiments.
Advanced Design and Experiment of a Micro Flywheel Energy Storage System With a High Temperature Superconductor Bearing
Authors: Lee Kangwon , Kim Bongsu , Ko Junseok , Jeong Sangkwon , Lee Seung S.
Published: April 2008

A micro flywheel energy storage system has been developed using a high temperature superconductor bearing. In the previous paper, the micro flywheel was fabricated and successfully rotated 38,000 rpm in the vacuum chamber. However, there are the large drag torque because of the non-axisymmetric magnetic flux of the motor/bearing magnet and the eddy current loss in the planar stator, which makes short spin-down time as 20~30 sec and coefficient of friction as 0.15. This paper presents the design, fabrication and electromagnetic analysis of the flywheel to reduce the large drag torque. The advanced flywheel is made up of motor and bearing magnet, aluminium disk, and magnetic screening disk. The maximum rotational speed is up to 51,000 rpm and furthermore the spin-down time is about 3 hr 20 min in the vacuum condition. From these results, the coefficient of friction is calculated as 0.001~0.002.
Locating Causes of Malfunctions in Energy Systems With Evolutionary Algorithms: A Global and a Local Approach
Authors: Toffolo Andrea , Lazzaretto Andrea
Published: April 2008

Energy system performance may differ from the expected one during actual operation because of the effects of faults, anomalies, wear and tear due to normal use. One of the main issues of diagnosis, i.e. the procedure to discover the causes of malfunctions, is to find the way back from measured altered performance to the original cause. Several procedures were proposed in the literature to solve the diagnostic problem, usually based on the comparison between a reference non-malfunctioning condition and an actual, possibly malfunctioning, condition. A different strategy is suggested in the paper. A direct search of the possible causes of malfunctions is performed by means of an evolutionary algorithm: a component fault is arbitrarily introduced in a model of the healthy system by substituting the reference characteristic curve with an altered one, and the algorithm is used to search for a combination of different kinds of performance modifiers that generates the same measured effects of the actual anomaly. A global and a local approach are proposed and applied to a real test case plant, also in presence of measurement noise. The local approach demonstrates to be more effective in terms of accuracy and computational effort.
Heat Removal and Thermophysical Properties of Biporous Evaporators
Authors: Semenic Tadej , Catton Ivan
Published: April 2008

This paper presents a study of different biporous evaporators as potential candidates for cooling high-power electronic devices. A biporous evaporator has two characteristic pore size distributions, which due to an enhancement in capillarity and vapor permeability greatly increase the critical heat flux (CHF) of the evaporator. In this work, eleven biporous evaporators are made by sintering together clusters of copper particles. Particles with diameters of 58, 76, 83, and 98μm are sintered into clusters with diameters of 302, 605, and 855μm. Clusters are subsequently sintered into evaporators with constant thickness-to-cluster diameter ratios of 3.3 and 0.32cm2 evaporator area. Finally, they are tested with degassed distilled water at 0.07bar. The highest CHF, 471W/cm2 at 149°C wall temperature and 104°C superheat, is measured for the 855/58 evaporator. A comparison of heat fluxes removed at a constant wall temperature of 125°C for all eleven evaporators shows that the highest heat flux of 388W/cm2 is removed with the 302/83 evaporator. A statistical regression analysis on heat fluxes at 125°C wall temperatures for all evaporators tested yields a correlation that relates the heat fluxes to cluster and particle diameters and is further used to predict a region of particle and cluster diameters with the highest heat flux.
Multi-Cell Homogenization of Elastic Periodic Domains
Authors: Gonella Stefano , Ruzzene Massimo
Published: April 2008

Recently, much attention has been devoted to the application of homogenization methods for the prediction of the dynamic behavior of periodic domains. One of the most popular techniques consists in the application of the Fourier Transform in space which allows the application of Taylor series approximations for low frequencies/long wavelengths. This method provides continuum equations which approximate the dynamic behavior of the considered periodic domain over a range of frequencies which is defined by the order of the considered Taylor series expansion. This technique is very effective, but suffers from two major drawbacks. First, the order of the Taylor expansion, and therefore the frequency range of approximation, is limited by the corresponding order of the continuum equations and by the number of boundary conditions which may be imposed in accordance with the physical constraints on the system. Second, the approximation at low frequencies does not allow capturing the band gap characteristics of the periodic domain. An attempt at overcoming the latter can be made by applying the Fourier series expansion to a macro cell spanning two (or more) irreducible unit cells of the periodic medium. This multi-cell approach allows the description of both average and intra-cell behavior of the domain, and approximates dispersion relations and corresponding dynamic properties at low frequencies and at frequencies close to the lower band gap. The resulting continuum equations are therefore capable of reproducing in part the band-gap characteristics of the structure. The proposed methodology is tested on simple one-dimensional and two-dimensional structures, which illustrate the method and show its effectiveness.
Kinetic Versus Static Frictional Torque Components in Threaded Fastener Applications
Authors: Nassar Sayed A. , Ganeshmurthy Saravanan , Yang Xianjie
Published: April 2008

This paper investigates the kinetic and static frictional torque components in threaded fasteners during the initial fastener tightening, subsequent torque audit, as well as during the loosening of previously tightened bolts. In less critical applications, the peak kinetic torque value is often used for predicting the bolt preload. The peak value of the tightening torque and its frictional components are mainly determined by the kinetic friction coefficients between the engaged threads and between the rotating nut (or head) and the joint surface. During subsequent quality inspection of the joint after its initial assembly, an audit residual torque value (in the tightening direction) is often used for predicting the residual fastener tension and joint clamp load, as well as for predicting the stability of the clamp load. In contrast with the peak kinetic torque, the audit torque and its thread and under head/nut frictional components are mainly determined by the static friction coefficients. In some cases, the careful application of a breakaway torque in the loosening direction (loosening torque) may be used as a measure for the residual clamp load; similar to the quality audit torque, the loosening torque is determined by the static friction coefficients of the bolted system. An experimental procedure and test set up are proposed to investigate the effect underhead contact radius, thread pitch, surface coating, and fastener head versus nut side tightening on the static and kinetic frictional torque components.
Study of the Effect of Hole Clearance and Thread Fit on the Self-Loosening of Threaded Fasteners
Authors: Nassar Sayed A. , Housari Basil A.
Published: April 2008

This study provides an experimental and theoretical investigation of the effect of hole clearance and thread fit on the self-loosening of tightened threaded fasteners that are subjected to a cyclic transverse service load. An experimental procedure and test set up are developed in order to collect real-time data on the rate of clamp load loss per cycle as well as the loosening rotation of the bolt head. Three levels of hole clearance are investigated; namely, 3%, 6%, and 10% of the bolt nominal diameter. For the commonly used 2A thread fit for a selected bolt size, three classes of the nut thread fit are considered; namely, 1B, 2B, and 3B. A simplified mathematical model is used for the analytical investigation of the effect of the hole clearance and thread fit on threaded fasteners self-loosening. The experimental and theoretical results are presented and discussed.
Magnetic Resonance Elastography Assessment of Focused Ultrasound Surgery in Cancer Models: A Pilot Study
Authors: Primak Svetlana V. , Le Yuan , Glaser Kevin J. , Reynold Carol A. , Lai Jinping , Roberts Lewis R. , Rossman Philip J. , Felmlee Joel P. , Ehman Richard L.
Published: April 2008

MRI guided focused ultrasound (FUS) has been shown to create thermal lesions where tissue stiffness changes significantly. To assess the correlation between tissue stiffness change and tissue ablation, a pilot animal based study was conducted to treat LNCaP tumors in vivo and Hep3B tumors immediately post mortem. MR elastography was used to analyze tissue stiffness before and after ablation. Treated tissue was excised immediately after each experiment and processed by routine histological analysis. Four prostate cancer tumors and four liver cancer tumors showed, on average, a threefold increase in stiffness due to FUS thermal treatment. Histology showed complete (100%) coagulation necrosis in these cases. These data suggest that MRE may be an effective means to assess tissue ablation.