bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effect of Elevated Temperatures on the Failure of Unfired Pressure Vessels
Authors: Langerman Michael A. , Larsen Gjermund , Pendleton Richard
Published: May 2008

The effect of elevated temperatures on the failure of pressure vessels constructed of mild steel was studied both analytically and numerically. This structural response issue is relevant to Homeland Security and tanks that are subjected to elevated temperatures from fires that result from blast or impact loading. Elevated temperature conditions may also be encountered during accidental fires, for example rural LPG tanks exposed to forest fires. For the analysis conducted, the material was assumed to behave in an elastic-plastic manner with linear hardening. The thermal loading for the results presented was based upon information relevant to a LPG (propane) vessel exposed to an external fire. Two-phase fluid conditions exist inside the vessel and, due to vapor/liquid stratification, the liquid occupies the lower region of the vessel whereas the vapor occupies the upper region of the tank. Due to the comparatively large thermal mass associated with the liquid phase, there can be a significant temperature gradient in the fluid and the wall between the lower regions of the tank and the upper regions occupied by the vapor. Results from the analyses indicate, as expected, that the pressure required to reach a fully plastic condition (tank failure) throughout the wall decreased almost linearly with increasing temperature. It was, however, somewhat surprising to find that the temperature gradient from the outside (hot) wall to the inside (cold) wall had little effect on the pressure required to reach the tank failure. Also considered in this study was the effect of tank wall thickness. A recent decision by ASME to decrease the design margin on its unfired pressure vessels from 4 to 1 to 3.5 to 1 allows the wall thickness on these vessels to be reduced by 12%. As discussed herein, results from analytical models indicate that this reduction in wall thickness will reduce the pressure required for tank failure by 0.6 MPa (∼90 psi). Results from the numerical model indicate that, when a two-dimensional temperature gradient is imposed on the wall adjacent to the liquid/vapor interface, a large thermal stress is induced that may increase the possibility for a BLEVE (Boiling Liquid Expanding Vapor Explosion), however more research is needed to confirm this possibilit. Results also indicate that wall thickness, in this case, has little effect on the wall reaching a fully plastic condition (assuming the internal tank vessel pressure to be at relief valve set pressure).
LES of Compressible Turbulent Annular Pipe Flow With a Rotating Wall
Authors: Lee Joon Sang , Xu Xiaofeng , Pletcher R. H.
Published: May 2008

Flow in an annular pipe with and without a wall rotating about its axis was investigated at moderate Reynolds numbers. The compressible filtered Navier-Stokes equations were solved using a second order accurate finite volume method. Low Mach number preconditioning was used to enable the compressible code to work efficiently at low Mach numbers. A dynamic subgrid-scale stress model accounted for the subgrid-scale turbulence. When the outer wall rotated, a significant reduction of turbulent kinetic energy was realized near the rotating wall and the intensity of bursting effects appeared to decrease. This modification of the turbulent structures was related to the vortical structure changes near the rotating wall. It has been observed that the wall vortices were pushed in the direction of rotation and their intensity increased near the non-rotating wall. The consequent effect was to enhance the turbulent kinetic energy and increased the intensity of the heat transfer rate there.
Investigation of the Spark Cycle Effect on Material Removal Rate in Wire Electrical Discharge Machining
Authors: Miller Scott F. , Shih Albert J.
Published: May 2008

The development of new, advanced engineering materials and the needs for precise and flexible prototype and low-volume production have made wire electrical discharge machining (EDM) an important manufacturing process to meet such demand. This research investigates the effect of spark on-time duration and spark on-time ratio, two important EDM process parameters, on the material removal rate (MRR) and surface integrity of four types of advanced material: porous metal foams, metal bond diamond grinding wheels, sintered Nd-Fe-B magnets, and carbon-carbon bipolar plates. An experimental procedure was developed. During the wire EDM, five types of constraints on the MRR due to short circuit, wire breakage, machine slide speed limit, and spark on-time upper and lower limits have been identified. An envelope of feasible EDM process parameters is created and compared across different work-materials. Applications of such process envelope to select process parameters for maximum MRR and for machining of micro features are presented.
Modeling of Metallic Sandwich Structures
Authors: Xue Zhenyu
Published: May 2008

All-metal sandwich construction holds promise for significant improvements in stiffness, strength and blast resistance for built-up plate structures. Analysis of the performance of sandwich plates under various loads, static and dynamic, requires modeling of face sheets and core with some fidelity. While it is possible to model full geometric details of the core for a few selected problems, this is unrealistic for larger complex structures under general loadings. A constitutive model can be proposed as an alternative means of modeling the sandwich core. The constitutive model falls within the framework of a compressible rate-independent, anisotropic elastic-plastic solid. In this paper, the model will be presented in details, along with numerical implementation in a finite element code, and benchmarks its performance against existing constitutive models.
Thermionic Electron Emission From Nanostructured Diamond
Authors: Chopra Vishal , Robinson Vance , Pfefferkorn Frank , Fisher T. S.
Published: May 2008

Unique features of electron emission from carbon-based nanostructures are studied to explore direct energy conversion materials and processes. These structures have been shown to produce highly efficient field emission (i.e., high electrical current at low applied fields) for electrical device applications. However, the commensurate transport and conversion of thermal energy has not been previously explored in detail. Understanding these concepts could enable development of devices with efficiencies that exceed those of other direct energy conversion technologies. The electron emission behavior at elevated temperatures, of two diamond-based devices with nanoscale features, is characterized. Bulk current measurements reveal work functions of 1 and 1.3 eV for a boron-doped diamond pyramid array and a phosphorus-doped diamond surface, respectively. An electron energy spectrometer has been designed in order to understand the emission behavior in more detail. The analyzer is integrated with a heat source that enables substrate temperatures up to 1000°C. Spectral measurements indicate higher work functions for both samples.
Quasi-Steady State Numerical Model for a Multilayer Thin Film Irradiated by a Moving Laser Source at High Peclet Numbers
Authors: Bianco Nicola , Manca Oronzio , Naso Vincenzo , Rotondo Giuseppe
Published: May 2008

A numerical analysis of the conjugate optical-thermal fields in an amorphous silicon thin film deposited on a glass substrate and irradiated by a moving Gaussian laser source is carried out. The velocity of the laser is assumed constant and quasi-steady state conditions are considered. Optical and thermophysical properties of materials are assumed temperature dependent. The conjugate optical and thermal models are solved by means of a finite volume numerical technique and the heat conduction along the direction of motion has been neglected. The optical field is considered locally one-dimensional and it has been solved by means of the matrix method. Results are given in terms of radiative coefficients, absorption function distribution and temperature profiles and fields. The effect of the relative velocity and of the thin film depth are analyzed. For the considered model, radiative coefficients profiles show that for the largest thin film thickness, reflectance values do not depend very much on the Peclet number and on the x coordinate. Temperature profiles point out that the maximum temperature values are attained for an intermediate thin film thickness among the three considered values. This is due to the interference effects within the thin film that cause the maximum energy absorption for this thickness.
Scale Analysis of Combined Radiation and Convection
Authors: Kottke Peter A. , Ferguson Timothy P.
Published: May 2008

Relationships predicting heat transfer results in limiting cases of the complicated problem of combined convection and radiation in boundary layer flows are sought using the method of scale analysis. Key nondimensional groups are developed that help identify the fundamental interaction between radiation and convection heat transfer for two cases of laminar, aiding, two-dimensional, forced and natural convection heat transfer from a semi-infinite vertical wall with radiation effects included. The first case considered is that of heat transfer from a gray wall with a specified heat flux to a nonparticipating medium. The second case is that of heat transfer from a black wall with a specified temperature to an optically thick, gray, non-scattering medium. The scale analysis results are presented in terms of the local Nusselt number and verified using similarity models.
Simulation of Multiphase Turbulent Fluid Flow Through an Electrolytic Cell
Authors: Akberov Roald , Ponyavin Valery , Chen Yitung , Hsieh Hsuan-Tsung , Pepper Darrell W.
Published: May 2008

A Finite Volume Method was applied to a two-dimensional model for multiphase turbulent fluid flow inside an electrolytic cell. The model is based on solving the momentum equations for the single continuous liquid phase. In the model, solid particles and hydrogen gas bubbles are treated as inert spherical particles. Once the momentum equations are solved, trajectories of the particles can be calculated by integrating the force balance on the particle, which can be expressed in a Lagrangian reference frame. Turbulence is modeled via utilizing the standard k-ε model. The paper also discusses the computational meshes, which can be used for the simulation. It is shown that usage of the boundary layer type elements decreases the total number of computational nodes while maintaining the same accuracy in calculation. It is also shown that minute changes in the geometry of the cell, such as an increase in the thickness of the plate, results in obtaining more favorable flow patterns for taking solid particles away from the electrolytic cell.
Hybrid Genetic Algorithm: A Robust Parameter Estimation Technique and Its Application to Heavy Duty Vehicles
Authors: Xiao Jie , Kulakowski Bohdan
Published: May 2008

This study aims at establishing an accurate yet efficient parameter estimation strategy for developing dynamic vehicle models that can be easily implemented for simulation and controller design purposes. Generally, conventional techniques such as Least Square Estimation (LSE), Maximum Likelihood Estimation (MLE), and Instrumental Variable Methods (IVM), can deliver sufficient estimation results for given models that are linear-in-the-parameter. However, many identification problems in the engineering world are very complex in nature and are quite difficult to solve by those techniques. For the nonlinear-in-the-parameter models, it is almost impossible to find an analytical solution. As a result, numerical algorithms have to be used in calculating the estimates. In the area of model parameter estimation for motor vehicles, most studies performed so far have been limited either to the linear-in-the-parameter models, or in their ability to handle multi-modal error surfaces. For models with nondifferentiable cost functions, the conventional methods will not be able to locate the optimal estimates of the unknown parameters. This concern naturally leads to the exploration of other search techniques. In particular, Genetic Algorithms (GAs), as population-based global optimization techniques that emulate natural genetic operators, have been introduced into the field of parameter estimation. In this paper, hybrid parameter estimation technique is developed to improve computational efficiency and accuracy of pure GA-based estimation. The proposed strategy integrates a GA and the Maximum Likelihood Estimation. Choices of input signals and estimation criterion are discussed involving an extensive sensitivity analysis. Experiment-related aspects, such as imperfection of data acquisition, are also considered. Computer simulation results reveal that the hybrid parameter estimation method proposed in this study shows great potential to outperform conventional techniques and pure GAs in accuracy, efficiency, as well as robustness with respect to the initial guesses and measurement uncertainty. Primary experimental validation is also implemented including interpretation and processing of field test data, as well as analysis of errors associated with aspects of experiment design. To provide more guidelines for implementing the hybrid GA approach, some practical guidelines on application of the proposed parameter estimation strategy are discussed.
Vehicle Consumption Evaluation Using Simulation Models Reproducing Gear Management Strategies
Authors: Capitani Renzo , Delogu Massimo , Orofino Luigi
Published: May 2008

The object of this article is the study of the estimated consumption of mean class vehicles through the development of a simulation model, which recreates the behavior of the test driver-vehicle on a predefined mission. The aim of such a model is to reproduce the management of the gears on a defined test ground allowing for the realization of a sensibility analysis regarding some vehicle parameters and to determine the optimum ones for the minimization of consumption depending upon the considered vehicle. The provisional model developed has been realized by integrating a simplified model of the dynamic of the vehicle with an expert system based on Artificial Neural Networks. It is able to reproduce logic and strategies of the test driver for the choice of the gear change.
Nanoparticulate and Interfacial Mechanics in Confined Geometries Typical of Chemical-Mechanical Planarization
Authors: Ng S. H. , Zettner C. M. , Zhou C. , Yoon I.-H. , Danyluk S. , Sacks M. , Yoda M.
Published: May 2008

Chemical-mechanical planarization (CMP), a surface preparation process used widely in integrated circuits manufacture, is currently the leading nanoscale manufacturing process worldwide, with an annual economic impact well in excess of $1 billion. Originally developed for glass polishing, CMP is used by the microelectronics industry to create silicon, silicon oxide, tungsten and copper surfaces with average roughnesses of O(10 mm). The process typically involves shearing a dilute abrasive silica or ceria nanoparticle-laden “slurry” between a compliant rough surface (the “pad”) and the surface to be polished (the “wafer”). The composition of the slurry can greatly affect material removal rates. Despite its importance, however, a lot still remains to be discovered about the fundamental mechanisms involved in this process. A multidisciplinary effort at Georgia Tech has focused upon the interfacial mechanics of this process and how nanoparticles chemomechanically wear SiO2, Si and Cu surfaces. It has been found, for example, that the wear rate of dielectric varies approximately as the particle diameter. The entrapment of particles at the asperity/dielectric interface is thought to produce the polishing, but the exact nature of this interaction is still unknown. An evanescent-wave visualization technique has therefore been developed to visualize the dynamics of fluorescent 300–500 nm diameter colloidal silica and polystyrene particles within a particle diameter of the “wafer” surface in a simplified model pad-wafer geometry. The technique has been used for the first time to the authors’ knowledge to directly measure the velocity and concentration of the interfacial particles—which presumably interact with and wear the wafer. Although the pad speeds in these studies are much lower than those encountered in the actual CMP process, the initial results suggest that there is negligible “slip” between the particle and fluid phase velocities at the wafer surface. The number of particles at the wafer surface appears, however, to be strongly affected by particle properties, including particle density and size.
Strategies for Improving Reliability of Solder Joints on Power Semiconductor Devices
Authors: Lu Guo-Quan , Liu Xingsheng , Wen Sihua , Calata Jesus Noel , Bai John G.
Published: May 2008

There has been a significant research effort on area-array flip-chip solder joint technology in order to reduce package footprint, enhance current handling capability, and improve heat dissipation. However, there is a lingering concern over cyclic fatigue of solder alloys by thermo-mechanical stresses arising from mismatched thermal expansion coefficients of expansion among the various components of the package. In this paper, some strategies taken to improve the reliability of solder joints on power devices in single-device and multi-chip packages are presented. A strategy for improving solder joint reliability by adjusting solder joint geometry, underfilling and utilization of flexible substrates is discussed with emphasis on triple-stacked solder joints that resemble the shape of an hourglass. The hourglass shape relocates the highest inelastic strain away from the weaker interface with the chip to the bulk region of the joint while the underfill provides a load transfer from the joints. Flexible substrates can deform to relieve thermo-mechanical stresses. Thermal cycling data show significant improvements in reliability when these techniques are used. The design, testing, and finite-element analyses of an interconnection structure, termed the Dimple-Array Interconnect (DAI), for improving the solder joint reliability is also presented. In the DAI structure, a solder is used to join arrays of dimples pre-formed on a metal sheet onto the bonding pads of a device. Finite-element thermo-mechanical analyses and thermal cycling data show that the dimple-array solder joints are more fatigue-resistant than the conventional barrel-shaped solder joints in flip-chip IC packages.
Wire Fatigue Models for Power Electronic Modules
Authors: Meyyappan Karumbu Nathan , Hansen Peter , McCluskey Patrick
Published: May 2008

This paper presents two, semi-analytical, physics-of-failure based life prediction model formulations for flexural failure of wires ultrasonically wedge bonded to pads at different heights. The life prediction model consists of a load transformation model and a damage model. The load transformation model determines the cyclic strain is created by a change in wire curvature at the heel of the wire resulting from expansion of the wire and displacement of the frame. The damage model calculates the life based on the strain cycle magnitude and the elastic-plastic fatigue response of the wire. The first formulation provides quick calculation of the time to failure for a wire of known geometry. The second formulation optimizes the wire geometry for maximum time to failure. These model formulations support virtual qualification of power modules where wire flexural fatigue is a dominant failure mechanism. The model has been validated using temperature cycling test results.
Application of an Advanced Frequency Domain Identification Method for Modelling of Flexible-Link Manipulators
Authors: Lai G. M. Y. , Ziaei K. , Wang D. W. L. , Heppler G. R.
Published: May 2008

This paper investigates the Comprehensive Identification from FrEquency Responses (CIFER) technique as a system identification tool for the Single Flexible Link (SFL) manipulator system. Frequency responses are identified for both the constrained and unconstrained motions. For the constrained case, two sets of frequency responses are identified based on actual contact force and an approximated contact force obtained through strain gauges readings. Identification results from CIFER® are compared to those from the Empirical Transfer Function Estimate (ETFE).
In-Plane Deformation Measurements Using Digital Image Correlation of Ultrasonic C-Scan Images
Authors: Regez Brad , Zhang Ying , Chu Tsuchin , Mahajan Ajay
Published: May 2008

The extension of digital image correlation method to ultrasonic C-scan acoustical speckle images of the bulk is presented in this paper. The approach discussed in this paper is ideally suited to composite materials such as particulate composites, fiber-reinforced plastics, and laminated composites. It can also be effectively employed for critical surfaces that are not within view, such as interfaces and back surfaces. Images taken prior to and after deformation are analyzed to estimate a deformation profile from changes in the image. The aim of the method is to find the displacements and strains of small subsets from the second image relative to the first one. This is accomplished by comparing the intensity levels of the subsets in the images. The speed and accuracy of the system is enhanced by the genetic algorithms(GAs) which are used to optimize correlation of images. An ultrasonic C-scan system was used to obtain the intensity images of the front or back surface of an isotropic or composite material. Three experimental tests were conducted to illustrate the application of Ultrasonic C-scan digital image correlation method. These tests include: 1) uniform translation, 2) small angle rotation, and 3) uniform deformation. A laminated carbon/epoxy composite panel (305×305×8 mm) was used for uniform translation and small angle rotation tests. A rubber specimen was used to perform the uniform axial deformation test. The results of correlated displacements (angles) are compared to the actual displacements (angles). The accuracy and applied limitation of the three experiments are also illustrated in this paper.
Habitat Operated Utilizing Solar Energy (HOUSE)©: A Grid-Independent 100% Solar-Powered Residential Dwelling
Authors: Martin Russell W. , Howell Stephen C. , Jones Rory J. , Bhavnani Sushil H.
Published: May 2008

It is quite a technological challenge to provide 100% of the electric and heating/cooling needs of a residence using solar energy alone. While the economics of using solar energy exclusively for all these needs is not currently feasible, it is worth exploring the engineering feasibility so as to provide a roadmap for future use as fossil fuel reserves continue to dwindle. A prototype 500 sq-ft Habitat Operated Utilizing Solar Energy (HOUSE©) was designed and constructed to provide all the amenities associated with comfortable living, including all necessary living spaces such as a living room, bedroom, kitchen, bathroom, and dining room. The house was powered by 36 roof-mounted photovoltaic modules in tandem with two 8’ × 4’ flat-plate collectors. Electric energy was stored in a 48V battery bank while thermal energy was stored in an 80-gal tank. The HOUSE was field-tested for a week in early October in an attempt to obtain performance data. The performance period included a variety of weather conditions from sunny and clear, to rainy and overcast. The paper provides information on insolation and use of energy during that period. The overall result for the week-long evaluation showed a net positive energy balance proving the technical feasibility of the concept. Data on air/water temperatures, and relative humidity will also be presented.
Parametric Study of Phase Change Suspension Flow in Microchannels
Authors: Hao Y. L. , Tao Y.-X.
Published: May 2008

A continuum model is applied to the numerical simulation of the laminar hydrodynamic and heat-transfer characteristics of suspension with phase change material (PCM) particles in a microchannel. The analytical/numerical formulation based on CFD modeling technique, and the computer code is developed. Local wall-to-suspension heat transfer coefficients are calculated by the simultaneous solution of the conservation of mass, momentum and thermal energy equations. By providing detailed information on the local behavior of the wall-to-suspension heat transfer coefficients, preliminary calculations expose that there exists a particle-depleted layer next to the wall under the laminar flow condition. It plays an important role on the heat transfer between the suspension and the wall under the laminar flow condition. The heat transfer coefficient increases and reaches a peak value in the melting region. The benefits on the enhancement of heat transfer and the reduction of wall temperature and mean temperature by employing the MCPCM particle are mainly in the melting region. The preliminary results agree very well with the experimental observations and measurement on the flow and heat transfer of microencapsulated PCM slurry in circular duct. It interprets the observation in the literature where heat transfer between the suspension and the wall is weaker in non-melting region and melted region than that between the pure fluid and the wall for laminar flow conditions.
An Integrated, Near Real-Time, Web-Based Data Acquisition and Management System for Air Quality Prediction for Las Vegas Valley, Nevada
Authors: Sun Lijian , Lei Steven , Hsieh Hsuan-Tsung , Chen Yitung , Pepper Darrell W.
Published: May 2008

Clark County, Nevada has been criticized by US Environmental Protection Agency (US EPA) for its un-attainment air quality problem for particulate matters (PM 10 and PM 2.5) and ozone (O3) and carbon monoxide (CO). The Department of Air Quality Management (DAQM), Clark County, the regulatory and enforcement agency, is required by the US EPA to measure and report to the public the impact of aeroallergens as well as visibility and haze issues. From the long-term observation, air quality in the Las Vegas Valley is also influenced by those pollution from the neighboring states, currently around 30 monitoring stations through out the county have been in service for years to continuously monitor meteorological condition and provide valuable air quality information to the public in a timely fashion. Since the existing monitoring system was not designed to collect and process large amount of data set at a short time period, the agency cannot flexibly acquire higher resolution data sets as well as any non-scheduled data collection. Meanwhile, the much-needed data presentation and reporting features were not considered for the past. To ensure that Clark County will reach and maintain attainment of all federal air quality standards, the Nevada Center for Advanced Computational Methods (NCACM) at University of Nevada, Las Vegas (UNLV) is required by the DAQM to design a new system that can provide a multi-function data acquisition and management system. By characterized the deficiencies in the existing system, the NCACM redesign the current system that will provide a web-based work environment with new communication, model simulation and database management modules. More remote control capabilities are also included in the new system. The application will be more scalable, flexible and maintainable. The system is defined into four distinct tiers, data acquisition, data repository, data analysis and forecasting and data presentation tiers. After the 9–11 terrorist attacks, emergency response for any major cities around the country becomes a vital issue for homeland security. Through the timely data acquisition support, the system can return high-resolution data from monitoring stations for efficient model simulation. While continuously meteorological data feeding through the network, the NCACM’s newly configured Beowulf PC-clustering system calculates the possible transportation scenario around the valley and returns the best emergency scenario analysis.
Singularity Issue in Dimensional Variation Diagnosis of Multi-Station Assembly Processes
Authors: Ding Yu , Gupta Abhishek , Apley Daniel W.
Published: May 2008

This paper presents a new method of diagnosing variation components of process error sources in a manufacturing system. Quite often in a complex multi-station assembly system only limited numbers of sensors are present due to which complete information of fixture errors is unavailable. This makes the system of variance components singular and not solvable by using regular least-squares estimation. The method suggests reformulation of the original error propagation model into a variation relation by using a matrix transformation. With the development of a new variation estimator and its diagnosability condition, some singular systems that are not diagnosable using traditional least squares methods become diagnosable. Difference between the new approach and the traditional approaches has been elaborated. Modified procedures of the new estimator are also presented to enhance its estimation performance. The idea is presented in the specific context of panel assembly processes, but the application of the idea should not be limited therein. Conclusions can be extended to general discrete-part manufacturing processes where fixtures are extensively used to ensure dimensional accuracy of the final product.
A Comparison of Two Solution Techniques for the Inverse Problem of Simultaneously Estimating the Spatial Variations of Diffusion Coefficients and Source Terms
Authors: Colac¸o Marcelo J. , Orlande Helcio R. B. , Dulikravich George S. , Rodrigues Fabio A.
Published: May 2008

This work deals with the simultaneous estimation of the spatially varying diffusion coefficient and of the source term distribution in a one-dimensional nonlinear diffusion problem. This work can be physically associated with the detection of material non-homogeneities such as inclusions, obstacles or cracks, heat conduction, groundwater flow detection, and tomography. Two solution techniques are applied in this paper to the inverse problem under consideration, namely: the conjugate gradient method with adjoint problem and a hybrid optimization algorithm. The hybrid optimization technique incorporates several of the most popular optimization modules; the Davidon-Fletcher-Powell (DFP) gradient method, a genetic algorithm (GA), the Nelder-Mead (NM) simplex method, quasi-Newton algorithm of Pshenichny-Danilin (LM), differential evolution (DE), and sequential quadratic programming (SQP). The accuracy of the two solution approaches was examined by using simulated transient measurements containing random errors in the inverse analysis.
A Discontinuous Finite Element Method for Non-Fourier Heat Conduction Problems
Authors: Ai X. , Li B. Q.
Published: May 2008

A discontinuous Galerkin finite element method is presented for the solution of non-Fourier heat conduction problems that arise from the thermal processing of thin films using the ultra-short pulsed lasers. Mathematical formulation is described in detail and computational procedures are given. Numerical example are given and compare with available solutions where available. The numerical solutions exhibit strong wave behavior and reflection and interactions of thermal waves at the boundaries in multi-dimensions.
Experimental Study of Frost Formation on a Flat Surface Under Nature Convection
Authors: Hao Y. L. , Tao Y.-X. , Iragorry J. , Castro D.
Published: May 2008

A series of experiments were conducted to investigate the frost formation and characteristics on a flat surface under natural convections. The process of frost formation and structures is visibly observed and measured by using of a microscope. The temperature distribution of the air around the frost layer is measured by using of the holographic interferometry technique. The influences of the main parameters are analyzed. Especially, the microscopic analysis of frost growth on the surface characteristics on the microscopic characteristics of a frost layer during the early growth period when sub-cooled droplets are formed and changed to the ice. The thickness and mass of frost layer are measured while frost formation is visualized simultaneously. The results show that the frost surface temperatures are much lower than the freezing temperature and close to the cold surface temperature at the early growth period. After the early growth period, the frost surface temperature is dominated by the convective heat transfer between the frost surface and surrounding air.
A Numerical Technique for Modeling Thermoelectric Cooler With Temperature Controller for Steady State CFD Applications
Authors: Karimanal Kamal V. , Ellsworth Michael J. , Refai-Ahmed Gamal
Published: May 2008

A Thermo Electric Cooler (TEC) model was incorporated to a CFD software program by imposing heat absorption, heat rejection and Joule heat generation source terms to the appropriate geometric regions. The above-mentioned source terms are functions of current input and local temperature. These functions were incorporated as User Defined Functions (UDF) to the software program. If the objective is to achieve a desired temperature at the centroid location of the heat absorption side (cold side), the current input to the TEC is an unknown that depends on the boundary conditions. Hence the current parameter was posed as an unknown variable in the UDF and was iteratively solved so that the set point temperature is attained. The source terms and the feedback control were implemented in Finite Volume Method (FVM) based CFD software Icepak. FVM simulation predictions were compared with the results from a 1-D global energy balance model that was solved using TK solver program. Acceptable agreement between the two approaches is reported. While the 1-D model can be used for quick calculation under assumed simplistic scenarios, the CFD implementation can be applied to system level flow and energy simulations.
Experimental and Numerical Study of Solidification in Constant and Oscillating Temperature Gradients
Authors: Shu Y. , Li B. Q.
Published: May 2008

Transient finite element models are developed to describe solidification of materials in constant and oscillating temperature gradients. Both moving grids and fixed methods are applied, with the former intended to model the near-planar solidification front, while the latter for complex solid-liquid interface morphology. Extensive numerical simulations are conducted for various configurations. To validate the model predictions, an experimental system has been set up with Succinonitrile (SCN) as a working fluid. The melt flows and solidification are measured using a laser PIV system. The measurements are compared well with numerical results obtained from the numerical models. Reasonably good agreement between the experimental measurements and numerical simulations is obtained.
Numerical Simulation of Hydrocarbon-Hydrogen Reaction Chemistry in a CVD Reactor
Authors: Garg R. K. , Gore J. P. , Fisher T. S.
Published: May 2008

In the present work, gas-phase reactions for three different hydrocarbon-hydrogen mixtures (CH4+H2, C2H2+H2 and C2H4+H2) in the presence of volumetric energy input were simulated in a chemical vapor deposition (CVD) reactor. The goal of the simulations is to estimate the concentrations of species responsible for the formation of carbon nanotubes (CNTs). These estimates are expected to aid in understanding fundamental mechanisms of CNT formation and in controlling the synthesis process through process parameters such as inlet composition and temperature of the mixture, reactor pressure and microwave power. The simulation employs gas-phase kinetics of the GRI-2.11 mechanism with only reactions involving neutral molecules that contain C and H atoms. The results indicate that the concentrations of H radicals and C atoms increase with increases in energy deposition rate.
Damage Relationships for BGA Reliability in Harsh Environments
Authors: Lall Pradeep , Islam Nokibul , Suhling Jeff , Darveaux Robert
Published: May 2008

Fine-Pitch BGAs and underfills have been used in benign office environments and wireless applications for a number of years, however their reliability in automotive underhood environment is not well understood. In this work, the reliability of fine-pitch PBGA packages has been evaluated in the automotive underhood environment. Experimental studies indicate that the CTE as measured by TMA typically starts to change at 10–15°C lower temperature than the Tg specified by DSC potentially extending the change in CTE well into the accelerated test envelope in the neighborhood of 125°C. High Tg substrates with glass-transition temperatures much higher than the 125°C high temperature limit are therefore not subject to the effect of high coefficient of thermal expansion close to the high temperature of the accelerated test. Darveaux’s damage relationships [1992, 1995, 2000] were derived on CBGA assemblies, with predominantly SMD pads and 62Sn36Pb2Ag solder. In addition to significant differences in the crack propagation paths for the two pad constructions, SMD pads fail significantly faster than NSMD pads in thermal fatigue. The thermal mismatch on CBGA’s is much larger than PBGA assemblies. Crack propagation in CBGA’s is often observed predominantly on the package side as opposed to both package and board side for PBGAs. In the present study, crack propagation data has been acquired on assemblies with 15 mm, 17 mm, and 23 mm size plastic BGAs with NSMD pads and 63Sn37Pb on high-Tg printed circuit boards. The data has been benchmarked against Darveaux’s data on CBGA assemblies. Experimental matrix also encompasses the effect of BT substrate thickness on reliability. Damage constants have been developed and compared against existing Darveaux Constants. Prediction error has been quantified for both sets of constants.
GL-Link: A Novel Telerobotics-Based Platform Supporting Distributed Mechatronic Research Via the Internet
Authors: Singh Surya P. N. , Waldron Kenneth J.
Published: May 2008

Mechatronics and robotics research efforts of large complexity are increasingly interdisciplinary involving collaboration between software, hardware, controls, and scientific teams. Traditionally, the level of integration has either required repeated site-visits or location of the teams at a common site. As the teams become increasingly diverse and disperse, there is a need for distributed operations platform that not only facilitates smooth communications, but also allows for remote experimentation and control of a common robot or device. By separating the principal design functions, a modular communications platform was developed to support the distance learning and experimental requirements of ambitious mechatronic development projects. This separation results in a modular system that is scalable and customizable to the particular conditions governing an experiment. The platform leverages off-the-shelf hardware and software and the presence of Internet connectivity. Where possible, open-source options were used to make the platform extensible to a variety of platforms and applications. The system is modular and consists of: a video observation/conferencing module, a file-transfer module, and a robot teleoperation module. This allowed multiple teams to test the operation of a robot independently and asynchronously without corrupting the work being conducted by another team member. It also allowed for new forms of interaction and reduced the need for travel between the multiple geographically-distributed research teams. Novel features of this work include a modular multiplatform architecture and an integration of basic telerobotics principles to extend PC-based collaboration/conferencing technologies from a basic communications platform to a means for supporting multi-site (robotics) research experiments. This paper describes the design considerations and evaluations associated with the development of the Great Little Inter link (GL-Link) architecture. This platform was motivated by robotics research ongoing between Stanford and Ohio State Universities. The platform was tested over several months as part of the design of a high-speed quadruped robot. Results from this trial highlight the impact of highly sensitive audio and video inputs and show the need for robustness to bandwidth fluctuations.
Mechanics of Direct Wafer Bonding
Authors: Turner K. T. , Spearing S. M.
Published: May 2008

Direct wafer bonding, also known as fusion bonding, has emerged as a key process in the manufacture of microelectromechanical systems (MEMS). The use of wafer bonding increases design flexibility, allows integration of dissimilar materials, and permits wafer-level packaging. While direct wafer bonding processes are becoming more prevalent in the fabrication of MEMS devices, failure during the bonding process is often a problem and is not completely understood. A modeling framework, based on the mechanics of the bonding process, has been on the mechanics of the bonding process, has been developed to correlate bonding failure to wafer geometry, surface condition, and etch patterns. The modeling approach is based on an energy balance between the reduction in surface energy as the bond is formed and the strain energy that is stored in the wafers as they conform to each other. The model allows the effect of flatness deviations, wafer geometry (i.e. thickness, diameter), wafer mounting, and etched features on the bonding process to be shown. Modeling results demonstrate that wafer bow, wafer thickness, and certain types of etch patterns are critical factors in controlling bonding success. Bonding experiments, in which specific flatness deviations and etch patterns have been introduced on wafers prior to bonding, have been carried out and compared to the modeling results. The understanding of the process gained through the modeling can be used to set tolerances on wafers, assist in mask layout, and guide the design of bonding equipment to ensure success in direct wafer bonding processes.
Simulation of the Milling Process for CAM Applications
Authors: Che´rif Mehdi , Furet Benoiˆt , Thomas Herve´ , Hascoe¨t Jean-Yves
Published: May 2008

CAD/CAM systems require technical data to model the tool and machined workpiece behavior during the cutting process. The large varieties of machining input data prevent exhaustive studies for each machining operation. The purpose of this paper is to analyze the most influent parameters (ie. rake angle, cutting speed and hone radius) on cutting force during the milling process in order to limit experiment testing while providing accurate data for the CAD/CAM requirement. Simulation results based on modified Altan’s approach are compared with experimental measurement for three different materials (AISI P20, AISI H11 and 2024 aeronautic alloy) and varying insert geometries (different rake angles and hone radius) are tested.
Adaptive Control of a Simulated MEMS Gyroscope
Authors: Khasawneh Qais A. , Batur C.
Published: May 2008

Micro Electro Mechanical Systems (MEMS) are playing a significant role in industry because of their small size, small weight, and low power consumption. The vibrating gyroscope is one of those MEMS devices that will have significant impact in stability control of cars. This paper studies the design and control of a vibrating gyroscope. The device has been constructed in Pro-E environment and its model has been simulated in finite element domain in order to approximate its dynamic characteristics with a lumped model. An adaptive feedback control system that guarantees the stability of the device and consistent measurement of angular velocity has been constructed and simulated.
Built-In Inspection Using Mechanical Energy Converting Elements
Authors: Volkovas Vitalijus
Published: May 2008

The paper presents a conversion model of the mechanical energy into the electrical one and shows that autonomic diagnostic devices can be developed on that basis. Built-in inspection uses these devices working on the conversion of the mechanical energy of vibration, applying for this reason piezoelectric matrices connected with the mechanical system, which are investigated theoretically and experimentally. It is shown that converters made of piezoelectric ceramics or film can work reliably enough by being placed directly in the objects to be inspected. Relative precision and abilities of the energy conversion for monitoring and diagnostic problem can be evaluated by simulating the dynamics of a general model according to the technical state of a mechanical system. It is suggested a concrete solution for the technical state monitoring and cracks diagnostics of constructive elements in different mechanical systems.
Thermal Performance Optimization of RF Packages for Wireless Communication
Authors: Chiriac Victor Adrian , Lee Tien-Yu Tom , Hause Vern
Published: May 2008

The increasing trend in power levels and associated densities leads to the need of design thermal optimization, either at the module level or at the system (module-board stack-up) level. The wireless communication industry is facing multiple challenges as it tries to promote smaller, faster and cost-effective packages, yet trying to cope with potential thermal bottlenecks. The present study investigates a new family of packages, whose thermal and electrical performances are far superior to the classic (standard) packages. A 3-D conjugate numerical study was conducted to evaluate the thermal performance of Gallium Arsenic (GaAs) die packaged in Quad Flat No Lead (QFN) packages for various wireless and networking applications. Two different QFN packages are investigated: a standard package and a Power package (PQFN) with thicker leadframe and solder die attach. The thermal impact of die attach material, leadframe thickness, die pad size, and board structure is evaluated and provides valuable information for product designers. Two powering scenarios are investigated: 1) one for standard operating parameters and 2) an alternative for extreme operating powering scenarios. Results indicate that the peak temperature reached on the die for 3×3 mm QFN under normal powering conditions is ∼138.5°C (or 119°C/W junction-to-air thermal resistance), while for the extreme scenario, the junction temperature is ∼186°C (or 125°C/W junction-to-air thermal resistance). In both cases, the top Au metal layer has a limited impact on lateral heat spreading. Under extreme powering conditions, the 5×5 mm PQFN package reaches a peak temperature of ∼126°C (66°C/W thermal resistance). A ∼32% reduction in peak temperature is achieved with the 5×5 PQFN package. The improvement is mainly due to the larger package size, high conductivity die attach material, thicker leadframe and more board thermal vias. A parametric study shows that the increase in leadframe thickness from 0.2 mm (8 mils) to 0.5 mm (20 mils) in the QFN package will lead to only 3% reduction in peak temperature. By comparison, for both packages, the die attach material (conductive epoxy vs. solder) will have a significant impact on the overall reduction in peak temperature (∼12%). Experimental measurements using an Infrared (IR) Microscope are performed to validate the numerical results. The results indicate good agreement (∼6% discrepancy) between the numerical model and the measurement.