bluuebunny/crossref_metadata_2025 huggingface dataset:
An Experiment to Determine the Accuracy of Squeeze-Film Damping Models in the Free-Molecule Regime
Authors: Sumali Hartono
Published: May 2009

Current published models for predicting squeeze film damping (SFD), which are based on different assumptions, give widely different results in the free-molecule regime. The work presented here provides experimental data for validating SFD models in that regime. The test device was an almost rectangular micro plate supported by beam springs. The structure was base-excited. The rigid plate oscillated vertically while staying parallel to the substrate. The velocities of the plate and of the substrate were measured with a laser Doppler vibrometer and a microscope. The damping ratio was calculated by performing modal analysis of the frequency response functions. The test structures were contained in a vacuum chamber with air pressures controlled to provide a five-order-of-magnitude range of Knudsen numbers. The damping coefficients from the measurements were compared with predictions from various published models. The results show that the continuum-base Reynolds equation predicts squeeze-film damping accurately if used with correct boundary conditions. The accuracy of molecular-based models depends heavily on the assumptions used in developing the models.
Curvature Based Metrics for Interpreting Warpage and Predicting Reliability in Second Level Interconnects
Authors: Meyyappan Karumbu Nathan , Cho Steve
Published: May 2009

The authors in this paper have proposed a new methodology to predict curvature from depth data. This is a whole field methodology that measures curvature by the method of fitting surfaces through moving patches. Ability to estimate curvature and localized bend modes or shapes can help identify process defects like solder joint non-wets, shorting and also predict board flexure induced stresses in second level interconnects. This methodology has been demonstrated through synthetic range data as well as true experimental data. Authors in this paper have proposed methods to reduce the impact of noise, which is unavoidable in real measurements.
CFD Analysis of a Continuous Inkjet Print Head for Direct Write Fabrication
Authors: Desai Salil , Lovell Michael
Published: May 2009

This paper investigates the fluid generation mechanism in a modified Continuous Inkjet Print (CIJ) method. The CIJ technique is utilized to deposit a variety of conductive nano particulate materials for building miniaturized devices that can sustain harsh environments. These include devices and structures that can sustain high temperature and humidity applications. Given the complex drop formation mechanism a CFD model is developed that is further validated using an ultrahigh speed photography experimental setup. Various input parameters such as frequency, voltage and fluid pressure can be tuned using the model for different fluid types to obtain an optimal drop formation. These findings can be useful for the fabrication of freeform miniaturized devices in 3 dimensional space.
An Advanced Real-Time Moire´ Interferometry System With Conductive Heating/Cooling and Its Application on a Creep Behavior of Solder
Authors: Cho Seungmin , Jang Changsoo , Han Bongtae
Published: May 2009

A new real-time moire´ interferometry system based on conductive heating and cooling is introduced. A special chamber is designed and fabricated using a high power thermoelectric cooler, which is connected to the compact moire´ interferometer to form the system. Compared with the conventional convection-based system, the proposed system provides a higher ramp rate while improving the temperature response to control signals. The system is applied to investigate the creep behavior of a eutectic solder material. A new solder joint configuration is designed and fabricated to produce a virtually uniform shear strain field. The deformation of solder joint is documented at a controlled ramp rate over several thermal cycles. The experimental results are analyzed and compared with those of finite element analyses to investigate the validity of solder constitutive models available in the literatures.
Designing Nonlinear Zeros to Reject Periodic Waveforms
Authors: Paden Brad E. , Mirnateghi Nasim , Gentili Luca , Marconi Lorenzo
Published: May 2009

In linear systems, designers use zeros for loop-shaping and the attenuation of disturbances. For example, jω-axis zeros can be used to reject sinusoids at a specific frequency such a 50Hz or 60Hz power line interference. In this paper we constructively design nonlinear zeros — nonlinear dynamics that reject a non-sinusoidal signal — for a class of disturbance cancellation problems involving input disturbances. Problems in this class, for example, arise in controlled mechanical systems wherein actuator forces and disturbance forces enter a feedback system at the same point. A key element of our approach is the synthesis of disturbance waveform models so that they may be included in controllers as internal models. The focus is on waveforms of “known shape” with unknown amplitude and phase. Our approach contrasts with linear repetitive control where complex periodic waveforms are rejected using linear internal models incorporating harmonic oscillators for the fundamental and a number of harmonics of the periodic waveform.
Modeling of Nonlinear Material Behavior in Microstructurally Engineered Ferroelectric Ceramics
Authors: Robbins Joshua , Chaplya Pavel M.
Published: May 2009

Ferroelectric ceramics can be tailored at the microscale to have an ordered arrangement of crystal axes. Such grain-oriented ceramics can exhibit material properties far superior to conventional ceramics with random microstructure. A microstructurally based numerical model has been developed that describes the 3D non-linear behavior of ferroelectric ceramics. The model resolves the polycrystalline structure directly in the topology of the problem domain. The developed model is used to predict the effect of microstructural modifications on material behavior. In particular, we examine the internal residual stress after poling for idealized configurations of random and grain-oriented microstructures. The results indicate that a grain-ordered microstructure produces a significant increase in remanent polarization without detriment to internal residual stress.
Behavior of NiMnGa Under Dynamic Magnetic Fields Considering Magnetic Diffusion and Eddy Current Power Loss
Authors: Wang Xiang , Dapino Marcelo J.
Published: May 2009

Prior experimental measurements by the authors demonstrated large reversible strains of up to –0.41% along the [001] crystal direction of a cylindrical Ni50Mn28.7Ga21.3 rod driven with a magnetic field along the same direction and no external restoring force. This represents an unusual configuration which can lead to solenoid transducers with enhanced energy density and bandwidth relative to standard electromagnet devices. Although a number of constitutive models have been developed which quantify magnetic field induced strain (MFIS) in these materials, models incorporating both the MFIS and transducer dynamics are scarce. This paper presents a transducer model that is built in three steps. In the first step, classic thermodynamics is used to calculate the volume fraction ξ of an ideal two-variant system as a function of magnetic fields and stresses. Bulk strains are then calculated through stochastic homogenization of the volume fraction. The transducer dynamics are quantified in the third step through calculation of magnetic diffusion in the sample, eddy current losses, and skin depth effects. The strain output is quantified at various magnetic field frequencies.
Path Planning for Cooperative Sensing Using Unmanned Vehicles
Authors: Tisdale John , Durrant-Whyte Hugh , Hedrick J. Karl
Published: May 2009

This work explores online path-planning for unmanned vehicles performing cooperative sensing. Much existing work employs receding-horizon optimization, where an objective function is repeatedly optimized over some short lookahead length. The use of receding horizon optimization often results in ad-hoc methods for dealing with the problem of myopic lookahead, where no value is visible in an agent’s planning horizon. This work examines the use of an algorithm for receding-horizon optimization that explicitly accounts for myopia by allowing for a variable lookahead length. Cooperation is maintained by ensuring that all agents plan to the same horizon, potentially with different strategies. This algorithm is used to develop trajectories for a team of unmanned vehicles searching for a target using a probabilistic framework. Simulation results are presented and discussed.
Wearable Engine-Driven Vapor-Compression Cooling System for Elevated Ambients
Authors: Ernst Timothy C. , Garimella Srinivas
Published: May 2009

The development of a wearable cooling system for use in elevated temperature environments by military, fire-fighting, chemical-response, and other hazardous duty personnel is underway. Such a system is expected to reduce heat-related stresses, increasing productivity and allowable mission duration, reduce fatigue, and lead to a safer working environment. The cooling system consists of an engine-driven vapor compression system assembled in a backpack configuration, to be coupled with a cooling garment containing refrigerant lines worn in close proximity to the skin. A 2.0 L fuel tank powers a small-scale engine that runs a compressor modified from the original air compression application to the refrigerant compression application here. A centrifugal clutch and reduction gear train system was designed and fabricated to couple the engine output to the refrigerant compressor and heat rejection fan. The system measured 0.318×0.273×0.152 m and weighed 4.46 kg. Testing was conducted in a controlled environment to determine performance over a wide range of expected ambient temperatures (37.7–47.5°C), evaporator refrigerant temperatures (22.2–26.1°C), and engine speeds (10,500–13,300 RPM). Heat removal rates of up to 300 W, which is the cooling rate for maintaining comfort at an activity level comparable to moderate exercise, were demonstrated at a nominal ambient temperature of 43.3°C. The system consumes fuel at an average rate of 0.316 kg/hr to provide nominal cooling of 178 W for 5.7 hrs between refueling.
Development of an Analytical Model to a Temperature Distribution of First Level Package With a Non-Uniformly Powered Die
Authors: Kaisare Abhijit , Agonafer Dereje , Haji-Sheikh A. , Chrysler Greg , Mahajan Ravi
Published: May 2009

Microprocessors continue to grow in capabilities, complexity and performance. Microprocessors typically integrate functional components such as logic and level two (L2) cache memory in their architecture. This functional integration of logic and memory results in improved performance of the microprocessor. However, the integration also introduces a layer of complexity in the thermal design and management of microprocessors. As a direct result of functional integration, the power map on a microprocessor is typically highly non-uniform and the assumption of a uniform heat flux across the chip surface has been shown to be invalid post Pentium II architecture. The active side of the die is divided into several functional blocks with distinct power assigned to each functional block. Previous work has been done which includes numerical analysis and thermal Based optimization of a typical package consisting of a non-uniformly powered die, heat spreader, TIM I &II and the base of the heat sink. In this paper, an analytical approach to temperature distribution of a first level package with a non-uniformly powered die is carried out for the first time. The analytical model for two layer bodies developed by Haji-Sheikh et al. is extended to this typical package which is a multilayer body. The solution is to begin by designating each surface heat flux as a volumetric heat source. An inverse methodology will be applied to solve the equations for various surfaces to calculate maximum junction temperature for given multilayer body. Finally validation of the analytical solution will be carried out using developed numerical model.
Interactive Sketch-Based Digital Prototyping by Using the Level-Set Method
Authors: Zhang Weihan , Leu Ming C.
Published: May 2009

This paper presents the development of a sketch-based interactive digital prototyping method by using the level-set method as the underlying technology. Various deformative operations (e.g., warping, smoothing) are developed by the level-set method to design 2D sketches. Fast and robust numerical techniques are utilized to support the real-time performance of level-set operations. B-spline function-based shape transformation method is developed to construct 3D volumetric data from multiple 2D sketches. Virtual prototypes are then visualized by reconstructing surface models from the volumetric data. Computational cost and memory requirement of the presented method are analyzed to evaluate its real-time performance. Example virtual prototypes are shown to demonstrate the capability of the developed method.
Bump Electromigration and Back End Design Rules
Authors: Nagaraj Vishal , Karajgikar Saket , Agonafer Dereje , Pekin Senol
Published: May 2009

As there is continuous demand for miniaturization of electronic devices, flip chip technology is predominantly used for high density packaging. The technology offers several advantages like excellent electrical performance and better heat dissipation ability. Original invention of flip chip packaging utilized ceramic substrates and high lead bumps. Low cost commercialization of this packaging technology, however, required organic laminate substrates coupled with SnPb eutectic bumped interconnects on the die side. While organic laminate flip chip packaging may be a good option for many low power applications, current carrying capability of the eutectic bumped interconnect causes a catastrophic failure mechanism called electromigration. Previously, researchers have identified and addressed few issues regarding electromigration. Electomigration leads to the formation of metal voids in the conductors which eventually increases the resistance drop across the conductor causing electrical opens. Electromigration is very significant at high current densities. Temperature is the other parameter of concern for electromigration. High current density causes temperature to rise due to Joule heating, there by reducing the life of package. In order to determine the factors responsible for high current densities, we formed a full factorial design of experiments (DOE) that contained parameters such as passivation opening, UBM size, UBM thickness and trace width. Finite Element Analysis (FEA) was performed in order to study the effect of above parameters on current crowding and temperature in the bumped interconnects. Based on the results, hierarchy of the most important parameters to be considered while selecting the appropriate flip chip technology is proposed.
Characterization of the Effect of Geometry on Single Cell Adhesion Strength Using a Microfluidic Device
Authors: Christ Kevin V. , Williamson Kyle B. , Masters Kristyn S. , Turner Kevin T.
Published: May 2009

Cell adhesion plays a crucial role in a number of fundamental physiological processes and is important in the development of implantable biomaterials. Cell adhesion strength has previously been measured using a range of techniques, including population assays (e.g., centrifugation [1], hydrodynamic flow [2]) and single-cell methods (e.g., AFM [3], micropipette manipulation [4]). Population studies are unable to provide detailed information about individual cell behavior, while the single-cell methods are often time-consuming and difficult to perform. Microfluidic channels present a way to generate well-defined stress fields on cells [5]. The small dimensions of these channels result in low Reynolds numbers that allow for the generation of sufficiently large stresses to detach well-spread cells under laminar flow conditions. In the present work, a microfluidic channel was used to controllably load adhered single-cells to detachment and measure the adhesion strength. Using this assay, the effect of cell geometry on adhesion strength was investigated.
Exploring the Basins of Attraction of Tapping Mode Atomic Force Microscopy With Capillary Force Interactions
Authors: Hashemi Nastaran , Paul Mark , Dankowicz Harry
Published: May 2009

We numerically explore the nonlinear dynamics of the oscillating cantilever tip in tapping mode atomic force microscopy. The cantilever dynamics are determined by complex force interactions between the sample surface and the oscillating cantilever tip which are dominated by attractive, adhesive, and repulsive contributions depending on the instantaneous position of the cantilever. We use a model proposed by Zitzler et al that includes a capillary force interaction due to the thin film of water that covers all surfaces as a result of ambient humidity. As the cantilever approaches the surface a meniscus is formed and as the cantilever retracts this water layer forms a neck and eventually breaks. This introduces hysteresis since the formation of the meniscus and the breaking of the water neck occur at different spatial locations during an oscillation of the cantilever. Using forward-time simulation with event handling techniques tailored for situations with rapid changes in force interactions we find three classes of steady-state dynamics: (i) a branch of solutions with periodic dynamics and large amplitude of oscillation; (ii) a branch of solutions with periodic dynamics and small amplitude of oscillation; (iii) windows of irregular aperiodic dynamics. We quantify the global basins of attraction for these solutions by performing a large set of numerical simulations over a wide range of initial conditions. Our findings provide a useful framework for further studies interested in controlling these dynamics.
Transforming Student Perspectives Through Summer Undergraduate Research
Authors: Issen Kathleen A. , Moosbrugger John C. , Howard Andrea J. , Ingraham Mathew D. , Reardon Bridget A. , Sabini Lisa M.
Published: May 2009

Undergraduate research is a commonly accepted method for increasing student interest in graduate study. An important outcome of this process is the transformation of student perspectives, such that students view themselves as potential graduate students. The Research Experience for Undergraduates (REU) site studied here seeks to accomplish this transformation through multidisciplinary research projects, community-building activities, and workshops, which expose students to graduate study, while increasing self-confidence and promoting exploration and risk taking. Based on direct student feedback, this paper describes the attributes of a successful program, and examines qualitative and quantitative assessments of the influence of summer residential undergraduate research experiences on the decision to pursue graduate study. Results indicate that students’ confidence in succeeding at graduate study and in conducting independent research increased significantly when provided with a well-advised research project, set in a learning based research environment, with a strong social community, and supplemented with seminars and workshops. The likelihood of a student pursuing a graduate degree increased slightly for an MS and significantly for a PhD. Students state that their REU experience was pivotal in their decision to attend graduate school.
Development of a Sustainability Scoring Method for Manufactured Automotive Products: A Case Study of Auto Body Panels
Authors: Ungureanu C. A. , Das S. , Jawahir I. S.
Published: May 2009

Undoubtedly, motor vehicles are among the most important, yet difficult to maintain and environmentally damaging consumer products on the planet. In light of the ongoing climate change discussion, sustainability considerations are currently taking a more prominent role in material selection decisions for automotive applications. This paper presents a new sustainability evaluation methodology for computing the potential benefits of using lighter materials, such as aluminum, in auto body applications, through a “Sustainability Scoring” method. When evaluating the “level of sustainability” built in any product, several major contributing factors (sustainability elements) need to be taken into consideration. Six major integral sustainability elements considered in this work are: product’s environmental impact, societal impact, functionality, resource utilization and economy, manufacturability and recyclability/remanufacturability. Each of these elements has corresponding sub-elements and influencing factors which are categorized as having varying levels of importance to the product. The paper compares the use of aluminum with the traditional use of steel alloys in a given automotive application using the newly developed comprehensive sustainability scoring method by considering all sustainability elements and sub-elements associated with a vehicle over its total life-cycle.
Processing and Performance Evaluation of Nanoclay Infused EPON828
Authors: Hosur Mahesh V. , Gebremedhin Orion , Jeelani Shaik
Published: May 2009

The field of polymer-clay nanocomposites has attracted considerable attention as a method of enhancing polymer properties and extending their utility. In this research, different nanocomposites have been manufactured by modifying the EPON828 resin system through the infusion of 0.5%, 1%, 1.5% and 2% by weight of clay (Nanocor® 1.30E) nanoparticles. Mechanical properties such as flexural, compressive, tensile and high strain rate strengths and moduli of polymer matrix were improved in nano structured materials owing to their unique phase morphology and improved interfacial interactions. A dynamic Mechanical analysis was performed to monitor changes in the thermal properties of the nanocomposite. Nanoclay reinforced epoxy showed consistent improvement in all the mechanical as well as Thermomechanical properties. High strain rate compressive modulus showed a progressive improvement over the neat values for all the strain rates used. SEM micrographs of the fracture surfaces for both tensile and flexural samples showed regular and continuous patterns of cracks for the neat samples. The nanophased samples on the other hand showed multiple irregular cracks which increased in densities with nanoclay loading.
Object Function Control Science Study for Homeland Security
Authors: Wynn Bear L. , Roth John T.
Published: May 2009

Firstly we put forward an object function control method and guideline, by which we can control the Function of object when we cannot control object itself. In such a case object function control will be beneficial to us forever and without any harm especially when armament system and high harm are used improperly. Then we use it to improve functions of the system and get safer methods so as to establish an integrated safeguard system, and the functions of the system and a more solid human security and stability in the establishment of the strategy, to create an integrated world of justice and peace in the security system. The object function control (constraint) includes: Main body control, Guest body control and Established body object control. Based on the goal of we can control the Function of object when we cannot control object itself, it showed a new technological means of the democracy, freedom, and peace of world. Based on the method of object function control, a new technical mode can be presented, which provides measures dealing with difficult problems (Such as to fight against the evil of the world and the international terrorism, safeguard the human justice and peace) and acceptable to many countries (Union) and becomes their strong support.
FE Modeling and Analysis of Patterning Micron Surface Structures by Laser Shock Peening
Authors: Warren A. W. , Guo Y. B.
Published: May 2009

Laser shock peening (LSP) is a potential fabrication process to pattern micron surface structures. The purpose of this paper is to model 3D shock pressure and dynamic mechanical behavior at high strain rates during laser patterning process. The 3D shock pressure was modeled using a user defined subroutine. The mechanical behavior at high strain rates is predicted by the Bammann, Chiesa, and Johnson (BCJ) model. A 3D FEA model of microscale LSP was created using the developed loading and material subroutines. For comparison, a direct input of measured material properties was also used. The results show that decreasing pulse time shifts the maximum transient stress from the surface to the subsurface. The rapid loading causes increased magnitudes of compressive stress throughout the depth. The BCJ model predicts higher stresses than the direct input method.
An Application of Computer Aided Engineering in Rubber Injection Mold With a Cold Runner System Design and Manufacturing
Authors: Rodkwan Supasit , Panyawipart Rungtham , Raksiri Chana , Eiamsa-ard Kunnayut
Published: May 2009

With a recent growth in the demand of the rubber products globally, the latest technology is adopted to improve the design and manufacturing of those rubber products in term of part quality and production lead time and cost. The cold runner system is one of the technologies which can assist in unfilling part problem and raw material saving. Nevertheless, with the lack of numerical tool with an ability to predict the behavior of rubber during the injection molding process, designers still need to use their experience and trial-and-error method to design the mold and the cold runner system. Therefore, in this research, the use of CAE and a cold runner system is applied to the design and manufacturing of rubber injection molding process with a gasket mold made of SBR as a case study. The empirical and simulated results agree well and the use of raw material in the actual system is decreased by 12% shot weight which can lead to the reduced cost of products. Finally, it can be seen that the use of CAE can assist the mold designers and manufacturers to get better understanding of flow pattern and behavior of rubber during the injection process so the better part quality can be obtained.
Using Weibull Analysis for Cases With an Unknown Susceptible Population
Authors: Murray Steve J. , Ray Rose M. , Grossman Helene L.
Published: May 2009

Weibull analysis is a powerful predictive tool for studying failure trends of engineering systems. [1] One noted shortcoming is that traditional techniques require the size of the susceptible population to be known. The method described in this paper allows for estimation of the size of the susceptible population using only failure data and no assumptions about total population size or susceptible portion. In the analysis of failures of mass-produced products, a large amount of failure data may be available, but all the conditions that define the susceptible population may never be known. For example, units with a particular usage condition may be expected to fail over time following a Weibull model, but the number of units subjected to that usage condition may never be known. To assume that the entire population is susceptible to the failure mode would greatly over-predict future failures, and the model could not be used to guide decision-making. By doing a least squares fit to the trend of failures versus time, a Weibull model can be fit to the data and then used to estimate the total number of susceptible units expected in the population. The ability to accurately estimate the size of the susceptible sub-population from failure data will be explored as a function of the size of the data set used, for known sets of failure data. For example, for a failure distribution that has increased, peaked, and then decreased to zero, almost the entire population has failed, so an estimate of the size of the susceptible population from this data is likely to be accurate. On the contrary, for only a few data points that show an increasing failure rate over time, little can be determined. Monte Carlo simulations will be used in order to estimate the error associated with this technique. Our analysis will show that predictions of total susceptible populations become similar to the actual susceptible populations when the predicted mean time to failure (MTTF) from the observed data is shorter than the observation time. In effect, predictions become accurate when it is clear to the observer that the number of failures per unit time has peaked.
Biomimetic Flow Sensing Using Artificial Lateral Lines
Authors: Yang Yingchen , Chen Nannan , Tucker Craig , Pandya Saunvit , Jones Douglas , Liu Chang
Published: May 2009

By mimicking fish lateral lines and fish sensing behaviors, we constructed an artificial lateral line and employed it for biomimetic flow sensing. Thirteen hot-film anemometers were mounted to the surface of a NACA0015 airfoil to constitute the artificial lateral line. The resulting fish-like platform was maneuvered by a 3-degree-of-freedom robotic arm for two-dimensional mobility in aquatic environments. Assisted with specially developed algorithms, two biologically relevant flow-sensing scenarios have been realized. They were tracking a nearby dipole source in still water by detecting the dipole flow field and tracking a distant stationary source in running water by detecting its hydrodynamic wake.
Hydrodynamic and Thermal Characteristics of Single-Phase and Two-Phase Micro-Pin-Fin Heat Sinks
Authors: Siu-Ho Abel M. , Qu Weilin , Pfefferkorn Frank
Published: May 2009

The pressure drop and heat transfer characteristics of single-phase and two-phase micro-pin-fin heat sinks were investigated experimentally. Fabricated from 110 copper, the heat sink contained an array of 1950 staggered square micro-pin-fins with 200×200 μm2 cross-section by 670 μm height. The ratios of longitudinal pitch and transverse pitch to pin-fin hydraulic diameter are equal to 2. Deionized water was employed as the cooling liquid. A coolant inlet temperature of 30 °C, and six maximum mass velocities, ranging from 183 to 420 kg/m2s, were tested. The corresponding inlet Reynolds number ranged from 45.9 to 105.9. General hydrodynamic and thermal characteristics of the two flow regimes of single-phase flow and flow boiling were described. The measured temperature distribution was used to evaluate single-phase heat transfer coefficient and Nusselt number. Predictions of the previous friction factor and heat transfer correlations that were developed for low Reynolds number (Re<1000) single-phase flow in short pin-fin arrays were compared to the present micro-pin-fin single-phase pressure drop and Nusselt number data, respectively. The Short et al friction factor correlation and the Kos¸ar et al. heat transfer correlation provided acceptable predictions.
Spectral Analysis of Deteriorated Offshore Structures
Authors: Karadeniz H.
Published: May 2009

In order to present an efficient, practical technique to determine progressive failure mechanism of structures, modelling of member deterioration by using a spring system is outlined. The procedure uses updates of member stiffness and mass matrices as well as the random load vector in incremental forms. In this procedure, the assembly process produces redistributions of the system stiffness and mass matrices, and the load vector. In the calculation of response spectral values, the original forms remain unchanged. Inversion of the stiffness matrix is calculated by using the Neumann expansion solution in which the original stiffness matrix is inverted only once so that a considerable computation time is saved in the whole calculation process. An incremental solution technique is presented for spectral analyses of both static and dynamic sensitive structures. In the case of dynamic analysis, special attention is paid to estimations of modified natural frequencies and mode shapes of deteriorated structures, which may affect response spectral values considerably. The technique, which is presented in the paper, is attractive in practical applications and can be efficiently used in the reliability calculation as well, and also it can be successfully used to determine a progressive failure mechanism of the structure.
Investigation of Hygroscopic Swelling of Polymers in Freezing Temperature
Authors: Park Seungbae , Zhang Haojun
Published: May 2009

It is well known that coefficients of thermal expansion and hygroscopic swelling vary with temperature. The most significant change takes place at the glass transition temperature of a polymer. The phenomenon of temperature-dependent CHS has been studied by several authors [1, 2] in polymers and polymer-based composites mainly at room temperature and above. However, effect of freezing temperature on hygroscopic swelling of polymers has not been demonstrated. In this study, the behavior of CHS at and below freezing temperature is investigated. Reported results are obtained using a new CHS measurement technique, the digital image correlation method.
On the Analysis of the Effects of Thermal and Time Dependent Interface Pressure Distribution on Slip Motion for Sandwich Elastic Beams
Authors: Olunloyo Vincent O. S. , Osheku Charles A.
Published: May 2009

Slip motion with sandwich elastic beams has been exploited for dissipating noise and vibration energy in machines, aero- and hydro-dynamic structures. While most of the original work on the modelling and analysis of the mechanism assume an environment of uniform pressure at the interface, experiments to date have confirmed that this is rarely the case. There have however been recent attempts to relax the restriction of uniform interface pressure to allow for more realistic pressure profiles that are encountered in practice. Even such attempts did not consider thermal and time dependent non uniform interface pressure effects. By employing the laminated beam theory, this paper investigates the effects of temperature variation and time dependent modulation on the non uniform linear interface pressure profile on slip motions in the case of sandwich elastic beams. In particular, closed form analytical expressions and results for dynamic and interfacial slip responses are reported for design analysis.
Qualification of SiP Products: Quasi-Static Cyclic Mechanical Bending
Authors: Farley D. , Zhou Y. , Dasgupta A. , Caers J. F. J. , de Vries J. W. C.
Published: May 2009

An LGA (Land Grid Array) laminate-based epoxy-molded RF SiP (system-in-package) containing four wirebonded and three flip-chip dice is qualified for quasi-static mechanical flexure using a PoF (Physics-of-Failure) approach. The process includes: design and execution of accelerated stress testing; failure analysis to identify the failure mode and mechanism; and mechanistic simulations to assess acceleration factors for extrapolation of the failures to field environments for selected failure mechanisms. Illustrative qualification results are presented for solder joint fatigue.
An Air-Brayton Nuclear-Hydrogen Combined-Cycle Peak- and Base-Load Electric Plant
Authors: Forsberg Charles
Published: May 2009

A combined-cycle power plant is proposed that uses heat from a high-temperature nuclear reactor and hydrogen produced by the high-temperature reactor to meet base-load and peak-load electrical demands. For base-load electricity production, air is compressed; flows through a heat exchanger, where it is heated to between 700 and 900°C; and exits through a high-temperature gas turbine to produce electricity. The heat, via an intermediate heat-transport loop, is provided by a high-temperature reactor. The hot exhaust from the Brayton-cycle turbine is then fed to a heat recovery steam generator that provides steam to a steam turbine for added electrical power production. To meet peak electricity demand, after nuclear heating of the compressed air, hydrogen is injected into the combustion chamber, combusts, and heats the air to 1300°C—the operating conditions for a standard natural-gas-fired combined-cycle plant. This process increases the plant efficiency and power output. Hydrogen is produced at night by electrolysis or other methods using energy from the nuclear reactor and is stored until needed. Therefore, the electricity output to the electric grid can vary from zero (i.e., when hydrogen is being produced) to the maximum peak power while the nuclear reactor operates at constant load. Because nuclear heat raises air temperatures above the auto-ignition temperatures of the hydrogen and powers the air compressor, the power output can be varied rapidly (compared with the capabilities of fossil-fired turbines) to meet spinning reserve requirements and stabilize the grid.
Mu-Synthesis for Magnetic Bearings: Why Use Such a Complicated Tool?
Authors: Maslen Eric H. , Sawicki Jerzy T.
Published: May 2009

The emergence of sophisticated formal control synthesis tools provokes important questions for any prospective user: why learn to use these new tools, what will they buy me? In synthesis of magnetic bearing controllers, it turns out that the range of stabilizing controllers is often quite narrow so that the difference between a poor controller and an “optimal” one may be small. Hence, the product of formal control synthesis tools often looks and performs much like what a reasonably clever control engineer would produce by hand. We argue here that the real value of these tools lies in a) generation of a performance benchmark which can be used to firmly establish the best performance relative to a specification and b) change of design parameter space to one which is relatively easy to maintain and represents a durable investment from an engineering process view.
Structural Integrity of Composite-Lined Hydrogen Storage Tanks at Operating Pressures
Authors: Guo Y. B. , Parham J. L.
Published: May 2009

Hydrogen may appear to be an attractive alternative fuel due to its obvious environmental and potentials of significant technical and economic advantages, the design and manufacture a safe and reliable hydrogen tank is the number one priority for development and deployment of hydrogen technology. Compared with aluminum-lined hydrogen tanks, composite tanks offer advantages of lightweight and conformability. Real life tank testing is very expensive and time consuming. In this study, a finite element analysis (FEA) tool has been developed to provide a more economical alternative for composite hydrogen tank analysis at operating pressures of 35 MPa, 45 MPa, and 70 MPa. It was found that the carbon-fiber/epoxy shell acts as the primary structural member, unlike an aluminum-lined tank where the liner acts performs this function. Critical portions of the tanks were found to be the top and bottom domes as well as the interaction between the liner and boss. Some slight plastic deformation was found to occur in the liner at 70 MPa, though under the 35 MPa and 45 MPa loads, the liner exhibited only elastic behavior. The shell elastically deformed in all loading cases, which results in very low residual stress and strain values following the load release. The results may help manufacturers improve tank safety in the design and manufacture of composite hydrogen.
Magnetorheological Flow in Pipes: An Exploration of the Time-Variation of Herschel-Bulkley Parameters
Authors: Letelier Mario F. , Stockle Juan S. , Siginer Dennis A.
Published: May 2009

In this paper it is analyzed the effects on the flow of the time-variation of Herschel-Bulkley model of fluid constitutive parameters. In this way, the influence of a varying magnetic field on the unsteady flow of a magnetic fluid is explored. Yield stress, viscosity and power index are assumed time-dependent. In particular, linear variations in time of these parameters are considered. The characteristics of the velocity field is analyzed for different values of the constants that determine the time structure of the constitutive parameters.
Computerized Planning of Multi-Probe Cryosurgical Treatment for Tumor With Complex Geometry
Authors: Deng Zhong-Shan , Liu Jing
Published: May 2009

To perform a cryosurgical procedure successfully, it is important to carefully design the optimal freezing parameters (such as the number of cryoprobes, the locations, the insertion paths and depths of cryoprobes) before cryosurgery. Failure to do so accurately could lead to either insufficient or excessive freezing. Due to the irregularly shaped tumors commonly encountered in clinics, multiple cryoprobes are often needed, which makes the parameter optimization rather difficult. Computerized planning tools would help to alleviate this difficulty. In this study, a three-dimensional cryosurgery planning tool is developed, based on the numerical algorithm presented in our recent works. This tool is developed with general purpose and applicable for the treatment planning of tumor with complex geometry. For demonstration purposes, several examples for typical cryosurgery cases using multiple cryoprobes are given and interpreted.
The Effectiveness-NTU Relationship of Microchannel Counter Flow Heat Exchangers With Axial Heat Conduction
Authors: Mathew B. , Hegab H.
Published: May 2009

In this paper the effect of axial heat conduction on the thermal performance of a microchannel heat exchanger with non-adiabatic end walls is studied. The two ends of the wall separating the coolant are assumed to be subjected to boundary condition of the first kind. As the end walls are not insulated heat transfer between the microchannel heat exchanger and its surroundings occur. Analytical equations have been formulated for predicting the axial temperature of the coolants and the wall as well as for determining the effectiveness of both fluids. The effectiveness of the fluids has been found to depend on the NTU, axial heat conduction parameter and end wall temperatures. The heat transfer through the end walls have been expressed in nondimensional terms. The nondimensional heat transfer from both ends of the wall also depends on the axial heat conduction parameter and temperature gradient at the end walls. A new parameter, performance factor, has been proposed for comparing the variation in effectiveness due to axial heat conduction coupled with heat transfer with the effectiveness without axial heat conduction. The effectiveness of both the hot and cold fluid for several cases of end wall temperatures and axial heat conduction parameter are analyzed in this paper for better understanding of heat transfer dynamics of microchannel heat exchangers.
Low-Invasive Estimation of Physical Properties in Numerically Ill-Conditioned MEMS
Authors: Spiewak S. A. , Lawrence E. M.
Published: May 2009

A prototype system for comprehensive evaluation of micro- and nano-electromechanical systems is presented. It features constitutive-empirical modeling methodology closely linked with symbolic, arbitrary precision computations. It is capable of resolving ambiguities created by numerical ill-conditioning in micro and nano scale systems. For precision low-invasive laboratory investigations or production (wafer level) metrology it employs laser interferometry and white light profilometry supported by extensive signal and system analysis software. Experimental results obtained with microfabricated beams and resonators illustrate the current performance of the system and hint its potential applications.
Criteria for Static Equilibrium in Discrete Element Methods
Authors: Tu Xuxin , Andrade Jose
Published: May 2009

In most DEM codes, the governing equation for static problems is solved in an explicit scheme that involves a set of motion equations with numerical damping. With such an explicit scheme, parameter calibration is demanded in order to obtain a converged solution and to achieve a state of static equilibrium. This paper presents two criteria, based on the homogenized stress equation, for evaluating the static force balance and the static moment balance, respectively. Numerical examples demonstrate that these two criteria play a critical role in calibrating the explicit scheme and preventing it from generating erroneous results.
FE Modeling of the Three-Layer Human Carotid Artery Under Impact Loadings
Authors: Zhao Aihong , Digges Ken , Field Mark , Richens David
Published: May 2009

Blunt traumatic rupture of the carotid artery is a rare but life threatening injury. The histology of the artery is key to understanding the aetiology of this injury. The carotid artery is composed of three layers known as the tunica intima, media, and adventitia, with distinct biomechanical properties. In order to examine the behaviour of the carotid artery under external load we have developed a three layer finite element model of this vessel. A rubber-like material model from LS-DYNA was selected for the FE model. The Arbitrary-Lagrangian Eulerian (ALE) approach was adopted to simulate the interaction between the fluid (blood) and the structure (carotid). To verify the FE model, the impact bending tests are simulated using this FE model. Simulation results agree with tests results well. Furthermore, the mechanical behaviour of carotid artery tissues under impact loading were revealed by the simulations. The results provide a basis for a more in-depth investigation of the carotid artery in vehicle crashes. In addition, it provides a basis for further work on aortic tissue finite element modeling.
Air-Coupled Ultrasound: A New Paradigm in NDE
Authors: Dayal Vinay , Hsu David K. , Kite Adam H.
Published: May 2009

In any ultrasonic investigation, the contact between the transducer and the object has always been a source of problem. With the introduction of the air-coupled ultrasonic probes the couplant is totally eliminated. The limitation of these probes is that they are of very low frequency and as a result they bring their set of restrictions. We present here a couple of results of our investigations of composite structures with air-coupled transducers. The resonance of structures is an important factor which is able to explain observations of air-coupled ultrasonic testing.
LES and RANS Simulation of the Turbulent Mixing of High-Density-Ratio Axisymmetric Jets
Authors: Dhakal Tej P. , Wolgemuth Nicole M. , Walters D. Keith
Published: May 2009

The turbulent mixing of axisymmetric jet flows is investigated using large-eddy simulation (LES) and Reynolds-averaged Navier-Stokes (RANS) computational fluid dynamics (CFD). The flowfield of interest consists of a round jet and a surrounding, coaxial annular jet ejected into a quiescent free stream. This flow situation arises, for example, in the flow of hydrogen and oxygen in rocket combustion systems. In such cases, the jets have significantly different densities, which has been found experimentally to strongly influence the downstream turbulent mixing dynamics. The goal of the present study is to evaluate the capacity of the LES and RANS methodologies to accurately predict jet mixing without the complicating effects of combustion. Simulations were performed for test cases matching an experimental study that has been documented in the open literature. Both air-air and hydrogen-air jet combinations were investigated, yielding density ratios ranging from 1.46 to 0.08. The LES and RANS results were compared to one another and to experimental measurements in terms of centerline decay and radial distribution of mean velocity and concentration. The results highlight the strengths and weaknesses of the two computational approaches for this class of problems.
A Principle to Generate Flow for Thermal Convective Base Sensor
Authors: Dinh Thien X. , Ogami Yoshifumi
Published: May 2009

This paper presents a millimeter scaled device which can generate a closed flow with magnitude velocity of order of m/s. The device consisting of a piezoelectric pump connecting to a closed network channel through a specific nozzle is investigated by using computational fluid dynamics (CFD). With this device, numbers of laminar jet-flow are produced depending on the structure of the channel. In this study, four laminar jet-flows are demonstrated. If the amplitude of the vibration of PZT membrane is large enough, in a jet flow, the self-similar of the axial velocity (along jet direction) to the half-widths of the jet is observed. The two remains components of the flow are small compared with the axial component. Moreover, each jet flow can vibrate almost freely in three dimensions. Therefore, this device promises a rich application into the sensors based on a flow.