bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling and Experimental Validation of Active Limited Slip Differential Clutch Dynamics
Authors: Ivanovic´ Vladimir , Deur Josˇko , Herold Zvonko , Hancock Matthew , Assadian Francis
Published: August 2009

This paper deals with modeling of an Active Limited Slip Differential (ALSD) which comprises a wet clutch actuated by an electromechanical mechatronic system consisting of a DC motor and ball-ramp mechanism. The structure of the proposed ALSD model is divided in two subsystems: (i) clutch axial force development model and (ii) clutch torque development model. The former includes DC motor dynamics; gear box kinematics and backlash; ball-ramp mechanism kinematics, friction, and compliance; fluid squeeze speed dynamics; and clutch pack axial compliance and damping. The latter includes structural compliance and inertias, as well as dynamic friction effects. Each submodel has a pure physical structure. This facilitates model parameterization through a series of relatively simple experimental procedures, which are also described in the paper. The final model has been validated under various operating conditions by using an ALSD test rig. The validation results point to a good modeling accuracy.
Heavy Truck and Bus Brake Testing: The Development and Use of a Forensic Tool
Authors: Ferrone Christopher W.
Published: August 2009

After an accident it is often necessary to check the brake push rod stroke adjustment and pneumatic integrity of the brake system of a truck or bus. In many instances, due to the traumatic accident damage, the brake system may not be able to be tested/checked by the conventional means. Test methods used at the scene of an accident may compromise or influence the brake stroke adjustment levels. A tool has been developed which eliminates these issues. This tool, when used to test air brakes (push-rod stroke) on a heavy truck or bus, will eliminate the common problems and difficulties that occur during brake stroke adjustment testing in a post-accident situation. • Checking brake push rod stroke with improper air pressure levels; • System leaks creating measurement inaccuracies; • Parking brake release issues; • System interruption due to traumatic accident damage. By using this tool an engineer can determine the brake push rod stroke adjustment level or diagnose a system failure in an efficient and nondestructive manner, by minimizing the alteration of post-accident conditions.
Torsional Vibration Analysis of Drillstrings in Blasthole Drilling
Authors: Aminfar Omid , Khajepour Amir
Published: August 2009

Reducing vibrations in well drilling has a significant effect on improving the overall performance of the drilling process. Vibrations may affect the drilling process in different ways, i.e., reducing durability of the drillstring’s elements, reducing the rate of penetration, and deviating the drilling direction. In rotary drilling, which is used to open mine and oil wells, torsional vibration of the drillstring is an important component of the overall system’s vibration that has received less attention in the literature. In this paper, we propose a finite element model for a sample blasthole drillstring used to open mine wells to investigate its torsional vibrations. Boundary conditions and elements’ specifications are applied to this model. In the model, the interaction between the insert and the rock is represented by a set of repetitive impulses according to the insert pattern. The steady-state response of the system to the repetitive impulses is found and natural frequencies, kinetic energy, and potential energy of the drillstring are calculated. The root mean square (RMS) of the total energy can be used as the measure for reducing the torsional vibration of the system. Finally, an optimum combination of inserts on the cone’s rows was found based on minimizing the total vibratory energy of the drillstring. The optimum design can reduce the torsional vibrations of the drillstring and improve the drilling performance.
Curve and Surface Fitting by Means of Rational B-Spline Functions
Authors: Carminelli Antonio , Catania Giuseppe
Published: August 2009

This paper presents a method to obtain the mathematical model of a free-form curve or a surface fitting a set of point coordinates by a rational B-spline (NURBS) formulation in the homogeneous R4 space. A method to evaluate the control points R4 coordinates is proposed by means of a two step process. In the first step, NURBS weights are evaluated by means of an optimization procedure making it possible to evaluate the best fitting parameterization as well. In the second step, the control point coordinates are computed by means of a linear least squares approach.
High Performance Engine Warm-Up Thermo-Fluid-Dynamic Analysis
Authors: Senatore Adolfo , Cardone Massimo , Buono Dario , Dominici Agostino
Published: August 2009

Luxury car market is characterized by a more and more increasing demand of high performance engines, and this requires high specific power outputs and a continuous evolution of technical solutions. This trend implies consequently, higher amounts of heat to be released from the cooling system. The latter requires special care in design since it must release as much heat as possible from the engine without compromising the aerodynamic performance of the car. In this paper the results of thermo-fluid-dynamic model of an 8 cylinder high-performance engine cooling system are shown. The model has been validated by both thermal and hydraulic experimental data. In particular, this study has been carried out on simulation of the warm up procedure and deep attention was given to the thermostat behavior and to the heat exchange phenomena during this procedure. The goal of this activity was not only to perform a dedicated simulation model to analyze the complex heat exchange phenomena and to highlight eventual critical aspects, but also to define a methodology to optimize the cooling system and its components.
Direct Numerical Simulations of Nucleate Boiling
Authors: Tryggvason Gretar , Thomas Siju , Lu Jiacai
Published: August 2009

Direct Numerical Simulations (DNS) of multiphase flows, where all continuum length and time scales are fully resolved have progressed enormously in the last few years. Increases in computer power and new algorithms now make it possible to follow the unsteady motion of several hundred particles (drops, bubbles and solids) for long enough times so that meaningful averages for the fluid mixture can be calculated. However, most progress has so far been made for disperse flow of two-fluid systems. See Prosperetti and Tryggvason (2007) for a review.
Mechanical Characterization of a Freestanding Polyvinyl Alcohol Hydrogel Membrane
Authors: Montiel Edgar J. , Wan Kai-Tak
Published: August 2009

The following study presents two methods established for characterizing the mechanical properties of polyvinyl alcohol hydrogel membranes. The first one, an instant deformation test with an automated machine allowed the determination of the elastic properties of the material, while the second permitted the determination of the viscoelastic properties with the use of the standard linear solid model while confirming the previously found elastic results. This is not trivial as clearly old fashioned tests such as the ASTM standard tension test where grips are used to hold the sample are not feasible to perform due to the fragile characteristics of this kind material that resemble delicate biological tissues. The results obtained are consistent with previous publications, where different methods where used, but an increase in the material strength was also found as the number of freezing/thawing cycles increased.
A Thermal Quadrupole-Based Model for Heat Diffusion in a Multilayered System: Application to Determination of Transient Performance of a Medium-Voltage Soft Starter
Authors: Volle Fabien , Garimella Suresh V. , Juds Mark A.
Published: August 2009

Adverse effects of starting-torque transients and high inrush currents in induction motors are typically mitigated by employing electronically controlled soft starting voltages through silicon controlled rectifiers (SCRs). However, the heat dissipation in the soft starter must be carefully managed in the design of motor drives. The objective of this study is to address the heat dissipation in the soft starter by implementing analytical solutions to the heat diffusion equations inside the soft starter. The transient analytical thermal model allows an estimation of the thermal system transfer function from the transient thermal impedance curve, and can be incorporated into a dynamic system model in order to determine the transient performance of a soft starter by evaluating the thyristor junction temperature for different switching time profiles, motor and load combinations, and “ON/OFF” cycles. Predictions from the model are validated by comparing against a coupled thermal and electrical model using a resistance/capacitance network approach.
Dynamic Model Fuzzy Transition in DMC Type Controllers for Varying Dynamics in Bioreactors
Authors: Cantero Katty M. , Sanjuan Marco E.
Published: August 2009

This research presents an approach to implement industrial type DMC (Dynamic Matrix Control) controllers in biological process where a fed-batch operation is required. In this type of operation a substantial change in the process dynamics occurs due to changes in volume, reaction rate, pressure, temperature, concentration, and other process variables. To compensate for changes in the dynamic, several matrix models are identified, and using a fuzzy supervisor a soft model transition is implemented, such that the controller and the process performance can adapt to the new operating conditions without affecting the process integrity. The control system design, its identification, and implementation are presented, focusing in the articulation between MPC (Model Predictive Control) and Fuzzy Supervision. The overall strategy is demonstrated at a simulation level using a benchmark fermentation process for Penicillin production in Fed-Batch mode. In this process glucose is used as a substrate, and a fungus, penicillium chrysogenum, is used in a fed-batch reactor to obtain penicillin. The model presents an unstructured approach to the reactor dynamic system, and the initial steps for this research required the development of an identification procedure for such zones.
Metamaterials With Tunable Stop Bands
Authors: Huang H. H. , Sun C. T.
Published: August 2009

Metamaterials are materials with manmade microstructures. Recently, researchers have looked at a class of metamaterials whose microstructures contain internal degrees of freedom that are different from those of the macro-medium. These metamaterials exhibit unusual dynamic behavior and if modeled as homogeneous solids then their effective mass densities would become negative in certain frequency range. Specifically, a new stop band in the vicinity of the local resonance frequency of the internal mass in the microstructure would result. In this paper, a one dimensional metamaterial is employed to investigate the meaning of the negative mass density in the material and the energy flow in and out of the microstructure. In addition, numerical solutions are used to illustrate the phenomenon.
Predicting the Thermal Boundary Resistance of Isolated and Closely-Spaced Si/Si1−XGeX Interfaces With Molecular Dynamics Simulations
Authors: Landry E. S. , Matsuura T. , McGaughey A. J. H.
Published: August 2009

Phonon scattering at an interface between two materials results in a thermal boundary resistance R, given by [1] R=ΔTq,(1) where ΔT and q are the temperature drop and heat flux across the interface. Predicting the thermal boundary resistance of semiconductor/semiconductor interfaces is important in devices where phonon interface scattering is a significant contributor to the overall thermal resistance (e.g., computer chips with high component density). Such predictions will also lead to improvements in the design of nanocomposite materials (e.g., superlattices) with low thermal conductivity, desirable in thermoelectric energy conversion applications [2].
Development of Combustion-Driven Thermoacoustic Engine
Authors: Shafrei Tehrany Najmeddin , Lin Chien Shung , Bloomquist Cory , Ahn Jeongmin , Matveev Konstantin
Published: August 2009

Miniature thermoacoustic engines driven by combustion and producing electricity are promising candidates for small-scale power devices. The elemental development of the system including a small thermoacoustic engine and a Swiss roll combustor is discussed in this work. A standing-wave thermoacoustic prime mover consists of a resonator with a stack of porous material inside where a temperature gradient is maintained. This engine generates acoustic power from heat. The sound energy can be converted in electricity by an electroacoustic transformer. The Swiss roll combustor utilizes the high energy density of hydrocarbon fuels in order to provide the necessary heat transfer required to generate acoustic power from the engine. Some results of this developmental study are presented.
Interaction of Dislocations With Interfaces in Nanoscale Multilayered Metallic Composites
Authors: Shao S. , Medyanik S. N.
Published: August 2009

Atomistic simulation studies of dislocation nucleation and propagation in nanoscale multilayered metallic systems (Cu-Ni and Cu-Nb) are performed. Nanoindentation model is used to generate dislocations at and near the surface. Interaction of the propagating dislocations with two types of interfaces (coherent and incoherent) is analyzed. In the case of coherent interface, Cu(111)-Ni(111), dislocations that initiate in Cu layer propagate through the interface into Ni. However, the interface acts as an obstacle for dislocation propagation and leads to a higher dislocation density near the interface. In the case of incoherent interface, Cu(111)-Nb(110), dislocations that initiate in Cu do not propagate into Nb and tend to accumulate in copper near the interface. In both cases, the interfaces provide mechanisms for strengthening the nanoscale multilayered metallic systems.
Impact of Piezoresistive Coefficient Uncertainty on Stress Measurement Using Silicon Multi-Resistor Sensor Rosettes
Authors: Jaeger Richard C. , Cho Chun-Hyung , Hussain Safina , Suhling Jeffrey C.
Published: August 2009

Multi-element resistor rosettes on silicon are widely utilized to measure integrated circuit die stress in electronic packages and other applications. Previous analyses of many sources of error have led to rosette optimization and the realization that temperature compensated stress extraction should be used whenever possible. However, error in stress extraction due to the inherent uncertainty in knowledge of the values of the piezoresistive coefficients has not been explored in detail. In this work, direct analysis of the sensitivities of the extracted stresses to uncertainties in the piezoresistive coefficients is presented. The sensitivities are found to be stress dependent and therefore vary widely from very small to very large over the die surface. The results indicate that temperature compensated rosette configurations should be utilized whenever possible. Study of these sensitivities may lead to new rosette optimizations.
Scenario-Based Design for Amorphous Systems
Authors: Kim Sun K. , Ishii Kosuke , Beiter Kurt A.
Published: August 2009

Designing amorphous systems is difficult. Not only does the design team have to deal with various building blocks, such as hardware, software, service, infrastructure, and policy, but there are communication challenges among team members with different domain-expertise. This research begins with the observation that, at the onset of an amorphous system-oriented project, design teams struggle because they are limited to knowledge of less than 4 W’s of the 6 W’s (Where, What, Who, When, Why, How) rather than detailed functional or structural specifications. The proposed scenario-based approaches enable design teams to effectively deal with ambiguity and to communicate their ideas among the team as well as with customers and managers through a common language. The framework is based on conventional dfX (Design for X), but new methods such as the Scenario Graph, the Scenario Menu, and Dynamic-Customer Value Chain Analysis (D-CVCA) help design teams through the exploration stage of a new system development. The integrated framework guides the design teams in visualizing scenarios, making decisions, and building a sound business model for an amorphous system.
Abrasive Waterjet Peening With Elastic Prestress: Effect of Boundary Conditions
Authors: Sadasivam Balaji , Hizal Alpay , Arola Dwayne
Published: August 2009

Abrasive Waterjet Peening (AWJP) has emerged as a potential surface treatment process for metal implants and prosthetic devices. An elastic tensile prestress has been shown to increase the magnitude and depth of residual stress that can be obtained. In the present investigation, the subsurface residual stress fields resulting from AWJ peening of Ti6Al4V with load control and displacement control elastic prestress were compared. Prestress ranged from 0 to 75% of the material’s yield strength and the subsurface residual stress distribution was quantified using the layer removal technique. Results showed that the surface residual stress was dependent on the boundary conditions for prestress levels less than 60% of the materials yield strength. The magnitude of surface residual stress and the stored elastic energy were up to 50% and 100% larger respectively when load controlled boundary conditions were used. However, the boundary condition did not affect the depth of compressive residual stress.
Static and Dynamic Analysis of a Bistable Micro-Actuator
Authors: Towfighian S. , Abdel-Rahman E. M. , Heppler G. R.
Published: August 2009

The static response of an electrostatic micro-catilever beam has been obtained by using Galerkin’s method. To make the system bi-stable, a controller has been added and the static response profile is presented using a multi-mode model for the beam. The number of mode shapes leading to convergence has been studied. The softening effect of adding more mode shapes has been investigated along with the effect of changing the system parameters on the static response. Decreasing the controller gain has been found to widen the voltage range of the bi-stability region and increasing the sensor amplification factor is shown to push the upper equilibrium point away from pull-in. Properly choosing these parameters can adjust the range of voltage for bi-stability. By doing a linearization about the stable fixed points, we also found the two natural frequencies for each stable equilibrium point. Finally, we have found the dynamic response of the bistable system using one- and three-mode-models. The basins of attraction for each stable fixed point and the exchange of energy between the two potential energy wells (equilibrium points), are demonstrated.
Gas Mixing Analysis in a Large-Scaled Saltstone Facility
Authors: Lee Si Y.
Published: August 2009

Computational fluid dynamics (CFD) methods have been used to estimate the flow patterns mainly driven by temperature gradients inside vapor space in a large-scaled Saltstone vault facility at Savannah River site (SRS). The purpose of this work is to examine the gas motions inside the vapor space under the current vault configurations by taking a three-dimensional transient momentum-energy coupled approach for the vapor space domain of the vault. The modeling calculations were based on prototypic vault geometry and expected normal operating conditions as defined by Waste Solidification Engineering. The modeling analysis was focused on the air flow patterns near the ventilated corner zones of the vapor space inside the Saltstone vault. The turbulence behavior and natural convection mechanism used in the present model were benchmarked against the literature information and theoretical results. The verified model was applied to the Saltstone vault geometry for the transient assessment of the air flow patterns inside the vapor space of the vault region using the potential operating conditions. The baseline model considered two cases for the estimations of the flow patterns within the vapor space. One is the reference baseline case. The other is for the negative temperature gradient between the roof inner and top grout surface temperatures intended for the potential bounding condition. The flow patterns of the vapor space calculated by the CFD model demonstrate that the ambient air comes into the vapor space of the vault through the lower-end ventilation hole, and it gets heated up by the Benard-cell type circulation before leaving the vault via the higher-end ventilation hole. The calculated results are consistent with the literature information. Detailed results and the cases considered in the calculations will be discussed here.
Multiscale Modeling of Nanoscale Systems Based on Space/Time Formulation
Authors: Qian Dong , Chirputkar Shardool U.
Published: August 2009

There has been an increasing interest in developing concurrent simulation technique based on coupled atomistic/continuum representations. An important challenge in implementing this technique in studying the nanoscale material systems is the incompatibility between the continuum and atomistic descriptions at the interface, which sometimes leads to artificial reflections and numerical errors. In this work, we present a space/time enrichment approach in which the enrichment scales are introduced on top of the continuum approximation. Using the partition-of-unity concept, we establish multiscale approximation based on the fine-scale physics that are associated with the particular application. Following this, a coupled solution scheme is developed and the coupled continuum/atomistic simulation method is derived within the framework of space/time discontinuous Galerkin method. A unique advantage of the developed methodology is that it allows one to directly address multiscale phenomena that are coupled in space and time. After an outline of the basic formulation, we illustrate the robustness of the method by focusing on finite temperature material systems. We show that the wave transmitting boundary conditions can be achieved simultaneously with energy conservation.
Application of a Genetic Optimization Method to a 2-D Constructal-Based Cooling Configuration
Authors: Robbe Mauro , Sciubba Enrico
Published: August 2009

The thermal performance of a 2-D section of a prismatic body cooled by internal tubes arranged in a bundle according to the prescriptions of Constructal Theory, is analyzed. The flow inside each tube is fully developed. The heat transfer from the slab to the coolant flowing inside the tubes and the average temperature of the slab provide the metric to evaluate the system thermal performance. In this initial study, all quantities are calculated by reducing the original 3d model to a simplified 2d geometry, corresponding to a section obtained by intersecting the slab with a plane normal to the mean flow direction. One of the possible 2D sections, at an arbitrarily chosen distance from the onset of the fully developed flow regime, has been parameterized to create a design template. A “design of experiment” based on the SOBOL algorithm is used to set an initial family of 2D slab configurations (i.e., different cooling tubes arrangements). A multi-objective genetic algorithm (MOGA II) is then used to optimize the slab thermal performance starting from the initial family set. The results confirm that Constructal Theory correctly predicts the “nearly-optimal” tube arrangement that ensures the minimal average temperature in the solid. However, at least one non-Constructal configuration exists that produces a “better optimum” than Constructal geometry. It is also found that, in the 2-D configuration analyzed here, the two objective functions of “minimum material temperature” and of “maximum heat rejection to the coolant” are concurrent, i.e., they share the same solution space.
Use of Nanoindentation to Determine Biphasic Material Properties of Articular Cartilage
Authors: Miller Gregory J. , Morgan Elise F.
Published: August 2009

Nanoindentation (NI) has been used with increasing frequency to characterize the mechanical properties of biological tissues. However, the majority of prior studies in this area have focused on hard tissues such as bone, enamel, and dentin [1]. For soft, hydrated tissues and biomaterials, methods of analyzing the force-displacement curves to obtain meaningful information on viscoelastic material properties are still under development. In particular, methods for using NI to quantify the biphasic material properties (aggregate modulus HA, permeability k, Poisson’s ratio ν) of tissues such as articular cartilage have not been established. Such methods could be applied in studies using small animal models to investigate biological and biomechanical mechanisms of articular cartilage degeneration and repair. The overall goal of this study was to develop the use of NI for characterization of the mechanical properties of soft, hydrated materials.
An Approach Experimentally Based Modeling and Simulation of Human Motion
Authors: Lee Jenchieh , Flashner Henryk , McNitt-Gray Jill
Published: August 2009

A computational approach for estimating three-dimensional human body motion from measurement of marker locations during motion is proposed. The proposed method computes the system’s kinematics while preserving important physical and dynamic properties. These properties include preserving the connection point (joint) between any two neighboring bodies and satisfying total body linear and angular momentum conservation laws. Four sets of equations are formulated for kinematic and dynamic properties of body segments. Attitude estimation is based on Wahba’s problem [1], and dynamic and kinematic constraints are included by utilizing penalty function method. An iteration process is presented to combine the four sets of estimation measure to ensure convergence to the optimal solution. Two examples are presented to demonstrate the performance of the proposed method: estimation of the kinematics of a chain of rigid bodies obtained by computer simulation, and estimation of motion in three dimension of a diver obtained using experimental measurements. The results of both examples show fast convergence of the algorithm to an optimal solution while satisfying the imposed the constraints.
Three-Axis Gimbal Surveillance Algorithms for Use in Small UAS
Authors: Ranganathan Jaganathan , Semke William H.
Published: August 2009

An active three-axis gimbal system is developed to allow small fixed wing Unmanned Aircraft Systems (UAS) platforms to estimate accurate position information by pointing at a target and also to track a known target location. Specific targets vary from a stationary point on the ground to aircraft in the national airspace. The payload developed to accomplish this at the University of North Dakota is the Surveillance by University of North Dakota Observational Gimbal (SUNDOG). This paper will focus on a novel, nonlinear closed form analytical algorithm developed to calculate the exact rotation angles for a three-axis gimbal system to point a digital imaging sensor at a target, as well as how to estimate accurate position of a target by using the pointing angles of a three-axis gimbal system. A kinematic analysis is done on a three-axis gimbal system to get the appropriate model of gimbal rotations in order to point at a certain location on the ground. The mathematical model includes an inertial coordinate system that has coordinates fixed to the Earth, a coordinate system that is body-fixed to the aircraft, and a third coordinate system that is fixed to the gimbal. Therefore, multiple three-dimensional transformations are required to accurately provide the necessary pointing angles to the gimbal system. The autonomous control system uses Global Positioning System (GPS), Inertial Measurement Unit (IMU), and other sensor data to estimate position and attitude during flight. Since the algorithm is entirely based on Inertial Measurement Unit (IMU) and Global Positioning System (GPS) device inputs, any error from these devices cause offset in the target location. Hence, an error analysis is carried out to find the offset distance and the operating range of the algorithm. The main advantage obtained in the three-axis gimbal system is that the orientation of the image will always be aligned in a specified direction for effective interpretation. The closed form expressions to the non-linear transformations provide simple solutions easily programmed without large computational expense. Experimental work will be carried out in a controlled environment and in flight testing to show the autonomous tracking ability of the gimbal system. Simulation and experimental data illustrating the effectiveness of the surveillance algorithms is presented.
Dynamic Recrystallization of Sn3.0Ag0.5Cu Pb-Free Solder Alloy
Authors: Holdermann Ken , Cuddalorepatta Gayatri , Dasgupta Abhijit
Published: August 2009

This study examines microstructural recrystallization in Sn3.0Ag0.5Cu (SAC305) solder joints due to isothermal, mechanical cycling. It is well known that after reflow SAC solder joints at length scales of 200 μm consist of only a few grains [1–3]. This coarse microstructure makes the joint mechanically inhomogeneous and anisotropic, and non-repeatable. Creep tests conducted on modified lap-shear SAC305 solder joints therefore show significant scatter in their results, because of piece-to-piece variability in the microstructural morphology [1]. However, results of cyclic fatigue tests of the same SAC305 solder joints show less significant scatter [4]. One possible hypothesis is that dynamic recrystallization occurs during the cycling, resulting in a much finer (and hence more isotropic, homogeneous and repeatable) microstructure. Recrystallization of solder has been reported to occur under thermal cycling [5–6]. The objective of this study is to assess the extent of recrystallization of SAC305 solder during isothermal mechanical cycling fatigue. Focused ion beam technology is used to prepare a very clean and even surface to reveal the SAC305 grains in modified lap-shear test specimens, both before and after isothermal mechanical cycling. Polarized light microscopy, scanning electron microscopy and focused ion beam microscopy are used to reveal the microstructure of these SAC305 solder joints. The results show that mechanical cycling produces the same type of recrystallization behavior of SAC solder, as has been reported in the literature for thermally cycled specimens [5–6]. The number of grains in the SAC305 solder joint changes from a few to hundreds, during mechanical cycling. As expected, the recrystallization is observed to be localized around cracks in the solder joint, where the local stresses are the highest. The minimal grain size near the cracked region is approximately 4–6 μm and the average grain size increases significantly with increasing distance from the crack face. The transition of solder from very few (non-homogeneous and anisotropic) to a homogenous recrystallized state may be one possible explanation for differences in the extent of scatter in the data from creep tests and isothermal mechanical fatigue tests.
Interface and Dynamic Indentation of Crosslinked Polyester Films
Authors: Ahuja Suresh
Published: August 2009

Nano-indentation is increasingly used to estimate the mechanical properties of polymeric films of nanometer-scale thickness. Hardness and modulus, as obtained on indentation are parameters that are strongly dependent upon tip geometry, elastic and inelastic material behavior, and specimen boundary conditions. The objective of this study was to analyze the mechanical response of nano-indentation loading on surfaces and interfaces of polymer films both linear and cross-linked. Polymer films on nano-indentation show confinement effect on their modulus and hardness. Reduced modulus and hardness in polyester and polycarbonate show strain softening that is associated polymer chain flexibility. The spatial constraints imposed to the plastic flow of the interface layer by the rigid indenter and substrate surfaces produce a dynamic effect, demonstrated by the loading rate dependence of the deformation response. In nano-indentation of cross-linked polymers, entanglements physical and chemical affect reduced modulus and hardness dependence on strain. Strain softening and strain hardening as well as dynamic frictional response are applied to indented polymer films consisting of surface, intermediate, and interface layers.
Binary Excitation of a High-Q Bulk Acoustic Microresonator by Actuation Polarity Inversion
Authors: Lee Joshua E.-Y. , Seshia Ashwin A.
Published: August 2009

We present a technique for independently exciting two resonant modes of vibration in a single-crystal silicon bulk mode microresonator using the same electrode configuration through control of the polarity of the DC actuation voltage. Applications of this technique may include built-in temperature compensation by the simultaneous selective excitation of two closely spaced modes that may have different temperature coefficients of resonant frequency. The technique is simple and requires minimum circuit overhead for implementation. The technique is implemented on square plate resonators with quality factors as high as 3.06 × 106.
Biomimetic Prosthetic Knee Using Antagonistic Muscle-Like Activation
Authors: Martinez-Villalpando Ernesto C. , Weber Jeff , Elliott Grant , Herr Hugh
Published: August 2009

The majority of commercial prosthetic knees are passive in nature and therefore cannot replicate the positive mechanical work exhibited by the natural human knee in early and late stance. In contrast to traditional purely dissipative prosthetic knees, we propose a biomimetic active agonist-antagonist structure designed to reproduce both positive and negative work phases of the natural joint while using series elasticity to minimize net energy consumption. We present the design and implementation of the active knee prosthesis prototype.
Microstructural Constitutive Equation for Sprain Analysis
Authors: Guo Zheying , De Vita Raffaella
Published: August 2009

A new constitutive equation is presented to describe the damage evolution process in parallel fibered collagenous tissues such as ligaments and tendons. The model is formulated by accounting for the fibrous structure of the tissues. The tissue’s stress is defined as the average of the collagen fiber’s stresses. The fibers are assumed to be undulated and straighten out at different stretches that are defined by a Weibull probability density function. After becoming straight each fiber is assumed to be linear elastic. Its waviness is defined by a Weibull distribution. Tissue’s damage is assumed to occur at the fiber level and is defined as a reduction in the fiber’s stiffness. The proposed model is validated by using experimental data published in the biomechanics literature by Provenzano et al. [1].
On Subharmonic Resonances of Geometric Nonlinear Vibrations of Nonuniform Beams
Authors: Caruntu Dumitru I.
Published: August 2009

Subharmonic resonances of nonlinear forced bending vibrations in the case of moderately large curvature of nonuniform cantilever beams of rectangular cross section and a sharp end are reported. Cantilevers of constant width and parabolic thickness variation are considered in this research. The method of multiple scales is directly applied to the governing partial-differential equation of motion and boundary conditions. Two problems, zeroth- and first-order, result. Using factorization method, the linear modes of the zeroth-order problem are obtained in terms of hypergeometric functions. The first-order problem provides the amplitude and phase evolution equation and consequently the regions where subharmonic responses exist.
Experimentally Based Modeling of Whole Body Movement During Contact
Authors: Munaretto Joseph M. , McNitt-Gray Jill L. , Flashner Henryk
Published: August 2009

In this paper, we investigated how the assumption of fixed segment lengths in two dimensional whole body dynamic models limits accuracy in reproducing experimental reaction forces and observed kinematics. A six segment whole body dynamic model of the musculoskeletal system was developed to simulate the measured forces and kinematic data during the contact phase of two somersaulting tasks performed by two Olympic level divers. Initial conditions and foot-surface model parameters were refined using optimization to ensure that change in whole body center of mass (CM) linear and angular momenta satisfied the impulse/momentum relationship for both dives and divers. Simulation results indicate that the assumption of fixed segment lengths increases error in prediction of the CM trajectory in the sagittal plane. Sensitivity analysis shows that a foot/surface model high in stiffness is more accurate in reproducing observed foot metatarsal displacement but is also more sensitive to the velocity of the metatarsals at contact than a less stiff foot-surface model. As a result, the assumption of a fixed foot segment length also affects the process of optimizing the initial conditions and foot-surface parameters. These findings suggest that a 2D representation of segment motion using fixed segment lengths is limited accuracy because the fixed length representation of segment kinematics does not reflect out of plane motion. Tracking the effect of error introduced by input kinematics on model performance is essential in the process of validating a 2D model of human movement during contact with the environment.
Project Based Activities to Attract Students to Marine Engineering and Technology Careers
Authors: Verma Alok K. , Erande Ameya S.
Published: August 2009

During the past several years, workforce issues have immerged as a dominant concern for shipbuilding and repair companies. Related issues include concern about “aging” of the workforce, lack of basic technical education, career transition processes, recruitment and training of the new workforce, retention and training of the incumbent workforce, image of the industry, and lack of career information for middle and high school students. Large turnover combined with retirement of aging workforce is anticipated to create large demands for qualified workforce. The Shipbuilding and Repair Career Day Events (SBRCD) project was conceived in response to this critical need of workforce in shipbuilding and repair industry. This project was funded by the National Shipbuilding research Program to increase awareness about careers in marine industry. The paper discusses the multi-pronged effort within the SBRCD project to inform and engage middle and high school students, teachers and counselors about career opportunities in this industry. The paper also discusses the design and development of four simulation activities known as marine kits to engage students in shipbuilding related projects. These activities are tied to Virginia Standards of Learning (SOL) so teachers can use them in classrooms without loosing time. The Marine Kits were pilot tested and results are discussed.
Modeling and Simulation of Shock and Drop Loading for Complex Portable Electronic Systems
Authors: Askari Farahani Farbod , Al-Bassyiouni Moustafa , Dasgupta Abhigit , Tolchinsky Sheldon
Published: August 2009

In this study, the transient response of electronic assemblies to mechanical loading encountered in drop and shock conditions are investigated. Many manufactures face design challenges when evolving new designs for high-strain rate life-cycle loading. Examples of high-strain rate loading include drop events, blast events, vibration, ultrasonic process steps, etc. New design iterations invariably bring new unexpected failure modes under such loading and costly trial-and-error design fixes are often necessary after the product is built. Electronics designers have long sought to address these effects during the design phase, with the aid of computational models. However, such efforts have been difficult because of the nonlinearities inherent in complex assemblies and complex dynamic material properties. Our goal in this study is to investigate the ability of finite element models to accurately capture the transient response of a complex portable electronic product under shock and drop loading. While many researchers have shown qualitative ability for such modeling, further work is still needed to demonstrate good quantitative agreement. The product consists of a circuit card assembly in a plastic housing. Dynamic loading, consisting of various shock profiles, is applied using an electrodynamic shaker. Limited number of drop tests are also conducted on a drop tower. The modeling is conducted in ABAQUS/Explicit. In-plane strains and accelerations are the parameters that are compared to assess the agreement between the model and the experimental results. The long-term goal of this study is to demonstrate a systematic methodology to predict failure modes during the design phase of future products.
Numerical Modeling of Microfluidic Two-Phase Electrohydrodynamic Instability
Authors: Narayanan Venkat R. T. , Li Jianbo , Zahn Jeffrey D. , Lin Hao
Published: August 2009

Organic-aqueous liquid (phenol) extraction is one of many standard techniques to efficiently purify DNA directly from cells. Effective dispersion of one fluid phase in the other increases the surface area over which biological component partitioning may occur, and hence enhances DNA extraction efficiency. Electrohydrodynamic (EHD) instability can be harnessed to achieve this goal and has been experimentally demonstrated by one of the co-authors (JDZ). In this work, analysis and simulation are combined to study two-phase EHD instability. In the problem configuration, the organic (phenol) phase flows into the microchannel in parallel with and sandwiched between two aqueous streams, creating a three-layer planar geometry; the two liquid phases are immiscible. An electric field is applied to induce instability and to break the organic stream into droplets. The Taylor-Melcher leaky-dielectric model is employed to investigate this phenomenon. A linear analysis is carried out with a Chebyshev pseudo-spectral method, whereas a fully nonlinear numerical simulation is implemented using a finite volume, immersed boundary method (IBM). The results from both models compare favorably with each other. The linear analysis reveals basic instability characteristics such as kink and sausage modes. On the other hand, the nonlinear simulation predicts surface deformation in the strongly nonlinear regime pertinent to droplet formation. These numerical tools will be used to investigate the effects of the applied electric field, geometry, and convective flow rate on mixing and dispersion. The eventual objective is to maximize surface area of the organic phase under given experimental conditions for optimized DNA extraction.
Nano-Filled Polymer Composites for Biomedical Applications
Authors: Ramos Maximiano V. , Frederick Armstrong , Al-Jumaily Ahmed M.
Published: August 2009

Polymer nanocomposites offer various functional advantages required for several biomedical applications. For example, polymer nanocomposites are biocompatible, biodegradable, and can be engineered to have mechanical properties suitable for specific applications. The key to the use of polymer nanocomposites for different applications is the correct choice of matrix polymer chemistry, filler type, and matrix-filler interaction. This paper discusses the results of a study in the processing and characterization of nono-filled polymer composites and focuses on the improvement of its properties for potential biomedical applications. The experimental procedure for the preparation of nano-filled polymer composite by ultrasonic mixing is described. Different types of nanofillers and polymer matrix are studied. Effects of processing parameters such as percent loading of fillers, mixing time on the mechanical properties of the composites are discussed. Preliminary results indicate improvement in shear and flexural properties, tensile and compressive properties, were observed in the prepared composites for some processing conditions.
Modelling MEMS Resonators Past Pull-In
Authors: Vyasarayani Chandrika P. , Abdel-Rahman Eihab M. , McPhee John , Birkett Stephen
Published: August 2009

In this paper, we develop a mathematical model of an electrostatic MEMS beam undergoing impact with a stationary electrode subsequent to pull-in. We model the contact between the beam and the substrate using a nonlinear foundation of springs and dampers. The system partial differential equation (PDE) is converted into coupled nonlinear ordinary differential equations (ODEs) using the Galerkin method. A numerical solution is obtained by treating all nonlinear terms as external forces.
Ab Initio Calculations of Infrared Absorption Cross Sections of CO2 Gas
Authors: Liang Zhi , Tsai Hai-Lung
Published: August 2009

An ab initio model is used to determine the infrared absorption cross sections of CO2 gas as a function of laser wavelength. The intra-molecular potential energy and electric dipole moment of the CO2 molecule as a function of molecular nuclear configurations are obtained by solving the Kohn-Sham (KS) equation. The rotational constants at different vibrational levels, the vibrational energy eigen values and transition dipole moments are determined by solving the pure vibrational Schro¨dinger equation. Using the Fermi’s Golden Rule and all the calculated ab initio results, the absorption cross sections of CO2 gas at room temperature and one atmosphere pressure are obtained. The calculated results have a good agreement with experimental results. Based on the calculated ab initio results, the infrared absorption cross sections of CO2 gas at higher pressures are calculated. The absorption spectra at high pressures are found to be much smoother due to the overlaps between neighboring absorption line shapes.
Effects of Circumferential Heating Variations and Channel Height on Heat Transfer Coefficient of Wetted Surfaces in a Single Inline Row Impingement Channel
Authors: Ricklick Mark , Kersten Stephanie , Krishnan V. , Kapat J. S.
Published: August 2009

High performance turbine airfoils are typically cooled with a combination of internal cooling channels and impingement channels. In such applications, the jets impinge against a target surface, and then exit along the channel formed by the jet plate, target plate, and side walls. Local convection coefficients are the result of both the jet impact, as well as the channel flow produced from the exiting jets. Numerous studies have explored the effects of jet array and channel configurations on both target and jet plate heat transfer coefficients. However, little work has been done in examining effects of circumferentially non-uniform heating on all channel walls, which is the kind of thermal boundary condition in real world applications. This paper examines the local and averaged effects of channel height and circumferential heating variations on heat transfer coefficients. High resolution local heat transfer coefficient distributions on target and side wall surfaces were measured using temperature sensitive paint and recorded via a scientific grade charge-coupled device (CCD) camera. Streamwise pressure distributions for both the target and side walls was recorded and used to explain heat transfer trends. Results are presented for average jet based Reynolds numbers between 17,000 and 45,000. All experiments were carried out on a large scale single row, 15 hole impingement channel, with X/D of 5, Y/D of 4, and Z/D of 1, 3 and 5.
Performance Characterization of a Traveling-Wave Electrohydrodynamic Micropump
Authors: Iverson Brian D. , Garimella Suresh V.
Published: August 2009

Microscale fluidic manipulation using traveling-wave, induction electrohydrodynamics is demonstrated. A three-phase traveling-wave device fabricated for the experiments provides a temporally and spatially varying electric field which helps induce ions in a fluid subject to a temperature gradient. These ions are moved as the traveling wave propagates, resulting in a drag force being exerted on the surrounding fluid. Repulsion-type electrohydrodynamic flow is visualized in a microchannel of depth 50 μm, and results are presented in terms of velocity measurements using particle image velocimetry.