bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparative Study on Evaluating Fatigue Performance of Forged Steel Versus Different Material Automotive Component
Authors: Jhala R. L. , Khandare S. S.
Published: May 2012

The overall objective of this paper is to compare and evaluate the fatigue performance of two competing manufacturing technologies for automotive component, namely forged steel and cast iron steering knuckle. The paper details the different experimental evaluation, mechanical properties and performance of two materials and components, their results for the steering Knuckle. Fatigue is the primary cause of failure of component due to the cyclic loading and presence of stress concentrations at the fillets and critical areas. The steering knuckle consisted of mainly sections namely spindle, strut mounting holes and hub mounting attachments. The masses of both steering knuckle were similar with the forged steel at 4.8 kg and the cast iron at 4.5 kgs. Also, the failure location of the steering knuckle used in this study was in the first step and second step fillet, which agrees with the typical failure location for an automotive steering knuckle. The paper concludes that the crack growth life for both steering knuckle was a significant portion of the fatigue life during the steering knuckle testing. The crack growth rate of the forged steel steering knuckle was slower than the cast iron steering knuckle. During steering knuckle fatigue tests, circumferential cracks developed in the first step and second step fillet of both forged steel and cast iron steering knuckles which was identified as the critical location from FEA.
Entropy Generation in Isothermal Laminar Flow Through Bifurcated Tubes With Wall Suction
Authors: Sciubba Enrico
Published: May 2012

The paper presents an analysis of the entropy generation in the bifurcation of a fluid-carrying tube in the presence of wall suction. The objective is to minimize the entropy generation rate due to the viscous flow within the tubes. Several simplifying assumptions are made to reduce the problem to a multi-objective optimization in 3 independent variables: the aspect ratio of the domain served by the flow, the diameter ratio of the primary and secondary branches, and the length of the secondary branch (the location of both the “source” of the fluid and the “sink”, i.e. the place of desired delivery of the fluid, being a datum). The wall suction is assumed to be proportional to the wetted area. For three different initial assumptions (constant Re, constant fluid velocity, constant fluid volume) it is shown that an “optimal shape” exists and is identified by the minimum entropy generation. But, this minimum is always higher than the value pertaining to the unsplit tube with no wall suction. The study demonstrates that, for a given design goal (i.e., for an assigned “function” the configuration is called to perform) Entropy Generation Minimization is a feasible “topological Lagrangian” for the bifurcation geometry.
Detection and Characterization of Pulsatile Flow Induced Acoustic Emissions in Stenosed Arterial Geometric Models
Authors: Gebreegziabher T. , Ayorinde E. , Singh T.
Published: May 2012

A Newtonian fluid is used in a simplified experimental hydraulic model of a cardiovascular system (CVS) to study pulsatile flow in arterial geometric models with different stages of stenosis (restriction rates) and understand the progression of stenosis and how the fluid flow properties in stenosed sections of arteries behave. In this study, 16mm long cylindrical stenosis models (orifices) with different restriction rates were pressed into the middle section of a 570 mm long arterial geometric model (polyethylene tube) one at a time. The arterial geometric models were connected to a solenoid or reciprocating pump (DC Voltage) capable of generating pulsatile flow at different pumping frequencies. The effects of pulsatile flow properties (pressure pulse, flow rate, etc) on acoustic emission (AE) signal levels using sensors for the detection of elastic waves in the arterial models for different restriction rates of stenoitic geometric models (orifices) at different pumping frequencies have been investigated. The results from this research show that there is a strong correlation between the flow properties of the Newtonian fluid in the arterial geometric models and the level of the flow induced AE signal indicators such as the waveforms, elastic energy, number of events, etc. Thus, as AE techniques can be used to predict flow characteristics in a given geometric model to assess the restriction level of a flow passage, the same principle could be applied in the detection of severe atherosclerosis or stenosis in large arteries — human external carotid arteries.
A Hybrid Approach to Force Balancing of Robotic Mechanisms
Authors: Huang J. , Ouyang P. R. , Cheng L. , Zhang W. J.
Published: May 2012

A hybrid approach to force balancing of robotic mechanisms which have at least two degrees of freedom is proposed. This hybrid approach is to combine adjusting kinematic parameters (AKP) and counterweights (CW) approaches, and it is called AKP+CW in short. The main motivation of the AKP+CW approach is that CW and AKP each has its own advantage and disadvantage, and thus a combined one may strengthen the both. This paper presents the force balancing principles and equations for the AKP+CW approach. Software called ADAMS is employed as a tool for the simulated experiment to verify the effectiveness of the proposed approach. The implication of the work described in this paper to the balancing of mechanisms in general is that many different force balancing methods may be combined based on the hybridization principle proposed in this paper to become a novel one.
Micromechanical Model for Examination and Characterization of Interfacial Response of Fibrous Composites
Authors: Sarkar Romit , Banerjee Rusha , Karami Ghodrat , Azarmi Fardad
Published: May 2012

A micromechanical model for a Representative Volume Element (RVE) of a composite material to study the interface adhesion is introduced. The composite constituents assumed to have elastic properties with unidirectional fiber arrangement. The characterization is performed to study the interface and the separation/delamination of layers and their impacts on the overall mechanical response and properties of the composite material. Finite element package ANSYS is used to simulate the conditions of the interface employing cohesive zone modeling. The impact of an increasing axial transverse loading force on the interface in terms of its separation is studied. The exponential traction-separation curve pioneered by Xu and Needleman [1] will be implemented. The RVE is periodically constrained to represent a common element within the continuum domain far from the locality influence of the force and for a homogenized mechanical behavior study of the interface. The examination of the characteristics of the cohesive zone element as a simulation tool for interface analysis gives us conditions of a closer simulation for tissue engineering analysis.
Experimental Investigations of Minimum Power Consumption Optimal Control for Variable Speed AMB Rotor
Authors: Barbaraci Gabriele , Pesch Alexander H. , Sawicki Jerzy T.
Published: May 2012

The purpose of this paper is to present a method for development of the optimal speed-dependent control matrix for a rotor supported on active magnetic bearings (AMBs) with the provision of minimum control power consumption over the operating speed range. The speed dependency of the optimal control matrix is the result of the dynamics of rotating machines. Most of published works on optimal control use a stationary optimal control matrix derived for the non-rotating system and thus neglecting the effect of gyroscopic phenomena. This paper employs the minimum energy consumption condition to derive the speed varying optimal control for rotating AMB rotor system. In the presented approach the control matrix is characterized by a second order polynomial matrix with the angular speed as a variable. This leads to a more compact and lower computational burden for controller implementation. Calculations are performed for a 4-axis AMB rotor test rig. Testing with rotor speed ramps is performed and experimental values for power consumption are presented. These results are compared to results with speed invariant optimal control and PID control.
Multi-Robot Cooperative Transportation of Objects Using Modified Q-Learning
Authors: Siriwardana Pallege Gamini Dilupa , Silva Clarence de
Published: May 2012

In cooperative multi-robot object transportation, several autonomous robots navigate cooperatively in either a static or a dynamic environment to transport an object to a goal location and orientation. The environment may consist of both fixed and removable obstacles and it will be subject to uncertainty and unforeseen changes within the environment. More than one robot may be required for handling heavy and large objects. This paper presents a modified Q-learning approach for object transportation utilizing cooperative and autonomous multiple mobile robots. A modified version of Q-learning is presented, which employs for effective robot coordination. A solution to the action selection conflicts of the robots is presented, which helps to improve the real time performance and robustness of the system. As required in the task, the paper presents an algorithm for object pose estimation, by utilizing the laser range finder and color blob tracking. The developed techniques are implemented in a multi-robot system in laboratory. Experimental results are presented to demonstrate the effectiveness of the developed multi-robot system and its underlying methodologies.
Optimization of Arrays of Rectangular Longitudinal Fins and Circular or Elliptical Cross-Section Spines
Authors: Razelos P. , Das S.
Published: May 2012

The purpose of this study is to illustrate a method for obtaining the thermal performance and optimum dimensions of arrays consisting of rectangular longitudinal fins, cylindrical and elliptical cross-section spines. Since the majority of fin problems in an array have constant boundary temperatures, our endeavor is focused on the analysis and optimization of these types of fins. The temperature distribution, heat released to the environment, and the fins’ optimum dimensions in the array have been determined. Our analysis is based on a new set of dimensionless parameters, which are more suitable than those frequently used in fin analyses in the available literature. The effects of the boundary temperature ratio on the temperature variation in the fin have been examined and the results are shown graphically. Three salient results are derived regarding the thermal characteristics of these types of fins. They are: (1) the fin’s heat dissipation is expressed exactly with the same expression which describes the optimum heat dissipated by a fin with insulated tip, having half the fin’s dimensionless height. (2) The optimum fins’ dimensionless height and thickness are identical with those obtained for a fin with adiabatic tip of twice the dimensionless height (3) The optimum semi-axes ratio of elliptical-cross section spines is uniquely defined. In addition, it is shown that this approach can be successfully applied to solve problems in several practical applications, including pin fins having elliptic-cross sections. Two examples serve to illustrate the usefulness of our method.
Effect of Microbeam Electrical Resistivity on Dynamic Pull-In Voltage of an Electrostatically Actuated Microbeam
Authors: Pasharavesh Abdolreza , Ahmadian M. T. , Alizadeh Vaghasloo Y. , Assempour A.
Published: May 2012

The dynamic pull-in voltage as a criterion for the system stability is one of the most important effects considered with the dynamics of microstructures. In this study effect of microbeam electrical resistivity on the pull-in voltage of an electrostatically actuated microbeam is investigated. Assuming Euler-Bernoulli theory for the microbeam, two coupled nonlinear partial differential equations are derived for the beam deflection and voltage. The one parameter Galerkin method is implemented to transform the equations to a set of nonlinear coupled ordinary differential equations. Obtained equations are solved implementing the differential quadrature method (DQM). Variation of dynamic pull-in voltage with changing the microbeam electrical resistivity with different boundary conditions and different configurations of voltage application, is investigated. Considering effect of resistivity on the deflection of the beam, it is observed that at a certain resistivity called critical resistivity there exists a jump in frequency with a peak in damping of the beam. Results indicate that the dynamic pull-in voltage increases when the microbeam electrical resistivity is increased and reaches the static pull-in voltage for resistivities higher than this critical resistivity.
Observer-Based Robust Control With Adaptive Perturbation Estimation for a Piezoelectric Actuator
Authors: Ghafarirad Hamed , Rezaei Seyed Mehdi , Abdullah Amir , Zareinejad Mohammad , Saadat Mozafar
Published: May 2012

Control of piezoelectric actuators is under the effects of hysteresis that could affect actuators micropositioning accuracy. In this paper a modified Prandtl-Ishlinskii (PI) operator and its inverse is utilized for both identification and real time compensation of the hysteresis effect. As a result, the actuator dynamic model would be transformed to the second order linear dynamic model. Considering the parametric uncertainties, PI estimation error and probably unmodeled dynamics, a variable structure controller coupled with adaptive perturbation estimation is proposed for trajectory tracking of the piezoelectric position. Requiring the velocity state of the actuator, a high-gain observer would estimate the full state from the only measurable position trajectory. The stability of the controller in the presence of the estimated state is demonstrated with the Lyapunov criterion. Comparing to the widely used proportional-integral controller, the experimental results depicts that the proposed approach is achieved in precisely tracking of multiple frequency trajectories.
Numerical Study of Flow and Heat Transfer Characteristics of Impinging Jets
Authors: Abdel-Salam Tarek M.
Published: May 2012

This study presents results for flow and heat transfer characteristics of two-dimensional rectangular impinging jets and three-dimensional circular impinging jets. Flow geometries under consideration are single and multiple impinging jets issued from a plane wall. Both confined and unconfined configurations are simulated. Effects of Reynolds number and the distance between the jets are investigated. Results are obtained with a finite volume computational fluid dynamics (CFD) code. Structured grids are used in all cases of the present study. Turbulence is treated with a two equation k-ε model. Different jet velocities have been examined corresponding to Reynolds numbers of 5,000 to 20,000. Results of the three-dimensional cases show that Reynolds number has no effect on the velocity distribution of the center jet. Results of both two-dimensional and three-dimensional cases show that Reynolds number highly affects the heat transfer and values of the Nusselt number. The maximum Nusselt number was always found at the stagnation point of the center jet.
FEM Analysis of a 0.50 Caliber Rifle Barrel
Authors: Anderson Gary A. , Lanoue Corey M. , Delfanian Fereidoon
Published: May 2012

In order to ensure rifle barrels have the features of high strength, durability, and light weight, the strength analysis of the barrels under hot temperatures and pressures is very important in the design. A finite element model incorporating the plastic deformation of a typical 0.50 caliber rifle barrel is constructed to determine the stresses caused by the mechanical loads and plastic deformation. According to the simulation results, the finite element analysis is proved to be a power analysis tool for future failure analysis of firearm barrels. The method provides a power tool for analysis of firearm barrels. The projectile was accelerated to 941.7 m/s in 1.430 ms with a pressure profile that reached a maximum of 469.3 MPa. Stresses as large as 1,410 MPa along the interior of the barrel were found where the leading edge of the projectile slides along the bore, but the largest stresses at the exterior of the barrel were found where the barrel wall is thinnest near the chamber.
Vibration Energy Harvesting of a Hydraulic Engine Mount Using a Turbine
Authors: Mohareri Omid , Arzanpour Siamak
Published: May 2012

The hydraulic engine mount (HEM) has been designed to provide a vibration isolation characteristic to control road and engine induced vibrations in vehicles by using two fluid passages known as decoupler and inertia track. These types of engine mounts are known for their best noise, vibration, and harshness (NVH) suppression performance among other different types of engine mounts. However, a low cost technique to recycle the dissipated energy of the system in the process of vibration suppression is significantly advantageous. A novel design structure in which the decoupler is replaced with a water turbine to capture and restore the vibration energy of the system is presented in this paper. The turbine design and selection has been done based on the upper and lower chamber pressures and the fluid flow rates in the system’s resonant frequency. The mount vibration isolation and energy generation performance is studied in both frequency and time domains. The simulation results demonstrate that a considerable amount of energy can be harvested from the engine vibration sources. This recent study demonstrates a novel energy harvesting technique in vehicles that require minimum design modifications of conventional hydraulic mounts.
Heat Transfer Performance of Superhydrophilic Nanostructured Cu Micropost Wicks for Micro Heat Pipes
Authors: Nam Youngsuk , Sharratt Stephen , Ju Y. Sungtaek
Published: May 2012

Micro-heat pipes incorporating advanced wicks are promising for the thermal management of power electronics. We report the heat transfer performance of superhydrophilic Cu micropost wicks fabricated on thin silicon substrates using electrochemical deposition and controlled chemical oxidation. For a fixed post diameter, the inter-post spacing and hence solid fraction is found to be a main design factor affecting the effective heat transfer coefficient and critical heat flux. The effective heat transfer coefficient as high as 20 W/cm2 K and the critical heat flux >500 W/cm2 over 2 mm × 2 mm heating areas are demonstrated. Copper oxide nanostructures formed on the micropost surfaces significantly enhance the critical heat flux without compromising the effective heat transfer coefficient. The advanced wick structures and experimental approaches developed in this work will help develop thin and lightweight thermal management solutions for high-power density semiconductor devices.
The Liquid Bridge Heat Switch Design With Considering the Pressure Behavior to Regulate the Thermal Resistance for the Temperature Control
Authors: Jeong Su-Heon , Nakayama Wataru , Lee Sun-Kyu
Published: May 2012

Various types of heat switch have been suggested as the promising solution of thermal management in the extremely low temperature condition. Recently, the heat switch based on the liquid for the room temperature condition has been investigated to control the thermal resistance of the electronic devices. The presented heat switch was composed of several micro channels. The key technology of the heat switch operation for room temperature is the fluid control. The existing studied indicates that the flow regulation was achieved by simple channel geometry design based on the burst pressure theory. In this research, the design of the liquid bridge heat switch was presented and the pressure characterization of the designed switch was carried out. The supplying liquid generates the liquid bridge between two plates. The thermal resistance between two plates depends on the liquid bridge diameter and height. The liquid bridge size control is achieved based on the pressure characterization.
Resonance Modelling and Control in Structures by Means of Magnetorheological Dampers
Authors: Letelier Mario F. , Siginer Dennis A. , Stockle Juan S. , Herrera Cristian
Published: May 2012

Many structures such as automobile bodies, bridges and buildings are subjected to external forces due to the nature of the environment in which they exist. When the external excitation frequency is similar to the structure’s natural frequency a resonance effect is generated, increasing the energy and the amplitude of the oscillation, often causing catastrophic situations. This paper presents a method to decrease such resonant oscillations using magnetorheological dampers.
Laminar Flow Model in Ducts of Circular Section With Arbitrary Axial Variation
Authors: Letelier Mario F. , Siginer Dennis A. , Stockle Juan S. , Huilcan Andy
Published: May 2012

Laminar flow inside a circular duct of variable section in the axial direction is modeled, assuming that the working fluid is Newtonian, incompressible, with laminar flow, a permanent state, and constant properties. The results describe the behavior of the stream function, the velocity field, and the pressure field, and graphic results are presented for each of those functions. The method used to solve the problem makes use of regular perturbations around the shape factor ε parameter. This research can be used for the design of new technological devices important to industry, optimizing processes in which fluids are transported, energy is transferred, etc.
Numerical Simulations as a Reliable Alternative for Landmine Explosion Studies: The AUTODYN Approach
Authors: Follett Stephanie , Hameed Amer , Darina S. , Hetherington John G.
Published: May 2012

In order to validate the numerical procedure, the explosion of a mine was recreated within the non-linear dynamics software, AUTODYN. Two models were created and analysed for the purposes of this study — buried and flush HE charge in sand. The explosion parameters — time of arrival, maximum overpressure and specific impulse were recorded at two stand-off distances above the ground surface. These parameters are then compared with LS-DYNA models and published experimental data. The results, presented in table format, are in reasonable agreement.
Vibration Suppression in a Cantilever Beam Using a String-Type Vibration Absorber
Authors: Issa Jimmy S. , Habchi Wassim F.
Published: May 2012

A string-type vibration absorber is proposed to suppress energy from a vibrating beam. A cantilever beam is considered with a harmonic force applied at its free end. The vibration absorber is a string attached to the beam at two different points. The string is rigidly connected to the fixed end of the beam and through a spring and damper to a second point on the beam. The finite element method is used to model the system and a reduced order model is obtained through modal reduction performed on both the string and the beam. The steady state amplitude of the transverse vibration of the beam is calculated using the first two modes of the beam-string system. It is found that the maximum amplitude at a given point of the beam occurs at a forcing frequency which is a root of a sixth order polynomial. The design of the vibration absorber is done in two steps. In the first, the spring stiffness, the position of the second attachment point of the string and a preliminary damping constant are calculated using a genetic algorithm approach where the objective function is the maximum displacement on the beam. Fine tuning is done in the second optimization step, by choosing an appropriate damping constant to further improve the design. To avoid buckling, the string tension is set to a value less than the lowest buckling force of the system. Numerical simulations of the beam’s maximum amplitude with and without absorber are shown to validate the proposed design.
Microflow Cytometer: Hydrodynamic Focusing and Separation of Sample Stream
Authors: Hashemi Nastaran , Howell Peter B. , Ligler Frances S.
Published: May 2012

Using grooves in the walls of a microchannel and two sheath streams, we have passively focused a sample stream in the center of the microchannel for optical analysis. Even though the sample stream is completely surrounded by sheath fluid, reversing the orientation of the grooves in the channel walls returns the sample stream to its original position with respect to the sheath streams. The use of this sheathing technique has already been demonstrated in a sensitive microflow cytometer; the unsheathing capability now provides the opportunity to recover particles from the sensor with minimal dilution or to recycle the sheath fluid for long-term unattended operation. The ability to reverse focused laminar flows opens a variety of options for combining target transport, processing and analysis procedures.
Elastic Polyether Polyurethane Foams Under Punching: Experiments, Theory and Simulations
Authors: Sabuwala Tapan , Dai Xiangyu , Gioia Gustavo
Published: May 2012

We carry out punching experiments on low-density elastic polyether polyurethane (EPP) foams. The punch is rigid and wedge-shaped, and the specimens are either cubic or brick-shaped. The experimental results display some striking features, most notably a mechanical response that remains linear up to a penetration of the punch of about 40% of the height of the specimen. At higher penetrations, the mechanical response turns abruptly nonlinear: for the cubic specimens, there is a momentary loss of stiffness; for the brick-shaped specimens, there is a sizable increase in stiffness. We formulate a simple theoretical model of the punching of low-density EPP foams. In this model, a cell of the microstruture of an EPP foam behaves as a bistable elastic structure under compression, so that there are two preferred values of strain corresponding to two configurational phases of the foam. We use the model to explain the most salient experimental observations. We also formulate a micromechanical, mean-field model of EPP foams, implement the model in a general-purpose finite element code, and carry out computational simulations of the punching experiments. The computational results are in good accord with the experimental results, and they allow us to verify some of the assumptions on which the theoretical model is predicated.
Thermoeconomic Cost Analysis of Central Solar Heating Plants Combined With Seasonal Storage
Authors: Lozano Miguel A. , Anastasia Antonio , Serra Luis M. , Verda Vittorio
Published: May 2012

The European Union and its Member States have committed themselves to achieving a 20% share of renewable energy by 2020. If the focus remains solely on solar thermal systems for domestic hot water (DHW) preparation, as in Spain, then the solar contribution will be very limited. Central Solar Heating Plants combined with Seasonal Storage (CSHPSS) systems enable high solar fractions of 50% and more. Most CSHPSS demonstration plants in Europe have been built in Central and North Europe, mainly in Denmark, Germany and Sweden. South Europe has little experience. This article presents a thermoeconomic cost analysis of CSHPSS systems. The objective of thermoeconomics is to explain the cost formation process of internal flows and products of energy systems. The costs obtained with thermoeconomics can be used to optimize the design of new plants and to control the production of existing plants. A simulation study on solar assisted district heating systems with high solar fractions and seasonal thermal energy storage was carried out with TRNSYS taking into consideration the meteorological conditions in Zaragoza (Spain). A CSHPSS plant was designed for a district of 500 dwellings with an annual thermal energy demand of 2,905 MWh/year. The process of cost formation has been analyzed considering the very specific features of the CSHPSS designed system: free solar energy, seasonal and DHW thermal energy storage, continuous variation of the operation due to highly variations of solar radiation and energy demands (hourly and seasonal). These features impose important difficulties in the calculation of the costs of internal flows and products in this type of systems.
A Novel Approach for the Design of a 1-DOF Nano-Telemanipulation System Involving a Virtual Slave and Environment Based on Passivity and Coupled Stability Theory
Authors: Samadzade S. , Habibnejad Korayem M. , Sarli N.
Published: May 2012

In a typical passivity-based controller design for a teleoperation task, a passive environment is frequently postulated. This assumption does not hold for nano environments and numerous researches in nano-telemanipulation have attributed this to the substantial van der Waals and capillary forces with respect to inertial forces in nanocosm. This non-passivity diminishes the applicability of most passivity-based methods for controller design unless the reflection of this active behavior to the operator is ignored. The focus of this paper is to present a control structure for an AFM-based telemanipulation system capable of addressing the three main issues in a fine fashion: stability, transparency and human perception. Specifically guaranteeing stability on the premise that the environment is non-passive is the main concern and treated by designing a suitable virtual coupling and haptic interface.
Design and Analysis of a High Power Density, Low Temperature Waste Heat Recovery System Using an Oil-Free Turboalternator
Authors: Walton James F. , Hunsberger Andrew , Heshmat Hooshang
Published: May 2012

In this paper the authors will present the design and preliminary test results for a distributed electric generating system that uses renewable energy source for economical load-following and peak-shaving capability in an oil-free, high-speed micro-turboalternator system using compliant foil bearings and a permanent magnet alternator. Test results achieved with the prototype system operating to full speed and under power generating mode will be presented. A comparison between predicted and measured electrical output will also be presented up to a power generating level of 25 kWe at approximately 55,000 rpm. The excellent correlation between design and test provides the basis for scale up to larger power levels. Based upon the turboalternator test results a thermodynamic cycle analysis of a system using low grade waste heat water at approximately 100 C will be reviewed. The tradeoff study results for a series of environmentally friendly refrigerant working fluids will also be presented including sensitivity to vaporization and condensing temperatures. Based on the cycle and pinch point analyses predicted maximum output power was determined. Finally a preliminary turbine design for the selected R134a working fluid was completed. The results of this study show that a net output power level of greater than 40 kW is possible for approximately 240 l/m flow of water at 100C is possible.
Prognostic Health Monitoring of Damage Progression in Leadfree Electronics Under Sequential Exposure to Thermal Aging and Thermal Cycling
Authors: Lall Pradeep , Vaidya Rahul , More Vikrant , Goebel Kai
Published: May 2012

Deployed electronic systems may be subjected to cyclic thermo-mechanical loads during storage and subsequent to deployment. Aging has been previously shown to affect the reliability and constitutive behavior of second-level leadfree interconnects. Prognostication of accrued damage and assessment of residual life is extremely critical for ultra-high reliability systems in which the cost of failure is too high. The presented methodology uses leading indicators of failure based on micro-structural evolution of damage to identify impending failure in electronic systems subjected to sequential stresses of thermal aging and thermal cycling. The methodology has been demonstrated on area-array ball-grid array test assemblies with Sn3Ag0.5Cu interconnects subjected to thermal aging at 125°C and thermal cycling from −55 to 125°C for various lengths of time and cycles. Damage equivalency methodologies have been developed to map damage accrued in thermal aging to the reduction in thermo-mechanical cyclic life based on damage proxies. Prognostic metrics including α-λ metric, sample standard deviation, mean square error, mean absolute percentage error, average bias, relative accuracy, and cumulative relative accuracy have been used to compare the performance of the damage proxies.
Wetting Characteristics of a Phospholipid Membrane Using Molecular Dynamics Simulation
Authors: Maroo Shalabh C. , Cho H. Jeremy , Wang Evelyn N.
Published: May 2012

Phospholipid molecules form bilayers in water due to their hydrophilic heads and hydrophobic tails. The electroporation of lipid bilayers (cell membranes) is a phenomenon where membranes are permeabilized by the application of electric fields. At some critical voltage, a dramatic increase in conductivity across the membranes is observed. This phenomenon is widely used in DNA and RNA transfer as well as targeted drug delivery systems. However, the membrane ruptures with a continuous increase in voltage where interaction between lipid and water molecules is an important factor in electroporation behavior. This study characterizes the wettability, of both the head and tail groups of lipid molecules, by calculating the contact angle of a water droplet on a planar phospholipid monolayer using molecular dynamics simulations. The water droplet completely spreads on the hydrophilic heads of the lipid, while forming an average contact angle of 136.05° on the hydrophobic tails. An analysis using the Young’s equation suggests that a difference in free energy of 116 mJ/m2 contributes to the overall energy barrier for water penetration across the lipid monolayer. We aim to control this permeabilization phenomenon to achieve water desalination.
Sub-Atmospheric Pressure Pool Boiling of Water on a Screen Laminate-Enhanced, Wavy-Fin Array
Authors: Laca P. J. , Wirtz R. A.
Published: May 2012

Saturated pool boiling on vertically oriented, copper, wavy-fin surfaces in water at reduced pressures is investigated. A lamination of fine-filament, wire mesh is an effective surface enhancement for boiling since the surface can be configured to provide a very high density of potential bubble nucleation sites. Two surfaces are considered: a 0.75mm thick 4-layer laminate with approximately 4000 pores per cm2 and a 0.42mm thick 8-layer laminate with approximately 26,000 pores per cm2. The results show that the 8-layer laminate outperforms the 4-layer laminate. At reduced pressures a reduction in performance is seen for both surfaces. A semi-empirical boiling model is developed. The model predicts the boiling performance of our data within an error of 30%. The model shows that shorter fins improve boiling performance.
Dynamics of Mechanically Over-Constrained Inertial Sensors
Authors: Spiewak Swavik , Selvakumar Arjun , Tabe Arjmand Mehdi , Lawrence Eric
Published: May 2012

Microsystems Technology based inertial sensors offer important advantages in low-invasive measurement of spatial motion with sub-micron accuracy. Their successful implementation hinges upon achieving very low distortion and noise at the low end of the frequency spectrum. Of particular importance is the Vibration Rectification Error (VRE) — an apparent shift in the signal bias that occurs when inertial sensors are subjected to vibration. A common approach to the reduction of VRE is assuring a highly symmetrical mechanical structure of sensors. Furthermore, a low cross-axis sensitivity is desirable. In accelerometers these properties are achieved by employing multiple flexures supporting the seismic mass. However, this may lead to mechanical over-constraining and multiple local equilibria rather than a single global one. Multiple equilibria combined with the nonlinearity of flexures create conditions for chaotic behavior, which can greatly degrade the sensors’ performance. We investigate representative architectures of high performance servo accelerometers, study the impact of over-constraining, and develop comprehensive dynamic models accounting for the presence of this condition. Given the complexity of spatial motion of the proof mass and resulting deformations in the flexures, we employ computer aided generation of constitutive, symbolic and scaleable models of the investigated sensors. We illustrate analytical investigations with numerical simulations and experimental results.
Performance Modeling of Micropost Wicks for Micro Heat Pipes at Low Heat Fluxes
Authors: Sharratt Stephen , Nam Youngsuk , Ju Y. Sungtaek
Published: May 2012

Well defined wick microstructures comprised of hexagonally packed cylindrical posts with varying solid fraction (.227–.534) are analyzed for heat transfer performance for heat pipe applications. The equilibrium free fluid surface profile under the influence of surface tension is calculated for each wick structure wetted with water. The fluid geometry is analyzed using a numerical solver so that the thermal performance (defined as a heat transfer coefficient) of the wick evaporator can be determined. Conduction through both the solid wick and liquid are considered and resistance to evaporation at the liquid-vapor interface is included. The analysis is compared to the results of a heat transfer experiment using water with a super-hydrophilic micro-manufactured copper post array. The equilibrium meniscus assumption is shown to be valid for heat fluxes less than ∼ 30 W/cm2. For low contact angles, ∼50% of the heat transfer is shown to occur within the region where fluid layer thickness is less than 2um. Heat transfer performance is shown to be a strong function of contact angle, especially for well wetting fluids. Solid fraction is shown to not be a good predictor of thermal performance. A non-dimensional normalized thin film area is presented and is a strong indicator of thermal performance. Evaporator heat transfer coefficients greater than 20 W/cm2K are predicted for large values of normalized thin film area. The modeling methods presented can be used as a design and analysis tool for predicting the effects of microscale geometry and topology on the heat transfer performance of microstructured wicks operating at low heat fluxes.
Distributed Cohesive Motion Control of Quadrotor Vehicle Formations
Authors: Bayezit I˙smail , Fidan Barıs¸ , Amini Mehdi M. , Shames Iman
Published: May 2012

In this paper, we focus on distributed cohesive motion control of 3-dimensional multi-vehicle systems considering individual agent dynamic behaviors as well as the overall multi-vehicle system. In this context, we examine maintenance of geometric formation of a swarm of autonomous quadrotor vehicles, i.e. maintenance of the distance between each agent pair in the swarm, during arbitrary maneuvers. A distributed scheme for the formation maintenance task is developed first. This coordination scheme is integrated with low level dynamic controllers designed for the agents considering practical kinematic and dynamic models for quadrotor vehicles. The distributed motion control scheme is implemented to move the vehicles whose initial positions satisfying the desired formation maintenance constraints are specified, to a set of final desired positions satisfying the same constraints cohesively without deviating from the desired geometric formation during motion. The developed coordination and control schemes are tested via a number of simulations.
The IGE Model: An Extension of the Ideal Gas Model to Include Chemical Composition as Part of the Equilibrium State
Authors: Paolini Christopher P. , Bhattacharjee Subrata
Published: May 2012

The TEST (The Expert System for Thermodynamics, www.thermofluids.net) web portal is a comprehensive thermodynamic courseware consisting of multimedia problems and examples, an online solution manual for educators, traditional thermodynamic charts and tables, fifteen chapters of animations to illustrate thermodynamic systems and fundamental concepts, and a suite of thermodynamic calculators called daemons for evaluating thermodynamic properties and analyzing thermodynamic problems.. The state module offers Java applets for evaluation of thermodynamic states of different working substances grouped into several material models according to underlying assumptions. Gas mixtures are modeled by the perfect gas (PG) or ideal gas (IG) mixture models. In this work, we extend the IG model mixture model into an ideal gas equilibrium (IGE) mixture model by incorporating chemical equilibrium calculations as part of the state evaluation process. Through a simple graphical interface users can set the atomic composition of a gas mixture. In the state panel, the known thermodynamic properties are entered. For a given pressure and temperature, the mixture’s Gibbs function is minimized subject to atomic constraints and the equilibrium composition along with thermodynamic properties of the mixture are calculated and displayed. What is unique about this approach is that equilibrium computations are performed in the background, without requiring any major change in the familiar user interface used in other state daemons. Properties calculated by this equilibrium state daemon are compared with results from other established applications such as NASA CEA and STANJAN. Also, two different algorithms, an iterative approach and a direct approach based on minimizing different thermodynamic functions in different situation are compared.
Numerical Analysis of a Hydrotreater Furnace Inlet Piping System
Authors: Huang Dui , Wu Bin , Magner Jeff , Gonzalez Martin R. , Zhou Chenn Q.
Published: May 2012

In the petroleum refining industry, the oil hydrotreater produces low-sulfur feed for the downstream units. An oil and hydrogen mixture is delivered by a piping system to the hydrotreater furnace. Uneven splitting and/or phase separations of the original stream can cause uneven heating as well as high furnace tube metal temperature, which can lead to shorten tube life and potentially tube rupture. In order to achieve better understanding of the current design, Computational Fluid Dynamics (CFD) had been used to determine the two-phase flow regime throughout the piping system and report the degree to which each flow split is uneven. In this study, a three dimensional multiphase CFD model of a hydrotreater furnace had been developed. The CFD model provides detailed velocity distribution and flow patterns together with the oil concentration and pressure drops at different location of the entire piping system. The degree of uneven splitting to all the outlets had also been evaluated quantitatively. The simulation results provide thorough understanding of the operating performance, while the parametric studies offer insight into the optimization of the current piping design.
A Neural Network Based Adaptive Tracking Controller for Nonholonomic Wheeled Mobile Robots With Unknown Dynamics
Authors: Mohareri Omid , Dhaouadi Rached
Published: May 2012

This paper presents the design, implementation and comparative analysis of an intelligent neural network based controller used for adaptive trajectory tracking of a wheeled mobile robot with unknown dynamics. In this proposed control scheme, the neural network is used to continuously tune the gains of the kinematic based controller in a backstepping structure. The online learning and adaptive capabilities of the neural network are utilized to achieve a smooth and fast robot tracking motion. The simulation results are used to verify the tracking performance of the proposed control algorithm and to compare it with the conventional backstepping controller.
Effect of Thermal Characteristics of Electronic Enclosures on Dynamic Data Center Performance
Authors: Ibrahim Mahmoud , Bhopte Siddharth , Sammakia Bahgat , Murray Bruce , Iyengar Madhusudan , Schmidt Roger
Published: May 2012

Data centers are the facilities that house large number of computer servers that dissipate high power. Considering the dynamics of the data centers, their efficient thermal management is a big challenge that needs to be addressed. Computational analysis using a CFD code is very useful technique that helps the engineer to understand and solve the data center cooling problem. Several ongoing numerical modeling research efforts assume the computer room air conditioning (CRAC) units as fixed flow devices with constant temperature boundary condition. In reality, CRAC supply temperature is governed by the thermal characteristic curve, as specified by vendor. In this paper, study is presented by incorporating the CRAC thermal characteristic curve in the numerical model. Case studies are presented to show how the segregated high and low powered clusters in a data center may affect the supply temperatures from the CRAC in their vicinity. Another concern that is crucial in analyzing data centers performance precisely is the effect of buoyancy and thermal mass on the facility environment. In some cases, the effect of thermal mass and buoyancy may cause unexpected behaviors such as temperature overshoot or rapid variations in temperature. Non-dimensional parameters are used to demonstrate the effects of thermal mass and buoyancy.
Efficiency of the High Contact Ratio Involute Spur Gears With Asymmetric Teeth
Authors: Karpat F. , Ekwaro-Osire S.
Published: May 2012

Gears with asymmetric teeth have unique potential for application in gearboxes, particularly when uni-directional loading is applied. Most recently, gears with asymmetric teeth have received much attention for use in applications that require high performance due to increased load capacity. Such applications include aircraft and wind turbine. These gears offer flexibility to designers due to their non-standard design. In asymmetric teeth, the geometry of the drive side is not to be symmetric to the coast side. In other words, the pressure angle on the drive side is greater or smaller than that on the coast side. Asymmetry between tooth sides provide vital in obtaining key properties, such as high load carrying capacity, low weight, low wear or low vibration. In order to effectively design asymmetric teeth, it is necessary to perform analyses on the efficiency of these gears under various loading. In this study, the results obtained on high contact ratio involute spur gears with asymmetric teeth are presented and discussed. The impact of a few design parameters, such as pressure angle or tooth height, on sliding velocities and friction is investigated and illustrated with numerical examples.
CFD Modeling of Indirectly Fired Integrated Oxygen-Free Gasification and Steam Generation System
Authors: Alyaser Monem , Nair Rajesh , Sathyamurthy Prabhu
Published: May 2012

This paper introduces a novel gasification reactor that uses a process of steam gasification of the carbonaceous feedstock by indirectly heating the reacting flow through a high temperature heat exchanger without the need for partial with pure oxygen. It demonstrates the importance of gasification as a method for increasing power plant efficiency and reducing emissions. A computational fluid dynamics (CFD) model was created to model this novel gasifier and the results of the model that illustrates the efficiency and advantages of the new gasifier. The heating fuel was assumed to be fully combusted at the inlet. The adiabatic flame temperature was assumed to be the inlet temperature of the heating gas. The gasification stream was modeled as a laminar flow, where the reaction is kinetically controlled. The standard Shrinking Core Model (SCM) included in the commercial CFD package Fluent was used to predict the char consumption. The coal conversion rates were found to be higher than expected. The results indicate that the gasification of coal with steam without partial combustion with pure oxygen using this new concept is feasible.