bluuebunny/crossref_metadata_2025 huggingface dataset:
Stress Analysis of Functionally Graded Cylinders Subjected to Thermo-Mechanical Loads Based on Bernstein Polynomials
Authors: Fallah Ali , Aghdam Mohammad Mohammadi , Pasharavesh Abdolreza
Published: May 2012

Stress analysis of thick walled functionally graded (FG) cylindrical pressure vessels subjected to uniform axisymmetric thermo-mechanical loads is presented using Bernstein polynomials. All thermal and mechanical properties except Poisson’s ratio of the FG vessels vary through the thickness with arbitrary functions of the radial coordinate. Based on the thermo-elasticity theory, the first law of thermodynamics and axisymmetric assumption, the governing equations of the semi-coupled thermo-elasticity problem reduce to a set of second order boundary value problem. Galerkin method together with Bernstein polynomials is used to obtain solution for the governing equations. The presented method is simple to implement, efficient and accurate. Predictions of some special cases for which analytical results are available in the literature are used to validate the method. Comparison of the results for stress and displacement components and temperature distribution with analytical results shows excellent agreement. Furthermore, predictions for radial displacement, stresses and temperature in various cylindrical pressure vessels with different material models are presented for future references.
Dynamic Performance of an Electromagnetically Actuated Valveless Micropump
Authors: Dinh Thien X. , Ogami Yoshifumi
Published: May 2012

The dynamic performance of a valveless electromagnetic micropump is studied by a fluid–diaphragm coupling model. The model includes fluid inertia and considers the electromagnetic action on the flexible diaphragm of the pump as a sinusoidal force. Fluid pressure acting on the diaphragm is obtained instantaneously with solving the coupling equation through a transient dynamic mesh simulation. This treatment avoids omitting the phase shift between pressure force and displacement of the diaphragm. Furthermore, the model removes almost empirical parameters. A MEMS prototype is fabricated and the measured backpressure attains to 2.5cmH2O when using a 65mA sinusoidal driving current at frequency of 30Hz.
Development of a New Void Fraction Correlation for Modeling Two-Phase Flow in Producing Geothermal Wells Using Artificial Neural Networks
Authors: A´lvarez del Castillo A. , Santoyo E. , Garci´a-Valladares O.
Published: May 2012

An artificial neural network (ANN) was used to develop a new empirical correlation to estimate void fractions for modeling two-phase flows in geothermal wells. Flowing pressure, wellbore diameter, steam quality, fluid density and viscosity, and Reynolds numbers were used as input data. An explicit relationship among the input data was obtained from an ANN model. A computational architecture based on, the Levenberg-Marquardt optimization algorithm, the hyperbolic tangent sigmoid transfer-function, and the linear transfer-function, was designed. A geothermal database containing thirty-two data sets logged in production well tests were used both to train and to validate the ANN. The best training results were obtained for an ANN architecture of five neurons in the hidden layer, which made possible to predict void fractions with a satisfactory efficiency (R2 = 0.992). From this ANN training pattern, a new empirical correlation was developed and coupled into a wellbore simulator for modeling two-phase flows in other geothermal wells (to avoid bias). Four well-known engineering correlations for calculating the void fraction were simultaneous evaluated. The simulated results (obtained with the five void fraction correlations) were statistically compared with measured field data. A better agreement between simulated and field data was systematically obtained for the new ANN correlation with matching errors less than 3%. These results suggest that the new empirical correlation can be reliable used to estimate void fractions in two-phase geothermal wellbores.
Energy Flow of Advanced IGCC With CO2 Capture Option
Authors: Kawabata Masako , Iki Norihiko , Kurata Osamu , Tsutsumi Atsushi , Koda Eiichi , Suda Toshiyuki , Matsuzawa Yoshiaki , Furutani Hirohide
Published: May 2012

Conventional IGCC (integrated gasification combined cycle) employs a cascaded energy flow with a high efficiency, yet it is difficult to achieve over 50% HHV (higher heating value). The current study proposes an alternative model of exergy recuperated Advanced IGCC (A-IGCC) to achieve higher plant efficiency by applying an autothermal reaction in the gasifier. This requires an additional heat supply from the gas turbine exhaust and the steam extracted from the steam turbine. System and performance analyses were studied on base IGCC and A-IGCC cases incorporating the heat (exergy) recuperation concept with an air-blown twin circulating fluidized bed gasifier for the gasification of sub-bituminous coal, both with and without the post combustion carbon dioxide (CO2) capture option. A-IGCC could deliver sufficient energy in the gasifier to the gas turbine without losing heat as resulted in IGCC. Chemical absorption methods using monoethanolamine (MEA) and methyldiethanolamine (MDEA) were selected as a CO2 absorbent. A-IGCC demonstrated a significantly higher system efficiency (51%) than IGCC (43%) without CO2 separation, provided the gas purification was at high temperature. The thermal efficiency penalty by CO2 capture was −8% using MDEA (56% absorption) and −11% using MEA (90% absorption).
Fast Prediction of Temperature Evolution in Electronic Devices for Run-Time Thermal Management Applications
Authors: Yang Yizhang , Sundaram Sridhar , Refai-Ahmed Gamal , Touzelbaev Maxat
Published: May 2012

Increase of non-uniform power density and high switching frequency has presented new challenges in predicting transient temperature response to fast-changing power inputs in advanced electronic devices. While the computational effort with direct calculation through the finite element model (FEM) is expensive, various methods of model reduction with drastically improved computing speed have been developed for calculation of dynamic thermal responses of the electronic systems. However, those methods’ still-considerable computational time consumption inhibits their practices in real-time temperature prediction and dynamic thermal management (DTM) applications. This work presents a fast algorithm for predicting temperature evolution in electronic devices subjected to multiple heat source excitations. It utilizes the equivalent thermal RC network for model reductions, and adopts recursive infinite impulse response (IIR) digital filters for accelerated computation in discrete time-domain. The algorithm is validated by comparison to existing convolution integral methods, yielding excellent agreement with several orders of magnitude improvement in computation efficiency. Due to its simplicity in implementation, the algorithm is very suitable for run-time evaluation of temperature response for dynamic power management applications.
Integration of GPS and Accelerometer Uncertainties to Improve the Estimation of the Pose of Autonomous Vehicles
Authors: Achicanoy M. Wilson O. , Rodriguez H. Carlos F.
Published: May 2012

Uncertainty fusion techniques based on Kalman filtering are commonly used to provide a better estimation of the state of a system. A comparison between three different methods to combine the sensor information in order to improve the estimation of the pose of an autonomous vehicle is presented. Two sensors and their uncertainty models are used to measure the observables states of a process: a Global Positioning System (GPS) and an accelerometer. Given that GPS has low sampling rate and the uncertainty of the position, calculated by double integration from the accelerometer signal, increases with time, first a resetting of the estimator based on accelerometer by the GPS measurement is done. Next, a second method makes the fusion of both sensor uncertainties to calculate the estimation. Finally, a double estimation is done, one for each sensor, and a estimated state is calculated joining the individual estimations. These methods are explained by a case study of a guided bomb.
An Analytical and Numerical Study of Rectangular Orifice Plate Micro-Flowmeters
Authors: Amnache A. , Omri M. , Fre´chette L. G.
Published: May 2012

The paper presents the design and analysis of differential pressure micro-flowmeter, for low flows of gases (0.1–120 mg/s) with different inlet pressure conditions (1–4 bars). The device consists of a planar micro orifice obstruction in a rectangular microchannel, with two pressure ports, upstream and downstream of the constriction. The particularities of this micro orifice is the small scale and the planar two-dimensional configuration, i.e. only in the width of the rectangular microchannel changes. A series of micro orifice sizes will be studied, with hydraulic diameters ranging from 200 to 465 μm and channel Reynolds numbers up to 7000. The geometric parameters of these micro orifices were determined to have a measurable pressure drop and to avoid choking. The calculation of the pressure drop through a micro orifice are represented using analytical equations, and modeled numerically using computational fluid dynamics to further investigate the flow patterns and 3D effects. The discharge coefficient is determined for each orifice micro-flowmeter by numerical analysis. This work aims to implement integrated mass flow measurements in micro chemical and fluidic devices that cannot use macroscopic mass flow meters, either due to their large volume, high cost, or inability to withstand harsh environments.
Design of a New 45 kWe High-Flux Solar Simulator for High-Temperature Solar Thermal and Thermo-Chemical Research
Authors: Krueger Katherine R. , Davidson Jane H. , Lipin´ski Wojciech
Published: May 2012

In this paper, we present a systematic procedure to design a solar simulator for high-temperature concentrated solar thermal and thermo-chemical research. The 45 kWe simulator consists of seven identical radiation units of common focus, each comprised of a 6.5 kWe xenon arc lamp close-coupled to a precision reflector in the shape of a truncated ellipsoid. The size and shape of each reflector is optimized by a Monte Carlo ray tracing analysis to achieve multiple design objectives, including high transfer efficiency of radiation from the lamps to the common focal plane and desired flux distribution. Based on the numerical results, the final optimized design will deliver 7.5 kW over a 6-cm diameter circular disc located in the focal plane, with a peak flux approaching 3.7 MW/m2.
Analysis of Mechanical Nonlinearities of a Micro-Beam in Longitudinal Mode
Authors: Arjmand Ehsan , Arzanpour Siamak , Bahreyni Behraad
Published: May 2012

Micro electrical mechanical systems inherently tend to behave nonlinearly in high power handling. Such nonlinearities arise from mechanical and electrical characteristics of the systems. In this study, the mechanical nonlinearities are focused and the longitudinal mode shape of a microbeam resonator with high quality factor is considered. The mechanical nonlinearities for this system are assumed to be cubic and quadratic. the method of multiple scale is used for perturbation analysis which leads us to obtain the function of displacement with respect to frequency which is beneficial to set an upper dynamic limit to avoid instability and, also, facilitates to make the system so-called almost linear.
Gas-Liquid Two-Phase Flow Simulation of Wetted Wall Flows in Packed Columns
Authors: Iso Yoshiyuki , Chen Xi
Published: May 2012

Gas-liquid two-phase interfacial flows on the wall like liquid film flows, which are the so-called wetted wall flows, are observed in many industrial processes such as absorption, desorption, and distillation. For the optimum design of packed columns widely used in those kind of processes, the accurate predictions of the details on the small scale behavior of wetted wall flows in packing elements are very important, especially in order to enhance the mass transfer between the gas and liquid and to prevent flooding and channeling of the liquid flow. The present study focuses on the effects of the change of liquid flow rate and the wall surface texture treatments on the characteristics of wetted wall flows which have the drastic flow transition between the film flow and rivulet flow. In this paper, the three-dimensional gas-liquid two-phase flow simulation by using the volume of fluid (VOF) model is applied into wetted wall flows. Firstly, present results showed that the hysteresis of the flow transition between the film flow and rivulet flow arose against the increasing or decreasing stages of the liquid flow rate. It was supposed that this transition phenomenon depends primarily on the history of flow pattern as the change of curvature of interphase surface which leads to the surface tension. Additionally, the applicability and accuracy of the present numerical simulation were validated by using the existing experimental and theoretical studies. Secondary, referring to the texture geometry used in an industrial packing element, the present simulations showed that surface texture treatments added on the wall can improve the prevention of liquid channeling and can increase the wetted area.
The Internet-Based Teleoperation: Motion and Force Predictions Using the Particle Filter Method
Authors: Lee Jae-young , Payandeh Shahram , Trajkovic´ Ljiljana
Published: May 2012

In this paper, we present motion and force predictions in Internet-based teleoperation systems using the particle filter method. The particle filter, also known as the sequential Monte Carlo (SMC) method, is a probabilistic prediction or estimation technique within a sequential Bayesian framework: Data at a current time step are predicted or estimated by recursively generating probability distribution based on previous observations and input states. In this paper, we first formulate the particle filter method using a prediction-based approach. Motion and force data flows, which may be impaired by the Internet delay, are formulated within a sequential Bayesian framework. The true motion and force data are then predicted by employing the prediction-based particle filter method using the impaired observations and previous input states. We performed experiments using a haptic device that interacts with a mechanics-based virtual 3D graphical environment. The haptic device is used as a master controller that provides positioning inputs to a 4-degree of freedom (4-DoF) virtual robotic manipulator while receiving feedback force through interactions with the virtual environment. We simulate the Internet delay with variations typically observed in a user datagram protocol (UDP) transmission between the master controller and the virtual teleoperated robot. In this experimental scenario, the particle filter method is implemented for both motion and force data that experience the Internet delay. The proposed method is compared with the conventional Kalman filter. Experimental results indicate that in nonlinear and non-Gaussian environments the prediction-based particle filter has distinct advantage over other methods.
An Electrostatic Torsional Microresonator With Improved Quality Factor
Authors: Rasouli Mohammad Amin , Bahreyni Behraad
Published: May 2012

In this paper, we propose two structures for electrostatically actuated torsional microresonators in order to improve their mechanical quality factor (Q). In order to attain higher Q-factors, various mechanisms that limit Q-value of microresonators are investigated. The dominant sources of energy loss were minimized through structural design considerations. Since anchor and support losses are known to be the dominant energy dissipation mechanisms for most resonators, including the torsional microresonators of this work, our main focus is to come up with design structures that lead to anchor loss reduction. Finite element analyses (FEA) were employed to verify the design principle. It is demonstrated that the results are in agreement with our expectations, validating the effectiveness of presented structures from the view point of anchor loss reduction and Q-factor boosting. To compare analytic and experimental results, the proposed structures are fabricated and will be tested.
Engineering Education Through Degree-Long Project: A New Project Based Learning Approach
Authors: Kim Jay , Lim Teik , Allemang Randall , Rost Bob
Published: May 2012

A new pedagogical approach called engineering education through degree-long project has been implemented in the mechanical engineering program at the University of Cincinnati as a part of the NSF CCLI project. The approach integrates selected courses across the undergraduate curriculum of the mechanical engineering program using a degree-long project (DLP) as the theme. Design of Formula SAE® race car was employed as the first DLP. In each course in the sequence, the concept of the DLP approach and the role of the assignment in the course in the overall DLP are explained to students. In early-year courses, assignments are simple problems designed to show how abstract concepts are eventually applied to engineering tasks. In later-year courses, more involved design projects are used aiming at nurturing the ability to solve open-ended engineering problems. In conducting the approach, the most difficult part was developing an interesting and challenging problem which is relevant to practical applications, especially in early year courses. Findings through student evaluations and a stake-holders workshop on the improvement of the approach are discussed.
A Novel Signal Mechanical Signal Processing Technique for Detection of Perturbations in Coupled Microresonators
Authors: Hajhashemi M. Sadegh , Bahreyni Behraad
Published: May 2012

In this paper we present a novel method for processing of the signals from sensor systems based on coupled micromechanical resonators. Microfabricated resonators typically have electrostatic or piezoelectric interfaces. Properly designed microresonators can be mechanically coupled to each other in order to realize a bandpass filter transfer function. We will demonstrate that it is possible to use coupled microresonators for sensing applications and propose a novel mechanical signal processing method to detect quantities of interest.
Development of Thermal Interface Materials for Harsh Environment Packaging of Superconducting Integrated Circuits
Authors: Thompson Corey , Gordon Matt , Malshe Ajay P. , Gupta Deep
Published: May 2012

Superconducting integrated circuits (SCICs) require cooling to about 4 K for proper circuit operation. Current efforts are being made to transfer SCIC technology from lab experiments to viable consumer and military products. In order for this to be feasible, SCICs must function in cryogen-free closed-cycle refrigerator (or cryocooler) based systems. Design constraints for SCICs utilizing rapid single-flux-quantum (RSFQ) logic require a maximum temperature gradient across the package of less than 50 mK for proper circuit operation when implemented in cryocooler mounted systems. Also, to achieve increased functional density and decreased signal delays, it is desired to implement multichip module (MCM) SCICs in which RSFQ signals are passed from chip-to-chip through a common MCM substrate. Satisfying these constraints requires innovative packaging and thermal interface materials for harsh environment packaging (low temperature, high vacuum). The objective of this modeling work is to: explain the role of underfill in harsh environment cryogenic packages, explore the role of polymers and nanocomposites in filling this role, and anticipate the role of manufacturing defects on thermal management of 4 K packages. A characteristic model is developed in COMSOL MultiPhysics that allows for investigation of the dependence of temperature gradients across the package on these variables. It is found that at 4 K thermal interface resistances act as major bottlenecks to heat removal from the active die. It is also shown that as bump diameter decreases below 100 microns due to device miniaturization, the need for effective thermal interface materials is exacerbated. A novel nanoengineered cryogenic adhesive (nECA) comprised of nanoparticles dispersed in an epoxy matrix is proposed to act as a heat transfer medium between chip and substrate. Incorporation of nECA into the FEA model of a single chip package reduces the overall temperature gradient from 78 mK to 44 mK. This advance in thermal management of low temperature SCICs is paramount for the advancement of MCM packaging requiring efficient removal of heat from densely packaged chips.
Domain Reduction Method for Periodic Nanostructure Modeling: Gold Nanorods, Carbon Nanotubes and Graphene Applications
Authors: Karpov Eduard G. , Qian Dong
Published: May 2012

A domain-reduction approach for the simulation of one- and two-dimensional nanocrystalline structures is demonstrated. In this approach, the domain of interest is partitioned into coarse and fine scale regions and the coupling between the two is implemented through a multiscale interfacial boundary condition. The atomistic simulation is used in the fine scale region, while the discrete Fourier transform is applied to the coarse scale region to yield a compact Green’s function formulation that represents the effects of the coarse scale domain upon the fine/coarse scale interface. This approach facilitates the simulations for the fine scale, without the requirement to simulate the entire coarse scale domain. Robustness of the proposed domain-reduction method is demonstrated via comparison and verification of the results with benchmark data from fully atomistic simulations. Demonstrated applications include deformation of crystalline Au (111) nanorods, CNT bending and buckling, and graphene nanoindentation.
A CFD Study on a Base and a Flow-Trimmed Low Specific Speed Centrifugal Compressor
Authors: Zhang Donghui , Di Liberti Jean-Luc , Cave Michael
Published: May 2012

A numerical study on a baseline and a 25% trimmed compressor is presented in this paper. The CFD results are compared with the test results and good agreements are reached. Both CFD and test results show that flow trimming reduces the compressor efficiency and flow range. For compressors with specific speed lower than 0.038, flow trimming is not recommended.
Characterization of Laser Processed Sub-Millimeter Lap Joints Between Copper and Aluminum Under Tensile Load
Authors: Mian A. , Hailat M. , Newaz G. , Patwa R. , Herfurth H.
Published: May 2012

This paper presents the results of laser joined copper-aluminum lap shear samples without filler materials using an IPG 500W SM fiber laser. The length of the processed laser joint was about 20 mm and the width was about 200 μm. Laser-joined samples were tested under tensile loading to determine joint strengths. In addition, finite element analysis (FEA) was conducted to understand the stress distribution within the bond area under such loading. The FEA model provides a full-field stress distribution in and around the joint that cause eventual failure. We are still working on the topic, and more data will be published soon.
Rainwater Harvesting as a Distributed Resource
Authors: Whear John H.
Published: May 2012

Explore the possibilities, difficulties, and benefits of large scale rainwater harvesting using recycled water distribution systems. This paper explores the growing use of recycled water and the possibilities that distribution systems have created. It investigates water quality of rainwater harvesting (RWH) systems and the quality of recycled water and their uses. It examines the amount of rain water available using aproximatly 10% of available roof area in the city and examines the benefits of large scale rainwater harvesting unique to San Antonio. An exhaustive search of published materials was conducted, coupled with communications with the Texas Water Development Board and the San Antonio Water System. Quality standards for recycled water were compared with known test results for harvested rainwater. With the use of mathematical models, a distributed rainwater harvesting systems was compared to a stand alone system. Connection to a distribution system reduces the cost of rainwater harvesting by eliminating the need for large amounts of storage, which can account for 50% of the total costs of a standalone system. With minor filtering and periodic quality checks, large structures may supply sufficient amounts of rainwater to justify being a source of water in a recycled water distribution system.
Dynamics of Double Hand Thoracic Spinal Manipulations by Different Chiropractors
Authors: Gudavalli Maruti Ram
Published: May 2012

This study presents the dynamic load characteristics of chiropractors delivering posterior to anterior double thenar thoracic spinal manipulations to a mannequin. A total of 36 thrusts were delivered by the three chiropractors to a mannequin that has similar shape and texture of a human. Two three-dimensional force transducers were used between the doctor’s hand and the mannequin. Parameters of the duration, rate of loading, preload and peak loads were extracted from the data for the three chiropractors. Average peak loads in the normal direction reached 247 N and 217N in the right and left hands. The shear forces reached 36 and 18N in the right and left hand. The rates of loading have reached 804N/s and 761N/s in the right and left hands. Average durations of thrust were 242msecs. The three doctors had distinct characteristics in pre loads, durations of loading and rates of loading.
Optimized Design of Regenerative Blowers for Enhanced Efficiency
Authors: Wang Chien-Hsiang , Choi Chang-Hwan
Published: May 2012

In this paper, we studied geometric effects of impeller blade angles and hub configurations on the energy conversion efficiency of regenerative blowers, using commercial CAD and CFD software. As a base geometry, a regenerative compressor, that was commercially available with accessible experimental data, was modeled and simulated. Both Pro/Engineering (PTC) and SolidWorks (Solidworks Corp.) were used for 3D geometrical modeling, and ANSYS-CFX (ANSYS, Inc.) was used for CFD flow simulation. The CFD flow simulation was performed at a constant impeller rotational speed of 3600 rpm, while the air flow rates varied from 60, 80, 100, to 120 cfm. The simulation results for the base geometry agree with the experimental data, confirming the validity of the modeling and simulation schemes. For the parametric study of the impeller blade angles and hub configurations for enhanced efficiency, the two geometrical design parameters were systematically investigated to find out optimal efficiency points. The result shows that the protrusion and shape of a hub are more impactful to the pump efficiency than the outflow angles of blades, and enhances the power efficiency more effectively.
Multi-Physics Modeling of an Electro-Thermally Actuated Micro-Cantilever for Scanning Probe Microscopy
Authors: Sattel Thomas , Roeser Dennis , Gutschmidt Stefanie
Published: May 2012

This article presents the nonlinear equations of motion and analysis of a smart micro-cantilever which was designed and fabricated for AFM (atomic force microscopy) technology. The model is derived from the mechanical continuum expressions and includes thermo-visco-elastic damping as well as the localized atomic force interaction between the tip and sample surface, which in turn is deduced from the Lennard-Jones potential. The modal dynamical system obtained from the continuum model and by means of the Galerkin decomposition is then numerically analyzed. The analysis begins with the study of equilibria and natural frequencies under the influence of the selected parameters, such as the direct current and gap between tip and sample. This is complemented by a brief dynamical analysis of the system in selected parameter domains. The multi-physics micro-cantilever exists in real life and these first results of work in progress serve our intentions of systematically investigating the static and dynamic behavior of the same experimentally in the future.
Assessment of the Efficacy of Learning Modules on FEM Instruction
Authors: Harnack Jacob , Xin X. J. , Cai Liang-Wu , Panthaki Malcolm
Published: May 2012

A module-based approach is promoted for introducing FEM applications into undergraduate engineering courses. A Learning Module (LM) is defined as a well-structured, compact, and self-sufficient learning resource that provides a learner the desired contents in a precise and concise manner, enabling the learner to learn efficiently and effectively. Each LM is designed to be equivalent to one week’s learning time. A navigatable and editable multi-media (NEMM) format of presentation for learning modules is proposed. Critical to the construction of a learning module is the principle of conceptual analysis which allows the extraction of general concepts, principles, and procedures from FEM software specifics. Two learning modules are developed, and their efficacy in FEM learning is assessed. The pedagogical foundations behind the module-based learning are explored from the cognitive science perspective. The advantages and disadvantages of the module-based learning are discussed.
A New Truly Meshless Method for Heat Conduction in Solid Structures
Authors: Ahmadi Eisa , Aghdam M. M. , Sheikhy Nasrin
Published: May 2012

In this study a new meshless method is presented for the analysis of heat transfer in heterogeneous solid structures. The presented meshless method is based on the integral form of energy equation for the sub-particles in the domain of the material. A micromechanical model based on the presented meshless method is presented for analysis of heat transfer, temperature distribution and steady-state effective thermal conductivities of fiber-matrix type of composite materials. Because the domain integration is eliminated in the presented meshless formulation, the computational efforts in presented method are decreased substantially. A small area of the composite system called the representative volume element (RVE) is considered as the solution domain. The fully bonded fiber-matrix interface is considered and contact thermal resistant is neglected in the fiber-matrix interface and so the continuity of temperature and reciprocity of heat flux is satisfied in the fiber-matrix interface. A direct interpolation method is employed for enforcement the appropriate boundary conditions to the RVE. Numerical results are presented for temperature distribution, heat flux and thermal conductivity. Numerical results show that presented meshless method is simple, effective, accurate and less costly method in micromechanical modeling of heat conduction in heterogeneous materials.
Modeling Flutter Using Deflection-Dependent Strain-Rate Damping
Authors: Norouzi Soroush , Arzanpour Siamak
Published: May 2012

Flutter is a flow-induced unstable motion in structures that has drawn researchers’ attention in the past decades due to its presence in numerous applications including aviation. Linear and nonlinear models of flutter have been developed. Linear models are simple and accurate for predicting the critical velocity at which flutter occurs. However, they are not capable of describing the post-flutter behavior of structures. Nonlinear models, on the other hand, can properly demonstrate the unstable motion accompanied with the occurrence of flutter but they are highly complicated. In fact, numerical solution of these equations requires extensive computations. As a result, having a model that is both simple and valid for post-flutter simulations is of critical importance. Linear models lose their accuracy when large deflections take place in the structure. This is when the unconsidered tensions that oppose large deflections come into play and render the behavior of the structure nonlinear. Usually, a type of damping relative to strain-rate is assumed for modeling structures under flutter. This paper introduces a deflection-dependant strain-rate damping coefficient to the linear flutter model, so as the deflections grow the restraining forces increase to limit the motion. The new sets of equations are derived and simulations are conducted to ensure the capability of the model to capture the post-flutter behavior. Results are then compared with the results of nonlinear simulation to demonstrate the new model’s compliance with those of nonlinearly-modeled systems.
Effect of Surface Roughness on Fouling of Calcium Carbonate: An Experimental Investigation
Authors: Izadi M. , Aidun D. K. , Marzocca P. , Lee H.
Published: May 2012

The effect of surface roughness on the fouling behavior of calcium carbonate is experimentally investigated. The real operating conditions of a tubular heat exchanger are simulated by performing prolonged experiments with duration of 3 to 7 days. The solution used is a mixture of sodium bicarbonate and calcium chloride in de-ionized water with the concentration of 0.4 g/l of each. An on-line fouling evaluation system was developed such that the fouling resistance for a selected solution could be measured in real time. The experiments are repeated with the same procedure for 90/10 Cu/Ni tubes with different internal surface roughness. After the experiment the surface is analyzed by analytical microscopy to investigate the morphology of the deposit layer. Comparison of the experimental results of smooth and rough surfaces shows that a combination of aragonite and calcite polymorphs are formed on rough surface while only dendritic porous aragonite crystals are formed on smooth surface. Accordingly, the deposit layer formed on rough surface is denser and has a higher thermal resistance comparing to that formed on smooth surface. The fouling factor-time curves of smooth and rough surfaces obtained by the current experimental study agree with the results found by the analytical microscopy of the surface and show higher fouling resistances for rough surface. Experimental data is significantly important for the design, and formulating operating, and cleaning schedules of the equipment.
Design of Hydractive Optimal Suspension for a Passenger Vehicle
Authors: Sarshari Ehsan , Asadi Navid , Yousefi Reza
Published: May 2012

In this study a hydractive suspension system is designed for a passenger car. By using a mathematical validated model with eight degrees of freedom for a vehicle which is equipped with hydractive suspension, optimal damping forces derived for suspension system on the base of optimal control theory which uses linear quadratic regulators for improving ride comfort of vehicle and saves vehicles stability at the same time. Existing limitations for applying damping forces and time lag of controlling component are considered. The results are being derived according to a bump excitation and nonlinearity effects of the hydractive suspension components. Simulation results for the hydractive optimal suspension demonstrate significant improvements of system behavior in all controlled modes in comparison with the passive suspension.
Optimizing Biased AC Electroosmosis Micropump by Hydrophobic Nanoparticle Monolayer
Authors: Islam Nazmul , Askari Davood
Published: May 2012

This paper describes the optimization of bidirectional micropump velocity by a deposition of hydrophobic nanoparticle (NP) monolayer. A nano-composite polymer coating contains a homogeneous mixture of Silicon NP in polydimithylsiloxane (PDMS) which will modify the micropump surface to a hydrophobic surface. For hydrophobic nature of PDMS, the monolayer coating will modify the hydrophilic surface of biased AC electroosmotic micropump to a hydrophobic surface. Based on the results obtained from our previous research work for the biased AC electroosmotic micropump, the pumping velocity was 300 micron/sec in 100μm channel thickness for applied voltage of 4.4V at 1 KHz frequency [1]. In that research, we had optimized the applied AC voltage, frequency, channel dimension, and electrode width. The main objective of this research is to investigate the micropump velocity through a surface modification process. Adding a thin monolayer will separate the electrode from the pumping liquid; thus eliminating the reaction on the electrode for applied voltage. In such case, we can apply high voltage to achieve high pumping rate.
Dynamic Simulation of a Beta-Type Stirling Engine With Cam-Drive Mechanism
Authors: Yu Ying-Ju , Cheng Chin-Hsiang
Published: May 2012

Dynamic simulation of a beta-type Stirling engine with cam-drive mechanism has been performed. A dynamic model associated with the cam-drive mechanism has been developed. Upon obtaining the gas pressure inside the chambers, the derived dynamic model is used to evaluate the transient rotational speed of the engine before the steady-state regime is reached. The torque of the engine can be calculated as long as the gas force, the inertia torque, the friction torque, and the load torque are evaluated. In this study, the mass moment of inertia of the flywheel is firstly calculated. The friction torque is assumed to be proportional to the time-varied rotational speed which is obtained by experiments. The weight of the individual parts of the engine has also been considered. An extensive parametric study of the engine under different geometrical and operating conditions has been performed and results are presented.
Heat Pulse Analysis in Single-Wall and Double-Wall Carbon Nanotubes
Authors: Chen Liang , Kumar Satish
Published: May 2012

This paper investigates thermal transport in single wall carbon nanotubes (SWCNTs) and the interfacial thermal interaction in double-wall carbon nanotubes (DWCNTs) using molecular dynamics (MD) simulation and wavelet methods. The simulations are performed on three groups of carbon nanotubes (CNTs), as shown in Figure 1: 200 nm SWCNTs, 200 nm DWCNTs with 50 nm cut in the middle, and 100 nm complete DWCNTs. A heat pulse is applied in the middle of the CNTs, and wavelike responses of temperature as well as its three components (radial, tangential, and longitudinal) along the CNTs are analyzed to explore the underlying thermal transport mechanism. Wavelet analysis is carried out on the three components of velocity to investigate the evolution of frequency spectrum along CNTs in time. The heat pulse analysis in SWCNTs shows that the longitudinal components propagate as the leading wave packet of heat at the largest speed but only carry a small fraction of the total energy. The high frequency radial components carry most of the energy and dominate in the middle diffusion regions. In DWCNTs, the radial components and tangential components carry most of the total energy while the longitudinal components carry only a small fraction of the total energy. We observe dramatic energy transfer from outer tube to inner tube of a DWCNT without any cut during the heating period. This energy transferred to inner tube is primarily contained in the slowly moving radial modes indicating that energy can be transferred effectively by the radial modes. However, the energy transfer between tubes of DWCNTs through tangential and longitudinal components is quite ineffective.
Three-Dimensional Multiphysics Analyses of a CPU Integrated Thermal Heat Sink
Authors: Al-Dojayli Maher , Chan Ellen , Leung Sunny , Naguib Hani , Dawson Francis , Adinkrah Vincent , Lakatos-Hayward Laszlo
Published: May 2012

Recent advances in electronic packaging have led to small, lightweight and highly efficient heat sink designs. Some of these attempts are aiming to integrate the heat sink with the packaging wall structure. In this paper, a three-dimensional multiphysics numerical model is developed for the integrated heat sink to carry out CFD and thermal analyses, stress analyses due to thermal expansion and modal analyses. Finite volumes were used to model the conjugate heat transfer (CHT) for the coupled fluid-structure fields representing the air and heat sink fin walls and base, respectively. In this analysis, both natural and forced convection analyses were considered. The predicted temperature distribution was then used to calculate the mechanical stresses due to thermal expansion, using finite elements. Lastly, modal analyses were conducted to calculate the natural frequencies of the model. The effect of varying the source heat generation rate, air flow speed, and some geometry features such as number of fins and fin’s height on the performance and structural integrity of the assembly have been studied.
Time Optimum Cam Synthesis With Manufacturing and Operation Constraints
Authors: Duerr Konrad , Seethaler Rudolf
Published: May 2012

Traditionally, cam profiles have been described in terms of harmonic functions or splines that are optimized to provide low residual oscillations and avoid constraints such as pressure angle. For automotive cams used in internal combustion engines, the designer usually manually manipulates the control points of the spline functions and checks for constraint violations by feeding the obtained cam profile through a dynamic simulation of the valve train. This is a lengthy and iterative process that cannot guarantee that the obtained cam profile is truly optimal, since constraint boundaries are usually only met at a few distinct points along the cam profile. However, a truly time optimal cam profile will need to follow constraints during the complete motion. This paper then shows a reverse design procedure, where cam profiles are defined in terms of the constraint functions. A valve lift profile is assembled that moves along the boundary of the feasible valve lift space. The resulting cam motion is constrained at all times and represents a time optimum cam profile in terms of the selected constraints. The proposed methodology is computationally efficient and runs effectively on standard office computers. Automotive cam designers can use the results of this approach as an initial starting point for their cam shape optimization.
Rear Door Heat Exchanger Cooling Performance in Telecommunication Data Centers
Authors: Mynampati Venkata Naga Poornima , Karajgikar Saket , Sheerah Ibraheem , Agonafer Dereje , Novotny Shlomo , Schmidt Roger
Published: May 2012

The increase in the data center server heat density waves a scope for developing improved cooling technologies without raising the power consumption. It is commonly observed that 40% of the total data center energy is consumed by its cooling equipments. For higher server density cabinets, typical air cooling techniques leads to a substantial increase in the power consumption. Rear door heat exchanger, an open looped cooling technique is one of the solutions for such scenarios. In this paper, emphasis is laid on the analytical determination of the optimum heat load after calculating the effectiveness of heat exchanger at given operating conditions of the data center and heat exchanger. Later, thermal analysis is performed and the working of heat exchanger is compared for different data center heat loads. Based on the results, a ‘rule of thumb’ is verified that rear door heat exchanger could be 100% efficient in cooling the cabinets of heat loads up to 27kW. Thus, for rack heat loads less than 27KW, CRAC units can be non-operational resulting in energy savings. Furthermore, effect of RDHx in different configuration is studied and compared.
Damage in Adhesive Joints During Low Cycle Fatigue
Authors: Ca´bulo-Pe´rez Iva´n C. , Casas-Rodri´guez Juan P.
Published: May 2012

The objective of this research is to study the damage behavior of bulk adhesive and single lap joint (SLJ) specimens during low cycle fatigue (LCF). Fatigue tests under constant stress amplitude were done and strain response was measured through cycles to failure using the bulk adhesive and SLJ data. A non linear damage model was used to fit experimental results. Identification of the damage parameters for bulk adhesive was obtained from the damage against accumulated plastic strain plot. It is shown that the plastic strain can be obtained from the constant stress test if the instantaneous elastic modulus, i.e. modulus affected by damage, is evaluated for each cycle. On the other hand, damage in SLJ was seen mainly in the adhesive for itself — no substrate failure — this fact is used to propose that fatigue response in the joint is due to continuum damage accumulation in the adhesive as the number of cycles increases. Damage behavior under compressive loads was not taken into account but good correlation of numerical and experimental data was obtained. It was found that damage evolution behaves in a non linear manner as the plastic deformation grows for each cycle: on fatigue onset an accelerated damage grow is observed, then a proportional evolution, and finally a rapid failure occurs; this characteristics were seen in both the SLJ and bulk adhesive specimen. So far, this research takes the damage model found in a standard adhesive specimen and assumes it is accurate enough to represent the damage behavior of the SLJ configuration.
Application of Adaptive Network-Based Fuzzy Inference System (ANFIS) in Aerodynamics Prediction of Low-Reynolds-Number Flapping Motion
Authors: Amiralaei M. R. , Partovibakhsh M. , Alighanbari H.
Published: May 2012

The objective of the present study is to develop an Adaptive Network-based Fuzzy Inference System (ANFIS) model to predict the unsteady lift coefficients of an airfoil. The airfoil performs a flapping motion in Low-Reynolds-Number (LRN) flow regime. Computational Fluid Dynamics (CFD) simulations of the flow field are conducted and the corresponding unsteady lift coefficients are used as the input data to ANFIS. The results show that the ANFIS model is capable of predicting the lift coefficients with very good accuracy, which could be of great value in the preliminary design stages.
Integrated System for Soft Tissue Dynamic Simulation
Authors: Zhao Xiaodong , Shan Baoxiang , Pelegri Assimina A.
Published: May 2012

An integrated system is built to model and simulate the dynamic response of soft tissues. The mathematical formulation employs finite element and model order reduction approaches to develop a state space model for soft tissues that allows for time-efficient numerical analysis. The stimulus device and signal processing routines are built in Matlab/Simulink and then integrated with the finite element state space model. This integrated system facilitates expeditious numerical evaluation of different soft tissue models subjected to dynamic excitation. It further elucidates the effect of different stimulus sources, as well as relative influences of different sources of uncertainty.
Experimental Model Identification and Controller Design of a Vapor Compression Cycle for Electronics Cooling
Authors: Catano Juan E. , Zhang Tiejun , Zhou Rongliang , Jensen Michael K. , Peles Yoav , Wen John T.
Published: May 2012

In this paper dynamic identification of the evaporator dynamics in a vapor compression cycle (VCC) subjected to imposed heat flux is studied. The imposed heat flux boundary condition at the evaporator represents a specific application of the VCC for electronics cooling. However, different models and control algorithms than traditional VCCs are required. First principle models are highly nonlinear and, hence, not practical for system control. A dynamic model identification of the refrigerant temperature at the exit of the evaporator, refrigerant pressure, and temperature of the heating element is performed by varying the expansion valve opening. It is shown that single-input single-output (SISO) identification is not sufficient to capture the dynamics of the evaporator, due to the coupling of the dynamics in the entire system. Including the effect of incoming mass flow rate into the evaporator to the model significantly improves the identification and prediction of the evaporator dynamics. Finally, a SISO controller based on the identified model, is designed and tested experimentally. The control objective is to maintain the temperature of the heating element below a set point, subjected to changes in heat flux.